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  • Title: Pyramidal cell axons show a local specialization for GABA and 5-HT inputs in monkey and human cerebral cortex.
    Author: DeFelipe J, Arellano JI, Gómez A, Azmitia EC, Muñoz A.
    Journal: J Comp Neurol; 2001 Apr 23; 433(1):148-55. PubMed ID: 11283956.
    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-HT(1A)-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 gamma-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.
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