Behavioral testing of progenies of Tx (hypothyroid) and growth hormone-treated Tx rats: an animal model for mental retardation.

Virgin Sprague-Dawley Holtzman rats were rendered Tx (hypothyroid) by radiothyroidectomy and maintained on 1.0 microgram T4 (thyroxine) per 100 g BW until pregnant. One-half of these Tx animals were administered 0.5 IU of growth hormone (GH) during the last 10-11 days of gestation as GH secretion is especially deficient in Tx rats. Untreated, food restricted to the level consumed by the Tx-only rats, GH-treated euthyroid, and T4-treated until pregnant animals served as controls. The animals were allowed to go through parturition and each litter was reduced to no more than 6 pups by removing pups for tissue weights and protein analyses at 1 and 5 days of age. The pups were weaned at 22 days of age and 2 animals per litter were utilized for behavioral testing between 40 and 60 days of age. At the end of the behavioral testing period the 60-day-old offspring were sacrificed to obtain tissue weights and protein concentrations. The behavioral tests were based on the ability of the animals to learn a Lashley's type 3 enclosed alley maze and their spontaneous activity was measured in stabilimeter cages. The animals were fasted overnight on alternate days and then given a food reward upon traversing the maze. This allowed for 10 separate trials in both the Lashley maze and the stabilimeters over the 20-day period from 40 to 60 days of age. Our previous studies have shown the fetuses and progenies of Tx-only mothers to have multiple metabolic defects including reduced rates of protein synthesis and tissue protein concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)