In rats predisposed to novelty-seeking, the CB1 antagonist AM251 reversed nicotine locomotor sensitization but failed to reduce nicotine-induced anxiety and actually made it worse when given later in abstinence.
Read this if you follow research on cannabinoid-based approaches to treating nicotine addiction.
CB1 blocker worsened anxiety when given during late abstinence
What the researchers found
Researchers used novelty-seeking (high-responder) rats that are predisposed to nicotine sensitization. After chronic adolescent nicotine exposure, these rats showed lasting behavioral sensitization and social anxiety even after 3 weeks of abstinence.
The CB1 antagonist AM251 was tested during abstinence. It successfully reversed locomotor sensitization to nicotine challenge even after prolonged abstinence. However, it completely failed to reverse nicotine-induced anxiety. When given later in abstinence (late phase), AM251 actually augmented anxiety and worsened associated molecular changes in the amygdala.
The amygdala showed persistent imbalances in neuropeptide Y and CRF systems, increased BDNF, and elevated spinophilin after nicotine, and AM251 did not correct these changes, instead worsening BDNF and spinophilin changes in the basolateral amygdala.
Why it matters
This study cautioned against using CB1 antagonists/inverse agonists for nicotine-related anxiety, even though they could reverse some addiction-related behaviors. The divergent effects on sensitization versus anxiety highlighted the complexity of cannabinoid system involvement in addiction.
The numbers in context
AM251 dose: 5 mg/kg. Short abstinence: 1 week. Long abstinence: 3 weeks. AM251 reversed locomotor sensitization but worsened anxiety during late abstinence.
How the study worked
Rat model using high-responder (novelty-seeking) phenotype. Chronic intermittent nicotine during adolescence. AM251 (CB1 antagonist, 5 mg/kg) administered during early (1 week) or late (3 weeks) abstinence. Measured locomotor sensitization, social anxiety, and amygdala neuropeptide/neuroplastic markers.
What this study cannot tell us
Animal study with a specific genetic phenotype (high-responder rats). Single dose and timing protocol for AM251. The novelty-seeking model may not generalize to all individuals. Only nicotine was tested.
How to read the evidence
Animal study with specific phenotype model. Provides mechanistic insight but limited direct clinical applicability.
When this study was published
Published in 2012. CB1 antagonists for addiction have largely been abandoned due to psychiatric side effects.
The bigger picture
This study was relevant to the broader question of whether CB1 antagonists could treat addiction. While rimonabant (another CB1 antagonist) had been explored for addiction and weight loss, psychiatric side effects led to its withdrawal. This study provided a mechanistic explanation for why CB1 blockade could worsen mood-related outcomes.
Questions still open
- Are novelty-seeking individuals particularly vulnerable to worsening anxiety from CB1 blockade? Would partial CB1 agonists fare better than antagonists? Does the timing of intervention matter for other cannabinoid-based addiction treatments?
Common questions
Could blocking the cannabinoid system help with nicotine addiction?
Why did the same drug help with one symptom but worsen another?
Read the original research
Nicotine-induced anxiety-like behavior in a rat model of the novelty-seeking phenotype is associated with long-lasting neuropeptidergic and neuroplastic adaptations in the amygdala: effects of the cannabinoid receptor 1 antagonist AM251.
Neuropharmacology, 63(8), 1335-45
Citation
Aydin, Cigdem; Oztan, Ozge; Isgor, Ceylan. (2012). Nicotine-induced anxiety-like behavior in a rat model of the novelty-seeking phenotype is associated with long-lasting neuropeptidergic and neuroplastic adaptations in the amygdala: effects of the cannabinoid receptor 1 antagonist AM251.. Neuropharmacology, 63(8), 1335-45. https://doi.org/10.1016/j.neuropharm.2012.08.016
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