Age-related changes in properties of cortically projecting basal forebrain neurons

Electrophysiological properties of basal forebrain (nucleus basalis area) neurons projecting directly to the frontal cortex were studied in urethane-anesthetized young and old male rats. Extracellular recordings demonstrated a total of 75 neurons (35 young and 40 old cells) which were antidromically activated by electrical stimulation of the frontal cortex. Post-antidromic orthodromic excitatory responses were seen, and the number of neurons showing such an orthodromic excitation was significantly smaller in aged rats. No significant differences were observed between young and aged rats in the threshold, latency or the conduction velocity of antidromic activation, or in the spontaneous firing rate of driven cells. The absolute refractory period was significantly longer and the degree of successful antidromic propagation into the somatodendritic complex was significantly lower in aged rats. The data provide evidence that there are marked changes with age in the physiological properties of basal forebrain neurons projecting to the frontal cortex.