Approach for quantifying the overall function of the ascending central neural integration to release vasopressin in...

Electrical stimulation of the intermediate portion of the solitary nucleus (SOL) is known to consistently elicit a pressor response and increase in the release of vasopressin (VP) in rats, when the cervical spinal cord and vago-sympathetic trunks are cut. The aim of the present study was to provide a methodological assessment for this technique, in order to quantify the central neuroendocrine function to release VP. Experiments were conducted on rats with cervical cordotomy and vagotomy, under 60% N2O anesthesia and artificial ventilation. The animals were maintained at their normal arterial blood pressure by infusing phenylephrine, which itself exerted little influence on the arterial plasma VP concentration (pVP) during SOL stimulation. In order to prevent blood loss, cross circulation with a donor rat was utilized in the blood sampling for pVP determination. We confirmed that this technique itself did not significantly affect the pVP level. A monopolar stimulus at a frequency of 50 Hz was found to produce the pressor response most effectively. The current spread of the stimulation (0.5 ms duration; 1 s on/1 s off; up to at least 120 microA) did not induce a false-positive pressor response mediated by other structures adjacent to the SOL. We suggest that electrical stimulation of the SOL in rats with cervical cordotomy and vagotomy, for observing the pressor response and/or increase of pVP, represents a rapid approach for screening the overall function of the ascending efferent part of the reflex mechanisms to release VP.