Prefrontal cortical projections to the rat dorsal raphe nucleus: Ultrastructural features and associations with serotonin and γ‐aminobutyric acid neurons

摘要: Studies of human brain indicate that both the ventromedial prefrontal cortex (PFC) and dorsal raphe nucleus (DRN) may be dysfunctional in major depressive illness, making it important to understand functional interactions between these regions. Anatomical studies have shown PFC projects DRN, although synaptic targets this excitatory pathway not yet been identified. Electrophysiological investigations rat DRN report most serotonin neurons are inhibited by electrical stimulation PFC, suggesting is more likely synapse onto neighboring γ-aminobutyric acid (GABA) than cells. We tested hypothesis electron microscopic examination sections dually labeled for biotin dextran amine anterogradely transported from immunogold-silver labeling tryptophan hydroxylase (TrH) or GABA. In majority axons either synapsed unlabeled dendrites failed form detectable synapses single sections. Other TrH- GABA-immunolabeled processes. Considerably tissue sampling was necessary detect GABA-labeled dendrites, latter connections common. other cases, terminals GABA-immunoreactive were closely apposed, without forming synapses, separated glial These results provide potential anatomical substrates whereby can directly indirectly regulate activity possibly contribute pathophysiology depression. J. Comp. Neurol. 468:518–529, 2004. © 2003 Wiley-Liss, Inc.