Repeated Exposure to the “Spice” Cannabinoid JWH-018 Induces Tolerance and Enhances Responsiveness to 5-HT1A Receptor Stimulation in Male Rats

Abstract

Naphthalen-1-yl-(1-pentylindol-3-yl)methanone (JWH-018) is a synthetic compound found in psychoactive “spice” products that activates cannabinoid receptors. Preclinical evidence suggests that exposure to synthetic cannabinoids increases 5-HT2A/2C receptor function in the brain, an effect which might contribute to psychotic symptoms. Here, we hypothesized that repeated exposures to JWH-018 would enhance behavioral responsiveness to the 5-HT2A/2C receptor agonist DOI. Male Sprague-Dawley rats fitted with subcutaneously (sc) temperature transponders received daily injections of JWH-018 (1.0 mg/kg, sc) or its vehicle for seven consecutive days. Body temperature and catalepsy scores were determined at 1, 2, and 4 h post-injection each day. At 1 and 7 days after the final repeated treatment, rats received a challenge injection of either DOI (0.1 mg/kg, sc) or the 5-HT1A receptor agonist 8-OH-DPAT (0.3 mg/kg, sc), then temperature and behavioral responses were assessed. Behaviors induced by DOI included wet dog shakes and back muscle contractions (i.e., skin jerks), while behaviors induced by 8-OH-DPAT included ambulation, forepaw treading, and flat body posture. On the first day of repeated treatment, JWH-018 produced robust hypothermia and catalepsy which lasted up to 4 h, and these effects were significantly blunted by day 7 of treatment. Repeated exposure to JWH-018 did not affect behaviors induced by DOI, but behavioral and hypothermic responses induced by 8-OH-DPAT were significantly augmented 1 day after cessation of JWH-018 treatment. Collectively, our findings show that repeated treatment with JWH-018 produces tolerance to its hypothermic and cataleptic effects, which is accompanied by transient enhancement of 5-HT1A receptor sensitivity in vivo.

Pharmacodynamic Effects, Pharmacokinetics, and Metabolism of the Synthetic Cannabinoid AM-2201 in Male Rats

“…The subcutaneous dose of 1.0 mg/kg AM-2201 induced a hypothermic response that reached 4°C, which is more robust than the effects observed after an equivalent intraperitoneal dose in rats (Banister et al, 2015b). The present findings agree with our previous results in rats where subcutaneous injections of AM-2201 (Schindler et al, 2017) or JWH-018 (Elmore and Baumann, 2018) induce hypothermia that is maximal after 1-2 hours and slowly returns to normal in a monophasic manner.…”

“…It is noteworthy that human users normally self-administer AM-2201 by smoking or vaping, but we were unable to use either of these routes. The subcutaneous route was chosen because our previous studies used this route to characterize the pharmacological effects of AM-2201 and other cannabinoids in rats (Schindler et al, 2017;Elmore and Baumann, 2018). Similar to the smoked and vaped routes of administration, the subcutaneous route largely bypasses first-pass metabolism in the liver.…”

“…Briefly, the proximal Silastic end of the catheter was advanced to the atrium while the distal vinyl end was exteriorized on the nape of the neck and plugged with a metal stylet. Immediately after catheter implantation, while still under anesthesia, rats received surgically implanted temperature transponders (model IPTT-300; Bio Medic Data Systems, Seaford, DE) to allow for the noninvasive measurement of body temperature (Elmore and Baumann, 2018). The temperature transponder emits radio frequency signals that are received by a compatible handheld reader system (DAS-7006/7r; Bio Medic Data Systems).…”

“…Groups of rats received subcutaneous injection of vehicle (control), or 0.1, 0.3, or 1.0 mg/kg AM-2201 on the lower back between the hips. The subcutaneous route of administration was chosen because our previous studies used this route when examining the effects of AM-2201 and other cannabinoids in rats (Schindler et al, 2017;Elmore and Baumann, 2018). Additionally, similar to the smoked route of administration, the subcutaneous route largely bypasses the first-pass metabolism in the liver.…”

“…On each test day, one investigator prepared drug solutions and administered the drug to rats, whereas another investigator performed the behavioral scoring without knowing the dose administered to each subject. During the 1-minute observation period, catalepsy behaviors were scored, as previously described, based on the following three overt symptoms: immobility, flattened body posture, and splayed limbs (Elmore and Baumann, 2018). Each symptom was scored as 1 5 absent, 2 5 present, or 3 5 continuous or intense, at each time point.…”