ScienceDaily (Oct. 28, 1999) — The latest neuroscience research shows that brains change along with behavior on the social ladder. According to a new study by Georgia State University biologists Don Edwards and Joanne Drummond, dominant and subordinate crayfish react to stressful situations by responding to the same brain chemical in two different ways depending on their changing social status.

Crayfish brains are often studied by neurobiologists wanting to know more about the role of serotonin, one of several substances known to affect mood and aggression. Crayfish fight a lot. When the fight's over, one becomes dominant over the other. Edwards' and Drummond's research, to be presented this weekend at the meeting of the Society for Neuroscience in Miami, shows that serotonin-containing crayfish nerve cells respond differently to natural stimuli in socially dominant and subordinate animals after a fight.

Previously, Edwards found that the nerve cells that trigger escape behavior are inhibited by serotonin in subordinate crayfish. But these same neurons are made more responsive by serotonin in dominant animals.This may be due to an imbalance between excitatory and inhibitory serotonin receptors in the crayfishes' escape nerve cells. These changes in serotonin's effect take about two weeks to develop following the fight that determines the animals' social status, and are largely reversible: if the loser can win, serotonin will revert to being excitatory. This new research indicates that the neural circuitry that excites the serotonin-containing nerve cells, and the patterns of serotonin release in the nervous system, differ in dominant and subordinate animals.

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