Central monoaminergic changes induced by morphine in hypoalgesic and hyperalgesic strains of domestic fowl

Analgesic Efficacy of Tramadol Compared With Meloxicam in Ducks (Cairina moschata domestica) Evaluated by Ground-Reactive Forces

The purpose of this study was to determine the efficacy of tramadol and meloxicam in an induced, temporary arthritis model in ducks as assessed by ground-reactive forces measured by a pressure-sensitive walkway (PSW) system. Twelve ducks (Cairina moschata domestica) were randomly separated into 3 equal groups of 4 birds each: water control, tramadol treatment, and meloxicam treatment. Baseline measurements were collected by having all ducks walk along a 3-m-long PSW in a custom-built corral before anesthesia and induction of arthritis. Arthritis was induced in all groups through injection, under anesthesia, of a 3% monosodium urate (MSU) solution into the intertarsal joint. One hour after MSU injection, birds were orally gavage fed 1 mL of tap water (control), tramadol (30 mg/kg), or meloxicam (1 mg/kg). After treatments, all ducks were reevaluated on the PSW at 1, 2, 3, 4, 8, and 24 hours post-MSU injection. The difference in maximum force was significantly greater in the control group than in both the tramadol- (P = .006) and meloxicam-treated (P = .03) individuals. Post hoc comparisons revealed differences between control and treated birds occurred only at the 3- and 4-hour time points after administration. No differences were found in the absolute difference in maximum force between tramadol- and meloxicam-treated birds at any time point (P > .05). Results of this study support the hypothesis that tramadol (30 mg/kg PO) and meloxicam (1 mg/kg PO) improve certain objective variables in an induced arthritis model in ducks. Our findings also support studies in other avian species that determined that both tramadol and meloxicam are effective analgesic drugs in some birds.

Opioid induced hyperalgesia in anesthetic settings

Pain is difficult to investigate and difficult to treat, in part, because of problems in quantification and assessment. The use of opioids, combined with classic anesthetics to maintain hemodynamic stability by controlling responses to intraoperative painful events has gained significant popularity in the anesthetic field. However, several side effects profiles concerning perioperative use of opioid have been published. Over the past two decades, many concerns have arisen with respect to opioid-induced hyperalgesia (OIH), which is the paradoxical effect wherein opioid usage may decrease pain thresholds and increase atypical pain unrelated to the original, preexisting pain. This brief review focuses on the evidence, mechanisms, and modulatory and pharmacologic management of OIH in order to elaborate on the clinical implication of OIH.

Avian analgesia

Avian analgesia is now recognized as a critical component of avian medicine and surgery. The need to recognize pain and to provide pain relief is the first step, and many anecdotal therapeutic doses have been extrapolated from other companion animals. Several published research investigations, using several species of birds, have begun to provide avian analgesia therapeutic information for clinical application. The challenge is to continue pushing this research forward with appreciation that there are approximately 10,000 known species of birds, perhaps 200 species commonly kept as pets, and that each species has a range of behaviors as varied as their species-specific PKs and PDs to each analgesic drug.

The evolution of vertebrate opioid receptors

The proteins that mediate the analgesic and other effects of opioid drugs and endogenous opioid peptides are known as opioid receptors. Opioid receptors consist of a family of four closely-related proteins belonging to the large superfamily of G-protein coupled receptors. The three types of opioid receptors shown unequivocally to mediate analgesia in animal models are the mu (MOR), delta (DOR), and kappa (KOR) opioid receptor proteins. The role of the fourth member of the opioid receptor family, the nociceptin or orphanin FQ receptor (ORL), is not as clear as hyperalgesia, analgesia, and no effect was reported after administration of ORL agonists. There are now cDNA sequences for all four types of opioid receptors that are expressed in the brain of six species from three different classes of vertebrates. This review presents a comparative analysis of vertebrate opioid receptors using bioinformatics and data from recent human genome studies. Results indicate that opioid receptors arose by gene duplication, that there is a vector of opioid receptor divergence, and that MOR shows evidence of rapid evolution.

Characterization of the chick carrageenan response

The present study characterized carrageenan inflammatory nociception in the 7-day-old domestic chick. The time course effects of foot withdrawal latency to a thermal stimulus and edema were examined over a 6-h period following an intraplantar carrageenan (0.0-1.0%) injection. Carrageenan-induced hyperalgesia and edema had a similar course of action, enduring for approximately 6 h, with a peak effect at approximately 2 h post carrageenan injection. Carrageenan inflammation was produced in a robust concentration dependent manner. Carrageenan hyperalgesia was induced at all concentrations tested and no carrageenan concentration effects were discerned. In a subsequent series of experiments we challenged the carrageenan inflammation model with systemic administration of the opioid agonist morphine, the nonsteroidal anti-inflammatory drug naproxen or the steroidal antiinflammatory drug dexamethasone. Morphine produced a dose dependent attenuation of carrageenan hyperalgesia but had no effect upon carrageenan inflammation. Naproxen produced a moderate attenuation of carrageenan inflammation and hyperalgesia. Dexamethasone dramatically attenuated both carrageenan hyperalgesia and inflammation. Collectively, these experiments characterize the chick carrageenan response and demonstrate the potential of the chick carrageenan inflammation model as a less expensive adjunct model of inflammatory nociception.

Influence of food restriction on dopamine receptor densities, catecholamine concentrations and dopamine turnover in chicken brain

To investigate further a putative role of dopamine in control of food restriction-induced behavioural stereotypies, chickens were fed during rearing on either a daily restricted ration recommended by a breeding company, twice the recommended restricted ration, or ad libitum food. They were killed at 60 days of age and their excised brains were dissected into six regions and homogenized. Densities of dopamine D1 and D2 receptors were assessed, after first estimating binding parameters for [3H]SCH 23390 (D1) and [3H]spiperone (D2) in chicken brain homogenates. Specific binding of both ligands was highest in basal telencephalon. Concentrations of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were also highest in basal telencephalon, whereas noradrenaline and adrenaline levels were highest in diencephalon. Dopamine concentration in basal telencephalon and noradrenaline concentration in diencephalon were increased significantly in response to food restriction, but no effect of feeding treatment was found in dopamine turnover, adrenaline levels, or D1 and D2 receptor densities in any brain region studied. The observed changes in brain catecholamine levels are consistent with roles for dopaminergic and adrenergic mechanisms in the control of food restriction-induced behavioural stereotypies in chickens.

Construct validation of behavioral indices of isolation stress and inflammatory nociception in young domestic fowl

Isolation from conspecifics can elicit a variety of behavioral responses in young domestic fowl that include increased vocalizations (VOC), ventral recumbency posturing (VRP), hypoalgesia, and hyperthermia. During tests of acute inflammatory nociception, chicks not only display several pain-related behaviors (i.e., footpecks and lifts), but also VOC and VRP. However, systematic evaluation of whether these behaviors reflect converging indices of stress and nociception remains to be conducted. In two separate experiments, 7-day-old chicks received intraplantar formalin (0.05%) or saline (0.05 ml) and were placed in sound-attenuating chambers with or without two conspecifics for a 3 min observation period. The following measures were recorded: VOC, footlift frequency (LFT), and duration (DUR, Experiment 2 only), pecks (PKS), ventral recumbency latency (VRL), body temperature (BTMP), and body weight (WGT). Principal component analyses revealed the presence of two oblique and nonmonotonically related components, one consisting of pain-related measures (i.e., LFT, DUR, and PKS) and the other consisting of stress-related measures (VOC, VRL, and BTMP). A third component, consisting of BTMP and WGT ostensibly reflects maturational variability in thermoregulatory capability. These findings support the construct validity of these behavioral indices of isolation stress and inflammatory nociception and are consistent with the notion of stress effects on nociceptive processing.

Effects of calcitonin on CNS monoamines following carrageenan-induced inflammation in rats

The present study examined the effects of systemically administered calcitonin (CT, 10 IU/0.25 ml, SC) on changes in CNS monoamines (MAs) following unilateral carrageenan (CARRA)-induced inflammation in the rat hindpaw. High-performance liquid chromatography with electrochemical detection (HPLC-EC) for MAs was performed on the whole brain and rostral spinal cord. Carrageenan-evoked inflammation significantly increased brain serotonin [5-hydroxytryptamine (5-HT)], norepinephrine (NE), and dopamine (DA) levels. CT significantly reduced these CARRA-induced elevations in brain MAs. Elevated spinal cord 5-HT and NE levels were observed in CARRA-treated animals. CT administration increased 5-HT and NE in both the CARRA-treated animals and their saline controls. Spinal cord DA levels were not affected by either CARRA or CT administration. These findings suggest the involvement of CNS monoaminergic substrates in CT-induced hypoalgesia in inflammatory nociception.

Morphine hyperalgesic effects on developmental changes in thermal nociception and respiration in domestic fowl (Gallus gallus)

Domestic fowl tested at 3, 5, and 7 days posthatch jumped from a heated grid more rapidly than animals tested at 14 days posthatch. Morphine (2.5 mg/kg) decreased jump latency in 14-day-old chicks but did not significantly affect jump latency in younger chicks. Respiration was lower in 3-day-old chicks than in the older groups but morphine depressed respiration at each age. In a second experiment morphine significantly decreased jump response latency in 5-day-old chicks when thermal stimulus intensity was lowered and morphine dose increased (5 mg/kg). Posttest respiration rate was depressed by morphine. Morphine hyperalgesia and respiratory depression were reversed by naloxone (5 mg/kg). However, naloxone alone increased jump response latency. Young domestic fowl are more sensitive and/or reactive to a noxious thermal stimulus and are less sensitive to morphine than 14-day-old chicks but morphine hyperalgesia was evident in both 5- and 14-day-old chicks. These hyperalgesic chicks may be tolerant at birth to morphine hypoalgesic effects on nociception.