Convergence of visceral and somatic afferents on single neurones in the reticular formation of the lower brain stem in dogs.

The reticular formation of the lower brain stem contains neuronal circuits for the generation of sympathetic tone, respiratory rhythm, muscle tone and the control of vigilance. In anesthetized dogs single neurone activities were recorded in the medial two-thirds of the reticular formation to investigate the organizing principles of this multifunctional system. The results from 110 recordings demonstrate that single neurones receive information from somatosensory afferents of skin, joints and muscles together with afferents from baro-, chemo- and lung inflation and deflation receptors. Whereas the composition of afferent spectra from somatosensory sources was different from neurone to neurone, baroreceptors had a more generalized activity-decreasing effect and chemoreceptors had a generalized activity-increasing influence, the former directing physiological systems to a trophotropic and the latter towards an ergotropic state. The functional significance of the results for the co-ordination of different physiological systems is discussed.