A subclass of prefrontal gamma-aminobutyric acid axon terminals are selectively altered in schizophrenia.

Abstract

In the primate cerebral cortex, morphologically and functionally diverse classes of local circuit neurons containing the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) differentially regulate the activity of pyramidal cells, the principal type of excitatory output neurons. In schizophrenia, GABA neurotransmission in the prefrontal cortex (PFC) appears to be disturbed but whether specific populations of GABA neurons are affected is not known. The chandelier class of GABA neurons are of particular interest because their axon terminals, which form distinctive arrays termed "cartridges," provide inhibitory input exclusively to the axon initial segment of pyramidal cells. Thus, chandelier cells are positioned to powerfully regulate the excitatory output of pyramidal neurons and, consequently, to substantially affect the patterns of neuronal activity within the PFC. In this study, an antibody directed against the GABA membrane transporter GAT-1 was used to label GABA axon terminals in postmortem human brains. The relative density of GAT-1-immunoreactive axon cartridges furnished by chandelier neurons was decreased by 40% in the PFC of schizophrenic subjects compared with matched groups of normal control and nonschizophrenic psychiatric subjects. In contrast, markers of the axon terminals of other populations of GABA neurons were not altered in the schizophrenic subjects. Furthermore, the density of GAT-1-immunoreactive axon cartridges was not altered in psychiatric subjects who had been treated with antipsychotic medications. The changes in GAT-1-immunoreactive axon cartridges of chandelier neurons in schizophrenia are likely to reflect altered information processing within the PFC and in its output connections to other brain regions and could contribute to the cognitive impairments seen in this disorder.