Adrenergic Mechanisms and Amphetamine Induced Abnormal Behaviour

Amphetamine reduces reward encoding and stabilizes neural dynamics in rat anterior cingulate cortex

Psychostimulants such as d-amphetamine (AMPH) often have behavioral effects that appear paradoxical within the framework of optimal choice theory. AMPH typically increases task engagement and the effort animals exert for reward, despite decreasing reward valuation. We investigated neural correlates of this phenomenon in the anterior cingulate cortex (ACC), a brain structure implicated in signaling cost-benefit utility. AMPH decreased signaling of reward, but not effort, in the ACC of freely-moving rats. Ensembles of simultaneously recorded neurons generated task-specific trajectories of neural activity encoding past, present, and future events. Low-dose AMPH contracted these trajectories and reduced their variance, whereas high-dose AMPH expanded both. We propose that under low-dose AMPH, increased network stability balances moderately increased excitability, which promotes accelerated unfolding of a neural 'script' for task execution, despite reduced reward valuation. Noise from excessive excitability at high doses overcomes stability enhancement to drive frequent deviation from the script, impairing task execution.

The protein kinase Cβ-selective inhibitor, enzastaurin, attenuates amphetamine-stimulated locomotor activity and self-administration behaviors in rats

RATIONALE

Pathological amphetamine (AMPH) use is a serious public health concern with no pharmacological treatment options. Protein kinase Cβ (PKCβ) has been implicated in the mechanism of action of AMPH, such that inhibition of PKCβ attenuates AMPH-stimulated dopamine efflux in vivo. With this in mind, inhibition of PKCβ may be a viable therapeutic target for AMPH use disorder.

OBJECTIVE

The purpose of this study is to demonstrate that selective pharmacological inhibition of PKCβ alters AMPH-stimulated behaviors in rats.

METHODS

Rats were administered intracerebroventricular (i.c.v.) injections of the PKCβ-selective inhibitor enzastaurin 0.5, 3, 6, or 18 h before evaluating AMPH-stimulated locomotion (0.32-3.2 mg/kg). Rats were trained to make responses for different doses of AMPH infusions or sucrose under a fixed ratio 5 schedule of reinforcement, and the effects of enzastaurin pretreatment 3 or 18 h prior to a self-administration session were determined. Also, the effect of enzastaurin on AMPH-stimulated PKC activity in the ventral striatum was evaluated.

RESULTS

A large dose of enzastaurin (1 nmol) decreased AMPH-stimulated locomotor activity 0.5 h following enzastaurin administration. Small doses of enzastaurin (10-30 pmol) attenuated AMPH-stimulated locomotor activity and shifted the AMPH dose-effect curve to the right following an 18-h pretreatment. Rats pretreated with enzastaurin 18 h, but not 3, prior to a self-administration session showed a decrease in the number of responses for AMPH, shifted the ascending limb of the amphetamine dose effect curve, and produced no change in responses for sucrose. AMPH-stimulated PKC activity was decreased following a 0.5- or 18-h pretreatment, but not a 3-h pretreatment of enzastaurin.

CONCLUSIONS

These results demonstrate that inhibition of PKCβ will decrease AMPH-stimulated behaviors and neurobiological changes and suggest that PKCβ is potentially a viable target for AMPH use disorder.

Animal Models of Tourette Syndrome-From Proliferation to Standardization

Tourette syndrome (TS) is a childhood onset disorder characterized by motor and vocal tics and associated with multiple comorbid symptoms. Over the last decade, the accumulation of findings from TS patients and the emergence of new technologies have led to the development of novel animal models with high construct validity. In addition, animal models which were previously associated with other disorders were recently attributed to TS. The proliferation of TS animal models has accelerated TS research and provided a better understanding of the mechanism underlying the disorder. This newfound success generates novel challenges, since the conclusions that can be drawn from TS animal model studies are constrained by the considerable variation across models. Typically, each animal model examines a specific subset of deficits and centers on one field of research (physiology/genetics/pharmacology/etc.). Moreover, different studies do not use a standard lexicon to characterize different properties of the model. These factors hinder the evaluation of individual model validity as well as the comparison across models, leading to a formation of a fuzzy, segregated landscape of TS pathophysiology. Here, we call for a standardization process in the study of TS animal models as the next logical step. We believe that a generation of standard examination criteria will improve the utility of these models and enable their consolidation into a general framework. This should lead to a better understanding of these models and their relationship to TS, thereby improving the research of the mechanism underlying this disorder and aiding the development of new treatments.

Abnormal neuronal activity in Tourette syndrome and its modulation using deep brain stimulation

Tourette syndrome (TS) is a common childhood-onset disorder characterized by motor and vocal tics that are typically accompanied by a multitude of comorbid symptoms. Pharmacological treatment options are limited, which has led to the exploration of deep brain stimulation (DBS) as a possible treatment for severe cases. Multiple lines of evidence have linked TS with abnormalities in the motor and limbic cortico-basal ganglia (CBG) pathways. Neurophysiological data have only recently started to slowly accumulate from multiple sources: noninvasive imaging and electrophysiological techniques, invasive electrophysiological recordings in TS patients undergoing DBS implantation surgery, and animal models of the disorder. These converging sources point to system-level physiological changes throughout the CBG pathway, including both general altered baseline neuronal activity patterns and specific tic-related activity. DBS has been applied to different regions along the motor and limbic pathways, primarily to the globus pallidus internus, thalamic nuclei, and nucleus accumbens. In line with the findings that also draw on the more abundant application of DBS to Parkinson's disease, this stimulation is assumed to result in changes in the neuronal firing patterns and the passage of information through the stimulated nuclei. We present an overview of recent experimental findings on abnormal neuronal activity associated with TS and the changes in this activity following DBS. These findings are then discussed in the context of current models of CBG function in the normal state, during TS, and finally in the wider context of DBS in CBG-related disorders.

Dual ameliorative effects of Ningdong granule on dopamine in rat models of Tourette's syndrome

Dopamine (DA) is a key neuromodulator in the brain that supports motor and cognitive functions. Here, we use apomorphine (Apo) and 3,3'-iminodipropionitrile (IDPN) to develop two rat models of Tourette's syndrome (TS), a common neuropsychiatric disorder characterized by stereotyped repetitive involuntary tics. The models enabled the assessment of unique ameliorative effects of Ningdong granule (NDG), a traditional Chinese medicine (TCM) preparation dedicated to the treatment of TS, on the striatal DA content of rats. By using high-performance liquid chromatography (HPLC), we found that long-term administration of NDG could, at least partially, restore the striatal dopamine alterations, either by increasing them after IDPN treatment or by decreasing them after Apo treatment. Taken together, our data indicated that NDG could ameliorate the abnormal striatal DA content dually, and the unique therapeutic property may be meaningful for the treatment of TS.

Dual regulating effects of gastrodin on extracellular dopamine concentration in rats models of Tourette's syndrome

PURPOSE

Evaluate the dual regulating effects of gastrodin on striatal extracellular dopamine (DA) concentration in Tourette's syndrome (TS) rat models, and explore the underlying pharmacological mechanisms.

MATERIALS AND METHODS

Seventy Wistar rats were randomly divided into control group and TS model group. The former was intraperitoneally injected with saline (0.9%), while in the later, the rats were injected with Apomorphine (Apo) and 3,3'-iminodipropionitrile (IDPN) respectively to manipulate two kinds of TS rat models. Both Apo and IDPN induced rats were further assigned to three conditions, and the related rats were treated respectively by oral gavage with saline, gastrodin and Haloperidol (Hal). Data of stereotypy of the rats were collected. After 8 weeks, the extracellular content of DA and HVA in striatum were examined by intracerebral microdialysis and follow-up high-performance liquid chromatography (HPLC), and the expression of dopamine transporter (DAT) was probed by Western blot.

RESULTS

Gastrodin improved the stereotyped behaviors in TS rats. Furthermore, it down-regulated the elevated striatal extracellular DA concentration in Apo-induced rats and up-regulated the decreased DA content in the rats exposed to IDPN. Meanwhile, a dramatic down-regulation was detected in DAT protein expression in Apo + GAS group, while an opposite profile was showed in the IDPN + GAS group.

CONCLUSIONS

The dual regulating effects of gastrodin on extracellular DA level have been established, and the related mechanisms would be the dual regulating effects of gastrodin on the expression of DAT, a glycoprotein in the regulation of the extracellular DA concentration.

Animal models of tic disorders: a translational perspective

Tics are repetitive, sudden movements and/or vocalizations, typically enacted as maladaptive responses to intrusive premonitory urges. The most severe tic disorder, Tourette syndrome (TS), is a childhood-onset condition featuring multiple motor and at least one phonic tic for a duration longer than 1 year. The pharmacological treatment of TS is mainly based on antipsychotic agents; while these drugs are often effective in reducing tic severity and frequency, their therapeutic compliance is limited by serious motor and cognitive side effects. The identification of novel therapeutic targets and development of better treatments for tic disorders is conditional on the development of animal models with high translational validity. In addition, these experimental tools can prove extremely useful to test hypotheses on the etiology and neurobiological bases of TS and related conditions. In recent years, the translational value of these animal models has been enhanced, thanks to a significant re-organization of our conceptual framework of neuropsychiatric disorders, with a greater focus on endophenotypes and quantitative indices, rather than qualitative descriptors. Given the complex and multifactorial nature of TS and other tic disorders, the selection of animal models that can appropriately capture specific symptomatic aspects of these conditions can pose significant theoretical and methodological challenges. In this article, we will review the state of the art on the available animal models of tic disorders, based on genetic mutations, environmental interventions as well as pharmacological manipulations. Furthermore, we will outline emerging lines of translational research showing how some of these experimental preparations have led to significant progress in the identification of novel therapeutic targets for tic disorders.

The disrupted basal ganglia and behavioural control: an integrative cross-domain perspective of spontaneous stereotypy

Spontaneous stereotypic behaviour (SB) is common in many captive animal species, as well as in humans with some severe psychiatric disorders, and is often cited as being related to general basal ganglia dysfunction. Despite this assertion, there is little in the literature examining SB specifically in terms of the basal ganglia mechanics. In this review, we attempt to fill this gap by offering an integrative, cross-domain perspective of SB by linking what we currently understand about the SB phenotype with the ever-growing literature on the anatomy and functionality of the basal ganglia. After outlining current models of SB from different theoretical perspectives, we offer a broad but detailed overview of normally functioning basal ganglia mechanics, and attempt to link this with current neurophysiological evidence related to spontaneous SB. Based on this we present an empirically derived theoretical framework, which proposes that SB is the result of a dysfunctional action selection system that may reflect dysregulation of excitatory (direct) and inhibitory (indirect and hyperdirect) pathways as well as alterations in mechanisms of behavioural switching. This approach also suggests behaviours that specifically become stereotypic may reflect inbuilt low selection threshold behavioural sequences associated with early development and the species-specific ethogram or, low threshold behavioural sequences that are the result of stress-induced dopamine exposure at the time of performance.

Comparison of rating scales used to evaluate L-DOPA-induced dyskinesia in the 6-OHDA lesioned rat

Abnormal involuntary movement (AIM) rating scales are frequently used to study the mechanisms underlying L-DOPA-induced dyskinesia (LID) in 6-OHDA lesioned rodents and the propensity of novel treatments for Parkinson's disease to induce or alleviate similar abnormal behaviours. Despite the existence of at least one well validated method, other AIM scales are also in use. Moreover, there have been developments and variations in the original scales and their methods of use, without re-validation. In this study, 6-OHDA medial forebrain bundle lesioned Sprague-Dawley rats were treated with chronic L-DOPA 6 mg/kg/day for 5 weeks followed by 12 mg/kg/day for another 5 weeks. Rats were assessed weekly by simultaneous ratings on four published AIM and stereotypy scales with concurrent recording of rotation, over 3 hours following L-DOPA injection. Three contemporary AIM scales have then been validated pharmacologically using agents that are known to reduce LID clinically and in primates (amantadine) or to interfere with the activity of L-DOPA (the D(1) and D(2) dopamine receptor antagonists, SCH-23390 and raclopride) respectively. We also demonstrate that AIM, stereotypic and rotational behaviour are distinct motor dysfunctions induced by chronic and acute treatment of L-DOPA, and should be assessed separately. The undertaking of assessments at multiple time points is essential especially when testing the efficacy of new potential anti-dyskinetic treatments. Importantly critical to all AIM and rotation testing is the internal validation of both the scale being used and the environment being used.

Increased responsiveness of mesolimbic and mesostriatal dopamine neurons to cocaine following repeated administration of a selective kappa-opioid receptor agonist

Previous data have shown that the repeated administration of kappa-opioid receptor agonists attenuates the acute behavioral effects of cocaine. The site and mechanism by which kappa-agonists interact with this psychostimulant, however, are unknown. Accordingly, the present microdialysis study characterized the effects of prior, repeated administration of the selective kappa-opioid receptor agonist U69593 on basal and cocaine-evoked DA levels within the nucleus accumbens (NAC) and caudate putamen (CPU). The influence of U69593 treatment on the locomotor-activating effects of an acute cocaine challenge was also assessed. Rats received once daily injections of U69593 (0.16-0.32 mg/kg/day) or vehicle (1.0 ml/kg/day) for 3 days. The behavioral and neurochemical effects produced by an acute cocaine challenge (20 mg/kg i.p.) were assessed 2 days following treatment cessation. Administration of cocaine to control animals increased locomotor activity. This effect was attenuated in animals which had previously received U69593 (0.32 mg/kg/day x 3 days). Prior administration of U69593 failed to modify basal DA levels in either the NAC or CPU. Thus, 2 days following the cessation of U69593 treatment, dialysate DA levels did not differ from that of controls. Administration of cocaine to vehicle-treated animals increased dialysate levels of DA in both brain regions. However, in animals previously exposed to U69593 (0.32 mg/kg/day x 3 days), a significant enhancement in the response of DA neurons to cocaine was seen. These data demonstrate that prior, repeated administration of a selective kappa-opioid receptor agonist attenuates the locomotor-activating effects of cocaine and increases cocaine-evoked DA overflow in terminal projection areas of mesostriatal and mesolimbic DA neurons. These findings indicate that the behavioral interactions of kappa-agonists with cocaine observed in this and previous studies cannot be attributed to a presynaptic inhibition of DA release. Rather, they suggest that postsynaptic or non-DA mechanisms mediate the interaction of these agents with cocaine.

Schizophrenia and psychostimulant abuse: a review and re-analysis of clinical evidence

The authors selected articles from those published between 1975 and 1994 that specifically documented psychostimulant abuse in patients determined to be schizophrenic according to recent and relatively uniform diagnostic criteria. These articles indicated that the incidence of psychostimulant abuse in schizophrenics is 2-5 times higher than that of the general public. Additionally, unlike the decline in stimulant use seen in older adults in the general population, high rates of abuse appeared to be maintained in schizophrenics. Although the incidence of abuse in this group was high, comparisons of abuse rates generated by self report with those obtained by urinalysis indicated that the frequency of abuse is being underestimated by 15-21%. Potential factors contributing to stimulant abuse in schizophrenics, including the disease process, and the influence of chronic neuroleptic medication, were evaluated. Results indicated that the incidence of psychostimulant abuse was neither a common property of psychiatric patients, nor exclusive to schizophrenics, but appeared to be related to chronic treatment with neuroleptic drugs. Symptom severity was generally similar in schizophrenic abusers and non-abusers, which also suggested a degree of independence from the disease process. In a majority of the studies surveyed, abuse of stimulants followed disease onset. It was also found that stimulant abuse was associated with marked increases in hospitalization in this patient group, including those known to be neuroleptic medication compliant. Possible explanations for the initiation and maintenance of psychostimulant abuse in schizophrenics are discussed in relation to clinical and preclinical evidence on drug addiction.

The psychology of perserverative and stereotyped behaviour

Many forms of psychopathology in higher animals and humans include the production of maladaptive, repetitive behaviour. Behaviour which is both repetitive and excessive in amount can be described as stereotyped whereas behaviour which represents a restriction of behavioural possibilities without excessive production can be described as perseverative. Both types of repetition can result from pathology in the neural mechanisms which control either the production of motor output or the organisation of behaviour at a higher level. A number of forms of repetitive behaviour can be induced environmentally. Confinement in adulthood results in a functional disorder which rapidly dissipates when normal conditions are restored but confinement in infancy may have a permanent effect on the organism's ability to interact in a flexible and creative way with its environment. The permanence of these disorders suggests that the environment can affect the way in which the nervous system develops. Repetitive behaviour is also a feature of mental illness including schizophrenia, autism, OCD, addiction and some neurological disorders including frontal lobe lesions, Tourette's syndrome and PD. In experimental studies in animals, stereotyped behaviour seems to be related mainly to excess dopaminergic activity in the basal ganglia while perserverative behaviour can be produced by lesions of the frontal lobes. It is supposed that the level of dopamine activity in the basal ganglia affects the baseline level of behavioural activation such that excess activation results in the excessive execution of the most probable response to the environment to the exclusion of other possibilities (i.e. stereotypy) while deficient activation results in the production of only a few responses which can exceed the necessary activation level (i.e. perseveration). In either case behaviour is 'stimulus-bound', being driven by only the most salient feature of the environment. The symptoms of PD result from inadequate levels of dopamine in the basal ganglia while the stimulant psychoses result from excessive availability of dopamine. The frontal lobes have a modulating effect on (i) the activation of motor activity by the basal ganglia, (ii) in the generation of self-initiated behaviour, i.e. volition, and (iii) in the neural mechanisms which permit different modes of neural function (e.g. perceiving, remembering or thinking) to be identified. Failures in these three functions could result in excessive and repetitive motor activity, stimulus-bound behaviour, the paucity of volitional and creative behaviour, and the perceptual and experiential symptoms of psychosis.

Electrical sensitization of the meso-limbic dopaminergic system in rats: a pathogenetic model for schizophrenia

To study whether it was possible to modify mesolimbic dopaminergic activity by intermittent electrical stimulations (IES), 44 rats were either electrically stimulated or sham-stimulated in the ventral tegmental area (VTA) once daily for 70 days. This was done through chronically implanted intracranial electrodes. The intensity of electrical stimulation was determined by the lowest current that elicited a definite motor response. Stimulated rats demonstrated a significantly potentiated behavioral response after 70 stimulations. Seven months after IES rats still demonstrated an increased sensitivity to electrical stimulations in the VTA. A new stimulation period only resulted in a modest additional fall in threshold values. There was a highly significant difference between the current needed to provoke a given response in sensitized rats and in sham-stimulated rats. The behavioral response to stimulation was suppressed both by the dopamine (DA) D2 receptor antagonists haloperidol and raclopride and by the DA D1 receptor antagonist SCH 23390. Furthermore, stimulated rats showed an enhanced response to stimulation with amphetamine and to a lesser extent with apomorphine. Between stimulation periods sensitized animals demonstrated a reduced social interaction. In conclusion intermittent electrical stimulations of the VTA resulted in a syndrome characterized by a hypersensitive response to electrical and pharmacological DA provocation combined with abnormal social interaction. This animal model has points of resemblance with recent interpretations of the DA hypothesis for schizophrenia.

Interactions between chronic haloperidol treatment and cocaine in rats: an animal model of intermittent cocaine use in neuroleptic treated populations

This experiment investigated the possibility that rats maintained on chronic haloperidol treatment would show increased behavioral responsiveness to cocaine, similar to that observed in human stimulant abusers who are chronically treated with neuroleptics. Thus, the effects on locomotion and stereotyped behavior of intermittent injections of cocaine were investigated in female rats receiving chronic haloperidol treatment. Daily injections of haloperidol (0.2 mg/kg, IP) or vehicle were administered for 6, 12 or 18 days prior to the start of testing with cocaine and were then continued throughout cocaine testing. All rats received four doses of cocaine (0.0, 3.0, 7.5, or 15.0 mg/kg, IP) in random order with an intervening vehicle day between successive drug days. The four dose sequence of cocaine was repeated a total of four times. Initial cocaine administration produced dose dependent increases in locomotion and stereotyped behavior. When the sequence of cocaine doses was repeated, differences among treatment groups emerged. Groups treated with haloperidol exhibited heightened locomotion in response to cocaine and with repeated injections, showed a higher rate of behavioral sensitization than control animals. These differences in the behavioral response to cocaine were maintained for at least 2 months following termination of daily haloperidol treatment. In order to examine the mechanisms underlying this heightened responsiveness to cocaine, apomorphine-induced locomotion (dose range, 0-250 micrograms/kg, SC) was determined. Regardless of dose, rats treated with haloperidol showed different temporal patterns of locomotion in response to apomorphine suggesting that the increased response to cocaine was related to changes in dopaminergic receptor sensitivity.

Stereotypy and asymmetry in mice

Mice ran in a circular runway. Number and direction of circuits were recorded. Most control mice ran about the same number of circuits in each direction. After 100 mumols/kg cocaine there were 3.5 times as many circuits and most mice ran most circuits in one direction. Some mice ran strongly in one direction after a first dose of cocaine and strongly in the other direction after a second dose. Hence, the primary influence toward unidirectional running is stereotypy rather than asymmetry.

Amperozide--a new putatively antipsychotic drug with a limbic mode of action on dopamine mediated behaviour

Amperozide, a new putatively antipsychotic drug, was found to exert a functional selectivity for the limbic system of the brain. Thus, amperozide was as active as both classical and atypical neuroleptics on hypermotility induced by a low dose of amphetamine. On the other hand, amperozide did not produce catalepsy, nor did it reverse amphetamine-induced stereotypies. Moreover, amperozide inhibited exploratory behaviour in mice. The present results indicate an antipsychotic effect of amperozide, with a minimal risk for EPS when used in the clinic.

Effects of systemic and intracranial amphetamine injections on behavior in the open field: a detailed analysis

Systemic injections of amphetamine result in profound changes in the behavior of animals in an open field. There is an increase in activity, certain species-typical behaviors are produced, and there is a tendency for any elicited behavior to be repeated in a stereotyped way. The present study examined the contributions of dopamine terminal regions to these effects in rats by microinjecting amphetamine directly into one of six discrete sites (medial frontal cortex, nucleus accumbens, anteromedial caudate nucleus, ventrolateral caudate nucleus, amygdala, or the region surrounding the area postrema) and making detailed behavioral observations. This data was compared with the behavior of systemically injected rats that were also observed in the open field. An observer recorded the occurrence of twelve categories of behavior and recorded photocell beam interruptions during five post-injection observation periods. The results confirmed and extended previous accounts of the behavior of systemically injected rats, adding increased snout contact with the environment as an additional effect of amphetamine. Intracranial injections produced changes in activity level from several of the injection sites but there was no increase in the species-typical behaviors associated with stereotypy. Changes in the occurrence of some recorded behaviors were produced by injections into most of the sites and these data are presented in detail.

Head-twitches induced by p-hydroxyamphetamine in mice

Head-twitches have been regarded as an experimental model of hallucination, and we have recently observed that p-hydroxyamphetamine (p-OHA) markedly induced head-twitches in mice. The present work was undertaken to study possible participation of a serotonergic system in the mechanism of head-twitches induced by p-OHA. Head-twitches induced by p-OHA continued for 20-80 min, and the peak time of this effect was approximately 30-40 min after the administration. The i.c.v. administration of p-OHA (20, 40, 80 and 160 micrograms/mouse) produced characteristic head-twitches in a dose-dependent manner. Simultaneous injection of serotonin (10 micrograms/mouse, i.c.v.) and p-OHA caused a 2-2.5-fold increase in the number of head-twitches compared with non-serotonin controls. Pretreatment with p-chlorophenylalanine (200 mg/kg, i.p. and 500 micrograms/mouse, i.c.v.), in contrast, reduced head-twitches as did the pretreatment with cyproheptadine or dimethothiazine. These results suggest that p-OHA-induced head-twitches may involve the central serotonergic system which may exert an excitatory effect on head-twitches.

Distribution and stress-induced increase of glutamate and aspartate levels in discrete brain nuclei of rats

Concentrations of glutamate and aspartate have been measured in 45 microdissected brain areas and nuclei in rat. Both amino acids are ubiquitously present and distributed unevenly in the central nervous system. Very high glutamate levels were found in the cerebellum and the insular cortex, high levels in neocortical and limbic cortical areas, and in the nuclei of the medial hypothalamus. Aspartate is distributed rather uniformly with the highest concentration in the hypothalamic arcuate nucleus and the lowest in the midbrain central gray matter and the cerebellum. Acute formalin (pain) stress elevated glutamate and aspartate levels in the cortical areas and substantia nigra significantly, but had minor or no effects on other brain nuclei. Increased locomotor and behavioral activities due to a high dose of amphetamine resulted in a 2-5-fold increase of glutamate and aspartate concentrations, particularly in the biogenic amine-containing brain nuclei.

Association of the mesencephalic locomotor region with locomotor activity induced by injections of amphetamine into the nucleus accumbens

Injections of amphetamine into the nucleus accumbens increased locomotor activity of rats. Subsequent injections of procaine into the midbrain, in the region of the pedunculopontine nucleus, significantly reduced the amphetamine-induced locomotor activity. Control experiments showed that procaine injections into the contralateral pedunculopontine nucleus had little or no effect, as well as ipsilateral injections dorsal and ventral to the pedunculopontine nucleus. These findings suggest that release of dopamine from amphetamine injections into the accumbens gives rise to ipsilateral descending influences on the region of the pedunculopontine nucleus, a major component of the mesencephalic locomotor region. Descending influences from the nucleus accumbens to mesencephalic locomotor region may serve as a link for limbic-motor integration in behavioral response initiation.

Lateralizing effects of apomorphine on taxis, postural support and rotation in rats

Subcutaneous injections of apomorphine, a dopamine receptor agonist, induced a lateralization of taxis for edges in 16% of rats and a reliable lateralization of postural support in 82% of rats. The relation among these effects and the lateralizing effects of apomorphine on rotational behavior were examined. Lateralized rotation did not reliably correlate with lateralized taxis. However, it correlated with a relatively large asymmetry of postural support. The lateralizing effects of apomorphine on taxis and rotation may reflect attentional and directional asymmetries, respectively. It is proposed that apomorphine can induce different types of lateralizations, including attentional, postural and directional, and that the lateralizing effects of apomorphine on posture and locomotor direction are interrelated. Regional brain interhemispheric asymmetries in the responsiviness of dopamine receptors may underlie different types of apomorphine-induced lateralizations.

Major psychosis and dopamine: controversial features and some suggestions

Three problems with the dopamine hypothesis of major psychosis are pointed out: the long time-course of neuroleptic therapy; the absence of tolerance to the antipsychotic effects of neuroleptic drugs, or of a supersensitivity psychosis on drug withdrawal; and the absence of potent psychotogenic properties in the direct dopamine agonists. A resolution of these paradoxes is suggested relying on a role for dopamine in learning processes at a relatively high (cognitive) functional level. The hypothesis proposed is also used to explain the origin of some of the more distinctive psychotic symptoms.

Enhancement of Behavioral Effect and Acute Toxicity of Methamphetamine by Qu nine in Rats

The behavioral effect and acute toxicity of methamphetamine were tested alone and in combination with quinine in rats. Quinine prolonged and increased the effect of methamphetamine. The enhancement of methamphetamine-induced stereotyped behavior was very marked when quinine was given prior to or simultaneously with methamphetamine. However, the time for onset of methamphetamine-induced stereotyped behavior was not affected by quinine. The mortality of methamphetamine was also potentiated markedly by quinine. The enhancement of the behavioral effect and the toxicity of methamphetamine may be due to inhibition of the metabolism of methamphetamine by quinine.

Alterations in cerebral dopamine function caused by administration of cis- or trans-flupenthixol for up to 18 months

Rats received either cis-flupenthixol (0.8-1.2 mg/kg per day) or trans-flupenthixol (0.9-1.2 mg/kg per day) continuously in drinking water for periods up to 18 months. cis-Flupenthixol, but not trans-flupenthixol, initially inhibited apomorphine-induced stereotyped behaviour but by 6 months and thereafter the stereotyped response was enhanced compared to age-matched control animals. Striatal and mesolimbic homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations were elevated for up to 3 months after starting cis-, but not trans-flupenthixol intake, but thereafter levels generally fell below those for age-matched control animals. Dopamine concentrations were not altered by cis- or trans-flupenthixol administration. The number of striatal [3H]spiperone binding sites (Bmax) was decreased by 40% after 1 months' administration of cis-flupenthixol but this gradually reversed, such that by 18 months a 40% increase in Bmax was apparent. Administration of trans-flupenthixol decreased Bmax up to 3 months but thereafter values were not different from those found in age-matched control animals. The dissociation constant (KD) for [3H]spiperone binding in striatum was not altered by 6 months cis-flupenthixol intake, but then increased as drug administration continued. trans-Flupenthixol administration did not alter striatal KD values. Bmax for [3H]spiperone binding to mesolimbic preparations was not altered by up to 12 months cis-flupenthixol intake, but was decreased after 18 months drug administration. cis-Flupenthixol administration had no effect on mesolimbic KD values. Administration of trans-flupenthixol for up to 18 months did not alter mesolimbic Bmax or KD values for [3H]spiperone binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulant drug effects in developmental disorders and hyperactivity--toward a resolution of disparate findings

An attempt is made to integrate data from a variety of clinical populations and from the animal literature. Evidence is presented suggesting that mentally retarded and autistic children generally show a poor response to stimulant medication, whereas hyperactive and normal children respond beneficially. Cognitive research in mentally retarded and autistic children is reviewed, and it is suggested that both diagnostic groups suffer from attentional difficulties, the mechanisms of which may be very similar. The literature on stimulant-induced stereotypy in animals is discussed, with emphasis on the clinical implications for autism and mental retardation. An attentional model is proposed to account for type of therapeutic response to stimulant medication. This is followed by a possible method for testing the model and by specific predictions relating to subject characteristics and response.

Methylphenidate in severely retarded residents and the clinical significance of stereotypic behavior

An attempt was made to evaluate a model predicting stimulant drug response based on attentional characteristics of the participants. Twenty-eight severely and profoundly mentally retarded residents took part in a double blind, placebo controlled trial of methylphenidate (Ritalin). Methylphenidate was administered, for one week each, in a low dose of 0.3 mg/kg and a high dose of 0.6 mg/kg. The results failed to show any clinically relevant differences between placebo and active drug conditions with the exception that methylphenidate caused a significant reduction in food consumption. A variety of subject characteristics, including level of stereotypy, hyperactivity, and IQ were unrelated to drug effect. One positive finding, unrelated to drug effects, was that subdivision of the group by degree of stereotypy provided substantial clinical information about individual subjects.

Amphetamine psychosis and schizophrenia: a dual model

Several of the behavioral consequences of acute and chronic amphetamine treatment were evaluated and related to the underlying neurochemical correlates of drug treatment. It was suggested that decreased noradrenergic activity after long-term amphetamine treatment influences stimulus sampling, whereas enhanced dopaminergic activity was responsible for the progressive augmentation of stereotypy and self-stimulation behavior observed after long-term exposure to amphetamine. It was hypothesized that amphetamine-induced psychosis and the symptomatology associated with schizophrenia are related to alterations in both norepinephrine and dopamine activity.

Contributions of alpha-adrenoreceptor blockade to extrapyramidal effects of neuroleptic drugs

Prazosin, phenoxybenzamine and clozapine, but not sulpiride, abolished the increase in flexor reflex activity induced by clonidine and they accelerated the noradrenaline utilization in the brain of rats. These findings indicate that the first three drugs block central alpha-adrenoreceptors. The alpha-methyltyrosine-induced disappearance of dopamine in the corpus striatum and the limbic system was decelerated by prazosin and phenoxybenzamine, was accelerated by sulpiride and was not significantly changed by clozapine. Prazosin and phenoxybenzamine almost completely reversed the sulpiride-induced increase in dopamine utilization. The reduction of the dopamine release following blockade of postsynaptic alpha-adrenoreceptors might prevent tardive dyskinesia. Blockade of postsynaptic alpha-adrenoreceptors might also increase the ultimate result of dopamine receptor stimulation in the corpus striatum but decrease that in the limbic system. Therefore, blockade of alpha-adrenoreceptors as well as of muscarinic receptors might explain why clozapine causes less extrapyramidal disturbances than other antipsychotic drugs.