Forgetting astrocytes – marijuana, memory, and the brain

My favorite thing about science are those discoveries that remind us we simply don’t know everything. A recent article by a group of researchers from Canada, China, and France (see original research article in the journal Cell here and a nice summary here) summarizes findings that reveal some surprises about the ways marijuana use affects short term memory.

Neuroscientists know a good deal about the way we form memories – long-term alterations in the way neurons in certain areas of the brain communicate known as long-term-depression and long-term-potentiation that are controlled, to a large extent, by chemicals (neurotransmitters) called GABA and Glutamate.

But as usual in human endeavors, we only know to look where we believe we need to. In the case of marijuana and memory, and after this study likely memory formation in general, we always thought that neurons were the sole players in this game. Like our old beliefs about genetics that stated that most of our genetic material is meaningless only to reveal that material to be crucial for gene regulations in a new science known as epigenetics, it seems that neurons are not the only important players in memory.

The scientists in this recent study were trying to figure out whether GABA or Glutamate were responsible for Marijuana’s (or more precisely THC‘s) effects on memory. To their surprise, they found out it was neither and kept looking, eventually realizing that the real culprits were cells called astrocytes, previously thought to be akin to the brain’s cleaning crew. Apparently, this cleaning crew might also be important for many crucial aspects of our daily functioning… Never assume, right?

The results of this research will no doubt produce some serious changes in the study of memory research as well as in research on the effects of THC and other drugs on memory – it broadens our search for the factors important in the primary and secondary effects of drugs and drug use, both short- and long-term. It could help us produce drugs with less side effects, find ways to counter undesirable effects of drug use, and develop treatments that specifically interfere with illicit drug use mechanisms. Exciting times.

3 Replies to “Forgetting astrocytes – marijuana, memory, and the brain”

  1. Dr Jaffe,

    Im wondering if the study showed how THC interacted with astrocytes and whether the effect on memory was proportional to THC or the # of Astrocytes?

    Thanks

    1. Great question Dr. Dean,
      What the researchers showed was that THC’s binding to astrocytes caused long-term-depression (LTD) in the communication between hippocampal neurons important for learning. LTD is the opposite of long-term-potentiation (LTP), which is believed to be important for memory coding. Unfortunately, since the experiment was designed as an all-or-nothing situation (mice either had CB1 receptors on their astrocytes or they did not), the study doesn’t tell us if there is a proportional effect here that is dependent on aspects of THC or astrocyte density. I am guessing future studies will examine that and my guess is that there will be differences found.
      thanks for the insightful question.
      Dr. J

  2. Dr. J
    This makes sense. And I might have a confirmation bias but this explains how many of my patients medicating with THC have lost motivation/ will to try other treatment options.
    Thank you for your thorough response and the work you do on this site. I will be tuning in for more.

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