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 neurofilament (NF) proteins and their intracellular distribution has been examined in primary cultures of neurons from embryonic rat cerebra. Northern blot analysis showed that in TH-deficient (THdef) neurons, the expression of all three NF mRNAs (NF-L, NF-M and NF-H) are retarded by 50-70% at days 7, 15 and 25 of culture compared with their TH-supplemented (THsup) counterparts. Western blot analysis also showed a decline of 60-80% in the expression of all the NF-proteins at all time points. Immunofluorescent staining of neurons 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 proximal axon region. The present neuronal culture system offers an excellent experimental model for studying the biochemical events responsible for the altered NF pathology in degenerating neurons.