8. The Chemistry of the Brain
To treat Tourette's Syndrome effectively we first have to know how it works. The genetics of the disease have already been discussed. However, it is important to note that the TIC gene isn’t the only gene involved with Tourette's syndrome. Tourette’s Syndrome is actually caused by many genes that are slightly abnormal. The TIC gene seems to enhance the effects of all the other genes.
Every thought begins in the brain. The brain consists of billions of brain cells, called neurons, which are structured into long chains to form nerves. During thought, an electrical pulse starts at one neuron and passes through many neurons along a predetermined pathway. However, neurons are not actually connected directly to each other. Between the neurons there is a very small gap called a synapse. The electrical impulse cannot cross the synapse, so chemical transmitters called neurotransmitters are used. When the electrical impulse arrives at the end of the neuron (a dendrite), a neurotransmitter is released which crosses the gap. The neurotransmitter is picked up by receptors on the post-synaptic membrane of the next neuron and sparks off another electrical impulse on the other side. This is how electrical impulses are transmitted throughout the brain.
Dopamine is one of the many neurotransmitters in the brain. In Tourette's patients, there seems to be an abnormality with the number of receptor sites on the post-synaptic neuron. Theory has it that the brain creates small impulses every now and again just to check that everything is functioning as it should. This requires the sending of an impulse down the neurons. In a normal person this impulse is so small that the action does not occur. However, in a Tourette's patient, the excess of receptors means that a larger than usual effect is seen and the spontaneous effects are observed as a tic.
Many medications for Tourette’s Syndrome are Dopamine Blockers. Once in the body they get into the synapses and bind with the Dopamine receptor sites. The Dopamine Blockers don’t trigger an impulse, they just sit there and stop Dopamine from binding to the receptor sites. They are called antagonists because they compete with the Dopamine for the sites. This reduces the number of available receptor sites in the synapse. The problem with most Dopamine Blockers is that they are indiscriminant and affect not only the nerves which cause the tics, but all other nerves too. This results in most medications causing drowsiness.
Dopamine can be converted in the body to Noradrenalin. Noradrenalin in the brain plays a crucial role in arousing the body, for example from sleep. Noradrenalin is released from the adrenal glands during stress. Its purpose is to increase heart rate and blood pressure, allowing more efficient breathing and conversion of food into energy. Noradrenalin can be the cause of sleeping difficulties and an increased appetite in Tourette's sufferers. Noradrenalin is also important for learning and the formation of memories.
Noradrenalin and Dopamine are part of the same chemical pathway. The body therefore has to choose which one it needs most. When a Tourette's sufferer is not on medication, the body produces a lot less Dopamine because the messages are getting through so easily. So the Dopamine is converted to Noradrenalinin in order to lower Dopamine levels to the body's idea of normal (actually lower levels than in non-Tourette's sufferers). So un-medicated Tourette's sufferers have higher than average Noradrenalin levels. When a Tourette's sufferer is on a Dopamine Blocker medication, the body converts Noradrenalin to Dopamine. This is because the body of a Tourette's sufferer "believes" that tics are the desirable normal state for the body to be in, and adapts to keep them. The body also stops producing as much Noradrenalin in order to increase Dopamine levels. Thus sedation is caused by the lack of Noradrenalin as well as by the medication. Hence, medicated Tourette's sufferers may feel their memory gets weaker if they are on large doses of anti-psychotics.
Serotonin is another type of neurotransmitter. It affects our sensitivity to pain, our appetite, our moods, our sexual behaviour and our memory. Low levels of Serotonin can also cause sleeplessness, irritability and forgetfulness. For this reason antidepressant drugs work to delay the breakdown of Serotonin and thus lift our mood. The best way to raise Serotonin levels is exercise. These effects can last up to several days.
It is well known that androgens (such as testosterone, the male sex hormone) affect Tourette's Syndrome. This is partly why Tourette's Syndrome affects three times as many males than females. The reason that these androgens aggravate Tourette's Syndrome is probably related to Serotonin levels.