Neuroendocrine mechanisms of environmental integration

Abstract

SYNOPSIS. In the dwarf Siberian hamster, Phodopus sungorus, the photoperiodic response can be modified by numerous environmental stimuli, including social interactions, dietary, and climatic changes. Photoperiodic information is processed in both the medial basal hypothalamus and the preoptic area. Transfer of animals from a long summer photoperiod to a short winter photoperiod results in decreases in the concentration of both norepinephrine and dopamine in both of these brain areas. Results from these studies indicate that both dietary supplements and social interactions can override the effects of day length on changes in brain neurotransmitters. Specifically, social interactions can override the decreases in norepinephrine and dopamine in the medial basal hypothalamus but not the preoptic area. Conversely, dietary manipulations override the decreases in the preoptic area but not in the medial basal hypothalamus. These results suggest that photoperiod is a general stimulus that depresses neurotransmitter activity in multiple brain areas including the medial basal hypothalamus, and preoptic area. Fine tuning information, such as dietary and social cues, is then processed in very specific areas of the brain and can override the photoperiod induced changes in these specific areas © 1993 by the American Society of Zoologists.