Effects of cholinergic depletion on evoked activity inthe cortex of young and aged rats

Abstract

Degeneration of cholinergic neurons in the basal forebrain is a neural marker ofAlzheimers disease and is associated with perceptual and cognitive deficits. An idea that hasattracted scientific scutiny is that aging makes the brain more susceptible to neurodegenerativediseases such as Alzheimers. The purpose of this study was to compare the effects of the loss ofcholinergic input from nucleus basalis of Meynert on evoked activity in the posteromedial barrelsubfield of the somatosensory cortex in young (2–2.5 months) and aged (28–30 months) maleFisher hybrid rats. The mean firing rate and receptive fields of single neurons in the posteromedialbarrel subfield of the somatosensory cortex were examined after selective lesions of cholinergicneurons in the nucleus basalis of Meynert with an immunotoxin, IgG 192-saporin.Functional properties of single neurons in young animals were affected much moresignificantly by cholinergic depletion than those in aged animals. In cholinergic-depleted younganimals, the mean firing rate of evoked activity and receptive field of posteromedial barrel subfieldneurons were significantly decreased. Cholinergic depletion caused a 14% decrease in evokedactivity and a 33% increase in receptive field size in young animals. The mean firing rate andreceptive field of single neurons were not affected by cholinergic depletion in aged animals. It isconcluded that functional properties of cortical sensory neurons in young animals are morevulnerable to cholinergic depletion than are those of aged animals and that cholinergic depletiondoes not further impact the properties of neurons exposed to the processes of aging.