A recent investigation in mice and rats discovered something that can reverse depressive symptoms by restoring certain impulses in a part of the brain that perceives scents.
The study’s findings were published in the journal Neuron.
Neurons, which convey information by “firing” or emitting electrical impulses, are a key component of the study.
Recent studies have shown that for clusters of neurons to coordinate their activity patterns in recurrent intervals (called oscillations) of shared quiet and activity, this synchronization is necessary for successful communication between brain areas.
One such rhythm is known as “gamma,” and it repeats up to 30 times per second, making it a crucial temporal pattern for the storing of complicated information, which may include emotions.
According to earlier research, depression is electrophysiologically marked by changes in gamma oscillations in brain areas that control the sense of smell, also linked to emotions, despite the fact that its origins are still not generally understood.
The olfactory bulb, which is situated next to the nasal cavity, is one of these areas and is hypothesized to be a source of gamma oscillations across the whole brain.
In order to test their hypothesis, the authors of the present study used genetic and cell signaling approaches to disable the function of the bulb.
They then noticed a rise in depressive-like behaviors in mice and used a device to amplify gamma signals in the brain at their normal rate in order to try and reverse the behaviors.
Corresponding study author Antal Berényi says that “Our experiments revealed a mechanistic link between deficient gamma activity and behavioral decline in mice and rat models of depression, with the signal changes in the olfactory and connected limbic systems similar to those seen in depressed patients. This work demonstrates the power of gamma-enhancement as a potential approach for countering depression and anxiety in cases where available medications are not effective.”
According to the experts, major depressive disorder is a widespread, serious mental illness that is frequently resistant to pharmacological therapy.
Since the beginning of the pandemic, the condition’s prevalence has sharply grown, with estimates of over 53 million additional cases.
An earlier animal model for the study of severe depression is bulb removal, however this procedure results in structural damage that might skew researchers’ understanding of the disease’s pathophysiology.
In order to prevent damage, the present study team created a reversible strategy.
They began with a single, modified DNA strand enclosed in a safe virus; this virus was then injected into mice’s olfactory bulb neurons, where it induced the cells to develop specific protein receptors on their surfaces.
This allowed the researchers to administer medication through injection to the mice, which traveled throughout the body but only caused the neurons in the altered drug-sensitive receptor-containing bulb to die.
In this manner, the researchers were able to turn off communication between the bulb partner brain areas selectively and reversibly.
These experiments showed that continuous suppression of olfactory bulb signals, particularly gamma, resulted in depressed behaviors that persisted for days after the intervention.
The scientists employed a number of established rodent tests, including measurements of the anxiety that is one of its primary symptoms, to demonstrate the impact of the lack of gamma oscillation in the olfactory bulb.
The profession utilizes a battery of tests to detect depressive behaviors since it is aware that there are few animal models of human mental illnesses.
The tests specifically examined the length of time that animals would stay in an open area (an indicator of anxiety), whether they would quit swimming sooner when submerged (an indicator of despair) if they would stop consuming sugar water (indicating a decrease in pleasure-seeking behavior), and whether they would refuse to enter a maze (signifying a desire to avoid stressful circumstances).
The scientists then utilized a specially designed apparatus to capture the olfactory bulb’s natural gamma oscillations and to send those timed signals back into the mice’s brains as closed loop electrical stimulation.
Gamma might be amplified or suppressed in healthy animals using the gadget.
Humans exhibited depressive-like responses when gamma oscillations in the olfactory lobe were suppressed.
In addition, feeding sad rats’ brains with an enhanced olfactory bulb signal led to the limbic system’s return to normal gamma function and a 40 percent (nearly normal) reduction in depression behaviors.
Senior author of the study, György Buzsáki, says that “No one yet knows how the firing patterns of gamma waves are converted into emotions. Moving forward, we will be working to better understand this link in the bulb, and in the regions it connects to, as behavior changes.”