Analgesic effect of benzodiazepines and flumazenil

The role of the lateral septum in neuropsychiatric disease

The lateral septum (LS) is a structure in the midline of the brain that is interconnected with areas associated with stress and feeding. This review highlights the role of the LS in anxiety, depression, and eating disorders and their comorbidity. There is a prevailing view that the LS is anxiolytic. This review finds that the LS is both anxiolytic and anxiogenic. Furthermore, the LS can promote and inhibit feeding. Given these shared roles, the LS represents a common site for the comorbidity of neuropsychiatric disorders, and therefore a potential pharmacological target. This is crucial since currently available treatments are not always effective. Corticotrophin-releasing factor 2 antagonists are potential drugs for the treatment of anxiety and anorexia and require further research. Furthermore, other drugs currently in trials for binge eating, such as alpha-adrenergic agonists, may in fact promote food intake. It is hoped that the advancements in chemo- and optogenetic techniques will allow future studies to profile the specific neural connections of the LS and their function. This information could facilitate our understanding of the underlying mechanisms, and therefore pharmacological targets, of these psychiatric conditions.

Novel Positive Allosteric Modulators of µ Opioid Receptor-Insight from In Silico and In Vivo Studies

Opioids are the drugs of choice in severe pain management. Unfortunately, their use involves serious, potentially lethal side effects. Therefore, efforts in opioid drug design turn toward safer and more effective mechanisms, including allosteric modulation. In this study, molecular dynamics simulations in silico and ‘writhing’ tests in vivo were used to characterize potential allosteric mechanism of two previously reported compounds. The results suggest that investigated compounds bind to μ opioid receptor in an allosteric site, augmenting action of morphine at subeffective doses, and exerting antinociceptive effect alone at higher doses. Detailed analysis of in silico calculations suggests that first of the compounds behaves more like allosteric agonist, while the second compound acts mainly as a positive allosteric modulator.

Reversal of oxycodone and hydrocodone tolerance by diazepam

The Centers for Disease Control has declared opioid abuse to be an epidemic. Overdose deaths are largely assumed to be the result of excessive opioid consumption. In many of these cases, however, opioid abusers are often polydrug abusers. Benzodiazepines are one of the most commonly co-abused substances and pose a significant risk to opioid users. In 2016, the FDA required boxed warnings - the FDA's strongest warning - for prescription opioid analgesics and benzodiazepines about the serious risks associated with using these medications at the same time. The point of our studies was to evaluate the interactions between these two classes of drugs. We investigated whether diazepam adds to the depressant effects of opioids or do they alter the levels of tolerance to opioids. In the present study, we have found that the antinociceptive tolerance that developed to repeated administration of oxycodone was reversed by an acute dose of diazepam. Antinociceptive tolerance to hydrocodone was also reversed by acute injection of diazepam; however, a fourfold higher dose of diazepam was required when compared to reversal of oxycodone-induced tolerance. These doses of diazepam did not potentiate the acute antinociceptive effect of either opioid. The same dose of diazepam that reversed oxycodone antinociceptive tolerance also reversed oxycodone locomotor tolerance while having no potentiating effects. These studies show that diazepam does not potentiate the acute effect of prescription opioids but reverses the tolerance developed after chronic administration of the drugs.

Reversal of morphine analgesic tolerance by ethanol in the mouse

The chronic use of opioids in humans, accompanied by the development of tolerance, is a dangerous phenomenon in its own right. However, chronic opioid use is often made more dangerous by the coconsumption of other substances. It has been observed that the blood level of opioids in postmortem analyses of addicts, who consumed ethanol along with the opioid, was much less than that observed in individuals who died from opioids alone. This relationship between ethanol and opioids led us to investigate the hypothesis that ethanol alters tolerance to opioids. In the present study, we report that ethanol significantly and dose-dependently reduced the antinociceptive tolerance produced by morphine and the cross-tolerance between [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) and morphine in the mouse tail-flick test. The reversal of morphine tolerance was partially blocked by both the gamma receptor blocker bicuculline and by the γ-aminobutyric acid (GABA)(B) receptor blocker phaclofen and the administration of both inhibitors completely reversed the effects of ethanol on morphine tolerance. Diazepam, like ethanol, decreased morphine tolerance. However, this inhibition was reversed by the GABA(A) antagonist bicuculline but not by the GABA(B) antagonist phaclofen. These findings have important implications for individuals who abuse opioids and ethanol as well as suggest a mechanism to reduce the amount of opioid needed in chronic pain treatment.

Evaluation of the Analgesic Effect of Aqueous Extract of Brugmansia suaveolens Flower in Mice: Possible Mechanism Involved

The study was conducted to test the aqueous extract of Brugmansia suaveolens (AEBs) flowers for their antinociceptive effects in mice. In the hot plate test, a significant increase in reaction time for two doses of AEBs at 60, 90, 120, and 150 min after treatment was noted. Pretreatment of animals with naloxone (5 mg/kg, intraperitoneally [IP]) left the antinociceptive effect of AEBs at a dose of 100 mg/kg unaffected at 60, 90, 120, and 150 min after treatment and at a dose of 300 mg/kg at 30 min but not at 90, 120, and 150 min. In the writhing test, the AEBs significantly inhibited acetic acid—induced abdominal constriction and was equally potent at both doses. Pretreatment with naloxone (5 mg/kg, IP) left the antinociceptive effect of both doses of AEBs unaffected. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg, IP) caused a significant change in the number of abdominal constrictions but did not change the antinociceptive effect of AEBs. Pretreatment of animals with methylene blue also did not change the effect of AEBs on the number of writhing movements in mice. Flumazenil (5 mg/kg, IP) antagonized the antinociceptive effects of diazepam and also reversed the antinociceptive effect of AEBs. AEBs showed a depressant effect on the central nervous system, and the treatment of mice with pentobarbital combined with AEBs increased the animals’ sleeping time in a dose-dependent manner. These results suggest that the antinociceptive activity of AEBs may be related in part to benzodiazepine receptors, although peripheral mechanisms cannot be excluded.

The antinociceptive effects and pharmacological properties of JM-1232(-): a novel isoindoline derivative

BACKGROUND

An isoindoline derivative, JM-1232(-) was developed as a sedative and analgesic drug. We performed the present study to investigate its antinociceptive effects on three different nociceptions in mice.

METHODS

Mail ddY mice were administered intraperitoneal (i.p.) JM-1232(-) 1,3 or 10 mg/kg (n = 8 for each dose in each test). Saline was used as a control. The hotplate or tail pressure test was performed for 120 min after i.p. drug injection. Acetic acid 0.6% solution in 10 mL/kg was i.p. administered 15 min after i.p. drug injection in the acetic acid test. The number of abdominal constriction episodes was counted for 10 min, starting 5 min after i.p. administration of the acid. When the analgesic effect was observed, naloxone or flumazenil was subcutaneously administered before administration of the maximum effective dose of JM-1232(-). Using the wheel running test, the number of wheel revolutions was recorded every 5 min for 120 min.

RESULTS

In the hotplate, tail pressure and acetic acid tests, i.p. JM-1232(-) produced significant antinociceptive effects with a 50% effective dose of 2.96 mg/kg (CI: 2.65-3.30 mg/kg), 3.06 mg/kg (CI: 2.69-3.47 mg/kg) and 2.27 mg/kg (CI: 1.46-3.53 mg/kg), respectively. In all tests, JM-1232(-)-induced antinociception was antagonized by flumazenil (5 mg/kg) but not by naloxone (10 mg/kg). In the running wheel test, there was no dose-dependent effect of JM-1232(-) on locomotor activity.

CONCLUSION

Systemically administered JM-1232(-) had antinociceptive effects on acute thermal, mechanical-induced pain, and visceral pain in mice. These effects might be mediated by benzodiazepine-gamma-aminobutyric acid type A receptors but not by opioid receptors.

The antinociceptive effects of midazolam on three different types of nociception in mice

Antinociceptive effects of systemically administered midazolam remain controversial. The present study was performed to investigate its antinociceptive effects on different types of nociception in mice. Four different doses of midazolam (1, 3, 10, and 30 mg/kg) were administered intraperitoneally (i.p.). Saline was used as a control. The hot plate test, tail pressure test, acetic acid writhing test, the running wheel test, and the balance beam test were performed following the drug administration. In the hot plate test and tail pressure test, i.p. midazolam produced significant antinociceptive effects with the 50% effective dose (ED(50)) of 3.46 mg/kg [confidence interval (CI), 1.99 - 6.01 mg/kg] and 3.52 mg/kg (CI, 2.77 - 4.47 mg/kg), respectively. In the acetic acid writhing test, i.p. midazolam also produced significant antinociceptive effects. In the running wheel test, no mice stopped running after saline or midazolam at 1, 3, or 10 mg/kg, but all mice stopped running 30 and 45 min after i.p. administration of midazolam at 30 mg/kg. In the balance beam test, 30 min after i.p. administration of saline or midazolam at 1, 3, and 10 mg/kg, all mice were able to stay on the beam for 90 s, none of them could with midazolam at 30 mg/kg. In conclusion, systemically administered midazolam had antinociceptive effects on acute thermal, acute mechanical, and acute inflammatory-induced nociception in mice. The antinociceptive potency of midazolam was the same for both acute thermal-induced nociception and mechanical-induced nociception.

Enhancement by benzodiazepines of the inhibitory effect of adenosine on skeletal neuromuscular transmission

1. Interactions of benzodiazepines with adenosine on the neuromuscular transmission were studied in mouse diaphragm preparations. 2. In tubocurarine (0.6-0.8 microM)-partially paralyzed preparations, diazepam (35 microM) and Ro 5-4864 (3-30 microM), a peripheral type benzodiazepine receptor agonist, potentiated the inhibitory effect of adenosine on indirect twitch responses. 3. The central type receptor agonist, clonazepam did not affect the inhibitory effect of adenosine. 4. The peripheral benzodiazepine receptor antagonist, PK11195 (1-10 microM) attenuated the adenosine inhibition and antagonized the potentiation by Ro 5-4864. 5. Ro 5-4864 failed to enhance further the inhibitory effect of adenosine in the presence of dipyridamole, an adenosine uptake inhibitor that also potentiated adenosine inhibition. 6. Neither Ro 5-4864 nor PK 11195 affected the inhibition produced by a stable adenosine analogue, 2-chloroadenosine, which is not a substrate for the adenosine uptake system. 7. Ro 5-4864 did not affect endplate potentials (e.p.ps) in the absence of adenosine, but reduced the amplitude of e.p.ps in the presence of adenosine without affecting miniature e.p.ps. 8. It is suggested that benzodiazepines potentiate the adenosine-effected presynaptic inhibition of neuromuscular transmission by an inhibition of adenosine uptake through activation of peripheral type benzodiazepine receptors.

Adenosine modulates the antinociceptive action of benzodiazepines

1. In the present study, adenosine modulation on the antinociceptive action of benzodiazepines (BZD) using the writhing test in mice was evaluated. 2. The i.c.v. BZDs tested (diazepam, midazolam and lorazepam) induced a dose-dependent antinociceptive action, that was not antagonized either by naloxone or by aminophylline. 3. The i.p. administration of adenosine-related compounds also produced a dose-dependent reduction in the number of writhings in mice. These effects were not antagonized by i.p. injection of naloxone but were antagonized by i.p. aminophylline. 4. The antinociceptive effect of BZDs was significantly enhanced by the administration of adenosine compounds, but this increased response was not modified by naloxone or by aminophylline. 5. The present findings could be explained by the fact that BZDs and adenosine-related compounds may interact in an additive manner, since the effects of these drugs may be due to a common mechanism of action or a common pathway.