Differential effects of i.c.v. microinfusion of agmatine on spatial working and reference memory in the rat

Agmatine alleviates ethanol withdrawal-associated cognitive impairment and neurochemical imbalance in rats

The present study aimed to investigate the role of agmatine in the neurobiology underlying memory impairment during ethanol withdrawal in rats. Sprague-Dawley rats were subjected to a 21-day chronic ethanol exposure regimen (2.4 % w/v ethanol for 3 days, 4.8 % w/v for the next 4 days, and 7.2 % w/v for the following 14 days), followed by a withdrawal period. Memory impairment was assessed using the passive avoidance test (PAT) at 24, 48, and 72 h post-withdrawal. The ethanol-withdrawn rats displayed a significant decrease in step-through latency in the PAT, indicative of memory impairment at 72 h post-withdrawal. However, administration of agmatine (40 µg/rat) and its modulators (L-arginine, arcaine, and amino-guanidine) significantly increases the latency time in the ethanol-withdrawn rats, demonstrating the attenuation of memory impairment. Further, pretreatment with imidazoline receptor agonists enhances agmatine's effects, while antagonists block them, implicating imidazoline receptors in agmatine's actions. Neurochemical analysis in ethanol-withdrawn rats reveals dysregulated glutamate and GABA levels, which was attenuated by agmatine and its modulators. By examining the effects of agmatine administration and modulators of endogenous agmatine, the study aimed to shed light on the potential therapeutic implications of agmatinergic signaling in alcohol addiction and related cognitive deficits. Thus, the present findings suggest that agmatine administration and modulation of endogenous agmatine levels hold potential as therapeutic strategies for managing alcohol addiction and associated cognitive deficits. Understanding the neurobiology underlying these effects paves the way for the development of novel interventions targeting agmatinergic signaling in addiction treatment.

Agmatine mitigates behavioral abnormalities and neurochemical dysregulation associated with 3-Nitropropionic acid-induced Huntington's disease in rats

Huntington's disease (HD) is a progressive neurodegenerative condition characterized by a severe motor incoordination, cognitive decline, and psychiatric complications. However, a definitive cure for this devastating disorder remains elusive. Agmatine, a biogenic amine, has gain attention for its reported neuromodulatory and neuroprotective properties. The present study was designed to examine the influence of agmatine on the behavioral, biochemical, and molecular aspects of HD in an animal model. A mitochondrial toxin, 3-nitro propionic acid (3-NP), was used to induce HD phenotype and similar symptoms such as motor incoordination, memory impairment, neuro-inflammation, and depressive-like behavior in rats. Rats were pre-treated with 3-NP (10 mg/kg, i.p.) on days 1, 3, 5, 7, and 9 and then continued on agmatine treatment (5 - 20 µg/rat, i.c.v.) from day-8 to day-27 of the treatment protocol. 3-NP-induced cognitive impairment was associated with declined in agmatine levels within prefrontal cortex, striatum, and hippocampus. Further, the 3-NP-treated rats showed an increase in IL-6 and TNF-α and a reduction in BDNF immunocontent within these brain areas. Agmatine treatment not only improved the 3-NP-induced motor incoordination, depression-like behavior, rota-rod performance, and learning and memory impairment but also normalized the GABA/glutamate, BDNF, IL-6, and TNF-α levels in discrete brain areas. Similarly, various agmatine modulators, which increase the endogenous agmatine levels in the brain, such as L-arginine (biosynthetic precursor), aminoguanidine (diamine oxidase inhibitor), and arcaine (agmatinase inhibitor) also demonstrated similar effects exhibiting the importance of endogenous agmatinergic pathway in the pathogenesis of 3-NP-induced HD like symptoms. The present study proposed the possible role of agmatine in the pathogenesis and treatment of HD associated motor incoordination, and psychiatric and cognitive complications.

Neuroprotection by agmatine: Possible involvement of the gut microbiome?

Agmatine, an endogenous polyamine derived from L-arginine, elicits tremendous multimodal neuromodulant properties. Alterations in agmatinergic signalling are closely linked to the pathogeneses of several brain disorders. Importantly, exogenous agmatine has been shown to act as a potent neuroprotectant in varied pathologies, including brain ageing and associated comorbidities. The antioxidant, anxiolytic, analgesic, antidepressant and memory-enhancing activities of agmatine may derive from its ability to regulate several cellular pathways; including cell metabolism, survival and differentiation, nitric oxide signalling, protein translation, oxidative homeostasis and neurotransmitter signalling. This review briefly discusses mammalian metabolism of agmatine and then proceeds to summarize our current understanding of neuromodulation and neuroprotection mediated by agmatine. Further, the emerging exciting bidirectional links between agmatine and the resident gut microbiome and their implications for brain pathophysiology and ageing are also discussed.

Agmatine prevents the manifestation of impulsive burying and depression-like behaviour in progesterone withdrawn female rats

Premenstrual dysphoric disorder (PMDD) is characterized by various physical and affective symptoms, including anxiety, irritability, anhedonia, social withdrawal, and depression. The present study investigated the role of the agmatinergic system in animal model of progesterone withdrawal in female rats. Chronic progesterone exposure of female rats for 21 days and its abrupt withdrawal showed enhanced marble burying, increased immobility time, and reduced no. of entries in open arm as compared to control animals. The progesterone withdrawal-induced enhanced marble burying anxiety and immobility time was significantly attenuated by agmatine (5-20 mg/kg, i.p.), and its endogenous modulators like L-arginine (100 mg/kg, i.p.), amino-guanidine (25 mg/kg, i.p.) and arcaine (50 mg/kg, i.p.) by their once-daily administration from day 14-day 21 of the protocol. We have also analysed the levels of agmatine, progesterone, and inflammatory cytokines in the hippocampal region of progesterone withdrawn rats. There was a significant decline in agmatine and progesterone levels and an elevation in cytokine levels in the hippocampal region of progesterone withdrawn rats compared to the control animals. In conclusion, the present studies suggest the importance of the endogenous agmatinergic system in progesterone withdrawal-induced anxiety-like and depression-like behaviour. The data also projects agmatine as a potential therapeutic target for the premenstrual dysphoric disorder.

Agmatine prevents development of tolerance to anti-nociceptive effect of ethanol in mice

Drug tolerance is directly correlated with drug abuse and physical dependence. The development of tolerance is manifested as the decline in pharmacological responses of drugs following repeated administration of the constant dose. The present study evaluated the effect of agmatine in ethanol-induced anti-nociception and tolerance in the tail-flick assay in mice. In an acute protocol, ethanol (1 and 2 g/kg, i.p. [intraperitoneally]) and agmatine (20 and 40 μg/mouse, i.c.v. [intracerebroventricularly]) produced significant analgesic effects in mice, as was evident from the increased baseline tail-flick latency when tested 20 minutes after their administration. Agmatine in a per se non-effective dose (5 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), and arcaine (25 μg/mouse, i.c.v.) significantly potentiated the anti-nociceptive effect of ethanol. Blood ethanol analysis showed no significant differences in blood ethanol concentration between ethanol/saline- and ethanol/agmatine-treated mice, suggesting that the effects of agmatine were not due to any possible effects on the pharmacokinetics of ethanol. In a separate study, mice were injected with ethanol (2 g/kg, i.p., 12%) or saline (1 mL/kg, i.p.) once daily for 9 days. On days 1, 3, 5, 7, and 9 of the experiment, they were subjected to the tail-flick test. Agmatine (5-20 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), arcaine (25 μg/mouse, i.c.v.), aCSF (2 μL/mouse, i.c.v.), or saline (1 mL/kg, i.p.) was administered daily prior to the first daily ethanol or saline injections, and reaction latencies were determined in the tail-flick assay. Injections of agmatine, L-arginine, and arcaine prevented the development of tolerance to ethanol-induced analgesia. Given that agmatine and its endogenous modulation can prevent tolerance to the anti-nociceptive effects of ethanol, these data suggest it as a possible new therapeutic strategy for the treatment of alcohol use disorder and associated complications.

Possible involvement of agmatine in neuropharmacological actions of metformin in diabetic mice

The risk of psychiatric and neurological disorders is significantly higher in patients with diabetes mellitus. Diabetic patients are more susceptible to depression, anxiety and memory impairment as compared with non-diabetic individuals. Metformin, a biguanide used for the management of type 2 diabetes mellitus (T2DM), promotes neurogenesis, enhances spatial memory function and protects the brain against oxidative imbalance beyond its effect on glucose metabolism. However, the exact mechanism of its neuropharmacological actions in T2DM is not known. We investigated the role of the agmatinergic system in neuropharmacological actions of metformin in diabetic mice. Diabetes was induced by the streptozotocin (STZ) injection and confirmed by high blood glucose levels. After 28 days, STZ treated mice exhibited memory impairment in radial arm maze, depression-like behavior in forced swim test and anxiety-like behavior in elevated plus maze along with increased expression of pro-inflammatory cytokines like TNF-α, IL-1β, IL-6, IL-10 also, reduced agmatine and BDNF levels in the hippocampus and prefrontal cortex compared to the control animals. Metformin and agmatine alone or in combination, by once-daily administration during 14-27 day of the protocol significantly reversed the STZ induced high blood glucose levels, memory impairment, depression and anxiety-like behaviors. It also reduced neuro-inflammatory markers and increased agmatine and BDNF levels in the hippocampus and prefrontal cortex. The present study suggests the importance of endogenous agmatine in the neuropharmacological action of metformin in diabetic mice. The data projects agmatine and metformin combination as a potential therapeutic strategy for diabetes associated memory impairment, depression, anxiety, and other comorbidities.

Reversal of lipopolysaccharide-induced learning and memory deficits by agmatine in mice

MATERIALS AND METHODS

Learning and memory functions in animals were evaluated by using Novel object recognition (NOR) and Morris water maze (MWM) tests. Following 7 days of LPS administration, animals were subjected to NOR test on Day-8 and MWM test on Days-9 to 13 for the assessment of recognition and spatial learning and memory, respectively.

RESULTS

LPS administration produced significant deficits in recognition and spatial memory in mice after seven days of LPS administration. In LPS pre-treated mice, agmatine treatment on Day-8 resulted in the increased exploration to the novel object. Agmatine treatment (Day 8-12) in mice showed reduction in the escape latency and time spent in the target quadrant (probe trial) in the MWM test. However, co-administration of agmatine with LPS in mice for 7 days showed higher discrimination index in NOR test on Day-8. This co-administration also decreased escape latency and time spent in the target quadrant in MWM test on Days 9-13 as compared to LPS control group.

CONCLUSION

Results implies the protective and curative effects of agmatine against LPS-induced loss of memory functions in experimental animals.HighlightsSubchronic but not acute lipopolysaccharides induce memory deficitsLipopolysaccharides impairs recognition and spatial memory in mice.Agmatine prevents lipopolysaccharides-induced loss of memory.Agmatine reverses deficits in learning and memory by lipopolysaccharides.

Agmatine improves the behavioral and cognitive impairments associated with chronic gestational ethanol exposure in rats

Chronic maternal ethanol exposure leads to poor intelligence, impaired cognition and array of neurological symptoms in offsprings and commonly referred as fetal alcohol spectrum disorder (FASD). Despite high prevalence and severity, the neurochemical basis of FASD remains largely unexplored. The present study evaluated the pharmacological effects of agmatine in cognitive deficits associated with FAS in rat's offsprings prenatally exposed to alcohol. Pregnant rats received ethanol in liquid modified diet during the entire gestational period of 21 days. Offsprings were treated with agmatine (20-80 mg/Kg, i.p.) during early postnatal days (PND: 21-35) and subsequently evaluated for anxiety in elevated plus maze (EPM), depression in forced swim test (FST) and learning and memory in Morris's water maze (MWM) during post adolescent phase. Hippocampal agmatine, BDNF, TNF-α and IL-6 levels were also analyzed in prenatally ethanol exposed pups. Offsprings prenatally exposed to ethanol demonstrated delayed righting reflex, reduced exploratory behavior along with anxiety, depression-like behavior and impaired memory. These behavioral abnormalities were correlated with a significant reduction in hippocampal agmatine and BDNF levels and elevation in TNF-α and IL-6 immunocontent. Chronic agmatine (40 and 80 mg/Kg, i.p.) administration for 15 days (PND: 21-35), improved entries and time spent in open arm of EPM, decreased immobility time in FST. It also reduced latency to reach the platform location; increased the number of entries, time spent in platform quadrant and also number of crossing over platform quadrant when subjected to MWM test in prenatally ethanol exposed offsprings. This study provides functional evidences for the therapeutic potential of agmatine in cognitive impairment and other neurological complications associated with FASD.

Effects of agmatine, glutamate, arginine, and nitric oxide on executive functions in children with attention deficit hyperactivity disorder

In this study, we aimed to investigate the effects of agmatine, nitric oxide (NO), arginine, and glutamate, which are the metabolites in the polyamine pathway,  on the performance of executive functions (EF) in attention deficit hyperactivity disorder (ADHD). The ADHD group included 35 treatment-naive children (6-14 years old) who were ewly diagnosed with ADHD. The control group consisted of 35 healthy children with the same age and sex, having no previous psychiatric disorders. In the study groups, Stroop test (ST) and trail making test (TMT) were used to monitor EF, and blood samples were collected to measure agmatine with ultra-high-performance liquid chromatography and NO, glutamate, and arginine with enzyme-linked immunosorbent assay (ELISA). The EFs were significantly impaired in the ADHD group. The agmatine and arginine levels of the ADHD group were significantly higher than their peers. The NO and glutamate levels were also higher in the ADHD group compared to the control group, but these differences did not reach statistical significance. Children with ADHD had more difficulties during EF tasks compared to healthy children. The elevated NO and glutamate levels may be related with the impairment during EF tasks. Therefore, agmatine and arginine may increase to improve EF tasks through its inhibitory effect on the synthesis of NO and glutamate. Further studies are needed about polyamine pathway molecules to shed light on the pathophysiology of ADHD.

Comparative Effectiveness of Agmatine and Choline Treatment in Rats with Cognitive Impairment Induced by AlCl3 and Forced Swim Stress

AIM

Endogenous agmatine has a significant role in learning and memory processes as a neurotransmitter. Various studies described the physiological role of endogenous agmatine in learning and memory of multiple cognitive tasks suggesting elevated levels of agmatine during the learning process in the rat brain. Dietary intake of choline showed correlation with cognitive functions in human subjects and treatment with choline supplements validated the ability to diminish learning and cognitive impairment dementias.

METHODS

36 Albino rats were equally divided into three groups previously: a) control-water, b) Test I - AlCl3 (100 mg/Kg body weight), and c) Test II - Forced swim stress (FSS) for 14 days. On the next day of AlCl3 and FSS last administration, animals were allocated into further three groups and received the following treatments: a. water was given orally to the control group, b. Agmatine (100 mg/Kg Body Weight) group, and c. Choline (100 mg/Kg Body Weight) group for the next 14 days. Behaviors were assessed in Light/Dark Box, Open Field, Novel Object Recognition Test (NOR), T Maze Test, and Morris Water Maze Test.

RESULTS

Animals administered with agmatine demonstrated increased time spent in bright areas of light/dark box and square crossed while improved spatial memory in Morris water maze and T maze test and enhanced discrimination of novel object in NOR were observed in learning and memory paradigms along with choline.

CONCLUSION

The present study determines that agmatine at the dose of (100 mg/kg body weight) attenuates memory and cognitive impairment in comparison with choline supplements.

Therapeutic Effect of Agmatine on Neurological Disease: Focus on Ion Channels and Receptors

The central nervous system (CNS) is the most injury-prone part of the mammalian body. Any acute or chronic, central or peripheral neurological disorder is related to abnormal biochemical and electrical signals in the brain cells. As a result, ion channels and receptors that are abundant in the nervous system and control the electrical and biochemical environment of the CNS play a vital role in neurological disease. The N-methyl-D-aspartate receptor, 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl) propanoic acid receptor, kainate receptor, acetylcholine receptor, serotonin receptor, α2-adrenoreceptor, and acid-sensing ion channels are among the major channels and receptors known to be key components of pathophysiological events in the CNS. The primary amine agmatine, a neuromodulator synthesized in the brain by decarboxylation of L-arginine, can regulate ion channel cascades and receptors that are related to the major CNS disorders. In our previous studies, we established that agmatine was related to the regulation of cell differentiation, nitric oxide synthesis, and murine brain endothelial cell migration, relief of chronic pain, cerebral edema, and apoptotic cell death in experimental CNS disorders. In this review, we will focus on the pathophysiological aspects of the neurological disorders regulated by these ion channels and receptors, and their interaction with agmatine in CNS injury.

Altered plasma arginine metabolome precedes behavioural and brain arginine metabolomic profile changes in the APPswe/PS1ΔE9 mouse model of Alzheimer's disease

While amyloid-beta (Aβ) peptides play a central role in the development of Alzheimer's disease (AD), recent evidence also implicates altered metabolism of L-arginine in the pathogenesis of AD. The present study systematically investigated how behavioural function and the brain and plasma arginine metabolic profiles changed in a chronic Aβ accumulation model using male APPswe/PS1ΔE9 transgenic (Tg) mice at 7 and 13 months of age. As compared to their wild-type (WT) littermates, Tg mice displayed age-related deficits in spatial water maze tasks and alterations in brain arginine metabolism. Interestingly, the plasma arginine metabolic profile was markedly altered in 7-month Tg mice prior to major behavioural impairment. Receiver operating characteristic curve analysis revealed that plasma putrescine and spermine significantly differentiated between Tg and WT mice. These results demonstrate the parallel development of altered brain arginine metabolism and behavioural deficits in Tg mice. The altered plasma arginine metabolic profile that preceded the behavioural and brain profile changes suggests that there may be merit in an arginine-centric set of ante-mortem biomarkers for AD.

Effects of withdrawal from repeated phencyclidine administration on behavioural function and brain arginine metabolism in rats

Phencyclidine (PCP) induces behavioural changes in humans and laboratory animals that resemble positive and negative symptoms, and cognitive impairments in schizophrenia. It has been shown repeated treatment of PCP leading to persistent symptoms even after the drug discontinuation, and there is a growing body of evidence implicating altered arginine metabolism in the pathogenesis of schizophrenia. The present study investigated the effects of withdrawal from repeated daily injection of PCP (2mg/kg) for 12 consecutive days on animals'behavioural performance and arginine metabolism in the hippocampus and prefrontal cortex in male young adult rats. Repeated PCP treatment reduced spontaneous alternations in the Y-maze and exploratory and locomotor activities in the open field under the condition of a washout period of 24h, but not 4days. Interestingly, the PCP treated rats also displayed spatial working memory deficits when tested 8-10days after withdrawal from PCP and showed altered levels of arginase activities and eight out of ten l-arginine metabolites in neurochemical- and region-specific manner. Cluster analyses showed altered relationships among l-arginine and its three main metabolites as a function of withdrawal from repeated PCP treatment in a duration-specific manner. Multiple regression analysis revealed significant neurochemical-behavioural correlations. Collectively, the results suggest both the residual and long-term effects of withdrawal from repeated PCP treatment on behavioural function and brain arginine metabolism. These findings demonstrate, for the first time, the influence of the withdrawal duration on animals' behaviour and brain arginine metabolism.

Agmatine ameliorates type 2 diabetes induced-Alzheimer's disease-like alterations in high-fat diet-fed mice via reactivation of blunted insulin signalling

The risk of Alzheimer's disease (AD) is higher in patients with type 2 diabetes mellitus (T2DM). Previous studies in high-fat diet-induced AD animal models have shown that brain insulin resistance in these animals leads to the accumulation of amyloid beta (Aβ) and the reduction in GSK-3β phosphorylation, which promotes tau phosphorylation to cause AD. No therapeutic treatments that target AD in T2DM patients have yet been discovered. Agmatine, a primary amine derived from l-arginine, has exhibited anti-diabetic effects in diabetic animals. The aim of this study was to investigate the ability of agmatine to treat AD induced by brain insulin resistance. ICR mice were fed a 60% high-fat diet for 12 weeks and received one injection of streptozotocin (100 mg/kg/ip) 4 weeks into the diet. After the 12-week diet, the mice were treated with agmatine (100 mg/kg/ip) for 2 weeks. Behaviour tests were conducted prior to sacrifice. Brain expression levels of the insulin signal molecules p-IRS-1, p-Akt, and p-GSK-3β and the accumulation of Aβ and p-tau were evaluated. Agmatine administration rescued the reduction in insulin signalling, which in turn reduced the accumulation of Aβ and p-tau in the brain. Furthermore, agmatine treatment also reduced cognitive decline. Agmatine attenuated the occurrence of AD in T2DM mice via the activation of the blunted insulin signal.

Interactions of nitric oxide with α2 -adrenoceptors within the locus coeruleus underlie the facilitation of inhibitory avoidance memory by agmatine

BACKGROUND AND PURPOSE

Agmatine, a putative neurotransmitter, plays a vital role in learning and memory. Although it is considered an endogenous ligand of imidazoline receptors, agmatine exhibits high affinity for α-adrenoceptors, NOS and NMDA receptors. These substrates within the locus coeruleus (LC) are critically involved in learning and memory processes.

EXPERIMENTAL APPROACH

The hippocampus and LC of male Wistar rat were stereotaxically cannulated for injection. Effects of agmatine, given i.p. or intra-LC, on acquisition, consolidation and retrieval of inhibitory avoidance (IA) memory were measured. The NO donor S-nitrosoglutathione, non-specific (L-NAME) and specific NOS inhibitors (L-NIL, 7-NI, L-NIO), the α2 -adrenoceptor antagonist (yohimbine) or the corresponding agonist (clonidine) were injected intra-LC before agmatine. Intra-hippocampal injections of the NMDA antagonist, MK-801 (dizocilpine), were used to modify the memory enhancing effects of agmatine, SNG and yohimbine. Expression of tyrosine hydroxylase (TH) and eNOS in the LC was assessed immunohistochemically.

KEY RESULTS

Agmatine (intra-LC or i.p.) facilitated memory retrieval in the IA test. S-nitrosoglutathione potentiated, while L-NAME and L-NIO decreased, these effects of agmatine. L-NIL and 7-NI did not alter the effects of agmatine. Yohimbine potentiated, whereas clonidine attenuated, effects of agmatine within the LC. The effects of agmatine, S-nitrosoglutathione and yohimbine were blocked by intra-hippocampal MK-801. Agmatine increased the population of TH- and eNOS-immunoreactive elements in the LC.

CONCLUSIONS AND IMPLICATIONS

The facilitation of memory retrieval in the IA test by agmatine is probably mediated by interactions between eNOS, NO and noradrenergic pathways in the LC.

Chronic agmatine treatment prevents behavioral manifestations of nicotine withdrawal in mice

Smoking cessation exhibits an aversive withdrawal syndrome characterized by both increases in somatic signs and affective behaviors including anxiety and depression. In present study, abrupt withdrawal of daily nicotine injections (2mg/kg, s.c., four times daily, for 10 days) significantly increased somatic signs viz. rearing, grooming, jumping, genital licking, leg licking, head shakes with associated depression (increased immobility in forced swim test) as well as anxiety (decreased the number of entries and time spent in open arm in elevated plus maze) in nicotine dependent animals. The peak effect was observed at 24h time point of nicotine withdrawal. Repeated administration of agmatine (40-80µg/mouse, i.c.v.) before the first daily dose of nicotine from day 5 to 10 attenuated the elevated scores of somatic signs and abolished the depression and anxiety like behavior induced by nicotine withdrawal in dependent animals. However, in separate groups, its acute administration 30min before behavior analysis of nicotine withdrawal was ineffective. This result clearly shows the role of agmatine in development of nicotine dependence and its withdrawal. In extension to behavioral experiments, brain agmatine analyses, carried out at 24h time point of nicotine withdrawal demonstrated marked decrease in basal brain agmatine concentration as compared to control animals. Taken together, these data support the role of agmatine as common biological substrate for somatic signs and affective symptoms of nicotine withdrawal. This data may project therapies based on agmatine in anxiety, depression and mood changes associated with tobacco withdrawal.

Dissociating effects of spatial learning from locomotor activity for ouabain-induced bipolar disorder-like rats

Whether ouabain, a Na+ - and K+-activated adenosine triphosphatase inhibitor, mimics cognitive impairments that can be dissociated from motor effects in the bipolar disorder-like animal model remains unclear. Ouabain and the vehicle aCSF were microinjected into the left lateral ventricle immediately, after 4h, and after 24h. The results showed that (a) locomotion responses of the Immediate group were significantly decreased compared to those of the aCSF group, particularly the first five minutes. (b) The ouabain-treated rats have longer latency and total distance traveled in the water maze task; however, the velocity was not affected for the ouabain group. (c) The analysis of covariance showed that the latency time (but not the total distance traveled and velocity) of the ouabain group was more impaired than that of the aCSF group, regardless of omitting total distance traveled and cross movement in the open field test. The latency might be more sensitive than the distance traveled and the velocity for assessing spatial learning. Dissociating the spatial learning from the movement may allow testing drug treatments of cognitive deficits independent of locomotor effects associated with bipolar disorder.

Agmatine improves cognitive dysfunction and prevents cell death in a streptozotocin-induced Alzheimer rat model

PURPOSE

Alzheimer's disease (AD) results in memory impairment and neuronal cell death in the brain. Previous studies demonstrated that intracerebroventricular administration of streptozotocin (STZ) induces pathological and behavioral alterations similar to those observed in AD. Agmatine (Agm) has been shown to exert neuroprotective effects in central nervous system disorders. In this study, we investigated whether Agm treatment could attenuate apoptosis and improve cognitive decline in a STZ-induced Alzheimer rat model.

MATERIALS AND METHODS

We studied the effect of Agm on AD pathology using a STZ-induced Alzheimer rat model. For each experiment, rats were given anesthesia (chloral hydrate 300 mg/kg, ip), followed by a single injection of STZ (1.5 mg/kg) bilaterally into each lateral ventricle (5 μL/ventricle). Rats were injected with Agm (100 mg/kg) daily up to two weeks from the surgery day.

RESULTS

Agm suppressed the accumulation of amyloid beta and enhanced insulin signal transduction in STZ-induced Alzheimer rats [experimetal control (EC) group]. Upon evaluation of cognitive function by Morris water maze testing, significant improvement of learning and memory dysfunction in the STZ-Agm group was observed compared with the EC group. Western blot results revealed significant attenuation of the protein expressions of cleaved caspase-3 and Bax, as well as increases in the protein expressions of Bcl2, PI3K, Nrf2, and γ-glutamyl cysteine synthetase, in the STZ-Agm group.

CONCLUSION

Our results showed that Agm is involved in the activation of antioxidant signaling pathways and activation of insulin signal transduction. Accordingly, Agm may be a promising therapeutic agent for improving cognitive decline and attenuating apoptosis in AD.

Putative agmatinase inhibitor for hypoxic-ischemic new born brain damage

Agmatine is an endogenous brain metabolite, decarboxylated arginine, which has neuroprotective properties when injected intraperitoneally (i.p.) into rat pups following hypoxic-ischemia. A previous screen for compounds based on rat brain lysates containing agmatinase with assistance from computational chemistry, led to piperazine-1-carboxamidine as a putative agmatinase inhibitor. Herein, the neuroprotective properties of piperazine-1-carboxamidine are described both in vitro and in vivo. Organotypic entorhinal-hippocampal slices were firstly prepared from 7-day-old rat pups and exposed in vitro to atmospheric oxygen depletion for 3 h. Upon reoxygenation, the slices were treated with piperazine-1-carboxamidine or agmatine (50 μg/ml agents), or saline, and 15 h later propidium iodine was used to stain. Piperazine-1-carboxamidine or agmatine produced substantial in vitro protection compared to post-reoxygenated saline-treated controls. An in vivo model involved surgical right carotid ligation followed by exposure to hypoxic-ischemia (8 % oxygen) for 2.5 h. Piperazine-1-carboxamidine at 50 mg/kg i.p. was given 15 min post-reoxygenation and continued twice daily for 3 days. Cortical agmatine levels were elevated (+28.5 %) following piperazine-1-carboxamidine treatment with no change in arginine or its other major metabolites. Histologic staining with anti-Neun monoclonal antibody also revealed neuroprotection of CA1-3 layers of the hippocampus. Until endpoint at 22 days of age, no adverse events were observed in treated pups' body weights, rectal temperatures, or prompted ambulation. Piperazine-1-carboxamidine therefore appears to be a neuroprotective agent of a new category, agmatinase inhibitor.

Effects of prolonged agmatine treatment in aged male Sprague-Dawley rats

Increasing evidence suggests that altered arginine metabolism contributes to cognitive decline during ageing. Agmatine, decarboxylated arginine, has a variety of pharmacological effects, including the modulation of behavioural function. A recent study demonstrated the beneficial effects of short-term agmatine treatment in aged rats. The present study investigated how intraperitoneal administration of agmatine (40mg/kg, once daily) over 4-6weeks affected behavioural function and neurochemistry in aged Sprague-Dawley rats. Aged rats treated with saline displayed significantly reduced exploratory activity in the open field, impaired spatial learning and memory in the water maze and object recognition memory relative to young rats. Prolonged agmatine treatment improved animals' performance in the reversal test of the water maze and object recognition memory test, and significantly suppressed age-related elevation in nitric oxide synthase activity in the dentate gyrus of the hippocampus and prefrontal cortex. However, this prolonged supplementation was unable to improve exploratory activity and spatial reference learning and memory in aged rats. These findings further demonstrate that exogenous agmatine selectively improves behavioural function in aged rats.

Participation of hippocampal agmatine in spatial learning: an in vivo microdialysis study

Agmatine, decarboxylated arginine, is widely distributed in mammalian brains and is considered as a novel putative neurotransmitter. Recent research demonstrates spatial learning-induced increases in agmatine in memory-related structures at the tissue and presynaptic terminal levels. By using the in vivo microdialysis technique coupled with highly sensitive liquid chromatography/mass spectrometry assay, we investigated dynamic changes of extracellular agmatine in the rat dorsal hippocampus before, during and after water maze training to find a fixed hidden platform on the first and forth day of testing. It was firstly noted that the basal level of extracellular agmatine was significantly elevated on day 4. While swimming per se had no effect, a rapid rise (2-6 folds) in extracellular agmatine was observed during water maze training regardless of testing day. Such learning-induced rise was found to successively lessen across the multiple blocks of training on day 1. However, this pattern was reversed on day 4 when the platform was removed during the final training trial. The present study, for the first time, demonstrates water maze training-induced increase of extracellular agmatine in the dorsal hippocampus. The results suggest a role of endogenous agmatine in the encoding and retrieval of spatial information.

Ageing alters behavioural function and brain arginine metabolism in male Sprague-Dawley rats

A growing body of evidence suggests the involvement of L-arginine and its metabolites in the ageing and neurodegenerative processes. The present study assessed behavioural performance in 4- (young), 12- (middle-aged) and 24- (aged) month-old male Sprague-Dawley rats, and investigated age-related changes in the activity of two key arginine metabolic enzymes, nitric oxide synthase (NOS) and arginase, and the levels of L-arginine and its downstream metabolites in a number of memory-related brain structures. Aged rats were less anxious and performed poorly in the water maze task relative to the young and middle-aged rats, and both middle-aged and aged rats displayed reduced exploratory activity relative to the young ones. There were significant age-related changes in NOS and arginase activities, and the levels of L-arginine, L-citrulline, L-ornithine, agmatine, putrescine, spermidine, spermine and glutamate, but not γ-aminobutyric acid, in the CA1, CA2/3 and dentate gyrus sub-regions of the hippocampus and the prefrontal, entorhinal, perirhinal, postrhinal and temporal (an auditory cortex) cortices in a region-specific manner. Cluster analyses revealed that the nine related neurochemical variables formed distinct groups, which changed as a function of ageing. Multiple regression analyses revealed a number of significant correlations between the neurochemical and behavioural variables. The present study further supports the involvement of arginine metabolism in the ageing process, and provides further evidence of the effects of animals' behavioural experience on arginine metabolism.

Agmatine, a metabolite of L-arginine, reverses scopolamine-induced learning and memory impairment in rats

Agmatine (l-amino-4-guanidino-butane), a metabolite of L-arginine through the action of arginine decarboxylase, is a novel neurotransmitter. In the present study, effects of agmatine on cognitive functions have been evaluated by using one trial step-down passive avoidance and three panel runway task. Agmatine (20, 40, 80 mg/kg i.p.) was administered either in the presence or absence of a cholinergic antagonist, scopolamine (1 mg/kg i.p.). Scopolamine significantly impaired learning and memory in both passive avoidance and three panel runway test. Agmatine did not affect emotional learning, working and reference memory but significantly improved scopolamine-induced impairment of learning and memory in a dose dependent manner. Our results indicate that agmatine, as an endogenous substance, may have an important role in modulation of learning and memory functions.

Agmatine, an endogenous ligand of imidazoline receptor protects against memory impairment and biochemical alterations in streptozotocin-induced diabetic rats

Agmatine, a polycationic amine synthesized via decarboxylation of l-arginine by arginine decarboxylase is reported to exhibit anti-hyperglycemic, antioxidant and memory enhancing effects. Therefore, we tested its influence against cognitive dysfunction in streptozotocin-induced diabetic rats using Morris water maze and object recognition paradigm. Lipid peroxidation and glutathione levels as parameters of oxidative stress and choline esterase (ChE) activity as a marker of cholinergic function were assessed in the cerebral cortex and hippocampus. Thirty days after diabetes induction rats showed a severe deficit in learning and memory associated with increased lipid peroxidation, decreased reduced glutathione, and elevated ChE activity. In contrast, chronic treatment with agmatine (5-10mg/kg, i.p. for 30 days) improved cognitive performance, lowered hyperglycemia, oxidative stress, and ChE activity in diabetic rats. Further, memory improving effects of agmatine were independent of adrenal I(2) imidazoline receptors. In a separate set, agmatine treatment for an initial 15 days after diabetes confirmation also significantly reduced memory impairment during training trials after 30 days of diabetes confirmation. Moreover, treatment during training trials (30 days after diabetes) also significantly reduced memory impairment in diabetic rats. In conclusion, the present study demonstrates that treatment with agmatine prevents changes in oxidative stress and ChE activity, and probably consequent memory impairment in diabetic rats.

Chronic difluoromethylornithine treatment impairs spatial learning and memory in rats

Recent evidence suggests that polyamines putrescine, spermidine and spermine are essential in maintaining normal cellular function. The present study investigated the effects of chronic treatment of difluoromethylornithine (DFMO, 3% in drinking water), a potent inhibitor of putrescine synthesis, for 54 consecutive days on animals'behavior and neurochemical levels in the CA1, CA2/3 and dentate gyrus sub-regions of the hippocampus and the prefrontal cortex. The DFMO group showed performance impairments in the place navigation and the probe test conducted 24 h after the training in the reference memory version of the water maze task, but not in the elevated plus maze, open field, object recognition, cued navigation and the working memory version of the water maze task when compared to the control group (drinking water only). DFMO treatment resulted in approximately 80-90% and 20% of reductions in the putrescine and spermidine levels, respectively, in the four brain regions examined, and a small reduction in agmatine level in the CA2/3, with no effects on spermine, glutamate and γ-aminobutyrate. The DFMO group showed decreased body weight relative to the control one. However, there were no significant differences between groups in the normalized brain, kidney and liver weights. The present study demonstrates that chronic treatment of DFMO depletes putrescine and decreases spermidine levels in the brain, inhibits growth, and impairs spatial learning and memory in the reference memory version of the water maze specifically. These findings merit further investigation to fully understand the functional role of endogenous polyamines in learning and memory.

Agmatine in the hypothalamic paraventricular nucleus stimulates feeding in rats: involvement of neuropeptide Y

BACKGROUND AND PURPOSE

Agmatine, a multifaceted neurotransmitter, is abundantly expressed in the hypothalamic paraventricular nucleus (PVN). Our aim was to assess (i) the effect of agmatine on feeding behaviour and (ii) its association, if any, with neuropeptide Y (NPY).

EXPERIMENTAL APPROACH

Satiated rats fitted with intra-PVN cannulae were administered agmatine, alone or jointly with (i) α₂-adrenoceptor agonist, clonidine, or antagonist, yohimbine; (ii) NPY, NPY Y₁ receptor agonist, [Leu³¹, Pro³⁴]-NPY, or antagonist, BIBP3226; or (iii) yohimbine and NPY. Cumulative food intake was monitored at different post-injection time points. Furthermore, the expression of hypothalamic NPY following i.p. treatment with agmatine, alone or in combination with yohimbine (i.p.), was evaluated by immunocytochemistry.

KEY RESULTS

Agmatine robustly increased feeding in a dose-dependent manner. While pretreatment with clonidine augmented, yohimbine attenuated the orexigenic response to agmatine. Similarly, NPY and [Leu³¹, Pro³⁴]-NPY potentiated the agmatine-induced hyperphagia, whereas BIBP3226 inhibited it. Moreover, yohimbine attenuated the synergistic orexigenic effect induced by the combination of NPY and agmatine. Agmatine increased NPY immunoreactivity in the PVN fibres and in the cells of the hypothalamic arcuate nucleus (ARC) and this effect was prevented by pretreatment with yohimbine. NPY immunoreactivity in the fibres of the ARC, dorsomedial, ventromedial and lateral nuclei of the hypothalamus was not affected by any of the above treatments.

CONCLUSIONS AND IMPLICATIONS

The orexigenic effect of agmatine is coupled to increased NPY activity mediated by stimulation of α₂-adrenoceptors within the PVN. This signifies the importance of agmatine or α₂-adrenoceptor modulators in the development of novel therapeutic agents to treat feeding-related disorders.

Spatial learning-induced increase in agmatine levels at hippocampal CA1 synapses

Agmatine, a metabolite of L-arginine, is considered as a novel putative neurotransmitter. It has been detected in axon terminals that synapse with pyramidal cells in the hippocampus, a brain region that is critically involved in spatial learning and memory. However, the role of agmatine in learning and memory is poorly understood. Recently, we demonstrated water maze training-induced increases in tissue levels of agmatine in the CA1 subregion of the hippocampus. This finding has raised an issue whether an endogenous agmatine could directly participate in learning and memory processes as a neurotransmitter. In the present study, quantitative immunogold-labeling and electron-microscopical techniques were used to analyze the levels of agmatine in CA1 stratum radiatum (SR) terminals (n = 600) of male Sprague-Dawley rats that had been trained to find a hidden escape platform in the water maze (WM) task or forced to swim (SW) in the pool with no platform presented. Agmatine levels were significantly increased by ∼85% in the synaptic terminals of SR of trained WM group compared with the SW control group (all P < 0.001). These results, for the first time, demonstrate spatial learning-induced elevation in agmatine levels at synapses in the hippocampus and provide evidence of its participation in learning and memory processing as a novel neurotransmitter.

The effects of exogenous testosterone on spatial memory in rats

Testosterone (T) is known to affect spatial abilities in men and women. Studies focusing on this relationship showed that both endogenous variability of T and administration of exogenous T, altered mental rotation and spatial visualization. Organizational and activational effects of T can be separately identified. The aim of our study was to evaluate the activational effects of exogenous T on spatial memory in male and female rats. T was administered 3 times a week over a two week period in either 1 mg/kg for low testosterone group or 10 mg/kg for high testosterone group. The Morris water maze was performed to assess the rat’s working and reference spatial memory. T and estradiol levels were measured in plasma. Increase in plasma T levels was confirmed in the experimental groups in comparison to the control groups (receiving sterile oil, 3 times a week over a two week period). Low dose T impaired working, but improved reference memory in female rats. In male rats the negative effects of T (both doses) on reference memory were shown. This experiment showed that the activational effects of exogenous testosterone on spatial memory of rats were gender and dose-dependent.

Repeated agmatine treatment attenuates nicotine sensitization in mice: modulation by alpha2-adrenoceptors

Agmatine [2-(4-aminobutyl)guanidine] is an endogenous amine proposed as a neurotransmitter/neuromodulator that binds to multiple target receptors in brain. Besides, many central and peripheral functions, agmatine have been implicated in the process of drug addiction. The purpose of the present study was to examine the effects of centrally injected agmatine on nicotine induced locomotor sensitization in Swiss male mice. Our data shows that repeated injections of nicotine (0.4 mg/kg, sc, twice daily for 7 days) gradually increased locomotion during 7 days development period or after 3 days (nicotine) withdrawal phase challenged with nicotine (0.4 mg/kg, sc) on day 11. Mice were pretreated with agmatine (40-80 microg, icv) or agents known to increase endogenous brain agmatine levels [e.g. an agmatine biosynthetic precursor, L-arginine (80 microg, icv), ornithine decarboxylase inhibitor, difluoromethyl-ornithine (50 microg, icv), diamine oxidase inhibitor, aminoguanidine (25 microg, icv) and agmatinase inhibitor, arcaine (50 microg, icv)] 30 min before daily first nicotine injection or during nicotine withdrawal phase. All these treatments attenuated the development as well as incubation of locomotor sensitization to nicotine. Coadministration of agmatine (20 microg, icv) and alpha(2)-adrenoreceptors agonist, clonidine (0.1 microg, icv) evoked synergistic inhibition of nicotine sensitization. Conversely, prior administration of alpha(2)-adrenoceptor antagonist, yohimbine (5mg/kg, ip) or idazoxan (0.4 mg/kg, ip) reversed the inhibitory effect of agmatine on nicotine sensitization. There was no significant difference in activity between mice injected with any of these agents/saline alone and saline/saline groups. These data indicate that agmatine attenuates nicotine induced locomotor sensitization via a mechanism which may involve alpha(2)-adrenergic receptors. Thus, agmatine might have therapeutic implications in the treatment of nicotine addiction and deserve further investigations.

Agmatine, an endogenous imidazoline receptor ligand modulates ethanol anxiolysis and withdrawal anxiety in rats

Present study investigated the role of agmatine in ethanol-induced anxiolysis and withdrawal anxiety using elevated plus maze (EPM) test in rats. The anxiolytic-like effect of ethanol was potentiated by pretreatment with imidazoline I(1)/I(2) receptor agonist agmatine (10-20 mg/kg, i.p.), imidazoline I(1) receptor agonists, moxonidine (0.25 mg/kg, i.p.) and clonidine (0.015 mg/kg, i.p.), imidazoline I(2) receptor agonist, 2-BFI (5 mg/kg, i.p.) as well as by the drugs known to increase endogenous agmatine levels in brain viz., L-arginine, an agmatine biosynthetic precursor (100 microg/rat, i.c.v.), ornithine decarboxylase inhibitor, DFMO (125 microg/rat, i.c.v.), diamine oxidase inhibitor, aminoguanidine (65 microg/rat, i.c.v.) and agmatinase inhibitor, arcaine (50 microg/rat, i.c.v.). Conversely, prior administration of I(1) receptor antagonist, efaroxan (1 mg/kg, i.p.), I(2) receptor antagonist, idazoxan (0.25mg/kg, i.p.) and arginine decarboxylase inhibitor, D-arginine (100 microg/rat, i.c.v.) blocked the anxiolytic-like effect of ethanol. Moreover, ethanol withdrawal anxiety was markedly attenuated by agmatine (10-20 mg/kg, i.p.), moxonidine (0.25 mg/kg, i.p.), clonidine (0.015 mg/kg, i.p.), 2-BFI (5 mg/kg, i.p.), L-arginine (100 microg/rat, i.c.v.), DFMO (125 microg/rat, i.c.v.), aminoguanidine (65 microg/rat, i.c.v.) and arcaine (50 microg/rat, i.c.v.). The anti-anxiety effect of agmatine in ethanol-withdrawn rats was completely blocked by efaroxan (1 mg/kg, i.p.) and idazoxan (0.25 mg/kg, i.p.). These results suggest that agmatine and imidazoline receptor system may be implicated in ethanol-induced anxiolysis and withdrawal anxiety and strongly support further investigation of agmatine in ethanol dependence mechanism. The data also project agmatine as a potential therapeutic target in overcoming alcohol withdrawal symptoms such as anxiety.

Behavioral effects of agmatine in naive rats are task- and delay-dependent

The present study systematically investigated the effects of agmatine administered i.p. in several commonly used behavioral tasks. In Experiment 1, pre-test treatment of agmatine (1 and 40 mg/kg) appeared to improve animals' performance in the water maze probe test conducted 24 h, but not 120 s, after training, when the effect was evaluated within subjects. In Experiment 2, pre-test agmatine treatment (40 mg/kg) did not affect animals' performance in the open field, and the place navigation, probe tests (1-4 and 6), reversal test and cued navigation in the water maze, but significantly facilitated performance in probe 5 which was conducted 96 h after training. In Experiment 3, rats with pre-test agmatine treatment (40 mg/kg) were less anxious relative to the controls, with no performance changes in the open field. In the water maze task, post-training agmatine treatment (40 mg/kg) did not affect place and cued navigation, but significantly improved animals' performance in the probe test conducted 24 h after training and the reversal test. In the working memory version of the task, agmatine treated rats took significantly less time and generated markedly shorter path length to reach the platform at the 180 s, but not 30 s, delay relative to the controls. In the object recognition task, rats with pre-test agmatine treatment (40 mg/kg) spent significantly more time exploring displaced objects, but not novel object, as compared to the controls. In Experiment 4, pre-test agmatine treatment (40 mg/kg) had no effect on the task acquisition in the delayed non-match to position task in the T-maze, but significantly facilitated performance at the 600 s delay. These results suggest that the behavioral effects of agmatine are task- and delay-dependent, and agmatine facilitates memory particularly when the task difficulty is increased due to memory trace decay and/or greater interference.