BRIEF HYPERCAPNIA ENHANCES SOMATOSENSORY ACTIVATION OF BLOOD-FLOW IN RAT

Activation of CBF by hypercapnia or functional stimulation has been at tributed to multiple mediators, most of which are thought to interfere with cerebrovascular reactivity in a closely time-related manner. Her e we describe that brief hypercapnia produces marked up-regulation of somatosensory activation of blood flow that outlasts carbon dioxide ex posure for at least 60 min. In chloralose-anesthetized, mechanically v entilated rats, somatosensory activation was carried out by electrical stimulation of the forepaw. Blood flow was measured in the contralate ral primary somatosensory cortex by laser-Doppler flowmetry (LDF). Und er control conditions, somatosensory stimulation increased LDF by 38.8 +/- 11.0%. Ventilation with 6% CO2 for 3 min caused a rise of LDF by 28.0 +/- 8.7%. Baseline CBF and P(a)co(2) returned to control values w ithin 20 min. Repetition of somatosensory stimulation after hypercapni a revealed a long-lasting up-regulation of the flow response: 25 min a fter hypercapnia, functional stimulation increased LDF by 86.0 +/- 18. 1%, and 60 min after hypercapnia even by 96.0 +/- 26.0%. This is the f irst demonstration of CO2-induced up-regulation of functional activati on of blood flow and an example of the importance of general physiolog ical variables for the modulation of the coupling process.