Study On Postnatal Development Of Auditory Evoked Potentials In Hypothyroidism Rats

Objectives:(1) To probe into the abnormal postnatal development of fast components of brainstem auditory evoked potentials (FC-BAEP), slow components of brainstem auditory evoked potentials (SC-BAEP) and middle latency responses (MLR) in hypothyroidsm rats.(2) To uncover the pathophysiological properties of the retardation of brain function development in hypo thy roidism.(3) To provide the basis for their clinical application in earlyexploration and objective evaluation of the brain hinders in hypothyroidism.Methods:15 pregnant SD rats were randomly divided into control, hypothyroidism and substitution teams. The rat pups of each team were further divided into AEP ( n=12 ), FT3-FT4 day 20 ( n=5 ), FT3-FT4 day 30 ( n=5 ), FT3-FT4 day 50 (n=5), FT3-FT4 day 70 ( n=5 ) and FT3-FT4 day 90 ( n=5 ) groups. Hypothyroidism of the rat pups was induced by 0.03% methimazole given in drinking water for the female rats from the pregnant day 17 to the postnatal day 30. L-T4 (2 ug/100 g/d) injected into abdominal cavityof the rat pups from postnatal day 1 to day 30 was used for substitution treatment. FC-BAEP, SC-BAEP and MLR was recorded by an evoked potentials recorder and serum FT3 and FT4 was determined by radioimmunoassay at postnatal da>s 20, 30, 50, 70 and 90.Results:(1) In control team, FC-BAEP, SC-BAEP and MLR had been recorded at postnatal day 20, and then their PL and IPL shortened step by step with age to adult values.(2) In hypothyroidism team, FC-BAEP, SC-BAEP and MLR had not been recorded at postnatal days 20. Their PL and IPL were significantly longer andtheir amplitudes were much smaller than that of control ones at postnatal days 30,50, 70 and 90.(3) In substitution team, FC-BAEP, SC-BAEP and MLR had been recorded at postnatal day 20. At postnatal days 20, 30, 50, 70 and 90, most PL, IPL and amplitudes were not significanty different from that of control ones, even several PL and IPL were shorter than that of control ones and their amplititudes were larger than that of control ones. But FC-BAEP and MLR's PL and IPL of a few waves were longer than that of control ones and their amplititudes were smaller than that of control ones.Conclusions:(1) There is a postnatal developmental process, consistent with FC-BAEP and MLR, for SC-BAEP, which suggests that there is a common way for postnatal development of whole auditory nervous system, and the effects of age on PL of SC-BAEP have to be calculated in application.(2) The postnatal development of FC-BAEP, SC-BAEP and MLR will be severely and irreversibly retarded in hypothyroidism Their PL and IPL are the objective and sensitive indoes for reflecting the brain hinders.(3) The retardation of brain function development in hypothyroidism can be improved significantly by the supplement of thyroxinepromptly.(4) The application of FGBAEP, especially combined with SGBAEP and MLR, is full of promise in arly exploration and objective evaluation of the retardation of brain function development in hypothyroidism.