On the environmental genetics of depressive symptoms : Focus on two serotonergic genes

Depression is a complex psychiatric disorder influenced by several genes, environmental factors, and their interplay. Serotonin receptor 2A (HTR2A) and tryptophan hydroxylase 1 (TPH1) genes have been implicated in vulnerability to depression and other psychiatric disorders, but the results have been inconsistent. The present study examined whether these two genes moderated the influence of different depressogenic environmental factors on subthreshold depressive symptoms (assessed on a modified version of Beck s Depression Inventory, BDI) and depression-related temperament, i.e., harm avoidance (assessed on the Temperament and Character Inventory, TCI). The environmental factors included measures of childhood and adolescence exposure, i.e., maternal nurturance and parental socioeconomic status, and adulthood social circumstances, i.e., perceived social support and urban/rural residence. The participants were two randomly selected subsamples (n = 1246, n = 341) from the longitudinal population-based Cardiovascular Risk in Young Finns study (n = 3596). Childhood environmental factors were assessed when the participants were 3 to 18 years of age, and three years after the baseline. Adulthood environmental factors and outcome measures were assessed 17 and 21 years later when the participants were 21 to 39 years of age. The T102C polymorphism of the HTR2A gene moderated the association between childhood maternal nurturance and adulthood depressive symptoms, such that exposure to high maternal nurturance predicted low depressive symptoms among individuals carrying the T/T or T/C genotypes, but not among those carrying the C/C genotype. Likewise, high parental SES predicted low adulthood harm avoidance in individuals carrying the T/T or T/C genotype, but not in C/C-genotype carriers. Individuals carrying the T/T or T/C genotype were also sensitive to urban/rural residence, such that they had lower depressive symptoms in urban than in rural areas, whereas those carrying the C/C genotype were not sensitive to urban/rural residence difference. HTR2A did not moderate the influence of social support. TheA779C/A218C haplotype of the TPH1 gene was not involved in the association between childhood environment and adulthood outcomes. However, individuals carrying A alleles of the TPH1 haplotype were more vulnerable to the lack of adulthood social support in terms of high depressive symptoms than their counterparts carrying no A alleles. Furthermore, individuals living in remote rural areas and carrying the A/A haplotype had higher depressive symptoms than those carrying other genotypes of the TPH1. The findings suggest that the HTR2A and TPH1 genes may be involved in the development of depression by influencing individual s sensitivity to depressogenic environmental influences.

GDNF family receptors in peripheral target innervation and hormone production

Glial cell line-derived neurotrophic factor (GDNF) family ligands: GDNF, neurturin, persephin and artemin, signal through a receptor tyrosine kinase Ret by binding first to a co-receptor (GFRα1-4) that is attached to the plasma membrane. The GDNF family factors can support the survival of various peripheral and central neuronal populations and have important functions also outside the nervous system, especially in kidney development. Activating mutations in the RET gene cause tumours in neuroendocrine cells, whereas inactivating mutations in RET are found in patients with Hirschsprung s disease (HSCR) characterized by loss of ganglionic cells along the intestine. The aim of this study was to examine the in vivo functions of neurturin receptor GFRα2 and persephin receptor GFRα4 using knockout (KO) mice. Mice lacking GFRα2 grow poorly after weaning and have deficits in parasympathetic and enteric innervation. This study shows that impaired secretion of the salivary glands and exocrine pancreas contribute to growth retardation in GFRα2-KO mice. These mice have a reduced number of intrapancreatic neurons and decreased cholinergic innervation of the exocrine pancreas as well as reduced excitatory fibres in the myenteric plexus of the small intestine. This study also demonstrates that GFRα2-mediated Ret signalling is required for target innervation and maintenance of soma size of sympathetic cholinergic neurons and sensory nociceptive IB4-binding neurons. Furthermore, lack of GFRα2 in mice results in deficient perception of temperatures above and below thermoneutrality and in attenuated inflammatory pain response. GFRα4 is co-expressed with Ret predominantly in calcitonin-producing thyroid C-cells in the mouse. In this study GFRα4-deficient mice were generated. The mice show no gross developmental deficits and have a normal number of C-cells. However, young but not adult mice lacking GFRα4 have a lower production of calcitonin in thyroid tissue and consequently, an increased bone formation rate. Thus, GFRα4/Ret signalling may regulate calcitonin production. In conclusion, this study reveals that GFRα2/Ret signalling is crucial for the development and function of specific components of the peripheral nervous system and that GFRα4-mediated Ret signalling is required for controlling transmitter synthesis in thyroid C-cells.

Zebrafish as a model of Parkinson's disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease among the elderly. Its etiology is unknown and no disease-modifying drugs are available. Thus, more information concerning its pathogenesis is needed. Among other genes, mutated PTEN-induced kinase 1 (PINK1) has been linked to early-onset and sporadic PD, but its mode of action is poorly understood. Most animal models of PD are based on the use of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP is metabolized to MPP+ by monoamine oxidase B (MAO B) and causes cell death of dopaminergic neurons in the substantia nigra in mammals. Zebrafish has been a widely used model organism in developmental biology, but is now emerging as a model for human diseases due to its ideal combination of properties. Zebrafish are inexpensive and easy to maintain, develop rapidly, breed in large quantities producing transparent embryos, and are readily manipulated by various methods, particularly genetic ones. In addition, zebrafish are vertebrate animals and results derived from zebrafish may be more applicable to mammals than results from invertebrate genetic models such as Drosophila melanogaster and Caenorhabditis elegans. However, the similarity cannot be taken for granted. The aim of this study was to establish and test a PD model using larval zebrafish. The developing monoaminergic neuronal systems of larval zebrafish were investigated. We identified and classified 17 catecholaminergic and 9 serotonergic neuron populations in the zebrafish brain. A 3-dimensional atlas was created to facilitate future research. Only one gene encoding MAO was found in the zebrafish genome. Zebrafish MAO showed MAO A-type substrate specificity, but non-A-non-B inhibitor specificity. Distribution of MAO in larval and adult zebrafish brains was both diffuse and distinctly cellular. Inhibition of MAO during larval development led to markedly elevated 5-hydroxytryptamine (serotonin, 5-HT) levels, which decreased the locomotion of the fish. MPTP exposure caused a transient loss of cells in specific aminergic cell populations and decreased locomotion. MPTP-induced changes could be rescued by the MAO B inhibitor deprenyl, suggesting a role for MAO in MPTP toxicity. MPP+ affected only one catecholaminergic cell population; thus, the action of MPP+ was more selective than that of MPTP. The zebrafish PINK1 gene was cloned in zebrafish, and morpholino oligonucleotides were used to suppress its expression in larval zebrafish. The functional domains and expression pattern of zebrafish PINK1 resembled those of other vertebrates, suggesting that zebrafish is a feasible model for studying PINK1. Translation inhibition resulted in cell loss of the same catecholaminergic cell populations as MPTP and MPP+. Inactivation of PINK1 sensitized larval zebrafish to subefficacious doses of MPTP, causing a decrease in locomotion and cell loss in one dopaminergic cell population. Zebrafish appears to be a feasible model for studying PD, since its aminergic systems, mode of action of MPTP, and functions of PINK1 resemble those of mammalians. However, the functions of zebrafish MAO differ from the two forms of MAO found in mammals. Future studies using zebrafish PD models should utilize the advantages specific to zebrafish, such as the ability to execute large-scale genetic or drug screens.

Interactions of nandrolone and psychostimulant drugs on central monoaminergic systems

It has been hypothesized that abuse of supra-therapeutic doses of anabolic androgenic steroids (AASs) can lead to dependence and function as a gateway to abuse of other drugs. This is supported by behavioral studies on animal models and psychiatric evaluations of human subjects, although their neurochemical effects remain largely unknown. A large body of evidence suggests that the ability of the drugs to induce a strong elevation of extracellular dopamine (DA) levels in the nucleus accumbens (NAc), especially, plays a crucial role in their reinforcing effects. -- This study had four main aims. The first was to explore the effects of nandrolone decanoate on dopaminergic and serotonergic activities in the brains of rats. The second aim was to assess whether or not nandrolone pre-exposure modulates the acute neurochemical and behavioral effects of psychostimulant drugs in experimental animals. The third was to investigate if the AAS-pre-treatment induced changes in brain reward circuitry are reversible. And the fourth main goal was to evaluate the role of androgen and estrogen receptors in the modulation of the dopaminergic and serotonergic effects of acute injections of stimulant drugs by sub-chronic nandrolone treatment. The results showed that nandrolone decanoate at doses, high enough to induce erythropoiesis, significantly increased the levels of DOPAC and 5-HT in the cerebral cortex. Co-administration of AAS and psychostimulant drugs showed that the increase in extracellular DA and 5-HT concentration evoked by amphetamine, MDMA and cocaine in the NAc was attenuated dose-dependently by pretreatment with nandrolone. Nandrolone pre-exposure also attenuated the ability of stimulants to cause increased stereotyped behavior and locomotor activity. Despite the significant decrease in nandrolone concentration in blood, the attenuation of cocaine’s effects remained unchanged after a fairly long period without nandrolone, suggesting that nandrolone effects could be long lasting. Blockade of androgen receptors with flutamide abolished the attenuating effect of nandrolone pretreatment on amphetamine-induced elevation of extracellular DA concentration. --- In conclusion, the results show that AAS-pretreatment is able to inhibit the reward-related neurochemical and behavioral effects of amphetamine, MDMA and cocaine in experimental animals. Furthermore, it seems that these effects could be long lasting and it appears that the ability of nandrolone to modulate reward-related effects of stimulants is dependent on activation of androgen receptors.

Microneurovascular free muscle transfer with cross-over nerve grafts in facial reanimation

Microneurovascular free muscle transfer with cross-over nerve grafts in facial reanimation Loss of facial symmetry and mimetic function as seen in facial paralysis has an enormous impact on the psychosocial conditions of the patients. Patients with severe long-term facial paralysis are often reanimated with a two-stage procedure combining cross-facial nerve grafting, and 6 to 8 months later with microneurovascular (MNV) muscle transfer. In this thesis, we recorded the long-term results of MNV surgery in facial paralysis and observed the possible contributing factors to final functional and aesthetic outcome after this procedure. Twenty-seven out of forty patients operated on were interviewed, and the functional outcome was graded. Magnetic resonance imaging (MRI) of MNV muscle flaps was done, and nerve graft samples (n=37) were obtained in second stage of the operation and muscle biopsies (n=18) were taken during secondary operations.. The structure of MNV muscles and nerve grafts was evaluated using histological and immunohistochemical methods ( Ki-67, anti-myosin fast, S-100, NF-200, CD-31, p75NGFR, VEGF, Flt-1, Flk-1). Statistical analysis was performed. In our studies, we found that almost two-thirds of the patients achieved good result in facial reanimation. The longer the follow-up time after muscle transfer the weaker was the muscle function. A majority of the patients (78%) defined their quality of life improved after surgery. In MRI study, the free MNV flaps were significantly smaller than originally. A correlation was found between good functional outcome and normal muscle structure in MRI. In muscle biopsies, the mean muscle fiber diameter was diminished to 40% compared to control values. Proliferative activity of satellite cells was seen in 60% of the samples and it tended to decline with an increase of follow-up time. All samples showed intramuscular innervation. Severe muscle atrophy correlated with prolonged intraoperative ischaemia. The good long-term functional outcome correlated with dominance of fast fibers in muscle grafts. In nerve grafts, the mean number of viable axons amounted to 38% of that in control samples. The grafted nerves characterized by fibrosis and regenerated axons were thinner than in control samples although they were well vascularized. A longer time between cross facial nerve grafting and biopsy sampling correlated with a higher number of viable axons. P75Nerve Growth Factor Receptor (p75NGFR) was expressed in every nerve graft sample. The expression of p75NGFR was lower in older than in younger patients. A high expression of p75NGFR was often seen with better function of the transplanted muscle. In grafted nerve Vascular Endothelial Growth Factor (VEGF) and its receptors were expressed in nervous tissue. In conclusion, most of the patients achieved good result in facial reanimation and were satisfied with the functional outcome. The mimic function was poorer in patients with longer follow-up time. MRI can be used to evaluate the structure of the microneurovascular muscle flaps. Regeneration of the muscle flaps was still going on many years after the transplantation and reinnervation was seen in all muscle samples. Grafted nerves were characterized by fibrosis and fewer, thinner axons compared to control nerves although they were well vascularized. P75NGFR and VEGF were expressed in human nerve grafts with higher intensity than in control nerves which is described for the first time.

FGF signaling in neurogenesis and patterning of the developing midbrain and anterior hindbrain

Embryonic midbrain and hindbrain are structures which will give rise to brain stem and cerebellum in the adult vertebrates. Brain stem contains several nuclei which are essential for the regulation of movements and behavior. They include serotonin-producing neurons, which develop in the hindbrain, and dopamine-producing neurons in the ventral midbrain. Degeneration and malfunction of these neurons leads to various neurological disorders, including schizophrenia, depression, Alzheimer s, and Parkinson s disease. Thus, understanding their development is of high interest. During embryogenesis, a local signaling center called isthmic organizer regulates the development of midbrain and anterior hindbrain. It secretes peptides belonging to fibroblast growth factor (FGF) and Wingless/Int (Wnt) families. These factors bind to their receptors in the surrounding tissues, and activate various downstream signaling pathways which lead to alterations in gene expression. This in turn affects the various developmental processes in this region, such as proliferation, survival, patterning, and neuronal differentiation. In this study we have analyzed the role of FGFs in the development of midbrain and anterior hindbrain, by using mouse as a model organism. We show that FGF receptors cooperate to receive isthmic signals, and cell-autonomously promote cell survival, proliferation, and maintenance of neuronal progenitors. FGF signaling is required for the maintenance of Sox3 and Hes1 expression in progenitors, and Hes1 in turn suppresses the activity of proneural genes. Loss of Hes1 is correlated with increased cell cycle exit and premature neuronal differentiation. We further demonstrate that FGF8 protein forms an antero-posterior gradient in the basal lamina, and might enter the neuronal progenitors via their basal processes. We also analyze the impact of FGF signaling on the various neuronal nuclei in midbrain and hindbrain. Rostral serotonergic neurons appear to require high levels of FGF signaling in order to develop. In the absence of FGF signaling, these neurons are absent. We also show that embryonic meso-diencephalic dopaminergic domain consists of two populations in the anterior-posterior direction, and that these populations display different molecular profiles. The anterior diencephalic domain appears less dependent on isthmic FGFs, and lack several genes typical of midbrain dopaminergic neurons, such as Pitx3 and DAT. In Fgfr compound mutants, midbrain dopaminergic neurons begin to develop but soon adopt characteristics which highly resemble those of diencephalic dopaminergic precursors. Our results indicate that FGF signaling regulates patterning of these two domains cell-autonomously.