Effects of Hypothermia on Ischaemic Depolarisation In Brain: A Comparison of Responses in Rat and Gerbil

The latency of development of ischaemic depolarization (LID) has been used to compare the relative effects of different levels of hypothermia on ischaemic responses in brains of rat and gerbil, using a model with imposed complete cessation of cerebral blood flow (CBF=0). At temperatures reducing from 37°C to 20°C, the LIDs were consistently shorter in the gerbil than in the rat. For example, at 37°C the LID in the gerbil was 0.71±01.2 min, and in the rat, 1.37±0.02 min respectively (P<0.01), whilst at 20°C, the values were 5.48±0.25 min and 7.30±0.76 min (P<0.01). However, the relative effects of hypothermia on each species were similar (by linear regression with slopes of -0.29 and -0.35 min/°C in the two species). There may be underlying differences in brain biophysics or structure between species, but in spite of this, applied hypothermia still imposes a similar depression on the development of ischaemic damage. Both models may thus be used in studies of brain hypothermia as long as the intrinsic differences are appreciated.