A social conditioned place preference test and pair maintenance in the monogamous zebra finch

Abstract

Social relationships are essential for a wide range of species, including humans. The mechanisms of pair formation and maintenance appear to be distinct, although relatively little is known about pair maintenance compared to bond formation. A social conditioned place preference (SCPP) test, a paradigm not often used, could be used to reveal differences in the mechanisms of bond formation and maintenance. Here we used the SCPP test across two experiments to investigate how the behavioral and neuroendocrine mechanisms of social affiliation change over the course of pair bonding in the monogamous zebra finch. In our procedure, we had three 30 min phases: preconditioning occurring on Day 1, followed by conditioning and postconditioning, both on Day 2. In our first experiment, we simply asked whether courting and paired dyads would form SCPPs in this assay. We found evidence that courting, but not paired birds, formed SCPPs. This was particularly evident for courting females. Courting and paired dyads also engaged in different behaviors during the conditioning phase. Despite these effects of social context on behavior, there was no clear relationship between these behavioral differences and the formation of SCPPs for courting males or females. We next tested whether pharmacological treatment with D1 and D2 receptor agonists would alter the effects of social context on the formation of SCPPs. Specifically, we hypothesized that treatment with a D1-agonist (SKF 38393) would block the formation of SCPPs in courting dyads and that activation of D2-like receptors (quinpirole) would induce SCPPs in already established pairs. In contrast with Experiment 1, we did not see any groups forming SCPPs, but paired males, regardless of pharmacological treatment, appeared to form aversions to the conditioning side. Furthermore, there was significantly less courtship and affiliative behavior in the second experiment. Combined, this leads us to suspect that coupling the SCPP with an s.c. injection made the entire procedure too aversive to reveal any SCPP. Despite this, there were subtle effects of pharmacological manipulation on social behavior during the conditioning phase. All together, the results from our two experiments (1) suggest that there are differences in the mechanisms by which courting and paired dyads relate to their partner in novel environments, (2) highlight the differences in social interactions between courting and paired birds, and (3) leave open the possibility that dopamine signaling differentially shapes social behavior and the formation of SCPPs in courting and paired birds.

Keywords: CPP; Copulations; Male song; NAc; Reinforcing properties; Reward.