Behavioural and Neuroendocrine Adaptations to Repeated Stress during Puberty in Male Golden Hamsters

Abstract

In adult animals, the consequences of stress are often severe and long lasting. Repeated subjugation in adult male golden hamsters inhibits aggression and increases submissive and avoidant behaviours. By contrast, subjugation during puberty enhances offensive aggression. The goals of this study were to characterize behavioural and neuroendocrine responses of naïve and repeatedly subjugated juveniles to social defeat and to assess potential recovery from social stress. From the onset of puberty on postnatal day 28 (P28) to mid puberty (P42), animals were either socially subjugated or placed in a clean and empty cage for 20 min daily. The subjugated and control groups were further divided into subgroups and sacrificed under basal conditions or after social defeat on P28, P35 (early puberty), P45 (mid puberty) and P70 (early adulthood). On P35 and P45, repeatedly subjugated juveniles showed a complete inhibition of olfactory investigation (i.e. risk assessment) towards aggressive adults. Repeatedly subjugated also animals had lower postdefeat cortisol levels than controls on P45. Interestingly, basal cortisol levels increased gradually during puberty but did not differ between treatment groups at any point. Repeated subjugation was also associated with increased tyrosine hydroxylase immunoreactivity (ir-TH) within the extended medial amygdala. After a 4-week recovery period, none of these variables differed between subjugated and control groups. In an additional experiment, subjugated adults also had increased ir-TH in the medial extended amygdala, suggesting that these neurones are particularly responsive to social stress. In conclusion, puberty may be a developmental period characterized by behavioural and neuroendocrine plasticity in stress responsiveness. Furthermore, peri-pubertal changes in stress hormones may explain why juvenile hamsters are more resilient to social stress than adults.

Stress, Aggression, and Puberty: Neuroendocrine Correlates of the Development of Agonistic Behavior in Golden Hamsters

“…For example, studies in juvenile hamsters have shown that long-term treatment with anabolic androgenic steroids increases attack frequency DeLeon et al, 2002]. On the other hand, socially subjugated juvenile male hamsters have decreased basal testosterone levels, and yet they perform a higher percentage of adult attacks than non-stressed controls and do not show a decrease in attack frequency [Wommack et al, , 2004. As such, these findings suggest that separate mechanisms control developmental changes in attack frequency and target.…”

Interactions between the neural regulation of stress and aggression

“…When stressful conditions are present during development, effects can be measured in the neural circuitries that regulate both aggression and stress, and in some brain regions those circuitries coincide. Repeated or chronic stress applied during puberty accelerates the progression of development of aggressive behaviors in male hamsters (Wommack et al, 2003;Delville et al, 2003), accompanied by neuroendocrine changes in brain regions like medial amygdala and bed nucleus of the stria terminalis (BNST) that are active in both stress and aggression (Wommack et al, 2004). Stressful conditions such as frustration (absence of reward) stimulates a significant increase in synaptic activity in the neural circuitry controlling aggression (David et al, 2004).…”

Differential responsiveness to fluoxetine during puberty.

“…In males, this time period is marked by an increase in testosterone levels, testicular development, and the emergence of sexual behaviors (Goldman & Swanson, 1975;Miller, Whitsett, Vandenbergh, & Colby, 1977;Vomachka & Greenwald, 1979;Wommack, Salinas, Melloni, & Delville, 2004). On the basis of these variables, puberty can be divided into three categories: early, mid, and late.…”