Demonstration of central γ-aminobutyrate-containing nerve terminals by means of antibodies against glutamate decar☐ylase

Abstract

A new procedure is described to obtain specific antibodies against mouse glutamate decar☐ylase using a purified glutamate decar☐ylase preparation obtained by affinity chromatography. Antibodies prepared against the Sepharose-bound glutamate decar☐ylase caused a concentration-dependent inhibition of glutamate decar☐ylase activity. Furthermore, the glutamate decar☐ylase antibodies gave a single precipitation band in double immunodiffusion, immunoelectrophoresis and in counterimmunoelectrophoresis analysis when reacted against crude extracts from mouse or rat brain. Immunohistochemical analysis in the rat brain demonstrated specific glutamate decar☐ylase-related immunofluorescence, presumably in γ-aminobutyrate-containing nerve terminals, but in no case in cell bodies in any part of the brain and the spinal cord. Two principal types of presumed γ-aminobutyrate-containing nerve terminals could be demonstrated. One type is strongly glutamate decar☐ylase immunoreactive, appears to have fairly large varicosities, may possibly make axosomatic and axodendritic contacts, and is confined mainly to the deep cerebellar nuclei, the nucleus vestibularis lateralis, the substantia nigra, the globus pallidus and the substantia innominata together with adjacent parts of the medial forebrain bundle and the dorsal part of the olfactory tubercle. In all these areas they are found in high densities. It is suggested, partly in agreement with previous findings that this type of γ-aminobutyrate-containing nerve terminal belongs to Golgi type I nerve cells (with long projections), contains high amounts of glutamate decar☐ylase enzyme protein and may mediate postsynaptic inhibition. The other type of γ-aminobutyrate-containing nerve terminal is weakly to moderately glutamate decar☐ylase immunoreactive, appears to have fine varicosities, may possibly make both axosomatic, axodendritic and axoaxonic contacts and is found all over the brain and the spinal cord in low to high densities. The distribution of this type correlates fairly well with the known distribution of glutamate decar☐ylase activity in the rat brain. It is suggested that this type of γ-aminobutyrate-containing nerve terminal mainly belongs to Golgi type II neurons (interneurons), contains relatively low amounts of glutamate decar☐ylase enzyme protein, and mediates both pre- and postsynaptic inhibition. The findings underline the existence of a new type of γ-aminobutyrate-containing Golgi type I neuron, controlling activity in the substantia innominata and in the outflow from Calleja's islands of the olfactory tubercle and the view that γ-aminobutyrate may play a role in synaptic processes in all parts of the brain and the spinal cord.