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Psychostimulants include a number of synthetic and natural compounds. The most prevalent and harmful (causing health damage, violence, death, etc.) are traditionally considered to be cocaine, amphetamine, and its derivative methamphetamine. In Europe, nearly 3 million young adults aged 15–35 (2.4% of this age population) are estimated to have used cocaine and about 1.5 million are estimated to have used amphetamines (1.2%) in the past year, and the trend of the stimulant use is increasing. Concerning their pharmacological effects, stimulants directly increase the dopamine concentrations in the NAC, mainly through axonal membrane monoamine-dopamine transporters (MATs) manipulation. Cocaine acts as short-term monoamine reuptake inhibitor, while amphetamines promote reverse transport (efflux) through MATs and also induce synaptic vesicle depletion (the blockage of VMATs), thus causing a massive prolonged accumbens dopamine increase. Psychostimulants show stimulatory and sympathomimetic effects and induce a loss of appetite. Food restriction (FR) increases stimulant (amphetamine, D1 agonist A77636) consumption and signs of reward, and increases amphetamine/cocaine intake and the reinstatement of drug-seeking behavior. Thus, the relationship between ghrelin/GHS-R1As and the pro-addictive effects of stimulants has been explored in a considerable number of preclinical studies and two clinical studies so far.
PRECLINICAL STUDIES—STIMULANTS | |||
Study Design | Results | Drug of Abuse | Reference |
Drug effect on the ghrelin blood concentrations | Total ghrelin blood levels were increased following drug single dose administration (in rats) | Methamphetamine | Crowley et al. [1] |
Methamphetamine and high doses of MDMA | Kobeissy et al. [2] | ||
Drug IVSA and extinction/anticipation significantly increased both acyl- and des-acyl ghrelin blood levels (in rats) Blockade of peripheral adrenergic ß1 receptors by atenolol attenuated the elevation in circulating ghrelin induced by cocaine |
Cocaine | You et al. [4][5] | |
Total ghrelin blood levels positively correlated with cue-induced cocaine-seeking behavior (in rats) | Cocaine (cue) | Tessari et al. [3] | |
Acyl-ghrelin administration effects | Systemic pretreatment with acute ghrelin augmented/sensitized acute cocaine-induced hyperlocomotion (in rats) | Cocaine | Wellman et al. [8] |
Systemic pretreatment with repeated ghrelin augmented/sensitized acute cocaine-induced hyperlocomotion (in rats) | Cocaine | Wellman et al. [9] | |
Central (NAC-core) pretreatment with ghrelin augmented/sensitized acute drug-induced hyperlocomotion (in rats) | Cocaine | [14] | |
Central (NAC-core) pretreatment with ghrelin augmented acute drug-induced hyperlocomotion and in co-administration with D1-agonist also the drug-induced behavioral senzitization (in rats) | Amphetamine | Jang et al. [15] | |
Systemic pretreatment with ghrelin increased development of drug-induced place preference (CPP) (in rats) | Cocaine | Davis et al. [16] | |
Central (VTA) pretreatment with ghrelin increased development of drug-induced place preference (CPP) (in rats) | Cocaine | Schuette et al. [17] | |
Central (VTA and NAC) pretreatment with ghrelin increased development of drug-CPP and this was attenuated when JMV2959 was centrally co-administered with ghrelin (in rats) | Cocaine | Dunn et al. [18] | |
Systemic and central (VTA) ghrelin augments cocaine-enhanced alcohol consumption (in rats) | Cocaine (alcohol) | Cepko et al. [20] | |
GHS-R1A antagonist administration | Systemic JMV2959 pretreatment decreased the drug-induced hyperlocomotion (in mice) | Cocaine and Amphetamine | Jerlhag et al. [23] |
Systemic JMV2959 pretreatment decreases the expression of drug-induced conditioned place preference expression (CPP) and accumbens dopamine release (in mice) | Cocaine and Amphetamine | Jerlhag et al. [23] | |
Repeated systemic JMV2959 pretreatment decreases the drug-induced hyperlocomotion (in mice) | Amphetamine | Suchankova et al. [24] | |
Systemic JMV2959 reduced systemic drug-induced increase of dopamine in the NAC-shell and in the VTA (in rats) | Amphetamine | Edvardsson et al. [27] | |
Systemic repeated JMV2959 together with cocaine decreased the drug-induced behavioral sensitization (in rats) | Cocaine | Clifford et al. [25] | |
Systemic JMV2959 pretreatment decreased the drug intravenous self-administration (IVSA) and drug-seeking behavior, plus the expression and also development of drug-induced conditioned place preference (CPP) (in rats) | Methamphetamine | Havlickova et al. [26] | |
Systemic JMV2959 pretreatment decreased the drug-induced CPP, as well as the body weight gain. However, acyl-ghrelin antibodies administration attenuated the weight gain but not the cocaine-CPP, which indicated, that the GHS-R1A effects on reward are independent from peripheral acyl-ghrelin binding (in mice) | Cocaine | Wenthur et al. [19] | |
Systemic JMV2959 pretreatment dose-dependently inhibited drug-IVSA, drug-seeking, and reinstatement of drug-seeking triggered by the drug (in rats) | Cocaine | You et al. [5] | |
Systemic JMV2959 pretreatment inhibited the brain stimulation reward (BSR) and drug-potentiated BSR maintained by optogenetic stimulation of VTA dopamine (in mice) | Cocaine | You et al. [5] | |
GHS-R1A knockout animals | GHS-R1A gene knockouts show reduced drug-induced behavioral sensitization (rats) | Cocaine | Clifford et al. [25] |
Ghrelin peptide gene (GHRL) knockout animals | GHRL gene knockouts showed reduced drug-induced hyperlocomotion as well as reduction of behavioral sensitization dopamine content in striatal dissections (30 min after cocaine) did not differ between GHRL knockouts and wild mice |
Cocaine | Abizaid et al. [36] |
CLINICAL STUDIES—STIMULANTS | |||
Study Design | Results | Drug of Abuse | Reference |
Genetic study | No association between pre-proghrelin gene (GHRL) variations and the drug dependence, but correlation between SNP on GHRL and emotional problems (depression, anxiety) was found (Korean population) | Methamphetamine | Yoon et al. [32] |
SNP located on the ghrelin receptor gene GHSR seemed associated with the drug dependence; no differences were found between drug-dependent and healthy participants in SNP on the pre-proghrelin gene (GHRL) (Swedish population) | Amphetamine | Suchankova et al. [33] | |
Ghrelin blood levels | In children with ADHD the total ghrelin blood levels were increased after two months treatment with the drug in comparison to basal pretreatment levels | Methylphenidate | Sahin et al. [35] |
No significant effect of intravenous drug administration in experienced cocaine users on the acyl- or total ghrelin blood levels was observed | Cocaine | Bouhlal et al. [34] |