Some Effects of Graded Changes in Central Chemoceptor Input By Local Temperature Changes on The Ventral Surface of Medulla

Abstract

We have attempted to examine the effects of rapid variations in the input from the central chemoceptive structures on the neural mechanisms regulating rate and depth of breathing without changing the chemical environment of the neuronal elements of these mechanisms. To that end we have taken advantage of results of Loeschcke and his collaborators. They have provided evidence suggesting that the central chemoceptive structures are located at circumscribed areas on the ventral surface of the medulla and shown that the central chemoreceptive function can be blocked by focal cooling of the “intermediate“ of these areas, (or S area), hereafter termed I_(S) area^1–4. The method of controlled cooling of regions in the central nervous system for the production of rapidly reversible block of synaptic transmission has proved a very useful tool in neurophys iological analysis of the functional organization of brain mechanisms^5–8. It has been well established that cooling a structure to a temperature of about 200C selectively blocks synaptic transmission with retained conduction in the nerve fibres (although at a somewhat slower rate). It was also known that the temperature gradient is steep (4 to 100C per mm) beneath a thermode on the brain surface or around a cryogenic probe thrust into deeper structures in the brain thus securing the spatial selectivity of the blocking effect^7–9.