Yanabel Grant

Levels of Neural Progenitors in the Hippocampus Predict Memory Impairment and Relapse to Drug Seeking as a Function of Excessive Methamphetamine Self-Administration

Methamphetamine affects the hippocampus, a brain region crucial for learning and memory, as well as relapse to drug seeking. Rats self-administered methamphetamine for 1 h twice weekly (intermittent-short-I-ShA), 1 h daily (limited-short-ShA), or 6 h daily (extended-long-LgA) for 22 sessions. After 22 sessions, rats from each access group were withdrawn from self-administration and underwent spatial memory (Y-maze) and working memory (T-maze) tests followed by extinction and reinstatement to methamphetamine seeking or received one intraperitoneal injection of 5-bromo-2′-deoxyuridine (BrdU) to label progenitors in the hippocampal subgranular zone (SGZ) during the synthesis phase. Two-hour-old and 28-day-old surviving BrdU-immunoreactive cells were quantified. I-ShA rats performed better on the Y-maze and had a greater number of 2-h-old SGZ BrdU cells than nondrug controls. LgA rats, but not ShA rats, performed worse on the Y- and T-maze and had a fewer number of 2-h-old SGZ BrdU cells than nondrug and I-ShA rats, suggesting that new hippocampal progenitors, decreased by methamphetamine, were correlated with impairment in the acquisition of new spatial cues. Analyses of addiction-related behaviors after withdrawal and extinction training revealed methamphetamine-primed reinstatement of methamphetamine-seeking behavior in all three groups (I-ShA, ShA, and LgA), and this effect was enhanced in LgA rats compared with I-ShA and ShA rats. Protracted withdrawal from self-administration enhanced the survival of SGZ BrdU cells, and methamphetamine seeking during protracted withdrawal enhanced Fos expression in the dentate gyrus and medial prefrontal cortex in LgA rats to a greater extent than in ShA and I-ShA rats. These results indicate that changes in the levels of the proliferation and survival of hippocampal neural progenitors and neuronal activation of hippocampal granule cells predict the effects of methamphetamine self-administration (limited vs extended access) on cognitive performance and relapse to drug seeking and may contribute to the impairments that perpetuate the addiction cycle.

κ Opioid Receptors in the Nucleus Accumbens Shell Mediate Escalation of Methamphetamine Intake

Given that the κ opioid receptor (KOR) system has been implicated in psychostimulant abuse, we evaluated whether the selective KOR antagonist norbinaltorphimine dihydrochloride (nor-BNI) would attenuate the escalation of methamphetamine (METH) intake in an extended-access self-administration model. Systemic nor-BNI decreased the escalation of intake of long-access (LgA) but not short-access (ShA) self-administration. nor-BNI also decreased elevated progressive-ratio (PR) breakpoints in rats in the LgA condition and continued to decrease intake after 17 d of abstinence, demonstrating that the effects of a nor-BNI injection are long lasting. Rats with an ShA history showed an increase in prodynorphin immunoreactivity in both the nucleus accumbens (NAc) core and shell, but LgA animals showed a selective increase in the NAc shell. Other cohorts of rats received nor-BNI directly into the NAc shell or core and entered into ShA or LgA. nor-BNI infusion in the NAc shell, but not NAc core, attenuated escalation of intake and PR responding for METH in LgA rats. These data indicate that the development and/or expression of compulsive-like responding for METH under LgA conditions depends on activation of the KOR system in the NAc shell and suggest that the dynorphin–KOR system is a central component of the neuroplasticity associated with negative reinforcement systems that drive the dark side of addiction.

Probing Active Cocaine Vaccination Performance through Catalytic and Noncatalytic Hapten Design

Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complementary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH (keyhole limpet hemocyannin) was found to elicit persistent high-titer, cocaine-specific antibodies and blunt cocaine-induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges, the vaccines protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse.

Locomotor Stimulant and Rewarding Effects of Inhaling Methamphetamine, MDPV, and Mephedrone via Electronic Cigarette-Type Technology

Although inhaled exposure to drugs is a prevalent route of administration for human substance abusers, preclinical models that incorporate inhaled exposure to psychomotor stimulants are not commonly available. Using a novel method that incorporates electronic cigarette-type technology to facilitate inhalation, male Wistar rats were exposed to vaporized methamphetamine (MA), 3,4-methylenedioxypyrovalerone (MDPV), and mephedrone (4-methylmethcathinone) in propylene glycol vehicle using concentrations ranging from 12.5 to 200 mg/ml. Rats exhibited increases in spontaneous locomotor activity, measured by implanted radiotelemetry, following exposure to methamphetamine (12.5 and 100 mg/ml), MDPV (25, 50, and 100 mg/ml), and mephedrone (200 mg/ml). Locomotor effects were blocked by pretreatment with the dopamine D1-like receptor antagonist SCH23390 (10 μg/kg, intraperitoneal (i.p.)). MA and MDPV vapor inhalation also altered activity on a running wheel in a biphasic manner. An additional group of rats was trained on a discrete trial intracranial self-stimulation (ICSS) procedure interpreted to assess brain reward status. ICSS-trained rats that received vaporized MA, MDPV, or mephedrone exhibited a significant reduction in threshold of ICSS reward compared with vehicle. The effect of vapor inhalation of the stimulants was found comparable to the locomotor and ICSS threshold-reducing effects of i.p. injection of mephedrone (5.0 mg/kg), MA (0.5–1.0 mg/kg), or MDPV (0.5–1.0 mg/kg). These data provide robust validation of e-cigarette-type technology as a model for inhaled delivery of vaporized psychostimulants. Finally, these studies demonstrate the potential for human use of e-cigarettes to facilitate covert use of a range of psychoactive stimulants. Thus, these devices pose health risks beyond their intended application for the delivery of nicotine.

Probing the Effects of Hapten Stability on Cocaine Vaccine Immunogenicity

Judicious hapten design has been shown to be of importance when trying to generate a viable vaccine against a drug of abuse. Hapten design has typically been predicated upon faithfully emulating the unique chemical architecture that each drug presents. However, the need for drug-hapten congruency may also compromise vaccine immunogenicity if the drug-hapten conjugate possesses chemical epitope instability. There has been no systematic study on the impact of hapten stability as it relates to vaccine immunogenicity. As a starting point, we have probed the stability of a series of cocaine haptens through varying several of its structural elements, including functionality at the C2-position, the nature of the linker, and its site of attachment. Accordingly, a hydrolytic stability profile of four cocaine haptens (GNNA, GNNS, GNE, and GNC) was produced, and these results were compared through each haptens immunological properties, which were generated via active vaccination. From this group of four, three of the haptens, GNE, GNNA, and GNC, were further examined in an animal behavioral model, and findings here were again measured in relationship to hapten stability. We demonstrate a corresponding relationship between the half-life of the hapten and its immunogenicity, wherein haptens presenting a fully representative cocaine framework elicited higher concentrations of cocaine-specific IgG in sera and also conferred better protection against cocaine-induced locomotor activity. Our results indicate that hapten half-life plays an important role in vaccine immunogenicity and this in turn can impact animal behavioral effects when challenged with a drug of abuse.

Escalation of intravenous self‐administration of methylone and mephedrone under extended access conditions

The recreational use of substituted cathinones continues to grow as a public health concern in the United States. Studies have shown that extended access to intravenous (i.v.) self‐administration of stimulants, such as cocaine and methamphetamine, results in escalation of drug intake relative to shorter access; however, little is known about the impact of extended access on self‐administration of entactogen class stimulants such as methylone and 4‐methylmethcathinone (mephedrone). Male Wistar rats were randomly assigned to short‐access (ShA, 2‐ h) and long‐access (LgA, 6‐ h) groups and trained to self‐administer methylone or mephedrone (0.5 mg/kg/infusion) using a fixed‐ratio 1 response contingency. The methylone‐trained groups were evaluated on a progressive‐ratio (PR) procedure incorporating dose‐substitution of methylone (0.125–2.5 mg/kg/infusion), mephedrone (0.125–2.5 mg/kg/infusion) or methamphetamine (MA; 0.01–0.5 mg/kg/infusion). Mephedrone‐trained rats were similarly evaluated on a PR with mephedrone and MA. Rats trained with LgA to methylone and mephedrone earned more infusions during acquisition compared with ShA groups. Mephedrone‐trained LgA rats reached significantly higher breakpoints than all other groups in mephedrone and MA PR tests. Methylone‐trained LgA rats exhibited a rightward shift of the peak effective dose but no overall efficacy change compared with methylone‐trained ShA rats. These findings show that the self‐administration of mephedrone escalates under LgA conditions in a manner similar to traditional stimulants whereas escalation of 6 h intakes of methylone is not accompanied by differences in PR performance. Thus mephedrone represents the greater risk for dysregulated drug consumption.

Repeated vapor inhalation of Δ9-tetrahydrocannabinol induces tolerance to hypothermia in female rats

Background and Purpose: Tolerance to the effects of Δ9-tetrahydrocannabinol (THC) emerges with repeated exposure, although it varies with dose, chronicity and the measure of interest. THC inhalation via an e-cigarette based system induces hypothermic and antinociceptive effects in rats. This study was conducted to determine if tolerance to these effects could be produced with repeated vapor inhalation. Experimental Approaches: Wistar rats were exposed to 30 minutes of vapor inhalation of the propylene glycol (PG) vehicle and then THC (200 mg/mL in PG) twice per day for four days. Female and male groups were compared for rectal temperature changes and tail-withdrawal latency from a noxious stimulus. A second female group was prepared with radiotelemetry devices for temperature and activity and then exposed to 30 minutes of PG (b.i.d., 4 days) and then THC (100 mg/mL; b.i.d., 5 days). Additional studies evaluated the effects of 4 mg/kg SR141716, AM251 or AM630 i.p. to determine CB1 and CB2 receptor contributions. Key Results: Female, but not male rats developed tolerance to the hypothermic and antinociceptive effects of THC after four days of THC vapor inhalation. The antagonist SR141716 blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. Initial hypothermia was not prevented by SR141716 or AM251 but the restoration of normal temperature was accelerated. Conclusions and Implications: Twice daily THC inhalation induces tolerance in female rats, providing further validation of the method. Blockade of the CB1 receptor shortens the maintenance of hypothermia and blocks antinociception after THC inhalation.Rationale A reduced effect of a given dose of Δ9-tetrahydrocannabinol (THC) emerges with repeated exposure to the drug. This tolerance can vary depending on THC dose, exposure chronicity and the behavioral or physiological measure of interest. A novel THC inhalation system based on e-cigarette technology has been recently shown to produce the hypothermic and antinociceptive effects of THC in rats. Objective To determine if tolerance to these effects can be produced with repeated vapor inhalation. Methods Groups of male and female Wistar rats were exposed to 30 minutes of inhalation of the propylene glycol (PG) vehicle or THC (200 mg/mL in PG) two or three times per day for four days. Rectal temperature changes and nociception were assessed after the first exposure on the first and fourth days of repeated inhalation. Results Female, but not male, rats developed tolerance to the hypothermic and antinociceptive effects of THC after four days of twice-daily THC vapor inhalation. Thrice daily inhalation for four days resulted in tolerance in both male and female rats. The plasma THC levels reached after a 30 minute inhalation session did not differ between the male and female rats. Conclusions Repeated daily THC inhalation induces tolerance in female and male rats, providing further validation of the vapor inhalation method for preclinical studies. Abbreviations PG, propylene glycol; THC; Δ9tetrahydrocannabinol;

Tolerance to hypothermic and antinoceptive effects of ∆9-tetrahydrocannabinol (THC) vapor inhalation in rats.

Rationale: A reduced effect of a given dose of &dgr;9‐tetrahydrocannabinol (THC) emerges with repeated exposure to the drug. This tolerance can vary depending on THC dose, exposure chronicity and the behavioral or physiological measure of interest. A novel THC inhalation system based on e‐cigarette technology has been recently shown to produce the hypothermic and antinociceptive effects of THC in rats. Objective: To determine if tolerance to these effects can be produced with repeated vapor inhalation. Methods: Groups of male and female Wistar rats were exposed to 30 min of inhalation of the propylene glycol (PG) vehicle or THC (200 mg/mL in PG) two or three times per day for four days. Rectal temperature changes and nociception were assessed after the first exposure on the first and fourth days of repeated inhalation. Results: Female, but not male, rats developed tolerance to the hypothermic and antinociceptive effects of THC after four days of twice‐daily THC vapor inhalation. Thrice daily inhalation for four days resulted in tolerance in both male and female rats. The plasma THC levels reached after a 30 min inhalation session did not differ between the male and female rats. Conclusions: Repeated daily THC inhalation induces tolerance in female and male rats, providing further validation of the vapor inhalation method for preclinical studies. HighlightsAn e‐cigarette based THC inhalation system produces hypothermia and antinociception in rats.Tolerance to THC emerges with repeated exposure.Repeated daily THC inhalation induces tolerance in female and male rats.This further validates vapor inhalation of THC in rats as a model of human consumption.

Prophylactic vaccination protects against the development of oxycodone self-administration

ABSTRACT Abuse of prescription opioids is a growing public health crisis in the United States, with drug overdose deaths increasing dramatically over the past 15 years. Few preclinical studies exist on the reinforcing effects of oxycodone or on the development of therapies for oxycodone abuse. This study was conducted to determine if immunopharmacotherapy directed against oxycodone would be capable of altering oxycodone‐induced antinociception and intravenous self‐administration. Male Wistar rats were administered a small‐molecule immunoconjugate vaccine (Oxy‐TT) or the control carrier protein, tetanus toxoid (TT), and trained to intravenously self‐administer oxycodone (0.06 or 0.15mg/kg/infusion). Brain oxycodone concentrations were 50% lower in Oxy‐TT rats compared to TT rats 30min after injection (1mg/kg, s.c.) whereas plasma oxycodone was 15‐fold higher from drug sequestration by circulating antibodies. Oxy‐TT rats were also less sensitive to 1–2mg/kg, s.c. oxycodone on a hot water nociception assay. Half of the Oxy‐TT rats failed to acquire intravenous self‐administration under the 0.06mg/kg/infusion training dose. Oxycodone self‐administration of Oxy‐TT rats trained on 0.15mg/kg/infusion was higher than controls; however under progressive ratio (PR) conditions the Oxy‐TT rats decreased their oxycodone intake, unlike TT controls. These data demonstrate that active vaccination provides protection against the reinforcing effects of oxycodone. Anti‐oxycodone vaccines may entirely prevent repeated use in some individuals who otherwise would become addicted. Vaccination may also reduce dependence in those who become addicted and therefore facilitate the effects of other therapeutic interventions which either increase the difficulty of drug use or incentivize other behaviors. HIGHLIGHTSNon‐medical use of prescription opioids such as oxycodone has reached epidemic levels.This study shows protective effects of an anti‐oxycodone vaccine in rats.Under lower dose conditions half of the rats did not acquire oxycodone self‐administration.Introducing a higher workload decreased intake under higher dose conditions.Anti‐oxycodone vaccination may reduce the incidence and severity of dependence.

Δ9-tetrahydrocannabinol Attenuates Oxycodone Self-Administration Under Extended Access Conditions

Growing nonmedical use of prescription opioids is a significant global problem which motivates research on ways to reduce therapeutic use and combat addiction. Medical marijuana availability has been associated epidemiologically with reduced opioid harms and cannabinoids have been shown to modulate effects of heroin or morphine in animal models. This study was conducted to determine if Δ9-tetrahydrocannabinol (THC) enhances the rewarding and/or antinociceptive effects of oxycodone. Male Wistar rats were trained to intravenously self-administer (IVSA) oxycodone (0.15 mg/kg/infusion) during 1 h or 8 h sessions. After acquisition of oxycodone IVSA, rats were exposed to THC by vapor inhalation (0, 100 or 200 mg/mL in the vehicle; 1 h and 8 h groups) or injection (0, 5 or 10 mg/kg, i.p., 8 h group) prior to IVSA sessions. Oxycodone intake was significantly decreased in rats following vaporized or injected THC compared with vehicle treatment prior to the session. Additional groups of male and female Wistar rats were assessed for nociception of a 52 °C hot water bath following inhalation of vaporized THC (50 mg/mL), oxycodone (100 mg/mL), the THC/oxycodone combination or the PG vehicle. Tail withdrawal latency was increased more by the THC/oxycodone combination compared to either drug alone. Similar additive effects on tail withdrawal latency were produced by injection of THC (5.0 mg/kg, i.p.) and oxycodone (2.0 mg/kg, s.c.). These data show additive effects of THC and oxycodone in rats and suggest the potential use of cannabinoids to enhance therapeutic efficacy and to reduce non-medical opioid abuse.