Some neurons in the brain are more susceptible to oxidative damage than others. Those neurons that contain dopamine1 and other oxidizable neurotransmitters, such as serotonin2, are especially vulnerable (as explained in the previous sections). For example, methylenedioxy-methamphetamine (“MDMA” or “ecstasy”) is another amphetamine-like drug3 that produces oxidative damage to serotonin neurons. While such damage has been shown in laboratory animals including primates, more recently, the neurotoxic effects of MDMA4 have been shown in the brains of human abusers. Although MDMA has been abused, there is clinical interest in its therapeutic use for the treatment (at lower doses) of certain mental health disorders.
Oxidative damage (caused by any means) in different parts of the brain can produce different neurological effects. For example, dopamine neurons are found in pathways that control voluntary movement. Oxidative damage to dopamine neurons in these pathways can cause movement problems. Similarly, movement disorders are associated with Parkinson’s disease and Huntington’s disease, in which dopamine neurons degenerate within an area of the brain called the basal ganglia. The basal ganglia are important in maintaining voluntary movement; degeneration within these structures results in tremors and tics. A few years ago scientists discovered an impurity (MPTP) in synthetic heroin that destroys dopamine neurons. It caused Parkinson’s disease in young men who were using the synthetic heroin. Another disease, Alzheimer’s Disease, involves the loss of neurons in the hippocampus, an area of the brain involved in memory. Oxidative damage to neurons in the hippocampus contributes to the memory problems in Alzheimer’s disease.
Other examples of oxidative damage to cells include:
- radiation damage to specific cells (accidental or for cancer treatment, or even UV rays from sunlight)
- damage to tumor cells by various anti-cancer drugs that form radicals easily
- damage to motor neurons in the brain and spinal cord due to a loss of the scavenging enzyme, superoxide dismutase in Lou Gehrig’s disease (Amyotrophic Lateral Sclerosis or ALS)
- damage to the liver and other organs by radicals formed from long-term alcohol use
- degeneration of many kinds of cells during normal aging, when levels of oxygen radical scavenging enzymes decrease
Definitions:
1 a neurotransmitter stored in vesicles of nerve terminals; it is a monoamine that is easily oxidized. This neurotransmitter is contained in neuron pathways important in brain stimulation, addiction and control of movement.
2 a neurotransmitter that is also oxidized easily by oxygen.
3 a substance that affects the structure or function of a cell or organism.
4 derivative of amphetamine that increases the release of serotonin into the synaptic space. It causes increased alertness and enhanced mood, but also causes toxicity to serotonin neurons.
