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Selective memory

Research shows that the similar injuries, but from separate causes, make the brain reorganize in different fashions, resulting in epilepsy or a stroke

For a considerable time, a mystery has intrigued neurologists: why do two brains with practically identical injuries develop separate illnesses? Why does the attack on and the death of the same group of neurons generate, in some cases, an epileptic person, and in others, the victim of a stroke? We are dealing with two clinical states that have nothing in common. The team led by Dr. Esper Abrão Cavalheiro of the Experimental Neurology Laboratory of the Federal University of São Paulo (Unifesp), the coordinator of a thematic project that is studying the rearranging of the nerve cells after brain damage that cause one of these two pathological cases, has formulated a good explanation for the puzzle. The answer seems to be in the event that causes the neuronal death. For Dr. Cavalheiro, similar or the same injuries, but resulting from diverse processes, make the brain circuits reorganize themselves in a different manner, giving birth to ailments with distinct characteristics.

It is as if the nervous system were capable of memorizing the reason for the aggression and was using this information as a parameter in its process of regeneration. “We observed in epileptic rats a reorganization of the neuronal circuits that did not happen in the animals that were victims of cerebral vascular accidents.” compares Dr. Cavalheiro, who is also the secretary of Policies and Programs for Science and Technology at the Ministry of Science and Technology (MCT). “This led us to the hypothesis that it is this rearrangement that determines the characteristic state of epilepsy (convulsion crises).” In the case of brain hemorrhage victims or strokes, the more fragile reorganization of the nerve cells ends up compromising the motor and cognitive functions, limitations that do not affect the epileptics.

Epilepsy is triggered off by abnormal electric activity of the neurons. On the other hand, the stroke occurs due to the clogging of one of the arteries which feeds the brain, in a process that is generally associated with risk factors such as hypertension, diabetes, and high levels of cholesterol. These two different causes, the electrical hyperactivity on one hand, and the prevention of blood form getting to the brain on the other, lead to an identical result – death of neurons, more evident in the hippocampus, an important structure of the temporal lobe related to emotions, learning and memory. Close to 80% of the neurons of the hippocampus can be put out of action by this process.

“These lesions are so similar that, immediately after the neuronal death, it is difficult to distinguish one from the other from the histological aspect (microscopic study of the tissues and organs)” states Cavalheiro. The researchers have to wait for a few weeks so that the particulars of each type of neural arrangement, more pronounced in the case of epilepsy, and less present in that of brain hemorrhaging, show themselves and are visible through the microscope lens. “What probably happens is that, besides the destruction of the neurons, the attack on the brain provokes other effects, yet unknown.

These ‘secondary’ effects, overshadowed by the magnitude of the neuronal deaths, will be the determining factors for the future evolution” explains the researcher. To understand in depth the mechanism of cerebral regeneration that results in epilepsy or brain hemorrhaging, Cavalheiro, a student of the theme for decades, brought together a team of specialists from Unifesp – Cícero Galli Coimbra, Débora Amado, Maria da Graça Naffah-Mazzacoratti and Maria José da Silva Fernandes – who carried out studies with laboratory mice. Each member of the group approached the question of the neuronal re-organization from a specific angle.

Coimbra is aiming to build an experimental model for the cerebral stroke, the process in which the blood circulation decreases, as a result of the hemorrhage or cardiac arrest, temporarily denying oxygen to the brain. In his work with laboratory animals, it has been observed that the neuronal death is accompanied by an intense inflammatory reaction, with the activation of the so-called glial cells. This type of scar tissue, which until recently was considered a simple support for the neurons, plays an active role in the process of the death and regeneration of tissue. Another discovery: victims of a ischemia who show signs of fever, apparently a benign reaction of the organism, have probably a greater chance of developing Alzheimer’s disease.

Chronic epileptics
The three women of Cavalheiro’s team have been investigating different aspects of the type of injury that turns an individual into a chronic epileptic. Maria da Graça is studying the biochemistry of the process, a series of events that precede and succeed neuronal death; Maria José, the cerebral metabolism; and Débora, the influence of the hormonal factors, which can facilitate or make difficult the death and the re-organization of the neurons.

In the study of the injuries associated with epileptic illness, the researchers made use of an experimental method established by Cavalheiro and the Polish Lechoslaw Turski. They administered a high dose of pilocarpine, a drug extracted from the South American plant Pilocarpus jaborandi, used as eyewash in the treatment of glaucoma, and that induced in the rats a state of neuronal excitement known as epileptic malady. The administration of the substance activates the neuronal receptors, which makes a greater quantity of calcium and sodium enter into the nerve cells. The result of the invasion is devastating. There is large destruction of the tissue and the genome of part of the surviving neurons modifies itself, provoking alterations in its cellular behavior. Modified, these cells make up the injury, the focus of future epileptic crises.

The space previously occupied by the neurons that died is filled by the glial cells. The brain then attempts to re-establish the connections (synapses) that were lost, and in this process the cells begin to make synapses with themselves, inciting or inhibiting each other. This is the so called “sprouting” of the mossy glandular fibers. The consequence of this irregular development is epilepsy.

In mice, the state of neuronal excitement lasts from 10 to 12 hours and leads to a high mortality index. The animals that survived this acute situation experienced a period free of crises that lasted on average 15 days. However, after this absence of convulsions, they went on to show spontaneous and recurring crises for the rest of their lives, with an average number of attacks of two to three per week. In the experiments on the induction of epilepsy through pilocarpine, Cavalheiro’s team noted that the brain of young mice support better crisis than those of adult mice. “These animals resist better the appearance of injuries and don’t show chronic crises, at least not until the third episode of the state of the epileptic illness.” says Maria da Graça.

The researchers still don’t know for certain why this happens. “A possible explanation would be the fact that the brain, during its development, consumes less energy when compared to an adult brain.” suggests Maria José. In another line of reasoning, the specialists believe that in the developing brain lots of receptors are still not active. “This means that the excitement set off by the crisis produces less damage than that which would be caused in an adult brain.” explains Maria da Graça.

Only two decades ago the factors which, in brain pathology terms, lead to the death of an enormous number of neurons were practically unknown and little was known about the intrinsic process of re-organization that the brain passes through after an injury. Nevertheless, over the last few years, research done here and abroad, has made strides in advancing knowledge. For example, today it is known that the neuronal death happens after the exaggerated liberation of a neuron transmitter called glutamate. This substance promotes the massive entrance of calcium and other elements into the cells, which die because of the excess of substances which, in normal quantities are indispensable for their existence.

Also, it is now known why the central nervous system doesn’t passively accept the destruction of neurons, but reacts to the aggression. “After suffering a grave injury, the brain creates connections totally unprecedented, and learns to live with this new circuitry. What we call an illness is in fact a vital reaction.” states Cavalheiro. “Our objective is to better understand the mechanisms of neuronal death and of the re-organization of the nervous system to interfere in the process.”

Fever after a stroke increases the risk of Alzheimer’s disease

In his studies with mice, the physician Cícero Galli Coimbra of Unifesp, has discovered that the equation stroke plus uncontrolled fever, years later can produce a greater number of individuals with Alzheimer’s disease. Characterized by the progressive loss and death of nerve cells in various parts of the brain, this disease, which has no cure, affects the memory and the capacity for learning. In its advanced stage, it is the main cause of schizophrenia, which occurs in 1% of the population over 65 years of age and is responsible for an yearly bill of US$ 100 billion in the United States.

“We verified that an ischemia followed by hyperthermia (fever) causes the death of neurons and the development of alterations typical of Alzheimer’s disease in animals.” says the researcher. Caused by a cardiac arrest or a stroke, the ischemia characterizes itself by a decrease in blood circulation and oxygen fed to the brain.

Coimbra’s finding should radically change the post- ischemic medical procedure. Many individuals who suffer brain strokes show fever during the first week of recovery due to pneumonia or other hospitalized complications. However, rarely to the doctors medicate with anti-fever drugs as they are accustomed to considering this fever as something benign or even as a good indicator of the organism’s response to antibiotics. They did not know that in the future these patients could develop an illness through the simple fact that their body temperature was not controlled after the stroke. “Today, 30% of the patients who suffer strokes show Alzheimer’s disease five years later.” reveals Coimbra.

The Unifesp doctor still does not know why this happens, but suggests a line of reasoning to attempt to explain the process. Hit almost concurrently by the stroke and the fever, the immunological system loses its capacity to distinguish friendly proteins from unfriendly proteins within the nervous system. Confused, the defense cells of the organism, years later, begin to attack the nervous system, triggering off Alzheimer’s disease.

An alternative explanation, proposed by other specialists, is that the binomial “stroke plus fever” causes a large liberation of free radicals. These ions tend to damage the mitochondrial DNA, accelerating the aging of mitochondrials which are the motors of the cells. With the characteristic performance of old machines, these organelles begin to demonstrate low performance and generate a lot of pollution, in other words, free radicals. In the end, this system feedback would lead to the beginning of Alzheimer’s disease.

No matter what the cause is, the discovery that ischemia followed by fever can lead to Alzheimer’s disease allows us to intentionally produce this disease situation in laboratory animals, in order to test drugs that might block or at least slow down this diseasey. “We already have the general lines of an experimental model. The next step is to quantify the process. For example, how does a second or third fever crisis increase the possibility of Alzheimer’s disease?” asks Coimbra. “And, simultaneously, to begin tests with drugs that are potential inhibitors of the disease, with substances recognized to be capable of helping in the re-generation of damaged DNA. The work with animals prepares the way for a clinical study, shortening the research time from fifty to five years.”

The project
Epileptic Genesis in Human Beings. Electrophysiological and Structural Characterization of Brain Tissue obtained in Surgeries for Epilepsy Treatment. Correlation with Clinical Alterations, Electro Encephalographs and Anatomy Pathology (00/08982-7);  Modality: Thematic project; Coordinator: Dr. Esper Abrão Cavalheiro – Unifesp; Investments: R$ 344,328.85 and US$ 459,055.48

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