Bringing back fading memories.

Bringing back fading memories

There are both joyous and sad memories. And there are those lost as a person ages--a loss that is exacerbated if the person has Alzheimer's disease. An inability to recall recent events can be disabling and frightening, and researchers are seeking ways to halt such age- and disease-related failures of short-term memory. Scientists in Sweden and the United States report this week that a substance called nerve growth factor may help improve impaired memory.

A protein produced by nerve cells, nerve growth factor was isolated in the early 1950s. Later, scientists observed that degenerative changes in the brains of Alzheimer patients occur in the same regions as those affected by the growth factor. On the basis this relationship, researchers at the University of Lund in Sweden and the University of California at San Diego recently tested the effects of infusing nerve growth factor into the aging brain, by studying changes in memory retention among aged rats.

As described in the Sept. 3 NATURE, the scientists repeatedly placed 2-year-old rats in a tank of water made opaque by a white powder, and observed the length of time it took for each rat to swim to a submerged platform on which it could stand. The "water maze task' is an established measure of how well rats retain prior knowledge of the platform's location, Anders Bjorklund of Lund told SCIENCE NEWS. He says that inability to learn the task is directly related to the degree of atrophy seen in the cholinergic system of a rat's brain. The network of cholinergic nerve cells--which release the chemical acetylcholine during message transmission between cells--is also affected in Alzheimer patients.

Two months before taking the water maze test, aged rats had been placed in the tank and categorized by whether or not they could memorize the platform's location. Those that could not were placed in the "impaired' group. About half the rats in this group were implanted with pumps containing nerve growth factor, while the remaining impaired rats served as controls, receiving a common blood protein as a placebo. After implantation, the rats were tested twice during a 28-day infusion period: about one week, and then three weeks, after nerve growth factor (or placebo) therapy began.

There was no change during the first week, but by the third week of therapy, performance of the rats given nerve growth factor was as good as that of the nonimpaired group, say the authors. They attribute this to "improved retention' of information learned during the first week's test. Along with the improved memory among the treated rats, the researchers found that cholinergic nerve cells on the side of the brain holding the implant increased in size.

Results from the short-term tests do not, however, show that nerve growth factor can improve the ability to learn new tasks or stop the gradual deterioration of overall memory, says Bjorklund.

This report follows an announcement last month that clinical trials are about to begin on another potential drug for Alzheimer's disease. Called tetra-hydro-aminoacridine (THA), the drug was synthesized nearly 80 years ago for other purposes. Last year, scientists reported that THA had improved memory function in a small group of patients (SN: 11/15/86, p.308). During the two-year clinical trials, about 300 Alzheimer patients will take the drug orally at U.S. research centers. THA is thought to block or slow the breakdown of the acetylcholine. Even if results from the clinical study confirm memory improvement due to the drug, experts have cautioned that THA probably will not stop the progressive destruction of brain cells that is characteristic of Alzheimer's.