Abstract:
Background: The role of noradrenergic system in the control of nociception is
documented in some vertebrate animals. However, there are no data showing
the role of this system on nociception in the marsh terrapins. Methodology: In
this study, the antinociceptive action of intrathecal administration of the a2-
adrenoreceptor agonist clonidine and a2-adrenoreceptor antagonist yohimbine
was evaluated in the African marsh terrapin using the formalin test. The interaction
of clonidine and yohimbine was also evaluated. Results: Intrathecal
administration of clonidine (37.5 or 65 lg/kg) caused a significant reduction in
the mean time spent in pain-related behavior. Yohimbine, at a dose of 25 lg/kg,
significantly blocked the effect of clonidine (65 lg/kg). However, administration
of yohimbine (40 or 53 lg/kg) caused a significant reduction in the mean time
spent in pain-related behavior. Intrathecal administration of yohimbine (53 lg/
kg) followed immediately by intrathecal injection of the serotonergic methysergide
maleate (20 lg/kg) resulted in a significant reversal of the antinociceptive
effect of yohimbine. Conclusion: The present study documented the intrathecal
administration of drugs in the marsh terrapin, a technique that can be applied
in future studies on these animals. The data also suggest the involvement of
both a2-adrenoreceptors and 5HT receptors in the modulation of nociception
in testudines.
