Hippocampal acetylcholine receptor activation-dependent long-term depression in streptozotocin-induced diabetic rats

Cholinergic innervation of the hippocampus correlates with memory formation. In a well-established animal model of type 1 diabetes mellitus, obtained by injecting young adult rats with streptozotocin (STZ), reductions have been reported in the expression of acetylcholine receptors and choline acetyltransferase. In this study, we showed that long-term synaptic depression (LTD) induced by carbachol (CCh), a nonselective cholinergic receptor agonist, at Schaffer collateral-CA1 synapses in hippocampal slices was significantly weaker in streptozotocin-induced diabetic rats (STZ rats) than in age-matched control rats. No significant change was observed in the paired-pulse ratio between before and 80 min after the application of CCh in control and STZ rats. Moreover, CCh-induced LTD in control and STZ rats was not affected by an NMDA receptor antagonist. Although the application of CCh down-regulated the surface expression of GluA2 in the hippocampus of control rats, but not STZ rats. Therefore, the present results suggest that acetylcholine receptor-mediated LTD in STZ rats requires the internalization of AMPA receptors on the postsynaptic surface and their intracellular effects in the hippocampus.

Involvement of trigeminal axons in nose-to-brain delivery of glucagon-like peptide-2 derivative

In our previous study, we created a glucagon-like peptide-2 (GLP-2) derivative with the functional sequence PAS-CPP to achieve efficient uptake by the respiratory epithelium and trigeminal nerve. By using octaarginine for cell penetrating peptides (CPP) and FFLIPKG, a reverse sequence of a part of the cathepsin D sequence for the penetration accelerating sequence (PAS), we found that the derivative was taken up by the cells through macropinocytosis and efficiently escaped from the endosomes and exited the cells. Moreover, it showed drug effects by intranasal (in.) administration at the same dose as intracerebroventricular (icv.) administration, which is direct drug administration into the brain. The purpose of this study was to elucidate the cause of the drug effect of in. administered PAS-CPP-GLP-2 at the same dose as that by icv. Administration. The present results suggested that although icv. Administered PAS-CPP-GLP-2 entered the cerebrospinal fluid, it barely penetrated the perivascular space of the brain, and therefore, only a small amount of the administered dose may have reached the site of action in the brain. In contrast, it was qualitatively suggested that in. administered PAS-CPP-GLP-2 migrates from the trigeminal nerve to the central nervous system via the principal sensory trigeminal nucleus and then through the trigeminal lemniscus. The present results show that nose-to-brain delivery by trigeminal axons, which is assumed to be a transcellular pathway, may be possible. As the drug can be delivered into the nerve, it is expected to be applied not only as a central delivery route but also for the treatment of neurological diseases.

Long-term exposure to high glucose induces changes in the expression of AMPA receptor subunits and glutamate transmission in primary cultured cortical neurons

Hyperglycemia, which occurs under the diabetic conditions, induces serious diabetic complications. Diabetic encephalopathy has been defined as one of the major complications of diabetes, and is characterized by neurochemical and neurodegenerative changes. However, little is known about the effect of long-term exposure to high glucose on neuronal cells. In the present study, we showed that exposure to glutamate (100 mM) for 7 days induced toxicity in primary cortical neurons using the MTT assay. Additionally, high glucose increased the sensitivity of AMPA- or NMDA-induced neurotoxicity, and decreased extracellular glutamate levels in primary cortical neurons. In Western blot analyses, the protein levels of the GluA1 and GluA2 subunits of the AMPA receptor as well as synaptophysin in neurons treated with high glucose were significantly increased compared with the control (25 mM glucose). Therefore, long-term exposure to high glucose induced neuronal death through the disruption of glutamate homeostasis.

Usefulness of cell-penetrating peptides and penetration accelerating sequence for nose-to-brain delivery of glucagon-like peptide-2

Neuropeptides are expected as therapeutic drug candidates for central nervous system (CNS) disorders. Intracerebroventricular (i.c.v.) administration of glucagon-like peptide-2 (GLP-2) has an antidepressant-like effect not only in depression model mice but also in treatment-resistant depression model mice. However, because i.c.v. administration is very invasive, research is progressing on brain delivery using intranasal administration as a non-invasive method. After intranasal administration of the drug, there are two routes to the brain. That of direct delivery from the paracellular route of olfactory epithelium to the brain via the olfactory bulb has been studied, and that of systemic absorption via the paracellular route of respiratory epithelium has been put to practical use. The high degree of vascularization and permeability of the nasal mucosa enables drug delivery via the paracellular route that leads to systemic delivery. Therefore, suppressing systemic absorption may increase drug delivery to brain, so we focused on the transcellular route. We created a GLP-2 derivative by adding cell-penetrating peptides (CPP) and penetration accelerating sequences (PAS), which are reported to provide efficient intracellular uptake, to GLP-2. However, to deliver GLP-2 by the transcellular route, GLP-2 must not only be taken up into cells but also move out of the cells. We investigated in vitro and in vivo function of PAS-CPP-GLP-2 to enable the translocation of GLP-2 directly from the nose to the brain. Derivatization of PAS-CPP-GLP-2 prevented its degradation. In the evaluation of intracellular dynamics, PAS-CPP-GLP-2 enhanced cellular uptake by macropinocytosis with CPP and promoted escape from endosomal vesicles by PAS. This study also showed that PAS-CPP-GLP-2 can move out of cells. Furthermore, only this PAS-CPP-GLP-2 showed an antidepression-like effect within 20 min of intranasal administration. Intranasal administered PAS-CPP-GLP-2 surprisingly showed the effect at the same dose with i.c.v. administration, but intravenous administered PAS-CPP-GLP-2 did not show the effect. These results suggested that PAS-CPP-GLP-2 can be efficiently delivered from the nose to the CNS and show a pharmacological effect, demonstrating the usefulness of PAS and CPP for nose-to-brain delivery of GLP-2.

GLP-2 restores impairments in spatial working memory and hippocampal LTD via the MEK/ERK pathway in juvenile-onset diabetes rats

Type 1 diabetic animal models, generated by injecting streptozotocin (STZ), have been widely used in research. We previously reported that juvenile-onset diabetes mellitus (JDM) rats, which were prepared by administering STZ to 17-day-old rats, developed cognitive impairments and hippocampal synaptic plasticity deficiencies, which were restored by glucagon-like peptide-1 (GLP-1). GLP-1 and GLP-2 are simultaneously derived from proglucagon and act through their own specific receptors. The present study was performed to investigate the potential of GLP-2 in JDM rats. The results obtained demonstrated that GLP-2 restored impairments in spatial working memory and hippocampal long-term depression (LTD) in JDM rats, and that the MEK1/2 inhibitor, U0126, inhibited this recovery. Therefore, GLP-2 has potential in the treatment of cognitive deficits in childhood-onset diabetes.

Fluorescein Permeability of the Blood-Brain Barrier Is Enhanced in Juvenile- but Not Young Adult-Onset Type 1 Diabetes in Rats

Clinically, neurological disorders, such as cognitive impairments and dementia, have been reported as diabetic complications, which are remarkable, especially in children with diabetes. The blood-brain barrier (BBB) is a physiologically dynamic regulatory barrier that maintains the consistency of the fluid microenvironment composition of the brain. However, the differences in BBB conditions between children and adults and the contribution of the BBB to the severity of cognitive impairments remain unclear. We generated adult-onset diabetes mellitus (DM) and juvenile-onset diabetes mellitus (JDM) diabetic rat models and investigated BBB functions in these models during the early stages of type 1 diabetes. We performed a BBB permeability assay using sodium fluorescein, a small-molecule fluorescent dye, to evaluate endothelial transport from the blood to the central nervous system. One week after diabetes onset, BBB permeability increased in the hippocampus and striatum of JDM rats, but no changes were observed in the frontal cortex and hypothalamus of JDM rats or for any region of DM rats. The double staining of tight junction proteins and astrocytes revealed no changes in the hippocampus and striatum of JDM rats. These results suggested that the observed increase in BBB permeability during early-stage diabetes onset in JDM rats, which did not depend on the expression of the interendothelial tight junction protein, claudin-5, may affect stylized neural development and cognitive function.

Cognitive and hippocampal synaptic profiles in monosodium glutamate-induced obese mice

Obesity is a growing worldwide public health issue and is associated with a range of comorbidities, including cognitive deficits. The present study investigated synaptic changes in the hippocampus during the development of obesity. The treatment of newborn mice with monosodium-L-glutamate (MSG, 2 mg/g) induced obesity and recognition memory deficits in the novel object recognition (NOR) test at 16-17 weeks, but not at 8-9 weeks. Hippocampal synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), and excitatory synaptic transmission at Schaffer collateral-CA1 (SC-CA1) synapses were compared between MSG-treated mice and age-matched control mice. LTP and fiber volley amplitudes were enhanced in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. Furthermore, the strength of paired-pulse facilitation (PPF) changed in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. These results suggest that enhanced LTP in the SC-CA1 synapses of MSG-induced obese mice involves presynaptic rather than postsynaptic mechanisms.

Glucagon-like peptide-2 rescues memory impairments and neuropathological changes in a mouse model of dementia induced by the intracerebroventricular administration of streptozotocin

Glucagon-like peptide 2 (GLP-2) is derived from the proglucagon gene expressed in the intestines, pancreas and brain. Our previous study showed that GLP-2 improved lipopolysaccharide-induced memory impairments. The current study was designed to further investigated the potential of GLP-2 in memory impairment induced by intracerebroventricular administration of streptozotocin (ICV-STZ) in mice, which have been used as an animal model of sporadic Alzheimer’s disease (AD). STZ was administered on alternate days (Day-1 and Day-3) in order to induce dementia in male ddY mice. ICV-STZ-treated mice were administered GLP-2 (0.6 μg/mouse, ICV) for 5 days from 14 days after the first ICV administration of STZ. In these mice, we examined spatial working memory, the biochemical parameters of oxidative stress, or neurogenesis. The GLP-2 treatment restored spatial working memory in ICV-STZ-treated mice. ICV-STZ-treated mice showed markedly increased thiobarbituric acid reactive species (TBARS) and decreased glutathione (GSH) levels, and GLP-2 significantly restored these ICV-STZ-induced changes. GLP-2 also significantly restored neurogenesis in the subgranular zone of the dentate gyrus in ICV-STZ-treated mice. We herein demonstrated that GLP-2 significantly restored ICV-STZ-induced memory impairments as well as biochemical and histopathological alterations, and accordingly, propose that the memory restorative ability of GLP-2 is due to its potential to reduce oxidative stress.

[Improving Effects of Peptides on Brain Malfunction and Intranasal Delivery of Those Derivatives to the Brain]

This review focuses on the anti-dementia and antidepressant-like effects of peptides including glucagon-like peptide (GLP)-1, GLP-2, neuromedin U (NmU), and oxytocin, and the intranasal delivery of these peptides to the brain. Intracerebroventricularly administered GLP-1, NmU, and oxytocin improved impairment of learning and memory in mice treated with lipopolysaccharide or β-amyloid protein. GLP-1 also improved impairment of learning and memory in juvenile diabetes model rats. On the other hand, GLP-2 exhibited antidepressant-like effects in mice during the forced-swim test, which were associated with 5-HT_1A, α₂, β₁, and D₂ receptors. GLP-2 also exerted antidepressant-like effects in adrenocorticotropic hormone (ACTH)-treated mice through restoration of the hypothalamic-pituitary-adrenal-axis and neurogenesis in the subgranular zone of the dentate gyrus. Because intracerebroventricular administration is invasive and the peptides are unable to penetrate the blood-brain barrier, we introduced our new method of intranasal administration to deliver the peptides to the brain. We prepared a GLP-2 derivative containing cell-penetrating peptides (CPPs) and a penetration accelerating sequence (PAS). Intranasally administered PAS-CPPs-GLP-2 was distributed throughout the brain, and exhibited antidepressant-like effects in both naive and ACTH-treated mice. The derivatives of GLP-1, NmU, and oxytocin with the PAS and CPPs were also distributed throughout the brain after intranasal administration, and improved impairment of learning and memory. We confirmed that our peptide derivatives were effectively delivered into the brain by intranasal administration. As such, these derivatives may be useful for the clinical treatment of psychiatric and neurological diseases.

Administration of a delta opioid receptor agonist KNT-127 to the basolateral amygdala has robust anxiolytic-like effects in rats

RATIONALE

We previously reported that systemic administration of a selective delta opioid receptor (DOP) agonist, KNT-127, produced potent anxiolytic-like effects in rats. Interestingly, DOPs are highly distributed in the basolateral region of the amygdala (BLA).

OBJECTIVES

In this study, we investigated the effect of intra-BLA administration of KNT-127 on anxiety-like behaviors in rats.

METHODS AND RESULTS

In the elevated plus maze test, bilateral injection of KNT-127 into the BLA significantly and dose-dependently increased time spent in the open arms. The magnitude of KNT-127 (0.08 μg/0.2 μl)-induced anxiolytic-like effects was similar to muscimol (0.1 μg/0.2 μl), which is a selective agonist for the gamma amino butyric acid type A receptors. Further, anxiolytic-like effects of KNT-127 were abolished by pretreatment with naltrindole, a selective DOP antagonist, suggesting that KNT-127-induced anxiolytic-like effects are mediated by DOPs. These anxiolytic-like effects were confirmed using another innate anxiety model, the open field test. Interestingly, intra-BLA administration of KNT-127 also induced anxiolytic-like effects in the contextual fear conditioning test. Moreover, these effects were also abolished by naltrindole pretreatment. Finally, we demonstrated that intra-BLA administration of KNT-127 facilitates extinction learning of contextual fear in conditioned rats.

CONCLUSIONS

Altogether, our findings clearly demonstrate that intra-BLA administration of KNT-127 in rats has robust anxiolytic-like effects not only in innate anxiety-like behavioral tests but also in the contextual fear conditioning test.

Effects of centrally administered glucagon-like peptide-2 on blood pressure and barosensitive neurons in spontaneously hypertensive rats

The central administration of glucagon-like peptide-2 (GLP-2) decreases blood pressure in rats. In the present study, we investigated the hypotensive effects of GLP-2 using spontaneously hypertensive rats (SHRs), an animal model of hypertension. The central administration of GLP-2 (0.6 μg) decreased mean arterial pressure (MAP) in SHRs (-24.1 ± 4.5%; P < 0.05), but not in normotensive Wistar-Kyoto (WKY) rats (-10.6 ± 7.4%; P > 0.05), whereas GLP-2 (6 μg) decreased MAP in WKY rats (-23.5 ± 4.2%; P < 0.05) and SHRs (-46.7 ± 11.6%; P < 0.01) under anesthesia with urethane and α-chloralose. Histological analyses revealed that the central administration of GLP-2 (6 μg) induced Fos immunoreactivity (Fos-IR) in the hypothalamic and medullary areas in WKY rats and SHRs. However, the distribution of Fos-IR in GABAergic neurons in the rostral ventrolateral medulla (RVLM) differed between WKY rats and SHRs. GLP-2 directly modulated the excitability of RVLM neurons in brainstem slices from SHRs, but not WKY rats. These results suggest that neuronal activity through the activation of GLP-2 receptors in the RVLM contributes to lowering blood pressure in SHRs.

Endogenous acetylcholine regulates neuronal and astrocytic vascular endothelial growth factor expression levels via different acetylcholine receptor mechanisms

Vascular endothelial growth factor (VEGF), a signaling molecule involved in angiogenesis, plays an important role in neuroprotection and neurogenesis. In the present study, we aimed to elucidate the mechanisms underlying endogenous acetylcholine (ACh)-induced VEGF expression in neurons and astrocytes, and identify the neuronal cells contributing to its expression in the medial septal area, a nuclear origin of cholinergic neurons mainly projecting to the hippocampus. The mRNA expression and secretion of VEGF were measured by RT-PCR and ELISA using mouse primary cultured cortical neurons and astrocytes. VEGF expression in the medial septal area was assessed by RT-PCR and immunostaining using mice treated with tacrine [9-amino-1,2,3,4-tetrahydro-acridine HCl (THA); 2.5 mg/kg, i.p.] once daily for 7 days. The THA treatment increased VEGF mRNA expression in neurons in a manner that was reversed by mecamylamine, a nicotinic ACh receptor (AChR) antagonist, whereas in mouse primary cultured astrocytes, carbachol, but not THA dose-dependently increased VEGF mRNA expression and secretion in a manner that was inhibited by scopolamine, a muscarinic AChR inhibitor. In in vivo studies, the administration of THA significantly increased the expression of VEGF in medial septal cholinergic neurons and the effects of THA were significantly blocked by mecamylamine. THA also significantly increased the expression levels of a phosphorylated form of VEGF receptor 2 (p-VEGFR2), an activated form of VEGFR2. The present results suggest that endogenous ACh plays an up-regulatory role for VEGF expression in neurons and astrocytes via different mechanisms. Moreover, endogenous ACh-induced increases in VEGF levels appear to activate VEGFR2 on medial septal cholinergic neurons via an autocrine mechanism.

Intranasal administration of neuromedin U derivatives containing cell-penetrating peptides and a penetration-accelerating sequence induced memory improvements in mice

Neuromedin U (NMU) is a neuropeptide that is expressed and secreted in the brain and gut. We previously demonstrated that the intracerebroventricular (i.c.v.) administration of NMU inhibited inflammation-mediated memory impairment in mice. In order to utilize NMU as a clinical treatment tool for inflammation-mediated amnesia, we herein focused on non-invasive intranasal delivery because the i.c.v. administration route is invasive and impractical. In the present study, we prepared two NMU derivatives containing cell-penetrating peptides (CPPs), octaarginine (R8), and each penetration-accelerating sequence, namely FFLIPKG (PASR8-NMU) and FFFFG (F4R8-NMU), for intranasal (i.n.) administration. In the Y-maze test, the i.c.v. administration of lipopolysaccharide (LPS) (10μg/mouse) significantly decreased spontaneous alternation behavior, and this was prevented by the prior administration of PASR8-NMU or F4R8-NMU (5.6μg/mouse, i.n.). Moreover, the administration of PASR8-NMU or F4R8-NMU (5.6μg/mouse, i.n.) just before the Y-maze test also improved LPS-induced memory impairment. Indocyanine green (ICG)-labeled PASR8-NMU (i.n.) was significantly observed in the hippocampus and paraventricular hypothalamic nucleus 30min after its i.n. administration. PASR8-NMU, but not F4R8-NMU guaranteed the stability of the administration liquid for 24h. These results suggest that PASR8-NMU is effective for i.n. delivery to the brain, and may be useful in the clinical treatment of inflammation-mediated amnesia.

Post-reexposure administration of riluzole attenuates the reconsolidation of conditioned fear memory in rats

Recently, we demonstrated that riluzole, which has been shown to block the glutamatergic system, facilitates fear extinction in rats. Here, we undertook experiments on contextual fear conditioning to clarify the actions of riluzole on the reconsolidation of fear memory in rats. We used the fast-acting benzodiazepine midazolam as a reconsolidation-inhibiting control drug. We demonstrated that riluzole (3 mg/kg) and midazolam (1 mg/kg) impaired the reconsolidation of contextual fear memory. Results from spontaneous recovery experiments also suggested that riluzole attenuated reconsolidation. Indeed, conditioned fear did not recover spontaneously 4 weeks after a short (3 min) reexposure and riluzole administration, whereas it recovered after a long (10 min) reexposure. Using western blotting, we demonstrated that a short reexposure increased the phosphorylation of cyclic adenosine monophosphate response element binding protein significantly in the dorsal part of hippocampus, but not in the medial prefrontal cortex. Interestingly, this phosphorylation was attenuated by riluzole with short reexposure. In addition, bilateral microinjection of riluzole (2 μM/0.2 μl/side) directly into the dorsal hippocampus clearly attenuated the reconsolidation. These findings suggested that the attenuating effect of riluzole on the reconsolidation of fear memory involves, at least in part, the dorsal part of the hippocampus. In conclusion, we demonstrated that riluzole attenuates the reconsolidation of fear memory in rats.

Post-reexposure administration of D-cycloserine facilitates reconsolidation of contextual conditioned fear memory in rats

The effect of D-cycloserine, a N-methyl-D-aspartate receptor partial agonist, on the reconsolidation of conditioned fear memory is not precisely understood. In this study, we clarified the effects of D-cycloserine on the reconsolidation in rats, by performing contextual fear conditioning with a mild fear-conditioning procedure and with post-reexposure administration of the drug. The D-cycloserine (15 mg/kg subcutaneously)-treated rats showed a persistent and greater fear response during the test session compared with the control group. In conclusion, we have confirmed that post-reexposure administration of D-cycloserine facilitates the reconsolidation of fear memory in rats.

Antidepressant-like effects exerted by the intranasal administration of a glucagon-like peptide-2 derivative containing cell-penetrating peptides and a penetration-accelerating sequence in mice

The intracerebroventicular (i.c.v.) administration of glucagon-like peptide-2 (GLP-2) to rodents was shown to have antidepressant-like effects in imipramine-resistant depression-model mice. In order to utilize GLP-2 as a clinical treatment tool for depression, we herein focused on the intranasal delivery that is non-invasive approach, because the i.c.v. administration is invasive and impractical. In the present study, we prepared a GLP-2 derivative containing cell penetrating peptides (CPPs) and a penetration accelerating sequence (PAS) (PAS-CPPs-GLP-2) for the intranasal (i.n.) administration. PAS-CPPs-GLP-2 (i.n.) exhibited antidepressant-like effects in the forced-swim test (FST) and tail suspension test (TST) in naïve mice as well as adrenocorticotropic hormone (ACTH) treated-mice. However, PAS-CPPs-GLP-2 (i.v.) and the GLP-2 derivative containing CPPs without a PAS (CPPs-GLP-2) (i.n.) did not affect the immobility time in the mouse FST. Moreover, fluorescein isothiocyanate (FITC)-labeled PAS-CPPs-GLP-2 (i.n.), but not FITC-labeled CPPs-GLP-2 (i.n.) was distributed through the mouse brain after the FST session. These results suggest that PAS-CPPs-GLP-2 is effective for i.n. delivery to the brain, and may be useful in the clinical treatment of major depression.

Neoechinulin A induced memory improvements and antidepressant-like effects in mice

Neoechinulin A is an isoprenyl indole alkaloid that exhibits scavenging, neurotrophic factor-like, and anti-apoptotic activities. However, the effectiveness of neoechinulin A in animal models of disease has not yet been explored. In the present study, we investigated the effects of neoechinulin A on memory impairment in lipopolysaccharide (LPS)-treated mice and its antidepressant-like effects in mice. In the Y-maze test, the intracerebroventicular (i.c.v.) administration of LPS (10μg/mouse) significantly decreased spontaneous alternation behavior, which was prevented by the prior administration of neoechinulin A (300ng/mouse, i.c.v.). None of the treatments altered the locomotor activity of mice. Moreover, the administration of neoechinulin A decreased the immobility time in the forced-swim test or tail suspension test, which was prevented by the prior administration of WAY100635 (an antagonist of 5-HT1A receptors) and parachlorophenylalanine (an inhibitor of tryptophan hydroxylase). These results suggest that neoechinulin A improves memory functions in LPS-treated mice, and also exerts antidepressant-like effects through changes in the 5-HT system.

Induction of c-Fos immunoreactivity in the amygdala of mice expressing anxiety-like behavior after local perfusion of veratrine in the prelimbic medial prefrontal cortex

Local perfusion of the sodium channel activator veratrine in mouse prelimbic medial prefrontal cortex (PL) induced c-Fos immunoreactivity in the sub-regions of amygdala. Co-perfusion of the NMDA receptor antagonist MK-801 diminished the c-Fos expression. Significant correlations were observed between c-Fos immunoreactivity and behavioral measures in the open-field test. The PL stimulation activates a neural network projecting to the amygdala via NMDA receptor-mediated glutamatergic neurotransmission. Anxiety-like behavior induced after the PL stimulation may be partly mediated through the activation of amygdala.

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.

Riluzole in the prelimbic medial prefrontal cortex attenuates veratrine-induced anxiety-like behaviors in mice

RATIONALE

We previously demonstrated in mice that the activation of prelimbic medial prefrontal cortex (PL) with the sodium channel activator veratrine induces anxiety-like behaviors via NMDA receptor-mediated glutamatergic neurotransmission. Riluzole directly affects the glutamatergic system and has recently been suggested to have an anxiolytic-like effect in both experimental animals and patients with anxiety disorders.

OBJECTIVES

We investigated the effects of co-perfusion of riluzole on veratrine-induced anxiety-like behaviors in mice.

METHODS

Extracellular glutamate levels were measured in 7-week-old male C57BL6 mice by using an in vivo microdialysis-HPLC/ECD system, and behaviors were assessed simultaneously in an open field (OF) test. Basal levels of glutamate were measured by collecting samples every 10 min for 60 min. The medium containing drugs was perfused for 30 min, and the OF test was performed during the last 10 min of drug perfusion. After the drug treatments, the drug-containing medium was switched to perfusion of control medium lacking drugs, and then samples were collected for another 90 min.

RESULTS

Riluzole co-perfusion attenuated veratrine-induced increase in extracellular glutamate levels in the PL and completely diminished veratrine-induced anxiety-like behaviors. Interestingly, riluzole perfusion alone in the PL did not affect the basal levels of glutamate and anxiety-like behaviors.

CONCLUSIONS

Our results suggest that compounds like riluzole that inhibit glutamatergic function in the PL are possible candidates for novel anxiolytics.

Lysophosphatidic acid induces anxiety-like behavior via its receptors in mice

Lysophosphatidic acid (LPA) is a potent bioactive lipid mediator with diverse biological properties. We previously found altered expression of the LPA-related genes in rodents after treatment with sertraline, which is widely used to treat anxiety disorders and depression. However, little is known about the behavioral effects of LPA. In the present study, we investigated the behavioral effects of intracerebroventricular injection of LPA in adult mice. LPA did not significantly affect spontaneous locomotor activity, suggesting that LPA does not induce hyperactivity, ataxia, or sedation. We next investigated the emotional effects of LPA via the hole-board test. LPA significantly increased the number of head-dips in a dose- and time-related manner. A significant induction of head-dip counts occurred 15 and 30 min after LPA administration. To clarify the involvement of LPA receptors, we examined the effect of the non-selective LPA1-4 receptor antagonist, 1-bromo-3(S)-hydroxy-4-(palmitoyloxy)butyl-phosphonate (BrP-LPA) co-administered with LPA. BrP-LPA dose-dependently inhibited LPA-induced head-dip counts. We next investigated anxiety-like behavior via the elevated plus-maze test. LPA significantly reduced the percentage of time spent in the open arms and BrP-LPA dose-dependently inhibited this anxiety-like behavior. In conclusion, LPA induced anxiety-like behavior in mice via LPA receptors. Our results suggest that LPA signaling plays an important role in regulating anxiety in mice.

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 Alzheimer's 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 H2 O2). 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 H2 O2 (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.

Neuronal Fos-like immunoreactivity associated with dexamethasone-induced hypertension in rats and effects of glucagon-like peptide-2

AIMS

Dexamethasone-induced hypertension models have been used to study the mechanisms of glucocorticoid induced hypertension, but the role of glucocorticoids in central cardiovascular regulation is not clearly understood. In the present study, we investigated the sites associated with dexamethasone-induced hypertension in the central nervous system in rats. We further investigated whether glucagon-like peptide-2 (GLP-2) was effective for dexamethasone-induced hypertension.

MAIN METHODS

Male Sprague–Dawley rats were treated with saline or dexamethasone (0.03mg/kg/day, s.c) for 10 days. GLP-2 (60 μg/kg, i.v.) was given to rats after dexamethasone treatment. We measured systolic blood pressure by a tail-cuff method in conscious rats, and arterial blood pressure in anesthetized rats. Immunohistochemical techniques were used to detection of the c-fos protein (Fos).

KEY FINDINGS

Fos-immunoreactivity (Fos-IR) in the dorsomedial hypothalamic nucleus (DMH) was higher in dexamethasone-treated rats than in saline-treated rats. However, Fos-IR in the infralimbic cortex, amygdala, and hippocampus was similar in saline-treated and dexamethasone-treated rats. Peripheral administration of GLP-2 reduced mean arterial blood pressure by 26%. After the peripheral administration of GLP-2, Fos-IR in the caudal ventrolateral medulla (CVLM) increased in dexamethasone-treated rats.

SIGNIFICANCE

Chronic dexamethasone treatment induced Fos-IR in the DMH. Peripheral administration of GLP-2 suppressed dexamethasone-induced hypertension in rats by enhancing inhibitory neuronal activity.

Kampo formulations, chotosan, and yokukansan, for dementia therapy: existing clinical and preclinical evidence

Cognitive deficits and behavioral and psychological symptoms of dementia (BPSD) are typical features of patients with dementia such as Alzheimer's disease (AD), vascular dementia (VD), and other forms of senile dementia. Clinical evidence has demonstrated the potential usefulness of chotosan (CTS) and yokukansan (YKS), traditional herbal formulations called Kampo medicines, in the treatment of cognitive disturbance and BPSD in dementia patients, although the indications targeted by CTS and YKS in Kampo medicine differ. The availability of CTS and YKS for treating dementia patients is supported by preclinical studies using animal models of dementia that include cognitive/emotional deficits caused by aging and diabetes, dementia risk factors. These studies have led not only to the concept of a neuronal basis for the CTS- and YKS-induced amelioration of cognitive function and emotional/psychiatric symptom-related behavior in animal models, but also to a proposal that ingredient(s) of Uncariae Uncis cum Ramulus, a medicinal herb included in CTS and YKS, may play an important role in the actions of these formulae in dementia patients. Further studies are needed to clarify the active ingredients of these formulae and their target endogenous molecules implicated in the anti-dementia drug-like actions.

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 60 min 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.

Increased systemic glucose tolerance with increased muscle glucose uptake in transgenic mice overexpressing RXRγ in skeletal muscle

Background

Retinoid X receptor (RXR) γ is a nuclear receptor-type transcription factor expressed mostly in skeletal muscle, and regulated by nutritional conditions. Previously, we established transgenic mice overexpressing RXRγ in skeletal muscle (RXRγ mice), which showed lower blood glucose than the control mice. Here we investigated their glucose metabolism.

Methodology/Principal Findings

RXRγ mice were subjected to glucose and insulin tolerance tests, and glucose transporter expression levels, hyperinsulinemic-euglycemic clamp and glucose uptake were analyzed. Microarray and bioinformatics analyses were done. The glucose tolerance test revealed higher glucose disposal in RXRγ mice than in control mice, but insulin tolerance test revealed no difference in the insulin-induced hypoglycemic response. In the hyperinsulinemic-euglycemic clamp study, the basal glucose disposal rate was higher in RXRγ mice than in control mice, indicating an insulin-independent increase in glucose uptake. There was no difference in the rate of glucose infusion needed to maintain euglycemia (glucose infusion rate) between the RXRγ and control mice, which is consistent with the result of the insulin tolerance test. Skeletal muscle from RXRγ mice showed increased Glut1 expression, with increased glucose uptake, in an insulin-independent manner. Moreover, we performed in vivo luciferase reporter analysis using Glut1 promoter (Glut1-Luc). Combination of RXRγ and PPARδ resulted in an increase in Glut1-Luc activity in skeletal muscle in vivo. Microarray data showed that RXRγ overexpression increased a diverse set of genes, including glucose metabolism genes, whose promoter contained putative PPAR-binding motifs.

Conclusions/Significance

Systemic glucose metabolism was increased in transgenic mice overexpressing RXRγ. The enhanced glucose tolerance in RXRγ mice may be mediated at least in part by increased Glut1 in skeletal muscle. These results show the importance of skeletal muscle gene regulation in systemic glucose metabolism. Increasing RXRγ expression may be a novel therapeutic strategy against type 2 diabetes.

The novel δ opioid receptor agonist KNT-127 produces antidepressant-like and antinociceptive effects in mice without producing convulsions

We previously reported that the δ opioid receptor (DOP) agonists SNC80 and TAN-67 produce potent antidepressant-like and antinociceptive effects in rodents. However, SNC80 produced convulsive effects. Recently, we succeeded in synthesizing a novel DOP agonist called KNT-127. The present study examined the convulsive, antidepressant-like, and antinociceptive effects of KNT-127 in mice. In contrast to SNC80, KNT-127 produced no convulsions at doses of up to 100mg/kg. In mice subjected to the forced swim test, a screening model for antidepressants, KNT-127 (1mg/kg, s.c.) significantly decreased the duration of immobility and increased the duration of swimming without influencing spontaneous locomotor activity. These behavioral changes were similar to that observed for the tricyclic antidepressant imipramine (6mg/kg). The antidepressant-like effect of KNT-127 in mice was antagonized by pretreatment with naltrindole (NTI), a selective DOP antagonist, or naltriben, a putative DOP(2) subtype antagonist. In addition, KNT-127 (3mg/kg, s.c.) significantly reduced the number of acetic acid-induced abdominal constrictions and the duration of licking time, respectively, in mice subjected to a writhing test and a formalin test. These antinociceptive effects were antagonized by pretreatment with either NTI or 7-benzylidenenaltrexone, a putative DOP(1) subtype antagonist. We propose that KNT-127 should be considered as a candidate compound for the development of DOP-based antidepressants and/or analgesics that lack convulsive effects.

Maternal stress affects postnatal growth and the pituitary expression of prolactin in mouse offspring

Maternal stress exerts long-lasting psychiatric and somatic on offspring, which persist into adulthood. However, the effect of maternal stress on the postnatal growth of pups has not been widely reported. In this study, we found that maternal immobilization stress (IS) during lactation resulted in low body weight of male mouse offspring, which persisted after weaning. Despite free access to chow, IS induced maternal malnutrition and decreased the serum insulin-like growth factor-1 (IGF-1) levels in the mothers and in the pups. mRNA expression analysis of anterior pituitary hormones in the pups revealed that growth hormone (GH) and prolactin (PRL), but no other hormones, were decreased by IS. Expression of the pituitary transcription factor PIT1 and isoforms of PITX2, which are essential for the development and function of GH-producing somatotropes and PRL-producing lactotropes, was decreased, whereas that of PROP1, which is critical for the earlier stages of pituitary development, was unchanged. Immunohistochemistry also showed a decrease in pituitary PRL protein expression. These results suggest that stress in a postpartum mother has persistent effects on the body weight of the offspring. Reduced PRL expression in the offspring's pituitary gland may play a role in these effects.

Antidepressant-like effects of glucagon-like peptide-2 in mice occur via monoamine pathways

In this study, we investigated whether glucagon-like peptide-2 (GLP-2) had antidepressant-like effects in mice, and whether these activities were associated with monoamine systems in mice. Antidepressant-like effects were evaluated based on the immobility time in the forced-swim test. GLP-2 (1.5-6 microg/mouse, i.c.v.) significantly reduced the immobility time in a dose-dependent manner without affecting locomotor activity in the wheel running test and memory function in the step-down passive avoidance test. These effects were inhibited by pretreatment with metergoline (an antagonist of non-specific 5-HT receptors), parachlorophenylalanine (an inhibitor of 5-HT synthase), NAN-190 (an antagonist of 5-HT1A receptors), yohimbine hydrochloride (an antagonist of alpha2 adrenoceptors), atenolol (an antagonist of beta1 receptors), and raclopride (an antagonist of D2 receptors), but not prazosin (an antagonist of alpha1 adrenoceptors), ICI118551 (an antagonist of beta2 adrenoceptors), and SCH23394 (an antagonist of D1 receptors). These results suggest that GLP-2 exerts antidepressant-like effects in the forced-swim test in mice, which are associated with 5-HT1A, alpha2, beta1 and D2 receptors.

The influences of juvenile diabetes on memory and hippocampal plasticity in rats: improving effects of glucagon-like peptide-1

Previous studies in children with diabetes found that hyperglycemia induces memory dysfunction. In this study, we investigated memory and synaptic plasticity in streptozotocine (STZ)-induced diabetic rats during the juvenile period. We further investigated the effects of glucagon-like peptide-1 (GLP-1) on the diabetes-induced profiles. STZ (85 mg/kg, i.p.) was administered to 17-day-old Wistar rats to induce type-1 juvenile diabetes mellitus (JDM). In the Y-maze test, JDM rats showed significant impairment of learning and memory, which were improved by GLP-1 (7-36) amide (1 microg/5 microl/rat, i.c.v.). Extracellular recording at Schaffer collateral synapses in the CA1 region of hippocampal slices showed that long-term potentiation and paired-pulse facilitation in JDM rats were similar to age-matched control rats. However, the input-output relation was strengthened, and long-term depression (LTD) and responses of N-methyl d-aspartic acid through NR2B subunits were weakened in the JDM rats. GLP-1 (7-36) amide (100 nM) increased the magnitude of LTD and the responses through NR2B in the JDM rats. These results indicate that the lack of LTD and NR2B responses may contribute to impairment of memory associated with JDM, suggesting the potential usefulness of GLP-1 in the treatment of memory dysfunction in JDM.

Macrophage-colony stimulating factor in obese adipose tissue: studies with heterozygous op/+ mice

OBJECTIVE

We examined the gene expression of macrophage-colony stimulating factor (M-CSF) in mice with diet-induced obesity and in genetically obese mice. We also examined the effect of decreased M-CSF signaling on the susceptibility to obesity and macrophage recruitment into the adipose tissue of mice.

RESEARCH METHODS AND PROCEDURES

The adipose tissue from mice with diet-induced obesity, obese KKA(y) mice, and ob/ob obese mice was used for RNA preparation. Production of M-CSF and monocyte chemoattractant protein-1 (MCP-1) was examined by quantitative real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay. The op/+ heterozygous mice, with decreased functional M-CSF expression, were placed on a high-fat diet or crossed with KKA(y) mice to study the susceptibility to obesity. The gene expression of macrophage markers in adipose tissue was examined.

RESULTS

The expression of M-CSF was not significantly changed in mice on a high-fat diet or in either type of genetic obesity (KKA(y) or ob/ob mice). No change in the degree of obesity or macrophage-related gene expression (F4/80, CD68, and MCP-1) in the adipose tissue was observed in op/+ mice compared with +/+ control mice, which were either treated with a high-fat diet or crossed with KKA(y) mice.

DISCUSSION

This study demonstrated that there was no significant change in the expression of M-CSF in the adipose tissue from obese mice and only a minor phenotypic change, such as macrophage infiltration, in the adipose tissue from op/+ mice, suggesting that M-CSF does not play a major role in macrophage recruitment in the adipose tissue of obese mice.