Single centre versus multi-centre pooled morbidity data in PCNL and the implications for informed consent.

Background: National and international outcome data following PCNL have been available for many years, but multi-centre data may not reflect the outcome from an individual surgeon or hospital.Methods: A combination of retrospective and prospective single centre data was collated from 2000-2016 and are compared to large single and multi-centre series.Results: Data were available on 801 unique cases performed between 2000 and 2016, mean age = 55.2 (SD = 14.8) (range = 17-93). The mean change in haemoglobin after PCNL was 1.65 g/dL ± 0.05, n = 630. Twenty-seven patients required a blood transfusion (3.37%). In 470 cases, data on pre-operative urine culture was available. One hundred and nineteen (25%) demonstrated evidence of bacteriuria pre-operatively. The most common isolated species were E. Coli and Proteus Mirabilis. Pre-operative urine infection was associated with a greater drop in haemoglobin following surgery, but this difference was not found to be statistically significant. Changes in serum creatinine and eGFR rise following surgery were calculated. The mean rise was found to be 15.21 µmol/L (SE = 2.08, n = 208). The mean drop in eGFR was estimated to be 7.35 ml/min/1.73 m2 (± 0.895, n = 205). Eight cases of 801 (1%) required admission to higher level care. There was one small bowel puncture and one pleural perforation recorded. Sub-selective embolization due to bleeding occurred in six cases (0 .75%) and there were no peri-operative deaths in this series. Published data comparing single centres with > 500 cases are presented.Conclusion: To facilitate transparent consent, single-centre rather than pooled outcome data should be utilized.

Live animal predictions of carcass components and marble score in beef cattle: model development and evaluation.

Until recently, beef carcass payment grids were predominantly based on weight and fatness categories with some adjustment for age, defined as number of adult teeth, to determine the price received by Australian beef producers for slaughter cattle. With the introduction of the Meat Standards Australia (MSA) grading system, the beef industry has moved towards payments that account for intramuscular fat (IMF) content (marble score (MarbSc)) and MSA grades. The possibility of a payment system based on lean meat yield (LMY, %) has also been raised. The BeefSpecs suite of tools has been developed to assist producers to meet current market specifications, specifically P8-rump fat and hot standard carcass weight (HCW). A series of equations have now been developed to partition empty body fat and fat-free weight into carcass fat-free mass (FFM) and fat mass (FM) and then into flesh FFM (FleshFFM) and flesh FM (FleshFM) to predict carcass components from live cattle assessments. These components then predict denuded lean (kg) and finally LMY (%) that contribute to emerging market specifications. The equations, along with the MarbSc equation, are described and then evaluated using two independent datasets. The decomposition of evaluation datasets demonstrates that error in prediction of HCW (kg), bone weight (BoneWt, kg), FleshFFM (kg), FleshFM (kg), MarbSc and chemical IMF percentage (ChemIMF%) is shown to be largely random error (%) in evaluation dataset 1, though error for ChemIMF% was primarily slope bias (%) in evaluation dataset 1, and BoneWt had substantial mean bias (%) in evaluation dataset 2. High modelling efficiencies of 0.97 and 0.95 for predicting HCW for evaluation datasets 1 and 2, respectively, suggest a high level of accuracy and precision in the prediction of HCW. The new outputs of the model are then described as to their role in estimating MSA index scores. The modelling system to partition chemical components of the empty body into carcass components is not dependent on the base modelling system used to derive empty body FFM and FM. This can be considered a general process that could be used with any appropriate model of body composition.

Live animal assessments of rump fat and muscle score in Angus cows and steers using 3-dimensional imaging.

The objective of this study was to develop a proof of concept for using off-the-shelf Red Green Blue-Depth (RGB-D) Microsoft Kinect cameras to objectively assess P8 rump fat (P8 fat; mm) and muscle score (MS) traits in Angus cows and steers. Data from low and high muscled cattle (156 cows and 79 steers) were collected at multiple locations and time points. The following steps were required for the 3-dimensional (3D) image data and subsequent machine learning techniques to learn the traits: 1) reduce the high dimensionality of the point cloud data by extracting features from the input signals to produce a compact and representative feature vector, 2) perform global optimization of the signatures using machine learning algorithms and a parallel genetic algorithm, and 3) train a sensor model using regression-supervised learning techniques on the ultrasound P8 fat and the classified learning techniques for the assessed MS for each animal in the data set. The correlation of estimating hip height (cm) between visually measured and assessed 3D data from RGB-D cameras on cows and steers was 0.75 and 0.90, respectively. The supervised machine learning and global optimization approach correctly classified MS (mean [SD]) 80 (4.7) and 83% [6.6%] for cows and steers, respectively. Kappa tests of MS were 0.74 and 0.79 in cows and steers, respectively, indicating substantial agreement between visual assessment and the learning approaches of RGB-D camera images. A stratified 10-fold cross-validation for P8 fat did not find any differences in the mean bias ( = 0.62 and = 0.42 for cows and steers, respectively). The root mean square error of P8 fat was 1.54 and 1.00 mm for cows and steers, respectively. Additional data is required to strengthen the capacity of machine learning to estimate measured P8 fat and assessed MS. Data sets for and continental cattle are also required to broaden the use of 3D cameras to assess cattle. The results demonstrate the importance of capturing curvature as a form of representing body shape. A data-driven model from shape to trait has established a proof of concept using optimized machine learning techniques to assess P8 fat and MS in Angus cows and steers.

Postweaning substitution of grazed forage with a high-energy concentrate has variable long-term effects on subcutaneous fat and marbling in Bos taurus genotypes.

The objective of this study was to quantify the effects and interactions of stage of growth and genotype on commercial carcass traits and intramuscular fat (IMF) content in 5 muscles of steers ( = 165) and to test the hypothesis that substituting pasture with a high-energy concentrate during the immediate postweaning period increases IMF. Cattle of 3 genotypes (Angus, Hereford, and Wagyu × Angus; = 55/genotype) were selected at weaning from commercial herds, targeting genotypic differences in marbling and subcutaneous fatness. Following weaning, steers were fed for 168 d within 2 different improved, temperate pasture-based nutritional systems: a forage-only system (FS) and forage with high-energy supplemented system (SS), with 2 replicates per system. The supplement was fed at a level of 1% of average BW adjusted every 2 wk to provide an estimated 50% of energy requirements for 168 d from weaning. Pasture on offer in both systems was managed to match the BW of the FS and SS steers during the postweaning treatment period to avoid confounding due to differences in growth rate during this period. Steers were then regrouped into 2 replicates and backgrounded on improved, temperate pasture for 158 d and then grain fed within 1 group for 105 d (short fed) or 259 d (long fed). Groups were slaughtered at commencement (d 0) and end of postweaning nutritional treatments (d 168), end of backgrounding (d 326), and after short (d 431) or long feedlotting (d 585). Serial slaughter stage had an effect on all traits assessed ( < 0.01). The FS steers had more rib fat ( < 0.01) and higher Meat Standards Australia marbling score ( < 0.05) and a tendency ( < 0.10) to have greater eye muscle area than the SS steers throughout the study. Genotypic differences were evident ( < 0.05) for all traits assessed except HCW, dressing percentage, rib fat depth, ossification score, ultimate pH, and IMF in the semitendinosus muscle. The results for marbling and IMF do not support the use of a high-energy feed as a substitute for an equivalent amount of energy from pasture during the immediate postweaning period to enhance development of marbling.

Modeling the relationship between scanned rump and 12th-rib fat in young temperate and tropical bovines: model development and evaluation.

A decision support tool for predicting subcutaneous fat depths called BeefSpecs, based on the Davis growth model (DGM), has been developed by the Cooperative Research Centre for Beef Genetic Technologies. Currently, the DGM predicts 12th-rib fat thickness (RFT, mm). To allow predictions of fat thickness at the P8 rump (P8FT, mm) site, the standard carcass fat measurement in the Australian beef industry, a relationship was developed between ultrasound RFT and P8FT in steers and heifers from temperate (Angus, Hereford, Shorthorn, and Murray Grey) and tropical (Brahman, Belmont Red, and Santa Gertrudis) breed types. Model development involved fitting various combinations of sex, breed type (BrT), BW, age, and RFT to produce 6 models. The models were challenged with data from 3 independent data sets: 1) Angus steers from 2.4 generations of divergent selection for and against residual feed intake; 2) 2 tropically adapted genotypes [Brahman and tropically adapted composites (combinations of Belmont Red, Charbray, Santa Gertrudis, Senepol, and Brahman breeds)]; and 3) a study using sires from Charolais, Limousin, Belgian Blue, and Black and Red Wagyu breeds and 3 genetic lines of Angus to create divergence in progeny in terms of genetic potential for intramuscular fat percent and retail beef yield. When challenged with data from Angus cattle, the mean biases (MB, mm) for models A to F were -1.23, -0.56, -0.56, -0.02, 0.14, and 0.04, and the root mean square errors of predictions (mm) were 1.53, 0.97, 0.97, 0.92, 0.93, and 0.91, respectively. When challenged with data from Brahman cattle, MB were 0.04, -0.22, -0.14, 0.05, -0.11, and 0.02 and root mean square errors of predictions were 1.30, 1.29, 1.27, 1.23, 1.37, and 1.29, respectively. Generally, model accuracy indicated by MB tended to be less for model E, which contained age rather than BW as a covariate. Models B and C were generally robust when challenged with data from Angus, Brahman, and Tropical Composite cattle as well as crossbred cattle with temperate sires. Model D, which did not contain age, performed the most consistently and was selected for inclusion in the DGM: P8FT, mm = -3.6 (+/-0.14) + 1.3 (+/-0.13) x sex + 0.11 (+/-0.13) x BrT + 0.014 (+/-4.8E(-4)) x BW + 0.96 (+/-0.01) x RFT - 0.73 (+/-0.08) x sex x BrT - 3.8E(-3) (+/-4.2E(-4)) x sex x BW - 0.09 (+/-0.01) x sex x RFT + 1.3E(-3) (+/-3.7E(-4)) x BrT x BW + 0.24 (+/-0.01) x BrT x RFT (adjusted R(2) = 0.86; SE = 0.013). Model D has been implemented in BeefSpecs to predict P8FT.

Characterization of a potassium-based leak conductance in the medial nucleus of the trapezoid body.

Principal neurons of the medial nucleus of the trapezoid body (MNTB) integrate the large, excitatory inputs from anteroventral cochlear nucleus (AVCN) bushy cells with conventional inhibitory inputs to produce an inhibitory output to the lateral and medial superior olive. This circuit is critical in the sound localization pathway of the auditory brainstem. Many ionic currents act in concert to produce the rapid phase-locked firing properties characteristic of MNTB principal neurons. We report here that MNTB neurons of the mouse possess a 2-4nS instantaneous potassium-based leak current, probably mediated by TWIK two-pore potassium leak channels. The function of the leak current was examined by modulating its magnitude with a dynamic clamp. The leak current modulates the resting voltage by 5mV/nS, reduces the input resistance of the cell by 5MOmega/nS and reduces the membrane time constant by 0.075 micros/nS. The leak current also modulates spike timing. Given leak channels are highly regulated, they are well placed to influence the firing properties, and action potential timing in principal neurons of the MNTB.

A randomized controlled trial of nephrostomy placement versus tubeless percutaneous nephrolithotomy.

PURPOSE: We established whether totally tubeless percutaneous nephrolithotomy with no nephrostomy or ureteral stent is a safe management technique. MATERIALS AND METHODS: Patients were randomized to have a nephrostomy placed (group 1 control) or none (group 2 treatment). A total of 25 patients were randomized to each group. Cases were considered uncomplicated and suitable for randomization if there was no significant bleeding or residual stone load, the pelvicaliceal system was intact and there was no evidence of a residual ureteral stone. The primary outcome measure was length of stay, and secondary outcomes were analgesic requirements and postoperative complications such as bleeding, infection or ureteral obstruction. Hospital readmission rates and stone clearance rates were also recorded. RESULTS: Mean stone size was 21.6 vs 17.5 mm. There were no transfusions in either group. Hemoglobin change was 2.03 vs 1.18 gm/dl and mean creatinine increase was 0.029 vs -0.111 mg/dl. There were no differences in hemorrhage, infection and serum parameters. There were no readmissions in either group. Mean length of stay was 3.4 vs 2.3 days (p <0.05). CONCLUSIONS: This trial demonstrates that percutaneous nephrolithotomy without nephrostomy or stent is a safe and well tolerated procedure in selected patients. Length of stay was reduced with no major complications in either group. We believe that totally tubeless percutaneous nephrolithotomy may be considered an accepted standard of care for selected cases and it is possible to reserve placement of a nephrostomy tube or internal ureteral stent for specific indications.

Brain-derived neurotrophic factor modulates cell excitability in the mouse medial nucleus of the trapezoid body.

Neurotrophins are a large class of trophic factors located throughout the central nervous system. While the role of neurotrophins in neuronal survival and axon guidance is well known, their secondary role in modulating synaptic transmission and cell firing properties is largely unexplored. In this study we examined the expression of neurotrophins in the mouse medial nucleus of the trapezoid body (MNTB) and investigated the effect of exogenous brain-derived neurotrophic factor (BDNF) application on the firing properties of MNTB principal cells. The expression levels of nerve growth factor, BDNF, neurotrophin-3, neurotrophin-4/5 and major receptor tyrosine kinase B was found to be moderate to high at postnatal day 12, indicating that the neurotrophins may have a role following synaptogenesis. A 2-h exposure to exogenous BDNF (100 ng/mL) had a significant effect on principal cell firing properties and voltage-gated potassium currents. Importantly, preincubation in BDNF increased the incidence of multifiring and rebounding cells, and significantly increased the number of action potentials fired in response to a single depolarizing step. BDNF exposure also significantly decreased underlying voltage-gated potassium currents, including both the low- and high-voltage-activated components. Our data show that the neurotrophins, specifically BDNF, may have a novel role in modulating cell excitability in the auditory brainstem.

Development of a robust central auditory synapse in congenital deafness.

Within the medial nucleus of the trapezoid body (MNTB) in the auditory brain stem, there is a large central synapse known as the calyx of Held, which mediates high-fidelity glutamatergic transmission. We investigated the effects of congenital deafness on the development of pre- and postsynaptic parameters of synaptic strength at the calyx of Held. Whole cell recordings of evoked excitatory postsynaptic currents (EPSCs) and immunohistochemistry of GluR1-4 subunits were performed using brain stem slices from congenitally deaf or hearing mice at postnatal days P5 and P12. In both hearing and deaf mice there was a similar developmental decrease in the NMDA component of the evoked EPSC. There was a concurrent increase in release probability and number of release sites, contributing to a fivefold increase in evoked AMPA-mediated EPSC amplitude. The increase in release probability is opposite to that found in previous studies at the calyx of Held in the rat. There was also a seven- to eightfold increase in the size of the readily releasable pool of vesicles and a decrease in tetanic depression. The postsynaptic glutamate receptor subunits were similarly developmentally regulated and unaffected by deafness. GluR1 and 4 dominated at both ages. There was a decrease in expression of GluR1-3 from P5 to P12 and a shift from GluR2 to GluR3, indicating that AMPA receptor complexes at P12 are predominantly calcium-permeable. These results demonstrate that early development at this robust synapse proceeds normally with congenital deafness, suggesting that auditory nerve activity does not affect the development of synaptic strength at the calyx of Held.

Presynaptic plasticity at two giant auditory synapses in normal and deaf mice.

Large calyceal synapses are often regarded as simple relay points, built for high-fidelity and high-frequency synaptic transmission and a minimal requirement for synaptic plasticity, but this view is oversimplified. Calyceal synapses can exhibit surprising activity-dependent developmental plasticity. Here we compare basal synaptic transmission and activity-dependent plasticity at two stereotypical calyceal synapses in the auditory pathway, the endbulb and the calyx of Held. Basal synaptic transmission was more powerful at the calyx than the endbulb synapse: the amplitude of evoked AMPA receptor-mediated excitatory postsynaptic currents (eEPSCs) was significantly greater at the calyx, as were the release probability, and the number of release sites. The quantal amplitude was smaller at the calyx, consistent with the smaller amplitude of spontaneous miniature EPSCs at this synapse. High-frequency trains of stimuli revealed that the calyx had a larger readily releasable pool of vesicles (RRP), less tetanic depression and less asynchronous transmitter release. Activity-dependent synaptic plasticity was assessed in congenitally deaf mutant mice (dn/dn). Previously we showed that a lack of synaptic activity in deaf mice increases synaptic strength at the endbulb of Held via presynaptic mechanisms. In contrast, we have now found that deafness does not affect synaptic transmission at the calyx synapse, as eEPSC and mEPSC amplitude, release probability, number of release sites, size of RRP, tetanic depression and asynchronous release were unchanged compared to normal mice. Synaptic transmission at the calyx synapse is more powerful and has less capacity for developmental plasticity compared to the endbulb synapse.

Phosphorylation regulates spontaneous and evoked transmitter release at a giant terminal in the rat auditory brainstem.

1. The role of phosphorylation in synaptic transmission was investigated at a large glutamatergic terminal, the endbulb of Held, on bushy cells in the rat anteroventral cochlear nucleus (AVCN). 2. Whole-cell recordings of excitatory postsynaptic currents (EPSCs) were used to examine the effects of kinase inhibitors and activators on low-frequency (baseline) evoked release, spontaneous release, paired-pulse facilitation (PPF) or depression (PPD), repetitive stimuli and recovery from depression. 3. Application of the kinase inhibitor H7 (100 microM) reduced low-frequency evoked EPSC amplitude (by 15 %) and simultaneously increased PPF (or reduced PPD), with no significant change in other aspects of transmission. H7 did not affect the amplitude or frequency of spontaneous miniature EPSCs. 4. Phorbol esters increased EPSC amplitude (by 50 %) with a concomitant decrease in PPF (or increase in PPD), and reduced the final EPSC amplitude during repetitive stimuli. The effect of phorbol esters was due exclusively to protein kinase C (PKC) activation, as the specific PKC inhibitor bis-indolylmaleimide (Bis) completely blocked the potentiating effect of phorbol esters on EPSC amplitude. 5. Significantly, phorbol esters did not increase the evoked EPSC amplitude at connections in which release was maximized using high extracellular calcium concentrations (4-6 mM). 6. Phorbol esters increased the frequency of spontaneous miniature EPSCs in physiological calcium (by 275 %), and in high extracellular calcium (by 210 %) when phorbol esters did not increase the evoked EPSC amplitude. 7. Our results are most consistent with the actions of H7 to decrease low-frequency release probability and phorbol esters to increase low-frequency release probability at the endbulb-bushy cell synaptic connection in the AVCN. The effects of H7 and phorbol esters on paired-pulse responses and tetanic depression appear to be largely consequential to these changes in low-frequency release probability.

GABA mediates presynaptic inhibition at glycinergic synapses in a rat auditory brainstem nucleus.

Many inhibitory nerve terminals in the mammalian anteroventral cochlear nucleus (AVCN) contain both glycine and GABA, but the reason for the co-localization of these two inhibitory neurotransmitters in the AVCN is unknown. We have investigated the roles of glycine and GABA at synapses on bushy cells in the rat AVCN, using receptor immunohistochemistry and electrophysiology. Our immunohistochemical results show prominent punctate labelling of postsynaptic clusters of glycine receptors and of the receptor clustering protein gephyrin over the surface of bushy cells. In contrast, weak diffuse membrane immunolabelling of GABAA receptors was observed. Whole-cell recordings from bushy cells in AVCN slices demonstrated that evoked inhibitory postsynaptic currents (IPSCs) were predominantly (81 %) glycinergic, based on the decrease in amplitude of the IPSCs in bicuculline (10 microM). This observation was supported by the effect of strychnine (1 microM), which was to decrease the evoked IPSC (to 10 % of control IPSC amplitude) and to produce a greater than 90 % block of spontaneous miniature IPSCs. These results suggest a minor role for postsynaptic GABAA receptors in bushy cells, despite a high proportion of GABA-containing terminals on these cells. Therefore, a role for metabotropic GABAB receptors was investigated. Activation of GABAB receptors with baclofen revealed a significant attenuation of evoked glycinergic IPSCs. The effect of baclofen was presynaptic, as indicated by a lack of change in the mean amplitude of spontaneous IPSCs. Significantly, the decrease in the amplitude of evoked glycinergic IPSCs observed following repetitive nerve stimulation was reduced in the presence of the GABAB antagonist, CGP 35348. This indicates that synaptically released GABA can activate presynaptic GABAB receptors to reduce transmitter release at glycinergic synapses. Our results suggest specific pre- versus postsynaptic physiological roles for GABA and glycine in the AVCN.

Release probability modulates short-term plasticity at a rat giant terminal.

1. Modulation of release probability is a major factor underlying short-term synaptic plasticity in the central nervous system. We have investigated the relationship between release probability ((Pr) and paired-pulse modulation at a large auditory calyceal synapse containing many transmitter release sites. Whole-cell patch electrode recordings were made of excitatory postsynaptic currents (EPSCs), evoked by stimulation of auditory nerve fibres giving rise to the endbulbs of Held. 2. Quantitative estimates of Pr and quantal amplitude were obtained using the recently developed variance-mean analysis technique. Release probability conditions were modulated by bath application of cadmium, elevated calcium and protein kinase C activation by phorbol esters. 3. Our results show that, under physiological conditions, most sites released neurotransmitter following a single presynaptic nerve impulse, with a mean Pr of 0.6. The mean quantal amplitude was 44 pA, which was consistent with the mean amplitude of miniature EPSCs (47 pA). 4. Under high release probability conditions with elevated calcium or phorbol esters, Pr at all sites approached 1.0. At these high Pr values, variance-mean analysis indicated a significant postsynaptic contribution to paired-pulse depression. The miniature EPSC amplitudes were decreased following stimulation in elevated calcium, confirming a postsynaptic component of paired-pulse depression at this glutamatergic connection. 5. A notable feature was the large variability between neurons in the relationship between paired-pulse ratio and Pr. Based on current models of vesicle release and ultrastructural evidence, we suggest that this variability may be partly due to morphological differences between endbulb specializations, particularly in the ratio of fusion-ready to reserve populations of vesicles at endbulb release sites.

Glycinergic miniature synaptic currents and receptor cluster sizes differ between spinal cord interneurons.

The structural features of a synaptic connection between central neurons play an important role in determining the strength of the connection. In the present study, we have examined the relationship between the structural and functional properties of glycinergic synapses in the rat spinal cord. We have analyzed the structure of glycinergic receptor clusters on rat ventral horn interneurons using antibodies against the glycine receptor clustering protein, gephyrin. We have examined the properties of quantal glycinergic currents generated at these synapses using whole cell patch-clamp recordings of miniature postsynaptic inhibitory currents (mIPSCs) in rat spinal cord slices in vitro. Our immunolabeling results demonstrate that there is a considerable variability in the size of glycine receptor clusters within individual neurons. Furthermore there are large differences in the mean cluster size between neurons. These observations are paralleled closely by recordings of glycinergic mIPSCs. The mIPSC amplitude varies significantly within and between neurons. Results obtained using combined immunolabeling and electrophysiological recording on the same neurons show that cells with small glycine receptor clusters concurrently exhibit small mIPSCs. Our results suggest that the differences in the size of glycinergic receptor clusters may constitute an important factor contributing to the observed differences in mIPSC amplitude among spinal cord interneurons.

A novel presynaptic inhibitory mechanism underlies paired pulse depression at a fast central synapse.

Several distinct mechanisms may cause synaptic depression, a common form of short-term synaptic plasticity. These include postsynaptic receptor desensitization, presynaptic depletion of releasable vesicles, or other presynaptic mechanisms depressing vesicle release. At the endbulb of Held, a fast central calyceal synapse in the auditory pathway, cyclothiazide (CTZ) abolished marked paired pulse depression (PPD) by acting presynaptically to enhance transmitter release, rather than by blocking postsynaptic receptor desensitization. PPD and its response to CTZ were not altered by prior depletion of the releasable vesicle pool but were blocked by lowering external calcium concentration, while raising external calcium enhanced PPD. We conclude that a major component of PPD at the endbulb is due to a novel, transient depression of release, which is dependent on the level of presynaptic calcium entry and is CTZ sensitive.

Quantal size is correlated with receptor cluster area at glycinergic synapses in the rat brainstem.

1. Whole-cell patch electrode recordings of glycinergic miniature inhibitory postsynaptic currents (mIPSCs) were obtained in neurons of the rat anteroventral cochlear nucleus (AVCN). Mean mIPSC peak amplitude was found to vary considerably between AVCN neurons (range, -19.1 to -317.9 pA; mean +/- s.d., -159.1 +/- 100.7 pA; 14 cells). 2. Immunolabelling of glycinergic receptor clusters in AVCN neurons was performed using antibodies against the glycine receptor clustering protein gephyrin. Measurements of the area of gephyrin immunoreactive clusters were obtained using confocal fluorescence microscopy. These measurements showed a large variability in cluster area, not only in the same cell (mean coefficient of variation, c.v., 0.66 +/- 0.18; 16 cells), but also in mean cluster area between cells (range, 0.21-0.84 microm2; 16 cells). 3. A possible relationship between mIPSC amplitude and receptor cluster area was investigated in a further series of experiments, in which mIPSCs recordings and immunolabelling of glycine receptor clusters were obtained for the same cells. In these experiments, AVCN neurons were identified using intracellular labelling with neurobiotin. Successful results using a combination of whole-cell recordings, neurobiotin identification and immunolabelling were obtained for a total of 10 AVCN neurons. Analysis of the results revealed a positive, statistically significant correlation between mean receptor cluster size and mean mIPSC amplitude (P < 0.05, 10 cells, Spearman's correlation test). 4. These results provide direct experimental evidence supporting a hypothesis of central glycinergic transmission in which synaptic strength may be regulated by changes in the size of the postsynaptic receptor region.

Signalling at the synapse: regulation of the post-synaptic response to quantal transmitter release.

Communication between neurones in the central nervous system occurs at specialized synaptic contacts. The strength of a synaptic signal is precisely regulated, and modification of synaptic strength is important in complex brain functions such as learning, and in the formation of appropriate neural maps during development. The fundamental building block of synaptic signalling is the post-synaptic current generated in response to the pre-synaptic release of a quantum of neurotransmitter. The present short review examines the factors that determine the quantal post-synaptic current, and provides direct evidence from a recent study in the author's laboratory that regulation of quantal size is important during development of excitatory transmission in the auditory system.

Developmental changes in EPSC quantal size and quantal content at a central glutamatergic synapse in rat.

1. Developmental changes in amplitude and time course of single-fibre-evoked and spontaneous EPSCs mediated by AMPA and NMDA receptors at the endbulb-bushy cell synapse of rats from 4 to 22 days of age were recorded using whole-cell patch-clamp methods in in vitro slices of cochlear nucleus. 2. The mean conductance of the AMPA component of evoked EPSCs increased by 66 %, while that of the NMDA component decreased by 61 %, for 12- to 18-day-old rats cf. 4- to 11-day-old rats. 3. The mean AMPA spontaneous EPSC conductance increased by 54 %, while mean NMDA spontaneous EPSC conductance decreased by 83 %, for 12- to 22-day-old rats cf. 4- to 11-day-old rats. The mean number of quanta contributing to peak evoked AMPA conductance also increased by 78 % in the older age group, after correction for the asynchrony of evoked quantal release. 4. The decay time constant of spontaneous AMPA EPSCs showed a small decrease in older animals, while the decay time constant of spontaneous NMDA EPSCs was markedly decreased in older animals. The decay time constants of evoked NMDA EPSCs showed a quantitatively similar decrease to that of spontaneous NMDA EPSCs. This suggests that AMPA receptor subunit composition is unlikely to undergo developmental change, while NMDA receptor subunit composition may be substantially altered during synaptic maturation. 5. These data are consistent with a developmentally increased efficacy of AMPA receptor-mediated synaptic transmission at the endbulb-bushy cell synapse, due to an increase in underlying AMPA-mediated quantal size and content during the same period as a transient co-localization of NMDA receptors.