Effects of central thermal stimuli on activity in cutaneous and muscle vasoconstrictor neurones supplying the cat hindlimb

Abstract

Cutaneous (CVC) and muscle vasoconstrictor neurones (MVC) exhibit characteristic reflex patterns upon somatic and visceral stimuli. Central thermal stimuli should be specific for CVC neurones and not affect MVC neurones. In the following the reactions of these sympathetic neurones to warming and cooling of hypothalamus and spinal cord are described. The hypothalamus was warmed and cooled by a water-perfused thermode which was positioned stereotaxically into the rostral part of the third ventricle, the spinal cord by a water-perfused U-shaped tubing positioned epidurally. Vasoconstrictor activity was recorded from postganglionic axons which have been isolated in bundles from peripheral skin and muscle nerves of the cat hindlimb. The following results were obtained: I) Hypothalamic and spinal cord wanning lead to a decrease of activity in CVC neurones in a graded manner. When both brain structures are warmed the decrease of activity is larger than the algebraic sLm~nation of the individual effects. 2) Central cooling leads to an increase of activity in the CVC neurones. This increase was very often transient and comparatively smaller than the effects upon central warming. 3) The activity in MVC neurones was either not influenced by central thermal stimuli or increased due to small decreases of systematic blood pressure (baroreceptor unloading). 4) During hypothalamic warming respiratory rhythmicity in the activity of many CVC neurones was enhanced.