Amygdalar inputs to ADH-secreting supraoptic neurones in rats

Effects of amygdala stimulation on the discharge activity of antidromically identified supra-optic neurosecretory neurones were studied in male rats anaesthetized with urethane. Stimulation of the medial and the basal amygdala produced excitation or inhibition of discharge activity both in phasically firing ("phasic") and in continuously firing ("continuous") neurones. More "phasic" neurones were excited than were inhibited after medial amygdala stimulation. On the other hand, fewer "continuous" neurones were excited by stimulation of the either amygdala area than were inhibited. This difference of responsiveness between "phasic" and "continuous" neurones is statistically significant. Synaptic inputs to supraoptic neurosecretory neurones after amygdala stimulation were also observed in rats with a lesion of the stria terminalis. Supraoptic nucleus stimulation activated antidromically 14 of the 336 amygdala neurones tested. Since "phasic" neurones have been identified as ADH-secreting neurones, it is concluded that ADH-secreting neurones in the rat supraoptic nucleus receive predominantly excitatory synaptic inputs from the medial amygdala and these amygdalar synaptic inputs are mediated by pathways which are at least in part monosynaptic and are not included in the stria terminalis.