Rotenone decreases intracellular aldehyde dehydrogenase activity: implications for the pathogenesis of Parkinson's disease

Repeated systemic administration of the mitochondrial complex I inhibitor rotenone produces a rodent model of Parkinson's disease (PD). Mechanisms of relatively selective rotenone‐induced damage to nigrostriatal dopaminergic neurons remain incompletely understood. According to the ‘catecholaldehyde hypothesis,’ buildup of the autotoxic dopamine metabolite 3,4‐dihydroxyphenylacetaldehyde (DOPAL) contributes to PD pathogenesis. Vesicular uptake blockade increases DOPAL levels, and DOPAL is detoxified mainly by aldehyde dehydrogenase (ALDH). We tested whether rotenone interferes with vesicular uptake and intracellular ALDH activity. Endogenous and F‐labeled catechols were measured in PC12 cells incubated with rotenone (0–1000 nM, 180 min), without or with F‐dopamine (2 μM) to track vesicular uptake and catecholamine metabolism. Rotenone dose dependently increased DOPAL, F‐DOPAL, and 3,4‐dihydroxyphenylethanol (DOPET) levels while decreasing dopamine and 3,4‐dihydroxyphenylacetic acid (DOPAC) levels and the ratio of dopamine to the sum of its deaminated metabolites. In test tubes, rotenone did not affect conversion of DOPAL to DOPAC by ALDH when NAD⁺ was supplied, whereas the direct‐acting ALDH inhibitor benomyl markedly increased DOPAL and decreased DOPAC concentrations in the reaction mixtures. We propose that rotenone builds up intracellular DOPAL by decreasing ALDH activity and attenuating vesicular sequestration of cytoplasmic catecholamines. The results provide a novel mechanism for selective rotenone‐induced toxicity in dopaminergic neurons.

     

Tyrosine Hydroxylase mRNA Expression by Dopaminergic Neurons in Culture: Effect of 1 -Methyl-4-Phenylpyridinium Treatment

To enable us to study expression of tyrosine hydroxylase [TH; tyrosine 3-monooxygenase; L-tyrosine tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] as a measure of dopaminergic neuron function in future experiments, methods were developed to quantify TH mRNA levels in cultures of dopaminergic mesencephalic cells. The model of selective dopaminergic toxicity of 1-methyl-4-phenylpyridinium (MPP+) was used to verify the specificity of our methods. Fetal (embryonic day 15) rat ventral mesencephalic cell cultures were treated with 15 microM MPP+ for 48 h, conditions previously shown to reduce the number of TH-immunoreactive neurons, TH activity, and dopamine uptake to 5-10% of control values. This treatment decreased the number of neurons labeled by TH in situ hybridization to 9% of untreated controls and caused a strong reduction of the abundance of TH mRNA in Northern blots. Our findings establish TH mRNA expression as a parameter for future studies of toxic and trophic effects on cultured dopaminergic neurons, and they support the view that MPP+ destroys dopaminergic neurons.     

Oxidation of 3,4-dihydroxyphenylacetaldehyde, a toxic dopaminergic metabolite, to a semiquinone radical and an ortho-quinone

The oxidation and toxicity of dopamine is believed to contribute to the selective neurodegeneration associated with Parkinson disease. The formation of reactive radicals and quinones greatly contributes to dopaminergic toxicity through a variety of mechanisms. The physiological metabolism of dopamine to 3,4-dihydroxyphenylacetaldehyde (DOPAL) via monoamine oxidase significantly increases its toxicity. To more adequately explain this enhanced toxicity, we hypothesized that DOPAL is capable of forming radical and quinone species upon oxidation. Here, two unique oxidation products of DOPAL are identified. Several different oxidation methods gave rise to a transient DOPAL semiquinone radical, which was characterized by electron paramagnetic resonance spectroscopy. NMR identified the second oxidation product of DOPAL as the ortho-quinone. Also, carbonyl hydration of DOPAL in aqueous media was evident via NMR. Interestingly, the DOPAL quinone exists exclusively in the hydrated form. Furthermore, the enzymatic and chemical oxidation of DOPAL greatly enhance protein cross-linking, whereas auto-oxidation results in the production of superoxide. Also, DOPAL was shown to be susceptible to oxidation by cyclooxygenase-2 (COX-2). The involvement of this physiologically relevant enzyme in both oxidative stress and Parkinson disease underscores the potential importance of DOPAL in the pathogenesis of this condition.     

Central dopaminergic and serotoninergic systems in the regulation of adrenal tyrosine hydroxylase.

Administration of the dopamine receptor agonists apomorphine, piribedil and bromocryptine caused an increase in adrenal tyrosine hydroxylase (TH; tyrosine-3-monooxygenase, EC 1.14.16.2) which could be partially abolished by prior injection of the dopamine blocker haloperidol. Injection of L-dihydroxyphenylalanine, along with the decarboxylase inhibitor carbidopa, also led to a highly significant increase in adrenal TH activity. Intraventricular injection of 5,7-dihydroxytryptamine (DHT), which destroys serotonin neurons, doubled adrenal TH activity in both normal and hypophysectomized rats. Splanchnicotomy abolished this effect of DHT. The increase in enzyme activity mediated by DHT could be partially prevented by peripheral administration of L-5-hydroxytryptophan together with carbidopa. Blockade of serotoninergic functions with the antagonist methiothepin also increased adrenal TH activity. The interrelationship between the dopamine and the presumed serotonin system was investigated. Intraventricular injection of 6-hydroxydopamine partially prevented the DHT-induced increase in adrenal TH activity. Administration of haloperidol to DHT-treated rats had the same effect. This suggests that an intact dopaminergic system is required. When DHT and either apomorphine or piribedil were adminstered simultancously the dopamine agonist-induced increase was potentiated. An intact serotoninergic system is therefore not required for dopamine function. Thus, the increase in adrenal TH activity is associated with either stimulation of central dopamine receptors or destruction of serotonin neurons. It is suggested that dopaminergic and serotoninergic systems are involved in the regulation of adrenal TH and that these systems have net excitatory and inhibitory roles, respectively. Furthermore, the present evidence favors the view that the interaction between the two systems is sequential, with the serotonin system preceding the dopamine one.     

N-Acetylcysteine Prevents the Increase in Spontaneous Oxidation of Dopamine During Monoamine Oxidase Inhibition in PC12 Cells

The catecholaldehyde hypothesis for the pathogenesis of Parkinson’s disease proposes that the deaminated dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) is toxic to nigrostriatal dopaminergic neurons. Inhibiting monoamine oxidase (MAO) should therefore slow the disease progression; however, MAO inhibition increases spontaneous oxidation of dopamine, as indicated by increased 5-S-cysteinyl-dopamine (Cys-DA) levels, and the oxidation products may also be toxic. This study examined whether N-acetylcysteine (NAC), a precursor of the anti-oxidant glutathione, attenuates the increase in Cys-DA production during MAO inhibition. Rat pheochromocytoma PC12 cells were incubated with NAC, the MAO-B inhibitor selegiline, or both. Selegiline decreased DOPAL and increased Cys-DA levels (p?<?0.0001 each). Co-incubation of NAC at pharmacologically relevant concentrations (1–10 µM) with selegiline (1 µM) attenuated or prevented the Cys-DA response to selegiline, without interfering with the selegiline-induced decrease in DOPAL production or inhibiting tyrosine hydroxylation. NAC therefore mitigates the increase in spontaneous oxidation of dopamine during MAO inhibition.

     

Does serotonin deficit mediate susceptibility to ADHD?

The onset of attention-deficit-hyperactivity-disorder (ADHD) in childhood is characterized by developmentally inappropriate levels of hyperactivity, impulsivity and inattention. A chronic deficit of serotonin (5-HT) at the synapse may trigger symptoms of ADHD. This review focuses on neuro-anatomical, experimental and clinical pharmacological evidence, as well as the genetic underpinnings of serotoninergic involvement in the etiology of ADHD. Neuro-anatomical investigations suggest that serotonin through the orbitofrontal–striatal circuitry may regulate behavioral domains of hyperactivity and impulsivity in ADHD. Studies from animal models of ADHD indicate intimate interplay between 5-HT and dopaminergic neurotransmission. Selective serotonin re-uptake inhibitors, as also non-stimulant drugs acting on the 5-HT system are, however, clinically effective. They impart less severe side effects in patients with no risk of addiction. Oral administration of l-tryptophan, the amino acid precursor of 5-HT, significantly alleviates ADHD symptoms. Given the multifactorial nature of ADHD, candidate gene and genome-wide association studies have suggested that serotoninergic gene variants are associated with increased risk of ADHD with each locus individually exerting a modest effect on overall risk.     

Selective dopaminergic vulnerability: 3,4-dihydroxyphenylacetaldehyde targets mitochondria

Parkinson's disease (PD) is a major cause of age-related morbidity and mortality, present in nearly 1% of individuals at ages 70-79 and approximately 2.5% of individuals at age 85. L-DOPA (L-dihydroxyphenylalanine), which is metabolized to dopamine by dopa decarboxylase, is the primary therapy for PD, but may also contribute to disease progression. Association between mitochondrial dysfunction, monoamine oxidase (MAO) activity, and dopaminergic neurotoxicity has been repeatedly observed, but the mechanisms underlying selective dopaminergic neuron depletion in aging and neurodegenerative disorders remain unclear. We now report that 3,4-dihydroxyphenylacetaldehyde (DOPAL), the MAO metabolite of dopamine, is more cytotoxic in neuronally differentiated PC12 cells than dopamine and several of its metabolites. In isolated, energetically compromised mitochondria, physiological concentrations of DOPAL induced the permeability transition (PT), a trigger for cell death. Dopamine was > 1000-fold less potent. PT inhibitors protected both mitochondria and cells against DOPAL. Sensitivity to DOPAL was reduced > or = 30-fold in fully energized mitochondria, suggesting that mitochondrial respiration may increase resistance to PT induction by the endogenous DOPAL in the substantia nigra. These data provide a potential mechanism of action for L-DOPA-mediated neurotoxicity and suggest two potentially interactive mechanisms for the selective vulnerability of neurons exposed to dopamine.     

Behavioural phenotyping of sodium-myo-inositol cotransporter heterozygous knockout mice with reduced brain inositol

Inositol plays a key role in dopamine, serotonin, noradrenaline and acetylcholine neurotransmission, and inositol treatment is reported to have beneficial effects in depression and anxiety. Therefore, a reduction in brain intracellular inositol levels could be a cause of some psychiatric disorders, such as depression or anxiety. To determine the behavioural consequences of inositol depletion, we studied the behaviour of sodium-dependent myo-inositol cotransporter-1 heterozygous knockout mice. In heterozygous mice, free inositol levels were reduced by 15% in the frontal cortex and by 25% in the hippocampus, but they did not differ from their wild-type littermates in cholinergic-mediated lithium-pilocarpine seizures, in the apomorphine-induced stereotypic climbing model of dopaminergic system function, in the Porsolt forced-swimming test model of depression, in amphetamine-induced hyperactivity, or in the elevated plus-maze model of anxiety. Reduction of brain inositol by more than 25% may be required to elicit neurobehavioural effects.     

Alterations in the Levels of Monoamines in Discrete Brain Regions of Clomipramine-Induced Animal Model of Endogenous Depression

It has been hypothesized that the dysfunction of the serotonergic and catecholaminergic neurotransmission is involved in the pathogenesis of depression. These hypotheses are being tested in a novel rat model of depression developed by the treatment of antidepressant-clomipramine neonataly from postnatal day 8 to 21. After the attainment of adulthood, these rats mimicked the features of the human endogenous depression showing significant decrease in the aggressive behavior and food intake. Biogenic amine estimations in these rats revealed that the levels of serotonin and noradrenaline were decreased significantly (P < 0.001) in frontal cortex, hippocampus, brain stem, septum and hypothalamus, while the levels of dopamine were decreased significantly (P < 0.001) only in the hippocampus compared to normal control and vehicle treated groups of rats. Our results demonstrate the dysfunction of serotonergic and noradrenergic neurotransmission, with lesser involvement of dopaminergic neurotransmission in the clomipramine induced experimental model of depression.     

The neurotoxicity of DOPAL: behavioral and stereological evidence for its role in Parkinson disease pathogenesis

Background

The etiology of Parkinson disease (PD) has yet to be fully elucidated. We examined the consequences of injections of 3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic metabolite of dopamine, into the substantia nigra of rats on motor behavior and neuronal survival.

Methods/Principal Findings

A total of 800 nl/rat of DOPAL (1 µg/200 nl) was injected stereotaxically into the substantia nigra over three sites while control animals received similar injections of phosphate buffered saline. Rotational behavior of these rats was analyzed, optical density of striatal tyrosine hydroxylase was calculated, and unbiased stereological counts of the substantia nigra were made. The rats showed significant rotational asymmetry ipsilateral to the lesion, supporting disruption of dopaminergic nigrostriatal projections. Such disruption was verified since the density of striatal tyrosine hydroxylase decreased significantly (p<0.001) on the side ipsilateral to the DOPAL injections when compared to the non-injected side. Stereological counts of neurons stained for Nissl in pars compacta of the substantia nigra significantly decreased (p<0.001) from control values, while counts of those in pars reticulata were unchanged after DOPAL injections. Counts of neurons immunostained for tyrosine hydroxylase also showed a significant (p = 0.032) loss of dopaminergic neurons. In spite of significant loss of dopaminergic neurons, DOPAL injections did not induce significant glial reaction in the substantia nigra.

Conclusions

The present study provides the first in vivo quantification of substantia nigra pars compacta neuronal loss after injection of the endogenous toxin DOPAL. The results demonstrate that injections of DOPAL selectively kills SN DA neurons, suggests loss of striatal DA terminals, spares non-dopaminergic neurons of the pars reticulata, and triggers a behavioral phenotype (rotational asymmetry) consistent with other PD animal models. This study supports the “catecholaldehyde hypothesis” as an important link for the etiology of sporadic PD.     

Whole blood serotonin and platelet activation in depressed post-myocardial infarction patients

Depression is an independent risk factor for post myocardial infarction (MI) mortality. Abnormalities in platelet function have been proposed as one of the mechanisms involved in increased cardiovascular risk among patients with depression post-MI. Depression in somatically healthy patients has been associated with increased platelet activation. Some but not all studies showed changes in blood serotonin level. Increased platelet activation and blood serotonin level have been associated with increased risk of cardiac events in patients with MI. The goal of this study was to investigate whether 1) depressed post-MI patients have higher markers of platelet activation as measured by plasma levels of beta-thromboglobulin (betaTG), platelet factor 4 (PF4) and soluble CD40 ligand (sCD40L) and higher serotonin (5-HT) levels than non-depressed post-MI patients and 2) treatment with the antidepressant mirtazapine decreases platelet activation. In this study, 25 depressed post-MI patients were asked for blood collection before start as well as after 8 weeks treatment with mirtazapine or placebo. The control group (n=22) consisted of non-depressed post-MI patients, matched for age, gender and time elapsed since MI. Plasma levels of betaTG, PF4 and sCD40L were not statistically different between the groups, but 5-HT levels were significantly higher in depressed patients. Treatment with mirtazapine resulted in a non-significant decrease in betaTG and PF4 and platelet 5-HT levels. Platelet and whole blood 5-HT, but not platelet activation was significantly increased in depressed post-MI patients. Treatment with mirtazapine showed a non-significant decrease in platelet activation and platelet 5-HT.     

Genetic Prediction of Antidepressant Drug Response and Nonresponse in Korean Patients

Genetic polymorphism contributes to variation in response to drug treatment of depression. We conducted three independent 6-week treatment studies in outpatients with major depressive disorder (MDD) to develop a pharmacogenomic model predicting response and nonresponse. We screened candidate genomic markers for association with response to selective serotonin reuptake inhibitors (SSRIs). No patients had received any antidepressant drug treatment in the current episode of depression. Outcome evaluation was blinded to drug and genotype data. The prediction model derived from a development sample of 239 completer cases treated with SSRIs comprised haplotypes and polymorphisms related to serotonin synthesis, serotonin transport, glutamate receptors, and GABA synthesis. The model was evaluated prospectively for prediction of outcome in a validation sample of 176 new SSRI-treated completer cases. The model gave a prediction in 60% of these cases. Predictive values were 85% for predicted responders and 86% for predicted nonresponders, compared to prior probabilities of 66% for observed response and 34% for observed nonresponse in those cases (both P<0.001). Convergent cross-validation was obtained through failure of the model to predict outcomes in a third independent sample of 189 completer cases who received non-SSRI antidepressants. We suggest proof of principle for genetic guidance to use or avoid SSRIs in a majority of Korean depressed patients.     

Evidence for involvement of protein kinase in the activation by adenosine 3':5'-monophosphate of brain tyrosine 3-monooxygenase.

Addition of adenosine 3':5'-monophosphate (cAMP) to high speed supernatant preparations obtained from rat brain caused a 3- to 4-fold increase in tyrosine 3-monooxygenase (tyrosine hydroxylase) activity. The tyrosine 3-monooxygenase remained in an activated state upon removal of the cAMP by passing the enzyme through a Sephadex G-25 column. Substances which inhibit cAMP-dependent protein kinase, namely, EDTA, ADP, and adenosine, and protein kinase modulator, each antagonized the activation of tyrosine 3-monooxygenase produced by cAMP. Furthermore, addition of partially purified brain cAMP-dependent protein kinase caused a several-fold increase in tyrosin 3-monooxygenase activity. The activation of tyrosine 3-monooxygenase by added cAMP and protein kinase required the presence of ATP and Mg-2+. These data suggests that the cAMP activation of tyrosine 3-monooxygenase may be mediated by a cAMP-dependent protein kinase.     

Pharmacological manipulation of serotonin levels in the nervous system of the opisthobranch mollusc Tritonia diomedea

Serotonin-related disorders can be treated by manipulating serotonin synthesis with the serotonin precursor 5-hydroxytryptophan (5-HTP) or other pharmacological agents. The mollusc Tritonia diomedea is a model for investigating the effects of altering serotonin content on the functions of identified neurons. We used high-performance liquid chromatography and immunohistochemistry to examine the amount and localization of 5-HTP, serotonin, and the serotonin breakdown product 5-hydroxyindolacetic acid (5-HIAA) in the Tritonia brain after various pharmacological treatments. Exposure to 5-HTP (2 mM for 30 min-1 h) caused an immediate and massive increase in total 5-HTP content, which lasted more than 20 h, and the widespread appearance of 5-HTP immunoreactivity in neurons. Serotonin levels rose gradually, but only a restricted number of additional neurons displayed serotonin immunoreactivity. 5-HTP treatment also caused an increase in the total amount of 5-HIAA and the appearance of 5-HIAA immunoreactivity throughout the brain. Treatment with the synthesis cofactor tetrahydrobiopterin, the initial precursor tryptophan, or serotonin itself had no persistent effect on total serotonin content. The amino acid decarboxylase inhibitor hydroxybenzylhydrazine (NSD-1015) also had no effect on the total serotonin content, although it caused an accumulation of 5-HTP. Thus, serotonin levels in the brain of T. diomedea appear to be maintained by a homeostatic mechanism that can be disrupted by 5-HTP.     

Oligomerization and Membrane-binding Properties of Covalent Adducts Formed by the Interaction of α-Synuclein with the Toxic Dopamine Metabolite 3,4-Dihydroxyphenylacetaldehyde (DOPAL)

Oxidative deamination of dopamine produces the highly toxic aldehyde 3,4-dihydroxyphenylacetaldehyde (DOPAL), enhanced production of which is found in post-mortem brains of Parkinson disease patients. When injected into the substantia nigra of rat brains, DOPAL causes the loss of dopaminergic neurons accompanied by the accumulation of potentially toxic oligomers of the presynaptic protein α-synuclein (aS), potentially explaining the synergistic toxicity described for dopamine metabolism and aS aggregation. In this work, we demonstrate that DOPAL interacts with aS via formation of Schiff-base and Michael-addition adducts with Lys residues, in addition to causing oxidation of Met residues to Met-sulfoxide. DOPAL modification leads to the formation of small aS oligomers that may be cross-linked by DOPAL. Both monomeric and oligomeric DOPAL adducts potently inhibit the formation of mature amyloid fibrils by unmodified aS. The binding of aS to either lipid vesicles or detergent micelles, which results in a gain of α-helix structure in its N-terminal lipid-binding domain, protects the protein against DOPAL adduct formation and, consequently, inhibits DOPAL-induced aS oligomerization. Functionally, aS-DOPAL monomer exhibits a reduced affinity for small unilamellar vesicles with lipid composition similar to synaptic vesicles, in addition to diminished membrane-induced α-helical content in comparison with the unmodified protein. These results suggest that DOPAL could compromise the functionality of aS, even in the absence of protein oligomerization, by affecting the interaction of aS with lipid membranes and hence its role in the regulation of synaptic vesicle traffic in neurons.     

Biogenic aldehyde(s) derived from the action of monoamine oxidase may mediate the antidipsotropic effect of daidzin

Daidzin, a major active principle of an ancient herbal treatment for 'alcohol addiction', was first shown to suppress ethanol intake in Syrian golden hamsters. Since then this activity has been confirmed in Wistar rats, Fawn hooded rats, genetically bred alcohol preferring P rats and African green moneys under various experimental conditions, including two-level operant, two-bottle free-choice, limited access, and alcohol-deprivation paradigms. In vitro, daidzin is a potent and selective inhibitor of mitochondrial aldehyde dehydrogenase (ALDH-2). However, in vivo, it does not affect overall acetaldehyde metabolism in golden hamsters. Using isolated hamster liver mitochondria and 5-hydroxytryptamine (5-HT) and dopamine (DA) as the substrates, we demonstrated that daidzin inhibits the second but not the first step of the MAO/ALDH-2 pathway, the major pathway that catalyzes monoamine metabolism in mitochondria. Correlation studies using structural analogs of daidzin led to the hypothesis that the mitochondrial MAO/ALDH-2 pathway may be the site of action of daidzin and that one or more biogenic aldehydes such as 5-hydroxyindole-3-acetaldehyde (5-HIAL) and/or DOPAL derived from the action of monoamine oxidase (MAO) may be mediators of its antidipsotropic action.     

Biogenic aldehyde(s) derived from the action of monoamine oxidase may mediate the antidipsotropic effect of daidzin

Daidzin, a major active principle of an ancient herbal treatment for ‘alcohol addiction’, was first shown to suppress ethanol intake in Syrian golden hamsters. Since then this activity has been confirmed in Wistar rats, Fawn hooded rats, genetically bred alcohol preferring P rats and African green moneys under various experimental conditions, including two-level operant, two-bottle free-choice, limited access, and alcohol-deprivation paradigms. In vitro, daidzin is a potent and selective inhibitor of mitochondrial aldehyde dehydrogenase (ALDH-2). However, in vivo, it does not affect overall acetaldehyde metabolism in golden hamsters. Using isolated hamster liver mitochondria and 5-hydroxytryptamine (5-HT) and dopamine (DA) as the substrates, we demonstrated that daidzin inhibits the second but not the first step of the MAO/ALDH-2 pathway, the major pathway that catalyzes monoamine metabolism in mitochondria. Correlation studies using structural analogs of daidzin led to the hypothesis that the mitochondrial MAO/ALDH-2 pathway may be the site of action of daidzin and that one or more biogenic aldehydes such as 5-hydroxyindole-3-acetaldehyde (5-HIAL) and/or DOPAL derived from the action of monoamine oxidase (MAO) may be mediators of its antidipsotropic action.     

Genetic load is associated with hypothalamic–pituitary–adrenal axis dysregulation in macaques

Dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis pathway is associated with several neuropsychiatric disorders, including post‐traumatic stress disorder (PTSD), major depressive disorder (MDD), schizophrenia and alcohol abuse. Studies have demonstrated an association between HPA axis dysfunction and gene variants within the cortisol, serotonin and opioid signaling pathways. We characterized polymorphisms in genes linked to these three neurotransmitter pathways and tested their potential interactions with HPA axis activity, as measured by dexamethasone (DEX) suppression response. We determined the percent DEX suppression of adrenocorticotropic hormone (ACTH) and cortisol in 62 unrelated, male rhesus macaques. While DEX suppression of cortisol was robust amongst 87% of the subjects, ACTH suppression levels were broadly distributed from ?21% to 66%. Thirty‐seven monkeys from the high and low ends of the ACTH suppression distribution (18 ‘high’ and 19 ‘low’ animals) were genotyped at selected polymorphisms in five unlinked genes (rhCRH, rhTPH2, rhMAOA, rhSLC6A4 and rhOPRM). Associations were identified between three variants (rhCRH‐2610C>T, rhTPH2 2051A>C and rh5‐HTTLPR) and level of DEX suppression of ACTH. In addition, a significant additive effect of the ‘risk’ genotypes from these three loci was detected, with an increasing number of ‘risk’ genotypes associated with a blunted ACTH response (P = 0.0009). These findings suggest that assessment of multiple risk alleles in serotonin and cortisol signaling pathway genes may better predict risk for HPA axis dysregulation and associated psychiatric disorders than the evaluation of single gene variants alone.     

Corticotropin releasing factor induces anxiogenic locomotion in trout and alters serotonergic and dopaminergic activity

Corticotropin releasing factor (CRF) and serotonin (5-HT) are strongly linked to stress and anxiety in vertebrates. As a neuromodulator in the brain, CRF has anxiogenic properties often characterized by increased locomotion and stereotyped behavior in familiar environments. We hypothesized that expression of anxiogenic behavior in response to CRF will also be exhibited in a teleost fish. Rainbow trout were treated with intracerebroventricular (icv) injections of artificial cerebrospinal fluid (aCSF), 500 or 2000 ng ovine CRF, or not injected. Treatment with either dose of CRF elicited greater locomotion and pronounced head shaking behavior but did not influence water column position. Locomotor and head shaking behaviors may be analogous to the increased stereotypy evoked by icv CRF in rats and may reflect the expression of stress/anxiety behavior. Injection with either aCSF or CRF produced significant increases in plasma cortisol. The absence of behavioral changes in aCSF-injected fish suggests that the behavioral responses following CRF were not due to cortisol. Treatment with 2000 ng CRF significantly increased serotonin, 5-HIAA and dopamine concentrations in the subpallium and raphé and increased 5-HIAA in the preoptic hypothalamus (POA). Concurrent effects of CRF on central monoamines, locomotion and head shaking in trout suggest that anxiogenic properties of CRF are evolutionarily conserved. In addition, positive linear correlations between locomotion and serotonergic and dopaminergic function in the subpallium, POA and raphé nuclei suggest a locomotory function for these monoamines.