Enhanced spontaneous locomotor activity in bovine GH transgenic mice involves peripheral mechanisms

clinical and experimental studies indicate a role for GH in mechanisms rela ted to anhedonia/hedonia, psychic energy, and reward. Recently we showed th at transgenic mice with general overexpression of bovine GH display increas ed spontaneous locomotor activity. In the present study, we investigated wh ether this behavioral change is owing to a direct action of GH in the centr al nervous system or to peripheral GH actions. A transgenic construct, cont aining the glial fibrillary acidic protein promoter directing specific expr ession of bovine GH to the central nervous system, was designed. The centra l nervous system-specific expression of bovine GH in the glial fibrillary a cidic protein-bovine GH transgenic mice was confirmed, but no effect on spo ntaneous locomotor activity was observed. Serum bovine GH levels were incre ased in glial fibrillary acidic protein-bovine GH transgenic mice but clear ly lower than in transgenic mice with general overexpression of bovine GH. In contrast to the transgenic mice with general overexpression. of bovine G H, glial fibrillary acidic protein-bovine GH mice did not display any diffe rence in serum IGF-I levels. The levels of free T-3 and the conversion of t he free T-4 to free T-3 were only increased in transgenic mice with general overexpression. of bovine GH, but serum corticosterone levels were similar ly increased in both transgenic models. These results suggest that free T-3 and/or IGF-I, affecting dopamine and serotonin systems in the central nerv ous system, may mediate the enhanced locomotor activity observed in transge nic mice with general overexpression of bovine GH.