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PubMed1984

Tail-flick related activity in medullospinal neurons.

Using the classification system of Fields et al. 131 neurons in the rostral ventromedial medulla (RVM) of lightly anesthetized rats were divided into 3 groups according to their response during tail-flick (TF) testing: those with an abrupt increase in activity prior to TF (on-cells); those with a sudden pause in activity prior to TF (off-cells); those with no change in activity prior to TF (neutral cells). Collision testing was performed using a cervical spinal cord stimulating electrode to determine whether these neurons projected to the cord. Conduction velocities were determined for all cord-projecting neurons. All 3 cell types projected to the cord and approximately 38% of cord-projecting neurons were flick-related (off-or on-cells). All projecting neurons were within or immediately adjacent to the nucleus raphe magnus. The mean conduction velocity of on-cell axons (17.7 m/s) was significantly greater than that of off-cell axons (10.7 m/s) and neutral cell axons (12.4 m/s). Conduction velocities for all cells were within the range for myelinated axons. These findings support the hypothesis that off-and on-cells in the RVM play a significant role in pain modulation at the spinal cord level.

Animals↗
PubMed1994

Electrophysiological evidence for projections of myelinated and non-myelinated primary vagal afferents to the rat insular cortex.

Two types of vagal evoked potentials were recorded in chloralose-anesthetized rats: a positive-negative one and a negative-positive one in granular and agranular insular cortical subareas, respectively, the former being more susceptible to barbiturate. Both potentials consisted of two subtypes which were distinct as to threshold and latency. Peripheral conduction velocities as well as thresholds of these two subtypes corresponded to myelinated and non-myelinated primary afferents, respectively. Thus, these two primary vagal afferents are probably both represented in two insular cortical subareas, through pharmacologically distinct pathways.

Anesthesia↗
PubMed1994

Bulbospinal sympathoexcitatory pathways in the rat.

Electrical stimulation of the rostral ventrolateral medulla (RVL) in the rat elicited a compound excitatory response on the renal sympathetic nerve (RSN) activity. Three shoulders (probably peaks) with mean latencies of 49, 59, and 71 ms were observed in the RSN excitatory response. Stimulation of the lateral funiculus at T4-T5 level evoked an excitatory response on the RSN with a mean latency of 42 ms. After subtracting the time needed for the impulse to run between the thoracic spinal cord and the recording site in the RSN, the calculated mean conduction velocities for the bulbospinal component of the sympathoexcitatory pathway activated by RVL stimulation were 7.4 m/s, 3.0 m/s, and 1.7 m/s. These conduction velocities corresponded with the axonal conduction velocities of intracellular recorded neurons in the RVL with pulse modulated activity and antidromically activated from the thoracic spinal cord (conduction velocities spanning from 1.1 m/s to 8.2 m/s). These findings are consistent with the idea that spontaneously active RVL barosensitive neurons with spinal projections are sympathoexcitatory and participate in mediating the sympathoexcitatory responses evoked on sympathetic nerves by RVL stimulation.

Animals↗
PubMed1979

Spinal evoked potential in man: a maturational study.

Summated evoked potentials to peroneal nerve stimulation which arise in the cauda equina and spinal cord afferent pathways were recorded from surface electrodes placed over the spine of 95 infants, children and adults. The conduction velocity of these potentials from lumbar to cervical recording sites was calculated. Additionally, segmental conduction velocities over peroneal nerve, caudal and rostral spinal cord were determined. In all age groups the speed of conduction up the spine was non-linear. It was slower over caudal spinal cord segments than over peripheral nerve or rostral cord. All these velocities were about half adult values in the newborn and progressively increased with age. The conduction velocity over peripheral nerve was within the adult range by 3 years of age. The speed of conduction over the spinal cord did not reach adult values until the 5th year. This suggests that spinal cord afferent pathways mature at a slower rate than peripheral nerve fibers.

Adolescent↗
PubMedDate not supplied

Role of pedal ganglia motor neurons in pedal wave generation in Aplysia.

Presumptive pedal ganglia motor neurons involved in pedal wave generation in the foot of Aplysia were examined. Pedal motor neurons fired tonicly in the absence of pedal waves, but exhibited bursting with constant phase angles during pedal wave generation. Motor neurons which burst both in and 180 degrees out of phase with the pedal wave were recorded. The relative latency of neurons firing at large phase angles was more variable than that of neurons firing at small phase angles. Pedal neurons did not make monosynaptic connections among themselves. Their firing both during and in the absence of pedal waves was due to synaptic input, presumably from interneurons which generate the oscillations underlying the pedal wave. Motor neurons firing in phase had common synaptic input of the same sign, while some motor neurons firing out of phase had common synaptic input of opposite sign. There also appeared to be polysynaptic connections among pedal motor neurons. Evidence suggesting polysynaptic feedback from the motor neurons to the oscillator interneurons was found. The results are consistent with a multineuronal oscillator in which different elements drive different groups of motor neurons. The pedal wave is the result of cyclic activation of the motor neurons by the oscillator network. Pedal motor neurons evoked several different types of tension changes in the foot when intracellularly stimulated. Fast and slow tension increases were observed. Some caused decreased tension in the foot when stimulated suggesting that they might be inhibitory motor neurons. Other neurons appeared to be involved in the central control of foot tonus. Pedal motor neurons had conduction velocities ranging from 36 to 136 cm.sec-1 and were found to have axons in more than one foot nerve branch. This property may contribute to the longitudinal spread of the pedal wave.

Animals↗
PubMed1979

Ascending projections of nociceptor-driven Lamina I neurones in the cat.

Single unit activity has been recorded from nociceptor-driven Lamina I neurones in the lumbar spinal cord of chloralose anaesthetized and gallamine paralysed cats. Ninety-four nociceptor-driven Lamina I neurones were identified by their superficial location in the dorsal horn and their ability to respond only to noxious stimulation of their cutaneous receptive fields. One-third of the Lamina I neurones responded only to noxious mechanical stimulation of the skin (Class 3a) and two-thirds responded to both mechanical and thermal noxious stimulation (Class 3b). Lissauer's tract was stimulated electrically two and three segments rostral to the recording sites. Ninety percent of the neurones tested showed a post-synaptic excitation mediated by fibres conducting at a mean velocity of 5.2 m/s (range 0.9--13.3 m/s). It is concluded that A delta and C afferent fibres running in Lissauer's tract excite nociceptor-driven Lamina I neurones. Ninety-six percent of the neurones tested showed a long period of inhibition (100--200 ms) following stimulation of large afferent fibres in the dorsal column. This inhibition was increased when the intensity of stimulation recruited Lissauer's tract fibres. Fifteen percent of the neurones tested were antidromically activated by Lissauer's tract stimulation from up to 3 segments rostal to their origin. A further 18.5% were antidromically excited by stimulation of deeper tracts. The mean conduction velocity of the axons of these projecting neurones was 8.6 m/s (range 3.8--16.5 m/s) and thus are small myelinated axons. The Class 3b neurones exhibited a significantly lower conduction velocity (7.5 +/- 2.8 (S.D.) m/s) than the Class 3a neurones (10.7 +/- 3.7 (S.D.) m/s). It is concluded that at least two-thirds of the population of nociceptor-driven Lamina I neurones are segmental interneurones.

Afferent Pathways↗
PubMed1990

Electrophysiological characterization of central sensory and motor pathway function in patients with moderate hemiparesis. II. Clinical results.

The central sensory and motor pathway function in patients with moderate hemiparesis and in healthy persons was selectively characterized by evaluation of latencies of short (R1) and long (R2) latency EMG responses as well as simultaneously recorded sensorimotor potentials (N19, N26) evoked by electrical stimulation of median and peroneal nerve (additionally, calculation of peripheral and central sensory/motor conduction times). This investigation procedure permits a noninvasive quantification of disturbed central sensory and motor pathway function in hemiparetic patients. The results found are in agreement to clinical, CT and other examination findings.

Adolescent↗
PubMed1980

Conductance changes and inhibitory actions of hippocampal recurrent IPSPs.

Intracellular recordings were obtained from CA1 pyramidal neurons in obliquely cut in vitro hippocampal slices. Recurrent IPSPs were elicited by antidromic stimulation of alvear fibers. The mechanisms by which IPSPs depress pyramidal cell excitability were investigated. Recurrent IPSPs could be reversed in sign by small hyperpolarizing currents applied through the recording electrode, indicating an increased membrane conductance. By using an AC bridge circuit it was found that the maximum impedance decrease usually occurred slightly before the peak of the IPSP. Otherwise the time course of the impedance change matched that of the IPSP itself. Inhibitory actions of the conductance increase were studied by adjusting the membrane potential to the IPSP equilibrium potential, thus allowing only the IPSP conductance to play an inhibitory role. Under these conditions non-linear summation of recurrent IPSPs with EPSPs originating in the apical dendrites could be demonstrated only during the initial 15--25 msec ofthe IPSP, which is the period of maximum conductance increase. The inhibition afforded by the hyperpolarization of the recurrent IPSP far outlasts the period of effective EPSP shunting by the inhibitory synaptic currents. The mechanisms of recurrent inhibition in the hippocampus thus appear similar to those operating in spinal motoneuron IPSPs.

Animals↗
PubMed1989

Electrophysiological evidence for axonal branching of ambiguous laryngeal motoneurons.

Laryngeal motoneurons in the nucleus ambiguous (NA) were identified antidromically by stimulation of the ipsilateral superior laryngeal nerve (S) and/or the recurrent laryngeal nerve (R). In some NA motoneurons, antidromic spikes elicited by both S and R stimulation collided with the spontaneously occurring discharges. In the same neuron, spikes evoked antidromically by stimulation of one laryngeal nerve always collided with antidromic spikes elicited by stimulation of the other laryngeal nerve. Of 105 NA neurons activated by S and R stimulation, 36 neurons satisfied the criteria, and were classified as NA neurons with branching axons (branching NA (B-NA) neurons). Those neurons activated by either S or R stimulation but not both were classified as NA neurons without branching axons (unbranched NA (UB-NA) neurons). Mean antidromic latencies of B-NA neurons were 0.79 +/- 0.20 ms to S stimulation and 1.91 +/- 0.45 ms to R stimulation and those values for UB-NA neurons were 0.84 +/- 0.17 ms to S stimulation and 2.10 +/- 0.53 ms to R stimulation respectively. None of these mean values were significantly different from one another. Conduction time in the unbranched portion of the branching axon was estimated according to the equation reported by Anderson and Yoshida. The mean conduction time for 20 B-NA neurons was 0.45 +/- 0.35 ms. The branching point in B-NA neurons was estimated on the basis of the conduction time in the unbranched stem portion and those times in two branches of a branching axon measured electrophysiologically. The results suggest that the majority of B-NA neurons bifurcate within a half axonal length.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1979

Conduction velocity through the somesthetic pathway in chronic renal failure.

The latencies of evoked potentials recorded at different levels of the peripheral and central nervous system by median nerve stimulation were measured before and after dialysis, and compared with similar recordings in normal volunteers. Abnormally slow conduction velocity was more often found in proximal rather than in distal segments of the peripheral pathway in patients with chronic renal failure. This abnormality was not correlated with the presence of clinical signs of neuropathy or low values of motor conduction velocity, neither was it affected by dialysis. These findings support the hypothesis of peripheral nerve dysfunction secondary to metabolic derangement in uraemic patients.

Adult↗
PubMed2003

Synaptic background noise controls the input/output characteristics of single cells in an in vitro model of in vivo activity.

In vivo, in vitro and computational studies were used to investigate the impact of the synaptic background activity observed in neocortical neurons in vivo. We simulated background activity in vitro using two stochastic Ornstein-Uhlenbeck processes describing glutamatergic and GABAergic synaptic conductances, which were injected into a cell in real time using the dynamic clamp technique. With parameters chosen to mimic in vivo conditions, layer 5 rat prefrontal cortex cells recorded in vitro were depolarized by about 15 mV, their membrane fluctuated with a S.D. of about 4 mV, their input resistances decreased five-fold, their spontaneous firing had a high coefficient of variation and an average firing rate of about 5-10 Hz. Brief changes in the variance of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) synaptic conductance fluctuations induced time-locked spiking without significantly changing the average membrane potential of the cell. These transients mimicked increases in the correlation of excitatory inputs. Background activity was highly effective in modulating the firing-rate/current curve of the cell: the variance of the simulated gamma-aminobutyric acid (GABA) and AMPA conductances individually set the input/output gain, the mean excitatory and inhibitory conductances set the working point, and the mean inhibitory conductance controlled the input resistance. An average ratio of inhibitory to excitatory mean conductances close to 4 was optimal in generating membrane potential fluctuations with high coefficients of variation. We conclude that background synaptic activity can dynamically modulate the input/output properties of individual neocortical neurons in vivo.

Animals↗
PubMed2000

Brainstem-evoked muscle potentials: their prognostic value in experimental spinal cord injury in the rat.

Recording myoelectric motor-evoked potentials is frequently used as an in vivo evaluation technique in experimental studies of spinal cord injury (SCI). The aim of the present study was to determine whether specific neuronal pathways conduct these potentials. Stainless steel screws were permanently implanted into the cranium of 18 rats for stimulation of brainstem-evoked muscle potentials (B-MPs). Twelve rats were subjected to spinal cord lesions that restricted the continuity of the spinal cord to different discrete sections of the lateral and/or ventral white matter (WM) of the left hemicord. Sham rats (n = 6) were subjected to laminectomy only. Left hind limb B-MPs and motor function (open field walking test) were recorded before surgery and weekly thereafter for six consecutive weeks. Motor function was severely affected by SCI in all rats but recovered significantly during the first 14 postoperative days. The degree of functional recovery depended not only on the amount of spared WM but also on the particular section of WM that had been spared. In contrast, B-MP amplitudes also were severely reduced by SCI, but did not recover during the survival period. Moreover, B-MP amplitudes correlated only weakly with the amount of sparedWM and were not influenced by which section ofWM had been spared. While functional recovery correlated significantly with the amount of spared WM, no correlation was found between B-MP amplitudes and functional recovery. B-MP conduction velocities were not affected by SCI. It is therefore believed that B-MPs have little prognostic value for experimental studies of SCI in the rat.

Analysis of Variance↗
PubMed1964

THE SELECTIVITY OF DRUGS BLOCKING GANGLIONIC TRANSMISSION IN THE RAT.

By comparing the effects on ganglionic transmission and on the pre- and post-ganglionic nerves in the isolated superior cervical ganglion preparation of the rat, the selectivity of several drugs was assessed quantitatively. Hexamethonium, tetraethylammonium, nicotine and tubocurarine blocked transmission in concentrations which did not affect nervous conduction and were considered to be highly selective in action. Atropine, amylobarbitone and paraldehyde depressed nervous conduction appreciably in ganglion-blocking doses, but not enough to account wholly for the block in transmission and they were therefore considered as being moderately selective. The ganglion blocking actions of mephenesin, procaine, methylpentynol, methylpentynol carbamate and benactyzine were nonspecific, showing general depression of neuronal activity. Ganglion block with bretylium was nonselective in its site of depression of the postganglionic neurone in concentrations which only partly depressed the preganglionic nerve.

Atropine↗
PubMed1997

Electrophysiological evidence that spinomesencephalic neurons in the cat may be excited via spinocervical tract collaterals.

Extracellular microelectrode recordings were made from spinomesencephalic tract (SMT) neurons in the lumbosacral spinal cord of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. The SMT cells were antidromically fired from the posterolateral parts of the superior colliculus and the intercollicular region, were located in laminae IV to VIII, and had response properties and axonal conduction velocities similar to those described previously. The effects of stimulating the dorsolateral funiculus of the cervical cord at C3 and rostral C1, below and above the termination of spinocervical tract (SCT) axons in the lateral cervical nucleus, were examined on 33 SMT cells. The strength of stimulation was adjusted so that at C3 it was above threshold for antidromic activation of SCT cells and at C1 was below threshold for activation of the same cells. Seven (21%) SMT neurons were excited from C3 but not from C1. The remaining 26 (79%) were excited from both C3 and rostral C1 and 23 (70% of these) were excited significantly more from C3. That is, 91% of the total sample were either excited only from C3 or more strongly from C3 than from rostral C1. We discuss the possible neuronal systems involved and conclude that the greater excitatory effects from C3 are most likely due to antidromic activation of the SCT. The shortest latency effects from C3 indicate a monosynaptic linkage between SCT cells with the fastest axons and the SMT. The longer latency actions may be due to monosynaptic connexions from SCT cells with slower conducting axons, to di- or polysynaptic actions from SCT cells with fast axons, or a combination of both. SMT cells are another population of spinal neurons, in addition to postsynaptic dorsal column, spinothalamic and dorsal horn spinocerebellar neurons, which receive excitation via SCT collaterals.

Animals↗
PubMed1987

Non-invasive assessment of the pyramidal tract and motor pathway of primates.

Non-invasive direct stimulation of the motor cortex of cynomolgus monkeys has been used to assess in awake and anesthetized animals the central and peripheral conduction times of the motor pathway and to measure the latencies of the descending spinal volley of the pyramidal tracts. Repetitive stimulation failed to induce convulsive activity or detectable pathological changes. Peripheral latencies were comparable with those obtained from F-wave analysis. Central conduction times for corticospinal tracts regulating the upper and lower limbs were 2.7 msec and 5.4 msec, respectively, the estimated conduction velocity (67.5 m/sec) corresponding to results obtained by invasive methods. These studies provide a new and apparently safe technique to assess non-invasively the functional status of the central motor pathway in primates, a method that might also find utility in clinical practice.

Animals↗
PubMed1994

4-Aminopyridine-sensitive neurologic deficits in patients with spinal cord injury.

4-Aminopyridine (4-AP) is a potassium channel blocking agent with the ability to restore conduction in demyelinated internodes of axons of the spinal cord. The present investigation sought to obtain electrophysiologic evidence of the effect of 4-AP in ameliorating central conduction deficits in a group of patients (n = 6) with spinal cord injury (SCI). The group was selected on the basis of having temperature-dependent central conduction deficits. 4-AP (24-25 mg total dose) was delivered intravenously at 6 mgh-1 or 15 mgh-1 while somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) were recorded as indices of central conduction. Two patients exhibited marked increases in the amplitude of cortical SEPs, and in one of these, 4-AP brought about a reduced central conduction time from L1 to cortex. Four patients revealed increased amplitude MEPs with concomitant reduction in latency indicative of enhanced conduction in corticospinal or corticobulbospinal pathways. Two of these patients demonstrated increased voluntary motor unit recruitment following 4-AP. Clinical examination revealed reduced spasticity (n = 2), reduced pain (n = 1), increased sensation (n = 1), improved leg movement (n = 3), and restored voluntary control of bowel (n = 1). These results support the hypothesis that 4-AP induces neurologic benefits in some patients with SCI. They are also consistent with the emerging concept that pharmaceutical amelioration of central conduction deficits caused by focal demyelination may contribute to the management of a select group of patients with compressive or contusive SCI.

4-Aminopyridine↗
PubMed1987

Cat hindlimb motoneurons during locomotion. I. Destination, axonal conduction velocity, and recruitment threshold.

Fine flexible wire microelectrodes chronically implanted in the fifth lumbar ventral root (L5 VR) of 17 cats rendered stable records of the natural discharge patterns of 164 individual axons during locomotion on a treadmill. Fifty-one out of 164 axons were identified as motoneurons projecting to the anterior thigh muscle group. For these axons, the centrifugal propagation of action potentials was demonstrated by the technique of spike-triggered averaging using signals recorded from cuff electrodes implanted around the femoral nerve. The axonal conduction velocity was measured from the femoral nerve cuff records. For 43/51 motoneurons, the corresponding target muscle was identified by spike-triggered averaging of signals recorded from bipolar EMG electrodes implanted in each of the anterior thigh muscles: vastus intermedius, medialis and lateralis, sartorius anterior and medialis, and rectus femoris. For 32/51 motoneurons, the recruitment threshold during locomotion was determined from the mean value of the rectified digitally smoothed EMG of the target muscle measured at the time when the motoneuron fired its first spike for each step. The recruitment threshold of every motoneuron was relatively constant for a given speed of walking, but for some units there were small systematic variations as a function of treadmill speed (range: 0.1-1.3 m/s). Recruitment thresholds were standardized with respect to the mean value of peak EMG activity of the target muscle during 16 s of walking at 0.5 m/s. For 28/51 motoneurons recorded in nine cats, recruitment thresholds (range: 3-93% of peak target muscle EMG) were linearly correlated (r = 0.51, P less than 0.02) to axonal conduction velocities (range: 57-117 m/s). In addition, for seven recorded pairs of motoneurons that projected to the same muscle in the same cat, the recruitment thresholds were ordered by relative conduction velocities. Taken together, these results are consistent with the notion that, in normal cat locomotion up to a medium trot, anterior thigh motoneurons are progressively recruited in an orderly fashion.

Action Potentials↗
PubMed1983

Heat exposure-induced changes in motor outflow component of reaction time.

Conduction velocity, absolute refractory period, and subnormal conduction period measures of the right ulnar motor nerve were obtained during a simple reaction time task. 6 young, healthy, right-arm dominant male subjects were tested following 30 min. exposure in ambient (20 degrees C) and hot (36 degrees C) room air conditions. Motor and premotor components of fractionated reaction time were tested on the same arm. Oral, right forearm skin and a four-site mean skin temperature were monitored. During heat exposure, forearm skin temperature increased 4.7 degrees C and mean skin temperature 2.9 degrees C. Oral temperature did not alter. Conduction velocity increased 11.4%, absolute refractory period decreased 22.7%, and subnormal conduction period decreased 14.1% in the hot condition. Concomitantly, a 5.2% increase in premotor reaction time and 12.2% decrease in motor reaction time were observed. Total RT did not alter significantly. It was concluded that different component parts of reaction time were differentially influenced by exposure to heat.

Adult↗