Effect of hypothalamic stimulation on mesencephalic neurons

The purpose of this study was to determine the effect of electrical stimulation of the lateral hypothalamus and preoptic area on second- and higher-order neurons in the ventral tegmental area of the mesencephalon. Single-unit responses were recorded by tungsten microelectrodes in anesthetized cats. Lateral hypothalamic stimulation caused short- and long-latency excitation as well as antidromic activation of ventral tegmental area neurons. However, half of the responsive neurons exhibited a suppression of firing, or inhibition, following stimulation. The short latency of onset of the suppression obtained in some of these neurons suggests the possibility that, in addition to a descending excitatory hypothalamic outflow, descending monosynaptic inhibitory pathways to the ventral tegmental area are also present.