Relationships Between Bulbar Respiratory, Vasomotor and Somatic Facilitatory and Inhibitory Areas

Abstract

[longdash]The effect of stimulation of the bulbar reticular formation in anesthetized cats was studied with respect to the simultaneous recordings of blood pressure, knee jerk reflex, and respiration. The respiratory responses were characterized as facilitatory when there was evidence of actual muscular contraction as with max. inspiratory apnea, tidal (submaximal) inspiratory apnea, and max. expiratory apnea. Inhibitory respiratory responses were indicated when mid-positional apnea or tidal expiratory apnea (due to elastic collapse of the thorax) were obtained. The distr. of those points eliciting each of the above responses in the bulbar reticular formation was descr. and it was found that points inhibiting respiration could be found throughout the length of the bulbar reticular formation. The distr. of points causing vasopressor responses was similarly descr. and these were located as descr. by previous authors. Vasodepressor points did not have nearly the consistency of distr. as the vasopressor points nor were they as exactly distr. as descr. by others. The distr. of points causing facilitation or inhibition of the knee jerk reflex were as descr. previously except that there is a great predominance of inhibitory points. Stimulation of any one point in the bulbar reticular formation will almost inevitably give rise to simultaneous vasomotor, respiratory, and knee jerk facilitatory or inhibitory effects but these effects are rarely parallel in all 3 functions. It is concluded that when knee jerk inhibition and respiratory apnea are evoked from a single point that a vasomotor response also always occurs but its direction is equivocal. In 48% of the cases knee jerk inhibition was associated with respiratory apnea (either inspiratory, expiratory, or mid-positional). This was by far the most common combination of all and was most often elicited in the dorsomedial reticular formation. It was not possible to associate facilitation of the knee jerk with any other kind of response. There seems to be some common mechanism which can inhibit the respiratory rhythm and recurrent (knee jerk) reflexes but there is no identity between the somatic facilitatory and inhibitory areas with inspiratory or expiratory points.