Retrograde HRP tracing combined with a pharmacohistochemical method for GABA transaminase for the identification of presumptive GABAergic projections to the habenula.

A pharmacohistochemical method for GABA-transaminase (GABA-T), the key enzyme for GABA metabolism, has been combined with retrograde tracing by horseradish peroxidase, to a study of projections to the lateral habenula. The results indicate that projections to the lateral habenula arise from both GABA-T intensive and non-GABA-T staining cells in the rostral entopeduncular nucleus and the lateral hypothalamus suggesting that these projections contain GABAergic elements, as indicated by previous work, but also involve other neurotransmitters. A few GABA-T intensive cells in the lateral preoptic area were also found to project to the lateral habenula by this double staining technique.