Neuroleptic-like effects of gamma-hydroxybutyrate: interactions with haloperidol and dizocilpine

Neurotoxic effects induced by gammahydroxybutyric acid (GHB) in male rats

Gammahydroxybutyric acid (GHB) is an endogenous constituent of the central nervous system that has acquired great social relevance for its use as a recreational 'club drug'. GHB, popularly known as 'liquid ecstasy', is addictive when used continuously. Although the symptoms associated with acute intoxication are well known, the effects of prolonged use remain uncertain. We examined in male rats the effect of repeated administration of GHB (10 and 100 mg/kg) on various parameters: neurological damage, working memory and spatial memory, using neurological tests, the Morris water maze and the hole-board test. The results showed that repeated administration of GHB, especially at doses of 10 mg/kg, causes neurological damage, affecting the 'grasping' reflex, as well as alteration in spatial and working memories. Stereological quantification showed that this drug produces a drastic neuronal loss in the CA1 hippocampal region and in the prefrontal cortex, two areas clearly involved in cognitive and neurological functions. No effects were noted after quantification in the periaqueductal grey matter (PAG), a region lacking GHB receptors. Moreover, NCS-382, a putative antagonist of GHB receptor, prevented both neurological damage and working- memory impairment induced by GHB. This suggests that the effects of administration of this compound may be mediated, at least partly, by specific receptors in the nervous system. The results show for the first time that the repeated administration of GHB, especially at very low doses, produces neurotoxic effects. This is very relevant because its abuse, especially by young persons, could produce considerable neurological alterations after prolonged abuse.

Behavioral effects of gamma-hydroxybutyrate, its precursor gamma-butyrolactone, and GABA(B) receptor agonists: time course and differential antagonism by the GABA(B) receptor antagonist 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP35348)

Gamma-hydroxybutyrate (GHB) is used therapeutically and recreationally. The mechanism by which GHB produces its therapeutic and recreational effects is not entirely clear, although GABA(B) receptors seem to play an important role. This role could be complex, because there are indications that different GABA(B) receptor mechanisms mediate the effects of GHB and the prototypical GABA(B) receptor agonist baclofen. To further explore possible differences in underlying GABA(B) receptor mechanisms, the present study examined the effects of GHB and baclofen on operant responding and their antagonism by the GABA(B) receptor antagonist 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP35348). Pigeons were trained to peck a key for access to food during response periods that started at different times after the beginning of the session. In these pigeons, GHB, its precursor gamma-butyrolactone (GBL), and the GABA(B) receptor agonists baclofen and 3-aminopropyl(methyl)phosphinic acid hydrochloride (SKF97541) decreased the rate of responding in a dose- and time-dependent manner. CGP35348 shifted the dose-response curve of each agonist to the right, but the magnitude of the shift differed among the agonists. Schild analysis yielded a pA(2) value of CGP35348 to antagonize GHB and GBL [i.e., 3.9 (3.7-4.2)] that was different (P = 0.0011) from the pA(2) value to antagonize baclofen and SKF97541 [i.e., 4.5 (4.4-4.7)]. This finding is further evidence that the GABA(B) receptor mechanisms mediating the effects of GHB and prototypical GABA(B) receptor agonists are not identical. A better understanding of the similarities and differences between these mechanisms, and their involvement in the therapeutic effects of GHB and baclofen, could lead to more effective medications with fewer adverse effects.

Behavioral effects and pharmacokinetics of gamma-hydroxybutyrate (GHB) precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) in baboons

RATIONALE

Gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are prodrugs for gamma-hydroxybutyrate (GHB). Like GHB, GBL and 1,4-BD are drugs of abuse, but their behavioral effects may differ from GHB under some conditions.

OBJECTIVES

The first study compared the behavioral effects of GBL (32-240 mg/kg) and 1,4-BD (32-240 mg/kg) with each other and to effects previously reported for GHB (32-420 mg/kg). A second study determined GHB pharmacokinetics following intragastric administration of GHB, GBL, and 1,4-BD.

METHODS

Operant responding for food, observed behavioral effects, and a fine-motor task occurred at multiple time intervals after administration of drug or vehicle. In a separate pharmacokinetics study, blood samples were collected across multiple time points after administration of GHB, GBL, and 1,4-BD.

RESULTS

Like GHB, GBL, and 1,4-BD impaired performance on the fine-motor task, but the onset of motor impairment differed across drugs. GBL and 1,4-BD dose dependently decreased the number of food pellets earned, but at lower doses than previously observed for GHB. Similar to GHB, both GBL and 1,4-BD produced sedation, muscle relaxation, gastrointestinal symptoms, and tremors/jerks. Administration of GBL and 1,4-BD produced higher maximum concentrations of GHB with shorter times to maximum concentrations of GHB in plasma when compared to GHB administration.

CONCLUSIONS

GBL and 1,4-BD produced behavioral effects similar to those previously reported with GHB and the time course of effects were related to blood levels of GHB. Given their higher potency and faster onset of effects, the abuse liability of GBL and 1,4-BD may be greater than GHB.

High fat diet and food restriction differentially modify the behavioral effects of quinpirole and raclopride in rats

Nutritional status can impact dopamine systems in a manner that might be important to understanding possible common neurobiological mechanisms that mediate abnormal compulsive food (e.g., obesity) and drug taking. Limiting food intake, for example, can increase sensitivity to the behavioral effects of indirect-acting dopamine receptor agonists. Much less is known regarding possible diet-induced changes in sensitivity to direct-acting dopamine receptor drugs. The present study investigated the effects of a high fat diet and of food restriction on sensitivity of rats to the behavioral effects of a direct-acting dopamine receptor agonist and a dopamine receptor antagonist. Free access to high fat chow increased sensitivity to quinpirole-induced yawning without changing sensitivity to raclopride-induced catalepsy or quinpirole-induced hypothermia. Food restriction (10 g/day) decreased sensitivity to quinpirole-induced yawning and raclopride-induced catalepsy without affecting sensitivity to quinpirole-induced hypothermia. Free access to a standard chow restored sensitivity to the behavioral effects of both drugs in rats that were previously food-restricted but not in rats that previously ate a high fat diet. These data confirm that food restriction can decrease sensitivity to behavioral effects of direct-acting dopamine receptor drugs, they provide evidence (i.e., no change in hypothermic effects) indicating that these changes are not due to pharmacokinetic mechanisms, and they provide initial evidence showing enhanced sensitivity to behavioral effects of dopamine receptor drugs in rats eating a high fat diet. These changes in sensitivity of dopamine systems could be relevant to understanding the impact of nutrition on therapeutic and recreational drug use.

Behavioral analyses of GHB: receptor mechanisms

GHB is used therapeutically and recreationally, although the precise mechanism of action responsible for its different behavioral effects is not entirely clear. The purpose of this review is to summarize how behavioral procedures, especially drug discrimination procedures, have been used to study the mechanism of action of GHB. More specifically, we will review several different drug discrimination procedures and discuss how they have been used to qualitatively and quantitatively study different components of the complex mechanism of action of GHB. A growing number of studies have provided evidence that the behavioral effects of GHB are mediated predominantly by GABAB receptors. However, there is also evidence that the mechanisms mediating the effects of GHB and the prototypical GABAB receptor agonist baclofen are not identical, and that other mechanisms such as GHB receptors and subtypes of GABAA and GABAB receptors might contribute to the effects of GHB. These findings are consistent with the different behavioral profile, abuse liability, and therapeutic indications of GHB and baclofen. A better understanding of the similarities and differences between GHB and baclofen, as well as the pharmacological mechanisms of action underlying the recreational and therapeutic effects of GHB, could lead to more effective medications with fewer adverse effects.

Cataleptic effects of gamma-hydroxybutyrate (GHB) and baclofen in mice: mediation by GABA(B) receptors, but differential enhancement by N-methyl-d-aspartate (NMDA) receptor antagonists

RATIONALE

Gamma-hydroxybutyrate (GHB) is a gamma-aminobutyric acid (GABA) analog that is used to treat narcolepsy but that is also abused. GHB has many actions in common with the GABA(B) receptor agonist baclofen, but their underlying GABA(B) receptor mechanisms may be different.

OBJECTIVE

The aim of this study is to further investigate a possible differential role of glutamate in GABA(B) receptor-mediated effects of GHB and baclofen.

MATERIALS AND METHODS

The experiments examined the effects of non-competitive antagonists at the N-methyl-d-aspartate (NMDA) subtype of glutamate receptors on GHB-induced catalepsy and compared these effects with those on baclofen-induced catalepsy.

RESULTS

In C57BL/6J mice, ketamine, phencyclidine (PCP), and dizocilpine (MK-801) all enhanced GHB-induced catalepsy. They did so with a potency order (i.e., MK-801 > PCP > ketamine) consistent with their relative potencies as NMDA antagonists but not as inhibitors of dopamine or organic cation transporters. Ketamine, PCP, and MK-801 enhanced catalepsy along inverted U-shaped dose-response curves likely because higher doses affected motor coordination, which limited their catalepsy-enhancing effects. Doses that were maximally effective to enhance GHB-induced catalepsy did not affect the cataleptic effects of baclofen.

CONCLUSIONS

The finding that NMDA receptor antagonists enhance the cataleptic effects of GHB but not those of baclofen is further evidence that the GABA(B) receptor mechanisms mediating the effects of GHB and GABA(B) agonists are not identical. Differential interactions of glutamate with the GABA(B) receptor mechanisms mediating the effects of GHB and baclofen may explain why GHB is effective for treating narcolepsy and is abused, whereas baclofen is not.

Synergistic interactions between 'club drugs': gamma-hydroxybutyrate and phencyclidine enhance each other's discriminative stimulus effects

Gamma-hydroxybutyrate (GHB) is often abused together with other 'club drugs', such as the N-methyl-D-aspartate (NMDA) receptor antagonists ketamine and phencyclidine (PCP). We recently found that the NMDA antagonist dizocilpine markedly enhanced GHB-induced catalepsy in rats. The present studies explored the generality of this interaction. Different groups of rats were trained to discriminate 2 mg/kg PCP or 3.2 mg/kg of the gamma-aminobutyric acid B receptor agonist baclofen from saline. In the PCP-trained rats, the dose-response (DR) curve for the discriminative stimulus (DS) effects of PCP was shifted 2.5-fold to the left by 178 mg/kg GHB, but not by baclofen. In the baclofen-trained rats, 2 mg/kg PCP shifted the DR curve for the baclofen-like DS effects of GHB 2.2-fold to the left, but did not shift the DR curve for baclofen. These results suggest that (i) NMDA antagonists potentiate not only the cataleptic effects of high doses of GHB, but also the DS effects of low doses, (ii) PCP and GHB enhance one another's DS effects, and (iii) this enhancement might be specific for GHB, because it did not occur with PCP and baclofen. These findings suggest that NMDA antagonists might potentiate the subjective effects of GHB in humans, and are further evidence that glutamatergic systems modulate effects of drugs of abuse.

Cataleptic effects of gamma-hydroxybutyrate (GHB), its precursor gamma-butyrolactone (GBL), and GABAB receptor agonists in mice: differential antagonism by the GABAB receptor antagonist CGP35348

RATIONALE

Gamma-hydroxybutyrate (GHB) is used to treat narcolepsy but is also abused. GHB has many actions in common with the GABA(B) receptor agonist baclofen.

OBJECTIVE

To further study the role of GABA(B) receptors in the effects of GHB.

MATERIALS AND METHODS

The experiments examined the ability of the GABA(B) receptor antagonist CGP35348 to attenuate GHB-induced catalepsy in comparison with its ability to attenuate the cataleptic effects of GABA(B) receptor agonists.

RESULTS

In C57BL/6J mice, GHB, the GHB precursor gamma-butyrolactone (GBL), and the GABA(B) receptor agonists baclofen and SKF97541 all produced catalepsy but differed in potency (i.e., SKF97541>baclofen>GBL>GHB) and in onset of action. The cataleptic effects of drug combinations were assessed at the time of peak effect of each compound, i.e., 60 min after CGP35348 and 60, 30, 30, and 15 min after baclofen, SKF97541, GHB, and GBL, respectively. At 100 mg/kg, CGP35348 shifted the dose-response curves of baclofen and SKF97541 to the right but not those of GHB and GBL; at 320 mg/kg, CGP35348 shifted the curves of all four compounds to the right.

CONCLUSIONS

The finding that CGP35348 was about threefold less potent to antagonize GHB and GBL than baclofen and SKF97541 is further evidence that the mechanisms mediating the effects of GHB and GABA(B) agonists are not identical. Differential involvement of GABA(B) receptor subtypes, or differential interactions with GABA(B) receptors, may possibly explain why GHB is effective for treating narcolepsy and is abused whereas baclofen is not.

Anti-aggressive effects of GHB in OF.1 strain mice: involvement of dopamine D2 receptors

Numerous studies indicate that gamma-hydroxybutyric acid (GHB) influences the endogenous dopamine system. Both GHB and most dopaminergic D(2) receptor antagonists are effective anti-aggressive agents in animal models. The present study aimed to investigate the effects of GHB on agonistic behaviour and to implicate D(2) dopamine receptor on these behaviours. For this purpose, the effects of GHB (80, 120 and 160 mg/kg, IP) and tiapride (60 mg/kg) administered alone or in combination were examined on agonistic behaviour elicited by 'isolation' in male mice. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. The administration of 80 and 120 mg/kg of GHB reduced threat without impairing motor activity, but the administration of 160 mg/kg of GHB or the co-administration of GHB+tiapride (a selective D(2) receptor antagonist) significantly reduced threat and attack but concomitantly increased immobility. The co-administration of GHB+tiapride had different effects to those observed by the administration of these drugs separately. It is concluded that the anti-aggressive effect of GHB appears to be mediated, at least in part, by D(2) dopamine receptors. This anti-dopaminergic activity is an indirect effect, probably induced by the activation of GHB receptors of low affinity, and in this way, this compound would reduce levels of dopamine without blockading of D(2) postsynaptic dopamine receptors.

Insulin replacement restores the behavioral effects of quinpirole and raclopride in streptozotocin-treated rats

Streptozotocin (STZ)-induced diabetes can modulate dopamine (DA) neurotransmission and thereby modify the behavioral effects of drugs acting on DA systems. Insulin replacement, and in some conditions repeated treatment with amphetamine, can partially restore sensitivity of STZ-treated rats to dopaminergic drugs. The present study sought to characterize the role of insulin and amphetamine in modulating the behavioral effects of drugs that selectively act on D2/D3 receptors. In control rats, quinpirole and quinelorane produced yawning, whereas raclopride and gamma-hydroxybutyric acid (GHB) produced catalepsy. Raclopride antagonized quinpirole- and quinelorane-induced yawning with similar potency. STZ treatment increased blood glucose concentration, decreased body weight, and markedly reduced sensitivity to quinpirole-induced yawning, quinelorane-induced yawning as well as to raclopride-induced catalepsy, while enhancing sensitivity to GHB-induced catalepsy. Repeated treatment with amphetamine partially restored sensitivity of STZ-treated rats to amphetamine-stimulated locomotion and also produced conditioned place preference, without affecting blood glucose and body weight changes. However, amphetamine treatment did not restore sensitivity to the behavioral effects of quinpirole, raclopride, or GHB, suggesting differential regulation of dopamine transporter activity and sensitivity of D2 receptors in hypoinsulinemic rats. Insulin replacement in STZ-treated rats normalized blood glucose and body weight changes and fully restored sensitivity to quinpirole-induced yawning, as well as to raclopride-induced catalepsy, while reducing sensitivity to GHB-induced catalepsy. Overall, these data indicate that changes in insulin status markedly affect sensitivity to the behavioral effects of dopaminergic drugs. The results underscore the importance of insulin in modulating DA neurotransmission; these effects might be especially relevant to understanding the co-morbidity of eating disorders and substance abuse.

Involvement of gamma-hydroxybutyrate (GHB) and GABA-B receptors in the acute behavioral effects of GHB in baboons

RATIONALE

Gamma-hydroxybutyrate (GHB) is used for the treatment of narcolepsy, but it is also a drug of abuse. The behavioral pharmacology of GHB is not well defined.

OBJECTIVES

The current study was conducted to characterize the behavioral effects of a range of GHB doses in baboons (N=4) and to evaluate whether a GABA-B receptor antagonist and a GHB receptor antagonist would block a behaviorally active dose of GHB.

METHODS

In the first experiment, GHB (32-420 mg/kg) or vehicle was administered via an intragastric catheter. Sixty min after dosing, subjects were presented with a fine-motor task and observed. Food pellets were available under a fixed-ratio schedule of reinforcement 20-h/day. In the second experiment, the GABA-B antagonist CGP36742 (10-56 mg/kg), the putative GHB antagonist NCS-382 (0.1-10 mg/kg), or vehicle were administered alone and then in combination with GHB (320 mg/kg).

RESULTS

GHB dose-dependently decreased the number of food pellets earned. Performance in the motor task was also impaired and accompanied by signs of sedation and gastrointestinal discomfort. Pretreatment with CGP36742 antagonized GHB-induced suppression of food-maintained behavior and performance on the fine-motor task. Signs of abdominal discomfort, ataxia, and muscle relaxation produced by GHB were also reduced by pretreatment with CGP36742. In contrast, pretreatment with NCS-382 sometimes restored performance in the fine-motor task and increased food-maintained behavior, but the effect was variable across doses and baboons. Some doses of NCS-382 appeared to exacerbate ataxia and gastrointestinal discomfort produced by GHB in some subjects.

CONCLUSIONS

These data indicate that while GABA-B receptors play a significant role in mediating the behavioral effects of GHB in baboon, the role of GHB receptors is less clear.

Streptozotocin-induced diabetes differentially modifies haloperidol- and γ-hydroxybutyric acid (GHB)-induced catalepsy

To examine whether dopamine-mediated behavioral effects are altered in diabetes, this study compared the cataleptic effects of the dopamine receptor antagonist haloperidol (0.032-0.56 mg/kg) and gamma-hydroxybutyric acid (GHB; 56-1000 mg/kg) in control and streptozotocin (STZ)-treated rats. Haloperidol and GHB produced catalepsy in control and diabetic rats; haloperidol was less potent in diabetic rats (D(50)=0.44 mg/kg) than in controls (D(50)=0.19 mg/kg), while GHB was more potent in diabetic rats (D(50)=392 mg/kg) than in controls (D(50)=550 mg/kg). In diabetic rats, the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist dizocilpine (0.32 mg/kg) further attenuated haloperidol-induced catalepsy (D(50)=1.2 mg/kg) and further enhanced GHB-induced catalepsy (D(50)=248 mg/kg). That haloperidol is less potent to produce catalepsy in diabetic rats is consistent with reports of altered dopamine receptor binding in diabetes.

Comparison of the behavioral effects of gamma-hydroxybutyric acid (GHB) and its 4-methyl-substituted analog, gamma-hydroxyvaleric acid (GHV)

Gamma-hydroxybutyrate (GHB), a metabolite of GABA, is a drug of abuse and a therapeutic. The illicit use of GHB precursors and analogs reportedly has increased worldwide. Gamma-hydroxyvaleric (GHV) is a 4-methyl-substituted analog of GHB that reportedly is abused and is marketed as a dietary supplement and replacement for GHB. The purpose of these studies was to compare the pharmacological and behavioral profiles of GHV and GHB. In radioligand binding studies, GHV completely displaced [(3)H]NCS-382 with approximately 2-fold lower affinity than GHB and did not markedly displace [(3)H]GABA from GABA(B) receptors at a 20-fold larger concentration. In drug discrimination procedures, GHV did not share discriminative stimulus effects with GHB or baclofen. GHV shared other behavioral effects with GHB, such as sedation, catalepsy, and ataxia, although larger doses of GHV were required to produce these effects. Lethality (50%) was observed after the largest dose of GHV (5600mg/kg), a dose that produced less-than-maximal catalepsy and ataxia. To the extent that large doses of GHV might be taken to in an attempt to produce GHB-like effects (e.g., hypnosis) GHV toxicity may pose a greater public health concern than GHB.

Novel gamma-hydroxybutyric acid (GHB) analogs share some, but not all, of the behavioral effects of GHB and GABAB receptor agonists

gamma-Hydroxybutyrate (GHB), a therapeutic for narcolepsy and a drug of abuse, has several mechanisms of action that involve GHB and GABA(B) receptors, metabolism to GABA, and modulation of dopaminergic signaling. The aim of these studies was to examine the role of GHB and GABA(B) receptors in the behavioral effects of GHB. Three approaches were used to synthesize GHB analogs that bind selectively to GHB receptors and are not metabolized to GABA-active compounds. Radioligand binding assays identified UMB86 (4-hydroxy-4-napthylbutanoic acid, sodium salt), UMB72 [4-(3-phenylpropyloxy)butyric acid, sodium salt], UMB73 (4-benzyloxybutyric acid, sodium salt), 2-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid (3-HPA), and 4-hydroxy-4-phenylbutyric acid as compounds that displace [(3)H]NCS-382 [5-[(3)H]-(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7] annulen-6-ylidene) ethanoic acid] from GHB receptors at concentrations that do not markedly affect [(3)H]GABA binding to GABA(B) receptors. In rats and pigeons, GHB discriminative stimulus effects were not mimicked or attenuated by UMB86, UMB72, or 3-HPA up to doses that decreased responding. In mice, GHB, GHB precursors (gamma-butyrolactone and 1,4-butanediol) and GABA(B) receptor agonists [SKF97541 [3-aminopropyl(methyl)phosphinic acid hydrochloride] and baclofen] dose-dependently produced hypolocomotion, catalepsy, ataxia, and loss of righting. The GABA(B) receptor antagonist CGP35348 (3-aminopropyl(diethoxymethyl)phosphinic acid) attenuated catalepsy and ataxia that was observed after GHB and GABA(B) receptor agonists SKF97541 and baclofen. UMB86, UMB72, UMB73, and 3-HPA, like GHB, produced hypolocomotion, ataxia, and loss of righting; however, catalepsy was never observed with these compounds, which is consistent with the cataleptic effects of GHB being mediated by GABA(B) receptors. Ataxia that was observed with UMB86, UMB72, UMB73, and 3-HPA was not antagonized by CGP35348, suggesting that ataxia induced by these analogs is not mediated by GABA(B) receptors and might involve GHB receptors.