Neuronal responses in the rat's thalamus to scrotal heating

Twenty-one single neurons from the rat's thalamus were recorded as they responded to scrotal skin thermal stimulation. Eighteen of them were warm and three inverse-warm cells. After the injection of Lidocain (Xylocain) into the scrotal skin, the response of each neuron was abolished. Eight neurons could be followed until the drug effect had disappeared; their responsiveness was fully restored. External application of Xylocain had the same effect as intracutaneous injection, apart from longer time intervals before the effect became apparent. From this, conclusions are drawn on the origin of the thalamic responses, and speculations are made on the functional role of warm and inverse-warm cells.