Heat-stress-induced hyperthermia alters CSF osmolality and composition in conscious rabbits

Amino acids have received increased attention with regard to their thermore gulatory effects and possible role as neurotransmitters within the thermore gulatory system. The purpose of the present work was to evaluate in conscio us rabbits the changes in cerebrospinal fluid (CSF) concentration of taurin e, GABA, aspartate, and glutamate during exposure to high ambient temperatu re (50 min, 40 degrees C) to investigate their involvement in heat stress ( HS). CSF and plasma osmolality and CSF concentrations of some cations and p roteins were also determined. HS animals underwent transient hyperthermia a nd thereafter fully recovered. This was accompanied by a significant rise i n CSF and plasma osmolality, CSF protein, calcium, taurine, and GABA. Artif icial CSF osmolality measurements after addition of CaCl2 or taurine demons trated that the increased CSF osmolality after HS is accounted for, only in part, by the increased concentrations of either calcium and taurine. It is suggested that, during HS, taurine and GABA are released in the extracellu lar space of brain tissues in higher amounts, possibly to counteract the re sulting hyperthermia.