Cortical cerebral blood flow governed by the basal forebrain: age-related impairments.

This study sought to compare resting and evoked increases in cortical microvascular perfusion elicited by electrical microstimulation of the basal forebrain (BF) in young (4-6 months) and aged (22-26 months) Sprague-Dawley rats. Regional cerebral blood flow (rCBF) was measured in chloralose-anesthetized rats for twelve bilateral regions using 14C-iodoantipyrine with regional brain dissection, while second-to-second changes in tissue perfusion were concurrently assessed using laser-doppler flowmetry (LDF). In young animals, BF stimulation elicited significant ipsilateral increases in CBF in parietal (+123%) and frontal (+107%) cortices, caudate nucleus (+63%) and thalamus (+59%) (p less than 0.05). The BF-elicited increases were preserved in frontal cortex and thalamus, but not in parietal cortex or caudate nucleus of aged animals. No frequency- or current-specific attenuations were observed in the spared frontal cortex of aged animals. However, there was a significant (+70%) age-related increase in the latency to reach maximal blood flow increases (p less than 0.05), without any change in the total time of increased blood flow. These findings support the hypothesis that cortical CBF is in part governed by BF neurons, and suggest that regionally selective, age-related impairments of cortical coupling of neuronal to dynamic vascular responses exist. It remains to be determined whether the mechanism of this impairment relates to an age-related impairment in coupling of blood flow and metabolism.