Hypoplastic heart induced by neonatal hypothalamic lesions in mice

To clarify whether the central nervous system has any influence on the growth of the heart, the growth patterns of mouse hearts with induced neonatal hypothalamic lesions were evaluated based on changes in weight gain, histological findings and cell proliferative kinetics. To prepare the mice with hypothalamic lesions, male Jcl-ICR strain mice were subcutaneously injected with monosodium L-glutamate (MSG), 2 mg/g of body weight, daily for 5 days after birth. Irreversible hypothalamic lesions caused by MSG, consisting of degeneration and necrosis of preoptic and arcuate nuclei, were histologically confirmed immediately after the MSG treatment. In mice with neonatal hypothalamic lesions, the heart was visibly smaller and considerably lighter than that in the normal mice throughout the growth. Light microscopic studies revealed no degenerative changes; however, myocardial cells became apparently hypertrophic in and after adolescence. The proliferative activity of the myocardial cells evaluated by mitotic activity and DNA synthesizing activity was continuously suppressed throughout the growth. These results confirmed that the hearts in the mice with neonatal hypothalamic lesions had much smaller numbers of myocardial cells than those in the normal mice, were significantly hypoplastic and had large numbers of hypertrophic myocardial cells in and after adolescence. This suggested that the hypothalamus played an important role in the growth of the heart.