Alterations in a molecular brain pathway that are activated by marijuana may give rise to the cognitive symptoms of schizophrenia, scientists at the University of Pittsburgh School of Medicine have said.
The researchers say that activation of the cannabinoid 1 receptor (CB1R), the site of action of the main chemical ingredient of marijuana, impairs signalling by gamma-aminobutyric acid (GABA), an important neurotransmitter essential for core cognitive processes such as working memory.
Writing about their observations in the Archives of General Psychiatry, the researchers have revealed that the use of marijuana in individuals with schizophrenia appears to worsen this deficit in GABA synthesis.
The researchers say that their suggest possible new drug targets that could help to improve function in people with the mental illness, given that reduced GABA is known to be present in schizophrenia.
"Heavy marijuana use, particularly in adolescence, appears to be associated with an increased risk for the later development of schizophrenia, and the course of illness is worse for people with schizophrenia who use marijuana," said Dr. David A. Lewis, corresponding author of the study and UPMC Endowed Professor in Translational Neuroscience, Western Psychiatric Institute and Clinic, University of Pittsburgh School of Medicine.
"We wanted to understand the biological mechanisms that could explain these observations, and with this study, I believe that we can narrow down at least part of the 'why' to CB1R, the receptor for both tetrahydrocannabinol (THC), the main psychoactive ingredient in marijuana, and the brains own cannabinoid chemical messengers," he added.