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Endocrinology Vol. 147, No. 11 5087-5093
Copyright © 2006 by The Endocrine Society

Orphanin FQ/Nociceptin Is a Physiological Regulator of Prolactin Secretion in Female Rats

Matthew Chesterfield, James Janik, Emily Murphree, Courtney Lynn, Erin Schmidt and Phyllis Callahan

Center for Neuroscience, Departments of Zoology (M.C., J.J., D.L., E.S., P.C.) and Mathematics and Statistics (E.M.), Miami University, Oxford, Ohio 45056

Address all correspondence and requests for reprints to: Phyllis Callahan, Center for Neuroscience, Department of Zoology, Miami University, Oxford, Ohio 45056. E-mail: Callahp{at}muohio.edu.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Orphanin FQ/nociceptin (OFQ/N), the most recently identified endogenous opioid peptide, stimulates prolactin secretion in both male and female rats. OFQ/N, however, did not elicit this stimulatory effect through the µ-, {delta}-, or {kappa}-opiate receptor subtype. The role OFQ/N plays in prolactin regulation under physiological conditions and its mechanism of action are not known. The purpose of these studies was to determine the physiological significance and pharmacological specificity of the prolactin secretory response to OFQ/N. In addition, the role of the tuberoinfundibular dopaminergic (TIDA) neurons in mediating this response was examined. Opioid receptor-like-1 (ORL-1) receptors were blocked by pretreatment with compound B (Comp B), a purported OFQ/N antagonist, or receptor synthesis was disrupted by pretreatment with ORL-1 receptor antisense oligonucleotides. The prolactin secretory response to OFQ/N administration in diestrous females was measured. Furthermore, the suckling-induced prolactin response was also determined after Comp B pretreatment. TIDA neuronal activity was quantified in diestrous female rats to determine whether OFQ/N stimulates prolactin release by inhibiting TIDA neurons. OFQ/N significantly inhibited the TIDA neurons by 1 min, preceding the prolactin secretory response. Both Comp B and antisense pretreatment blocked the stimulatory effects of OFQ/N on prolactin release, and Comp B abolished the suckling-induced prolactin response. These studies indicate that OFQ/N is a potent stimulus for prolactin secretion in female rats and that it mediates this effect by rapid and transient inhibition of TIDA neuronal activity. Furthermore, OFQ/N plays a physiologically significant role in the regulation of prolactin secretion during lactation, and it mediates its effects via actions at the ORL-1 receptor subtype.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
PROLACTIN (PRL) IS best characterized for its role in lactation, but it plays many important biological roles in reproduction and homeostasis in mammalian systems (1), including involvement in angiogenesis, osmoregulation, luteal function in rodents, and immune function (2). PRL secretion is regulated through complex interactions among many different hypothalamic factors, but the primary regulator of PRL release is hypothalamic dopamine (3). The hypothalamus contains three dopaminergic systems involved in the regulation of PRL secretion: the tuberohypophyseal dopaminergic (THDA), the periventricular hypothalamic dopaminergic (PHDA), and the tuberoinfundibular dopaminergic (TIDA) neurons. TIDA neurons originate in the A12 region of the dorsomedial arcuate nucleus and terminate in the median eminence of the hypothalamus, and these play the principal role in PRL regulation (1, 3). In addition to dopamine, regulation of PRL release involves a number of other factors, including opiate peptides, which stimulate PRL secretion, at least in part, by inhibiting TIDA neuronal activity (1).

Orphanin FQ/nociceptin (OFQ/N) is a heptadecapeptide that exhibits high amino acid sequence homology to the classic endogenous opiates, especially dynorphin (4, 5). However, OFQ/N lacks the N-terminal region necessary to bind to the classic opiate receptors, µ, {delta}, or {kappa}, and binds to its own unique receptor, opioid receptor-like-1 (ORL-1) (4, 5); this receptor does not bind any of the classic opiates (6). We have previously reported that OFQ/N administration stimulates PRL secretion in both male and female rats (7), and this effect was not blocked by naloxone, indicating it was not mediated by the classic opiate receptors (8). In situ hybridization and immunocytochemical studies have revealed that the OFQ/N peptide and its mRNA are localized throughout the hypothalamus, particularly in the arcuate nucleus (9). High levels of OFQ/N receptor mRNA have also been localized in the arcuate nucleus (10) (reviewed in Ref. 11). These results provide anatomic evidence to support the hypothesis that OFQ/N, like the other opiates, inhibits TIDA neuronal activity, thus stimulating prolactin release. Indeed, Shieh and Pan, (12) reported that OFQ/N administration produced a decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence of the hypothalamus in ovariectomized rats.

One limitation to elucidating the physiological significance and pharmacological specificity of OFQ/N's effects has been the lack of availability of a specific ORL-1 antagonist. Although [Phe1{psi}(CH2-NH)Gly2]NC(1–13)NH2 acted as a selective OFQ/N antagonist in a number of assays (13, 14, 15, 16, 17, 18), results from our laboratory (8) support other studies demonstrating that this drug acts as an OFQ/N agonist (19, 20, 21, 22, 23, 24, 25, 26). Similarly, acetyl-RYYRIK-NH2, a hexapeptide reported to antagonize the stimulation of [35S]GTP{gamma}S binding to G proteins in rat brain membranes (27), not only failed to block the PRL secretory response to OFQ/N but also acted as an agonist (28). In vivo agonist activity of acetyl-RYYRIK-NH2 has also been reported by others (29, 30, 31).

The homology between the other opiate peptides and OFQ/N, as well as between their receptors, coupled with the localization of OFQ/N (10, 32, 33) (see Refs. 34 and 35 for reviews) and its receptor (9, 36) (see Refs. 34 and 35 for reviews) in the hypothalamus support a neuroendocrine role for OFQ/N. The objectives of this study were 1) to determine whether OFQ/N stimulated PRL secretion via actions on the ORL-1 receptor by blocking the receptor with a reported, specific OFQ/N receptor antagonist, (1-[3R,4R)-1-(cyclooctylmethyl)-3-(hydroxymethyl) peperidin-4-yl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) [compound B (Comp B)] (37), and by blocking OFQ/N receptor synthesis with antisense oligonucleotides; 2) to carefully examine the time course of the PRL secretory response to OFQ/N and to determine whether TIDA neuronal activity plays a role in mediating the PRL increase; and 3) to determine the involvement of OFQ/N in mediating the important and potent physiological response of PRL to suckling by blocking the OFQ/N receptor pharmacologically with Comp B. Results indicate that OFQ/N stimulates PRL secretion by rapidly and transiently inhibiting TIDA neurons and that OFQ/N is involved in the PRL secretory response to suckling.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals
Experiments were performed using female Sprague Dawley rats (200–225 g) in the diestrous stage of the estrous cycle or primiparous females between d 7 and 10 postpartum (lactation study). Experiments were performed between 0830 and 1000 h to minimize the impact of any diurnal PRL secretion. Animals were housed under conditions of controlled lighting (12 h light and 12 h dark; lights on at 0600 h) and temperature (21 C) with food and water provided ad libitum. All animal experimental protocols were approved by the Miami University Institutional Animal Care and Use Committee.

OFQ/N specificity
To determine the specificity of the PRL secretory response to OFQ/N, virgin, female rats were implanted with chronic intracerebroventricular (icv) cannulations into the right lateral ventricle under ketamine (Ketaset, 80 mg/kg, im; Fort Dodge Laboratories, Inc., Fort Dodge, IA) and xylazine (14 mg/kg, im; Rugby Laboratories, Inc. Rockville Centre, NY) anesthesia, following the coordinate system of Pellegrino et al. (38), as previously described (39). After surgery, females were housed one per cage and were subjected to daily vaginal smears; only rats exhibiting two consecutive estrous cycles were used in the diestrous stage. On the day of the experiment, animals were pretreated with 0.1 or 1.0 µg Comp B (in 5-µl volume, icv), a purported specific ORL-1 receptor antagonist (37) (generously provided by T. Satoh, Banyu Pharmaceuticals, Co., Ltd., Tsukuba-city, Japan). Ten minutes later, OFQ/N (55 pmol, 5 µl, icv; Sigma Chemical Co., St. Louis, MO) was injected. An initial blood sample was withdrawn immediately before Comp B administration. Additional samples were withdrawn immediately before and 10, 20, 30, and 60 min after the OFQ/N administration.

A second approach was used to demonstrate that OFQ/N mediated its effects on PRL secretion through actions on the ORL-1 receptor. Separate groups of animals were pretreated with antisense oligonucleotide sequences to one of the three exons of the ORL-1 receptor. The control animals were pretreated with a missense sequence for exon 3 following the protocol described by Leventhal et al. (40). Briefly, the oligonucleotide sequences (2 µl, icv) (Table 1Go) (Invitrogen Life Technologies, Inc., Grand Island, NY) were injected on d 1, 3, and 5, and experiments were performed on d 6. On the day of the experiment, all animals received OFQ/N (55 pmol, 5 µl icv). A separate group of animals was tested for their response to OFQ/N only. Blood samples were withdrawn immediately before and 10, 20, 30, and 60 min after the OFQ/N.


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  		TABLE 1. Oligonucleotide sequences used to block OFQ/N receptor translation (40 )

 
Serial blood samples were withdrawn into heparinized (1000 U/ml) syringes and replaced with an equal volume of sterile, heparinized saline (40 U/ml). Blood samples were transferred into heparinized tubes and centrifuged (1000 x g), and the plasma was collected. Plasma was stored frozen at –20 C until hormone concentrations were determined in aliquots of the samples by RIA. At the conclusion of the experiment, proper cannula placement was visually confirmed by the presence of 0.1% toluidine blue in the ventricular system.

Role of OFQ/N during lactation
A potential physiological role for OFQ/N in the regulation of PRL secretion was examined by determining the effects of Comp B on the suckling-induced PRL increase. Females received icv cannulations on d 2 postpartum, and litters were culled to eight pups on the day of this surgery. After at least a 5-d recovery period and 1 d before being used in an experiment, animals were implanted with an iv cannula into the left jugular vein under isoflurane (Abbott Laboratories, North Chicago, IL) anesthesia as previously described (39, 41, 42). On the day of the experiment, postpartum females (d 7–10 of lactation) were separated from their pups for 6 h to ensure a robust suckling response (43). After the 6 h of separation, dams were injected with 0.1 or 1.0 µg Comp B (5 µl, icv) or saline (control). Ten minutes after injection, an initial blood sample was withdrawn from the dams. Dams were returned to their pups, and the suckling period was recorded from the time when at least four pups were suckling (43). Additional blood samples were withdrawn after 5, 10, 15, and 30 min of suckling.

Neurochemical studies
The effects of OFQ/N administration on TIDA, THDA, and PHDA neuronal activity were examined by measuring the ratio of DOPAC/dopamine in the median eminence and neurointermediate lobe (reviewed in Refs. 44 and 45) at 1 and 3 min after administration of the minimum stimulatory dose of OFQ/N (55 pmol, 5 µl, icv) (7) or saline. Animals were killed by rapid decapitation. Trunk blood was collected and plasma PRL levels were measured by RIA. The brains were rapidly removed and placed in ice-cold saline. The median eminence was quickly dissected following the guidelines of Palkovits and Brownstein (46), transferred to a 1.5-ml Eppendorf tube, and frozen in liquid nitrogen. The neurointermediate lobe was removed from the anterior lobe of the pituitary and transferred to a separate 1.5-ml Eppendorf tube and frozen on liquid nitrogen. All tissue was stored at –80 C until assayed.

Detection of amines was as previously described (47). Briefly, microdissected tissue was placed in 100 µl (median eminence) or 50 µl (neurointermediate lobe) catecholamine buffer [0.2 mM EDTA (disodium), 50 mM NaH2PO4 (monobasic), and 1.0 mM heptane sulfonic acid] and sonicated on ice for 1–2 sec. The tissue was centrifuged (10,000 x g) for 5 min at 4 C. An aliquot of the supernatant was used to determine the concentration of dopamine and DOPAC by HPLC coupled to coulochemical detection. Samples were injected onto a C-18, 3-µm, reversed-phase column (Varian, Walnut Creek, CA). Column effluent was monitored by a coulometric detector (ESA, Chelmsford, MA). The first electrode was set at a potential of –175 mV, the second electrode was set at a potential of +175 mV, and the guard cell was set at +250 mV. The lower limit of detection was 25 pg for dopamine and DOPAC. A mobile phase consisting of 93% catecholamine buffer and 7% methanol was pumped through a Waters 2695 separations module at a flow rate of 1 ml/min, maintaining column pressure at 3000 {psi}. Chromatographic data were collected on Waters Millennium Chromatography Manager Software (Waters, Milford, MA), and peak heights of unknowns were calculated based on dopamine or DOPAC standards. The tissue pellet was solubilized in 1.0 N NaOH and assayed for protein (48). Amine concentrations are expressed in nanograms per milligram protein.

Hormone assay
Plasma PRL concentrations were measured in duplicate samples by double-antibody RIA using reagents purchased from the National Hormone and Peptide Program and Dr. A. F. Parlow. Plasma PRL concentrations were expressed as nanogram equivalents of the reference preparation RP-3. The lower limit of detection was 0.8 ng/ml, and the upper detection limit was 400 ng/ml. All samples from a single study were included in one RIA, and the intraasay coefficient of variation was 5%.

Statistical analysis
All statistical analyses were performed using Windows version 8 SAS software. The probability of a type 1 error was held at 0.05 within any set of comparisons in each data set. DOPAC/dopamine ratios were analyzed using a two-sample t test with no assumption of equal variance. All hormone data were tested for normality and, except for the PRL response to suckling (see Fig. 4Go), data were log transformed to achieve normality. A one-tailed, two-sample t test was performed to determine the effects of OFQ/N at 1 and 3 min after OFQ/N administration (see Fig. 1BGo). The effects of Comp B on the PRL secretory response to OFQ/N (see Fig. 2Go) were analyzed by a paired t test to determine the effects of Comp B pretreatment within a group, and by a two-sample t test to determine the difference between the control group and the 0.1 or 1.0 µg Comp B pretreated group. All other hormone data were analyzed by repeated-measures ANOVA.


Figure 4
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  		FIG. 4. The effects of pretreatment with saline (control) or 1 or 10 µg Comp B (5 µl, icv) on the suckling-induced PRL secretory response. After 6 h of separation from their pups, postpartum dams (d 7–10) were injected with 1.0 or 10 µg Comp B (5 µl, icv) or saline (control). Ten minutes after Comp B injection, an initial blood sample was withdrawn from the dams (sample 1). Dams were returned to their pups, and the suckling period was recorded from the time when at least four pups were suckling. Additional blood samples were withdrawn after 5, 10, 15, and 30 min of suckling (samples 2–5). Suckling produced a significant increase in PRL levels (P < 0.0001) for the entire duration of the suckling bout. Both doses of Comp B significantly blocked the PRL secretory response to suckling at all sampling times. *, Significantly different from basal levels (sample 1), P < 0.001; {dagger}, significantly different from saline controls at the same sample time, P < 0.0005.

 

Figure 1
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  		FIG. 1. A, The effect of saline (control) or 55 pmol OFQ/N (5 µl, icv) on the activity of the TIDA neurons in diestrous female rats. Animals were killed 1 or 3 min after injection. There was no significant difference between control levels at 1 min (n = 6) or 3 min (n = 5) after OFQ/N injection, so these values were pooled. OFQ/N produced a significant decrease in the DOPAC/dopamine (DA) ratio in the median eminence by 1 min (*, P < 0.001), but activity returned to control levels by 3 min. B, The PRL secretory response to saline (control) or 55 pmol OFQ/N (5 µl, icv). Diestrous females were injected with saline or OFQ/N and killed 1 or 3 min later. Although PRL levels were not affected by OFQ/N administration 1 min after the injection, PRL levels were significantly elevated by 3 min (*, P < 0.0001).

 

Figure 2
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  		FIG. 2. The effects of pretreatment with saline (control) or 0.1 or 1.0 µg Comp B (5 µl, icv) on the OFQ/N-induced PRL secretory response in diestrous females. The initial blood sample was taken before any drug administration (–12 min). Immediately after this first blood sample was taken, animals were injected with Comp B or saline (arrow). Ten minutes later, a second blood sample was withdrawn (–1 min). Immediately after this sample, animals were injected with 55 pmol OFQ/N (arrow). Additional blood samples were taken 10, 20, 30, and 60 min after the OFQ/N injection. OFQ/N (55 pmol) produced a significant increase in female rats pretreated with either 0.1 or 1.0 µg Comp B, although the response was significantly attenuated compared with saline-pretreated controls. *, Significantly different from preinjection levels (at –1 min) at P = 0.002 (0.1-µg dose) and P < 0.001 (1.0-µg dose); {dagger}, significantly different from saline/OFQ/N at the same time at P = 0.009 (0.1-µg dose) and P < 0.001 (1.0-µg dose).

 

   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
OFQ/N Effects on TIDA neurons
OFQ/N produced a significant decrease in TIDA neuronal activity in female rats at 1 min after OFQ/N administration (P < 0.001) (Fig. 1AGo), but PRL levels were not elevated at this time (Fig. 1BGo). By 3 min, TIDA neuronal activity returned to control levels, but PRL levels were significantly elevated at this time (P < 0.001) (Fig. 1BGo), indicating that the TIDA neuronal inhibition preceded the PRL secretory response. Determination of DOPAC/dopamine levels in the neurointermediate lobe revealed that OFQ/N administration did not affect the THDA or PHDA neurons (data not shown).

OFQ/N receptor specificity
To determine the specificity of the PRL secretory response to OFQ/N, we pretreated the animals with Comp B, a purported specific ORL-1 receptor antagonist (37). Although OFQ/N produced a significant increase in circulating PRL levels in animals pretreated with either 0.1 µg (P = 0.002) or 1.0 µg (P < 0.001) Comp B, the response was significantly attenuated compared with saline-pretreated controls (P = 0.009 or 0.001 after the 0.1- or 1.0-µg dose, respectively) (Fig. 2Go). To further demonstrate specificity of the OFQ/N-induced PRL increase, animals were pretreated with antisense oligonucleotides to the OFQ/N receptor (41). Pretreatment with antisense targeted against exons 1 or 2 of the receptor blocked the OFQ/N-induced PRL response (P < 0.001), whereas the antisense targeting exon 3 as well as the missense sequence did not block the stimulatory effects of OFQ/N on PRL release (Fig. 3Go).


Figure 3
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  		FIG. 3. The effects of pretreatment with a missense oligonucleotide sequence or with antisense oligonucleotides targeted against exon 1, 2, or 3 of the OFQ/N receptor on the PRL response to OFQ/N in diestrous female rats. Oligonucleotide sequences (2 µl, icv) (Table 1Go) were injected on d 1, 3, and 5, and experiments were performed on d 6. On the day of the experiment, all animals received OFQ/N (55 pmol, 5 µl icv), including a group of animals that did not receive any pretreatment (OFQ/N, dashed line). Blood samples were withdrawn immediately before and 10, 20, 30, and 60 min after the OFQ/N injection. Pretreatment with antisense targeted against exon 1 or 2 of the receptor blocked the OFQ/N-induced PRL response, but antisense targeting exon 3 and the missense sequence did not block the stimulatory effects of OFQ/N on PRL release. *, Significantly different from basal levels at time 0, P < 0.001; {dagger}, significantly different from PRL levels in animals pretreated with missense or with antisense against exon 3, P < 0.001.

 
OFQ/N involvement in the suckling-induced PRL response
To demonstrate the potential physiological role of OFQ/N, the effect of Comp B pretreatment on the suckling-induced PRL secretory response was determined (Fig. 4Go). Suckling produced a robust, significant increase in PRL levels (P < 0.0001). Both doses of Comp B significantly reduced the PRL secretory response to suckling for the duration of the suckling period (all P values < 0.0005), indicating that endogenous OFQ/N is important in the suckling-induced PRL response.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The results of this study demonstrate, for the first time, that TIDA neuronal inhibition follows a time course consistent with mediating the PRL response to OFQ/N indicating that OFQ/N, like the other opiates, inhibits TIDA neuronal activity, at least transiently, to initiate the PRL secretory response. Furthermore, we demonstrated that (1-[3R,4R)-1-(cyclooctylmethyl)-3-(hydroxymethyl) peperidin-4-yl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) (Comp B) was effective in blocking the PRL secretory response to OFQ/N administration. This is the first purported OFQ/N antagonist (37) that has been effective in blocking the stimulatory effects of OFQ/N on PRL release. Additional evidence that Comp B is an effective OFQ/N antagonist was recently provided by Trapella et al. (49) who synthesized and characterized effective analogs of this drug. However, it must be noted that Koizumi et al. (50) reported that Comp B induced mesolimbic dopamine release in mice that was not mediated through the ORL-1 receptor. Previous work from our laboratory indicated that both [Phe1{psi}(CH2-NH)Gly2]NC(1–13)NH2 (13, 14, 15, 16, 17, 18) and acetyl-RYYRIK-NH2 (27), drugs reported to act as OFQ/N antagonists, acted as agonists and stimulated PRL secretion (8, 28). In contrast, Comp B not only blocked the PRL secretory response to OFQ/N administration but also blocked the suckling-induced PRL increase. This strongly indicates that OFQ/N, like the other opiates (43, 47) (see Ref. 1 for review), plays a physiological role in regulating PRL secretion. Finally, our results confirm that OFQ/N does indeed act through its own specific receptor because antisense nucleotide sequences directed against functional portions of the OFQ/N receptor also blocked the PRL secretory response to OFQ/N.

PRL secretion is a complex process and is regulated by a number of hypothalamic and systemic factors (see Refs. 1 and 3 for review). However, the TIDA neurons are primary inhibitors of PRL secretion, and these neurons are inhibited, even if only transiently, when PRL release is increased (for review see Refs. 1 and 3). Our results indicate that OFQ/N rapidly and transiently inhibits the TIDA neurons and that this inhibition precedes the increase in PRL. Interestingly, TIDA neuronal activity returns to control levels by 3 min, a time at which PRL levels are starting to increase. Indeed, when TIDA neuronal activity was measured at 10 min, when the PRL increase was at its peak, TIDA neurons were not inhibited (51). Furthermore, PRL levels remain elevated for 20–30 min (7, 8, 51), even though TIDA neuronal activity is no longer inhibited. Taken together, these results suggest that inhibition of dopamine is an initial mechanism of OFQ/N and the sustained PRL response is dependent on other, nondopaminergic mechanisms. Netti et al. (52) provided additional support that dopaminergic inhibition is important in mediating the OFQ/N-induced PRL increase. Male rats that were depleted of hypothalamic catecholamines still had increased PRL secretion after OFQ/N administration, suggesting PRL-releasing factors were involved. The releasing factors responsible for the sustained PRL increase are not known, but serotonin antagonists did not inhibit the PRL secretory response to OFQ/N (51), indicating that serotonin is not involved. A number of other hypothalamic factors are known to stimulate PRL secretion (see Ref. 1 for review) and could certainly be involved in maintaining the PRL increase. For example, histamine is involved in mediating the morphine-induced PRL increase in male rats (53, 54), and vasoactive intestinal polypeptide stimulation of PRL release was blocked by naloxone (55), suggesting that these releasing factors are also involved in mediating opiate action on PRL secretion.

The time course of the TIDA neuronal response was very rapid; i.e. inhibition occurred by 1 min. By 3 min, TIDA neuronal activity was not different from control levels. Shieh and Pan (12) also reported a significant inhibitory effect of OFQ/N on DOPAC accumulation in the median eminence, but they used ovariectomized, estrogen-replaced female rats, and they measured this decrease after administration of much higher doses of OFQ/N, i.e. more than 1800 times higher than the dose we used in this study. They also reported PRL levels increased at 60 min only and the magnitude of the response was much lower than reported here and in our previous studies (7, 8). One possible explanation for the discrepancy between our results and theirs is that their animals were ovariectomized for 1 wk before estrogen replacement. We have previously reported that the magnitude of the response in intact, cycling females is much greater than in males (7), and this appears to be due to effects mediated by estrogen (Callahan, P., unpublished). It is possible that the 1 wk of estrogen deprivation altered the sensitivity of the TIDA neurons and/or the anterior pituitary gland, causing a less robust PRL secretory response to OFQ/N.

OFQ/N is the endogenous ligand for the opioid-like orphan receptor, ORL-1 (4, 5, 6, 56), and high levels of OFQ/N receptor mRNA have been localized in the arcuate nucleus (10) (see Ref. 11 for review). Blocking the ORL-1 receptor subtype with either dose of Comp B significantly reduced the PRL secretory response to OFQ/N and abolished the suckling-induced PRL increase. Similarly, administration of antisense nucleotide sequences to the ORL-1 receptor abolished the PRL secretory response to OFQ/N. The antisense probes used in this study have been used to block OFQ/N-induced hyperphagia in male rats (40). Although we expected all the antisense sequences to effectively block the stimulatory effect of OFQ/N, this was not the case. Interestingly, antisense oligonucleotides targeting exons 2 and 3 of the ORL-1 receptor antagonized OFQ/N-mediated analgesia but had no effect on OFQ/N-induced hyperphagia, and antisense targeting exon 1 did not block OFQ/N-induced analgesia but did block hyperalgesia induced by OFQ/N (57). Supporting our results, Shieh and Pan (12) reported antagonism of the OFQ/N-induced PRL increase after treatment with antisense to exon 3, but they did not inject any other antisense sequences. One possibility for the differences in response to the different antisense oligonucleotide pretreatments is that there are splice variants of the ORL-1 receptor. One of the splice variants in the rat contains an 81-bp insertion with a stop codon that prevents translation of exon 3 but may still encode a functional, truncated receptor (see Ref. 58 for review). Animals pretreated with antisense targeting exon 3 still responded to OFQ/N administration, indicating that a functional ORL-1 receptor was likely still synthesized.

Finally, these results provide evidence that OFQ/N, like the other endogenous opiates (43, 47), plays a physiologically significant role in PRL regulation because Comp B blocked the suckling-induced PRL increase. Suckling, the most potent physiological stimulus for PRL secretion in mammalian species, is associated with a decrease in TIDA neuronal activity (see Ref. 1 for review). Therefore, Comp B may prevent the suckling-induced inhibition in TIDA neurons, and this possibility is currently being investigated. Interestingly, blocking any of the endogenous opiates abolished the suckling-induced PRL increase (43, 47). Our hypothesis is that the endogenous opiates elicit effects on TIDA neurons as well as other neurons that regulate PRL secretion during lactation. In support of this hypothesis, Soaje et al. (59) demonstrated an interaction among endogenous opioids, serotonin, and {gamma}-aminobutyric acid at the end of pregnancy in rats. Although the mechanisms regulating PRL release during lactation are not known (reviewed in Ref. 1), it is clear based on this and previous studies (43, 47) (reviewed in Ref. 1) that the endogenous opiates are involved in mediating the suckling-induced PRL increase and that TIDA neuronal inhibition is one mechanism through which the PRL increase occurs. Several releasing factors are also involved in the PRL response to suckling, e.g. vasopressin, oxytocin, TRH, and/or another unidentified PRL-releasing factor, but the interaction of the opiates with these releasing factors during lactation remains largely unknown (reviewed in Ref. 1).

In conclusion, OFQ/N is a potent stimulus for PRL secretion in female rats, and it mediates this effect by rapid and transient inhibition of TIDA neuronal activity. Furthermore, OFQ/N plays a physiologically significant role in the regulation of PRL secretion during lactation, and it mediates its effects via actions at the ORL-1 receptor subtype.


   Acknowledgments
 
We thank Ms. Laura Howard for technical review of the manuscript.


   Footnotes
 
This work was supported by National Institutes of Health Grant HD 46479 to J.J. and P.C.

Disclosure summary: all authors have nothing to declare.

First Published Online August 3, 2006

Abbreviations: Comp B, Compound B; DOPAC, 3,4-dihydroxyphenylacetic acid; icv, intracerebroventricular; OFQ/N, orphanin FQ/nociceptin; ORL-1, opioid receptor-like-1; PHDA, periventricular hypothalamic dopaminergic; PRL, prolactin; THDA, tuberohypophyseal dopaminergic; TIDA, tuberoinfundibular dopaminergic.

Received May 26, 2006.

Accepted for publication July 24, 2006.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Freeman ME, Kanyicska B, Lerant AA, Nagy GM 2000 Prolactin: structure, function, and regulation of secretion. Physiol Rev 80:1523–1631[Abstract/Free Full Text]
  2. Goffin V, Binart N, Touraine P, Kelly PA 2002 Prolactin: the new biology of an old hormone. Ann Rev Physiol 64:47–67[CrossRef][Medline]
  3. Ben-Jonathan N, Hnasko R 2001 Dopamine as a prolactin (PRL) inhibitor. Endocr Rev 22:724–763[Abstract/Free Full Text]
  4. Meunier JC, Mollereau C, Tool L, Suaudeau C, Moisand C, Alvinerie P, Butour JL, Guillemot JC, Ferrara P, Monsarrat B, Mazarguil H, Vassart G, Permenteir M, Constentin K 1995 Isolation and structure of the endogenous agonist of the opioid receptor-like ORL1 receptor. Nature 377:532–535[CrossRef][Medline]
  5. Reinscheid RK, Nothacker HP, Courson A, Ardati A, Henningsen RA, Bunzow JR, Grandy DK, Langen H, Monsma FJ, Civelli O 1995 Orphanin FQ: a neuropeptide that activates an opioid-like G-protein coupled receptor. Sci 270:792–794[Abstract/Free Full Text]
  6. Mollereau C, Parmentier M, Mailleux P, Butour JL, Moisand C, Chalon P, Caput D, Vassart G, Meunier JC 1994 ORL1, a novel member of the opioid receptor family. FEBS Lett 341:33–38[CrossRef][Medline]
  7. Bryant W, Janik J, Baumann M, Callahan P 1998 Orphanin FQ stimulates prolactin and growth hormone release in male and female rats. Brain Res 807:228–233[CrossRef][Medline]
  8. Bryant W, Callahan P, Murphree E, Janik J 2002 [Phe1{psi}(CH2-NH)Gly2]NC(1–13)NH2 does not antagonize orphanin FQ/nociceptin-induced prolactin release. Brain Res Bull 57:695–703[CrossRef][Medline]
  9. Neal CR, Mansour A, Reinscheid R, Nothacker HP, Civelli O, Akil H, Watson SJ 1999b Opioid receptor-like (ORL1) receptor distribution in the rat central nervous system: comparison of ORL1 receptor mRNA expression with 125I-[14Tyr]-orphanin FQ binding. J Comp Neurol 412:563–605
  10. Neal CR, Mansour A, Reinscheid R, Nothacker HP, Civelli O, Akil H, Watson SJ 1999 Localization of orphanin FQ (nociceptin) peptide and messenger RNA in the central nervous system of the rat. J Comp Neurol 406:503–547[CrossRef][Medline]
  11. Mollereau C, Mouledous L 2000 Tissue distribution of the opioid receptor-like (ORL1) receptor. Peptides 21:907–917[CrossRef][Medline]
  12. Shieh KR, Pan JT 2001 Effects of orphanin FQ on central dopaminergic neuronal activities and prolactin secretion. Am J Physiol Regul Integr Comp Physiol 280:R705–R712
  13. Calo G, Guerrini R, Bigoni R, Rizzi A, Biannchi C, Regoli D, Salvadori S 1998 Structure-activity study of the nociceptin (1–13)-NH2 terminal tetrapeptide and discovery of a nociceptin receptor antagonist. J Med Chem 41:3360–3366[CrossRef][Medline]
  14. Chu SP, Xu NS, Li P, Wang JQ 1999 The nociceptin receptor-mediated inhibition of the rat rostral ventrolateral medulla neurons in vitro. Eur J Pharmacol 364:49–53[CrossRef][Medline]
  15. Guerrini R, Calo G, Rizzi A, Bigoni R, Bianchi C, Salvadori S, Regoli D 1998 A new selective antagonist of nociceptin receptor. Br J Pharmacol 123:163–165[CrossRef][Medline]
  16. Madeddu P, Salis MB, Milia AF, Emanueli C, Guerrini R, Regoli D, Calo G 1999 Cardiovascular effects of nociceptin in unanesthetized mice. Hypertension 33:914–919[Abstract/Free Full Text]
  17. Meis S, Pape HC 1998 Postsynaptic mechanisms underlying responsiveness of amygdaloid neurons to nociceptin/orphanin FQ. J Neurosci 18:8133–8144[Abstract/Free Full Text]
  18. Varani K, Calo G, Rizzi A, Merighi S, Toth G, Guerrini R, Salvadori S, Borea PA, Regoli D 1998 Nociceptin receptor binding in mouse forebrain membranes: thermodynamic characteristics and structure activity relationships. Br J Pharmacol 125:1485–1490[CrossRef][Medline]
  19. Carpenter KJ, Dickenson AH 1998 Evidence that [Phe1{psi}(CH2-NH)Gly2] nociceptin-1–13-NH2, a peripheral ORL-1 receptor antagonists, acts as an agonist in the rat spinal cord. Br J Pharmacol 125:949–951[CrossRef][Medline]
  20. Chiou LC 1999 [Phe1{psi}(CH2-NH)Gly2]-nociceptin-(1–13)NH2 activation of an inward rectifier as a partial agonist of ORL1 receptors in rat periaqueductal gray. Br J Pharmacol 128:103–107[CrossRef][Medline]
  21. Grisel JE, Farrier DE, Wilson SG, Mogil JS 1998 [Phe1{Psi}(CH2-NH)Gly2]NC(1–13)NH2 acts as an agonist of the orphanin FQ/nociceptin receptor in vivo. Eur J Pharmacol 357:R1–R3
  22. Kapusta DR, Chang JK, Kenigs VA 1999 Central administration of [Phe1{psi}(CH2-NH)Gly2]-nociceptin-(1–13)NH2 and orphanin FQ/nociceptin (OFQ/N) produce similar cardiovascular and renal responses in conscious rats. J Pharmacol Exp Ther 289:173–180[Abstract/Free Full Text]
  23. Okawa H, Nicol B, Bigoni R, Hirst RA, Calo G, Guerrini R, Rowbotham DJ, Smart D, McKnight AT, Lambert DG 1999 Comparison of the effects of [Phe1{psi}(CH2-NH)Gly2]-nociceptin-(1–13)NH2 in rat brain, rat vas deferens and CHO cells expressing recombinant human nociceptin receptors. Br J Pharmacol 127:123–130[CrossRef][Medline]
  24. Schlicker E, Wethwein S, Kathmann M, Bauer U 1998 Nociceptin inhibits noradrenaline release in the mouse brain cortex via presynaptic ORL1 receptors. Naunyn-Schmiedebergs Arch Pharmacol 358:418–422[CrossRef][Medline]
  25. Xu ES, Wiesenfeld-Hallin A, Xu XJ 1998 [Phe1{Psi}(CH2-NH)Gly2]NC(1–13)NH2, a proposed antagonist of the nociceptin receptor, is a potent and stable agonist in the rat spinal cord. Neurosci Lett 249:127–130[CrossRef][Medline]
  26. Yakimova KS, Pierau RK 1999 Nociceptin orphanin FQ: effects on thermoregulation in rats. Methods Find Exp Clin Pharmacol 21:345–352[CrossRef][Medline]
  27. Berger H, Albrecht E, Wallukat G, M Bienart M 1999 Antagonism by acetyl-RYYRIK-NH2 of G protein activation in rat brain preparations and of chronotropic effect on rat cardiomyocytes evoked by nociceptin/orphanin FQ. Br J Pharm 126:555–558[CrossRef][Medline]
  28. Janik J, Krupica T, Dengler L, Murphree E, Callahan P 2003 Acetyl-RYYRIK-NH2, a purported orphanin FQ antagonist does not block the orphanin FQ induced prolactin secretory response in female rats. Neurosci Lett 345:149–152[CrossRef][Medline]
  29. Malinowska B, Kozlowska H, Berger H, Schlicker E 2000 Acetyl-RYYRIK-NH2 is a highly efficacious OP4 receptor agonist in the cardiovascular system of anesthetized rats. Peptides 21:1875–1880[CrossRef][Medline]
  30. Berger H, Bigoni R, Albrecht E, Richter RM, Krause M, Bienart M, Calo G 2000 The nociceptin/orphanin FQ receptor ligand acetyl-RYYRIK-amide exhibits antagonistic and agonistic properties. Peptides 21:1131–1139[CrossRef][Medline]
  31. Berger H, Calo G, Albrecht E, Guerrini R, Bienert M 2000b [NPhe1]NC(1–13)NH2 selectively antagonizes nociceptin/orphanin FQ-stimulated G protein activation in rat brain. J Pharmacol Exp Ther 294:428–433
  32. Mollereau C, Simon MJ, Soularue P, Liners F, Vassart G, Meunier JC, Parmetier M 1996 Structure, tissue distribution, and chromosomal localization of the prepronociceptin gene. Proc Natl Acad Sci USA 93:8666–8670[Abstract/Free Full Text]
  33. Nothacker HP, Reinscheid RK, Mansour A, Henningsen RA, Ardati A, Monsma FJ, Watson SJ, Civelli O 1996 Primary structure and tissue distribution of the orphanin FQ precursor. Proc Natl Acad Sci USA 93:8677–8682[Abstract/Free Full Text]
  34. Henderson G, McKnight AT 1997 The orphan opioid receptor and its endogenous ligand-nociceptin/orphanin FQ. Trends Pharmacol Sci 18:293–300[Medline]
  35. Reinscheid RK, Nothacker HP, Civelli O 2000 The orphanin FQ/nociceptin gene: structure, tissue distribution of expression and functional implications obtained from knockout mice. Peptides 21:901–906[CrossRef][Medline]
  36. Dooley CT, Houghten RA 1996 Orphanin FQ: receptor binding and analog structure activity relationships in rat brain. Life Sci 59:23–29
  37. Kawamoto H, Ozaki S, Itoh Y, Miyaji M, Arai S, Nakashima H, Kato T, Ohta H, Iwasawa Y 1999 Discovery of the first potent and selective small molecule opioid receptor-like (ORL-1) antagonist: (1-[3R,4R)-1-(cyclooctylmethyl)-3-(hydroxymethyl)peperidin-4-yl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) (J-113397). J Med Chem 42:5061–5063[CrossRef][Medline]
  38. Pellegrino LJ, Pellegrino AS, Cushman AJ 1979 A stereotaxic atlas of the rat brain. 2nd ed. New York: Plenum Press
  39. Kehoe L, Parman R, Janik J, Callahan P 1993 Opiate receptor subtype involvement in the stimulation of prolactin release by ß-endorphin in female rats. Neuroendocrinol 57:875–883[Medline]
  40. Leventhal L, Mathis JP, Rossi GC, Pasternak GW, Bodnar RJ 1998 Orphan opioid receptor antisense probe blocks orphanin FQ-induced hyperphagia. Eur J Pharmacol 349:R1–R3
  41. Janik J, Callahan P, Rabii J 1992 The role of the µ1 opiate receptor subtype in the regulation of prolactin and growth hormone secretion by ß-endorphin in female rats: studies with naloxonazine. J Neuroendocrinol 4:701–708[CrossRef]
  42. Callahan P, Janik J, Grandison L, Rabii J 1988 Morphine does not stimulate prolactin release during lactation. Brain Res 442:214–222[CrossRef][Medline]
  43. Jaworski RP, Callahan P, Janik J 1997 Immunoneutralization of ß-endorphin blocks prolactin release during suckling without affecting tuberoinfundibular dopaminergic neural activity. Life Sci 61:1301–1311[CrossRef][Medline]
  44. Moore KE, Lookingland KJ 1995 Dopaminergic neuronal systems in the hypothalamus. In: Bloom FE, Kupfer DJ, eds. Psychopharmacology: the fifth generation of progress. New York: Raven Press; 245–256
  45. Lookingland KJ, Moore KE 2006 Functional neuroanatomy of hypothalamic dopaminergic neuroendocrine systems. In: Dimmett SB, Bentivoglio M, Bjorklund A, Hokfelt T, eds. Handbook of chemical neuroanatomy. Vol 21. New York: Elsevier; 433–521
  46. Palkovits M, Brownstein MJ 1988 Maps and guide to microdissection of the rat brain. New York: Elsevier
  47. Callahan P, Klosterman S, Prunty D, Tompkins J, Janik J 2000 Immunoneutralization of endogenous opioid peptides prevents the suckling-induced prolactin increase and the inhibition of tuberoinfundibular dopaminergic neurons. Neuroendocrinology 71:268–276[CrossRef][Medline]
  48. Lowry OH, Rosebrough NJ, Farr AL, Randall R 1951 Protein measurement with the folin phenol reagent. J Biol Chem 193:265–278[Free Full Text]
  49. Trapella C, Guerrini R, Piccagli L, Calo G, Carra G, Spagnolo B, Rubini S, Fanton G, Hebbes C, McDonald J, Lambert DG, Regoli D, Severo S 2006 Identification of an achiral analogue of J-11397 as potent nociceptin/orphanin FQ receptor antagonist. Bioorg Med Chem 14:692–704[CrossRef][Medline]
  50. Koizumi M, Sakoori K, Midorikawa N, Murphy NP 2004 The NOP (ORL1) receptor antagonist compound B stimulates mesolimbic dopamine release and is rewarding in mice by a non-NOP-receptor mediated mechanism. Br J Pharmcol 143:53–62[CrossRef][Medline]
  51. Kraska A, Bryant W, Murphree E, Callahan P, Janik J 2005 Lack of involvement of dopamine and serotonin during orphanin FQ/nociceptin (OFQ/N)-induced prolactin secretory response. Life Sci 77:1465–1479[CrossRef][Medline]
  52. Netti C, Rapetti D, Sibilia V, Pagani F, Pecile A, Guidobono F 2002 Endocrine effects of centrally injected nociceptin in the rat. Brain Res 938:55–61[CrossRef][Medline]
  53. Netti C, Guidobono F, Sibilia V, Cazzamalli E, Villa I, Pecile A 1989 Effects of brain histamine depletion on stimulated prolactin release in rats. Agents Actions 27:117–119[CrossRef][Medline]
  54. Netti C, Guidobono F, Sibilia V, Pagani F, Villa I, Pecile A 1990 A selective role for brain histamine in prolactin release induced by opiates. Agents Actions 30:223–225[CrossRef][Medline]
  55. Kato Y, Iwasaki Y, Iwasaki J, Abe H, Yanaihara N, Imura H 1978 Prolactin release by vasoactive intestinal polypeptide in rats. Endocrinology 103:554–558[Abstract]
  56. Lan WY, Pu L, Ling K, Shao J, Cheng A, Ma L, Pei G 1997 Molecular characterization and functional expression of opioid receptor-like1 receptor. Cell Res 7:69–77[CrossRef][Medline]
  57. King MA, Rossi GC, Chang AH, Williams L, Pasternak GW 1997 Spinal analgesic activity of orphanin FQ/nociceptin and its fragments. Neurosci Lett 223:113–116[CrossRef][Medline]
  58. Mogil JS, Pasternak GW 2001 The molecular and behavioral pharmacology of the orphanin FQ/nociceptin peptide and receptor family. Pharmacol Rev 53:381–415[Abstract/Free Full Text]
  59. Soaje M, Bregonzio C, Caron RW, Deis RP 2004 Neurotransmitters involved in the opioid regulation of prolactin secretion at the end of pregnancy in rats. Neuroendocrinology 80:11–20[CrossRef][Medline]



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C. D. Foradori, M. Amstalden, L. M. Coolen, S. R. Singh, C. J. McManus, R. J. Handa, R. L. Goodman, and M. N. Lehman
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