Biology subjects

Townsend, E. A.

Publications and source records attributed to Townsend, E. A..

7 recordsLinked to original sources

bioRxiv2024

Nor-LAAM loaded PLGA Microparticles for Treating Opioid Use Disorder

The treatment landscape for opioid use disorder (OUD) faces challenges stemming from the limited efficacy of existing medications, poor adherence to prescribed regimens, and a heightened risk of fatal overdose post-treatment cessation. Therefore, there is a pressing need for innovative therapeutic strategies that enhance the effectiveness of interventions and the overall well-being of individuals with OUD. This study explored the therapeutic potential of nor-Levo--acetylmethadol (nor-LAAM) to treat OUD. We developed sustained release nor-LAAM-loaded poly (lactic-co-glycolic acid) (PLGA) microparticles (MP) using a hydrophobic ion pairing (HIP) approach. The nor-LAAM-MP prepared using HIP with pamoic acid had high drug loading and exhibited minimal initial burst release and sustained release. The nor-LAAM-MP was further optimized for desirable particle size, drug loading, and release kinetics. The lead nor-LAAM-MP (F4) had a relatively high drug loading (11 wt.%) and an average diameter (19 {micro}m) and maintained a sustained drug release for 4 weeks. A single subcutaneous injection of nor-LAAM-MP (F4) provided detectable nor-LAAM levels in rabbit plasma for at least 15 days. We further evaluated the therapeutic efficacy of nor-LAAM-MP (F4) in a well-established fentanyl-addiction rat model, and revealed a marked reduction in fentanyl choice and withdrawal symptoms in fentanyl-dependent rats. These findings provide insights into further developing long-acting nor-LAAM-MP for treating OUD. It has the potential to offer a new effective medication to the existing sparse armamentarium of products available to treat OUD.

bioengineering↗

bioRxiv2021

Lack of effect of different pain-related manipulations on opioid self-administration, reinstatement of opioid seeking, and opioid choice in rats

Rationale and Objective: Pain-related factors increase risk for opioid addiction, and opioid-induced pain relief may function as a negative reinforcer to increase opioid taking and seeking. However, experimental pain-related manipulations generally do not increase opioid self-administration in rodents. This discrepancy may reflect insufficient learning of pain-relief contingencies or confounding effects of pain-related behavioral impairments. Here we determined if pairing noxious stimuli with opioid self-administration would promote pain-related reinstatement of opioid seeking or increase opioid choice over food. Methods: In Experiment 1, rats self-administered fentanyl in the presence or absence of repeated intraplantar capsaicin injections in distinct contexts to model context-specific exposure to cutaneous nociception. After capsaicin-free extinction in both contexts, we tested if capsaicin would reinstate fentanyl seeking. In Experiment 2, rats self-administered heroin after intraperitoneal (i.p.) lactic acid injections to model acute visceral inflammatory pain. After lactic acid-free extinction, we tested if lactic acid would reinstate heroin seeking. In Experiment 3, we tested if repeated i.p. lactic acid or intraplantar Complete Freund Adjuvant (CFA; to model sustained inflammatory pain) would increase fentanyl choice over food. Results: In Experiments 1-2, neither capsaicin nor lactic acid reinstated opioid seeking after extinction, and lactic acid did not increase heroin-induced reinstatement. In Experiment 3, lactic acid and CFA decreased reinforcement rate without affecting fentanyl choice. Conclusions: Results extend the range of conditions across which pain-related manipulations fail to increase opioid seeking in rats and suggest that enhanced opioid-addiction risk in humans with chronic pain involves factors other than enhanced opioid reinforcement and relapse.

neuroscience↗

bioRxiv2021

Opioid withdrawal produces sex-specific effects on fentanyl-vs.-food choice and mesolimbic transcription

BackgroundOpioid withdrawal is a key driver of opioid addiction and an obstacle to recovery. However, withdrawal effects on opioid reinforcement and mesolimbic neuroadaptation are understudied and the role of sex is largely unknown. MethodsMale (n=10) and female (n=9) rats responded under a fentanyl-vs.-food "choice" procedure during daily 2h sessions. In addition to the daily choice sessions, rats were provided extended access to fentanyl during 12h sessions. After two weeks of this self-administration regimen, the nucleus accumbens (NAc) and ventral tegmental area (VTA) of a subset of rats were subjected to RNA sequencing. In the remaining rats, a third week of this self-administration regimen was conducted, during which methadone effects on fentanyl-vs.-food choice were determined. ResultsPrior to opioid dependence, male and female rats similarly allocated responding between fentanyl and food. Abstinence from extended fentanyl access elicited a similar increase in somatic withdrawal signs in both sexes. Despite similar withdrawal signs and extended access fentanyl intake, opioid withdrawal was accompanied by a maladaptive increase in fentanyl choice in males, but not females. Behavioral sex differences corresponded with transcriptional hyperfunction in the NAc and VTA of opioid-withdrawn females relative to males. Methadone blocked withdrawal-associated increases in fentanyl choice in males, but failed to further decrease fentanyl choice in females. ConclusionsThese results provide foundational evidence of sex-specific neuroadaptations to opioid withdrawal, which may be relevant to the female-specific resilience to withdrawal-associated increases in opioid choice and aid in the identification of novel therapeutic targets.

neuroscience↗

bioRxiv2020

Effects of Kappa Opioid Receptor Agonists on Fentanyl vs. Food Choice in Male and Female Rats: Contingent vs. Non-Contingent Administration

RationaleStrategies are needed to decrease the abuse liability of mu opioid receptor (MOR) agonists. One strategy under consideration is to combine MOR agonists with kappa opioid receptor (KOR) agonists. ObjectivesThe effects of KOR-agonists (U50488, nalfurafine) on fentanyl-versus-food choice were compared under conditions where the KOR agonists were added to the self-administered fentanyl (contingent delivery) or administered as pretreatments (non-contingent delivery) in male and female rats. The effects of increasing and decreasing the magnitude of the alternative food reinforcer were also determined. MethodsRats were trained to respond under a concurrent schedule of fentanyl (0, 0.32-10 g/kg/infusion) and food reinforcement. In Experiment 1, U50488 and nalfurafine were co-administered with fentanyl as fixed-proportion mixtures (contingent administration). In Experiment 2, U50488 (1-10 mg/kg) and nalfurafine (3.2-32 g/kg) were administered as acute pretreatments (non-contingent administration). nor-BNI (32 mg/kg) was administered prior to contingent and non-contingent KOR-agonist treatment in Experiment 3. Experiment 4 evaluated the effects of increasing and decreasing the magnitude of the non-drug reinforcer. ResultsBoth U50488 and nalfurafine decreased fentanyl choice when administered contingently, demonstrating that KOR agonists punish opioid choice. Non-contingent U50488 and nalfurafine administration decreased rates of fentanyl and food self-administration without altering fentanyl choice. Both contingent and non-contingent U50488 and nalfurafine effects on fentanyl choice were attenuated by nor-BNI. Fentanyl choice was sensitive to increases and decreases in the magnitude of the non-drug reinforcer. ConclusionsThese results demonstrate that the effects of KOR agonists on fentanyl reinforcement are dependent upon the contingencies under which they are administered.

animal behavior and cognition↗

bioRxiv2019

Comparison of Chemotherapy Effects on Mechanical Sensitivity and Food-Maintained Operant Responding in Male and Female Rats

ObjectiveChemotherapies of varying classes often cause neuropathy and debilitating chemotherapy-induced neuropathic pain (CINP) sufficient to limit treatment and reduce quality of life for many patients battling cancer. There are currently no effective preventative or alleviative treatments for CINP. Preclinical models have been developed to test candidate CINP treatments; however, studies using these models rarely provide direct comparisons of effects of different chemotherapies or assess the degree to which chemotherapies produce clinically relevant signs of pain-depressed behavior.\n\nMethodsMale and female Sprague-Dawley rats received four injections of vehicle, paclitaxel, oxaliplatin, vincristine, or bortezomib on alternate days. Mechanical hypersensitivity, body weight, and food-maintained operant responding were evaluated before, during, and for up to 42 days after initiation of treatment. Morphine potency and effectiveness to reverse chemotherapy-induced effects were also evaluated.\n\nResultsAll four chemotherapies produced dose-dependent and sustained mechanical hypersensitivity in all rats. Vincristine and oxaliplatin produced transient weight loss and decreases in food-maintained operant responding in all rats, whereas paclitaxel and bortezomib produced lesser or no effect. At four weeks after treatment, operant responding was depressed only in paclitaxel-treated males. Morphine reversed mechanical hypersensitivity in all rats but failed to reverse paclitaxel-induced depression of operant responding in males.\n\nConclusionsChemotherapy treatments sufficient to produce sustained mechanical hypersensitivity failed to produce sustained or morphine-reversible behavioral depression in rats. Insofar as pain-related behavioral depression is a cardinal sign of CINP in humans, these results challenge the presumption that these chemotherapy-dosing regimens are sufficient to model clinically relevant CINP in rats.

pharmacology and toxicology↗

bioRxiv2019

Lorcaserin maintenance fails to attenuate heroin vs food choice in rhesus monkeys

BackgroundThe current opioid crisis has reinvigorated preclinical research in the evaluation of non-opioid candidate treatments for opioid use disorder (OUD). Emerging evidence suggests 5-HT2C receptor agonists may attenuate the abuse-related effects of opioids. This study evaluated effectiveness of 7-day treatment with the clinically available 5-HT2C agonist lorcaserin on heroin-vs.-food choice in rhesus monkeys. Lorcaserin effects were compared to effects produced by saline substitution and by 7-day treatment with the opioid antagonist naltrexone.\n\nMethodsAdult male (1) and female (6) rhesus monkeys were trained to respond under a concurrent schedule of food delivery (1g pellets, fixed-ratio 100 schedule) and intravenous heroin injections (0-0.032 mg/kg/injection, fixed-ratio 10 schedule) during daily 2h sessions. Heroin choice dose-effect functions were determined daily before and following 7-day saline substitution or 7-day continuous treatment with naltrexone (0.0032-0.032 mg/kg/h, IV) or lorcaserin (0.032-0.32 mg/kg/h, IV).\n\nResultsUnder baseline conditions, increasing heroin doses maintained a dose-dependent increase in heroin choice. Both saline substitution and 7-day naltrexone treatment significantly attenuated heroin choice and produced a reciprocal increase in food choice. Continuous lorcaserin treatment significantly increased heroin choice.\n\nConclusionsIn contrast to saline substitution and naltrexone, lorcaserin treatment was ineffective to reduce heroin-vs.-food choice. These preclinical results do not support the therapeutic potential of lorcaserin as a candidate OUD treatment.

neuroscience↗

bioRxiv2019

Effectiveness and selectivity of a heroin conjugate vaccine to attenuate heroin, 6-acetylmorphine, and morphine antinociception in rats: Comparison with naltrexone

BackgroundOne emerging strategy to address the opioid crisis includes opioid-targeted immunopharmacotherapies. This study compared effectiveness of a heroin-tetanus toxoid (TT) conjugate vaccine to antagonize heroin, 6-acetylmorphine (6-AM), morphine, and fentanyl antinociception in rats.\n\nMethodsAdult male and female Sprague Dawley rats received three doses of active or control vaccine at weeks 0, 2, and 4. Vaccine pharmacological selectivity was assessed by comparing opioid dose-effect curves in 50{degrees}C warm-water tail-withdrawal procedure before and after active or control heroin-TT vaccine. Route of administration [subcutaneous (SC) vs. intravenous [IV)] was also examined as a determinant of vaccine effectiveness. Continuous naltrexone treatment (0.0032-0.032 mg/kg/h) effects on heroin, 6-AM, and morphine antinociceptive potency was also determined as a benchmark for minimal vaccine effectiveness.\n\nResultsThe heroin-TT vaccine decreased potency of SC heroin (5-fold), IV heroin (3-fold), and IV 6-AM (3-fold) for several weeks without affecting IV morphine or SC and IV fentanyl potency. The control vaccine did not alter potency of any opioid. Naltrexone dose-dependently decreased antinociceptive potency of SC heroin, and treatment with 0.01 mg/kg/h naltrexone produced similar, approximate 8-fold decreases in potencies of SC and IV heroin, IV 6-AM, and IV morphine. The combination of naltrexone and active vaccine was more effective than naltrexone alone to antagonize SC heroin but not IV heroin.\n\nConclusionsThe heroin-TT vaccine formulation examined is less effective, but more selective, than chronic naltrexone to attenuate heroin antinociception in rats. Furthermore, these results provide an empirical framework for future preclinical opioid vaccine research to benchmark effectiveness against naltrexone.

pharmacology and toxicology↗