Electrophysiological responses of neurons of the ventral tegmental area to electrical stimulation of amygdala and lateral septum

Abstract

Extracellular recordings were obtained from neurons in the ventral tegmental area of urethaneanesthetized rats. Neurons were divided into two types based on the criteria that the Type A neurons had long duration action potentials (>2.6 ms) and slow firing rates (<6 Hz) and Type B neurons shorter duration action potentials and a wider range of firing rates, assumed in previous studies to be dopaminergic and non-dopaminergic neurons. The effects of single pulse stimuli delivered to the ipsilateral lateral septum, or the basolateral or central amygdala, on activities of the two types of neurons were investigated. The results were as follows: (i) A high proportion (70–95%) of the two types of neurons responded to stimulation of the amygdala or septum, (ii) Equal numbers of Type A neurons were initially activated or suppressed by stimulation of either the amygdala or septum whereas a larger number of Type B neurons were suppressed than were activated by stimulation of the basolateral amygdala or lateral septum, (iii) Eighty-two percent of Type A neurons and 62% of Type B neurons had converging inputs from the amygdala and septum, the inputs being synergistic or asynergistic equally for both types of neurons, (iv) A majority of the responses had rather long onset latencies, prolonged durations, and complex sequences of activation and suppression, suggestive of mediation by multisynaptic pathways. The converging suppressive and activating inputs suggest that the amygdala and septum exert modulatory influences on the two types of neurons which project from the ventral tegmental area to forebrain structures, contributing to goal-directed behaviors.