Dopamine terminals synapse on callosal projection neurons in the rat prefrontal cortex

Dopamine (DA) afferents to the prefrontal cortex (PFC) play an important ro le in the cognitive functions subserved by this cortical area. Within the P FC, DA terminals synapse onto the distal dendrites of both local circuit ne urons and pyramidal projection cells. We have previously demonstrated in th e rat PFC that some of the dendrites and spines postsynaptic to DA terminal s arise from pyramidal neurons that project to the nucleus accumbens. Howev er, it is not known whether the pyramidal cells that give rise to callosal intercortical connections of the PFC also receive DA synaptic input. To add ress this question, retrograde tract tracing using an attenuated strain of pseudorabies virus (PRV-Bartha) was combined with immunocytochemistry for t yrosine hydroxylase (TH) to identify DA terminals in the PFC. Thirty-six to 40 hours following injection of PRV into the contralateral PFC, numerous c allosal projection neurons were extensively labeled throughout their dendri tic trees, with no evidence of PRV trans-synaptic passage. In tissue prepar ed for electron microscopy, labeling for PRV was distributed throughout pyr amidal cell somata and extended into distal dendrites and dendritic spines. Some PRV-labeled dendrites and spines received symmetric synaptic input fr om terminals containing peroxidase labeling for TH. These results demonstra te that DA terminals synapse onto the distal dendrites of callosally projec ting PFC neurons and suggest substrates through which DA may modulate inter hemispheric cortical communication. J. Comp. Neurol. 425:275-283, 2000. (C) 2000 Wiley-Liss, Inc.