Because these young neurons are typically more excitable than their more mature counterparts, exercise should result in more anxiety, not less. The researchers found that exercise also strengthens the mechanisms that prevent these brain cells from firing.The impact of physical activity on the ventral hippocampus specifically has not been deeply explored, said senior author Elizabeth Gould, Princeton's Dorman T. Warren Professor of Psychology. By doing so, members of Gould's laboratory pinpointed brain cells and regions important to anxiety regulation that may help scientists better understand and treat human anxiety disorders, she said.From an evolutionary standpoint, the research also shows that the brain can be extremely adaptive and tailor its own processes to an organism's lifestyle or surroundings, Gould said.A higher likelihood of anxious behaviour may have an adaptive advantage for less physically fit creatures. Anxiety often manifests itself in avoidant behaviour and avoiding potentially dangerous situations would increase the likelihood of survival, particularly for those less capable of responding with a "fight or flight" reaction, she said.Gould, who also is a professor in the Princeton Neuroscience Institute, said that understanding how the brain regulates anxious behaviour gives potential clues about helping people with anxiety disorders and also says something about how the brain modifies itself to respond optimally to its own environment.For the experiments, one group of mice was given unlimited access to a running wheel and a second group had no running wheel. Natural runners, mice will dash up to 4 kilometers a night when given access to a running wheel, Gould said. After six weeks, the mice were exposed to cold water for a brief period of time.The brains of active and sedentary mice behaved differently almost as soon as the stressor occurred, an analysis showed. In the neurons of sedentary mice only, the cold water spurred an increase in "immediate early genes," or short-lived genes that are rapidly turned on when a neuron fires. The lack of these genes in the neurons of active mice suggested that their brain cells did not immediately leap into an excited state in response to the stressor.Instead, the brain in a runner mouse showed every sign of controlling its reaction to an extent not observed in the brain of a sedentary mouse. There was a boost of activity in inhibitory neurons that are known to keep excitable neurons in check. At the same time, neurons in these mice released more of the neurotransmitter gamma-aminobutyric acid, or GABA, which tamps down neural excitement. The protein that packages GABA into little travel pods known as vesicles for release into the synapse also was present in higher amounts in runners.The results have been published in the Journal of Neuroscience.Source: ANI