Effects of the combined oral administration of NSAIDs and dextromethorphan on behavioral symptoms indicative of arthritic pain in rats.

The effects of combined single oral treatments with non-steroidal anti-inflammatory drugs (NSAIDs) and the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dextromethorphan (DM) on arthritic pain were examined in a rat model of adjuvant-induced arthritis. Although 12.5-100 mg/kg doses of DM alone produced no reliable effects, treatments with ibuprofen (IB, 50 and 100 mg/kg but not 12.5 or 25 mg/kg) produced mild analgesia in arthritic rats as determined using the Randall-Sellito test. IB showed a dose-response relationship which appeared to plateau at doses of 50 and 100 mg/kg. Adding 50 mg/kg DM to each IB dose resulted in significantly greater analgesic activity than IB alone at doses of 25, 50 and 100 mg/kg. A similar interaction between 50 mg/kg DM and 50 mg/kg IB occurred with respect to spontaneous pain behavior. Adding 25 mg/kg DM to 25 mg/kg IB likewise increased analgesia as measured by both the Randall-Sellito and spontaneous pain behavior tests (both P < 0.05). Five more NSAIDs were evaluated using the Randall-Sellito test, which included naproxen (NP), piroxicam (PIR), etodolac (ET), diclofenac (DC), and ketorolac (KE). For all six NSAIDS, the addition of 50 mg/kg DM reliably increased their analgesic potency, as indicated by reliable increases in previously effective NSAID doses (all six NSAIDs) as well as previously ineffective NSAID doses (IB, NP, DC, and PIR). These data demonstrate that DM greatly potentiates the analgesic activity of IB, DC, NP, PIR, ET, and KT and increases the peak effect over the NSAIDs alone. Similiar to DM's previously demonstrated enhancement of opioid analgesia in acute pain, the combination of DM and an NSAID may represent a novel analgesic approach to improved management of arthritic pain.

Development of water-immersion produced analgesia.

Nociceptive and antinociceptive systems change dramatically during the first 10 days of life in rats. The present studies sought to determine whether exposure to water stress can produce analgesia during this period, and when in the ontogeny changes in magnitude and duration of such stress-induced analgesia occur. It was found that exposure to water reliably induced analgesia as early as 3 days postnatally. This analgesia increased in magnitude and duration at the age of 17-20 days, when supra-spinal descending inhibition develops, and depended on the temperature of the water and duration of exposure.

Intrathecal treatment with dextrorphan or ketamine potently reduces pain-related behaviors in a rat model of peripheral mononeuropathy.

The therapeutic effects of dextrorphan and ketamine, two non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, on neuropathic pain-related behaviors were examined in rats with peripheral mononeuropathy induced by loose ligation of the common sciatic nerve (chronic constrictive injury, CCI). Four daily intrathecal treatments (beginning 1 h after nerve ligation) with dextrorphan or ketamine (12.5-100 nmol) reliably attenuated hyperalgesia to radiant heat and spontaneous pain-related behaviors in CCI rats. Thermal hyperalgesia also was reduced in CCI rats receiving a single intrathecal treatment with either dextrorphan or ketamine (50 and 100 nmol for each compound) on day 3 after nerve ligation when thermal hyperalgesia was well developed. Since both dextrorphan and ketamine are currently utilized in other clinical applications, the results suggest a new therapeutic utility of these 'old' compounds in treatment of neuropathic pain syndromes resulting from peripheral nerve injury.

The development of analgesic, pro- and anti-convulsant opiate effects in the rat.

Evidence indicates that the neonate is capable, if not perceiving nociception, then at least reacting to nociceptive stimuli. These responses can be inhibited by opiates such as morphine. The analgesic potency of morphine in rat pups increases with maturation, due to (a) the proliferation of opiate receptors and (b), the maturation of supraspinal descending inhibition which becomes functional at 3 weeks post-natally. Tolerance to repeated injections of morphine in pups is less pronounced than in adults since it is masked by several processes, it has been demonstrated to occur within the first two weeks of life. Toxic effects of morphine in the neonate, as can be demonstrated both in behavior and EEG, differ from those in adults. Thus, convulsions induced by morphine which have been reported to occur in adults, were absent in pups. Excitatory effects of morphine in behavior develop in 3 different stages. During the first week morphine caused behavioral activation which is not mediated by specific opiate receptors. In the second week morphine produces EEG spikes in a dose-dependent fashion, but at this age these spikes were not reversible by opiate antagonists. Opiate specific EEG spikes and other opiate specific excitatory effects start to predominate during the third week of life.

The effects of systemic morphine on behavior and EEG in newborn rats.

Early studies suggested that newborn animals are far more susceptible to the convulsant effect of systemic morphine than adult animals. The present study reassessed morphine's (0, 6, 12.5, 25, 50, 100 and 300 mg/kg) toxic effects, making use of electroencephalographic (EEG) recordings, behavioral observations and the specific opiate antagonist naloxone in immature rats (postnatal days 1, 3, 6, 12 and 24). Although morphine had opiate-specific effects (such as inhibition of activity at low doses), non-specific effects (such as hyperactivity) elicited by the highest doses, predominated in the 3 youngest age groups. At day 12 high doses of morphine first produced Straub tail and catatonia. At this age morphine produced EEG spikes that were not reversed by naloxone. Only at day 24 were electrographic spikes temporarily inhibited by naloxone. Behavioral convulsions were never observed, at any age. These findings indicate that morphine is less toxic in newborns than suggested previously.

Calcitonin gene-related peptide enhances substance P-induced behaviors via metabolic inhibition: in vivo evidence for a new mechanism of neuromodulation.

The present study examined the effects of intrathecal (i.t.) injection of calcitonin gene-related peptide (CGRP) on caudally directed biting and scratching induced by i.t. substance P (SP), bombesin (BBS), strychnine (STR), and kainic acid (KA). CGRP alone (5.25, 10.5 and 21 nmol) had no effect on these behaviors, but CGRP pretreatment produced a dose-related enhancement of behaviors induced by SP or BBS, but not by KA or STR. 2-Amino-5-phosphonovaleric acid (APV, 25 nmol), a selective N-methyl-D-aspartate (NMDA) receptor antagonist, did not block the CGRP potentiation of SP and BBS induced behaviors. CGRP, however, failed to enhance scratching and biting induced by a SP analogue [pGlu5-Mephe8-MeGly9]SP(5-11) (Dime-C7) that is resistant to enzymatic degradation by SP endopeptidase. These findings demonstrate that CGRP potentiates SP induced behavioral responses via inhibition of neuropeptide degradation and that this mechanism may serve as a physiological mechanism of SP modulation.

The development of stimulation-produced analgesia (SPA) in the rat.

The present study studied the development of stimulation produced analgesia (SPA) from the periaqueductal gray (PAG) in rats. A monopolar stimulating electrode was lowered into the dorsal or ventral PAG of animals aged 7, 14, 21, or 90-120 days. Constant current cathodal pulses (100 Hz, 100 microseconds) were delivered, starting 10 s before analgesia was tested by the tail-flick (TF) test and continuing throughout each TF trial or until cut-off (7 s). Current intensity was increased stepwise (3-200 microA). It was found that SPA can be elicited starting at 21 days, but not earlier. However, supraspinal modulation of nociception is still immature at 3 weeks after birth. First, stimulation intensities needed to produce SPA are higher in 21-day-old pups than in adult animals. Second, in 21-day-old pups, but not in adults effective current intensities in the dorsal PAG are higher than in the ventral PAG. Third, naltrexone decreases SPA from the ventral PAG in 21-day-old pups, but not in adult animals. These findings indicate that supraspinal modulation of nociception develops only 3 weeks after birth, with the ventral PAG maturing prior to the dorsal PAG, and that the contribution of endogenous opioids to SPA does not remain constant throughout the ontogeny of rats.

The role of serotonin in analgesia elicited by morphine in the periaqueductal gray matter (PAG).

The serotonergic antagonist, methysergide, administered into the periaqueductal gray matter (PAG), inhibited the antinociceptive effect of morphine, but not of glutamate, also administered into the PAG. At this dose methysergide did not alter the pain threshold when administered by itself. The implications for serotonin's role in the modulation of nociception in the PAG are discussed.

Evidence for opiate tolerance in newborn rats.

It has been reported that tolerance to the antinociceptive effect of morphine does not develop in rats younger than 15 days of age. This may be due to a masking effect of rapidly proliferating opiate receptors during the first 2 postnatal weeks. Newborn rats received morphine (20 mg/kg) or equivolume saline on postnatal days 5, 6, 7, 8 and antinociception was assessed on each day. On day 9, animals of both groups were injected with 0, 0.25, 0.50, 1, 2, 4, 8 or 20 mg/kg of morphine. Antinociception, tested by the tail-flick method, did not diminish over days 5-8, yet on day 9 a rightward shift in the dose-response curve occurred. Thus, tolerance in rats occurs to morphine induced antinociception earlier than 15 days postnatally.

Paradoxical opiate specific paralytic effects of high doses of intracerebroventricular etorphine and fentanyl in rats.

Injections of high doses of etorphine (0.0625, 0.25, or 1.0 mumol) or equimolar fentanyl into the cerebral ventricles of rats induced a sequence of motor effects including catatonia, a novel flaccid paralysis, and recurrent catatonia. These effects were dose related, naloxone reversible, and reveal an opiate specific organization of a central motor hierarchy.

Gall stone dissolution with methyl tert-butyl ether: how to avoid complications.

Fifty of 52 patients with cholesterol gall bladder stones were treated with methyl tert-butyl ether. In 48 of 50 (96%) patients the stones dissolved after an average interval of 9.5 hours. Mean stone size was 1.7 cm (0.5-3.3 cm), mean stone number was 14.6 (1-70). Twelve patients (24%) complained of nausea, a burning sensation, or vomiting. In one patient bile leakage occurred and another suffered haematobilia (4%). The puncture set was improved, and a special basket was developed to extract stones that had escaped into the cystic duct. To prevent bile leakage or haemorrhage from the incision channel, a tissue adhesive was injected into the channel or ceruletid was administered subcutaneously before removing the catheter to induce contraction of the gall bladder. Thus we were able to treat 44 patients without any complications. Nausea and vomiting could be reduced if the treatment time was kept short and the perfusion volume was as low as possible. Methyl tert-butyl ether treatment is a successful treatment of gall bladder stones with few complications.

The role of glutamate in opiate descending inhibition of nociceptive spinal reflexes.

The present experiment examined descending inhibition of the nociceptive tail-flick reflex produced by microinjection of morphine and glutamate into the periaqueductal gray (PAG) matter and the neurotransmitters mediating the inhibition at the level of the nucleus raphe magnus (NRM). The longlasting opiate analgesia was significantly reduced by microinjection of excitatory amino acid antagonists 1-(p-chlorobenzoyl)-piperazine-2,3-dicarboxylate (PCB, 3.25 mumol) or DL-2-amino-5-phosphono-valerate (APV, 25.38 mumol) into the NRM, whereas the short-lived glutamate analgesia was not. This indicates that although both opiate and non-opiate analgesia may originate in the PAG, the former is relayed through the NRM, whereas the latter is relayed by additional or different nuclei in the medulla. Two observations shed light on the question which receptors mediate the above effect in the NRM. First, PCB blocked morphine analgesia at doses that were 8 times lower than doses of APV that were effective. Second, analgesia produced by injection of glutamate into the NRM was antagonized by PCB (3.25 mumol), whereas APV (25.38 mumol) failed to do so. Together these results indicate that kainate/quisqualate, but not N-methyl-D-aspartate (NMDA), receptors are implicated in the NRM as a relay station in opiate descending inhibition.

Spinal paralysis and catalepsy induced by intrathecal injection of opioid agonists.

The intrathecal administration of high (1.05 mumol) doses of D-Ala2-Met5-enkephalinamide (DAMA), D-Ala2-Leu5-enkephalinamide (DADLE), Try-D-Thr-Gly-Phe-Leu-Thr, MR2034-TA, dextrorphan tartrate, U50,488H, levorphanol tartrate, methadone hydrochloride, and 1-methyl-4-phenyl-4-propionoxypiperidine induced spinal hypokinesia. The first 5 of these compounds caused spinal paralysis, whereas the other compounds and lower doses of the first 4 induced waxy catalepsy that was restricted to the hindquarters of rats. The paralysis induced by DAMA was not reversible by IT injections of 50 micrograms naltrexone, indicating, together with the paralytic effects of dextrorphan, that traditional opiate receptors are not involved in this behavioral effect. The spinal catalepsy induced by 0.26 mumol of DAMA was prevented by IT pretreatment with 10 micrograms of naltrexone. In view of this finding and the observation that spinal catalepsy can be induced by agonists of all opiate receptor classes, it seems likely that spinal catalepsy is produced by activation of specific opiate receptors, although the subtype remains to be established.

Opioid inhibition of kainic acid-induced scratching: mediation by mu and sigma but not delta and kappa receptors.

Scratching induced by intrathecal (IT) administration of kainic acid (0.5 nmol) to rats was inhibited by IT pretreatment with the selective mu agonists levorphanol (30 and 90 nmol), [D-Ala2,N-Met-Phe4,Gly5-ol]-enkephalin (DAGO, 0.4 and 1.1 nmol), or morphine (90 nmol), the mixed mu-delta agonist [D-Ala2,D-Leu5]-enkephalinamide (DADLE, 10 and 30 nmol), or the sigma/phenycyclidine (PCP) agonists dextrorphan (90 nmol) or (+)-N-allyl-N-normetazocine ([+]-NAM, 90 nmol). The kappa agonists dynorphin (1.1 nmol) and ethylketocyclazocine (EKC, 90 nmol) had no significant effect, nor did the selective delta agonist [D-Pen2,D-Pen5]-enkephalinamide (DPDPE, 90 nmol). The nonopioids (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([+]-3-PPP, 90 nmol) and PCP (90 nmol), selective for sigma and PCP sites, respectively, both antagonized kainic-induced scratching. Levorphanol- and DADLE-induced attenuation of scratching was partially antagonized by naltrexone. These findings suggest that opioid inhibition of kainic acid-induced scratching is mediated by classical mu receptors as well as sigma and PCP sites.

Is substance P a primary afferent neurotransmitter for nociceptive input? II. Spinalization does not reduce and intrathecal morphine potentiates behavioral responses to substance P.

Scratching elicited by the intrathecal (i.t.) administration of substance P (SP) into the lumbosacral spinal cord of rats was not reduced by spinalization or i.t. pretreatment with the analgesic morphine. Spinalization also did not affect scratching elicited by i.t. kainic acid and potentiated scratching elicited by i.t. strychnine, picrotoxin, and L-glutamic acid. Intrathecal morphine did, however, reduce scratching elicited by i.t. strychnine and kainic acid. These findings demonstrate that the scratching elicited by i.t. SP and other neuroexcitatory agents is a spinally mediated response. That this response, when elicited by SP, is not inhibited by the analgesic morphine strongly suggests that SP does not elicit scratching by action at the primary afferent synapse and that the response is not indicative of pain.

Is substance P a primary afferent neurotransmitter for nociceptive input? I. Analysis of pain-related behaviors resulting from intrathecal administration of substance P and 6 excitatory compounds.

Intrathecal (i.t.) injection of substance P (SP), capsaicin, kainic acid, picrotoxin, strychnine, morphine, and L-glutamic acid in rats induced rhythmic scratching movements with the hindlimbs, biting, and, with some of these compounds, vocalization and myoclonic twitches. Although biting was directed to the dermatome corresponding to the injection site, scratching was aimed at anterior dermatomes. Presumably painful chemical stimulation produced by cutaneous and subcutaneous application of capsaicin or acetic acid never elicited scratching. Vocalization was never elicited by SP. When vocalization occurred following i.t. picrotoxin and morphine, it was correlated with myoclonic twitches rather than with scratching and/or biting. These findings indicate that scratching (a) is not pain-related and, (b) when elicited by the i.t. administration of the compounds listed above, does not result from activation of nociceptive primary afferent synapses.

Is substance P a primary afferent neurotransmitter for nociceptive input? III. Valproic acid and chlordiazepoxide decrease behaviors elicited by intrathecal injection of substance P and excitatory compounds.

Intrathecal (i.t.) injections of substance P (SP) and kainic acid in rats produced rostrally directed scratches with the hindlimbs and caudally directed bites or licks. These behaviors, together with myoclonic twitches and vocalization, were also produced by I.T. morphine and strychnine. Intrathecal valproic acid (VA) significantly reduced all behaviors when these occurred spontaneously, and VA and chlordiazepoxide both reduced these behaviors when they were evoked by a light cotton swab tap to the lumbosacral region, in rats treated with the excitatory compounds. Since neither anticonvulsant affected the thermal or mechanical pain threshold at these doses, these results suggest that (a) the behaviors elicited by i.t. injection of the excitatory compounds are not responses to perceived pain, but rather the expression of a spinal convulsive-like state, and (b), since scratching and biting were the only behaviors produced by SP, this peptide is neither necessary nor sufficient for the elicitation of pain at the spinal level. Although our experiments do not rule out other roles for SP in pain processes such as that of a neuromodulator, it is unlikely that this compound is a traditional primary afferent neurotransmitter of pain.

Is substance P a primary afferent neurotransmitter for nociceptive input? IV. 2-Amino-5-phosphonovalerate (APV) and [D-Pro2,D-Trp7,9]-substance P exert different effects on behaviors induced by intrathecal substance P, strychnine and kainic acid.

Intrathecal (i.t.) pretreatment with 2-amino-5-phosphonovalerate (APV), an NMDA receptor antagonist, diminished scratching with the hindlimbs, vocalization, biting or licking, and myoclonic twitches produced by i.t. strychnine, kainic acid, or morphine in rats. APV did not diminish these behaviors when produced by i.t. substance P (SP). The SP analogue [D-Pro2,D-Trp7,9]-substance P (DPDT) failed to affect any behaviors produced by all of these compounds at non-paralytic doses. At these doses, neither APV nor DPDT changed the thermal and mechanical pain thresholds. These results indicate that SP does not produce scratching at the primary afferent synapse in the spinal cord, that hindlimb scratching in rats is neither necessary nor sufficient to infer the presence of pain in rats, and that SP may not be involved uniquely, if at all, in the transmission of nociceptive information at the primary afferent synapse.

Dissolution of calcified cholesterol stones and of brown and black pigment stones of the gallbladder.

The influence of different solvents on cholesterol and pigment stones was investigated in vitro. Stone analysis was performed chemically, with infrared spectroscopy (IRS), scanning electron microscopy, energy-dispersive X-microanalysis (EDXA) and wave-length-dispersive X-microanalysis (WDXA). Each set of stones came from one source: eight human calcified cholesterol stones (CHS), eight fragments of bovine radiopaque Ca-bilirubinate stones (BBIL), and two complete BBIL. CHS and BBIL fragments were treated with (1) a buffered, alkaline 1% ethylenediamine tetraacetate solution (BA-EDTA; pH 9.5); (2) with BA-EDTA and monooctanoin preparation (GMOC) alternately; (3) with GMOC alone, and (4) with methyl-tert-butyl ether (MTBE). The complete BBIL were treated with BA-EDTA and MTBE. Furthermore, two human black pigment stones (BPS) were incubated in BA-EDTA. Calcified cholesterol stones are not dissolved by GMOC alone, nor by alternating treatment with BA-EDTA. They are dissolved by MTBE. MTBE is unsuitable for complete Ca-bilirubinate stones but MTBE, GMOC and GMOC/BA-EDTA alternately disaggregate stone fragments. This means that stone fragments behave differently from complete Ca-bilirubinate stones, which is important for further in vitro investigations. Ca-bilirubinate and black pigment stones are disaggregated in BA-EDTA. These results were confirmed with six CHS, 12 BBIL and 12 BPS from 5 further patients, incubated in the most eligible solvent for any individual stone type.

Absence of side-effects in the anticonvulsant action of cortically applied antagonists of N-methyl-D-aspartate.

Three compounds reportedly blocking the N-methyl-D-aspartate (NMDA) receptor, namely 2-amino-5-phosphonovalerate, gamma-D-glutamylglycine and 3-hydroxy-2-quinoxalinecarboxylic acid, were injected subdurally onto the cortex of freely moving rats. All 3 compounds effectively suppressed behavioral and electrographic seizure activity induced by strychnine, morphine and picrotoxin that were administered via the same route. The cortical application of the NMDA-receptor antagonists did not induce behavioral or electrographic changes, and behavioral side-effects commonly observed following intracerebroventricular administration of these compounds were absent. The anatomical separation of anticonvulsant action and side-effects induced by these compounds suggests that this class of compounds may eventually be useful as antiepileptic drugs.