BASAL FOREBRAIN CONTROL OF CORTICAL BLOOD-FLOW AND TISSUE-GASES IN CONSCIOUS AGED RATS

Cholinergic projections from the basal forebrain are capable of influe ncing local cortical blood flow (CoBF). The effect of age on this infl uence was investigated by measuring CoBF and tissue gas partial pressu res (PtO2, PtCO2) by mass spectrometry in conscious young adult (2-4 m onths) and aged (22-28 months) Fischer 344 rats. Electrical stimulatio n (50 mu A) of the substantia innominata (SI) increased frontal (+ 100 .9%) and parietal (+ 28.4%) CoBF in young rats, but the effects were l ess in aged rats (frontal, + 48.6%, P < 0.05; parietal, + 18.9%, diffe rence N.S.). Frontal PtO2 was increased in young but not aged rats (P < 0.01.). During standard hypercapnia, changes in CoBF, PtO2 and PtCO2 did not differ between young and aged rats. Under physostigmine infus ion (0.15 mg/kg/h, i.v.), the CoBF increases to SI stimulation were ap proximately doubled in both cortices, in young and aged rats, and PtO2 increases were also significantly greater. However, frontal PtO2 incr eases were significantly smaller in aged (+ 7.6%) than in young (32.7% ) rats, as were frontal PtCO2 reductions. We conclude: (i) the influen ce of the SI on frontal CoBF and PtO2 is substantially reduced with ag e; (ii) although physostigmine treatment potentiates this influence in both groups, the beneficial effects are relatively limited for aged r ats.