Treatment outcomes of gemcitabine plus nab-paclitaxel in pancreatic cancer patients with malignant ascites.

BACKGROUND: Gemcitabine plus nab-paclitaxel (GnP) therapy has been shown to improve the prognosis in patients with metastatic pancreatic cancer (PC); however, the efficacy and safety of GnP in PC patients with malignant ascites (MA) remains unknown. METHODS: We retrospectively investigated PC patients with peritoneal dissemination who had received GnP as first-line chemotherapy at our institution between March 2015 and August 2021. The following patient data were reviewed: patient characteristics, overall survival (OS), progression-free survival (PFS), objective response rate (ORR), adverse events (AEs), and relative dose intensity (RDI). The severity of MA was categorized based on the CT findings as grade 1 (small), grade 2 (moderate), or grade 3 (massive). RESULTS: A total of 189 patients were included; the study endpoints were compared between patients with each ascites grade and 41 patients without MA. The MA was classified as grade 1 in 85 patients, grade 2 in 41 patients, and grade 3 in 22 patients. In the patients with MA, the median OS, PFS and ORR were 11.2 months, 5.7 months and 24.3%, respectively. The OS and PFS decreased with increasing the severity of MA; in particular, patients with grade 2 and 3 showed a poorer prognosis. There were no differences in AEs, except for anorexia, or the RDI according to the severity of MA. CONCLUSION: GnP showed moderate efficacy with manageable safety profile in PC patients with MA. However, PC patients with moderate to massive ascites still have a dismal prognosis, and further development of effective treatments is needed.

Fibroblast inhibition by tocilizumab enabled gemcitabine/nab-paclitaxel rechallenge for pancreatic cancer.

Interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) pathway inhibition may overcome chemoresistance of metastatic pancreatic cancer (MPC). We sought to determine the safety and recommended dose of tocilizumab (TCZ), an IL-6 receptor monoclonal antibody, and biological correlates of tumor shrinkage in patients with gemcitabine (GEM)/nanoparticle albumin-bound paclitaxel (nab-PTX)-refractory MPC. This phase 1 study enrolled 10 patients with MPC who had progressed after GEM/nab-PTX. Patients initially received TCZ 8 mg/kg on Day 1 and nab-PTX 100 mg/m2 + GEM 750 mg/m2 on Days 2, 9, and 16. Before and at the end of Cycle 1, biopsy of liver metastases was performed 3-5 h after levofloxacin (LVFX) administration to measure LVFX infiltration into tumor tissue. No dose-limited toxicities occurred, and the recommended dosage of TCZ was determined to be 8 mg/kg. Treatment-emergent adverse events occurred in 80% of patients, of which decreased neutrophil count was the most common. Tumor reduction during Cycle 1 was observed in four patients, who were defined as responders. In paired-biopsy samples, responder-related biological activities were an increase of cleaved PARP expression of tumor nuclei (p = 0.01), a decrease of proliferative cancer-associated fibroblasts (CAFs) (p = 0.08), and an increase of LVFX infiltration in the tumor (p = 0.04). A decrease of phosphorylated STAT3 expression (p = 0.02) favored an increase in LVFX infiltration. In conclusion, TCZ + GEM/nab-PTX-rechallenge had a manageable safety profile and showed preliminary activity via inhibition of CAF and improved intratumoral drug infiltration in MPC.

A prospective multicenter phase II study of FOLFIRINOX as a first-line treatment for patients with advanced and recurrent biliary tract cancer.

Given the promising activity and tolerability of FOLFIRINOX as a second-line treatment for advanced biliary tract cancer (BTC), it can be an attractive first-line treatment option as well. This is a single-arm, open-label, multicenter phase II study to evaluate the safety and efficacy of FOLFIRINOX as a first-line treatment for patients with advanced BTC. Primary endpoint was progression-free survival (PFS), and the secondary endpoints included overall survival (OS), tumor response and safety. This study defined primary endpoint might be met when the lower limit value of 80% confidence interval [CI] of the median PFS ≥ 6.0 months. Between June 2016 and March 2020, 35 BTC patients (21 intrahepatic, 10 extrahepatic, 2 gallbladder, 2 ampulla) including 26 unresectable and 9 recurrent disease were enrolled. After a median follow-up of 13.9 months, the median PFS and OS were 7.4 (80% CI, 5.5-7.5) and 14.7 (80% CI, 11.8-15.7) months, respectively. Complete response was achieved in 1 (2.9%) and partial response in 10 (28.6%), giving an objective response rate of 31.4% and disease control rate of 74.3%. Major grade 3-4 adverse events included neutropenia (54.3%), leukopenia (34.4%), febrile neutropenia (17.1%), thrombocytopenia (8.6%), cholangitis (8.6%), anemia, nausea, diarrhea, and peripheral sensory neuropathy (2.9% each). FOLFIRINOX was well tolerable in patients with advanced BTC, however, this study did not meet the primary endpoint to conduct a phase III trial. Thus, further explorations are required to find a subset of patients and/or certain clinical scenario which might be beneficial from FOLFIRINOX.

Cavitation with low-energy sonication during focused ultrasound thalamotomy for a patient with tremor-dominant Parkinson's disease: a potential risk.

We report a patient with tremor-dominant Parkinson's disease who had a mild cavitation bioeffect during magnetic resonance-guided focused ultrasound thalamotomy. During the aligning phase with low-energy sonication, cavitation caused mild dysarthria and paresthesia, prompting treatment cessation. At the same time, tremor and rigidity improved. MRI revealed extensive high-intensity lesions in the thalamus 1 day after the procedure followed by steroid infusion, which resulted in resolution of adverse events. Tremor and rigidity improved 1.5 years after the procedure. Although cavitation can relieve tremors and rigidity, it should be carefully monitored due to potential permanent adverse events by unpredictable and unknown behaviors.

Transgenic poplar trees overexpressing AtGolS2, a stress-responsive galactinol synthase gene derived from Arabidopsis thaliana, improved drought tolerance in a confined field.

Drought is an abiotic stress that limits plant growth and productivity, and the development of trees with improved drought tolerance is expected to expand potential plantation areas and to promote sustainable development. Previously we reported that transgenic poplars (Populus tremula × P. tremuloides, T89) harboring the stress-responsive galactinol synthase gene, AtGolS2, derived from Arabidopsis thaliana were developed and showed improved drought stress tolerance in laboratory conditions. Herein we report a field trial evaluation of the AtGolS2-transgenic poplars. The rainfall-restricted treatments on the poplars started in late May 2020, 18 months after transplanting to the field, and were performed for 100 days. During these treatments, the leaf injury levels were observed by measuring photosynthetic quantum yields twice a week. Observed leaf injury levels varied in response to soil moisture fluctuation and showed a large difference between transgenic and non-transgenic poplars during the last month. Comparison of the leaf injury levels against three stress classes clustered by the machine learning approach revealed that the transgenic poplars exhibited significant alleviation of leaf injuries in the most severe stress class. The transgenes and transcript levels were stable in the transgenic poplars cultivated in the field conditions. These results indicated that the overexpression of AtGolS2 significantly improved the drought stress tolerance of transgenic poplars not only in the laboratory but also in the field. In future studies, molecular breeding using AtGolS2 will be an effective method for developing practical drought-tolerant forest trees.

Efficacy of chemotherapy for patients with metastatic or recurrent pancreatic adenosquamous carcinoma: A multicenter retrospective analysis.

BACKGROUND/OBJECTIVES: Pancreatic adenosquamous carcinoma (PASC) is a rare variant of pancreatic ductal adenocarcinoma (PDAC). The usual treatment for metastatic or recurrent PASC is systemic chemotherapy in accordance with the PDAC treatment strategy. This study aimed to investigate the efficacy of chemotherapy, especially the benefit of recent combination therapies, in patients with metastatic or recurrent PASC. METHODS: We conducted a multicenter retrospective analysis of 116 patients with metastatic or recurrent PASC treated with first-line chemotherapy between April 2001 and December 2017 at 24 Japanese institutions. RESULTS: Combination chemotherapies included gemcitabine + nab-paclitaxel (GnP, n = 28), fluorouracil/leucovorin + irinotecan + oxaliplatin (FFX, n = 10), gemcitabine + S-1 (GS, n = 10), and others (n = 9). Monotherapies included gemcitabine (n = 51) and S-1 (n = 8). The median overall survival (OS) was 6.5, 7.3, and 4.3 months for the whole cohort, the combination therapy group, and the monotherapy group, respectively. Multivariate analysis indicated that combination therapy showed a better trend in OS than monotherapy (hazard ratio = 0.68; 95% confidence interval, 0.38-1.20). GnP or FFX were selected in 58.7% of patients after FFX was approved in Japan, and revealed a median OS, median progression-free survival, and objective response rate of 7.3 months, 2.8 months, and 26.9% in GnP and 7.2 months, 2.3 months, and 20.0% in FFX respectively. CONCLUSIONS: This study suggests that combination therapy may be more effective than monotherapy. GnP and FFX showed similar and clinically meaningful efficacy for patients with metastatic or recurrent PASC.

Endoscopic duodenal stent placement versus gastrojejunostomy for unresectable pancreatic cancer patients with duodenal stenosis before introduction of initial chemotherapy (GASPACHO study): a multicenter retrospective study.

BACKGROUND: Endoscopic duodenal stent placement is an alternative technique to gastrojejunostomy for gastric outlet obstruction due to pancreatic cancer. We compared the efficacy of endoscopic duodenal stent placement with that of gastrojejunostomy for treating patients with pancreatic cancer who are candidates for intensive combination chemotherapies as the first line of treatment. METHODS: This retrospective observational study included 100 patients from 18 institutions in Japan. Inclusion criteria were as follows: (1) cytologically or histologically confirmed adenocarcinoma of the pancreas, (2) good performance status, (3) gastric outlet obstruction scoring system score of 0-1 and (4) no history of treatment for pancreatic cancer. RESULTS: There was no significant difference in the background characteristics of patients in the endoscopic duodenal stent placement (n = 57) and gastrojejunostomy (n = 43) groups. The median overall survival in the endoscopic duodenal stent placement and gastrojejunostomy groups was 5.9 and 6.0 months, respectively. Clinical success was achieved in 93 cases; the median time to food intake resumption was significantly shorter in the endoscopic duodenal stent placement group (median: 3 days, n = 54) than in the gastrojejunostomy group (median: 5 days, n = 43). Chemotherapy was introduced in 63% of the patients in both groups after endoscopic duodenal stent placement or gastrojejunostomy. Chemotherapy was started earlier in the endoscopic duodenal stent placement group (median: 14 days) than in the gastrojejunostomy (median: 32 days) group. CONCLUSIONS: Endoscopic duodenal stent placement showed similar or better clinical outcomes than gastrojejunostomy. Thus, it might be a promising option in patients with good performance status.

Evaluation of potential impacts on biodiversity of the salt-tolerant transgenic Eucalyptus camaldulensis harboring an RNA chaperonic RNA-Binding-Protein gene derived from common ice plant.

We recently reported that a genetic transformation of the RNA-Binding-Protein (McRBP), an RNA chaperone gene derived from common ice plant (Mesembryanthemum crystallinum), alleviated injury and loss of biomass production by salt stress in Eucalyptus camaldulensis in a semi-confined screen house trial. In this study, we assessed the potential environmental impact of the transgenic Eucalyptus in a manner complying with Japanese biosafety regulatory framework required for getting permission for experimental confined field trials. Two kinds of bioassays for the effects of allelopathic activity on the growth of other plants, i.e., the sandwich assay and the succeeding crop assay, were performed for three transgenic lines and three non-transgenic lines. No significant differences were observed between transgenic and non-transgenic plants. No significant difference in the numbers of cultivable microorganisms analyzed by the spread plate method were observed among the six transgenic and non-transgenic lines. These results suggested that there is no significant difference in the potential impact on biodiversity between the transgenic McRBP-E. camaldulensis lines and their non-transgenic comparators.

Microvascular Decompression for Glossopharyngeal Neuralgia in the Semi-Sitting Position: A Report of Two Cases.

The semi-sitting position is well known to neurosurgeons. However, there are few reports of microvascular decompression surgery for glossopharyngeal neuralgia performed using the semi-sitting position. The semi-sitting position is not widely adopted in Japan, but it is considered to be a very useful neurosurgical position. Microvascular decompression surgery for glossopharyngeal neuralgia is a relatively rare procedure, and the semi-sitting position is very effective, considering the possibility of intraoperative cardiac arrest and postoperative complications of lower cranial nerve palsy. This report describes two cases of glossopharyngeal neuralgia operated in the semi-sitting position. Microvascular decompression was performed on both patients, and postoperative pain controls were good and no complications were observed. We show that the use of the semi-sitting position to perform microvascular decompression for glossopharyngeal neuralgia provides an excellent surgical view of the brainstem.

Spatiotemporal regulation of GABA concentration in extracellular space by gliotransmission crucial for extrasynaptic receptor-mediated improvement of sensory tuning performance in schizophrenia.

In schizophrenic patients, sensory tuning performance tends to be deteriorated (i.e., flattened sensory tuning), for which impaired intracortical tonic inhibition arising from a reduction in GABA concentration in extracellular space might be responsible. The δ subunit-containing GABAA receptor, located on extrasynaptic sites, is known to be involved in mediating tonic inhibitory currents in cortical pyramidal cells and is considered to be one of the beneficial therapeutic targets for the treatment of schizophrenia. The transporter GAT-1 in glial (astrocytic) membrane controls concentration of GABA molecules by removing them from extracellular space. We speculated that the upregulation of extrasynaptic receptors might compensate for the impaired tonic inhibition and thus improve their sensory tuning performance, in which the astrocytic GABA transporter might play an important role. To test our hypothesis, we simulated a schizophrenic neural network model with a GABAergic gliotransmission (i.e., GABA transport by transporters embedded in astrocytic membranes) mechanism that modulates local ambient (extracellular) GABA levels in a neuronal activity-dependent manner. Upregulating extrasynaptic GABA receptors compensated the impaired tonic inhibition and sharpened the sensory tuning, provided that ambient GABA molecules around stimulus-sensitive pyramidal cells were actively removed during sensory stimulation. We suggest that the upregulation of extrasynaptic GABA receptors can improve the performance of sensory tuning in schizophrenic patients, for which spatiotemporal regulation of ambient GABA concentration by gliotransmission may be crucial.

Magnetic resonance-guided focused ultrasound ablation of hypothalamic hamartoma as a disconnection surgery: a case report.

We report the case of a patient with hypothalamic hamartoma (HH) who was successfully treated with magnetic resonance-guided focused ultrasound (MRgFUS) for ablation as a disconnection surgery. A 26-year-old man with gelastic epilepsy had been diagnosed with HH at 3 years of age, and antiepileptic drugs were administered due to worsening episodes. Magnetic resonance imaging showed a sessile parahypothalamic hamartoma and MRgFUS ablation was performed, creating an oval-shaped lesion at the boundary area of the HH. Dramatic improvements in seizure symptoms were noted, and he was seizure-free on decreased antiepileptic drugs without any adverse events over the 1-year follow-up period.

Talipes Equinus Deformity Caused by Fibrous Gastrocnemius Muscle Contracture After Direct Contusion in Football Players: Report of Two Cases.

Two main causes of gastrocnemius contracture have been considered: 1) congenital deformities in pediatric patients, such as limb-length discrepancy, cerebral palsy, flatfoot, and clubfoot; and 2) secondary conditions such as immobilization for trauma or a nonfunctional limb. Talipes equinus deformity caused by fibrous gastrocnemius contracture after a direct muscle contusion is extremely rare. We describe 2 cases of talipes equinus deformity caused by fibrous gastrocnemius muscle contracture after a direct contusion in football players. Both of the players had a talipes equinus deformity with a severe restriction of ankle dorsiflexion, and a cord-like structure was observed at the proximal part of the lateral gastrocnemius head. Both patients' histological examinations revealed fibrous tendon-like tissue within the structure. After discission of the cord-like structures, the restriction of ankle dorsiflexion was completely resolved, and the patients were able to fully return to playing football without any discomfort in their calves.

[A case of ferroportin disease with phenotype A gene mutation in SCL40A1 resembling phenotype B manifestation influenced by alcohol consumption].

A 57-year-old man had been detected to have an elevated transaminase level. He had a history of alcohol consumption, and abdominal ultrasonography revealed an increase in the echogenicity of the liver;hence, he was diagnosed as having alcoholic liver disease. He restricted his alcohol intake, but the elevated transaminase level did not improve. Further medical examination was performed. He was found to have hyperferritinemia (serum ferritin, 6574ng/mL) and high transferrin saturation (TSAT, 90.5%). Computed tomography (CT) revealed high CT values of the liver and spleen (94 and 84HU, respectively). These findings differed from the characteristics of a typical alcoholic liver disease. Liver biopsy revealed iron deposition within the hepatocytes and Kupffer cells and liver fibrosis (F1-2). From the gene analysis of HFE, HJV, TFR2, HAMP, and SLC40A1 genes, he was heterozygous for the G>A (G490D) mutation in the ferroportin gene (SLC40A1). He was diagnosed as having ferroportin disease. It was reported that patients with a G490D mutation exhibited ferroportin disease A, which occurs owing to a loss-of-function mutation of SLC40A1. However, he was considered to have some characteristics of ferroportin disease B, which occurs owing to a gain-of-function mutation of SLC40A1. In this case, alcohol consumption might affect the progression of iron deposition in the liver. Therapeutic venesection was performed, and his hyperferritinemia with high TSAT gradually improved. In the course of the disease, other organ damages and progression of liver fibrosis did not occur.

Alternate Endpoints for Phase II Trials in Advanced Neuroendocrine Tumors.

BACKGROUND: In phase II trials for neuroendocrine tumors (NETs), the objective response rate (ORR) is traditionally used as a primary endpoint. However, the validity of the ORR as a primary endpoint has never been systematically examined. Therefore, a literature-based analysis of phase II trials for NETs was performed to identify valid alternative endpoints for predicting median progression-free survival (PFS) in clinical trials for NETs. MATERIALS AND METHODS: Phase II trials of medical treatment for advanced NETs were identified based on a systematic search using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. RESULTS: A total of 22 trials were identified, and 1,310 patients and 27 treatment arms were included in the analysis. There was no significant relationship between the ORR and median PFS (r = .374; 95% confidence interval [CI], -0.051 to 0.800; p = .085). Conversely, 12-month PFS rates showed very strong correlations with median PFS (r = .929; 95% CI, 0.831-1.027; p < .001). CONCLUSION: The results of the present analysis indicate that the ORR is not significantly correlated with median PFS and suggest that 12-month PFS rates are good alternate endpoints for screening phase II trials for NETs. IMPLICATIONS FOR PRACTICE: Phase II trials are screening trials that seek to identify agents with sufficient activity to continue development. Thus, earlier endpoints are preferable, and the objective response rate (ORR) has been traditionally used as a surrogate endpoint in phase II trials for neuroendocrine tumors (NETs). However, the present study showed that the ORR was not significantly correlated with median progression-free survival (PFS). On the other hand, the 12-month PFS rate showed very strong correlation with median PFS and is considered a good alternate endpoint for screening phase II trials for NETs.

Development and evaluation of novel salt-tolerant Eucalyptus trees by molecular breeding using an RNA-Binding-Protein gene derived from common ice plant (Mesembryanthemum crystallinum L.).

The breeding of plantation forestry trees for the possible afforestation of marginal land would be one approach to addressing global warming issues. Here, we developed novel transgenic Eucalyptus trees (Eucalyptus camaldulensis Dehnh.) harbouring an RNA-Binding-Protein (McRBP) gene derived from a halophyte plant, common ice plant (Mesembryanthemum crystallinum L.). We conducted screened-house trials of the transgenic Eucalyptus using two different stringency salinity stress conditions to evaluate the plants' acute and chronic salt stress tolerances. Treatment with 400 mM NaCl, as the high-stringency salinity stress, resulted in soil electrical conductivity (EC) levels >20 mS/cm within 4 weeks. With the 400 mM NaCl treatment, >70% of the transgenic plants were intact, whereas >40% of the non-transgenic plants were withered. Treatment with 70 mM NaCl, as the moderate-stringency salinity stress, resulted in soil EC levels of approx. 9 mS/cm after 2 months, and these salinity levels were maintained for the next 4 months. All plants regardless of transgenic or non-transgenic status survived the 70 mM NaCl treatment, but after 6-month treatment the transgenic plants showed significantly higher growth and quantum yield of photosynthesis levels compared to the non-transgenic plants. In addition, the salt accumulation in the leaves of the transgenic plants was 30% lower than that of non-transgenic plants after 15-week moderate salt stress treatment. There results suggest that McRBP expression in the transgenic Eucalyptus enhances their salt tolerance both acutely and chronically.

Reducing variability in motor cortex activity at a resting state by extracellular GABA for reliable perceptual decision-making.

Interaction between sensory and motor cortices is crucial for perceptual decision-making, in which intracortical inhibition might have an important role. We simulated a neural network model consisting of a sensory network (NS) and a motor network (NM) to elucidate the significance of their interaction in perceptual decision-making in association with the level of GABA in extracellular space: extracellular GABA concentration. Extracellular GABA molecules acted on extrasynaptic receptors embedded in membranes of pyramidal cells and suppressed them. A reduction in extracellular GABA concentration either in NS or NM increased the rate of errors in perceptual decision-making, for which an increase in ongoing-spontaneous fluctuations in subthreshold neuronal activity in NM prior to sensory stimulation was responsible. Feedback (NM-to-NS) signaling enhanced selective neuronal responses in NS, which in turn increased stimulus-evoked neuronal activity in NM. We suggest that GABA in extracellular space contributes to reducing variability in motor cortex activity at a resting state and thereby the motor cortex can respond correctly to a subsequent sensory stimulus. Feedback signaling from the motor cortex improves the selective responsiveness of the sensory cortex, which ensures the fidelity of information transmission to the motor cortex, leading to reliable perceptual decision-making.

Extracellular GABA assisting in organizing dynamic cell assemblies to shorten reaction time to sensory stimulation.

Until recently, glia, which exceeds the number of neurons, was considered to only have supportive roles in the central nervous system, providing homeostatic controls and metabolic supports. However, recent studies suggest that glia interacts with neurons and plays active roles in information processing within neuronal circuits. To elucidate how glia contributes to neuronal information processing, we simulated a sensory neuron-glia (neuron-astrocyte) network model. It was investigated in association with ambient (extracellular) GABA level, because the astrocyte has a major role in removing extracellular GABA molecules. In the network model, transporters, embedded in plasma membranes of astrocytes, modulated local ambient GABA levels by actively removing extracellular GABA molecules which persistently acted on receptors in membranes outside synapses and provided pyramidal cells with inhibitory currents. Gap-junction coupling between astrocytes mediated a concordant decrease in local ambient GABA levels, which solicited a prompt population response of pyramidal cells (i.e., activation of an ensemble of pyramidal cells) to a sensory stimulus. As a consequence, the reaction time of a motor network, to which axons of pyramidal cells of the sensory network project, to the sensory stimulus was shortened. We suggest that the astrocytic gap-junction coupling may assist in organizing dynamic cell assemblies by coordinating a reduction in local ambient GABA levels, thereby shortening reaction time to sensory stimulation.

Climatic changes and potatoes: How can we cope with the abiotic stresses?

Climate change triggers increases in temperature, drought, and/or salinity that threaten potato production, because they necessitate specific amounts and quality of water, meanwhile lower temperatures generally support stable crop yields. Various cultivation techniques have been developed to reduce the negative effects of drought, heat and/or salinity stresses on potato. Developing innovative varieties with relevant tolerance to abiotic stress is absolutely necessary to guarantee competitive production under sub-optimal environments. Commercial varieties are sensitive to abiotic stresses, and substantial changes to their higher tolerance levels are not easily achieved because their genetic base is narrow. Nonetheless, there are several other possibilities for genetic enhancement using landraces and wild relatives. The complexity of polysomic genetics and heterozygosity in potato hamper the phenotype evaluation over abiotic stresses and consequent conventional introgression of tolerance traits, which are more challenging than previous successes shown over diseases and insects resistances. Today, potatoes face more challenges with severe abiotic stresses. Potato wild relatives can be explored further using innovative genomic, transcriptomic, proteomic, and metabolomic approaches. At the field level, appropriate cultivation techniques must be applied along with precision farming technology and tolerant varieties developed from various breeding techniques, in order to realize high yield under multiple stresses.

Perceptual judgments via sensory-motor interaction assisted by cortical GABA.

Recurrent input to sensory cortex, via long-range reciprocal projections between motor and sensory cortices, is essential for accurate perceptual judgments. GABA levels in sensory cortices correlate with perceptual performance. We simulated a neuron-astrocyte network model to investigate how top-down, feedback signaling from a motor network (Nmot) to a sensory network (Nsen) affects perceptual judgments in association with ambient (extracellular) GABA levels. In the Nsen, astrocytic transporters modulated ambient GABA levels around pyramidal cells. A simple perceptual task was implemented: detection of a feature stimulus presented to the Nsen. The Nmot showed distinct perceptual behaviors: hit, fault, and miss. A hit is a correct response to the stimulus, a fault is a wrong response to the stimulus, and a miss is no response to the stimulus. In hits, the feedback signaling increased the gain of Nsen pyramidal cells and accelerated the reaction speed of Nmot pyramidal cells to the stimulus. Without feedback signaling, the Nsen but not Nmot responded to the stimulus, resulting in a miss. With too strong feedback signaling, the Nmot resulted in a fault, namely, stimulus-insensitive but not stimulus-sensitive pyramidal cells wrongly responded. Balancing the feedforward and feedback signaling formed a coherent, ongoing-spontaneous neuronal state, by which the highest hit rate was achieved. A transient reduction in local ambient GABA levels, triggered by the stimulus, contributed to accelerating the reaction speed under noisy environmental conditions. Adjusting the basal ambient GABA level ensured high hit rates. We suggest that motor cortex feedback may accelerate reaction speed to sensory stimulation by promoting coherency in ongoing-spontaneous neuronal activity between sensory and motor cortices, thereby achieving prompt perceptual judgments. Spatiotemporal modulation of ambient GABA levels, possibly by astrocytic transporters, assists in making reliable perceptual judgments.

Improved Perceptual Learning by Control of Extracellular GABA Concentration by Astrocytic Gap Junctions.

Learning of sensory cues is believed to rely on synchronous pre- and postsynaptic neuronal firing. Evidence is mounting that such synchronicity is not merely caused by properties of the underlying neuronal network but could also depend on the integrity of gap junctions that connect neurons and astrocytes in networks too. In this perspective, we set out to investigate the effect of astrocytic gap junctions on perceptual learning, introducing a model for coupled neuron-astrocyte networks. In particular, we focus on the fact that astrocytes are rich of GABA transporters (GATs) which can either uptake or release GABA depending on the astrocyte membrane potential, which is a function of local neural activity. We show that GABAergic signaling is a crucial component of intracolumnar neuronal synchronization, thereby promoting learning by neurons in the same cell assembly that are activated by a shared sensory cue. At the same time, we show that this effect can critically depend on astrocytic gap junctions insofar as these latter could synchronize extracellular GABA levels around many neurons and throughout entire cell assemblies. These results are supported by extensive computational arguments and predict that astrocytic gap junctions could improve perceptual learning by controlling extracellular GABA.