Higher environmental temperature-induced change in synaptosomal acetylcholinesterase activity of brain regions

Exposure of adult male albino rats to higher environmental temperature (HET) at 35 degrees for 2-12 hr or at 45 degrees for 1-2 hr increases hypothalamic synaptosomal acetylcholinesterase (AChE) activity. Synaptosomal AChE activity in cerebral cortex of rats exposed to 35 degrees for 12 hr and in cerebral cortex and pons-medulla of rats exposed to 45 degrees for 1-2 hr are also activated. AChE activity of synaptosomes prepared from normal rat brain regions incubated in-vitro at 39 degrees or 41 degrees for 0.5 hr increases significantly in cerebral cortex and hypothalamus. The activation of AChE in pons-medulla is also observed when this brain region is incubated at 41 degrees for 0.5 hr. Increase of (a) the duration of incubation at 41 degrees and (b) the incubation temperature to 43 degrees under in-vitro condition decreases the synaptosomal AChE activity. Lineweaver-Burk plots indicate that (a) in-vivo and in-vitro HET-induced increases of brain regional synaptosomal AChE activity are coupled with an increase of Vmax without any change in Km (b) very high temperature (43 degrees under in-vitro condition) causes a decrease in Vmax with an increase in Km of AChE activity irrespective of brain regions. Arrhenius plots show that there is a decrease in transition temperature in hypothalamus of rats exposed to either 35 degrees or 45 degrees; whereas such a decrease in transition temperature of the pons-medulla and cerebral cortex regions are observed only after exposure to 45 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)