Identification of acetylcholinesterase-reactive neurons and neuropil in neostriatal transplants

Abstract

To identify and describe neurons in neostriatal transplants that synthesize acetylcholinesterase (AChE), the present study has utilized the irreversible AChE inhibitor diisopropylfluorophosphate (DFP) combined with AChE histochemistry. Dissociated suspensions of tissue taken from the striatal ridge of embryos at 14 days of gestation were transplanted into the neostriatum of adult rats 5 days after intrastriatal kainic acid lesions. Two types of AChE neurons have been identified in transplants treated with DFP. One type resembled the large intensely reactive AChE neuron that is thought to be a cholinergic interneuron of the normal neostriatum. The other type resembled smaller, less reactive AChE neurons of the neostriatum, as well as medium-sized, lightly reactive AChE neurons of the globus pallidus. Qualitative observations suggest that these less reactive AChE neurons were more numerous in transplants compared to the normal neostriatum. Both AChE neuronal types were found in segregated clusters throughout the grafts. Transplants processed for AChE histochemistry without DFP treatment contained two types of AChE neuropil. Dark areas of AChE neuropil similar in intensity to the normal neostriatum were found between larger areas of lighter AChE neuropil. These results demonstrate that neostriatal transplants contain AChE neurons and suggest that these neurons contribute to the AChE reactivity within the graft.