AUTORADIOGRAPHIC COMPARISON OF [ 3 H](-)NICOTINE, [ 3 H]CYTISINE AND [ 3 H]EPIBATIDINE BINDING IN RELATION TO VESICULAR ACETYLCHOLINE TRANSPORT SITES IN THE TEMPORAL CORTEX IN ALZHEIMER’S DISEASE W. SIHVER,*†‡ P.-G. GILLBERG,§k A.-L. SVENSSON¶ and A. NORDBERG¶ *PET Center Uppsala, Uppsala University, Uppsala, Sweden †Department of Neuroscience, Division of Medical Pharmacology, Uppsala University, Box 593, S-75124 Uppsala, Sweden §Department of Pharmacology, Pharmacia and Upjohn, S-75182 Uppsala, Sweden k Department of Neuroscience, Division of Neurology, University Hospital, S-75185 Uppsala, Sweden ¶Karolinska Institutet, Division of Molecular Neuropharmacology, Department of Clinical Neuroscience, Occupational Therapy and Elderly Care Research, Geriatric Clinic, Huddinge University Hospital, S-14186 Huddinge, Sweden Abstract —The laminar binding distribution of three nicotinic receptor agonists, [ 3 H](-)nicotine, [ 3 H]cytisine, and [ 3 H]epibati- dine, and their relation to the [ 3 H]vesamicol binding, which is known to represent the vesicular acetylcholine transport sites, was performed employing in vitro autoradiography on the medial temporal cortex (Brodmann area 21). Autopsied brain tissue from nine Alzheimer patients and seven age-matched controls were used. The binding pattern of the three nicotinic ligands in the normal cortex was in general similar, showing binding maxima in the cortical layers I, III and V. The binding of [ 3 H](-)nicotine, [ 3 H]cytisine, and [ 3 H]epibatidine was lower in the older controls and more uniform throughout the layers as compared with younger controls. There was a significant age-related decrease in the binding of the three nicotinic ligands within the controls (age range: 58 to 89 years; P [3H](-)nicotine  0.002, P [3H]epibatidine  0.010, P [3H]cytisine  0.037). In the older controls, the [ 3 H]epibatidine binding was much decreased as compared with that of [ 3 H](-)nicotine and [ 3 H]cytisine. This may indicate a higher selectivity of [ 3 H]epibatidine for a nicotinic receptor subtype that is particularly affected by aging. The laminar binding pattern of [ 3 H]vesamicol showed one maximum in the outer cortical layers II/III. The [ 3 H]vesamicol binding did not change with aging. The binding of all ligands was significantly decreased in all layers of the temporal cortex in Alzheimer’s disease, but the [ 3 H]vesamicol binding decreased only half as much as the nicotinic receptors. Also, choline acetyltransferase activity was percentually more reduced than [ 3 H]vesamicol binding in Alzheimer’s disease. The cortical laminar binding pattern of all 3 H-ligands was largely absent in the Alzheimer’s disease cases. The less severe loss of vesicular acetylcholine transport sites as compared with the loss of the nicotinic receptors and choline acetyltransferase activity may suggest that vesamicol binding sites might be more preserved in presynaptic terminals still existing and thereby expressing compensatory capacity to maintain cholinergic activity.  1999 IBRO. Published by Elsevier Science Ltd. Key words: human temporal cortex, nicotinic receptor binding, vesicular acetylcholine transport sites, Alzheimer’s disease, quantitative autoradiography. The cerebral nicotinic acetylcholine receptors (nAChRs) are of great interest in relation to their involvement in cognitive function and memory. 90 Neuronal nAChRs are ligand-gated ion channel receptors consisting of ligand-binding a- and structural b-subunits. To date, nine human nAChR subunits have been cloned: a2, a3, a4, a5, a6, a7, b2, b3, and b4 (for a review, see Ref. 28). The nAChRs are located both presynaptically to facilitate neurotransmitter release 88,95,96 and postsynaptically to mediate responses. 9,74 The physio- logical function of their different combinations is still unknown. Autoradiographical studies of high-affinity nAChRs indicate their heterogeneous distribution in the human cerebral cortex with nicotinic agonists such as [ 3 H]nicotine, 54,63,94 [ 3 H]cytisine, 71,79 and [ 3 H]epibatidine. 79 [ 3 H]Epibatidine has been found to bind with subnanomolar affinity in human brain. 35,43 These three nAChR ligands are suggested to bind to one common binding site, which most probably represents a nAChR subtype that consists of a4 subunits. 79 This subunit seems to be one of the most affected in Alzheimer’s disease (AD). 91 A reduction in the number of nAChRs in the cerebral cortex of AD brains has been detected both by in vitro methods in post mortem brain tissue 20,53 and by in vivo methods using positron emis- sion tomography. 57,59 In a few studies, nicotine has improved attention and information processing in patients with AD. 51,73 In AD, further cholinergic deficiencies have been observed in presynaptic terminals, such as reduced choline acetyltrans- ferase (ChAT) activity, 19,32 reduced binding to high-affinity choline uptake transporter, 60,67 and reduced synthesis 22,82 and release of acetylcholine (ACh). 52 The density of the presynap- tic vesicular ACh transporter (VAChT) binding sites deter- mined by [ 3 H]vesamicol was also shown to be decreased in brains of patients with AD, 18,38 but increased in the study by Ruberg et al. 72 The aim of the present study was to compare the binding of [ 3 H](-)nicotine, [ 3 H]cytisine, and [ 3 H]epibatidine in relation to the [ 3 H]vesamicol binding in the temporal cortex of controls and patients with AD by in vitro autoradiography. Nicotinic and vesamicol receptors in Alzheimer cortex 685 685 Neuroscience Vol. 94, No. 3, pp. 685–696, 1999 Copyright  1999 IBRO. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306-4522/99 $20.00+0.00 PII: S0306-4522(99)00295-X Pergamon ‡To whom correspondence should be addressed. Tel.: + 46-18-4713373; fax: + 46-18-4713370. E-mail address: wiebke.sihver@pet.uu.se (W. Sihver) Abbreviations: ACh, acetylcholine; AD, Alzheimer’s disease; ApoE, apoli- poprotein E; ChAT, choline acetyltransferase; nAChR, nicotinic acetyl- choline receptor; VAChT, vesicular acetylcholine transporter.