Similarity between (+)-amphetamine and amfonelic acid

Rats, trained to discriminate the CNS stimulant (+)-amphetamine (1.0 mg/kg) from saline in a two-lever drug administration task, were challenged with various doses of the structurally dissimilar CNS stimulant amfonelic acid. Amfonelic acid was found to substitute for the amphetamine stimulus and was found to be 1.5 times more potent than amphetamine.     

The effects of (+)-amphetamine and fenfluramine on feeding in starved and satiated mice

(+)-Amphetamine and fenfluramine depressed both the food intake during the first 2 h of feeding of mice adapted to feed between 12:00 and 15:00 daily and the food intake of free feeding mice between 24:00 and 02:00 (lighting on, 09:00–21:00) in a dose-dependent manner. Higher doses of each drug were needed to produce a significant depression in the latter case. However, (+)-amphetamine (0.5–2 mg/kg) markedly increased the negligible food intake of free feeding mice between 12:00 and 14:00, an effect which rapidly disappeared at higher doses. Fenfluramine at doses up to 40 mg/kg had no effect on the feeding of these mice. Nevertheless, as caffeine (10–40 mg/kg) also increased feeding, behavioural arousal might be an important factor in this anomalous feeding response, although a specific action by (+)-amphetamine and caffeine on the feeding centres of the satiated mouse cannot be ruled out.     

Sex- and dose-dependency in the pharmacokinetics and pharmacodynamics of (+)-methamphetamine and its metabolite (+)-amphetamine in rats

These studies investigated how (+)-methamphetamine (METH) dose and rat sex affect the pharmacological response to METH in Sprague-Dawley rats. The first set of experiments determined the pharmacokinetics of METH and its pharmacologically active metabolite (+)-amphetamine (AMP) in male and female Sprague-Dawley rats after 1.0 and 3.0 mg/kg METH doses. The results showed significant sex-dependent changes in METH pharmacokinetics, and females formed significantly lower amounts of AMP. While the area under the serum concentration-time curve in males increased proportionately with the METH dose, the females showed a disproportional increase. The sex differences in systemic clearance, renal clearance, volume of distribution, and percentage of unchanged METH eliminated in the urine suggested dose-dependent pharmacokinetics in female rats. The second set of studies sought to determine the behavioral implications of these pharmacokinetic differences by quantifying locomotor activity in male and female rats after saline, 1.0, and 3.0 mg/kg METH. The results showed sex- and dose-dependent differences in METH-induced locomotion, including profound differences in the temporal profile of effects at higher dose. These findings show that the pharmacokinetic and metabolic profile of METH (slower METH clearance and lower AMP metabolite formation) plays a significant role in the differential pharmacological response to METH in male and female rats.     

The effects of chronic administration and withdrawal of (+)-amphetamine on seizure threshold and endogenous catecholamine concentrations and their rates of biosynthesis in mice

The i.v. pentylenetetrazol seizure threshold was increased by 2.5 mg/kg and decreased by 15 mg/kg of a single (+)-amphetamine dose. After 7 consecutive days of amphetamine administration, tolerance developed to the decrease but not to the increase in seizure threshold. At 12–48 h after the last dose of 2.5 mg/kg seizure threshold was decreased, and at 36–48 h after the last dose of 15 mg/kg seizure threshold was increased. After acute and chronic administration of (+)-amphetamine (2.5 mg/kg) endogenous concentrations of whole brain dopamine (DA) were increased and returned to normal levels during the withdrawal period (12–48 h); endogenous norepinephrine (NE) levels were unchanged by acute and chronic drug treatment and during withdrawal. The rates of DA and NE synthesis were increased by chronic amphetamine administration at 24–48 h after drug withdrawal. An acute dose of (+)-amphetamine (15 mg/kg) decreased endogenous levels of DA and NE; normal levels of DA were detected with chronic drug treatment and during withdrawal, with NE remaining slightly depressed. The rates of synthesis of DA and NE were increased by acute and chronic amphetamine treatment and returned to normal 24–48 h after withdrawal. The rebound reversal in seizure threshold after (+)-amphetamine withdrawal suggests an abstinence syndrome that may be interpreted as evidence for the development of physical dependence to (+)-amphetamine after chronic drug administration.     

6-Hydroxydopamine lesion of the dopamine mesocorticolimbic cell bodies increases (+)-amphetamine self-administration

The effect of 6-OHDA lesions of the dopaminergic mesocorticolimbic cell bodies on intravenous (+)-amphetamine self-administration in the rat was assessed. An acquisition paradigm was used in which the rat had to discriminate between an active and an inactive lever. Each press on the active lever delivered 7.5 g/kg (+)-amphetamine. The lesioned animals acquired this discrimination faster and hence self-administered a larger amount of drug. Thus dysfunction of dopaminergic neurons can induce an enhanced vulnerability to drugs which may be abused by humans.     

Acute exposure to caffeine selectively disrupts context conditioning in rats

RATIONALE AND OBJECTIVE: Acute caffeine administration has both beneficial and adverse effects on learning and memory; however, the brain regions underlying these effects remain unclear. Several experiments were conducted to examine the effects of acutely administered caffeine on the acquisition and expression of hippocampal-dependent and hippocampal-independent forms of conditioned fear. METHODS: In the first experiment, caffeine (10, 20, or 30 mg/kg; IP) or vehicle was administered to rats 15 min prior to classical fear conditioning, which consisted of ten tone-shock pairings. Freezing to the conditioning context was measured 24 h later, whereas tone-elicited fear was measured 48 h later. A second experiment examined possible state-dependent effects of caffeine by administering caffeine (30 mg/kg) or vehicle 15 min before conditioning and before testing. RESULTS: Pretreatment of acute caffeine severely impaired the acquisition of context conditioning, a hippocampal-dependent task. Tone conditioning, a hippocampal-independent task, was only modestly and non-significantly affected by caffeine (4-21% suppression compared with controls). The disruption of context conditioning was dose-dependent: 10 mg/kg had little effect on context or tone conditioning, whereas doses of 20 and 30 mg/kg caffeine severely disrupted context conditioning (73-87% suppression). In two subsequent experiments, it was found that caffeine's selective disruption of context conditioning could not be attributed to the fact that it is a weaker form of learning than tone conditioning or to state-dependent learning. CONCLUSIONS: Considered together, these results suggest that acute administration of caffeine may preferentially disrupt the acquisition of hippocampal-dependent learning, including context conditioning.     

Effects of intra-amygdala R(+) 7-OH-DPAT on intra-accumbens d-amphetamine-associated learning I. Pavlovian conditioning

We have previously obtained evidence that the mesoamygdaloid dopamine projection modulates the acquisition of a conditioned response (CR) elicited by presentation of a conditioned stimulus (CS) predicting the availability of a natural (sucrose) reward. This property was found to be dependent upon D₃, but not D₁ or D₂, dopamine receptor activation. The aim of the present study was to determine whether the mesoamygdaloid dopamine projection is similarly involved in the acquisition of a drug-associated CR. Thus, two groups of rats with guide cannulae aimed at the nucleus accumbens and amygdala were trained using a Pavlovian conditioning procedure in which an initially neutral CS was paired with a computer-controlled, bilateral intra-accumbens infusion of d-amphetamine (the unconditioned stimulus; US). Conditioning sessions were conducted in standard operant chambers, with each session consisting of a single CS-US trial. For one group of rats, CS presentation was positively correlated with the drug US (Paired group), while for the second group CS and US presentations were negatively correlated (Unpaired group). During training, locomotor activity was recorded and was utilised as the measure both of the unconditioned (UR) and conditioned response (CR). A within-subjects design was utilised to investigate the effect of post-session bilateral intra-amygdala administration of R(+) 7-OH-DPAT on the development of the drug-associated CR. Hence, both Paired and Unpaired groups were exposed to two different CSs which were presented on alternate sessions. Post-session bilateral intra-amygdala administration of R(+) 7-OH-DPAT (10 nmol) followed sessions in which one CS was presented, while intra-amygdala vehicle followed sessions in which the alternate CS was presented. The development of a CR occurred only in the presence of a CS that had been positively correlated with presentation of the drug US. Post-session, intra-amygdala administration of R(+) 7-OH-DPAT enhanced the acquisition of this CR. However, R(+) 7-OH-DPAT was without effect upon the unconditioned response to intra-accumbens d-amphetamine. Our previous data indicate a comparable effect of R(+) 7-OH-DPAT on conditioning to a CS associated with a non-drug, natural reward. Therefore, taken together, these findings suggest that D₃ dopamine receptors within the amygdala modulate specifically the acquisition of Pavlovian conditioned responses, regardless of whether drug or natural rewards constitute the US. Received: 28 November 1997/Final version: 9 April 1998     

The transport of (+)-amphetamine by the neuronal noradrenaline carrier

Summary PC-12 cells (a clonal line of rat phaeochromocytoma cells) take up noradrenaline by a transport system which is identical with the neuronal amine transport system (uptake₁). The uptake of ³H-noradrenaline into reserpine-pretreated PC-12 cells (monoamine oxidase inhibited) was saturable (K_m=0.6±0.1 mol/l), dependent on sodium and chloride, and competitively inhibited by (+)-amphetamine (K_i=0.18±0.04 mol/l), cocaine (K_i=0.55±0.15 mol/l) and desipramine (K_i=4.3±0.6 nmol/l). The uptake and accumulation of ³H (+)-amphetamine showed characteristics comparable to those of ³H-noradrenaline, since the uptake of ³H (+)-amphetamine (0.1 mol/l) was reduced by omission of sodium or chloride from the incubation medium. The sodium-sensitive component of uptake and accumulation of ³H (+)-amphetamine was fully inhibited by cocaine and desipramine. The IC₅₀ of desipramine for inhibition of the sodium-sensitive component of the 1-min uptake of ³H (+)-amphetamine (20 nmol/l) was about 2 nmol/l, i.e., identical with the K_i for inhibition of uptake of ³H-noradrenaline. At concentrations above 1 mol/l, desipramine additionally caused an inhibition of the sodium-independent permeation of ³H (+)-amphetamine into PC-12 cells.Hence, by using a homogeneous population of cells endowed with uptake₁, it is possible to demonstrate — besides a pronounced lipophilic entry — a carrier-mediated uptake of ³H (+)-amphetamine.Some of the results were communicated to the German Pharmacological Society (Bönisch 1981). This study was supported by the Deutsche Forschungsgemeinschaft (Bo 521)     

Viral restoration of dopamine signaling to the dorsal striatum restores instrumental conditioning to dopamine-deficient mice

Introduction Instrumental responding was evaluated to determine whether mice lacking dopamine [dopamine-deficient mice (DD mice)] could learn to preferentially press a visually cued, active lever for food reward over an inactive lever. Results When DD mice were treated with 3,4-L-dihydroxyphenalanine (L-dopa) to restore dopamine signaling systemically, they were able to learn to press the active lever as well as control mice, whereas mice lacking dopamine would not perform the task. Importantly, DD mice treated with caffeine (to stimulate locomotor and feeding behaviors) also failed to show preference for the active lever and were slower to retrieve rewards after making a reinforced operant response. Selective restoration of dopamine signaling to the nigrostriatal pathway of DD mice via viral-mediated gene transfer completely restored learning and performance of this simple instrumental task. Furthermore, the virally treated DD mice were willing to lever press as much as control mice for reward in progressive-ratio and high fixed-ratio schedules of reinforcement. Conclusion These results suggest that the deficit in goal-directed behavior observed in mice without dopamine signaling is the result of decreased motivation to obtain reward, and that dopamine signaling in the dorsal striatum is sufficient to restore normal goal-directed behavior on a variety of operant responding tasks. This work was supported in part by the Institutional Grant for Neurobiology: GM07108-29 (SR) and by the National Institute of General Medical Sciences Grant: PHS NRSA T32 GM07270 (TSH).     

The effect of amantadine and (+)-amphetamine on motility in rats after inhibition of monoamine synthesis and storage

The effect of amantadine and (+)-amphetamine on motility was investigated by subcutaneous administration to rats. Amantadine 50 and 100 mg/kg induced a moderate increase of motility. (+)-amphetamine 1, 2.5 and 5 mg/kg showed a more potent locomotor stimulant effect. A stereotyped licking was found during the hypermotility induced by (+)-amphetamine 5 mg/kg.Pretreatment with the catecholamine synthesis inhibitor -methyl-p-tyrosine inhibited the effect of (+)-amphetamine but not that of amantadine. Reserpine potentiated the effects of both amantadine and (+)-amphetamine. Tetrabenazine antagonized the hyperactivity produced by (+)-amphetamine but potentiated amantadine induced hyperactivity. The locomotor stimulant effect of amantadine seems to differ in certain respects from that of amphetamine.     

Studies in mice on the antagonism of (+)-amphetamine anorexia by alpha-methyl-p-tyrosine methyl ester HCl.

Experiments were carried out in mice to investigate the individual roles of dopamine and noradrenaline in both the production of (+)-amphetamine anorexia and in its antagonism by α-methyl-p-tyrosine methyl ester HCl. The anorexia resulting from (+)-amphetamine pretreatment (2 mg/kg, s.c.) was potentiated by intracerebroventricular injection of dopamine (8 μg) and noradrenaline (8 μg). Neither catecholamine, however, produced any anorectic effects when given alone at these dose levels. The anorexia produced by (+)-amphetamine was antagonised by α-methyl-p-tyrosine methyl ester HC1 (40–160 mg/kg, i.p.) and the submaximal antagonism at 80 mg/kg α-methyl-p-tyrosine was reversed by l-DOPA (40 and 80 mg/kg, i.p.) and by intracerebroventricular dopamine (4 and 8 μg). Noradrenaline, in intracerebroventricular doses of up to 8 μg, failed to produce this reversal. These results indicate that, although a role for both dopamine and noradrenaline may be implicated in the production of (+)-amphetamine anorexia and in its antagonism by α-methyl-p-tyrosme, the noradrenergic component is dependent upon a fully functional dopaminergic system.     

Increased synthesis of adrenomedullary catecholamines induced by caffeine and theophylline

Summary Caffeine or theophylline, 20 mg/kg i.p., was given to rats. Thirty minutes after the injection of either drug, adrenal dopamine increased 80 and 50%, respectively. This increase was prevented by a C-7 spinal cord transection made 24 h before. In transected animals adrenal dopamine decreased after caffeine; no statistically significant decreases in adrenaline + noradrenaline were observed. It is concluded that caffeine and theophylline activate the tyrosine hydroxylase by a mechanism which depends on a normal or increased nerve impulse flow. In addition, release of adrenal catecholamines may occur both via neurogenic stimulation and directly.     

(+)-Amphetamine oral 'drug taking behavior' in naive and tolerant rats

The drinking behavior of naive rats changes predictably in a free choice experiment involving water vs. 0.02%, 0.01% and 0.003% (+)-amphetamine solutions: The higher the concentration of the amphetamine solution, the sooner a number of rats quit drinking it, and the less is ingested by those still drinking it. Physically dependent rats having undergone three withdrawals immediately reject (+)-amphetamine solution in a free choice test with water available. The avoidance of withdrawal symptoms does not motivate further self-administration. Therefore, (+)-amphetamine self-administered in drinking water is neither a reinforcer for naive nor for physically dependent rats in sustaining drug taking behavior. In acute and chronic experiments, the transition from increased motor activity to stereotypical behavior could be demonstrated and evidence was produced that tolerance develops to the (+)-amphetamine-induced increase in motor activity.     

Dose-dependent and baseline-dependent conditioning with d-amphetamine in the place conditioning paradigm

The place conditioning paradigm was used to evaluate the positively reinforcing effects of d-amphetamine. During conditioning, female rats were injected (IP) with saline or one of five doses (0.625–5 mg/kg) of d-amphetamine (d-A) and confined to the initially non-preferred side of the testing apparatus. The highest dose of d-A failed to produce a significant preference. The four middle doses of the drug induced a similar preference. A significant increase from baseline was observed on the 4th post-conditioning test day in the five drug groups and controls when given an injection of 1.5 mg/kg d-A 15 min prior to placement in the chamber. Control and drug groups were separated into high and low initial preference sub-groups. Place preferences were more readily induced by d-A in the sub-groups with initially high baseline preferences. These findings as well as those of others led us to conclude that the place conditioning paradigm is a somewhat problematic way of measuring drug reinforcement and that the effects observed may not solely be the result of the conditioning of the drug's reinforcing properties to a particular environment.     

Effects of caffeine, caffeine-associated stimuli, and caffeine-related information on physiological and psychological arousal

RATIONALE: To test the classical conditioning and expectancy theories of placebo effects. OBJECTIVE: Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. METHOD: Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. RESULTS: Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. CONCLUSIONS: Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.     

Effect of caffeine on physiological sleep tendency and ability to sustain wakefulness at night

Marked sleepiness occurs during typical night shift work hours and this reduced alertness is associated with marked performance deficits. The effect of caffeine (versus placebo) upon sleepiness at night was studied using objective measures of physiological sleep tendency and ability to sustain wakefulness. Both measures show caffeine to reduce sleepiness at a single dose roughly the equivalent of two to four cups of coffee. Despite impressive objective differences in alertness with caffeine, subjects did not consistently differentiate between drug conditions on subjective alertness assessments. The use of CNS stimulants to promote alertness during night shift hours should be considered, particularly for occupations for which alertness is critical.     

Reinforcing effects of caffeine and theobromine as found in chocolate

Rationale  

Although in a previous study we showed that caffeine and theobromine were the main psychopharmacologically active constituents in a 50-g bar of chocolate, mere activity does not guarantee a role in our liking for the food.     

Catecholaminergic involvement in the effects of amphetamine isomers on seizure susceptibility

The (+)-amphetamine (2.5 mg/kg) increase in pentylenetetrazol seizure was abolished by pretreatment with reserpine, α-methyltyrosine methyl ester (α-MT), FLA-63 or 6-hydroxydopa. All treatments except reserpine antagonized the increase in seizure threshold produced by (-)-amphetamine (4 mg/kg). Only reserpine +α-MT antagonized the decrease in seizure threshold produced by (+)-amphetamine (15 mg/kg). These results indicate that amphetamine alterations in PLZ seizure susceptibility are mediated indirectly via the release of newly synthetized and/or granular stores of catecholamines.     

Tramadol and caffeine produce synergistic interactions on antinociception measured in a formalin model

Drug combinations have been used in clinical practice for the main purpose of increasing therapeutic effect efficacy. The aim of this study was to determine the antinociceptive effect of tramadol and caffeine administered separately or in combination, as well as their synergistic interaction. The formalin test was used. Nociceptive behavior was evaluated by flinching response of the formalin-treated paw. Rats were divided into five groups and received tramadol alone (4.9-49.6 mg/kg, s.c.), caffeine alone (1-17.8 mg/kg, p.o.), or combinations of tramadol (4.9, 8.8, 15.6 and 20.8 mg/kg, s.c.) and caffeine (1, 3.16 and 10 mg/kg, p.o.). Tramadol showed dose-dependent antinociceptive effect in both phases of the formalin test. Caffeine only presented antinociceptive effect in the second phase and this effect was also dose-dependent. In Phase 1, combinations of tramadol and caffeine showed antinociceptive effect similar to that of tramadol alone. In Phase 2, the dose-response curve shifted to the left with the combination of tramadol and each dose of caffeine. Synergism analysis resulted in synergistic effect in ten combinations and antagonism in two combinations. In conclusion, the synergism observed in the majority of tramadol and caffeine combinations used in this study suggests that this drug combination is useful in the treatment of pain.     

In vitro studies on the mechanism by which (+)-norfenfluramine induces serotonin and dopamine release from the vesicular storage pool

(+)-Norfenfluramine is the main metabolite of the serotoninergic anorectic agent (+)-fenfluramine. Both compounds inhibit 5-HT reuptake and stimulate its release, although they induce release from different pools, with (+)-norfenfluramine acting primarily on the cytoplasmic pool. Moreover, (+)-norfenfluramine was more potent than the parent drug in inducing dopamine release. In order to investigate whether (+)-norfenfluramine induces a Ca²⁺-dependent vesicular release, like some amphetamine derivatives, in the present study we preloaded synaptosomes with the [³H]neurotransmitter ([³H]5-HT or [³H]dopamine), superfused (washed) them for 47 min in the absence of pargyline and then exposed them to the releasing stimulus. With this protocol, the cytoplasmic pool should be absent and the [³H]neurotransmitter should mainly be stored in synaptic vesicles, where (+)-norfenfluramine should act to induce release. This was confirmed by a significant decrease of (+)-norfenfluramine-induced [³H]5-HT and [³H]dopamine release after reserpine pretreatment. The dose-response curves of (+)-norfenfluramine-induced [³H]5-HT release were superimposable in hippocampus and hypothalamus, and also superimposable on the curve for (+)-fenfluramine-induced [³H]5-HT release; the dopamine releasing potency of (+)-norfenfluramine in the striatum was more than ten times lower. The [³H]5-HT release induced by (+)-norfenfluramine was partly (about 50%) but significantly Ca²⁺-dependent, and it was also markedly (68%) inhibited by Cd²⁺, a non-specific blocker of voltage-dependent Ca²⁺ channels, suggesting that the Ca²⁺-dependent release is mediated by entry of Ca²⁺ into the synaptosomes through these channels. The [³H]dopamine release induced by 5 μM (+)-norfenfluramine was completely Ca²⁺-independent whereas at higher concentrations (10 and 20 μM) it was only slightly (20%) Ca²⁺-dependent. We have no clear explanation why (+)-norfenfluramine has these different effects on serotoninergic and dopaminergic synaptosomes. Received: 6 April 1998 / Accepted: 9 June 1998