The study was designed to investigate the involvement of noradrenergic and serotonergic receptor systems in the modulation of formalin-induced pain-related behaviour in the Speke's hinged tortoise. Intradermal injection of 100 μL of formalin at a dilution of 12.5% caused pain-related behaviour (hindlimb withdrawal) that lasted for a mean time of 19.28 min (monophasic response). Intrathecal administration of clonidine (α -adrenergic receptor agonist) and yohimbine (α -adrenergic receptor antagonist) at a dose of 40 μg/kg and 37.5 μg/kg or 50 μg/kg, respectively, caused a highly significant reduction in the duration of the formalin-induced pain-related behaviour. The effect of clonidine was reversed by intrathecal administration of yohimbine at a dose of 26.7 μg/kg. The effect of yohimbine at a dose of 50 μg/kg was reversed by intrathecal injection of 20 μg/kg of the serotonergic receptor antagonist methysergide maleate. When performing antagonistic reactions, the administration of the antagonist was followed immediately by that of the agonist. The study indicates that for experimental purposes, intrathecal route of drug administration through the atlanto-occipital joint is effective in tortoises. The data also suggest that testudines have noradrenergic and serotonergic systems that appear to play a role in the modulation of pain in this species.

BackgroundThe 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.MethodologyIn this study, the antinociceptive action of intrathecal administration of the α2-adrenoreceptor agonist clonidine and α2-adrenoreceptor antagonist yohimbine was evaluated in the African marsh terrapin using the formalin test. The interaction of clonidine and yohimbine was also evaluated.ResultsIntrathecal administration of clonidine (37.5 or 65 μg/kg) caused a significant reduction in the mean time spent in pain-related behavior. Yohimbine, at a dose of 25 μg/kg, significantly blocked the effect of clonidine (65 μg/kg). However, administration of yohimbine (40 or 53 μg/kg) caused a significant reduction in the mean time spent in pain-related behavior. Intrathecal administration of yohimbine (53 μg/kg) followed immediately by intrathecal injection of the serotonergic methysergide maleate (20 μg/kg) resulted in a significant reversal of the antinociceptive effect of yohimbine.ConclusionThe 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 α2-adrenoreceptors and 5HT receptors in the modulation of nociception in testudines.

The biggest challenge in utilization of analgesics in reptiles has always been species specificity in respect to their effectiveness. Some analgesics considered to be generally effective in reptiles are not effective in certain reptile species. Mostly, pain in reptiles is commonly treated by use of non-steroidal anti-inflammatory drugs (NSAIDs), opioids and alpha-2 agonists (Sladky & Mans, 2012). There is also a plethora of potential analgesics for reptiles that are currently available and used in other vertebrate species. Tricyclic antidepressants for example are

Some of the most commonly used analgesic drugs in animals are of questionable efficacy or present adverse side effects among the various species of reptiles. Tricyclic antidepressants have been demonstrated to have antinociceptive effects in several animal models of pain and could be a good alternative for use in reptiles. The aim of the study was to investigate the antinociceptive effects of nortriptyline and desipramine hydrochloride in Speke's hinge-back tortoise. A total of 24 animals weighing 600-1000 g were used for nociceptive tests, i.e., formalin, capsaicin, and hot plate tests. Drugs were administered intracoelomically 30 min before starting the tests. The time spent in nocifensive behavior and the associated observable effects during the tests were recorded. Only the highest dose of 40 mg/kg of nortriptyline hydrochloride caused statistically significant decrease in nocifensive behavior in both the formalin and the capsaicin test. Desipramine hydrochloride at doses of 20 and 40 mg/kg caused statistically significant decrease in nocifensive behavior in the formalin test. Also, desipramine hydrochloride at doses of 15, 20, and 60 mg/kg caused statistically significant decrease in nocifensive behavior in the capsaicin test. None of the doses used for both drugs had any statistically significant effect on nocifensive behavior in the hot plate test. The results show that nortriptyline and desipramine hydrochloride have significant antinociceptive effects in the chemical but not thermal inflammatory pain-related behavior in the Speke's hinge-back tortoise. The most common associated side effect following administration of the higher doses of either of the drugs is excessive salivation. K E Y W O R D S antinociception, capsaicin test, desipramine hydrochloride, formalin test, nortriptyline hydrochloride, tortoise 1 | INTRODUCTION Reptile analgesia is a developing field in reptile medicine. It's generally agreed that analgesia should be an