Behavioral and neurochemical effects of dietary methyl donor deficiency combined with unpredictable chronic mild stress in rats.

Methyl donor deficiencies and chronic stress cause depression independently, but their interaction has never been thoroughly evaluated. In our study, methyl donor deficient diet and chronic stress condition consisted respectively of a B2, B9, B12, and choline-free diet and a chronic mild stress procedure. Rats were randomly assigned to six groups with three "diet" conditions (free-feeding, pair-fed and methyl donor deficient diet) and two "stress" conditions (no-stress and stress) and were evaluated in the open-field, the elevated plus-maze and the forced swimming test. After the behavioral evaluation, corticosterone and homocysteine plasma levels were measured and dopamine, DOPAC, serotonin, 5HIAA concentrations were evaluated in several brain areas. Rats given a methyl donor deficient diet for 11 weeks causing elevated plasma homocysteine levels were compared to pair-fed and free-feeding rats with or without unpredictable chronic mild stress. Regardless of stress environmental conditions, the methyl donor deficient diet decreased plasma corticosterone levels and caused disinhibition in the elevated plus-maze condition relative to both control groups. However, stress potentiated the effects of the deficient regimen on rearing in the open-field and climbing in the forced swim test. The dietary changes involved in behavior and plasma corticosterone could be caused by homocysteine-induced decreases in dopamine and 5-hydroxytryptamine metabolites in selective brain regions and it can be noted that regardless of stress-conditions, methyl donor deficient diet decreases DOPAC/dopamine and 5HIAA/serotonin ratios in striatum and hypothalamus and selectively 5HIAA/serotonin ratio in the sensorimotor cortex. Our experimental data is particularly relevant in the context of neuropsychiatric disorders frequently associated with folate deficiency and hyperhomocysteinemia.

Preventive antioxidant effects of cocoa polyphenolic extract on free radical production and cognitive performances after heat exposure in Wistar rats.

The preventive effects of ACTICOA powder (AP), a cocoa polyphenolic extract, on free radicals produced by leucocytes in rats after heat exposure (HE) and its protective effects on subsequent cognitive impairments were assessed. AP or vitamin E, the antioxidant reference, was orally administered to rats for 14 d before HE at 40 degrees C temperature during 2 h. The day after HE, free radical production by leucocytes in rats treated with AP or vitamin E was significantly reduced as compared to control. Unlike controls, AP- and vitamin E-treated rats discriminated between active lever and inactive levers in a light extinction paradigm. In the Morris water maze, escape latencies before reaching the hidden platform by AP- and vitamin E-treated rats decreased throughout testing. The daily oral administration of AP or vitamin E protected rats from cognitive impairments after HE by counteracting the overproduction of free radicals.

The endogenous androgen-regulated sialorphin modulates male rat sexual behavior.

In sexually mature male rats, sialorphin is synthesized under androgenic control and its surge endocrine secretion is evoked in response to environmental acute stress. These findings led us to suggest that this signaling mediator might play a role in physiological and behavioral integration, especially reproduction. The present study investigates the effects induced by sialorphin on the male sexual behavior pattern. Intact male rats were treated in acute mode, with sialorphin at the 0.3, 1, and 3 microg/kg doses, before being paired with receptive female for 45 min. The data obtained show that sialorphin increased, in a dose-related manner, the occurrence of intromissions across the successive ejaculatory sequences. The rats treated with the highest 3 microg/kg dose significantly ejaculated less often compared to controls; however, 80% of them achieved up to three ejaculations. Further analyses of mount bouts for rats achieving three ejaculations reveal that there were significant stimulatory effects of sialorphin, at all doses, on the frequency of intromissions before ejaculation and on the propensity of males to engage in investigatory behavior directed to the female during the post-ejaculatory interval. Thus, sialorphin has the ability to modulate, at doses related to physiological circulating levels, the male rat mating pattern, that is, exerting a dual facilitative or inhibitory dose-dependent effect on the sexual performance, while stimulating the apparent sexual arousal or motivation. These findings led us to speculate that the endogenous androgen-regulated sialorphin helps modulate the adaptative balance between excitatory and inhibitory mechanisms serving appropriate male rat sexual response, depending on the context.

Effects of the light--dark cycle on a water tank social interaction test in mice.

Mice were exposed to a water tank interaction test in which food could be obtained either by wading in the water or by attacking littermates. A tank with progressively rising water levels caused mice in groups of four to differentiate into those willing to wade (carrier mice) from those unwilling to wade (noncarrier mice). Noncarrier mice could only obtain food by stealing it from carrier mice or from other noncarrier mice. It was found that mice during the dark period of the light--dark cycle were more willing to wade in the search for food rather than attempt to steal food from other mice. Because mice are generally more active during the dark period, this result suggests that higher activity levels increase the willingness to share the work load, a form of altruism, rather than promote parasitic behavior and aggression.

Behavioral differentiation of mice exposed to a water tank social interaction test.

Male or female C57BL/6J mice were exposed to a water tank in which food could be obtained only by wading in the water towards a feeder. Behavioral differentiation occurred in that three distinct categories could be distinguished: major carriers (transporting over 80% of the food pellets), sporadic carriers (transporting less than 20% of the food pellets) and non-carriers. In the elevated + -maze, major carriers were more willing to explore open spaces than non-carriers. Sporadic carriers showed some evidence of the same tendency of decreased anxiety, but in a minor way. The willingness of mice to become carriers is associated with their willingness to explore novel areas. This test may be useful for the assessment of anxiolytic compounds in a social situation.