[Analysis of reflex thermoregulatory reactions induced by thermal stimulation of the trigeminal zone]

In anesthetized rabbits, the activity of thermoreceptors, the neuronal activity in the preoptic area of hypothalamus (POAH), and the efferent outflow in sympathetic fibres of the auricular nerve were studied during thermal stimulation of the skin innervated by the trigeminal nerve. Among 79 receptors 8 responded to warming of the skin and 38 responded to cooling with the maximal activity at the skin temperature 22-21 degrees C. The activity of 46 POAH neurons out of 94 correlated with the skin temperature: 34 neurons increased the frequency of firing during cooling and 12 during warming. The firing rate in the sympathetic ganglion cells and postganglionic fibers increased by 50-100% during cooling causing vasoconstriction of the rabbit's ear, while warming of the receptive zone reduced the activity by 56-48% or abolished it, leading to vasodilatation.