Fearfulness and sex in F2 Roman rats: males display more fear though both sexes share the same fearfulness traits

Abstract

The pattern of sex differences in a large sample (about 400 for each sex) of F2-generation rats, derived from inbred Roman high- and low-avoidance strains differing in fearfulness and brain functioning, was investigated. We obtained measures from responses to a battery of novel/threatening tests [open field (OF), plus maze (PM), hole board (HB), activity (A), and acoustic startle reflex (ASR)] as well as learned fear paradigms [classical fear conditioning (CFC) and shuttlebox avoidance conditioning (SAC)]. The results showed that almost all behaviors assessed fit with a pattern of unidirectional sex effects characterized by male rats as being more fearful than females: males defecated more than females in the OF, PM, HB, ASR, and CFC; ambulated less in the OF, PM, A, and SAC; showed more self-grooming in PM and HB; explored the open arms of the PM and the holes of the HB less; displayed enhanced ASR; and showed poorer performance in the SAC task. We applied two factor analyses to each sex showing that, in general, they shared a common three-factor structure: a Learned Fear Factor comprising SAC and CFC responding, a Fear of Heights/Open Spaces Factor with the highest loadings for open arm behavior in the PM, and an Emotional Reactivity Factor, mainly grouping defecations, ambulation, and self-grooming. These results indicate that the essential components of fearful behavior are similar for both sexes in an inbred but genetically heterogeneous population.