Effects of cholinergic depletion on evoked activity in the cortex of youngand aged rats

Degeneration of cholinergic neurons in the basal forebrain is a neural mark er of Alzheimer's disease and is associated with perceptual and cognitive d eficits. An idea that has attracted scientific scutiny is that aging makes the brain more susceptible to neurodegenerative diseases such as Alzheimer' s. The purpose of this study was to compare the effects of the loss of chol inergic input from nucleus basalis of Meynert on evoked activity in the pos teromedial barrel subfield of the somatosensory cortex in young (2-2.5 mont hs) and aged (28-30 months) male Fisher hybrid rats. The mean firing rate a nd receptive fields of single neurons in the posteromedial barrel subfield of the somatosensory cortex were examined after selective lesions of cholin ergic neurons in the nucleus basalis of Meynert with an immunotoxin, IgG 19 2-saporin. Functional properties of single neurons in young animals were affected much more significantly by cholinergic depletion than those in aged animals. In cholinergic-depleted young animals, the mean firing rate of evoked activit y and receptive field of posteromedial barrel subfield neurons were signifi cantly decreased. Cholinergic depletion caused a 14% decrease in evoked act ivity and a 33% increase in receptive field size in young animals. The mean firing rate and receptive field of single neurons were not affected by cho linergic depletion in aged animals. It is concluded that functional propert ies of cortical sensory neurons in young animals are more vulnerable to cho linergic depletion than are those of aged animals and that cholinergic depl etion does not further impact the properties of neurons exposed to the proc esses of aging. (C) 1999 ISDN. Published by Elsevier Science Ltd. All right s reserved.