Basal forebrain control of cortical blood flow and tissue gases in conscious aged rats

Cholinergic projections from the basal forebrain are capable of influencing local cortical blood flow (CoBF). The effect of age on this influence was investigated by measuring CoBF and tissue gas partial pressures (PtO 2, PtCO 2) by mass spectrometry in conscious young adult (2–4 months) and aged (22–28 months) Fischer 344 rats. Electrical stimulation (50 μA) of the substantia innominata (SI) increased frontal (+100.9%) and parietal (+28.4%) CoBF in young rats, but the effects were less in aged rats (frontal, +48.6%, P < 0.05; parietal, +18.9%, difference N.S.). Frontal PtO 2 was increased in young but not aged rats ( P < 0.01.). During standard hypercapnia, changes in CoBF, PtO 2 and PtCO 2 did not differ between young and aged rats. Under physostigmine infusion (0.15 mg/kg/h, i.v.), the CoBF increases to SI stimulation were approximately doubled in both cortices, in young and aged rats, and PtO 2 increases were also significantly greater. However, frontal PtO 2 increases were significantly smaller in aged (+7.6%) than in young (32.7%) rats, as were frontal PtCO 2 reductions. We conclude: (i) the influence of the SI on frontal CoBF and PtO 2 is substantially reduced with age; (ii) although physostigmine treatment potentiates this influence in both groups, the beneficial effects are relatively limited for aged rats.