CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) - Volume 12, Issue 7, 2013

The aetiology of suicide is complex and still not completely understood. The present communication, which consists of two parts, aims to shed some light on the role of amino acidergic neurotransmission in suicide. In the first part we provide an overview of the literature showing that with the exception of certain gamma-aminobutyric acid transporters, virtually all components of the glutamate-glutamine- gamma-aminobutyric acid cycle are, in some way or other, abnormal in suicide victims, which indicates a prominent involvement of the glutamatergic and gammaaminobutyric acidergic neurotransmitter systems in suicidal behaviour. In the second part we present own immunohistochemical findings showing that densities of glutamine synthetase expressing glial cells in the mediodorsal thalamus as well as in the dorsolateral prefrontal and orbitofrontal cortex of schizophrenic suicide completers are significantly elevated compared with controls and non-suicide individuals with schizophrenia, thus calling into question the belief that cerebral glutamine synthetase deficit is indicative of suicidal behaviour.

In recent years, the hypothalamus, amygdala and hippocampus have attracted increased interest with regard to the effects of stress on neurobiological systems in individuals with depression and suicidal behaviour. A large body of evidence indicates that these subcortical regions are involved in the pathogenetic mechanisms of mood disorders and suicide. The current neuroimaging techniques inadequately resolve the structural components of small and complex brain structures. In previous studies, our group was able to demonstrate a structural and neuronal pathology in mood disorders. However, the impact of suicide remains unclear. In the current study we used volumetric measurements of serial postmortem sections with combined Nissl-myelin staining to investigate the hypothalamus, amygdala and hippocampus in suicide victims with mood disorders (n = 11), non-suicidal mood disorder patients (n = 9) and control subjects (n = 23). Comparisons between the groups by using an ANCOVA showed a significant overall difference for the hypothalamus (p = 0.001) with reduced volumes in non-suicidal patients compared to suicide victims (p = 0.018) and controls (p = 0.006). To our surprise, the volumes between the suicide victims and controls did not differ significantly. For the amygdala and hippocampus no volume changes between the groups could be detected (all p values were n. s.). In conclusion our data suggest a structural hypothalamic pathology in non-suicidal mood disorder patients. The detected differences between suicidal and non-suicidal patients suggest that suicidal performances might be related to the degree of structural deficits.

This paper provides a review of the literature on neuroimaging studies of suicidal behaviour, and discusses the relevance of these studies for our understanding of suicidal behaviour. Main findings from molecular imaging studies include a reduced prefrontal perfusion or metabolism and a blunted increase in activation when challenged in association with a history of suicide attempts. Moreover, impairment of the prefrontal serotonergic system in association with suicidal behaviour is demonstrated in a number of studies. Recent structural and functional imaging studies show changes in cortical and subcortical areas and their connections. A number of methodological issues hamper the interpretation of findings. Nevertheless, when findings from studies using divergent techniques are taken together there is increasing evidence of the involvement of a fronto-cingulo-striatal network in suicidal behaviour. This involvement is supported additionally by findings from neuropsychological studies, which demonstrate changes in decision-making processes in association with suicidal behaviour that rely on the same network. Further study is needed to translate the increasing knowledge from neuroimaging studies in clinical tools for the prediction and prevention of suicidal behaviour.

We report recent postmortem findings from the Magdeburg Brain Bank related to the evaluation of impaired activity of neuronal networks relevant for depression. Chronic changes in ribosomal DNA transcriptional activity have been revealed by the quantitative evaluation of silver-stained nucleolar organising regions (AgNORs). Abnormalities in AgNOR parameters have been found in neurons of the prefrontal limbic regions, the amygdala, the external globus pallidus, and the serotonergic dorsal raphe nucleus (DRN). The impact of the processes leading to suicide has been clearly accentuated in opposition to the weak influence of unipolar-bipolar dichotomy, which was only revealed in one area (the anterior cingulate cortex). The impact of suicide was most pronounced in the DRN. Our AgNOR studies show that the influence of psychotropic medication (antidepressants and typical neuroleptics, among others) is limited in the prevention of abnormal neuronal activity specific for suicide.

During the past years suicide statistics in Germany showed a dramatic decrease of suicide rates. Such a reduction in a comparatively short time period is not explainable by an altered frequency of major psychiatric disorders or certain neurobiological conditions that may underlie suicide; other factors causing or leading to suicide and their modification have to be considered. This overview illustrates various risk factors for suicide different from neurobiology. Epidemiological aspects and the effect of political, social and economic contributions to suicide rates are exemplified. With regard to the incidence of major psychiatric disorders the paper focuses on physical illnesses and their risk of suicide. Finally the significance of changes in the accessibility of suicide methods is discussed.

Suicide is a major public health concern and each year about one million people die by suicide worldwide. Recent studies suggest that suicide may be associated with specific neurobiological abnormalities. Earlier studies of neurobiology of suicide focused on abnormalities of the serotonergic mechanism. These studies suggested that some serotonin receptor subtypes may be abnormal in the postmortem brain of suicide victims. Since these receptors are linked to signal transduction pathways, abnormalities of signaling mechanisms have been recently studied in the postmortem brain of suicide victims. Of particular interest is the 5-hydroxytryptamine2Areceptor-linked phosphoinositide signaling system. Several studies have focused on the abnormalities on the component of this signaling system and these studies suggest the abnormalities of G proteins, the effectors phospholipase C and the second or the third messenger systems, such as protein kinase A. Further studies revealed abnormalities in the downstream transcription factors such as the cyclic AMP response element binding protein and some of the targeted genes of these transcription factors. The most important gene in this aspect which has been studied in the suicide is the brain-derived neurotrophic factor. Here we critically review the studies focusing on these components of the phosphoinositide signaling system in the postmortem brain of both adult and teenage suicide victims. These studies provide a better understanding of the signal transduction abnormalities in suicide focusing on the phosphoinositide signaling pathway. These studies may lead to new therapeutic agents targeting specific sites in this signaling cascade.

Hypothalamic-Pituitary-Adrenal (HPA) axis hyperactivity measured with the dexamethasone suppression test and the dexamethesone/CRH test may have some predictive power for suicidal behavior in patients with mood disorders. Increased prolactin (PRL) levels may be related both to physiological and pathological conditions. HPA-axis abnormalities and increased levels of PRL may coexist, and common neuroendocrine changes may activate both HPA axis and PRL release. HPA-axis hyperactivity is presumably present in a large subpopulation of depressed subjects. Suicidal behavior is considered to be a form of inward-directed aggression, and aggressive behavior has been connected to high androgen levels. However, lower plasma total testosterone levels have also been reported in subjects with depression and higher suicidality. Lipid/immune dysregulations, the increased ratio of blood fatty acids, and increased PRL levels may each be associated with the increased production of pro-inflammatory cytokines, which have been reported in patients with major depression and patients engaging in suicidal behavior. Although no studies have been done to determine whether ante-mortem physical stress may be detected by raised post-mortem PRL, this would be of great interest for physicians.

Immune dysfunction, including monocytosis, increased blood levels of interleukin-1 (IL-1), interleukin-6 (IL- 6) and tumor necrosis factor-alpha (TNF-alpha), as well as an increased microglial density in certain brain areas, have been described in schizophrenia and depression. Interestingly, similar immune alterations have been observed in suicide patients regardless of their underlying psychiatric diagnosis. This review summarizes relevant data from previous studies that have examined peripheral blood, cerebrospinal fluid and human brains (using postmortem histology and in vivo positron emission tomography) to investigate immune mechanisms in suicidal patients.

We discuss whether the observed findings indicate that microgliosis and monocyte-macrophage system activation may be a useful marker of disease acuity/severity or whether they instead indicate a distinct neurobiology of suicide. Notably, pathophysiological mechanisms could change during the long-term course of psychiatric diseases. Therefore, different patterns of immune activation may be observed when comparing newly diseased patients with those who are chronically ill.

Suicide is a significant worldwide public health problem. Understanding the neurobiology is important as it can help us to better elucidate underlying etiological factors and provide opportunities for intervention. In recent years, many lines of research have suggested that the polyamine system may be dysregulated in suicidal behaviors. Initial research in animals provided evidence of a dysfunctional polyamine stress response system, while later work using post-mortem human brain tissue has suggested that molecular mechanisms may be at play in the suicide brain. In this review, we will describe the research that suggests the presence of alterations in the polyamine system in mental disorders and behavioral phenotypes, with particular attention to work on suicide. In addition, we will also describe potential avenues for future work.

The antidepressant effect of a compound formed by co-ultramicronized palmitoylethanolamide (PEA) and luteolin (PEA+luteolin) was investigated in a mouse model of anxiety/depressive-like behavior. 129Sv/Ev mice were subjected to 6 weeks of corticosterone administration, and then behavior, neurogenesis, neuroplasticity, neurotrophic and apoptotic proteins expression were evaluated. The effect of PEA+luteolin compound treatment (1mg/kg, i.p.), on depression-like behaviour was assessed using different paradigms such as open field, novelty suppressed feeding, forced swim test and elevated plus maze. In particular in the open field, novelty suppressed feeding and elevated plus maze the time spent in the open arm was employed as an indicator of anxiety; forced swim test was used to evaluate the antidepressant capacity of PEA+luteolin on immobility time as an indicator of depression. Adult hippocampal neurogenesis and neuroplasticity were evaluated by immunohistochemical techniques; brain-derived neurotrophic factor and apoptotic protein (Bax and Bcl2) expression were studied by immunostaining and Western blot analysis. For the first time we demonstrated that PEA+luteolin compound exerts a significant antidepressant effect a low dose and may be considered as a novel therapeutic strategy in depression.

Inflammation in Parkinson’s disease (PD) is a continuous process and might be implicated in the progression of neuronal degeneration. Taking this into account, we proposed a new protocol with multiple and consecutive intranigral lipopolysaccharide (LPS) administration in order to analyze its effects on cognitive behavior. Additionally, striatal concentrations of the neurotransmitters dopamine (DA) and serotonin and their respective metabolites were assessed in three different time-points with the purpose of identifying the consecutive and cumulative effects of LPS infusions. We demonstrated that with a minimum administered dose there was stabilization of neuronal damage as revealed by absence of synergic effect on DA concentration. Although the DA decrease (–43%) generates an animal model of early phase of PD, without apparent motor impairment, the LPS group exhibited deficit in episodic-like memory behavior from the first time-point until the last one, indicating persisted disturbances in memory-recognition responses. These findings provide evidence that multiple intranigral LPS infusions are not sufficient to cause cumulative and progressive damage to dopaminergic neurons, but confirm that the LPS model can be adopted as a useful tool providing insight about the cognitive impairment observed in pre-motor phase of PD.

Ischemia reperfusion injuries can be threatening to end organ viability and can progress, with mortal and morbid outcomes. In particular, neural tissues are highly sensitive to hypoxia and reperfusion stress. This study aimed to determine the neuroprotective effects of rosuvastatin on spinal cord ischemia reperfusion injury. Forty male Sprague– Dawley rats were divided into four equal groups: group I (control), group II (sham with simple laparotomy), group III (ischemia-reperfusion), group IV (ischemia-reperfusion group with continuous rosuvastatin utilization), and group V (ischemia-reperfusion group with rosuvastatin-withdrawal after reperfusion). Spinal cord ischemia was induced by clamping the aorta below the left renal artery and above the aortic bifurcation. Reperfusion was provided after 72^nd hours of ischemia. After reperfusion, blood samples and spinal cord tissue samples were taken from all the rats. Oxidative and antioxidant markers from both serum and tissue samples were evaluated, and tissues were examined histopathologically. There were no significant differences between the control and sham groups. A notable increase in oxidative markers was observed in group III compared to group I. In addition, a significant decrease in antioxidant markers was detected in group III. However, there was a marked preservation in the tissue and blood samples of groups IV and V compared to group III in terms of oxidative damage. Additionally, definitive prophylaxes were seen in the histopathological examination of the tissue samples in groups IV and V compared with group III. These significant findings show that rosuvastatin has a considerable protective effect on neural tissue against oxidative damage. Likewise, the early withdrawal of rosuvastatin has a clear neuroprotective effect similar to that of continuous therapy. Nevertheless, other systematic effects and beneficial neural effects of statins should be investigated in further clinical trials.

Motor complications (dyskinesias and motor fluctuations) are a common and disabling problem of dopaminergic therapy in Parkinson’s disease, which are often difficult to treat with the current therapeutic strategies. It has been proposed that continuous dopaminergic delivery could reduce the emergence of motor complications, which has been tried with levodopa intestinal infusion or subcutaneous apomorphine infusion. In selected refractory cases, surgical approaches such as deep brain stimulation should be considered. Ongoing clinical and preclinical research tried to lead the field into the discovery of other therapeutic targets and strategies that might prevent or reduce motor complications. These include drugs targeting non-dopaminergic systems (e.g. glutamatergic, serotonergic, noradrenergic, adenosinergic and cholinergic systems), gene therapy for delivering neurotrophic factors or critical enzymes for dopamine synthesis, and cell therapy. These studies found variable results, some of them promising, with the possibility of new therapeutic armamentarium in the management of Parkinson’s disease in the near future.

Probenecid (PROB) has been widely used for long time for different clinical purposes, from gout treatment to designs as a coadjutant for antibiotic agents. Among its many properties, the ability of PROB to preserve high concentrations of several metabolites and other agents in the CNS, together with its relative lack of side-effects, have made this drug a valuable pharmacological tool for clinical and basic research. Nowadays, biomedical research offers evidence about new targets for PROB that may help to explain its many beneficial actions. In this regard, despite most of its protective actions in the brain have been largely related to its capacity to accumulate the inhibitory metabolite kynurenic acid to further inhibit the glutamate-related excitotoxicity in different animal models of neurological disorders, in this review we describe the basic aspects of PROB’s pharmacokinetics and mechanisms of action and discuss other alternative targets recently described for this drug that may complement its pattern of activity in the CNS, including its role as anti-inflammatory and anti-nociceptive agent when targeting different key proteins.

The brain-derived neurotrophic factor (BDNF) and its high affinity receptor tropomyosin-receptor-kinase B (TrkB) play a critical role in neuronal differentiation and survival, synapse plasticity, and memory. Indeed, both have been implicated in the pathophysiology of numerous diseases. Although the remarkable therapeutic potential of BDNF has generated much research over the past decade, the poor pharmacokinetics and adverse side effect profile have limited its clinical usefulness of BDNF. Small compounds that mimic BDNF’s neurotrophic signaling and overcome the pharmacokinetic and side effect barriers may have greater therapeutic potential. The purpose of this review is to provide a survey of the various strategies taken towards the development of small molecule mimetics for BDNF and the selective TrkB agonist. A particular focus was placed on TrkB agonist 7, 8-dihydroxyflavone, which modulates multiple functions and has demonstrated remarkable therapeutic efficacy in a variety of central nervous system disease models. Two other small molecules included in this review are adenosine A2A receptor agonists that indirectly activate TrkB, and TrkB binding domains of BDNF, loop II-LM22A compounds that directly activate TrkB. These alternative molecules have shown promise in preclinical studies and may be included in prospective clinical investigations.