Distribution of GABAAreceptor alpha 1 subunit‐like immunoreactivity in comparision with that of enkephalin and substance P in the rat forebrain

The γ-aminobutyric acid-A receptor consists of several subunits. In this immunohistochemical study we investigated the regional distribution of the α1 subunit with an antibody directed against a specific amino acid sequence (1-9) of the α1 subunit. We compared the distribution pattern of the α1 subunit-like immunoreactivity with that of substance P- and enkephalin-like immunoreactivities in adjacent sections of the rat forebrain. α1 subunit-like immunoreactivity appeared in the form of varicosities and fibers. A band-like terminal staining pattern (woolly fibers) that has been shown by others for substance P- and enkephalin-like immunoreactivity is also observed for α1 subunit-like immunoreactivity. In contrast to substance P and enkephalin, numerous α1 subunit-like immunoreactive perikarya were found. The highest density of α1 subunit-like immunoreactive fibers and perikarya was found in the pallidal areas and the substantia nigra pars reticulata whereas the nucleus accumbens and the caudate putamen displayed a low density. α1 subunit-like immunoreactive neurons resembled typical pallidal neurons. Some of these neurons were pericellularly stained with enkephalin-like immunoreactive varicosities in the dorsal pallidum. The distribution pattern of α1 subunit-like immunoreactivity reflects a partial overlap with the substance P and enkephalin system although a differential distribution to each of these peptides was observed for cell bodies, fibers, and axon terminals. © 1995 Wiley-Liss, Inc.