Functional and Structural Basis of Thermoreception

Abstract

This chapter illustrates the functional and structural basis of thermoreception. Cutaneous warm and cold receptors have been investigated in various homoiotherms and poikilotherms. In biophysical terms, warm (cold) receptors are defined by an overshoot (transient inhibition) on dynamic warming and a transient inhibition (overshoot) on dynamic cooling. At constant temperatures, thermoreceptors show a static discharge with a bell-shaped temperature frequency curve. The static discharge does not allow an unequivocal discrimination between warm and cold receptors. Specific thermoreceptors are insensitive to mechanical stimulation. The dynamic overshoot is up to 30 times higher than the static discharge. For a given temperature change, the dynamic response is relatively small for warm receptors in the rat's scrotum, medium for the cold receptors in the cat's nose and large for warm receptors in the cat's nose and in the labial region of Boa constrictor . In certain single fibers from the ampullae of Lorenzini in the dogfish, a spontaneous inversion from cold to warm sensitivity of unknown origin has been observed. Ionized calcium inhibits cold receptor activity but enhances the activity of warm receptors. Direct comparisons have been made, between peripheral and central neural events following thermal stimulation of the rat scrotum.