Effects of simultaneous application of opposing brain-stem stimuli on respiration and blood pressure in anesthetized cats

The effect of simultaneous stimulation of paired brain-stem sites, one of which elicited an increase and the other a decrease in respiration or in blood pressure, was assessed in cats anesthetized with Nembutal or chloralose. Sites of stimulation were dispersed from posterior hypothalamus to medulla oblongata. Under Nembutal anesthesia, alterations of respiratory amplitude or rate in opposite directions were found upon single stimulation of sixteen pairs of sites. Simultaneous stimulation of these paired opposing sites yielded the following patterns in terms of respiration: (a) algebraic summation or cancellation of opposing effects; (b) a response equivalent to that seen upon stimulation of one site of the pair, representing simple dominance; or (c) a response of markedly greater magnitude than that seen upon single stimulation, representing exaggeration. Under chloralose anesthesia, eleven pairs of sites exerted opposing effects on blood pressure, and eight of these pairs also altered respiratory rate in opposite directions. Simultaneous stimulation resulted in either (a) algebraic summation or (b) an exaggerated response; simple dominance was not observed in cats anesthetized with chloralose. An exaggerated response in one function (e.g., blood pressure) was usually accompanied by an algebraic summation of the other (e.g., respiration). Thus the functions of blood pressure and respiration are capable of exhibiting several types of response to simultaneous opposing stimuli, when sites of stimulation are dispersed through several areas of the brain stem in anesthetized cats. The two functions may reveal independence in their patterns of response to simultaneous stimulation of the same pair of brain-stem areas.