Indexed on: 01 Nov '59Published on: 01 Nov '59Published in: Pflügers Archiv - European Journal of Physiology
In cats lightly anesthetized with Presuren, their isolated carotidsinuses were perfused either with buffered KCN- or NaCN-Ringer-solutions (0,1–1,5 mg. in a 0,01–0,001 M solution, pH 7,3) or with arterial blood from a donor cat breathing nitrogen. The effects of increased chemoceptor activity on single lumbar α or γ motoneurones (Triceps surae) were studied.1. Spontaneous activity of γ motoneurones increases with chemoceptor stimulation. The same behaviour is observed in gastrocnemius muscle spindle discharges provided their efferent innervation is intact.2. This somatomotor activation is, as a rule, more pronounced than the vasomotor activation by chemoceptor excitation.3. The excitatory effect of the chemoceptors on γ motoneurones is stronger than the concurrent suppressor effect of the carotid sinus baroceptors when both are stimulated simultaneously.4. If the γ-muscle spindle-loop is interrupted, chemoceptor stimulation leads to facilitation of tonic stretch reflex responses of α motoneurones. With efferent as well as afferent pathways intact, the muscle frequently develops active tension changes and sometimes rhythmic movements.5. It is concluded that parts of the reticular activating motor system in the lower brain stem are excited by the afferent chemoceptor impulses.