Stimulation of the septal complex increases local cerebral blood flow in the hippocampus in anesthetized rats

The effects of focal stimulation, either electrically or chemically, of the septal complex (i.e. the medial septal nucleus and the nucleus of the diagonal band) on the local hippocampal cerebral blood flow (Hpc CBF) measured by laser Doppler flowmetry were examined in anesthetized rats. Electrical stimulation of the septal complex produced a current-dependent increase in Hpc CBF that was accompanied by an increase in extracellular acetylcholine (ACh) release in the hippocampus. Microinjection of L-glutamate (50-100 nmol) into the septal complex also produced an increase in Hpc CBF. The L-glutamate-induced vasodilative response of Hpc CBF was markedly attenuated after administration of nicotinic cholinergic blocking agent, mecamylamine (2 mg/kg, i.v.). It was suggested that the cholinergic septohippocampal nerve fibers act as an intracerebral vasodilative neural system by releasing ACh from the nerve terminals in the hippocampus and by activating the nicotinic cholinergic receptor.