Effect of short exposure to cold on plasma thyroxine in Coturnix quail: role of the infundibular complex and its neural afferents.

Exposure of control quail to low ambient temperature (4 degrees) for a short duration (15 min) led to a rapid increase in plasma thyroxine (T4) levels. A peak appeared 40 min after the cold began and was followed by a progressive and slow decline. T4 levels were elevated in birds maintained for up to 3 hr at 4 degrees. Restraint stress could be accompanied by a slight and late decrease in thyroxine concentration, indicating that glucocorticoids could partly inhibit thyroid function. Both cold and restraint stresses elicited sustained adrenocortical activation. No thyroid response to cold appeared after complete or partial neural deafferentation of the hypothalamus, indicating that cold signals were conveyed to the thyrotropic centers from peripheral and/or deep thermoreceptors through neural posterior-lateral afferents to the hypothalamus. No thalamic relay appeared to be necessary since normal thyroidal stimulation was observed after thalamic-hypothalamic disconnection. Such a response persisted in hemispherectomized quail.