An assessment of the spontaneous activity of rats administered morphine, phencyclidine, or nicotine using automated and observational methods

Nicotine's Effects on Schizophrenia-like Symptoms in a Mice Model: Time Matters

Tobacco consumption in schizophrenia (SCHZ) patients is highly prevalent. Data support the occurrence of sequential events during comorbidity establishment, and both smoking first, SCHZ second and SCHZ first, smoking second sequences have been proposed. To investigate whether these two possibilities lead to distinct outcomes of comorbidity, we used a phencyclidine-induced SCHZ model and nicotine exposure as a surrogate of smoking. C57Bl/6 mice were submitted to a protocol that either began with 4 days of phencyclidine exposure or 4 days of nicotine exposure. This period was followed by 5 days of combined phencyclidine + nicotine exposure. Locomotor sensitization and pre-pulse inhibition (PPI) were assessed due to their well-known associations with SCHZ as opposed to rearing, an unrelated behavior. Nicotine priming potentiated phencyclidine-evoked sensitization. However, nicotine exposure after SCHZ modeling did not interfere with phencyclidine's effects. In the PPI test, nicotine after SCHZ modeling worsened the phencyclidine-evoked deficiency in males. In contrast, nicotine priming had no effects. Regarding rearing, nicotine priming failed to interfere with phencyclidine-mediated inhibition. Similarly, phencyclidine priming did not modify nicotine-mediated inhibition. The present results indicate that the sequence, either SCHZ-first or nicotine-first, differentially impacts comorbidity outcomes, a finding that is relevant for the identification of mechanisms of nicotine interference in the neurobiology of SCHZ.

Intranasal (2R, 6R)-hydroxynorketamine for acute pain: Behavioural and neurophysiological safety analysis in mice

Ketamine is known for its antinociceptive effect and is also used for treatment-resistant depression. However, the efficacy and safety of (2R, 6R)-hydroxynorketamine (HNK), a ketamine metabolite has been sparingly investigated for acute pain management. The current study aims at investigating the antinociceptive effect of intranasal (2R, 6R)-HNK using pre-clinical models of acute pain. Additionally, the behavioural and neurophysiological safety analyses were carried out for the effective time window. Antinociceptive efficacy of (2R, 6R)-HNK was evaluated using the hot plate test and Hargreaves' plantar test. The formalin test was carried out in both the acute and tonic phases. The neurophysiological and behavioural safety analyses were carried out separately for the haemodynamic function, cortical electroencephalography (EEG), and spontaneous behavioural functions. Analgesic effect of (2R, 6R)-HNK was evident by a significant increase in paw-withdrawal latency in both Hargreaves' and hot plate tests. Additionally, the (2R, 6R)-HNK showed a significant ameliorative effect on pain-related behaviour in the second phase of the formalin test. (2R, 6R)-HNK exhibited an anxiolytic effect without causing any significant changes in locomotor activity and haemodynamic parameters. Power spectral density (PSD) analysis of electroencephalogram revealed no significant changes except a comparative increase in the gamma band range. Both the locomotor functions in the open field test and the PSD value of delta wave indicated no sedative effect at the given dose of (2R, 6R)-HNK. The results demonstrated the pain-alleviating effect of (2R, 6R)-HNK without compromising the neurophysiological and behavioural function. Therefore, intranasal (2R, 6R)-HNK is suggested as a safe candidate for further clinical study in the management of acute pain.

Sustained Functioning Impairments and Oxidative Stress with Neurobehavioral Dysfunction Associated with Oral Nicotine Exposure in the Brain of a Murine Model of Ehrlich Ascites Carcinoma: Modifying the Antioxidant Role of Chlorella vulgaris

Simple Summary

Nicotine is the major psychoactive component considered to underlie tobacco’s addictive nature, and its dependence has been linked to several drawbacks on behavior and brain health. The purpose of this study was to investigate the mechanisms triggered by oral nicotine that cause brain tissue damage, as well as the supportive role of Chlorella vulgaris microalgae supplementation in Ehrlich ascites carcinoma in mice. The results revealed pronounced neurobehavioral alterations, increased mortality rate, oxidative stress, DNA damage, and augmented inflammatory response in the brain tissue alongside the microstructural alteration caused by nicotine. Chlorella vulgaris was quite successful in reducing the negative effects of nicotine. It acts as an antioxidant anti-inflammatory and restores nearly normal tissue architectures. As a result, we believe it should be supplemented to cancer patients consuming regular nicotine doses.

Abstract

Background: This study provides a model for studying the mechanism(s) responsible for the nervous tissue damage and misfunctioning that occurred due to oral nicotine exposure, considered a stress factor, during the presence of Ehrlich ascites carcinoma bearing in the mouse model (EAC). The mitigating role of Chlorella vulgaris (CV) against nicotine-induced brain damage was evaluated. Methods: Eighty Swiss female mice were classified into four groups, these were the control, the CV group, the nicotine group(100 µg/kg), and the combination group. Oxidant/antioxidant status, proinflammatory cytokines levels, DNA damage, quantitative microscopical lesions, and Caspase 3, Bcl-2 proteins were assessed in the current study. Levels of dopamine (DA) and gamma-aminobutyric acid (GABA) were also evaluated. Results: Nicotine was found to cause pronounced neurobehavioral alterations, increase the mortalities oxidative stress DNA damage, and augment the inflammatory response in brain tissue alongside the microstructural alteration. The administration of CV with nicotine in EAC-bearing mice rescued the detrimental effects of nicotine. Conclusions: CV aids in reducing the harmful effects of nicotine and returns the conditions caused by nicotine to near-control levels. Thus, we are in favor of giving it to cancer patients who are taking daily dosages of nicotine even by smoking cigarettes or being exposed to second-hand smoke.

High fructose corn syrup alters behavioural and neurobiological responses to oxycodone in rats

There are indications that sugars in the diet can play a role in vulnerability to opioid abuse. The current study examined a range of neuro-behavioural interactions between oxycodone (OXY) and high fructose corn syrup (HFCS). Male Sprague-Dawley rats had access to HFCS (0 or 50%) over 26 days in their home cages and were subsequently tested on place conditioning induced by 0, 0.16 and 2.5 mg/kg OXY (3 pairings of drug and saline, each 30 min), as well as on locomotor responses to 0, 0.16 and 2.5 mg/kg OXY, and in-vivo microdialysis was employed to measure dopamine (DA) levels in the nucleus accumbens (NAc) in response to 0 and 2.5 mg/kg OXY. A complex set of interactions between HFCS exposure and responses to OXY were observed: HFCS increased place preference induced by OXY, it enhanced the suppressant effect of OXY on locomotion, and it attenuated OXY-induced elevation in DA overflow in the NAc. Taken together, these findings suggest that nutrition has the potential to influence some responses to opioids which may be relevant to their abuse.

Neurobiology of rodent self-grooming and its value for translational neuroscience

Self-grooming is a complex innate behaviour with an evolutionarily conserved sequencing pattern and is one of the most frequently performed behavioural activities in rodents. In this Review, we discuss the neurobiology of rodent self-grooming, and we highlight studies of rodent models of neuropsychiatric disorders--including models of autism spectrum disorder and obsessive compulsive disorder--that have assessed self-grooming phenotypes. We suggest that rodent self-grooming may be a useful measure of repetitive behaviour in such models, and therefore of value to translational psychiatry. Assessment of rodent self-grooming may also be useful for understanding the neural circuits that are involved in complex sequential patterns of action.

Sex differences in adult cognitive deficits after adolescent nicotine exposure in rats

This study was designed to determine whether deficits in adult serial pattern learning caused by adolescent nicotine exposure persist as impairments in asymptotic performance, whether adolescent nicotine exposure differentially retards learning about pattern elements that are inconsistent with "perfect" pattern structure, and whether there are sex differences in rats' response to adolescent nicotine exposure as assessed by a serial multiple choice task. The current study replicated the results of our initial report (Fountain et al., 2008) using this task by showing that adolescent nicotine exposure (1.0mg/kg/day nicotine for 35days) produced a specific cognitive impairment in male rats that persisted into adulthood at least a month after adolescent nicotine exposure ended. In addition, sex differences were observed even in controls, with additional evidence that adolescent nicotine exposure significantly impaired learning relative to same-sex controls for chunk boundary elements in males and for violation elements in females. All nicotine-induced impairments were overcome by additional training so that groups did not differ at asymptote. An examination of the types of errors rats made indicated that adolescent nicotine exposure slowed learning without affecting rats' cognitive strategy in the task. This data pattern suggests that exposure to nicotine in adolescence may have impaired different aspects of adult stimulus-response discrimination learning processes in males and females, but left abstract rule learning processes relatively spared in both sexes. These effects converge with other findings in the field and reinforce the concern that adolescent nicotine exposure poses an important threat to cognitive capacity in adulthood.

Differential behavioral profiling of stimulant substances in the rat using the LABORAS™ system

Preclinical testing requires rapid and reliable evaluation of the main in vivo effects of novel test substances usually in rodents. Nevertheless, the techniques primarily used up to now involve either automated measurement of motor activity or direct observation of behavioral effects by extensively trained investigators. The advantages of these approaches are respectively high-throughput and comprehensive behavioral assessment. Nevertheless, motor activity is only one aspect of animal behavior and it cannot predict the full neurobehavioral profile of a substance, whereas direct observation is time-consuming. There is thus a need for novel approaches that combine the advantages of both automatic detection and comprehensive behavioral analysis. In the present study, we used the LABORAS™ system to analyze motor and non-motor behavior in rats administered various stimulant substances with or without known psychotomimetic properties or abuse liability (amphetamine, cocaine dizocilpine (MK-801), ketamine, modafinil and nicotine). The data show that LABORAS™ clearly detects the stimulating effects on motor behaviors of amphetamine, cocaine, dizocilpine and ketamine in a dose- and time-dependent manner. Differential effects of these test substances on non-motor behaviors, such as grooming, eating and drinking could also be detected. Nicotine displayed only slight stimulating effects on locomotion, whereas modafinil was virtually without effect on the behaviors evaluated by the system. These data with different stimulant substances suggest that LABORAS™ presents an advantage over classical methods performing automated measurements restricted to locomotion. Furthermore, the procedure is considerably more rapid than behavioral observation procedures. Characterization of the behavioral profile of test substances using LABORAS™ should therefore accelerate preclinical studies. In addition, the multi-faceted parameters measured by LABORAS™ permit a more detailed comparison of the behavioral profiles of novel substances with standard reference substances, thereby providing important indicators for orienting further substance evaluation and supporting drug development.

Assessing carrageenan-induced locomotor activity impairment in rats: comparison with evoked endpoint of acute inflammatory pain

BACKGROUND

Most animal models currently used to evaluate antinociceptive efficacy of analgesics rely on the assessment of evoked pain behaviours as primary endpoints.

METHODS

Here, we have developed and characterized the carrageenan-induced locomotor activity impairment (CLAIM) model to objectively assess non-evoked inflammatory pain behaviour in rats. In this model, 100 µL of 1% carrageenan was subcutaneously injected into the plantar aspect of the right hind paw and exploratory behaviour in the novel testing chamber was recorded using an automated locomotor activity system.

RESULTS

Carrageenan-injected animals exhibited an exploratory behavioural deficit 2-7 h following injection compared to saline-injected animals. The severity of impairment was carrageenan dose related, and sensitive to the light intensity in the testing room. The effects of standard analgesics on CLAIM were examined 2 or 3 h following carrageenan injection. Diclofenac and ibuprofen, in a dose range exerting no effect on locomotor activity in naïve rats, exhibited dose-related reversal of CLAIM (ED(50) = 1.5 and 5.0 mg/kg, respectively), with comparable efficacy on carrageenan-induced thermal hyperalgesia (ED(50) = 2.0 and 6.0 mg/kg, respectively). Gabapentin and duloxetine produced no reversal of CLAIM, or attenuation of thermal hyperalgesia. Efficacy discrepancy was noted for morphine on thermal hyperalgesia and CLAIM. Additionally, amphetamine dose dependently reversed CLAIM, and similarly increased locomotor activity in normal animals.

DISCUSSION AND CONCLUSION

The results presented here demonstrate that CLAIM provides an objective assessment of non-evoked pain behaviours for acute inflammatory pain. The pharmacological profile of standard analgesics supports that CLAIM model can be used to identify agents to treat acute inflammatory pain in the clinic.

Genetically expressed HIV-1 viral proteins attenuate nicotine-induced behavioral sensitization and alter mesocorticolimbic ERK and CREB signaling in rats

The prevalence of tobacco smoking in HIV-1 positive individuals is 3-fold greater than that in the HIV-1 negative population; however, whether HIV-1 viral proteins and nicotine together produce molecular changes in mesolimbic structures that mediate psychomotor behavior has not been studied. This study determined whether HIV-1 viral proteins changed nicotine-induced behavioral sensitization in HIV-1 transgenic (HIV-1Tg) rats. Further, we examined cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). HIV-1Tg rats exhibited a transient decrease of activity during habituation, but showed attenuated nicotine (0.35mg/kg, s.c.)-induced behavioral sensitization compared to Fisher 344 (F344) rats. The basal levels of phosphorylated CREB and ERK2 were lower in the PFC of HIV-1Tg rats, but not in the NAc and VTA, relative to the controls. In the nicotine-treated groups, the levels of phosphorylated CREB and ERK2 in the PFC were increased in HIV-1Tg rats, but decreased in F344 animals. Moreover, repeated nicotine administration reduced phosphorylated ERK2 in the VTA of HIV-1Tg rats and in the NAc of F344 rats, but had no effect on phosphorylated CREB, indicating a region-specific change of intracellular signaling. These results demonstrate that HIV-1 viral proteins produce differences in basal and nicotine-induced alterations in CREB and ERK signaling that may contribute to the alteration in psychomotor sensitization. Thus, HIV-1 positive smokers are possibly more vulnerable to alterations in CREB and ERK signaling and this has implications for motivated behavior, including tobacco smoking, in HIV-1 positive individuals who self-administer nicotine.

DRD2-related TaqIA polymorphism modulates motivation to smoke

INTRODUCTION

TaqIA polymorphism, a genetic variant associated with the expression level of dopamine D2 receptors in the brain, has been linked to various aspects of smoking behavior, including smoking prevalence, affective withdrawal symptoms, and smoking cessation outcome. However, its involvement in motivation to smoke cigarettes has not been elucidated.

METHODS

The present study examined the possible differences in self-reported reasons to smoke and craving for smoking in 160 smokers participating in a clinical trial.

RESULTS

Individuals with at least one A1 allele of the TaqIA polymorphism were more likely to report smoking for stimulating effects and to reduce negative affect compared with those lacking an A1 allele. The association of the A1 genotype with a higher probability and stronger motive to smoker to enhance cognitive functioning was evident in female but not in male smokers. Female A1 carriers also expected a greater likelihood of smoking for pleasure than those without an A1 allele. A1 subjects reported stronger craving for cigarettes during early days and the last phase of a 6-week abstinence period.

DISCUSSION

These results support the idea that dopaminergic transmission plays an important role in the neurobiological basis of reasons for smoking and that the TaqIA variant is one of the genetic factors underlying individual differences in these aspects. These findings also have implications for improving treatment strategies to help individuals quit smoking by controlling their motivation to continue cigarette consumption.

Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine

Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.

Chronic nicotine exposure has dissociable behavioural effects on control and beta2-/- mice

Nicotine exerts beneficial effects on various neurological and psychiatric pathologies, yet its effects on cognitive performance remain unclear. Mice lacking the beta2 subunit of the nicotinic receptor (beta2-/-) show characteristic deficits in executive functions and are suggested as reliable animal models for some specific endophenotypes of human pathologies, notably ADHD. We use beta2-/- and their controls to investigate the consequences of chronic nicotine exposure on cognitive behaviour. We show that in control mice, this treatment elicits somewhat slight effects, particularly affecting nocturnal activity and self-grooming. By contrast, in beta2-/- mice, chronic nicotine treatment had restorative effects on exploratory behaviour in the open-field and affected rearing, but did not modify motor functions. We confirmed that beta2-/- mice exhibit impaired exploratory and social behaviour, and further demonstrated their nocturnal hyperactivity. These data support the proposal that beta2-/- mice represent a relevant model for cognitive disorders in humans and that nicotine administered chronically at low dose may relieve some of these.

Psychopharmacological approaches to modulating attention in the five-choice serial reaction time task: implications for schizophrenia

RATIONALE

In schizophrenia, attentional disturbance is a core feature which may not only accompany the disorder, but may precede the onset of psychiatric symptoms.

OBJECTIVES

The five-choice serial reaction time task (5CSRTT) is a test of visuo-spatial attention that has been used extensively in rats for measuring the effects of systemic and central neurochemical manipulations on various aspects of attentional performance, including selective attention, vigilance and executive control. These findings are relevant to our understanding of the neural systems that may be compromised in patients with schizophrenia.

METHODS

The 5CSRTT is conducted in an operant chamber that has multiple response locations, in which brief visual stimuli can be presented randomly. Performance is maintained using food reinforcers to criterion levels of accuracy. Various aspects of performance are measured, including attentional accuracy and premature responding, especially under different attentional challenges.

RESULTS

The effects of systemic and intra-cerebral infusions of selective dopamine, serotonin and cholinergic receptor agents on the 5CSRTT are reviewed with a view to identifying attention-enhancing effects that may be relevant to the treatment of cognitive deficits in schizophrenia. In addition, some novel agents such as modafinil and histamine receptor agents are also considered. Examining the effects of selective neurochemical lesions helped define the neural locus of attentional effects. Similarly, findings from microdialysis studies helped identify the extracellular changes in neurotransmitters and their metabolites in freely moving rats during performance of the 5CSRTT.

CONCLUSIONS

The monoaminergic and cholinergic systems have independent but complementary roles in attentional function, as measured by the 5CSRTT. These functions are predominantly under the control of the prefrontal cortex and striatum. These conclusions are considered in the context of their application towards therapeutic approaches for attentional disturbances that are typically observed in schizophrenic patients.

Phencyclidine exacerbates attentional deficits in a neurodevelopmental rat model of schizophrenia

Schizophrenia is characterized by severe abnormalities in cognition, including disordered attention. In the rat, neonatal ventral hippocampal (NVH) lesions induce behavioral abnormalities at adulthood thought to simulate some aspects of the symptomatology of schizophrenia. Here, we compared the effects of NVH and adult ventral hippocampal (AVH) lesions on attentional performance as assessed by the five-choice serial reaction time task (5-CSRTT). NVH-lesioned rats were slower to acquire the task than AVH-lesioned and control animals. When training was complete, NVH- and AVH-lesioned animals exhibited stable but disrupted performance under standard conditions, thus emphasizing an implication of VH in visual attentional processes. Variations in task parameters induced a significantly greater disruption in NVH- and AVH-lesioned groups as compared to controls. NVH-lesioned rats were also hyper-responsive to the disruptive effects of a high dose of phencyclidine (PCP) (3 mg/kg). In contrast, amphetamine (0.4-0.8 mg/kg) had a similar effect in control and VH-lesioned rats. Thus, NVH-lesioned rats were impaired in the acquisition of stable performance in the 5-CSRTT, and were hypersensitive to the cognitive-impairing effects of PCP.

Persistent and delayed behavioral changes after nicotine treatment in adolescent rats

Despite the increasing use of tobacco by adolescents, few animal studies have addressed the neurobehavioral consequences of nicotine exposure during this period. We administered nicotine to adolescent rats via continuous infusion on postnatal days (PN) 30 through 47.5, using a dosage regimen that maintains plasma levels similar to those found in smokers or in users of the transdermal nicotine patch. Behavior in a novel open field and learning a passive avoidance task were assessed during nicotine treatment and for 2 weeks post-treatment. On PN44, during nicotine exposure, female rats showed decreased grooming, an effect not seen in males; this effect is opposite to the effects of nicotine in adult rats. Two weeks after cessation of nicotine administration, females showed deficits in locomotor activity and rearing, whereas males again were unaffected; the behavioral deficits appeared at the same age at which gender-selective brain cell damage emerges. In contrast, nicotine exposure enhanced passive avoidance, with the effect intensifying and persisting throughout the post-treatment period. These results reinforce the concept that developmental vulnerability to nicotine extends into adolescence, with patterns of drug effects different from those in earlier or later periods. The correlation of neurochemical with behavioral effects strengthens the connection between adolescent nicotine exposure and persistent functional changes that may influence drug habituation, learning and memory.

Antinociceptive and behavioral activation responses elicited by d-Pro(2)-endomorphin-2 in the ventrolateral periaqueductal gray are sensitive to sex and gonadectomy differences in rats

Sex differences have been observed in antinociception after morphine administered into either the lateral ventricles, rostral ventromedial medulla, or ventrolateral periaqueductal gray such that male rats exhibit significantly greater antinociception than female rats. Adult gonadectomy produced small, but significant changes in morphine antinociception relative to same-sex sham-operated controls. The present study examined whether sex and adult gonadectomy differences were observed in antinociceptive responses after D-Pro(2)-Endomorphin-2 (1-50 microg) elicited from the ventrolateral periaqueductal gray (vlPAG) on the tail-flick and jump tests in rats, and compared these effects with morphine antinociception. D-Pro(2)-Endomorphin-2 antinociception in the vlPAG was significantly greater in estrous-phase, sham-operated and ovariectomized female rats relative to sham-operated and castrated male rats on the tail-flick, but not jump test that differed markedly from the greater magnitude of morphine antinociception noted for male rats on both tests. In testing whether D-Pro(2)-Endomorphin-2's antinociceptive sex differences were secondary to alterations in activity, similar decreases in the pattern of total activity were observed after D-Pro(2)-Endomorphin-2 in the vlPAG in male and female rats. In evaluating whether male and female rats differed in their behavioral activation responses after D-Pro(2)-Endomorphin-2 in the vlPAG, significantly more excessive grooming, seizures, barrel rolls and explosive running behaviors were observed after D-Pro(2)-Endomorphin-2 in male, but not female rats during the precise periods of time when they were failing to display robust antinociceptive responses on the tail-flick test. Thus, the different patterns of sex differences after D-Pro(2)-Endomorphin-2 in the vlPAG appear to be attributable to sex-dependent alterations in behavioral activation rather than nociceptive processing per se.

Reductions in locomotor activity following central opioid receptor subtype antagonists in rats

Opioid agonists produce biphasic (decreases then increases) effects upon activity in rats. General opioid antagonists typically suppress activity. Selective opioid antagonists reduce weight and food intake. However, the latter effects cannot fully account for the former effects. To assess the possibility that selective opioid antagonists might decrease weight by increasing activity, the present study examined whether central administration of either mu (beta-funaltrexamine: 20 micrograms), mu1 (naloxonazine: 50 micrograms), delta1 ([D-Ala2,Leu5,Cys6]enkephalin: 40 micrograms), delta2 (naltrindole isothiocyanate: 20 micrograms), or kappa1 (nor-binaltorphamine: 20 micrograms) opioid antagonists altered total, ambulatory, or stereotypic activity. Each of the antagonists significantly reduced total (mu: 18%, mu1: 31%, delta1: 42%, delta2: 37%, kappa1: 31%), ambulatory (mu: 17%, mu1: 27%, delta1: 34%, delta2: 37%, kappa1: 31%), and stereotypic (mu: 19%, mu1: 34%, delta1: 49%, delta2: 37%, kappa1: 31%) activity on the first day. All three activity measures were reduced by delta1 and delta2 antagonism on the second day, whereas mu antagonism reduced total and stereotypic activity on the second day. The activity reductions induced by selective opioid receptor subtype antagonists parallel effects induced by general opioid antagonism, and suggest that antagonist-induced weight loss effects independent of intake reductions are not due to antagonist-induced hyperactivity.

Antiparkinsonian action of dextromethorphan in the reserpine-treated mouse

Dextromethorphan has been reported to be a weak antagonist of the ion channel associated with the NMDA receptor, and to have putative antiparkinsonian activity in man. This study looked at the effects of dextromethorphan in normal and monoamine-depleted mice, to determine whether it exhibited a behavioural profile with regard to motor activity that was consistent with NMDA receptor blockade. In normal mice, 5-80 mg/kg i.p. dextromethorphan caused modest muscle relaxation at the highest dose in all animals; hyperlocomotion and stereotypy were evident at 40 mg/kg i.p. in a fraction of mice (4/14). In 24 h reserpine-treated mice, locomotion was reinstated by the dopamine D1 receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine hydrochloride (SKF 38393, 30 mg/kg i.p.), the dopamine D2 receptor agonist N-n-propyl-N-phenylethyl-p-(3-hydroxyphenyl)ethylamine (RU 24213, 5 mg/kg s.c.) and L-3,4-dihydroxyphenylalanine (L-DOPA, 150 mg/kg i.p. in conjunction with benserazide 100 mg/kg i.p.). Dextromethorphan alone (10-40 mg/kg i.p.) caused non-significant arousal of monoamine-depleted mice, but potentiated synergistically movements elicited by SKF 38393 and L-DOPA, though not RU 24213. The possible use of dextromethorphan as an adjunct to L-DOPA in the treatment of Parkinson's disease in man, is discussed.

Effects of morphine on different aspects of social play in juvenile rats

To clarify the influence of opioids on social play, the effects of morphine on playful and non-playful social behavior in juvenile rats was investigated under different conditions. Environmental variables employed were different (dim and intense) levels of illumination during testing, familiarity to the test cage, and different periods of social isolation prior to testing. Under dim light conditions, morphine markedly increased playful social behavior, such as pinning, boxing/wrestling and following/chasing, whereas non-playful social behavior such as social exploration and contact behavior was hardly affected. This effect of morphine was independent of duration of previous isolation and dose-dependent, with a maximal effect at 1.0 mg/kg. The mechanism of this effect is interpreted as an action on the rewarding aspects of play. A dose of 0.1 mg/kg of morphine abolished the initial suppression of play induced by unfamiliarity to the test cage, without influencing total levels of play. This may be an effect of morphine on the integration of sensory stimuli. Under intense light conditions, whereas playful behavior was completely suppressed, morphine itself hardly affected such behavior, but decreased some aspects of non-playful social behavior. These results suggest that in juvenile rats playful and non-playful forms of social behavior are differentially regulated. In addition, opioid systems may be involved at different levels in the regulation of social play.

Biphasic effects of intraaccumbens mu-opioid peptide agonist DAMGO on locomotor activities

The effects of bilateral microinjections of mu-opioid receptor agonist DAMGO (0.00, 0.01, 0.1, or 1.0 microgram/side) were tested in rats for 120 min in activity monitors. The horizontal movement, rearing, and stereotypy times in seconds were measured during 12 consecutive 10-min time blocks. DAMGO (0.01, 0.1, and 1.0 microgram) resulted in biphasic effects, inhibition followed by activation for each of the three measures. These data replicate the behavioral effects of ICV DAMGO except that the duration of the behavioral effects were longer with Acb injections.

Behavioral effects of the mu-opioid peptide agonists DAMGO, DALDA, and PL017 on locomotor activities

The relative role of central mu-opioid receptor agonists Tyr-D-Ala-Gly-N-Methyl-Phe-Gly-ol (DAMGO), Tyr-D-Arg-Phe-Lys (DALDA), and Tyr-Pro-MePhe-D-Pro (PL017) (0.00, 0.01, 01, or 1.0 micrograms, ICV) on behavior was investigated in rats for 60 min in activity monitors. DAMGO (0.1 and 1.0 micrograms) and PL017 (1.0 micrograms) resulted in biphasic effects, inhibition followed by hyperactivity for linear locomotor, whereas the 0.01-micrograms dosage was associated with hyperactivity. On the other hand, DALDA (0.1 and 1.0 micrograms) suppressed locomotor activity over the 60-min session.

Quantitative analysis of spider locomotion employing computer-automated video tracking

The locomotor activity of adult specimens of the wolf spider Pardosa amentata was measured in an open-field setup, using computer-automated colour object video tracking. The x,y coordinates of the animal in the digitized image of the test arena were recorded three times per second during four consecutive 12-h periods, alternating between white and red (lambda > 600 nm) illumination. Male spiders were significantly more locomotor active than female spiders under both lighting conditions. They walked, on average, twice the distance of females, employed higher velocities, and spent less time in quiescence. Both male and female P. amentata were significantly less active in red light (simulated dark environment) than in white light. The results also revealed that P. amentata administers its walking velocity and periods of quiescence according to consistent distributions, which can be approximated by simple mathematical expressions. It was found that this species spends exponentially decreasing time at increasing velocities. The number of quiescent periods, however, follow a power decay distribution at increasing quiescent period duration.

Morphine-induced hyperactivity in rats--a rebound effect?

The behavioural nature of the delayed hyperactivity induced by systemic administration of morphine was studied in rats. Different components of motility induced by morphine with or without naloxone or haloperidol at different times were analyzed by observation and quantified by an Opto-Varimex-3 Activity Meter. By this automatic recording system motility was discriminated into horizontal and two different vertical components and the total distance run by each of the rats was quantified by a computer program. Simultaneously the running pattern was recorded by a XY-plotter. By means of these recordings, three subsequent phases of behaviour could be recorded after morphine (15 mg/kg i.p.): 1. a depressed phase (akinesia) lasting 1.5-2 h, followed, 2. by an intermediate phase for 1-1.5 h, still dominated by akinesia but interrupted by sudden bursts of hyperactivity. Finally, 3. a hyperactivity phase lasted for 1.5-2 h, characterized by an equal enhancement of locomotor activity and stereotypy. After 30 mg/kg of morphine the hyperactivity was predominantly characterized by locomotor activity and stereotypy and rearing were less prominent than after the smaller dose. Naloxone (2 mg/kg i.p.) given at the beginning of the hyperactivity phase significantly antagonized rearing but not other motility parameters. However, coadministration of naloxone (2 mg/kg i.p.) simultaneously with morphine (15 mg/kg) clearly antagonized akinesia and completely prevented the development of the delayed hyperactivity. Haloperidol (0.2 mg/kg i.p.) at the beginning of the hyperactivity phase clearly antagonized all of the motility parameters seen during this phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral effects of opioid peptide agonists DAMGO, DPDPE, and DAKLI on locomotor activities

The effects of the mu-selective agonist DAMGO (ICV doses of 0.00, 0.01, 0.1, or 1.0 micrograms), the delta-selective agonist DPDPE (ICV doses of 0.00, 0.1, 1.0, or 10.0 micrograms), and the kappa-selective agonist DAKLI (ICV doses of 0.00, 0.01, 0.1, or 1.0 micrograms) were tested in rats for 60 min in an activity monitor. The durations in seconds of linear locomotor time, rearing time, stereotypy time, and margin time (thigmotaxis) were measured during six 10-min time blocks. DAMGO (0.1 and 1.0 micrograms) resulted in biphasic effects, inhibition followed by hyperactivity for linear locomotor, rearing, and stereotypy times, and an inhibition of thigmotaxis. DPDPE (10.0 micrograms) was associated with monophasic potentiation of linear locomotor activity and mixed effects in stereotypy times. DAKLI did not effect horizontal, rearing, or margin times; only stereotypy times resulted in mixed effects of DAKLI. The differential behavioral profiles were discussed in reference to the three opioid receptor subtypes.

Neurotransmitter regulation of dopamine neurons in the ventral tegmental area

Over the last 10 years there has been important progress towards understanding how neurotransmitters regulate dopaminergic output. Reasonable estimates can be made of the synaptic arrangement of afferents to dopamine and non-dopamine cells in the ventral tegmental area (VTA). These models are derived from correlative findings using a variety of techniques. In addition to improved lesioning and pathway-tracing techniques, the capacity to measure mRNA in situ allows the localization of transmitters and receptors to neurons and/or axon terminals in the VTA. The application of intracellular electrophysiology to VTA tissue slices has permitted great strides towards understanding the influence of transmitters on dopamine cell function, as well as towards elucidating relative synaptic organization. Finally, the advent of in vivo dialysis has verified the effects of transmitters on dopamine and gamma-aminobutyric acid transmission in the VTA. Although reasonable estimates can be made of a single transmitter's actions under largely pharmacological conditions, our knowledge of how transmitters work in concert in the VTA to regulate the functional state of dopamine cells is only just emerging. The fact that individual transmitters can have seemingly opposite effects on dopaminergic function demonstrates that the actions of neurotransmitters in the VTA are, to some extent, state-dependent. Thus, different transmitters perform similar functions or the same transmitter may perform opposing functions when environmental circumstances are altered. Understanding the dynamic range of a transmitter's action and how this couples in concert with other transmitters to modulate dopamine neurons in the VTA is essential to defining the role of dopamine cells in the etiology and maintenance of neuropsychiatric disorders. Further, it will permit a more rational exploration of drugs possessing utility in treating disorders involving dopamine transmission.

The ontogeny of phencyclidine-induced wall climbing and locomotor activity

Wall climbing behavior is an age-specific behavior that is elicited during postnatal Days 7 through 17 by various stimuli that include heat, odors, shock, and the catecholaminergic agonists apomorphine, amphetamine, and clonidine. In a previous study, a significant amount of wall climbing behavior was observed during ataxia and activity testing following phencyclidine (PCP) administration in Day 19 but not Day 40 rat pups. The present study describes the ontogeny of PCP-induced wall climbing behavior and locomotor activity. Frequency and duration of wall climbing bouts and locomotor activity were recorded on Days 5, 12, 19, 26, 33, or 40 following PCP treatment. On Day 12, all doses of PCP induced significant amounts of wall climbing behavior. A similar pattern of results was observed on Day 5 although these effects were not statistically significant. After Day 12, PCP-induced wall climbing behavior declined precipitously. PCP increased locomotor activity at all ages tested with maximum activities observed on Day 19. These results demonstrate that PCP-elicited wall climbing behavior follows an ontogenetic profile similar to that previously reported for other stimuli and that there are robust ontogenetic differences in the locomotor response to PCP.

Systemic and microiontophoretic administration of morphine differentially effect ventral pallidum/substantia innominata neuronal activity

In vivo electrophysiological recording techniques were employed to examine responses of ventral pallidum/substantia innominata (VP/SI) neurons to systemic and local administration of morphine. Using a cumulative dosing protocol, intravenous administration (0.1-30 mg/kg i.v.) produced a suppression of firing in 82% of neurons tested. The suppression was dose-related and blocked by the opioid antagonist, naloxone. In contrast, microiontophoretic applications of morphine resulted in current-related suppression (32% of neurons tested) or excitation (26%). Concurrent application of naloxone attenuated or blocked both effects of local morphine application. It was demonstrated that acute tolerance did not develop with repeated morphine exposures following either systemic or local administration. The present findings establish the sensitivity of VP/SI neurons to morphine and provide functional relevance at the level of a single neuron for opioid peptides and their receptors in this region. As reported for most other opioid-receptive brain areas, neuronal rate suppression was the predominate response observed, and it is proposed that excitations to iontophoresed morphine reflect a disinhibitory phenomenon. The differential morphine-induced rate changes, and number of responding neurons, observed with systemic vs. iontophoretic morphine administration suggest that extra-VP/SI regions that also are opioid sensitive can subsequently direct neuronal responsiveness to opioids within the VP/SI.

Muscarinic antagonists attenuate dizocilpine-induced hypermotility in mice

Pretreatment of mice with the muscarinic receptor antagonists scopolamine and atropine attenuated the hypermotility (but not the depression of rearing) induced by a low dose of dizocilpine maleate [(+)-MK-801; 0.1 mg/kg, i.p.], a non-competitive NMDA antagonist. In contrast, the muscarinic blockers failed to affect hypermotility induced by equieffective doses of phencyclidine (1 mg/kg, i.p.) or d-amphetamine (2 mg/kg, i.p.). These results suggest differences between the mechanism of behavioral activation produced by dizocilpine and phencyclidine, and demonstrate the potential of muscarinic blockade for diminishing the behavioral toxicity of NMDA antagonists.

The effects of intraperitoneally administered phencyclidine on the central nervous system: behavioral and neurochemical studies

The effects of intraperitoneally (IP) injected phencyclidine (phencyclohexyl piperidine; PCP) on the metabolism of dopamine (DA) and cholecystokinin-like immunoreactivity (CCK-LI) in the rat brain were investigated in connection with PCP-induced behavioral changes. The predominant behavior change elicited by 2.5 mg/kg PCP was locomotion, while with higher doses (5 and 10 mg/kg) sniffing, swaying and falling were observed in addition to the enhanced locomotor activity. Backpedaling and rotation were observed in 10 mg/kg PCP-treated rats. IP injection of PCP caused a dose-related increase in the levels of DA and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the medial frontal cortex (MFC) and anterior cingulate cortex (ant.CC) without any changes in the nucleus accumbens (NAc) or striatum. CCK-LI in the MFC, ant.CC and NAc was decreased in a dose-dependent manner following IP injection of PCP. These findings support the evidence that PCP selectively activates the mesocortical DA systems. Furthermore, our results indicate a functional relationship between the mesocortical DA neurons and intrinsic CCK containing cortical neurons, and the change in the activity of the intrinsic CCK-containing cortical neurons in these two areas, perhaps due to an alteration in DA transmission, might be involved in behavioral changes after PCP injection.

Evidence for an involvement of D1 and D2 dopamine receptors in mediating nicotine-induced hyperactivity in rats

Previous studies have suggested that repeated exposure of rats to the drug or to the experimental environment is necessary to observe nicotine-induced locomotor stimulation. In the present study the role of habituation to the experimental environment on the stimulant effect of nicotine in rats was examined. In addition, the role of dopamine receptors in mediating nicotine-induced locomotor stimulation was investigated by examining the effects of selective D1 and D2 dopamine receptor antagonists on activity induced by nicotine. Locomotor activity was assessed in male Sprague-Dawley rats tested in photocell cages. Nicotine (1.0 mg/kg) caused a significant increase in locomotor activity in rats that were habituated to the test environment, but had only a weak and delayed stimulant action in rats that were unfamiliar with the test environment. The stimulant action of nicotine was blocked by the central nicotinic antagonist mecamylamine but not by the peripheral nicotinic blocker hexamethonium, indicating that the response is probably mediated by central nicotinic receptors. Nicotine-induced hyperactivity was blocked by the selective D1 antagonist SCH 23390, the selective D2 antagonist raclopride and the D1/D2 antagonist fluphenazine. Pretreatment with the D2 agonist PHNO enhanced nicotine-induced hyperactivity, whereas the D1 agonist SKF 38393 had no effect. The results indicate that acute nicotine injection induces a pronounced hyperactivity in rats habituated to the test environment. The effect appears to be mediated by central nicotine receptors, possibly located on dopaminergic neurons, and also requires the activation of both D1 and D2 dopamine receptors.

The effects of the phencyclidine analogs BTCP and TCP on nigrostriatal dopamine neuronal activity

Extracellular single unit recording techniques were used to evaluate the effects of two phencyclidine (PCP) derivatives. N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and N-[1-(2-thiophenyl)cyclohexyl]piperidine (TCP) on the electrophysiological activity of antidromically identified nigrostriatal dopamine (DA) neurons in chloral hydrate-anesthetized rats. I.v. BTCP produced a dose-dependent decrease in the firing rate of identified nigrostriatal DA neurons whereas TCP elicited a dose-dependent biphasic effect which was characterized by an activation of cell firing at low doses followed by a reversal of the response with larger doses. A hemitransection of the brain anterior to the substantia nigra significantly reduced the inhibitory effect of BTCP while this surgical procedure did not affect the response to TCP. However, iontophoretic application of BTCP induced a current-dependent inhibition of the spontaneous activity of cells while local application of TCP had no effect on the firing rate of these cells. These data indicate that PCP analogs are able to interact with the nigrostriatal DAergic pathway through distinct and opposing mechanisms. The results are discussed in light of recent observations that BTCP is selective for the DA uptake site while TCP is selective for the high affinity PCP binding site.

Gait topography in rat locomotion

Gait topography has been quantified and normative data established for free, spontaneous locomotion in rats. The normal walking pattern has been compared for male and female rats and for three rat strains. The normal walking gait was found to be symmetrical, and measures of stride width (SW) and stride length (SL) were consistent, with coefficients of variability ranging between 10 and 21%. A study of gait ontogeny found that for both male and female rats, SL increased as a linear function of body weight, whereas SW increased curvilinearly. The results indicate that repeated measures of gait topography were not subject to interference from habituation. A sex difference in gait ontogeny was observed. The developmental pattern is similar for both sexes, but males increase both SL and SW faster than females. It is proposed that gait topography may yield valuable information in activity studies.

Effects of ketamine on tunnel maze and water maze performance in the rat

The NMDA receptor, which has been implicated in memory formation, is noncompetitively blocked by ketamine. The present study examines the effect of ketamine (0, 3, 6, 12, and 25 mg/kg body wt; ip) on tunnel maze and water maze performance in Wistar rats. In the hexagonal tunnel maze (HTM) high doses of ketamine (12 and 25 mg/kg) decreased locomotor activity. Moreover, ketamine induced perimeter walking (6, 12, and 25 mg/kg) and attenuated exploratory efficiency (25 mg/kg). When the HTM was converted into a modified six-arm radial maze, ketamine impaired short-term but not long-term memory. In the Morris water maze, rats injected with ketamine (12 and 25 mg/kg) acquired a spatial navigation task more slowly than controls. When the escape platform was removed, the drug-treated rats did not preferentially search for it in the area where the platform had been during the acquisition phase. However, when the escape platform was visible, no differences in the performance of ketamine-treated and control rats could be found. In summary, ketamine seems to attenuate some but not all forms of learning in the tunnel maze and it impairs the acquisition of a spatial navigation task.

Comparison of the effects of the acute administration of dexoxadrol, levoxadrol, MK-801 and phencyclidine on body temperature in the rat

Some of the dioxolanes produce pharmacological effects that have much in common with phencyclidine and phencyclidine-like drugs. Dioxadrol can be resolved into two enantiomers, dexoxadrol and levoxadrol. Dexoxadrol has an affinity for phencyclidine receptors that is much greater than that of levoxadrol, but dexoxadrol and levoxadrol have nearly equal affinities for sigma receptors. The systematic analysis of the relative potencies of dexoxadrol and levoxadrol can be used as an approach to define effects mediated by phencyclidine vs sigma receptors. Compounds that act on phencyclidine receptors, as well as affecting behavior, alter body temperature in the rat. The purpose of the present study was to compare and contrast the effects of the acute administration of dexoxadrol, levoxadrol, MK-801 and phencyclidine on body temperature in the rat. Dexoxadrol and levoxadrol (5.0, 10.0, 20.0 or 40.0 mg/kg), MK-801 (0.12, 0.6 or 1.2 mg/kg) or phencyclidine (5.0, 10.0 or 20.0 mg/kg) were administered subcutaneously and body temperature was measured. Both dexoxadrol and MK-801 produced hyperthermia but levoxadrol did not affect body temperature. In contrast to the hyperthermic effects of dexoxadrol and MK-801, phencyclidine produced hypothermia. These findings indicate that hypothermia induced by phencyclidine is not due to interactions with phencyclidine receptors and, while dexoxadrol, MK-801 and phencyclidine may share some similar receptor binding and behavioral characteristics, they can be differentiated on the basis of their effects on body temperature.

Mesolimbic and mesocortical dopamine activation induced by phencyclidine: contrasting pattern to striatal response

The effects of acute administration of phencyclidine, an indirect dopamine agonist, on biochemical indices of dopaminergic activation were examined in mesocortical, mesolimbic and nigrostriatal regions of the rat. High doses (10 mg/kg) of phencyclidine resulted in a marked increase in levels of the dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid in all mesolimbic and mesocortical sites examined, as well as in the ventral tegmental area, source of the dopaminergic innervation of mesolimbic/cortical sites. In contrast, levels of both metabolites decreased in the striatum and tended to decrease in the substantia nigra, source of the striatal dopaminergic innervation. The metabolite response to phencyclidine was dose-related. These data indicate that the mesolimbic and mesocortical dopaminergic neurons are activated by phencyclidine. Since the firing rate of both A10 (ventral tegmental area) and A9 (substantia nigra) dopamine neurons has previously been shown to be increased by phencyclidine, these data suggest that phencyclidine results in a differential regulation of presynaptic release of dopamine in mesolimbic/cortical as opposed to nigrostriatal dopaminergic regions.

A simple and rapid method for assessing similarities among directly observable behavioral effects of drugs: PCP-like effects of 2-amino-5-phosphonovalerate in rats

Directly observable behavioral effects of the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (AP5) (10-1,000 mg/kg IP, 0.18-5.6 mumol/rat ICV) and of phencyclidine (PCP) (3.2-56 mg/kg IP, 0.032-3.2 mg/rat ICV), ketamine (10-100 mg/kg), amphetamine (1-18 mg/kg), apomorphine (0.1-5.6 mg/kg), chlordiazepoxide (1-100 mg/kg), and pentobarbital (3.2-56 mg/kg) were studied in rats. Pharmacologically specific results were obtained rapidly and reliably, using a cumulative dosing procedure. Cluster analysis grouped the drug treatments, on the basis of their similarities in producing different behavioral activities, into three main clusters; characteristically, stimulant drugs (amphetamine, apomorphine) produced sniffing and gnawing; PCP-like drugs (PCP, ketamine) produced locomotion, sniffing, swaying and falling; sedative drugs (pentobarbital, chlordiazepoxide) produced loss of righting. The behavioral effects of ICV administration of AP5 were more similar to the effects of PCP-like drugs than to the effects of either stimulant or sedative drugs, thus supporting the hypothesis that the behavioral effects of PCP-like drugs may result from reduced neurotransmission at excitatory synapses utilizing NMDA preferring receptors. The present procedure is simple, rapid and may provide a useful approach in the classification of behaviorally active drugs.

The role of reward pathways in the development of drug dependence

In commenting on the discovery of "opiate" receptors, Goldstein (1976) said: "It seemed unlikely, a priori, that such highly stereospecific receptors should have been developed by nature to interact with alkaloids from the opium poppy" (p. 1081). Endogenous opioid peptides and opioid receptor systems have now been identified in invertebrates that are unlikely to have had ancestors exposed to opium poppies (Kavaliers et al., 1983; Kream et al., 1980; Leung and Stefano, 1984; Stefano et al., 1980). Moreover, endogenous opioids play a role in stress-induced feeding in the slug (Kavaliers and Hirst, 1986) just as they play a role in stress-induced feeding in rodents (Lowy et al., 1980; Morley and Levine, 1980). If we are to understand the actions of opiates and other drugs of abuse we must understand them in terms of their abilities to interact with neural systems that evolved in the service of primitive biological functions, long before any serious incidence of addiction itself. The most primitive axes of the biological substrates of behavior are the axes of approach and withdrawal. Addictive drugs appear to be able to activate the mechanisms of approach, which is termed "positive reinforcement" and to inhibit the mechanisms of withdrawal, which is termed "negative reinforcement." Anatomically distinct sets of pathways have evolved to serve these two forms of reward. Activation of the medial forebrain bundle and associated structures serves positive reinforcement and induces forward locomotion. Approach and forward locomotion are the unconditioned responses to positive reinforcing stimuli such as food and sex partners, and approach to environmental objects and positive reinforcement is induced by electrical stimulation of this structure. The locomotor stimulating effects and the positive reinforcing effects of opiates and psychomotor stimulants result from their activation of this mechanism; stimulants activate the mechanism at the level of dopaminergic synapses of the nucleus accumbens, frontal cortex, and perhaps other forebrain structures, while opiates activate the system at two points: at the level of the dopaminergic synapse and at the level of the afferents to the dopaminergic cell bodies. Ethanol, nicotine, caffeine and phencyclidine stimulate both locomotor activity and dopamine turnover, but their sites of interaction with reward pathways have not yet been identified. Benzodiazepines and barbiturates stimulate locomotor activity without stimulating dopamine turnover; they may interact with reward pathways at a synapse efferent to the dopaminergic link in the pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

A quantitative study of normal locomotion in the rat

Three variables of locomotion; stride length, stride frequency and velocity have been measured in forty-eight rats. Median values were found to be 11.3 cm, 2.4 Hz and 24.2 cm/sec respectively. The results are assessed both as independent variables and in terms of their interaction. It was found that the two variables used to increase velocity (stride length and stride frequency) were not deployed equally during normal walking velocities (10-50 cm/sec). It is proposed that the study of these three readily quantifiable variables, particularly the relationships between velocity and stride frequency may be useful for the evaluation of locomotion in the assessment of neuropharmacologically active agents.

An automatic device for measuring speed of movement and time spent at rest: its application to testing dopaminergic drugs

We describe a device to measure speed of movement and time at rest for use with a commercially available infrared photobeam activity monitor. This system is a reliable substitute for a human observer and provides additional measures of activity that can help in interpreting how psychoactive drugs alter behavior. The effects of graded doses of d-amphetamine, haloperidol and (-)3-(3-hydroxyphenyl)-N-n-propylpiperidine, (-)-3-PPP, were studied with the device, and the results confirmed that these drugs differentially alter speed of movement and time at rest.

Comparison of the pharmacologic effects of N-allylnormetazocine and phencyclidine: sensitization, cross-sensitization, and opioid antagonist activity

The effects of phencyclidine (PCP) on locomotor activity were compared to those of the stereoisomers of N-allylnormetazocine (NAN) after acute administration to rats. PCP produced swaying and falling movements, increased sniffing behavior, and enhanced horizontal locomotor activity. d-NAN also induced swaying, falling, sniffing behavior and locomotion, and decreased rearing behavior. l-NAN decreased rearing activity, depressed locomotion, antagonized morphine antinociception and precipitated the morphine-withdrawal syndrome. Sensitization to drug-induced sniffing, rearing and locomotion developed after four daily injections of PCP, d-NAN or l-NAN in rats. Rats which were sensitized to PCP-induced locomotion, sniffing, and rearing were also cross-sensitized to both d-NAN and l-NAN. Animals sensitized to the effects of either d- or l-NAN exhibited cross-sensitization to PCP. There was little evidence that the cross-sensitization between the three agents was stereoselective. These data indicate that the acute effects of PCP are similar to those of d-NAN, but differ from l-NAN, the only agent of the three with opioid antagonist properties. The data further indicate that as sensitization to the motor effects develops during repeated administration of PCP, d-NAN or l-NAN, the differences among the three agents become less apparent.

Reduction in locomotor activity of arthritic rats as parameter for chronic pain: effect of morphine, acetylsalicylic acid and citalopram

Arthritis was induced in rats by plantar injection of a suspension of killed mycobacteria in Viscoleo. Non-treated rats served as controls. The locomotor activities of the rats were measured weekly during the following four weeks. The exploratory activity was determined in the daytime in activity cages and spontaneous locomotor activity was measured during the night in the same cages. From one week to four weeks after treatment in one hind paw the arthritic rats showed significantly lower exploratory activity than the control rats, whereas the spontaneous locomotor activity in the arthritic rats was not significantly reduced. After treatment in two hind paws both activities were significantly smaller in the arthritic group than in the control group. The low exploratory activity level of the arthritic rats was not changed by acetylsalicylic acid but was significantly increased by morphine and citalopram in doses which did not influence the exploratory activity of the control rats. The results suggest that reduction of the locomotor activity of arthritic rats might be a reliable parameter for chronic pain.