CHOLINERGIC AND GABAERGIC SEPTOHIPPOCAMPAL PROJECTION NEURONS IN MICE- A RETROGRADE TRACING STUDY COMBINED WITH DOUBLE IMMUNOCYTOCHEMISTRYFOR CHOLINE-ACETYLTRANSFERASE AND PARVALBUMIN

The present experiments were directed to determine the proportions of the cholinergic and GABAergic septo-hippocampal projection neurons in NMRI mice. For the labeling of the septal neurons we used a double imm unocytochemical method combined with retrograde transport of wheatgerm agglutinin apo-horseradish peroxidase-gold (WAHG) injected unilateral ly into the hippocampus. Monoclonal antibodies against choline acetylt ransferase (ChAT) and parvalbumin (PARV) were used as markers for chol inergic and GABAergic neurons in the medial septum/diagonal band compl ex (MS/DB). Both antibodies were visualized in the same section using the ABC detection system with diaminobenzidine and 4-chloro-1-naphtol as chromogens. Cholinergic and PARV-containing neurons are coexsisting in the MS/DB. About 38% of all retrogradely labeled neurons were ChAT -positive whereas only 10% of all retrogradely labeled cells were immu nostained for PARV. On the other hand, 40% of all ChAT-positive neuron s and about 24% of all PARV-positive neurons were retrogradely labeled . No double immunolabeled neurons were detected. The proportion of GAB Aergic neurons may have been underestimated because immunostaining for PARV only labels a subpopulation of GABAergic neurons. The present re sults were compared with those of previous studies in rats. They may s erve as a basis of further comparative studies in mice.