Regulation of cerebral blood flow response to somatosensory stimulation through the cholinergic system: a positron emission tomography study in unanesthetized monkeys

The effects of scopolamine, a muscarinic cholinergic receptor antagonist and physostigmine, a cholinesterase inhibitor, on the regional cerebral blood flow (rCBF) response to vibrotactile stimulation of the forepaw were studied in the brain of unanesthetized monkeys using ¹⁵O-labeled water and high resolution positron emission tomography. Before scopolamine administration, vibrotactile stimulation produced a significant increase in the rCBF response in the contralateral somatosensory cortex of the monkey brain. Intravenous administration of scopolamine at doses ranging from 1 to 500 μg/kg resulted in a dose-dependent reduction of the rCBF response. The rCBF response abolished by scopolamine (50 μg/kg) was recovered by administration of physostigmine (10 μg/kg). On the other hand, the regional cerebral metabolic rate of glucose (rCMRglc) response, measured with [¹⁸F]-2-fluoro-2-deoxy-d-glucose, to the same stimulation was unchanged by administration of either scopolamine and/or physostigmine. These results suggested that cholinergic mechanisms might be involved in regulation of the coupling between neuronal activity and rCBF response, not between the activity and rCMRglc response.