Thermosensitivity of Preoptic Neurons and Hypothalamic Integrative Function in Hibernators and Nonhibernators

Mammalian Hibernation: An Escape from the Cold

“…One of these suggests that at least on theoretical grounds, two additional interactive neuronal pools which are active only during the hibernating phase may be responsible in exerting active inhibition or facilitation on thermogenesis in the cold, allowing the occurrence and termination, respectively, of hibernation (South et al 1978). Although this supposition is weakened by the current lack of a precise definition on the nature and anatomical specificity of these neurons, it is nevertheless consistent with the observation that in the nonhibernating phase, euthermic hibernators show equivalent hypothalamic thermosensitivity to that seen in the nonhibernating species (Wiinnenberg et al 1978) but are capable of exhibiting a wider range of thermosensitivity during the hibernating phase. It is therefore apparent that seasonal alterations in CNS thermoregulatory sensitivity and responsiveness to thermal and chemical challenges may occur and such alterations may provide clues as to the selective activation or depression of CNS neuronal mechanisms governing thermoregulation.…”

“…During entry into hibernation, there is a further, progressive decline in Tset and thermosensitivity, resulting in corresponding decreases of metabolic rate and body temperature (HelIer et al 1978). Electrophysiological recordings from the diencephalon in hedgehogs, Erinaceus europaeus (Wiinnenberg et al 1978), indicate suppression of neuronal activities prior to any significant decrease in body temperature during entry into hibernation. Other studies have also shown that during entry into hibernation, suppression of electrical activities occurs first in the neocortex, followed by those in the midbrain reticular formation, and lastly in areas of the limbic system (Wiinnenberg et al 1978;Beckman and Stanton 1982).…”

“…Electrophysiological recordings from the diencephalon in hedgehogs, Erinaceus europaeus (Wiinnenberg et al 1978), indicate suppression of neuronal activities prior to any significant decrease in body temperature during entry into hibernation. Other studies have also shown that during entry into hibernation, suppression of electrical activities occurs first in the neocortex, followed by those in the midbrain reticular formation, and lastly in areas of the limbic system (Wiinnenberg et al 1978;Beckman and Stanton 1982). During hibernation, at a brain temperature of 6.1 °C (Strumwasser 1960), spontaneous electrical activity remains in most, if not all brain areas, but especially in the motor and sensory cortex, medial preoptic area, septum, and the ventromedial nucleus of the hypothalamus although the magnitude of EEG has decreased to about 100/0 of that observed in euthermia.…”