Chronic THC Altered Cerebellar Synaptic Plasticity in Mice Through an ERK-Linked Mechanism
Tolerance to a movement effect does not mean cerebellar signaling has returned to an unchanged state. A mouse study found altered synaptic properties after repeated THC exposure and implicated ERK-related signaling.
The recordings examined a defined connection
Researchers investigated parallel-fiber to Purkinje-cell synapses in the cerebellum. They measured transmission and plasticity in THC-tolerant animals and tested sensitivity to a cannabinoid agonist and an adenosine-receptor intervention.
Several properties changed together
The abstract reports increased baseline release probability, altered excitatory currents and reduced sensitivity to cannabinoid inhibition. An ERK-pathway inhibitor prevented the reported changes in transmission and plasticity.
The mechanism does not determine a clinical diagnosis
Synaptic long-term potentiation is an experimental property of neural connections, not a direct measure of a person's learning, motor skill or addiction. A pathway inhibitor's effect also does not establish a safe way to reverse cannabis tolerance in patients.
The results support a circuit-level account of adaptation under this regimen. They do not prove permanent brain injury, nor do they show that motor tolerance protects every other function. The species, exposure schedule, recorded connection and pharmacological manipulation are necessary parts of any explanation of the finding.
Related: interpreting cannabis tolerance claims.
Research cited
Tonini R; Ciardo S; Cerovic M; Rubino T; Parolaro D; Mazzanti M; Zippel R. ERK-dependent modulation of cerebellar synaptic plasticity after chronic Delta9-tetrahydrocannabinol exposure. The Journal of neuroscience : the official journal of the Society for Neuroscience (2006). doi:10.1523/JNEUROSCI.5469-05.2006. Findings discussed from the study abstract.
