THC Adaptation Followed Different Kinase Pathways Across Mouse Brain Regions
Repeated THC exposure did not engage the same adaptation pathway throughout the mouse brain. A study of receptor-regulating proteins found that ERK signaling helped explain changes in some regions, while other regions largely relied on different mechanisms.
What the researchers measured
The investigators examined G protein-coupled receptor kinases, known as GRKs, and beta-arrestins after chronic THC exposure. These proteins help regulate receptor responsiveness. The brain regions included the striatum, cerebellum, hippocampus and prefrontal cortex. This was laboratory research in mice, rather than a study measuring impairment in cannabis users.
Where ERK inhibition changed the result
Chronic THC significantly activated particular GRK and beta-arrestin subunits in the regions examined. Genetic and pharmacological approaches that inhibited ERK activation prevented these changes in the striatum and cerebellum. The hippocampal and prefrontal changes were mostly ERK-independent. ERK activation in those latter regions instead accompanied changes in transcription-related proteins and brain-derived neurotrophic factor.
Why a regional mechanism matters
The authors linked the striatal and cerebellar findings to mechanisms potentially underlying tolerance to reduced movement. That interpretation does not establish that every THC effect becomes tolerant through the same pathway. Nor does a molecular finding identify the degree of adaptation in an individual person.
For evidence interpretation, the useful question is which region, protein and behavioral outcome were actually studied. A broad statement that THC tolerance is caused by ERK alone would lose the regional distinctions central to these results.
Related: interpreting cannabis tolerance claims.
Research cited
Rubino T; Viganò D; Premoli F; Castiglioni C; Bianchessi S; Zippel R; Parolaro D. Changes in the expression of G protein-coupled receptor kinases and beta-arrestins in mouse brain during cannabinoid tolerance: a role for RAS-ERK cascade. Molecular neurobiology (2006). doi:10.1385/MN:33:3:199. Findings discussed from the study abstract.
