A new study explains how marijuana impairs working memory. The component THC removes AMPA receptors for the neurotransmitter glutamate in the hippocampus. This means that there are fewer receivers for the information crossing between neurons.
The research is also significant because it adds to the growing evidence for the role of astrocytes in neural transmission of information.
This is shown by the finding that genetically-engineered mice who lack type-1 cannabinoid receptors in their astroglia do not show impaired working memory when exposed to THC, while those who instead lacked the receptors in their neurons do. The activation of the cannabinoid receptor expressed by astroglia sends a signal to the neurons to begin the process that removes AMPA receptors, leading to long-term depression (a type of synaptic plasticity that weakens, rather than strengthens, neural connections).
(2012). Acute Cannabinoids Impair Working Memory through Astroglial CB1 Receptor Modulation of Hippocampal LTD.
Cell. 148(5), 1039 - 1050.