Exploring the Role of Oxytocin in Rodent Defensive Behaviours

Abstract

Although evidence implicates oxytocin (OT) in anxiety regulation, little is known about where this occurs in the brain or if this system is altered by social affiliation. I hypothesized that infusions of OT into the lateral septum (LS), a brain structure implicated in anxiety, would decrease rats’ anxiety-related defensive responses. Twenty male rats were administered bilateral injections of OT or saline into the LS before undergoing the elevated plus-maze (EPM) and novelty-induced suppression of feeding test (NSFT). OT infusions marginally increased the percentage of time spent on the open arms in the EPM. Surprisingly, in the NSFT novel-cage test, OT-treated rats began consuming the wafer later than controls. Thus, the effects of OT infusions on anxiety appeared test-specific. In Experiment 2, I hypothesized that social housing would reduce rats’ defensive behaviours and that this effect would map onto an increase in the functionality of the OT system, as indexed by a higher number of OT-immunoreactive (-ir) cells in the hypothalamic regions where OT is predominantly produced; i.e., the paraventricular nucleus (PVN) and supraoptic nucleus. Twenty male rats were either single- or pair-housed for five weeks, then anxiety was measured using the EPM and a modified NFST. One week later, their brains were processed for OT-immunoreactivity. Pair-housed rats took less time to initiate consumption of the wafer in the NSFT, but their behavioural profiles in the EPM did not differ from those of single-housed rats. Relative to single-housed rats, pair-housed rats had more OT-ir cells in the ventral parvocellular region of the PVN, which correlated negatively with their latency to begin consuming the wafer on Day 1 of the NSFT. These findings suggest that social housing upregulates the OT system which, in turn, influences rats’ defensive behaviours. Overall, my findings confirm the involvement of OT in behavioural defense regulation however, further research is needed to understand how OT influences defensive behaviours under different threat contexts.