FURTHER OBSERVATIONS ON THE DISTRIBUTION AT THE LEVEL OF THE PONS OF DESCENDING NERVE FIBERS SUBSERVING HEAT REGULATING FUNCTIONS

Abstract

Information regarding the lateral distribution of descending nerve fibers subserving heat regulation was gained by studying dogs for extended periods after placing graded transverse lesions in the pons. In addition to a complete hemisection on one side, a transverse section must extend across the midline and involve a considerable portion of the medial tissue of the opposite half of the stern before the animal''s heat regulating ability is in any way affected. Even then there is no grossly detectable asymmetry in the responses of the heat regulating mechanisms on the 2 sides of the body. When enough of the opposite medial tissue is involved, the heat maintenance mechanism is impaired or permanently eliminated before heat loss ability is detectably altered. The retention of either heat maintenance or heat loss powers in chronic prepns. following an incomplete trausection of the pons is dependent on the functional activity of nerve libers descending through the unsevered tissue, and not to the activity of subsidiary medullary neurons. This is evident from the fact that these functions are eliminated permanently when transection is completed by an opposite hemisection of the midbrain. Of considerable significance to localization studies is the fact, that descending fibers which subserve heat regulating functions may be temporarily paralyzed by the traumatic sequelae of an acute lesion. The assay of heat regulation deficits on acute or subchronic prepns. is therefore entirely unreliable.