Long-term effects of propylthiouracil-induced neonatal hypothyroidism.

Hypothyroidism was induced in neonatal Sprague-Dawley rats by adding propylthiouracil to the lactating female's food and water. Behavioral evaluation on a 6-item battery occurred from 70 to 114 days of age. Results indicated long-lasting behavioral changes in the neonatal hypothyroid animals characterized by increased activity and decreased performance on avoidance and escape learning. Serum thyroxine levels were reduced in the hypothyroid animals throughout the 120-day period. Experimental animals also had fewer synaptic contacts in the cerebellar cortex when analyzed at 90 days of age.