A research group led by Associate Professor Fumitaka Kimura of the Graduate School of Medicine, Osaka University has elucidated that multiple mechanisms are involved in the formation of neural circuits in the cerebral cortex.At the same time, it was discovered for the first time in the world that substances similar to cannabinoids, the active ingredient of cannabis, sort out unnecessary synapses, and that ingestion of cannabis cuts down to the synapses that are originally needed and destroys neural circuits.Published in the American scientific journal "Journal of Neuroscience".

 Until now, it was known that neural activity before and after synapses greatly affects the formation of neural circuits, but it was unclear what kind of neural activity was specifically involved.Especially in the formation of projections from the thalamus to the cerebral cortex, it is more complicated, and after wide projections can be made to the immature cerebral cortex, unnecessary projections are removed as the cerebral cortex grows, leaving only the correct projection destination2. Stage changes occur, but the mechanism has not been elucidated.

 In other parts of the cerebral cortex, the research group found that there is a rule called "STDP" in which the firing sequence of cells before and after synapses determines the strength of synapses, and this rule suddenly changes at some stage during circuit formation. I was discovering to do.Therefore, this time, we focused on the possibility that the rules would change at the synapses of the thalamus and cerebral cortex as well.

 As a result, when the thalamus-cortex projection is possible, the pre-synaptic activity first strengthens the synapse, the projection extends over a wide area, and then the synchronized activity weakens the synapse. Discovered that extra projections are organized.We also found that cannabinoids released from nerve cells during synaptic weakening pruned unwanted neural projections.

 Next, when cannabinoids were externally administered to mice, it was confirmed that neural projection was similarly regressed.It was also found that genetically lacking cannabinoid receptor function left the projections undisturbed.

 This result suggests that there is a substance similar to cannabinoid in the brain, and by stopping this function and suppressing the breakdown of neural circuits, it may be applied to the treatment of brain damage and dementia.At the same time, scientifically demonstrating that cannabis impairs the normal development of the brain is expected to contribute to raising awareness of the reduction of abuse of cannabis and dangerous drugs in the future.

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