Effects of ablation of N- and R-type Ca(2+) channels on pain transmission.

Recently several mutant mouse lines lacking neuronal voltage-dependent Ca(2+) channels (VDCCs) have been established by the use of gene targeting in embryonic stem cells. Pain-related behaviors in Ca(v)2.2 (alpha(1B)) and Ca(v)2.3 (alpha(1E)) knockout mice were studied to gain further insight into the mechanism of pain transmission, where VDCCs are thought to play important roles. We review here the data from these recent studies. Ca(v)2.3-/- mice showed normal responses to acute painful stimuli, and reduced responses to the somatic inflammatory pain stimuli. Ca(v)2.3+/- mice exhibited reduced symptoms of visceral inflammatory pain. Ca(v)2.3-/- mice showed abnormal behavior related to the descending antinociceptive mechanism activated by the intraperitoneal injection of acetic acid. Ca(v)2.2-/- mice showed variable acute nociceptive responses depending on the mutant lines. However, all the lines of Ca(v)2.2-/- mice exhibited reduced responses in the phase 2 of the formalin test, suggesting a suppression of inflammatory pain. Furthermore Ca(v)2.2-/- mice showed markedly reduced neuropathic pain symptoms after spinal nerve ligation. Impaired antinociception, similar to that seen in the Ca(v)2.3-/- mice, was also observed in the Ca(v)2.2-/- mice. Therefore, it is suggested that these mutant mice could provide novel models to delineate the nociceptive and antinociceptive mechanisms.