Cutaneous vasoconstriction in conscious rabbits during alerting responses detected by hippocampal θ-rhythm

We determined whether alerting stimuli cause cutaneous vasoconstriction in conscious rabbits. We compared ear blood flow with renal, mesenteric, and femoral flows at rest and in response to nonnoxious alerting stimuli, which induced θ-rhythm (4-9 Hz) in the simultaneously recorded hippocampal electroencephalogram (EEG). θ-Inducing stimuli (e.g., whistles and fur touches) reduced ear flow by 95 ± 6%, commencing 1-2 s after the EEG change and lasting 45 s. Renal flow did not significantly change with alerting stimuli, mesenteric and femoral flows slightly decreased, arterial pressure transiently rose (+10 ± 3 mmHg), and heart rate fell (-43 ± 9 beats/min). At rest, the coefficient of variation for ear flow (62 ± 6%) was greater than for other flows (P < 0.01). Phentolamine (1 mg/kg iv) reduced this coefficient to 29 ± 4% (P 0.01). Our study demonstrates that alerting responses in conscious rabbits are associated with selective cutaneous vasoconstriction, without increase in flow to skeletal muscle.