Attenuation of reinstatement of methamphetamine-, sucrose-, and food-seeking behavior in rats by fenobam, a metabotropic glutamate receptor 5 negative allosteric modulator

This study investigated whether fenobam, a negative allosteric modulator (NAM) of the metabotropic glutamate receptor 5 (mGluR5), could effectively attenuate relapse-like behavior in a rat model of methamphetamine addiction. Given that current pharmacological options for methamphetamine addiction are limited, researchers evaluated fenobam due to its previous history of being well-tolerated in human clinical trials. The researchers trained rats to self-administer methamphetamine, then subjected them to extinction training, and finally measured the ability of fenobam (at various doses) to prevent the reinstatement of drug-seeking behavior triggered by drug cues or an acute priming dose of the drug. Additionally, the study assessed whether fenobam impacts the pursuit of natural reinforcers—sucrose and food—to determine if the drug's effects are specific to addiction or representative of broader behavioral inhibition.

Fenobam treatment at doses of 10 and 15 mg/kg significantly decreased the number of active lever presses during both drug-primed and cue-induced methamphetamine reinstatement sessions. These results suggest that targeting mGluR5 receptors is a viable strategy for reducing relapse-like behaviors in preclinical models. However, the study also found that fenobam effectively attenuated cue-induced reinstatement of sucrose and food-seeking behaviors across all doses tested (5, 10, and 15 mg/kg). The researchers noted that fenobam did not significantly impact locomotor activity at the 10 mg/kg dose, arguing against generalized motor impairment, but the suppression of both drug and natural reward-seeking suggests a broader influence on appetitive motivation.

While the study confirms that mGluR5 inhibition can curb methamphetamine-seeking, the broad suppression of appetitive behaviors presents a challenge for clinical translation. If a potential medication reduces an individual's motivation to pursue essential natural rewards, it may not be an ideal candidate for addiction treatment. These findings highlight the importance of refining mGluR5-targeting compounds to achieve higher specificity for drug-associated cues while preserving normal motivated behavior.