The heightened behavioral responding exhibited by isolates in the elevated plus maze (reduced risk assessment, avoidance of the aversive open arms) probably enhanced their sensitivity to the anxiolytic-like properties of handling. Individual housing and a lack of either handling or habituation all increase responding to anxiolytics in the elevated plus maze (for review see Hogg, 1996). Of course, the elevated plus maze measures only a facet of the multidimensional construct of emotionality (Ramos, 2008). The open field may measure aspects of anxiety that are both shared and distinct from the elevated plus maze. In the open field, two negatively related measures of emotionality (Hall, 1934) – novelty-induced ambulation and defecation – were exacerbated in isolates. Here, the use of multiple measures strengthened our understanding of the emotional consequences underlying both adverse and beneficial early-life manipulations. Results from these measures provide converging lines of evidence to conclude that isolates have an anxiogenic-, whereas handled rats have an anxiolytic-like behavioral profile.
