A single prolonged stress paradigm produces enduring impairments in social bonding in monogamous prairie voles

Abstract

Traumatic events such as natural disasters, violent crimes, tragic accidents, and war, can have devastating impacts on social relationships, including marital partnerships. We developed a single prolonged stress (SPS) paradigm, which consisted of restraint, forced swimming, and ether anesthesia, to establish an animal model relevant to post-traumatic stress disorder. We applied a SPS paradigm to a monogamous rodent, the prairie vole (Microtus ochrogaster) in order to determine whether a traumatic event affects the establishment of pair bonds. We did not detect effects of the SPS treatment on anhedonic or anxiety-like behavior. Sham-treated male voles huddled with their partner females, following a 6day cohabitation, for a longer duration than with a novel female, indicative of a pair bond. In contrast, SPS-treated voles indiscriminately huddled with the novel and partner females. Interestingly, the impairment of pair bonding was rescued by oral administration of paroxetine, a selective serotonin reuptake inhibitor (SSRI), after the SPS treatment. Immunohistochemical analyses revealed that oxytocin immunoreactivity (IR) was significantly decreased in the supraoptic nucleus (SON), but not in the paraventricular nucleus (PVN), 7days after SPS treatment, and recovered 14days after SPS treatment. After the presentation of a partner female, oxytocin neurons labeled with Fos IR was significantly increased in SPS-treated voles compared with sham-treated voles regardless of paroxetine administration. Our results suggest that traumatic events disturb the formation of pair bond possibly through an interaction with the serotonergic system, and that SSRIs are candidates for the treatment of social problems caused by traumatic events. Further, a vole SPS model may be useful for understanding mechanisms underlying the impairment of social bonding by traumatic events.

Keywords: PTSD; Paroxetine; Partner preference; SSRI; Serotonin; Social behavior.

Fig. 1

Experimental schedules. (A) Experiment 1 was designed to clarify the effects of SPS on behaviors. Subjects were individually housed 4 days before the SPS treatment (at Day 0). They were tested for sucrose preference at Day –1 and Day 7. Subjects were cohabitated with a female for 6 days (box with oblique lines, Day 8–14) and investigated for partner preference at Day 14. (B) Experiment 2 was designed to clarify whether paroxetine prevented the disturbance of pair bonding by the SPS treatment. Subjects were orally administrated with paroxetine between Day 1 and 10 (gray box), and cohabitated with a female vole for 3 days (box with oblique lines, Day 7–10). At Day 11, subjects were tested for partner preference and individually housed for 3 days. Brains were prepared at Day 14, 90 min after subjects were presented to their partner female. (C) Experiment 3 was performed to prepare brains from SPS- and sham- treated voles without stimulations 7 days after SPS treatment. a, Three of sham-treated voles and one SPS-treated vole were eliminated due to a technical problem. A sham-treated vole showing no sucrose preference was also eliminated from the analysis.; b, Three voles were died during the SPS treatment.; c, Totally 7 voles were eliminated because of technical trouble and death.; d, Two of sham-treated voles showing sexual behavior to stimulus voles were eliminated from the analysis.; e, One vole in each treatment was eliminated because of a technical problem.; f, Brain of sham-treated vole administrated with H₂ O was eliminated because of inadequate perfusion.

Fig. 2

SPS treatment did not induce either anhedonia or anxiety-like behavior. (A) Anhedonia test. Both sham- and SPS- treated voles preferred to drink water containing 1% sucrose. n = 8 for sham treatment, n = 11 for SPS treatment. (B) Open field test. SPS-treated voles spent time in the center area as much as sham-treated voles did. n = 11 for sham treatment, n = 10 for SPS treatment.

Fig. 3

SPS treatment disturbed pair bonding. (A) Duration of huddling behavior. SPS-treated voles huddled with their partner female as much as with a stranger female, whereas sham-treated voles significantly spent more time to huddle with their partner female than a stranger female. (B) Duration to spent in a chamber containing a partner or stranger female. SPS-treated voles preferred to stay in the chamber containing a stranger female than one containing partner female. Contrarily, sham-treated voles spent more time in the chamber containing their partner than one with a stranger female. **, P < 0.01. (C) The numbers of entries into chambers. There was no difference among conditions. n = 9 for sham treatment, n = 9 for SPS treatment.

Fig. 4

Prevention of SPS-mediated impairment in pair bonding by paroxetine administration. (A) Duration of huddling behavior. When paroxetine was orally administrated, SPS-treated voles significantly spent more time to huddle with their partner female than a stranger female. When only distilled water was administrated, SPS-treated voles did not show the partner preference. (B) Duration to spent in a chamber containing a partner or stranger female. SPS-treated voles indiscriminately spent time in a chamber containing a partner or stranger female, regardless of whether they were administrated with paroxetine. **, P < 0.01. n = 11 for SPS treatment and administrated with paroxetine, n = 11 for SPS treatment and administrated with the vehicle.

Fig. 5

Immunoreactivities of oxytocin and cFos at the PVN (A, C, E) and SON (B, D, F). Oxytocin IR (bluish gray) was observed at somatic bodies, while cFos IR (brown) was in nuclei. The surrounded area is magnified at the right bottom in (A). An arrow indicates a cell double- labeled with oxytocin and cFos IRs. The number of such cells was counted. Open arrowheads show cells labeled with oxytocin IR but not cFos. (A, B) SPS-treated voles administrated with only vehicle. (C, D) SPS-treated voles administrated with paroxetine. (E, F) Voles without any treatment nor administration. v, 3rd ventricle; ot, optic tract. Bars, 100 μm..

Fig. 6

Immunoreactivities of oxytocin (A–D) and vasopressin (E–H). Immunoreactivities were observed at somatic bodies and neurites in the PVN (A, B, E, F) and SON (C, D, G, H). Localization of oxytocin and vasopressin was similar between sham- (A, C, E, G) and SPS- (B, D, F, H) treated voles. Oxytocin IR at the SON appeared to be higher in sham-treated voles than SPS-treated voles (C, D). Bars, 100 μm. v, 3rd ventricle; ot, optic tract.