The M-Cholinergic Brain Reaction in Dependence on the Environmental Temperature for Cold-Blooded and Warm-Blooded Animals

During artificial incubation of slices of the sensorimotor cortex of guinea pigs and the telencephalon of turtles, microiontophoretic application of acetylcholine to neurons revealed a significantly lower frequency of spike responses in the nerve cells of turtles compared with guinea pig cells. This difference was attributed to the different rate of the M-cholinergic response in the temperature ranges of 27–29 and 34–36°C, as found previously in hypothermic experiments. Although experiments on guinea pig and turtle neurons were performed in the same temperature range (32–34°C), the genetically determined structure of neuronal membranes reflects the natural temperature dependence of both species: guinea pig membranes with a constant habitat temperature of 38°C have a higher density of K⁺ channels than turtles with a preferred temperature of 28–32°C. The difference in K⁺ channel representation was determined by a significantly longer activation after-effect in turtle neurons in response to glutamate-induced spike activation. The low density of K⁺ channels on membranes and the low rate of the M-cholinergic response, which closes them at the onset of any adaptive act, prevent neurons from forming high-frequency and long-lasting impulse sequences to regulate behavior over a wide range in turtles with a preferred temperature of 28–32°C.