Journal of Neuroscience, Vol 7, 65-76, Copyright © 1987 by Society for Neuroscience
Coexistence of GABA receptors and GABA-modulin in primary cultures of rat cerebellar granule cells
FM Vaccarino, H Alho, MR Santi and A Guidotti
GABA-modulin (GM), a basic polypeptide purified from rat brain
synaptosomes, which is an allosteric inhibitor of GABA recognition sites,
has been detected in primary cultures of cerebellar interneurons enriched
in granule cells by immunohistochemistry, using a specific antibody raised
in rabbit injected with GM purified from rat brain synaptosomes. In these
cultures, GM is expressed by the granule cells, which are postsynaptic to
GABAergic interneurons, but not by glial cells. In rat cerebellar sections
anti-GM antiserum intensely strains the granular cell layer and Purkinje
cell dendrites and cell bodies. GM has been purified from the cerebellar
granule cell cultures and appears to be identical under biochemical,
immunological, and functional criteria to authentic GM purified from rat
brain synaptosomes. Granule cell cultures devoid of GABAergic neurons
contain the GABA/BZ/Cl- receptor complex; in fact, intact cell monolayers,
incubated in physiological buffer at 25 degrees C, express 3H-muscimol and
3H- flunitrazepam binding sites, which are comparable to the sites detected
in cell membrane preparations and which modulate each other reciprocally.
It is concluded that GM might participate in the supramolecular
organization of the GABA receptor complex, perhaps functioning as a
modulator of this receptor protein.