Reduced expression and altered distribution of neurofilaments in neurons cultured in thyroid hormone-deficient medium

The effect of thyroid hormone (TH) deficiency on the expression of neurofil ament (NF) proteins and their intracellular distribution has been examined in primary cultures of neurons from embryonic rat cerebra. Northern blot an alysis showed that in TH-deficient (THdef) neurons, the expression of all t hree NF mRNAs (NF-L, NF-M and NF-H) are retarded by 50-70% at days 7, 15 an d 25 of culture compared with their TH-supplemented (THsup) counterparts. W estern blot analysis also showed a decline of 60-80% in the expression of a ll the NF-proteins at all time points. Immunofluorescent staining of neuron s from THdef and THsup cultures at days 7, 15, and 25 with monoclonal anti NF-L antibody showed that with age, TH deficiency reduced the localization of NF-L in the cell body with a corresponding increase in the hillock and p roximal axon region. The present neuronal culture system offers an excellen t experimental model for studying the biochemical events responsible for th e altered NF pathology in degenerating neurons. (C) 2000 Lippincott William s & Wilkins.