Anesthesiology
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The authors examined in vivo the effects of general anesthetics on evoked substance P release (primary afferent excitability) and c-Fos expression (neuronal activation) in superficial dorsal horn. ⋯ General anesthetics at anesthetic concentrations block spinal neuron activation through a mechanism that is independent of an effect on small primary afferent peptide release. The effect of fentanyl alone and the synergistic effect of isoflurane and nitrous oxide on substance P release suggest a correlative rationale for the therapeutic use of these anesthetic protocols by blocking nociceptive afferent transmitter release and preventing the initiation of cascade, which is immediately postsynaptic to the primary afferent.