D-amphetamine Sulfate Research Articles

Extinction procedures abolish conditioned stimulus control but spare sensitized responding to amphetamine

The effect of extinction on previously established environment-specific sensitization of the locomotor activating effects of 1.0mg/kg d-amphetamine sulfate was studied in an attempt to investigate the relation between sensitization and conditioning of the drug effect. During the conditioning phase, groups of eight rats each were administered drug, i.p., prior to being placed in activity boxes and saline in their home cages (paired group), drug in the home cages and saline in the activity boxes (unpaired group), or saline in both environments. Evidence for conditioning and environment-specific sensitization was found following the conditioning phase in tests during which animals were administered saline or amphetamine, respectively. On a final test for environment-specific sensitization that followed the extinction phase (during which all animals received saline injections in both the activity boxes and the home cages), sensitized responding to amphetamine was found in both the paired and unpaired groups, suggesting that prior to extinction the expression of sensitization in the unpaired group had been under inhibitory control.

Methodological issues in drug-drug conditioning in rats: nonassociative factors in heart rate and avfail.

Sodium pentobarbital injections followed 30 min later by d-amphetamine sulfate produce an effect over trials in the form of an increase in heart rate in response to pentobarbital in relation to rats that receive the 2 drugs 24 hr apart (long-delayed control: Revusky, Davey, & Zagorski, 1989). This study found equivalent increases in heart rate in forward and backward groups in relation to a long-delayed control regardless of whether training or testing was carried out in a heart rate recording apparatus or in the home cage, which suggests that a drug interaction due to drug administrations in forward and backward groups has yet to be eliminated in accounting for the heart rate effect. Comparison of backward and long-delayed controls in a drug-drug procedure that used a taste aversion test revealed that both forward and delayed pairings can produce attenuated aversions in relation to a backward group regardless of whether the unconditional stimulus is amphetamine (Experiment 1) or lithium chloride (Experiment 2).

Dietary influences on the acute effects of anorectic drugs

The effects of acute administration of d-amphetamine sulfate (0.0, 0.5, 1.0 and 2.0 mg/kg) and dl-fenfluramine hydrochloride (0.0, 1.5, 3.0 and 6.0 mg/kg) on food intake were examined in male Sprague-Dawley rats fed either a high-carbohydrate diet (carbohydrate equaled 65% of total calories) or a high-fat diet (fat equaled 65% of total calories). Animals were given ad lib access to the diets throughout the experiment. Drug injections were given at 0900 on experimental days and food intakes were measured at 1, 3 and 6 h postinjection. Amphetamine led to dose-related decreases in food intake for animals on both diets. The effects of amphetamine were most noticeable at 1 and 3 h postinjection. No differences in amphetamine's effects on food intake were found as a function of diet. Fenfluramine injections also led to dose-related reductions in food intake for animals in both dietary conditions. In contrast to amphetamine, however, fenfluramine led to greater reductions in food intake for rats fed the high-fat diet than for rats fed the high-carbohydrate diet. These data demonstrate that dietary variables must be considered when evaluating the anorectic actions of psychopharmacological agents.

Nuclear magnetic resonance determination of flow, lactate, and phosphate metabolites during amphetamine stimulation of the rat brain

The effects of amphetamine on rat cerebral blood flow, lactate, and phosphate levels were studied using in vivo nuclear magnetic resonance (NMR) spectroscopy. Proton NMR imaging was used to determine the region of brain being studied. Blood flow was estimated by detecting the washout of trifluoromethane using 19F NMR. A dose of 20 mg/kg D-amphetamine sulphate stimulated flow fourfold over control values for at least 1 h. Even though amphetamine stimulated a large increase in flow, there were no significant changes in levels of inorganic phosphate, ATP, phosphocreatine, pH or Mg2+ as determined by 31P NMR. This was true for doses of 10 and 20 mg/kg D-amphetamine sulphate. No significant changes occurred in 1H NMR detected levels of lactate with a 20 mg/kg dose of amphetamines. Lactate levels increased slightly 30 min after administration of 10 mg/kg D-amphetamine sulphate. The results call into question the central role of changes in levels of phosphates in coupling increased cortical activity to increases in metabolism.

Effects of dietary tyrosine on L-dopa- and amphetamine-induced changes in locomotor activity and neurochemistry in mice

Recent findings suggest that intraperitoneal injections of L-tyrosine at high doses (100 mg/kg) alters amphetamine-induced changes in behavior by restoring amphetamine-induced decreases in whole brain norepinephrine (NE). The present study examined the motor effects of L-dihydroxyphenylalanine (L-dopa) and d-amphetamine sulfate in mice after treatment with a basal casein diet supplemented with L-tyrosine. The basal diet supplemented with 1–4% L-tyrosine, or 1–4% L-phenylalanine, produced no changes in motor activity in otherwise untreated mice. Whereas L-dopa (25–100 mg/kg) following inhibition of extracerebral decarboxylase by Ro 4-4602 (25 mg/kg) slightly decreased activity in diet control (casein) animals, this drug treatment enhanced motor activity in a dose-related fashion when L-tyrosine was added to the diet. Increases in motor activity following low doses of amphetamine (0.75–1.5 mg/kg) in casein control mice were antagonized by dietary L-tyrosine, but a higher dose of d-amphetamine (3 mg/kg) interacted with the addition of L-tyrosine producing an increase in motor activity. Neurochemical changes observed in brain concentrations of tyrosine, dopamine (DA), norepinephrine (NE), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), tryptophan, serotonin (5-HT) and 5-hydroxy-indoleacetic acid (5-HIAA) following drug and diet treatment suggest that 5-HT systems, in addition to catecholamine systems, may be involved in mediating these effects.

Role of D-1 and D-2 receptor stimulation in sensitization to amphetamine-induced circling behavior and in expression and extinction of the Pavlovian conditioned response

Circling behavior was measured in female rats treated with amphetamine (1.25 mg/kg d-amphetamine sulfate, IP) on 3 consecutive days. On days 4 and 5 saline was substituted for amphetamine. While the amphetamine-induced response was attenuated by both a D-1 (SCH 23390) and a D-2 (metoclopramide) antagonist. sensitization to amphetamine was attenuated by the D-1 antagonist only. In addition, expression of a placebo-like response observed on day 4 (characterized previously as a Pavlovian conditioned response) was attenuated by both the D-1 and D-2 antagonists without disrupting extinction of the response.

Effects of paraventricular hypothalamic microinjections of phenylpropanolamine and d-amphetamine on mash intake in rats

The present experiment compared the effects of unilateral microinjections (40, 80 and 160 nmol/0.5 μl) of phenylpropanolamine (PPA: d,1-norephedrine) and d-amphetamine sulfate within the paraventricular hypothalamus (PVN) on consumption of a palatable sweetened-mash diet in 15-hour food-deprived adult male rats. Intracranial microinjections were administered 5 minutes prior to each 30-minute feeding trial. PPA, at a dose of 160 nmol, suppressed feeding by 42%, whereas a similar dose of amphetamine suppressed feeding by 49%. Amphetamine or PPA doses of 40 and 80 nmol were without significant effect on feeding behavior. A relatively high dose of 160 nmol amphetamine was required to suppress feeding after injection into the PVN whereas much lower amphetamine concentrations are required to suppress feeding after injection into the perifornical hypothalamus. In contrast, PPA has some anorexic activity within the PVN but not within the perifornical hypothalamus.

Dose effects on heart rate conditioning when pentobarbital is the CS and amphetamine is the US

If sodium pentobarbital is injected into rats 30 min prior to d-amphetamine sulphate on four or five occasions, there is a learned effect of pentobarbital on heart rate. The conditioned response is a higher heart rate than found in rats with a control history of exposure to the same drugs. In Experiment 1, when the pentobarbital dose was 32 mg/kg throughout, this effect was obtained with amphetamine doses of 2, 4, 8, or 16 mg/kg. In Experiment 2, when the amphetamine dose was 12 mg/kg throughout, pentobarbital doses of 16 and 32 mg/kg yielded conditioning, while 8 mg/kg yielded equivocal results.

Haloperidol prevents the reinstatement of amphetamine-rewarded runway responding in rats

Animals were trained to traverse a straight-alley once each day for a reward of 1.0 mg/kg SC d-amphetamine sulfate. After 14 days of acquisition, extinction trials were initiated in which the amphetamine reward was replaced by injections of physiological saline. After running speeds had decreased to less than one third those of preextinciton values, rats recieved a single amphetamine-rewarded trial either in the absence or presence of haloperidol (0.075, 0.15 or 0.3 mg/kg IP). Twenty-four hours later, animals were tested for reinstatement of operant running in a single drug-free Test trial. Animals that were nondrugged during the amphetamine-rewarded trial demonstrated a statistically reliable increase in running speed on the Test trial relative to extinction baseline speeds. In contracts, animals that were unde the influence of medium or high doses of haloperidol during the amphetamine-rewarded trial failed to show Test day increases in running speed. This result did not stem from some residual sedative or performance impairing quality of the drug since a “motor control group” administered a high dose of haloperidol shortly after a rewarded trial, was able to demonstrate unimpaired reinstatement of operant running on Test day (i.e., 24 hr later). These findings support the view that dopamine systems play a role in the neural substrates underlying the incentive motivational properties of amphetamine reinforcement.

Histological and ultrastructural evidence thatd-amphetamine causes degeneration in neostriatum and frontal cortex of rats

d-Amphetamine sulfate, continuously administered for 3 days subcutaneously via an implanted minipump, induced neural degeneration in Long-Evans and Sprague-Dawley rats at doses between 20 and 60 mg/kg/day. Using Fink-Heimer silver staining, axonal degeneration was detected in the neostriatum and the dorsal agranular insular cortex and degenerating pyramidal cells were observed in portions of the somatosensory neocortex in both strains. In contrast, dense axonal degeneration largely confined to layers 2 and 3 of frontal motor areas (Fr1, Fr2 and Fr3 of Zilles36) with occasional degenerating cells was seen reliably in Long-Evans rats but rarely in Sprague-Dawley rats. In the electron microscope, cortical degeneration consisted mainly of disrupted cell bodies and dark processes, including axons making asymmetric synapses. Damage in all cortical areas represents damage to non-monoamine neurons and processes since tyrosine hydroxylase and serotonin immunolabeling were normal. In contrast, the damage in neostriatum probably includes damage to dopamine axonal terminals since tyrosine hydroxylase immunolabeling was patchy with many swollen and distorted labeled axons. Serotonin and Leu-enkephalin labeling were normal. Electron microscopy confirmed that the neostriatum contained many tyrosine hydroxylase-labeled axons that were swollen and disrupted, although other labeled processes made normal symmetric synapses onto spines and dendrites. Additional degeneration found only in amphetamine-treated rats included many dark, shrunken profiles. Some of these appeared to be astrocytic processes and a few were myelinated axons, suggesting that some non-monoamine, possibly cortical afferents, are also degenerating in the neostriatum. Since similar degrees of behavioral activation, weight loss and lethality were seen in both strains, a genetic predisposition constrain amphetamine-induced motor cortex damage but not neostriatal damage.

Acute effects of d-amphetamine in a monkey operant behavioral test battery

The acute effects of d-amphetamine were assessed using a battery of complex food-reinforced operant tasks that included responding in delayed matching-to-sample (DMTS, n=6), conditioned position responding (CPR, n=7), progressive ratio (PR, n=8), temporal response differentiation (TRD, n=4), and incremental repeated acquisition (IRA, n=9) tasks. Performance in these tasks is thought to depend upon specific brain functions such as short-term memory and attention (DMTS), color and position discrimination (CPR), motivation to work for food (PR), time perception (TRD), and learning (IRA). d-Amphetamine sulfate (0.01–1.0 mg/kg IV), given 15-min presession produced significant dose-dependent decreases in the number of reinforcers obtained in each task. Response accuracy was significantly decreased at doses of 0.3 and 1.0 mg/kg for TRD and at 1.0 mg/kg for CPR when compared to saline injections. Accuracy was not consistently affected in the DMTS or IRA tasks. Response rates decreased or response latencies increased significantly at doses of 0.3 and 1.0 mg/kg in the PR and DMTS tasks. A dose of 0.1 mg/kg for the IRA and TRD tasks, 0.3 mg/kg for DMTS and 1.0 mg/kg for the CPR tasks significantly decreased percent task completed. Thus, the relative sensitivities of these tasks for detecting d-amphetamine behavioral effects were IRA = TRD > PR = DMTS > CPR. These results indicate that in monkeys, performance of operant tasks designed to model learning ability and time perception is more sensitive to the disruptive effects of d-amphetamine than is performance in tasks designed to model motivation, short-term memory and attention, which is more sensitive than tasks that model color and position discrimination.

Ontogeny of the enhanced behavioral response to amphetamine in amphetamine-pretreated rats

Repeated administration of amphetamine to adult rats results in enhanced behavioral responses to subsequent amphetamine exposure. These experiments were designed to determine the earliest age at which behavioral sensitization to amphetamine could be detected. Rats from both sexes (n = 6-8/group) at ages of 1, 7, 21 or 49 postnatal days (PNDs) were injected with either d-amphetamine sulfate (5 mg/kg) or saline, SC, twice daily for 5 consecutive days. Stereotyped behavior and locomotor activity responses to a challenge dose of d-amphetamine (2.5 mg/kg), or saline, IP, were assessed for a total of 90 min, 15 days after the last dose of pretreatment. Amphetamine-induced stereotyped behavior was significantly enhanced only when amphetamine pretreatment was initiated at PND 49, but not at the earlier ages of PND 1, 7 or 21. There was no apparent sex difference in this effect. Correspondingly, amphetamine-induced locomotor activity was reduced in both sexes of the same age group (PND 49), but not in groups pretreated earlier, when compared to the saline-pretreated rats. These results suggest that amphetamine sensitization may be a late-developing effect, one which occurs sometime after the 3rd week of postnatal life.

Effects of haloperidol on anorexia induced by 1-norephedrine and d-amphetamine in adult rats

Although amphetamine anorexia has been linked to activation of dopaminergic receptors within the lateral aspects of the hypothalamus, the receptor type by which phenylpropanolamine (PPA: the racemic mixture of d- and l-norephedrine) induces anorexia has not been identified. In the present experiment, separate groups of adult male rats were pretreated (IP) with either 0.9% saline or haloperidol (either 0.4 or 0.8 mg/kg) 45 minutes prior to treatment (IP) with either saline or 20 mg/kg l-NEP (the active enantiomer of PPA) and were then allowed 180 minutes access to food and water. Treatment with 20 mg/kg l-NEP induced comparable reductions in food intake of approximately 30% in rats pretreated with either dose of haloperidol or saline. In a sub-experiment, it was demonstrated that 1.0 mg/kg d-amphetamine sulfate reduced food intake by 25%, but this anorexic action was completely attenuated by 0.8 mg/kg haloperidol given 45 minutes prior to feeding. These results add to a growing body of literature that documents important differences between the mechanisms by which amphetamine and PPA produce their anorexic actions.

Effects of perifornical hypothalamic microinjections of phenylpropanolamine and amphetamine on latency to feed and mash intake in rats

To determine whether phenylpropanolamine (PPA) and amphetamine act on a common satiety mechanism, the present experiment compared the effect of unilateral microinjections (40, 80, and 160 nmol) of phenylpropanolamine hydrochloride (PPA: d,l-norephedrine) and of d-amphetamine sulfate within the perifornical hypothalamus (PFH) on consumption of a palatable sweetened-mash diet in adult male rats. Microinjection of d-amphetamine (40–160 nmol) within the PFH induced dose-dependent anorexia, whereas PPA microinjections were without effect on feeding. These results document that amphetamine and PPA do not act at a common CNS site, such as the PFH, to induce anorexia.

Enhanced dopamine receptor activation in accumbens and frontal cortex has opposite effects on medial forebrain bundle self-stimulation

This study was undertaken to investigate the effects of activating dopamine receptors in accumbens and prefrontal cortex on self-stimulation behavior in the medial forebrain bundle. The experiments were carried out in rats chronically implanted with one stimulating electrode in medial forebrain bundle and two bilaterally-placed cannulas for giving injections into accumbens or prefrontal cortex. After completion of training, animals classified as responders and non-responders were given drug tests. The non-responders were tested to determine the effects of the treatment on motor activity. The self-stimulation task involved the depression of a lever to obtain a stimulus of 0.25 s duration, 60 Hz sine waves applied to the medial forebrain bundle. Dopamine receptor activation in accumbens or prefrontal cortex was induced with bilateral injections in these structures of a mixture containing 5 mg dopamine, 10 mg d-amphetamine sulfate and 5 mg pargyline mixed in 0.5 ml saline containing 0.1% ascorbic acid (dopamine + d-amphetamine sulfate +4-pargyline, the cocktail). Each injection was of 2 μl/side, yielding a concentration of 20 μg of dopamine, 40 μg of d-amphetamine sulfate and 20 μg of pargyline/injection. The bilateral injections were given immediately before the self-stimulation session which lasted 12 h, starting in late afternoon. The effects of saline containing the ascorbate were determined in control sessions. Saline injected bilaterally in accumbens or prefrontal cortex of self-stimulators or non-self-stimulators had no effects on the response-rate of self-stimulators or on the gross motor activity of non-responders. In contrast, the cocktail of dopamine + d-amphetamine sulfate + pargyline injected in accumbens of self-stimulators induced a complex response which included first a facilitation, then a prolonged suppression and then again one or two episodes of facilitation interspersed with periods of suppression of self-stimulation and then a return to baseline rates. The same cocktail of dopamine + d-amphetamine sulfate + pargyline injected bilaterally in accumbens of non-self-stimulators resulted also in a complex response including as a first component a facilitation of responding, but the complex effect was of shorter duration and lower magnitude, never raising the rate of lever-pressing to levels meeting self-stimulation criteria. The same cocktail of dopamine + d-amphetamine sulfate + pargyline injected in prefrontal cortex of self-stimulators simply attenuated or suppressed responding, and the effect lasted for most of the session. The same effect was seen in non-self-stimulators indicating a decrease in gross motor activity. These data are interpreted to mean that dopamine receptors in accumbens are part of the circuitry mediating reinforcing effects of brain stimulation while dopamine receptors in prefrontal cortex are not. Furthermore, the sequence of prolonged facilitation and prolonged depression may possibly have reflected the initial large increase in released dopamine and then the decrease that could have resulted from extremely high utilization during the extended facilitatory period.

Effect of direct and indirect dopamine agonists on brain extracellular ascorbate levels in the striatum and nucleus accumbens of awake rats

Systemic administration of direct and indirect dopamine agonists resulted in increased extracellular ascorbic acid levels in the striatum and, to a lesser degree, in the nucleus accumbens as measured by in vivo voltammetry. Intraperitoneal d-amphetamine sulfate (5mg/kg) increased ascorbate concentrations in striatal extracellular fluid. Amphetamine also increased extracellular ascorbate levels in the nucleus accumbens although more gradually and to a lesser extent. Intraperitoneal phenethylamine hydrochloride (20 mg/kg) following pargyline hydrochloride pretreatment (20 mg/kg) increased extracellular ascorbate levels in the striatum significantly above the small increase seen in the nucleus accumbens. The direct acting dopamine agonists Ly-141865 and Ly-163502 when given i.p. at 1 mg/kg, resulted in increased extracellular ascorbate concentrations in both brain areas, again with a significantly greater effect in the striatum. These results indicate that brain extracellular ascorbate levels can be modulated by dopaminergic neuro-transmission and that this modulation is quantitatively different in different dopamine-containing brain structures.

Microinjections of Sch-23390 into the ventral tegmental area and substantia nigra pars reticulata attenuate the development of sensitization to the locomotor activating effects of systematic amphetamine

Pre-exposure of rats to systemic injections of d-amphetamine sulfate in the presence of bilateral injections of Sch-23390 (0.5 or 1.0 μg/side) into the ventral tegmental area (VTA) attenuated the acute locomotor effects of amphetamine and blocked the development of sensitization to amphetamine in a test when only amphetamine was administered, in a dose-dependent manner. Similar, but less potent, effects were observed following injections into substantia nigra pars reticulata. These findings suggest that dopamine released from somatodendritic regions brings about changes in local circuitry in the VTA that underlie the development of sensitization to amphetamine, and that Sch-23390 acts at D 1 receptors in these regions to block these changes.

Chemical antagonism of red-winged blackbird habituation to fright-producing auditory stimuli

We studied the feasibility of improving the efficacy of fright-producing auditory stimuli as wild bird repellents by chemically antagonizing habituation to the stimulus. Red-winged blackbirds ( Agelaius phoeniceus) were fed mealworms containing a 10 mg/kg dose of d-amphetamine sulfate and exposed to a prerecorded blackbird distress call. Heart rate (HR) and behavioral activity responses (BAR) of these birds were measured and compared to the responses of untreated birds. After an initial strong response, the HR and BAR of control birds diminished despite repeated applications of the distress call until, after 30 applications, they were near the baseline values. The HR and BAR of birds treated with d-amphetamine sulfate remained at elevated levels throughout. The treated birds' responses demonstrated that d-amphetamine sulfate was effective as an habituation antagonist. The results suggest that a nonlethal level of a central nervous system stimulant could be used to antagonize habituation of wild birds to auditory repellents, thereby enhancing their effectiveness in control programs.

Effects of repeated activation by FG-7142 of mesocortical dopamine systems

An aberrant response to stress of the prefrontal cortex (PFC) may underlie psychotic symptoms. To study the normal response we repeatedly activated PFC dopamine (DA) systems by administering FG-7142 10 mg/kg/ip or vehicle daily for ten days to rats. On the 11 th day rats received an injection of FG-7 142 or vehicle (ie. 4 groups: V/V, V/FG, FG/V, and FG/FG) and were placed in photocell monitors. One day and one week later their response to d-amphetamine sulfate 0.75 mg/kg ip was evaluated. On day 11, only the V/FG group demonstrated the usual inhibition of exploratory activity by FG-7142. On day 12 both the V/FG and the FG/FG rats showed an augmented amphetamine locomotor response but on day 19 this augmentation was evident only in the FG/FG group. Our results suggest: (1) repeated FG-7142 treatment induces behavioral tolerance to its acute locomotor inhibitory effects, (2) while a single activation of the PFC DA system increases sensitivity to amphetamine induced locomotion, the effect is prolonged by repeated PFC DA activation.

Measurement and quantification of stereotypy in freely behaving subjects: An information analysis

Stereotypy is typically defined as abnormal, repetitive, and purposeless motor behavior. In this study, stereotypy was more rigorously and generally defined in terms ofH, the typical metric for entropy, and was measured using computer-driven analyses of filtered and digitized video records. This technique was validated using rats treated with d-amphetamine, which has been shown to be an effective stimulant of traditionally defined stereotypy in a wide variety of species. Rats were treated with 0, 1, 2, and 4 mg/kg body weight d-amphetamine sulfate, and their unrestrained behavior was recorded on videotape. Our results confirm previous research that found stereotypy to occur at high doses of amphetamine. However, the present measure of stereotypy brought out additional complexities. Our results indicate that stereotypy occurred at significant levels with low drug doses, and, furthermore, that stereotypy in general was highly dependent upon the level of behavioral complexity considered. Finally, we discuss the advantages of the present metric for studying stereotypy.