Thermoregulation mediated by conditioned heart-rate changes in pigeons

Abstract

Pigeons were subjected to an apparent heat (44 °C) or cold (30 °C) load by means of a thermode located next to their thermosensitive spinal cord. They were then able to obtain brief thermonormality (40 °C) spells if they changed their heart-rate by a preset amount above (or below) their baseline heartrate. In the final experiments the animals increased (or decreased) their heart-rate by about 25% within 12 training sessions, thereby achieving a partial thermoregulation: they were able to maintain their spinal temperature at a normal level for about 25% of the time. Extinction sessions, in which the heart-rate changes did not have any thermoregulatory effect, and control sessions, in which thermonormality periods were given independently of the heart activity, yielded baseline heart-rates. It is concluded that the cardiac activity related to thermoregulation may be subject to modification through learning and thus may not differ fundamentally in this respect from some homeothermic behavioural responses.This work was supported by the Interdisciplinary Research Fund of the Ruhr-Universität and the Deutsche Forschungsgemeinschaft through its Sonderforschungsbereich 114. We thank Dr. I. Schmidt (Bad Nauheim) for much advice and discussion and Dr. J. Emmerton, Miss A. Lohmann and Mrs. D. Hagenkötter for assistance of various kinds.