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

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.

Effects of delta9-tetrahydrocannabinol on reward and anxiety in rats exposed to chronic unpredictable stress.

Although cannabis derivatives produce clear subjective motivational responses in humans leading to drug-seeking behaviour, the reinforcing attributes of these subjective effects are difficult to define in experimental animals. The aim of this study was to examine how exposure to chronic unpredictable stress (CUS) will affect reward function and anxiety after acute administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) in rats. Male rats were exposed to either 10 days of CUS or no stressor. Alterations in brain reward function were assessed with the intracranial self-stimulation (ICSS) paradigm, and anxiety responses were measured with the elevated plus maze. CUS did not affect baseline brain stimulation reward thresholds. Delta(9)-THC did not exhibit reinforcing actions in the ICSS paradigm neither in nonstressed nor in stressed animals. More importantly, in nonstressed animals, both the low and the high dose of Delta(9)-THC exerted anxiolytic-like effects. In stressed animals, however, only the high dose of THC induced an anxiolytic-like response, whereas the low dose induced anxiogenic effects. The present results provide clear evidence for an anxiolytic effect of Delta(9)-THC both in stressed and in nonstressed animals, and indicate that environmental conditions, such as stressful experiences, do not alter the behavioural effects of Delta( 9)-THC in the ICSS paradigm.