Sensitization of the tail-flick reflex following exposure to either a single prolonged test trial or behavioral testing under the analgesic influence of morphine

Anti-hypersensitive effect of intramuscular administration of αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] in rats of neuropathic pain

αO-conotoxin GeXIVA (GeXIVA) is a potent antagonist of α9α10 nicotinic acetylcholine receptors (nAChRs), which has four Cys residues and three disulfide isomers. Among the 3 isomers, both GeXIVA[1,2] (bead isomer) and GeXIVA[1,4] (ribbon isomer) showed potent block on α9α10 nAChRs with close low nanomolar IC50s. Here we report that anti-hypersensitive effects of the bead and ribbon isomers in the chronic constriction injury (CCI) model of neuropathic pain and acute pain model of tail flick test. Treatment was started and continued for 7 or 14days after the development of hyperalgesia which was induced by CCI surgery. GeXIVA[1,2] and GeXIVA[1,4] significantly reduced mechanical allodynia in CCI rats without tolerance, in which GeXIVA[1,2] remained up to two weeks after intramuscular administration of the toxins was ceased. The pain reliever effect of GeXIVA[1,2] on neuropathic rats was slightly better than GeXIVA[1,4]. The two isomers did not suppress the acute thermal pain behaviors significantly when they were tested in the tail flick model by intramuscular bolus injection. Both GeXIVA[1,2] and GeXIVA[1,4] had no significant effect on performance of rats in the accelerating rotarod test after intramuscular injections. This suggests that αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] may offer new strategies to the treatment of neuropathic pain.

The Antinociceptive Effect of Acupressure in Rats

Acupuncture and acupressure points correlate well with sites on the body that have low transcutaneous electrical resistance (TER). Using lightly sedated, adult Sprague-Dawley rats, we identified an acupoint (i.e. site with low TER) located on the hind limb of the rat and compared the effects of acupressure at this site on the nociceptive threshold to an adjacent, non-acupoint site (i.e. site with high TER). Focal pressure (55.42±2.2 g) was applied to the site for 10 minutes and the tail flick response (TFR) was determined by draping the distal portion of the tail over a heated wire (75±5°C). Three trials were performed during each of three randomized conditions (i.e. acupoint, placebo and control) and the trials were averaged. All rats tested (5/5) showed a statistically significant increase in TFR following 10 minutes of acupressure at the acupoint compared to placebo or control trials (p=0.007). Acupressure at the placebo point resulted in a TFR that was not statistically different from the control. Systemic administration of naloxone completely abolished the tail-flick inhibition induced by acupressure at the acupoint. These data suggest that acupressure elicits an antinociceptive effect in rats that is mediated by the endogenous release of opioids.

Application of neurobehavioral toxicology methods to the military deployment toxicology assessment program

The military Tri-Service (Army, Navy & Marines, Air Force) Deployment Toxicology Assessment Program (DTAP) represents a 30-year (1996-2026) planning effort to implement comprehensive systems for the protection of internationally deployed troops against toxicant exposures. A major objective of DTAP is the implementation of a global surveillance system to identify chemicals with the potential to reduce human performance capacity. Implementation requires prior development of complex human risk assessment models, known collectively as the Neurobehavioral Toxicity Evaluation Instrument (NTEI), based on mathematical interpolation of results from tissue-based and in vivo animal studies validated by human performance assessment research. The Neurobehavioral Toxicity Assessment Group (NTAG) at the Naval Health Research Center Detachment-Toxicology (NHRC-TD), Dayton, OH, and associated academic institutions are developing and cross-validating cellular-level (NTAS), laboratory small animal (NTAB), nonhuman primate (GASP), and human-based (GASH) toxicity assessment batteries. These batteries will be utilized to develop and evaluate mathematical predictors of human neurobehavioral toxicity, as a function of laboratory performance deficits predicted by quantitative structural analysis relationship (QSAR-like) properties of potential toxicants identified by international surveillance systems. Finally, physiologically-based pharmacokinetic (PBPK) and pharmacodynamic (PBPD) modeling of NTAS, NTAB, GASP, GASH data will support multi-organizational development and validation of the NTEI. The validated NTEI tool will represent a complex database management system, integrating global satellite surveillance input to provide real-time decision-making support for deployed military personnel.