Elsevier

Physiology & Behavior

Volume 61, Issue 4, April 1997, Pages 477-484
Physiology & Behavior

Neuroendocrine Correlates of Separation Stress in the Siberian Dwarf Hamster (Phodopus sungorus)

https://doi.org/10.1016/S0031-9384(96)00456-8Get rights and content

Abstract

Castro, W. L. R. and K. S. Matt. Neuroendocrine correlates of separation stress in the Siberian dwarf hamster (Phodopus sungorus). Physiol Behav 61(4) 477–484, 1997.—Siberian dwarf hamsters form monogamous male-female pair bonds. Disruption of the pair bond results in increases in body mass and behavioral alterations similar to profiles seen in human atypical depression. We examined behavioral and neuroendocrine correlates associated with separation of the male from his mate. Animals were paired (n = 28 pairs) for 3 weeks, then 15 pairs were separated and 13 pairs remained as controls. Behaviors of the males were observed in a novel environment following 3 weeks of pairing and 4 weeks of separation. The 5-min behavioral test monitored exploratory, territorial behavior, and locomotor activity. Separated males showed a significant increase in body mass (p < 0.01), paralleled by an increase in food consumption (p < 0.01). Separated males had decreased seminal vesicle mass (p < 0.05) and testicular mass (p < 0.05). Behavioral analysis revealed that separated males showed no significant differences in grooming, scent-marking, alert on 2 feet, or escape behavior when compared to paired males. Separated males did show significant increases in inactivity (p < 0.05). Plasma cortisol levels were significantly increased in separated animals (p < 0.05), but there were no significant effects on testosterone. Resting levels of plasma norepinephrine and epinephrine were less in separated males, but this was significant only for norepinephrine (p < 0.05). In conclusion, separation stress was accompanied by increased hypothalamic-pituitary-adrenal axis function and decreased peripheral sympathetic nervous system activity and decreased reproductive profiles.

Section snippets

Animals

Fifty-six adult (3-month-old) male and female Siberian dwarf hamsters (Phodopus sungorus) from the breeding colony at Arizona State University were used for the experiment. Hamsters were housed in large polycarbonate cages (48 × 26.7 × 12.7 cm) containing loose wood shavings for bedding. Food (Purina Laboratory Chow 5001) and water were supplied ad lib. Animals were maintained at 23°C on a 16 h light: 8 h dark cycle, lights on at 0400 h. Daily light cycles were produced by overhead “cool-white”

Body Weights, Food Consumption

Initially, animals did not differ in body mass at day −21 (week −3) before pairing and throughout the first 3 weeks (weeks −3 to 0). A 2-way MANOVA for weeks 1–4 revealed that body mass significantly increased across time in separated males compared to that in paired control animals (p < 0.01). One week after separation, separated animals had increased body mass compared to paired controls (p < 0.05) and this remained elevated to the end of the study (p < 0.01) (Fig. 1A).

Food consumption was

Discussion

Analysis of our data indicates that physiological and behavioral changes seen in separated males are associated with increased plasma levels of cortisol, suggesting an increase in HPA axis activity. This increased HPA axis activity suggests that the separation paradigm results in a physiological state that is similar to that of chronic stress. Associated with this upregulation of HPA axis activity was a decrease in the hypothalamic-pituitary-gonadal (HPG) axis, as demonstrated in decreases in

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