To investigate scrapie agent neuroinvasion from the oral cavity, else C57BL/6J, LT��, and muMT null mice were inoculated in the tongue with the RML scrapie agent at two different doses, and mice were monitored for the following: (i) the onset of clinical disease, (ii) PrPSc deposition in brain and spleen, and (iii) scrapie agent replication in brain and spleen. Following intratongue (i.t.) inoculation, all three strains of mice were susceptible to prion disease, but there was no difference in incubation periods (P > 0.05, Bonferroni t test) between the C57BL/6J mice and the LT�� null mice (167 �� 0.6 days versus 161 �� 8.6 days) or between the C57BL/6J mice and the muMT null mice (146 �� 7.8 days versus 144 �� 13.4 days) (Table (Table1).1). The distribution of PrPSc in brain and spleen tissue in the i.

t.-inoculated mice was similar to the tissue distribution described following i.c. inoculation into these three murine hosts. PrPSc was found in the brain and spleen tissue of C57BL/6J mice and in the brain tissue of LT�� and muMT null mice but not in the spleen tissue of LT�� and muMT null mice following i.t. inoculation (Fig. 1A and B, lanes 9 to 12; also data not shown). Measurement of scrapie agent infectivity following i.t. inoculation of the RML scrapie agent from the same brain and spleen samples that were analyzed for PrPSc by Western blotting (Fig. (Fig.1)1) revealed that brain and spleen homogenates of symptomatic C57BL/6J mice induced onset of disease in recipient mice at 110 to 129 days and 128 to 135 days, respectively (Fig. (Fig.2B).2B).

In LT�� null mice that developed scrapie following i.t. inoculation, brain homogenates induced onset of disease in recipient mice between 113 and 134 days, which was a level of scrapie infection similar to that found in the brain tissue of C57BL/6J mice. The spleen from one of the symptomatic LT�� null mice following i.t. inoculation did not cause disease in recipient mice after 375 days postinoculation. However, the spleen from a second symptomatic mouse did cause clinical disease at 135 and 181 days postinoculation in the scrapie infectivity assay (Fig. (Fig.2B).2B). PrPSc was not detected in the spleen from this second mouse (Fig. (Fig.1B,1B, lane 11) even though spleen homogenates from C57BL/6J Dacomitinib mice that also induced scrapie after 135 days postinoculation had evidence of PrPSc in the spleen (Fig. (Fig.1B,1B, lane 9). The spleen from this LT�� null mice was the only one out of a total of six spleens from LT�� null inoculated mice that showed evidence of scrapie infection (Fig. (Fig.2;2; also data not shown from LT�� null mice following i.p. inoculation), and PrPSc was not found in eight spleens from LT�� null mice inoculated with the RML scrapie agent (Fig. (Fig.1B).1B).