Temperature Dependence of Thermal and Nonthermal Regulation: Hypothalamic Thermo- and Osmoregulation in the Duck

Abstract

Temperature dependence of central interneurons was assumed first by Hammel in 1965 to account for the influence of hypothalamic temperature (T_hy) on thermoregulatory activities. Specific thermosensory inputs were assumed to be generated in the hypothalamic thermointegrative network, without involving thermoreceptors in the strict sense of the word, by a Q₁₀ ≥ 1 for transmission of cold signals and a Q₁₀ ≫ 1 for transmission of warm signals from peripheral thermoreceptors. A more general view of this idea has been suggested by the unexpected disclosure of inappropriate thermoregulatory responses to thermal stimulation of the avian hypothalamus (Simon et al. 1976). While not compatible with the idea of temperature dependence as a specific mode of temperature transduction, inappropriate thermoresponsiveness of the avian hypothalamus could be accounted for by assuming a Q₁₀ > 1 for warm signal transmission and a Q₁₀ ≫ 1 for cold signal transmission at the hypothalamic level. Inherent to both hypotheses is the assumption of an overall Q₁₀ > 1 of intrahypothalamic transmission and, consequently, a decrease in gain of input-to-effector coupling with decreasing T_hy (Simon et al. 1986).