Expression of prion protein (PrP) gene in rat tissues and cell lineswas investigated by reverse transcriptase polymerase chain reaction (RNA-peR) and Northern blot analyses. PrP cDNA clones were generated usingRNA-PCR from RNA preparation of neuronal cell line (HVI6-3), whichwere immortalized from rat embryonic hippocampal cells. These clonescontained 5 upstream region and an in-frame ATG codon which had notbeen reported previously in rat and were used as hydridization probes.RNA-PCR analyses showed that PrP mRNA was present in rat embryonichippocampal neuronal cell lines (HV3-3 and HVI6-3) and a rat glioma cellThe second experiment in the present study was carried out on four different groups (calves, heifers, lactating and pregnant cows) to study the physiological changes which may occur in each group after vaccination with