Conduction Velocity Spectrum Research Articles

Physiological and anatomical identification of the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract in monkeys

Physiological and anatomical criteria were used to clearly establish the existence of a pretectal relay of visual information to the ipsilateral inferior olive in the macaque monkey. After injection of horseradish peroxidase into the inferior olivary nucleus, retrogradely labelled neurons were found in the nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN). The labelled cells were distributed in a sparse band arching below the margin of the brachium of the superior colliculus between the dorsal and lateral borders of the brainstem at the caudal edge of the pulvinar. Various types of cells could be distinguished. More superficially the cells were extremely spindle shaped, cells deeper within the midbrain had more compact somata. NOT-DTN neurons in the same region were also found to respond with short latencies to electrical stimulation of both the inferior olive and the optic chiasm. All neurons in the NOT-DTN which were antidromically activated from the inferior olive were also found to have direction specific binocular visual responses. Such neurons were excited by ipsiversive motion and suppressed by contraversive motion, regardless of whether large area random dot stimuli moved across the visual field or small single dots moved across the fovea. Direct retinal input to these neurons was via slowly conducting fibers (3-9 m/s) from the monkey's optic tract conduction velocity spectrum. As shown previously for non-primates, NOT-DTN cells may also in the monkey carry a signal representing the velocity error between stimulus and retina (retinal slip), and relay this signal into the circuitry mediating the optokinetic reflex.

Effects of roll tilt of the animal and neck rotation on different size vestibulospinal neurons in decerebrate cats with the cerebellum intact

In decerebrate cats with the cerebellum intact we recorded the activity of lateral vestibulospinal neurons projecting to lumbosacral segments of the spinal cord (IVS neurons) and related the resting discharge, as well as the response characteristics of these neurons to roll tilt of the animal and neck rotation, with the cell size inferred from the conduction velocity of the corresponding axons. A slight negative correlation was found between resting discharge rate and conduction velocity of the whole population of IVS neurons responsive and unresponsive to animal tilt and neck rotation, so that the faster the conduction velocity, the lower was the unit discharge at rest. This correlation, however, was found only for the dorsocaudal LVN neurons, which contributed to the majority of IVS units, but not for the rostroventral LVN neurons. Moreover, it affected the units unresponsive but not those responsive to vestibular stimulation; the opposite, however, occurred for the units tested to neck stimulation. These findings indicate that the static properties of the IVS neurons can only in part be related to cell size. If we consider the IVS neurons responsive to roll tilt of the animal (76 neurons) and neck rotation (75 neurons) at the standard parameters of 0.026 Hz, +/- 10 degrees, no significant correlation was found between gain (impulses X s-1 X deg-1) of the labyrinth or neck responses and conduction velocity of the axons. Thus, due to the presence of slight negative relation between resting discharge and conduction velocity of the axons, larger neurons exhibited a greater percentage modulation (sensitivity) to the labyrinth and neck inputs than smaller neurons; this correlation involved particularly the dcLVN neurons. These findings suggest that the afferent pathways driven during dynamic stimulation of labyrinth and neck receptors produce an higher number or density of synaptic contacts on IVS neurons of increasing size. No significant differences in the means of resting discharge, conduction velocity, gain and sensitivity were found between all the IVS units responding to labyrinth and neck inputs. These findings indicate that the effectiveness of the two inputs was almost comparable and did not vary in different units as a function of cell size. The IVS neurons were mainly excited during side-down animal tilt and side-up neck rotation. Although these neurons showed the same spectrum of conduction velocity as those displaying the opposite response patterns, the response gains of the predominant populations of units were on the average higher than those obtained from the remaining populations of units.(ABSTRACT TRUNCATED AT 400 WORDS)

Motor nerve conduction velocity spectrum: A further development of the double pulse stimulation technique

Motor nerve conduction velocity spectrum: A further development of the double pulse stimulation technique

Axonal refractory period of single short toe extensor motor units in neuropathies and neuromuscular diseases.

Electromyographic recordings were carried out on 36 patients with neuropathies and neuromuscular disorders with a selectivity permitting identification of single motor unit potentials during maximal voluntary effort and after supramaximal nerve stimulation. The axonal conduction velocity and refractory period of 117 motor units were determined and the findings were compared to those in previously studied normal subjects. The axonal conduction velocity spectrum was 15-52 m/s. Fifteen per cent of all motor units had axonal conduction velocities below 30 m/s which is below the normal range. When test stimulus strength was 10% above the axonal threshold at rest the refractory period was 1.88 +/- 0.43 ms which is slightly longer than the corresponding value in healthy subjects (1.67 +/- 0.25 ms). The relationship between the axonal conduction velocity and refractory period observed in healthy subjects did not hold for these patients. Thirty-eight per cent of all motor motor units with axonal conduction velocities within the normal range had refractory periods longer than 2.0 ms which was only infrequently observed in healthy subjects. When test stimulus strength was 50% above the axonal threshold at rest the refractory period was 1.16 +/- 0.42 ms which was significantly longer (p less than 0.02) than in healthy subjects (0.64 +/- 0.21 ms). At this stimulus strength 40% of all motor units with axonal conduction velocities within the normal range had refractory periods above 1.0 ms which was never the case in healthy subjects. The significance of these findings with regard to the clinical application of the Hopf technique for determining the conduction velocity spectrum of peripheral motor nerves is discussed.

Neurotoxicology of vincristine in the cat. Electrophysiological studies.

Cats were given vincristine sulfate (50 micrograms/kg i.v. every 4 days) and studied after 7-29 injections when neurological deficits became evident. The conduction velocity spectrum of individual afferent nerves from soleus muscles was shifted toward slower velocities. Relatively few functional muscle spindles or other proprioceptors which responded to muscle stretch were encountered. Those primary endings of soleus muscle spindles which did respond were significantly reduced in dynamic but not length sensitivity. Length sensitivity of secondary endings was unchanged. Thresholds of secondary but not primary endings were elevated. The average conduction velocity of soleus motor axons was reduced 30% but no deficit was detected in motor nerve terminal function. Indirectly-elicited contractile tension of the soleus muscles of the neuropathic cats was not significantly lower than that in untreated animals. Amplitudes of spinal monosynaptic reflexes were unaffected. These data indicate, that in the cat, neurological impairment results partly from dysfunction in muscle spindles and peripheral nerves.

The conduction velocity and central projections of retinofugal fibers in the rabbit

In anesthetized and paralyzed rabbits, action potentials were elicited antidromically following electrical stimulation of optic tract terminals at the geniculate level (LGN). The conduction velocity spectrum extended from 7 m.s −1 to 34 m.s −1. The distribution of conduction velocities indicated four major modes at 10, 18, 22 and 26 m.s −1. Antidromic compound action potentials exhibited good correlation between the conduction latency and the major modes of the distribution histogram. These results suggest that the rabbit optic tract is composed of four classes of fibers varying in their conduction velocities. The central projections of retinofugal axons were studied with electrical stimulations of the Superior Colliculus (CS) and the LGN while recording from the same optic tract fiber. Antidromic spikes could be elicited from all conduction velocity groups and 71% of axons responded to both sites of stimulation. This finding indicates that most retinofugal fibers branch to and innervate both CS and LGN. Further, there is a tendency for fast-conducting axons to have their receptive field located eccentrically relative to the optic axis of the eye.

Axonal refractory period of single short toe extensor motor units in man.

The aim of this study was to test the reliability of the commonly used blocking technique for measuring the conduction velocity spectrum of the peripheral motor nerve in man, as first described by Hopf in 1962. Electromyographic recordings were carried out with a selectivity permitting identification of single motor unit potentials. The conduction velocity of the single alpha motor axon was determined by a direct technique and by the blocking technique. the refractory period was determined by comparison of the results of these two techniques. The refractory period was studied in relation to the strength of the testing stimulus, axonal conduction velocity, skin temperature and age of the subject. When the strength of the test stimulus increased from 10% to 50% above the axonal threshold, the refractory period decreased from 1.7 to 0.6 ms. An inverse relationship between the axonal conduction velocity and the refractory period was observed. When skin temperature was 4 degrees C subnormal the refractory period was significantly prolonged; at 10 degrees C subnormal it was more than doubled. The same relationship between axonal conduction velocity and the refractory period was observed in both young and elderly subjects. The significance of these findings for the clinical application of the blocking technique is discussed.

Some observations on the efferent innervation of rat soleus muscle spindles

In the small segmental tail muscles of the rat beta fibres provide exclusively the dynamic fusimotor control, while gamma fibres provide exclusively the static fusimor control. The present experiments were made to investigate the fusimotor innervation of spindles in a large muscle of the rat, the soleus, and thus to determine the occurrence and significance of beta innervation in this muscle. Our results have revealed no case of beta innervation in the rat soleus. As a consequence of our experimental method, however, we would not claim that beta innervation does not exist in the soleus, only that it must play an insignificant role relative to that seen in the tail segmental muscles. Investigations of the fusimotor innervation of eight spindles were sufficiently complete to warrant detailed illustration. The number of gamma fibres ranged from two to four. In every case the slowest conducting gamma fibre was dynamic. However, the conduction velocity spectra for the static and dynamic gamma fibres to rat soleus overlap to such an extent that it is impossible to use conduction velocity as the sole guide to functional gamma fibre classification. The pooled results from the eight spindles fully investigated provide a ratio of static to dynamic gamma fibres of approximately 1:1. Other evidence discussed in the paper suggests that in the muscle nerve the ratio is considerably higher. These differences are reconciled if the dynamic gamma fibres branch more profusely and innervate more spindles than do the static gamma fibres.

Analysis of Activity in A and C Fibres Under Mechanical and Thermal Stimulation of the Skin Receptor Field

A conduction velocity spectrum in nerve fibres of 0.15 to 90 m/sec was found by means of electrophysiological methods of analysis and computer-aided processing of experimental data. A greater portion of the non-myelinated fibres in the cutaneous nerve proved to be afferent. Patterns of afferent impulse flows entering the central nervous system are determined under various mechanical and thermal stimulations of cat's cutaneous receptive field. Differences of these flows are considered to be the reasons for various sensation modalities. The mechanism of cutaneous mechanoreceptor excitation under temperature stimuli is discussed. Special attention is paid to the contraction of cutaneous collagen under cooling. Experimental data on the change of cutaneous mechanical properties and the electrophysiological changes corroborating the thermomechanical hypothesis of receptor excitation are given.

Optic nerve axon diameters measured in the cat retina: Some functional considerations

Because of the arrangement of axon bundles in the fibre layer of the cat's retina, it is possible to obtain electronmicroscopic sections of axon bundles which contain exclusively either axons arising from the area centralis, or axons arising from peripheral retina. From electronmicrographs of such sections we have constructed axon diameter spectra for central and peripheral axon samples. The centrally originating axons are markedly smaller than peripheral axons, in good agreement with their slower conduction velocity (described in an accompanying paper). The diameter spectra of both peripheral and area centralis axon samples are unimodal, in contrast to the two conduction velocity groups known to exist within each axon population. Alternative explanations of this discrepancy between diameter and conduction velocity spectra are discussed.