On the regulator of spike activity in cortical neurons under hypothermic conditions

In sensorimotor cortical slices of guinea pig in the course of cooling incubating fluid from 34 to 21-22{degrees}C it was shown that hypothermia exerted both increase and decrease of spontaneous activity in different neurons. On hypothermic increase of firing level spike responses of soma to iontophoretic application of glutamate to dendritic locus appeared with shorter latencies and with longer latencies - on hypothermic decrease of spontaneous activity. At the same time hypothermia did not influence on the evoked spike reactions to iontophoretic application of glutamate straight to the soma. It means that hypothermic disorders of neuronal activity are not connected with changes in sensitivity to glutamate but determined by changes of amplitude of glutamatergic excitation while propagating along dendritic branches. The changes in spontaneous activity began at 30{degrees}C along with the decreased spike reactions to iontophoretic applications of acetylcholine and efficacy of dendro-somatic propagation. At the same temperature the fall of spike amplitude was initiated and increased with further hypothermia. It is proposed that the basis for hypothermic changes of neuronal activity is the decreased rate of M-cholinergic process at 27-29{degrees}C which leads both to attenuation of conductive function of dendrites and imbalance of K+ ion homeostasis. Peculiarities of hypothermic regulation of neuronal spike activity depend on individual functional properties of cortical neurons.