Dopaminergic control of the septal-hippocampal cholinergic pathway

Apomorphine given subcutaneously is known to decrease the turnover rate of acetylcholine (TR(ACh) in the hippocampus. Blockade of dopaminergic receptors by intraseptal haloperidol or destruction of dopaminergic terminals by intraseptal 6-hydroxydopamine results in an increase in TR(ACh) in the hippocampus. Specific destruction of the dopaminergic neurons projecting to the septum by the injection of 6-hydroxydopamine into the A10 mesencephalic cell group also results in an increased TR(ACh) in the hippocampus. None of the above treatments affects TR(ACh) in the cortex. Thus, it appears that dopaminergic neurons exert a tonic inhibitory effect on the ACh metabolism of the septal-hippocampal pathway, but do not affect that of cholinergic neurons projecting from the septum to the cortex. It can be inferred that this decrease in the rate of metabolism may be associated with a regulation of the rate of neuronal firing.