Phencyclidine and (+)-MK-801-induced circling preference: correlation with monoamine levels in striatum of the rat brain

Sex-related differences in intravenous ketamine effects on dissociative stereotypy and antinociception in male and female rats

Ketamine, a multimodal dissociative anesthetic drug, is widely used to treat various conditions including acute pain and treatment-resistant depression. We previously reported that subanesthetic doses of intravenous (i.v.) ketamine produced transient dissociative stereotypy and antinociception in male rats. However, sex-related differences in the effects of i.v. ketamine on these measures are not well characterized. Adult male and female Sprague-Dawley rats (10 weeks old) received an i.v. bolus saline or ketamine (2 and 5 mg/kg), and dissociative stereotypy (head weaving, ataxia, and circling) and natural behaviors (horizontal activity, rearing, and grooming) were quantified over a 10-min period. Ten minutes after the behavioral observation, antinociception was measured using a tail flick test. The i.v. ketamine administration increased head weaving, ataxia, circling, and horizontal activity while decreasing rearing and grooming behaviors in male and female rats. Following 5 mg/kg ketamine administration, ataxia was greater in female rats, while head weaving was greater in male rats. Among the female rats, head weaving was greater in the low estrogen group (diestrus phase) as compared to the high estrogen group (proestrus/estrus phase). Ketamine doses (2 and 5 mg/kg) produced antinociception in male and female rats, and female rats were more sensitive to the antinociceptive effects of 2 mg/kg ketamine. The current findings suggest that i.v. ketamine administration, a clinically relevant route of administration, may produce sex-related differences in dissociative behaviors and analgesia between males and females.

Quantifying free behaviour in an open field using k-motif approach

Quantification and parametrisation of movement are widely used in animal behavioural paradigms. In particular, free movement in controlled conditions (e.g., open field paradigm) is used as a “proxy for indices of baseline and drug-induced behavioural changes. However, the analysis of this is often time- and labour-intensive and existing algorithms do not always classify the behaviour correctly. Here, we propose a new approach to quantify behaviour in an unconstrained environment: searching for frequent patterns (k-motifs) in the time series representing the position of the subject over time. Validation of this method was performed using subchronic quinpirole-induced changes in open field experiment behaviours in rodents. Analysis of this data was performed using k-motifs as features to better classify subjects into experimental groups on the basis of behaviour in the open field. Our classifier using k-motifs gives as high as 94% accuracy in classifying repetitive behaviour versus controls which is a substantial improvement compared to currently available methods including using standard feature definitions (depending on the choice of feature set and classification strategy, accuracy up to 88%). Furthermore, visualisation of the movement/time patterns is highly predictive of these behaviours. By using machine learning, this can be applied to behavioural analysis across experimental paradigms.

Aripiprazole, A Drug that Displays Partial Agonism and Functional Selectivity

BACKGROUND

The treatment of schizophrenia is challenging due to the wide range of symptoms (positive, negative, cognitive) associated with the disease. Typical antipsychotics that antagonize D2 receptors are effective in treating positive symptoms, but extrapyramidal side-effects (EPS) are a common occurrence. Atypical antipsychotics targeting 5-HT2A and D2 receptors are more effective at treating cognitive and negative symptoms compared to typical antipsychotics, but these drugs also result in side-effects such as metabolic syndromes.

OBJECTIVE

To identify evidence in the literature that elucidates the pharmacological profile of aripiprazole.s.

METHODS

We searched PubMed for peer reviewed articles on aripiprazole and its clinical efficacy, side-effects, pharmacology, and effects in animal models of schizophrenia symptoms.

RESULTS

Aripiprazole is a newer atypical antipsychotic that displays a unique pharmacological profile, including partial D2 agonism and functionally selective properties. Aripiprazole is effective at treating the positive symptoms of schizophrenia and has the potential to treat negative and cognitive symptoms at least as well as other atypical antipsychotics. The drug has a favorable side-effect profile and has a low propensity to result in EPS or metabolic syndromes. Animal models of schizophrenia have been used to determine the efficacy of aripiprazole in symptom management. In these instances, aripiprazole resulted in the reversal of deficits in extinction, pre-pulse inhibition, and social withdrawal. Because aripiprazole requires a greater than 90% occupancy rate at D2 receptors to be clinically active and does not produce EPS, this suggests a functionally selective effect on intracellular signaling pathways.

CONCLUSION

A combination of factors such as dopamine system stabilization via partial agonism, functional selectivity at D2 receptors, and serotonin-dopamine system interaction may contribute to the ability of aripiprazole to successfully manage schizophrenia symptoms. This review examines these mechanisms of action to further clarify the pharmacological actions of aripiprazole.

Animal Models of Psychosis: Current State and Future Directions

Psychosis is an abnormal mental state characterized by disorganization, delusions and hallucinations. Animal models have become an increasingly important research tool in the effort to understand both the underlying pathophysiology and treatment of psychosis. There are multiple animal models for psychosis, with each formed by the coupling of a manipulation and a measurement. In this manuscript we do not address the diseases of which psychosis is a prominent comorbidity. Instead, we summarize the current state of affairs and future directions for animal models of psychosis. To accomplish this, our manuscript will first discuss relevant behavioral and electrophysiological measurements. We then provide an overview of the different manipulations that are combined with these measurements to produce animal models. The strengths and limitations of each model will be addressed in order to evaluate its cross-species comparability.

Comparison of the MK-801-induced increase in non-rewarded appetitive responding with dopamine agonists and locomotor activity in rats

Systemic administration of the noncompetitive N-methyl-D-aspartate (NMDA)- receptor antagonist, MK-801, has been proposed to model cognitive deficits similar to those seen in patients with schizophrenia. Evidence has shown that MK-801 increases the probability of operant responding during extinction, possibly modeling perseveration, as would be seen in patients with schizophrenia. This MK-801-induced behavioral perseveration is reversed by dopamine receptor antagonism. To further explore the role of dopamine in this behavioral change, the current study sought to determine if the MK-801-induced increase in non-rewarded operant responding could be mimicked by dopamine agonism and determine how it was related to locomotor activity. Male Long Evans rats were treated systemically with MK-801, cocaine, GBR12909 or apomorphine (APO) and given a single trial operant extinction session, followed by a separate assessment of locomotor activity. Both MK-801 (0.05 mg/kg) and cocaine (10 mg/kg) significantly increased responding during the extinction session and both increased horizontal locomotor activity. No dose of GBR-12909 (5, 10 or 20 mg/kg) was found to effect non-rewarded operant responding or locomotor activity. APO (0.05, 0.5, 2 or 5 mg/kg) treatment produced a dose-dependent decrease in both operant responding and locomotor activity. These results suggest the possibility that, rather than a primary influence of increased dopamine concentration on elevating bar-pressing responses during extinction, other neurotransmitter systems may be involved.

Neonatal tryptophan depletion and corticosterone supplementation modify emotional responses in adult male mice

The serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis are crucially involved in the regulation of emotions. Specifically, spontaneous and/or environmentally mediated modulations of the functionality of these systems early in development may favour the onset of depressive- and anxiety-related phenotypes. While the independent contribution of each of these systems to the emergence of abnormal phenotypes has been detailed in clinical and experimental studies, only rarely has their interaction been systematically investigated. Here, we addressed the effects of reduced serotonin and environmental stress during the early stages of postnatal life on emotional regulations in mice. To this aim, we administered, to outbred CD1 mouse dams, during their first week of lactation, a tryptophan deficient diet (T) and corticosterone via drinking water (C; 80μg/ml). Four groups of dams (animal facility rearing, AFR; T treated, T; C treated, C; T and C treated, TC) and their male offspring were used in the study. Maternal care was scored throughout treatment and adult offspring were tested for: anhedonia (progressive ratio schedule); anxiety-related behaviour (approach-avoidance conflict paradigm); BDNF, dopamine and serotonin concentrations in selected brain areas. T, C and TC treatments reduced active maternal care compared to AFR. Adult TC offspring showed significantly increased anxiety- and anhedonia-related behaviours, reduced striatal and increased hypothalamic BDNF and reduced dopamine and serotonin in the prefrontal cortex and their turnover in the hippocampus. Thus, present findings support the view that neonatal variations in the functionality of the serotonergic system and of HPA axis may jointly contribute to induce emotional disturbances in adulthood.

Effects of hallucinogenic agents mescaline and phencyclidine on zebrafish behavior and physiology

Mescaline and phencyclidine (PCP) are potent hallucinogenic agents affecting human and animal behavior. As their psychotropic effects remain poorly understood, further research is necessary to characterize phenotypes they evoke in various animal models. Zebrafish (Danio rerio) are rapidly emerging as a new model organism for neuroscience research. Here, we examine the effects of mescaline (5-20mg/l) and PCP (0.5-3mg/l) in several zebrafish paradigms, including the novel tank, open field and shoaling tests. Mescaline and PCP dose-dependently increased top activity in the novel tank test, also reducing immobility and disrupting the patterning of zebrafish swimming, as assessed by ethograms. PCP, but not mescaline, evoked circling behavior in the open field test. At the highest doses tested, mescaline markedly increased, while PCP did not affect, zebrafish shoaling behavior. Finally, 20mg/l mescaline did not alter, and 3mg/l PCP elevated, whole-body cortisol levels. Overall, our studies indicate high sensitivity of zebrafish models to hallucinogenic compounds with complex behavioral and physiological effects.

Comparison of the MK-801-induced appetitive extinction deficit with pressing for reward and associated pERK1/2 staining in prefrontal cortex and nucleus accumbens

Administration of the noncompetitive N-methyl-d-aspartate (NMDA)-receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) has been shown to produce extinction deficits on appetitive operant tasks. The present study sought to further explore this by comparing extinction pressing to pressing for the primary reward and examining associated neural correlates to determine if the MK-801 extinction profile resembled the behavioral and neural profile associated with pressing for primary reward. Immunohistochemical labeling of phosphorylated extracellular signal-regulated kinase-1 and -2(pERK1/2) in the prelimbic (PrL) and infralimbic (IL) cortices and nucleus accumbens shell (AcbSh) and core (AcbC) was examined after rewarded or extinction lever pressing conditions. A dose-response curve revealed a within-day extinction deficit following administration of 0.05 mg/kg MK-801. All doses of MK-801 were associated with reduced IL pERK1/2 staining but only the 0.05 mg/kg dose was associated with elevated AcbSh pERK1/2 labeling. Extinction pressing under the influence of MK-801 was elevated compared to that seen during rewarded pressing-whether on MK-801 or saline. Rewarded pressing following saline or MK-801 was associated with elevated pERK1/2 in the PrL with no similar patterns in the MK-801/extinction group. There was more pERK1/2 labeling in the AcbSh of the MK-801 extinction group than any other condition. These data suggest that the MK-801-induced extinction deficit may be due to the combination of an underactive cortical behavioral inhibition system and an overactive AcbSh reward system.

Intra-accumbens injection of a dopamine aptamer abates MK-801-induced cognitive dysfunction in a model of schizophrenia

Systemic administration of the noncompetitive NMDA-receptor antagonist, MK-801, has been proposed to model cognitive deficits similar to those seen in patients with schizophrenia. The present work investigated the ability of a dopamine-binding DNA aptamer to regulate these MK-801-induced cognitive deficits when injected into the nucleus accumbens. Rats were trained to bar press for chocolate pellet rewards then randomly assigned to receive an intra-accumbens injection of a DNA aptamer (200 nM; n = 7), tris buffer (n = 6) or a randomized DNA oligonucleotide (n = 7). Animals were then treated systemically with MK-801 (0.1 mg/kg) and tested for their ability to extinguish their bar pressing response. Two control groups were also included that did not receive MK-801. Data revealed that injection of Tris buffer or the random oligonucleotide sequence into the nucleus accumbens prior to treatment with MK-801 did not reduce the MK-801-induced extinction deficit. Animals continued to press at a high rate over the entire course of the extinction session. Injection of the dopamine aptamer reversed this MK-801-induced elevation in lever pressing to levels as seen in rats not treated with MK-801. Tests for activity showed that the aptamer did not impair locomotor activity. Results demonstrate the in vivo utility of DNA aptamers as tools to investigate neurobiological processes in preclinical animal models of mental health disease.

Behavioral and molecular biomarkers in translational animal models for neuropsychiatric disorders

Modeling neuropsychiatric disorders in animals poses a significant challenge due to the subjective nature of diverse often overlapping symptoms, lack of objective biomarkers and diagnostics, and the rudimentary understanding of the pathophysiology. Successful translational research requires animal models that can inform about disease mechanisms and therapeutic targets. Here, we review behavioral and neurobiological findings from selected animal models, based on presumed etiology and risk factors, for schizophrenia, bipolar disorder, and major depressive disorder. We focus on the use of appropriate statistical tools and newly developed Research Domain Criteria (RDoC) to link biomarkers from animal models with the human disease. We argue that this approach will lead to development of only the most robust animal models for specific psychiatric disorders and may ultimately lead to better understanding of the pathophysiology and identification of novel biomarkers and therapeutic targets.

Dopamine-mediated MK-801-induced elevation in food-based extinction responding in rats and associated changes in region-specific phosphorylated ERK

RATIONALE

The current study examined the effect of the noncompetitive N-methyl-D: -aspartate (NMDA) receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) on the extinction of food-based operant responding.

OBJECTIVES

Experiments were carried out to determine (1) the nature of the elevated responding when rats were under the influence of MK-801, (2) the effect of combined and separate D1- and D2-like dopaminergic antagonists (SCH 23390 and haloperidol) on this MK-801-induced behavioral effect and (3) the neural correlates on and off MK-801 using immunohistochemical localization of the phosphorylated forms of the extracellular signal-regulated kinase-1 and -2.

METHODS

Male Long Evans rats were trained using operant conditioning procedures then treated with the various compounds, and resultant extinction pressing was measured.

RESULTS

A moderate dose (0.1 mg/kg) of MK-801 produced a persistent, elevated lever pressing throughout the entire 30-min extinction session. When animals were pretreated with combined or separate dopamine (DA) D1- or D2-like receptor antagonists, extinction responding under MK-801 was significantly reduced. Examination of pERK1/2 labeling in MK-801-treated animals showed reduced staining in the infralimbic and piriform cortices and elevated staining in the nucleus accumbens compared with controls.

CONCLUSIONS

These data show that MK-801 elevates food-based extinction behavior that can be reduced by DA receptor antagonists. The disrupted extinction behavior may be mediated, in part, by disinhibition of corticostriatal circuits.

Neonatal quinpirole treatment enhances locomotor activation and dopamine release in the nucleus accumbens core in response to amphetamine treatment in adulthood

Neonatal quinpirole treatment to rats produces long-term increases in D(2) receptor sensitivity that persists throughout the animal's lifetime, a phenomenon referred to as D(2) priming. Male and female Sprague-dawley rats were administered quinpirole (1 mg kg(-1)) or saline from postnatal days (P)1-11. At P60, all animals were given an injection of quinpirole (100 microg kg(-1)), and results showed that rats neonatally treated with quinpirole demonstrated enhanced yawning in response to quinprole, verifying D(2) receptor priming because yawning is a D(2) receptor mediated event. Beginning 1-3 days later, locomotor sensitization was tested through administration of d-amphetamine (1 mg kg(-1)) or saline every other day over 14 days, and horizontal activity and turning behavior were analyzed. Findings indicated that D(2)-priming enhanced horizontal activity in response to amphetamine in females compared to males at Days 1 and 4 of locomotor sensitization testing, and D(2)-priming enhanced turning in response to amphetamine. Seven to ten days after sensitization was complete, microdialysis of the NAcc core was performed using a cumulative dosing regimen of amphetamine (0.1-3.0 mg kg(-1)). D(2)-primed rats administered amphetamine demonstrated a 500% increase in accumbal DA overflow compared to control rats administered amphetamine. Additionally, amphetamine produced a significant increase in NE overflow compared to controls, but this was unaffected by D(2) priming. These results indicate that D(2) receptor priming as is produced by neonatal quinpirole treatment robustly enhances behavioral activation and accumbal DA overflow in response to amphetamine, which may underlie increases in psychostimulant use and abuse within the psychotic population where increased D(2) receptor sensitivity is a hallmark.

Interaction between orexinergic neurons and NMDA receptors in the control of locus coeruleus-cerebrocortical noradrenergic activity of the rat

Several studies suggest that NMDA glutamate receptors may play an important role in the activation of a number of brain regions by orexin (OX). We hypothesized that OX and NMDA receptors may interact with cerebrocortical noradrenergic neuron originating from the locus coeruleus (LC). To test this hypothesis, using rats as experimental animals, we examined (i) in vitro effects of MK801 on OXA-evoked norepinephrine release from rat cerebrocortical slices, (ii) in vivo interaction between OXA and the NMDA receptor antagonist, MK801 on norepinephrine release from the prefrontal cortex assessed using microdialysis and (iii) MK801 and OXA-modulation of the electroencephalogram (EEG). We have found that MK801 produced a concentration-dependent inhibition of OXA-evoked norepinephrine release from rat cerebrocortical slices with the IC(50) of 0.9 microM. Moreover, we have also found that icv OXA dose-dependently stimulated norepinephrine release from the rat prefrontal cortex saturating at 213% of baseline. In addition, ip MK801 0.1 mg/kg also significantly increased norepinephrine release in prefrontal cortex to 213%. However, these increases in norepinephrine release were significantly reduced by approximately 70% by simultaneous administration of icv OXA 1 nmol and ip MK801 0.1 mg/kg. Both OXA and MK801 decreased sleep and increased wakefulness, but co-administration caused a return to base-line sleep state. These findings strongly indicate that there is a significant interaction between orexinergic neurons and NMDA receptors in the control of LC-cerebrocortical noradrenergic activity.

Analysis of behavioral asymmetries in the elevated plus-maze and in the T-maze

When studying functional asymmetries in normal laboratory rats, several behavioral tests have been applied and proven their utility, including turning in rotometers or open-fields, handedness in paw usage, T-maze alternation, and others. Here, we analyzed male Wistar rats in two tests, namely the elevated plus-maze and the T-maze. In these tests, behavioral asymmetries are rather likely to occur, since the animals have to show several types of turns towards the left or right when ambulating through these environments. In a first study using the plus-maze, we provide detailed data on (A) the types of turns which the animals showed when changing their direction within arms (i.e., 180 degrees turns), and (B) the types of turns when proceeding from one arm to an adjacent one (i.e., 90 degrees turns). With respect to asymmetry, we found moderate biases in favor of the right. On the 1st day of plus-maze testing, there was a trend for more rightward turns within arms. On the 2nd day of testing, there was a trend for turns towards the right when alternating between arms of the plus-maze. In a 2nd study, we asked for asymmetries in the plus-maze in animals, which had been treated acutely with the psychostimulatory amphetamine analogue 3,4-methylene-dioxymethamphetamine (MDMA). Psychostimulants drugs, especially amphetamine, have repeatedly been used before in work on functional asymmetry, since they can enhance or reveal asymmetries in normal rats. MDMA had dose-dependent effects on activity, which affected turns within arms, and turns between arms; however, there was only sparse evidence with respect to asymmetry. Interestingly, and if at all, asymmetry was in favor of the right. Finally, we present data for behavior in the T-maze, where we used a spontaneous test version, that is, the animals could explore the maze but had no task to solve. Asymmetries were measured as turns within the start arm (180 degrees), and as left- or rightward turns between arms (90 degrees ) at the T-point of the maze. In both measures, we again obtained evidence for asymmetries in favor of the right. This work supports previous studies showing that the T-maze is suitable to analyze behavioral asymmetries in rats. In addition, it provides new evidence with respect to the elevated plus-maze, indicating that this standard tool of anxiety research may also be useful in research on behavioral asymmetries and their underlying brain mechanisms. Behavioral biases in favor of the right, as shown here, have often been reported before, especially with Wistar rats. Such biases should be taken into account, since they can serve as an approach to study brain/behavior relationships, and since they may affect the outcome of physiological manipulations or behavioral trainings.

Intracerebral administration of 2,4-diclorophenoxyacetic acid induces behavioral and neurochemical alterations in the rat brain

Although, the mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) neurotoxicity remains unknown, the monoaminergic system appears to mediate some of its effects in rats as we previously reported. In this study; we examined the 2,4-D effects on locomotor activity, circling behavior and monoamine levels after the injection into the basal ganglia of male adult rats. These effects were compared with those induced after selective lesions of dopaminergic neurons with 6-hydroxydopamine (6-OHDA). 2,4-D-injected into one striatum (100 microg/rat) produced a marked depression in locomotor activity and elicited a moderate circling towards the ipsilateral side at 6 and 24 h postinjection. These behavioral changes were accompanied by a decrease and an increase of serotonin (5-HT) and homovanillic acid (HVA) levels, respectively. 2,4-D administration (100 microg/rat) into the nucleus accumbens, induced similar behavioral and neurochemical patterns to the intrastriatal 2,4-D injection, although rats did not present notorious turning. When 2,4-D was injected into one medial forebrain bundle (MFB, 50 microg/rat), animals presented ipsilateral circling, while locomotor activity was unchanged at 3 and 7 days post-injection. These last rats also exhibited diminished levels of striatal 5-HT, dopamine (DA) and their metabolites without changes in the substantia nigra (SN). Animals sacrificed 3 and 7 days after a 6-OHDA injection into one of the MFB, presented progressive depletion of dopamine in striatum and SN. 2,4-D as well as 6-OHDA-treated rats into one of the MFB were challenged with low dose (0.05 mg/kg s.c.) of apomorphine (only at 7 days post-injection) to evaluate a possible DA-receptor supersensitivity. Only 6-OHDA treated rats showing a vigorous contralateral rotation activity. These results indicate that 2,4-D induced a regionally-specific neurotoxicity in the basal ganglia of rats. The neurotoxic effects of 2,4-D on basal ganglia by interacting with the monoaminergic system depended not only on the exact location of the 2,4-D injection, but also on the dose and time period of post-injection. Toxicity produced by 2,4-D appears to be different in monoaminergic terminals, axonal fibers, and cell bodies.

Apoptosis induction by phencyclidine in the brains of rats of different ages

We examined whether acute administration of phencyclidine (PCP), an antagonist of the N-methyl-D-aspartate (NMDA) receptor-channel complex, can cause neuronal toxicity that is associated with apoptosis. Three- and 24-month-old rats were placed in locomotor activity chambers. PCP (50 mg/kg) or saline (0.15 M NaCl) were simultaneously administered to the treated and age-matched controls. After observing changes of locomotor activities, the animals were killed 24 h after treatment. The brains were processed for in situ analysis of apoptosis either by propidium iodide (PI) staining, or for the terminal dUTP nick-end labelling (TUNEL) method. The regional distribution of apoptotic nuclei was established using PI staining. Apoptosis was additionally confirmed and quantified by the TUNEL technique. PI and TUNEL staining revealed that PCP-mediated neurotoxicity in the prefrontal and enthorhinal cortices, the striatum and hippocampus was associated with a significant number of neurons exhibiting apoptotic morphology. We found that the total number of apoptotic cells was higher in the brains of 24-month-old rats. Compared to the respective controls the number of apoptotic cells was 3.8-fold greater in the cortex of old rats, followed by the striatum (three-fold), and hippocampus (1.4-fold). Accordingly, we concluded that ageing was accompanied by DNA-damage that was most pronounced in the prefrontal cortical neurones. The most prominent elevation in the degree of apoptosis in the young-treated compared to young-untreated rats was detected in the striatum. Comparison of the number of TUNEL-positive cells in treated-aged versus treated-young rats revealed that in all the examined regions of the brain PCP exerted a stronger apoptotic effect in younger animals.

Immunohistochemical and neurochemical studies on nigral and striatal functions in the circling (ci) rat, a genetic animal model with spontaneous rotational behavior

Asymmetrical spontaneous turning behavior or circling phenomena are often related to components of the dopaminergic system, particularly to an imbalance of nigrostriatal function. When a rotational preference is observed, it is typically in a direction away from the brain hemisphere with higher striatal dopaminergic transmission. We have recently described a rat mutant (ci) with spontaneous circling behavior and other signs of functional brain asymmetry. Neurochemical determinations showed that mutants of both genders have significantly lower concentrations of dopamine and dopamine metabolites in the striatum ipsilateral to the preferred direction of rotation. In the present study, we used immunohistochemical, neurochemical, and autoradiographic techniques to characterize the dopaminergic abnormalities of the ci rat mutant in more detail. Age-matched non-affected controls of the same strain were used for comparison. Immunohistochemical labeling of dopaminergic neurons and fibers in substantia nigra pars compacta, ventral tegmental area, and striatum did not indicate any significant neurodegeneration or asymmetry that could explain the lateralization in dopamine levels in striatum of ci rats. Neurochemical determinations substantiated that ci rats of both genders have a significant imbalance in striatal dopamine metabolism, but a similar significant lateralization was also seen in non-affected female controls. Comparison of dopamine, serotonin, noradrenaline and several monoamine metabolite levels in substantia nigra, striatum, nucleus accumbens and frontal cortex of ci rats and controls did not disclose any marked difference between affected and non-affected animals which was consistently found in both genders. Quantitative autoradiographic determination of binding densities of dopamine transporter and D1 and D2 receptors in several parts of the striatum and substantia nigra indicated that ci rats have a significantly higher binding density of dopamine transporter and receptors than controls. Taken together, ci mutant rats of both genders exhibit an asymmetry in striatal dopamine and metabolite levels and an enhanced dopamine transporter and receptor binding, but the link of these differences in dopaminergic parameters with the rotational behavior of the animals is not clear yet. The lack of any significant dopaminergic cell loss in the substantia nigra and the locomotor hyperactivity observed in the mutants clearly suggest that the ci rat is not suited as a model of Parkinsonism but rather constitutes a model of a hyperkinetic motor syndrome.

Destruction of the noradrenergic system with DSP4 potentiates the behavioral effects of MK-801 in rats

In this study we investigated the effect of lesioning the noradrenergic systems on the behavioral effects of (5R, 10S)-(+)-5-Methyl-10,11-dihydro-5H-dibenzo [a, d] cyclohepten-5,10-imine hydrogen maleate--MK-801, in rats. The noradrenergic system was lesioned with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride--DSP4 (60 mg/kg IP). MK-801 increased the locomotor activity and rearing. DSP4 significantly further increased the hyperlocomotor activity, circling (especially to the left side), sniffing, rolling, and falling that were induced by MK-801. These results showed that destruction of the noradrenergic system increased MK-801-hyperlocomotor activity, ataxia and stereotypy.

Modulation of phencyclidine-induced changes in locomotor activity and patterns in rats by serotonin

To test the hypothesis that serotonergic modulation of the effects of phencyclidine (PCP) are due to circuit- rather than receptor-based interactions between glutamatergic and serotonergic systems, multivariate profiles of rat behavior were assessed after treatments with the 5-hydroxytryptamine (5-HT) 5-HT2 receptor antagonist ketanserin (1.0 mg/kg), the 5-HT2 receptor agonist (1(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) (DOI; 0.27 mg/kg), various doses of PCP (0.75 to 10.125 mg/kg), or combinations thereof. Ketanserin blocked all effects of DOI, but reduced the effects of PCP only on locomotion. Depending on the dose, PCP was observed to increase or decrease locomotion and the roughness of the rats' patterns of locomotion. In any case, DOI always increased the activity and decreased the roughness of locomotor paths in PCP-treated rats. Thus, co-administration of DOI and PCP did not yield a shift in the dose-effect curve for either drug, but instead resulted in a new behavioral profile consistent with a circuit-based dynamic interaction.

Behavioral and neurochemical dysfunction in the circling (ci) rat: a novel genetic animal model of a movement disorder

One of the crucial breakthroughs in research on parkinsonism was the observation of circling behaviour in rodents after unilateral intranigral injection of 6-hydroxydopamine. This Ungerstedt model remains one of the basic animal models of Parkinson's disease. We report here the first mutant rat strain with abnormal circling behaviour and several other features reminiscent of the Ungerstedt Parkinson model. The neurological disorder in the novel mutant rat strain is determined monogenetically by a recessive autosomal gene termed circling (ci). Mutant rats of both genders exhibit an intense asymmetric circling in an open-field or rotometer, which is enhanced by treatment with amphetamine. Neurochemical determinations show that mutants of both genders have significantly lower concentrations of dopamine and dopamine metabolites in the striatum ipsilateral to the preferred direction of rotation. Furthermore, in a forelimb-reaching test for assessing the skilled motor capacities of rats, ci rats show a marked deficit on the side contralateral to the preferred direction of turning, which is analogous to motor deficits previously described for rats subjected to unilateral 6-hydroxydopamine lesions. The new mutant rat strain thus exhibits remarkable similarities to the Ungerstedt model and could be used to study the endogenous processes, particularly the genetic components, that might eventually lead to progressive motor dysfunctions.

Drug-induced circling preference in rats. Correlation with monoamine levels

Drugs of abuse, such as phencyclidine (PCP), methamphetamine (METH), and cocaine (COC) are known to affect several behaviors in rats, such as motor activity, stereotypy, and circling. In this study, we evaluated whether these drugs produce circling preferences in the presence or absence of unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the caudate nucleus. Adult male CD rats were lesioned with 10 micrograms 6-OHDA/site. Animals were dosed with PCP (15 mg/kg, ip) its congener (+) MK-801 (0.15 mg/kp, ip), METH (2 mg/kg, ip) COC (60 mg/kp, ip), or apomorphine (0.2 mg/kg, ip). Circling preference was recorded in control and lesioned rats for 2 h before animals were sacrificed to determined monoamine levels by HPLC/EC. In control animals, administration of these drugs produced 60-70% left circling. In lesioned animals, these drugs produced 78-90% ipsilateral (toward the lesion) circling, except apomorphine, which produced 60-80% contralateral (away from the lesion) circling. Dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations significantly decreased ipsilaterally in lesioned caudate nucleus (CN) and substantia nigra (SN). However, no significant changes were observed in nucleus accumbens (NA) and olfactory tubercles (OT). These data demonstrate that drugs of abuse like PCP, its congener (+) MK-801, METH, and COC produce a greater preference to turn toward the left than the right, a finding similar to that found in human psychosis. Since 6-OHDA lesions enhanced the circling bias and depleted DA and its metabolites DOPAC and HVA, it also suggests that the dopaminergic system may be involved in the circling behavior.