Opposing changes in serotonin and norepinephrine transporter mRNA levels after serotonin depletion

Bacillus subtilis-based probiotic promotes bone growth by inhibition of inflammation in broilers subjected to cyclic heating episodes

Heat stress as an environmental stressor causes abnormal bone remodeling and microarchitectural deterioration. The objective of this study was to investigate the effects of a Bacillus subtilis–based probiotic on bone mass of broilers subjected to cycling high ambient temperature. One hundred and twenty 1-day-old Ross 708 male broiler chicks were randomly assigned to 2 dietary treatments (12 pens per treatment): control diet and the control diet plus 250-ppm probiotic consisting of 3 strains of Bacillus subtilis. Room temperature was gradually decreased from 35°C on day 1 by 0.5°C/d until day 15, when ambient temperature was increased from 28°C to 32°C for 10 h (07:00 h–17:00 h) daily until day 44. Samples of blood, leg bones (tibia and femur), and brains (raphe nuclei and hypothalamus) were collected at day 43, while latency to lie test was conducted at day 44. Compared with controls, probiotic supplementation increased bone mineral content, weight, size, weight to length index, and reduced robusticity index in the tibia and femur (P < 0.05) of broilers subjected to heat stress. Serum concentrations of c-terminal telopeptide of type I collagen (CTX) were reduced (P = 0.02) by the probiotic supplementation, while ionized calcium, phosphate, and osteocalcin were not affected (P > 0.05). Moreover, tumor necrosis factor-α (TNF-α) in probiotic fed broilers was decreased (P = 0.003) without changes of plasma interleukin (IL)-6, IL-10, interferon-γ, and corticosterone concentrations. There were no treatment effects on the concentrations of peripheral serotonin and central serotonin and catecholamines (norepinephrine, epinephrine, and dopamine) as well as their metabolites. These results may indicate that dietary supplementation of Bacillus subtilis–based probiotic increases bone growth in broilers under a cyclic heating episode probably via inhibition of bone resorption, resulting from downregulation of the circulating TNF-α and CTX. Dietary probiotic supplementation may be a management strategy for increasing skeletal health of broilers under hot weather.

Effects of acute combined serotonin and dopamine depletion on cue-induced drinking intention/desire and cognitive function in patients with alcohol dependence

BACKGROUND

Alcohol cues can precipitate the desire to drink and cause relapse in recovering alcohol-dependent patients. Serotonin and dopamine may play a role in alcohol cue-induced craving. Acute combined tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) depletion (CMD) in the diet attenuates the synthesis of serotonin and dopamine in the human brain. However, no study of the effects of acute CMD has been previously conducted. Therefore, we investigated whether the attenuation of serotonin and dopamine synthesis changes cue-induced alcohol craving in recently abstinent alcoholics.

METHODS

In this double-blind, randomized, placebo-controlled, crossover design, 12 male patients who met the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria for alcohol dependence were divided into two conditions: (1) monoamine depletion (i.e., consumption of a concentrated amino acid beverage that resulted in a rapid and significant decrease in plasma-free Tyr/Phe/Trp) and (2) balanced condition (i.e., consumption of a similar beverage that contained Tyr/Phe/Trp). The participants were scheduled for two experimental sessions, with an interval of ≥7 days. The cue-induced craving test session was conducted 6h after each amino acid beverage administration. Drinking urge, blood pressure, heart rate, working memory, and attention/psychomotor performance were assessed before and after administration.

RESULTS

Compared with the balanced condition, the monoamine depletion condition significantly increased drinking intention/desire and diastolic blood pressure. Cognitive performance was not different between the two conditions.

CONCLUSIONS

Acute combined serotonin and dopamine depletion may increase drinking intention/desire and diastolic blood pressure without influencing cognitive function.

Adult raphe-specific deletion of Lmx1b leads to central serotonin deficiency

The transcription factor Lmx1b is essential for the differentiation and survival of central serotonergic (5-HTergic) neurons during embryonic development. However, the role of Lmx1b in adult 5-HTergic neurons is unknown. We used an inducible Cre-LoxP system to selectively inactivate Lmx1b expression in the raphe nuclei of adult mice. Pet1-CreER^T2 mice were generated and crossed with Lmx1b^flox/flox mice to obtain Pet1-CreER^T2; Lmx1b^flox/flox mice (which termed as Lmx1b iCKO). After administration of tamoxifen, the level of 5-HT in the brain of Lmx1b iCKO mice was reduced to 60% of that in control mice, and the expression of tryptophan hydroxylase 2 (Tph2), serotonin transporter (Sert) and vesicular monoamine transporter 2 (Vmat2) was greatly down-regulated. On the other hand, the expression of dopamine and norepinephrine as well as aromatic L-amino acid decarboxylase (Aadc) and Pet1 was unchanged. Our results reveal that Lmx1b is required for the biosynthesis of 5-HT in adult mouse brain, and it may be involved in maintaining normal functions of central 5-HTergic neurons by regulating the expression of Tph2, Sert and Vmat2.

Lmx1b is required for maintenance of central serotonergic neurons and mice lacking central serotonergic system exhibit normal locomotor activity

Central serotonergic neurons have been implicated in numerous animal behaviors and psychiatric disorders, but the molecular mechanisms underlying their development are not well understood. Here we generated Lmx1b (LIM homeobox transcription factor 1 beta) conditional knock-out mice (Lmx1b(f/f/p)) in which Lmx1b was only deleted in Pet1 (pheochromocytoma 12 ETS factor-1)-expressing 5-HT neurons. In Lmx1b(f/f/p) mice, the initial generation of central 5-HT neurons appeared normal. However, the expression of both 5-HT-specific and non-5-HT-specific markers was lost in these neurons at later stages of development. The loss of gene expression is concomitant with downregulation of Lmx1b expression, with the exception of serotonin transporter Sert and tryptophan hydroxylase TPH2, whose expression appears to be most sensitive to Lmx1b. Interestingly, the expression of Pet1 is tightly coupled with expression of Lmx1b during later stages of embryonic development, indicating that Lmx1b maintains Pet1 expression. In Lmx1b(f/f/p) mice, almost all central 5-HT neurons failed to survive. Surprisingly, Lmx1b(f/f/p) mice survived to adulthood and exhibited normal locomotor activity. These data reveal a critical role of Lmx1b in maintaining the differentiated status of 5-HT neurons. Lmx1b(f/f/p) mice with normal locomotor function should provide a unique animal model for examining the roles of central 5-HT in a variety of animal behaviors.

Neuroimaging and electrophysiological studies of the effects of acute tryptophan depletion: a systematic review of the literature

RATIONALE

There is a growing psychopharmacological literature on the use of Acute Tryptophan Depletion (ATD) for experimental modulation of the serotonergic system. To date, no systematic review has been undertaken assessing the neurophysiological effects following this acute central 5-HT manipulation.

MATERIALS AND METHODS

A comprehensive MEDLINE, EMBASE, PsycINFO search was performed for reports on neural substrates of Acute Tryptophan Depletion in healthy individuals and in clinical population.

RESULTS

Twenty-eight placebo-controlled studies were included in the review. Although tryptophan depletion reduced plasma serotonin levels in all studies, significant effects on mood were only observed in studies with recovered depressed patients. In functional neuroimaging studies ATD was consistently found to modulate cortical activity in prefrontal areas implicated in mnemonic and executive functions and in orbitofrontal, cingulate, and subcortical regions associated with emotional processing. Electrophysiological studies indicated that ATD has a significant effect on both "selective" and "involuntary" attention.

CONCLUSIONS

The combination of ATD with modern brain imaging techniques allows the investigation of the neurophysiological effects of reduced 5-HT synthesis on global brain activity, executive functions, memory, attention, and affect.

Selective serotonin depletion does not regulate hippocampal neurogenesis in the adult rat brain: differential effects of p-chlorophenylalanine and 5,7-dihydroxytryptamine

Serotonin is suggested to regulate adult hippocampal neurogenesis, and previous studies with serotonin depletion reported either a decrease or no change in adult hippocampal progenitor proliferation. We have addressed the effects of serotonin depletion on distinct aspects of adult hippocampal neurogenesis, namely the proliferation, survival and terminal differentiation of hippocampal progenitors. We used the serotonin synthesis inhibitor p-chlorophenylalanine (PCPA) or the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to deplete serotonin levels. 5,7-DHT selectively decreased hippocampal serotonin levels, while PCPA resulted in a significant decline in both serotonin and norepinephrine levels. We observed a robust decline in the proliferation and survival of adult hippocampal progenitors following PCPA treatment. This was supported by a decrease in the number of doublecortin-positive cells in the neurogenic niche in the hippocampus. In striking contrast, 5,7-DHT did not alter the proliferation or survival of adult hippocampal progenitors and did not alter the number of doublecortin-positive cells. The terminal differentiation of adult hippocampal progenitors was not altered by either PCPA or 5,7-DHT treatment. An acute increase in serotonin levels also did not influence adult hippocampal progenitor proliferation. These results suggest that selective serotonin depletion or an acute induction in serotonin levels does not regulate adult hippocampal neurogenesis, whereas treatment with PCPA that induces a decline in both serotonin and norepinephrine levels results in a significant decrease in adult hippocampal neurogenesis. Our results highlight the need for future studies to examine the role of other monoamines in both the effects of stress and antidepressants on adult hippocampal neurogenesis.

Effects of tryptophan depletion on the serotonin transporter in healthy humans

BACKGROUND

Lowering of brain serotonin by acute tryptophan depletion (TD) frequently leads to transient symptoms of depression in vulnerable individuals but not in euthymic healthy subjects with a negative family history of depression. The effects of TD on regional serotonin transporter binding potential (5-HTT BP), an index of 5-HTT density and affinity, were studied in healthy individuals using 3-(11)C-amino-4-(2-dimethylaminomethylphenylsulfanyl)benzonitrile ([11C]DASB) positron emission tomography (PET). Adaptive decreases in 5-HTT density and/or affinity during TD would be a possible compensatory mechanism to maintain sufficient extracellular serotonin levels during TD, thereby preventing a depressive relapse.

METHODS

Regional noninvasive 5-HTT BP was found in 25 healthy subjects using [11C]DASB PET. Fourteen subjects were scanned twice, once after TD and once after sham depletion, and 11 other healthy subjects were scanned twice to measure test-retest reliability of the method.

RESULTS

None of the healthy subjects experienced depressive symptoms during TD and there was no difference in regional 5-HTT BP during TD as compared with sham depletion.

CONCLUSIONS

Acute changes in 5-HTT density or affinity are unlikely to play a role in protecting healthy subjects against mood symptoms during TD. Other mechanisms that may be associated with greater resilience against acute lowering of extracellular serotonin should be explored to gain further insight into the neurochemical basis of different vulnerabilities to short-term depressive relapse.

Discovering endophenotypes for major depression

The limited success of genetic studies of major depression has raised questions concerning the definition of genetically relevant phenotypes. This paper presents strategies to improve the phenotypic definition of major depression by proposing endophenotypes at two levels: First, dissecting the depressive phenotype into key components results in narrow definitions of putative psychopathological endophenotypes: mood bias toward negative emotions, impaired reward function, impaired learning and memory, neurovegetative signs, impaired diurnal variation, impaired executive cognitive function, psychomotor change, and increased stress sensitivity. A review of the recent literature on neurobiological and genetic findings associated with these components is given. Second, the most consistent heritable biological markers of major depression are proposed as biological endophenotypes for genetic studies: REM sleep abnormalities, functional and structural brain abnormalities, dysfunctions in serotonergic, catecholaminergic, hypothalamic-pituitary-adrenocortical axis, and CRH systems, and intracellular signal transduction endophenotypes. The associations among the psychopathological and biological endophenotypes are discussed with respect to specificity, temporal stability, heritability, familiality, and clinical and biological plausibility. Finally, the case is made for the development of a new classification system in order to reduce the heterogeneity of depression representing a major impediment to elucidating the genetic and neurobiological basis of this common, severe, and often life-threatening illness.

Expression of brain and platelet serotonin transporters in sublines of rats with constitutionally altered serotonin homeostasis

By selective breeding, two sublines of rats, termed Wistar-Zagreb 5HT rats, with constitutionally high or low values of platelet serotonin (5HT) level and activity of platelet serotonin transporter (5HTt) have been developed. Previous studies demonstrated significant differences between the sublines in the expression of platelet 5HTt at the level of both mRNA and protein. Neurochemical and behavioural studies demonstrated differences in functional activity of brain 5HTt indicating that, similarly to platelets, differences in mRNA level might be expected in brains of selected animals. In this work, semi-quantitative RT-PCR method for measuring the 5HTt expression in rat tissues was described and then used to quantify the 5HTt mRNA in brains and platelets of animals from high-5HT and low-5HT sublines. Three different housekeeping genes: GAPDH, beta-actin and cyclophylin B, were used as internal standards to normalise 5HTt signals. Significant differences in platelet 5HTt mRNA between the sublines were confirmed, as contrasted to only a tendency toward higher 5HTt mRNA levels in midbrain of animals from the high-5HT subline. Results indicate differences in transcriptional regulation of central and peripheral 5HT transporters, suggesting that homeostatic control in the brain counteract more efficiently the selection pressure than in the periphery.