Respiratory suppression by focal cooling of ventral medullary surface in anesthetized rats; functional and neuroanatomical correlate.

Bilateral cooling of the parapyramidal region in the rostral ventral medullary surface (VMS) elicited a reduction in respiratory frequency and phrenic inspiratory activity in halothane anesthetized rats. A distinct cluster of neurons (nucleus parapyramidalis superficialis) was found in a superficial layer (10-15 microns from the surface) just beneath the area where cooling produced suppression of respiration. The rat VMS layer contains neural substrates which regulate the respiratory rhythm generation and inspiratory neural output.