Immunohistochemical and neurochemical studies of hippocampal cholinergic neurones after ischaemia.

We investigated alterations in cholinergic neurones in the gerbil hippocampus after ischaemia. The cholinergic function of acetylcholine (ACh) release fluctuated over the test period. Choline acetyltransferase (ChAT) immunoreactivity decreased slightly on day 1 and no ChAT immunoreactivity was observed on or after day 4 after ischaemia. Since ChAT immunoreactivity is a marker of cholinergic terminal survival, post-ischaemic cholinergic dysfunction on and after day 4 was accompanied by the destruction of terminals. However, dysfunction of the cholinergic system without destruction of the terminals is possible since mild ischaemia decreases ACh release in spite of retaining intact ChAT immunoreactivity. In the morphological study, delayed neuronal death in the stratum pyramidale was observed from day 4. The present study shows that presynaptic cholinergic dysfunction occurs in the early stage prior to pyramidal cell death.