Dorsal hippocampal canine tissue had a greater propensity to form neurospheres when cultured in the Neural Colony Forming Cell Assay. In this assay, cells at clonal density are cultured in a semi-solid medium that precludes cell fusion events, restricting neurosphere growth to de novo cell division [20]. However, because our canine hippocampus-derived neurospheres were limited to a maximum of 100 microns, and neural stem cells from the rat or mouse brain grow to produce neurospheres of up to 2 mm in this assay [18], our results are more consistent with differences arising from the endogenous neural precursor population rather than from bona fide neural stem cells