Not Enough Neuronal Survival

Many conditions and diseases are caused by not enough neurons surviving in certain areas of the nervous system and a drop in their numbers.  A lot of research is going on into the subject of neuronal survival in the hope of finding treatments for these conditions. 

Parkinson's Disease

Parkinson's Disease is a neurodegenerative disease characterised by the loss of neurons that secrete dopamine in an area of the brain called the substantia nigra. 

The substantia nigra secretes dopamine onto the cells in the caudate and putamen (the striatum) which inhibits them, when these neurons are lost so is the inhibition.  As the striatum in responsible for inhibiting motor actions the result is an increase in the inhibition of motor activity.  

Symptoms include:

• A tremor, often in one hand.  This is often the first sign of the disease.
• Slowing of movements.  Performing movements takes longer than it used to, this is known as bradykinesia.
• Stiffness in muscles.  Activities such as getting up become harder to do.

A PET scan showing the loss of dopaminergic neuron activity in the substantia nigra (red and yellow) in Parkinson's disease.

Huntington's Disease

Huntington's disease differs from the others in that it is inherited through a faulty gene on chromosome 4.  If a person has a parent with Huntington's they have a 50% chance of developing the disease themselves. 

This gene causes the production of a mutant form of the protein huntingtin which causes aggregation and damage of neurons.

The aggregation caused by the mutant huntingtin protein.

The symptoms of Huntington's are caused by gradual damage and loss of neurons in the striatum and cerebral cortex area of the brain.  This leads to symptoms like:

• Memory loss
• Confusion
• Personality changes
• Mood changes
• Clumsiness and uncontrolled movements
• Dementia
• Weight loss
• Depression and anxiety
• Difficulties with speaking and swallowing

Huntington's does not start to show in an individual until they are between 30-50 years old.  By this time they may well have passed the faulty gene onto their children.

Alzheimer's Disease

Alzheimer's diease is the most common cause of dementia.  It is caused by the abnormal secretion of amyloid protein by neurons which then causes the formation of "plaques" and "tangles" in the brain which lead to cell death.

This scan shows the huge loss of brain tissue that occurs in Alzheimer's disease.

 Symptoms include:

• Confusion and forgetting things, such as names and appointments easily.
• Mood swings.
• Becoming withdrawn.

Motor Neuron Disease

In motor neuron disease the upper and lower motor neurons degenerate leading to the muscles that they innervate wasting away or becoming weak.  This causes problems with movement, breathing, speech and swallowing.  It remains a mystery why this occurs, suggestions for it are that free radicals cause the damage or an excess of the neurotransmitter glutamate.

Parkinson's Disease Image from Wikimedia Commons https://commons.wikimedia.org/wiki/File:PET_scan_Parkinson%27s_Disease.jpg, in public domain

Huntington's Disease Image from Wellcome Images https://images.wellcome.ac.uk/, image reference: B0003893, licence: Creative Commons 2.0

Alzheimer's Disease Image from Wikimedia Commons https://commons.wikimedia.org/wiki/File:Alzheimer%27s_disease_-_MRI.jpg, in public domain