This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Adams, V. L. Articles by Lehman, M. N. Search for Related Content PubMed PubMed Citation Articles by Adams, V. L. Articles by Lehman, M. N.

Morphological Plasticity in the Neural Circuitry Responsible for Seasonal Breeding in the Ewe

Departments of Physiology and Pharmacology (V.L.A., R.L.G.) and Neurobiology and Anatomy (A.K.S.), West Virginia University Health Sciences Center, Morgantown, West Virginia 26506; Reproductive Sciences Program (F.J.K.), Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor Michigan 48109; and Department of Anatomy and Cell Biology (L.M.C., M.N.L.), University of Western Ontario, London, Ontario N6A 5C1, Canada

Address all correspondence and requests for reprints to: Dr. Robert L. Goodman, Department of Physiology and Pharmacology, PO Box 9229, West Virginia University, Morgantown, West Virginia. E-mail: bgoodman{at}hsc.wvu.edu.

An increase in the response of GnRH neurons to estrogen negative feedback is responsible for seasonal anestrus in the ewe, but the underlying neural mechanisms remain largely unknown. Neural plasticity may play an important role because the density of synaptic input to GnRH neurons changes with seasons. Moreover, the transition from breeding to anestrous season requires thyroid hormones, which are also required for neuronal development. In the first experiment, we examined whether the decrease in synapses on GnRH neurons is critical for the transition to anestrus by comparing synaptic input in thyroidectomized and thyroid-intact controls, using electron microscopic analysis. Thyroidectomized ewes remained in the breeding season, but the number of synaptic contacts on their GnRH cells was not different from those in thyroid-intact ewes that were anestrus. The next experiment tested whether there was a seasonal change in morphology of the A15 dopaminergic neurons that mediate estrogen negative feedback during anestrus by analyzing synapsin-positive close contacts onto A15 neurons with confocal microscopy. There was a 2-fold increase in these close contacts onto dendrites of A15 neurons in anestrus and a corresponding increase in the length of A15 dendrites at this time of year. The increase in dendritic length was blocked by thyroidectomy, but this procedure did not significantly affect synaptic input to A15 neurons. These results provide initial evidence that the seasonal change in synapses on GnRH neurons is not sufficient for the transition into anestrus but that plasticity of the A15 dopaminergic neurons mediating estrogen negative feedback may contribute to this seasonal alteration.

This article has been cited by other articles:

				S. R. Singh, S. M. Hileman, J. M. Connors, C. J. McManus, L. M. Coolen, M. N. Lehman, and R. L. Goodman Estradiol Negative Feedback Regulation by Glutamatergic Afferents to A15 Dopaminergic Neurons: Variation with Season Endocrinology, October 1, 2009; 150(10): 4663 - 4671. [Abstract] [Full Text] [PDF]

				A. L. Bogusz, S. L. Hardy, M. N. Lehman, J. M. Connors, S. M. Hileman, J. H. Sliwowska, H. J. Billings, C. J. McManus, M. Valent, S. R. Singh, et al. Evidence that {gamma}-Aminobutyric Acid Is Part of the Neural Circuit Mediating Estradiol Negative Feedback in Anestrous Ewes Endocrinology, June 1, 2008; 149(6): 2762 - 2772. [Abstract] [Full Text] [PDF]

				C. J McManus, M. Valent, S. L Hardy, and R. L Goodman Does nitric oxide act in the ventromedial preoptic area to mediate oestrogen negative feedback in the seasonally anoestrous ewe? Reproduction, July 1, 2007; 134(1): 137 - 145. [Abstract] [Full Text] [PDF]

				C. A. Christian and S. M. Moenter Estradiol Induces Diurnal Shifts in GABA Transmission to Gonadotropin-Releasing Hormone Neurons to Provide a Neural Signal for Ovulation J. Neurosci., February 21, 2007; 27(8): 1913 - 1921. [Abstract] [Full Text] [PDF]