A LONGITUDINAL-STUDY OF CENTRAL AND PERIPHERAL-NERVE CONDUCTION IN HYPOTHYROID RATS

In order to detect the dysfunction of central and peripheral nervous s ystems among rats with varied duration of hypothyroidism and to elucid ate the pattern of recovery after thyroxine replacement, a series of B AEP and PNCS (Peripheral Nerve Conduction Study) were conducted and co mpared with age-matched controls. BAEP and PNCS were performed in thre e groups of hypothyroid animals 1, 3 and 5 months after thyroidectomy, respectively. Following initial electrophysiological assessment, thyr oxine replacement was administered to each group of hypothyroid rats, and BAEP and PNCS were performed at two month intervals, up to two suc cessive normal studies, or six months after the initiation of therapy, whichever came first. For BAEP prolonged I-V interpeak latency was th e most consistent abnormal finding in all groups of hypothyroid rats, and longer hypothyroid stales correlated well with more severe central conduction disorder. Nevertheless, these abnormalities usually return ed to normal after thyroxine replacement if the duration of hypothyroi dism was less than 5 months. Regarding PNCS, all groups of thyroidecto mized rats showed normal conduction before and after thyroxine therapy . The present study indicates that, in rats: (1) the peripheral nervou s system seems to be more resistant to hypothyroidism than the central nervous system, or (2) the pathogenesis of central and peripheral ner ve dysfunction in hypothyroid rats may occur through different mechani sms. (C) 1997 Elsevier Science B.V.