Effects of the imidazobenzodiazepine RO15-4513 on the stimulant and depressant actions of ethanol on spontaneous locomotor activity

The purpose of this study was to investigate the effects of the imidazobenzodiazepine RO15-4513, a partial inverse agonist at benzodiazepine (BDZ) receptors, on the stimulant and depressant actions of ethanol in mice. For comparative purposes, another BDZ inverse agonist, FG-7142, was examined as well. Neither RO15-4513 nor FG-7142 influenced the low-dose excitatory effects of ethanol on spontaneous locomotor activity. However, both RO15-4513 and FG-7142 significantly antagonized the depressant effects of ethanol, and this antagonism was completely reversed by pretreatment with the BDZ receptor antagonist, RO15-1788. These data suggest that RO15-4513 is capable of antagonizing only some of the behavioral effects of ethanol, and in particular, those responses to ethanol that are mediated by modulation of the GABA/BDZ-chloride channel receptor complex.     

Blockade of the locomotor stimulant effects of cocaine and methamphetamine by glutamate antagonists

The AMPA antagonist, NBQX, produced dose-dependent blockade of the locomotor stimulant effects of cocaine and methamphetamine in male, Swiss-Webster mice at doses which did not alter spontaneous locomotion. A similar finding was obtained with the competitive NMDA antagonist, NPC 12626, although blockade was only observed at the highest dose studied. The NMDA antagonists, (+)-HA-966 and 7-chlorokynurenic acid (7-CKA), which act at the strychnine-insensitive modulatory site of the NMDA receptor, only blocked the stimulatory effects of methamphetamine and with (+)-HA-966, blockade was only achieved at a dose that decreased spontaneous locomotor activity. These results provide evidence for the involvement of glutamatergic input in the control of behavior involving mesolimbic dopamine. Along with other findings these results suggest that glutamate receptors may be a target for the development of pharmacological therapies for the treatment of psychomotor stimulant abuse and for other disorders involving hyperfunction of the mesolimbic dopamine system (eg. schizophrenia).     

Measuring naloxone antagonism of discriminative opioid stimulus

The numerous studies of opioids as discriminative stimuli, beginning in 1971, have shown specificity, similarity of several opioids, differences in potency (fentanyl greater than heroin greater methadone greater than morphine), and antagonism by naloxone and naltrexone. The discriminative opioid stimulus is differentiated from those of other classes of drugs, such as sedatives and anxiolytics. Greater potency of the opioid stimulus has been found in rats after subcutaneous (s.c.) than intraperitoneal administration. The discriminative opioid stimulus and its antagonism by naloxone or naltrexone have been demonstrated in rats, squirrel monkeys, gerbils, and pigeons. A few studies have quantified the competitive agonist-antagonist interaction at the receptor by calculating the pA2, which reflects the dose of the antagonist that requires doubling the agonist dose to obtain the original agonist response. The pA2 for naloxone is the same in groups of rats trained to discriminate different doses of morphine (1, 2, or 4 mg/kg s.c.) from saline. Higher pA2 values in tests after fentanyl and methadone than after heroin and morphine in rats trained to discriminate fentanyl (0.04 mg/kg s.c.) from saline reflect greater susceptibility of the synthetic than the natural exogenous opioids to antagonism by naloxone. Different pA2 values are usually interpreted as indicating differences among populations of receptors.     

Immobilization of sika deer with medetomidine and ketamine, and antagonism by atipamezole

Forty wild sika deer (Cervus nippon) were immobilized with medetomidine and ketamine and reversed by atipamezole in summer and fall captures from September 1994 to October 1995. For large yearling and older deer, mean +/- SD doses of 57.0+/-15.6 microg/kg medetomidine and 1.64+/-0.49 mg/kg (male) or 4.02+/-1.16 mg/kg (female) of ketamine were administered by intramuscular injection. For calves and small yearlings, 69.3+/-7.0 microg/kg medetomidine and 2.69+/-0.44 mg/kg ketamine were administered. While immobilized, deer were easy to handle, and muscles were well relaxed. After intramuscular administration of atipamezole (about 5 times the dose of medetomidine), deer recovered rapidly and smoothly.     

Physiological response of gray wolves to butorphanol-xylazine immobilization and antagonism by naloxone and yohimbine

Captive gray wolves (Canis lupus) were immobilized (loss of consciousness) with 2.0 mg/kg xylazine hydrochloride (XYL) and 0.4 mg/kg butorphanol tartrate (BUT) administered intramuscularly. Induction time was 11.8 +/- 0.8 min (mean +/- SE). Immobilization resulted in bradycardia, respiratory depression, and normotension. Fifteen min after induction, six wolves were given either 0.05 mg/kg naloxone hydrochloride (NAL) and 0.125 or 0.250 mg/kg yohimbine hydrochloride (YOH), or an equal volume of saline (control) intravenously. Antagonism resulted in shortened recovery times compared to control animals (P less than 0.03); there was no difference in recovery times between the YOH doses (P greater than 0.05). Antagonism caused increases in heart rate (HR) and respiratory rate (RR), but no changes in MABP. Eight other wolves were similarly immobilized, but given only NAL. This resulted in partial antagonism with the animals appearing to be sedated with XYL only. Three wolves given only 0.4 mg/kg BUT assumed a state described as "apathetic sedation." Three other wolves sedated with only 2.0 mg/kg XYL showed a profound sedation characterized by recumbency, bradycardia and shallow, but regular, respiration. This study demonstrated that (1) BUT and XYL together, but not separately, can completely immobilize wolves, (2) this combination can be rapidly antagonized by NAL and YOH, and (3) there appeared to be no adverse cardiopulmonary reactions to any of the drugs used.     

Differential effects on morphine analgesia and naloxone antagonism by biogenic amine modifiers.

The stimulation of dopaminergic receptors, inhibition of serotonin synthesis or blockade of muscurinic receptors by various modifiers led to inhibition of morphine analgesia in mice. Blockade of dopaminergic receptors or the increase in serotonergic or cholinergic activity resulted in the enhancement of morphine analgesia. Serotonergic and cholinergic systems are proposed as positive and the dopaminergic system as negative modulators of morphine analgesia. The modulation of naloxone antagonism was much more complicated than that of morphine analgesia and often the effect of biogenic amine-modifiers on antagonism differed from that on analgesia. The fact that biogenic amine-modifiers do not affect morphine analgesia and naloxone antagonism by a similar pattern suggest that interaction of narcotics and narcotic antagonists with analgesic receptors may not be exactly the same.     

Lack of Fas antagonism by Met in human fatty liver disease

Hepatocytes in fatty livers are hypersensitive to apoptosis and undergo escalated apoptotic activity via death receptor-mediated pathways, particularly that of Fas-FasL, causing hepatic injury that can eventually proceed to cirrhosis and end-stage liver disease. Here we report that the hepatocyte growth factor receptor, Met, plays an important part in preventing Fas-mediated apoptosis of hepatocytes by sequestering Fas. We also show that Fas antagonism by Met is abrogated in human fatty liver disease (FLD). Through structure-function studies, we found that a YLGA amino-acid motif located near the extracellular N terminus of the Met alpha-subunit is necessary and sufficient to specifically bind the extracellular portion of Fas and to act as a potent FasL antagonist and inhibitor of Fas trimerization. Using mouse models of FLD, we show that synthetic YLGA peptide tempers hepatocyte apoptosis and liver damage and therefore has therapeutic potential.     

Immobilization of white-tailed deer with xylazine hydrochloride and ketamine hydrochloride and antagonism by tolazoline hydrochloride

Fourteen penned and 17 free-ranging white-tailed deer (Odocoileus virginianus Rafinesque) were singularly or repeatedly immobilized with 100 mg xylazine hydrochloride (HCl) and 300 mg ketamine HCl. The mean times from intravenous injection to ambulation for 1.0, 2.0, and 4.0 mg/kg body weight doses of tolazoline HCl were 13.5, 10.5, and 9.2 min. Deer not receiving tolazoline HCl recovered in an average of 168 min. Heart rates significantly (P less than 0.001) increased from 47 to 83 beats/min after tolazoline HCl administration, representing a return to normal rate. Tolazoline HCl had no effect on respiratory rate. A total of 85 reversals with tolazoline HCl resulted in no apparent adverse reactions.     

Excitatory actions of propofol and ketamine in the snail Lymnaea stagnalis

This study compares the actions of the intravenous anaesthetics propofol and ketamine on animal behaviour and neuronal activity in the snail Lymnaea stagnalis, particularly in relation to excitatory effects observed clinically. When injected into the whole animal, neither agent induced total anaesthesia. Rather, behavioural activity was enhanced by propofol (10(-5) M) and ketamine (10(-7) M), indicating excitatory effects. When superfused over the isolated central nervous system (CNS), differential effects were produced in two identified neurons, right pedal dorsal 1 (RPeD1) and visceral dorsal 4 (VD4). Resting membrane properties were largely unaffected. However, spike after hyperpolarisation was significantly reduced in RPeD1, but not VD4, with some evidence of increased excitability. In addition, an intrinsic bursting property (post-stimulus burst) in VD4 was altered by propofol (10(-7) M). The results suggest significant excitatory components in the actions of some intravenous anaesthetics, as well as a potential role in modifying excitation and bursting mechanisms in the CNS.     

The involvement of nitric oxide in the analgesic effects of ketamine

We investigated the contribution of NO-cyclic GMP (cGMP) pathway to the antinociceptive effects of ketamine in mice by using the nitric oxide synthase inhibitor, nitro(g)- L-arginine methyl ester (L-NAME). Intraperitoneal (i.p.) (1, 5 or 10 mg/kg) or intrathecal (i.th.) (10, 30 or 60 microg/mouse) administration of ketamine produced dose-dependent antinociceptive effects in the acetic acid-induced writhing and formalin tests but not in the tail-flick nor in hot-plate tests. Pretreatment of mice with L-NAME (10 mg/kg, i.p.) which produced no antinociception on its own, significantly inhibited the antinociceptive effect of ketamine (1, 5 or 10 mg/kg, i.p.). However, L-NAME (30 microg/mouse) was given intrathecally, it neither modified the antinociceptive effect of i.th. ketamine (10, 30 or 60 microg/mouse) nor did it produce an antinociceptive effect alone. These data suggest that the activation of the NO-cGMP pathway probably at the supraspinal level, but not spinal level, contributes to the antinociceptive effects of ketamine.     

Effects of naloxone on anti-conflict and hyperphagic actions of diazepam

Rats were treated with diazepam (DZP) with or without co-administration of naloxone (NLX). Animals were subsequently tested in two settings. Sated rats were tested for food consumption in their home cages for a 1 hr period following injection. Food was then removed and on the following day the fasted animals were placed in an open field for 15 min. A single food pellet (5–6 g) was secured in the center of the open field. Animals were observed and scored on frequency of rearing, grooming, urination, number of approaches to the food, amount of food eaten and x? g food eaten per approach to the food pedestal.DZP treatment increased food consumption by sated animals in their home cages. Naloxone blocked this effect. In the open field, DZP, reduced novelty induced grooming, increased the amount of food eaten and x? g food eaten per approach to the food pedestal. Co-administration of NLX had no affect on these parameters. The primary effect of NLX appears to be on consumatory behavior $\text{per se}$ and not on the anti-conflict properties of DZP.     

Functional diversity for body actions in the mesencephalic locomotor region

1. Download : Download high-res image (240KB)
2. Download : Download full-size image

     

Morphine-like analgesic actions of enkephalin-like peptides containing the Tyr-Arg unit

The analgesic actions of some synthetically prepared peptides having the Tyr-D-Arg unit at the N terminal portion of met- and leu-enkephalin were measured by the intra-cisternal injection method in mice. Among them, Tyr-D-Arg-Gly-Phe (DR-4) induced the most potent naloxone-reversible analgesia and was also effective by s.c. injection. DR-4 showed the good affinity to mu-receptor, and the resistance to the enzymatic degradation.     

Effect of ambient temperature on the thermoregulatory and locomotor stimulant effects of 4-methylmethcathinone in wistar and sprague-dawley rats

The drug 4-methylmethcathinone (4-MMC; aka, mephedrone, MMCAT, "plant food", "bath salts") is a recent addition to the list of popular recreational psychomotor-stimulant compounds. Relatively little information about this drug is available in the scientific literature, but popular media reports have driven recent drug control actions in the UK and several US States. Online user reports of subjective similarity to 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") prompted the current investigation of the thermoregulatory and locomotor effects of 4-MMC. Male Wistar and Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1-10 mg/kg ) using an implantable radiotelemetry system under conditions of low (23°C) and high (27°C) ambient temperature. A reliable reduction of body temperature was produced by 4-MMC in Wistar rats at 23°C or 27°C with only minimal effect in Sprague-Dawley rats. Increased locomotor activity was observed after 4-MMC administration in both strains with significantly more activity produced in the Sprague-Dawley strain. The 10 mg/kg s.c. dose evoked greater increase in extracellular serotonin, compared with dopamine, in the nucleus accumbens. Follow-up studies confirmed that the degree of locomotor stimulation produced by 10 mg/kg 4-MMC was nearly identical to that produced by 1 mg/kg d-methamphetamine in each strain. Furthermore, hypothermia produced by the serotonin 1(A/7) receptor agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) was similar in each strain. These results show that the cathinone analog 4-MMC exhibits thermoregulatory and locomotor properties that are distinct from those established for methamphetamine or MDMA in prior work, despite recent evidence of neuropharmacological similarity with MDMA.     

NR2B‐deficient mice are more sensitive to the locomotor stimulant and depressant effects of ethanol

The NR2B subunit of N‐methyl d ‐aspartate glutamate receptors influences pharmacological properties and confers greater sensitivity to the modulatory effects of ethanol. This study examined behavioral responses to acute ethanol in a conditional knockout mouse model that allowed for a delayed genetic deletion of the NR2B subunit to avoid mouse lethality. Mice lacking the NR2B gene (knockout) were produced by mating NR2B[f/f] mice with CAMKIIa‐driven tTA transgenic mice and the tetO‐CRE transgenic mice. Adult male and female offspring representing each of the resultant genotypes (knockout, CAM, CRE and wildtype mice) were tested for open‐field locomotor activity following acute low‐ and high‐dose ethanol challenge as well as loss of righting reflex. Findings indicate that male and female mice lacking the NR2B subunit exhibited greater overall activity in comparison to other genotypes during the baseline locomotor activity test. NR2B knockout mice exhibited an exaggerated stimulant response to 1.5 g/kg (i.p.) and an exaggerated depressant response to 3.0 g/kg (i.p.) ethanol challenge. In addition, NR2B knockout mice slept longer following a high dose of ethanol (4.0 g/kg, i.p.). To evaluate pharmacokinetics, clearance rates of ethanol (1.5, 4.0 g/kg, i.p.) were measured and showed that female NR2B knockouts had a faster rate of metabolism only at the higher ethanol dose. Western blot analyses confirmed significant reduction in NR2B expression in the forebrain of knockout mice. Collectively, these data indicate that the NR2B subunit of the N‐methyl d ‐aspartate glutamate receptor is involved in regulating low‐dose stimulant effects of ethanol and the depressant/hypnotic effects of ethanol.     

Field immobilization of feral 'Judas' donkeys (Equus asinus) by remote injection of medetomidine and ketamine and antagonism with atipamezole

The Judas technique is a method used for landscape control of feral donkeys (Equus asinus) in northern Australia. Central to the success of any Judas program is the safe, efficient, and humane attachment of the telemetry device. For feral donkeys, this involves the use of field immobilization. We examine the replacement of the current chemical capture agent, succinylcholine, with contemporary immobilization agents to achieve positive animal welfare outcomes. A combination of medetomidine and ketamine delivered by remote injection from a helicopter was used to capture 14 free-ranging feral donkeys for the fitting of telemetry collars in Western Australia in November 2010. Dose rates of 0.14 mg/kg medetomidine and 4.1 mg/kg ketamine were appropriate to immobilize animals in 9 min (± SD = 3). Mean recovery time (total time in recumbency) was 21 min (± 14). All animals recovered uneventfully after being administered atipamezole, a specific antagonist of medetomidine, intramuscularly at 0.35 mg/kg. Physiologic parameters were recorded during recumbency, with environment-related hyperthermia being the only abnormality recognized. No significant complications were encountered, and this drug combination represents an efficient approach to capturing wild donkeys. This new method allows a rapid, safe, cost-effective approach to the immobilization of feral donkeys for use as Judas animals. This drug combination will replace the relatively inhumane succinylcholine for the field immobilization of feral donkeys.