Biologists have cured mice of fears transplantation of neurons
Chinese scientists have shown that transplantation of embryonic neurons in the amygdala of mice allows them to better deal with these fears.
The article was published in the journal Neuron.
Generalization of fear and the inability to get rid of traumatic memories lead to the development of post-traumatic stress disorder and other associated with fears of mental disorders. For the treatment of such disorders in humans using both behavioral and pharmacological therapies. However, despite the fact that many of these treatments are initially very successful, have a significant proportion of patients with serious disorders after some time there is a relapse.
The same phenomenon has been described in rodents. Mice taught to fear a certain sound is due to the fact that the learning process is accompanied by shocks, can heal from traumatic memories during the so-called “decay of fear.” If the mouse repeatedly hear the same sound, not accompanied by shocks, the fear gradually fades. However, fear often spontaneously return if the mouse you hear that sound some time later.
Interestingly, young mice during a certain critical period of spontaneous return of fear is not happening. The end of this critical period coincides with the time formirovaniyu the brain perineuronal nets — extracellular matrix surrounding synapses. In previous studies it was shown that pharmacological destruction of the perineuronal nets around inhibitory neurons of the amygdala (a structure which plays a key role in the perception of emotions and fears) leads to the disappearance of spontaneous return of fear. On this basis, the authors suggested that the “rejuvenation” of the neurons of the amygdala can lead to the same effect.
To test this hypothesis, the researchers decided to transplant in the amygdala of adult mice embryonic neurons, of which in the course of development formed Mature neurons of this brain structure. As control was used a group of mice that transplanted embryonic neurons dead. After transplantation, mice from both groups formed a fear of a certain sound. For different sub-groups of mice the formation of fear was performed after 7, 14, 21 or 28 days after transplantation. Once the mice had learned to fear the tone, the authors caused them to fade out of fear, which lasted for two days. Then, a week later, the researchers again lost the mice a terrible sound and looked, whether there will be a spontaneous return of fear.
The authors also conducted an additional experiment, which tested, does not transplant embryonic neurons of the amygdala to get rid of old fears permanently. It is carried out transplantation of neurons after the formation in mice of fear. However, it turned out that these mice when they heard the terrible sound after transplantation, still continued to fear him. However, the attenuation of fear subsequently took from them much more effectively, and a spontaneous return of fear was observed less frequently than mice in the control group.
Histological analysis of the amygdala has helped to explain why the effect of the disappearance of the spontaneous return of fear was observed only two weeks after transplantation, but not earlier and not later. It turned out that the transplanted neurons over time, they pass all the required stages of maturation to form functional synapses with existing neurons. Transplanted cells cause a decrease in the synthesis of perineuronal nets and, apparently, as a consequence, increase the synaptic plasticity of the neurons of the amygdala. This noticeable the number of synapses formed about two weeks after the transplant, when the transplanted neurons are represented by a mixture of Mature and immature cells. One week after transplantation, the number of new synapses is still very small, and the transplanted neurons are mostly immature. And after 3 and 4 weeks after transplantation of the neurons, in contrast, are already “too Mature”.
The authors hope that in the future the obtained results can help in the treatment of phobias and post-traumatic stress disorder in humans.
Recently, scientists have proposed a way to treat phobias, allowing you to get rid of fear without colliding with it causing an unpleasant stimulus. This method is based on the “reprogramming” of traumatic memories with more pleasant with the reward system. Another recently proposed method based on interference in the process of reconsolidation traumatic memories.