Pre-exposure to ethanol, but not to caffeine and nicotine, induced place preference and self-administration of the NMDA receptor antagonist-benzodiazepine combination, Zoletil®

Pituitary Adenylate Cyclase-Activating Polypeptide: A Potent Therapeutic Agent in Oxidative Stress

Stroke is a life-threatening condition that is characterized by secondary cell death processes that occur after the initial disruption of blood flow to the brain. The inability of endogenous repair mechanisms to sufficiently support functional recovery in stroke patients and the inadequate treatment options available are cause for concern. The pathology behind oxidative stress in stroke is of particular interest due to its detrimental effects on the brain. The oxidative stress caused by ischemic stroke overwhelms the neutralization capacity of the body's endogenous antioxidant system, which leads to an overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and eventually results in cell death. The overproduction of ROS compromises the functional and structural integrity of brain tissue. Therefore, it is essential to investigate the mechanisms involved in oxidative stress to help obtain adequate treatment options for stroke. Here, we focus on the latest preclinical research that details the mechanisms behind secondary cell death processes that cause many central nervous system (CNS) disorders, as well as research that relates to how the neuroprotective molecular mechanisms of pituitary adenylate cyclase-activating polypeptides (PACAPs) could make these molecules an ideal candidate for the treatment of stroke.

Evaluation of the abuse potential of AM281, a new synthetic cannabinoid CB1 receptor antagonist

AM281 (1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide) is a new synthetic cannabinoid CB1 receptor antagonist. Similar to other cannabinoid antagonists, AM281 has been suggested to have therapeutic indications. However, recent reports have suggested that cannabinoid CB1 receptor antagonists may share similar behavioral effects with other drugs of abuse such as cocaine and amphetamine. These reports cast doubts on the safety profile of AM281. Thus, in the present study we evaluated the abuse potential (rewarding and reinforcing effects) of AM281 through two of the most widely used animal models for assessing the abuse potential of drugs: the conditioned place preference (CPP) and self-administration (SA) tests. Experiments were performed in Sprague-Dawley rats in various dosages [CPP (0.1, 0.5 or 2.5mg/kg), SA (0.005, 0.025 or 0.1mg/kg/infusion)]. We also delved into the consequences of repeated drug exposure on the subsequent response to the drug. Thus, parallel experiments were carried out in rats pretreated with AM281 for 7 or 14 days. Our findings indicated that AM281, at any dose, did not induce CPP and SA in drug-naïve rats. Interestingly, significant CPP (0.5mg/kg of AM281), but not SA, was observed in 14 days pretreated rats. These observations suggest that AM281 per se has no or minimal rewarding and reinforcing properties, but alterations in neuronal functions and behavior due to repeated AM281 exposure may contribute in part to the abuse potential of this drug. In view of this finding, we advocate the careful use, monitoring, and dispensation of AM281.

Conditioned place preference and self-administration induced by nicotine in adolescent and adult rats

Nicotine addiction is a worldwide problem. However, previous studies characterizing the rewarding and reinforcing effects of nicotine in animal models have reported inconsistent findings. It was observed that the addictive effects are variable on different factors (e.g. route, dose, and age). Here, we evaluated the rewarding and reinforcing effects of nicotine in different routes of administration, across a wide dose range, and in different age groups. Two of the most widely used animal models of drug addiction were employed: the conditioned place preference (CPP) and self-administration (SA) tests. Nicotine CPP was evaluated in different routes [intraperitoneal (i.p.) and subcutaneous (s.c.)], doses (0.05 to 1.0 mg/kg) and age [adolescent and adult rats]. Similarly, intravenous nicotine SA was assessed in different doses (0.01 to 0.06 mg/kg/infusion) and age (adolescent and adult rats). In the CPP test, s.c. nicotine produced greater response than i.p. The 0.2 mg/kg dose produced highest CPP response in adolescent, while 0.6 mg/kg in adult rats; which were also confirmed in 7 days pretreated rats. In the SA test, adolescent rats readily self-administer 0.03 mg/kg/infusion of nicotine. Doses that produced nicotine CPP and SA induced blood nicotine levels that corresponded well with human smokers. In conclusion, we have demonstrated that nicotine produces reliable CPP [0.2 mg/kg dose (s.c.)] in adolescents and [0.6 mg/kg dose (s.c.)] in adults, and SA [0.03 mg/kg/infusion] in adolescent rats. Both tests indicate that adolescent rats are more sensitive to the rewarding and reinforcing effects of nicotine.

Adolescent nicotine or cigarette smoke exposure changes subsequent response to nicotine conditioned place preference and self-administration

Nicotine/cigarette addiction starts young. Indeed, most smokers started when they were adolescents. Adolescence has been implicated to be a critical period for nicotine/cigarette addiction, thus it is important to understand the consequences of such early exposure. In the present study, we sought to characterize the effects of adolescent nicotine or cigarette smoke pre-exposure on the subsequent addictive effects of nicotine. The rewarding and reinforcing effects of nicotine were evaluated in drug-naïve, nicotine pre-exposed, or cigarette smoke pre-exposed adolescent and adult rats, through the conditioned place preference (CPP) and the self-administration (SA) tests. In the CPP test, drug-naïve adolescent rats demonstrated CPP for the 0.2mg/kg dose of nicotine, while drug-naïve adult rats showed CPP for the relatively higher dose of 0.6mg/kg. Pre-exposed adolescent rats showed diminished response for the 0.2mg/kg, instead significant CPP was observed for the higher dose (0.6mg/kg) of nicotine. No significant change was observed in pre-exposed adult rats. Interestingly, cigarette smoke pre-exposed adolescent rats showed substantially higher nicotine CPP (0.6mg/kg) than to its nicotine-pre-exposed or adult counterpart. In the SA test, drug-naïve adolescent rats reliably produced stable nicotine (0.03mg/kg/infusion) self-administration, but drug-naïve adult rats did not. Surprisingly, however, nicotine or cigarette smoke pre-exposed adolescent and adult rats showed decreased nicotine self-administration. These results conform with the growing notion that adolescents are more sensitive to the addictive effects of nicotine and that nicotine or cigarette smoke exposure during this period produces complex behavioral changes which may influence subsequent response to nicotine.