Small litter size impairs spatial memory and increases anxiety- like behavior in a strain-dependent manner in male mice.

Early life overfeeding is associated with cognitive decline and anxiety-like behaviors in later life. It is not clear whether there are individual differences in the effects of early life overfeeding and what the underlying mechanistic pathways are. We investigated the long-lasting effects of small litter size, an experimental manipulation to induce neonatal overfeeding, in two strains of mice, C57BL/6 and NMRI. We measured body weight, learning and memory, anxiety-related behaviors, interleukin-(IL)-1ß and brain-derived-neurotrophic-factor (BDNF) levels in the hippocampus, and both basal and stress corticosterone levels in adult mice which have been nursed in small litters compared with those from control litters. Our findings showed that small litter size led to increased body weight in both strains of mice. Small litter size significantly decreased spatial memory and hippocampal BDNF levels, and increased hippocampal IL-1ß, in NMRI mice, but not C57BL/6 mice. Interestingly, we found that small litter size resulted in a significant increase in anxiety-like behaviors and stress-induced corticosterone in NMRI mice, whereas small litter size reduced anxiety-like symptoms and stress-induced corticosterone levels in C57BL/6 mice. These data show that small litter size, which is life-long associated with increased body weight, affects memory and anxiety-related behaviors in a strain-dependent manner in male mice. This suggests that there are individual differences in the developmental consequences of early life overfeeding.

Adolescent fluoxetine treatment decreases the effects of neonatal immune activation on anxiety-like behavior in mice.

Experimental studies have shown conflicting effects of neonatal infection on anxiety-like behaviors and hypothalamic-pituitary-adrenal (HPA) axis activity in adult rats. We investigated for the first time whether neonatal exposure to lipopolysaccharide (LPS) is associated with increased levels of anxiety-like behaviors in mice. Moreover, there have been several studies showing that adolescent fluoxetine (FLX) treatment can influence HPA axis development and prevent occurrence of psychiatric disorders induced by common early-life insults. In the present study, we also investigated the effects of adolescent FLX exposure following neonatal immune activation on anxiety-like behavior in mice. Neonatal mice were treated to LPS (50µg/kg) or saline on postnatal days (PND) 3 and 5, then male and female mice of both neonatal intervention groups received oral administration of FLX (5 and 10mg/kg/day) or water via regular drinking bottles during the adolescent period (PNDs 35-65). The results showed that postnatal immune challenge increased anxiety-like behavior in the open field, elevated plus-maze and light-dark box in adult mice (PND 90). Furthermore, the adolescent FLX treatment inhibited the anxiety-like behavior induced by neonatal infection in both sexes. However, this study indicates the negative effects of the FLX on normal behavioral symptoms in male control mice. Taken together, the current data provide experimental evidence that neonatal infection increases anxiety levels in male and female mice in adulthood. Additionally, the findings of this study support the hypothesis that an early pharmacological intervention with FLX may be an effective treatment for reducing the behavioral abnormalities induced by common early-life insults.

Neonatal NMDA receptor blockade alters anxiety- and depression-related behaviors in a sex-dependent manner in mice.

There is increasing evidence that N-methyl-D-aspartate (NMDA) receptor blockade in the neonatal period has a long-lasting influence on brain and behavior development and has been linked to an increased risk for neuropsychiatric disorders in later life. We sought to determine whether postnatal NMDA receptor blockade can affect normal development of body weight, corticosterone levels, anxiety- and depression-related behaviors in male and female mice in adulthood. For this purpose, male and female NMRI mice were treated with either saline or phencyclidine (PCP; 5 and 10 mg/kg, s.c.) on postnatal days (PND) 7, 9, and 11, and then subjected to different behavioral tests, including open field, elevated plus-maze, elevated zero-maze, light-dark box, tail suspension test and forced swimming test in adulthood. The results indicated that neonatal PCP treatment reduced body weight during neonatal and adulthood periods, and did not alter baseline corticosterone levels in both male and female mice. Moreover, this study obtained some experimental evidence showing the PCP at dose of 10 mg/kg increases stress-induced corticosterone levels, anxiety- and depression-related behaviors in males, while decreasing levels of anxiety without any significant effect on depression in female mice in adulthood. These data support the argument that neonatal NMDA receptor blockade can lead to behavioral abnormalities and psychiatric diseases in adulthood. Collectively, our findings suggest that neonatal exposure to PCP may have profound effects on the development of anxiety- and depression-related behaviors in a sex- and dose-dependent manner in mice.