Paraventricular vasopressin-containing neurons project to brain stem and spinal cord respiratory-related sites

We studied in the rat projections of vasopressin-containing neurons of the paraventricular nucleus (PVN) to phrenic nuclei and to the pre-Botzinger complex (pre-BotC). In addition, we determined vasopressin receptor expression within the pre-BotC and the physiological effects of vasopressin on respiratory drive and arterial blood pressure when injected into the pre-BotC. Retrograde tracing with cholera toxin B subunit (CT-b) showed that a subpopulation of vasopressin-containing PVN neurons project to phrenic nuclei and the pre-BotC. The latter region, identified by expression of neurokinin-1 receptors, contained a subpopulation of neurons that were immunoreactive for the vasopressin type 1 receptor (V1R). Microinjection of vasopressin in the pre-BotC (0.2 nmol/200 nl) significantly increased diaphragm electromyographic activity and frequency discharge (P < 0.05). In addition, vasopressin increased blood pressure and heart rate (P < 0.05). These data indicate that PVN vasopressin-containing neurons innervate respiratory-related regions of the medulla oblongata and spinal cord and when vasopressin is released at these sites, it may increase respiratory drive via activation of the distinct V1R. (C) 2002 Elsevier Science B.V. All rights reserved.