LOCAL CEREBRAL HYPERTHERMIA INDUCES SPONTANEOUS THROMBOSIS AND ARTERIOLAR CONSTRICTION IN THE PIA MATER OF THE MOUSE

The effect of local cerebral hyperthermia on responses of pial microve ssels of the mouse was investigated. A set protocol was followed, invo lving the performance of a craniotomy on anaesthetized animals and usi ng intravital microscope-television closed circuitry. Controlled hyper thermic exposure was applied regionally by heating the brain surface w ith irrigating artificial cerebrospinal fluid. Microvascular responses such as changes in diameter, thrombosis and embolism were monitored a nd video-taped observations were further viewed and analysed. When bot h brain surface and core body temperatures were kept at 37-degrees-C, no changes in pial microvessels were noted. With core body temperature kept at 37-degrees-C and at a brain surface temperature of 43.1-degre es-C, passing emboli and arteriolar constriction were observed. A few minutes later, visible thrombosis was prevalent. Further spontaneous t hrombo-embolic activity continued and at the end of a 50-min hyperther mic exposure, arterioles attained a constriction of 37%. Thrombus form ation was sometimes massive enough to occlude fully the microvessel. T he protocol followed in this study can be adopted to other small anima l species and for a variety of experimental procedures involving hyper thermia and the pial microcirculation.