Animal Studies

Monosodium glutamate induces behaviors thought to reflect headache and nausea in rats. We explored the effects of the N-methyl-D-aspartate receptor antagonist (2R)-amino-5-phosphonovaleric acid, the inotropic glutamate receptor antagonist kynurenic acid, and the CGRP receptor antagonist olcegepant, on monosodium glutamate-induced increases in nocifensive, headache-like and nausea behaviours. Effects of these antagonists on motor function were examined with a rotarod. The effect of the dopamine receptor antagonist metoclopramide and the serotonin 3 receptor antagonist ondansetron on nausea behaviour was also assessed. (2R)-amino-5-phosphonovaleric acid, and to a lesser extent, kynurenic acid and olcegepant, reduced nocifensive and headache-like behaviours evoked by monosodium glutamate. No alteration in motor function by (2R)-amino-5-phosphonovaleric acid, kynurenic acid or olcegepant was observed. No sex-related differences in the effectiveness of these agents were identified. Nausea behaviour was significantly more pronounced in male than in female rats. Olcegepant, ondansetron and metoclopramide ameliorated this nausea behaviour in male rats. Ondansetron and metoclopramide also reduced headache-like behaviour in male rats. These findings suggest that peripheral N-methyl-D-aspartate receptor activation underlies monosodium glutamate-induced headache-like behaviour but does not mediate the nausea behaviour in rats.

Massive rotator cuff tears (MRCTs) of the shoulder cause disability and pain among the adult population. In chronic injuries, the tendon retraction and subsequently the loss of mechanical load lead to muscle atrophy, fat accumulation, and fibrosis formation over time. The intrinsic repair mechanism of muscle and the successful repair of the torn tendon cannot reverse the muscle degeneration following MRCTs. To address these limitations, we developed an electroconductive matrix by incorporating graphene nanoplatelets (GnPs) into aligned poly(l-lactic acid) (PLLA) nanofibers. This study aimed to understand 1) the effects of GnP matrices on muscle regeneration and inhibition of fat formation in vitro and 2) the ability of GnP matrices to reverse muscle degenerative changes in vivo following an MRCT. The GnP matrix significantly increased myotube formation, which can be attributed to enhanced intracellular calcium ions in myoblasts. Moreover, the GnP matrix suppressed adipogenesis in adipose-derived stem cells. These results supported the clinical effects of the GnP matrix on reducing fat accumulation and muscle atrophy. The histological evaluation showed the potential of the GnP matrix to reverse muscle atrophy, fat accumulation, and fibrosis in both supraspinatus and infraspinatus muscles at 24 and 32 wk after the chronic MRCTs of the rat shoulder. The pathological evaluation of internal organs confirmed the long-term biocompatibility of the GnP matrix. We found that reversing muscle degenerative changes improved the morphology and tensile properties of the tendon compared with current surgical techniques. The long-term biocompatibility and the ability of the GnP matrix to treat muscle degeneration are promising for the realization of MRCT healing and regeneration.

TRPV1, a capsaicin- and heat-activated ion channel, is expressed by peripheral nociceptors and has been implicated in various inflammatory and neuropathic pain conditions. Although pharmacological modulation of TRPV1 has attracted therapeutic interest, many TRPV1 agonists and antagonists produce thermomodulatory side effects in animal models and human clinical trials, limiting their utility. These on-target effects may result from the perturbation of TRPV1 receptors on nociceptors, which transduce signals to central thermoregulatory circuits and release proinflammatory factors from their peripheral terminals, most notably the potent vasodilative neuropeptide, calcitonin gene-related peptide (CGRP). Alternatively, these body temperature effects may originate from the modulation of TRPV1 on vascular smooth muscle cells (vSMCs), where channel activation promotes arteriole constriction. Here, we ask which of these pathways is most responsible for the body temperature perturbations elicited by TRPV1 drugs in vivo. We address this question by selectively eliminating TRPV1 expression in sensory neurons or vSMCs and show that only the former abrogates agonist-induced hypothermia and antagonist-induced hyperthermia. Furthermore, lesioning the central projections of TRPV1-positive sensory nerve fibers also abrogates drug-mediated thermomodulation, whereas eliminating CGRP has no effect. Thus, TRPV1 drugs alter core body temperature by modulating sensory input to the central nervous system, rather than through peripheral actions on the vasculature. These findings suggest how mechanistically distinct TRPV1 antagonists may diminish inflammatory pain without affecting core body temperature.

As a progressive chronic condition, osteoarthritis (OA) causes substantial pain and impairment. Secrete proinflammatory cytokines are essential mediators involved in the pathophysiology of OA. In this regard, the clinical effectiveness of autologous conditioned serum (ASC) has been shown through its injection into OA tissues. This study aimed to assess the effectiveness and concentration level of ACS components produced by Nano-carbon glass beads. Intravenous whole blood was obtained from each New Zealand male rabbit by 10-ml syringes, comprising 33 medical-grade Nano carbon-coated glass beads. Serum retrieving was performed after 6-8 h incubation (37 C, 5% Co), and then centrifuged. The ACS was then injected into OA rabbits to assess its function.

Severe traumatic brain injury (TBI) is a multifactorial injury process involving respiratory, cardiovascular and immune functions in addition to the brain. Thus, live animal models are needed to study the molecular, cellular and systemic mechanisms of TBI. The ethical use of laboratory animals requires that the benefits of approaches be carefully weighed against potential harm to animals. Welfare assessments adapted to severe TBI research are lacking. Here, we introduce a scoresheet to describe and monitor potential distress in animals, which includes general welfare (body weight, general appearance and spontaneous behaviour) and TBI-specific indices (respiratory function, pain, locomotor impairment, wound healing). Implementation of this scoresheet in Sprague-Dawley rats subjected to severe lateral fluid percussion TBI revealed a period of suffering limited to four days, followed by a recovery to normal welfare scores within 10-15 days, with females showing a worse impact than males. The scores indicate that animal suffering in this model is transitory compared with TBI consequences in humans. The scoresheet allows for the implementation of refinement measures including (1) analgesia during the initial period following TBI and (2) humane endpoints set (30% weight loss, score ≥90 and/or respiratory problems). This animal scoresheet tailored to TBI research provides a basis for further refinement of animal research paradigms aimed at understanding or treating the sequelae of severe TBI.

The activation of heme oxygenase 1 (HO-1)/carbon monoxide (CO) inhibits chronic inflammatory pain, but its role in the central nervous system (CNS) is not entirely known. We evaluated whether the treatment with an HO-1 inducer, cobalt protoporphyrin IX (CoPP), or a CO-releasing molecule, tricarbonyldichlororuthenium(II)dimer (CORM-2), modulates the nociceptive, apoptotic and/or oxidative responses provoked by persistent inflammatory pain in the CNS. In C57BL/6 male mice with peripheral inflammation caused by complete Freund's adjuvant (CFA), we assessed the effects of CORM-2 and CoPP on the expression of protein kinase B (Akt), the apoptotic protein BAX, and the antioxidant enzymes HO-1 and NADPH quinone oxidoreductase 1 (NQO1) in the periaqueductal gray matter (PAG), amygdala (AMG), ventral hippocampus (VHPC) and medial septal area (MSA). Our results showed that the increased expression of p-Akt caused by peripheral inflammation in the four analyzed brain areas was reversed by CORM-2 and CoPP therapies. Both treatments also normalized the upregulation of BAX induced by CFA on the VHPC and MSA. Oxidative stress, demonstrated with the decreased expression of HO-1 on the PAG and AMG, was normalized in CORM-2 and CoPP treated animals. CoPP also increased the expression of HO-1 on VHPC, and both treatments up-regulated the NQO1 levels on the PAG of CFA-injected animals. In conclusion, both CORM-2 and CoPP treatments inhibited the nociceptive and apoptotic responses generated by peripheral inflammation and/or potentiated the antioxidant responses in several brain areas revealing the new modulatory effects of these treatments in the CNS of animals with chronic inflammatory pain.

Arylcyclohexylamines is an ever-growing class of new psychoactive substances, including an increasing number of ketamine analogues. N-Ethylnorketamine (NENK) is a new synthetic ketamine analogue that has emerged as an abused drug, but little is known about the pharmacological profile of NENK. In this study, we investigated the anesthetic and analgesic activity, abuse liability of NENK compared with ketamine. The ED values of anesthetic activity for NENK and ketamine were 96.9, 69.4mg/kg, respectively. The ED values of analgesic activity for NENK and ketamine were 45.9 and 23.6mg/kg, respectively. NENK induced significant conditioned place preference at a minimum dose of 10.0mg/kg in mice, an effect comparable to that of ketamine (3.0mg/kg). Acute injections of NENK or ketamine at 30.0mg/kg enhanced locomotor activity, and repeated treatments with this dose induced locomotor sensitization after withdrawal. Taken together, these results clearly demonstrated that NENK has lower anesthetic and analgesic activity compared to ketamine, but has significant abuse liability.

A newly deorphanized G protein-coupled receptor, GPR171, is found to be highly expressed within the periaqueductal gray, a pain-modulating region in the brain. Our recent research has shown that a GPR171 agonist increases morphine antinociception in male mice and opioid signaling in vitro. The objective of this study was to evaluate the effects of combination treatment in females as well as whether chronic treatment can be used without exacerbating morphine-induced tolerance and withdrawal in female and male mice. Our results demonstrate that activation of GPR171 with an agonist attenuates morphine tolerance in both female and male mice on the tail-flick test, but not the hotplate test. Importantly, the GPR171 agonist in combination with morphine does not exacerbate morphine-induced tolerance and withdrawal during long-term morphine treatment. Taken together, these data suggest that the GPR171 agonist may be combined with morphine to maintain antinociception while reducing the dose of morphine and therefore reducing side effects and abuse liability. The outcome of this study is clearly an important step toward understanding the functional interactions between opioid receptors and GPR171 and developing safer therapeutics for long-term pain management.