Rats Depleted Of Salt Become Sensitized To Amphetamine, Show Unusual Growth Of Brain Cells

The researchers, headed by University of Washington psychologist Ilene Bernstein, discovered that nerve cells in the nucleus accumbens of sensitized rats have more branches and were 30 percent to 35 percent longer than normal. The nucleus accumbens, located in the forebrain, is involved in the reward and motivation system in rats and in humans. It is associated with regulating motivated behaviors of such natural drives as those for food and salt, and for artificial rewards provided by drugs.

The findings are published in the current issue of the Journal of Neuroscience.

"This number, 30 to 35 percent, is startling and implies an ability for neurons to make more connections," said Bernstein.

The research was triggered by several recent papers. One reported that rats sensitized to amphetamine showed this type of neuron growth. A second found that rats deprived of food seemed to be amphetamine sensitized. When an animal or person becomes sensitized their behavior changes. With amphetamine, animals and people become hyperactive. Rats that are salt sensitized drink and eat salt more rapidly and in greater quantities. Why they behave this way is unknown, Bernstein said.

"That research and ours seem to indicate that being hungry or sodium deprived enough can change an animal's or a person's response to a drug even if they have not been exposed to the drug previously," she said.

"We don't know if this holds up in humans. But the same part of the brain and the response to drugs holds up across species. The same systems are involved in rats and humans when it comes to amphetamines and cocaine. This suggests evidence of a common natural substrate to natural and artificial rewards that is worth further investigation."

She added that the findings also point to questions that need to be explored. These include determining how long cross sensitization persists and whether physical challenges such as salt depletion alter people's responses to drugs.

"There is differential response among people who are challenged or stressed based on their history.