The effects and mechanisms of heat stress on mammalian oocyte and embryo development

The sum of nonspecific physiological responses exhibited by mammals in response to the disruption of thermal balance caused by high-temperature environments is referred to as heat stress (HS). HS affects the normal development of mammalian oocyte and embryos and leads to significant economic losses. Therefore, it is of great importance to gain a deep understanding of the mechanisms underlying the effects of HS on oocyte and embryonic development and to explore strategies for mitigating or preventing its detrimental impacts in the livestock industry. This article provides an overview of the negative effects of HS on mammalian oocyte growth, granulosa cell maturation and function, and embryonic development. It summarizes the mechanisms by which HS affects embryonic development, including generation of reactive oxygen species (ROS), endocrine disruption, the heat shock system, mitochondrial autophagy, and molecular-level alterations. Furthermore, it discusses various measures to ameliorate the effects of HS, such as antioxidant use, enhancement of mitochondrial function, gene editing, cultivating varieties possessing heat-resistant genes, and optimizing the animals'rearing environment. This article serves as a valuable reference for better understanding the relationship between HS and mammalian embryonic development as well as for improving the development of mammalian embryos and economic benefits under HS conditions in livestock production.

Alterations in the brain serotonin system and serotonin-regulated behavior during aging in zebrafish males and females

The brain serotonin (5-HT) system performs a neurotrophic function and supports the plasticity of the nervous system, while its age-related changes can increase the risk of senile neurodegeneration. Zebrafish brain is highly resistant to damage and neurodegeneration due to its high regeneration potential and it is a promising model object in searching for molecular factors preventing age-related neurodegeneration. In the present study alterations in 5-HT-related behavior in the home tank and the novel tank diving test, as well as 5-HT, 5-HIAA levels, tryptophan hydroxylase (TPH), monoamine oxidase (MAO) activity and the expression of genes encoding TPH, MAO, 5-HT transporter and 5-HT receptors in the brain of 6, 12, 24 and 36 month old zebrafish males and females are investigated. Marked sexual dimorphism in the locomotor activity in the novel tank test is revealed: females of all ages move slower than males. No sexual dimorphism in 5-HT-related traits is observed. No changes in 5-HT and 5-HIAA levels in zebrafish brain during aging is observed. At the same time, the aging is accompanied by a decrease in the locomotor activity, TPH activity, tph2 and htr1aa genes expression as well as an increase in the MAO activity and slc6a4a gene expression in their brain. These results indicate that the brain 5-HT system in zebrafish is resistant to age-related alterations.

RGS2 and female common diseases: a guard of women's health

Currently, women around the world are still suffering from various female common diseases with the high incidence, such as ovarian cancer, uterine fibroids and preeclampsia (PE), and some diseases are even with the high mortality rate. As a negative feedback regulator in G Protein-Coupled Receptor signaling (GPCR), the Regulator of G-protein Signaling (RGS) protein family participates in regulating kinds of cell biological functions by destabilizing the enzyme-substrate complex through the transformation of hydrolysis of G Guanosine Triphosphate (GTP). Recent work has indicated that, the Regulator of G-protein Signaling 2 (RGS2), a member belonging to the RGS protein family, is closely associated with the occurrence and development of certain female diseases, providing with the evidence that RGS2 functions in sustaining women's health. In this review paper, we summarize the current knowledge of RGS2 in female common diseases, and also tap and discuss its therapeutic potential by targeting multiple mechanisms.

Age-Related Alterations in the Level and Metabolism of Serotonin in the Brain of Males and Females of Annual Turquoise Killifish (Nothobranchius furzeri)

The annual turquoise killifish (Nothobranchius furzeri) is a laboratory model organism for neuroscience of aging. In the present study, we investigated for the first time the levels of serotonin and its main metabolite, 5-hydroxyindoleacetic acid, as well as the activities of the key enzymes of its synthesis, tryptophan hydroxylases, and degradation, monoamine oxidase, in the brains of 2-, 4- and 7-month-old male and female N. furzeri. The marked effect of age on the body mass and the level of serotonin, as well as the activities of tryptophan hydroxylases and monoamine oxidase in the brain of killifish were revealed. The level of serotonin decreased in the brain of 7-month-old males and females compared with 2-month-old ones. A significant decrease in the tryptophan hydroxylase activity and an increase in the monoamine oxidase activity in the brain of 7-month-old females compared to 2-month-old females was shown. These findings agree with the age-related alterations in expression of the genes encoding tryptophan hydroxylases and monoamine oxidase. N. furzeri is a suitable model with which to study the fundamental problems of age-related changes of the serotonin system in the brain.

Fermented Angelica sinensis activates Nrf2 signaling and modulates the gut microbiota composition and metabolism to attenuate D-gal induced liver aging

Aging is an inevitable physiological process associated with an imbalance in the oxidative defense system. Angelica sinensis, a kind of traditional Chinese medicine (TCM), has anti-oxidant effects and has been considered as a potential supplement in anti-aging treatment. Nevertheless, it has the disadvantages of slow efficacy and long duration of treatment. Fermentation, as an efficient biotechnological approach, is beneficial for improving the nutritional capacity of the material. Fermented TCMs are considered to be more effective. In this study, fermented Angelica sinensis (FAS) and non-fermented Angelica sinensis (NFAS) were used to investigate changes in the chemical constituents. Furthermore, the improvement effect of FAS on D-galactose-induced aging in mice and the potential mechanisms were explored. The results revealed that FAS and NFAS had different constituents under the influence of fermentation, such as 3-phenyllactic acid, L-5-hydroxytryptophan, taxifolin and methyl gallate. These elevated constituents of FAS might help increase the ability of FAS to improve aging. The aging model was established by intraperitoneal injection of D-galactose (2.5 g kg^-1 day^-1) for 44 days, and FAS (3 g kg^-1 day^-1) was administered daily by oral gavage after 2 weeks of induction with D-galactose. FAS was observed to significantly ameliorate changes associated with liver aging, such as reduction of MDA, AGEs and 8-OHdG. The contents of pro-inflammatory cytokines containing TNF-α, IL-1β and IL-6 were significantly suppressed in the FAS group. In addition, FAS activated Nrf2 signaling better than NFAS, improved the expression of Nrf2, HO-1, NQO1, GCLC, GCLM and GSS, and further increased the activities of SOD, CAT and other antioxidant enzymes in the liver. Simultaneously, it had a certain repair effect on the liver tissues of mice. The intestinal microbiota analysis showed that FAS could regulate the microbiota imbalance caused by aging, increase the ratio of Firmicutes/Bacteroidetes by 95% and improve the relative abundance of beneficial bacteria related to Nrf2 signaling, such as Lactobacillus. Besides, fecal metabolite analysis identified uric acid as an evidential metabolite, suggesting that FAS participates in purine metabolism to improve aging. Therefore, the regulation of intestinal microbiota and metabolism may be one of the important mechanisms of FAS in alleviating hepatic oxidative stress via the gut-liver axis. The results of this study could provide information for the future development of postbiotic products that may have beneficial effects on the prevention or treatment of aging.

Age-Related Changes in Central Nervous System 5-Hydroxytryptamine Signalling and Its Potential Effects on the Regulation of Lifespan

Serotonin or 5-hydroxytryptamine (5-HT) is an important neurotransmitter in the central nervous system and the periphery. Most 5-HT (~99%) is found in the periphery where it regulates the function of the gastrointestinal (GI) tract and is an important regulator of platelet aggregation. However, the remaining 1% that is found in the central nervous system (CNS) can regulate a range of physiological processes such as learning and memory formation, mood, food intake, sleep, temperature and pain perception. More recent work on the CNS of invertebrate model systems has shown that 5-HT can directly regulate lifespan.This chapter will focus on detailing how CNS 5-HT signalling is altered with increasing age and the potential consequences this has on its ability to regulate lifespan.

The role of serotonin in declarative memory: A systematic review of animal and human research

The serotonergic system is involved in diverse cognitive functions including memory. Of particular importance to daily life are declarative memories that contain information about personal experiences, general facts, and events. Several psychiatric or neurological diseases, such as depression, attention-deficit-hyperactivity disorder (ADHD), and dementia, show alterations in serotonergic signalling and attendant memory disorders. Nevertheless, understanding serotonergic neurotransmission and its influence on memory remained a challenge until today. In this systematic review, we summarize recent psychopharmacological studies in animals and humans from a psychological memory perspective, in consideration of task-specific requirements. This approach has the advantage that comparisons between serotonin (5-HT)-related neurochemical mechanisms and manipulations are each addressing specific mnemonic circuits. We conclude that applications of the same 5-HT-related treatments can differentially affect unrelated tasks of declarative memories. Moreover, the analysis of specific mnemonic phases (e.g., encoding vs. consolidation) reveals opposing impacts of increased or decreased 5-HT tones, with low 5-HT supporting spatial encoding but impairing the consolidation of objects and verbal memories. Promising targets for protein synthesis-dependent consolidation enhancements include 5-HT₄ receptor agonists and 5-HT₆ receptor antagonists, with the latter being of special interest for the treatment of age-related decline. Further implications are pointed out as base for the development of novel therapeutic targets for memory impairment of neuropsychiatric disorders.

Age-Related Alterations in the Behavior and Serotonin-Related Gene mRNA Levels in the Brain of Males and Females of Short-Lived Turquoise Killifish (Nothobranchius furzeri)

Short-lived turquoise killifish (Nothobranchius furzeri) have become a popular model organism for neuroscience. In the present paper we study for the first time their behavior in the novel tank diving test and the levels of mRNA of various 5-HT-related genes in brains of 2-, 4- and 6-month-old males and females of N. furzeri. The marked effect of age on body mass, locomotor activity and the mRNA level of Tph1b, Tph2, Slc6a4b, Mao, Htr1aa, Htr2a, Htr3a, Htr3b, Htr4, Htr6 genes in the brains of N. furzeri males was shown. Locomotor activity and expression of the Mao gene increased, while expression of Tph1b, Tph2, Slc6a4b, Htr1aa, Htr2a, Htr3a, Htr3b, Htr4, Htr6 genes decreased in 6-month-old killifish. Significant effects of sex on body mass as well as on mRNA level of Tph1a, Tph1b, Tph2, Slc6a4b, Htr1aa, 5-HT2a, Htr3a, Htr3b, Htr4, and Htr6 genes were revealed: in general both the body mass and the expression of these genes were higher in males. N. furzeri is a suitable model with which to study the fundamental problems of age-related alterations in various mRNA levels related with the brains 5-HT system.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Procognitive profiling of a serotonin 5-HT6 receptor antagonist in a complex model system in rats: A novel translational approach for clinical prediction

INTRODUCTION

The serial clinical failures of novel cognitive enhancer candidates point out the lack of predictive power in the preceding animal experimentation. For a more predictive profiling of putative procognitive drugs in rodents, we recently elaborated a methodical approach which consists of three fundamental steps: 1. teaching various learning tasks representing different cognitive domains to the same cohort of animals with the aim to create a population with 'widespread knowledge'. 2. Applying a cognitive deficit-inducing intervention to transform this cohort of animals to a 'patient population'. 3. Testing putative procognitive drugs with a 'clinical trial-like' design on the wide spectrum of cognitive (dys)functions in the actual 'patient population'. The present study has been the first trial to test the feasibility and utility of the proposed system.

METHODS

The population with 'widespread knowledge' consisted of 2 year old male Long-Evans rats with a learning history in five-choice serial reaction time task (5-CSRTT, attentional paradigm), Morris water maze (MWM, spatial learning), a cooperative task carried out in pairs (social learning), and a skill-learning task, "pot-jumping". For inducing cognitive deficit, thus creating a 'patient population' we increased the difficulty of the tasks. For the cognitive enhancer mechanism to test in the system we chose a serotonin 5-HT₆ receptor antagonist compound, RO4368554. Animals were randomly assigned to vehicle- and drug treated groups based on their baseline learning performance and their response in a pilot test of increase in task difficulty. During the 13-day long treatment with 3 mg/kg ip. RO4368554 all the learning paradigms were repeatedly run with increased difficulty supplemented with a novel object recognition test (NOR, episodic memory).

RESULTS

In the 5-CSRTT, reducing the stimulus duration from 1 s to 0.25 s caused a significant decrease in the percentage of correct responses (from 52 % to 31 % in the control group) which was not affected by the 5-HT₆ receptor antagonist treatment (correct responses decreased from 58 % to 31 %). In the MWM, replacing the escape platform to a new location did not mean a hard challenge for the rats. Members of both groups could find it within a relatively short time: mean escape latencies were 83 s and 65 s at the first replacement trial and 58 s and 74 s at the second one in the control and drug-treated groups, respectively. In the cooperation paradigm, where the rats had to perform simultaneous nose-pokes to get a reward, task difficulty was increased by requiring two consecutive simultaneous nose-poking from the animals. This caused a fall in the percentage of successful trials in both groups (from 48 % to 12 % and from 50 % to 20 % in the saline - and drug-treated group, respectively), however, by the end of the treatment RO4368554-treated animals showed significantly higher performance (29 %) than saline treated rats (2%). The NOR test, carried out with a 5 -h delay, revealed poor recognition memory in both groups (discrimination index (DI) values were 0.13 and 0.06 for saline and RO4368554, respectively). Performance in the pot jumping test was also not improved by the drug-treatment.

CONCLUSIONS

The applied study design allowed parallel measurements of the action of the test compound on several cognitive functions and to follow its time course. RO4368554 did not show notable effects on impaired attention and visual recognition; nor did it affect spatial and procedural learning, but it exerted beneficial effect on cooperative behaviour. The revealed activity pattern highlight the cognitive domain most sensitive to the particular drug effect and may give hints for further target validating and clinical studies.

Silencing of RGS2 enhances hippocampal neuron regeneration and rescues depression-like behavioral impairments through activation of cAMP pathway

Depression is one of the most common mental disorders with an increasing incidence. However, factors involved in depression are so complex, thus it is difficult to find effective strategies to reverse the impairments. This study aims to verify the role of regulator of G protein signaling 2 (RGS2) in the mouse mode of unpredictable mild stress-induced depression-like behaviors. Knockdown of RGS2 was achieved by transfection of siRNA-RGS2 in mouse hippocampal (HT-22) cells in vitro and injection of recombinant adenovirus expressing siRNA-RGS2 in mice in vivo. An aberrant high expression of RGS2 was found in mice with depression-like behaviors through immunohistochemical analysis. Silencing of RGS2 or Forskolin (activator of cAMP pathway) developed sweet water consumption, reduced inflammation and oxidative stress injury, and attenuated cognitive impairment and neuronal damage in mice with depression-like behaviors. Furthermore, regeneration was enhanced and apoptosis was repressed in mouse hippocampal neurons in the presence of RGS2 knockdown and Forskolin. Mechanistic studies indicated that silencing of RGS2 promoted the activation of cAMP pathway, thus rescuing depression-like behaviors of mice. Collectively, our study uncovered the role of RGS2-dependent cAMP pathway in regulation of cognitive impairment and hippocampal neuron regeneration in depression-like behaviors of mice, which may be a potential therapeutic target for impairments and symptoms associated with depression.

The serotonin system in the hippocampus CA3 involves in effects of CSDS on social recognition in adult female mandarin voles (Microtus mandarinus)

Chronic social defeat stress (CSDS) exacerbated the development of stress-related psychiatric disorders, and the social recognition dysfunction is the core feature of many psychiatric disorders. However, the effects of CSDS on female social recognition and the underlying neural mechanisms remain unclear. Using highly aggressive adult female mandarin voles (Microtus mandarinus) as animal model, the aim of this work is to investigate the effects of CSDS on social recognition in adult female rodents and the neurobiological mechanisms underlying these effects. Our results indicate the CSDS disrupted the normal social recognition in adult female voles. Meanwhile, defeated voles exhibited increased neural activity in the DG, CA1 and CA3 of the hippocampus. Furthermore, CSDS reduced levels of serotonin (5-HT) and serotonin 1A receptors (5-HT_1AR) in the CA3. We also discovered that microinjection of 8-OH-DPAT into the CA3 effectively reversed the social recognition deficits induced by CSDS, and an infusion of WAY-100635 into the CA3 of control female voles impaired social recognition. Moreover, targeted activation of the 5-HT neuron projection from the DRN to CA3 by long-term administration of CNO significantly prevented the CSDS induced social recognition deficits. Taken together, our study demonstrated that CSDS induced social recognition deficits in adult female voles, and these effects were mediated by the action of 5-HT on the 5-HT_1AR in the hippocampus CA3. The projection from the DRN to CA3 may be involved in social recognition deficits induced by CSDS.

Aerobic exercise upregulates the BDNF-Serotonin systems and improves the cognitive function in rats

Aerobic exercise (AE) benefits brain health and behavior. Serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) are known to mediate and shape cognitive processes. Both systems share some actions: BDNF is involved in the maturation and function of 5-HT neurons. In turn, 5-HT is involved in neuroplasticity phenomena mediated by BDNF and stimulated by exercise. The aim of this work was to study the long-term effects of AE on BDNF- 5-HT systems and cognitive function in rats at different ages. A lifelong moderate-intensity aerobic training program was designed, in which aerobically exercised (E) and sedentary control (C) rats were studied at middle (8 months) and old age (18 months) by means of biochemical, immunohistochemical and behavioral assays. The levels and expression of BDNF, 5-HT, serotonin transporter (SERT) and 5-HT_1A receptor were determined in selected brain areas involved in memory and learning. Immunopositive cells to neuronal nuclear protein (NeuN) in the hippocampus CA1 area were also quantified. The cognitive function was evaluated by the object recognition test (ORT). Results indicate that AE enhanced spatial and non-spatial memory systems, modulated by age. This outcome temporarily correlated with a significant upregulation of cortical, hippocampal and striatal BDNF levels in parallel with an increase in the number of hippocampal CA1-mature neurons. AE also increased brain and raphe 5-HT levels, as well as the expression of SERT and 5-HT_1A receptor in the cortex and hippocampus. Old AE rats showed a highly conserved response, indicating a remarkable protective effect of exercise on both systems. In summary, lifelong AE positively affects BDNF-5-HT systems, improves cognitive function and protects the brain against the deleterious effects of sedentary life and aging.

Chronic activation of 5-HT4 receptors or blockade of 5-HT6 receptors improve memory performances

5-HT4 and 5-HT6 serotonergic receptors are located in brain structures involved in memory processes. Neurochemical and behavioural studies have demonstrated that acute activation of 5-HT4 receptors (5-HT4R) or blockade of 5-HT6 receptors (5-HT6R) improves memory. To evaluate the potential of these two receptors as targets in the treatment of memory disorders encountered in several situations (ageing, Alzheimer's disease, schizophrenia, etc.), it is necessary to assess whether their beneficial effects occur after chronic administration, and if such treatment induces adverse effects. The goal of this study was to assess the effects of chronic 5-HT4R or 5-HT6R modulation on recognition memory, and to observe the possible manifestation of side effects (modification of weight gain, locomotor activity or exploratory behaviour, etc.). Mice were treated for 14 days with a 5-HT4R partial agonist (RS-67333) or a 5-HT6R antagonist (SB-271046) at increasing doses. Memory performances, locomotor activity, and exploration were assessed. Both chronic 5-HT4R activation and 5-HT6R blockade extended memory traces in an object recognition test, and were not associated with any adverse effects in the parameters assessed. Chronic modulation of one or both of these receptors thus seems promising as a potential strategy for the treatment memory deficits.

Serotonin: from top to bottom

Serotonin is a monoamine neurotransmitter, which is phylogenetically conserved in a wide range of species from nematodes to humans. In mammals, age-related changes in serotonin systems are known risk factors of age-related diseases, such as diabetes, faecal incontinence and cardiovascular diseases. A decline in serotonin function with aging would be consistent with observations of age-related changes in behaviours, such as sleep, sexual behaviour and mood all of which are linked to serotonergic function. Despite this little is known about serotonin in relation to aging. This review aims to give a comprehensive analysis of the distribution, function and interactions of serotonin in the brain; gastrointestinal tract; skeletal; vascular and immune systems. It also aims to demonstrate how the function of serotonin is linked to aging and disease pathology in these systems. The regulation of serotonin via microRNAs is also discussed, as are possible applications of serotonergic drugs in aging research and age-related diseases. Furthermore, this review demonstrates that serotonin is potentially involved in whole organism aging through its links with multiple organs, the immune system and microRNA regulation. Methods to investigate these links are discussed.

Age effects on serotonin receptor 1B as assessed by PET

Previous imaging studies have suggested that there is an age-related decline in brain serotonin (5-hydroxytryptamine) measures in healthy subjects. This paper addresses whether the availability of 5-hydroxytryptamine receptor 1B (5-HT(1B)) is seen to decrease with aging via PET imaging.

METHODS

Forty-eight healthy control subjects (mean age ± SD, 30 ± 10 y; age range, 18-61 y; 33 men, 15 women) underwent (11)C-P943 scanning on a high-resolution PET tomograph. Regions were examined with and without gray matter masking, the latter in an attempt to control for age-related gray matter atrophy on nondisplaceable binding potential (BP(ND)) as determined by a validated multilinear reference tissue model.

RESULTS

5-HT(1B) BP(ND) decreased in the cortex at an average rate of 8% per decade without and 9% with gray matter masking. A negative association with age was also observed in all individual cortical regions. Differences in the putamen and pallidum (positive association) were significant after adjustment for multiple comparisons. No sex- or race-related effects on 5-HT(1B) BP(ND) were found in any regions.

CONCLUSION

These findings indicate that age is a relevant factor for 5-HT(1B) in the cortex of healthy adults.

Behavioral, neurochemical and histological alterations promoted by bilateral intranigral rotenone administration: a new approach for an old neurotoxin

Rotenone exposure in rodents provides an interesting model for studying mechanisms of toxin-induced dopaminergic neuronal injury. However, several aspects remain unclear regarding the effects and the accuracy of rotenone as an animal model of Parkinson's disease (PD). In order to counteract these limitations, this study characterized a precise neurotoxin-delivery strategy employing the bilateral intranigral administration protocol of rotenone as a reliable model of PD. We performed bilateral intranigral injections of rotenone (12 μg) and subsequent general activity (1, 10, 20, and 30 days after rotenone) and cognitive (7, 8, 15, and 30 days after rotenone) evaluations followed by neurochemical and immunohistochemical tests. We have observed that rotenone was able to produce a remarkable reduction on the percentage of tyrosine hydroxylase immunoreactive neurons (about 60%) within the substantia nigra pars compacta. Dopamine (DA) was severely depleted at 30 days after rotenone administration, similarly to its metabolites. In addition, an increase in DA turnover was detected at the same time-point. In parallel, striatal serotonin and its metabolite were found to be increased 30 days after the neurotoxic insult, without apparent modification in the serotonin turnover. Besides, motor behavior was impaired, mainly 1 day after rotenone. Furthermore, learning and memory processes were severely disrupted in different time-points, particularly at the training and test session (30 days). We now provide further evidence of a time-dependent neurodegeneration associated to cognitive impairment after the single bilateral intranigral administration of rotenone. Thus, it is proposed that the current rotenone protocol provides an improvement regarding the existing rotenone models of PD.