Takayoshi Mamiya

Role of Tumor Necrosis Factor-α in Methamphetamine-Induced Drug Dependence and Neurotoxicity

Tumor necrosis factor-α (TNF-α), a proinflammatory cytokine, is now emerging as an important modulator of the function of the CNS. Methamphetamine (METH) is a widely abused psychostimulant that causes euphoria, hyperactivity, and drug dependence. High doses of METH cause long-term neurotoxicity in dopaminergic neurons. In this study, we investigated a role of TNF-α in METH-induced dependence and neurotoxicity. Repeated treatment with METH (2 mg/kg for 5 d) in rats induced a significant increase in TNF-α mRNA and protein expression in the brain. Exogenous TNF-α (1-4 μg) blocked locomotor-stimulating and rewarding effects of METH, as well as METH (4 mg/kg; four times at 2 hr intervals)-induced dopaminergic neurotoxicity in mice. To examine a role of endogenous TNF-α in behavioral and neurochemical effects of METH, we used mice with targeted deletions of the TNF-α gene. TNF-α-(-/-) mice showed enhanced responses to the locomotor-sensitizing, rewarding, and neurotoxic effects of METH compared with wild-type mice. We also examined the role of TNF-α in METH-induced dopamine (DA) release and uptake in vitro and in vivo in C57BL/6 mice. Exogenous TNF-α (4 μg) attenuated the METH-induced increase in extracellular striatal DA in vivo and potentiated striatal DA uptake into synaptosomes in vitro and in vivo. Furthermore, TNF-α activated vesicular DA uptake by itself and diminished the METH-induced decrease in vesicular DA uptake. Our findings suggest that TNF-α plays a neuroprotective role in METH-induced drug dependence and neurotoxicity by activating plasmalemmal and vesicular DA transporter as well as inhibiting METH-induced increase in extracellular DA levels.

Silibinin prevents amyloid β peptide‐induced memory impairment and oxidative stress in mice

Background and purpose:u2002 Accumulated evidence suggests that oxidative stress is involved in amyloid β (Aβ)‐induced cognitive dysfunction. Silibinin (silybin), a flavonoid derived from the herb milk thistle (Silybum marianum), has been shown to have antioxidative properties; however, it remains unclear whether silibinin improves Aβ‐induced neurotoxicity. In the present study, we examined the effect of silibinin on the memory impairment and accumulation of oxidative stress induced by Aβ25–35 in mice.

[Gly14]-humanin improved the learning and memory impairment induced by scopolamine in vivo

Humanin is a very recently discovered 24 amino acid linear polypeptide, which protects against cell death induced by either familial Alzheimers disease mutant of amyloid precursor protein, presenilin‐1 or presenilin‐2 in vitro. However, it has remained uncertain whether humanin is a useful drug for the animal model of learning and memory deficit. In this study, we evaluated the effects of [Gly14]‐humanin, a more potent humanin analogue, on the scopolamine HBr (1u2003mgu2003kg−1 s.c.)‐induced impairment of spontaneous alternation behaviour in the Y‐maze, an index of short‐term memory in mice. [Gly14]‐Humanin (1000u2003pmolu20035u2003μl−1 i.c.v.) reversed the impairment without affecting the number of arm entries. These results suggest that (I) [Gly14]‐humanin is a beneficial drug for the impairment of learning and memory and (II) it modulates the learning and memory function mediated via cholinergic systems in mice.

Usp46 is a quantitative trait gene regulating mouse immobile behavior in the tail suspension and forced swimming tests

The tail suspension test (TST) and forced swimming test (FST) are widely used for assessing antidepressant activity and depression-like behavior. We found that CS mice show negligible immobility in inescapable situations. Quantitative trait locus (QTL) mapping using CS and C57BL/6J mice revealed significant QTLs on chromosomes 4 (FST) and 5 (TST and FST). To identify the quantitative trait gene on chromosome 5, we narrowed the QTL interval to 0.5 Mb using several congenic and subcongenic strains. Ubiquitin-specific peptidase 46 (Usp46) with a lysine codon deletion was located in this region. This deletion affected nest building, muscimol-induced righting reflex and anti-immobility effects of imipramine. The muscimol-induced current in the hippocampal CA1 pyramidal neurons and hippocampal expression of the 67-kDa isoform of glutamic acid decarboxylase were significantly decreased in the Usp46 mutant mice compared to control mice. These phenotypes were rescued in transgenic mice with bacterial artificial chromosomes containing wild-type Usp46. Thus, Usp46 affects the immobility in the TST and FST, and it is implicated in the regulation of GABA action.

Silibinin attenuates cognitive deficits and decreases of dopamine and serotonin induced by repeated methamphetamine treatment

Cognitive deficits are a core feature of patients with methamphetamine (METH) abuse. It has been reported that repeated METH treatment impairs long-term recognition memory in the novel object recognition test (NORT) in mice. Recent studies indicate that silibinin, a flavonoid derived from the herb milk thistle, has potent neuroprotective effects in cell cultures and several animal models of neurological diseases. However, its effect on the cognitive deficit induced by METH remains unclear. In the present study, we attempt to clarify the effect of silibinin on impairments of recognition memory caused by METH in mice. Mice were co-administered silibinin with METH for 7 days and then cognitive function was assessed by NORT after 7-day withdrawal. Tissue levels of dopamine and serotonin as well as their metabolites in the prefrontal cortex and hippocampus were measured 1 day after NORT. Silibinin dose-dependently ameliorated the impairment of recognition memory caused by METH treatment in mice. Silibinin significantly attenuated the decreases in the dopamine content of the prefrontal cortex and serotonin content of the hippocampus caused by METH treatment. We also found a correlation between the recognition values and dopamine and serotonin contents of the prefrontal cortex and hippocampus. The effect of silibinin on cognitive impairment may be associated with an amelioration of decreases in dopamine and serotonin levels in the prefrontal cortex and hippocampus, respectively. These results suggest that silibinin may be useful as a pharmacological tool to investigate the mechanisms of METH-induced cognitive impairments.

Neuronal mechanism of nociceptin-induced modulation of learning and memory: Involvement of N -methyl- D -aspartate receptors

Nociceptin (also called orphanin FQ) is an endogenous heptadecapeptide that activates the opioid receptor-like 1 (ORL1) receptor. Nociceptin system not only affects the nociception and locomotor activity, but also regulates learning and memory in rodents. We have previously reported that long-term potentiation and memory of ORL1 receptor knockout mice are enhanced compared with those in wild-type mice. Here, we show the neuronal mechanism of nociceptin-induced modulation of learning and memory. Retention of fear-conditioned contextual memory was significantly enhanced in the ORL1 receptor knockout mice without any changes in cued conditioned freezing. Inversely, in the wild-type mice retention of contextual, but not cued, conditioning freezing behavior was suppressed by exogenous nociceptin when it was administered into the cerebroventricle immediately after the training. ORL1 receptor knockout mice exhibited a hyperfunction of N-methyl-D-aspartate (NMDA) receptor, as evidenced by an increase in [3H]MK-801 binding, NMDA-evoked 45Ca2+ uptake and activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity and its phosphorylation as compared with those in wild-type mice. The NMDA-induced CaMKII activation in the hippocampal slices of wild-type mice was significantly inhibited by exogenous nociceptin via a pertussis toxin-sensitive pathway. However, the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor GluR1 subunit at Ser831 and Ser845, and NMDA receptor subunit NR2B at Thr286 were phosphorylated similarly after NMDA receptor stimulation in both type of mice. The expressions of GluR1 and GluR2 also did not change, but the levels of polysialylated form of neuronal cell adhesion molecule (N-CAM) were reduced in the ORL1 receptor knockout as compared with wild-type mice. These results suggest that nociceptin system negatively modulates learning and memory through the regulation of NMDA receptor function and the expression of N-CAM.

Nociceptin system plays a role in the memory retention: involvement of naloxone benzoylhydrazone binding sites.

We investigated the role of nociceptin system in learning and memory in mice. The deficiency of nociceptin receptors and nociceptin itself did not affect the alternation behavior in the Y-maze test. In the passive avoidance test, the step-through latencies of nociceptin receptor knockout mice were longer than those of wild-type mice. Nociceptin shortened the step-through latency in wild-type mice. This impairment on passive avoidance task was reversed by naloxone benzoylhydrazone (NalBzoH), indicating that the amnesic effects of nociceptin may be mediated through the NalBzoH recognition sites. These suggest that nociceptin system plays an important role in the memory retention of passive avoidance task, and NalBzoH-recognized sites are involved in nociceptin-induced impairment of the memory retention.

Silibinin Attenuates Amyloid β25–35 Peptide-Induced Memory Impairments: Implication of Inducible Nitric-Oxide Synthase and Tumor Necrosis Factor-α in Mice

In Alzheimer’s disease (AD), the deposition of amyloid peptides is invariably associated with oxidative stress and inflammatory responses. Silibinin (silybin), a flavonoid derived from the herb milk thistle, has potent anti-inflammatory and antioxidant activities. However, it remains unclear whether silibinin improves amyloid β (Aβ) peptide-induced neurotoxicity. In this study, we examined the effect of silibinin on the fear-conditioning memory deficits, inflammatory response, and oxidative stress induced by the intracerebroventricular injection of Aβ peptide25–35 (Aβ25–35) in mice. Mice were treated with silibinin (2, 20, and 200 mg/kg p.o., once a day for 8 days) from the day of the Aβ25–35 injection (day 0). Memory function was evaluated in cued and contextual fear-conditioning tests (day 6). Nitrotyrosine levels in the hippocampus and amygdala were examined (day 8). The mRNA expression of inducible nitric-oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α) in the hippocampus and amygdala was measured 2 h after the Aβ25–35 injection. We found that silibinin significantly attenuated memory deficits caused by Aβ25–35 in the cued and contextual fear-conditioning test. Silibinin significantly inhibited the increase in nitrotyrosine levels in the hippocampus and amygdala induced by Aβ25–35. Nitrotyrosine levels in these regions were negatively correlated with memory performance. Moreover, real-time RT-PCR revealed that silibinin inhibited the overexpression of iNOS and TNF-α mRNA in the hippocampus and amygdala induced by Aβ25–35. These findings suggest that silibinin (i) attenuates memory impairment through amelioration of oxidative stress and inflammatory response induced by Aβ25–35 and (ii) may be a potential candidate for an AD medication.

Ferulic acid attenuated cognitive deficits and increase in carbonyl proteins induced by buthionine-sulfoximine in mice.

beta-Amyloid peptide (Abeta), the major constituent of the senile plaques observed in the brains of Alzheimers disease patients, is cytotoxic to neurons and plays a central role in the pathogenesis of this disease. Previous studies have suggested that oxidative stress is involved in the mechanisms of Abeta-induced neurotoxicity in vivo. Here, we used a mouse model of brain dysfunction induced by dl-buthionine-(S,R)-sulfoximine (BSO: 3micromol/3microL/mouse, i.c.v.), an inhibitor of glutathione synthesis. In the novel object recognition test, we found impairments of exploratory preference in the retention trial but not the training trial 24h after BSO treatment, suggesting that BSO produces cognitive dysfunction in mice. In the forebrain of this model, we observed increase in carbonyl protein levels, an index of biochemical oxidative damage of proteins, compared to vehicle-treated mice. Pretreatment with ferulic acid (5mg/kg, s.c.) once a day for 6 days inhibited the induction of deficits in memory and increase in carbonyl protein levels by BSO. These findings suggest that pretreatment with FA may attenuate the memory deficits and increase the carbonyl protein levels induced by BSO in mice.

MAGE-D1 Regulates Expression of Depression-Like Behavior through Serotonin Transporter Ubiquitylation

The ubiquitin–proteasome system (UPS) controls the stability of most cellular proteins. The polymorphism of UPS-related genes is associated with major depression disorder, but less is known about the molecule that plays a role in depression by modulating the UPS. Melanoma antigen gene-D1 (MAGE-D1) interacts with RING E3 ubiquitin ligase and is implicated in protein degradation. MAGE-D1 may thus play an important role in the CNS via ubiquitylation. Here, we clarified a novel role of MAGE-D1 in emotional functions, namely its modulation of ubiquitylation to the serotonin transporter (SERT). The MAGE-D1 knock-out and knockdown by small interfering RNA (siRNA) in the prefrontal cortex showed depression-like behavior, such as a decrease in exploratory behavior in both the home cage and novel apparatus, a decrease in social interaction, increased immobility time during forced swimming and tail suspension, and a decrease in sucrose preference without any anxiety, or cognitive or motor dysfunction. Acute and chronic (28 d) administration of sertraline (10 mg/kg) and imipramine (20 mg/kg) reversed all or part of depression-like behavior in knock-out mice. In these mice, the serotonergic function in the prefrontal cortex and hippocampus was hypoactive, accompanied by hyperexpression of SERT attributable to a decrease in ubiquitylation. Furthermore, MAGE-D1 binds to SERT via the necdin homology domain. MAGE-D1 overexpression in cells resulted in a decrease in serotonin uptake activity and the protein level of SERT but an increase in ubiquitylated SERT. Together, the present findings suggest a novel role for MAGE-D1 in depressive behaviors: modulating SERT ubiquitylation.