Intravenous self-administration of diazepam in rats

Adinazolam, a Benzodiazepine-Type New Psychoactive Substance, Has Abuse Potential and Induces Withdrawal Symptoms in Rodents

Adinazolam (ADZ) is a benzodiazepine-type new psychoactive substance (NPS) with anxiolytic, anticonvulsant, and antidepressant effects. High ADZ doses have been reported to impair psychomotor performance and memory; however, the abuse potential and drug dependence of ADZ have not yet been fully investigated. In this study, we evaluated whether ADZ has abuse potential and leads to drug dependence and withdrawal symptoms. The intravenous self-administration (IVSA) test revealed that ADZ (0.01, 0.03, and 0.1 mg/kg/infusion) was self-administered significantly above vehicle levels, suggesting the reinforcing effect of ADZ. Furthermore, we revealed that treatment discontinuation following chronic ADZ administration (3 and 6 mg/kg) caused several somatic withdrawal symptoms in mice, including body tremor. Moreover, it induced motivational withdrawal signs, such as anxiety-related behavior in the elevated plus maze (EPM) test and memory deficits in the Y-maze test. After the IVSA test, an enzyme-linked immunosorbent assay (ELISA) showed that ADZ administration significantly increased the dopamine contents in the thalamus, nucleus accumbens (NAc), and ventral tegmental area (VTA). This finding was also supported by the results of the Western blot. Taken together, our results suggest that ADZ has abuse potential and can lead to drug dependence and withdrawal syndrome.

Reinforcing effectiveness of midazolam, ethanol, and sucrose: behavioral economic comparison of a mixture relative to its component solutions

Benzodiazepines (BZs) are relatively safe when administered alone. However, these drugs can produce severe side effects when coadministered with ethanol. Despite these adverse consequences, rates of concurrent BZ and ethanol misuse are increasing, and it is unclear whether this behavior is maintained by an enhanced reinforcing effect of the mixture. To address this issue, the current study compared the reinforcing effectiveness of sucrose solutions mixed with midazolam, ethanol, or both. Eight male rats were trained to orally self-administer solutions of either sucrose (S), sucrose+midazolam (SM), sucrose+ethanol (SE), or sucrose+midazolam+ethanol (SME). The response requirement was increased between sessions until the number of reinforcers earned was zero and the relationship between response requirement and reinforcers earned was analyzed using the exponential model of demand. Although baseline intake was similar across drug conditions, consumption of SM was least affected by increases in cost, indicating that it possessed the highest reinforcing effectiveness (i.e. least elastic). The reinforcing effectiveness of S, SE, and SME did not differ significantly. The finding that the reinforcing effectiveness of the SME was less than that of SM does not support the supposition that BZ and ethanol coadministration is maintained by a higher reinforcing effectiveness of the mixture.

Abuse-related effects of subtype-selective GABAA receptor positive allosteric modulators in an assay of intracranial self-stimulation in rats

RATIONALE

GABA_A positive allosteric modulators (GABA_A PAMs), such as diazepam and zolpidem, are used clinically for anxiety and insomnia, but abuse liability is a concern. Novel GABA_A PAMS may have lower abuse liability while retaining clinical utility.

OBJECTIVE

The present study compared abuse-related effects of the non-selective GABA_A PAM diazepam, the α1-selective GABA_A PAM zolpidem, and three novel GABA_A PAMs (JY-XHe-053, XHe-II-053, and HZ-166) using intracranial self-stimulation (ICSS) in rats. These novel compounds have relatively low efficacy at α1-, α2-, and α3-containing GABA_A receptors, putative in vivo selectivity at α2/α3-containing GABA_A receptors, and produce anxiolytic-like effects with limited sedation in non-human primates.

METHODS

Adult, male Sprague-Dawley rats (n = 17) were each implanted with a bipolar electrode in the medial forebrain bundle and trained to respond under a fixed-ratio 1 schedule of reinforcement for electrical brain stimulation. The potency and time course of effects were compared for diazepam (0.1-10 mg/kg), zolpidem (0.032-3.2 mg/kg), and the three novel compounds (JY-XHe-053, XHe-II-053, and HZ-166; all 3.2-32 mg/kg).

RESULTS

Zolpidem and diazepam produced transient facilitation of ICSS at small doses and more sustained rate-decreasing effects at larger doses. JY-XHe-053 and HZ-166 produced weak and inconsistent ICSS facilitation, whereas XHe-II-053 had no effect on ICSS.

CONCLUSIONS

These results support a key role for α1-containing GABA_A receptors in mediating GABA_A PAM-induced ICSS facilitation. These results are concordant with drug self-administration studies in monkeys in suggesting that GABA_A PAMs with low α1 efficacy and putative α2/α3 selectivity have lower abuse liability than high-efficacy non-selective or α1-selective GABA_A PAMs.

Anabolic-androgenic steroid dependence? Insights from animals and humans

Anabolic-androgenic steroids (AAS) are drugs of abuse. They are taken in large quantities by athletes and others to increase performance, with negative health consequences. As a result, in 1991 testosterone and related AAS were declared controlled substances. However, the relative abuse and dependence liability of AAS have not been fully characterized. In humans, it is difficult to separate the direct psychoactive effects of AAS from reinforcement due to their systemic anabolic effects. However, using conditioned place preference and self-administration, studies in animals have demonstrated that AAS are reinforcing in a context where athletic performance is irrelevant. Furthermore, AAS share brain sites of action and neurotransmitter systems in common with other drugs of abuse. In particular, recent evidence links AAS with opioids. In humans, AAS abuse is associated with prescription opioid use. In animals, AAS overdose produces symptoms resembling opioid overdose, and AAS modify the activity of the endogenous opioid system.

Morphine deprivation increases self-administration of the fast- and short-acting mu-opioid receptor agonist remifentanil in the rat

Opiate dependence and withdrawal have long been hypothesized to enhance the reinforcing effects of opiates; however, opiate agonist self-administration in these states has yet to be systematically assessed. To address this issue, the reinforcing property of the short-acting mu-opioid agonist, remifentanil, was assessed in morphine-dependent (MD), morphine-dependent and -withdrawn (MW), and nondependent, control (C) rats. Dependence was established by twice daily administration of increasing doses of morphine for 4 days (10, 20, 30, and 40 mg/kg s.c.) and then maintained with a daily injection of the large dose. Morphine deprivation-induced withdrawal (defined by weight loss and hyperalgesia) was apparent 24, but not 12, h after morphine treatment. Remifentanil self-administration (0.4, 0.8, 1.6, 3.2, or 6.4 mug/kg/infusion) was assessed over 20 successive, daily, 1-h sessions, either 12 or 24 h after the maintenance dose of morphine. Compared with the control group, the MD group demonstrated suppressed remifentanil self-administration, whereas the MW group exhibited enhanced responding for every dose of remifentanil. The increased responding observed in the MW group compared with the control and MD groups resulted in an upward shift in the remifentanil dose-response curve, an effect that was expressed only after repeated exposure to the contingency, demonstrating that morphine withdrawal ultimately enhances the reinforcing effects of remifentanil.

Testosterone and nucleus accumbens dopamine in the male Syrian hamster

Most drugs of abuse increase dopamine (DA) in nucleus accumbens (Acb). However, the effects of anabolic androgenic steroids (AAS) on Acb DA have not been examined. We determined the effects of subcutaneous (sc) testosterone (T) on Acb DA in male hamsters. The effects of sc amphetamine were also examined for comparison. In addition, Acb DA was evaluated during intracerebroventricular (ICV) T infusion, designed to mimic T intake during ICV T self-administration in drug-naïve and drug-preexposed animals. Acb DA was measured using in vivo microdialysis and HPLC-EC. T (7.5 or 37.5 mg/kg), amphetamine (1 or 5 mg/kg), or vehicle was injected sc and Acb DA monitored for 4h. In the ICV experiment, T (1 or 2 microg/infusion) or vehicle was infused ICV every 6 min for 4h and Acb DA monitored. ICV T preexposure was accomplished by repeating the same ICV T infusion (1 microg/infusion) daily for 14 days, and T infusion was accompanied by microdialysis on 15th day. Neither sc nor ICV T administration increased Acb DA. At high dose (2 microg/infusion), ICV T decreased Acb DA. Likewise, daily ICV infusion of T for 15 days did not alter Acb DA. In contrast, sc amphetamine significantly increased Acb DA at both doses. Therefore, unlike many drugs of abuse, AAS does not increase Acb DA levels. The reduction in DA at high T doses is likely due to autonomic depressant effects of AAS. We suggest that AAS act via mechanism distinct from those of stimulants, but may share neural substrates with other drugs of abuse.

Reinforcing aspects of androgens

Are androgens reinforcing? Androgenic-anabolic steroids (AAS) are drugs of abuse. They are taken in large quantities by athletes and others to increase performance, often with negative long-term health consequences. As a result, in 1991, testosterone was declared a controlled substance. Recently, Brower [K.J. Brower, Anabolic steroid abuse and dependence. Curr. Psychiatry Rep. 4 (2002) 377-387.] proposed a two-stage model of AAS dependence. Users initiate steroid use for their anabolic effects on muscle growth. With continued exposure, dependence on the psychoactive effects of AAS develops. However, it is difficult in humans to separate direct psychoactive effects of AAS from the user's psychological dependence on the anabolic effects of AAS. Thus, studies in laboratory animals are useful to explore androgen reinforcement. Testosterone induces a conditioned place preference in rats and mice, and is voluntarily consumed through oral, intravenous, and intracerebroventricular self-administration in hamsters. Active, gonad-intact male and female hamsters will deliver 1 microg/microl testosterone into the lateral ventricles. Indeed, some individuals self-administer testosterone intracerebroventricularly to the point of death. Male rats develop a conditioned place preference to testosterone injections into the nucleus accumbens, an effect blocked by dopamine receptor antagonists. These data suggest that androgen reinforcement is mediated by the brain. Moreover, testosterone appears to act through the mesolimbic dopamine system, a common substrate for drugs of abuse. Nonetheless, androgen reinforcement is not comparable to that of cocaine or heroin. Instead, testosterone resembles other mild reinforcers, such as caffeine, nicotine, or benzodiazepines. The potential for androgen addiction remains to be determined.

Testosterone reinforcement: intravenous and intracerebroventricular self-administration in male rats and hamsters

RATIONALE

Anabolic steroids are drugs of abuse. However, the potential for addiction remains unclear. Testosterone induces conditioned place preference in rats and oral self-administration in hamsters.

OBJECTIVES

To determine if male rats and hamsters consume testosterone by intravenous (IV) or intracerebroventricular (ICV) self-administration.

METHODS

With each nose-poke in the active hole during daily 4-h tests in an operant conditioning chamber, gonad-intact adult rats and hamsters received 50 microg testosterone in an aqueous solution of beta-cyclodextrin via jugular cannula. The inactive nose-poke hole served as a control. Additional hamsters received vehicle infusions.

RESULTS

Rats ( n=7) expressed a significant preference for the active nose-poke hole (10.0+/-2.8 responses/4 h) over the inactive hole (4.7+/-1.2 responses/4 h). Similarly, during 16 days of testosterone self-administration IV, hamsters ( n=9) averaged 11.7+/-2.9 responses/4 h and 6.3+/-1.1 responses/4 h in the active and inactive nose-poke holes, respectively. By contrast, vehicle controls ( n=8) failed to develop a preference for the active nose-poke hole (6.5+/-0.5 and 6.4+/-0.3 responses/4 h). Hamsters ( n=8) also self-administered 1 microg testosterone ICV (active hole:39.8+/-6.0 nose-pokes/4 h; inactive hole: 22.6+/-7.1 nose-pokes/4 h). When testosterone was replaced with vehicle, nose-poking in the active hole declined from 31.1+/-7.6 to 11.9+/-3.2 responses/4 h within 6 days. Likewise, reversing active and inactive holes increased nose-poking in the previously inactive hole from 9.1+/-1.9 to 25.6+/-5.4 responses/4 h. However, reducing the testosterone dose from 1 microg to 0.2 microg per 1 microl injection did not change nose-poking.

CONCLUSIONS

Compared with other drugs of abuse, testosterone reinforcement is modest. Nonetheless, these data support the hypothesis that testosterone is reinforcing.

Lack of reinforcing effect of the benzodiazepine and tricyclic antidepressant combination of diazepam and dothiepin

Fixed combinations of a tricyclic antidepressant (TCA) with a benzodiazepine (BZD) for the treatment of depressive syndromes enjoy remarkable acceptance among patients and prescribing physicians. In order to investigate if the widespread use of one such fixed TCA-BZD combination might be due to its high positive reinforcing effect, we tested each drug alone and in combination in an operant conditioning paradigm (fixed ratio 1 time-out 150 s) of intravenous self-administration in rats and compared their reinforcing effects to that of cocaine. Diazepam proved to be of only moderate reinforcing strength. Dothiepin alone was ineffective as a reinforcer but essentially abolished the reinforcing effect of diazepam when given in combination with it. These data indicate that the widespread acceptance of the fixed diazepam-dothiepin combination by the therapeutic community is not due to an increase in the positive reinforcing effect of diazepam by dothiepin but that, in contrast, addition of dothiepin might even decrease diazepam's moderately positive reinforcing effect.

Analgesia and abuse potential: an accidental association or a common substrate?

The fact that centrally acting analgesics have abuse potential commensurate with their analgesic activity raises the question of whether these effects are related. The abuse potential of drugs depends on their ability to produce reinforcing effects, which are mediated by a neural system that includes the ventral tegmental dopamine cells and their connections with the ventral striatum. Morphine and amphetamine are both powerful analgesics and have high abuse potential. Their analgesic and reinforcing effects are mediated by similar receptors, similar sites of action, and overlapping neural substrates. These coincidences suggest that reinforcers may produce analgesia by transforming the aversive affective state evoked by pain into a more positive affective state. The implications of this hypothesis and its relation to other known mechanisms of analgesia are discussed. The hypothesis predicts that drugs with reinforcing effects should produce analgesia. A survey of drugs acting through 21 classes of receptors reveals that in 13 classes there is evidence for both analgesic and reinforcing effects that are approximately equipotent. The GABA(A) agonists were found to be the only drugs with confirmed abuse potential that lack analgesic activity. The interpretation of this and several other anomalous cases is discussed.

Effects of repeated intravenous administration of diazepam on food intake in rats

Effects of repeated intravenous (i.v.) administration of diazepam on food intake were investigated in freely moving rats implanted with a chronic i.v. cannula. Diazepam (0.2 and 2 mg/kg) was automatically injected i.v. at 3-h intervals for 3 consecutive days. Food intake was measured twice daily, ie for the light phase (7 00-19 00) and dark phase (19 00-7 00). Food intake during the light phase was increased in a dose-dependent manner following diazepam. Each injection of diazepam provoked hyperphagia, followed by a compensatory hypophagia until the next diazepam injection. Body weight, however, was increased significantly in rats treated with diazepam. When diazepam (2 mg/kg) was automatically injected at 3-h intervals for 10 consecutive days, tolerance did not develop to the hyperphagia and body weight was increased significantly following diazepam injection. After cessation of diazepam injection, both food intake and body weight decreased. These findings suggest that such excessive i.v. treatment with diazepam induces hyperphagia showing no tolerance accompanied by an increase in body weight, thus resulting in a trend toward obesity in rats.

Benzodiazepine-induced decreases in extracellular concentrations of dopamine in the nucleus accumbens after acute and repeated administration

In vivo microdialysis was used to assess the effects of acute and repeated injections of the benzodiazepine midazolam on extracellular dopamine (DA) concentrations in the nucleus accumbens. Acute administration of midazolam (5 mg/kg, SC) elicited a 22% decrease in extracellular DA in the nucleus accumbens but failed to affect DA concentrations in the striatum. Similarly, six spaced intravenous infusions of midazolam, at a dose that has previously been found to support self-administration (0.05 mg per infusion), produced a 50% decrease in extracellular DA in the nucleus accumbens. In order to assess the effects of subchronic midazolam injections, two groups of rats were given injections of saline or midazolam (5 mg/kg, SC) for 14 days (two injections per day). A subsequent challenge injection of midazolam (5 mg/kg) decreased extracellular DA in the nucleus accumbens by 25% in both groups, indicating that neither tolerance nor sensitization occurred during the repeated drug administration. These experiments indicate (1) that midazolam differentially affects meso-accumbens and nigrostriatal DA neurons, and (2) that the midazolam-induced decrease in extracellular DA in the nucleus accumbens is not affected by repeated drug administration. The data further suggest that the rewarding effects of midazolam are not associated with increased release of DA in the nucleus accumbens.

Social behavior, dominance, and social deprivation of rats determine drug choice

Relationships between social deprivation, dominance, and voluntary intake of ethanol (ETOH) and diazepam (D) were studied in male adult Wistar rats. Social behavior was registered by tetradic encounters in the open field prior to the rats' drug experiences. Social deprivation was induced by individual housing (LI) and contact caging (C). Nondeprived rats were housed in groups of four individuals (G) each. Social deprivation facilitated ETOH intake: LI rats consumed 30% more ETOH than G. Increase of deprivation by change of housing condition additionally raised ETOH consumption. ETOH experiences did not affect subsequent D choice. However, rats with a high ETOH consumption also preferred D. Individual drug disposition correlated with social dominance (in G: to social activity). Even in individual isolation dominant rats took less drugs than subordinate ones, but these rats raised their ETOH consumption when the housing conditions were changed. After nine months of voluntary ETOH intake and subsequently nine months without access to ETOH the rats showed signs of "behavioral dependence." Compared to naive animals they took twice as much ETOH and even after adulterating ETOH by quinine a high preference was perpetuated. During this state modifying social factors were no longer effective.

Diazepam effects on the exploratory behaviour of rats in an elevated runway: evidence for biphasic effects of benzodiazepines

The purpose of this study was to test the validity of the fear-reduction model of benzodiazepine (BZ) action on the exploration of novelty. According to this hypothesis an animal given a tranquilizer should selectively increase the amount of investigative behaviour in the more novel portion of an elevated maze. To permit comparison of the same behaviours at both ends of the maze, an elevated runway was built with a wall running lengthwise along the midline of one end. In the first experiment, male Sprague-Dawley rats treated with diazepam (2.0 mg/kg, i.p., -30 min) compared to saline-treated animals, increased the time spent exploring the open end of the runway but not the wall end of the runway, thus supporting the fear-reduction model. However, saline-treated animals, made less fearful by repeated prior exposure to the runway, did not show a similar increase in open-end exploration. Instead, they habituated to the novelty of the runway, as grooming and sitting still replaced investigation. In Experiment 2, exploration was rewarded by adding to the open end of the runway a patch of litter soiled by a female rat. This produced a behavioural pattern in naive saline-treated rats very similar to that seen in naive diazepam-treated rats in the first experiment. In Experiment 3, diazepam potentiated the habituation of rats previously familiarized with the runway. The initial increase and subsequent decrease in exploration caused by diazepam were encompassed by the biphasic model of BZ action more adequately than either the fear-reduction or reward-enhancement models.

Neurophysiology and neurochemistry of drug dependence: a review

To understand the neurophysiological and neurochemical mechanisms of drug dependence, the functional significance of dopamine, noradrenaline and endogenous opioid peptides in the mediation of natural, self-stimulation and pharmacological reinforcement are discussed. Data on search of system(s), mediator(s) and neurons of reinforcement as well as my own notions on reinforcement as a critical element in organization and regulation of the organism's adaptive activity in variable environments are presented. The role of chronic drug-induced stable modification of central neurochemical systems' functioning as a basis for the alteration of endogenous reinforcement processes and raising drug dependence are examined in detail for main addictive drugs, opiates and psychomotor stimulants.

Effects of ritanserin on the rewarding properties of d-amphetamine, morphine and diazepam revealed by conditioned place preference in rats

The possibility that 5-HT2 receptors mediate the reinforcing properties of d-amphetamine, morphine and diazepam was investigated in rats, using ritanserin, a 5-HT2 antagonist, and the conditioned place preference paradigm. Ritanserin 1 or 2.5 mg/kg did not cause place conditioning. Place preference induced by 1.5 mg/kg d-amphetamine and 2 mg/kg morphine was inhibited and attenuated respectively by pretreatment with 2.5 mg/kg ritanserin. Diazepam- (1 mg/kg) induced place preference was completely blocked by both doses of ritanserin. Ritanserin pretreatment failed to influence amphetamine-induced hyperlocomotion, morphine-induced analgesia and diazepam-induced increased open arm exploration of rats on the elevated plus maze. These data are discussed in terms of (a) the possibility that serotoninergic mechanisms have a role in mediating reinforcement and (b) the relationship between appetitive properties and specific behavioral effects of psychostimulants, opiates and anxiolytics.

Drug-induced place preference in rats with 5,7-dihydroxytryptamine lesions of the nucleus accumbens

The conditioned place preference (CPP) paradigm was used to determine a role for serotonin in the nucleus accumbens in the mediation of the rewarding properties of D-amphetamine morphine and diazepam. The effect of these drugs on CPP was examined in controls and in animals with 5,7-dihydroxytryptamine lesions of the nucleus accumbans. The results from control animals confirmed that D-amphetamine (1.5 mg/kg, i.p.), morphine (2.0 mg/kg, i.p.) and diazepam (1.0 mg/kg, i.p.) produced place preference for a distinctive environment that had previously been paired with injections of the drug. In animals with 80% reduction of 5-hydroxytryptamine content of the nucleus accumbens, D-amphetamine CPP was unchanged and morphine CPP was attenuated compared with controls. Diazepam CPP was not apparent in animals with the lesion. In separate experiments, characteristic behavioural effects of the drugs under study were examined in control and in animals with lesion. The results showed a tendency for increased amphetamine hyperlocomotion, enhanced morphine activity and analgesia and decreased diazepam anti-anxiety effect in animals with lesions. Thus, the 5,7-dihydroxytryptamine lesions of the nucleus accumbens differently influenced the CPP induced by the drugs studied and, with the exception of diazepam, the various behavioural effects elicited by each drug. The findings suggest that serotonin-containing neurones of the nucleus accumbens are a component of the neural circuitry that mediates the rewarding properties of morphine, probably of diazepam, but not of D-amphetamine.