Presynaptic and postsynaptic GABAA receptors in rat suprachiasmatic nucleus

M. A. Belenky, N. Sagiv, J. M. Fritschy, Y. Yarom

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43 Scopus citations

Abstract

The mammalian suprachiasmatic nucleus (SCN), the brain's circadian clock, is composed mainly of GABAergic neurons, that are interconnected via synapses with GABAA receptors. Here we report on the subcellular localization of these receptors in the SCN, as revealed by an extensively characterized antibody to the α3 subunit of GABAA receptors in conjunction with pre- and postembedding electron microscopic immunocytochemistry. GABAA receptor immunoreactivity was observed in neuronal perikarya, dendritic processes and axonal terminals. In perikarya and proximal dendrites, GABAA receptor immunoreactivity was expressed mainly in endoplasmic reticulum and Golgi complexes, while in the distal part of dendrites, immunoreaction product was associated with postsynaptic plasma membrane. Many GABAergic axonal terminals, as revealed by postembedding immunogold labeling, displayed GABAA receptor immunoreactivity, associated mainly with the extrasynaptic portion of their plasma membrane. The function of these receptors was studied in hypothalamic slices using whole-cell patch-clamp recording of the responses to minimal stimulation of an area dorsal to the SCN. Analysis of the evoked inhibitory postsynaptic currents showed that either bath or local application of 100 μM of GABA decreased GABAergic transmission, manifested as a two-fold increase in failure rate. This presynaptic effect, which was detected in the presence of the glutamate receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione and the selective GABAB receptor blocker CGP55845A, appears to be mediated via activation of GABAA receptors. Our results thus show that GABAA receptors are widely distributed in the SCN and may subserve both pre- and postsynaptic roles in controlling the mammalian circadian clock.

Original languageEnglish
Pages (from-to)909-923
Number of pages15
JournalNeuroscience
Volume118
Issue number4
DOIs
StatePublished - 6 Jun 2003
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by BMBF. We thank Dr. Gary Pickard (Colorado State University) for valuable comments and critical reading of the manuscript. We also thank Dr. Ezra Rahamim for the opportunity to use freeze-substitution equipment and Naomi Feinstein for help with quantitative analysis.

Funding

This work was supported by BMBF. We thank Dr. Gary Pickard (Colorado State University) for valuable comments and critical reading of the manuscript. We also thank Dr. Ezra Rahamim for the opportunity to use freeze-substitution equipment and Naomi Feinstein for help with quantitative analysis.

FundersFunder number
Bundesministerium für Bildung und Forschung

    Keywords

    • Circadian clock
    • Electrophysiology
    • GABA
    • GABA receptors
    • Immunocytochemistry
    • Suprachiasmatic nucleus

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