Pyramidal cell axons show a local specialization for GABA and 5-HT inputs in monkey and human cerebral cortex

Academic Article

Abstract

  • Various mechanisms are thought to control excitation of pyramidal cells of the cerebral cortex. With immunocytochemical methods, we found that the proximal portions of numerous pyramidal cell axons (Pyr-axons) in the human and monkey neocortex are immunoreactive for the serotonin (5-HT) receptor 5-HT-1A. With double-labeling experiments and confocal laser microscopy, we found that most (93.4%) of the 5-HT1A-immunoreactive Pyr-axons present in layers II and III were innervated by parvalbumin-immunoreactive chandelier cell axon terminals. In addition, Pyr-axons were compartmentalized: 5-HT-1A receptors were found proximal to inputs from chandelier cells. Although we found close appositions between GABAergic chandelier cell axon terminals and Pyr-axons, suggesting synaptic connections, we did not observe 5-HT-immunoreactive fibers in close proximity to the Pyr-axons. These results suggested that Pyr-axons are under the influence of 5-HT in a paracrine manner (via 5-HT-1A receptors) and, more distally, are under the influence of γ-aminobutyric acid (GABA) in a synaptic manner (through the axons of chandelier cells). The local axonal specialization might represent a powerful inhibitory mechanism by which the responses of large populations of pyramidal cells can be globally controlled by subcortical serotonin afferents, in addition to local inputs from GABAergic interneurons. © 2001 Wiley-Liss, Inc.
  • Authors

    Published In

    Digital Object Identifier (doi)

    Author List

  • DeFelipe J; Arellano JI; Gómez A; Azmitia EC; Muñoz A
  • Start Page

  • 148
  • End Page

  • 155
  • Volume

  • 433
  • Issue

  • 1