Intra-abdominal pressure response to medullary stimulation in cats

Abstract

The interior of medulla was stimulated electrically and the intra-abdominal pressure responses studied in anesthetized cats. The most reactive areas were located at the levels of lower medulla. The response pattern was grouped into three types, i.e., tonic, tonic-spasmodic, and spasmodic abdominal contractions. The tonic abdominal contraction was characterized by a slowly building-up response during the period of stimulation. The reactive areas were located in the lateral reticular formation, and in the medial longitudinal fascicle at levels caudal to the obex. The tonic-spasmodic response was a spasmodic abdominal contraction superimposed on the tonic increase of intra-abdominal pressure. The reactive areas were found in the region between the tractus solitarius and the spinal tract of trigeminus. The spasmodic abdominal contraction was a strong alternate increase and decrease of the intra-abdominal pressure at a rate of approximately 1 per second, which looked like coughing. The reactive points were found in the similar areas to those for the tonic-spasmodic abdominal contraction. The reactive areas in the medial longitudinal fascicle at the levels caudal to the obex were supposed to represent the efferent pathways for the response.