Prior nicotine exposure changed how THC affects the brain differently by age and sex | Research

The takeaway

Chronic nicotine pre-exposure altered THC-induced brain activation and behavior in rats, with effects depending on whether the animals were adolescent or adult, male or female.

Addiction researchers, adolescent health specialists, and those studying tobacco-cannabis co-use.

Nicotine pre-exposure potentiated THC brain activation in all regions; effects varied by age and sex

What the researchers found

In 112 rats, chronic nicotine followed by a washout period altered responses to THC challenge. In adult males, nicotine pre-exposure reduced THC-induced locomotor suppression. In adolescent females, nicotine potentiated THC suppression. THC increased brain c-Fos in multiple regions, and nicotine pre-exposure further amplified this effect. Brain activation patterns differed by age (greater in adults) and sex (greater in females).

Why it matters

Cannabis and tobacco are frequently co-used, especially by adolescents. This study reveals that prior nicotine exposure creates lasting changes in how the brain responds to cannabis, and that the effects are dramatically different depending on age and sex.

The numbers in context

112 rats; 14 days nicotine + 14 days washout + THC challenge; THC increased c-Fos in caudate, nucleus accumbens, amygdala, hypothalamus, thalamus; nicotine pre-exposure potentiated c-Fos in all regions.

How the study worked

Animal study with 112 male and female adolescent and adult Sprague-Dawley rats receiving 14 days of nicotine (1 mg/kg/day) followed by 14-day washout, then acute THC challenge (5 mg/kg). Locomotor activity and c-Fos brain mapping assessed.

What this study cannot tell us

Animal study with synthetic nicotine and THC; fixed dose protocol may not reflect human use patterns; 14-day washout is a specific timeframe; only one THC dose tested.

How to read the evidence

Preliminary: animal study; cannot directly translate age/sex interactions to human co-use patterns.

When this study was published

Published 2020.

The bigger picture

The age and sex differences suggest that adolescents and females may be particularly sensitive to nicotine-cannabis interactions. This has implications for understanding why co-use patterns develop and why outcomes may differ across demographics.

Questions still open

Does vaping nicotine before cannabis use produce the same cross-sensitization? Are adolescent females at particular risk from combined tobacco-cannabis use?

Common questions

Does prior nicotine use change how THC affects the brain?

Yes. In this rat study, prior nicotine exposure created lasting changes in THC-induced brain activation that persisted even after a 2-week nicotine-free washout period.

Were adolescents and adults affected differently?

Dramatically. Nicotine reduced THC locomotor effects in adult males but potentiated them in adolescent females, suggesting age and sex are critical factors in nicotine-cannabis interactions.

Read the original research

Effects of chronic nicotine exposure on Δ9-tetrahydrocannabinol-induced locomotor activity and neural activation in male and female adolescent and adult rats.

Pharmacology, biochemistry, and behavior, 194, 172931

View on PubMed ↗Publisher’s paper ↗

Citation

Miladinovic, T; Manwell, L A; Raaphorst, E; Malecki, S L; Rana, S A; Mallet, P E. (2020). Effects of chronic nicotine exposure on Δ9-tetrahydrocannabinol-induced locomotor activity and neural activation in male and female adolescent and adult rats.. Pharmacology, biochemistry, and behavior, 194, 172931. https://doi.org/10.1016/j.pbb.2020.172931