Somatosensory regulation of regional hippocampal blood flow in anesthetized rats

The effect of noxious or non-noxious mechanical stimulation of various cutaneous areas on cerebral blood flow in hippocampus was examined with laser Doppler flowmetry in urethane-anesthetized artificially-ventilated rats. Noxious mechanical stimulation (pinching) of the skin on the face, forepaw, chest, or hindpaw for 20s increased regional hippocampal blood flow (Hpc-BF) and systemic blood pressure, but non-noxious mechanical stimulation (brushing) had no such effect. After the spinal cord was transected at T1 level a forepaw pinch caused no change in blood pressure but still increased Hpc-BF. This suggests that cutaneous noxious stimulation can induce pressor-independent increases in Hpc-BF. The increase in Hpc-BF induced by a forepaw pinch in T1-transected rats was partially reduced by intravenous administration of mecamylamine (2 mg/kg), a nicotinic cholinergic receptor antagonist. Atropine (0.5 mg/kg), a muscarinic cholinergic antagonist was ineffective. These data indicate that the cholinergic vasodilative system is involved in the somatically-induced increase in Hpc-BF via activation of the nicotinic cholinergic receptors.