Heat thermosensivity of the brain and spinal cord in Greenfinches

Abstract

Heat thermosensitivity of 13 brain areas and of the thoracic and lumbar parts of the spinal cord was studied in freely-moving Greenfinches at different ambient temperatures . Ofthe brain areas studied, clear vasomotor responses were observed only during local heating of the anterior hypothalamus (POA/POM) and dorsal medulla. The thresholds were 40.9 ±0.1 ° C (POA/POM) and 41 .8 ±0.4°C (medulla). No respiratory responses could be elicited by local brain heating . By contrast, spinal heating elicited both vasodilation and panting . During thoracic stimulation the vasomotor threshold was 41 .7 ± 0.2°C, and the panting threshold was 44.3 ± 0.1°C . During lumbar stimulation the reaction thresholds were higher by 1 .2 to 1 .5 °Cand the reactions were weaker. However, lumbar heating retained the ability to activate vasomotor reactions even in moderate hyperthermia. The data suggest that, as in other birds, the spinal cord of passerine birds plays a pivotal role in central thermosensitivity. The mammalian-like hypothalamic thermosensors of birds, on the other hand, may have a role in specific control of brain temperature.