Adenosine receptor agents and conditioned place preference

The effect of Coriandrum sativum seed extract on the learning of newborn mice by electric shock: interaction with caffeine and diazepam

Coriander has been recommended for the relief of pain, anxiety, flatulence, and loss of appetite. In traditional medicine, it is believed that coriander can induce some degree of amnesia in a child when his/her mother uses coriander during the pregnancy. We evaluated the effect of Coriandrum sativum seed extract on learning in second-generation mice. Ethanolic extract (2%) of coriander (100 mg/kg intraperitoneal) was dissolved in sunflower oil (oil) as a vehicle and injected into the control group mother mice during breastfeeding for 25 days at 5-day intervals. After feeding the newborn mice, their learning was evaluated using a step-through passive avoidance task with 0.4 mA electric shock for 2 or 4 seconds. While coriander extract showed a negative effect in the short term (1 hour) after the training session, it potentiated the mice's learning in later assessments (24 hours post-training [P = 0.022] and 1 week post-training [P = 0.002] by a 4-second shock). Low-dose caffeine (25 mg/kg ip after training) improved the learning after 1 hour (P = 0.024); while diazepam (1 mg/kg ip) suppressed learning at all time points after the 4-second shock training (1 hour, P = 0.022; 24 hours, P = 0.002; and 1 week, P = 0.008). No modification in the pain threshold was elicited by electric stimuli both in coriander and control groups. In conclusion, coriander does not improve learning within a short period of time after training; however, learning after coriander administration can be improved in the long term.

Methylxanthines and drug dependence: a focus on interactions with substances of abuse

This chapter examines the psychostimulant actions of methylxanthines, with a focus on the consequences of their excessive use. Consumption of methylxanthines is pervasive and their use is often associated with that of substances known to produce dependence and to have abuse potential. Therefore, the consequences of this combined use are taken into consideration in order to evaluate whether, and to what extent, methylxanthines could influence dependence on or abuse of other centrally active substances, leading to either amplification or attenuation of their effects. Since the methylxanthine that mostly influences mental processes and readily induces psychostimulation is caffeine, this review mainly focuses on caffeine as a prototype of methylxanthine-produced dependence, examining, at the same time, the risks related to caffeine use.

Effect of breastfeeding piperine on the learning of offspring mice: interaction with caffeine and diazepam

Piperine, the main alkaloid of black pepper (Piper nigrum), has been suggested to display several pharmacological properties, including pain relief, anticonvulsant, antidepressant-like, antianxiety, sedative, and anti-inflammatory effects. This study was designed to investigate the effect of piperine on learning in mice and the interaction of the effect with caffeine and diazepam. Piperine (100 mg/kg intraperitoneally) was injected into the mouse mothers or nursing dams during breastfeeding for 25 days at five-day intervals. After feeding the newborn mice, their learning was evaluated using a step-through passive avoidance task. Mouse learning was assessed 1 hr and 24 hr and 1 week after a training session. Piperine increased learning in the first (1 hr: 243.33 s vs 55.17 s, P = 0.002) and third assessments (1 week: 226 s vs 97 s, P < 0.05) post-training, but no significant change was seen at the second (24 hr) assessment. Piperine improved the effect of a low dose of caffeine (25 mg/kg intraperitoneally after a shock of 2 s duration) in a first assessment (295.17 s vs 149.17 s, P = 0.026) compared to a higher dose of caffeine. Piperine reversed diazepam (1 mg/kg intraperitoneally) suppression of learning 24 hours after training by a 4 s shock (298 s vs 135.67 s, P = 0.03). According to the results, piperine alone significantly increased learning 1 hour and 1 week after training assessments, and learning can be improved in the short term when followed by piperine administration. It was also shown that piperine can potentiate the effect of a low dose of caffeine and can reverse the effect of diazepam.

Theophylline inhibits tolerance and sensitization induced by morphine: a conditioned place preference paradigm study in female mice

The effect of theophylline on reward properties of morphine was examined in the present study. A biased conditioned place preference paradigm was used to study the effects of theophylline on the development of conditioned place preference by morphine in sensitized and tolerant female mice. Subcutaneous injection of morphine (0.5-10 mg/kg) induced conditioned place preference in mice, while intraperitoneal administration of theophylline (2.5-100 mg/kg) did not induce conditioned place preference or conditioned place aversion. Theophylline (2.5-100 mg/kg) in combination with morphine (5 mg/kg), during conditioning sessions, decreased the acquisition of morphine conditioned place preference dose independently. Administration of theophylline (2.5-100 mg/kg) before testing also caused a significant reduction of the expression of morphine-induced conditioned place preference in a dose-independent manner. Administration of morphine (12.5, 25 or 50 mg/kg) daily, for 3 days, produced tolerance to conditioned place preference induced by the drug (5 mg/kg). Administration of theophylline (2.5 and 10 mg/kg) 1 h before morphine (12.5, 25 mg/kg), during development of tolerance, abolished morphine tolerance. A higher dose of theophylline (100 mg/kg), however, did not alter morphine tolerance. In addition, theophylline (2.5, 10 and 100 mg/kg) failed to reduce tolerance to a higher dose of morphine (50 mg/kg). Daily administration of morphine (5 mg/kg) for 3 days followed by a 5-day interval caused sensitization to morphine place conditioning. When theophylline was administered (2.5, 10 and 100 mg/kg) 1 h before morphine (5 mg/kg), during development of sensitization, inhibition of morphine-induced sensitization was demonstrated. The effect of theophylline was dose independent. It is concluded that while theophylline has no effect by itself, it reduced both the acquisition and expression of morphine conditioned place preference. In addition, theophylline reduced the acquisition of morphine conditioned place preference in morphine-sensitized and morphine-tolerant mice.

Effect of imipramine on the expression and acquisition of morphine-induced conditioned place preference in mice

The effect of imipramine and alpha-adrenoceptor agonists and antagonists on the acquisition or expression of morphine-induced conditioned place preference (CPP) was studied in mice. An unbiased CPP paradigm was used to study the effect of the agents. In the first set of experiments, the drugs were used during the development of CPP by morphine or they were used alone in order to see if they induce CPP or conditioned place aversion (CPA). Our data showed that intraperitoneal injection of morphine sulphate (2.5-10 mg/kg) induced CPP in mice. Imipramine (0.5-2.5 mg/kg), phenylephrine (0.5-2 mg/kg), yohimbine (0.5-2 mg/kg) or prazosin (0.1-1 mg/kg) did not influence CPP, but clonidine (0.002-0.05 mg/kg) induced CPA. Yohimbine increased, while clonidine and prazosin reversed, morphine-induced CPP. Phenylephrine did not influence the CPP induced by morphine. In the second set of experiments, when the drugs were used before testing on Day 6, in order to test their effects on the expression of morphine-induced CPP, imipramine (0.5-5 mg/kg) reversed morphine-induced CPP and this reversal was blocked by naloxone (2 mg/kg). Clonidine and prazosin reversed, while yohimbine decreased morphine-induced CPP. Phenylephrine did not alter the morphine response. Furthermore, yohimbine and prazosin reversed the imipramine effect. None of the drugs influenced locomotion. However, prazosin or yohimbine in combination with morphine altered locomotor activity during the acquisition of CPP. Yohimbine by itself increased locomotion. It is concluded that imipramine can induce CPA through an opioid receptor mechanism and alpha-adrenoceptor agents may influence morphine CPP.

The effect of 7-nitroindazole on the acquisition and expression of D-methamphetamine-induced place preference in rats

The present study investigated the role of nitric oxide (NO) in the rewarding effects of D-methamphetamine using 7-nitroindazole, a potent inhibitor of neuronal nitric oxide synthase (nNOS), as determined by the conditioned place preference paradigm. Male Sprague-Dawley rats treated with D-methamphetamine (1 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed marked place preference for the drug-paired side. The administration of 7-nitroindazole (12.5-50 mg/kg) 30 min prior to the exposure to D-methamphetamine dose-dependently attenuated the acquisition of D-methamphetamine-induced conditioned place preference. In addition, when it was acutely administered 30 min prior to the testing session of an already established D-methamphetamine-induced conditioned place preference, 7-nitroindazole (12.5-50 mg/kg) attenuated the expression of this conditioned response in a dose-dependent manner, while 7-nitroindazole (25 and 50 mg/kg) alone showed no place preference effects. These findings indicate that nitric oxide (NO) is involved in the rewarding properties of methamphetamine and suggest that selective nNOS inhibitors maybe useful in the management of methamphetamine abuse.

Central adenosine A(2A) receptors: an overview

Recent advances in molecular biology, biochemistry, cell biology and behavioral pharmacology together with the development of more selective ligands to the various adenosine receptors have increased our understanding of the functioning of central adenosine A(2A) receptors. The A(2A) receptor is one of four adenosine receptors found in the brain. Its expression is highest in striatum, nucleus accumbens and olfactory tubercles, although it also occurs in neurons and microglia in most other brain regions. The receptor has seven transmembrane domains and couples via Gs to adenyl cyclase stimulation. Antagonistic interactions between A(2A) receptors and dopamine D(2) receptors have been described, as stimulation of the A(2A) receptor leads to a reduction in the affinity of D(2) receptors for D(2) receptor agonists. The A(2A) receptor is thought to play a role in a number of physiological responses and pathological conditions. Indeed, A(2A) receptor antagonists may be useful for the treatment of acute and chronic neurodegenerative disorders such as cerebral ischemia or Parkinson's disease. A(2A) receptor agonists may treat certain types of seizures or sleep disorders. This review discusses the characteristics, distribution, pharmacochemical properties and regulation of central A(2A) receptors, as well as A(2A) receptor-mediated behavioural responses and their potential role in various neuropsychiatric disorders.

Adenosine A(2) receptors inhibit morphine self-administration in rats

In the present study, the effect of adenosine receptor agonists and antagonists on morphine self-administration was investigated. Intravenous administration of morphine (0.3-3 mg/kg/injection) induced dose-dependent self-administration. The adenosine receptor antagonists, theophylline (2.5, 5, 10 mg/kg) and 3, 7-Dimethyl-1-propargylxanthine (DMPX; 0.25, 0.5, 1 mg/kg), when injected 1 h before the start of the test, reduced the number of self-administered morphine infusions. The adenosine receptor antagonists when administered in the training period (11 days) greatly increased the number of morphine infusions, however, they did not induce any response by themselves. 5'-N-ethylcarboxamido-adenosine (NECA; 0.5, 1 mg/kg) and 4-[2-[[6-Amino-9-(N-ethyl-beta-D-ribofuranuronamidosyl)-9H-purin-2 -yl ]amino] ethyl]benzenepropanoic acid (CGS21680; 0.001, 0.01, 0.025, 0. 05 mg/kg), given 1 h before the start of the test, increased morphine self-administration. Although the adenosine agonists, when injected during training period (11 days), reduced morphine self-administration. Furthermore, NECA, but not CGS21680, induced significant self-administration. The adenosine A(1) receptor agonist, N(6)-cyclohexyladenosine (CHA; 0.01, 0.1, 0.25, 0.5 and 1 mg/kg), and the adenosine A(1) receptor antagonist, 8-phenyletheophylline (2, 4, 6, 8 mg/kg), themselves neither altered morphine infusion nor induced any response. These results indicate a role for adenosine A(2) receptors in the expression and/or development of morphine self-administration.

Measuring reward with the conditioned place preference paradigm: a comprehensive review of drug effects, recent progress and new issues

This review gives an overview of recent findings and developments in research on brain mechanisms of reward and reinforcement from studies using the place preference conditioning paradigm, with emphasis on those studies that have been published within the last decade. Methodological issues of the paradigm (such as design of the conditioning apparatus, biased vs unbiased conditioning, state dependency effects) are discussed. Results from studies using systemic and local (intracranial) drug administration, natural reinforcers, and non-drug treatments and from studies examining the effects of lesions are presented. Papers reporting on conditioned place aversion (CPA) experiments are also included. A special emphasis is put on the issue of tolerance and sensitization to the rewarding properties of drugs. Transmitter systems that have been investigated with respect to their involvement in brain reward mechanisms include dopamine, opioids, acetylcholine, GABA, serotonin, glutamate, substance P, and cholecystokinin, the motivational significance of which has been examined either directly, by using respective agonist or antagonist drugs, or indirectly, by studying the effects of these drugs on the reward induced by other drugs. For a number of these transmitters, detailed studies have been conducted to delineate the receptor subtype(s) responsible for the mediation of the observed drug effects, particularly in the case of dopamine, the opioids, serotonin and glutamate. Brain sites that have been implicated in the mediation of drug-induced place conditioning include the 'traditional' brain reward sites, ventral tegmental area and nucleus accumbens, but the medial prefrontal cortex, ventral pallidum, amygdala and the pedunculopontine tegmental nucleus have also been shown to play important roles in the mediation of place conditioning induced by drugs or natural reinforcers. Thus, although the paradigm has also been criticized because of some inherent methodological problems, it is clear that during the past decade place preference conditioning has become a valuable and firmly established and very widely used tool in behavioural pharmacology and addiction research.