Early life low intensity stress experience modifies acute stress effects on juvenile brain cell proliferation of European sea bass (D. Labrax)

• Juvenile sea bass brain is characterized by extensive active cell proliferation.
• Early life adversity (UCLIS) did not change juvenile brain cell proliferation.
• Acute stress reduced mitotic activity in teleost hippocampus, amygdala, cerebellum.
• Acute stress increased plasma cortisol in all cases (non-UCLIS, UCLIS juveniles).
• Early UCLIS modified acute stress plasticity of brain cell proliferation responses.

Early life adversity may be critical for the brain structural plasticity that in turn would influence juvenile behaviour. To address this, we questioned whether early life environment has an impact on stress responses latter in life, using European sea bass, Dicentrarchus labrax, as a model organism. Unpredictable chronic low intensity stress (UCLIS), using a variety of moderate intensity stressors, was applied during two early ontogenetic stages, flexion or formation all fins. At juvenile stage, fish were exposed to acute stress and plasma cortisol, brain mRNA expression of corticosteroid receptors’ genes (gr1, gr2, mr) and brain cell proliferation (using BrdU immunohistochemistry) were determined in experimental and matched controls. UCLIS treatment specifically decreased brain gr1 expression in juveniles, but had no effect on the juvenile brain cell proliferation pattern within the major neurogenic zones studied of dorsal (Dm, Dld) and ventral (Vv) telencephalic, preoptic (NPO) areas, periventricular tectum gray zone (PGZ) and valvula cerebellum (VCe). In contrast, exposure to acute stress induced significant plasma cortisol rise, decreases of cerebral cell proliferation in juveniles, not previously exposed to UCLIS, but no effect detected on the expression levels of gr1, gr2 and mr in all groups of different early life history. Interestingly, juveniles with UCLIS history showed modified responses to acute stress, attenuating acute stress-induced cell proliferation decreases, indicating a long-lasting effect of early life treatment. Taken together, early life mild stress experience influences an acute stress plasticity end-point, cerebral cell proliferation, independently of the stress-axis activation, possibly leading to more effective coping styles.