In our previous experiments using retinal injection of scrapie in a 2 μl volume, transgenic mice expressing anchored PrP only in neurons (tgNSE) showed spread of PrPres from retina to brain following the optic system, whereas mice expressing anchored PrP only in astrocytes (tgGFAP) showed very slow spread by a random cell-to-cell diffusing mechanism not involving nerves or blood vessels[17]. This evidence concerns the gene PRNP and scrapie.