Tissue transplant boosts memory in rats.

Tissue transplant boosts memory in rats

Memory problems caused by longterm alcohol use in rats can be mostly reversed with transplants of brain tissue rich in a neurotransmitter already implicated in the memory deficits of Alzheimer's disease, according to a report in the March 30 NATURE.

Similar transplants eventually may help humans whose memory is muddled from years of heavy drinking or as a result of Alzheimer's disease, say Thomas Arendt and his colleagues of the Institute of Psychiatry in London, England. Although it is unclear if the rats provide a model for any specific type of memory disturbance in alcoholics, "the rats' memory problems were produced in much the same way as human alcoholics develop severe memory problems," says neuropsychologist and study participant Jeffrey A. Gray.

The investigators provided 78 male rats with an alcohol solution as the only fluid in an otherwise normal diet for 28 weeks. Another 16 rats drank only water with their food during the same period. Four weeks after the alcohol-treated rats returned to water, they made many more errors on memory tests in which they had to remember which four arms of an eight-spoked maze contained sugar pellets.

But about nine weeks after receiving transplants of fetal rat brain tissue to two brain areas -- the outer layer of the frontal part of the brain and an inner structure concerned with memory function known as the hippocampus -- 12 alcohol-treated rats performed nearly as well as water-only rats on maze trials. The fetal tissue contained large amounts of acetylcholine, a chemical that helps transmit information from one brain cell to another.

"The transplants must act on general memory rehearsal or retrieval mechanisms in the brain", says Gray, since the animals recovered the ability to use visual, tactile and spatial orientation cues, and avoided both unbaited arms and those from which a sugar pellet had already been taken.

Alcohol-treated rats given tissue transplants with acetylcholine to only one of the brain areas showed minimal memory recovery. Rats that received tissue with the neurotransmitter noradrenaline, but not acetylcholine, in one or both brain areas did not improve on maze trials.

Acetylcholine and its chemical precursors have been implicated in the memory loss associated with diseases of aging, such as Alzheimer's disease, says Gray, but the clinical effectiveness of drugs that alter acetylcholine levels has not been clearly demonstrated.

The persistent memory deficits of alcohol-treated animals mimic the irreversible memory loss seen in chronic alcoholics who develop Korsakoff's psychosis, says Gray. The rats' brains, however, do not show damage typical of the Korsakoff brain. "This evidence questions whether the brain damage observed in humans with Korsakoff's psychosis is related to their memory problems," notes Gray. -- B Bower