Enhancement of central cholinergic sprouting by prior injury: correlation with endogenous trophic content of hippocampus.

Injury to neural tissue elicits the release of neurotrophic substances which support the survival of cultured cholinergic neurons. The aim of the present report was to determine the effect of prior hippocampal injury on the sprouting of mature intrinsic cholinergic septal afferents in vivo. Levels of choline acetyltransferase (CAT) in intrahippocampal iris implants were used as an index of cholinergic regeneration. The results show that prelesioning the hippocampus 1 week prior to insertion of the iris increased CAT levels of implants left for 8 days in situ. Levels of iris CAT were correlated with the trophic content of the surrounding hippocampal tissue. These observations suggest that endogenous trophic factors released as a consequence of neural injury facilitate cholinergic sprouting in vivo.