[Reaction of the hypothalamic neurosecretory centers in the rat to cooling and the administration of thyroliberin].

Three experiments were performed on Wistar male rats. In experiment N1 rats were maintained at the temperature of +5 degrees C during two hours, resultant in intensity of the thyroliberin synthesis. In test N2 synthetic thyroliberin in a dose of 8 micrograms was injected to intact rats 30 minutes before decapitation to decrease the requirement in the intrinsic hormone synthesis. In test N3 thyroliberin was injected to rats over the cooling process to compensate partially the need in the intrinsic hormone synthesis. The functional condition of the hypothalamic supraoptic-, suprachiasmatic-, paraventricular-, ventromedial and arcuate nuclei (SON, SCN, PVN, VMN, AN) was evaluated by morphometry. SON and SCN remained unchanged under cooling. In both tests thyroliberin injections reduced the nucleoli sizes in the nuclear cells. The AN response was different from that of other centers, i. e. in experiment N1 the AN activity decreased; in tests N2 and N3 the effect of thyroliberin injected was not revealed. The PVN and VMN cell activation was noted in experiment N1, whereas the activity of the same nuclei was markedly lowered in test N2. An increase in the activity of these nuclei in experiment N3 was slightly reduced under exogenous thyroliberin injection. It is suggested that the PVN and VMN synergy plays an essential role in the organism response to the change in the thyroliberin synthesis.