EXERCISE PRESSOR RESPONSES AND THE BRAINSTEM

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Isometric muscular exercise causes increases in heart rate, blood pressure and ventilation. At least part of this response is reflexly evoked. This reflex may be conveniently studied in acute animal models utilizing stimulation of cut ventral roots to achieve muscular contraction which in turn evokes a cardiovascular response similar in many ways to that observed during isometric exercise. This reflex is often called the "exercise pressor reflex" as a convenient operational definition. The proposed research will investigate the specific location, electrophysiological response characteristics and immunocytochemical properties of cells which may contribute to the reflex. Brainstem areas for study includes: (a) caudal ventrolateral medulla including the area in or near the lateral reticular nucleus (LRN), (b) the nucleus ambiguus (NA), (c) rostral ventrolateral medulla including the areas analogous to the C1 area in the rat, and (d) medial medulla including the raphe nuclei, the "dorsomedial pressor region", the nucleus of the tractus solitarius and the inferior olive. The cells of these areas will be evaluated for responses to: (1) muscular contraction, (2) baroreceptor input, (3) chemoreceptor input, (4) stimulation of the "subthalamic locomotor area", or "defence area", and also will be evaluated for (5) contribution to sympathetic or parasympathetic outflow, and (6) neurotransmitter content and effects of various neurotransmitters. It is thought that a fundamental reciprocal inhibition relationship might exist between the muscular contraction-evoked pressor reflex and various depressor reflexes; and therefore, key points in both types of reflexes will be studied. The analysis techniques will include the use of 1) both extra and intracellular single cell electrical recording 2) immunocytochemical labelling and 3) microinjection and microiontophoresis to identify various transmitter substances. The studies will yield a further understanding of processes underlying pressor reflexes and their reciprocal relationship with depressor reflexes. Furthermore, the techniques of immunocytochemical labelling, intracellular recording and microiontophoresis are areas for career development training.