Some neurons predisposed to Huntington's.Some neurons predisposed to Huntington's
Researchers long have suspected that a buildup of certain natural chemicals or an oversensitivity to them in the brain is at least partly responsible for Huntington's disease Huntington's disease, hereditary, acute disturbance of the central nervous system usually beginning in middle age and characterized by involuntary muscular movements and progressive intellectual deterioration; formerly called Huntington's chorea. , an inherited neurological disorder afflicting about 25,000 in the United States. According to theory, these compounds flood the bundles of neurons deep within the forebrain forebrain: see brain. and kill some nerve cells, causing the progressive memory loss, angry rages and muscle spasms that mark the disease.
Now, researchers from the University of Michigan (body, education) University of Michigan - A large cosmopolitan university in the Midwest USA. Over 50000 students are enrolled at the University of Michigan's three campuses. The students come from 50 states and over 100 foreign countries. in Ann Arbor report new data concerning the exact target sites on the cells where these chemicals act. In the Aug. 19 SCIENCE they describe experiments comparing the number of receptors for six chemicals in brain tissue taken from patients who died of Huntington's and from normal brains.
The two main chemicals believed responsible for the nerve cell degeneration -- quinolinic acid and glutamate glutamate /glu·ta·mate/ (gloo´tah-mat) a salt of glutamic acid; in biochemistry, the term is often used interchangeably with glutamic acid.
1. A salt of glutamic acid. -- occur naturally and play essential roles at their normal concentrations in the body. Quinolinic acid is a breakdown product of the amino acid amino acid (əmē`nō), any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. tryptophan tryptophan (trĭp`təfăn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. ; glutamate has a metabolic function Metabolic function
Those processes necessary for the maintenance of a living organism.
Mentioned in: Stress Reduction as well as acting as a neurotransmitter in the brain.
But too much of either chemical kills certain cells, and past studies have shown quinolinic acid and glutamate bind to the receptor site for a chemical abbreviated NMDA NMDA
N-methyl-D-asparate . In support of this, the Michigan scientists traced glutamate binding and found that brains with Huntington's had 93 percent fewer NMDA receptors.
This indicates that cells with those receptors had died, explains principal investigator Anne Young. "Glutamate has been hypothesized to be responsible for cell death in Huntington's," she says. "But nobody had actually measured the [NMDA] receptors in post-Huntington's brains."
Not all neurons inside the basal ganglia, a knot of several kinds of nerve cells in the forebrain, degenerate in Huntington's victims. Some cells almost completely die off, while others are unscathed. Several years ago, scientists from the University of Maryland University of Maryland can refer to:
In two studies comparing a total of 13 Huntington's brains to 12 controls, Young and her colleagues found decreased numbers of receptors for five other chemicals, although none as pronounced as the decrease in NMDA receptors. Receptors for two other compounds were diminished by 67 percent and those for three others by 55 percent or less. Young plans to do the same type of comparison on patients who died before the disease progressed as far as in the Huntington's brains in the current study.
In the end, the Michigan researchers suggest that some cells may be more vulnerable to damage from glutamate and quinolinic acid because they contain more NMDA receptors where the compounds can bind to the cell. Finding a way to block those receptors, they say, might slow the disease, for which there is still no cure.