Early life stress experience may blunt hypothalamic leptin signalling.

The aim of this study was to investigate whether neonatal maternal separation (MS) - chronic stress experience in early life - affects the anorectic efficacy of leptin in the offspring at adolescence. Sprague-Dawley pups were separated from the dam daily for 3 h during postnatal day 1-14 or left undisturbed as non-handled controls (NH). NH and MS male pups received an intraperitoneal leptin (100 µg/kg) or saline on postnatal day (PND) 28, and then food intake and body weight gain were recorded. The hypothalamic levels of leptin-signalling-related genes, phosphorylated signal transducer and activator of transcription-3 (pSTAT3) and protein-tyrosine phosphatase 1B (PTP1B) were examined at 40 min after a single injection of leptin on PND 39 by immunohistochemistry and Western blot analysis. Leptin-induced suppressions in food intake and weight gain was observed in NH pups, but not in MS. Leptin increased pSTAT3 in the hypothalamic arcuate nucleus of NH pups, but not of MS. Interestingly, basal levels of the hypothalamic PTP1B and pSTAT3 were increased in MS pups compared with NH controls. The results suggest that neonatal MS experience may blunt the anorectic efficacy of leptin later in life, possibly in relation with increased expressions of PTP1B and/or pSTAT3 in the hypothalamus.

Hypothalamic NPY, AGRP, and POMC mRNA responses to leptin and refeeding in mice.

Food deprivation (FD) increases hypothalamic neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels and decreases proopiomelanocortin (POMC) mRNA levels; refeeding restores these levels. We determined the time course of changes in hypothalamic NPY, AGRP, and POMC mRNA levels on refeeding after 24 h FD in C57BL mice by in situ hybridization. After 24 h deprivation, mice were refed with either chow or a palatable mash containing no calories or were injected with murine leptin (100 microg) without food. Mice were perfused 2 or 6 h after treatment. Food deprivation increased hypothalamic NPY mRNA (108 +/- 6%) and AGRP mRNA (78 +/- 7%) and decreased hypothalamic POMC mRNA (-15 +/- 1%). Refeeding for 6 h, but not 2 h, was sufficient to reduce (but not restore) NPY mRNA, did not affect AGRP mRNA, and restored POMC mRNA levels to ad libitum control levels. Intake of the noncaloric mash had no effect on mRNA levels, and leptin administration after deprivation (at a dose sufficient to reduce refeeding in FD mice) was not sufficient to affect mRNA levels. These results suggest that gradual postabsorptive events subsequent to refeeding are required for the restoration of peptide mRNA to baseline levels after food deprivation in mice.

Dextromethorphan increases tyrosine hydroxylase mRNA in the mesencephalon of adolescent rats.

Dextromethorphan (DM), an antitussive widely available in over-the-counter, has been abused mostly in teenage groups at high doses. To examine effects of DM on the reward pathway, we injected a high dose of DM (40 mg/kg; intraperitoneally) into the adolescent rat and measured tyrosine hydroxylase (TH) mRNA by in situ hybridization in the ventral tegmental area (VTA) and the substantia nigra (SN). Remarkable increases in the level of TH mRNA were observed in the VTA and SN 2 h after DM injection. Stereotyped behavior and ataxia increased, and rearing decreased by DM administration. These results suggest that DM-induced increase in TH mRNA expression in mesencephalon contribute to the reinforcing property and the behavioral effects of DM.

Neuropeptide Y mRNA and serotonin innervation in the arcuate nucleus of anorexia mutant mice.

The anorexia (anx) mutation causes reduced food intake in preweanling mice, resulting in death from starvation within 3-4 weeks. In wild-type rodents, starvation induces increased neuropeptide Y (NPY) mRNA levels in the arcuate nucleus that promotes compensatory hyperphagia. Despite severely decreased body weight and food intake at 3-weeks age, anx/anx mice do not show elevated NPY mRNA levels in the hypothalamic arcuate nucleus compared to wild-type/heterozygous littermates. The NPY mRNA levels can be upregulated in normal mice at this chronological age, because 24-h food deprivation increased arcuate NPY mRNA in wild-type littermates. The unresponsiveness of NPY expression in the arcuate of anx/anx mice was paralleled by serotonergic hyperinnervation of the arcuate nucleus, comparable to the serotonergic hyperinnervation previously reported in the rest of the anx/anx brain. This result is consistent with the hypothesis that wasting disorders are accompanied by disregulation of NPY mRNA expression in the arcuate nucleus, and suggests that reduced food intake, the primary behavioral phenotype of the anx/anx mouse, may be the result of altered hypothalamic mechanisms that normally regulate feeding.