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

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Abstract
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.