Effects of environmental enrichment and social isolation on sucrose consumption and preference: associations with depressive-like behavior and ventral striatum dopamine.

Little attention has been directed towards environmental control of sensitivity to natural reward and its possible relationship with other motivated behaviors, besides the well-known effects of environmental enrichment and social isolation on drug self-administration and locomotor sensitization to psychostimulants. Here, we investigate the effects of these rearing conditions on sucrose consumption and preference, and tissue levels of striatal dopamine. The possible relationship among sucrose intake, immobility behavior in the forced swimming test, and dopamine concentration was explored through correlation and regression analyses. Even though all animals preferred sucrose over water, we found, that during postnatal period, isolated rats consumed more sucrose than control or enriched littermates. In isolated rats sucrose intake correlated positively with ventral but not with dorsal striatum dopamine, even when striatal dopamine did not differ among groups. Especially in isolated animals immobility behavior was positively predicted by differences in sucrose intake. The dopamine concentration did not correlate with immobility behavior. Taken together, the present data support previous findings regarding the effects of early life events upon reward-sensitivity and depressive-like behavior, and also provide further evidence about the relationship between these motivated behaviors and the likely role of ventral striatum dopamine in regulating them.