Isradipine blocks cocaine's ability to facilitate pressing for intracranial stimulation

Isradipine augmentation of virtual reality cue exposure therapy for tobacco craving: a triple-blind randomized controlled trial

Preclinical research with rodents suggests that the L-type calcium channel blocker isradipine can enhance long-term extinction of conditioned place preference for addictive substances when it is administered in conjunction with extinction training. Although isradipine alone, which is FDA-approved for hypertension, has not shown a direct effect on craving in human drug users, its potential to augment behavioral treatments designed to reduce craving remains unknown. We conducted a triple-blind, randomized placebo-controlled pilot clinical trial of isradipine combined with a novel virtual reality cue exposure therapy (VR-CET) approach with multimodal cues that targeted craving. After 24 hours of abstinence, 78 adults with an ongoing history of daily cigarette use received isradipine (n = 40) or placebo (n = 38) and reported craving levels after each of 10 trials of VR-CET. Consistent with pre-registered hypotheses, the isradipine group had significantly lower mean craving across cue exposure trials at the medication-free 24-hour follow-up (d = -0.42, p = 0.046). There were no serious adverse events; however, side effects such as headache and dizziness occurred more frequently in the isradipine group. The findings of the current study support follow-up clinical trials that specifically test the efficacy of isradipine-augmented VR-CET for reducing smoking relapse rates after an initial quit attempt. clinicaltrials.gov: NCT03083353.

Augmented behavioral response and enhanced synaptosomal calcium transport induced by repeated cocaine administration are decreased by calcium channel blockers

Recent studies suggest that calcium influx via L-type calcium channels is necessary for psychostimulant-induced behavioral sensitization. In addition, chronic amphetamine upregulates subtype Cav1.2-containing L-type calcium channels. In the present studies, we assessed the effect of calcium channel blockers (CCBs) on cocaine-induced behavioral sensitization and determined whether the functional activity of L-type calcium channels is altered after repeated cocaine administration. Rats were administered daily intraperitoneal injections of either flunarizine (40 mg/kg), diltiazem (40 mg/kg) or cocaine (20 mg/kg) and the combination of the CCBs and cocaine for 30 days. Motor activities were monitored on Day 1, and every 6th day during the 30-day treatment period. Daily cocaine administration produced increased locomotor activity. Maximal augmentation of behavioral response to repeated cocaine administration was observed on Day 18. Flunarizine pretreatment abolished the augmented behavioral response to repeated cocaine administration while diltiazem was less effective. Measurement of tissue monoamine levels on Day 18 revealed cocaine-induced increases in DA and 5-HT in the nucleus accumbens. By contrast to behavioral response, diltiazem was more effective in attenuating increases in monoamine levels than flunarizine. Cocaine administration for 18 days produced increases in calcium uptake in synaptosomes prepared from the nucleus accumbens and frontal cortex. Increases in calcium uptake were abolished by flunarizine and diltiazem pretreatment. Taken together, the augmented cocaine-induced behavioral response on Day 18 may be due to increased calcium uptake in the nucleus accumbens leading to increased dopamine (DA) and serotonin (5-HT) release. Flunarizine and diltiazem attenuated the behavioral response by decreasing calcium uptake and decreasing neurochemical release.

Cocaine-induced alterations in dopamine receptor signaling: Implications for reinforcement and reinstatement

The transition from casual drug use to addiction, and the intense drug craving that accompanies it, has been postulated to result from neuroadaptations within the limbic system caused by repeated drug exposure. This review will examine the implications of cocaine-induced alterations in mesolimbic dopamine receptor signaling within the context of several widely used animal models of addiction. Extensive evidence indicates that dopaminergic mechanisms critically mediate behavioral sensitization to cocaine, cocaine-induced conditioned place preference, cocaine self-administration, and the drug prime-induced reinstatement of cocaine-seeking behavior. The propagation of the long-term neuronal changes associated with recurring cocaine use appears to occur at the level of postreceptor signal transduction. Repeated cocaine treatment causes an up-regulation of the 3',5'-cyclic adenosine monophosphate (cAMP)-signaling pathway within the nucleus accumbens, resulting in a dys-regulation of balanced D1/D2 dopamine-like receptor signaling. The intracellular events arising from enhanced D1-like postsynaptic signaling mediate both facilitatory and compensatory responses to the further reinforcing effects of cocaine.

Research with rats germane to medication for alcoholism: consequences of noncompliance

Results of prior work indicate that (a) rats take stable, toxic levels of ethanol when they receive a daily regimen of limited opportunities to take both water and sweetened ethanol solution and (b) the combination of isradipine plus naltrexone persistently reduces those intakes. What are the effects of periodically missing doses of isradipine, naltrexone, or both? That is, what are the effects of differing levels of compliance? To get relevant information, rats were placed on a daily regimen, leading them to take, by choice, large amounts of ethanol (>2.0 g of ethanol per kilogram of body weight during 2 h a day). After being on this regimen for more than 60 days and after 28 days of no opportunity to take ethanol, 55 rats were divided into five groups. The opportunity to drink was then reinstated. One group received placebos, and another group received the combination of isradipine plus naltrexone daily. The other three groups received doses periodically, thereby conforming to good, moderate, and poor compliance. After abstinence, the intakes for rats receiving placebos rapidly returned to high levels. Intakes for rats receiving daily isradipine plus naltrexone did not return to high levels. The intakes for the other three groups were intermediate to intakes of the reference groups, corresponding to frequency of medication. When medication was not given, intakes approached placebo control levels, but the combination of isradipine plus naltrexone was effective when given subsequently. Daily dosing clearly is effective in reducing intakes, and suspension of dosing leads to higher intakes. A missed day of dosing, however, has limited consequences, provided that administration of medication is resumed.

Amlodipine, a calcium channel inhibitor, and cocaine and ethanol's reinforcing effects

The effects of amlodipine (from 0.1 to 3.0 mg/kg) on rats' pressing for rewarding brain stimulation, with and without cocaine administration, were assessed. None of the doses reliably modified the effects of cocaine. Also, amlodipine was given to two groups of rats taking alcohol: one group that was regularly taking a sweetened alcoholic beverage and the other taking an unsweetened alcoholic beverage. The only discernible effects of amlodipine on alcohol intake were associated with the highest dose and only with rats taking the sweetened beverage. The effects of this high dose could easily be attributable to behavioral toxicity elicited by the dose. In contrast, and confirming previous work, isradipine, another calcium channel inhibitor, produced reliable reductions on both cocaine's and alcohol's reinforcing effects. Despite the similarity of isradipine and amlodipine, isradipine apparently has some unique features with respect to cocaine and alcohol.

Responding for rewarding brain stimulation: cocaine and isradipine plus naltrexone

Rats, fixed with chronically indwelling electrodes for electrical intracranial stimulation (ICS) of the lateral hypothalamus, were taught to press a bar for ICS. Once pressing rates became stable, during daily 20-min sessions, rats were given cocaine (5 or 20 mg/kg) before the sessions. When given daily, cocaine consistently enhanced rates of pressing. When a combination of small doses of isradipine (e.g., 1 mg/kg) and naltrexone (3 mg/kg) were given before cocaine administration. the combination blocked cocaine's enhancement of pressing for ICS. The combination, however, neither reduced rates of pressing below those observed under placebos (i.e., baseline conditions) nor reduced rates when no cocaine was given. Naltrexone and isradipine (in the dose used in the combination) by themselves did not block cocaine's effects. This profile of effects indicates that a combination of isradipine and naltrexone is apt to be useful in treating cocaine use disorders.