Brain, Vol. 125, No. 7, 1483-1495,
July 2002
© 2002 Guarantors of Brain
Nicotinic receptor abnormalities in the cerebellar cortex in autism
1 MRC/University of Newcastle Upon Tyne Development in Clinical Brain Ageing and 2 Department of Neuropathology, Newcastle General Hospital, Newcastle upon Tyne, UK, 3 Cure Autism Now, Los Angeles, CA and 4 Children’s Neurology Service, Harvard Medical School, Massachusetts’s General Hospital, Boston, MA, USA
Correspondence to: E. K. Perry, MRC Building, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne NE4 6BE, UK E-mail: e.k.perry{at}ncl.ac.uk
Autism is a common developmental disorder associated with structural and inferred neurochemical abnormalities of the brain. Cerebellar abnormalities frequently have been identified, based on neuroimaging or neuropathology. Recently, the cholinergic neurotransmitter system has been implicated on the basis of nicotinic receptor loss in the cerebral cortex. Cerebellar cholinergic activities were therefore investigated in autopsy tissue from a series of autistic individuals. The presynaptic cholinergic enzyme, choline acetyltransferase, together with nicotinic and muscarinic receptor subtypes were compared in the cerebellum from age-matched mentally retarded autistic (eight), normal control (10) and non-autistic mentally retarded individuals (11). The nicotinic receptor binding the agonist epibatidine (the high affinity receptor subtype, consisting primarily of 
3 and 4, together with ß2 receptor subunits) was significantly reduced by 40–50% in the granule cell, Purkinje and molecular layers in the autistic compared with the normal group (P < 0.05). There was an opposite increase (3-fold) in the nicotinic receptor binding -bungarotoxin (to the 7 subunit) which reached significance in the granule cell layer (P < 0.05). These receptor changes were paralleled by a significant reduction (P < 0.05) and non-significant increase, respectively, of 4 and 7 receptor subunit immunoreactivity measured using western blotting. Immunohistochemically loss of 4 reactivity was apparent from Purkinje and the other cell layers, with increased 7 reactivity in the granule cell layer. There were no significant changes in choline acetyltransferase activity, or in muscarinic M1 and M2 receptor subtypes in autism. In the non-autistic mentally retarded group, the only significant abnormality was a reduction in epibatidine binding in the granule cell and Purkinje layers. In two autistic cases examined histologically, Purkinje cell loss was observed in multiple lobules throughout the vermis and hemispheres. This was more severe in one case with epilepsy, which also showed vermis folial malformation. The case with less severe Purkinje cell loss also showed cerebellar white matter thinning and demyelination. These findings indicate a loss of the cerebellar nicotinic 4 receptor subunit in autism which may relate to the loss of Purkinje cells, and a compensatory increase in the 7 subunit. It remains to be determined how these receptor abnormalities are involved in neurodevelopment in autism and what is the relationship to mental function. Since nicotinic receptor agonists enhance attentional function and also induce an elevation in the high affinity receptor, nicotinic therapy in autism may be worth considering.
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