KELTY, J.D.*; NOSEWORTHY, P.; FEDER, M.E.; ROBERTSON, R.M.; RAMIREZ, J.M.: Effect Of Heat Pretreatment On Spontaneous Glutamatergic And Glycinergic Synaptic Transmission During Subsequent Thermal Stress In The Mouse Pre-B-tzinger Complex

Brief exposure to sublethal high temperature induces protection against a variety of stresses (e.g., high temperature, oxidation, hypoxia) in many organisms. The breadth of protection conferred in this way suggests potential importance in defending the mammalian central nervous system against the detrimental effects of ischemia and hypoxia. As part of our investigation into the effects of hyperthermia on neuronal function, we used standard whole-cell patch clamp techniques to determine whether thermal pretreatment alters the frequency of spontaneous glutamatergic and glycinergic synaptic transmission between neurons of the mouse pre-B�tzinger complex during subsequent hyperthermia. Without thermal pre-treatment, heating the tissue from 30˚ to 40˚C increased the frequency of spontaneous miniature postsynaptic currents elicited by both glutamate and glycine by 1104.1 � 86.3% and 3582.8 � 142.6%, respectively. However, a 15 min thermal pretreatment at 39.5˚ – 41˚C one hour prior to such hyperthermia significantly reduced the increase in frequency of spontaneous transmission via glutamate to 456.5 � 43.4% above 30˚C baseline (p < 0.005) and via glycine to 1120.9 � 94.8% above baseline (p < 0.0005). Two hours following thermal pretreatment, hyperthermia-induced increases in spontaneous transmission frequency remained significantly lower than those in tissues undergoing hyperthermia for the first time (p < 0.005 for both neurotransmitters). These data indicate that exposure of nervous tissue to temperatures experienced during high fever or heat stroke induces an acclimatory response opposing extreme deviation from normal frequencies of spontaneous synaptic transmission.