Cutaneous vascular bed is not involved in arterial pressure changes elicited by increasing or decreasing the activity of inhibitory vasomotor neurons in caudal ventrolateral medulla in rabbits

We determined whether caudal ventrolateral medulla (CVLM) vasodepressor neurons tonically inhibit vasomotor tone in the ear in anesthetized rabbits. Injection of L-glutamate (10 nmol in 100 nl) into the CVLM decreased arterial pressure and increased superior mesenteric conductance. Ear conductance decreased (0.43 ± 0.06 to 0.33 ± 0.05 cm s^-1 per mmHg, n = 15 injections, 12 rabbits, P < 0.01). Conversely, bilateral injection of γ-aminobutyric acid (100 nmol in 100 nl) increased arterial pressure and decreased superior mesenteric conductance. At the same time ear conductance increased (0.39 ± 09 to 0.48 ± 0.27 cm s^-1 per mmHg, n = 8 injections, eight rabbits, P < 0.05). Results suggest that ear vessels are not tonically inhibited by the CVLM vasodepressor neurons. Presympathetic motoneurons regulating cutaneous flow may be excited, rather than inhibited, by the CVLM neurons. (C) 2000 Elsevier Science Ireland Ltd.