An electrophysiological study of inputs to neurons of the ventral tegmental area from the nucleus accumbens and medial preoptic-anterior hypothalamic areas.

Extracellular recordings were obtained from neurons in the ventral tegmental area (VTA) of urethane-anesthetized rats. Neurons were divided into two types based on the latencies of antidromic activation following electrical stimulation of the nucleus accumbens (NAcc), and on the durations of action potentials. Type A neurons had longer latencies for antidromic activation (mean 15.9 msec) and longer durations of action potentials (> 2.6 msec), while type B neurons had shorter latencies (mean 4.5 msec) and shorter duration of action potentials (< 2.6 msec). Electrical stimulation of the medial preoptic-anterior hypothalamic areas (mPOA-AHA) and NAcc produced the following effects on the two types of VTA neurons: (i) the majority of both type A and B neurons were suppressed by mPOA-AHA stimulation with onset latencies of less than 10 msec; (ii) 42% of type B neurons were also suppressed by NAcc stimulation, with onset latencies of less than 10 msec; (iii) type A neurons were suppressed (33%) or activated (43% by NAcc stimulation, the onset latencies usually being longer than 10 msec; (iv) 71% of type A neurons tested had convergent inputs from the mPOA-AHA and NAcc, usually suppressed-suppressed or suppressed-activated, while 45% of type B neurons had convergent inputs from these two areas, usually suppressed-suppressed.