Effects of heroin on lever pressing for intracranial self-stimulation,food and water in the rat

Male rats maintained with continuous access to levers for intracranial self-stimulation (ICSS), water, and food were subjected to five consecutive daily injections of heroin (5 mg/kg). Rates of lever pressing for ICSS were increased in 8 rats, 2–6 hrs after administration of heroin. Rates of lever pressing for water and food were not significantly changed during this period. Naloxone (5 mg/kg) pretreatment attenuated by 82% the facilitative effect of heroin on ICSS. A second group of 8 rats maintained at reduced ICSS rates failed to show an increase in lever pressing for ICSS with heroin. The facilitative effect of heroin described in this study is consistent with previously reported studies describing the effects of morphine on ICSS.     

Phencyclidine-induced head-weaving and head-twitch through interaction with 5-HT1 and 5-HT2 receptors in reserpinized rats

Phencyclidine mainly produced head-weaving and head-twitches at doses of 5-7.5 mg/kg and of 7.5-12.5 mg/kg, respectively. Phencyclidine-induced head-twitches and head-weaving were blocked by pretreatment with ritanserin (1 mg/kg), a selective serotonin (5-HT)2 receptor antagonist and with pindolol (20 mg/kg, s.c.), a 5-HT1 receptor antagonist, respectively. In reserpine-pretreated rats, the degree of utilization of 5-HT and the number of 5-HT1 ([3H]5-HT) and 5-HT2 ([3H]ketanserin) binding sites were significantly increased compared with the figures for the vehicle-pretreated rats. The intensity of phencyclidine-induced head-weaving (at the dose of 2.5 mg/kg) and head-twitch (at the doses of 2.5 and 5 mg/kg) was significantly increased in reserpine-pretreated rats compared with that of vehicle-pretreated rats. Furthermore, in the reserpine-pretreated rats, the intensity of phencyclidine (1.25 mg/kg)-induced head-weaving and head-twitches was increased in combination with imipramine, while the intensity of phencyclidine (2.5 mg/kg)-induced head-weaving and head-twitch was decreased by pretreatment with mianserin, a non-selective 5-HT receptor antagonist. These results indicate that phencyclidine induced head-weaving by interacting with 5-HT1 receptors, indirectly after the release of 5-HT and/or with some other mechanisms and induced head-twitch by interacting with 5-HT2 receptors directly and/or indirectly.     

Mechanisms of PCA-induced hypothermia,ejaculation, salivation and irritability in rats

Injections of p-chloroamphetamine (PCA, 5 mg/kg) induced hypothermia, ejaculation, salivation and irritability in male rats kept at an ambient temperature of 20±1°C. PCA-induced hypothermia was attenuated by pretreatment with the 5-hydroxytryptamine (5-HT) uptake blockers Lundbeck 10–171 (Lu 10–171, 10 mg/kg) and chlorimipramine (CMI, 20 mg/kg) and the 5-HT synthesis inhibitor parachlorophenylalanine (PCPA, 150 mg/kg daily for 3 days); it was potentiated by pretreatment with the noradrenaline uptake blocker Lundbeck 5-003 (Lu 5-003, 10 mg/kg) and the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (AMPT, 50 mg/kg every 3 hr for 9 hr). PCA-induced ejaculation was attenuated by pretreatment with Lu 10–171 and CMI. PCA-induced salivation was attenuated by pretreatment with Lu 10–171 and CMI and potentiated by pretreatment with Lu 5-003. PCA-induced irritability was potentiated by pretreatment with PCPA. These results suggest that both 5-HT and the catecholamines play a role in PCA-induced hypothermia, ejaculation, and salivation.     

Effects of ritanserin on the rewarding properties of d-amphetamine, morphine and diazepam revealed by conditioned place preference in rats

The possibility that 5-HT₂ receptors mediate the reinforcing properties of d-amphetamine, morphine and diazepam was investigated in rats, using ritanserin, a 5-HT₂ antagonist, and the conditioned place preference paradigm. Ritanserin 1 or 2.5 mg/kg did not cause place conditioning. Place preference induced by 1.5 mg/kg d-amphetamine and 2 mg/kg morphine was inhibited and attenuated respectively by pretreatment with 2.5 mg/kg ritanserin. Diazepam- (1 mg/kg) induced place preference was completely blocked by both doses of ritanserin. Ritanserin pretreatment failed to influence amphetamine-induced hyperlocomotion, morphine-induced analgesia and diazepam-induced increased open arm exploration of rats on the elevated plus maze. These data are discussed in terms of (a) the possibility that serotoninergic mechanisms have a role in mediating reinforcement and (b) the relationship between appetitive properties and specific behavioral effects of psycho-stimulants, opiates and anxiolytics.     

Toxicity of polycyclic aromatic hydrocarbons. III. Effects of beta-naphthoflavone pretreatment on hepatotoxicity of compounds produced in the ozonation or NO2-nitration of phenanthrene and pyrene in rats

Male Sprague-Dawley rats were treated ip with beta-naphthoflavone (BNF, 40 mg/kg/day) in dimethylsulfoxide (DMSO, 26.7 mg BNF/ml) for three days. At 24 hr after the pretreatment DMSO (3.0 ml/kg), phenanthrene (150 mg/kg), ozonized or nitrated products of phenanthrene (150 mg/kg), pyrene (150 mg/kg), or ozonized or nitrated products of pyrene (150 mg/kg) were injected ip. Phenanthrene, pyrene, and their ozonized or nitrated products were dissolved in DMSO (50 mg/ml). No increase in the level of aspartate aminotransferase (AST), alanine aminotransferase (ALT) or sorbitol dehydrogenase (SDH) was seen in the pretreated rats 48 hr after the treatment. This is in contrast to what was seen in previous work without the BNF pretreatment. BNF pretreatment induced a small but significant increase in gamma-glutamyl transpeptidase (GGTP) levels. No treatment group receiving BNF differed from another with respect to GGTP. A decrease in lactate dehydrogenase (LDH) levels was noted in the nitro-PAH treatment groups; the same phenomenon was observed earlier in rats treated with nitro-PAH without BNF treatment. These results suggest that the mixed-function oxidase systems specifically induced by BNF have a protective effect against the hepatotoxicity of the oxonized or nitrated products of phenanthrene and pyrene.     

Effectiveness of lofexidine in blocking morphine-withdrawal signs in the rat

Discontinuation of chronic morphine infusion in rats 3esulted in the reliable occurrence of withdrawal body shakes. This sign of narcotic withdrawal was dose-dependently reduced by lofexidine (0.04–0.64 mg/kg) and clonidine (0.01–0.16 mg/kg). As with clonidine, the activity of lofexidine was not prevented by naloxone (5 mg/kg). In addition, diarrhea induced by naloxone (5 mg/kg) in morphine dependent rats was also prevented by lofexidine or clonidine pretreatment. These data suggest that lofexidine, like clonidine, may reduce the narcotic withdrawal syndrome in humans.     

Effects of lithium on behaviour induced by phencyclidine and amphetamine in rats

d-Amphetamine and phencyclidine (PCP) have both been reported to produce manic-like sequela in humans, effects that are reportedly antagonized by lithium. To test the hypothesis that the acute effects of these drugs in rats may serve as models of mania, the behaviors, induced by d-amphetamine (3 mg/kg) or PCP (5 mg/kg) were quantified on behavioral rating scales subsequent to chronic dietary pretreatment with lithium carbonate or control diet. On day 14 of pretreatment, PCP-induced stereotyped behaviors and ataxia were potentiated in rats receiving lithium (plasma levels 1.0±0.23 mEq/l). PCP-induced locomotor activity was not affected by lithium pretreatment. Stereotypies and locomotion induced by d-amphetamine were also not significantly affected by lithium pretreatment. These results suggest that neither PCP nor amphetamine administered acutely to rats will be useful models to explore the manic-like symptoms produced by these drugs in humans.     

The effect of chronic lithium pretreatment on rat brain muscarinic receptor regulation

The effect of two weeks of lithium (Li) pretreatment on up and down regulation of muscarinic receptors in rat brain was measured in two groups of rats. After two weeks of feeding 0.2% LiCl in ground pellets, one group of rats was injected with atropine (3 mg/kg daily for 5 days) and another group with diisopropyl fluorophosphate, a cholinesterase inhibitor (1.2 mg/kg). Li pretreatment completely abolishes the significant 23% rise in QNB binding induced by atropine but does not prevent the significant 16% decline in QNB binding induced by DFP. These results suggest that chronic Li pretreatment prevents supersensitivity but does not prevent subsensitivity of rat brain muscarinic receptors.     

Effects of zinc sulphate pretreatment on gastric acid secretion and lesion formation in rats infused intravenously with graded doses of methacholine.

The effects of intraperitoneal pretreatment with zinc sulphate (22, 44 or 88 mg/kg) were studied on gastric acid secretion and lesion formation induced by methacholine (125, 250 or 500 microgram/kg/h) infused intravenously in rats with stomachs perfused in situ. Graded infusions of methacholine produced dose-dependent increases in gastric acid secretion and lesion incidence in saline-pretreated control rats. These effects were progressively reduced by increasing pretreatment doses of zinc sulphate. The relationship between these findings and the action of zinc on gastric mast cells is discussed.     

Evidence for dissociable mechanisms of amphetamine-and stress-induced behavioral sensitization: effects of MK-801 and haloperidol pretreatment

The present study examined the ability of pretreatment with MK-801 or haloperidol to block the induction of behavioral sensitization to amphetamine challenge by repeated immobilization stress in male Sprague-Dawley rats. Fifteen minutes before each of ten 30-min restraint sessions, rats were administered saline, MK-801 (0.01, 0.10 or 0.25 mg/kg IP) or haloperidol (0.10 or 0.25 mg/kg IP). Control rats received the same injection regimen without restraint. An additional experiment examined the ability of MK-801 to block the induction of sensitization by repeatedd-amphetamine. In this experiment, rats were administered saline or MK-801 (0.25 mg/kg IP) 15 min before each of ten amphetamine injections (1.0 mg/kg IP, administered under the same regimen as immobilization stress). Four days after the final immobilization or amphetamine injection, rats were tested for locomotor response to novelty, saline andd-amphetamine (1.5 mg/kg IP). Exposure to repeated immobilization stress significantly enhanced the locomotor response to amphetamine challenge but not to saline challenge whether rats were pretreated with saline, MK-801 or haloperidol. Secondary analysis of dose effects in each pretreatment group revealed that at 0.25 mg/kg, repeated MK-801 in itself induced sensitization to the response to amphetamine in control rats and potentiated stress-induced sensitization in restrained rats. In contrast, the sensitization induced by repeated amphetamine was attenuated by MK-801 pretreatment. Neither dose of haloperidol affected the locomotor response to saline or amphetamine in control or stressed rats. These results indicate that the effects of MK-801 on the induction of sensitization are complex and suggest that amphetamine-and stress-induced behavioral sensitization may arise through different mechanisms.     

Effects of GABA antagonists on the pentobarbital-induced depression of respiration and cough in rats

In order to determine the possible involvement of GABA-ergic mechanisms in the modulation of the cough reflex, the effects of GABA antagonists on the pentobarbital-induced depression of respiration and cough were examined in a comparative study in rats. The cough reflex was induced by application of electrical stimulation to the tracheal mucosa by the puncture electrode-induced cough method. The 50% antitussive dose (AtD50) of pentobarbital was calculated by the "up and down" method. Pentobarbital (10 mg/kg, IP) caused a reduction of tidal volume, which was counteracted by pretreatment with picrotoxin (3 mg/kg, IP) or bicuculline (3 mg/kg, IP). However, neither picrotoxin nor bicuculline were able to counteract the reduction in frequency of respiration. The AtD50 of pentobarbital was 1.95 mg/kg when administered IP. The AtD50 of pentobarbital was not altered after pretreatment of rats with picrotoxin (1.85 mg/kg, IP) or with bicuculline (1.55 mg/kg). These results suggest that GABA-ergic mechanisms may not be involved in the cough-depressant effect of pentobarbital.     

Role of kinin and prostaglandin in cutaneous thermal nociception

Involvements of kinin and prostaglandin and their interaction in noxious thermal stimuli were investigated in noninflamed and inflamed rats. The nociceptive response was evaluated from the escape latency of foot withdrawal to the thermal stimuli with a beam of light. The escape latency in kininogens-deficient Brown Norway (B/N-) Katholiek rats was significantly longer than that in the normal strain, B/N-Kitasato rats. The latency in B/N-Kitasato rat was prolonged by administration of a bradykinin (BK) B2 receptor antagonist, FR173657 (30 mg/kg, p.o.), whereas it was shortened by pretreatment with a kininase II inhibitor, captopril (10 mg/kg, i.p.). Both agents did not affect the latency in B/N-Katholiek rats. In normal Sprague-Dawley (SD) rat, administration of indomethacin did not change the escape latency against the thermal stimuli. In contrast, administration of indomethacin or a relatively cyclooxygenase-1-selective inhibitor, mofezolac (10 mg/kg, p.o.) significantly reduced numbers of writhing reaction in mice induced by acetic acid solution. Injection of lipopolysaccharide (1 mg/kg, i.v.) resulted in shortening escape latency at 8 h after the injection in B/N-Kitasato rats. This hyperalgesia could be reversed by pretreatment of the rats with indomethacin, a cyclooxygenase-2-selective inhibitor JTE-522 (10 mg/kg, p.o.), or FR173657, but not with mofezolac. The hyperalgesia was not seen in B/N-Katholiek rats. These results indicate that kinin has major participation in peripheral skin thermal nociception under noninflamed condition, although cyclooxygenases may have little participation. Prostaglandins produced by cyclooxygenase-2 could coordinate with BK to elicit hyperalgesia during inflammation induced by lipopolysaccharide.     

Sex-related differences in cadmium-induced alteration of drug action in the rat

3 days after pretreatment of rats of both sexes with cadmium (2 mg/kg, i.p.) the duration of hypnosis induced by hexobarbital (75 mg/kg, i.p.) was potentiated in males but not females. Likewise, similar treatment with cadmium leads to significant inhibition of the metabolism of hexobarbital by hepatic microsomal enzymes obtained from male but not female animals. These data suggest that there is a sex-related difference in the ability of cadmium to alter drug action in rats.     

Effect of LSD on prepulse inhibition and spontaneous behavior in the rat. A pharmacological analysis and comparison between two rat strains.

The goal of the present study was to better delineate the mechanisms of action of the prototypical hallucinogen LSD. LSD (0.03, 0.1 and 0.3 mg/kg, s.c.) produced locomotor hyperactivity, disruption of PPI and a number of behaviors indicative of 5-HT activation such as wet-dog shakes, back muscle contractions and forepaw treading. These various behavioral effects of LSD were studied in both Sprague-Dawley and Wistar rats, although with the exception of back muscle contractions which were more prominent in Sprague-Dawley rats, no major strain differences were detected. The PPI disruption induced by LSD (0.1 mg/kg) in Sprague-Dawley rats was completely reversed by pretreatment with the selective 5-HT(2A) antagonist MDL 100907 (0.5 and 1 mg/kg, s.c.). In contrast, pretreatment with antagonists at 5-HT(2C), (SB 242084 (0.5 mg/kg, i.p.)); 5-HT(2B/2C) (SDZ SER 082 (1 mg/kg, s.c.)); 5-HT(1A), ((+)-WAY 100135 (1 and 20 mg/kg, s.c.)) and 5-HT(6) receptors, (RO 04-6790 (30 mg/kg, i.p.)), all failed to influence LSD-induced disruption of PPI. The dopamine DA(2like) receptor antagonist, haloperidol (0.1 and 0.2 mg/kg, s.c.), was without effect against an LSD-induced disruption of PPI. Finally, selective blockade of 5-HT(2A) but not 5-HT(2C) receptors completely abolished the locomotor hyperactivity induced by LSD. These findings provide empirical evidence to support the view that the hallucinogenic effects of LSD are mediated by a direct agonist effect at 5-HT(2A) receptors.     

CP-154,526, a CRF type-1 receptor antagonist,attenuates the cue-and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior in rats

Rationale Previous studies from our laboratory and others have indicated a role for the hypothalamo-pituitary-adrenal (HPA) axis in the extinction/reinstatement animal model of cocaine relapse Objective This present study was designed to investigate the potential role for the HPA axis in the cue- and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior by determining the effects of ketoconazole and the corticotropin-releasing hormone (CRF) type 1 receptor antagonist, CP-154,526, on these behaviors. Materials and methods Male Wistar rats were trained to self-administer methamphetamine (0.03 mg/kg/infusion). The delivery of methamphetamine was paired with the presentation of a tone and the illumination of a house light. Once stable responding was reached, the rats were placed into extinction. The effects of pretreatment with ketoconazole (25, 50, or 100 mg/kg, i.p.) or CP-154,526 (20 or 40 mg/kg, i.p.; 3 μg, i.c.v) on cue-induced reinstatement were then evaluated. Results Cue-induced reinstatement was not significantly attenuated by pretreatment with peripherally administered CP-154,526 or by pretreatment with ketoconazole. However, centrally administered CP-154,526 (3 μg, i.c.v.) significantly attenuated cue-induced reinstatement. In a separate group of rats, CP-154,526 (20 mg/kg, i.p.) attenuated methamphetamine-induced reinstatement (0.12 mg/kg priming infusion); whereas a higher dose (40 mg/kg) was necessary to attenuate reinstatement induced by a priming infusion of 0.24 mg/kg/infusion. Ketoconazole (50 mg/kg) did not affect reinstatement induced by a 0.12 mg/kg priming infusion and, therefore, was not tested at the higher methamphetamine priming dose. Conclusions These data suggest an important role for CRF in the cue- and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior.     

Effect of pretreatment with tricresylphosphates and phenobarbital on the metabolism and toxicity of procaine in rats.

We examined the effects of pretreatment with phenobarbital and tricresylphosphates, TOCP and TCP, on the metabolism and toxicity of procaine in rats. A single administration of procaine at a dose of 250 mg/kg intraperitoneally to adult rats caused convulsion, however, phenobarbital (80 mg/kg intraperitoneally daily, 4 days) pretreatment protected against the toxicity or procaine. In contrast, pretreatment of rats with TOCP (10 mg/kg per os) or TCP (10 mg/kg per os) revealed a higher incidence of toxicity as compared to control rats. Mortality in procaine-treated rats was significantly decreased with phenobarbital-pretreatment and, conversely, increased with TOCP and TCP. Paralysis, convulsion and death were induced at the brain level of procaine of 0.303 +/- 0.025, 0.480 +/- 0.026 and 0.565 +/- 0.018 mumole/g brain wet weight, respectively. Toxic effects of procaine were, therefore, concluded to be due to the accumulation of the drug in the brain.     

Complete blockade and attenuation of 5-hydroxytryptamine induced analgesia following NA depletion in rats and mice

The effect of pretreatment with the noradrenaline neurotoxin, N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP4), upon the analgesia induced by various doses of 5-hydroxytryptamine (5-HT) was examined in rats and mice. DSP4 treatment (2 X 50 mg/kg, intraperitoneally) of rats caused a complete blockade of 5-HT induced analgesia in the tail-flick, hot-plate and shock titration tests. DSP4 treatment (1 X 50 mg/kg, intraperitoneally) of mice caused a partial blockade of 5-HT induced analgesia in the hot-plate test, but no significant blockade in the tail-flick test. These results are discussed with regard to serotonergic-noradrenergic interactions and the species discrepancy in nociceptive testing.     

The effect of cholinergic antagonists on increases of spontaneous locomotor activity and body weight induced by the administration of morphine to tolerant rats

Increases both in spontaneous locomotor activity and in body weight were observed after the administration of morphine-HCl (100 mg/kg, i. p.) to tolerant rats. These signs were inhibited by pretreatment of the morphine-tolerant rats with cholinergic antagonists; the inhibition by scopolamine was greater than that by methscopolamine or atropine. These results suggest that both central and peripheral cholinergic mechanisms participate in the increases both in spontaneous locomotor activity and in body weight of tolerant rats after morphine administration.Portions of this work were presented at the 42nd and 43rd meeting of Japanese Pharmacological Society in Kanto district, May 23, 1970 and October 24, 1970 and in Jap. J. Pharmacol. 20, 455–457 (1970), as a preliminary report.     

Involvement of nitric oxide in the protective effects of dehydroepiandrosterone sulphate on stress induced neurobehavioral suppression and brain oxidative injury in rats

The involvement of nitric oxide (NO) in the effects of dehydroepiandrosterone sulphate (DHEAS) on restraint stress induced neurobehavioral and brain oxidative/nitrosative stress markers was investigated in rats. Exposure of rats to restraint stress suppressed behavioral activity in the elevated plus maze and this was associated with increases in malondialdehyde (MDA) and decrease in reduced glutathione (GSH) and brain NO metabolite (NOx) levels in brain homogenates. Pretreatment with DHEAS (5-40mg/s.c.) reversed the stress induced changes in behavioral and oxidative stress markers and also brain NOx levels. The beneficial effect of DHEAS (40mg/kgs.c.) was blocked by pretreatment with nitric oxide synthase inhibitor, L-NAME (50mg/kgi.p.) while pretreatment of rats with NO-precursor l-Arginine (100mg/kg i.p.) produced potentiation of action of sub effective dose of DHEAS (5mg/kgs.c.). The DHEAS effects were stress specific as these behavioral and biochemical parameters were not much influenced in non-stressed rats. These observations suggest that pretreatment with DHEAS has a protective effect on restraint stress induced alteration of neurobehavioral changes and brain oxidative injury in rats and NO-dependent mechanisms may be involved in this effect.     

Phencyclidine-induced wet-dog shakes observed in rats after withdrawal from reserpine treatment

This study was designed to assess the involvement of serotonergic neurons in phencyclidine (PCP)-induced wet-dog shakes in rats after termination of reserpine treatment. Administration of L-5-hydroxytryptophan (7.5-12.5 mg/kg) to rats 30 min following pretreatment with pargyline induced wet-dog shakes which included head shake and whole body shake. p-Chloroamphetamine (PCA) (5 mg/kg) alone also produced wet-dog shakes in the vehicle-pretreated rats, but PCP (2.5-7.5 mg/kg) and tryptophan (100 mg/kg) alone did not. The number of wet-dog shakes significantly increased after the injection of PCA (2.5 and 5 mg/kg) in the reserpine-pretreated rats, in which the 5-hydroxyindoleacetic acid/serotonin (5-HT) ratio was significantly higher and postsynaptic 5-HT receptors were also in a state of supersensitivity, compared to that of the vehicle-pretreated rats. PCP (2.5-7.5 mg/kg) also produced wet-dog shakes in a dose-dependent fashion in rats after pretreatment with reserpine. Furthermore, PCP-induced wet-dog shakes were potentiated by imipramine, a 5-HT-uptake blocker, and prevented by mianserin, a 5-HT receptor-blocker. Tryptophan (100 mg/kg) alone produced wet-dog shakes in the reserpine-pretreated rats and it was enhanced in combination with imipramine. These results may indicate that the PCP-induced wet-dog shakes after reserpine withdrawal are due to an increased release of 5-HT from the functional pool and supersensitivity of postsynaptic 5-HT receptors.