Effect of immobilization stress on brain polyamine levels in spontaneously hypertensive and Wistar-Kyoto rats

Putrescine as indicator of manganese neurotoxicity: Dose-response study in human SH-SY5Y cells

Disrupted polyamine metabolism with elevated putrescine is associated with neuronal dysfunction. Manganese (Mn) is an essential nutrient that causes neurotoxicity in excess, but methods to evaluate biochemical responses to high Mn are limited. No information is available on dose-response effects of Mn on putrescine abundance and related polyamine metabolism. The present research was to test the hypothesis that Mn causes putrescine accumulation over a physiologically adequate to toxic concentration range in a neuronal cell line. We used human SH-SY5Y neuroblastoma cells treated with MnCl2 under conditions that resulted in cell death or no cell death after 48 h. Putrescine and other metabolites were analyzed by liquid chromatography-ultra high-resolution mass spectrometry. Putrescine-related pathway changes were identified with metabolome-wide association study (MWAS). Results show that Mn caused a dose-dependent increase in putrescine over a non-toxic to toxic concentration range. MWAS of putrescine showed positive correlations with the polyamine metabolite N8-acetylspermidine, methionine-related precursors, and arginine-associated urea cycle metabolites, while putrescine was negatively correlated with γ-aminobutyric acid (GABA)-related and succinate-related metabolites (P < 0.001, FDR < 0.01). These data suggest that measurement of putrescine and correlated metabolites may be useful to study effects of Mn intake in the high adequate to UL range.

Ginsenoside rb1 modulates level of monoamine neurotransmitters in mice frontal cortex and cerebellum in response to immobilization stress

Cerebral monoamines play important roles as neurotransmitters that are associated with various stressful stimuli. Some components such as ginsenosides (triterpenoidal glycosides derived from the Ginseng Radix) may interact with monoamine systems. The aim of this study was to determine whether ginsenoside Rb1 can modulate levels of the monoamines such as dihydroxyphenylalanine (DOPA), dopamine (DA), norepinephrine (NE), epinephrine (EP), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydorxytryptamine (5-HT), 5-hydroxindole-3-acetic acid (5-HIAA), and 5-hydroxytryptophan (5-HTP) in mice frontal cortex and cerebellum in response to immobilization stress. Mice were treated with ginsenoside Rb1 (10 mg/kg, oral) before a single 30 min immobilization stress. Acute immobilization stress resulted in elevation of monoamine levels in frontal cortex and cerebellum. Pretreatment with ginsenoside Rb1 attenuated the stress-induced changes in the levels of monoamines in each region. The present findings showed the anti-stress potential of ginsenoside Rb1 in relation to regulation effects on the cerebral monoaminergic systems. Therefore, the ginsenoside Rb1 may be a useful candidate for treating several brain symptoms related with stress.

Evidence of altered polyamine concentrations in cerebral cortex of suicide completers

Recent studies have implicated alterations in the expression of polyamine-related genes in the brains of suicide completers including widespread downregulation of spermidine/spermine N1-acetyltransferase, the key enzyme in polyamine catabolism, suggesting compensatory mechanisms attempting to increase brain levels of polyamines. Given the complexity of the polyamine system, quantification of the levels of the polyamines is an essential step in understanding the downstream effects of dysregulated gene expression. We developed a method using high-resolution capillary gas chromatography (GC) in combination with mass spectrometry (MS) for quantitation of polyamines from post-mortem brain tissue, which allowed us to accurately measure spermidine and putrescine concentrations in post-mortem brain tissues. Using this method, we analyzed putrescine and spermidine levels in a total of 126 samples from Brodmann areas 4, 8/9, and 11, from 42 subjects, comprising 16 suicide completers with major depression, 13 non-depressed suicide completers, and 13 control subjects. Both putrescine and spermidine levels fell within the expected nanomolar ranges and were significantly elevated in the brain of suicide completers with a history of major depression as compared with controls. These results were not accounted by possible confounders. This is the first GC-MS study to analyze the expression of putrescine and spermidine from post-mortem brain tissue and confirms the hypothesis raised by previous studies indicating alterations in putrescine and spermidine levels in suicide/major depression.

Global disturbances in autonomic function yield cardiovascular instability and hypertension in the chromogranin a null mouse

We reported previously that chromogranin A (Chga) knockout (KO) mice are hypertensive and hyperadrenergic. Here we sought to determine the basis of such alterations by probing physiological, biochemical, and pharmacological responses to perturbations of the autonomic nervous system. In the conscious state, KO mice had substantially elevated basal high blood pressure (BP) and heart rate (HR); immobilization stress caused increments in systolic BP and HR in both wild-type (WT) and KO mice, with higher maxima but blunted increments in the KO state. Catestatin (CST; CHGA(352-372)) selectively diminished stress-induced increments in BP and HR in KO mice, implicating CST as an antihypertensive peptide, even in stressful conditions. Heightened plasma catecholamines in KO mice returned to WT level after CST. Stress caused further increments in catecholamines in WT mice but no change in KO mice. KO mice displayed diminished baroreflex sensitivity in response to either phenylephrine or sodium nitroprusside, accounting for exaggerated pressor and depressor responses to these compounds; baroreceptor function was normalized by CST. To probe the relative roles of endogenous/basal sympathetic vs. parasympathetic tone in control of BP and HR, we used the muscarinic-cholinergic antagonist atropine or the beta-adrenergic antagonist propranolol; HR and BP responses to each antagonist were exaggerated in KO animals. We conclude that ablation of Chga expression results in global disturbances in autonomic function, both sympathetic and parasympathetic, that can be abrogated (or rescued), at least in part, by replacement of CST. The results point to mechanisms whereby CHGA and its CST fragment act to control cardiovascular homeostasis.

Profiling brain expression of the spermidine/spermine N1-acetyltransferase 1 (SAT1) gene in suicide

Altered stress reactivity is considered to be a risk factor for both major depressive disorder and suicidal behavior. The authors have sought to expand their previous findings implicating altered expression of spermidine/spermine N(1)-acetyltransferase 1 (SAT1), the rate-limiting enzyme involved in catabolism of the polyamines spermidine and spermine in the polyamine stress response (PSR), across multiple brain regions between control individuals and depressed individuals who have died by suicide. Microarray expression of probesets annotated to SAT1 were examined across 17 brain regions in 13 controls and 26 individuals who have died by suicide (16 with a diagnosis of major depression and 10 without), all of French-Canadian origin. Profiling conducted on the Affymetrix U133A/B chipset was further examined on a second chipset (U133 Plus 2.0) using RT-PCR, and analyzed in a second, independent sample. A reduction in SAT1 expression identified through multiple probesets was observed across 12 cortical regions in depressed individuals who have died by suicide compared with controls. Of these, five cortical regions showed statistically significant reductions which were supported by RT-PCR and analysis on the additional chipset. SAT1 cortical expression levels were also found to be significantly lower in an independent sample of German subjects with major depression who died by suicide in comparison with controls. These findings suggest that downregulation of SAT1 expression may play a role in depression and suicidality, possibly by impeding the normal PSR program or through compensation for the increased polyamine metabolism accompanying the psychological distress associated with depressive disorders.

Suicide neurobiology

In this review, we examine the history of the neurobiology of suicide, as well as the genetics, molecular and neurochemical findings in suicide research. Our analysis begins with a summary of family, twin, and adoption studies, which provide support for the investigation of genetic variation in suicide risk. This leads to an overview of neurochemical findings restricted to neurotransmitters and their receptors, including recent findings in whole genome gene expression studies. Next, we look at recent studies investigating lipid metabolism, cell signalling with a particular emphasis on growth factors, stress systems with a focus on the role of polyamines, and finally, glial cell pathology in suicide. We conclude with a description of new ideas to study the neurobiology of suicide, including subject-specific analysis, protein modification assessment, neuroarchitecture studies, and study design strategies to investigate the complex suicide phenotype.

Age-related changes in polyamines in memory-associated brain structures in rats

Polyamines putrescine, spermidine and spermine are positively charged aliphatic amines and have important roles in maintaining normal cellular function, regulating neurotransmitter receptors and modulating learning and memory. Recent evidence suggests a role of putrescine in hippocampal neurogenesis, that is significantly impaired during aging. The present study measured the polyamine levels in memory-related brain structures in 24- (aged), 12- (middle-aged) and 4- (young) month-old rats using liquid chromatography/mass spectrometry and high performance liquid chromatography. In the hippocampus, the putrescine levels were significantly decreased in the CA1 and dentate gyrus, and increased in the CA2/3 with age. Significant age-related increases in the spermidine levels were found in the CA1 and CA2/3. There was no difference between groups in spermine in any sub-regions examined. In the parahippocampal region, increased putrescine level with age was observed in the entorhinal cortex, and age did not alter the spermidine levels. The spermine level was significantly decreased in the perirhinal cortex and increased in the postrhinal cortex with age. In the prefrontal cortex, there was age-related decrease in putrescine, and the spermidine and spermine levels were significantly increased with age. This study, for the first time, demonstrates age-related region-specific changes in polyamines in memory-associated structures, suggesting that polyamine system dysfunction may potentially contribute to aged-related impairments in hippocampal neurogenesis and learning and memory.

Exogenous agmatine has neuroprotective effects against restraint-induced structural changes in the rat brain

Agmatine is an endogenous amine derived from decarboxylation of arginine catalysed by arginine decarboxylase. Agmatine is considered a novel neuromodulator and possesses neuroprotective properties in the central nervous system. The present study examined whether agmatine has neuroprotective effects against repeated restraint stress-induced morphological changes in rat medial prefrontal cortex and hippocampus. Sprague-Dawley rats were subjected to 6 h of restraint stress daily for 21 days. Immunohistochemical staining with beta-tubulin III showed that repeated restraint stress caused marked morphological alterations in the medial prefrontal cortex and hippocampus. Stress-induced alterations were prevented by simultaneous treatment with agmatine (50 mg/kg/day, i.p.). Interestingly, endogenous agmatine levels, as measured by high-performance liquid chromatography, in the prefrontal cortex and hippocampus as well as in the striatum and hypothalamus of repeated restraint rats were significantly reduced as compared with the controls. Reduced endogenous agmatine levels in repeated restraint animals were accompanied by a significant increase of arginine decarboxylase protein levels in the same regions. Moreover, administration of exogenous agmatine to restrained rats abolished increases of arginine decarboxylase protein levels. Taken together, these results demonstrate that exogenously administered agmatine has neuroprotective effects against repeated restraint-induced structural changes in the medial prefrontal cortex and hippocampus. These findings indicate that stress-induced reductions in endogenous agmatine levels in the rat brain may play a permissive role in neuronal pathology induced by repeated restraint stress.

Novel stressors affected catecholamine stores in socially isolated normotensive and spontaneously hypertensive rats

Catecholamines in some central (hypothalamus and hippocampus) and peripheral tissues (adrenal glands and heart auricles) of long-term socially isolated normotensive and spontaneously hypertensive rats exposed to novel immobilization stress were determined by a simultaneous single isotope radioenzymatic assay. Long-term isolation (21 days) produced depletion of hypothalamic norepinephrine (NE) stores and hippocampal dopamine (DA) stores in both normotensive and spontaneously hypertensive rats. Acute immobilization stress (2 h) significantly decreased NE and DA stores in hypothalamus and hippocampus of naive normotensive and spontaneously hypertensive rats controls. However, novel immobilization stress applied to normotensive rats previously subjected to long-term isolation produced no changes in catecholamine levels in hypothalamus, while resulting in somewhat higher depletion of NE stores in hypothalamus of spontaneously hypertensive rats treated in the same way. Novel immobilization stress decreased NE and DA stores in hippocampus of normotensive but was without effect on NE and DA stores of spontaneously hypertensive rats. Social isolation did not affect catecholamine stores in peripheral tissues but novel immobilization stress produced a significant decrease in catecholamine content. The results suggest that some central and peripherals tissues of spontaneously hypertensive rats and normotensive rats differ with regard to catecholamine content and that there are certain differences in their responsiveness to stress.

In vivo basal and amphetamine-induced striatal dopamine and metabolite levels are similar in the spontaneously hypertensive, Wistar–Kyoto and Sprague–Dawley male rats

Nigrostriatal alterations are proposed to partially underlie the hypertension and hyperactivity exhibited by the spontaneously hypertensive rat (SHR). Here, in vivo microdialysis was used to measure baseline and d-amphetamine (AMPH)-stimulated striatal dopamine (DA) and metabolite levels in adult male SHR, Wistar-Kyoto (WKY), and Sprague-Dawley (SD) rats. At approximately 19 weeks of age, baseline levels of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were measured after which time, each rat was injected intraperitoneally with 2 mg/kg AMPH and samples were collected for the subsequent 200 min. There were no significant strain differences in baseline levels of DA, HVA, and 5-HIAA. The baseline level of DOPAC was decreased in the WKY relative to the SD. AMPH treatment altered DA, DOPAC, HVA, and 5-HIAA to a similar extent in all strains; thus, there were no significant strain differences, nor did the area under the curve (AUC) for DA levels differ between strains. AUC for DOPAC was significantly smaller for the WKY relative to the SD strain, likely due to the lower baseline level. At the single dose of amphetamine used here, the results indicate that in vivo DA levels in the SHR are similar to the WKY and SD strains.