Teiichi Nishiki

A CACNB4 mutation shows that altered Cav2.1 function may be a genetic modifier of severe myoclonic epilepsy in infancy

Mutations of SCN1A, encoding the voltage-gated sodium channel alpha1 subunit, represent the most frequent genetic cause of severe myoclonic epilepsy in infancy (SMEI). The purpose of this study was to determine if mutations in other seizure susceptibility genes are also present and could modify the disease severity. All coding exons of SCN1B, GABRG2, and CACNB4 genes were screened for mutations in 38 SCN1A-mutation-positive SMEI probands. We identified one proband who was heterozygous for a de novo SCN1A nonsense mutation (R568X) and another missense mutation (R468Q) of the CACNB4 gene. The latter mutation was inherited from his father who had a history of febrile seizures. An electrophysiological analysis of heterologous expression system exhibited that R468Q-CACNB4 showed greater Ba(2+) current density compared with the wild-type CACNB4. The greater Ca(v)2.1 currents caused by the R468Q-CACNB4 mutation may increase the neurotransmitter release in the excitatory neurons under the condition of insufficient inhibitory neurons caused primarily by the SCN1A mutation.

Antidepressant-like effect of sildenafil through oxytocin-dependent cyclic AMP response element-binding protein phosphorylation

Oxytocin (OT) levels in plasma increase during sexual response and are significantly lower in patients with depression. A drug for the treatment of sexual dysfunction, sildenafil, enhances the electrically evoked release of OT from the posterior pituitary. In this study, we showed that sildenafil had an antidepressant-like effect through activation of an OT signaling pathway. Application of sildenafil reduced depression-related behavior in male mice. The antidepressant-like effect was blocked by an OT receptor (OTR) antagonist and was absent in OTR knockout (KO) mice. Sildenafil increased the phosphorylation of cAMP response element-binding protein (CREB) in the hippocampus. The OTR antagonist inhibited sildenafil-induced CREB phosphorylation and sildenafil had no effect on CREB phosphorylation in OTR KO mice. These results suggest sildenafil to have an antidepressant-like effect through the activation of OT signaling and to be a promising drug for the treatment of depression.

CACNA1A variants may modify the epileptic phenotype of Dravet syndrome.

Dravet syndrome is an intractable epileptic syndrome beginning in the first year of life. De novo mutations of SCN1A, which encode the Na(v)1.1 neuronal voltage-gated sodium channel, are considered the major cause of Dravet syndrome. In this study, we investigated genetic modifiers of this syndrome. We performed a mutational analysis of all coding exons of CACNA1A in 48 subjects with Dravet syndrome. To assess the effects of CACNA1A variants on the epileptic phenotypes of Dravet syndrome, we compared clinical features in two genotype groups: 1) subjects harboring SCN1A mutations but no CACNA1A variants (n=20) and 2) subjects with SCN1A mutations plus CACNA1A variants (n=20). CACNA1A variants detected in patients were studied using heterologous expression of recombinant human Ca(v)2.1 in HEK 293 cells and whole-cell patch-clamp recording. Nine CACNA1A variants, including six novel ones, were detected in 21 of the 48 subjects (43.8%). Based on the incidence of variants in healthy controls, most of the variants seemed to be common polymorphisms. However, the subjects harboring SCN1A mutations and CACNA1A variants had absence seizures more frequently than the patients with only SCN1A mutations (8/20 vs. 0/20, p=0.002). Moreover, the former group of subjects exhibited earlier onset of seizures and more frequent prolonged seizures before one year of age, compared to the latter group of subjects. The electrophysiological properties of four of the five novel Ca(v)2.1 variants exhibited biophysical changes consistent with gain-of-function. We conclude that CACNA1A variants in some persons with Dravet syndrome may modify the epileptic phenotypes.

Therapy for hyperthermia-induced seizures in Scn1a mutant rats

Purpose:  Mutations in the SCN1A gene, which encodes the α1 subunit of voltage‐gated sodium channels, cause generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy of infancy (SMEI). N1417H‐Scn1a mutant rats are considered to be an animal model of human FS+ or GEFS+. To assess the pharmacologic validity of this model, we compared the efficacies of eight different antiepileptic drugs (AEDs) for the treatment of hyperthermia‐induced seizures using N1417H‐Scn1a mutant rats.

Inhalation of 10% carbon dioxide rapidly terminates Scn1a mutation-related hyperthermia-induced seizures

The aim of this study was to assess the anticonvulsant effect of carbon dioxide (CO2) on Scn1a mutation-related febrile seizures. We examined physiological changes in the blood gas levels after the induction of hyperthermia-induced seizures (HISs), which were associated with the Scn1a missense mutation. We determined the efficacy of inhalation of 5% or 10% CO2 to treat HISs. HISs were evoked in Scn1a mutant and wild-type (WT) rats by hot water baths. To determine the anticonvulsant effect of CO2 inhalation, rats were placed in a chamber filled with air or mixed gas containing 5% CO2 or 10% CO2 for 3 min, immediately after the induction of HISs. We also analyzed the blood gas levels at the end of inhalation of CO2. Hot water bathing induced a significant reduction in the partial pressure of CO2 (pCO2) and respiratory alkalosis in the WT and Scn1a mutant rats. HISs were evoked in 100% of the Scn1a mutant rats within 5 min, but in none of the WT rats. The Scn1a mutant rats demonstrated a higher HISs susceptibility associated with respiratory alkalosis than the WT rats. Inhalation of 10% CO2 shortened the seizure duration from 62.6±12.1 s to 15.5±1.0 s. Blood gas analysis after the inhalation of 10% CO2 demonstrated an elevated pCO2 level and respiratory acidosis. Inhalation of 10% CO2 demonstrated a potent and fast-acting anticonvulsant effect against HISs.

Possible role of cortactin phosphorylation by protein kinase Cα in actin-bundle formation at growth cone

Cortactin contributes to growth cone morphogenesis by forming with dynamin, ring‐shaped complexes that mechanically bundle and stabilise F‐actin. However, the regulatory mechanism of cortactin action is poorly understood.

Oxytocin Inhibits Corticosterone-induced Apoptosis in Primary Hippocampal Neurons

Stress is an adaptive and coordinated response to endogenous or exogenous stressors that pose an unpleasant and aversive threat to an individuals homeostasis and wellbeing. Glucocorticoids, corticosterone (CORT) in rodents and cortisol in humans, are adrenal steroids which are released in response to stressful stimuli. Although they help individuals to cope with stress, their overexposure in animals has been implicated in hippocampal dysfunction and neuronal loss. Oxytocin (OT) plays an active role in adaptive stress-related responses and protects hippocampal synaptic plasticity and memory during stress. In this study, we showed that OT protects primary mouse hippocampal neurons from CORT-induced apoptosis. OT receptors (OTR) were expressed in primary mouse hippocampal neurons and glial cells. CORT induced apoptosis in hippocampal neurons, but had no effect on apoptosis in glial cells. OT inhibited CORT-induced apoptosis in primary hippocampal neurons. OT was unable to protect primary hippocampal neurons prepared from OTR KO mice from CORT-induced apoptosis. These results indicate that OT has inhibitory effects on CORT-induced neuronal death in primary hippocampal neurons via acting on OTR. The findings suggest a therapeutic potential of OT in the treatment of stress-related disorders.

Sildenafil exerts oxytocin-receptor-mediated antidepressant effects in male mice via a pathway involving MAP kinase and CREB phosphorylation in hippocampus

P3-t05 Pattern separation related activity in dentate gyrus is associated with subjective mood: A functional MRI study Takeshi Fujii 1 , Daisuke N. Saito 1,2, Hisakazu T. Yanaka 1,2, Hirotaka Kosaka 3, Hiroshi Oikawa 1, Hidehiko Okazawa 1 1 Biomedical Imaging Research Center, University of Fukui, Japan 2 Research and Education Program for Life Science, University of Fukui, Fukui, Japan 3 Department of Neuropsychiatry, Faculty of Medical Sciences, University of Fukui, Fukui, Japan

Assembly and disassembly of the complex of synaptotagmin 1 and syntaxin 1 under physiological conditions

cell patch-clamp recordings in adult rat spinal cord slices. In this study, we examined the firing patterns of the SG neurons receiving CA-sensitive afferent fibers. In current-clamp mode, SG neurons discharged action potentials in response to a just supra-threshold current pulse. SG neurons tested were classified into five types: delayed firing, sustained repetitive firing, phasic firing, initial firing and other firing (e.g. single). Most (78%) of the CA-sensitive SG neurons were the delayed and sustained repetitive firing types, although CA-insensitive cells were also found in these two types of SG neurons. In the initial firing type, CA-sensitive neurons were not detected except for one cell. A previous study explored the relationship between the morphological class of SG neurons and their firing pattern, has shown that vertical cells exhibit the delayed or sustained firing type, and radial cells exhibit the phasic firing type. Moreover, central cells are reported to exhibit the initial firing pattern of discharge. In combination with previous studies, the present results suggest that activation of spinal TRPA1 presynaptically facilitates miniature excitatory synaptic transmission from primary afferents onto mainly delayed firing and sustained repetitive firing type neurons which are morphologically classified vertical and radial cells.

P3-o09 Oxytocin mediates mating-induced antidepressant effect in male mice

Oxytocin (OXT) is known as a regulator of depression, anxiety and trust behaviors in central nervous system. Moreover, recent studies have shown that OXT mediates mating-induced anxiolysis in male rats. However, it is unclear whether OXT is involved in the antidepressant effect by mating behavior. In the present study, we examined the effect of mating on depression behaviors in wild-type (WT) and OXT receptor-deficient male mice (OXT-R KO). The depression behaviors were measured by forced swim test. Each animal was examined the duration of immobility during swimming for 6 min. In WT male mice, the duration of immobility was significantly reduced at after termination of the mating behavior. In OXT-R KO mice, in contrast, the duration of immobility were not reduced compared with that before mating behavior. These results suggest that OXT is involved in mating-induced antidepressant effect in male mice.