Anxiety-induced antinociception in the mouse

RESUMO

It has been suggested that exposure to the elevated plus-maze (EPM) apparatus induces antinociceptive effects in mice as measured by the tail-flick assay,, which are not blocked by the opiate antagonist naltrexone. The a) if exposure limited to the open or the enclosed arm of the EPM would alter this effect; b) whether or not pharmacologically induced anxiety (1.0 mg/kg pentylenetetrazole, PTZ) would also reduce nociceptions c) if exposure to the EPM would alter visceral pain, as measured by the abdominal contortion test. The simultaneous exposure to both the open and enclosed arms of the EPM, but not the exposure limited to each type of arm, led to statistically significant increases in tail withdrawal latencies (TWL). Indeed, 10 min after exposure to both arms, TWL values (means ñ SEM) were 10.31 ñ 0.87 s as compared to a baseline value of 5.46 ñ 0.53 s. The acute administration of PTZ significantly increased TWL. Conversely, EPM-induced antinociception was not detected by the abdominal contortion test. These results confirm the existence of EPM-induced antinociceptive effects demonstrated by others and show that they may be multiple determinants