Intracerebellar cannabinoid administration impairs delay but not trace eyeblink conditioning

Chronic cannabis use affects cerebellum dependent visuomotor adaptation

BACKGROUND

Cannabis is one of the most commonly used substances in the world. However, its effects on human cognition are not yet fully understood. Although the cerebellum has the highest density of cannabinoid receptor type 1 (CB1R) in the human brain, literature on how cannabis use affects cerebellar-dependent learning is sparse. This study examined the effect of chronic cannabis use on sensorimotor adaptation, a cerebellar-mediated task, which has been suggested to depend on endocannabinoid signaling.

METHODS

Chronic cannabis users (n = 27) with no psychiatric comorbidities and healthy, cannabis-naïve controls (n = 25) were evaluated using a visuomotor rotation task. Cannabis users were re-tested after 1 month of abstinence (n = 13) to assess whether initial differences in performance would persist after cessation of use.

RESULTS

Cannabis users showed lower adaptation rates compared to controls at the first time point. However, this difference in performance did not persist when participants were retested after one month of abstinence (n = 13). Healthy controls showed attenuated implicit learning in the late phase of the adaptation during re-exposure, which was not present in cannabis users. This explains the lack of between group differences in the second time point and suggests a potential alteration of synaptic plasticity required for cerebellar learning in cannabis users.

CONCLUSIONS

Overall, our results suggest that chronic cannabis users show alterations in sensorimotor adaptation, likely due to a saturation of the endocannabinoid system after chronic cannabis use.

The mouse at the popcorn stage of development

In mice, rats, and rabbits vigorous jumping and hyperexcitability occur at the popcorn stage of postnatal development. In view of subcortical structures appearing before cortical ones, the trait is deemed to occur at the maturation time of ascending excitatory projections from the brainstem and to disappear at the maturation time of descending inhibitory projections from the forebrain. There is evidence that the popcorn stage may be due in part to the lack of a cholinergic influence on dopamine systems. Based mostly on results found in adult mice and rats, there may also be a role for cortico-subcortical systems that include the cerebellum and basal ganglia requiring the influence of biogenic amines, glutamate, and endocannabinoids.

Differential effects of two early life stress paradigms on cerebellar-dependent delay eyeblink conditioning

Early life stress paradigms have become prominent in the animal literature to model atypical development. Currently, two models have prevailed within the literature: (1) limited bedding or nesting and (2) maternal separation or deprivation. Both models have produced aberrations spanning behavior and neural circuitry. Surprisingly, these two models have yet to be directly compared. The current study utilized delay eyeblink conditioning, an associative learning task with a well-defined cerebellar circuit, to compare the behavioral effects of standard limited bedding (postnatal day 2–9, n = 15) and maternal separation (60 min per day during postnatal day 2–14, n = 13) early life stress paradigms. Animals in all groups exhibited robust learning curves. Surprisingly, facilitated conditioning was observed in the maternal separation group. Rats that underwent limited bedding did not differ from the control or maternal separation groups on any conditioning measures. This study contributes to a clearer understanding of early life stress paradigms and the claims made about their mechanisms, which if better clarified can be properly leveraged to increase translational value.