출생 초기 Thyroxine 투여가 흰쥐 소뇌에서 BDNF와 TrkB함유 조롱박세포의 생후 발달 및 BDNF 단백 양에 미치는 영향

Abstract

Thyroid hormones (TH) are essential for the development of the brain. Furthermore, TH modulate the expression of neurotrophins or their receptors. Brain-derived neurotrophic factor (BDNF) and its receptor trkB are enriched in the mammalian central nervous system. This study investigated the effect of early thyroxine (T4) treatment on the postnatal development of BDNF- and trkB- immunoreactive (IR) Purkinje cell and BDNF protein amount in the rat cerebellum. In addition, electron microscopic finding of BDNF-IR Purkinje cell at P10 was examined. Newborn Sprague-Dawley rats were randomly divided into two groups and treated during first 10 postnatal days, either with a daily subcutaneous injection of 0.05ml 7.5㎍ L-thyroxine sodium salt in buffered 0.9% saline (group T) or with an identical volume of normal saline (group C). The number of BDNF-and trkB-IR Purkinje cells and protein amount of BDNF were significantly higher in the group T than in the group C at P10. At P10, electron microscopic observations of BDNF-IR Purkinje cells revealed numerous short segments of rough endoplasmic reticulum (rER), many of which showed a tendency of parallel alignment in the group T compared to the group C. A similar developmental pattern of BDNF- and trkB-IR Purkinje cells was observed in the group T and C on and after P15. However, in the group T, the number of BDNF-and trkB-IR Purkinje cells and protein amount of BDNF were significantly decreased at P30 compared to P15. Based on the results, it can be suggested that the increase of protein amount of BDNF and BDNF-and trkB-IR Purkinje cell by early postnatal T4 treatment is transient during early postnatal life, and these morphological alterations are not kept until adolescence