Regulation of cortical blood flow by the dorsal raphe nucleus: topographic organization of cerebrovascular regulatory regions.

We examined in rat: (1) the time-course and magnitude of change in cortical blood flow (CoBF) following electrical stimulation of the dorsal raphe nucleus (DRN) and (2) whether DRN lesions affect resting CoBF or the cerebrovascular response to CO2. Animals were anesthetized (chloralose), paralyzed, and artificially ventilated. The effect of stimulus frequency (1-200 Hz) and intensity (10-100 microA) on arterial pressure, heart rate, and CoBF was examined; lesions were made electrolytically. CoBF was measured using a laser-Doppler flowmeter with the probe placed extradurally over the parietal sensorimotor cortex. The DRN was computer reconstructed in three dimensions from Nissl stained coronal sections for localization of electrode placements. Brief stimuli (8 s; n = 6) elicited frequency and intensity-dependent increases in arterial pressure, heart rate, and CoBF. Sustained intermittent trains of stimuli of rostral DRN (200 Hz; 1 s on/1 s off; 70 microA) elicited a decrease (85 +/- 12% of baseline; n = 9) in CoBF (p less than 0.05) while stimulation in caudal DRN resulted in increased CBF (126 +/- 13% of baseline; n = 9). Phenylephrine infusion (0.1-1 microgram; i.v.; n = 8) increased arterial pressure and CoBF less than that elicited by brief DRN stimulation (p less than 0.05). DRN lesions did not affect resting CoBF (140 +/- 25 perfusion units (PU) before; 127 +/- 16 PU after DRN lesion; p greater than 0.05, n = 5) or mean arterial pressure (127 +/- 13 before; 120 +/- 11 after); nor did it affect the cerebrovascular response to change in arterial PCO2. Sustained intermittent stimulation of the DRN can evoke either increases or decreases in CoBF depending on the anatomical sublocalization. The DRN does not tonically maintain resting CoBF, nor participate in the cerebrovascular response to change in PCO2.