Fig. 7.

VTA nondopamine neuron reciprocal input to cortex: intracellular recordings. A, Similar to that in the extracellular recordings in Figure 3, stimulation of the IC (arrowheads indicate stimulus artifact) consistently evoked intracellularly recorded VTA non-DA spikes at short latency. In this example, the driven spike (filled circle) appeared to be orthodromic because a spontaneous spike occurred within a spontaneous-spike to driven-spike interval that was less than twice the latency of the driven spike plus the refractory period. In addition, a small EPSP preceded the driven spike. The spike at thefar right was a spontaneous spike and was not time-locked to successive stimuli. B, This VTA non-DA spike doublet was driven antidromically from the IC. Spike doublets occurred more with intracellular than with extracellular recordings. Note that there is little or no EPSP preceding the doublet of short latency spikes even though the spontaneous spikes are accompanied by EPSPs. C, The doublet of IC-driven spikes is extinguished by a spontaneous spike that occurs within an interval that was less than twice the latency of the first driven spike plus the refractory period. The asterisk indicates where the spikes would have occurred in the absence of collision. The calibration bars in A apply to B andC.