Influence of cold adaptation on the activity of thermoresponsive neurons in thalamus and midbrain of the rat.

A group of 25 rats was adapted to cold by housing for five weeks at +3 degrees C. Using thermal stimuli of the scrotal skin, 53 recordings of warm-responsive thalamic and midbrain neurons were analyzed and compared with 84 control recordings from non-adapted rats. The activity of the analyzed neurons is characterized by a steep increase of firing rate above a certain temperature threshold zone. Between scrotal skin temperatures of 36 degrees and 38 degrees C the percentage of neurons with firing rates above the basal rate is higher, both in the thalamic and midbrain population of the cold adapted rats. It is concluded that after cold-adaptation the increase of firing rate starts on average at a lower temperature. The results are discussed in the context of findings of other authors on peripheral structures and on effector behaviour.