Modification of the antinociceptive effect of morphine by centrally administered diazepam and midazolam

The Perioperative Use of Benzodiazepines for Major Orthopedic Surgery in the United States

BACKGROUND

Despite numerous indications for perioperative benzodiazepine use, associated risks may be exacerbated in elderly and comorbid patients. In the absence of national utilization data, we aimed to describe utilization patterns using national claims data from total hip/knee arthroplasty patients (THA/TKA), an increasingly older and vulnerable surgical population.

METHODS

We included data on 1,863,996 TKAs and 985,471 THAs (Premier Healthcare claims data, 2006-2019). Benzodiazepine utilization (stratified by long- and short-acting agents) was assessed by patient- and health care characteristics, and analgesic regimens. Given the large sample size, standardized differences instead of P values were utilized to signify meaningful differences between groups (defined by value >0.1).

RESULTS

Among 1,863,996 TKA and 985,471 THA patients, the utilization rate of benzodiazepines was 80.5% and 76.1%, respectively. In TKA, 72.6% received short-acting benzodiazepines, while 7.9% received long-acting benzodiazepines, utilization rates 68.4% and 7.7% in THA, respectively. Benzodiazepine use was particularly more frequent among younger patients (median age [interquartile range {IQR}]: 66 [60-73]/64 [57-71] among short/long-acting compared to 69 [61-76] among nonusers), White patients (80.6%/85.4% short/long-acting versus 75.7% among nonusers), commercial insurance (36.5%/34.0% short/long-acting versus 29.1% among nonusers), patients receiving neuraxial anesthesia (56.9%/56.5% short/long-acting versus 51.5% among nonusers), small- and medium-sized (≤500 beds) hospitals (68.5% in nonusers, and 74% and 76.7% in short- and long-acting benzodiazepines), and those in the Midwest (24.6%/25.4% short/long-acting versus 16% among nonusers) in TKA; all standardized differences ≥0.1. Similar patterns were observed in THA except for race and comorbidity burden. Notably, among patients with benzodiazepine use, in-hospital postoperative opioid administration (measured in oral morphine equivalents [OMEs]) was substantially higher. This was even more pronounced in patients who received long-acting agents (median OME with no benzodiazepines utilization 192 [IQR, 83-345] vs 256 [IQR, 153-431] with short-acting, and 329 [IQR, 195-540] with long-acting benzodiazepine administration). Benzodiazepine use was also more frequent in patients receiving multimodal analgesia (concurrently 2 or more analgesic modes) and regional anesthesia. Trend analysis showed a persistent high utilization rate of benzodiazepines over the last 14 years.

CONCLUSIONS

Based on a representative sample, 4 of 5 patients undergoing major orthopedic surgery in the United States receive benzodiazepines perioperatively, despite concerns for delirium and delayed postoperative neurocognitive recovery. Notably, benzodiazepine utilization was coupled with substantially increased opioid use, which may project implications for perioperative pain management.

Effect of midazolam on the quality and duration of anaesthetic recovery in healthy dogs undergoing elective ovariohysterectomy or castration

OBJECTIVE

To determine whether the use of a single dose of midazolam affects quality and duration of the recovery period in healthy dogs undergoing elective castration or ovariohysterectomy.

STUDY DESIGN

Prospective, randomized, placebo-controlled, masked clinical trial.

ANIMAL POPULATION

Seventy-four client-owned dogs undergoing neutering.

METHODS

Following cage demeanour scoring using a simple descriptive scale (SDS), dogs were premedicated with acepromazine (0.03 mg kg^-1) and pethidine (3 mg kg^-1) intramuscularly (quadriceps muscle). Twenty minutes later sedation was scored with an SDS. Male dogs were induced with midazolam (0.25 mg kg^-1) (group M) or an equivalent amount of Hartmann's solution (group P) and propofol intravenously (IV). Female dogs were induced with propofol alone and were administered midazolam (group M) or Hartmann's solution (group P) 5 minutes before intraoperative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Intraoperative analgesia was provided with morphine (0.3 mg kg^-1 IV) prior to the start of surgery. Male dogs were administered intratesticular lidocaine (1 mg kg^-1). All dogs were administered meloxicam (0.2 mg kg^-1 IV) at the end of the procedure, and recovery was scored with an SDS following extubation and 30 minutes later. Time to extubation, head lift, sternal position and standing and complications during recovery were recorded. Data are presented as median (range).

RESULTS

Time to standing was significantly longer in animals in group M [56 (13-179) minutes] than in group P [44 (4-137) minutes], and the early recovery score in group M [3 (2-6)] was overall worse than in group P [3 (1-5)]. Significantly more dogs in group M (n = 30) than in group P (n = 22) displayed hypotension.

CONCLUSIONS AND CLINICAL RELEVANCE

The administration of midazolam prolonged time to standing and had a mild negative effect on the quality of recovery in a pooled population of healthy male and female dogs undergoing neutering.

Effects of midazolam on cardiovascular responses and isoflurane requirement during elective ovariohysterectomy in dogs

Background

A prospective, randomized, placebo-controlled, blinded clinical study was conducted to determine whether a single dose of midazolam affects the cardiovascular response to surgical manipulation of the ovaries during elective ovariohysterectomy. Thirty-nine client-owned dogs undergoing elective ovariohysterectomy were recruited. After scoring cage demeanour, dogs were premedicated with acepromazine (0.03 mg kg^-1) and pethidine (3 mg kg^-1) intramuscularly into the quadriceps muscle and 20 min later sedation was scored. Anaesthesia was induced with propofol intravenously (IV) to effect. The study treatment (group M: midazolam (0.25 mg kg^-1); or group P: placebo (Hartmann’s solution) (0.125 ml kg^-1)) was administered IV before the intra-operative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Morphine (0.3 mg kg^-1 IV) was administered prior to the start of surgery. The vaporizer setting was adjusted according to the depth of anaesthesia. If an end-tidal isoflurane concentration (FE’Iso) above 1.6% was required additional analgesia was provided with fentanyl (2 μg kg^-1). Dogs received meloxicam (0.2 mg kg^-1 IV) at the end of procedure. Heart rate, mean arterial blood pressure, respiratory rate and end-tidal partial pressure of carbon dioxide as well as FE’Iso were recorded and analysed.

Results

A statistical significant difference between groups was detected in FE’Iso, with group M requiring a significantly lower FE’Iso than group P (14.3%) after administration of midazolam. No differences between groups was shown for percentage change in heart rate and mean arterial blood pressure, or end-tidal carbon dioxide and requirement for mechanical ventilation, or rescue analgesia. There was no statistically significant difference in the incidence of complications in group M and P. Group M received significantly more succinylated gelatin solution pre-administration of midazolam than group P, but no differences in fluid administration post-administration of the study treatment (midazolam/placebo) were detected. No statistical significant difference was demonstrated for the use of anticholinergic agents, dobutamine or noradrenaline.

Conclusion

No significant effect on cardiovascular parameters could be observed with administration of midazolam, but a modest (14.3%) isoflurane-sparing effect was detected.

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.

Midazolam exacerbates morphine tolerance and morphine-induced hyperactive behaviors in young rats with burn injury

Midazolam and morphine are often used in pediatric intensive care unit (ICU) for analgesia and sedation. However, how these two drugs interact behaviorally remains unclear. Here, we examined whether (1) co-administration of midazolam with morphine would exacerbate morphine tolerance and morphine-induced hyperactive behaviors, and (2) protein kinase C (PKC) would contribute to these behavioral changes. Male rats of 3-4 weeks old were exposed to a hindpaw burn injury. In Experiment 1, burn-injured young rats received once daily saline or morphine (10mg/kg, subcutaneous, s.c.), followed 30min later by either saline or midazolam (2mg/kg, intraperitoneal, i.p.), for 14 days beginning 3 days after burn injury. In Experiment 2, young rats with burn injury were administered with morphine (10mg/kg, s.c.), midazolam (2mg/kg, i.p.), and chelerythrine chloride (a non-specific PKC inhibitor, 10nmol, intrathecal) for 14 days. For both experiments, cumulative morphine anti-nociceptive dose-response (ED50) was tested and hyperactive behaviors such as jumping and scratching were recorded. Following 2 weeks of each treatment, ED50 dose was significantly increased in rats receiving morphine alone as compared with rats receiving saline or midazolam alone. The ED50 dose was further increased in rats receiving both morphine and midazolam. Co-administration of morphine and midazolam also exacerbated morphine-induced hyperactive behaviors. Expression of the NR1 subunit of the N-methyl-d-aspartate (NMDA) receptor and PKCγ in the spinal cord dorsal horn (immunohistochemistry; Western blot) was upregulated in burn-injured young rats receiving morphine alone or in combination with midazolam, and chelerythrine prevented the development of morphine tolerance. These results indicate that midazolam exacerbated morphine tolerance through a spinal NMDA/PKC-mediated mechanism.

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.

The effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test: anxiolysis vs. pain modulation

The aim of the present study was to evaluate, by means of quantitative and multivariate analyses, the effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test as well as whether such changes are associated with drug-induced effects on anxiety and/or nociception. To this purpose, ten groups of male Wistar rats were intraperitoneally injected with saline, diazepam (0.25, 0.5 and 2 mg/kg), FG-7142 (1, 4 and 8 mg/kg) or morphine (3, 6 and 12 mg/kg). The mean number and mean latency to first appearance were calculated for each behavioral component. In addition, multivariate cluster and adjusted residual analyses based on the elaboration of transition matrices were performed. Three main behavioral categories were identified: exploratory (walking, sniffing), primary noxious-evoked (hind paw licking, front paw licking, shaking/stamping) and escape (climbing, jumping). Although no significant modifications in the latencies of the primary noxious-evoked components were induced by treatment with diazepam or FG-7142, significant effects were provoked by morphine treatment. Multivariate analyses showed that diazepam-induced anxiolysis redirected the rat's behavior toward a more purposeful and effective escape strategy. In contrast, the high level of anxiety induced by FG-7142 caused the behavioral structure to become disorganized and not purposefully oriented. Changes in the organization of behavioral components were observed in morphine-treated animals and mainly consisted of modifications in the primary noxious-evoked and escape components. The findings suggest that the effects of diazepam on the structure of the rat's response to pain in the hot-plate test are more likely attributable to anxiolysis than pain modulation.

Antinociceptive property of intrathecal and intraperitoneal administration of a novel water-soluble isoindolin-1-one derivative, JM 1232 (-) in rats

Antinociceptive effects of a new water-soluble sedative agent, an isoindolin-1-one derivative, (-)-3-[2-(4-methyl-1-piperazinyl)-2-oxoethyl]-2-phenyl-3,5,6,7-tetrahydrocyclopenta[f]isoindol-1-(2H)-one (JM 1232 (-)) were studied in two different nociceptive models of rats. Sprague-Dawley rats with lumbar intrathecal catheters were tested for their thermal tail withdrawal response and for their paw flinches by formalin injection after intrathecal administration of various doses of JM 1232 (-). The effects of intraperitoneal administration were also investigated. In addition, behavioral side effects were examined. When antinociceptive effects were observed, the effects of pretreatment with flumazenil or naloxone for the maximum effective dose were evaluated. Eight rats were used in each dose of each group. Intrathecal JM 1232 (-) increased the tail flick latency and decreased the number of flinches in both phases 1 and 2 of the formalin test. These changes were antagonized by intrathecal flumazenil but not by naloxone. Intraperitoneal JM 1232 (-) had no effects on the tail flick latency, but decreased the number of flinches in both phases 1 and 2 of the formalin test. The latter was antagonized by intraperitoneal flumazenil and naloxone with bigger effects of flumazenil. Intraperitoneal JM 1232 (-) 3000 microg induced reversible motor disturbance. In conclusion, intrathecal JM 1232 (-) exerts antinociceptive effects on acute thermal and inflammatory stimuli through benzodiazepine-GABA(A) receptors in the spinal cord. Intraperitoneal JM 1232 (-) was antinociceptive only against inflammatory stimulus and this is mediated mainly by benzodiazepine-GABA(A) receptors, but partially by micro-opioid receptors in the brain.

Midazolam attenuates the antinociception induced by d-serine or morphine at the supraspinal level in rats

Our recent study has shown that the intracerebroventricular administration of d-serine, an endogenous and selective agonist for the glycine site of the N-methyl-d-aspartate receptor, alone or in combination with morphine, leads to the potentiation of antinociception on the tail-flick response. Although there is a variety of information concerning the effects of benzodiazepines on opioid-induced antinociception, little is known about the effect of benzodiazepines on the N-methyl-d-aspartate receptor agonist-induced antinociception. To clarify the analgesic interactions among the benzodiazepine/GABA(A), N-methyl-d-aspartate and opioid receptors at the supraspinal level, we investigated the effects of intracerebroventricular administration of midazolam, a benzodiazepine receptor agonist, on the antinociception evoked by the intracerebroventricular application of d-serine or morphine. The intracerebroventricular administration of midazolam alone produced hyperalgesia on the tail-flick response in a benzodiazepine receptor antagonist, flumazenil-reversible manner. The antinociception induced by the intracerebroventricular application of d-serine or morphine was attenuated by the intracerebroventricular administration of midazolam. In addition, this inhibitory effect of midazolam on the antinociception of d-serine or morphine was antagonized by the intracerebroventricular administration of flumazenil. Together with the facts that d-serine and midazolam act as selective agonists for the glycine site of the N-methyl-d-aspartate receptor and benzodiazepine/GABA(A) receptor, respectively, these observations suggest a functional interaction between the NMDA and benzodiazepine/GABA(A) receptors in the regulation of antinociception at the supraspinal level.

Analgesic effects of systemic midazolam: comparison with intrathecal administration

PURPOSE

Midazolam has antinociceptive effects when administered intrathecally, while its effects associated with systemic administration remain controversial. In the present study, the antinociceptive properties of systemically vs intrathecally administered midazolam were investigated in a rat model of thermal and inflammatory pain.

METHODS

One hundred seventy-six (n = 8 animals per dose escalation) male Sprague-Dawley rats were instrumented with lumbar intrathecal catheters. Tail withdrawal in response to thermal stimulation, or paw flinching and shaking in response to sc hind paw formalin injection were compared following intrathecal injection of midazolam (1, 3, 10, 30, or 100 microg in 10 microL) or ip administration (3, 30, 300, or 3,000 microg in 300 microL). Saline 10 microL or 300 microL was used as a control. Behavioural side effects and motor disturbance were also examined.

RESULTS

Intrathecal administration of midazolam increased tail flick latency dose dependently (P < 0.05) with a 50% effective dose (ED50) of 1.60 microg, whereas ip administration did not increase latency. Both intrathecal and ip routes of administration decreased the number of paw flinches in both phases 1 and 2 of the formalin test (P < 0.05). The ED50s were 1.26 microg [confidence interval (CI), 0.35-3.18 microg], (phase 1) and 1.20 microg (CI, 0.29-3.71 microg), (phase 2) with intrathecal administration, and 11.6 microg (CI, 2.5-19.3 microg), (phase 1) and 52.2 microg (CI, 18.3-102.7 microg), (phase 2) with ip administration.

CONCLUSION

Systemically administered midazolam induced antinociception for inflammatory pain only, while intrathecal administration elicited antinociceptive effects on both acute thermal and inflammatory-induced pain.

Involvement of cholecystokininergic systems in anxiety-induced hyperalgesia in male rats: behavioral and biochemical studies

Keeping in mind the increased pain complaints reported in anxious or depressive patients, our goal was to investigate in rats the consequences of an experimentally provoked state of anxiety/depression on pain behavior and on its underlying mechanisms. We therefore used a model of social defeat consisting of a 30 min protected confrontation followed by a 15 min physical confrontation, repeated during 4 d, that elicited symptoms close to those observed in humans with anxiety or depression. Indeed, 5 d later, animals subjected to social-defeat confrontation were characterized by a decrease of sweet-water consumption and of body weight, and a hyperactivity of the hypothalamic-pituitary-adrenal axis, suggesting that the social-defeat procedure induced a prolonged state of anxiety. Rats subjected to the social-defeat procedure showed an enhanced nociceptive behavior to the subcutaneous administration of formalin, 5 d after the last confrontation session. Because chronic treatment with the established anxiolytic chlordiazepoxide (10 mg.kg(-1).d(-1)) prevented hyperalgesia, this strongly suggested that this experimental procedure might be a suitable animal model of "anxiety-induced hyperalgesia." Hyperalgesia associated with anxiety not only was related to a significant increase of CCKLM [cholecystokinin (CCK)-like material] in frontal cortex microdialysates but also was prevented by a CCK-B receptor antagonist [4-[[2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2[[(tricyclo[3.3[12,17]dec-2-yloxy)-carbonyl]amino]-propyl]amino]-1-phenyethyl]amino]-4-oxo-[R-(R*, R*)]-butanoate N-methyl-D-glucamine (CI-988)] (2 mg/kg), strongly supporting the involvement of central CCKergic systems in these phenomena. Finally, combined treatments with CI-988 and morphine completely suppressed pain-related behavior, supporting the idea that the association of both compounds might represent a new therapeutic approach to reduce the increase of pain complaints highly prevalent among anxious or depressive patients.

Benzodiazepine system is involved in hyperalgesia in rats induced by the exposure to extremely low frequency magnetic fields

Many reports demonstrate that extremely low frequency magnetic fields (ELF MFs, 60 Hz) may be involved in hyperalgesia. In a previous investigation, we suggested that MFs may produce hyperalgesia and such a response may be regulated by the benzodiazepine system. In order to further confirm this effect of MFs, we used diazepam and/or flumazenil with MFs exposure. When testing the pain threshold of rats using hot plate tests, MFs or diazepam (0.5 microg, i.c.v.; a benzodiazepine receptor agonist) induced hyperalgesic effects with the reduction of latency. These effects were blocked by a pretreatment of flumazenil (1.5 mg/kg, i.p.; a benzodiazepine receptor antagonist). When the rats were exposed simultaneously to MFs and diazepam, the latency tended to decrease without statistical significance. The induction of hyperalgesia by co-exposure to MFs and diazepam was also blocked by flumazenil. However, the pretreatment of GABA receptor antagonists such as bicuculline (0.1 microg, i.c.v.; a GABA(A) antagonist) or phaclofen (10 microg, i.c.v.; a GABA(B) antagonist) did not antagonize the hyperalgesic effect of MFs. These results suggest that the benzodiazepine system may be involved in MFs-induced hyperalgesia.

Sedation with Midazolam Leads to Reduced Pain After Dental Surgery

Our principal objective in this study was to evaluate the potential pain reducing effect of i.v. midazolam in patients undergoing oral surgery. One-hundred-twenty-five patients with impacted mandibular third molars requiring removal under local anesthetic were randomized into 2 groups. The first group (n = 64) was administered i.v. midazolam by titration until a clinical end-point of conscious sedation followed by local anesthetic before surgery; the second group (n = 61) was the control and was administered only local anesthetic before surgery. The surgery was performed in a standardized manner in both groups by the same surgeon. Outcome measures were four primary end-points: pain intensity as assessed by a 100-mm visual analogue scale and a 4-point categorized scale hourly for 8 h, time to first analgesic, total analgesic (ibuprofen) consumption over the first 48 h, and a 5-point categorical patient global assessment scale (0 = poor, 1 = fair, 2 = good, 3 = very good, and 4 = excellent). Throughout the 8-h investigation period, patients in the midazolam group reported significantly lower pain intensity scores than those in the control group (19.0 +/- 13.2 mm versus 28.1 +/- 12.8 mm, P < 0.05). The patients in the midazolam group also reported significantly longer time to first analgesic (165.5 +/- 56.5 min versus 202.2 +/- 79.0 min, P < 0.05), less analgesic consumption (1275 +/- 364 mg versus 1688 +/- 407 mg, P < 0.001) and better patient global assessment (3.34 +/- 0.8 versus 2.4 +/- 0.9, P < 0.001). We conclude that systemically administered midazolam is effective in reducing postoperative pain after third molar surgery.

IMPLICATIONS

In this observer blinded study, we found that i.v. midazolam treatment (0.09 mg/kg) has a pain-reducing effect after third molar surgery, thus improving postoperative pain management.

A review of methadone deaths in Jefferson County, Alabama

Interpretation of the concentration of a drug is more difficult when a combination of drugs is present in a decedent's blood. An increase in deaths resulting from co-intoxication with methadone and a benzodiazepine led the authors to perform a retrospective study of cases examined at the Jefferson County Coroner/Medical Examiner Office. They found 101 deaths wherein methadone was detected in the blood. Based on the drugs detected in the blood, these 101 cases were grouped into four categories: (1) pure methadone intoxication, (2) intoxication with methadone and benzodiazepine, (3) intoxication with methadone and other drugs excluding benzodiazepine, and (4) intoxication with methadone, benzodiazepines, and other drugs. Methadone was the sole intoxicant in 15 cases, with a mean concentration of 0.27 mg/L. Benzodiazepines were the most frequently detected co-intoxicant (60 of 101 cases). Benzodiazepine was the only co-intoxicant in 30 cases, and the mean methadone concentration in those 30 cases was 0.599 mg/L. Higher levels of methadone may occur in acute intoxication with methadone and benzodiazepine because benzodiazepines compete with methadone for methadone receptors. Higher levels of methadone may occur with chronic abuse of methadone and benzodiazepines because over time, benzodiazepines inhibit the hepatic enzymes that metabolize methadone.

Effect of pre-operative anxiolysis on postoperative pain response in patients undergoing total abdominal hysterectomy

In a double blind, placebo-controlled trial, we have assessed the effects of pre-operative anxiolysis on postoperative pain scores in 112 ASA I-II women, aged 18-65 years, scheduled to undergo total abdominal hysterectomy. Subjects were randomly allocated to receive either oral diazepam 10 mg (n=56) or placebo (n=56) pre-operatively. Postoperative anxiety, pain scores, analgesic consumption, and sedation were evaluated at several time points during the first 24 h following surgery. Postoperative pain scores were found to be significantly higher in the diazepam group. Trait and state anxiety showed a significant effect on pain scores, independent of the treatment group. No difference was found between the groups in morphine consumption, but there was a significant reduction in morphine consumption with time.

Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.

The effects of diazepam dependence and withdrawal on morphine-induced antinociception and changes in locomotion in male and female rats

Male and female rats were exposed for 3 weeks to diazepam (DZ)-filled or empty capsules (CTR) prior to the daily administration of morphine (MOR, 5 mg/kg, IP) for 5 days. Thereafter, capsules were removed and 48 h later MOR was injected for the next 5 days. The tail-flick latency (TFL) was measured prior to and 15, 30, and 60 min after MOR assessed analgesia. Locomotion (LOC) was determined before and 15 min after injection. Prior to MOR injection (baseline), male rats were more sensitive to the thermal stimulus and were less active than female rats. Daily MOR injections neither affected the baseline TFL nor LOC. Regardless of gender, MOR produced greater analgesia in DZ-dependent and withdrawn rats than in CTR. MOR analgesia was greater in DZ-dependent male than in female rats. Gender differences in MOR analgesia were not of statistical significance in DZ-withdrawn rats. The first dose of MOR produced more depression of LOC in DZ-dependent female than in male rats. Across the time of MOR injections, female DZ-dependent and withdrawn rats were less active than CTR. LOC increased with repeated administration of MOR in all groups of rats. In summary, DZ dependence and withdrawal enhanced MOR analgesia in rats of both sexes. Regardless of chronic treatment, MOR produced more analgesia and less depression of LOC in male than in female rats. It is suggested that a decrease in the function of the GABAergic system plays a role in alteration of MOR analgesia.

Spinal and supraspinal midazolam potentiates antinociceptive effects of isoflurane

The effects of lumbar intrathecal (i.t.) and intracerebroventricular (i.c.v.) midazolam on nociception during isoflurane anaesthesia were studied in rats using the tail-flick test. Rats received i.t. midazolam 2 and 4 microg or i.c.v. midazolam 4 and 8 microg during 1.1, 1.2 and 1.3% isoflurane or without isoflurane. Neither i.t. nor i.c.v. midazolam alone at doses studied influenced nociceptive responses. 1.1% isoflurane showed a minimum antinociceptive effect which was not influenced by i.t. or i.c.v. midazolam. 1.2 and 1.3% isoflurane produced moderate antinociception which was markedly potentiated by both i.t. and i.c.v. midazolam. The effects of midazolam shown in the present study are different from the reported effects of midazolam on opioid-induced antinociception; where spinally administered midazolam potentiates and supraspinal midazolam inhibits the antinociceptive effects of morphine. The present results suggest that midazolam potentiates isoflurane-induced antinociception at doses where no effect is seen alone.

Low doses of epidural ketamine or neostigmine, but not midazolam, improve morphine analgesia in epidural terminal cancer pain therapy

STUDY OBJECTIVE

To examine analgesia and adverse effects of combination epidural pain therapy consisting of administration of morphine with either low dose of ketamine, neostigmine, or midazolam in terminal cancer pain patients.

DESIGN

Randomized double-blind study.

SETTING

Teaching hospital.

PATIENTS

48 terminal cancer patients suffering from chronic pain.

INTERVENTIONS

Patients were randomized to one of four groups (n = 12). The concept of visual analog scale (VAS), which consisted of a 10-cm line with 0 equaling "no pain at all" and 10 equaling "the worst possible pain" was introduced. All patients were taking oral amitriptyline 50 mg at bedtime. Pain was initially treated with epidural morphine 2 mg twice daily (12-hr intervals) to maintain the VAS below 4/10. Afterwards, VAS scores > or = 4/10 at any time were treated by adding the epidural study drug (2 ml), which was administered each morning, just after the 2-mg epidural morphine administration. The control group (CG) received 2 mg of epidural morphine (2 ml). The ketamine group (KG) received 0.2 mg/kg epidural ketamine (2 ml). The neostigmine group (NG) received 100 micrograms epidural neostigmine (2 ml). The midazolam group (MG) received 500 micrograms epidural midazolam (2 ml). Patients received the study drugs on a daily basis.

MEASUREMENTS AND MAIN RESULTS

Duration of effective analgesia was measured as time from the study drug administration to the first patient's VAS score > or = 4/10 recorded in days. The groups were demographically the same. The VAS pain scores prior to the treatment were also similar among groups. Only the patients in the KG demonstrated lower VAS scores compared to the MG (p = 0.018). Time since the epidural study drug administration until patient complaint of pain VAS > or = 4/10 was higher for both the KG and NG compared to the CG (KG > CG, p = 0.049; NG > CG; p = 0.0163). Only the KG used less epidural morphine compared to the CG during the period of study (25 days) (p = 0.003).

CONCLUSION

The association of either low-dose epidural ketamine or neostigmine (but not midazolam) to epidural morphine increased the duration of analgesia in the population studied (gt;20 days) compared to the CG and MG (8 to 10 days) when administered in the early stages of terminal cancer pain therapy, without increasing the incidence of adverse effects.

Diazepam alters caffeine-induced effects on beta-endorphin levels in specific rat brain regions

The present study was conducted to evaluate the effects of caffeine and the benzodiazepine agonist diazepam, and a combination of both on beta-endorphin (beta-EN) levels in specific rat brain regions. Male Sprague-Dawley rats (150-200 g) adapted to a 12-hour light: 12-hour dark illumination cycle were used in this study. Caffeine (10 mg/kg), diazepam (2 mg/kg) or a combination of caffeine (10 mg/kg) and diazepam (2 mg/kg) were administered intraperitoneally to rats at 11:00 hr. Control animals were injected with saline. Animals were sacrificed by decapitation 1 h after injection, the brains were immediately removed; the cortex, hippocampus, hypothalamus and midbrain were dissected and their B-EN levels measured by radioimmunoassay. Caffeine administration significantly increased B-EN levels in the cortex. Similarly, administration of diazepam alone resulted in a significant increase of B-EN levels in cortex. However, concurrent administration of diazepam and caffeine resulted in higher increase of B-EN levels in cortex. No significant changes in B-EN levels were detected in hippocampus and midbrain after administration of either caffeine or diazepam alone. On the other hand, when diazepam and caffeine were concurrently administered a significant increase of B-EN levels were observed in the midbrain. Moreover, administration of diazepam alone resulted in a significant increase of B-EN levels in hypothalamus. This increase was still observed following concurrent administration of diazepam and caffeine. These results clearly indicate that diazepam alters caffeine-induced effects on B-EN in specific rat brain regions.

Majonoside-R2, a major constituent of Vietnamese ginseng, attenuates opioid-induced antinociception

The effects of majonoside-R2 on antinociceptive responses caused by the mu-opioid receptor agonist morphine and the selective kappa-opioid receptor agonist U-50, 488H were examined by the tail-pinch test in mice. Intraperitoneal (IP) or intracerebroventricular (ICV) injection of majonoside-R2 (3.1-6.2 mg/kg, IP or 5-10 micrograms/mouse, ICV) and diazepam (0.1-0.5 mg/kg, IP or 0.5-1.0 microgram/mouse, ICV), as well as an opioid receptor antagonist naloxone (2 mg/kg, IP or 5 micrograms/mouse, ICV), dose-dependently attenuated the antinociception caused by subcutaneously administered morphine and U-50,488H. Moreover, when co-administered ICV or intrathecally (IT) with morphine (4 micrograms/mouse) or U-50,488H (60 micrograms/mouse), majonoside-R2 (5-20 micrograms/mouse) also exhibited antagonism against the antinociceptive action of these opioid receptor agonists in the tail-pinch test. The inhibitory effects of majonoside-R2 (10 micrograms/mouse, ICV) and diazepam (1 microgram/mouse, ICV) were reversed by flumazenil (2.5 micrograms/mouse, ICV), a selective benzodiazepine receptor antagonist, and picrotoxin (0.25 microgram/mouse, ICV), a GABA-gated chloride channel blocker. These results suggest that majonoside-R2 attenuates the opioid-induced antinociception by acting at the spinal and supraspinal levels, and that the GABAA receptor complex at the supraspinal level is involved in the effect of ICV administered majonoside-R2.

Midazolam does not influence intravenous fentanyl-induced analgesia in healthy volunteers

The effects of saline and intravenous midazolam (0.5, 1, and 2 mg per 70 kg) in combination with intravenous fentanyl (0.1 mg/70 kg) were examined on pain induced by a cold pressor test. Healthy volunteers (six females, six males) were enrolled in a prospective, double-blind, randomized, crossover trial in which mood and psychomotor performance were also examined. Five minutes and 135 min postinjection subjects immersed their forearm in ice cold water for 3 min while assessments of pain were recorded. During the first immersion, subjects reported significantly lower pain intensity and bothersomeness ratings after having been injected with fentanyl, relative to the saline condition, but the addition of midazolam neither increased nor decreased pain reports. During the second immersion (approximately 2.5 h postinjection) pain ratings did not differ between the drug and saline conditions. Mood-altering and psychomotor-impairing effects of the drug combination were dose related. We conclude that midazolam at the doses and route of administration tested neither potentiates nor decreases the analgesia produced by fentanyl in a cold-pressor pain assay.

An investigation of the potential morphine sparing effect of midazolam

The effect of a bolus and continuous infusion of midazolam on postoperative morphine consumption was assessed in a placebo-controlled, double-blind, randomly allocated trial of 50 patients undergoing elective abdominal hysterectomy. Patients in the trial group received a bolus dose of midazolam 5 mg.70 kg-1 at induction followed by an infusion at a rate of 1 mg.70 kg-1.h-1 over the next 48 h. Morphine consumption in the midazolam group was significantly lower in the first 12 h postoperatively (p < 0.02) but there was no significant difference between the two groups thereafter. Patients in the midazolam treated group had lower pain scores over the first 24 h. Also, a significantly greater number of patients in the midazolam group required no antiemetic medication over the 48 h study period (p < 0.05). Assessment of sedation revealed no significant difference between groups. We conclude that low dose midazolam has a significant, but short-lived, morphine sparing effect.

The possible involvement of GABAA systems in the antinarcotic effect of majonoside-R2, a major constituent of Vietnamese ginseng, in mice

The effect of majonoside-R2 on morphine- and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine- and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated CI- channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

The spinal potentiating effect and the supraspinal inhibitory effect of midazolam on opioid-induced analgesia in rats

The authors investigated the effects of spinal and supraspinal administration of the benzodiazepine receptor agonist midazolam alone and with opioids on tests of nociception (tail-flick and hot-plate tests) and motor function (catalepsy) in rats. At the spinal level, the dose-response curves for peak effect and area under the curve for morphine were shifted to the left (indicating potentiation) by a submaximal dose of intrathecal (i.t.) midazolam (20 micrograms) in both nociceptive tests. Additionally, 2.5 micrograms of i.t. midazolam, a dose having no effect when given alone, increased antinociception in both tests when given with i.t. morphine. Isobolographic analysis confirmed that i.t. injection of midazolam potentiated antinociception induced by i.t. morphine. At the supraspinal level, intracerebroventricular (i.c.v.) injection of 4 micrograms of midazolam inhibited morphine antinociception, i.e., the dose-response curve for morphine in the hot-plate test shifted to the right. Midazolam did not affect morphine antinociception in the tail-flick test. Catalepsy occurred only when the highest doses of i.t. or i.c.v. morphine or midazolam were injected alone. The differing effect of midazolam on morphine-induced antinociception suggests that different mechanisms are involved in the spinal cord and brain.

Effect of the NMDA-antagonist, MK 801, on benzodiazepine-opioid interactions at the spinal and supraspinal level in rats

1. Benzodiazepines potentiate morphine antinociception at the spinal level via GABAergic mechanisms. At the supraspinal level, the inhibitory effect of midazolam on morphine antinociception cannot be easily explained by GABAA receptor activation. Since excitatory amino acids play a role in central transmission, we investigated the effect of dizocilpine (MK 801) on this interaction in spinal cord and brain. 2. In rats with an intrathecal or intracerebroventricular catheter, the mechanisms of the antinociceptive effect of benzodiazepine-morphine combinations were tested during thermal nociceptive tests. 3. The principal findings of this study were that at the spinal level, midazolam potentiation of morphine antinociception can be antagonized by the NMDA antagonist, MK 801 (10 micrograms), as assessed by hot-plate and tail-flick tests. When drugs were administered supraspinally, midazolam inhibited morphine antinociception only in the hot-plate test, an effect also inhibited by MK 801. In the tail-flick assay, midazolam failed to influence the morphine response. 4. The NMDA antagonist significantly affected midazolam antinociception at the spinal level, but was not effective following i.c.v. administration of the drugs. MK 801 had no effect on morphine antinociception after i.t. and i.c.v. administration of the drugs. 5. The paradoxical effect of midazolam on morphine antinociception and its reversal by MK 801 might be due to modulation at various levels of the neuraxis and/or modulation of different pathways mediated via both GABAA and NMDA receptor mechanisms.

Mechanisms of the influence of midazolam on morphine antinociception at spinal and supraspinal levels in rats

The mechanisms for the combined antinociceptive effect of midazolam and morphine administered at spinal (intrathecal, i.t.) and supraspinal (intracerebroventricular, i.c.v.) levels were investigated in rats. Nociceptive test results showed that co-administration of midazolam and morphine at the spinal level potentiated morphine-induced antinociception, and that this interaction was blocked by intraperitoneal (i.p.) naloxone and reversed by i.t. bicuculline and i.p. flumazenil. Also, bicuculline and flumazenil blocked midazolam-induced antinociception at the spinal level, and naloxone completely reversed morphine antinociception. In contrast, when drugs were injected intracerebroventricularly, midazolam inhibited the antinociceptive effect of morphine (as determined by the hot-plate test). The inhibitory effects of i.c.v. midazolam upon i.c.v. morphine antinociception were partly blocked by flumazenil and bicuculline. Midazolam-induced antinociception was increased by bicuculline and decreased by flumazenil; naloxone i.p. blocked both i.c.v. morphine antinociception and i.c.v. morphine-midazolam antinociception. Results after i.t. injection may be due to an interaction between morphine and midazolam/GABAA receptor-activated systems. At the supraspinal level, this interaction may also activate other systems that are distinct from those governing the individual action of each agonist.

The protective effects of stress control may be mediated by increased brain levels of benzodiazepine receptor agonists

Control over stress protects against many of the deleterious effects of stress exposure, but the endogenous mediators responsible for these prophylactic effects have remained elusive. Using behavioral pharmacology, in vitro radioligand binding and neurochemical analyses, we demonstrate that exposure to escapable stress results in brain and behavior changes reminiscent of benzodiazepine administration. The stress control group shows significant protection against picrotoxinin-induced seizures, reductions in [35S]t-butylbicyclophosphorothionate (TBPS) binding and a 3-fold increase of benzodiazepine-like substances in brain in comparison to both yoked-inescapable shock and non-shock controls. These observations suggest that coping behavior leads to the release of endogenous benzodiazepine-like compounds in brain which protect the organism from stress pathology.

Diazepam attenuates hyperexcitability and mechanical hypersensitivity of dorsal horn convergent neurones during reperfusion of the rat's tail following ischaemia

We have investigated the involvement of the GABAA-benzodiazepine receptor complex in nociceptive activity of convergent neurones in the spinal cord during ischaemia and reperfusion of their receptive fields on the rat's tail. In enflurane anaesthetized rats, extracellular recordings were made from convergent neurones located throughout the dorsal horn before, during and after 30 min of ischaemia. Following intrathecal saline pretreatment, there was a significant increase in spontaneous firing rate during ischaemia (219 +/- 21%, P < 0.02, n = 10) which persisted during reperfusion. After 10 min of reperfusion, the neurones exhibited a greater response than before ischaemia to both innocuous brush (54 +/- 11%, P < 0.05, n = 10) and noxious pinch (72 +/- 14%, P < 0.02, n = 10) and the enhanced sensitivity persisted over the 60-min reperfusion period. During reperfusion, receptive field size increased in most neurones tested. Intrathecal diazepam (100 and 500 micrograms) abolished the hyperexcitability and the hypersensitivity to both innocuous and noxious mechanical stimulation during reperfusion. The highest dose of diazepam (500 micrograms) also attenuated the increase in spontaneous firing rate during ischaemia. Diazepam, at the doses tested, had no effect on receptive field enlargements during reperfusion. The effect of 100 micrograms of diazepam was partially reversed by flumazenil (1 mg/kg i.p.) but not by naloxone (1 mg/kg i.p.). In the absence of ischaemia, diazepam had no effect on spontaneous firing rate nor on the responses to innocuous or noxious mechanical stimulation. Our results support an antinociceptive role for benzodiazepines in the dorsal horn elements responsible for reperfusion hyperalgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of midazolam and naloxone in rats tested for sensitivity/reactivity to formalin pain in a familiar, novel or aversively conditioned environment

Rats tested for sensitivity/reactivity to formalin-induced pain in either an aversively conditioned or a novel environment displayed immediate but transient hypoalgesic responses that were insensitive to either a benzodiazepine (midazolam) or an opioid antagonist (naloxone). Exposure to the aversively conditioned, but not to the novel environment also provoked a more enduring hypoalgesic response that was abolished by either midazolam or naloxone. The results were taken to mean that fear is sufficient but not necessary for the production of hypoalgesic responses to environmental stimuli.

Inhibition of morphine tolerance and dependence by diazepam and its relation to the CNS Met-enkephalin levels

The effect of diazepam on the development of morphine tolerance and dependence was investigated. Male Sprague-Dawley rats were rendered tolerant and dependent by subcutaneous implantation of six morphine pellets. Diazepam (0.025, 0.25 or 2.5 mg/kg body weight) was once daily injected intraperitoneally into rats starting on the first day of implantation. Antinociception was measured by tail-flick (TF) and hot plate (HP) tests, and the extent of sedation determined by a rotarod test before and one hour after diazepam injections everyday for 5 days. Physical dependence on morphine was assessed by an antagonist-precipitated abstinence syndrome on the fifth day of treatment by injecting naloxone 10 mg/kg subcutaneously. Diazepam (0.025-2.5 mg/kg body weight) did not produce significant antinociception or sedation (sensorimotor impairment) in rats implanted with placebo pellets. Diazepam (0.25 and 2.5 mg/kg) inhibited tolerance to TF antinociception in rats implanted with morphine pellets. Sedation as evidenced by sensorimotor impairment induced by morphine pellet implantation was not influenced by diazepam (0.025-2.5 mg/kg). Diazepam administration (0.25 mg/kg) also decreased the degree of jumping behavior observed following naloxone injection in morphine pellet implanted rats. Serum morphine concentration in morphine-diazepam treated rats was not significantly different from that in morphine-saline treated rats. Finally, a decrease in the Met-enkephalin levels observed in the hypothalamus, hippocampus, cortex and spinal cord of morphine dependent rats was reversed by injecting diazepam along with morphine pellet implantation. These results suggest that diazepam inhibits morphine tolerance and dependence, and also prevents morphine-induced decrease in the CNS Met-enkephalin levels in morphine dependent rats.

Effect of chronic maternal diazepam treatment on the development of stress-induced antinociception in young rats

The use and abuse of benzodiazepines is widespread and we have begun to address whether maternal exposure to these drugs influences the development of opioid systems. We have studied the effect of maternal diazepam treatment on stress-induced antinociception in the neonatal offspring. Diazepam (1 or 10 mg/kg) was administered twice daily to mothers from conception. Pre- and postweanling rat pups were assessed for opioid-mediated stress-induced antinociception by 3-min swimming and measuring nociception using the tail immersion test. In preweanling rats there was stress-induced antinociception in both vehicle- and diazepam-treated animals but in diazepam-treated groups (1 and 10 mg/kg) this was insensitive to reversal by the opioid antagonist naloxone, suggesting that nonopioid systems are operating this response. In postweanling rats a similar insensitivity to naloxone was observed in 1 mg/kg diazepam-treated groups; with 10 mg/kg diazepam there was no significant antinociception. The results suggest that maternal diazepam treatment interferes with the development of stress-mediated responses and that part of this toxicity is due to actions on opioid systems in the CNS.

Attenuation of reperfusion hyperalgesia in the rat by systemic administration of benzodiazepines

1. An investigation into whether reperfusion hyperalgesia is modulated by prior systemic administration of two benzodiazepine agonists (diazepam and chlordiazepoxide), and an antagonist (flumazenil) was conducted. 2. Transient ischaemia was induced in conscious rats by applying an inflatable tourniquet to the base of the tail; when the rats exhibited a co-ordinated escape response, the tourniquet was deflated and reperfusion of the tail was allowed. Reperfusion hyperalgesia manifested as a decrease in tail flick latency, following tail immersion in 49 degrees C water, after the release of the tourniquet. 3. Intraperitoneal administration of diazepam, chlordiazepoxide and flumazenil had no effect on the co-ordinated escape to the noxious ischaemic stimulus nor on tail flick latency after application of a sham tourniquet. 4. The hyperalgesia evident during reperfusion, was abolished by diazepam (1 and 5 mg kg-1) and chlordiazepoxide (5 and 25 mg kg-1). The antihyperalgesic effects of both diazepam (5 mg kg-1) and chlordiazepoxide (25 mg kg-1) were inhibited by flumazenil (1 mg kg-1). 5. Rotarod performance was impaired in rats given diazepam and chlordiazepoxide at the same doses at which the benzodiazepines were antihyperalgesic. The impairment to motor function did not extend to the motor systems involved in the tail flick response. 6. In conclusion, benzodiazepines have antinociceptive properties during hyperalgesia.

Pentobarbital, diazepam, and ethanol abolish the interphase diminution of pain in the formalin test: evidence for pain modulation by GABAA receptors

There are two phases to the behavioral response to injection of formalin. After an initial vigorous response, a period of reduced pain occurs 10 to 15 min after formalin, followed by reemergence of pain-related behaviors. These phases are believed to represent acute chemical stimulation of afferent neurons followed by injury-related inflammatory pain. Pentobarbital (10, 15, or 25 mg/kg), diazepam (0.5, 1.5, or 5.0 mg/kg), or ethanol (0.5, 1.0, or 1.5 g/kg) attenuated the diminution of pain between the two phases, so that pain was continuous throughout 60 min of testing, but had no effect on pain scores during the peaks of either phase. The effects of pentobarbital and diazepam were blocked by picrotoxin (2.5 mg/kg), which itself had no effect. Ro 15-1788 also blocked the effect of diazepam. Picrotoxin did not effectively antagonize the effect of ethanol. A high dose of picrotoxin (5.0 mg/kg) caused seizures in some rats and also eliminated the interphase depression of pain. The results suggest that the biphasic time course of formalin pain is produced by a central antinociceptive mechanism that is inhibited by GABAA receptors.

Dynorphin A(1-17) mediates midazolam antagonism of morphine antinociception in mice

Studies have shown that midazolam acts in the brain to antagonize the antinociception produced by morphine. The purpose of this study was to determine if spinal dynorphin A(1-17) (Dyn) was involved in the antagonistic effects of midazolam. A number of drugs when administered intracerebroventricularly (ICV) to mice release Dyn in the spinal cord to antagonize morphine-induced antinociception. In the present study using the mouse tail-flick test, midazolam administered ICV produced a dose related reduction of the antinociception induced by morphine given intrathecally (IT). The antagonistic action of midazolam against morphine-induced antinociception involved the release of Dyn in the spinal cord, as evidenced by the following results. 1) Administration of naloxone, nor-binaltorphimine and dynorphin antiserum, IT, eliminated the antagonistic effect of midazolam, given ICV, against morphine. Treatment with these opioid antagonists and dynorphin antiserum is known to inhibit the action of spinally released Dyn. 2) Production of desensitization to the effect of spinal Dyn by pretreating with morphine, 10 mg/kg subcutaneously 3 h before the tail-flick test, abolished the antagonistic action of midazolam given ICV. A 3-h pretreatment with midazolam, ICV, also produced desensitization to the antianalgesic action of Dyn given IT. 3) Elimination of the Dyn component of action of midazolam by administration of naloxone, nor-binaltorphimine and dynorphin antiserum, IT, uncovered slight antinociceptive activity of midazolam, given ICV. Coadministration of flumazenil (a benzodiazepine antagonist), bicuculline (a GABA antagonist) and picrotoxin (a chloride ion channel blocker) inhibited the midazolam effect.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Respiratory mu-opioid and benzodiazepine interactions in the unrestrained rat

Interactions of mu-opioid receptors with the benzodiazepine system were studied by examining the modulatory effects of flumazenil (a benzodiazepine antagonist) and alprazolam (a benzodiazepine agonist) on the respiratory effects of the opioid peptide dermorphin. Dermorphin, 1-30 nmol administered i.c.v., to conscious, unrestrained rats decreased ventilation rate (VR) and minute volume (MV) dose-dependently. The ventilatory depression was antagonized by naloxone and by the benzodiazepine antagonist flumazenil. The benzodiazepine alprazolam potentiated the respiratory inhibition of a small (1 nmol) dose of dermorphin but antagonized that of a higher dose (3 nmol). The results suggest that the benzodiazepine/GABA receptor complex modulates respiratory depression induced by central mu-receptor stimulation in the rat.

Does midazolam inhibit the development of acute tolerance to the analgesic effect of alfentanil?

Alfentanil-midazolam analgesic interactions were studied in rats with continuous infusions or bolus injections of the drugs. Analgesia was determined by measuring the threshold of motor response to noxious pressure. The continuous constant-rate infusion of alfentanil demonstrated that after an initial peak, the analgesia profoundly declined due to the development of acute tolerance. When alfentanil (250 micrograms.kg-1.h-1) was given together with midazolam (3 mg.kg-1.h-1), the decline in the analgesic effect of alfentanil was attenuated. Following the 4 h period of the constant-rate (250 micrograms.kg-1.h-1) infusion of alfentanil, when acute tolerance was already developed, midazolam (3 mg.kg-1) given as a bolus injection enhanced the alfentanil-induced anesthesia. At the same time, when alfentanil was given as a bolus injection (30 micrograms.kg-1) with or without midazolam (3 mg.kg-1) also by bolus injection, no changes were seen to indicate an enhancement of the analgesic effect of alfentanil by midazolam. The results suggest that midazolam attenuates the development of acute tolerance to the analgesic effect of alfentanil.

Can midazolam diminish sufentanil analgesia in patients with major trauma? A retrospective study with 43 patients

Benzodiazepine agonists in combination with opioid analgesics are commonly used for combined analgesia and sedation in intensive care patients as well as for anesthesia. In animals, studies indicate either agonistic or antagonistic interactions of benzodiazepine agonists and opioids. This retrospective study of 43 patients evaluated the possible clinical relevance of benzodiazepine-opioid interactions related to pain management. We observed an increase of greater than 50% of the maximal sufentanil infusion rate in significantly more patients in group 2 (13 patients vs 6 patients; chi 2: p = 0.04) and a decrease of the sufentanil infusion rate in eight group 1 patients, but only in one patient in group 2 (chi 2: p = 0.03). We believe that an interaction between midazolam and sufentanil on nociceptive transmission and/or a rapid development of tolerance to sufentanil may be responsible for the observed difference. Contrary to the common clinical impression that midazolam potentiates opioid analgesia, these results indicate that systemic co-administration of midazolam over a period of more than three days can diminish sufentanil efficacy.

Effects of diazepam on nociception in rats

Acute i.p. injection of diazepam (1 mg/kg) resulted in a moderate increase in the tail-flick latency in rats. Tolerance to this diazepam effect developed after 10 days of diazepam treatment (1 mg kg-1 day-1). The benzodiazepine antagonist Ro 15-3505 only partially reversed the effect of diazepam on nociception. Naloxone (5 mg/kg i.p.) failed to affect the effect of diazepam on nociception, while the kappa antagonist MR 2266 fully antagonized the diazepam-induced increase of the tail-flick latency. Diazepam injected intracerebroventricularly (1, 5, 20 micrograms/rat) did not alter basal nociceptive threshold, however, diazepam injected intrathecally (20 micrograms/rat) prolonged the tail-flick latency. Furthermore, intracerebroventricular injection of muscimol partially antagonized the i.p. diazepam-induced increase of the tail-flick latency. These results suggest that benzodiazepine receptor sites are partially involved in the effect of diazepam on nociception and indicate that an indirect kappa-opioid-receptor-mediated mechanism may be involved. The anatomical site of diazepam action on tail-flick latency seems to be at the spinal level. Descending axons to the spinal cord from brain areas reached by intracerebroventricular injection of muscimol seem to modulate the effect of diazepam effect on nociception.

Central and peripheral benzodiazepine receptors: involvement in an organism's response to physical and psychological stress

The present review discusses the current knowledge of the molecular pharmacology and neuroanatomical and subcellular localization of both the central benzodiazepine/GABA-chloride ionophore receptor complex and the peripheral benzodiazepine receptor. It then reviews all of the literature to date on how these two receptor sites are modulated by environmental stress. The possible role of these sites in learning and memory is also discussed. Finally, a theoretical model is presented which examines the differential, and perhaps complementary, alterations of these two sites in an organism's response to stress.

Benzodiazepine-induced antagonism of opioid antinociception may be abolished by spinalization or blockade of the benzodiazepine receptor

The mechanisms underlying benzodiazepine antagonism of opioid antinociception were studied using the tail flick test and the hot plate test in mice. Both single-dose and repeated diazepam treatment antagonized the antinociceptive effect of morphine. The specific benzodiazepine antagonist flumazenil completely reversed the antagonism between diazepam and morphine. Mid-thoracic spinalization also abolished the antagonism, indicating that the antagonism takes place at higher levels in the CNS. Neither diazepam nor midazolam showed any affinity for opioid mu or kappa receptors in membranes prepared from mouse forebrain. Taken together with the results of other studies of interactions between GABAergic drugs and opioids, the results indicate that a benzodiazepine receptor-mediated mechanism at higher levels in the CNS, possibly in the brainstem, blocks the effect of opioids on nociceptive transmission.

GABAergic mechanisms in morphine-induced hypothermia

Morphine produced a hypothermic effect in restrained rats which was antagonized by naloxone. This effect was completely inhibited by gamma-acetylenic-GABA, an inhibitor of GABA transaminase and by baclofen, a specific GABAB agonist. Pretreatment with diazepam, an agonist of the benzodiazepine receptor, partially inhibited morphine-induced hypothermia. Flumazenil, a benzodiazepine receptor blocker, potentiated the action of morphine on body temperature. A role of brain GABA in the thermoregulatory effects of morphine is proposed on the basis of these results.

Does midazolam sedation in oral surgery affect the potency or duration of diflunisal analgesia?

A randomized cross-over study was carried out to determine whether midazolam in doses used for conscious sedation had any effect on the potency or duration of diflunisal, a non-narcotic analgesic used for postoperative pain in oral surgery. Thirty-two Hong Kong Chinese patients of either sex, aged between 16 and 28 years, were given either midazolam to supplement local anaesthesia or local anaesthesia alone at one visit and the alternative at the other visit, for surgical removal of bilateral symmetrically impacted third molars. Surgery was carried out on one side only at each visit. Diflunisal was given for postoperative pain relief. Midazolam had no effect on the potency or duration of action of diflunisal. Independent of the method, more patients had better pain relief following the second procedure than following the first, probably due to a degree of adaptation to the pain, at the second visit.

Diazepam attenuates morphine antinociception test-dependently in mice

The influence of diazepam on the antinociceptive effect of morphine was studied using four different nociceptive tests in mice. In the tail flick test, diazepam induced a dose-dependent reduction of the morphine effect, with an almost total reversed morphine effect following diazepam 2 mg/kg. The effect could not be explained by altered tail skin temperature or pharmacokinetic changes. Diazepam 1 mg/kg and higher induced sedation and significantly impaired the performance in a rotarod test, a dose of 0.5 mg/kg diazepam was therefore used in the other nociceptive tests. This dose of diazepam significantly attenuated the antinociceptive effect of morphine in the constant temperature hot plate test and the tail flick test. In the increasing temperature hot plate test and in the formalin test, no effect of diazepam on the nociceptive effect of morphine was observed. The results indicate that diazepam antagonizes the effect of morphine dependent upon the test employed. No antagonism could be observed in tests with a long-lasting stimulus, and a response integration probably at a rather high level in the CNS. In the two tests showing antagonism, the stimulus is more short-lasting, and at least for the tail flick test, the integration takes place at a lower level in the CNS.

Interaction of midazolam and morphine in the spinal cord of the rat

The antinociceptive properties, as measured by the tail-flick and hot-plate tests, and the motor effects of an intrathecally-administered benzodiazepine agonist midazolam, alone, and in combination with morphine, was examined in rats. Midazolam alone produced a weak but dose-dependent (20-60 micrograms) antinociceptive effect in addition to a clear motor dysfunction at larger doses (60-100 micrograms). An inactive dose of intrathecally-administered midazolam (20 micrograms) produced a leftward shift in the dose-response curve for intrathecally administered morphine, in the thermal antinociceptive tests. This supra-additive effect was antagonized by naloxone (1 mg/kg). The data suggest a synergistic interaction between mu- and GABAA-receptors in the spinal processing of thermally-evoked pain.

Duodenal infusion of fat, cholecystokinin secretion and satiety in the pig

The influence of the cholecystokinin (CCK) antagonist L-364,718 (0.1 mg/kg) on short-term control of food intake was studied in 6 pigs. Arterial injection of L-364,718 abolished the inhibition of intake to CCK octapeptide infusion (4 micrograms/kg/hr; from 42% p less than 0.001, to 97% of control intake), but did not alter control intake (99%). Injection of L-364,718 also abolished the inhibition of intake to duodenal infusion of emulsified fat (12 g/hr; from 76% p less than 0.001 to 105%) and of monoglyceride (24 g/hr; from 64% p less than 0.001 to 101%), but did not alter the inhibition to oleic acid (60 g/hr; 48% p less than 0.01 and 61% p less than 0.02), to glycerol (127 g/hr; 84% p less than 0.05 and 89%) or to glucose (144 g/hr; 78% p less than 0.02 and 69% p less than 0.001). These results suggest that monoglyceride-induced CCK secretion is mainly responsible for the satiety to duodenal fat in the pig, but that there is also a CCK-independent effect via the fatty acid. The results further indicate that intake of a normal barley-based diet (2% fat) is controlled via CCK-independent mechanisms.

Interactions between anticholinesterase poisoning and opioid analgesia and locomotion in mice

Interactions between anticholinesterases and opioid drugs on antinociception and locomotor behaviour have been studied in the mouse. The anticholinesterase di-isopropylfluorophosphate (DFP) (1 mg/kg), pyridostigmine (1 mg/kg) and neostigmine (200 micrograms/kg) or drugs used to treat anticholinesterase poisoning (atropine, pralidoxime and diazepam) were not antinociceptive. DFP, at doses which produced marked neurotoxicity (2 mg/kg), produced antinociception which was not mediated by opioid receptors. The antinociceptive effects of alfentanil, but not fentanyl or morphine, were potentiated by DFP, whereas pyridostigmine and neostigmine were without effect. The potentiating activity of DFP was unaffected by atropine, pralidoxime and diazepam. DFP (1 mg/kg) produced a small degree of hypolocomotion whilst atropine and pralidoxime produced marked hyperlocomotion. Diazepam alone and with DFP, atropine, pralidoxime or opioid drugs produced marked motor incapacitation. Hyperlocomotion induced by morphine and alfentanil was reduced by DFP but fentanyl hyperlocomotion was unaffected. Treatment of DFP toxicity with atropine and pralidoxime reversed the effects on alfentanil locomotion but failed to alter DFP's action upon morphine or fentanyl locomotion. Atropine and pralidoxime treatment alone did not affect fentanyl hyperlocomotion, attenuated alfentanil hyperlocomotion and produced marked hypolocomotion in morphine-treated mice. Opioids and anticholinesterases do not exhibit common interactions and their effects are dependent on both opioid, anticholinesterase and the behaviour studied.

Zopiclone potentiates the antinociceptive effect of morphine in rats

The antinociceptive effect of morphine, as determined by the tail-flick test, was dose-dependently increased by the intraperitoneal injection of zopiclone. The benzodiazepine antagonists Ro 15-1788 (flumazepil) and Ro 15-3505, when intraperitoneally injected, significantly antagonized the effect of intraperitoneal injection of zopiclone on morphine antinociception. Intrathecal injection of zopiclone potentiated morphine antinociception, while the intracerebroventricular injection of zopiclone failed to enhance morphine antinociception and the intracerebroventricular injection of flumazepil to antagonize the intraperitoneal-zopiclone-induced increase in morphine antinociception. These results suggest that benzodiazepine sites are specifically involved in the potentiating effect of zopiclone on morphine antinociception. The anatomical locations of the receptors involved seem to be at the spinal level.

Reversal of the effects of centrally-administered morphine on colonic motility in dogs by the benzodiazepine receptor antagonist RO 15-1788

The effects of intravenous (i.v.) and intracerebroventricular (i.c.v.) administration of morphine on jejunal and colonic motility were investigated in conscious dogs chronically prepared with strain gage transducers and compared to those of i.c.v. DAGO, a highly selective opiate mu agonist. Morphine i.v. (100 micrograms/kg) and i.c.v. (10 micrograms/kg) administered 3 hrs after a meal stimulated colonic motility for 3-5 hrs and induced a phase 3 on the jejunum, which appeared after a 15-60 min delay following i.c.v. administration. These effects were reproduced by DAGO administration at doses of 2 micrograms/kg i.v. and 0.2 micrograms/kg i.c.v. The effects of i.v., but not those of i.c.v., morphine and DAGO on jejunal and colonic motility were blocked by a previous administration of naloxone (100 micrograms/kg i.v.). The colonic stimulation but not the jejunal phase 3 induced by i.c.v. morphine and DAGO were blocked by RO 15-1788 (1 mg/kg i.v.), a selective benzodiazepine antagonist. The colonic stimulation induced by i.v. morphine or DAGO was not modify by i.v. RO 15-1788. It is concluded that i.c.v. administration of mu agonist involved benzodiazepine but not opiate receptors to stimulate colonic motility in dogs.