From the earliest moment of development to the last stages of your life, your brain and immune system are involved in a constant, ever-changing dialogue. Each influences the other in specific and profound ways.
The growth of the human brain and its health are dependent on proper immune function from infancy. Conversely, the premature demise of brain cells in diseases such as Alzheimer's, Parkinson's, and ALS is linked to immune system breakdown.
Biological communication between your body's many systems relies on messenger molecules which travel between cells and act in concert with one another. In this chapter, you will learn about the ongoing chemical dialogue between the brain and the immune system, a connection that depends on two languages: the neurotransmitters of the brain, and the immunotransmitters of the immune system.
First, though, let's take a look at the regional control center for monitoring this vital biological dialogue, a brain structure known as the hypothalamus.
The hypothalalnus is an area of the brain no larger than a pea, yet its complex communication pathways connect your brain with your endocrine, cardiovascular, and immune systems. Like a master conductor in a biological symphony, the hypothalamus orchestrates the production and release of thyroid, stress, growth, and sex hormones. It also controls the amount of insulin released by the pancreas.
Furthermore, this tiny brain structure links our emotions to our bodily responses. For instance, anger, depression, and anxiety are all mediated by chemical communicatlon signals that originate in the hypothalamus. These signals include neurotransmitters and substances known as "hormone-releasing factors," or neuropeptides -- protein-like substances which regulate body temperature, level of alertness, blood pressure, respiratory rate, appetite, and reproductive functions.
Now, in addition to commanding this vast spectrum of responses, recent scientific discoveries have linked the hypothalamus to immune function as well. Research has demonstrated that this part of the brain exchanges a significant amount of information with the body's immune system via their respective neurotransmitters and immunotransmitters.
Hypothalamic messengers allow the brain to directly influence the immune system and either increase or decrease its activity. The immune system even has receptor sites for these neurotransmitters. The receptor sites are found on white blood cells, lymph nodes, and various other immune organs.
Conversely, the brain's hypothalamus is directly and continuously influenced by the immune system. Certain brain region's are specifically designed to receive immunotransmitters, and in this way the immune system can profoundly influence brain metabolism, the electrical activity of neurons, and the synthesis and release of neurotransmitters.
This elaborate biological communication network, which we refer to as the brain-immune connection, is the basis of your well-being or your vulnerability to a particular disease. As you will see throughout The Brain Wellness Plan, your health depends on the ongoing ability of the brain and the immune system to communicate effectively in both directions.
When mystery novelist Agatha Christie's favorite detective, Hercule Poirot, is up against a tough case to solve, he often looks for answers in "the little grey cells." These little grey cells are the neurons in our brains.
Neuron, the word for the brain's most basic cellular unit, is Greek for "string." Indeed, people during the Greek and Roman eras drew a parallel between man, who is manipulated by the gods, and puppets on strings. However, even early on, physicians such as Hippocrates (ca. 460-877 B.C.) managed to persuade at least some in the scientific community that diseases were not punishments from the gods, but the result of natural causes.
Today, we are able to use tools such as digitized computer microscope systems to actually see what is happening in the brain, leading us to understand a great deal about brain function and to closely map specific disease pathways.
Essentially, the brain relies on efficient connections between neighboring neurons to process information it receives from sense organs such as your eyes, ears, and skin, as well as from sense organs such as your eyes, ears, and skin, as well as from within your body. That way, your brain can keep track of what's going on in your body's external and internal environments and instruct other bodily systems to respond accordingly.
Your emotional and physical health depends on how well your brain cells communicate with one another-and with the rest of your body-via neurotransmitters.
Neurotransmitters are the brain's pony express messengers, chemicals that leap across the tiny gaps, or synapses, between brain cells. If there is a match between the neurotransmitter's password and the chemical gates of the receptors of the receiving cell, the event causes the receiving neuron to either fire or shut down, depending on the message received.
In other words, each of your neurons has certain receptors on their cell surfaces, which we call membranes, and these receptors act as receiving platforms for messages from various neurotransmitters. This exacting process requires a specific match between the receptor and the neurotransmitter, much as every lock requires a specific key.
Once a specific neurotransmitter binds to a neuron receptor, it sets a chain reaction into motion within the cell. These chemical reactions in turn then regulate and control every cellular process, producing specific biological effects.
Receptors found in neuron membranes are highly specialized in terms of their structure, and that structure is dependant upon the condition of the cell membrane. The cell membrane, which is composed mostly of proteins and lipids, is in a constant state of flux. Changes in cell membranes actually occur from moment to moment, and are uniquely affected by factors such as the emotions, diet, and the immune system. Even slight alterations in this specialized cell membrane design can have negative consequences on the ability of neurotransmitters to produce the desired effects, and can ultimately cause disease.
For example, patients with Alzheimer's suffer massive destruction of the brain cells that release a memory-enhancing neurotransmitter called acetylcholine. That discovery has prompted recent efforts to try to make up for that loss by administering drugs and nutritional agents that boost the brain's acetylcholine content.
In Parkinson's disease, brain damage mainly targets a particular set of dopamine-producing neurons, shortchanging the body of the dopamine neurotransmitter so essential for controlling muscle movements and balance. One of the most effective drug therapies for patients with Parkinson's is L-Dopa, which helps restore a normal level of that crucial neurotransmitter.
In Part II of The Brain Wellness Plan, we describe each neurological disease in relationship to the chemical messengers involved in the brain-immune communication relay systems. Right now though, we'll simply profile a few of the most important neurotransmitters to emerge among the more than fifty to have been discovered and studied in recent years.
The biological complexity of the brain's communication system is matched in intricacy and efficiency by the immune system's complicated communication network. Like the brain, the immune system's different components "speak" to one another - and with the rest of the body - through its chemical messengers, the immunotransmitters.
At its most basic level, the function of the immune system is to protect us from the harmful effects of bacteria, viruses, parasites, and environmental toxins. This enormous task is carried out by various components of the immune system, which must work in close harmony with one another for best results.
The most important of these immune system components are the lymphocytes, or white blood cells, which fight bacteria, fungi, and other foreign bodies. Lymphocytes include both T cells and B cells.
In addition, throughout this book you will read about another important type of white blood cell, the macrophage. Macrophages are the immune system's foot soldiers, capable of engaging in hand-to-hand battle and literally gobbling up invaders to destroy them.
The number of white blood cells called into battle depends, of course, on the severity of the invasion. Your immunotransmitters play a vital role in goading the immune system components into action and in regulating the scope of the battle.
Because the immune system plays such a complex role in defending our bodies, it has developed a highly specialized form of communication to allow its various cellular components to coordinate their ferocious activity, This communication relies on immunotransmitters called cytokines.
Cytokines are to the immune system what neurotransmitters are to the brain. Just as the brain relies on neurotransmitters to exchange information among its own neurons and with the rest of the body, so your immune system's ability to relay messages between its components and throughout the body depends on cytokines.
The three types of cytokines you will read about most in this book will be the interleukins, tumor necrosis factor (TNF), and interferons. All these natural proteins are capable of mounting and amplifylng immune responses to a variety of biological challenges.
When your body is threatened by invasion, cytokines signal your immune system to mobilize reserve troops of white blood cells. When the invasion is over, it is up to your cytokines to put out the word to stop mobilizing the troops.
In other words, these immunotransmitters coordinate your white blood cells, boosting their activity at times of infection, injury, or other demands and reining them back in after battle. In this regard, we can think of cytokines as the body's Paul Revere molecules, calling the immune system's troops out as needed.
In the past, scientists catalogued neurotransmitters as chemical messengers limited only to transmitting information between neurons in the brain. As we explained earlier, however, recent investigations at top research institutions worldwide have dispelled that notion - we now understand that there is a two-way chemical dialogue between the brain and the immune system. Each can influence the other directly.
For example, the neurotransmitters norepinephrine and serotonin have receptors on various components of the immune system and are therefore able to influence immune response in specific ways.
Conversely, in certain areas of the brain, neurons have receptors for cytokines. As you will see in the next chapter, when cytokines are unleashed by the immune system, they can profoundly alter the way important neurotransmitters are released or inhibited.
Another good example of the brain's influence on the immune system is through the cortisol hormone. Cortisol is produced via the hypothalamus. When you suffer stress, your hypothalamus produces a substance called "corticotropin-releasing factor" (CFR) which then stimulates the release of cortisol from your adrenal glands. Cortisol plays such a pivotal role in the brain-immune connection that it has fallen under close scrutiny for its relationship to such diverse disease states as depression, chronic fatigue syndrome, and Alzheimer's.
Why is cortisol so important? The increased level of cortisol triggered by stress - an adaptive response that no doubt evolved to help us suvive attacks by predators or enemy tribes - allows your body to muster a coordinated defense to the event. That defense may include heightened awareness, increased heart rate, and increased blood flow to muscles.
Cortisol also has the ability to alter the immune system's production of white blood cells, and to cause them to migrate to particular regions of the body during times of injury, infection, and stress.
You rarely see the immune system's components in the brain, because an overzealous immune response activated to fight off invading toxins or viruses is all too capable of killing off healthy (and irreplaceable) brain cells in the process.
However, as Drs. Wolfgang J. Streit and Carol A. Kincaid-Colton explain in their November 1995 article in Scientific American, scientists are in the throes of discovering mounting evidence for an extensive defense network that functions like the brain's own private immune system.
Studies examining the way certain "microglia" cells respond to antibodies in the brain demonstrate that these normally mild-mannered cells can perform amazing, Superman-like feats.
Within minutes of disturbances in their environment, microglia cells rush to surround damaged neurons and produce some of the same deadly chemicals that immune system cells manufacture to eat up invaders.
As in the immune system, some of those protective chemicals used by the brain's microglia also end up destroying healthy bystander cells in the course of battle. This has aroused new suspicions that overzealous microglia may contribute to certain neurologic disorders.
The possible good news? Finding ways to specifically inhibit microglia activity or block their products might yield new therapies for treating patients with neurological illnesses.
Now that you understand a bit about your body's essential chemical messengers and how they function to keep you healthy, we will discuss the various roles that neurotransmitters and immunotransmitters play in causing the breakdowns of the brain-immune connection that is the hallmark of neurological disease.
