SELECTIVE ACTIVATION OF VASOMOTOR COMPONENT OF SAP SPECTRUM BY NUCLEUS-RETICULARIS VENTROLATERALIS IN RATS

We evaluated the contribution of the rostral nucleus reticularis ventr olateralis (NRVL) to the vasomotor component in the spectrum of system ic arterial pressure (SAP) signals by quantifying the transfer functio n between electrical stimulation of this medullary nucleus and the SAP response. Sprague-Dawley rats anesthetized with pentobarbital sodium, paralyzed with pancuronium, and mechanically ventilated were used. Br oad-band stimulation of the NRVL with computer-generated rectangular c urrent pulses (10-50 mu A, 1 ms), at a mean spike rate of 50 pulses/s and randomized modulation frequency of 0-3 Hz, elicited a site-specifi c and intensity-related presser response. Intriguingly, the correspond ing autospectrum of SAP signals exhibited prevailing power density onl y in the lower frequency range (0-0.8 Hz). This low-pass response char acteristic was confirmed by the observation that 90% of the total magn itude of transfer function between NRVL stimulation and SAP response c oncentrated between 0 and 0.6 Hz. The magnitude of NRVL-SAP transfer f unction was significantly reduced by phentolamine or prazosin but appr eciably enhanced by yohimbine. We conclude that the NRVL may contribut e to the very-low (0-0.25 Hz)- and low (0.25-0.8 Hz)-frequency compone nts of the SAP spectrum, which are believed to reflect sympathetic mod ulation on vasomotor activity via a-adrenergic neurotransmission.