Rectification of ATP-gated current of rat P2X2 and P2X7 receptors depends on the cytoplasmic N-terminus.

The phenotypes of ATP-gated currents thought ionotropic P2X channels depend on the composition of the oligomeric receptor. We constructed chimeric P2X2/P2X7 receptors to study the effect of cytoplasmic domains on rectification of current flow through the open channel. We found that the identity of the N-terminus determines the pattern of rectification, with chimeric receptors containing the N-terminus of the P2X2 receptor displaying inward rectification, and chimeric receptors containing the N-terminus of the P2X7 receptor displaying slightly outward rectification. In contrast, rectification of current through chimeric receptors with swapped C-termini always mimicked the wild-type receptor. Thus, our findings suggest that the N-terminus of P2X receptors regulate ion flow through the channel pore and are responsible in part for determining current rectification.

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 ß-nicotinamide mononucleotide (ß-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.

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.

Astrocytes with previous chronic exposure to amyloid ß-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 ß-peptide (Aß) 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 Aß 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 Aß1-40 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 Aß1-40 is attributable to a small number of synapses with higher release probability.

Location analysis of presynaptically active and silent synapses in single-cultured hippocampal neurons.

A morphologically present but non-functioning synapse is termed a silent synapse. Silent synapses are categorized into "postsynaptically silent synapses," where AMPA receptors are either absent or non-functional, and "presynaptically silent synapses," where neurotransmitters cannot be released from nerve terminals. The presence of presynaptically silent synapses remains enigmatic, and their physiological significance is highly intriguing. In this study, we examined the distribution and developmental changes of presynaptically active and silent synapses in individual neurons. Our findings show a gradual increase in the number of excitatory synapses, along with a corresponding decrease in the percentage of presynaptically silent synapses during neuronal development. To pinpoint the distribution of presynaptically active and silent synapses, i.e., their positional information, we employed Sholl analysis. Our results indicate that the distribution of presynaptically silent synapses within a single neuron does not exhibit a distinct pattern during synapse development in different distance from the cell body. However, irrespective of neuronal development, the proportion of presynaptically silent synapses tends to rise as the projection site moves farther from the cell body, suggesting that synapses near the cell body may exhibit higher synaptic transmission efficiency. This study represents the first observation of changes in the distribution of presynaptically active and silent synapses within a single neuron.

Liver toxicity of intravenous heparin treatment in patients with acute ischemic stroke.

OBJECTIVE: Serum alanine aminotransferase (ALT), which is an indicator of liver dysfunction, may increase during treatment in patients in the acute phase of stroke. However, the cause of the ALT elevation is unclear, as multiple medications are often being used. We investigated the relationship between medications used in acute ischemic stroke, including cerebral infarction and transient ischemic attack, and ALT elevation. METHODS: The subjects were 230 patients who had been diagnosed with cerebral infarction or TIA and treated at the Stroke Care Unit of Fukuoka University Hospital. We investigated ALT abnormalities that occurred from the start of the treatment over the subsequent 14 days. We also followed patients for an additional seven days to confirm the peak ALT levels. A binomial logistic regression analysis was performed to evaluate the association between medications used during the period and ALT elevation. RESULTS: The incidence of ALT abnormality was 23.9% (55/230). ALT elevation was mostly mild and peaked within 21 days of treatment initiation in 93.2% of the patients, excluding indeterminate patients. A binary logistic regression analysis showed that unfractionated heparin (odds ratio [OR] 2.759, 95% confidence interval [CI] 1.328-5.729, p = 0.007) was extracted as a cause of ALT elevation. In a receiver operating characteristic (ROC) analysis for the administration period of unfractionated heparin, the cut-off value (area under the ROC curve) for ALT elevation was 6 days (0.575). Significant factors contributing to ALT elevation caused by unfractionated heparin included an unfractionated heparin administration period of ≥ 6 days (OR 2.951, 95% CI 1.244-7.000, p = 0.014) and edaravone combination (OR 2.594, 95% CI 1.159-5.808, p = 0.021). CONCLUSION: In the acute phase of stroke, we believe that unfractionated heparin discontinuation is not necessary when hepatotoxicity of unfractionated heparin is suspected. However, physicians should be aware of the risk of liver toxicity when unfractionated heparin is administered for more than six days or when edaravone is used in combination.

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.

Hippocampal neurons in direct contact with astrocytes exposed to amyloid ß25-35 exhibit reduced excitatory synaptic transmission.

Amyloid ß protein (Aß) is closely related to the progression of Alzheimer's disease because senile plaques consisting of Aß cause synaptic depression and synaptic abnormalities. In the central nervous system, astrocytes are a major glial cell type that contribute to the modulation of synaptic transmission and synaptogenesis. In this study, we examined whether astrocytes exposed to Aß fragment 25-35 (Aß25-35) affect synaptic transmission. We show that synaptic transmission by hippocampal neurons was inhibited by astrocytes exposed to Aß25-35. The Aß25-35-exposed astrocytes lowered excitatory postsynaptic release and the size of the readily releasable synaptic pool. The number of excitatory synapses was also reduced. However, the number of excitatory synapses was unchanged unless there was direct contact between Aß25-35-exposed astrocytes and hippocampal neurons. These data indicate that direct contact between Aß25-35-exposed astrocytes and neurons is critical for inhibiting synaptic transmission in the progression of Alzheimer's disease.