Clonidine impairs sustained attention and memory in Alzheimer's disease

We investigated the effect of the alpha2-agonist, clonidine (orally: 0.5 an d 2 mu g/kg), administration on parameters assessing attention and shea-ter m recognition memory in Alzheimer's disease patients. Clonidine 2 mu g/kg, but not 0.5 mu g/kg, disrupted memory accuracy in delayed matching to sampl e test delay-dependently in nine out of 28 patients. The volumes of the hip pocampus and the entorhinal cortex of those Alzheimer's disease patients wh o were sensitive to clonidine administration were larger than those whose p erformance was unaffected by clonidine. These two groups of Alzheimer's dis ease patients performed equally in measures of attention after placebo or c lonidine administration. Clonidine 2 mu g/kg disrupted attention only at le vers of testing that were demanding for the individual patients. Our results suggest that the disruptive effect of clonidine on short-term m emory in Alzheimer's disease patients may be mediated via the hippocampus a nd the entorhinal cortex. Furthermore, the deleterious effect of clonidine on effortful attention is mediated via different brain systems from those i nvolved in the modulation of memory function. (C) 1999 IBRO. Published by E lsevier Science Ltd.