It has been reported that oligodendrocytes do not contain nuclear T3 receptors, 
which is in apparent contradiction with the well-known effects of thyroid 
hormones on myelination. In this study we have reexamined the presence of 
receptors in this cell population, using pure rat oligodendrocyte cultures. T3 
binding was also studied with the use of pure rat astrocytes as well as in mixed 
neuronal-glial cultures. The latter are mainly neuronal during the first days in 
culture and essentially glial thereafter. Binding studies carried out in intact 
cells demonstrated the presence of high affinity-low capacity binding sites for 
thyroid hormones in pure cultures of oligodendrocytes. The maximal binding 
capacity was 50-60 fmol/100 micrograms DNA and the dissociation constant (Kd) 
0.13 nM. Pure rat astrocyte cultures also contained high affinity sites for 
thyroid hormones, although receptor concentrations was 2-3 times lower than in 
oligodendrocytes or neurons. This was confirmed in pure cultures of chick 
astrocytes and in neuronal-glial cultures during the astroglial period. The 
relative affinity of the receptor for thyroid hormone analogs was 
triiodothyroacetic acid = T3 greater than T4 greater than tetraiodothyroacetic 
acid in oligodendrocyte and astrocyte nuclei, and the sedimentation coefficient 
of the receptor was approximately 3.8S in both cell types. These results 
demonstrate that nuclear T3 receptors similar to those found in neurons and 
astrocytes are also present in oligodendrocytes. This suggests that the effects 
of thyroid hormones on myelination could result from a direct action of the 
hormone in the oligodendrocytes.