EVIDENCE FOR A HIPPOCAMPAL-SEPTAL GLUTAMATERGIC PATHWAY IN THE RAT

Kainic acid lesions of the hippocampal formation resulted in degeneration of axons and terminals in the lateral septal nuclei and in the nucleus accumbens. The degeneration of the hippocampal-septal projection was associated with a selective reduction in the synaptosomal Na-dependent uptake of L-[3H]glutamate (-30 to 40%) and in the concentration of L-glutamate in the P2 fraction (-20%). Presynaptic neurochemical markers for cholinergic, GABAergic and noradrenergic neurons in the septal nuclei were not reduced by the hippocampal lesion. Transection of the hippocampal-septal projection at the fornix reduced the synaptosomal uptake of L-[3H]glutamate 40% but did not significantly reduce [3H]GABA uptake in the septal nuclei. The hippocampal-septal pathway, an excitatory projection, may thus be glutamatergic.