Methamphetamine neurotoxicity increased CB1 cannabinoid receptor expression across multiple brain regions in rats, altering how they responded to cannabinoid drugs in anxiety and cognition tests.
Read this if you are interested in how methamphetamine use changes the brain's response to cannabis.
Meth exposure increased CB1 receptors in 5 brain regions and reversed cannabinoid anxiety effects
What the researchers found
Rats were exposed to a neurotoxic methamphetamine regimen (4 doses of 4 mg/kg in one day) and examined three weeks later.
Meth-exposed rats showed significantly increased CB1 receptor expression in the prefrontal cortex, caudate-putamen, basolateral amygdala, hippocampal CA1 region, and perirhinal cortex.
Behavioral responses to the cannabinoid agonist WIN 55,212-2 were altered: it produced anxiolytic (anti-anxiety) effects in meth-exposed rats but anxiogenic (anxiety-inducing) effects in controls. Meth-exposed animals also showed reduced cannabinoid effects on exploration and short-term recognition memory.
Some cannabinoid effects (locomotor reduction, acoustic startle) were not altered by meth exposure.
Why it matters
Cannabis is the most common secondary drug among meth users. Understanding how meth neurotoxicity alters the cannabinoid system could explain different cannabis responses in meth users and has implications for dual-use populations.
The numbers in context
Meth regimen: 4 mg/kg x 4 doses in one day. CB1 increased in prefrontal cortex, caudate-putamen, basolateral amygdala, CA1, and perirhinal cortex. Cannabinoid agonist produced opposite anxiety effects in meth-exposed vs control rats.
How the study worked
Rats received a neurotoxic meth regimen (4 mg/kg x 4, 2 hours apart). Three weeks later, CB1 receptor expression was measured by immunohistochemistry in multiple brain regions. A separate group was tested with the cannabinoid agonist WIN 55,212-2 in behavioral paradigms (open field, object recognition, startle reflex).
What this study cannot tell us
Animal study using a specific neurotoxic meth protocol that may not reflect typical human meth use patterns. Three-week post-exposure timepoint may not reflect longer-term changes. Rats were drug-naive before the experiment.
How to read the evidence
Preclinical study with a specific neurotoxic meth protocol. Well-controlled but limited to animal models with no human validation.
When this study was published
Published in 2010. Research on drug interactions at the receptor level has continued to develop but remains primarily preclinical.
The bigger picture
Drug interactions at the neural level can explain why people who use multiple substances may have different responses to each. Meth-induced changes in the cannabinoid system could influence vulnerability to cannabis effects and vice versa.
Questions still open
- Do human meth users show similar CB1 receptor upregulation? Could cannabinoid system changes contribute to the high rate of cannabis co-use in meth users? Would CBD or THC have different effects in meth-experienced individuals?
Common questions
Why would meth increase cannabinoid receptors?
Does this explain why meth users often use cannabis?
Read the original research
Methamphetamine neurotoxicity increases brain expression and alters behavioral functions of CB₁ cannabinoid receptors.
Journal of psychiatric research, 44(14), 944-55
Citation
Bortolato, Marco; Frau, Roberto; Bini, Valentina; Luesu, William; Loriga, Roberta; Collu, Maria; Gessa, Gian Luigi; Ennas, M Grazia; Castelli, M Paola. (2010). Methamphetamine neurotoxicity increases brain expression and alters behavioral functions of CB₁ cannabinoid receptors.. Journal of psychiatric research, 44(14), 944-55. https://doi.org/10.1016/j.jpsychires.2010.03.002
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