The role of N-type Ca2+ channels in nociceptive transmission was examined in genetically engineered mice lacking the α1B subunit of N-type channels and in their heterozygote and wild-type littermates. In α1B-deficient mice, N-type channel activities in dorsal root ganglion neurons and spinal synaptoneurosomes were eliminated without compensation by other types of voltage-dependent Ca2+ channels. The α1B-deficient mice showed a diminution in the phase 2 nociceptive responses more extensively than in the phase I-nociceptive responses of the formalin test. The α1B-deficient mice exhibited significantly increased thermal nociceptive thresholds in the hot plate test, but failed to increase mechanical nociceptive thresholds in the tail pinch test. These results suggest a crucial role of N-type channels in nociceptive transmission, especially for persistent pain like phase 2 of the formalin test and for nociception induced by thermal stimuli.
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