Age-related alterations in responses of nucleus basalis magnocellularis neurons to peripheral nociceptive stimuli

The present study investigated the effects of peripheral noxious stimuli on the spontaneous activity of the nucleus basalis magnocellularis (nbM) neurons in young, adult and old rats. Single unit extracellular recordings from the nbM neurons were obtained with glass micropipettes in urethane-anesthetized rats. A total of 104 units were antidromically identified as nbM-cortical neurons. Noxious but not innocuous mechanical stimulation elicited responses in 72% of the 104 neurons. Most of them were excited. The receptive fields were usually very large and bilateral. Most of the neurons also responded to noxious thermal, chemical and electrical stimuli. No marked differences were observed in the incidence of neurons having different spontaneous firing rates, firing patterns and response type among the three age groups. However, the latency of responses evoked by noxious thermal or electrical stimulation and the threshold of excitatory responses evoked by electrical stimulation were increased with aging. The duration and peak-firing rate of excitatory responses evoked by noxious thermal, chemical or electrical stimulation were decreased in old rats. These findings indicate that there might be some functional changes in the nbM neurons and its projection pathway with aging, which impair their responsive ability to peripheral nociceptive stimuli.