Social status controls somatostatin neuron size and growth

Many animal species show flexible behavioral responses to environmental and social changes. Such responses typically require changes in the neural sub strate responsible for particular behavioral states. We have shown previous ly in the African cichlid fish, Haplochromis burtoni, that changes in socia l status, including events such as losing or winning a territorial encounte r, result in changes in somatic growth rate. Here we demonstrate for the fi rst time that changes in social status cause changes in the size of neurons involved in the control of growth. Specifically, somatostatin-containing n eurons in the hypothalamus of H. burtoni increase up to threefold in volume in dominant and socially descending animals compared with cell sizes in su bordinate and socially ascending fish. Because somatostatin is known to be an inhibitor of growth hormone release, the differences in cell size sugges t a possible mechanism to account for the more rapid growth rates of subord inate and socially ascending animals compared with those of dominant or soc ially descending fish. These results reveal possible mechanisms responsible for socially induced physiological plasticity that allow animals to shift resources from reproduction to growth or vice versa depending on the social context.