. Bonner zoologische Monographien. Zoology. 55 Warm Ree. -> Cold- Rec. ->. > Pa >Va THERMOREGULATORY RESPONSES Fig. 33: Proposed model for thermoregulatory system for hibernators (adapted from Luecke and South 1972). Neurons in the hypothalamus (Hy) having firing rates which are strongly temperature dependent (Q10 » 1) over the range of normal Tb (= Hi Q10 — sensory neurons). The Lo Q10 — sensory neurons are assumed to have firing rates over the range of Tb; they are not strongly temperature depen- dent. Both synapse with and facilitate or inhibit the neurons which activate regulat
. Bonner zoologische Monographien. Zoology. 55 Warm Ree. -> Cold- Rec. ->. > Pa >Va THERMOREGULATORY RESPONSES Fig. 33: Proposed model for thermoregulatory system for hibernators (adapted from Luecke and South 1972). Neurons in the hypothalamus (Hy) having firing rates which are strongly temperature dependent (Q10 » 1) over the range of normal Tb (= Hi Q10 — sensory neurons). The Lo Q10 — sensory neurons are assumed to have firing rates over the range of Tb; they are not strongly temperature depen- dent. Both synapse with and facilitate or inhibit the neurons which activate regulatory responses. Hammel (1967) suggests that the cold sensory neurons could be suppressed during hibernation by an inhibitory signal from the reticular activating system (RAS) which would remove central control over Tb. Throughout the period of deep hibernation active thermoregu- latory control is present (defense against cold). The subcortical structures remain in active control. Their electrical activity is characterized by inter- mittent localized bursts or spikes. The nature of the stimuli responsible for spontaneous arousal is still moot. No specific electrical activity in the brain has been found which induces the arousal process; once initi- ated, it is coordinated by the limbic system and may be expressed as a generalized sympathetic discharge (South et al. 1972 a). Summary: Beside the physical, chemical and behavioural temperature regulation, hibernators possess the ability to voluntarily lower the Th. Brown fat plays a role as a source of thermogenesis in awake mammals, during arousal and probably during torpor itself. Cold adaptation raises the basal metabolism and simultaneously, in several species, increases the readiness for hibernation. Torpor may start at low and at high T;1. The fall of Ti, is controlled. During deep torpor, temperature regulation is possible. The peripheral and central thermoreceptors are still excitable at 0° C. In several species, centra
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