Elsevier

Neuroscience

Volume 42, Issue 2, 1991, Pages 497-507
Neuroscience

In situ hybridization histochemistry reveals a diversity of GABAA receptor subunit mRNAs in neurons of the rat spinal cord and dorsal root ganglia

https://doi.org/10.1016/0306-4522(91)90392-2Get rights and content

Abstract

The distribution and relative abundance of gene transcripts for diverse GABAA receptor subunits (α1–3,5, β1–3, γ2) in neurons of the rat cervical spinal cord and dorsal root ganglia were determined by in situ hybridization histochemistry using35S-labeled 60mer oligonucleotide probes. The receptor proteins (mapped by benzodiazepine receptor radioautography and immunohistochemistry with [3H]flumazenil and a monoclonal antibody for the β2 + β3 subunits, respectively) were most abundant in the dorsal horn (layers II and III) and in layer X around the central canal. Although diverse receptor subunit mRNAs were detected (to varying degrees) in neurons throughout layers II-X of the spinal cord, motoneurons in layer IX were particularly strongly labeled. The γ2 mRNA was the most ubiquitous and abundant of the subunit variants investigated. The labeling of motoneurons in layer IX was particularly strong for α2, moderate for β3 and γ2 and extremely weak for α1 and α3. In layers VII, VIII and X the β3 and γ2 transcripts were moderately expressed whereas the α1 and β2 transcript levels differed markedly among the cells of these layers. Although the mRNAs of all subunit variants could be detected in layers IV-VI, only α3, α5, β3 and γ2 hybridization signals were observed in layers II and III. In the dorsal root ganglia, whereas α2 transcripts were abundant in virtually all large sensory neurons and to a much lower degree in the small diameter cells, γ2 transcripts were confined to a subpopulation of large and small neurons. Furthermore, β2 and α1 transcripts were even more restricted in their distribution.

The findings provided a basis for the mediation of synaptic inhibition in the spinal cord by diverse GABAA receptors and further strong evidence for the long-established view that presynaptic inhibition of inter- and motoneurons, via axoaxonic synapses between GABAergic interneurons and primary afferent terminals, is mediated by GABAA receptors. The physiological roles and pharmacological implications of this receptor diversity have yet to be determined.

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