Following several days of continuous administration d-amphetamine acquires hallucinogenlike properties

Antipsychotics for Amphetamine Psychosis. A Systematic Review

Background: Among individuals experiencing amphetamine psychosis, it may be difficult to rule out schizophrenia. The use of antipsychotics for the treatment of amphetamine psychosis is sparse due to possible side effects. Some arguments disfavor their use, stating that the psychotic episode is self-limited. Without treatment, some individuals may not fully recover from the psychosis and may develop full-blown psychosis, emotional, and cognitive disturbance. This review aims to investigate the clinical benefits and risks of antipsychotics for the treatment of amphetamine psychosis. Methods: Electronic search on trials on antipsychotic drugs for amphetamine psychosis from their inception to November 2018 was conducted in PubMed, Scopus, Google Scholar, EBSCOhost, ProQuest, Cochrane Review Database, Medline Ovid, and EMBASE following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. The Cochrane risk-of-bias tool assessed the risk of bias, the methodological quality of individual trials was assessed by the Oxford Quality Scoring System, and the quality of evidence for recommendations was judged by the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). The results were synthesized qualitatively and quantitatively. Results: The investigation of six randomized controlled trials of 314 participants showed that aripiprazole, haloperidol, quetiapine, olanzapine, and risperidone were able to reduce or control the psychotic episode (positive and negative symptoms) induced by amphetamine use with no adverse event. Although the side-effect profile of these agents varied, no drug was clinically superior to others. Conclusions: This review suggests that antipsychotics seem to be efficacious for amphetamine psychosis on both positive and negative symptoms. Practitioners need to tailor their use based on risks for side effects individually.

An Argument for Amphetamine-Induced Hallucinations in an Invertebrate

Hallucinations – compelling perceptions of stimuli that aren’t really there – occur in many psychiatric and neurological disorders, and are triggered by certain drugs of abuse. Despite their clinical importance, the neuronal mechanisms giving rise to hallucinations are poorly understood, in large part due to the absence of animal models in which they can be induced, confirmed to be endogenously generated, and objectively analyzed. In humans, amphetamine (AMPH) and related psychostimulants taken in large or repeated doses can induce hallucinations. Here we present evidence for such phenomena in the marine mollusk Tritonia diomedea. Animals injected with AMPH were found to sporadically launch spontaneous escape swims in the absence of eliciting stimuli. Deafferented isolated brains exposed to AMPH, where real stimuli could play no role, generated sporadic, spontaneous swim motor programs. A neurophysiological search of the swim network traced the origin of these drug-induced spontaneous motor programs to spontaneous bursts of firing in the S-cells, the CNS afferent neurons that normally inform the animal of skin contact with its predators and trigger the animal’s escape swim. Further investigation identified AMPH-induced enhanced excitability and plateau potential properties in the S-cells. Taken together, these observations support an argument that Tritonia’s spontaneous AMPH-induced swims are triggered by false perceptions of predator contact – i.e., hallucinations—and illuminate potential cellular mechanisms for such phenomena.

Withdrawal from continuous amphetamine administration abolishes latent inhibition but leaves prepulse inhibition intact

RATIONALE

Schizophrenia has been associated with dysregulation of dopamine (DA) transmission and impairment in a number of experimental tasks, including sensorimotor gating assessed using prepulse inhibition (PPI) and selective attention assessed using latent inhibition (LI). We have demonstrated in previous studies that after withdrawal from escalating (ESC) dosages of amphetamine (AMPH), animals exhibited disruption of LI but no alteration of PPI. Moreover, these animals always showed behavioural sensitization to an AMPH challenge.

OBJECTIVE

In this study, we were interested in testing whether a different administration schedule would elicit disruption of both LI and PPI.

METHODS

Animals were treated with continuous AMPH release (via osmotic mini-pumps at a dosage of 10 mg kg(-1) day(-1) for 7 days) and tested for their performance in L and PPI during withdrawal in a drug free state. Rats received AMPH treatment during the induction phase in their home cages or in the activity chambers. Following withdrawal, the expression of behavioural sensitization to an AMPH challenge was tested in both cases in the activity chambers.

RESULTS

Animals pretreated with AMPH from both groups did not exhibit behavioural sensitization. Withdrawal from continuous administration induced LI attenuation with no effect on PPI.

CONCLUSIONS

These findings are similar to what was previously found with respect to an ESC AMPH regime. The only difference between the schedules was that the ESC AMPH schedule led to behavioural sensitization whereas the continuous AMPH did not. It is suggested that the expression of sensitization may not be a prerequisite for observed LI disruption.

Prolonged exposure of rats to intravenous methamphetamine: behavioral and neurochemical characterization

The translational value of preclinical models of methamphetamine abuse depends in large part on the degree to which the drug regimens used in animals produce methamphetamine exposure patterns similar to those experienced by human methamphetamine abusers. To approximate one common form of methamphetamine abuse, we studied the effects of a schedule of intravenous methamphetamine administration in rats which included 2 weeks of progressively more frequent drug injections (0.125 mg/kg/injection) followed by 40 maintenance days during which animals received 40 daily injections (at 15-min intervals), with the dose gradually increasing (0.125-0.25 mg/kg per injection) every 5-10 days. This treatment produced an emerging behavioral profile characterized by gradually more continuous periods of activation consisting of progressively more intense, focused stereotypy interrupted by episodic bursts of locomotion. We also assessed markers of dopamine neurotransmission (dopamine transporter, vesicular monoamine transporter, and dopamine D1 and D2 receptors) at 15 min and (including dopamine levels) at 6 and 30 days following cessation of methamphetamine treatment. All dopamine components measured in caudate-putamen were significantly reduced at 15 min and 6 days after the final methamphetamine injection. Dopamine D1 and D2 receptors fully recovered after 30 days of drug abstinence, whereas dopamine and the dopamine transporter exhibited significant but incomplete recovery by this time point. In contrast, only the vesicular monoamine transporter exhibited no evidence of recovery over the 30-day withdrawal period. These data are discussed in terms of damage to dopamine terminals and compensatory adjustments in mechanisms maintaining functional dopaminergic transmission.

An escalating dose "binge" model of amphetamine psychosis: behavioral and neurochemical characteristics

Stimulant-induced psychosis is most frequently associated with a chronic, high-dose, multiple daily ("binge") exposure pattern of stimulant abuse. To simulate these conditions, rats were exposed to escalating doses of amphetamine (Escalating Dose phase, 1.0-8.0 mg/kg) before multiple daily injections of relatively high doses of the drug (Run phase, 8.0 mg/kg/2 hr x 4 injections). Behavior was monitored continuously during the course of these treatments as well as during subsequent amphetamine challenges at various times after discontinuation of drug treatment. With the Escalating Dose-Run pattern of administration, a unique behavioral profile emerged in which tolerance occurred to the amount of time spent engaged in continuous focused stereotypy simultaneous with a profound increase in ambulatory activity that appeared agitated and disorganized. Parallel in vivo microdialysis studies showed progressively declining extracellular dopamine and serotonin responses, both within and between successive runs, whereas the norepinephrine response remained relatively unaltered. We propose that this model more closely resembles clinical manifestations of amphetamine psychosis and that the alterations may reflect a shift in the relative activation of mesolimbic and nigro-striatal dopamine pathways.

Stimulant-induced psychosis, the dopamine theory of schizophrenia, and the habenula

While one of the original underpinnings of the dopamine theory of schizophrenia was the paranoid psychosis which often develops during the binges or speed runs of chronic amphetamine addicts (and, more recently, in cocaine addicts), neurochemical studies of such drug abusers or from animals given continuous stimulants in an effort to model stimulant psychoses have not played a major role in the further evolution of this theory. One clear persisting alteration produced by continuous amphetamine is a neurotoxicity to dopaminergic innervations in caudate. Yet continuous cocaine administration apparently does not induce a similar neurotoxicity and this makes this effect a poor candidate for an underpinning of stimulant psychoses. However, it has recently been found that both continuous amphetamine and cocaine induce a strong pattern of degeneration which is highly confined to the lateral habenula and its principal output pathway, fasciculus retroflexus. This finding has led to a reconsideration of the role of these structures in psychoses. The habenula, as the chief relay nucleus of the descending dorsal diencephalic system (consisting of stria medullaris, habenula and fasciculus retroflexus), is an important link between limbic and striatal forebrain and lower diencephalic and mesencephalic centers. Studies of glucose utilization have consistently shown the habenula to be highly sensitive to dopamine agonists and antagonists. Lesions of habenula produce a wide variety of behavioral alterations. The dorsal diencephalic system has major and predominantly inhibitory connections onto dopamine-containing cells and it mediates part of the negative feedback from dopamine receptors onto dopamine cell bodies. It represents one of the major inputs in brain to the raphe nuclei and has anatomical and functional connections to modulate important functions such as sensory gating through thalamus, pain gating through central gray and raphe and motor stereotypies and reward mechanisms through substantia nigra and the ventral tegmental area. It is argued that alterations in these pathways are ideal candidates for producing the behaviors which occur during psychosis and that future considerations of the circuitry underlying psychoses need to include this highly important but relatively neglected system.

A silicone pellet for continuous cocaine: comparison with continuous amphetamine

An inexpensive silicone pellet is described for the continuous administration of cocaine for up to 5 days. Rats implanted with this pellet show minimal skin irritation and go through distinct behavioral stages, with an initial period of hyperactivity followed by motor stereotypies. Then, at 3-4 days after implantation, a variety of hallucinogen-like ("late-stage") behaviors appear, including limb flicks, sudden startle responses, and repetitive mid-air grasping movements. Compared to continuous d-amphetamine, continuous cocaine induces decreased motor stereotypies but heightened "late-stage" behaviors.

Time-dependent changes in the sensitivity of dopamine neurons to low doses of apomorphine following amphetamine infusion

Changes in dopamine autoregulatory mechanisms following a chronic infusion of amphetamine were studied. Rats were infused with D-amphetamine (4.8 mg/day) for 7 days by osmotic minipumps, and were studied at various times after withdrawal. In contrast to no changes in the spontaneous firing rate of single dopamine cells, the potency of apomorphine in the substantia nigra was markedly decreased soon after withdrawal, followed by an increase 7 days later. The ventral tegmental area showed no changes in either spontaneous firing rate or sensitivity to apomorphine following a 7-day withdrawal. Moderate decreases in striatal and tubercle dopamine concentrations were not accompanied by any significant decrease in basal dopamine synthesis. Under intact impulse-flow, the sensitivity of terminal dopamine synthesis to low doses of apomorphine was decreased immediately following withdrawal; by Day 7 supersensitivity was observed. Direct assessment of terminal autoreceptors following a 7-day withdrawal revealed normo- and supersensitivity of these receptors in the striatum and olfactory tubercle, respectively. Possible mediating mechanisms as well as implications of these findings for the development of characteristic behavioral syndromes during and after amphetamine infusion are discussed.

Patterns of locomotor and stereotypic behavior during continuous amphetamine administration in rats

The present study examined the behavioral effects of continuous subcutaneous infusion of amphetamine (AMPH) to rats. Saline and 3 AMPH doses were infused for 96 hr (0.2 mg/kg/hr, 0.55 mg/kg/hr, 0.9 mg/kg/hr; n = 12). Locomotor behavior, grooming, gnawing and licking, sniffing, and head-bobbing were recorded for each animal for 1 hr in the light cycle and 1 hr in the dark cycle. The low dose AMPH animals exhibited increased locomotor activity. The medium and high dose groups developed similar behavioral patterns consisting of increased grooming and sniffing and changes in circadian rhythms of activity. Although most behaviors exhibited were similar to those discussed in previous literature describing the effects of chronic amphetamine, the pattern of the behaviors was not. Furthermore, continuous administration of AMPH seems to reliably increase the frequency of behaviors which are rarely observed after acute or chronic amphetamine. This finding has important implications since administration of AMPH to rats has been suggested to be an animal model of schizophrenia.

Comparison of stimulants and hallucinogens on shuttle avoidance in rats

Rats were trained to a high level of performance of a conditioned avoidance response in a shuttlebox to test effects of several classical stimulants in comparison to a variety of hallucinogens. A previously-reported biphasic pattern of effects of mescaline on shuttle avoidance was replicated and extended to 12 other hallucinogens of both phenylethylamine and indolealkylamine classes. Response patterns of hallucinogens could be differentiated from 3 stimulants and from a methoxyamphetamine compound that lacks hallucinogenic activity.

Continuous low-level apomorphine administration induces motor abnormalities and hallucinogen-like behaviors

Continuous low-level (0.825 mg/kg/h for 20 h) administration of AP through SC in-dwelling silicone reservoirs in the rat induced behavioral and biochemical changes that were similar to those induced by low levels (0.1 mg/kg) of acutely administered AP (decreased behavioral activity and decreased dopamine metabolism in the striatum). With longer periods of continuous AP exposure (40 h or more) the activity-depressing effects of low-level AP diminished. Concurrently a novel behavioral syndrome emerged characterized by limb flicks, body shakes, sudden orienting responses, and motor abnormalities, such as tremors of the jaw muscles, chewing movements, prominent tongue extensions, and body 'tics'. This behavioral syndrome became more apparent following cessation of drug treatment. These novel behavioral changes, which were accompanied by increased behavioral responsiveness to acutely administered AP and amphetamine, were correlated with increased levels of dopamine, homovanillic acid, and 3,4-dihydroxyphenylacetic acid in the striatum but not the nucleus accumbens. This novel behavioral syndrome appears to reflect a rebound increase in dopaminergic mechanisms in striatum following their chronic suppression by low levels of AP.

Self-injurious behavior in rats produced by intranigral microinjection of GABA agonists

Bilateral injection of the GABA agonist muscimol (10-300 ng) into the caudal substantia nigra (pars reticulata) of rats produced dose-dependent stereotyped gnawing and self-biting. Limiting the opportunity to gnaw on inanimate objects shifted the dose-response curve for muscimol-induced self-injurious behavior (SIB) to the left and increased the maximum incidence of SIB. Microinjection of muscimol (30 ng) into the rostral and caudal regions of the substantia nigra were equally effective in producing SIB, though the incidence of SIB decreased sharply when muscimol was injected 1 mm rostral or caudal to the substantia nigra. Bilateral intranigral injection of THIP (100-1000 ng) and (+/-)baclofen (100-1000 ng) induced a low incidence of SIB. However, neither IP administration of picrotoxin (5 mg/kg) or simultaneous microinjection of (+)bicuculline methiodide (BMI; 300 or 1000 ng) along with muscimol (30 ng) blocked muscimol-induced SIB. In fact, (+)BMI increased the occurrence of self-biting and reduced the latency to onset of SIB. The involvement of GABAergic mechanisms in muscimol-induced SIB is discussed.

Electrophysiological evidence for A10 dopamine autoreceptor subsensitivity following chronic D-amphetamine treatment

Extracellular single unit recording techniques were used to determine whether chronic treatment with D-amphetamine (AMP) causes a subsensitivity of dopamine (DA) autoreceptors on A10 DA neurons in the rat ventral tegmental area. Either once daily or twice daily intraperitoneal (i.p.) administration of 5.0 mg/kg AMP for 1 week significantly reduced the ability of intravenous (i.v.) AMP and apomorphine (APO) to suppress the firing of A10 DA neurons when tested 24-32 h after the final administration of i.p. AMP. For both of these treatment regimens, the dose-response curves for AMP and APO induced suppression were shifted approximately 4-fold to the right of control. Following an 8 day abstinence period, only the rats that received twice daily AMP injections exhibited subsensitivity to i.v. AMP and APO; the degree of subsensitivity was reduced by 50% as compared to that observed 24-32 h post-treatment. These results were not due to acute tolerance phenomena since a single i.p. injection of AMP 24-32 h before testing failed to alter sensitivity to i.v. AMP and APO. Rather, the results indicate that chronic AMP treatment reduces the sensitivity of A10 DA neurons to DA agonists. DA autoreceptor subsensitivity was demonstrated further by the finding that the ability of microiontophoretically applied DA to suppress A10 DA neuronal activity was markedly reduced (5.8-fold shift of the dose-response curve) by chronic AMP treatment (2 X 5 mg/kg/day). In contrast, there was no alteration in the ability of iontophoretic gamma-amino butyric acid (GABA) to suppress A10 DA activity in chronic AMP rats. Chronic AMP-treatment also increased the number of spontaneously active A10 DA neurons as well as their basal firing rate. It is suggested that the ability of chronic AMP treatment to decrease the auto-regulatory ability of A10 DA neurons may be related to the phenomena of behavioral sensitization and AMP psychosis.

Continuous amphetamine intoxication: an animal model of the acute psychotic episode

When amphetamines are administered to humans every few hours for several days, either during the 'speed runs' of addicts or in controlled laboratory settings, the psychosis which reliably results is similar to paranoid schizophrenia in a number of important aspects. This unique regimen of drug intake, which involves the continuous presence of stimulants over a prolonged period of time, can be simulated in animals using subcutaneously implanted slow-release silicone pellets containing d-amphetamine base. Monkeys and rats implanted with these pellets develop stages of behavioural alterations which are somewhat similar in sequence to those observed in humans who have received frequent doses of amphetamine. An initial period of hyperactivity and exploratory behaviour is followed by the gradual development of motor stereotypies which become virtually incessant. A period of relative inactivity then appears which is followed, at 4-5 days after pellet implantation, by a late stage. This final stage is characterized by 'wet-dog' shakes, parasitotic-like grooming episodes, and a variety of other forms of hallucinatory-like behaviour. At about the same time there are distinctive and partially irreversible alterations in dopaminergic innervations of the caudate nucleus, but not in mesolimbic dopamine innervation of the nucleus accumbens or in several other neurotransmitter systems. Continuous amphetamine administration may reproduce some aspects of the prolonged excitation which accompanies an acute psychotic episode and may be a fruitful model for the clarification of the dopamine theory of schizophrenia.

Self-injurious behavior produced in rats by daily caffeine and continuous amphetamine

Self-biting (SB) is an unusual behavioral effect of high doses of certain amphetamine-like drugs in rats. This bizarre behavior has received little attention, perhaps because the high doses of drug required and the dramatic disturbance of the animals' behavioral repertoire have raised the possibility that SB is a high dose phenomenon. However, we have found that continuous administration of very low amounts of amphetamine reliably produces SB in rats, and that this behavioral change can be very selective. We compared SB produced by continuous amphetamine to SB produced by daily caffeine; the latter has been proposed as an animal model for self-injurious behavior (SIB) in the Lesch-Nyhan syndrome. Subcutaneous silicone pellets containing amphetamine base were implanted for 4.5 days; caffeine was administered daily for 10 days. The amphetamine pellets produced the highest rate of SB (75% vs 40%) with the least toxic effects (no deaths vs three deaths). Neither drug produced stereotypy. The dopamine antagonist haloperidol was only marginally effective in controlling SB produced by daily caffeine but the dopamine antagonist pimozide (which has a longer duration of action) prevented SB by amphetamine pellet rats. Continuous release amphetamine pellets may provide an alternative to the caffeine model of SIB in humans, particularly for the Lesch-Nyhan syndrome.

The late stage following continuous amphetamine administration to rats is correlated with altered dopamine but not serotonin metabolism

In previous experiments rats pretreated with slow-release d-amphetamine (d-Amp) pellets for 4 1/2 days, given a 12-hr drug-free period, and then injected with d-Amp have been found to show a behavioral syndrome which has similarities to that induced by acute injections of the hallucinogens LSD and mescaline. The present results indicate that rats administered this same drug regimen have large decreases in Dopamine (DA), dihydroxyphenyl acetic acid (Dopac), and homovanillic acid (HVA) in caudate nucleus, smaller decreases in DA with no changes in Dopac and HVA levels in nucleus accumbens, but no alterations in 5-hydroxytryptamine (5HT) and 5-hydroxyindole acetic acid (5HIAA) levels in caudate, accumbens, brainstem and hippocampus. Increased 5HIAA levels are found in rats sacrificed with pellets intact following 3 days of continuous d-Amp administration, while sleep deprived and in motor stereotypies. The late and hallucinatory stage following continuous d-amp is correlated more closely with alterations in dopamine than of 5HT.

Opposed stages of continuous amphetamine administration: parallel alterations in motor stereotypies and in vivo spiroperidol accumulation

Rats pretreated with different regimens of chronic d-amphetamine (d-Amp) administration were injected 24 h after cessation of chronic d-Amp with either d-Amp (to test the degree to which it now elicited motor stereotypies) or with [3H]spiroperidol (to study in vivo accumulation in 7 brain regions). Rats pretreated with 28 daily injections of d-Amp subsequently evidenced heightened stereotypies to d-Amp whereas other rats pretreated with the same amount of d-Amp for 28 days using slow-release pellets showed decreased stereotypies to d-Amp. In neither of these chronic groups was spiroperidol accumulation altered. But the administration of d-Amp continuously over briefer periods induced large and phasic alterations in both d-Amp induced stereotypes and in spiroperidol accumulation. Rats given continuous d-Amp for 24 h, allowed a 24 h drug-free period, and then injected evidenced a large potentiation of both stereotypies and in vivo accumulation of spiroperidol in the caudate nucleus, whereas after 5 days of continuous d-Amp administration rats showed attenuated stereotypies and decreased [3H]spiroperidol accumulation in the caudate, accumbens, and substantia nigra. These results imply that brief periods of continuous d-Amp administration produce large and phasic changes in dopamine systems.

Rapid decline of stereotyped behavior in rats during constant one week administration of amphetamine via implanted ALZET osmotic minipumps

Groups of rats were subcutaneously implanted with ALZET 2001 type osmotic minipumps containing d-amphetamine. Three doses of amphetamine (calculated as 0.47, 0.94 and 1.41 mg/kg/hour; measured values were approximately 50% lower), continuously released for 7 days, initially produced locomotor stimulation and stereotyped behavior slightly increasing over the first few days. During the later days, however, locomotor stimulation and stereotyped behavior markedly declined indicating tolerance development. These results contrast the often reported development of sensitization to the behavioral effect of amphetamine observed with repeated injections.

Chronic methylxanthine treatment in rats: a comparison of Wistar and Fischer 344 strains

Caffeine, theophylline or aminophylline were administered chronically to rats of both sexes, in the weight range 30-245 g. Self-injurious behaviour was noted only rarely in Wistar rats allowed free access to food, but developed over 3 to 4 weeks in half of the animals given a restricted diet of about one third of the intake of control rats. Fischer rats showed self-injurious behaviour more readily, 87% of animals showing signs within 9 days even on an ad lib diet. It is suggested that Fischer rats treated with methylxanthines may provide a model of the Lesch-Nyhan syndrome. Behavioural observations made during the period of methylxanthine treatment suggest that an activation of both the dopamine and 5-hydroxytryptamine neurone systems may be produced. Further work will seek a relationship between these systems and self-injurious behaviour.

Decreased spiroperidol and LSD binding in rat brain after continuous amphetamine

Rats were implanted with a silicone tubing pellet continuously releasing amphetamine base for several days. After five days of this treatment specific binding of spiroperidol (dopamine receptors) and LSD (serotonin receptors) was decreased in the corpus striatum and frontal cortex. In the striatum the number of dopamine receptors was decreased while the affinity was unchanged. These results indicate that dopamine and serotonin receptors can be regulated by the release of their own neurotransmitter.