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 microvessels of the mouse was investigated. A set protocol was followed, involving the performance of a craniotomy on anaesthetized animals and using intravital microscope-television closed circuitry. Controlled hyperthermic exposure was applied regionally by heating the brain surface with irrigating artificial cerebrospinal fluid. Microvascular responses such as changes in diameter, thrombosis and embolism were monitored and video-taped observations were further viewed and analysed. When both brain surface and core body temperatures were kept at 37° C, no changes in pial microvessels were noted. With core body temperature kept at 37° C and at a brain surface temperature of 43.1° C, passing emboli and arteriolar constriction were observed. A few minutes later, visible thrombosis was prevalent. Further spontaneous thrombo-embolic activity continued and at the end of a 50-min hyperthermic exposure, arterioles attained a constriction of 37%. Thrombus formation was sometimes massive enough to occlude fully the microvessel. The protocol followed in this study can be adopted to other small animal species and for a variety of experimental procedures involving hyperthermia and the pial microcirculation.