Excitation by dopamine of putative oxytocinergic neurones in the rat supraoptic nucleus in vitro: evidence for two classes of continuously firing neurones.

Neurones from the supraoptic nucleus in the rat hypothalamic slice preparation in vitro have been recorded from using conventional extracellular techniques. Neurones which fired in a slow continuous manner (putative oxytocinergic cells) increased their firing pattern in response to dopamine applied in the perfusate or pressure ejected onto the slice. Of these neurones, 85% were inhibited by spiperone, haloperidol or cis-flupenthixol applied in the bath. A small proportion (approximately 15%) of neurones excited by dopamine (DA) were not affected by these DA antagonists but were inhibited strongly by (+/-)-sulpiride. Similar results were also obtained on a small number of cells recorded from an 'island-slice' preparation, utilized to isolate the observed responses to an area immediately adjacent to the supraoptic nucleus. These results may be relevant to earlier work on in vivo anaesthetized preparations using intracerebroventricular injections of DA and antagonists, and indicate that such substances may act directly on a synapse(s) within the magnocellular nucleus in addition to other possible actions within the neurohypophyseal tract. The differential response to the dopamine antagonists indicate that the majority of continuously firing neurones in the supraoptic nucleus are of the DI receptor class, but the presence of possible D2 receptors on a small proportion of these neurones suggests that a second type of continuously firing neurone may exist in this nucleus.