Nest Making and Oxytocin Comparably Promote Wound Healing in Isolation Reared Rats

Background: Environmental enrichment (EE) fosters attachment behavior through its effect on brain oxytocin levels in the hippocampus and other brain regions, which in turn modulate the hypothalamic-pituitary axis (HPA). Social isolation and other stressors negatively impact physical healing through their effect on the HPA. Therefore, we reasoned that: 1) provision of a rat EE (nest building with Nestlets®) would improve wound healing in rats undergoing stress due to isolation rearing and 2) that oxytocin would have a similar beneficial effect on wound healing. Methodology/Principal Findings: In the first two experiments, we provided isolation reared rats with either EE or oxytocin and compared their wound healing to group reared rats and isolation reared rats that did not receive Nestlets or oxytocin. In the third experiment, we examined the effect of Nestlets on open field locomotion and immediate early gene (IEG) expression. We found that isolation reared rats treated with Nestlets a) healed significantly better than without Nestlets, 2) healed at a similar rate to rats treated with oxytocin, 3) had decreased hyperactivity in the open field test, and 4) had normalized IEG expression in brain hippocampus. Conclusions/Significance: This study shows that when an EE strategy or oxytocin is given to isolation reared rats, the peripheral stress response, as measured by burn injury healing, is decreased. The findings indicate an association between the effect of nest making on wound healing and administration of the pro-bonding hormone oxytocin. Further elucidation of this animal model should lead to improved understanding of how EE strategies can ameliorate poor wound healing and other symptoms that result from isolation stress

Nestlet “treatment” of isolation reared rats.

<p>Twice weekly cages are changed and replaced with a new Nestlet (A), the Nestlet is shredded by the rat prior to forming the nest (B), and then the rat spends time resting in the formed nest (C).</p

Entrez Gene ID Numbers and Primer Sequences of Genes Used for Quantitative Polymerase Chain Reaction Experiments

<p>Entrez Gene ID Numbers and Primer Sequences of Genes Used for Quantitative Polymerase Chain Reaction Experiments</p

Degree of impaired burn healing rats in each condition.

<p>For each rat, the number of pixels comprising the width of the maximum gap of unhealed tissue was normalized to the width of its back. The average normalized pixels of unhealed tissue were significantly greater for the isolation-reared rats (middle column) compared with both the group-reared rats (first column) and the isolation reared rats treated with Nestlets (third column). Average±S.E.M., *p<.05, ** <i>P</i><0.01.</p

Gene expression changes in the hippocampus by condition.

<p>Rats treated with Nestlets had significantly higher gene expression compared to isolation reared rats without Nestlets for cfos and junb (compare columns 3 and 4 for these genes). Gene expression of rats treated with Nestlets returned to that of group reared rats for these genes (compare columns 1 and 4 for cfos and junb). Group reared rats treated with Nestlets showed an increase in these genes above the expression level for group reared rats not treated with Nestlets (compare columns 1 and 2) even though there was no additional benefit to their wound healing (since wound healing was maximal for the group reared rats without the Nestlets). Average±SEM, *p<0.05, **p<.01, ***p<.001.</p

Effect of Nestlet treatment on open field test behavior.

<p>Ambulatory time was significantly lower for isolation reared rats treated with Nestlets (column 4) compared to untreated isolation reared rats (column 3) and not different from group reared rats (column 1) or group reared rats treated with Nestlets (column 2). Average±SEM.,*<i>P</i><0.05, ** <i>P</i><0.01, ***<i>P</i><0.001.</p

Example of healing in rats in the different conditions examined

<p>(A). 92% of group reared rats healed well (n = 12, column 1, 2B, and top row 2C), 12% of isolation reared rats healed well (n = 8, middle column 2B, and middle row 2C), and 64% of isolation reared rats treated with Nestlets healed well (n = 11 see third column 2B, and bottom row 2C).* <i>P</i><0.05, ** <i>P</i><0.01, *** <i>P</i><0.001.</p

Time series analysis of Nest Building and Oxytocin effect on wound healing.

<p>Panel A shows an example of wound healing over six weeks from weaning (PN20 to PN62) in the four conditions examined. Panel B shows that group reared rats had significantly better healing compared to isolation reared rats by 21 days post burn injury, while Nestlet and oxytocin treated rats showed similar healing to group reared rats by 28 days post burn injury. The difference between Nestlet treated, oxytocin treated, and group reared rats compared to isolation reared rats continued until 42 days post burn injury. Average±S.E.M., *p<.05, ** p<0.01, ***p<0.001.</p