Localizaion of functionally different premortor neurons for the presympathetic neurons in the rostral ventrolateral medulla of rabbits.

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Whether the functionally different premotor neurons for the sympathetic preganglionic neurons are located in different area in the rostral ventrolateral medulla (RVLM) or not was studied in anesthetized and immobilized rabbits. Blood flow of muscles of a forelimb and a hind limb, kidney and skin of an ear was measured with laser or ultrasonic Doppler flow meters. Conductance of each vascular bed was calculated by the flow and the mean arterial pressure. Effects of micro-injection of neuroexcitatory or neuroinhibitory agents into the rostral ventrolateral medulla on conductance of vascular beds were investigated. The effective area for forelimb and hid limb muscle vascular conductance is localized in the caudal part of the RVLM,whereas for the kidney the effective area was located in the rostral part of the RVLM.Neurons thaht control the skin blood flow were located medial part of the RVLM.These effective areas, however, had a considerable overlap each other. Because the preganglionic neurons that innervate the vessels of the forelimb muscles are located at the same spinal segments of those innervate to vessels of the ear skin, we concluded that the premotor neurons for the sympathetic preganlionic neurons are located according to their function but not their axons projected.