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Inflammation of the Brain and Memory Problems

chemo

Neurological disorders typically involve memory issues. Most of the problems are attributed to plaques that build up in the brain (which are typically prions), yet some causes are unknown. New research however sheds some light on at least one cause of memory problems. As it turns out brain inflammation can rapidly disrupt our ability to retrieve complex memories of similar but distinct experiences.

Their study specifically identifies how immune system signaling molecules, called cytokines, impair communication among neurons in the hippocampus (which is an area of the brain critical for discrimination memory). The findings offer insight into why cognitive deficits occurs in people undergoing chemotherapy and those with autoimmune or neurodegenerative diseases.

Moreover, since cytokines are elevated in the brain in each of these conditions, the work suggests potential therapeutic targets to alleviate memory problems in these patients. Offering — for the first time ever — a treatment for conditions specifically caused by cytokines.

“Our research provides the first link among immune system activation, altered neural circuit function and impaired discrimination memory,” said Guzowski, the James L. McGaugh Chair in the Neurobiology of Learning & Memory. “The implications may be beneficial for those who have chronic diseases, such as multiple sclerosis, in which memory loss occurs and even for cancer patients.”

What he found interesting is that increased cytokine levels in the hippocampus only affected complex discrimination memory, the type that lets us differentiate among generally similar experiences — what we did at work or ate at dinner, for example. Interestingly enough, a simpler form of memory processed by the hippocampus — which would be akin to remembering where you work — was not altered by brain inflammation.

In the study researchers exposed rats to two similar but discernable environments over several days. They received a mild foot shock daily in one, making them apprehensive about entering that specific site. Once the rodents showed that they had learned the difference between the two environments, some were given a low dose of a bacterial agent to induce a neuroinflammatory response, leading to cytokine release in the brain. Those animals were then no longer able to distinguish between the two environments.

Afterward, the researchers explored the activity patterns of neurons — the primary cell type for information processing — in the rats’ hippocampi using a gene-based cellular imaging method. In the rodents that received the bacterial agent (and exhibited memory deterioration), the networks of neurons activated in the two environments were very similar, unlike those in the animals not given the agent (whose memories remained strong).

This finding suggests that cytokines impaired recall by disrupting the function of these specific neuron circuits in the hippocampus.

“The cytokines caused the neural network to react as if no learning had taken place,” said Guzowski, associate professor of neurobiology & behavior. “The neural circuit activity was back to the pattern seen before learning.”

The work may also shed light on a chemotherapy-related mental phenomenon known as “chemo brain,” in which cancer patients find it difficult to efficiently process information. UCI neuro-oncologists have found that chemotherapeutic agents destroy stem cells in the brain that would have become neurons for creating and storing memories.

Right now they’re looking for a simple intervention, such as an anti-inflammatory or steroid drug, that could lessen post-chemo inflammation. Bota will test this approach on patients, pending the outcome of animal studies.

“It will be interesting to see if limiting neuroinflammation will give cancer patients fewer or no problems,” she said. “It’s a wonderful idea, and it presents a new method to limit brain cell damage, improving quality of life. This is a great example of basic science and clinical ideas coming together to benefit patients.”

Who knows, inflammation of the brain may play a part in other neurological degenerative diseases. This research would then help find a way to stave off the progression (if only temporarily). Even if this isn’t the case and this can’t help people in the general sense, there are plenty of chemotherapy patients that would be happy to hear this news and that alone is a big deal.

Sources
Czerniawski J, & Guzowski JF (2014). Acute neuroinflammation impairs context discrimination memory and disrupts pattern separation processes in hippocampus. The Journal of neuroscience : the official journal of the Society for Neuroscience, 34 (37), 12470-80 PMID: 25209285

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