Background: Progressive supranuclear palsy (PSP) is a progressive neurodegenerative disorder involving motor and cognitive dysfunction. Currently, there is no effective treatment either for symptomatic relief or disease modification. This relates, in part, to a lack of knowledge of the underlying neurochemical abnormalities, including cholinergic receptor status in the basal ganglia. Aim: To measure muscarinic M2 and M4 receptors in the basal ganglia in PSP. Methods: The muscarinic M2 (presynaptic) and M4 (postsynaptic) receptors in the striatum, pallidum and adjacent insular cortex were autoradiographically measured in pathologically confirmed cases of PSP (n = 18), and compared with cases of Lewy body dementias (LBDs; n = 45), Alzheimer's disease (AD; n = 39) and controls (n = 50). Results: In cases of PSP, there was a reduction in M2 and M4 receptors in the posterior caudate and putamen compared to controls, but no significant changes in the pallidum. Cases with AD showed lower M2 receptors in the posterior striatum. Groups with LBD and AD showed higher M2 binding in the insular cortex compared with controls. Conclusions:The results suggest loss of posterior striatal cholinergic interneurones in PSP, and reduction in medium spiny projection neurones bearing M4 receptors. These results should be taken in the context of more widespread pathology in PSP, but may have implications for future trials of cholinergic treatments.

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The long-term care and management of psychoses in the elderly graphic changes which have resulted in a "graying of the population", the number of older individuals with chronic psychiatric illnesses (ego schizophrenia; bipolar mood disorder) is also increasing. The same demographic trends are causing a significant increase in the incidence of neurodegenerative disorders (ego Alzheimer's Disease) which are frequently characterized by behavioural changes in addition to their cognitive stigmata. This presentation will describe the prevalence and phenomenology of psychiatric syndromes and neurodegenerative illnesses in the elderly population, and will detail the differential diagnosis which the psychiatrist must invoke in order to arrive at a satisfactory diagnosis in the individual patient.