Sachie Sasaki-Hamada

Riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines.

In this study, we investigated the anxiolytic-like effect of riluzole using three different innate anxiety models in rats. In the elevated plus-maze test, riluzole significantly increased the time spent in, and entries into, the open arm after 60xa0min administration. This finding was supported by results obtained from light/dark and open-field tests. The magnitude of the anxiolytic-like effects of riluzole in each of the behavioral models was similar to those produced by a benzodiazepine, diazepam, suggesting that riluzole has a robust anxiolytic-like activity in rats. To clarify the involvement of sodium channels in this anxiolytic activity, we examined the effect of a co-administered sodium channel activator, veratrine. The anxiolytic-like action of riluzole was diminished by veratrine in the elevated plus-maze, light/dark and open-field tests. Based on these results, it is suggested that the anxiolytic mechanism of riluzole is clearly distinct from that of diazepam. In addition, to examine whether riluzole directly and non-selectively affected the GABA(A)-benzodiazepine receptor complex, we performed three behavioral tests (footprint analysis, Y-maze test and the ethanol-induced sleeping time test) that are closely related to the GABA(A)-benzodiazepine pathways. In contrast to diazepam, riluzole produced no significant effects in these tests. Here, we provide the first report demonstrating that riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines.

Glucagon‐like peptide‐1 protects synaptic and learning functions from neuroinflammation in rodents

Glucagon‐like peptide‐1 (GLP‐1) is derived from the processing of proglucagon in intestinal L‐cells and releases insulin from pancreatic β‐cells as an incretin. The GLP‐1 receptor has been proposed as a possible therapeutic target for the treatment of Alzheimers disease, in which neuroinflammation is critical in the pathogenesis. The present study investigates whether GLP‐1 (7–36) amide, an active fragment of GLP‐1, protected against synaptic impairments induced by inflammation‐related injurious agents (lipopolysaccharide [LPS], interleukin‐1β [IL‐1β], and H2O2). In the Y‐maze test, LPS (10 μg/mouse, i.c.v) significantly decreased the percentage alternation. Pretreatment with GLP‐1 (7–36) amide (0.09–0.9 nmol/mouse, i.c.v.) prevented an impairment in spontaneous alternation performance. Pretreatment with LPS (10 μg/ml, 2 hr) impaired LTP induction but not paired‐pulse facilitation in the CA1 region of rat hippocampal slices. This impairment was prevented by cotreatment with GLP‐1 (7–36) amide (50 nM). IL‐1β (0.57 nM) or H2O2 (50 μM) also impaired LTP induction. This impairment was prevented by GLP‐1 (7–36) amide (50 nM). These results suggest that GLP‐1 (7–36) amide improves the synaptic impairments induced by inflammation‐related injurious agents in the CA1 region of the hippocampus.

Diabetes onset influences hippocampal synaptic plasticity in streptozotocin-treated rats.

Children with type 1 diabetes mellitus (DM) are at risk of developing cognitive difficulties. Although a diabetes onset of patient influences cognitive difficulties, synaptic properties related to the age of diabetes onset remain unknown. Here we showed that synaptic plasticity including long-term potentiation (LTP) or long-term depression (LTD), and excitatory synaptic transmission at Schaffer collateral-CA1 (SC-CA1) synapses in hippocampal slices were affected by age of onset in rats with streptozotocin-induced diabetes (STZ-rats), compared with age-matched control rats. LTP was impaired and the ratio of AMPA receptor-mediated EPSCs relative to N-methyl-d-aspartate (NMDA) receptor-mediated EPSCs (the AMPA/NMDA ratio) decreased in young adult-onset STZ-rats, whereas LTD was impaired and both AMPA receptor-mediated and NMDA receptor-mediated EPSCs increased in juvenile-onset STZ-rats. Furthermore, impaired LTD of juvenile-onset STZ-rats was restored with an NMDA receptor antagonist. These results suggest that the pathophysiology of diabetes-induced cognitive difficulties varies with the age of diabetes onset.

Glucagon-like peptide-2 but not imipramine exhibits antidepressant-like effects in ACTH-treated mice.

We investigated the effectiveness of glucagon-like peptide-2 (GLP-2) against refractory depression in adrenocorticotropic hormone (ACTH)-treated mice as a model of tricyclic antidepressant (TCA)-resistant depression. Chronic ACTH treatment (0.45 mg/kg, s.c., 14 days) weakened the antidepressant-like effects of imipramine (20 mg/kg, i.p., 6 days) in the forced-swim test (FST). Conversely, GLP-2 (3 μg/mice, i.c.v., 6 days) induced antidepressant-like effects in the ACTH-treated mice in the FST. ACTH-treatment increased basal serum corticosterone levels, with an additional increase induced by the FST. Imipramine or GLP-2 had no effect on the basal corticosterone level, but GLP-2 attenuated the additional increase caused by the FST. Moreover, GLP-2 increased 5-HT levels, but not 5-HIAA. These results suggest that GLP-2 induced antidepressant-like effects under imipramine-resistant conditions through increase in 5-HT levels.

Chemical profiling with HPLC-FTMS of exogenous and endogenous chemicals susceptible to the administration of chotosan in an animal model of type 2 diabetes-induced dementia

In our previous study, the daily administration of chotosan (CTS), a Kampo formula consisting of Uncaria and other 10 different crude drugs, ameliorated cognitive deficits in several animal models of dementia including type 2 diabetic db/db mice in a similar manner to tacrine, an acetylcholinesterase inhibitor. The present study investigated the metabonomics of CTS in db/db mice, a type 2 diabetes model, and m/m mice, a non-diabetes control strain, to identify the exogenous and endogenous chemicals susceptible to the administration of CTS using high performance liquid chromatography equipped with an orbitrap hybrid Fourier transform mass spectrometer. The results obtained revealed that the systemic administration of CTS for 20 days led to the distribution of Uncalia plant-derived alkaloids such as rhynchophylline, hirsuteine, and corynoxeine in the plasma and brains of db/db and m/m mice and induced alterations in four major metabolic pathways; i.e., (1) purine, (2) tryptophan, (3) cysteine and methionine, (4) glycerophospholipids in db/db mice. Moreover, glycerophosphocholine (GPC) levels in the plasma and brain were significantly higher in CTS-treated db/db mice than in vehicle-treated control animals. The results of the in vitro experiment using organotypic hippocampal slice cultures demonstrated that GPC (10-30 μM), as well as tacrine, protected hippocampal cells from N-methyl-d-aspartate-induced excitotoxicity in a manner that was reversible with the muscarinic receptor antagonist scopolamine, whereas GPC had no effect on the activity of acetylcholinesterase in vitro. Our results demonstrated that some CTS constituents with neuropharmacological activity were distributed in the plasma and brain tissue following the systemic administration of CTS and may subsequently have affected some metabolic pathways including glycerophospholipid metabolism and cognitive function in db/db mice. Moreover, the present metabonomic analysis suggested that GPC is a putative endogenous chemical that may be involved in the tacrine-like actions of CTS in the present diabetic animal model.

The impairment in spatial learning and hippocampal LTD induced through the PKA pathway in juvenile-onset diabetes rats are rescued by modulating NMDA receptor function

Childhood- or early adulthood-onset type 1 diabetes is associated with modest impairments in cognition, and has an elevated risk of cognitive decline. Although an earlier onset age of diabetes has been identified as one of the strongest risk factors associated with cognitive dysfunction, little is known about the effects of cognitive performance associated with hippocampal function. Our previous study showed impaired working memory and hippocampal long-term depression (LTD) deficits in juvenile-onset diabetes mellitus (JDM) rats. Here, we demonstrated that treatment with the NMDA open-channel blocker, memantine, rescued hippocampal LTD and hippocampal-dependent memory in JDM rats. In addition, the impairment in LTD was attributed to a malfunction in NR2B-containing NMDA receptors. JDM rats exhibited excessive PKA activity, which may play a role in altered NMDA receptor function and impaired LTD. The changes in NR2B-containing NMDA receptors and PKA activity may be involved in learning impairments in JDM rats. Our findings suggest that NMDA open-channel blockers offer a potential strategy to treat cognitive deficits in childhood-onset diabetes.

Immunohistochemical determination of the site of hypotensive effects of glucagon-like peptide-2 in the rat brain.

Proglucagon-derived glucagon-like peptide-2 (GLP-2) is released from enteroendocrine cells and neurons. GLP-2 regulates energy absorption and epithelial integrity in the gastrointestinal tract, but its effect on blood-pressure regulation remains unknown. In the present study, we found that GLP-2 administered both peripherally and centrally dose-dependently reduced mean arterial blood pressure (MAP) in male Wistar rats anesthetized with urethane and α-chloralose. Immunohistochemical detection of the c-fos protein (Fos) revealed that the peripherally and centrally administered GLP-2 induced Fos-immunoreactivity (Fos-IR) in the nucleus of the solitary tract (NTS) and the caudal ventrolateral medulla (CVLM). In contrast, Fos-IR in brainstem catecholamine neurons decreased after the administration of GLP-2. These results suggest that GLP-2 acts on specific brain nuclei to inhibit sympathetic nerve activity and this leads to hypotension.

Immunohistochemical determination of the site of antidepressant-like effects of glucagon-like peptide-2 in ACTH-treated mice.

The intracerebroventicular administration (i.c.v.) of glucagon-like peptide-2 (GLP-2) had antidepressant-like effects on saline-treated mice in the forced-swim test. The GLP-2 treatment (3 μg, i.c.v.) for 6 days, but not that of imipramine had antidepressant-like effects on adrenocorticotropic hormone (ACTH)-treated mice. The immunohistochemical detection of the c-fos protein (Fos) revealed that the administration of GLP-2 induced Fos-immunoreactivity (Fos-IR) in the dorsomedial hypothalamic nucleus in saline-treated and ACTH-treated mice, and also in the hippocampal dentate gyrus in ACTH-treated mice, but not in saline-treated mice. In contrast, Fos-IR in the paraventricular nucleus of the hypothalamus decreased after the administration of GLP-2 to ACTH-treated mice. In ACTH-treated mice, the chronic administration of GLP-2 affected hippocampal neurogenesis, in addition to Fos-IR in hypothalamic GABAergic neurons and corticotrophin-releasing factor-containing neurons. These results suggest that GLP-2 acts on specific brain regions to regulate stress conditions, and induces antidepressant-like effects under imipramine-resistant conditions, which may be associated with the modulation of the hypothalamic-pituitary-adrenal-axis.

Glucagon-like peptide-2-induced memory improvement and anxiolytic effects in mice

We investigated the effectiveness of glucagon-like peptide-2 (GLP-2) on memory impairment in lipopolysaccharide (LPS)-treated mice, and anxiety-like behavior in adrenocorticotropic hormone (ACTH)-treated mice. In the Y-maze test, LPS (10 µg/mouse, i.c.v.) significantly decreased spontaneous alternation, which was prevented by pretreatment with GLP-2 (0.01-0.3 µg/mouse, i.c.v.). The GLP-2 treatment just before the Y-maze test also improved LPS-induced memory impairment. Continuous treatment with GLP-2 (3 µg/mouse, i.c.v.) had no effect on the open-field test in saline-treated or ACTH-treated mice. Chronic ACTH treatment did not cause anxiogenic effects in the elevated plus-maze test. GLP-2 showed weak anxiolytic-like effects in the elevated plus-maze test in ACTH-treated, but not saline-treated mice. Moreover, GLP-2 increased 5-HT, but not 5-HIAA and tryptophan hydroxylase 2 levels in the amygdala of ACTH-treated mice. Pharmacological depletion of 5-HT prevented the anxiolytic effects of GLP-2. These results suggest that GLP-2 protected and improved memory function in LPS-treated mice, and also had anxiolytic effects due to changes in the 5-HT system.

Characterization of the hypotensive effects of glucagon-like peptide-2 in anesthetized rats

Glucagon-like peptide-2 (GLP-2) is a proglucagon-derived peptide released from enteroendocrine cells and neurons. We recently reported that GLP-2 induced hypotension. In the present study, we characterized the mechanisms of GLP-2-induced hypotension. GLP-2 was administered peripherally or centrally to male Wistar rats anesthetized with urethane and α-chloralose. The rats were vagotomized or systemically pretreated with atropine, prazosin, or propranolol before the GLP-2 administration. The central and peripheral administration of GLP-2 reduced mean arterial blood pressure (MAP). The maximum change of MAP (maximum ΔMAP) was reduced by vagotomy or prazosin, but not propranolol. The effects of the central but not peripheral administration of GLP-2 were reduced by atropine. These results suggest that GLP-2 modulates vagal afferent inputs and inhibits the sympathetic nervous system in the brain to induce hypotension.