EXPRESSION OF ACETYLCHOLINESTERASE MESSENGER-RNA IN HUMAN BRAIN - AN IN-SITU HYBRIDIZATION STUDY

The distribution of messenger RNA coding for acetylcholinesterase was studied in human post mortem brain and rhesus monkey by in situ hybrid ization histochemistry and compared to the distribution of acetylcholi nesterase activity. Acetylcholinesterase messenger RNA had-similar to acetylcholinesterase enzymatic activity-a widespread distribution in h uman brain. Acetylcholinesterase messenger RNA positive cells correspo nded to perikarya rich in acetylcholinesterase activity in most but no t all regions. Examples for mismatches included the inferior olive and human cerebellar cortex. The presence of hybridization signals in cer ebral cortex and an enrichment in layer III and V of most isocortical areas confirmed that perikaryal acetylcholinesterase in cerebral corte x is of postsynaptic origin and not derived from cholinergic projectio ns. In striatum the expression of high levels of acetylcholinesterase messenger RNA was restricted to a small population of large striatal n eurons. In addition, low levels of expression were found in most mediu m sized striatal neurons. Cholinergic neurons tended to express high l evels of acetylcholinesterase messenger RNA whereas in cholinoceptive neurons the levels were moderate to low. However, some noncholinergic neurons like dopaminergic cells in substantia nigra, noradrenergic cel ls in locus coeruleus, serotoninergic cells in raphe dorsalis, GABAerg ic cells in thalamic reticular nucleus, granular cells in cerebellar c ortex and pontine relay neurons expressed levels comparable to choline rgic neurons in basal forebrain. It is suggested that neurons expressi ng high levels of acetylcholinesterase messenger RNA may synthesize ac etylcholinesterase for axonal transport whereas neurons with an expres sion of acetylcholinesterase confined to somatodendritic regions tend to contain lower levels of acetylcholinesterase messenger RNA.