Physiological properties of individual cerebral axons studied in vivo for as long as one year

1985 ◽  
Vol 54 (5) ◽  
pp. 1346-1362 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Conduction Velocity ◽  
Cortical Neurons ◽  
Refractory Period ◽  
Antidromic Activation ◽  
Conduction Velocities ◽  
Supernormal Period ◽  
Velocity Changes ◽  
The Stability ◽  
Over Time

The long-term stability of conduction velocity and recovery processes were studied in a fast-conducting (corticotectal) and in a more slowly conducting (visual callosal) axonal system. Chronic microelectrode recording methods were used in conjunction with antidromic activation via electrical stimulation at one or more axonal site. These methods enabled 54 axons to be studied for greater than 20 days and seven of these cells to be studied for 101-448 days. The conduction velocities of corticotectal axons were characteristic of myelinated axons and were very stable over time. The conduction velocities of most callosal axons were characteristic of nonmyelinated axons, and 68% of callosal axons had conduction velocities that were stable over long periods of time. Of the remaining callosal axons, approximately one third showed an increase in conduction velocity (8-14%), whereas two thirds showed a progressive and systematic decrease in conduction velocity (6-81%). These changes in conduction velocity were distributed along the callosal axon, rather than limited to a single segment of axon. Although the refractory period of callosal and corticotectal axons showed considerable variability over time, the minimal interval between two conducted impulses was stable. The stability of this property was remarkable because the minimal interspike intervals of different axons with similar conduction velocities often differed greatly. Callosal axons show a supernormal period of increased conduction velocity following the relative refractory period and a subsequent subnormal period of decreased conduction velocity following a burst of prior impulses. In different callosal axons the magnitude of the velocity changes (percent change) differs greatly, even among axons of the same conduction velocity. For a given axon, however, these properties are very stable over time. These results on axonal properties may be useful in studies requiring the examination of extracellular responses of individual neurons over long periods of time. Antidromic latency provides a useful means of identifying a cell, particularly when conduction times are long. The stability of the minimal interspike interval and the supernormal period within individual axons make them suitable as ancillary criteria in identifying individual neurons. These three measures are independent of spike amplitude and waveform, and together they provide a "signature" by which individual cortical neurons can be identified over periods that represent a significant portion of the lifespan of adult mammals.

Comparison of the Effects of Racemic Bupivacaine, Levobupivacaine, and Ropivacaine on Ventricular Conduction, Refractoriness, and Wavelength

2002 ◽  
Vol 96 (3) ◽  
pp. 641-650 ◽  
Author(s):  
Antoine G. M. Aya ◽  
Jean E. de La Coussaye ◽  
Emmanuelle Robert ◽  
Jacques Ripart ◽  
Philippe Cuvillon ◽  
...  
Keyword(s):  
Conduction Velocity ◽  
Refractory Period ◽  
Cycle Length ◽  
Left Ventricular ◽  
Effective Refractory Period ◽  
Potency Ratio ◽  
Dependent Effect ◽  
Intergroup Comparison ◽  
Conduction Velocities ◽  
Ventricular Conduction

Background The study was designed to compare the effects of equimolar concentrations of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, anisotropy, duration and homogeneity of refractoriness, and wavelengths, and to provide a potency ratio for effects on conduction velocity. Methods Isolated frozen rabbit hearts (which leave a thin layer of surviving epicardial muscle) were treated with 0.1, 1, and 10 mum racemic bupivacaine, levobupivacaine, or ropivacaine. Left ventricular longitudinal and transverse conduction velocities, anisotropic ratio, minimum pacing cycle length, use dependency, duration and dispersion of ventricular effective refractory period, and wavelengths were studied. A high-resolution mapping system was used for data acquisition. In addition to two-way analysis of variance for repeated measures, data for conduction velocities were fitted simultaneously using a nonlinear mixed-effect modeling program to allow intergroup comparison. Results Each agent induced a concentration- and use-dependent slowing of conduction velocities, with no change of the anisotropic ratio. The use-dependent effect of levobupivacaine is similar to that of racemic bupivacaine concerning longitudinal conduction velocity. Fitting of conduction velocities provided a racemic bupivacaine to levobupivacaine and to ropivacaine ratio of 1:1.38 for concentration effect at 1,000-ms pacing cycle length, and 1:0.74 for use-dependent effect at 600-ms pacing cycle length. Racemic bupivacaine and levobupivacaine prolonged the ventricular effective refractory period, whereas ropivacaine did not. No dispersion in ventricular effective refractory period values occurred. All three agents induced significant decreases in wavelengths. This effect was not different among groups. Conclusions Differences among racemic bupivacaine, levobupivacaine, and ropivacaine at equimolar concentrations are mainly caused by the use-dependent effects on conduction velocities and the concentration-dependent effects on ventricular effective refractory period. Therefore, one must take into account the corresponding pacing rates when comparing the potency ratios of local anesthetics.

scholarly journals Propylene Glycol Stabilizes the Linear Response of Glutamate Biosensor: Potential Implications for In-Vivo Neurochemical Monitoring

Chemosensors ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 58 ◽  
Author(s):  
Gaia Rocchitta ◽  
Andrea Bacciu ◽  
Paola Arrigo ◽  
Rossana Migheli ◽  
Gianfranco Bazzu ◽  
...  
Keyword(s):  
Propylene Glycol ◽  
System Level ◽  
Linear Region ◽  
Excitatory Neurotransmitter ◽  
Glutamate Oxidase ◽  
The Central Nervous System ◽  
The Stability ◽  
Main Components ◽  
Over Time

L-glutamate is one the most important excitatory neurotransmitter at the central nervous system level and it is implicated in several pathologies. So, it is very important to monitor its variations, in real time in animal models’ brain. The present study aimed to develop and characterize a new amperometric glutamate biosensor design that exploits the selectivity of Glutamate Oxidase (GluOx) for l-glutamate, and the capability of a small molecule as propylene glycol (PG), never used before, to influence and extend the stability and the activity of enzyme. Different designs were evaluated by modifying the main components in their concentrations to find the most suitable design. Moreover, enzyme concentrations from 100 U/ml up to 200 U/ml were verified and different PG concentrations (1%, 0.1% and 0.05%) were tested. The most suitable selected design was Ptc/PPD/PEI(1%)2/GlutOx5/PG(0.1%) and it was compared to the same already described design loading PEDGE, instead of PG, in terms of over-time performances. The PG has proved to be capable of determining an over-time stability of the glutamate biosensor in particular in terms of linear region slope (LRS) up to 21 days.

scholarly journals Separating Spike Count Correlation from Firing Rate Correlation

2016 ◽  
Vol 28 (5) ◽  
pp. 849-881 ◽  
Author(s):  
Giuseppe Vinci ◽  
Valérie Ventura ◽  
Matthew A. Smith ◽  
Robert E. Kass
Keyword(s):  
Firing Rate ◽  
Cortical Neurons ◽  
Experimental Manipulation ◽  
Response Variability ◽  
Spike Count ◽  
Firing Rates ◽  
Area V4 ◽  
Rate Correlation ◽  
Over Time

Populations of cortical neurons exhibit shared fluctuations in spiking activity over time. When measured for a pair of neurons over multiple repetitions of an identical stimulus, this phenomenon emerges as correlated trial-to-trial response variability via spike count correlation (SCC). However, spike counts can be viewed as noisy versions of firing rates, which can vary from trial to trial. From this perspective, the SCC for a pair of neurons becomes a noisy version of the corresponding firing rate correlation (FRC). Furthermore, the magnitude of the SCC is generally smaller than that of the FRC and is likely to be less sensitive to experimental manipulation. We provide statistical methods for disambiguating time-averaged drive from within-trial noise, thereby separating FRC from SCC. We study these methods to document their reliability, and we apply them to neurons recorded in vivo from area V4 in an alert animal. We show how the various effects we describe are reflected in the data: within-trial effects are largely negligible, while attenuation due to trial-to-trial variation dominates and frequently produces comparisons in SCC that, because of noise, do not accurately reflect those based on the underlying FRC.

scholarly journals Propylene Glycol Stabilizes the Linear Response of Glutamate Biosensor: Potential Implications for In-Vivo Neurochemical Monitoring

2018 ◽  
Author(s):  
Gaia Rocchitta ◽  
Andrea Bacciu ◽  
Paola Arrigo ◽  
Rossana Migheli ◽  
Gianfranco Bazzu ◽  
...  
Keyword(s):  
Propylene Glycol ◽  
System Level ◽  
Excitatory Neurotransmitter ◽  
Glutamate Oxidase ◽  
Temporal And Spatial ◽  
The Stability ◽  
Main Components ◽  
Very High ◽  
Over Time

L-glutamate is one the most important excitatory neurotransmitter at central nervous system level and it is implicated in several pathologies. So, it is very important to monitor its variations, in real time in animal models’ brain. Amperometric biosensors have been used because of their very high temporal and spatial resolution, and because suitable for a short to mid-term implantation. The present study aimed to develop and characterize a new glutamate biosensor design that exploits the selectivity of Glutamate Oxidase (GluOx) for l-glutamate, and the capability of a small molecule as propylene glycol (PG) to influence and extend the stability and the activity of enzyme. Different designs were evaluated by modifying the main components in their concentrations to find the most suitable design. Moreover, enzyme concentrations from 100 U/ml up to 200 U/ml were verified and different PG concentrations (1%, 0.1% and 0.05%) were tested. The most suitable selected design was Ptc/PPD/PEI(1%)2/GlutOx5/PG(0.1%) and it was compared to the same already described design loading PEDGE, instead of PG, in terms of over-time performances. PG has proved to be capable of determining an over-time stability of the glutamate biosensor in particular in terms of linear region slope (LRS) up to 21 days.

Composition of α-tocopheryl acetate with micellar nanocarriers and the possibility of its use as a biologically active additive

2020 ◽  
Vol 42 (4) ◽  
pp. 292-306
Author(s):  
N.M. Permyakova ◽  
◽  
T.B. Zheltonozhskaya ◽  
V.I. Karpovskyi ◽  
R.V. Postoi ◽  
...  
Keyword(s):  
Diblock Copolymer ◽  
Biological Action ◽  
Ethanol Solution ◽  
Biologically Active ◽  
Tocopheryl Acetate ◽  
Similar Process ◽  
Salting Out ◽  
The Stability ◽  
Over Time

Based on the asymmetric diblock copolymer (DBC) poly(ethylene oxide)/polyacrylic acid, effective, biocompatible and biodegradable micellar carriers were obtained for the delivery of vitamin E analogue, α-tocopheryl acetate (α-TOCA), in living organisms. The monitoring of the stability of micellar structures of the block copolymer and its composition with α-TOCA over time, in a saline solution and when the pH of the solution changes, was carried out. The stability of DBC micelles over time at pH = 3.5, partial disaggregation of micelles at pH = 9 and an increase in their aggregation in physiological solution were shown. The high stability of the α-TOCA/DBC composition formed in situ in time in the range of pH=3.5-9 and a significant decrease in its solutions of salting out effects in the presence of NaCl were established. The thermodynamic parameters of the process of the micelle formation of the pure α-TOCA in water/ethanol solution (95/5 v/v) as well as the size and morphology of its micellar structures were determined by light scattering and TEM methods. The initial α-TOCA micelles in water/ethanol solution were stable over a wide pH range, but their stability was much lower and the sensitivity to the presence of NaCl was much higher than that of DBC micelles. The dialysis method revealed the gradual release of the drug from the micellar carrier through a semipermeable membrane into the surrounding aqueous and aqueous-saline media. However, the rate and efficiency of α-TOCA release from the DBC micelles in an aqueous medium were significantly lower compared to a similar process of drug release from the pure α-TOCA dispersion. Thus, a possibility of providing of long-term controlled release of α-TOCA in the living organism due to the use of DBC micelles has been proven. Based on in vivo tests of the biological action of the composition on pregnant sows, its high bioavailability, rapid absorption, active participation in metabolic processes and positive effect on the reproductive qualities of sows compared to pure α-TOCA, were displayed, which improves the safety and productivity of newborn piglets. Key words: diblock copolymer, α-tocopheryl acetate, micellar carrier, encapsulation/release, biological action.

In Vivo Assessment of Conduction Velocity and Refractory Period of Denervated Muscle Fibers

2005 ◽  
Vol 29 (6) ◽  
pp. 436-439 ◽  
Author(s):  
Christian Hofer ◽  
Claudia Forstner ◽  
Michaela Modlin ◽  
Heidrun Jager ◽  
Winfried Mayr ◽  
...  
Keyword(s):  
Conduction Velocity ◽  
Refractory Period ◽  
Muscle Fibers ◽  
Denervated Muscle ◽  
In Vivo Assessment

scholarly journals Implantable microcoils for intracortical magnetic stimulation

2016 ◽  
Vol 2 (12) ◽  
pp. e1600889 ◽  
Author(s):  
Seung Woo Lee ◽  
Florian Fallegger ◽  
Bernard D. F. Casse ◽  
Shelley I. Fried
Keyword(s):  
Cortical Neurons ◽  
Magnetic Stimulation ◽  
Pyramidal Neurons ◽  
Brain Slices ◽  
Behavioral Responses ◽  
Wide Range ◽  
Cortical Pyramidal Neurons ◽  
Over Time

Neural prostheses that stimulate the neocortex have the potential to treat a wide range of neurological disorders. However, the efficacy of electrode-based implants remains limited, with persistent challenges that include an inability to create precise patterns of neural activity as well as difficulties in maintaining response consistency over time. These problems arise from fundamental limitations of electrodes as well as their susceptibility to implantation and have proven difficult to overcome. Magnetic stimulation can address many of these limitations, but coils small enough to be implanted into the cortex were not thought strong enough to activate neurons. We describe a new microcoil design and demonstrate its effectiveness for both activating cortical neurons and driving behavioral responses. The stimulation of cortical pyramidal neurons in brain slices in vitro was reliable and could be confined to spatially narrow regions (<60 μm). The spatially asymmetric fields arising from the coil helped to avoid the simultaneous activation of passing axons. In vivo implantation was safe and resulted in consistent and predictable behavioral responses. The high permeability of magnetic fields to biological substances may yield another important advantage because it suggests that encapsulation and other adverse effects of implantation will not diminish coil performance over time, as happens to electrodes. These findings suggest that a coil-based implant might be a useful alternative to existing electrode-based devices. The enhanced selectivity of microcoil-based magnetic stimulation will be especially useful for visual prostheses as well as for many brain-computer interface applications that require precise activation of the cortex.

Formation and Structure of Casein Micelles in Lactating Mammary Tissue

1970 ◽  
Vol 28 ◽  
pp. 150-151
Author(s):  
Robert J. Carroll ◽  
Marvin P. Thompson ◽  
Harold M. Farrell
Keyword(s):  
Size Distribution ◽  
G Protein ◽  
Milk Proteins ◽  
Mammary Tissue ◽  
Colloidal System ◽  
Casein Micelles ◽  
The Stability

Milk is an unusually stable colloidal system; the stability of this system is due primarily to the formation of micelles by the major milk proteins, the caseins. Numerous models for the structure of casein micelles have been proposed; these models have been formulated on the basis of in vitro studies. Synthetic casein micelles (i.e., those formed by mixing the purified αsl- and k-caseins with Ca2+ in appropriate ratios) are dissimilar to those from freshly-drawn milks in (i) size distribution, (ii) ratio of Ca/P, and (iii) solvation (g. water/g. protein). Evidently, in vivo organization of the caseins into the micellar form occurs in-a manner which is not identical to the in vitro mode of formation.

On the Robustness of Solution Strategy Classifications

2010 ◽  
Vol 31 (2) ◽  
pp. 68-73 ◽  
Author(s):  
María José Contreras ◽  
Víctor J. Rubio ◽  
Daniel Peña ◽  
José Santacreu
Keyword(s):  
Individual Differences ◽  
Study Strategies ◽  
Solution Strategy ◽  
Specific Test ◽  
Spatial Tasks ◽  
The Stability ◽  
Strategy Changes ◽  
Over Time

Individual differences in performance when solving spatial tasks can be partly explained by differences in the strategies used. Two main difficulties arise when studying such strategies: the identification of the strategy itself and the stability of the strategy over time. In the present study strategies were separated into three categories: segmented (analytic), holistic-feedback dependent, and holistic-planned, according to the procedure described by Peña, Contreras, Shih, and Santacreu (2008) . A group of individuals were evaluated twice on a 1-year test-retest basis. During the 1-year interval between tests, the participants were not able to prepare for the specific test used in this study or similar ones. It was found that 60% of the individuals kept the same strategy throughout the tests. When strategy changes did occur, they were usually due to a better strategy. These results prove the robustness of using strategy-based procedures for studying individual differences in spatial tasks.

On the Stability of Evaluative Conditioning Effects

2013 ◽  
Vol 44 (6) ◽  
pp. 380-389 ◽  
Author(s):  
Sabine Förderer ◽  
Christian Unkelbach
Keyword(s):  
Evaluative Conditioning ◽  
Indirect Measures ◽  
The Stability ◽  
Over Time

Evaluative conditioning (EC) refers to valence changes in neutral stimuli (CSs) through repeated pairing with liked or disliked stimuli (USs). The present study examined the stability of EC effects in the course of 1 week. We investigated how this stability depends on memory for US valence and US identity. We also investigated whether CSs evaluations occurring immediately after conditioning (i.e., evaluative consolidation) are necessary for stable EC effects. Participants showed stable EC effects on direct and indirect measures, independent of evaluations immediately after conditioning. EC effects depended on memory for US valence but not for US identity. And although memory decreased significantly over time, EC effects remained stable. These data suggest that evaluative consolidation is not necessary, and that conditioned preferences and attitudes might persist even when people do not remember the concrete source anymore.

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