Amphetamine psychosis and schizophrenia: a dual model

Capillary electrophoresis-laser-induced fluorescence detection of amphetamine in the brain

Prefrontal cortex microdialysis was done in rats that had received intraperitoneal amphetamine (AMPH). Samples were derivatized with 10(-4) M fluorescein isothiocyanate and incubated for 18 h. AMPH was separated by capillary electrophoresis (CE) and detected by laser-induced fluorescence detection (LIFD) from 30 to 150 min after injection. The limit of mass detection was 3 amol, which is three orders of magnitude lower than that in gas chromatography-mass spectrometry, and the limit of concentration detection was 3 x 10(-9) M. The results showed that CE-LIFD is a good method for detecting AMPH in brain dialysates of rats.

Antagonism of amphetamine-induced disruption of latent inhibition in rats by haloperidol and ondansetron: implications for a possible antipsychotic action of ondansetron

Latent inhibition (LI) is a behavioural phenomenon whereby preexposure to a stimulus without reinforcement interferes with the formation of subsequent associations to that stimulus. Using preexposure to a tone stimulus which subsequently serves as a conditioned stimulus for suppression of licking, we have confirmed that LI is disrupted by a low dose of amphetamine. Haloperidol was able to prevent this effect of amphetamine. Ondansetron, a selective and potent 5HT3 receptor antagonist, was also shown to be effective at blocking the amphetamine-induced disruption of LI at a dose of 0.01 mg/kg, but not at 0.1 mg/kg. In addition, it was demonstrated that ondansetron could enhance LI; using only ten preexposures, no LI was obtained in the saline group, but was apparent in animals given ondansetron, an effect which has been previously shown with haloperidol. Haloperidol, at the higher dose used, reduced suppression of licking, however, ondansetron at the effective dose had no such effect. It is concluded that ondansetron is able to attenuate increases in dopamine activity, produced pharmacologically with amphetamine without affecting baseline dopamine activity. The implications of these findings for a possible antipsychotic action of ondansetron are discussed.

Effects of methamphetamine and ethanol on learning and brain neurotransmitters in rats

The interactions of methamphetamine (MAMP) and ethanol (EtOH) on multiple active/passive avoidance performance and neurotransmitters in different brain regions were examined. After the acquisition schedules, rats were retrained under the influence of MAMP (2 mg/kg/day, IP), EtOH (2 g/kg/day, IP), and in combination over 20 days in rats (n = 6 per group). As a function of progress of drug treatment, MAMP-EtOH mixtures disrupt the learned avoidance performance and produced severe impairment of discriminative behavior caused by enhancement of excitability induced by MAMP when compared with MAMP only. At withdrawal, MAMP-EtOH-induced impairments of performance significantly persisted, whereas MAMP-only-induced impairments slightly recovered. At the eleventh day drug withdrawal, MAMP-only-induced alterations of neurotransmitter levels at different regions were alleviated by EtOH, but these did not return to normal levels. These data provide support for the direct antagonistic and indirect additive interactions following constant daily treatment with a combination of MAMP and EtOH. EtOH may be an important factor in MAMP abuse to MAMP-induced psychosis or neurotoxicity.

Dopaminergic and noradrenergic modulation of amphetamine-induced changes in auditory gating

Dopaminergic and noradrenergic mediation of central sensory gating were assessed in Sprague-Dawley rats using a condition-test paradigm in which auditory evoked potentials were recorded. In this paradigm, unmedicated rats 'gate', i.e. suppress the response to the second of a pair of clicks delivered at a 0.5 s interval. Amphetamine-treated rats fail to gate; in this respect, they resemble schizophrenic humans. Previous studies had indicated noradrenergic involvement in the mediation of auditory gating in rats. In this study, we used selective antagonists to assess the contribution of alpha- and beta-adrenergic receptors, and dopamine D1- and D2-receptors, to amphetamine-induced alterations in gating. Both the alpha-antagonist, phentolamine, and the beta-antagonist, timolol, normalized gating by potentiating amphetamine-induced decreases in the amplitude of the test response. SCH 23390, a D1-receptor antagonist, also normalized gating, but by elevating the amphetamine-reduced amplitude of the conditioning response. Sulpiride did not significantly alter amphetamine-induced changes in gating. Thus, both noradrenergic alpha- and beta-receptors and dopamine D1-receptors appear to modulate gating. However, their dissimilar means of normalizing gating suggests that noradrenergic and dopaminergic drugs act via different mechanisms and possibly different neuroanatomical loci.

The effects of amphetamine preexposure on electrical kindling of the hippocampus and related transfer phenomena

Earlier research has established that repeated amphetamine administration can interact synergistically with the processes responsible for the genesis of kindled seizures after intermittent electrical stimulation of the amygdala. In this study, the effects of amphetamine preexposure on primary hippocampal kindling, secondary kindling of the contralateral amygdala, and rekindling of the original hippocampal focus were evaluated. It was shown that amphetamine treatment did not modify kindling rates when electrodes were situated in the dorsal hippocampus. However, transfer kindling of the contralateral amygdala evolved after fewer afterdischarges, and rekindling of the dorsal hippocampus progressed significantly faster in amphetamine-pretreated animals. The effects of amphetamine on ventral hippocampal kindling were also determined, and it was found that although epileptogenesis developed more rapidly relative to the dorsal region of this structure, kindling rates were not affected by amphetamine preexposure. These results were related to the possibility that the amygdala might have a unique function in the relationship between kindling- and stimulant-induced sensitization effects.

Concurrent medical illness in the schizophrenic patient. Epidemiology, diagnosis, and management

The management of the medically ill schizophrenic patient presents a dual dilemma for the physician. The patient may have a serious medical illness that must be diagnosed and effectively treated, yet the patient's psychiatric disorder may interfere with effective management. Thus, undiagnosed and untreated medical illness can result in significant morbidity for schizophrenic patients. Because schizophrenic patients may appear to be less cooperative than medical patients without concurrent psychiatric illness, they can cause countertransference reactions on the part of physicians and nursing staff that can interfere with treatment. Schizophrenic patients also have deficits in the processing of sensory information. These deficits require the staff to make changes in management in order to facilitate the patient's ability to cooperate with treatment and to give reliable informed consent. A host of other factors complicate the medical management and treatment of schizophrenic patients. Such factors include medication side effects of psychotropic medication, the potential interactions between medications used to treat the patient's physical illness with psychotropics, pregnancy in the female patient, and the strength of the patient's support system. The ability to successfully diagnose and treat concurrent medical illness in the schizophrenic patient will depend on the physician's ability to be flexible and to understand the implications of the patient's underlying disorder for his relationship to hospital staff. This paper reviews some of the relevant literature and describes possible treatment strategies integrating what we know about schizophrenia with medical management.

Acute and long-term amphetamine treatments alter extracellular ascorbate in neostriatum but not nucleus accumbens of freely moving rats

The ability of amphetamine to alter the extracellular level of ascorbate, an apparent modulator of neostriatal function, was assessed voltammetrically in the neostriatum and nucleus accumbens of awake, behaving rats. Whereas acute administration (1.0 and 5.0 mg/kg d-amphetamine) produced a dose-dependent rise in neostriatal ascorbate, there was no change in the nucleus accumbens. Vehicle injections had no significant effect on ascorbate levels in either location. Administration of 5.0 mg/kg d-amphetamine for one week enhanced neostriatal ascorbate release even further, but this effect returned to acute levels when treatment continued for a second week. Multiple amphetamine injections for up to two weeks failed to alter extracellular ascorbate in the nucleus accumbens. The results of these experiments confirm a site-specific action of amphetamine on ascorbate release and suggest complex changes in the extracellular level of this substance in the neostriatum with long-term treatment.

Effects of cat exposure and cat odors on subsequent amphetamine-induced stereotypy

The effect of exposure to a cat, as a predatory stressor, was examined in male and female rats during subsequent tests of amphetamine-induced stereotypy in which cat odors were present or absent. Rats in Group C/O were given a 15-min exposure session to a male cat while they were protected in a wire cage. They were then given an IP injection of d-amphetamine (1 mg/kg) and tested 30 min later for stereotypy in the presence of cat odors (soiled cat litter). Rats in Group NC/O were given a no-cat-exposure control session, and amphetamine tested with cat odors. Groups C/NO and NC/NO were both tested without cat odors (fresh litter), with the former group having been previously exposed to a cat. During the 90-min test sessions, female rats showed significantly more stereotypy than males. More importantly, the male subjects in group C/O exhibited significantly more stereotypy than the males in the other groups, and group NC/NO males showed the least amount of stereotypy. These findings clearly indicate that amphetamine reactivity is influenced by prior exposure to a predator, the presence of predatory odors during testing, and the subject's sex.

Effects of lithium on an amphetamine animal model of bipolar disorder

1. This study examines the effects of chronic lithium administration on changes induced by amphetamine administration and withdrawal on open field locomotor activity of rats, and considered as an animal model of behaviors displayed in bipolar disorders. 2. For 21 days, rats were administered either single daily intraperitoneal injections (IP) of 0.9% saline, 0.15 mEq/kg, or 1.5 mEq/kg lithium chloride (LiCl). From day 7 to day 16, half of the animals in each group consisting of 12 rats were administered twice daily IP injections of either 1.5 mg/kg d-amphetamine or 0.9% saline. From day 17 to 21, d-amphetamine was withdrawn. 3. Neither dose of LiCl significantly altered the increases in activity levels produced by amphetamine. The withdrawal of amphetamine lead to an immediate return to baseline activity levels which neither dose of LiCl significantly affected. 4. The absence of interactive effects suggests that the influence of lithium and amphetamine on activity are mediated by different neurotransmitter systems.

Sensitization to amphetamine and tolerance to cocaine and phencyclidine stimulation in mice

Amphetamine (1.0-7.0 mg/kg), cocaine (5.0-40.0 mg/kg) and phencyclidine (1.0-7.0 mg/kg) increased acoustic startle responding in mice. These drugs, however, had varying effects on habituation of the startle response after repeated exposure to the auditory stimulus. The primary effect of phencyclidine was to disrupt the habituation process, whereas increased startle responding after cocaine developed without modification of the habituation curve. Amphetamine facilitated acoustic startle at all doses, and after administration of 3.0 mg/kg a significant response sensitization as a function of repeated stimulus presentation was evident. Consistent with previous reports the excitatory effects of cocaine and amphetamine on acoustic startle were blocked by pretreatment with haloperidol. Haloperidol, which decreased startle responding, attenuated the facilitating effects of PCP on acoustic startle as well. Chronic exposure to amphetamine, cocaine and phencyclidine had differential effects on startle responding. The facilitating effects of amphetamine on startle were further enhanced after long-term exposure to the drug and the sensitizing effect of repeated amphetamine exposure was observed only when animals were tested with amphetamine. In contrast, tolerance developed after chronic exposure to both cocaine and phencyclidine, and the response attenuation was evident when animals were tested for acoustic startle after cocaine, amphetamine and phencyclidine.

Stressor invoked exacerbation of amphetamine-elicited perseveration

The provocation of stimulus preservation induced by amphetamine in a Y-maze was appreciably enhanced in animals that had been exposed to uncontrollable shock, whereas controllable shock did not influence performance. The enhancement of the stimulus perseveration was evident irrespective of whether the stressor was applied immediately or 72 hr prior to the perseveration test, provided that the stimulus complex in which shock was delivered was similar to that in which the perseveration test was conducted. When the two environments were distinctively different from one another the enhancement of stimulus perseveration was evident immediately after shock exposure, but not 72 hr after shock. It is suggested that stressors may have long-term effects of amphetamine-elicited perseveration, but the expression of such an effect is dependent upon the stimulus context in which the behavior is examined. Moreover, it is suggested that evaluation of amphetamine-induced behavioral changes, and possibly amphetamine-elicited and idiopathic psychosis, should consider the stress history of the organism.

Biochemical and behavioral changes in rats during and after chronic d-amphetamine exposure

Two groups of rats were implanted with ALZET minipumps to deliver vehicle or a theoretical amount of 1 mg/kg per h of d-amphetamine (A) for 12 days. After 3 days of A-exposure, motor movements and stereotypic behavior were markedly increased. Subsequent testing during A-exposure showed that motor movements and stereotypic behavior remained significantly increased but declined. After removal of the pumps, these effects disappeared and no differences at rest, during stress or A challenge, were apparent in either group. Animals sacrificed after 3 days of drug exposure, showed a drastic decrease in cardiac, but not adrenal, catecholamine levels. In the brain, norepinephrine (NE) levels were markedly decreased in the frontal cortex, hypothalamus, caudate, pons-medulla and cerebellum. Epinephrine (E) levels were unaffected and dopamine (DA) levels were decreased in most areas without reaching statistical significance. Plasma corticosterone levels were similar in both groups. Animals in both groups sacrificed about 25 days after pump removal were biochemically similar. Under our conditions, A-exposure produced marked behavioral and biochemical changes but there was no evidence of residual abnormalities after cessation of drug treatment.

Dopamine-sensitive alternation and collateral behaviour in a Y-maze: effects of d-amphetamine and haloperidol

The degree of alternation of arm choice in a Y-maze was examined on 15-min tests over 4 days in rats treated (IP) with saline, amphetamine (0.5 or 2.0 mg/kg) or pretreated with haloperidol (0.08 mg/kg) in each condition prior to test. On day 1 amphetamine-treated animals chose arms at random, but from day 2-4 those receiving the higher dose perseverated their choice. Controls maintained alternation. These effects could be prevented by haloperidol pretreatment. Amphetamine treatment increased the frequency of rearing at the middle, choice-point of the maze more than at the end of an arm. The increase at the mid-point was suppressed by haloperidol pretreatment from day 1 and at the end of an arm from day 2. Amphetamine induced an increase in head-turning/"looking" that was suppressed by haloperidol from day 2. The effect of haloperidol in increasing the duration of an item of looking or rearing at the end of an arm also started later in testing. Two effects are postulated to have occurred: (i) a conflict on day 1 between novelty-controlled sensory or attentional effects that leads to an alternation of arm choice and amphetamine-induced dopaminergic activity that facilitates an alternation of behavioural responses. The result was random choice and increased rearing at the choice point. (ii) On days 2-4 the drug-induced effects on switching motor responses came to control behaviour.

Atypical neuroleptics clozapine and thioridazine enhance amphetamine-induced stereotypy

The effects of the atypical neuroleptics clozapine and thioridazine and the typical neuroleptic pimozide on amphetamine-induced behavior were examined. Pimozide, as expected, blocked both amphetamine-induced locomotion and stereotypy. Thioridazine and clozapine antagonized the increases in locomotion produced by amphetamine, but produced increases in amphetamine-induced stereotypy and lowered the threshold dose for stereotypy. It is suggested that the increased stereotypy might partly account for the decreased locomotion, and that this might be a primary effect of these atypical neuroleptics. The data would also suggest that the use of amphetamine-induced stereotypy as a model for psychosis is inappropriate, as clozapine and thioridazine, which enhance stereotypy, are antipsychotic.

Sensitization to the effects of repeated amphetamine administration on intracranial self-stimulation: evidence for changes in reward processes

The effects of daily administration of 1.0 mg/kg of D-amphetamine for 20 consecutive days on self-stimulation responding from the substantia nigra, and nucleus accumbens were evaluated at several current intensities. Raising current intensity increased rates of responding when electrodes were situated in these areas, and amphetamine significantly enhanced rates of responding from both brain regions. Moreover, the drug-induced response enhancements were facilitated further after repeated drug/test pairings. Although response sensitization was observed at several current intensities, it developed sooner at the lower current levels indicating that the sensitizing effect of repeated drug administration on self stimulation responding was not due to variations in locomotor activity or arousal levels induced by amphetamine treatment. Furthermore, sensitization was observed at current levels that engendered both high and low levels of responding, suggesting that the sensitization was unrelated to the rate dependent effects of the drug. Rather, it was argued that repeated amphetamine treatment sensitized animals to the rewarding properties of electrical brain stimulation. Possible neurochemical and behavioral mechanisms that may be involved in the development of reverse tolerance after repeated amphetamine treatment were discussed.

Effects of chronic intermittent and continuous amphetamine administration on acoustic startle

Acoustic startle was evaluated after mice were exposed to two different schedules of long-term amphetamine treatment. Under one schedule, mice received two daily subcutaneous injections of d-amphetamine for 7 consecutive days, whereas the other consisted of continuous administration of amphetamine via a subcutaneously implanted minipump. The enhanced acoustic startle observed after a test dose of d-amphetamine (3.0 mg/kg) was further facilitated when animals were exposed to long-term intermittent amphetamine administration. In contrast, the enhanced startle response to amphetamine was attenuated when mice received chronic continuous exposure to amphetamine. Possible behavioral and neurochemical mechanisms that may be involved in the development of tolerance after continuous amphetamine administration, and reverse tolerance after intermittent amphetamine treatment were discussed.

Dopamine and schizophrenia: an analysis of the theory

The postulated relationship of dopamine to schizophrenia ranks among the most important contemporary theories pertinent to the biological bases of behavior. However, as an examination of the relevant research literature makes clear, the theory has not yet been convincingly validated. This lack of validation is due, in part, to a failure to address the following questions: Is dopamine hyperactivity an etiological and/or a symptom factor in schizophrenia; do laboratory measures used to test the theory truly parallel the relevant clinical phenomena; is attenuated dopamine activity a necessary and/or sufficient condition for remission of schizophrenic symptoms? Analysis of these questions not only provides a departure point for examining the theory, but sets the stage for a reformulation of the theory itself.

The behavioral and biochemical effects of lithium on dopaminergic agonist-induced supersensitivity

Dopaminergic behavioral supersensitivity may be induced by chronic treatment with either dopaminergic agonists or antagonists. We demonstrate that the development of agonist-induced supersensitivity is resistant to chronic lithium exposure. Furthermore, chronic lithium alone enhances the stereotypic response to acute dopamine agonist administration and this effect of lithium summates with the behavioral augmentation caused by chronic amphetamine exposure. Although marked dopamine-related behavioral changes occur, chronic treatment with amphetamine, lithium, or both had no effect on levels of DA, DOPAC, HVA, and 3MT in either the striatum or nucleus accumbens. These results suggest that chronic amphetamine treatment with or without lithium does not affect presynaptic dopamine metabolism as assessed by metabolite levels. Furthermore, amphetamine-induced behavioral supersensitivity is not a simple function of changes in dopamine metabolism.

The effects of chronic amphetamine administration on the acquisition and extinction of an active and passive avoidance response in mice

Long-term amphetamine treatment had no effect on the acquisition or retention of an active or passive avoidance response. In both tasks, however, mice withdrawn from chronic amphetamine administration showed a resistance to extinction relative to control animals. These findings were related to the effects of long-term amphetamine administration on attentional processes. Possible neurochemical mechanisms governing the attentional deficits induced by chronic exposure to amphetamine were discussed.

Amphetamine: differential effects on defensive flight and motor behavior in the rat

As in previous research, hooded rats treated with an acute high dose of d-amphetamine sulfate (5 mg/kg free base) showed a dramatic defensive flight reaction to a novel stimulus (mechanical robot) that did not elicit flight from saline controls. Both the defense response and stereotypy behavior (repetitive movements and oral, licking chewing) were assessed at eight time periods after injection: 1, 15, 30, 45, 75, 105, 135, and 165 min. The defense response peaked early (15-30 min) after injection and showed a significant decline by 75 min, with no reemergence as stereotypy subsided. Stereotypy peaked later (45 min) and did not decline until 105 min. Tests in the absence of the robot provided a control for motor effects of the drug. Whereas stereotypy occurred in both Robot and No Robot conditions, the defense response occurred only in the Robot condition. These results were thought to provide further evidence that the effects of amphetamine on defensive flight could not be attributed to purely motor reactions. Thus, amphetamine-induced defensive flight may be an appropriate pharmacological model of affective psychosis. As such, it may be helpful in establishing differential pharmacological profiles for affective versus motor potencies of potential antipsychotic compounds.

Centrally mediated effects of neurohypophyseal hormones

The neurohypophyseal hormones oxytocin and vasopressin cause a variety of biological effects in animals which are mediated by central nervous system mechanisms. Among the best studied of these effects is the modulation of both memory processes and the development of drug tolerance and dependence. Neurohypophyseal hormones have also been shown to alter various physiological parameters such as heart rate and body temperature following central administration. In addition, these peptides can profoundly alter spontaneous, unlearned behavior in several rodent species. Many of the centrally mediated effects of neurohypophyseal hormones have been shown to be elicited at sites within the brain stem and the limbic system where vasopressin and oxytocin occur in cell bodies, axons and nerve terminals, suggesting a physiological role for these peptide effects. The various central effects of neurohypophyseal hormones involve different mechanisms which can be distinguished from one another on the basis of required dose, time-course of action, and structure-activity relationships. Thus, alterations of spontaneous behavior are mediated by putative receptors closely related to vasopressin receptors in blood vessels responsible for the peripheral pressor response while the effects on memory processes are mediated by a mechanism which is not closely related to those involved in the peripheral hormonal effects of the peptides. The influence of neurohypophyseal hormones on memory and attention may be useful clinically. A potential role for these peptides in mental disorders is discussed.

Behavioural tolerance to amphetamine and other psychostimulants: the case for considering behavioural mechanisms

An hypothesis is presented about the nature of behavioural tolerance in animals to stimulant drugs. It is suggested that, in many behavioural procedures, tolerance is due to behavioural adaptation to those drug effects which cause disruption of ongoing rewarded behaviour. This unitary hypothesis accounts for the available data on tolerance and cross-tolerance to stimulants more effectively than all of the other more conventional explanations which are based upon dispositional or functional concepts, the most common of which are described, evaluated, and found to be inadequate. Furthermore, it is suggested that attempts to explain tolerance in terms of changes in synaptic functioning are subject to very considerable problems of interpretation and that an analysis of behavioural mechanisms may be of greater value in understanding the process of behavioural tolerance. Evidence for the basic behavioural hypothesis is outlined in some detail, and a theoretical justification presented for its major assumptions. Operant studies of chronic stimulant effects on behaviour have often produced very complex patterns of data, considerable differences being reported both between subjects and between studies. A speculative model is presented which attempts to account for this pattern of data in tolerance studies.

Stress-induced facilitation of acoustic startle after d-amphetamine administration

Administration of d-amphetamine enhanced the startle response to an auditory stimulus. In contrast to saline treated mice, startle activity after amphetamine administration did not wane with repeated exposure to the auditory stimulus. Rather, the effects of amphetamine on startle activity increased as a function of stimulus presentation. Whereas exposure to isolation stress or inescapable shock had no effect on startle activity, both types of stress potentiated the effects of amphetamine on startle arousal. The observation that stress sensitized animals to later amphetamine administration is consistent with the effects of stress on other amphetamine behaviors, e.g., stereotypy. Results were related to the development of dopamine post-synaptic receptor supersensitivity after exposure to stress and were discussed in terms of the role played by stress in the expression of behavioral arousal, in the etiology of schizophrenia.

Potentiation of d-amphetamine and L-dopa-induced acoustic startle activity after long-term exposure to amphetamine

The startle response to an auditory stimulus was potentiated by treatment with d-amphetamine sulfate. Administration of L-dopa after pretreatment with the extracerebral decarboxylase inhibitor MK-486 also increased startle activity. After long-term exposure to amphetamine the startle response to L-dopa and d-amphetamine was enhanced. These findings are consistent with the consequences of long-term amphetamine administration on other amphetamine-induced behaviors (e.g. stereotype), and are discussed in terms of the effects of long-term amphetamine treatment on pre- and postsynaptic dopamine receptors and serotonin.