In 2006 the National Toxicology Program (NTP) of the FDA shifted to the 
preferred use of Wistar-Han rats from the more commonly used Sprague-Dawley (SD) 
strain - and industry followed. While European laboratories preferred the 
Wistar-Han line, there was a paucity of relevant historical control data in many 
US research institutions for the new "industry standard" rat strain. In 2010 the 
NTP reversed its decision and shifted back to SD rats because of reproductive 
issues with the Wistar strain. For post hoc comparative analyses, we report 
minimal practical differences in Functional Observational Battery (FOB) data 
from a large sample of male and female Wistar-Han and SD rats. In summarizing 
data from the preclinical safety evaluations of the CNS effects of new drugs 
using the FOB, it is crucial to understand the value of not only how the 
functional expression of drug effects in the rat are predictive of the human 
response, but also how and why they differ. What we can predict from the 
behavioral and physiological response of the designated test system to drug 
administration is the foundation of "generalizability" to the human's response. 
Here, we conclude that the use of either SD or WH rat strains in standard CNS 
safety studies provide equivalent supportive data for CNS safety assessment 
required for IND approval under the harmonized guidelines.