Intracerebral temperature alterations associated with focal seizures.

Because focal seizures produce an increase in local cerebral metabolism and blood flow, we wanted to determine whether they might lead to changes in brain temperature. We induced focal neocortical seizures by microinjection of 4-aminopyridine (4-AP) into the rat motor cortex. The temperature on the dura immediately over the injection site, or 8 mm away, was measured with a thermocouple and in some experiments relative blood flow was monitored with a laser Doppler probe. In animals that did not receive 4-AP, brain and rectal temperature remained fairly constant at 33.5 and 37.2 degrees C, respectively, over a 2 h monitoring period. In animals treated with 4-AP, brain temperature over the seizure focus rose an average of 0.3 degrees C, within a few seconds of seizure onset, while rectal temperature remained constant. The seizure-induced temperature rise was preceded by an increase in cortical blood flow. The temperature, but not blood flow, was also elevated 8 mm away from the seizure focus. When blood flow was increased independently of neuronal activity, by elevating pCO(2), brain temperature also rose by about 0.3 degrees C. Focal seizures in anesthetized rats produce a small, but statistically significant increase in local brain temperature, as a result of increased blood flow that brings brain temperature closer to body temperature. In humans, seizures could actually cause a reduction in brain temperature, because brain temperature is normally higher than body temperature.