Effects of sweetening agents on morphine-induced analgesia in mice by formalin test

Assessment of Pain Associated with the Injection of Sodium Pentobarbital in Laboratory Mice (Mus musculus)

The AVMA Guidelines for the Euthanasia of Animals considers injection of barbiturates to be an acceptable method of euthanasia in rodents but states there is a potential for pain when administered intraperitoneally. This study examined the potential for pain in mice by assessing visceral pain after intraperitoneal administration and acute pain by using a paw-lick test. Male and female mice (n = 160) intraperitoneally received a euthanizing dose of sodium pentobarbital at a concentration of 5, 50, or 390 mg/mL and were observed for writhing, peritoneum-directed behaviors (PDB), loss of righting reflex, and time to death. Writhing was not observed in any animal. There was no significant difference in the number of mice exhibiting PDB or in the rate of PDB for responders receiving either saline or the 390-mg/mL solution. There was a significant treatment effect on time, with greater concentration and dose resulting in more rapid loss of righting reflex and death. In the second set of experiments, the same solutions were injected subcutaneously into the plantar hindpaw of male and female mice (n = 84). The number of responders, latency until the first lick, and the number of licks per responder were recorded. The number of responders was increased in the 50-mg/mL group; however, there was no difference in latency or the number of licks per responder. These results show that intraperitoneal injection of sodium pentobarbital for euthanasia in mice did not result in increased behavioral signs of pain, and animals lose consciousness more rapidly than the onset of pain seen in the pawlick test. Therefore, although sodium pentobarbital is capable of inducing inflammation, euthanasia through intraperitoneal administration is rapid and does not result in overt signs of pain when compared with injection of saline.

The effect of quinine in two bottle choice procedures in C57BL6 mice: Opioid preference, somatic withdrawal, and pharmacokinetic outcomes

Previous reports assessing morphine effects in two bottle choice (TBC) paradigms often use taste adulterants such as sweeteners (e.g., saccharin) and/or bitterants (e.g., quinine) to demonstrate morphine preference with C57BL6 mice. The effect of these additional components on the morphine preference of C57BL6 remains poorly understood. Thus, we sought to elucidate the interrelationship of morphine and quinine in the TBC paradigm. As expected, when morphine was included in the opposite bottle from quinine, a preference for the morphine solution was observed. Conversely, when quinine was included in each bottle, or when fentanyl without quinine was used, no preference was observed. All opioid-drinking mice displayed withdrawal signs, and morphine was detectable in plasma and brain. When these results were compared to previous results via conversion to quinine preference scores, quinine was revealed to determine largely the measured morphine preference. Thus, quinine is effective to drive morphine consumption and engender dependence but may confound the ability to measure oral abuse liability of morphine. Together, these results suggest future TBC procedures should consider the effect of quinine upon measured preference for compounds in the opposite bottle, and that excessively high quinine concentrations appear to influence preference more so than the opposite solute when using C57BL6 mice. Alternative conditions to assess oral abuse liability may be necessary to complement and confirm results from TBC experiments utilizing morphine or other opioids.

Antinociceptive actions of peripheral glucose administration

The effects of intraperitoneal (ip) D-glucose administration on antinociception were studied in male Long-Evans rats. Rats were assessed for antinociception using the hot-water tail-withdrawal procedure (54±0.2 °C) to determine if peripheral administration of D-glucose (300, 560, or 720 mg/kg) would enhance morphine-mediated antinociception (MMA) (1.0, 3.0, 4.2, 5.6, and 10.0mg/kg cumulative-dosing regime) and if D-glucose (560, 720, or 1000 mg/kg) alone could produce antinociceptive activity that was naloxone (0.32 mg/kg) reversible. Additionally, the actions of D-glucose on MMA were compared with a stereoisomer, L-glucose, which is not metabolized. The results of these studies demonstrate that peripheral administration of D-glucose significantly enhances MMA and that D-glucose alone produces antinociceptive actions that are potentially mediated by the endogenous opioid system. Furthermore, L-glucose failed to have an effect on MMA suggesting that the alterations in antinociception seen with D-glucose are not due to stressors such as osmolality or injection. The current studies provide evidence that D-glucose alteration of antinociception is not simply a response to taste or gustation.

Chronic sucrose intake reduces the antagonist effect of β-funaltrexamine on morphine-induced antinociception in female but not in male rats

Chronic ingestion of a sweet-tasting sucrose solution enhances the pain relieving actions of opioid agonists. These results, taken in conjunction with research demonstrating that sucrose stimulates the production and release of endogenous opioid peptides, have led to the hypothesis that the effects of palatable foods and fluids on pain sensitivity are mediated by the endogenous opioid system. To assess this hypothesis, two studies determined if chronic sucrose intake would block the antagonist effects of the micro-selective opioid antagonist beta-funaltrexamine (beta-FNA) on morphine-induced antinociception. Female and male Long-Evans rats were maintained on chow and water, or chow, water and a 32% sucrose solution. In Experiment 1, after four weeks on the diets, female rats received 0 or 10 mg/kg (subcutaneously (s.c.)) beta-FNA, while in Experiment 2, male and female rats received 0, 5 or 20 mg/kg beta-FNA. Six days later, rats were tested for morphine-induced antinociception using the hot-water tail-withdrawal test. Morphine, administered using a cumulative dose regime (1.0, 3.0, 5.6, 10.0 and 31.0 mg/kg s.c.), led to dose-dependent increases in tail-withdrawal latencies in male and female rats. Males were more sensitive to the pain relieving properties of morphine than females. Sucrose intake increased, while beta-FNA decreased the analgesic actions of morphine in males and females. beta-FNA was less effective in blocking the antinociceptive actions of morphine in sucrose-fed female rats than in females fed only chow. In contrast, diet had minimal effects on responses to beta-FNA in male rats.

Anti-inflammatory and anti-nociceptive effects of the ethanolic extracts of Alkanna frigida and Alkanna orientalis

Alkanna species are used in Iranian traditional medicine for treatment of rheumatoid arthritis and other inflammatory diseases. This study was designed to evaluate the anti-inflammatory and anti-nociceptive effects of Alkanna frigida and Alkanna orientalis ethanolic extracts via the carrageenan-induced paw edema test and formalin test in rat and mouse, respectively. Ethanolic extracts of plant root were prepared and were injected intraperitoneally 60 min before carrageenan-induced inflammation or formalin-induced nociception at 100, 200 and 400 mg/kg. Anti-inflammatory effects of plants were monitored for 3 h after carrageenan injection and anti-nociceptive effects were evaluated during the first hour after formalin injection. Diclofenac, a well-known anti-inflammatory and anti-nociceptive agent, was used as a positive control. Our results show that, in contrast to Alkanna orientalis, ethanolic extract of Alkanna frigida significantly decreases carrageenan-induced inflammation at 400 mg/kg, especially 3 h after inflammation induction. Both Alkanna frigida and Alkanna orientalis ethanolic extracts possess a remarkable anti-nociceptive effect at each dose (100, 200 and 400 mg/kg) in a dose-dependent manner during the first hour after formalin injection.The present findings provide more evidence for the potential anti-nociceptive effect of Alkanna sp. and the anti-inflammatory effect of Alkanna frigida. It supports their traditional indication in the treatment of pain and inflammatory-related diseases. These useful effects may result from the inhibitory interaction of the plant ethanolic extract with cyclooxygenase-2 enzyme and the subsequent reduction in prostaglandin production.

Oral sucrose and a pacifier for pain relief during simple procedures in preterm infants: a randomized controlled trial

BACKGROUND AND OBJECTIVES

Previous randomized trials of the analgesic effects of sucrose, glucose, and a pacifier in term neonates have shown that the pacifier resulted in lower pain scores than glucose or sucrose, but the pacifier with and without sucrose did not differ. The current study was designed to assess the analgesic effect of pharmacologic (sucrose, water) and a non-pharmacologic measures (pacifier) in preterm infants and to find whether there is any synergism between these intervention in relieving pain during painful procedures.

PATIENTS AND METHODS

In this double-blind, randomized, controlled study, 36 preterm infants (mean 31 weeks gestational age, range 27 to 36 weeks) were randomly allocated to six different regimens (0.5 mL sterile water with pacifier, 0.5 mL sterile water without pacifier, 0.5 mL sucrose 24% with pacifier, 0.5 mL sucrose 24% without pacifier, pacifier alone and control group) during a stay in intensive care of up to 15 days. Pain scores were measured with the Premature Infant Pain Profile (PIPP), a validated behavioral acute pain scale.

RESULTS

Of all the regimens, the lowest pain scores occurred with the use of 24% sucrose solution combined with pacifier. The mean pain score for the combination of sucrose with pacifier was 0.7 as compared to 1.4 for the sterile water with pacifier group (P<.05).

CONCLUSION

The synergistic effect of the combination of sucrose and non-nutritive sucking was clinically effective and safe in relieving the pain of simple procedures such as venipuncture or heel stick in preterm and term infants, but further research is needed on these interventions alone and in combination with other behavioral interventions in neonates.

Kangaroo mother care diminishes pain from heel lance in very preterm neonates: a crossover trial

BACKGROUND

Skin-to-skin contact, or kangaroo mother care (KMC) has been shown to be efficacious in diminishing pain response to heel lance in full term and moderately preterm neonates. The purpose of this study was to determine if KMC would also be efficacious in very preterm neonates.

METHODS

Preterm neonates (n = 61) between 28 0/7 and 31 6/7 weeks gestational age in three Level III NICU's in Canada comprised the sample. A single-blind randomized crossover design was employed. In the experimental condition, the infant was held in KMC for 15 minutes prior to and throughout heel lance procedure. In the control condition, the infant was in prone position swaddled in a blanket in the incubator. The primary outcome was the Premature Infant Pain Profile (PIPP), which is comprised of three facial actions, maximum heart rate, minimum oxygen saturation levels from baseline in 30-second blocks from heel lance. The secondary outcome was time to recover, defined as heart rate return to baseline. Continuous video, heart rate and oxygen saturation monitoring were recorded with event markers during the procedure and were subsequently analyzed. Repeated measures analysis-of-variance was employed to generate results.

RESULTS

PIPP scores at 90 seconds post lance were significantly lower in the KMC condition (8.871 (95%CI 7.852-9.889) versus 10.677 (95%CI 9.563-11.792) p < .001) and non-significant mean differences ranging from 1.2 to1.8. favoring KMC condition at 30, 60 and 120 seconds. Time to recovery was significantly shorter, by a minute(123 seconds (95%CI 103-142) versus 193 seconds (95%CI 158-227). Facial actions were highly significantly lower across all points in time reaching a two-fold difference by 120 seconds post-lance and heart rate was significantly lower across the first 90 seconds in the KMC condition.

CONCLUSION

Very preterm neonates appear to have endogenous mechanisms elicited through skin-to-skin maternal contact that decrease pain response, but not as powerfully as in older preterm neonates. The shorter recovery time in KMC is clinically important in helping maintain homeostasis.

TRIAL REGISTRATION

(Current Controlled Trials) ISRCTN63551708.

Mechanisms of the placebo effect of sweet cough syrups

The review discusses the large placebo effect associated with cough medicines and speculates on the observation that most cough medicines are formulated as sweet syrups rather than capsules or tablets. The review proposes that the major benefit of cough medicines for treatment of cough associated with common cold is related to the placebo effect rather than the pharmacological effect of an active ingredient. The placebo effect is discussed in terms of physiological effects of cough syrups associated with the taste of the medicine and true placebo effects associated with belief in the therapy. The idea is developed that a sweet taste may modulate cough at the level of the nucleus tractus solitarius, possibly by influencing the production of endogenous opioids.

Phytochemical investigation and anti-inflammatory activity of aerial parts of Stachys byzanthina C. Koch

From the aerial parts of Stachys byzanthina C. Koch., an acyclic diterpene ester, phytyl nonadecanoate, was isolated for the first time. In addition, two normal alkanes, one fatty acid and two sterols were also identified. Stuctures were established by conventional methods of analysis and confirmed by 1H, 13C NMR and mass spectral analysis. Anti-inflammatory effects of acetone and methanolic extracts of aerial parts of Stachys byzanthina C. Koch. were investigated in this study. For assessment of anti-inflammatory properties, two well-characterized inflammatory models, formalin test and carrageenan-induced paw edema were used. Intraperitoneal injections of either acetone or methanolic extract of Stachys byzanthina C. Koch. (50, 100 and 200 mg/kg), 30 min before formalin injection, had no effects against the first phase of the formalin-induced pain, but all three doses caused a significant blockade on the second phase (p < 0.01). The recording of the early phase started immediately after formalin injection and lasted for 10 min (0-10 min). The late response was recorded 20 min after formalin injection and lasted for 10 min (20-30 min). In the carrageenan-induced paw edema, both extracts revealed dose-related inhibitory effects on carrageenan-induced rat paw edema over the dose range 50-200 mg/kg. The anti-inflammatory activities of these extracts were similar to a high dose of indomethacin (5 mg/kg) in both carrageenan-induced paw edema and formalin-induced paw licking. In conclusion, the present data provide further evidence for an important role of extracts of Stachys byzanthina C. Koch. in the inhibition of pain and inflammatory processes.

Oral sucrose and pain relief for preterm infants

The frequency of painful procedures performed on preterm infants in the neonatal intensive care unit (NICU) presents a challenge to nurses who are attempting to provide effective pain relief, and to the infants themselves who may suffer adverse consequences in response to repeated painful procedures. One new pain relief intervention under study is the administration of oral sucrose, which may activate endogenous opioid systems within the body. Studies with preterm infants that have examined the use of oral sucrose as an analgesic during heelsticks and venipunctures have shown that sucrose is effective in reducing pain. Sucrose may also be combined with nonnutritive sucking to provide significant pain relief. The use of oral sucrose is now recommended with a wide range of painful procedures in the NICU. Promising results have been observed in studies with both term and preterm infants, but less research has occurred with preterm infants. Additional research is warranted to determine the most effective approaches for the administration of sucrose, to examine the effectiveness of sucrose with additional types of painful procedures, and to examine the effects of long-term repeated use of sucrose.

Chronic sucrose intake augments antinociception induced by injections of mu but not kappa opioid receptor agonists into the periaqueductal gray matter in male and female rats

Chronic intake of a palatable sucrose solution enhances the antinociceptive potency of systemically administered mu, and kappa opioid receptor agonists. To investigate whether the effects of sucrose on the actions of opioid drugs are mediated within the central nervous system (CNS), antinociception was examined following the administration of mu and kappa opioid receptor agonists into the periaqueductal gray area (PAG). Male and female Long-Evans rats consumed either water and ground chow, or water, chow and a 32% (w/v) sucrose solution. After adaptation to the dietary conditions, a guide cannula was stereotaxically implanted into the PAG. Injections of the mu agonist, morphine (0.0, 2.5, 5.0, 10.0 and 20.0 microg), into the PAG led to dose-related increases in antinociceptive responses on a tail flick test in both male and female rats. Rats which had consumed sucrose displayed significantly greater levels of antinociception than rats not given the sugar. Antinociceptive responses to morphine did not differ as a function of sex. Injections of the kappa agonist, spiradoline (0, 100, 300, 600 microg), into the PAG increased tail flick latencies in male and female rats. However, antinociceptive responses did not vary as a function of diet in rats injected with spiradoline. In both diet conditions, spiradoline led to greater levels of antinociception in female rats than in male rats. These results support the hypothesis that intake of palatable foods and fluids act within the CNS to moderate the behavioral actions of opioid drugs.

Potentiation by nitric oxide synthase inhibitor and calcium channel blocker of aspartame-induced antinociception in the mouse formalin test

By applying a 12 day regimen of the non-calorific sweetener, aspartame, in combination with representative compounds of the calcium channel blocker and nitric oxide synthase inhibitor, we tried to investigate using a formalin-test in mice the relative role of aspartame on pain and its mechanism of action. Verapamil (2, 3.5, 5, 7.5 mg/kg) induced significant (P < 0.01) antinociception in both phases of the formalin test. L-Nitro-arginine-methyl-ester (L-NAME) at the doses used, induced significant (P < 0.01) antinociception in early phase (1, 2, 5, 10 mg/kg) and late phase (5, 10 mg/kg). Twelve days of treatment in animals by aspartame (0.16% w/v) significantly induced antinociception in both phases of the formalin test. Both verapamil (5 mg/kg) and L-NAME (10 mg/kg) significantly (P < 0.01) potentiated aspartame-induced antinociception in both phases of formalin test. The present findings support the hypothesis that the activation of NMDA receptors by aspartame modulates pain-related behaviour via a nitric oxide/cGMP/glutamate release cascade. It is concluded that aspartame would be a good analgesic agent if it would be used in combination with a calcium channel blocker or NOS inhibitor.

Saccharin effects on morphine-induced antinociception in the mouse formalin test

This study was performed to investigate the role of sweetness and taste sensations of the non-caloric sweetener saccharin on pain and morphine antinociception by the formalin test in mice. The formalin test was chosen because it measures the response to a long-lasting nociceptive stimulus and thus may closely resemble clinical pain. The total time (seconds) spent licking and biting the injected paw (indices of nociception) during periods of 0-5 min (early phase) and 10-30 min (late phase) were measured as an indicator of pain and inflammatory responses. A 12 days pretreatment of animals with saccharin (0.04%, 0.08%, 0.16%) produced complex effects on the action of morphine. All doses significantly potentiated the low dose (1.5 mgkg(-1)) of morphine-induced analgesia in the early phase significantly but antagonized the effect of morphine (3 mgkg(-1)). The effect of high doses of morphine (6-9 mgkg(-1)) was antagonized by the low dose of saccharin (0.04%), but the effect of morphine (6 mgkg(-1)) was potentiated with high concentrations of saccharin (0.08% and 0.16%). All doses of saccharin decreased the analgesic effect of morphine at a dose of 9 mgkg(-1). Analgesic effects of low doses of morphine (1.5-3 mgkg(-1)) were decreased by all doses of saccharin in the late phase. Different concentrations of saccharin also affected the antagonistic effect of naloxone (0.4 mgkg(-1)) on morphine-induced analgesia in both phases of the formalin test. The high dose of saccharin (0.16%) potentiated the effect of naloxone in the late phase. The results obtained suggest that sweet sensation is an important factor in mediating morphine analgesic properties. It is therefore inappropriate to use different concentrations of sweet saccharin solutions interchangeably.

Intake of a palatable sucrose solution modifies the actions of spiradoline, a kappa opioid receptor agonist, on analgesia and feeding behavior in male and female rats

Previous research has shown that rats consuming a sucrose solution and chow are more sensitive to the analgesic actions of morphine, a selective mu opioid agonist, and the anorectic actions of opioid antagonists, than rats eating only chow. However, from these data, it cannot be determined if sucrose intake only modifies the behavioral consequences of drugs that act at the mu opioid receptor, or if the sugar also alters the actions of opioid drugs that act at other opioid receptor subtypes. Thus, the present experiments examined the effects of sucrose intake on the actions of spiradoline, a selective kappa opioid agonist, on analgesia and food intake in male and female Long-Evans rats. In Experiment 1, male and female rats consumed either chow, a 32% sucrose solution and water, or only chow and water. After 3 weeks, antinociceptive responses on the tail-flick test were determined after spiradoline injections (0.0, 0.3, 1.0, and 3.0 mg/ kg, s.c.). Rats fed sucrose were more sensitive to the analgesic actions of spiradoline than rats fed only chow. In Experiment 2, drug-naive male and female rats were maintained under the same dietary conditions as in Experiment 1. Food intake was measured 1, 2, 4, and 6 h after spiradoline injections (0.0, 0.3, 1.0, and 3.0 mg/kg, s.c.). Spiradoline led to significant dose-related decreases in food intake for males and females in both dietary conditions. However, the anorectic effects of the drug were more pronounced in rats fed sucrose than in those eating only chow. These results support the hypothesis that intake of palatable foods and fluids alters the activity of the endogenous opioid system.

Interaction between calcium channel blockers and sweetening agents on morphine-induced analgesia in mice by formalin test

1. Calcium is known to be an important ion in the modulation of nociception and inflammation. Previous research has shown that mice drinking sweet-tasting solutions such as sucrose, saccharin and aspartame exhibit significant changes in morphine-induced analgesia in both phases of the formalin test. 2. In this study, the role of calcium channel blockers on the effectivity of a 12-day regimen of different sweetening agents (sucrose 32%, saccharin 0.08% and aspartame 0.16%) on the alteration of the morphine response has been investigated. 3. Male albino mice weighing 20-27 g were used for experiments. Animals were given 12 days to adapt to dietary conditions. Animals were given morphine (1.5, 3, 6, 9 mg/kg) subcutaneously 30 min before observation. Nifedipine (5 mg/kg), verapamil (5 mg/kg) and diltiazem (10 mg/kg) were administered intraperitoneally 20 min before morphine injection. 4. Recording of the early phase started immediately and lasted for 10 min after formalin injection. Recording of the late response started 20 min after formalin injection and lasted for 10 min. 5. Calcium channel blockers potentiated the antinociceptive effects of sweetening agents and diminished the antagonistic effects of these compounds on morphine-induced analgesia in the early and late phases of the formalin test. 6. It is proposed that calcium has a role for the interactive effects of sweetening agents and morphine on pain sensitivity.

Interaction between lead acetate and morphine on antinociception in mice by formalin test

1. In this study, the effects of lead acetate on two types of pain (nociception and inflammation) induced by formalin and its interactions with opioid system and morphine-induced analgesia were examined. Male albino mice weighing 22-27 g were used in the experiments. 2. To study nociception, the formalin test was selected. Morphine was administered subcutaneously 30 min before formalin injection. Lead acetate treatment was administered 90 min before any injection. Comparisons between groups were made by analysis of variance and then by Newman-Keuls test. Differences with P < or = 0.05 was considered statistically significant. 3. Different doses of morphine induced antinociception in both phases of the formalin test. Lead acetate induced non-dose-dependent nociception in the early phase and dose-dependent analgesia in the late phase. 4. Pretreatment with lead acetate antagonized the effect of morphine in the early phase. In the other hand, the effect of lead acetate in the early phase was reduced by morphine and its effect eliminated in the late phase. 5. It is concluded that lead can modulate pain response and interact with morphine-induced antinociception. Additional research to find the mechanisms of these effects are suggested.

Endogenous opiates: 1997

This paper is the twentieth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1997 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.