Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats

The use of Δ⁹-tetrahydrocannabinol (THC) by inhalation using e-cigarette technology grows increasingly popular for medical and recreational purposes. This has led to development of e-cigarette based techniques to study the delivery of THC by inhalation in laboratory rodents. Inhaled THC reliably produces hypothermic and antinociceptive effects in rats, similar to effects of parenteral injection of THC. This study was conducted to determine the extent to which the hypothermic response depends on interactions with the CB₁ receptor, using pharmacological antagonist (SR141716, AM-251) approaches. Groups of rats were implanted with radiotelemetry devices capable of reporting activity and body temperature, which were assessed after THC inhalation or injection. SR141716 (4 mg/kg, i.p.) blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. SR141716 was unable to block the initial hypothermia caused by THC inhalation, but temperature was restored to normal more quickly. Alterations in antagonist pre-treatment time, dose and the use of a rat strain with less sensitivity to THC-induced hypothermia did not change this pattern. Pre-treatment with SR141716 (4 mg/kg, i.p.) blocked hypothermia induced by i.v. THC and reversed hypothermia when administered 45 or 90 min after THC (i.p.). SR141716 and AM-251 (4 mg/kg, i.p.) sped recovery from, but did not block, hypothermia caused by vapor THC in female rats made tolerant by prior repeated THC vapor inhalation. The CB₂ antagonist AM-630, had no effect. These results suggest that hypothermia consequent to THC inhalation is induced by other mechanisms in addition to CB₁ receptor activation.

Effects of active anti-methamphetamine vaccination on intravenous self-administration in rats

BACKGROUND

d-Methamphetamine (METH) addiction is a serious public health concern for which successful treatment remains elusive. Immunopharmacotherapy has been shown to attenuate locomotor and thermoregulatory effects of METH. The current study investigated whether active vaccination against METH could alter intravenous METH self-administration in rats.

METHODS

Male Sprague-Dawley rats (Experiment 1: N=24; Experiment 2: N=18) were vaccinated with either a control keyhole-limpet hemocyanin conjugate vaccine (KLH) or a candidate anti-METH vaccine (MH6-KLH) or. Effects of vaccination on the acquisition of METH self-administration under two dose conditions (0.05, 0.1mg/kg/inf) and post-acquisition dose-substitution (0, 0.01, 0.05, 0.20mg/kg/inf, Experiment 1; 0.01, 0.05, 0.10, 0.15mg/kg/inf, Experiment 2) during steady-state responding were investigated. Plasma METH concentrations were determined 30min after an acute challenge dose of 3.2mg/kg METH.

RESULTS

Active vaccination inhibited the acquisition of METH self-administration under the 0.1mg/kg/inf dose condition, with 66% of the MH6-KLH-vaccinated rats compared to 100% of the controls reaching criteria, and produced transient and dose-dependent effects on self-administration during the maintenance phase. Under the 0.05mg/kg/inf dose condition, MH6-KLH-vaccinated rats initially self-administered more METH than controls, but then self-administration decreased across the acquisition phase relative to controls; a subsequent dose-response assessment confirmed that MH6-KLH-vaccinated rats failed to acquire METH self-administration. Finally, plasma METH concentrations were higher in MH6-KLH-vaccinated rats compared to controls after an acute METH challenge, and these were positively correlated with antibody titers.

CONCLUSIONS

These data demonstrate that active immunopharmacotherapy for METH attenuates the acquisition of METH self-administration.

The novel recreational drug 3,4-methylenedioxypyrovalerone (MDPV) is a potent psychomotor stimulant: self-administration and locomotor activity in rats

Recreational use of the cathinone derivative 3,4-methylenedioxypyrovalerone (MDPV; "bath salts") has increased worldwide in past years, accompanied by accounts of health and legal problems in the popular media and efforts to criminalize possession in numerous jurisdictions. Minimal information exists on the effects of MDPV in laboratory models. This study determined the effects of MDPV, alongside those of the better studied stimulant d-methamphetamine (METH), using rodent models of intravenous self-administration (IVSA), thermoregulation and locomotor activity. Male Wistar rats were trained to self-administer MDPV or METH (0.05 mg/kg/infusion, i.v.) or were prepared with radiotelemetry implants for the assessment of body temperature and activity responses to MDPV or METH (0-5.6 mg/kg s.c.). METH and MDPV were consistently self-administered within 10 training sessions (mg/kg/h; METH Mean = 0.4 and Max = 1.15; MDPV Mean = 0.9 and Max = 5.8). Dose-substitution studies demonstrated that behavior was sensitive to dose for both drugs, but MDPV (0.01-0.50 mg/kg/inf) showed greater potency and efficacy than METH (0.1-0.25 mg/kg/inf). In addition, both MDPV and METH increased locomotor activity at lower doses (0.5-1.0 mg/kg, s.c.) and transiently decreased activity at the highest dose (5.6 mg/kg, s.c.). Body temperature increased monotonically with increasing doses of METH but MDPV had a negligible effect on temperature. Stereotypy was associated with relatively high self-administered cumulative doses of MDPV (∼1.5 mg/kg/h) as well as with non-contingent MDPV administration wherein the intensity and duration of stereotypy increased as MDPV dose increased. Thus, MDPV poses a substantial threat for compulsive use that is potentially greater than that for METH.

Reciprocal inhibitory effects of intravenous d-methamphetamine self-administration and wheel activity in rats

BACKGROUND

Some epidemiological and cessation studies suggest physical exercise attenuates or prevents recreational drug use in humans. Preclinical studies indicate that wheel activity reduces cocaine self-administration in rats; this may, however, require the establishment of compulsive wheel activity.

METHODS

Effects of concurrent wheel activity on intravenous d-methamphetamine (METH) self-administration were examined in male Wistar and Sprague Dawley rats with negligible prior wheel experience. Wistar rats self-administered METH (0.05 mg/kg/inf) under a fixed-ratio 1 (FR1) schedule with concurrent access to an activity wheel during sessions 1-14, 8-21 or 15-21. Control rats which did not self-administer METH had access to an activity wheel during sessions 1-14, 8-21 or 15-28. Sprague Dawley rats self-administered METH (0.1 mg/kg/inf) under FR1 for 14 sessions with either concurrent access to a locked or an unlocked activity wheel.

RESULTS

METH self-administration was lower when the wheel was available concurrently from the start of self-administration training in both strains, even though Sprague Dawley rats self-administered twice as many METH infusions and ran one-sixth as much on the wheel compared to Wistar rats. Wheel access initiated after 7 or 14 days had no effect on METH self-administration in Wistar rats. Wheel activity was significantly reduced in these groups compared with the group with concurrent wheel and METH access for the first 14 sessions.

CONCLUSIONS

These data show that METH self-administration is reduced by exercise if initiated from the start of self-administration and that prior METH self-administration experience interferes with the value of exercise as a reinforcer.