Changes of acetylcholinesterase activity in the brain following septal lesions in the rat

Loss of hippocampal acetylcholinesterase staining after fornix lesion in the monkey

Cholinergic denervation of the hippocampal formation has been extensively studied in rodents but not in primates. Therefore we studied the changes in acetylcholinesterase histochemical staining of the hippocampus occurring after bilateral transection of the fornices in the cynomolgus monkey. Animals were sacrificed 1.5, 6, 13, and 23 weeks after surgery. We found a 40-50% reduction in the density of acetylcholinesterase-positive fibers in the four analyzed regions (dentate gyrus, CA3, CA1, and subiculum) 1.5 week after surgery and a 60-80% reduction at longer time intervals. The characteristic diffuse AChE staining found in hippocampi from control animals disappeared after fornix lesion, except in the inner third of the molecular layer of the dentate gyrus. We did not find any evidence of spontaneous cholinergic reinnervation over the 6-month period. Thus, as in rats, fornix lesion produces dramatic changes in hippocampal AChE staining, presumably caused by a massive cholinergic denervation. However, in contrast to rodents, spontaneous reinnervation does not seem to occur in the months following the lesion in primates.

Acetylcholinesterase activity and acetylcholine effects in the cerebello-rubro-thalamic pathway of the cat

Unilateral transections of the brachium conjunctivum (BC) of cats resulted, after 2-3 weeks, in marked loss of acetylcholinesterase (AChE) activity from the contralateral red nucleus (RN) and ventral tier nuclei of the thalamus (VA-VL). Significant changes in activity were not observed in other locations. Sensitivity of RN neurons to iontophoretically applied acetylcholine (ACh) was studied under conditions which should maximize ACh sensitivity, including AChE inhibition, but ACh was found to have only a weak depressant effect on excitability or no effect at all. Intravenous physostigmine usually increased spontaneous activity of RN neurons, and sometimes increased potentials evoked by electrical stimulation of cerebellar nuclei, to a small extent. Anticholinergic drugs were found not to influence such evoked responses, except to reverse the effects of physostigmine. It is concluded that ACh is not a major transmitter in the excitatory cerebello-rubral tract in spite of the relationship of AChE to this pathway.