The effect of tryptophan on the cortisol response to social stress is modulated by the 5-HTTLPR genotype.

OBJECTIVE: The S'/S' (S/S, S/Lg and Lg/Lg) variant of the serotonin (5-HT) transporter gene linked polymorphic region (5-HTTLPR) is associated with less efficient neurotransmission and may be more reactive to 5-HT manipulations. We tested the effects of l-tryptophan supplements on the cortisol response induced by a social stressor in S'/S' and L'/L' (La/La) carriers. METHODS: In a double-blind parallel design, 25 S'/S' carriers and 21 L'/L' carriers were randomised to take l-tryptophan (2.8g/d) or placebo supplements for six days. At day 7 participants were exposed to the Trier Social Stress Test. Salivary cortisol and subjective mood states were monitored before, during and after the stress procedure. RESULTS: S'/S' carriers who took l-tryptophan supplements had a significantly lower cortisol response to stress than S'/S' carriers who took placebo. Tryptophan had no effect on cortisol in L'/L' carriers and no effect on subjective mood states in either genotype group. CONCLUSION: Tryptophan attenuates the cortisol response to acute social stress depending on 5-HTTLPR genotype. S'/S' carriers may indeed be more reactive to 5-HT manipulations.

Object recognition testing: rodent species, strains, housing conditions, and estrous cycle.

The object recognition task (ORT) allows assessing learning and memory processes in rodents. In this study, two areas in which knowledge about the ORT could be extended were addressed; i.e. generality to species and strains, and intervening variables including housing and estrous cycle. Regarding generality to species and strains, the ORT performance of golden hamsters was assessed. The hamsters showed sufficient exploration times, object recognition performance, and a retention-interval dependent decline similar to rats and mice. Subsequently, we tested three mouse strains which have not been described before in the ORT; i.e. OF1, NMRI, and SJL mice. OF1 and NMRI strains performed equally well, whereas the SJL strain showed low exploration times and no memory retention. Therefore, the SJL strain is unsuited for ORT experiments using a 1h retention interval and a fixed (3 min) trial duration. Furthermore, the sensitivity to a pharmacological memory deficit model (scopolamine) was tested in three rat strains. Each strain showed a dose dependent relationship, but the least effective dose of scopolamine differed among the three strains, the effect being greater in the order of Wistar, Long-Evans, Hooded Lister rats. Finally, to investigate potential intervening variables in the ORT, the effects of housing conditions and estrous cycle were investigated with rats. Single housing resulted in absolute higher performance than social housing. Furthermore, females in pro-estrus/estrus showed better performance compared to females in met-estrus/di-estrus. Taken together, object recognition appears to be a common ability of rodent species, but different strains have different memory capacities and sensitivities to scopolamine, individual housing leads to higher performance, and performance of females is dependent on the estrous cycle phase. Thus, rodent species, strain, housing, and estrous cycle should be taken into consideration in ORT studies.

The efficacy of n-3 fatty acids DHA and EPA (fish oil) for perinatal depression.

Depressive symptoms are common during pregnancy and the post-partum period. Although essential n-3 PUFA may have beneficial effects on depression, it remains unclear whether they are also effective for perinatal depression. The purpose of the present study was to assess the efficacy of n-3 supplementation for perinatal depression, by performing a meta-analysis on currently available data. After a thorough literature search, we included seven randomised controlled trials in the meta-analysis, all with EPA and/or DHA supplementation. Most studies were judged to be of low-to-moderate quality, mainly due to small sample sizes and failure to adhere to Consolidated Standards of Reporting Trials guidelines. Some studies were not primarily designed to address perinatal depression. A total of 309 women on n-3 fatty acid supplementation were compared with 303 women on placebo treatment. n-3 Supplementation was not found to be significantly more effective than placebo at post-treatment with a pooled effect size (Hedges's g) of - 0.03 (95 % CI - 0.18, 0.13; P = 0.76) using a fixed-effects model. Heterogeneity was low-to-moderate (I2 = 30 %). In a subgroup analysis of three small studies of pregnant women with major depression, there was some indication of effectiveness (effect size 0.17; 95 % CI - 0.21, 0.55). In conclusion, the question of whether EPA and DHA administration is effective in the prevention or treatment of perinatal depression cannot be answered yet. Future research should focus on women who are clinically depressed (or at risk). The quality of research in this area needs to improve.

Influence of chronic mild stress on the behavioural effects of acute tryptophan depletion induced by a gelatin-based mixture.

Several types of stress can increase vulnerability to developing depression. This depression may be caused by the effects of stress on the serotonergic system, which may make the system more vulnerable. The aim of this experiment was to evaluate whether chronic mild stress (CMS) resulted in long-lasting vulnerability of the serotonergic system, reflected by stronger behavioural responses to a serotonergic challenge with acute tryptophan depletion (ATD) several weeks after the CMS had ended. Male Wistar rats were exposed to 3 weeks of CMS followed by a 2-week resting period. CMS resulted in blunted weight gain and lower sucrose consumption. After the resting period, rats were repeatedly treated with a gelatin-based protein-carbohydrate mixture, either with or without L-tryptophan, to acutely challenge the serotonergic system and the rats were tested in several tests of anxiety-related and depression-related behaviour and memory. CMS and ATD both influenced behaviour on some tests, but overall this CMS procedure did not result in increased sensitivity to ATD, as there were no CMSxATD interaction effects on behaviour. In conclusion, CMS did not result in long-lasting vulnerability of the serotonergic system, measured by the behavioural response to ATD several weeks after the CMS had ended.