[Evaluation of perfusion technics of the magnocellular nucleus of the hypothalamus in vitro and in vivo].

In suckled rats, OT necessary for the occurrence of the neurosecretory bursts on OT cells, is probably released inside the magnocellular nuclei. In order to demonstrate this in vivo release and to precise the mechanism involved, perifusions were realized in vivo on lactating rats and in vitro with isolated magnocellular nuclei. In vivo, the push-pull perifusion of a single supraoptic nucleus (SON) was realized simultaneously with the recording of the electrical activity of OT cells in the contralateral nucleus. This would allow to determine the possible relationships between the amount of OT released in the SON and the electrical activity of OT cells (bursting activation during suckling or continuous activation during an hyperosmotic stimulation). Results obtained showed 1) that OT was released in vivo inside the SON, 2) that this release was specifically increased during the milk ejection reflex and 3) that this increase was only detectable inside the SON. However, this technique did not permit to determine either the mechanism of OT release or the neuron elements (perikaryon, dendrites, axon collaterals) responsible for this release. That is for why, in vitro perifusions were undertaken with isolated magnocellular nuclei. The first stage was to determine the stimulus able to induce a reproducible increase of OT release. Among the chemical stimuli (neurotransmitters, K+) only K+ at a 56 mM concentration increased OT release by SON but this increase was small and non significant. Repetitive electrical stimulations with short pulses (0.2 to 5 msec) were ineffective even if the pulse intensity was raised up to 10 mA and the frequency up to 80 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)