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The effects of 6 months' ethanol consumption by mice on hippocampal GABAergic neurons were investigated by means of an immunocytochemical method using GABA antibodies. Although ethanol treatment did not modify body or brain weights in our experimental conditions, two differences were observed in ethanol-treated mice, as compared to controls: a decrease in the labelling intensity of immunopositive neurons and fibers in the dorsal and the ventral parts of the hippocampus; and a decrease in the number of immunopositive neurons. This neuronal loss was statistically significant in the ventral hippocampus only, where it reached about 25% in the stratum radiatum. It is concluded that chronic ethanol consumption leads to a decrease in GABA content of hippocampal neurons and to a loss of GABAergic neurons, mostly in the ventral part of the hippocampus. These alterations in GABAergic transmission could be related to the well known functional deficits observed in chronic alcoholism.

The distribution of GABA-immunoreactive neurons and axonal varicosities was investigated in the hippocampal region of the rat brain by means of an indirect peroxidase immunocytochemical method with recently developed anti-GABA antibodies. The immunolabeling was found to be restricted to nervous structures: neuronal cell bodies, dendrites and axon terminals. Myelinated axons showing GABA-immunoreactivity were also observed. GABA-immunoreactive neurons were found in great number in the stratum pyramidale, the superficial part of the stratum oriens and the deep part of the stratum radiatum in the Ammon's horn. Less were found in the other regions; rare labeled cells were observed in the superficial part of the stratum radiatum and the middle part of the stratum oriens. The dentate gyrus exhibited numerous labeled cells in the granular layer, few in the hilus, rare in the molecular layer. A high density of GABA-immunoreactive terminals was found at the limit of the stratum oriens with the alveus, in the stratum pyramidale and in the stratum lacunosum. A lower density of labeled fibers was observed in the other areas. The somata and proximal dendrites of pyramidal and granular cells were encompassed by characteristic pericellular arrangements of GABA-immunoreactive varicosities. Ultrastructural observations revealed a diffuse immunoreaction product spread over the cytoplasm and the nucleus without specific relationship with the organelles, and immunoreactive aggregates in the cytoplasm. Labeled dendrites often showed enlargements displaying the immunoreaction whereas thinner segments were devoid of it. They received numerous asymmetrical synapses from unlabeled axon terminals. GABA-immunoreactive terminals were filled with small clear vesicles with immunopositive membranes and were observed in symmetrical contact with somata and dendrites.