The brain stem is essential for mediating energetic response to starvation. Brain stem TSH-releasing hormone (TRH) is synthesized in caudal raphe nuclei innervating brain stem and spinal vagal and sympathetic motor neurons. Intracisternal injection (ic) of a stable TRH analog RX77368 (7.5-25 ng) dose-dependently stimulated solid food intake by 2.4- to 3-fold in freely fed rats, an effect that lasted for 3 h. By contrast, RX77368 at 25 ng injected into the lateral ventricle induced a delayed and insignificant orexigenic effect only in the first hour. In pentobarbital-anesthetized rats, RX77368 (50 ng) ic induced a significant bi-peak increase in serum total ghrelin levels from the basal of 8.7 ± 1.7 ng/ml to 13.4 ± 2.4 ng/ml at 30 min and 14.5 ± 2.0 ng/ml at 90 min, which was prevented by either bilateral vagotomy (-60 min) or atropine pretreatment (2 mg/kg, -30 min) but magnified by bilateral adrenalectomy (-60 min). TRH analog ic-induced food intake in freely fed rats was abolished by either peripheral atropine or ghrelin receptor antagonist (D-Lys-3)-GHRP-6 (10 µmol/kg), or ic Y1 receptor antagonist 122PU91 (10 nmol/5 µl). Brain stem TRH mRNA and TRH receptor 1 mRNA increased by 57-58% and 33-35% in 24-48 h fasted rats and returned to the fed levels after a 3 h re-feeding. Natural food intake in overnight fasted rats was significantly reduced by ic TRH antibody, ic Y1 antagonist, and peripheral atropine. These data establish a physiological role of brain stem TRH in vagal-ghrelin-mediated stimulation of food intake, which involves interaction with brain stem Y1 receptors.