Morphology and intracellular responses of an identified dorsal raphe projection neuron.

Stimulation of ventral medial tegmentum elicits an antidromic action potential and an inhibitory postsynaptic potential in dorsal raphe projection neurons. The inhibitory postsynaptic potential is not wholly due to activation of recurrent inhibitory circuits as it is not monosynaptic and its onset precedes the antidromic action potential. Light microscopic examination of horseradish peroxidase-filled projection neurons reveals a neuron type with radiating, poorly branched dendrites and terminal dendritic thickets. The axon of the exemplary neuron presented is seen to leave the nucleus but gives off a single collateral while still within the parent cell's dendritic domain.