Parkinson disease (PD) is characterized by a slowing of voluntary movements, bradykinesia, muscular rigidity and tremor at rest.  These abnormalities result from a reduction of neurons that make dopamine in the pars compacta of the substantia nigra.  The axons of these neurons normally release this neurotransmitter where they synapse, in parts of the basal ganglia called the caudate nucleus and putamen or, collectively, the corpus striatum.  Dopamine usually works as an inhibitory neurotransmitter in the corpus striatum where it acts on cholinergic neurons. 

Lewy bodies, a hyaline inclusion, are seen microscopically in the cytoplasm of residual neurons in the substantia nigra of nearly all patients with Parkinsonism. The  loss of neurons results in a grossly evident depigmentation of the substantia nigra because those dopaminergic neurons also contain the pigment neuromelanin in their cytoplasm.

There are various causes for the loss of dopaminergic neurons in the substantia nigra and the resultant signs of PD.  Some evidence exists for involvement of genetic factors in the pathogenesis of PD.  For example, several large families with an autosomal, dominant inheritance pattern of PD have now been described, and the first genetic locus for PD has been identified in one of those families

Alzheimer Disease

Alzheimer disease (AD) is the most common cause of dementia in western civilization. It affects more women than men, and the clinical course generally lasts approximately five years.  The younger the individual is at the onset of the disease, the more severe the deficits for the patient.  One famous contemporary who suffers from the disease is former U.S. President Ronald Reagan.

The cerebral cortex and some other forebrain regions atrophy so severely that the brain may weigh less than 1000g at death. Shrinkage is most pronounced in the frontal and temporal lobes.  The insula and the medial part of the temporal lobe tend to demonstrate the highest  number of neuritic plaques.  The greater the number of plaques the higher the degree of dementia.  The disease often causes vacuolization of the subpial layers of the temporal and parietal lobes.  The spongy state is associated with neuronal loss and is similar to the effects of Creutzfeldt-Jakob disease.

Researchers continue to search for causes and cures for AD.  The gene that codes for the B-amyloid protein located on chromosome 21 is implicated in the 20% of  patients for whom there is a family history of AD.  Head injury has been implicated in 3 to 5 % of AD cases.  There is a 70 to 90% decrease in the production of the enzyme that makes acetylcholine.  Other neurotransmitter abnormalities have also been implicated.

Multiple Sclerosis

Multiple sclerosis (MS) is the most common demyelinating disease afflicting humans.   It is a chronic disease affecting more women than men often leading to progressive neurological deterioration and ataxic paraplegia.  MS has cycles of remission and relapses with remission occurring less frequently as the disease progresses.  Lesions occur in all parts of the CNS white matter appearing gray and translucent.  Some of the more prominent structures affected are the medial longitudinal fasciculus and the optic tract and chiasm.  Damage to the neurons in these structures can lead to optic neuritis (with complete loss of vision in one eye), diplopia (double vision) and problems coordinating eye and head movements.  Onset of the disease is usually between the ages of 20 and 40 years of age.

Histologically there is a large decrease in the number of oligodendrocytes with 90% of the patients having antibodies to these cells.  Many times there is a cuffing of blood vessels due to the high number of lymphocytes, macrophages and plasma cells found in plaques.  Macrophages take a principal role in stripping and phagocytosis of myelin from intact axons.  Efforts to link this autoimmune disease with a virus have been unsuccessful perhaps do to the difficulty of isolating and culturing virus from MS patients.

Huntington Disease

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

Multiple sclerosis (MS) is the most common demyelinating disease afflicting humans.   It is a chronic disease affecting more women than men often leading to progressive neurological deterioration and ataxic paraplegia.  MS has cycles of remission and relapses with remission occurring less frequently as the disease progresses.  Lesions occur in all parts of the CNS white matter appearing gray and translucent.  Some of the more prominent structures affected are the medial longitudinal fasciculus and the optic tract and chiasm.  Damage to the neurons in these structures can lead to optic neuritis (with complete loss of vision in one eye), diplopia (double vision) and problems coordinating eye and head movements.  Onset of the disease is usually between the ages of 20 and 40 years of age.

Histologically there is a large decrease in the number of oligodendrocytes with 90% of the patients having antibodies to these cells.  Many times there is a cuffing of blood vessels due to the high number of lymphocytes, macrophages and plasma cells found in plaques.  Macrophages take a principal role in stripping and phagocytosis of myelin from intact axons.  Efforts to link this autoimmune disease with a virus have been unsuccessful perhaps do to the difficulty of isolating and culturing virus from MS patients.

Huntington Disease

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

Alzheimer disease (AD) is the most common cause of dementia in western civilization. It affects more women than men, and the clinical course generally lasts approximately five years.  The younger the individual is at the onset of the disease, the more severe the deficits for the patient.  One famous contemporary who suffers from the disease is former U.S. President Ronald Reagan.

The cerebral cortex and some other forebrain regions atrophy so severely that the brain may weigh less than 1000g at death. Shrinkage is most pronounced in the frontal and temporal lobes.  The insula and the medial part of the temporal lobe tend to demonstrate the highest  number of neuritic plaques.  The greater the number of plaques the higher the degree of dementia.  The disease often causes vacuolization of the subpial layers of the temporal and parietal lobes.  The spongy state is associated with neuronal loss and is similar to the effects of Creutzfeldt-Jakob disease.

Researchers continue to search for causes and cures for AD.  The gene that codes for the B-amyloid protein located on chromosome 21 is implicated in the 20% of  patients for whom there is a family history of AD.  Head injury has been implicated in 3 to 5 % of AD cases.  There is a 70 to 90% decrease in the production of the enzyme that makes acetylcholine.  Other neurotransmitter abnormalities have also been implicated.

Multiple Sclerosis

Multiple sclerosis (MS) is the most common demyelinating disease afflicting humans.   It is a chronic disease affecting more women than men often leading to progressive neurological deterioration and ataxic paraplegia.  MS has cycles of remission and relapses with remission occurring less frequently as the disease progresses.  Lesions occur in all parts of the CNS white matter appearing gray and translucent.  Some of the more prominent structures affected are the medial longitudinal fasciculus and the optic tract and chiasm.  Damage to the neurons in these structures can lead to optic neuritis (with complete loss of vision in one eye), diplopia (double vision) and problems coordinating eye and head movements.  Onset of the disease is usually between the ages of 20 and 40 years of age.

Histologically there is a large decrease in the number of oligodendrocytes with 90% of the patients having antibodies to these cells.  Many times there is a cuffing of blood vessels due to the high number of lymphocytes, macrophages and plasma cells found in plaques.  Macrophages take a principal role in stripping and phagocytosis of myelin from intact axons.  Efforts to link this autoimmune disease with a virus have been unsuccessful perhaps do to the difficulty of isolating and culturing virus from MS patients.

Huntington Disease

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

Multiple sclerosis (MS) is the most common demyelinating disease afflicting humans.   It is a chronic disease affecting more women than men often leading to progressive neurological deterioration and ataxic paraplegia.  MS has cycles of remission and relapses with remission occurring less frequently as the disease progresses.  Lesions occur in all parts of the CNS white matter appearing gray and translucent.  Some of the more prominent structures affected are the medial longitudinal fasciculus and the optic tract and chiasm.  Damage to the neurons in these structures can lead to optic neuritis (with complete loss of vision in one eye), diplopia (double vision) and problems coordinating eye and head movements.  Onset of the disease is usually between the ages of 20 and 40 years of age.

Histologically there is a large decrease in the number of oligodendrocytes with 90% of the patients having antibodies to these cells.  Many times there is a cuffing of blood vessels due to the high number of lymphocytes, macrophages and plasma cells found in plaques.  Macrophages take a principal role in stripping and phagocytosis of myelin from intact axons.  Efforts to link this autoimmune disease with a virus have been unsuccessful perhaps do to the difficulty of isolating and culturing virus from MS patients.

Huntington Disease

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.

This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades.  Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period.  As the disease progresses it leads to dementia and usually death from incurrent infection.  There is a high incidence of suicide among patients with HD.

Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen  The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave.  In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes.  The gene for this disease has been isolated to the short arm of chromosome 4.