STUDIES ON REGENERATION OF THE NEURONAL NETWORK IN CEREBROVASCULAR DEMENTIA MODEL

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We investigated changes in signal transduction pathways via muscarinic acetylcholine receptor (mAChR) in hippocampal slices after microsphere embolism (ME) in this term of research project. Our findings demonstrated that stimulation of mAChR fails to activate MAP kinase in the ipsilateral, but not in the contralateral hippocampus of ischemic rats. The stimulation of mAChR with carbachol induced tyrosine phosphorylation of the Gα_<q/11> subunit in the contralateral, but not in the ipsilateral hippocampus. These results suggest that failure in mAChR-induced tyrosine phosphorylation of the Gα_<q/11> subunit in the ischemic hippocampus may be involved in alterations of ERK signal transduction.We further examined alterations in factors involved in the regeneration of the neuronal network in the hippocampus of rats with ME.The immunohistochemical study showed increases in GAP-43, a marker of axonal sprouting ; synaptophysin, a inarker of presynaptic nerve ; and BDNF, a neurotrophic factor and a decrease in the amount of L1, an adhesion molecule in some areas of the hippocampal ischemic penumbra of such animals. These results suggest that some, but not all, factors for regeneration of the neuronal network in the ischemic penumbra respond to sustained cerebral ischemia for a certain period. Immunochemical analysis, however, showed decreases in the absolute amounts of GAP-43 and L1 proteins in the ipsilateral hippocampus of the ME animal. The lack of an increase in L1 in the ischemic penumbra of the hippocampus of the ME animal suggests that production of cell adhesion molecules in response to cerebral ischemia may play a role in the regeneration of the neuronal network of the central nervous system after ischemic brain injury.