Aspirin influences mouse pial microvascular responses to regional hyperthermia

Pial microvascular responses to a hyperthermic exposure, at 44°C for 45 min, applied to the brain surface of anesthetized mice were observed and recorded by intravital videomicroscopy. The hyperthermic exposure was applied by heated artificial cerebrospinal fluid (ACSF). The effect of aspirin (100 mg/kg, i.p.), given 60 min prior to hyperthermic exposure was also studied. Mice were anesthetized (urethane, 1-2 mg/g, i.p.), the trachea was intubated and a craniotomy was performed. A cranial well was affixed on the animal's head, to which ACSF was delivered and drained. Microvascular responses such as changes in diameter, thrombosis and embolism were monitored. With core body temperature kept at 37°C and at a brain surface temperature of 43.3 ± 1.0°C, passing emboli were first observed in arterioles and then shortly afterwards in venules. A few minutes later, visible thrombi were prevalent. Arteriolar constriction was also noted. Further thrombo-embolic activity continued and by the end of a 45-min exposure arterioles attained a 21% constriction. Aspirin, compared to control, delayed the appearance of the first observable response (18.6 ± 4.2 vs 11.5 ± 4.5 min, P < 0.05) in arterioles and reduced arteriolar constriction (5 vs 24%, P < 0.01) at that time. No significant differences were noted between the two groups on the venular side. The protocol and experimental set-up described can be employed in a variety of studies when thermic treatments, whether hypo or hyper, and pial microcirculation are of interest.