Effects of hypergravity exposure on the developing central nervous system:Possible involvement of thyroid hormone

The present study examined the effects of hypergravity exposure on the deve loping brain and specifically explored the possibility that these effects a re mediated by altered thyroid status. Thirty-four timed-pregnant Sprague-D awley rats were exposed to continuous centrifugation at 1.5 G (HG) from ges tational Day 11 until one of three key developmental points: postnatal Day (P) 6, P15, or P21 (10 pups/dam: 5 males/5 females). During the 32-day cent rifugation, stationary controls (SC, n = 25 dams) were housed in the same r oom as HG animals. Neonatal body, forebrain, and cerebellum mass and neonat al and maternal thyroid status were assessed at each time point. The body m ass of centrifuged neonates was comparatively lower at each time point. The mass of the forebrain and the mass of the cerebellum were maximally reduce d in hypergravity-exposed neonates at P6 by 15.9% and 25.6%, respectively. Analysis of neonatal plasma suggested a transient hypothyroid status, as in dicated by increased thyroid stimulating hormone (TSH) level (38.6%) at P6, while maternal plasma TSH levels were maximally elevated at P15 (38.9%). N either neonatal nor maternal plasma TH levels were altered, suggesting a mo derate hypothyroid condition. Thus, continuous exposure of the developing r ats to hypergravity during the embryonic and neonatal periods has a highly significant effect on the developing forebrain and cerebellum and neonatal thyroid status (P < 0.05, Bonferroni corrected). These data are consistent with the hypothesized role of the thyroid hormone in mediating the effect o f hypergravity in the developing central nervous system and begin to define the role of TH in the overall response of the developing organism to alter ed gravity.