Fig. 9.
Interactions among hippocampal, MD, and VTA inputs converging on the same PFC neurons. A, FF-evoked firing probabilities in PFC←Hipp neurons that also responded with an orthodromic monosynaptic action potential after stimulation of the MD. Application of a conditioning pulse to the MD 10 or 50 msec before a test pulse to the MD (gray bars) significantly reduced the evoked firing probability relative to that observed when the FF was stimulated alone (gray hatched bar). Burst stimulation of the VTA also attenuated FF-evoked firing (black bars). However, application of a conditioning pulse to the MD 10 msec before an FF test pulse significantly (*p < 0.05) attenuated the VTA-mediated inhibition. Stars denote significant difference versus firing probability evoked by FF single-pulse stimulation.B, Location of all neurons observed in this study (open stars) that responded with an orthodromic, monosynaptic action potential after stimulation of the FF and the MD. Numbers beside each plate correspond to millimeters from bregma. C, Diagram of the stimulation protocol used in this experiment. Here the VTA was stimulated in a burst pattern (1) 10 msec before administering MD–FF sequential-pulse stimulation (2, 3). Both the MD and FF were stimulated with single pulses that were separated by 10 or 50 msec.