Kamikihito reduces β-amyloid25-35-induced axon damage via neurotrophic factors

The Japanese herbal medicine kamikihito (KKT) is widely used for insomnia, anorexia, anemia, and depression. Recently, the efficacy of KKT against Alzheimer's disease (AD) has been demonstrated in clinical and non-clinical studies. To address the mechanism underlying the effect of KKT on AD, we examined the effects of KKT in β-amyloid (Aβ)25-35-exposed primary cultured neurons. The effects of KKT on Aβ25-35-induced neurotoxicity were assessed by immunocytochemical assays and Sholl analysis of neurites, and the influence of KKT on neurotrophic factor (NF) gene expression was examined using RT-PCR analysis. As a result, Aβ25-35 exposure attenuated the arborization of neurites of single cultured hippocampal neurons, and KKT treatment for 3 days ameliorated the Aβ25-35-induced impairment of tau-positive axon outgrowth. This ameliorative effect of KKT was largely abolished by the Trk inhibitor K252a, and expression of NFs, nerve growth factor (Ngf), brain-derived neurotrophic factor (Bdnf), neurotrophin-3 (NT-3) was significantly increased by KKT. These results indicate that KKT ameliorates axonal atrophy via NFs signaling, providing a mechanistic basis for treatment of AD with KKT.

The Effects of Ninjinyoeito on Impaired Spatial Memory and Prefrontal Cortical Synaptic Plasticity through α-Amino-3-hydroxy-5-4-isoxazole Propionic Acid Receptor Subunit in a Rat Model with Cerebral Ischemia and β-Amyloid Injection

Ninjinyoeito (NYT), a traditional Japanese medicine, is effective for improving physical strength and treating fatigue and anorexia. Recently, a clinical report revealed that NYT ameliorates cognitive dysfunction in Alzheimer's disease (AD) patients, although the mechanisms remain unclear. AD is a neurodegenerative disorder accompanied by a progressive deficit in memory. Current therapeutic agents are largely ineffective in treating cognitive dysfunction in AD patients. In this study, we investigated the effects of NYT on spatial memory impairment in a rat model of dementia. Rats were prepared with transient cerebral ischemia and intraventricular injection of β-amyloid1-42 for 7 days (CI + Aβ). NYT was orally administered for 7 days after cerebral ischemia. We evaluated spatial memory using the Morris water maze and investigated the expression of α-amino-3-hydroxy-5-4-isoxazole propionic acid receptor subunits, the phosphorylation level of glutamate receptor A (GluA)1 at serine sites S831 and S845, and the Ca2+/calmodulin-dependent protein kinase II (CaMKII) in the hippocampus and prefrontal cortex of CI + Aβ rats. In the CI + Aβ rats, NYT treatment shortened the extended time to reach the platform. However, NYT did not restore the decrease in the hippocampal GluA1, GluA2, or CaMKII expression but increased prefrontal cortical phosphorylation levels of S845-GluA1 and CaMKII. Therefore, NYT may alleviate spatial memory impairment by promoting glutamatergic transmission involved in the phosphorylation of S845-GluA1 and CaMKII in the prefrontal cortex of CI + Aβ rats. Our results suggest that NYT is a valuable treatment for AD patients.

Protein Kinase A Is Responsible for the Presynaptic Inhibition of Glycinergic and Glutamatergic Transmissions by Xenon in Rat Spinal Cord and Hippocampal CA3 Neurons

The effects of a general anesthetic xenon (Xe) on spontaneous, miniature, electrically evoked synaptic transmissions were examined using the "synapse bouton preparation," with which we can clearly evaluate pure synaptic responses and accurately quantify pre- and postsynaptic transmissions. Glycinergic and glutamatergic transmissions were investigated in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xe presynaptically inhibited spontaneous glycinergic transmission, the effect of which was resistant to tetrodotoxin, Cd2+, extracellular Ca2+, thapsigargin (a selective sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor), SQ22536 (an adenylate cyclase inhibitor), 8-Br-cAMP (membrane-permeable cAMP analog), ZD7288 (an hyperpolarization-activated cyclic nucleotide-gated channel blocker), chelerythrine (a PKC inhibitor), and KN-93 (a CaMKII inhibitor) while being sensitive to PKA inhibitors (H-89, KT5720, and Rp-cAMPS). Moreover, Xe inhibited evoked glycinergic transmission, which was canceled by KT5720. Like glycinergic transmission, spontaneous and evoked glutamatergic transmissions were also inhibited by Xe in a KT5720-sensitive manner. Our results suggest that Xe decreases glycinergic and glutamatergic spontaneous and evoked transmissions at the presynaptic level in a PKA-dependent manner. These presynaptic responses are independent of Ca2+ dynamics. We conclude that PKA can be the main molecular target of Xe in the inhibitory effects on both inhibitory and excitatory neurotransmitter release. SIGNIFICANCE STATEMENT: Spontaneous and evoked glycinergic and glutamatergic transmissions were investigated using the whole-cell patch clamp technique in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xenon (Xe) significantly inhibited glycinergic and glutamatergic transmission presynaptically. As a signaling mechanism, protein kinase A was responsible for the inhibitory effects of Xe on both glycine and glutamate release. These results may help understand how Xe modulates neurotransmitter release and exerts its excellent anesthetic properties.

Ninjinyoeito Prevents Onset of Depression-Like Behavior and Reduces Hippocampal iNOS Expression in Senescence-Accelerated Mouse Prone 8 Mice

Late-life depression is a globally prevalent disorder. Ninjinyoeito (NYT), a traditional Japanese herbal medicine, attenuates depressive symptoms in older patients. However, the mechanisms underlying the antidepressive effect of NYT are unknown. In this study, we investigated the mechanism of the action of NYT using senescence-accelerated mouse prone 8 (SAMP8) mice, which exhibit accelerated aging. SAMP8 mice were treated with NYT starting at 12 weeks of age. Twelve-week-old SAMP8 mice did not show prolonged immobility time in the tail suspension test compared with age-matched SAMR1 mice (normal aging control). At 34 weeks of age, vehicle-treated SAMP8 mice displayed prolonged immobility time compared with SAMR1 mice. NYT-treated SAMP8 mice showed a shorter immobility time than that of vehicle-treated SAMP8 mice. Notably, NYT decreased hippocampal inducible nitric oxide synthase (iNOS) expression in SAMP8 mice. There was no difference in iNOS expression between SAMR1 and vehicle-treated SAMP8 mice. Subchronic (5 days) administration of an iNOS inhibitor, 1400 W, shortened the immobility time in SAMP8 mice. These results suggest that NYT prevents an increase in immobility time of SAMP8 mice by decreasing iNOS levels in the hippocampus. Therefore, the antidepressive effect of NYT in older patients might be mediated, at least in part, by the downregulation of iNOS in the brain. Our data suggest that NYT is useful to prevent the onset of depression with aging.

Astrocyte Ca2+ signaling is facilitated in Scn1a+/- mouse model of Dravet syndrome

Dravet syndrome (DS) is an infantile-onset epileptic encephalopathy. More than 80% of DS patients have a heterozygous mutation in SCN1A, which encodes a subunit of the voltage-gated sodium channel, Nav1.1, in neurons. The roles played by astrocytes, the most abundant glial cell type in the brain, have been investigated in the pathogenesis of epilepsy; however, the specific involvement of astrocytes in DS has not been clarified. In this study, we evaluated Ca2+ signaling in astrocytes using genetically modified mice that have a loss-of-function mutation in Scn1a. We found that the slope of spontaneous Ca2+ spiking was increased without a change in amplitude in Scn1a+/- astrocytes. In addition, ATP-induced transient Ca2+ influx and the slope of Ca2+ spiking were also increased in Scn1a+/- astrocytes. These data indicate that perturbed Ca2+ dynamics in astrocytes may be involved in the pathogenesis of DS.

Establishment of autaptic culture with human-induced pluripotent stem cell-derived astrocytes

Although astrocytes are involved in the pathogenesis of CNS diseases, how they induce synaptic abnormalities is unclear. Currently, in vitro pathological astrocyte cultures or animal models do not reproduce human disease phenotypes accurately. Induced pluripotent stem cells (iPSCs) are replacing animal models in pathological studies. We developed an autaptic culture (AC) system containing single neuron cultures grown on microislands of astrocytes. AC with human iPSC-derived astrocytes (HiA) was established. We evaluated the effect of astrocytes on the synaptic functions of human-derived neurons. We found a significantly higher Na⁺ current amplitude, membrane capacitance, and number of synapses, as well as longer dendrites, in HiAACs compared with neuron monocultures. Furthermore, HiAs were involved in the formation and maturation of functional synapses that exhibited excitatory postsynaptic currents. This system can facilitate the study of CNS diseases and advance the development of drugs targeting glial cells.

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We developed an autaptic culture with human iPSCs-derived astrocytes

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Neurons in HiAACs developed after culture and formed functional synapses

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EPSC and mEPSC were recorded showing HiAs promoted synapse formation/maturation

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Autaptic cultures can be used to analyze synaptic activity and human CNS disease

Quantitative Analysis of Presynaptic Vesicle Luminal pH in Cultured Neurons

Newly generated synaptic vesicles (SVs) are re-acidified by the activity of the vacuolar-type H⁺-ATPases. Since H⁺ gradient across SV membrane drives neurotransmitter uptake into SVs, precise measurements of steady-state vesicular pH and dynamics of re-acidification process will provide important information concerning the H⁺-driven neurotransmitter uptake. Indeed, we recently demonstrated distinct features of steady state and dynamics of vesicular pH between glutamatergic vesicles and GABAergic vesicles in cultured hippocampal neurons. In this article, we focus on an experimental protocol and setup required to determine steady-state luminal pH of SVs in living neurons. This protocol is composed of efficient expression of a pH-sensitive fluorescent protein in the lumen of SVs in cultured neurons, and recordings of its fluorescence changes under a conventional fluorescent microscope during local applications of acidic buffer and ionophores-containing solution at a given pH. The method described here can be easily applied for measuring luminal pH of different types of secretory organelles and other acidic organelles such as lysosomes and endosomes in cultured cell preparations.

Kamishoyosan potentiates pentobarbital-induced sleep in socially isolated, ovariectomized mice

ETHNOPHARMACOLOGICAL RELEVANCE

Sleep disorders are among the most common symptoms in both peri- and post-menopausal women. Kamishoyosan (KSS) is a Kampo medicine prescribed for the treatment of sleep disorders in menopausal women in Japan. However, its precise mechanism of action remains unclear.

AIM OF THE STUDY

In the present study, we developed a new animal model of menopausal sleep disorders by inducing social isolation stress in ovariectomized mice. Using pentobarbital-induced sleeping time as an index, we aimed to investigate the effects of KSS and involvement of the benzodiazepine receptors.

MATERIALS AND METHODS

Eight-week-old, female ddY mice were ovariectomized or subjected to a sham operation (control) and housed in social isolation or groups for 9 weeks. The animals were divided into four groups, group-housed sham-operated, isolated sham-operated, group-housed ovariectomized, and socially isolated ovariectomized. Pentobarbital (50 mg/kg) was administered intraperitoneally (i.p.). Sleeping time was considered the period between the loss of righting reflex and its return (up to 180 min). KSS was administered orally (p.o.) 60 min before the test. Diazepam and flumazenil were administered i.p. 30 and 45 min before the test, respectively. On the day after administration, the mice were euthanized, and their uteri were weighed.

RESULTS

Socially isolated, ovariectomized mice had shorter sleeping times than mice in all other groups. In mice with intact ovaries, diazepam (1 mg/kg, i.p.) considerably prolonged the pentobarbital-induced sleeping time, but KSS (30-1000 mg/kg, p.o.) did not. However, KSS (100 mg/kg, p.o.) significantly prolonged the pentobarbital-induced sleeping time in socially isolated ovariectomized mice. The prolongation of sleeping time mediated by KSS was reversed by flumazenil (3 mg/kg, i.p.).

CONCLUSIONS

KSS potentiated pentobarbital-induced sleep in socially isolated, ovariectomized mice, and the benzodiazepine receptors are possibly involved in its pharmacological mechanism. These findings suggest that KSS is beneficial for the treatment of menopausal sleep disorders.

Ibudilast suppresses oxaliplatin-induced mechanical allodynia and neurodegeneration in rats

Oxaliplatin is a key drug used in the management of solid tumors, such as colorectal cancer; however, it causes peripheral neuropathy. In this study, we investigated the effect of ibudilast, a phosphodiesterase inhibitor, on oxaliplatin-induced mechanical allodynia and histological changes in rats. Ibudilast (7.5 mg/kg, i.p., 5 times per week) reduced mechanical allodynia and histological changes induced by oxaliplatin (4 mg/kg, i.p., twice a week). In contrast, ibudilast (0.01-10 μM) had no effect on oxaliplatin-induced tumor cytotoxicity in murine colon adenocarcinoma 26 cells. These findings suggest that ibudilast could be useful for preventing oxaliplatin-induced peripheral neuropathy in clinical settings.

The novel mitochondria activator, 10-ethyl-3-methylpyrimido[4,5-b]quinoline-2,4(3H,10H)-dione (TND1128), promotes the development of hippocampal neuronal morphology

Adenosine triphosphate (ATP) is the most vital energy source produced mainly in the mitochondria. Age-related mitochondrial dysfunction is associated with brain diseases. Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor for energy production in mitochondria. Here, we examined how the novel NAD+-assisting substance, 10-ethyl-3-methylpyrimido[4,5-b]quinoline-2,4(3H,10H)-dione (TND1128), modulates the morphological growth of cultured mouse hippocampal neurons. The morphological growth effect of TND1128 was also compared with that of β-nicotinamide mononucleotide (β-NMN). TND1128 induced the branching of axons and dendrites, and increased the number of excitatory synapses. This study provides new insight into TND1128 as a mitochondria-stimulating drug for improving brain function.

Inhibitory synaptic transmission is impaired at higher extracellular Ca2+ concentrations in Scn1a+/- mouse model of Dravet syndrome

Dravet syndrome (DS) is an intractable form of childhood epilepsy that occurs in infancy. More than 80% of all patients have a heterozygous abnormality in the SCN1A gene, which encodes a subunit of Na+ channels in the brain. However, the detailed pathogenesis of DS remains unclear. This study investigated the synaptic pathogenesis of this disease in terms of excitatory/inhibitory balance using a mouse model of DS. We show that excitatory postsynaptic currents were similar between Scn1a knock-in neurons (Scn1a+/- neurons) and wild-type neurons, but inhibitory postsynaptic currents were significantly lower in Scn1a+/- neurons. Moreover, both the vesicular release probability and the number of inhibitory synapses were significantly lower in Scn1a+/- neurons compared with wild-type neurons. There was no proportional increase in inhibitory postsynaptic current amplitude in response to increased extracellular Ca2+ concentrations. Our study revealed that the number of inhibitory synapses is significantly reduced in Scn1a+/- neurons, while the sensitivity of inhibitory synapses to extracellular Ca2+ concentrations is markedly increased. These data suggest that Ca2+ tethering in inhibitory nerve terminals may be disturbed following the synaptic burst, likely leading to epileptic symptoms.

Valproic acid-exposed astrocytes impair inhibitory synapse formation and function

Valproic acid (VPA) is widely prescribed to treat epilepsy. Maternal VPA use is, however, clinically restricted because of the severe risk that VPA may cause neurodevelopmental disorders in offspring, such as autism spectrum disorder. Understanding the negative action of VPA may help to prevent VPA-induced neurodevelopmental disorders. Astrocytes play a vital role in neurodevelopment and synapse function; however, the impact of VPA on astrocyte involvement in neurodevelopment and synapse function has not been examined. In this study, we examined whether exposure of cultured astrocytes to VPA alters neuronal morphology and synapse function of co-cultured neurons. We show that synaptic transmission by inhibitory neurons was small because VPA-exposed astrocytes reduced the number of inhibitory synapses. However, synaptic transmission by excitatory neurons and the number of excitatory synapses were normal with VPA-exposed astrocytes. VPA-exposed astrocytes did not affect the morphology of inhibitory neurons. These data indicate that VPA-exposed astrocytes impair synaptogenesis specifically of inhibitory neurons. Our results indicate that maternal use of VPA would affect not only neurons but also astrocytes and would result in perturbed astrocyte-mediated neurodevelopment.

A Japanese herbal medicine attenuates anxiety-like behavior through GABAA receptor and brain-derived neurotrophic factor expression in a rat model of premenstrual syndrome

Inochinohaha White (IHW) is a Japanese herbal medicine for treating women with anxiety associated with premenstrual syndrome (PMS). In this study, we examined the effects of IHW on anxiety-like behavior in rats undergoing progesterone withdrawal (PWD), a model for PMS. Female rats were injected daily with progesterone for 21 days. Water and ethanol extracts of IHW (WE-IHW and EE-IHW, respectively) were administered orally 15 days after the initiation of progesterone injections. Anxiety-like behavior in an elevated plus maze was evaluated 48 h after the final injection of progesterone. PWD induced anxiety-like behavior, and EE-IHW (300 mg/kg), but not WE-IHW, significantly attenuated this behavior. Administration of the GABA agonists, diazepam or muscimol, significantly attenuated PWD-induced anxiety-like behavior. To investigate the underlying mechanisms of IHW action, we analyzed GABAA receptor expression in the amygdala of these rats. EE-IHW ameliorated the PWD-induced decrease in GABAA receptor β2-subunit mRNA, although β2-subunit protein was unchanged. Brain-derived neurotrophic factor (BDNF) has been reported to have anxiolytic effects and enhance GABAergic synaptic transmission. We found that EE-IHW increased BDNF levels in a dose-dependent manner. Our results suggest that EE-IHW attenuates PWD-induced anxiety-like behavior by increasing GABAA receptor-mediated signaling via increases in β2-subunit and BDNF in the amygdala.

Presynaptically silent synapses are modulated by the density of surrounding astrocytes

Astrocytes, comprising the primary glial-cell type, are involved in the formation and maturation of synapses, and thus contribute to sustainable synaptic transmission between neurons. Given that the animals in higher phylogenetic tree have brains with a higher density of glial cells with respect to neurons, there is a possibility that the relative astrocytic density directly influences synaptic transmission. However, the notion has not been tested thoroughly. Here we addressed it, by using a primary culture preparation where single hippocampal neurons are surrounded by a variable but a countable number of cortical astrocytes in dot-patterned microislands, and recording synaptic transmission by patch-clamp electrophysiology. Neurons with a higher astrocytic density showed a higher amplitude of the evoked excitatory postsynaptic current than that of neurons with a lower astrocytic density. The size of the readily releasable pool of synaptic vesicles per neuron was significantly larger. The frequency of spontaneous synaptic transmission was higher, but the amplitude was unchanged. The number of morphologically identified glutamatergic synapses was comparable, but the percentage of functional ones was increased, indicating a lower ratio of presynaptically silent synapses. Taken together, the higher astrocytic density enhanced excitatory synaptic transmission by increasing the fraction of functional synapses through presynaptic un-silencing.

Effect of Yokukansan and Yokukansankachimpihange on Aggressive Behavior, 5-HT Receptors and Arginine Vasopressin Expression in Social Isolation-Reared Mice

The traditional herbal medicines yokukansan (YKS) and yokukansankachimpihange (YKSCH) are prescribed for neurosis, insomnia or night crying and irritability in children. YKSCH comprises YKS and two additional herbs, a chimpi and a hange, and is used to treat digestive function deficiencies. However, the differences between the effects of YKS and YKSCH on brain function are unclear. The present study examined the effects of YKS and YKSCH on aggressive behavior in mice reared under a social isolation (SI) condition. Mice were housed individually for 6 weeks. YKS and YKSCH were administered orally for 2 weeks before aggression tests. SI increased aggressive behavior against naïve mice, and YKS, but not YKSCH, significantly attenuated this aggressive behavior. Because serotonin (5-HT)_2A and 5-HT_3A receptor antagonists are reported to have anti-aggressive effects, the mRNA levels of these receptors were examined. YKS attenuated the SI-induced increase in 5-HT_2A and 5-HT_3A receptor mRNA in the amygdala. On the other hand, YKSCH attenuated the SI-induced increase in 5-HT_1A receptor mRNA. YKS and YKSCH did not affect 5-HT and its metabolite 5-hydroxyindoleacetic acid content in the amygdala. However, YKSCH increased the mRNA level of arginine vasopressin (AVP), which is a neuropeptide that has been implicated in aggression, in the amygdala. These results suggest that YKS ameliorates aggressive behavior by decreasing 5-HT_2A and 5-HT_3A receptor expression. The YKSCH-induced increase in AVP may disrupt the anti-aggressive effect of YKS. YKS may be more effective than YKSCH for treating irritability if digestive function deficiencies are not considered.

Pioneer Factor NeuroD1 Rearranges Transcriptional and Epigenetic Profiles to Execute Microglia-Neuron Conversion

Minimal sets of transcription factors can directly reprogram somatic cells into neurons. However, epigenetic remodeling during neuronal reprogramming has not been well reconciled with transcriptional regulation. Here we show that NeuroD1 achieves direct neuronal conversion from mouse microglia both in vitro and in vivo. Exogenous NeuroD1 initially occupies closed chromatin regions associated with bivalent trimethylation of histone H3 at lysine 4 (H3K4me3) and H3K27me3 marks in microglia to induce neuronal gene expression. These regions are resolved to a monovalent H3K4me3 mark at later stages of reprogramming to establish the neuronal identity. Furthermore, the transcriptional repressors Scrt1 and Meis2 are induced as NeuroD1 target genes, resulting in a decrease in the expression of microglial genes. In parallel, the microglial epigenetic signature in promoter and enhancer regions is erased. These findings reveal NeuroD1 pioneering activity accompanied by global epigenetic remodeling for two sequential events: onset of neuronal property acquisition and loss of the microglial identity during reprogramming.

Dependence and Homeostasis of Membrane Impedance on Cell Morphology in Cultured Hippocampal Neurons

The electrical impedance of cell membranes is important for excitable cells, such as neurons, because it strongly influences the amount of membrane potential change upon a flow of ionic current across the membrane. Here, we report on an investigation of how neuronal morphology affects membrane impedance of cultured hippocampal neurons. Microfabricated substrates with patterned scaffolding molecules were used to restrict the neurite growth of hippocampal neurons, and the impedance was measured via whole-cell patch-clamp recording under the inhibition of voltage-dependent ion channels. Membrane impedance was found to depend inversely on the dendrite length and soma area, as would be expected from the fact that its electrical property is equivalent to a parallel RC circuit. Moreover, we found that in biological neurons, the membrane impedance is homeostatically regulated to impede changes in the membrane area. The findings provide direct evidence on cell-autonomous regulation of neuronal impedance and pave the way towards elucidating the mechanism responsible for the resilience of biological neuronal networks.

The Japanese Angelica acutiloba root and yokukansan increase hippocampal acetylcholine level, prevent apoptosis and improve memory in a rat model of repeated cerebral ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

Japanese Angelica acutiloba root (Angelica root) is included in several Kampo medicines including Yokukansan (YKS). Angelica root and YKS are used for the treatment of a variety of psychological and neurodegenerative disorders. Development of safe and effective therapeutic agents against cerebrovascular disorders will improve the treatment of patients with dementia.

AIM OF THE STUDY

The effect of Angelica root and YKS on ischemia-impaired memory has not yet been fully investigated. The present study investigated whether Angelica root is also involved in memory improving and neuroprotective effect of YKS in a model of cerebrovascular ischemia.

MATERIALS AND METHODS

Male Wistar rats grouped into sham rats received saline, and other three groups subjected to repeated cerebral ischemia induced by 4-vessel occlusion (4-VO), received a 7-day oral administration of either saline, Angelica root or YKS. Memory was evaluated by eight-arm radial maze task. Acetylcholine release (ACh) in the dorsal hippocampus was investigated by microdialysis-HPLC. Apoptosis was determined by terminal deoxynucleotidyl transferase (TdT)-mediated fluorescein-deoxyuridine triphosphate (dUTP) nick-end labeling.

RESULTS

Ischemia induced apoptosis, reduced release of ACh, and impaired the memory (increased error choices and decreased correct choices). Angelica root and YKS improved the memory deficits, upregulated the release of ACh and prevented 4-VO-induced hippocampal apoptosis.

CONCLUSION

The dual ACh-increasing and neuroprotective effect of Angelica root could make it a promising therapeutic agent useful for the treatment of symptoms of cerebrovascular dementia. Angelica root could be one of the components contributing to the memory-improving and neuroprotective effects of YKS.

The Traditional Japanese Herbal Medicine Hachimijiogan Elicits Neurite Outgrowth Effects in PC12 Cells and Improves Cognitive in AD Model Rats via Phosphorylation of CREB

Hachimijiogan (HJG) is a traditional herbal medicine that improves anxiety disorders in patients with dementia. In this study, we tested the hypothesis that HJG exerts neurotrophic factor-like effects to ameliorate memory impairment in Alzheimer disease (AD) model rats. First, we describe that HJG acts to induce neurite outgrowth in PC12 cells (a rat pheochromocytoma cell line) like nerve growth factor (NGF) in a concentration-dependent manner (3 μg/ml HJG, p < 0.05; 10–500 μg/ml HJG, p < 0.001). While six herbal constituents of HJG, Rehmannia root, Dioscorea rhizome, Rhizoma Alismatis, Poria sclerotium, Moutan bark, and Cinnamon bark, could induce neurite outgrowth effects, the effect was strongest with HJG (500 μg/ml). Second, we demonstrated that HJG-induced neurite outgrowth was blocked by an inhibitor of cAMP response element binding protein (CREB), KG-501 (10 μM, p < 0.001). Moreover, HJG was observed to induce CREB phosphorylation 20–90 min after treatment (20 min, 2.50 ± 0.58-fold) and CRE-mediated transcription in cultured PC12 cells (500 μg/ml, p < 0.01; 1000 μg/ml, p < 0.001). These results suggest a CREB-dependent mechanism underlies the neurotrophic effects of HJG. Finally, we examined improvements of memory impairment following HJG treatment using a Morris water maze in AD model animals (CI + Aβ rats). Repeated oral administration of HJG improved memory impairment (300 mg/kg, p < 0.05; 1000 mg/kg, p < 0.001) and induced CREB phosphorylation within the hippocampus (1000 mg/kg, p < 0.01). Together, our results suggest that HJG possesses neurotrophic effects similar to those of NGF, and can ameliorate cognitive dysfunction in a rat dementia model via CREB activation. Thus, HJG could potentially be a substitute for neurotrophic factors as a treatment for dementia.

Astrocytes with previous chronic exposure to amyloid β-peptide fragment 1-40 suppress excitatory synaptic transmission

Synaptic dysfunction and neuronal death are responsible for cognitive and behavioral deficits in Alzheimer's disease (AD). It is well known that such neurological abnormalities are preceded by long-term exposure of amyloid β-peptide (Aβ) and/or hyperphosphorylated tau prior. In addition to the neurological deficit, astrocytes as a major glial cell type in the brain, significantly participate in the neuropathogenic mechanisms underlying synaptic modulation. Although astrocytes play a significant key role in modulating synaptic transmission, little is known on whether astrocyte dysfunction caused by such long-term Aβ exposure affects synapse formation and function. Here, we show that synapse formation and synaptic transmission are attenuated in hippocampal-naïve neurons co-cultured with astrocytes that have previously experienced chronic Aβ_1-40 exposure. In this abnormal astrocytic condition, hippocampal neurons exhibit decrements of evoked excitatory post-synaptic currents (EPSCs) and miniature EPSC frequency. Furthermore, size of readily releasable synaptic pools and number of excitatory synapses were also significantly decreased. Contrary to these negative effects, release probability at individual synapses was significantly increased in the same astrocytic condition. Taken together, our data indicate that lower synaptic transmission caused by astrocytes previously, and chronically, exposed to Aβ1-40 is attributable to a small number of synapses with higher release probability.

Overexpression of Swedish mutant APP in aged astrocytes attenuates excitatory synaptic transmission

Amyloid precursor protein (APP), a type I transmembrane protein, has different aspects, namely, performs essential physiological functions and produces β‐amyloid peptide (Aβ). Overexpression of neuronal APP is responsible for synaptic dysfunction. In the central nervous system, astrocytes – a major glial cell type – have an important role in the regulation of synaptic transmission. Although APP is expressed in astrocytes, it remains unclear whether astrocytic overexpression of mutant APP affects synaptic transmission. In this study, the effect of astrocytic overexpression of a mutant APP on the excitatory synaptic transmission was investigated using coculture system of the transgenic (Tg) cortical astrocytes that express the human APP695 polypeptide with the double mutation K670N + M671L found in a large Swedish family with early onset Alzheimer's disease, and wild‐type hippocampal neuron. Significant secretion of Aβ 1–40 and 1–42 was observed in cultured cortical astrocytes from the Tg2576 transgenic mouse that genetically overexpresses Swedish mutant APP. Under the condition, Tg astrocytes did not affect excitatory synaptic transmission of cocultured wild‐type neurons. However, aged Tg astrocytes cultured for 9 weeks elicited a significant decrease in excitatory synaptic transmission in cocultured neurons. Moreover, a reduction in the number of readily releasable synaptic vesicles accompanied a decrease in the number of excitatory synapses in neurons cocultured with aged Tg astrocytes. These observations indicate that astrocytic expression of the mutant APP is involved in the downregulation of synaptic transmission with age.

Unidirectional signal propagation in primary neurons micropatterned at a single-cell resolution

The structure and connectivity of cultured neuronal networks can be controlled by using micropatterned surfaces. Here, we demonstrate that the direction of signal propagation can be precisely controlled at a single-cell resolution by growing primary neurons on micropatterns. To achieve this, we first examined the process by which axons develop and how synapses form in micropatterned primary neurons using immunocytochemistry. By aligning asymmetric micropatterns with a marginal gap, it was possible to pattern primary neurons with a directed polarization axis at the single-cell level. We then examined how synapses develop on micropatterned hippocampal neurons. Three types of micropatterns with different numbers of short paths for dendrite growth were compared. A normal development in synapse density was observed when micropatterns with three or more short paths were used. Finally, we performed double patch clamp recordings on micropatterned neurons to confirm that these synapses are indeed functional, and that the neuronal signal is transmitted unidirectionally in the intended orientation. This work provides a practical guideline for patterning single neurons to design functional neuronal networks in vitro with the direction of signal propagation being controlled.

Activation of Rheb, but not of mTORC1, impairs spine synapse morphogenesis in tuberous sclerosis complex

Mutations in the Tsc1 or Tsc2 genes cause tuberous sclerosis complex (TSC). Tsc1 and Tsc2 proteins form a complex that inhibits mammalian target of rapamycin complex 1 (mTORC1) signalling through Rheb-GTPase. We found that Tsc2^+/− neurons showed impaired spine synapse formation, which was resistant to an mTORC1 inhibitor. Knockdown of mTOR also failed to restore these abnormalities, suggesting mTORC may not participate in impaired spinogenesis in Tsc2^+/− neurons. To address whether Rheb activation impairs spine synapse formation, we expressed active and inactive forms of Rheb in WT and Tsc2^+/− neurons, respectively. Expression of active Rheb abolished dendritic spine formation in WT neurons, whereas inactive Rheb restored spine synapse formation in Tsc2^+/− neurons. Moreover, inactivation of Rheb with farnesyl transferase inhibitors recovered spine synapse morphogenesis in Tsc2^+/− neurons. In conclusion, dendritic spine abnormalities in TSC neurons may be caused through activation of Rheb, but not through of mTORC1.

A human Dravet syndrome model from patient induced pluripotent stem cells

BACKGROUND

Dravet syndrome is a devastating infantile-onset epilepsy syndrome with cognitive deficits and autistic traits caused by genetic alterations in SCN1A gene encoding the α-subunit of the voltage-gated sodium channel Na(v)1.1. Disease modeling using patient-derived induced pluripotent stem cells (iPSCs) can be a powerful tool to reproduce this syndrome's human pathology. However, no such effort has been reported to date. We here report a cellular model for DS that utilizes patient-derived iPSCs.

RESULTS

We generated iPSCs from a Dravet syndrome patient with a c.4933C>T substitution in SCN1A, which is predicted to result in truncation in the fourth homologous domain of the protein (p.R1645*). Neurons derived from these iPSCs were primarily GABAergic (>50%), although glutamatergic neurons were observed as a minor population (<1%). Current-clamp analyses revealed significant impairment in action potential generation when strong depolarizing currents were injected.

CONCLUSIONS

Our results indicate a functional decline in Dravet neurons, especially in the GABAergic subtype, which supports previous findings in murine disease models, where loss-of-function in GABAergic inhibition appears to be a main driver in epileptogenesis. Our data indicate that patient-derived iPSCs may serve as a new and powerful research platform for genetic disorders, including the epilepsies.

Long-term culture of astrocytes attenuates the readily releasable pool of synaptic vesicles

The astrocyte is a major glial cell type of the brain, and plays key roles in the formation, maturation, stabilization and elimination of synapses. Thus, changes in astrocyte condition and age can influence information processing at synapses. However, whether and how aging astrocytes affect synaptic function and maturation have not yet been thoroughly investigated. Here, we show the effects of prolonged culture on the ability of astrocytes to induce synapse formation and to modify synaptic transmission, using cultured autaptic neurons. By 9 weeks in culture, astrocytes derived from the mouse cerebral cortex demonstrated increases in β-galactosidase activity and glial fibrillary acidic protein (GFAP) expression, both of which are characteristic of aging and glial activation in vitro. Autaptic hippocampal neurons plated on these aging astrocytes showed a smaller amount of evoked release of the excitatory neurotransmitter glutamate, and a lower frequency of miniature release of glutamate, both of which were attributable to a reduction in the pool of readily releasable synaptic vesicles. Other features of synaptogenesis and synaptic transmission were retained, for example the ability to induce structural synapses, the presynaptic release probability, the fraction of functional presynaptic nerve terminals, and the ability to recruit functional AMPA and NMDA glutamate receptors to synapses. Thus the presence of aging astrocytes affects the efficiency of synaptic transmission. Given that the pool of readily releasable vesicles is also small at immature synapses, our results are consistent with astrocytic aging leading to retarded synapse maturation.

Cholinergic involvement and synaptic dynamin 1 expression in Yokukansan-mediated improvement of spatial memory in a rat model of early Alzheimer's disease

The aim of this study was to investigate the effect of Yokukansan (YKS) on the impairment of spatial memory and cholinergic involvement in a rat model of early-phase Alzheimer's disease (AD). In this model, rats underwent four-vessel transient cerebral ischemia and then were treated with beta amyloid oligomers injected intracerebroventricularly once daily for 7 days. These animals showed memory impairment in an eight-arm radial maze task without histological evidence of apoptosis but with a decrease in expression of hippocampal dynamin 1, an important factor in synaptic vesicle endocytosis. Oral administration of YKS for 2 weeks significantly increased the number of correct choices and decreased the number of error choices in the eight-arm radial maze task (P < 0.05). Moreover, YKS significantly increased high K⁺-evoked potentiation of acetylcholine (ACh) release (P < 0.05) and significantly increased the expression of dynamin 1 (P < 0.01) in the hippocampus. The ameliorative effect of YKS on spatial memory impairment in our rat model of early-phase AD may be mediated in part by an increase in ACh release and modulation of dynamin 1 expression, leading to improved synaptic function. Future studies will determine whether YKS is similarly useful in the treatment of memory defects in patients diagnosed with early-stage AD.

Neuroprotective effects of citidine-5-diphosphocholine on impaired spatial memory in a rat model of cerebrovascular dementia

Citidine-5-diphosphocholine or citicoline (CDP-choline) is used as a neuroprotective and memory-enhancing drug in cerebral stroke, Alzheimer's disease, and other neurovascular diseases. Non-clinical studies have demonstrated the neuroprotective effects of CDP-choline in ischemic animal models. However, the relationship between the neuroprotective effect and the memory enhancing effect of CDP-choline is still unknown. No studies have demonstrated the ameliorative effect on impaired spatial memory and the suppressive effect on neuronal cell death of CDP-choline in the same model. In this study, we examined the effect of CDP-choline on impaired spatial memory and hippocampal CA1 neuronal death in rats subjected to repeated cerebral ischemia, and we compared the mechanism of CDP-choline to that of donepezil. Seven days post administration of CDP-choline (100, 300, 1000 mg/kg per day, p.o.) or donepezil increased correct choices and reduced error choices in an eight-arm radial maze task in a dose-dependent manner. Neuronal cell death of caspase-3 protein-positive neurons in the hippocampus were reduced by repeated administration of CDP-choline at the highest dose. These results suggest that CDP-choline has ameliorative effects on the impairment of spatial memory via hippocampal neuronal cell death in a rat model of cerebral ischemia.

Regulation of Rap2A by the ubiquitin ligase Nedd4-1 controls neurite development

Nedd4-1 is a "neuronal precursor cell expressed and developmentally downregulated protein" and among the most abundant E3 ubiquitin ligases in mammalian neurons. In analyses of conventional and conditional Nedd4-1-deficient mice, we found that Nedd4-1 plays a critical role in dendrite formation. Nedd4-1, the serine/threonine kinase TNIK, and Rap2A form a complex that controls Nedd4-1-mediated ubiquitination of Rap2A. Ubiquitination by Nedd4-1 inhibits Rap2A function, which reduces the activity of Rap2 effector kinases of the TNIK family and promotes dendrite growth. We conclude that a Nedd4-1/Rap2A/TNIK signaling pathway regulates neurite growth and arborization in mammalian neurons.

Decreased acetylcholine release is correlated to memory impairment in the Tg2576 transgenic mouse model of Alzheimer's disease

Acetylcholine (ACh) release is one of the key factors in memory mechanisms. To clarify whether beta-amyloid (Abeta) induces a disturbance of the cholinergic system leading to memory impairment, we examined memory impairment and measured hippocampal ACh release in Tg2576 (Tg) mice that over-express the Swedish mutant amyloid precursor protein (APPsw). Furthermore, we examined Abeta burden with aging. Tg mice aged 9-11 months, but not aged 4-6 months, showed memory impairment in the 8-arm radial maze behavior test. Spontaneous ACh release was not altered in Tg mice compared with age-matched control mice at 4-6 or 9-11 months of age. On the other hand, high-K(+)-evoked ACh release was decreased in Tg mice aged 9-11 months, but not in Tg mice aged 4-6 months. Hippocampal Abeta increased in an age-dependent manner, but evident amyloid plaques were not found in the hippocampus of Tg mice aged 11 months. These results suggest that memory impairment in Tg mice could be attributed to cholinergic synapse dysfunction that could not be caused predominantly by amyloid plaques. Measuring ACh release in this model might be a useful index for the screening of new drugs to treat the early-phase of Alzheimer's disease.

Cannabidiol prevents a post-ischemic injury progressively induced by cerebral ischemia via a high-mobility group box1-inhibiting mechanism

We examined the cerebroprotective mechanism of cannabidiol, the non-psychoactive component of marijuana, against infarction in a 4-h mouse middle cerebral artery (MCA) occlusion model. Cannabidiol was intraperitoneally administrated immediately before and 3h after cerebral ischemia. Infarct size and myeloperoxidase (MPO) activity, a marker of neutrophil, monocyte/macropharge, were measured at 24h after cerebral ischemia. Activated microglia and astrocytes were evaluated by immunostaining. Moreover, high-mobility group box1 (HMGB1) was also evaluated at 1 and 3 days after MCA occlusion. In addition, neurological score and motor coordination on the rota-rod test were assessed at 1 and 3 days after cerebral ischemia. Cannabidiol significantly prevented infarction and MPO activity at 20h after reperfusion. These effects of cannabidiol were not inhibited by either SR141716 or AM630. Cannabidiol inhibited the MPO-positive cells expressing HMGB1 and also decreased the expression level of HMGB1 in plasma. In addition, cannabidiol decreased the number of Iba1- and GFAP-positive cells at 3 days after cerebral ischemia. Moreover, cannabidiol improved neurological score and motor coordination on the rota-rod test. Our results suggest that cannabidiol inhibits monocyte/macropharge expressing HMGB1 followed by preventing glial activation and neurological impairment induced by cerebral ischemia. Cannabidiol will open new therapeutic possibilities for post-ischemic injury via HMGB1-inhibiting mechanism.

Delta 9-tetrahydrocannabinol-induced catalepsy-like immobilization is mediated by decreased 5-HT neurotransmission in the nucleus accumbens due to the action of glutamate-containing neurons

Delta(9)-tetrahydrocannabinol (THC) has been reported to induce catalepsy-like immobilization, but the mechanism underlying this effect remains unclear. In the present study, in order to fully understand the neural circuits involved, we determined the brain sites involved in the immobilization effect in rats. THC dose-dependently induced catalepsy-like immobilization. THC-induced catalepsy-like immobilization is mechanistically different from that induced by haloperidol (HPD), because unlike HPD-induced catalepsy, animals with THC-induced catalepsy became normal again following sound and air-puff stimuli. THC-induced catalepsy was reversed by SR141716, a selective cannabinoid CB(1) receptor antagonist. Moreover, THC-induced catalepsy was abolished by lesions in the nucleus accumbens (NAc) and central amygdala (ACE) regions. On the other hand, HPD-induced catalepsy was suppressed by lesions in the caudate putamen (CP), substantia nigra (SN), globus pallidus (GP), ACE and lateral hypothalamus (LH) regions. Bilateral microinjection of THC into the NAc region induced catalepsy-like immobilization. This THC-induced catalepsy was inhibited by serotonergic drugs such as 5-hydroxy-L-tryptophan (5-HTP), a 5-HT precursor, and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), a 5-HT receptor agonist, as well as by anti-glutamatergic drugs such as MK-801 and amantadine, an N-methyl-d-aspartate (NMDA) receptor antagonist. THC significantly decreased 5-HT and glutamate release in the NAc, as shown by in vivo microdialysis. SR141716 reversed and MK-801 inhibited this decrease in 5-HT and glutamate release. These findings suggest that the THC-induced catalepsy is mechanistically different from HPD-induced catalepsy and that the catalepsy-like immobilization induced by THC is mediated by decreased 5-HT neurotransmission in the nucleus accumbens due to the action of glutamate-containing neurons.

A shared vesicular carrier allows synaptic corelease of GABA and glycine

The type of vesicular transporter expressed by a neuron is thought to determine its neurotransmitter phenotype. We show that inactivation of the vesicular inhibitory amino acid transporter (Viaat, VGAT) leads to embryonic lethality, an abdominal defect known as omphalocele, and a cleft palate. Loss of Viaat causes a drastic reduction of neurotransmitter release in both GABAergic and glycinergic neurons, indicating that glycinergic neurons do not express a separate vesicular glycine transporter. This loss of GABAergic and glycinergic synaptic transmission does not impair the development of inhibitory synapses or the expression of KCC2, the K+ -Cl- cotransporter known to be essential for the establishment of inhibitory neurotransmission. In the absence of Viaat, GABA-synthesizing enzymes are partially lost from presynaptic terminals. Since GABA and glycine compete for vesicular uptake, these data point to a close association of Viaat with GABA-synthesizing enzymes as a key factor in specifying GABAergic neuronal phenotypes.

Differential modulation of evoked and spontaneous glycine release from rat spinal cord glycinergic terminals by the cyclic AMP/protein kinase A transduction cascade

The mechanisms underlying cyclic AMP modulation of action potential-dependent and -independent (spontaneous) release of glycine from terminals synapsing onto sacral dorsal commissural nucleus neurons of lamina X were studied in spinal cord slices using conventional patch-clamp recordings. 3-Isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, and forskolin increased the amplitude of evoked inhibitory postsynaptic currents (eIPSCs) in a sensitive manner to protein kinase A (PKA) inhibition (with KT-5720). Direct activation (with adenosine 3',5'-cyclic-monophosphothioate, Sp-isomer) and inhibition (with adenosine 3',5'-cyclic-monophosphothioate, Rp-isomer) of PKA increased and decreased the eIPSC amplitude, respectively. Paired pulse experiments and direct injection of PKA inhibitor fragment 6-22 amide (PKI(6-22)) into the recording neuron revealed that these effects on eIPSC amplitude occurred presynaptically, indicating that evoked glycine release is regulated by presynaptic cAMP via changes in PKA activity. Increasing cAMP also increased spontaneous release of glycine, causing an increased frequency of miniature IPSCs (mIPSCs). In contrast to the effects on evoked release, this response was not solely mediated via PKA, as it was not occluded by PKA inhibition, and both direct inhibition and direct activation of PKA actually enhanced mIPSC frequency. Direct inhibition of cAMP (with SQ 22536) did, however, reduce mIPSC frequency. These results suggest cAMP modulation of evoked and spontaneous release involves different presynaptic mechanisms and proteins.

Distinct profiles of refilling of inhibitory neurotransmitters into presynaptic terminals projecting to spinal neurones in immature rats

Corelease of glycine and GABA from the single synaptic terminal (synaptic bouton) is well accepted in immature rat spinal cord and brainstem. However, it raises the question of how glycine and GABA are accumulated in the same synaptic vesicles and coreleased. To address this issue, spontaneous miniature inhibitory postsynaptic currents (mIPSCs) and focally evoked IPSCs (eIPSCs) mediated via a single synapse were recorded from synaptic bouton preparations of the rat immature sacral dorsal commissural nucleus (SDCN) neurones by whole-cell patch recording. Focal stimulation of a single synaptic bouton revealed that three different quantal releases occur from a single synaptic bouton: i.e. pure glycine, pure GABA, and mixed. Prolonged treatment with bafilomycin A1, a vacuolar-type H+/ATPase inhibitor, to the SDCN neurone greatly suppressed frequency and amplitude of the mIPSCs. During washing out of bafilomycin A1, complete recovery in the amplitude of glycinergic mIPSCs was observed, while that of GABAergic and mixed mIPSCs was incomplete. These observations indicate that three types of vesicles coexist in single synaptic terminals, and that refilling of glycine into the synaptic vesicle predominantes over GABA after pretreatment with bafilomycin A1 in immature rats. This could be explained by the decrease in the cytosolic concentration of GABA, or by the presence of subtypes of vesicular inhibitory amino acid transporter in the synaptic vesicle membrane.

Developmental switch from GABA to glycine release in single central synaptic terminals

Early in postnatal development, inhibitory inputs to rat lateral superior olive (LSO) neurons change from releasing predominantly GABA to releasing predominantly glycine into the synapse. Here we show that spontaneous miniature inhibitory postsynaptic currents (mIPSCs) also change from GABAergic to glycinergic over the first two postnatal weeks. Many 'mixed' mIPSCs, resulting from co-release of glycine and GABA from the same vesicles, are seen during this transition. Immunohistochemistry showed that a large number of terminals contained both GABA and glycine at postnatal day 8 (P8). By P14, both the content of GABA in these mixed terminals and the contribution of GABA to the mixed mIPSCs had decreased. The content of glycine in terminals increased over the same period. Our results indicate that switching from GABAergic to glycinergic inputs to the LSO may occur at the level of a single presynaptic terminal. This demonstrates a new form of developmental plasticity at the level of a single central synapse.

GABAB receptor transduction mechanisms, and cross-talk between protein kinases A and C, in GABAergic terminals synapsing onto neurons of the rat nucleus basalis of Meynert

The transduction mechanisms underlying presynaptic GABAB receptor-mediated inhibition of transmitter release have been characterized for a variety of synapses in the central nervous system (CNS). These studies have suggested a range of transduction mechanisms, including a role for second messengers such as protein kinases A (PKA) and C (PKC). In the present study, we have examined the intracellular signalling pathways underlying baclofen-induced inhibition of GABA release from terminals synapsing onto rat basalis of Meynert neurons using patch-clamp recordings. Baclofen, a selective GABAB receptor agonist, reversibly decreased both evoked and spontaneous, miniature, GABAergic inhibitory postsynaptic currents (eIPSCs and mIPSCs, respectively). Such baclofen actions were completely abolished by CGP55845A, a selective GABAB receptor antagonist, and by staurosporine, a non-selective PKA and PKC inhibitor. The mIPSC frequency was still decreased by baclofen even in the presence of 4 AP, a K+ channel blocker, and Cd2+, a voltage-dependent calcium channel blocker. Pharmacological activation or inhibition of PKC activity affected basal GABA release and mildly affected the response to baclofen. Inhibition of the cAMP/PKA cascade also affected basal GABA release and, in a subset of neurons, occluded the effects of baclofen, suggesting that the GABAB receptor-mediated inhibitory action on GABA release was mediated via decreases in PKA activity. In addition, PKA inhibition occluded the effects of PKC modulation on both basal GABA release and on the response to baclofen. Our results characterize the transduction pathway of baclofen at these nucleus basalis of Maynert (nBM) synapses and show, for the first time, some cross-talk between the cAMP/PKA and PKC pathways in mammalian presynaptic nerve terminals.

A distinct distribution of functional presynaptic 5-HT receptor subtypes on GABAergic nerve terminals projecting to single hippocampal CA1 pyramidal neurons

5-HT is known to modify the excitability of GABAergic interneurons projecting to hippocampal CA1 neurons. In this study we investigate the presence and functionally characterize the 5-HT receptor subtypes found on the presynaptic nerve terminals of these GABAergic neurons. Using conventional whole-cell patch recording, we confirmed that the 5-HT(1A) agonist, 8-hydroxy-2-dipropylaminotetralin, presynaptically decreased electrically evoked GABA release while the 5-HT(3) agonist, m-chlorophenylbiguanide (mCPBG), presynaptically facilitated release. Using the 'synaptic bouton preparation', where CA1 neurons are acutely isolated with functional nerve terminals/boutons remaining adherent, we next showed that these receptor subtypes are found presynaptically. We next used the technique of focal stimulation of a single bouton in this preparation to further investigate the distribution of these 5-HT receptor subtypes. We found that all boutons contained inhibitory 5-HT(1A) receptors while a subset of boutons showed both 5-HT(1A) and excitatory 5-HT(3) receptors. No boutons were detected which contained only 5-HT(3) receptors. Our studies show that presynaptic 5-HT receptor subtypes are found presynaptically and are not uniformly distributed. This provides another potential mechanism whereby 5-HT can modulate GABA release and hence the excitability of hippocampal neurons.

[Recent advances of strategy for the brain functions--a targeting for tiny presynaptic boutons]

Recent advances in our knowledge of synaptic transmission have been achieved using brain slice preparations. Since the complexes of neuronal networks often make multiple synaptic contacts to a single postsynaptic neuron, the electrical stimulation of presynaptic nerve bundle simultaneously activates not only plural presynaptic axons but also the collateral pathways. Accordingly, the mechanisms of transmitter release from a single presynaptic nerve terminal are poorly understood. Recently, a more simplified preparation of cultured neurons has been developed and the properties of transmitter release were clearly studied. However, little information exists as to whether the release properties and presynaptic modulation of single native terminals behave similarly to terminals formed in culture preparations. We have then develop a mechanical dissociation technique of single CNS neurons attaching functional native excitatory and inhibitory synaptic terminals (boutons). These dissociated neurons exhibit spontaneous synaptic activities, and their presynaptic modulation has been extensively studied. We further visualized single presynaptic boutons onto a synaptic bouton preparation and electrical stimulation was selectively given to one of the boutons. Here we show how such an electrophysiological approach allows us to understand the transmitter release in a single presynaptic element in the CNS. We discuss the pharmacological and physiological prospects.