Distribution and projection of single units in the cat preoptic region responding to stimulation of the medial amygdala.

Neuronal responses were recorded extracellularly in the preoptic region of 11 male castrate cats following stimulation in the 'medial' group of amygdalar nuclei (medial, basomedial, basolateral). The latency of responses varied with the site of stimulation and could be explained if connections to the preoptic region were made through both the stria terminalis and the ventral amygdalofugal pathway. Projection of 13% of orthodromically excited preoptic units to the medial basal hypothalamus was established by collision tests following stimulation in these regions. The amygdalar excitation was probably exerted through the amygdalofugal pathway. In 5/6 cats the amygdalar stimulation was successfully used to raise plasma LH levels. In one cat no preoptic units projecting to the medial basal hypothalamus were found and in the cat which failed to increase plasma LH in response to amygdala stimulation, 5 such units were found. We conclude the pathway from the amygdala through the preoptic region to the hypothalamus may not be the way in which amygdalar stimulation affects LH release in the cat. Projection of 10% of orthodromically excited preoptic units in the medial forebrain bundle was established by collision tests in 3 cats. These identified units were driven from amygdalar sites thought to project to the preoptic region by ventral amygdalofugal pathways.