Distribution of gamma-aminobutyric acid-immunoreactive neurons in the septal region of the rat brain.

The distribution of gamma-aminobutyric acid-immunoreactive (GABA-I) elements was examined in the septal region of the rat brain. The indirect peroxidase-antiperoxidase technique was used with anti-GABA antibodies in normal and colchicine-pretreated rats, with or without use of detergent in the incubation medium. Intraventricular injection of colchicine did not result in any change in the staining of neuronal perikarya. Intraseptal injections increased the intensity of labelling of GABA-I cell bodies in the lateral septal nucleus and increased the number of labelled cells in the medial septal nucleus and diagonal band of Broca (dbB). Triton X-100 added to the incubation media decreased the intensity of staining and number of GABA-I somata in all septal nuclei with a concentration-dependent effect. No change was observed concerning GABA-I varicosities. The septal area, including the lateral, medial, and triangular septal nuclei; the anterior rudiment of the hippocampus; the island of Calleja magna; the septofimbrial nucleus; the bed nucleus of the stria terminalis; and the dbB showed a strong reaction to anti-GABA antibodies with regard to GABA-containing surrounding structures. GABA-I axonal varicosities were observed in all the regions with an uneven distribution. The highest density was found in the dorsal and ventral parts of the lateral septal nucleus and in a band situated between the dbB and the nucleus accumbens. Labelled varicosities were frequently observed surrounding GABA-I and nonimmunoreactive cell bodies. GABA-I somata ranged from 10 to 30 micron in diameter. Small neurons were present in great number at the ventricular border and in the zona limitans. Medium-size and large neurons were mostly observed in the medial part of the dorsal lateral nucleus and in the intermediate lateral nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)