Because iodothyronine deiodinases play a crucial role in the regulation of the 
available intracellular T(3) concentration, it is important to determine their 
cellular localization. In brain, the presence of type III iodothyronine 
deiodinase (D3) seems to be important to maintain homeostasis of T(3) levels. 
Until now, no cellular localization pattern of the D3 protein was reported in 
chicken brain. In this study polyclonal antisera were produced against specific 
peptides corresponding to the D3 amino acid sequence. Their use in 
immunocytochemistry led to the localization of D3 in the Purkinje cells of the 
chicken cerebellum. Both preimmune serum as well as the primary antiserum 
exhausted with the peptide itself were used as negative controls. Extracts of 
chick cerebellum and liver were made in the presence of Triton X-100 to 
solubilize the membrane-bound deiodinases. Using these extracts in Western blot 
analysis, a band of the expected molecular weight ( approximately 30 kDa) could 
be detected in both tissues. Using a full-length (32)P-labeled type III 
deiodinase cRNA probe, we identified a single mRNA species in the cerebellum 
that was of the exact same size as the hepatic control mRNA (+/-2.4 kb). RT-PCR, 
followed by subcloning and sequence analysis, confirmed the expression of D3 
mRNA in the chicken cerebellum. In this study we provide the first evidence of 
the presence of the D3 protein in a neuronal cell type, namely Purkinje cells, 
by means of immunocytochemical staining. We were able to detect a protein 
fragment corresponding to the expected molecular mass (30 kDa) for type III 
deiodinase by means of Western blot analysis. RT-PCR as well as Northern blot 
analysis confirmed the presence of D3 mRNA in the cerebellum.