Temperature Preference and Responses of Cutaneous Temperature-Sensitive Neurons during Bullfrog Development

Abstract

The mean temperature selected by bullfrog tadpoles, Rana catesbeiana, in a continuous thermal gradient increased as a function of development; from 24 C at TaylorKollros stages X-XII, to 29 C at stages XIX-XX, to 32 C at stages XXIV-XXV. The variance of the selected body temperature decreased and the frequency at the modal temperature increased as development proceeded. Responses of a total of 29 cold-and three warm-sensitive neurons were characterized. As development progressed, the temperature at which static impulse frequency occurred in individual cutaneous coldsensitive neurons increased from a low of 16 C at stage XIII to as high as 32 C at stage XXV. The average static maximum temperature of these cold-sensitive units was less than the mean selected body temperature at each developmental stage studied (17 C at XIII-XIV, 25 C at XIX-XX, and 27 C at XXIV-XXV) but paralleled the developmental changes in thermal preference. We hypothesize that the ontogeny of the final thermal preferendum of bullfrogs is dependent on the developmental changes in the thermal characteristics of peripheral cold-sensitive neurons as well as possible changes in peripheral warm-sensitive neurons and neurons within the central nervous system.