Chronic administration of a norepinephrine antagonist prevents and partially reverses escalation of cocaine self-administration

Anxiety is a critical component of the development and maintenance of drug addiction; however, anti-anxiety medications such as benzodiazepines and beta-blockers (β-adrenergic receptor antagonists) are not used for the treatment of substance use disorder, except for the management of acute withdrawal syndrome. Preclinical studies have shown that beta-blockers may reduce stress-induced relapse; however, the effect of beta blockers on the escalation and maintenance of drug intake has not been tested. To address this issue, we chronically administered the β-adrenergic receptor antagonist propranolol during the escalation or maintenance of cocaine intake in a model of extended access (6 h) to cocaine self-administration (0.5 mg/kg). The behavioural specificity of propranolol was tested using a non-drug reward (saccharin). Daily administration of propranolol (15 mg/kg) prevented the development of escalation of cocaine self-administration and partially reversed self-administration after the establishment of escalation of intake. Moreover, propranolol dose-dependently decreased the motivation for cocaine tested under a progressive ratio schedule of reinforcement during the development of escalation and after maintenance. Finally, propranolol administration had no effect on the escalation and maintenance of saccharin self-administration. These results demonstrate that chronic treatment with propranolol provides therapeutic efficacy in reducing cocaine self-administration during the development and after the establishment of escalation of cocaine self-administration in an animal model relevant to cocaine use disorder. These results suggest that beta blockers should be further investigated as a target for medication development for the treatment of cocaine use disorder.

Carboxymethyl cellulose-alginate interpenetrating hydroxy ethyl methacrylate crosslinked polyvinyl alcohol reinforced hybrid hydrogel templates with improved biological performance for cardiac tissue engineering

Cardiac tissue engineering is an emerging approach for cardiac regeneration utilizing the inherent healing responses elicited by the surviving heart using biomaterial templates. In this study, we aimed to develop hydrogel scaffolds for cardiac tissue regeneration following myocardial infarction (MI). Two superabsorbent hydrogels, CAHA2A and CAHA2AP, were developed employing interpenetration chemistry. CAHA2A was constituted with alginate, carboxymethyl cellulose, (hydroxyethyl) methacrylate, and acrylic acid, where CAHA2AP was prepared by interpenetrated CAHA2A with polyvinyl alcohol. Both hydrogels displayed superior physiochemical characteristics, as determined by attenuated total reflection infrared spectroscopy spectral analysis, differential scanning calorimetry measurements, tensile testing, contact angle, water profiling, dye release, and conductivity. In vitro degradation of the hydrogels displayed acceptable weight composure and pH changes. Both hydrogels were hemocompatible, and biocompatible as evidenced by direct contact and MTT assays. The hydrogels promoted anterograde and retrograde migration as determined by the z-stack analysis using H9c2 cells grown with both gels. Additionally, the coculture of the hydrogels with swine epicardial adipose tissue cells and cardiac fibroblasts resulted in synchronous growth without any toxicity. Also, both hydrogels facilitated the production of extracellular matrix by the H9c2 cells. Overall, the findings support an appreciable in vitro performance of both hydrogels for cardiac tissue engineering applications.

Validation of a nicotine vapor self-administration model in rats with relevance to electronic cigarette use

The debate about electronic cigarettes is dividing healthcare professionals, policymakers, manufacturers, and communities. A key limitation in our understanding of the cause and consequences of vaping is the lack of animal models of nicotine vapor self-administration. Here, we developed a novel model of voluntary electronic cigarette use in rats using operant behavior. We found that rats voluntarily exposed themselves to nicotine vapor to the point of reaching blood nicotine levels that are similar to humans. The level of responding on the active (nicotine) lever was similar to the inactive (air) lever and lower than the active lever that was associated with vehicle (polypropylene glycol/glycerol) vapor, suggesting low positive reinforcing effects and low nicotine vapor discrimination. Lever pressing behavior with nicotine vapor was pharmacologically prevented by the α4β2 nicotinic acetylcholine receptor partial agonist and α7 receptor full agonist varenicline in rats that self-administered nicotine but not vehicle vapor. Moreover, 3 weeks of daily (1 h) nicotine vapor self-administration produced addiction-like behaviors, including somatic signs of withdrawal, allodynia, anxiety-like behavior, and relapse-like behavior after 3 weeks of abstinence. Finally, 3 weeks of daily (1 h) nicotine vapor self-administration produced cardiopulmonary abnormalities and changes in α4, α3, and β2 nicotinic acetylcholine receptor subunit mRNA levels in the nucleus accumbens and medial prefrontal cortex. These findings validate a novel animal model of nicotine vapor self-administration in rodents with relevance to electronic cigarette use in humans and highlight the potential addictive properties and harmful effects of chronic nicotine vapor self-administration.

Oxycodone self-administration and withdrawal behaviors in male and female Wistar rats

RATIONALE

Over the last decade, oxycodone has become one of the most widely abused drugs in the USA. Oxycodone use disorder (OUD) is a serious health problem that has prompted a need to develop animal models of OUD that have both face and predictive validity. Oxycodone use in humans is more prevalent in women and leads to pronounced hyperalgesia and irritability during withdrawal. However, unclear is whether current animal models of oxycodone self-administration recapitulate these characteristics in humans.

OBJECTIVES

We assessed the face validity of a model of extended-access oxycodone self-administration in rats by examining the escalation of oxycodone intake and behavioral symptoms of withdrawal, including irritability-like behavior and mechanical nociception, in male and female Wistar rats.

RESULTS

Both male and female rats escalated their oxycodone intake over fourteen 12-h self-administration sessions. After escalation, female rats administered more drug than male rats. No differences in plasma oxycodone levels were identified, but males had a significantly higher level of oxycodone in the brain at 30 min. Extended access to oxycodone significantly decreased aggressive-like behavior and increased defensive-like behaviors when tested immediately after a 12-h self-administration session, followed by a rebound increase in aggressive-like behavior 12 h into withdrawal. Tests of mechanical nociception thresholds during withdrawal indicated pronounced hyperalgesia. No sex differences in irritability-like behavior or pain sensitivity were observed.

CONCLUSIONS

The present study demonstrated the face validity of the extended access model of oxycodone self-administration by identifying sex differences in the escalation of oxycodone intake and pronounced changes in pain and affective states.

Dopamine D3 Receptor Antagonism Reverses the Escalation of Oxycodone Self-administration and Decreases Withdrawal-Induced Hyperalgesia and Irritability-Like Behavior in Oxycodone-Dependent Heterogeneous Stock Rats

Prescription opioids, such as oxycodone, are highly effective analgesics for clinical pain management, but approximately 25% of patients who are prescribed opioids misuse them, and 5%–10% develop an opioid use disorder (OUD). Effective therapies for the prevention and treatment of opioid abuse and addiction need to be developed. The present study evaluated the effects of the highly selective dopamine D₃ receptor antagonist VK4-116 ([R]-N-[4-(4-[3-chloro-5-ethyl-2-methoxyphenyl]piperazin-1-yl)-3-hydroxybutyl]-1H-indole-2-carboxamide) on oxycodone addictive-like behaviors. We used a model of extended access to oxycodone self-administration and tested the effects of VK4-116 on the escalation of oxycodone self-administration and withdrawal-induced hyperalgesia and irritability-like behavior in male and female rats. Pretreatment with VK4-116 (5–25 mg/kg, i.p.) dose-dependently decreased the escalation of oxycodone self-administration and reduced withdrawal-induced hyperalgesia and irritability-like behavior in opioid-dependent rats. These findings demonstrate a key role for D₃ receptors in both the motivation to take opioids and negative emotional states that are associated with opioid withdrawal and suggest that D₃ receptor antagonism may be a viable therapeutic approach for the treatment of OUD.