Neurobehavioral effects of hypothyroidism on the next generation in the rat

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Mother rats were treated with MMI (anti-thyroid drug) by adding it to the drinking water at the concentrations of 0, 0.002, or 0.02% from the gestational day 15 to the postnatal day 21. Twelve weeks after the birth, all rats received a target detection task or a differential reinforcement of low rate (DRL) 20 s task in an operant chamber.1, Target detection task : The target (light) was presented after an ITI. If the rats responded to the target within a time limit, a food pellet was delivered as a reward (hit response). The ITIs were 10, 17.4, 30, and 52.5 s and the time limits were 16, 8, and 4 s. As the results, male and female rats treated with 0.02% MMI reduced % hit response. The hit response was decreased as the ITI and the time limit became shorter. Rats need to prepare to the new target and respond to it quickly under the conditions of shorter ITIs and shorter time limits. We propose that hypothyroid rats do not sustain attention to a target.2, DRL 20 s task : In this test, rats need to respond to the lever after more than or equal to 20 s since the previous response to receive a food reward. The male rats treated with 0.02% MMI displayed a tendency not to be able to wait for 20 s and control their behavior. Taken together, these data give support to the idea that thyroid hormone inhibition causes impulsiveness.