5-HT2A serotonin agonists like psilocybin are known to induce neuroplastic changes - this is most evident to users in the form of rapid cognitive schema formation (since we actually experience that happening), but it stands to reason that it happens throughout the nervous system.

https://www.researchgate.net/publication/45695149_The_Neurobiology_of_Psychedelic_Drugs_Implications_for_the_Treatment_of_Mood_Disorders

https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2021.724606/full

It's definitely unfortunate that there was such a backlash against this research in the 60s/70s.