GABAergic Neurotransmission in the Premammillary Nucleus of the Turkey Hypothalamus Regulates Reproductive Seasonality and the Onset of Photorefractoriness.

BACKGROUND/AIMS: Photoperiod is a major environmental cue in temperate-zone birds which synchronizes breeding with the time of year that offers the optimal environment for offspring survival. Despite continued long photoperiods, these birds eventually become refractory to the stimulating photoperiod and their reproductive systems regress. In this study, we characterized the role of γ-aminobutyric acid (GABA)ergic neurotransmission in modulating the response of the premammillary nucleus (PMM) to a gonad stimulatory photoperiod and the onset of photorefractoriness. METHODS AND RESULTS: Bilateral ablation of the PMM blocked the light-induced neuroendocrine response from occurring in photosensitive turkeys. Microarray analyses revealed an increase in GABAergic activity in the PMM of photorefractory birds as opposed to photosensitive ones, and this enhanced GABAergic activity appeared to inhibit the photoperiodic signal. Additionally, GABAA and GABAB receptors were expressed by dopamine-melatonin neurons in the PMM, and the administration of the GABA receptor agonist baclofen blocked the photoperiodic reproductive neuroendocrine responses. CONCLUSIONS: Consistent with the present findings, we propose that the long-sought-after mechanism underlying photorefractoriness is linked to the inhibitory actions of GABA. We suggest that (1) GABAergic interference with photoperiodic entrainment in the PMM initiates the photorefractory state and terminates the annual breeding season in temperate-zone birds, and (2) the PMM is a site of photoreception and photorefractoriness that controls the initiation and termination of avian reproductive seasonality.

[Montirelin hydrate (NS-3), a TRH analog, improved disturbance of consciousness in cats: electroencephalographical studies].

Central effects of montirelin hydrate (NS-3) were electroencephalographically investigated in cats with experimentally induced disturbance of consciousness. All experiments were conducted under the gallamine-immobilized and artificially ventilated acute experimental condition. NS-3 and TRH produced EEG activation in cats with lesions in the midbrain reticular formation in a dose-dependent manner. Similar effects were observed in cats with bilateral lesions of the posterior hypothalamic area. These effects of NS-3 were 30 to 100 times more potent than those of TRH. NS-3 at doses higher than 0.003 mg/kg restored the suppressed EEG dose-dependently in cats with cerebral ischemia produced by clamping the bilateral common carotid arteries and basilar artery. TRH showed no effect at a dose of 10 mg/kg. These results indicate that NS-3 might be an effective drug for treating the disturbance of consciousness.

[Antidiuretic activity of blood and certain approaches to the pharmacologic correction of the hypothalamo-neurohypophyseal system in burn injuries]. / Antidiureticheskaia aktivnost' krovi i nekotorye puti medikamentoznoi korrektsii gipotalamo-neirogipofizarnoi sistemy pri termicheskoi travme.

The time-course of changes in the antidiuretic activity of plasma in response to burn injury has been assayed in intact rabbits and in those with an altered body reactivity induced by a preliminary injury to the anterior and posterior hypothalamus. It was demonstrated that in control animals and in rabbits with an injury to the anterior hypothalamus, the burn led to a phasic activation of the hypothalamo-neurohypophyseal system. In animals with an injury to the posterior hypothalamus, the burn, in contrast, inhibited the activation of the system, while the phasic pattern of the responses remained unchanged. The experiments on rats have shown that the decreased activity of the hypothalamo-neurohypophyseal system induced by the pharmacological blockade of the supraoptic nuclei of the hypothalamus raised the body resistance in burn injury.