Behavioral effects of systemic transforming growth factor-alpha in Syrian hamsters

The growth factor, transforming growth factor-alpha (TGF-α) is strongly expressed in the hypothalamic circadian pacemaker, the suprachiasmatic nucleus (SCN). TGF-α is one of several SCN peptides recently suggested to function as a circadian output signal for the regulation of locomotor activity rhythms in nocturnal rodents. When infused in the brain, TGF-α suppresses activity. TGF-α suppresses other behaviors as well including feeding, resulting in weight loss. Elevated TGF-α is correlated with some cancers, and it is possible the TGF-α and its receptor, the epidermal growth factor receptor (EGFR), mediate fatigue and weight loss associated with cancer. If true for cancers outside of the brain, then systemic TGF-α should also affect behavior. We tested this hypothesis in hamsters with intraperitoneal injections or week-long subcutaneous infusions of TGF-α. Both treatments suppressed activity and infusions caused reduced food consumption and weight loss. To identify areas of the brain that might mediate these effects of systemic TGF-α, we used immunohistochemistry to localize cells with an activated MAP kinase signaling pathway (phosphorylated ERK1). Cells were activated in two hypothalamic areas, the paraventricular nucleus and a narrow region surrounding the third ventricle. These sites could not only be targets of TGF-α produced in the SCN but could also mediate effects of elevated TGF-α from tumors both within and outside the central nervous system.