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H R Koerber

Publications and source records attributed to H R Koerber.

At least 37 records · Page 2Linked to original sources
PubMed1991

Modulation of synaptic transmission at Ia-afferent fiber connections on motoneurons during high-frequency stimulation: role of postsynaptic target.

1. High-frequency stimulation of single group Ia-fibers results in modulation of excitatory postsynaptic potential (EPSP) amplitude recorded in target motoneurons. This can be either positive (EPSP amplitude increases in response to successive stimuli in the high-frequency burst) or negative (decrease in EPSP amplitude). We have investigated whether the magnitude of modulation is associated with the stimulated afferent, the responding motoneuron, or the amplitude of the EPSP. 2. In agreement with previous findings, we found that positive modulation tends to occur at connections generating small EPSPs and negative modulation, at those producing large EPSPs. Because large EPSPs generally are evoked in motoneurons with low values of rheobase, we found, as anticipated, that connections on low rheobase motoneurons are prone to negative modulation during high-frequency stimulation, whereas those on high rheobase motoneurons (which tend to generate small EPSPs) are prone to positive modulation. 3. In experiments where the projection of multiple afferents to a single motoneuron was studied, we found that amplitude modulation was similar despite differences in EPSP amplitude. Thus in a given motoneuron there is no relationship between modulation and amplitude, in contrast to the existence of such a relationship in the population of connections as a whole. 4. In the converse experiments where the projection of single afferents to multiple motoneurons was studied, we found marked variability in the modulation patterns with clear indications that amplitude and modulation are correlated as in the entire population of Ia/motoneuron connections. 5. We tested the constancy of modulation patterns evoked in a given motoneuron by comparing the modulation patterns evoked in motoneurons by single fibers, and by stimulation of the heteronymous nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Modulation of synaptic transmission at Ia-afferent connections on motoneurons during high-frequency afferent stimulation: dependence on motor task.

1. Monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in medial gastrocnemius motoneurons by maximal group Ia stimulation of the heteronymous lateral gastrocnemius-soleus nerve in anesthetized cats. Three different patterns of high-frequency stimulation were delivered to the nerve, and the EPSPs were averaged in register (1, 2, . . ., n) for each. 2. One pattern ("Burst") consisted of 32 shocks delivered every 2 s at an interstimulus interval of 6 ms (167 Hz). The second pattern ("Stepping") was a frequency-modulated burst of 52 shocks derived from a recording of a spindle during stepping and was delivered every 2 s. The third pattern ("Paw Shake") was from an extensor spindle afferent recorded during rapid paw shake and was delivered in groups of six bursts with an interburst interval of 75 ms and a 3-s pause between groups of six bursts. The EPSPs in each burst were averaged in register (1, 2, . . ., n) so that the relative amplitude of each EPSP in the burst could be ascertained. The EPSP produced by low-frequency stimulation of the nerve (18 Hz) was also recorded for each motoneuron. 3. The initial EPSP in most bursts was larger than the EPSP measured as a result of low-frequency stimulation. This potentiation, defined as the ratio of the amplitude of the initial EPSP of the response to that of the low-frequency control, was found to vary systematically as a function of amplitude of the control EPSP as well as the stimulus paradigm used.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1991

Tuning of spinal networks to frequency components of spike trains in individual afferents.

Cord dorsum potentials (CDPs) evoked by primary afferent fiber stimulation reflect the response of postsynaptic dorsal horn neurons. The properties of these CDPs have been shown to vary in accordance with the type of primary afferent fiber stimulated. The purpose of the present study was to determine the relationships between frequency modulation of the afferent input trains, the amplitude modulation of the evoked CDPs, and the type of primary afferent stimulated. The somata of individual primary afferent fibers were impaled in the L7 dorsal root ganglion of alpha-chloralose-anesthetized cats. Action potentials (APs) were evoked in single identified afferents via the intracellular microelectrode while simultaneously recording the response of dorsal horn neurons as CDPs, or activity of individual target interneurons recorded extracellularly or intracellularly. APs were evoked in afferents using temporal patterns identical to the responses of selected afferents to natural stimulation of their receptive fields. Two such physiologically realistic trains, one recorded from a hair follicle and the other from a slowly adapting type 1 receptor, were chosen as standard test trains. Modulation of CDP amplitude in response to this frequency-modulated afferent activity varied according to the type of peripheral mechanoreceptor innervated. Dorsal horn networks driven by A beta afferents innervating hair follicles, rapidly adapting pad (Krause end bulb), and field receptors seemed "tuned" to amplify the onset of activity in single afferents. Networks driven by afferents innervating down hair follicles and pacinian corpuscles required more high-frequency activity to elicit their peak response. Dorsal horn networks driven by afferents innervating slowly adapting receptors including high-threshold mechanoreceptors exhibited some sensitivity to the instantaneous frequency, but in general they reproduced the activity in the afferent fiber much more faithfully. Responses of synaptically coupled dorsal horn neurons belonging to either hair follicle or SA1 fiber-driven networks to frequency-modulated input were in agreement with the CDP results, confirming that CDP amplitude modulation is a true reflection of EPSP amplitude modulation in at least a subset of dorsal horn neurons comprising the network.

Action Potentials↗
PubMed1990

Correlation of monosynaptic field potentials evoked by single action potentials in single primary afferent axons and their bouton distributions in the dorsal horn.

The relationship between structure and function of the projections of single identified primary cutaneous axons was investigated by recording cord dorsum potentials at 4 sites in response to electrical stimulation of the single axon and visualizing the boutons of the axon stained by intracellular injection of horseradish peroxidase. The rostrocaudal extent of boutons differed from fiber to fiber ranging from 4.14-11.50 mm; their location in the dorsal horn also varied in agreement with the known somatotopy of the presynaptic neuropil and dorsal horn neurons. Rostrocaudal distributions of cord dorsum potentials and boutons of individual fibers revealed good agreement. Cord dorsum potential amplitude and length of the spinal projection were positively correlated with number of boutons, but no correlation with bouton density was found. The spinal projection of afferents innervating slowly adapting type 1 mechanoreceptors exhibited a greater rostrocaudal extent (mean: 8.48 mm) than those innervating rapidly adapting mechanoreceptors (i.e., hair follicle and field receptors: mean: 5.87 mm). Although the mean total number of boutons was greater for axons with slowly adapting receptors (7,250/fiber) than for axons of rapidly adapting receptors (4,677/fiber), no differences in the longitudinal density of boutons (boutons/mm) were observed. Likewise, summed amplitudes of cord dorsum potentials at the 4 recording electrodes were larger for SA1 afferents than for those of field and hair follicle afferents. A major role for the number of boutons in determining these differences is supported by the finding that the calculated average contribution per bouton to cord dorsum potentials (expressed as an amplitude coefficient a) was similar for slowly and rapidly adapting afferents. No evidence was found for regions in which boutons did not contribute to the cord dorsum potential.

Action Potentials↗
PubMed1989

Mismatches between peripheral receptor type and central projections after peripheral nerve regeneration.

The central projections of axotomized fibers were assessed to investigate how well these matched the modality of the reinnervated receptor. Our results using intrafiber injection of horseradish peroxidase (HRP) and cord dorsum potentials evoked by intracellular stimulation of single afferents indicate that regenerating fibers can innervate inappropriate receptors. Mismatches included: (i) reinnervation of muscle receptors by cutaneous afferents, and vice versa; (ii) reinnervation of low threshold cutaneous receptors by nociceptive afferents; and (iii) reinnervation of slowly adapting receptors by fibers normally supplying rapidly adapting receptors.

Action Potentials↗
PubMed1988

Properties of somata of spinal dorsal root ganglion cells differ according to peripheral receptor innervated.

1. Intracellular recordings were made in the somata of dorsal root ganglion cells in the L7 or S1 DRG in cats anesthetized with alpha-chloralose. The properties of the action potentials (amplitude, duration, peak rate of rise), duration of afterhyperpolarization (AHP), magnitude of inward rectification, and axonal conduction velocity were measured. The adequate stimulus was determined, and the extent to which these properties are correlated was investigated. 2. All cells with receptive fields could be classified as mechanoreceptors. Most cells with A-beta-axons (greater than 36 m/s) could be activated by gentle mechanical stimulation but a small minority with conduction velocity in the low end of the A-beta-range were nociceptors. Cells with A-delta-axons (2-36 m/s) innervated either the very sensitive Down hair follicles (D-hairs) or high-threshold mechanoreceptors (HTMRs). In addition a group of A-delta-fibers was found for which no receptive field could be described. Their spikes, AHPs, and membrane properties were indistinguishable from those of cells supplying HTMRs (see below) and they were lumped together with A-delta-HTMRs. 3. A-beta-neurons exhibited smaller, briefer spikes than A-delta-neurons, even those supplying D-hairs. Peak rate of rise (dV/dt)max and inward rectification were significantly larger in A-beta-cells than in A-delta s, whereas AHP duration and input resistance were smaller. However, the values of these parameters in cells of a given conduction velocity range were generally associated with receptor type. 4. A-delta-HTMRs exhibited spikes of greater amplitude and duration, longer AHP duration, and smaller inward rectification than D-hairs. The long duration of these spikes was due largely to a prominent hump on their descending limb. Input resistance was similar in both groups of cells. 5. A-beta-HTMRs differed from A-beta-cells innervating low threshold receptors in the same general way that A-delta-HTMRs differed from D-hairs. However, A-beta-LTMRs supplying different receptor types (e.g., slowly adapting type I, Pacinian corpuscles, etc.) exhibited no correlation between receptor type and electrophysiology of the soma. 6. These differences in spike parameters occur at the level of the membrane rather than in the degree of somal invasion because the largest amplitude spikes also exhibited the slowest time course (i.e., in HTMRs). Systematic variation in AHP duration and inward rectification also suggest differences in the proportions of ionic channel types among these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Functional specialization of central projections from identified primary afferent fibers.

1. Somata of primary afferent fibers were impaled in the L7 or S1 dorsal root ganglion in cats anesthetized with alpha-chloralose. Individual cells (n = 182) were characterized according to receptive field (RF) and by the peripheral mechanoreceptor they innervated. They were then stimulated intracellularly while recording the evoked cord dorsum potentials (CDPs) simultaneously at four sites. CDPs were recorded in response to single fiber stimulation while varying both the frequency and the numbers of action potentials (APs) evoked per trial. Stimulus parameters included: 1) single APs evoked at both high (18 Hz) and low (0.67 Hz) frequencies, 2) pairs of APs (50-ms ISI) delivered at 0.67 Hz, and 3) trains of four APs (20-ms ISI) also delivered at 0.67 Hz. The properties of the CDPs and their relationship to receptor type innervated by the fiber were determined. 2. CDPs evoked by 18-Hz stimulation consisted of an axon fiber spike followed at a short latency [600 +/- 9.9 (SEM) microseconds] by the onset of a monophasic negative wave. A-beta-afferent fibers innervating slowly adapting type 1 and 2 receptors (SA1 and SA2) evoked the largest amplitude CDPs followed by field and hair follicle afferents while A-delta-fibers rarely produced measurable CDPs at this frequency of stimulation. 3. The magnitude of the CDP varied at the four recording sites with clear evidence in individual experiments that the projections of individual fibers are somatotopically organized. 4. CDPs evoked by 0.67-Hz stimulation had the same onset latency but were larger in amplitude and had longer time-to-peak and durations than those elicited by high frequency stimulation. Under these conditions A-beta-fibers innervating hair follicles produced the largest CDPs followed by field receptors and SA1s and SA2s. A-beta- and A-delta-fibers innervating high threshold mechanoreceptors (HTMRs) and A-delta-fibers innervating down hair follicles (D-hairs) produced CDPs of amplitude and duration similar to those evoked by slower A-beta-fibers. 5. The response to a test stimulus delivered 50 ms after a conditioning stimulus to the same single fiber was always depressed in the case of A-beta-fibers supplying rapidly adapting receptors. The conditioning stimulus exerted relatively little effect on the response to the test stimulus for A-beta- fibers innervating slowly adapting receptors. The test response to stimulation of A-beta- and A-delta- fibers innervating HTMRs was consistently facilitated while stimulation of A-delta- D-hairs evoked either marked facilitation or slight depression.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1987

Morphologically unusual feline spinocervical tract neurons.

Intracellular horseradish peroxidase studies of spinocervical tract neurons in the cat have demonstrated that they have dendritic arbors primarily confined to laminae III through V. In the present intracellular staining study of this class of neuron we retrieved one cell with its soma in lamina I which arborized in laminae I through III and another cell with a soma in lamina III and a dendritic arbor which extended from lamina I through V. These data indicate therefore that a small proportion of neurons forming the spinocervical tract do not have dendritic arbors that are confined to laminae III through V. These two cells were capable of receiving monosynaptic input from primary afferent fibers innervating mechanical nociceptors and C-fibers.

Animals↗
PubMed1987

Excitatory actions of single impulses in single hair follicle afferent fibres on spinocervical tract neurones in the cat.

1. In cats under chloralose anaesthesia single dorsal root ganglion cells with axons innervating hair follicles were stimulated intracellularly to produce single impulses. At the same time single spinocervical tract (s.c.t.) neurones were recorded extracellularly, from their axons in the upper lumbar cord. 2. When the receptive field of the afferent fibre was contained within the impulse firing zone of the s.c.t. cell, a single afferent impulse increased the probability of firing of the neurone. In thirty-nine pairs of units, where the afferent fibre had a group II conduction velocity, coupling was very efficient and for seventeen pairs the single afferent impulse produced one or more impulses in the s.c.t. cell in at least 90% of trials. The mean number of impulses evoked in s.c.t. cells by a single group II afferent impulse was 1.47. The latencies of the impulses ranged from 1.5 to 14.0 ms, with times to peak and total durations of 2.5-17.5 ms and 4.5-28.0 ms respectively. For two pairs of units where the afferent fibre had a group III conduction velocity the effectiveness of single afferent impulses was much less and the latencies, but not the durations, of the impulses were longer (12 and 17 ms). 3. When the receptive field of the hair follicle afferent fibre was outside, but close to, the firing zone of the s.c.t. neurone there was no indication that single afferent impulses affected the probability of neuronal discharge for thirteen of fifteen pairs of units. Weak excitation was observed in two pairs and this was clear only when two or more afferent impulses were employed. 4. There was a tendency for hair follicle afferent fibres with their receptive fields at or near the centre of the s.c.t. cell's firing zone to be most effective, producing shorter latency responses with more impulses at higher frequencies. When the afferent's field was peripherally located in the s.c.t. neurone's firing zone there was a wide range of responses but these included those with the longest latencies and very few impulses. 5. The results are discussed with reference to previous work on the spinocervical tract and to the known actions of single impulses on other neuronal types. Suggestions are made for the possible excitatory neuronal circuits linking hair follicle afferent fibres to the s.c.t. neurones.

Action Potentials↗
PubMed1987

Actions of trains and pairs of impulses from single primary afferent fibres on single spinocervical tract cells in cat.

1. In cats under chloralose anaesthesia single lumbosacral dorsal root ganglion cells of hair follicle afferent fibres were stimulated intracellularly to produce trains or pairs of impulses. At the same time, single spinocervical tract (s.c.t.) neurones were recorded extracellularly, from their axons in the upper lumbar spinal cord. Afferent fibre-neurone pairs were chosen in which the receptive field of the fibre was contained within the excitatory receptive field (firing zone) of the neurone. 2. Trains of impulses of 2.0 Hz were less effective in increasing the probability of s.c.t. cell firing than trains at 0.67 Hz, and this latter rate was usually less effective than trains at 0.33 Hz. 3. Successive responses to individual members of a train of hair follicle afferent impulses were variable. In some pairs of units succeeding responses declined until a fairly consistent plateau was reached. In others there was no decline and the responses remained irregular. 4. Pairs or short trains of impulses revealed two phenomena: over the first 5 ms or so following an impulse in a group II hair follicle afferent fibre, a second or small group of impulses produced a greater response from the s.c.t. neurone but at intervals of 25-200 ms there was a profound depression of the responses evoked by the second member of a pair of impulses. For A delta afferent fibres the early facilitation lasted for at least 25 ms. 5. It is concluded that a single impulse in a single hair follicle afferent fibre from within the excitatory receptive field of a s.c.t. neurone has complex actions on transmission through that neurone. An initial excitatory influence is followed by a long-lasting depression that influences transmission through the system for at least 1500 ms. Possible mechanisms underlying this depression are discussed.

Action Potentials↗
PubMed1987

An intracellular study of spinocervical tract cell responses to natural stimuli and single hair afferent fibres in cats.

1. Intracellular recordings were made from spinocervical tract (s.c.t.) neurones in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. In one series of experiments the cells' receptive fields were examined with the use of natural stimuli. Hair movement within the impulse firing zone of the cell evoked excitatory post-synaptic potentials (e.p.s.p.s) from which impulses were generated; in addition, in the majority of s.c.t. cells tested, areas were found within the impulse firing zone where hair movement elicited both e.p.s.p.s and inhibitory post-synaptic potentials (i.p.s.p.s). Outside the firing zones, both regions evoking e.p.s.p.s and regions evoking i.p.s.p.s were observed in all neurones examined in detail (ten cells). The responses of these neurones to a variety of natural stimuli showed the receptive fields of s.c.t. cells to be more complex than previously thought. 3. In a second series of experiments, intracellular recordings from s.c.t. cells were combined with intracellular recording and stimulation of single dorsal root ganglion cells belonging to group II hair follicle afferent fibres. When the afferent fibres innervated skin within the impulse firing zone of the s.c.t. cell, single afferent impulses evoked e.p.s.p. complexes consisting of both mono- and polysynaptic components; no i.p.s.p.s were observed in response to single hair follicle afferent impulses or to trains. Although the monosynaptic e.p.s.p. component was often large and had a fast rise time, s.c.t. cell impulses usually arose from the later components. Afferent fibres innervating the central region of the s.c.t. cell firing zones tended to evoke relatively large e.p.s.p.s with fast rise times. The rise times and amplitudes of the e.p.s.p.s evoked by afferent fibres from the periphery, however, varied between afferent fibres but included the slowest and smallest in the total sample of synaptically coupled pairs. Afferent fibres from outside the s.c.t. cell's firing zone were usually ineffective in setting up post-synaptic potentials, but one group III hair follicle afferent fibre, from an inhibitory receptive field component, gave rise to i.p.s.p.s. 4. The effects of pairs and trains of afferent impulses at intervals of 10, 25, 50, 100 and 200 ms were examined. At 25 ms the response to the second afferent impulse was profoundly less than that evoked by the first and was still substantially reduced at 200 ms interval. In all synaptically coupled pairs studied, the e.p.s.p. complex evoked by the second afferent impulse was smaller in amplitude than that evoked by the first.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Somal action potential duration differs in identified primary afferents.

In the present study we examined action potentials recorded from somata in the cat L7 and S1 dorsal root ganglia. We found (i) that there is a characteristic spike duration for each receptor type (e.g. Golgi tendon organ, D-hair) and (ii) that, for a given peripheral fiber conduction velocity, somata whose axons supply low-threshold cutaneous receptors exhibit spikes with shorter durations than those innervating high-threshold cutaneous receptors. These results suggest that there may be significant differences in somal membrane composition which are specific to the physiological receptor types innervated.

Action Potentials↗
PubMed1986

Fine structure of collateral axons originating from feline spinocervical tract neurons.

In adult cats, 7 spinocervical tract neurones were intracellularly labelled with horseradish peroxidase and ultrastructural properties of collateral axons of 3 of them were examined. The terminations of collateral axons formed boutons which made synaptic associations predominantly with the somata and proximal dendrites of dorsal horn neurones. Collateral axons of one spinocervical tract neurone formed synaptic associations with a cell which projected via the dorsal columns.

Afferent Pathways↗
PubMed1985

Axonotmesis as treatment for neurotmesis.

The effect of proximal nerve crush on regeneration after unrepaired nerve transection was studied in feline cutaneous nerves. Delays between the initial transection and the subsequent nerve crush varied between 0 (immediate crush) and 13 months. A survival time of 6 to 12 months after the crush was allowed for regeneration to complete. Data from these animals was compared with data from animals in which the nerve was simply transected. Four measures of regeneration success were used to assess the degree of functional recovery: (i) the number of fibers crossing the neuroma and regenerating down the distal stump; (ii) the conduction velocity and diameter of individual fibers in the distal stump relative to their conduction velocity and diameter in the proximal stump; (iii) the number of fibers reinnervating cutaneous mechanoreceptors; and (iv) the number of cutaneous type I mechanoreceptors present after regeneration. As a whole, the data showed a statistically significant increase in the number of fibers entering the distal stump and in the number of fibers reinnervating the skin when the nerve was crushed 6 months after transection compared with nerves that were only transected. There was also an increase in the size and conduction velocity of fibers in the distal stump of nerves that had been crushed 4 to 6 months after transection.

Animals↗
PubMed1985

Light and electron microscopy of contacts between primary afferent fibres and neurones with axons ascending the dorsal columns of the feline spinal cord.

In addition to primary afferent fibres, the dorsal columns of the cat spinal cord contain ascending second-order axons which project to the dorsal column nuclei. The aim of the present study was to obtain morphological evidence that certain primary afferent axons form monosynaptic contacts with cells of origin of this postsynaptic dorsal column pathway. In ten adult cats, neurones with axons ascending the dorsal columns were retrogradely labelled with horseradish peroxidase using a pellet implantation method in the thoracic dorsal columns. In the lumbosacral regions of the same animals, primary afferent fibres were labelled intra-axonally with ionophoretic application of horseradish peroxidase. Tissue containing labelled axons was prepared for light and combined light and electron microscopy. Ultrastructural examination demonstrated that slowly adapting (Type I), hair follicle, Pacinian corpuscle and group Ia muscle spindle afferents formed monosynaptic contacts with labelled cells and light microscopical analysis suggested that they also received monosynaptic input from rapidly adapting (Krause) afferents. This evidence suggests that sensory information from large-diameter cutaneous and muscle spindle afferent fibres is conveyed disynaptically via the postsynaptic dorsal column pathway to the dorsal column nuclei. Some of the input to this pathway is probably modified in the spinal cord as the majority of primary afferent boutons forming monosynaptic contacts were postsynaptic to other axon terminals. The postsynaptic dorsal column system appears to constitute a major somatosensory pathway in the cat.

Animals↗
PubMed1983

A quantitative evaluation of suture and tubulization nerve repair techniques.

The radial and sural nerves in cats were transected and either left unrepaired, repaired with 11-0 epineurial sutures, sutured and treated with topical application of Kenalog, or tubulated with hypoantigenic collagen. One year later the nerves were examined electrophysiologically, using single unit recording techniques, and histologically, by light microscopy. The results indicate that regeneration through the neuroma was comparable in all four groups, but that reinnervation of sensory structures in the skin was most successful in the tubulated nerves.

Animals↗
PubMed1982

Somatotopic organization of hindlimb cutaneous nerve projections to cat dorsal horn.

1. The dorsal horn lamina III-IV projections of 10 hindlimb nerves innervating most of the hindlimb have been studied in the cat using transganglionic transport of horseradish peroxidase (HRP). The somatotopic organization of whole cutaneous nerve projections was largely in register with the somatotopic organization of dorsal horn cells. That is, nerves projected to areas of dorsal horn where their innervation fields overlap the receptive fields of dorsal horn cells. 2. However, long-ranging projections were observed that were more extensive than predicted from the somatotopy of dorsal horn cells: these long-ranging projections may reflect the presence of normally ineffective synapses (synapses that do not cause postsynaptic discharge during receptive-field mapping of dorsal horn cells,) or a misconception of dorsal horn cell somatotopy in S2 and caudal segments, or the existence of a functionally separate cell group in ventral lamina IV and lamina V of these segments. 3. The cutaneous innervation fields of homologous nerves possessed high bilateral symmetry, as did their lamina III-IV projection fields. The degree of separation or overlap of two cutaneous nerves' projection fields was predictable from the degree of separation or overlap of their cutaneous innervation fields.

Animals↗