Biomedical subjects

D H Edwards

Publications and source records attributed to D H Edwards.

At least 37 records · Page 2Linked to original sources

PubMed1998

Effect of temperature on a voltage-sensitive electrical synapse in crayfish.

The effects of temperature on transmission through the voltage-sensitive giant motor synapse (GMS) were investigated in crayfish both experimentally and in computer simulation. The GMS is part of the fast reflex escape pathway of the crayfish and mediates activation from the lateral giant (LG) command neurone to the motor giant (MoG) flexor motoneurone. The investigation was motivated by an apparent mismatch between the temperature sensitivity of the activation time constant of the GMS, with a Q10 reported to be close to 11, and that of the active membrane properties of LG and MoG, which are thought to have Q10 values close to 3. Our initial hypothesis was that at cold temperatures the very slow activation of the GMS conductance would reduce the effectiveness of transmission compared with higher temperatures. However, the reverse was found to be the case. Effective transmission through the GMS was reliable at low temperatures, but failed at an upper temperature limit that varied between 12 degrees C and 25 degrees C in isolated nerve cord preparations. The upper limit was extended above 30 degrees C in semi-intact preparations where the GMS was less disturbed by dissection. The results of experiments and simulations both indicate that transmission becomes more reliable at low temperatures because the longer-duration presynaptic spikes are able to drive more current through the GMS into the MoG, which is more excitable at low temperatures. Conversely, effective transmission is difficult at high temperatures because the transfer of charge through the GMS is reduced and because the input resistance of MoG is lowered as its current threshold is increased. The effect of the high Q10 of the GMS activation is to help preserve effective transmission through the synapse at high temperatures and so extend the temperature range for effective operation of the escape circuit.

Action Potentials↗

PubMed1997

Neuronal adaptations to changes in the social dominance status of crayfish.

The effect of superfused serotonin (5-HT; 50 microns) on the synaptic responses of the lateral giant (LG) interneuron in crayfish was found to depend on the social status of the animal. In socially isolated animals. 5-HT persistently increased the response of LG to sensory nerve shock. After social isolates were paired in a small cage, they fought and determined their dominant and subordinate status. After 12 d of pairing, 5-HT reversibly inhibited the response of LG in the social subordinate and reversibly increased the response of LG in the social dominant crayfish. The effect of 5-HT changed approximately linearly from response enhancement to inhibition in the new subordinate over the 12 d of pairing. If, after 12 d pairing, the subordinate was reisolated for 8 d, the response enhancement was restored. If the subordinate, instead, was paired with another subordinate and became dominant in this new pair, the inhibitory effect of 5-HT changed to an enhancing effect over the next 12 d of pairing. If, however, two dominant crayfish were paired and one became subordinate, the enhancing effect of 5-HT persisted in the new subordinate even after 38 d pairing. These different effects of serotonin result from the action of two or more molecular receptors for serotonin. A vertebrate 5-HT, agonist had no effect on social isolates but reversibly inhibited the response of LG in both dominant and subordinate crayfish. The inhibitory effects of the agonist developed approximately linearly over the first 12 d of pairing. A vertebrate 5-HT2 agonist persistently increased the response of LG in isolate crayfish and reversibly increased the response of the cell in dominant and subordinate crayfish. Finally, although neurons that might mediate these effects of superfused 5-HT are unknown, one pair of 5-HT-immunoreactive neurons appears to contact the LG axon and initial axon segment in each abdominal ganglion in its projection caudally from the thorax.

Adaptation, Physiological↗

PubMed1997

Serotonin, social status and aggression.

Serotonin, social status and aggression appear to be linked in many animal species, including humans. The linkages are complex, and, for the most part, details relating the amine to the behavior remain obscure. During the past year, important advances have been made in a crustacean model system relating serotonin and aggression. The findings include the demonstration that serotonin injections will cause transient reversals in the unwillingness of subordinate animals to engage in agonistic encounters, and that at specific synaptic sites involved in activation of escape behavior, the direction of the modulation by serotonin depends on the social status of the animal.

Aggression↗

PubMed1997

The Bacillus subtilis DivIVA protein targets to the division septum and controls the site specificity of cell division.

The Bacillus subtilis divIVA gene, first defined by a mutation giving rise to anucleate minicells, has been cloned and characterized. Depletion of DivIVA leads to inhibition of the initiation of cell division. The residual divisions that do occur are abnormally placed and sometimes misorientated relative to the long axis of the cell. The DivIVA phenotype can be suppressed by disruption of the MinCD division inhibitor, suggesting that DivIVA controls the topological specificity of MinCD action and thus septum positioning. A DivIVA-GFP fusion targets to new and used sites of cell division, consistent with it having a direct role in topological specification.

Adenosine Triphosphatases↗

PubMed1997

Ca2+ sequestration as a determinant of chaos and mixed-mode dynamics in agonist-induced vasomotion.

We have investigated the contribution of smooth muscle Ca2+ stores to chaotic vasomotion in isolated rabbit ear resistance arteries. In preparations constricted by histamine, exposure to cyclopiazonic acid (CPA) and thapsigargin (TSG), which inhibit the Ca2+-adenosinetriphosphatase (ATPase) pump of the sarcoplasmic reticulum, first induced then abolished highly characteristic mixed-mode oscillatory behavior. The fractal dimension of the vasomotion, which reflects the minimum number of contributing dynamic variables, remained between 2 and 4 until the point at which oscillations disappeared completely. By contrast, ryanodine, which attenuates Ca2+-induced Ca2+ release, decreased the fractal dimension of the responses to <2 in a graded concentration-dependent fashion by selectively suppressing a slow subcomponent of the overall rhythmic activity. CPA-associated oscillations were insensitive to ryanodine but could be abolished by verapamil and modulated in an inhibitory or stimulatory fashion by charybdotoxin, which blocks Ca2+-activated K+ channels, and by ouabain, which blocks the Na+-K+-ATPase. We conclude that there is nonlinear cross talk between CPA/TSG-sensitive Ca2+ stores and a membrane oscillator that regulates Ca2+ influx and that the kinetics of Ca2+ uptake by the CPA/TSG-sensitive pool can be distinguished dynamically from the kinetics of Ca2+ release from its ryanodine-sensitive subcomponent.

Animals↗

PubMed1997

Entrained ion transport systems generate the membrane component of chaotic agonist-induced vasomotion.

We have analyzed the contribution of membrane ion transport systems to chaotic vasomotion induced by histamine in isolated rabbit ear resistance arteries. Dynamic complexity was monitored as a fractal correlation dimension that provides an estimate of the minimum number of control variables contributing to an irregular time series and generally took a value between 2 and 4. A distinct subcomponent of the overall oscillatory activity (frequency approximately 0.06 Hz) was selectively suppressed by blockade of Ca(2+)-activated K+ channels (KCa) with tetraethylammonium, Ca(2+)-activated Cl- channels with low extracellular Cl- concentration and niflumic acid, the Na(+)-K+ adenosine-triphosphatase (ATPase) with ouabain, and Na+/Ca2+ exchange with low-Na+ buffer. Each of these interventions caused a fall in average fractal dimension to a value < 2, whereas inhibition of voltage-dependent K+ channels with 4-aminopyridine or the Ca(2+)-ATPase extrusion pump with vanadate were without effect on the form and complexity of the vasomotion. There was no systematic correlation between the changes in fractal dimension induced by the various interventions and their effects on perfusion pressure. Our findings suggest that nonlinearity in the kinetics of multiple coupled ion transport systems leads to entrainment and the emergence of a composite membrane oscillator, thus accounting for the low fractal dimension of the vasomotion observed in these arteries.

Animals↗

PubMed1997

Excitation of identified serotonergic neurons by escape command neurons in lobsters.

Serotonin-containing neurosecretory neurons in the first abdominal ganglion (A1 5-HT cells) of the lobster (Homarus americanus) ventral nerve cord have been shown previously to function as 'gain setters' in postural, slow muscle, command neuron circuitries. Here we show that these same amine neurons receive excitatory input from lateral (LG) and medial (MG) giant axons, which are major interneurons in phasic, fast muscle systems. Activation of either LG or MG axons elicits short-latency, non-fatiguing, long-lasting excitatory postsynaptic potentials (EPSPs) in A1 5-HT cells which follow stimulus frequencies of up to 100 Hz in a 1:1 fashion. Single spikes triggered in either giant axon can produce EPSPs in the A1 5-HT cells of sufficient magnitude to cause the cells to spike and to fire additional action potentials after variable latencies; action potentials elicited in this way reset the endogenous spontaneous spiking rhythm of the A1 5-HT neurons. The giant-axon-evoked EPSP amplitudes show substantial variation from animal to animal. In individual preparations, the variation of EPSP size from stimulus to stimulus was small over the first 25 ms of the response, but increased considerably in the later, plateau phase of each response. When tested in the same preparation, EPSPs in A1 5-HT cells evoked by firing the LG axons were larger, longer-lasting and more variable than those triggered by firing the MGs. Firing A1 5-HT cells through an intracellular electrode, prior to activation of the giant fiber pathway, significantly reduced the size of LG-evoked EPSPs in A1 5-HT cells. Finally, morphological and physiological results suggest that similarities exist between giant fiber pathways in lobsters and crayfish. The possible functional significance of an involvement of these large amine-containing neurosecretory neurons in both tonic and phasic muscle circuitries will be discussed.

Animals↗

PubMed1996

The effect of social experience on serotonergic modulation of the escape circuit of crayfish.

The neuromodulator serotonin has widespread effects in the nervous systems of many animals, often influencing aggression and dominance status. In crayfish, the effect of serotonin on the neural circuit for tailflip escape behavior was found to depend on the animal's social experience. Serotonin reversibly enhanced the response to sensory stimuli of the lateral giant (LG) tailflip command neuron in socially dominant crayfish, reversibly inhibited it in subordinate animals, and persistently enhanced it in socially isolated crayfish. Serotonin receptor agonists had opposing effects: A vertebrate serotonin type 1 receptor agonist inhibited the LG neurons in dominant and subordinate crayfish and had no effect in isolates, whereas a vertebrate serotonin type 2 receptor agonist enhanced the LG neurons' responses in all three types of crayfish. The LG neurons appear to have at least two populations of serotonin receptors that differ in efficacy in dominant, subordinate, and socially isolate crayfish.

Animals↗

PubMed1996

Endoscopic fluorescence detection of high-grade dysplasia in Barrett's esophagus.

BACKGROUND & AIMS: Early detection and treatment of esophageal cancer in Barrett's esophagus may improve patient survival if dysplasia is effectively detected at endoscopy. Typically, four-quadrant pinch biopsy specimens are taken at 2-cm intervals. This study was conducted to determine whether laser-induced fluorescence spectroscopy could be used to detect high-grade dysplasia in patients with Barrett's esophagus. METHODS: Four hundred ten-naonometer laser light was used to induce autofluorescence of Barrett's mucosa in 36 patients. The spectra were analyzed using the differential normalized fluorescence (DNF) index technique to differentiate high-grade dysplasia from either low-grade or nondysplastic mucosa. Each spectrum was classified as either premalignant or benign using two different DNF indices. RESULTS: Analysis of the fluorescence spectra from all patients collectively using the DNF intensity at 480 nm (DNF480) index showed that 96% of nondysplastic Barrett's esophagus samples were classified as benign, all low-grade dysplasia samples as benign, 90% of high-grade dysplasia samples as premalignant, and 28% of low-grade with focal high-grade dysplasia samples as premalignant. Using the two DNF indices concurrently, all patients with any high-grade dysplasia were classified correctly. CONCLUSIONS: Laser-induced fluorescence spectroscopy has great potential to detect high-grade dysplasia in Barrett's esophagus when using the DNF technique.

Adult↗

PubMed1996

Uniform growth and neuronal integration.

1. The cable equations were analyzed to determine the effects of two patterns of uniform growth on the passive and active integrative properties of neurons. 2. During uniform isoelectrotonic growth, the diameters of all neuronal processes increase as the square of their increase in length, while the specific electrical properties and branch terminal conditions of the neuron remain constant. An analytic inductive proof is given to show that, for any neuron, uniform isoelectrotonic growth increases the input conductance everywhere by the cube of the growth factor, but leaves the active and passive spread of membrane potential within the neuron unchanged. The spread of membrane voltage is unchanged because this pattern of growth enables both the axial and membrane currents everywhere in the cell to increase by the cube of the growth factor. Synaptic inputs would evoke the same responses in the isoelectrotonically larger cell as in the smaller cell if the total postsynaptic conductance of the synapse increased with the dendritic membrane area. 3. During uniform isometric growth, the diameter and lengths of all processes increase by the same factor, while the specific electrical properties and branch terminal conditions remain constant. This pattern of uniform growth increases the input conductance by the square of the growth factor, and also increases the attenuation, delay, and low-pass filtering of the cell's responses. Voltage attenuation increases with isometric growth because the axial current increases in proportion to growth, while the membrane current increases in proportion to the square of the growth factor. Isometric growth reduces the ability of distal synaptic inputs to affect the membrane potential at proximal integrating sites, even after the synaptic conductance has increased to compensate for the increased input conductance. 4. These two patterns of uniform growth help define the consequences of all types of uniform growth for neuronal integration and responsiveness.

Electrophysiology↗

PubMed1996

Comparison of chaotic and sinusoidal vasomotion in the regulation of microvascular flow.

OBJECTIVE: In order to elucidate the physiological consequences of irregular vasomotion on microvascular flow we have compared the theoretical hydrodynamic consequences of sinusoidal and chaotic fluctuations in the diameter of a single resistance vessel. METHODS: In initial experimental studies vasomotion was induced by histamine in isolated rabbit ear resistance arteries (approximately 150 microns diameter) perfused with physiological buffer under both controlled-flow and controlled-pressure conditions. The phase relationships between the observed oscillations in flow and pressure were used to validate a theoretical electrical circuit in which vasomotion was simulated as sinusoidal or as chaotic fluctuations in distal resistance, with compliance incorporated as a parallel capacitance. RESULTS: In both the experimental and theoretical situation, oscillations in flow led those in pressure by approximately 90 degrees in controlled-flow mode, whereas they were approximately 180 degrees out of phase in controlled-pressure mode. In the theoretical model an increase in the amplitude of sinusoidal or chaotic diameter fluctuations enhanced flow, but "paradoxically" increased both time-averaged resistance and conductance. The model showed that with sinusoidal fluctuations the "efficiency" of perfusion (i.e., flow/viscous work expended in perfusing the vessel undergoing vasomotion) exhibited a peak whose magnitude was a function of vasomotion amplitude and the proximal capacitance in the circuit, and was attributable to transient release of charge from this capacitance. This phenomenon was not observed in simulations with chaotic vasomotion. Hydrodynamic effects specific to the presence of chaotic dynamics (e.g., abrupt increases or decreases in flow under the variation of a single parameter) were also evident when the intrinsic complexity of the vasomotion, rather than its amplitude, was varied. CONCLUSIONS: The model suggests (i) that vasomotion may serve to increase flow, (ii) that conductance provides a more accurate physiological measure of the functional consequences of active vasomotion than resistance, (iii) that chaotic vasomotion dissipates transients more readily than sinusoidal vasomotion, thereby conferring greater stability to microcirculatory perfusion and (iv) that specific modes of chaotic vasomotion may influence flow independently of their amplitude.

Animals↗

PubMed1995

Complexity of chaotic vasomotion is insensitive to flow and pressure but can be regulated by external control.

We have previously shown that irregular vasomotion induced by histamine in isolated rabbit ear resistance arteries is chaotic. Consistently, in the present study, such activity was found to respond in a highly unpredictable fashion to changes in flow under conditions of controlled-flow perfusion, although its fractal dimension, calculated by a standard correlation technique, was effectively independent of flow rate and remained < 4. As this statistic provides an estimate of the number of control variables that generate a chaotic time series, flow thus appears to modulate vasomotion without fundamentally contributing to its genesis. External modification of the dynamics was attempted by a negative feedback loop that regulated pump speed through an error signal derived from perfusion pressure. Irregular responses were converted to either periodic or steady-state behavior in approximately 60% of cases with an associated fall in fractal dimension. Conversely, unsuccessful control was often associated with an increase in fractal dimension, reflecting the additional complexity introduced by the feedback loop. Furthermore, control was more readily achieved in the presence of NG-nitro-L-arginine methyl ester, when time- and flow-dependent changes in endothelium-derived relaxing factor synthesis would not be expected to complicate the overall dynamics. The study suggests that vascular chaos may be economically "controlled" under both physiological and pathophysiological conditions.

Animals↗

PubMed1995

Angiographic contrast media relax isolated rabbit aorta through an endothelium-independent mechanism that may not depend on the presence of the iodine atom.

Systemically administered iodinated angiographic contrast media evoke vasodilatation through mechanisms that are at present poorly understood. In the current investigation we have evaluated the role of the vascular endothelium in responses to an iso-osmolar formation of the non-ionic dimer iodixanol and a hyperosmolar formulation of the non-ionic monomer iopromide. Isolated rabbit aortic ring preparations with endothelium intact or removed by gentle abrasion were mounted in organ baths containing oxygenated Holman's solution, and cumulative concentration-response curves for relaxation to the contrast media were constructed after pre-constriction by phenylephrine (300 nM) in the presence of indomethacin to inhibit prostaglandin synthesis. Endothelial denudation did not influence the ability of either iodixanol or iopromide to relax the aortic ring preparations. Iopromide was significantly more potent than iodixanol when expressed in terms of iodine concentration (mg I ml-1), but both agents were equipotent when expressed in terms of molarity (mM). We conclude that relaxation of isolated rabbit aortic rings to iodixanol and iopromide under conditions where there is no fluid flow is endothelium-independent, and therefore not mediated by release of the potent endogeneous nitrovasodilator endothelium-derived relaxing factor (EDRF). Furthermore, their relaxant activity under the in vitro experimental conditions employed is attributable to a direct action on vascular smooth muscle by factors in addition to osmolality, and may depend on features that are not specifically associated with the presence of the iodine atom.

Angiography↗

PubMed1994

The effect of neuronal growth on synaptic integration.

The way in which the dimensions of neurons change during postembryonic development has important effects on their electrotonic structures. Theoretically, only one mode of growth can conserve the electrotonic structures of growing neurons without employing changes in membrane electrical properties. If the dendritic diameters of a neuron increase as the square of the increase in dendritic lengths, then the neuron's electrotonic structure is conserved. We call this special mode of allometric growth "isoelectrotonic growth." In this study we compared the developmental changes in morphology of two identified invertebrate neurons with theoretical growth curves. We found that a cricket neuron, MGI, grows isoelectrotonically and thereby preserves its electrotonic properties. In contrast, the crayfish neuron, LG, grows in nearly isometric manner resulting in an increase in its electrotonic length.

Animals↗

PubMed1994

EDRF suppresses chaotic pressure oscillations in isolated resistance artery without influencing intrinsic complexity.

It is now widely recognized that nonlinear oscillatory systems can exhibit simple periodicity, characteristic repetitive patterns of odd and even integral periodicity and specific pathways for the transition to irregular, so-called "chaotic," dynamics. In the present study we have identified such behavior in the highly irregular rhythmic vasomotor activity induced by histamine in isolated rabbit ear resistance arteries, thus suggesting a deterministic rather than random etiology. In this experimental model nonlinearity arises at the level of the vascular smooth muscle cell, since oscillatory behavior was not abolished by endothelial denudation. To quantify the complexity of the responses induced by histamine, we applied the analysis of Grassberger and Proccacia (Physica D 9: 189-208, 1983) to calculate a scaling parameter known as fractal dimension, which estimates the minimum number of control variables participating in the genesis of an irregular time-varying signal. The findings suggest the involvement of at least three such variables, because its average numerical value was generally found to be between 2 and 3. Neither the absolute concentration of histamine employed nor pharmacological manipulation (i.e., stimulation/inhibition) of endothelium-derived relaxing factor (EDRF) activity significantly affected the fractal dimension of the pressure fluctuations, although both influenced their superficial form. Histamine and EDRF consequently do not determine the fundamental interactions responsible for generating the chaotic nature of the responses and may be regarded as permissive and modulatory influences, respectively. The well-known unpredictability of nonlinear systems to perturbation may explain why EDRF can either suppress or enhance rhythmic vasomotor activity in different artery types.

Acetylcholine↗

PubMed1994

Fractal analysis of role of smooth muscle Ca2+ fluxes in genesis of chaotic arterial pressure oscillations.

We have investigated the role of vascular smooth muscle Ca2+ fluxes in the genesis of chaotic pressure oscillations induced by histamine in isolated resistance arteries from the rabbit ear. The responses exhibited distinct "fast" and "slow" components, with periods of 5-20 s and 1-5 min, respectively, which could be dissociated pharmacologically. The fast subsystem involved ion movements at the cell membrane and was inhibited by both low (< 2 mM) and high (> 5 mM) extracellular Ca2+ concentration ([Ca2+]o) by verapamil (which inhibits voltage-dependent Ca2+ influx) and by charybdotoxin (ChTX) and apamin (which block Ca(2+)-activated K+ channels). In contrast, the slow subsystem was intracellular and was selectively attenuated by ryanodine, which inhibits Ca(2+)-induced Ca2+ release from sarcoplasmic reticulum. The effects of these interventions on the complexity of the responses were quantified by calculating their fractal dimension, a parameter that estimates the minimum number of independent variables contributing to an irregular time series. Its mean value was generally > 2 under control conditions but decreased to < 2 in a concentration-dependent fashion in the presence of verapamil, ChTX, apamin, or ryanodine and when [Ca2+]o was outside the range of 2-3 mM. Each intervention thus removed one dimension of complexity from the mechanisms generating the rhythmic activity. We conclude that the interaction of a fast membrane oscillator, which involves Ca2+ influx, Ca(2+)-activated K+ efflux, and therefore presumably changes in membrane potential, and a slow intracellular oscillator involving Ca2+ sequestration and release from stores is responsible for vascular chaos in our model. The coupling between these subsystems is likely to be mediated by cytosolic [Ca2+].

Animals↗

PubMed1994

The onset of response habituation during the growth of the lateral giant neuron of crayfish.

1. The postembryonic development of the crayfish LG tailflip command neuron's response to mechanosensory input was studied with standard electrophysiological techniques in animals between 1 and 12 cm long. 2. LG neurons are present in each abdominal hemisegment where they receive direct and indirect excitatory input from mechanosensory afferents. In both small and large crayfish, electrical stimulation of an abdominal ganglionic nerve containing those afferents evoked a compound excitatory postsynaptic potential (EPSP) with an early, reliable alpha component and a later, depression-prone beta wave. It is known that the alpha and beta components are produced by inputs from primary mechanosensory afferents and interneurons, respectively. 3. In crayfish < 2 cm long, LG was excited by the alpha component. When superthreshold, the alpha component triggered a single spike; additional excitation provided by the later beta wave presumably was preempted by refractoriness following the alpha spike and by recurrent inhibition of LG excited by the spike. LG was excited reliably by the alpha component in response to repeated superthreshold stimulation. 4. In crayfish between 2 and 3 cm, LG was excited more readily by the beta wave than by the alpha component. LG's beta spike response habituated to repeated stimulation at 1 Hz, and the beta EPSP depressed whereas the alpha component was largely unchanged. The appearance of the cellular substrates of habituation correlates with the reported onset of behavioral habituation of the tailflip response. Higher stimulus levels brought the alpha EPSP to threshold. Repetitive stimulation at these levels reliably evoked LG spikes from the alpha EPSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1994

Changes in synaptic integration during the growth of the lateral giant neuron of crayfish.

1. The effect of growth on the electrotonic structure and synaptic integrative properties of the lateral giant (LG) interneuron was assessed from anatomic and electrophysiological measurements of LGs in small (1-2.4 cm) and large (9-11.2 cm) crayfish and from calculated responses of mathematical models of these neurons. Postsynaptic responses of small and large LGs were compared with model responses to determine whether the differences in the neurons' responses result from growth-related changes in their physical characteristics. 2. LG neurons in the terminal abdominal ganglia of small and large crayfish are similar in shape but differ in size according to an approximately isometric pattern of growth. The soma diameter of the large LG is 2.2 times larger than the small LG, the major ipsilateral dendrite is 2.8 times longer and 3.6 times greater in diameter, and the axon is 7.6 times longer and 4.5 times greater in diameter. The projected area of the major ipsilateral dendrite of LG in the horizontal plane of the terminal abdominal ganglion is 27 times larger in the large than in the small crayfish. 3. LG's input resistance was nearly 80% smaller in the large (167 K omega) than in the small (742 K omega) crayfish when measured at or near the initial axon segment. The cell's membrane time constant displayed an opposite relationship, with the value in the large crayfish (20.9 ms) nearly two-and-a-half times larger than the value in the small crayfish (8.6 ms). 4. Simultaneous recordings were made from the distal portion of the ipsilateral dendrite and the initial axon segment of small and large LGs to determine how excitatory postsynaptic potentials (EPSPs) are attenuated or filtered by the electrotonic properties of the different sized cells. In the small LG, the fast alpha and the slower beta components of compound EPSPs evoked by sensory nerve stimulation were similarly attenuated. In the large LG, the alpha component of the compound EPSP was much more attenuated and smoothed than the slower beta component. 5. Multicompartment models of small and large LGs were constructed and used to test whether differences in the two neurons' physical properties could account for the differences in their passive response properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗