Effect of Partner Separation on PVN Vasopressin Cells and Behavior in Mongolian Gerbils Open Access
Jiang, Jinrun (Spring 2024)
Abstract
Introduction: Plasticity of the paraventricular nucleus of the hypothalamus (PVN) vasopressin (VP) cell group has previously been demonstrated in prairie voles, such that cell numbers are different based on pair-bonding status. Whether this bond status-dependent plasticity occurs in other socially monogamous species is unknown. Here we explored the effect of partner separation on a spectrum of behaviors as well as on vasopressin anatomy and function in the PVN.
Methods: Sixteen male Mongolian gerbils were randomly assigned to either a Paired or Separated group and were allowed to cohabitate with an opposite-sex partner for two weeks. After cohabitation, subjects were run through a set of behavior tests, and were either separated from their partner (Separated group) or remained with their partner (Paired) for four weeks, and tested again through the same set of behavior tests. Lastly, an immediate early gene (IEG) social interaction test was run before brains were collected for immunohistochemical staining of VP-ir and Fos-ir cells to visualize neural activity of interest.
Results: In a reproductive context, separated male Mongolian gerbils showed increased time spent investigating and acting prosocially toward an opposite-sex conspecific. In a non-reproductive social context, males did not show behavior changes after they were separated from their partner. Within a non-social context, separated males traveled a lesser amount of distance compared to paired males. Separated males had higher PVN VP-ir cell counts, which positively correlated with the amount of time spent investigating an opposite-sex conspecific, compared to paired males.
Conclusion: Our results suggest that partner separation does not generally alter behavior in non-reproductive contexts, such as non-social anxiety-like behavior and interaction toward same-sex conspecifics. However, subjects that were separated from their partners exhibited more prosocial and investigative behaviors in a reproductive context, and the investigative behavior positively correlated with VP cell densities in the PVN. We also found that separated males had higher VP densities in the PVN than males who remained paired, suggesting that there is an increase in PVN VP density following separation from the partner, possibly to increase investigation of opposite-sex conspecifics to find a new mate and/or to alleviate stress.
Table of Contents
INTRODUCTION 1
MATERIALS AND METHODS 4
Animals 4
Experimental Design 4
Figure 1: General Experimental Timeline 5
Behavioral Tests 6
Social Approach Test 6
Table 1: Ethogram for Behavioral Scoring in Social Interaction and Resident Intruder Tests. 7
Resident Intruder Test 7
Social Interaction Test 7
Open Field Test 8
Immediate-early gene experimental design 8
Histology and Immunohistochemistry 9
Perfusion and fixation 9
Sectioning 9
Immunohistochemistry procedure 9
Antibody Composition 10
Data Acquisition and Analysis 10
Effects of partner separation on nonreproductive behaviors 11
Figure 2: Pair bonded males exhibited more aggression in the social interaction test at Timepoint 2, after a total of 6 weeks of being pair bonded. Separated males did not show a change in aggression toward a novel, opposite-sex conspecific between the time they were pair bonded (Test 1) and after they had been separated from their partner for 4 weeks (Test 2). 12
Effects of partner separation on reproductive social behavior 12
Figure 3: Investigation of a novel, opposite-sex intruder increased between the time they were pair bonded (Test 1) and after they had been separated from their partner for 4 weeks (Test 2). Behavior did not differ from Test 1 to Test 2 for paired males. 14
Figure 4: Separated males spent more time engaging in prosocial contact with a novel, opposite-sex conspecific on neutral territory compared to paired males. 14
Figure 5: Separated males spent more time investigating a novel, opposite-sex conspecific on neutral territory compared to paired males. 15
Effects of partner separation on PVN VP function 15
Figure 6: PVN VP density, but not PVN VP-Fos colocalization, differ between paired and separated males. 16
Effects of partner separation on PVN VP neuroanatomy 16
Figure 7: The total number of PVN VP neurons positively correlated with the time spent investigating a novel, opposite-sex conspecific on neutral territory. 17
DISCUSSION 17
Behavioral consequences of pair bonding 17
PVN vasopressin and social behavior 19
PVN vasopressin and stress 22
CONCLUSION 24
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