PMC

In the Naïve group, body weight increased over time. Chronic social defeat inhibited weight gain and this effect was not altered by clomipramine. After 4 weeks of clomipramine administration, body weight was still significantly lower in subordinate tree shrews. *p<0.05, **p<0.01.

(A) All groups preferred 5% sucrose to water, but preference was significantly higher in the Naïve group compared to the Sub+Sal group. Normal sucrose preference was restored in the Sub+Clo group. (B) In the unstressed Naïve Group, locomotor activities were stable. Stress induced an unstable fluctuation in locomotor activity in both Sub+Sal and Sub+Clo groups, but the Sub+Clo group exhibited locomotor activity levels similar to the Naïve group by the recovery phase. *p<0.05.

(A) In the Naïve group, the concentration of urinary cortisol remained constant throughout the entire experiment. In the Sub+Sal group, stress induced a sustained elevation in urinary cortisol. Similarly, urinary free cortisol was elevated throughout the whole stress period in the Sub+Clo group. (B) On Week 7, urinary cortisol rhythm was measured in all groups. Clomipramine reduced urinary cortisol at 16:00–17:00, the time of peak activity for tree shrews. (C) Self-grooming behavior of both Sub+Sal and Sub+Clo groups were increased after 1 week social defeat. From 2 to 6 weeks, the number of autogrooming behavior in Sub+Sal group animals showed fluctuated relative to Sub+Clo group.

(A) Micrograph showing the positions of the stimulating electrode (S) and the recording electrode (R) in the tree shrew hippocampal CA1 (scale bar: 350 µm). (B) LTP induced by high-frequency stimulation (HFS) in Naïve (N = 4 animals, n = 6 slices), Sub+Sal (N = 4, n = 5), and Sub+Clo tree shrews (N = 4, n = 7). Inset above: Typical fEPSPs recorded at baseline and 50−60 min post-HFS (horizontal bar: 5 ms, vertical bar: 0.5 mV for each group). (C) There was no significant difference in LTP at 50−60 min post-HFS between the Sub+Sal and Sub+Clo group. Both groups exhibited impaired LTP compared to the Naïve group. *p<0.05 compared to the Naïve group.

The experiment included three experimental groups, Naïve, Subordinate+Saline (Sub+Sal), and Subordinate+Clomipramine (Sub+Clo), and four phases. Phase 1 consisted of a 7 day stress-free period during which the animals adapted to the experimental environment. Phase 2 was the social defeat (SD) phase during which animal pairs in the Sub+Sal and Sub+Clo groups housed separately in connected cages were allowed direct access to fight for social dominance. In contrast, Naïve group tree shrews remained undisturbed. Phase 3 was the drug administration plus SD phase lasting 28 days during which the subordinate (Sub) tree shrews were exposed to daily social defeat stress as before but also treated daily with oral clomipramine (50 mg/kg/day) or saline (1 ml/kg/day). The final recovery phase consisted of a 7 day period with neither social defeat nor drug treatment.