IMMUNOCYTOCHEMICAL STUDY ON THE DISTRIBUTION OF GABA-LIKE IMMUNOREACTIVE NEURONS IN RAT LOCUS CERULEUS WITH KARYOMETRY AND SYNAPTOLOGY

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Distribution of GABA-like immunoreactive neurons in the rat locus ceruleus was investigated by applying the peroxidase-antipcroxidase method with a GABA-antiserum to the thin, consecutive frontal paraffin sections counterstained with cresyl violet. Nuclear sizes of 1155 immunoreactive neurons in and around locus ceruleus on alternate 240 sections and 313 noradrenergic neurons in both divisions were measured and analysed statistically. The density of distribution of GABA-like immunoreactive neurons was low in the dorsal division (12.5%, 354/2815) and perinuclcar zone (16.4%, 539/3285), but rather high in the ventral division (55.6%, 262/470). Intrinsic GABAergic neurons could be divided into medium-sized and small ones (3.9% and 8.6% of total neurons in the dorsal division, respectively) (P < 0.005). Both types of total immunoreactive neurons (Mean nuclear volume±Standard error) (169.8±5.6μm^3 and 99.3±2.5μm^3) within locus ceruleus were significantly smaller than noradrenergic ones (220.2±5.5μm^3 and 126.9±4.5μm^3). Immunoelectron microscopy showed that only 7.5% (19/253) of axo-somatic boutons on immunonegative mcdium-sized neurons were GABAergic. From these observations, it is suggested that the organized GABA system, different in size from a noradrenergic system, is distributed all over the locus ceruleus.