Parkinson’s disease

The Second Brain and Parkinson’s disease

Parkinson’s disease is a disorder of the motor system correlated with a loss of dopamine in the brain and characterized by tremors, muscular rigidity, and a reduction in voluntary movement. It is classified as a degenerative dementia and is the second most common neurodegenerative disease. Chapter 16 defines dementia as an acquired and persistent syndrome of intellectual impairment characterized by memory and other cognitive deficits and impairment in social and occupational functioning. Dementia is not a singular disorder and the DSM uses this definition as the criteria for assigning a diagnosis. Parkinson’s disease is very common affecting approximately 1% of the population. That number is expected to rise as more people are living longer and the occurrence of the disease rises dramatically in old age.

Parkinson’s disease is caused by a progressive cell death in the substantia nigra. There is a decrease in the release of dopamine into the striatum because of this cell death. Dopamine plays a main role in the control of voluntary movement and the decrease in production of this neurotransmitter is the cause of some of the symptoms of the disease. Symptoms vary from person to person even though cell degeneration in the brain is well defined. Parkinson’s disease gives us a look into the general problems and neural changes that come with getting older since most of the symptoms take place as we age naturally. The signs of the disease begin slowly with a tremor or slight stiffness of the limbs, movement becomes slower, the face turns mask like, eye blinking slows or stops, and a lack of emotion is seen. The posture may slump, a walking shuffle where the arms hang motionless at the side develops, speech becomes slow and monotone, and swallowing becomes difficult often causing drooling. The rate at which symptoms worsen varies with their on again off again qualities and it often takes 10 to 20 years to completely incapacitate the afflicted person.

There are four major symptoms of Parkinson’s disease: tremor, rigidity, loss of spontaneous movement (akinesia), and disturbances of posture. Positive symptoms, the appearance of abnormal behavior, are very common with this disease and are inhibited in the normal brain but released as the disease progresses. There are three main positive symptoms. First there is a tremor at rest, alternating movement of the limbs that stops during voluntary movement or sleep. Second there is muscular rigidity in the limbs and all movement must be done in a series of steps. This often looks like slow motion and the afflicted person is unable to speed the movement up. Last is akathesia, small involuntary movements or changes in posture that occur for no apparent reason. These cannot be controlled, consist of a turning of the head or eyes to one side, and can last for a few minutes or hours. Negative symptoms, the loss of normal behavior, have five groups: Disorders of posture and equilibrium, disorders of righting, disorders of locomotion, speech disturbances, and akinesia. Cognitive symptoms of the disease often mirror the motor symptoms.

There is no known cure for this disease and treatment for it is based on current symptoms and psychological factors. Drug therapy is also used to increase the amount of activity in the remaining dopamine receptors and to suppress others that activate due to the decrease in dopamine. The main problem with this type of treatment is that as the disease progresses the drugs no longer have the same effect. Two other treatments have been shown to be effective in treating the positive symptoms of the disease. Lesioning the globus pallidis helps with muscle rigidity and tremors. Deep brain stimulation, neurosurgery in which electrodes implanted in the brain stimulate a target area with a low voltage electrical current to facilitate behavior, also helps with rigidity and tremors. Both of these treatments can be used together for maximum relief.

The enteric nervous system (ENS) controls gastrointestinal motility, contains dopamine neurons, and is connected to the CNS through afferent and efferent pathways in the PNS and SNS. This connection is the pathophysiology of Parkinson’s disease. Research has shown that the GI problems that occur in Parkinson’s disease are directly related to the loss of dopamine in the substantia nigra and the presence of Lewy bodies (LB), a circular fibrous structure found in several neurodegenerative disorders that forms within the cytoplasm of neurons and is thought to result from abnormal neurofilament metabolism. Patients with PD were autopsied and various tissue samples were taken and then a gram stain was performed. These LB were found not only in the brain but also in the GI tract, colon, olfactory bulb and other areas as well. This leads researchers to believe that the lesions that are found in the ENS occur early in PD and that the LB spread to other areas of the body thus progressing the disease even faster. This spreading worsens symptoms and makes some treatment processes harder to perform because the LB takes over new cells as well.

　

Chaumette, T., Derkinderen, P., Duyckaerts, C., Lebouvier, T., & Paillussion, S. (2009)

The Second brain and Parkinson’s Disease. European Journal of Neuroscience,

30, 735-741. doi: 10.1111/j.1460-9568.2009.06873.x