Axonal sprouting of noradrenergic locus coeruleus neurons following repeated stress and antidepressant treatment

Antidepressants escitalopram and venlafaxine up-regulate BDNF promoter IV but down-regulate neurite outgrowth in differentiating SH-SY5Y neurons

Antidepressants are used to treat depression and some anxiety disorders, including use in pregnant patients. The pharmacological actions of these drugs generally determine the uptake and metabolism of a series of neurotransmitters, such as serotonin, norepinephrine, or dopamine, along with an increase in BDNF expression. However, many aspects of antidepressant action remain unknown, particularly whether antidepressants interfere with normal neurodevelopment when taken by pregnant women. In order to reveal cellular and molecular implications crucial to the functioning of pathways related to antidepressant effects, we performed an investigation on neuronally differentiating human SH-SY5Y cells. To our knowledge, this is the first time human SH-SY5Y cells in cultures of purely neuronal cells induced by controlled differentiation with retinoic acid are followed by short-term 48-h exposure to 0.1-10 μM escitalopram or venlafaxine. Treatment with antidepressants (1 μM) did not affect the electrophysiological properties of SH-SY5Y cells. However, the percentage of mature neurons exhibiting voltage-gated sodium currents was substantially higher in cultures pre-treated with either antidepressant. After exposure to escitalopram or venlafaxine, we observed a concentration-dependent increase in activity-dependent BDNF promoter IV activation. The assessment of neurite metrics showed significant down-regulation of neurite outgrowth upon exposure to venlafaxine. Identified changes may represent links to molecular processes of importance to depression and be involved in neurodevelopmental alterations observed in postpartum children exposed to antidepressants antenatally.

Noradrenergic depletion causes sex specific alterations in the endocannabinoid system in the Murine prefrontal cortex

Brain endocannabinoids (eCB), acting primarily via the cannabinoid type 1 receptor (CB1r), are involved in the regulation of many physiological processes, including behavioral responses to stress. A significant neural target of eCB action is the stress-responsive norepinephrine (NE) system, whose dysregulation is implicated in myriad psychiatric and neurodegenerative disorders. Using Western blot analysis, the protein expression levels of a key enzyme in the biosynthesis of the eCB 2-arachidonoylglycerol (2-AG), diacylglycerol lipase-α (DGL-α), and two eCB degrading enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH) were examined in a mouse model that lacks the NE-synthesizing enzyme, dopamine β-hydroxylase (DβH-knockout, KO) and in rats treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4). In the prefrontal cortex (PFC), DGL-α protein expression was significantly increased in male and female DβH-KO mice (P < 0.05) compared to wild-type (WT) mice. DβH-KO male mice showed significant decreases in FAAH protein expression compared to WT male mice. Consistent with the DβH-KO results, DGL-α protein expression was significantly increased in male DSP-4-treated rats (P < 0.05) when compared to saline-treated controls. MGL and FAAH protein expression levels were significantly increased in male DSP-4 treated rats compared to male saline controls. Finally, we investigated the anatomical distribution of MGL and FAAH in the NE containing axon terminals of the PFC using immunoelectron microscopy. MGL was predominantly within presynaptic terminals while FAAH was localized to postsynaptic sites. These results suggest that the eCB system may be more responsive in males than females under conditions of NE perturbation, thus having potential implications for sex-specific treatment strategies of stress-related psychiatric disorders.

Norepinephrine and serotonin are required for vagus nerve stimulation directed cortical plasticity

Vagus nerve stimulation (VNS) paired with forelimb training drives robust, specific reorganization of movement representations in the motor cortex. This effect is hypothesized to be mediated by VNS-dependent engagement of neuromodulatory networks. VNS influences activity in the locus coeruleus (LC) and dorsal raphe nucleus (DRN), but the involvement of these neuromodulatory networks in VNS-directed plasticity is unknown. We tested the hypothesis that cortical norepinephrine and serotonin are required for VNS-dependent enhancement of motor cortex plasticity. Rats were trained on a lever pressing task emphasizing proximal forelimb use. Once proficient, all rats received a surgically implanted vagus nerve cuff and cortical injections of either immunotoxins to deplete serotonin or norepinephrine, or vehicle control. Following surgical recovery, rats received half second bursts of 0.8 mA or sham VNS after successful trials. After five days of pairing intracortical microstimulation (ICMS) was performed in the motor cortex contralateral to the trained limb. VNS paired with training more than doubled cortical representations of proximal forelimb movements. Depletion of either cortical norepinephrine or serotonin prevented this effect. The requirement of multiple neuromodulators is consistent with earlier studies showing that these neuromodulators regulate synaptic plasticity in a complimentary fashion.

Molecular mechanism of noradrenaline during the stress-induced major depressive disorder

Chronic stress-induced depression is a common hallmark of many psychiatric disorders with high morbidity rate. Stress-induced dysregulation of noradrenergic system has been implicated in the pathogenesis of depression. Lack of monoamine in the brain has been believed to be the main causative factor behind pathophysiology of major depressive disorder (MDD) and several antidepressants functions by increasing the monoamine level at the synapses in the brain. However, it is undetermined whether the noradrenergic receptor stimulation is critical for the therapeutic effect of antidepressant. Contrary to noradrenergic receptor stimulation, it has been suggested that the desensitization of β-adrenoceptor is involved in the therapeutic effect of antidepressant. In addition, enhanced noradrenaline (NA) release is central response to stress and thought to be a risk factor for the development of MDD. Moreover, fast acting antidepressant suppresses the hyperactivation of noradrenergic neurons in locus coeruleus (LC). However, it is unclear how they alter the firing activity of LC neurons. These inconsistent reports about antidepressant effect of NA-reuptake inhibitors (NRIs) and enhanced release of NA as a stress response complicate our understanding about the pathophysiology of MDD. In this review, we will discuss the role of NA in pathophysiology of stress and the mechanism of therapeutic effect of NA in MDD. We will also discuss the possible contributions of each subtype of noradrenergic receptors on LC neurons, hypothalamic-pituitary-adrenal axis (HPA-axis) and brain derived neurotrophic factor-induced hippocampal neurogenesis during stress and therapeutic effect of NRIs in MDD.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Altered expression of tyrosine hydroxylase in the locus coeruleus noradrenergic system in citalopram neonatally exposed rats and monoamine oxidase a knock out mice

In rodents, noradrenergic (NE) locus coeruleus (LC) neurons are well known to express tyrosine hydroxylase (TH) immunoreactivity. However, due to its very low enzyme activity, NE cortical fibers do not typically express TH immunoreactivity, thus dopamine-β-hydroxylase (DBH) immunoreactivity is commonly utilized as a marker for NE cortical fibers. In this study, we performed double and/or triple immunofluorescent staining using antibodies against TH, DBH, and/or norepinephrine transporter (NET) to investigate the altered NE TH expression of cortical fibers in citalopram (CTM)-exposed rats and monoamine oxidase (MAO) A knock out (KO) mice. We have noted the following novel findings: (1) neonatal exposure to the selective serotonin reuptake inhibitor (SSRI) CTM enhanced NE TH immunoreactive fibers throughout the entire neocortex, and a few of them appeared to be hypertrophic; (2) slightly enhanced NE cortical TH immunoreactive fibers were also noted in MAO A KO mice, and many of them revealed varicosities compared with the rather smooth NE cortical TH immunoreactive fibers in wild-type (WT) mice; (3) LC dendrites of MAO A KO mice exhibited beaded morphology compared with the smooth LC dendrites in WT mice. Our findings suggest that both genetic and environmental factors during early development may play a critical role in the regulation and proper function of NE TH expression in the neocortex.

Effects of postnatal isolation rearing and antidepressant treatment on the density of serotonergic and noradrenergic axons and depressive behavior in rats

The development of monoaminergic axons is affected by pharmacological and environmental manipulations during early periods of brain development. In addition, it has been proposed that changes in the density of monoaminergic axons are involved in the pathophysiology of depression. The present experiments examined the effects of neonatal treatment with antidepressants on the density of monoaminergic axons containing 5-HT or noradrenaline (NA) and depressive behavior in rats. In this study, clomipramine (CL) was used as an antidepressant, because a large amount of data has been accumulated on the effects of neonatal CL treatment on monoaminergic neurons and depressive behavior. It was also examined whether the effects of neonatal CL treatment could be further modified by environmental conditions. In the present experiments, postweaning isolation rearing (Iso) was examined as an environmental condition, because postweaning Iso is reported to change the density of 5-HT axons in the rat brain. Unexpectedly, neonatal CL treatment alone had no effect on the density of 5-HT or NA axons or depressive behavior. Postweaning social Iso rearing reduced the density of 5-HT axons in the central nucleus and basolateral nucleus of the amygdala and CA3 of the hippocampus. In the prelimbic area and infralimbic area of medial prefrontal cortex and the dentate gyrus of the hippocampus, the density of 5-HT axons was not affected by social Iso alone, but was reduced when animals were socially isolated after neonatal CL treatment. Postweaning Iso, but not neonatal CL treatment, increased immobility in the forced swim test in adolescence/early adulthood. These findings suggest that postweaning social Iso alters the density of monoaminergic axons, particularly 5-HT axons, and induces a possible model of depression, while neonatal CL treatment alone has no effect on the density of NA or 5-HT axons or depressive behavior in adolescence/early adulthood.

A pilot study of vagus nerve stimulation (VNS) for treatment-resistant anxiety disorders

BACKGROUND

Vagus nerve stimulation (VNS) is an effective anticonvulsant device and has shown antidepressant effects in chronic treatment resistant depression. Because the vagus nerve sends information to brain regions important in anxiety regulation (locus coeruleus, orbitofrontal cortex, insula, hippocampus and amygdala), this pathway might be involved in perceiving or manifesting various somatic and cognitive symptoms that characterize anxiety disorders. On the basis of this reasoning and reports of anxiolytic effects of VNS in patients treated for epilepsy and depression, we organized an open-label pilot acute trial of adjunctive VNS on top of stable medications, followed by long-term follow-up, to assess the safety and potential efficacy of VNS for patients with treatment resistant anxiety disorders.

METHODS

Eleven adult outpatients with treatment resistant obsessive-compulsive disorder (OCD), panic disorder (PD), or posttraumatic stress disorder (PTSD) were recruited. Patients had failed several medication trials as well as cognitive behavioral therapy (CBT). All patients were rated with the Hamilton Anxiety Scale (HAM-A) and the clinical global impressions improvement scale (CGI-I). Patients with OCD were also rated with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). Patients were maintained on their current psychotropic medications at fixed doses during the acute 12-week phase. Changes in medications and VNS stimulus parameters were allowed during the long-term follow-up. Response was defined as a 50% or greater improvement on the HAM-A for all patients and a 25% or greater improvement on the Y-BOCS for patients with OCD.

RESULTS

Eleven patients were recruited. Seven patients had a primary diagnosis of OCD, two had PTSD, and one had PD. One OCD patient changed their mind and was never implanted. One patient with OCD withdrew consent before the end of the acute phase, so long-term results were available for nine patients. Three patients were acute responders, based on the HAM-A, and there was some improvement in anxiety ratings over time (with statistically significant improvements at 14 of 18 quarters during long-term follow-up). Of the seven patients with OCD who received stimulation, three were acute responders, based on the Y-BOCS, and there was some improvement in Y-BOCS scores over time (with statistically significant improvements at 7 of 18 quarters during long-term follow-up). VNS was relatively well tolerated. Four years after implantation, four patients (diagnoses two OCD, one PD, one PTSD) were still receiving VNS with continued and sustained improvement in anxiety scores compared with their baseline scores.

CONCLUSIONS

These patients with treatment-resistant anxiety disorders generally tolerated VNS treatment, and there was evidence of acute and long-term improvement in some patients. These open data suggest that further double-blind studies assessing the VNS role in treating anxiety disorders, particularly OCD, may be warranted.

Administration of oral methylphenidate during adolescence prevents suppressive development of dopamine projections into prefrontal cortex and amygdala after an early pharmacological challenge in gerbils

The enduring effects of postweaning subchronic methylphenidate (MP) treatment and/or previous early preweaning methamphetamine (MA) application on dopamine (DA) fiber density were investigated in multiple cortical and subcortical areas of the gerbil brain. The study aimed to explore three questions: (1) is the development of DA fiber innervation in control animals sensitive to a clinically relevant subchronic treatment with MP? (2) Is the development of DA fiber innervation in the forebrain altered by a single early MA challenge? (3) If so, might the subsequent institution of a therapeutically relevant MP application scheme interfere with such early induced alternative developmental trajectories for DA fiber innervation? For this purpose, gerbils pretreated both with saline and MA (50 mg/kg, i.p.) on day 14 received either H(2)O or MP (5 mg/kg) orally on days 30 to 60. On day 90, DA fibers were immunohistochemically detected and quantified. As a result, MP on its own did not have any significant influence on the postnatal development of the DA fiber systems, whereas it prevented a previously MA triggered suppressive development of DA fiber innervation in the prefrontal cortex and amygdala complex (30% less fiber innervation in both areas). Thus, MP prevented previously initiated miswiring of DA fibers from actually being implemented in the gerbil forebrain. During earlier studies, rather complex miswiring has been documented in response to an early preweaning MA challenge. This miswiring was associated with functional deficits resembling some of the symptoms of patients with ADHD. Therefore, morphogenetic properties of MP need further attention.

Mitochondrial dysfunction as the molecular basis of bipolar disorder: therapeutic implications

Multiple lines of evidence, such as impaired energy metabolism in the brain detected by magnetic resonance spectroscopy, a possible role of maternal inheritance, co-morbidity with mitochondrial diseases, the effects of mood stabilisers on mitochondria, increased mitochondrial DNA (mtDNA) deletion in the brain, and association with mtDNA mutations/polymorphisms or nuclear-encoded mitochondrial genes, suggest that mitochondrial dysfunction is an important component of bipolar disorder. Global reduction of mitochondria-related gene expression in the postmortem brains of patients with bipolar disorder may also be an indicator, but such findings are affected by sample pH and thus need to be interpreted with caution. A recently developed animal model carrying mtDNA deletion in neurons suggested that accumulation of mtDNA deletions causes bipolar disorder-like phenotypes. The next step in the study of mitochondrial dysfunction in bipolar disorder should be clarification of how mitochondrial dysfunction, a nonspecific risk factor, can cause specific symptoms of bipolar disorder. Two hypothetical mechanisms are mtDNA neuroplasticity and nonvisual photoreception impairment. Further study of mitochondrial dysfunction in bipolar disorder is expected to be useful for the development of new mood stabilisers.

Age-dependent interactive changes in serotonergic and noradrenergic cortical axon terminals in F344 rats

In the frontal cortex of aging rats, we found an increase in sprouting of the noradrenergic (NA) axons originated from the locus coeruleus (LC). The serotonergic (5-HT) axons originating from the dorsal raphe (DR) share the same cortical area and their age-dependent changes and interactions with NA axons were still unclear. To compare quantitatively the extent of axonal sprouting of DR and LC neurons in the frontal cortex, we extracellularly recorded from both DR and LC neurons in the same animals and antidromically stimulated 32 cortical sites (a pair of stimulating electrodes was moved at 100-mum intervals from 500 to 2000 microm in depth). In addition, to examine the effects of degeneration of 5-HT axons on NA axons, and vice versa, we used specific neurotoxins for 5-HT (PCA) or NA (DSP-4) axons. We also used noradrenaline uptake inhibitor (maprotiline) to verify the effects of NA on degeneration of 5-HT axons. Results suggested that 5-HT axons sprouted between 15 and 17 months of age and noradrenaline accelerated the age-dependent change of 5-HT axons.

Locus coeruleus neurons originate in alar rhombomere 1 and migrate into the basal plate: Studies in chick and mouse embryos

We investigated in the mouse and chick the neuroepithelial origin and development of the locus coeruleus (LoC), the most important noradrenergic neuronal population in the brain. We first studied the topography of the developing LoC in the hindbrain, using as markers the key noradrenergic marker gene Dbh and the transcription factors Phox2a and Phox2b (upstream of Dbh). In both mouse and chicken, LoC neurons first appear arranged linearly along the middle one-third of the alar plate of rhombomere 1 (r1), collinear to a reference ventricular longitudinal band that early on expresses Phox2a and Phox2b in the alar plate of r2 and later expands to r1. Double-labeling experiments with LoC markers (Dbh or Phox2a) and either alar (Pax7 and Rnx3) or basal (Otp) genetic markers suggested that LoC cells migrate from their origin in the alar plate to a final position in the lateral basal plate. To corroborate these suggestions experimentally and determine the precise origin of the LoC, we fate mapped the LoC in the chick at stage HH11 by using quail-chick homotopic grafts. The experimental results confirmed that the LoC originates in the alar plate throughout the rostrocaudal extent of r1 and ruled out a rostrocaudal translocation. They also corroborated a ventralward tangential migration of LoC cells into the lateral basal plate, where the postmigratory LoC primordium is located. Comparisons with neighboring alar r1-derived cell populations established that LoC neurons originate outside the cerebellum, in a matrix area intercalated dorsoventrally between the sources of the prospective vestibular and trigeminal columns.

Brain plasticity and functional losses in the aged: scientific bases for a novel intervention

Aging is associated with progressive losses in function across multiple systems, including sensation, cognition, memory, motor control, and affect. The traditional view has been that functional decline in aging is unavoidable because it is a direct consequence of brain machinery wearing down over time. In recent years, an alternative perspective has emerged, which elaborates on this traditional view of age-related functional decline. This new viewpoint--based upon decades of research in neuroscience, experimental psychology, and other related fields--argues that as people age, brain plasticity processes with negative consequences begin to dominate brain functioning. Four core factors--reduced schedules of brain activity, noisy processing, weakened neuromodulatory control, and negative learning--interact to create a self-reinforcing downward spiral of degraded brain function in older adults. This downward spiral might begin from reduced brain activity due to behavioral change, from a loss in brain function driven by aging brain machinery, or more likely from both. In aggregate, these interrelated factors promote plastic changes in the brain that result in age-related functional decline. This new viewpoint on the root causes of functional decline immediately suggests a remedial approach. Studies of adult brain plasticity have shown that substantial improvement in function and/or recovery from losses in sensation, cognition, memory, motor control, and affect should be possible, using appropriately designed behavioral training paradigms. Driving brain plasticity with positive outcomes requires engaging older adults in demanding sensory, cognitive, and motor activities on an intensive basis, in a behavioral context designed to re-engage and strengthen the neuromodulatory systems that control learning in adults, with the goal of increasing the fidelity, reliability, and power of cortical representations. Such a training program would serve a substantial unmet need in aging adults. Current treatments directed at age-related functional losses are limited in important ways. Pharmacological therapies can target only a limited number of the many changes believed to underlie functional decline. Behavioral approaches focus on teaching specific strategies to aid higher order cognitive functions, and do not usually aspire to fundamentally change brain function. A brain-plasticity-based training program would potentially be applicable to all aging adults with the promise of improving their operational capabilities. We have constructed such a brain-plasticity-based training program and conducted an initial randomized controlled pilot study to evaluate the feasibility of its use by older adults. A main objective of this initial study was to estimate the effect size on standardized neuropsychological measures of memory. We found that older adults could learn the training program quickly, and could use it entirely unsupervised for the majority of the time required. Pre- and posttesting documented a significant improvement in memory within the training group (effect size 0.41, p<0.0005), with no significant within-group changes in a time-matched computer using active control group, or in a no-contact control group. Thus, a brain-plasticity-based intervention targeting normal age-related cognitive decline may potentially offer benefit to a broad population of older adults.

Identification of novel electroconvulsive shock-induced and activity-dependent genes in the rat brain

Electroconvulsive shock (ECS) has been used as an effective treatment for patients suffering from major depression disorders and schizophrenia. However, the exact mechanisms underlying the action of ECS are poorly understood. Using high-density oligonucleotide microarrays, we identified 60 ECS-induced genes whose gene products are involved in the neuronal signaling, neuritogenesis and tissue remodeling. In situ hybridization and depolarization-dependent expression assay were performed to characterize 4 genes (lysyl oxidase, Ab1-046, SOX11, and T-type calcium channel 1G subunit) which have not yet been reported to be induced by ECS. Interestingly, the induction of these genes was observed mainly in the dentate gyrus of hippocampal formation and piriform cortex, where ECS-induced neural activation is highlighted, and depolarization of cultured cortical neurons also induced the expression of these genes. Taken together, our results suggest that therapeutic actions of ECS may be manifested by the activity-dependent induction of genes related to the plastic changes of the brain such as neuronal signaling neuritogenesis, and tissue remodeling.

Opposite morphological responses of partially denervated cortical serotonergic and noradrenergic axons to repeated stress in adult rats

We examined plastic changes in serotonin (5-HT) axons following repeated stress in the adult rat brain, and compared stress-induced changes between 5-HT and noradrenaline (NA) axons. We locally injected the specific neurotoxin to 5-HT axons or to NA axons into the frontal cortex to cause partial denervation. The animals were mildly restrained from 1 day after the neurotoxin injection and this stress was repeated daily for 20 min during the first 2 days and for 40 min during the next 11 days. On the fourteenth day after injection, the brains were removed to visualize 5-HT and NA axons by immunohistochemistry. Repeated stress did not significantly alter the denervation area of 5-HT or NA axons, but the density of 5-HT axons was increased whereas that of NA axons was decreased in cortical regions outside the denervation site. In addition, the expression of brain-derived neurotrophic factor (BDNF) was increased in cortical regions where the 5-HT axon density was increased in response to stress. These results suggest that repeated stress causes opposite changes in the morphology of partially denervated 5-HT and NA axons in the cerebral cortex. The stress-induced increase in BDNF expression may contribute to 5-HT axon sprouting following repeated stress.

Interaction between serotonergic and noradrenergic axons during axonal regeneration

The present experiments focused on the morphological interaction between serotonergic (5-HT) and noradrenergic (NA) axons during regeneration following partial axonal denervation in the cerebral cortex in adult rats. The denervation paradigm used employed two neurotoxins, one for 5-HT and one for NA axons, infused together at one cortical site while a single neurotoxin to either 5-HT or NA was infused at the symmetrical cortical site in the other hemisphere. This treatment enabled us to assess the role of 5-HT or NA axons in the regeneration of the other monoaminergic axon. 5-HT axon regeneration became apparent as early as 28 days after the toxin injection, whereas the regeneration of NA axons was not evident even at 60 days after the toxin injection. Since NA axons revealed marked regeneration in the cortical site with denervation of 5-HT axons, intact 5-HT axons may be inhibitory on the regeneration of NA axons. In contrast, since the regeneration of 5-HT axons was suppressed in the absence of NA axons, NA axons appear to exert a facilitatory effect on 5-HT axon regeneration. These results suggest that the role of 5-HT axons in the regeneration of NA axons is opposite to that of NA axons in the regeneration of 5-HT axons. In addition, the regeneration of 5-HT axons occurred much faster than that of NA axons in response to axonal damage. The differential roles of 5-HT and NA axons in axonal regeneration may play a role in a variety of physiological functions related to these monoamines and possibly in the pathophysiology of clinical depression.

Coupling Between "Hand" Primary Sensorimotor Cortex and Lower Limb Muscles After Ulnar Nerve Surgical Transfer in Paraplegia

Previous neuroimaging evidence revealed an "invasion" of "hand" over "lower limb" primary sensorimotor cortex in paraplegic subjects, with the exception of a rare patient who received a surgical motor reinnervation of hip-thigh muscles by the ulnar nerve. Here, the authors show that a functional reorganization of cortico-muscular and cortico-cortical oscillatory coupling was related to the recovery of the rare patient, as a paradigmatic case of long-term plasticity in human sensorimotor cortex after motor reinnervation of paraplegic muscles. This conclusion was based on electroencephalographic and electromyographic data collected while the patient and normal control subjects performed isometric muscle contraction of the left hand or lower limb. Cortico-muscular and cortico-cortical coupling was estimated by electroencephalographic-electromyographic coherence and directed transfer function of a multivariate autoregressive model.

Novel objects in a holeboard probe the role of the locus coeruleus in curiosity: support for two modes of attention in the rat

Idazoxan, an alpha 2 adrenoceptor antagonist (2 mg/kg), enhanced novel object investigation in a holeboard in rats as previously reported (V. Devauges & S. J. Sara, 1990). Two weeks of 10 min/day in 37 degrees C water increased dopamine-beta-hydroxylase staining density in the locus coeruleus but did not enhance novel object investigation. In contrast to idazoxan, however, the warm water treatment increased rearing, center entries, and activity, a pattern previously described during tonic infusion of norepinephrine into the hippocampus. Correlations among dopamine-beta-hydroxylase measures and behavior reinforced these tonic norepinephrine/behavior associations. The behavioral effects across the idazoxan and warm water experiments support G. Aston-Jones et al.'s (1999) 2 modes of attention hypothesis for locus coeruleus function: Phasic locus coeruleus activity promotes focused attention; tonic locus coeruleus activity promotes scanning attention.

Nerve growth factor-induced neurite sprouting in PC12 cells involves sigma-1 receptors: implications for antidepressants

One theory concerning the action of antidepressants relates to the drugs' ability to induce an adaptive plasticity in neurons such as neurite sprouting. Certain antidepressants are known to bind to sigma-1 receptors (Sig-1R) with high affinity. Sig-1R are dynamic endoplasmic reticulum proteins that are highly concentrated at the tip of growth cones in cultured cells. We therefore tested the hypotheses that Sig-1R might participate in the neurite sprouting and that antidepressants with Sig-1R affinity may promote the neuronal sprouting via Sig-1R. The prototypic Sig-1R agonist (+)-pentazocine [(+)PTZ], as well as the Sig-1R-active antidepressants imipramine and fluvoxamine, although ineffective by themselves, were found to enhance the nerve growth factor (NGF)-induced neurite sprouting in PC12 cells in a dose-dependent manner. A Sig-1R antagonist N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE100) blocked the enhancements caused by these Sig-1R agonists. In separate experiments, we found that NGF dose and time dependently increased Sig-1R in PC12 cells. Chronic treatment of cells with (+)PTZ, imipramine, or fluvoxamine also increased Sig-1R. These latter results suggested that NGF induces the neurite sprouting by increasing Sig-1R. Indeed, the overexpression of Sig-1R per se in PC12 cells enhanced the NGF-induced neurite sprouting. Furthermore, antisense deoxyoligonucleotides directed against Sig-1R attenuated the NGF-induced neurite sprouting. Thus, when taken together, our results indicate that Sig-1R play an important role in the NGF-induced neurite sprouting and that certain antidepressants may facilitate neuronal sprouting in the brain via Sig-1R.

Morphological brain changes in depression: can antidepressants reverse them?

Structural neuroimaging and postmortem histopathological studies of the brain have revealed morphological changes in cortical and subcortical regions in individuals diagnosed with depression. Moreover, these regions are known to be functionally altered in mood disorders. This indicates that the morphological changes might be directly involved in the pathophysiology of depression, and implies that antidepressants may be able to regulate or reverse the detected structural abnormalities. Work with animal models has shown that antidepressants are capable of inducing structural alterations in dendrites and axons and changes in the numbers of neural cells. However, there have been no studies in the human brain that have directly addressed whether antidepressant treatment can reverse or regulate the depression-related structural changes. Nevertheless, experience with lithium in bipolar disorder and antipsychotics in schizophrenia suggests that treatment with psychotropic drugs can result in structural changes that are consistent with reversion towards normal values. Clearly, ascertaining the role of the reversal of structural changes in the therapeutic actions of antidepressants will require further longitudinal studies and careful comparisons between those patients with mood disorder who are treated with antidepressants and those who are not.

A novel pharmacological concept in an animal model of psychosis

OBJECTIVE

We have analysed pharmacologically induced perturbation of functional and structural neurogenesis in the prefrontal cortex (PFC) and hippocampus.

METHOD

Juvenile gerbils received a single dose of methamphetamine (METH, 50 mg/kg, i.p.). In adults the following parameters were quantitatively investigated: prefrontal dopaminergic and GABAergic innervation densities (immunocytochemistry), morphogenesis of pyramidal cells (Golgi), dentate granule cell proliferation (BrdU-labelling), working memory and behavioural inhibition (delayed response, open-field).

RESULT

A single challenge of METH continuously suppresses granule cell proliferation in adult gerbils and initiates rewiring of neuronal networks in the PFC which run concurrently with the development of severe deficits in PFC-related behaviours.

CONCLUSION

It appears that a continuous remodelling of neuronal circuits is an inherent property of the brain, the biological significance of which seems to be to ascertain adaptive interaction between brain and environment. Learning more about drug-induced neuronal reorganization might be basic for understanding the genesis of psychotic conditions in the brain. This presentation is based both on own research and on a review of the literature.

The unknown mechanism of the overtraining syndrome: clues from depression and psychoneuroimmunology

When prolonged, excessive training stresses are applied concurrent with inadequate recovery, performance decrements and chronic maladaptations occur. Known as the overtraining syndrome (OTS), this complex condition afflicts a large percentage of athletes at least once during their careers. There is no objective biomarker for OTS and the underlying mechanism is unknown. However, it is not widely recognised that OTS and clinical depression [e.g. major depression (MD)] involve remarkably similar signs and symptoms, brain structures, neurotransmitters, endocrine pathways and immune responses. We propose that OTS and MD have similar aetiologies. Our examination of numerous shared characteristics offers insights into the mechanism of OTS and encourages testable experimental hypotheses. Novel recommendations are proposed for the treatment of overtrained athletes with antidepressant medications, and guidelines are provided for psychological counselling.

Restraint stress-induced alterations in the levels of biogenic amines, amino acids, and AChE activity in the hippocampus

Inspite of large number of studies on the neurochemical changes in the stress, an equivocal case is yet to be made for the role of a specific neurotransmitter in this important neurobiological disorder. The difficulty arises from the fact that there is no single neurotransmitter system appears to be responsible for the stress induced damage to the hippocampal neurons. The present study evaluates the effect of restraint stress on the alterations in the levels of biogenic amines, aminoacids and acetylcholinesterase activity in the hippocampus. Male Wistar rats of 45 days old were subjected to 6 hours of daily restraint stress over a period of 21 days. Immediately after the last session of stress, rats were sacrificed and neurotransmitter levels were estimated in the hippocampus. A significant (p < 0.001) decrease in the levels of noradrenaline, dopamine, 5-hydroxytryptamine and acetylcholinesterase activity in the stressed rats was observed compared to controls. However, levels of glutamate was significantly (p < 0.001) increased in stressed rats. These results indicate that chronic restraint stress decreases aminergic and cholinergic neurotransmission, and increases the glutamatergic transmission in the hippocampus.

Induction and adaptation of Fos expression in the rat brain by two types of acute restraint stress

The present study was designed to examine whether both induction and adaptation of brain Fos expression during acute stress depend on the intensity and duration of stressors. For this purpose, different durations of two types of acute stress, mild (restraint) and severe (immobilization) stress, were employed. Stress-induced Fos expression was analyzed quantitatively by immunohistochemistry. Adaptation of Fos expression to the acute stressors was not apparent in the hypothalamic paraventricular nucleus (PVN) or locus coeruleus (LC) but was observed in the amygdala, hippocampus, and cerebral cortex. A higher level of Fos expression was seen in the PVN, LC, and amygdala, following severe stress than was seen following mild stress. In the hippocampus, the dentate gyrus showed reduced Fos expression in response to stressors, although both mild and severe acute stress increased Fos expression in other regions of the hippocampus. The cingulate cortex showed increased Fos expression during mild stress, whereas long-duration severe stress reduced Fos expression. In the somatosensory cortex, both stressors increased Fos expression. These results indicate that the PVN and LC are relatively resistant to adaptation to acute stress compared to other brain regions. In addition, the PVN, LC, and amygdala may play important roles in the perception of the severity of stress.

Prolonged c-Jun expression in the basolateral amygdala following bulbectomy: possible implications for antidepressant activity and time of onset

Olfactory bulbectomy is a well established animal model of depression. Neurochemical and behavioral alterations observed following olfactory bulbectomy, are due, in part, to the neurodegeneration of specific brain structures. Amygdaloid dysfunction in particular, is known to play a substantial role in the syndrome of the olfactory bulbectomized rat. The present study examined both short- and long-term alterations in immediate early gene expression, tyrosine hydroxylase and serotonin immunoreactivity, and classical silver staining, following olfactory bulbectomy in the basolateral amygdala. The results indicated no consistent change in Fos expression observed over the experimental period. Following bulbectomy, long term (up to 64 days post-lesion) Jun expression, not coincident with silver staining, was observed in the basolateral nucleus. The basolateral nucleus was also intensely immunoreactive for serotonin at this timepoint post-bulbectomy. Thus, following bulbectomy long term alterations in Jun expression occurs in the serotonin rich basolateral amygdala. As a site of action for antidepressant compounds, alterations at the immediate early gene level in this region may have implications both for the model, and antidepressant drug action therein.

The stress-reaction process and the adaptive modification and reorganization of neuronal networks

On the basis of a comprehensive definition of the stress-reaction process (SRP), the neurobiological and psychological consequences of this process, which are elicited by either controllable or uncontrollable stress, are described. We conclude that controllable stress triggers the stabilization and facilitation of neuronal networks involved in the generation of appropriate patterns of appraisal and coping, whereas uncontrollable stress favors the extinction of inappropriate patterns and the reorganization of neuronal connections underlying certain inappropriate behaviors. Both controllable and uncontrollable stress-reaction processes are therefore inherent challenges to the development and essential prerequisites of the adaptation of an individual's behavior to the demands of the ever-changing external world. The overabundance, as well as the lack, of either kind of SRP may lead to different psychodevelopmental failures and psychiatric disturbances.

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With the increasing application of imaging techniques, characteristic changes in the structure and functional activity of certain neuronal networks and transmitter Systems have been discovered in the brains of patients suffering from various psychiatric disorders. These findings have often been assumed to support biological concepts of the genetic background and causation of these disorders. However, several lines of research are converging to indicate that the initially established genetically programmed neuronal Connectivity is further elaborated, fine tuned and modified by usedependent neuronal and synaptic plasticity. In all socially organized species in general and in human subjects in particular, psychosocial experiences appear to represent the most important trigger of use-dependent adjustments of neuronal Connectivity through the facilitation, modification and reorganization of neuronal networks. In experimental animals, changes in psychosocial rearing conditions were shown to cause profound and persistent changes in the cytoarchitecture, dendritic arborization and synapse formation in individual brain regions as well as in the maturation of monoaminergic afferences. Based on these findings, the mechanisms of the biological affixation of psychosocial experiences are described and the implications of experience dependent neuronal and synaptic plasticity in the prevention and the therapy of mental disorders are outlined.

Self-stimulation of lateral hypothalamus and ventral tegmentum increases the levels of noradrenaline, dopamine, glutamate, and AChE activity, but not 5-hydroxytryptamine and GABA levels in hippocampus and motor cortex

Self-stimulation (SS) rewarding experience induced structural changes have been demonstrated in the hippocampal and motor cortical pyramidal neurons. In the present study, we have evaluated whether these changes are accompanied by neurochemical alterations in the hippocampus and motor cortex in SS experienced rats. Self-stimulation experience was provided one hour daily over a period of 10 days through stereotaxically implanted bipolar stainless steel electrodes, bilaterally in lateral hypothalamus and substantia nigra-ventral tegmental area. Self-stimulation experience resulted in a significant (P < 0.001) increase in the levels of noradrenaline, dopamine, glutamate and AChE activity but not 5-hydroxytryptamine and GABA levels in hippocampus and motor cortex. Such alterations in the levels of neurotransmitters may enhance the cognitive functions in the SS experienced rats.

Influence of water immersion stress on peripheral nerve recovery in the rat

An experimental study was performed to investigate the relationship between stress and peripheral nerve recovery. Male Wistar rats weighing 200-250 g were used. The sciatic nerve was crushed unilaterally with an aneurysm clip. Stress was applied by water immersion for 3 h, three times a week, from 1 week preoperatively, and continued for 6 or 8 weeks. The animals' walking tracks were measured every week to evaluate nerve function, and a sciatic functional index (SFI) was calculated. Specimens for histological examination were taken from the nerve at a site distal to the crush injury. By 3 weeks postoperatively, the SFI in the non-stress groups had recovered, but it remained at significantly lower levels in the stress groups (P < 0.01). Histological studies showed that the recovery of nerve fibers was retarded and regenerating axons were smaller in the stress groups. Peripheral nerve recovery after crush injury was suppressed by water-immersion stress.

Stress and the adaptive self-organization of neuronal connectivity during early childhood

A conceptual framework is proposed for a better understanding of the biological role of the stress-response and the relationship between stress and brain development. According to this concept environmental stimuli (in children mainly psychosocial challenges and demands) exert profound effects on neuronal connectivity through repeated or long-lasting changes in the release of especially such transmitters and hormones which contribute, as trophic, organizing signals, to the stabilization or destabilization of neuronal networks in the developing brain. The increased release of noradrenaline associated with the repeated short-lasting activation of the central stress-responsive systems in the course of the stress-reaction-process to psychosocial challenges which are felt to be controllable acts as a trigger for the stabilization and facilitation of those synaptic and neuronal pathways which are activated in the course of the cognitive, behavioral and emotional response to such stressors. The long-lasting activation of the central stress-responsive systems elicited by uncontrollable psychosocial conflicts in conjunction with the activation of glucocorticoid receptors by the sustained elevation of circulating glucocorticoid levels favors the destabilization of already established synaptic connections and neuronal pathways in associative cortical and limbic brain structures. The facilitation and stabilization of neuronal pathways triggered by the experience of controllable stress is thus opposed, attenuated or even reversed in the course of lon-lasting uncontrollable stress. This destabilization of previously established synaptic connections and neuronal pathways in cortical and limbic brain structures is a prerequisite for the acquisition of novel patterns of appraisal and coping and for the reorganization of the neuronal connectivity in the developing brain. Alternating experiences of repeated controllable stress and of long-lasting uncontrollable stress are therefore needed for the "self-adjustment" of neuronal connectivity and information processing the developing brain to changing environmental (psychosocial) demands during childhood. The brain structures and neuronal circuits involved in the regulation of behavioral responding become thus repeatedly reoptimized and refitted, not the changing conditions of life per se but rather to those conditions which are still able to activate the central stress responsive systems of an individual at a certain developmental stage.

Long-term stress degenerates, but imipramine regenerates, noradrenergic axons in the rat cerebral cortex

Exposed to a forced walking stress for 2 weeks, some rats became persistently inactive (depression-model rats), whereas others gradually recovered from exhaustion (spontaneous recovery rats). We also studied rats exposed to short-term stress, rats without stress, and the model rats treated with imipramine or saline. We examined the density of noradrenergic axons in the frontal cortex using retrograde labeling of the locus coeruleus with horseradish peroxidase injected into the cortex and immunohistochemical staining of cortical axons with dopamine beta-hydroxylase antiserum. The density was significantly lower in the depression-model rats, but tended to be higher in the recovery rats and short-term stressed rats. Chronic treatment with imipramine significantly increased the density in the model rats. There was also a correlation between the density of noradrenergic axons and the recovery rate of activity. Our results suggest that cortical noradrenergic degeneration is involved in the pathogenesis of depression.

Changes in CSF spaces differ in endogenous and neurotic depression. A planimetric CT scan study

Regional planimetric measurements of internal and external CSF spaces were performed in CT scans of 23 patients with endogenous depression (ICD 9, 296.1) and 28 patients with neurotic depression (ICD 9, 300.4) as compared to 56 control individuals without neuropsychiatric disorder. In female patients with endogenous depression, but not in men, the bilateral upper cortical sulci were widened, especially in the frontal regions, and the third ventricle was enlarged. In contrast, the female neurotic depressed group showed no enlargement of CSF spaces, but a narrowing of the Sylvian fissure and of the basal frontal lobe reaching level of significance in the right fronto-temporal region (P = 0.005). No narrowing of CSF spaces was observed in women with endogenous depression. A discriminant analysis of significantly changed CSF regions resulted in a correct classification in 82.4% of depressed women in either the endogenous or the neurotic group. Determination of divergent types of brain pathology might prove as a useful tool in validating the differential classification of these two main subtypes of affective disorders.

Degeneration of locus coeruleus axons in stress-induced depression model

Antidepressants such as desipramine induce axonal regeneration of brain noradrenergic neurons. This novel action of antidepressants suggests the involvement of degeneration or retraction of brain noradrenergic axons in the pathophysiology of clinical depression. The present study was designed to further confirm this view in an animal model of stress-induced depression. The depression model was produced by exposing rats to prolonged forced walking stress. To see if axonal degeneration of noradrenergic neurons occurred in the depression model, the density of noradrenergic axons in the cerebral cortex was assessed by three different methods, antidromic stimulation technique, retrograde tracing with horseradish peroxidase and immunohistochemical staining with dopamine-beta-hydroxylase antiserum. These methods all assured of degenerative changes of noradrenergic axon terminals in the depression model. Furthermore, it was found that repeated treatments of the depression-model rats with imipramine could cause regeneration of cortical noradrenergic axons. These findings support the view that degeneration or retraction of noradrenergic axons is involved in the pathophysiology of depression.