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Biomedical subjects

R B Leonard

Publications and source records attributed to R B Leonard.

At least 73 records · Page 4Linked to original sources
PubMed1979

The cells of origin of the primate spinothalamic tract.

Spinothalamic tract cells in the lumbar, sacral and caudal segments of the primate spinal cord were labelled by the retrograde transport of horseradish peroxidase (HRP) injected into the thalamus. The laminar distribution of stained spinothalamic cells in the lumbosacral enlargement differed according to whether the HRP was injected into the lateral or the medial thalamus. Lateral injections labelled cells in most laminae, but the largest numbers of cells were in laminae I and V. The highest concentrations of cells labelled from the medial thalamus were in laminae VI-VIII. Ninety percent or more of the stained spinothalamic cells in the lumbosacral enlargement were contralateral to the injection site. In the conus medullaris stained spinothalamic cells were most numerous in laminae I, V and VI following lateral thalamic injections of HRP. Many of the cells of the conus were in Stilling's nucleus. Twenty-three percent of the cells in the conus were ipsilateral to the injection site in the lateral thalamus. Only a few cells in the conus were labelled by medial thalamic injections. The total number of spinothalamic cells from L5 caudally was estimated to be at least 1,200-2,500. An injection of HRP into the midbrain resulted in laminar distribution of labelled cells much like that produced by a lateral thalamic injection. The types of spinothalamic tract cells and the sizes of their somata were determined for different laminae. The cell types resemble those already described from Golgi and other studies of the spinal cord gray matter. The spinothalamic tract cells in lamina I included Waldeyer cells and numerous small fusiform, pyriform or triangular cells. Those in lamina II included limitrophe and central cells. Spinothalamic cells in lamina III were central cells. Most of the labelled cells in laminae IV-X were polygonal, although there were also flattened cells in these layers. The smallest spinothalamic cells were in laminae I-III, while the largest were in laminae V and VII-IX. Spinothalamic cells in the conus medullaris included cells like those in the lumbosacral enlargement, but also a special cell type in Stilling's nucleus. Some cells in the conus had dendrites that crossed the midline. Spinothalamic axons could sometimes be traced to the ventral white commissure within one or a few sections. In longitudinal sections, most labelled axons were in the ventral part of the lateral funiculus on the side of the injection, although a few were in the ventral funiculus or on the contralateral side. The axons were widely dispersed, and a few were located adjacent to the pia-glial membrane.

Animals↗
PubMed1979

Nuclei in which functionally identified spinothalamic tract neurons terminate.

The approximate level of termination of the axons of individual, functionally characterized spinothalamic tract neurons within the monkey thalmus was mapped by antidromic activation using a monopolar electrode which was moved in a systematic grid of tracks through the thalamus. The course of individual axons could be followed through several thalamic levels, and in a few cases branches to both the VPL nucleus and to the intralaminar nuclei were demonstrated. Most of the axons studied, however, projected just to the VPLc or VPLo nuclei. The spinothalamic tract cells that projected to the VPLc nucleus included representative of all known functional categories: low threshold, wide dynamic range, high threshold and "deep." It is speculated that these different classes of spinothalamic projections could make contributions to such sensory modalities as touch, proprioception and pain.

Animals↗
PubMed1979

The organization of the electromotor nucleus and extraocular motor nuclei in the stargazer (Astroscopus y-graecum).

The organization of the oculomotor and electromotor systems was examined in the stargazer, a teleost. The electromotor system in these animals is a derivative of the oculomotor system. The extraocular motor nuclei and nerves consist of approximately equal numbers of motoneurons and axons (about 100 per muscle). In contrast, electromotor axons appear to branch several times within the intracranial portion of the IIIrd nerve. The topographical organization of the motoneurons was examined using retrograde transport of horseradish peroxidase injected into the electric organ or eye muscles. Electromotor and oculomotor neurons form distinct populations. Each electric organ receives a strong ipsilateral and a weak contralateral innervation. Individual eye muscles receive unilateral innervations with the expected laterality. Within the oculomotor nucleus there is some topographical separation of motoneurons innervating each muscle. Antidromic field potentials confirm the identity of the electromotor nucleus.

Animals↗
PubMed1979

Locomotion in the decerebrate stingray.

Stingrays swim with an active elevation-depression sequence of the pectoral fin resembling an extension-flexion sequence. During forward locomotion this sequence passes caudally along the pectoral fin. Immediately following high decerebration, stingrays are capable of locomotion, and the pattern of muscle activity closely resembles that of intact animals. Spontaneous and midbrain evoked rhythmic motoneuron discharges can be recorded in paralyzed decerebrated animals. In contrast to dogfish sharks, stringrays with high spinal transections do not locomote.

Animals↗
PubMed1979

Responses of primate spinothalamic neurons to graded and to repeated noxious heat stimuli.

1. The responses of primate spinothalamic tract cells innervating the glabrous skin of the foot to noxious thermal stimuli have been examined. 2. Of the 41 cells studied, 98% responded to noxious thermal stimuli. Heating the cutaneous receptive field with a series of stimuli from 35 to 43, 47, and 50 degrees C produced a graded increase in discharge rate. The responses were characterized by an onset, which occurred after the temperature change had either slowed or stopped, an acceleration in the discharge up to a peak, and then an adaptation to a new base-line level. The time constants of adaptation were faster than those reported for C polymodal nociceptors. 3. No systematic differences were found in the responses to noxious thermal stimuli of cells with wide dynamic range receptive fields and of cells with narrow dynamic range, high-threshold receptive fields. There were also no differences in the responses of cells located in the marginal zone and of cells located in the neck of the dorsal horn. 4. The relationship between peak frequency and final skin temperature with a 30 s stimulus duration can best be described by a power function with an exponent of 2.1. An increase in the stimulus duration to 120 s resulted in an increase in the exponent of the power function to 3.2. 5. Repetition of the series of 30-s heat stimuli resulted in an increase in peak frequency, total impulse count, and background activity. Repetition of stimuli having a duration of 120 s produced an increase in the peak frequency at 43 and 45 degrees C, a smaller increase at 47 degrees C, and a decrease at 50 degrees C. Background activity was increased by the lower temperature stimuli, but was decreased following higher temperature stimuli. 6. In six additional cells, the skin was heated with three consecutive presentations at each temperature level (43, 45, 47, and 50 degrees C) for 30 s. No change was observed in the peak frequencies of the responses to successive stimuli of the same intensity. However, the exponent of the power function relating the average peak frequency for the six cells to changes in skin temperature was 3.9. This exponent was larger than that seen when two series of graded heat stimuli of 120 s duration were used, indicating more sensitization despite the fact the total time of exposure to noxious heat was less. 7. A role for both high-threshold and wide dynamic range spinothalamic cells in transmitting nociceptive information to the diencephalon is postulated.

Adaptation, Physiological↗
PubMed1978

Spinothalamic tract neurons in the substantia gelatinosa.

The substantia gelatinosa of the mammalian spinal cord is generally believed to be a closed system; that is its neurons are thought to project only to the substantia gelatinosa of the same or the contralateral side. Experiments in monkeys, using injections of the marker enzyme horseradish peroxidase, show that at least some neurons of the substantia gelatinosa project to the thalamus and thus belong to the spinothalamic tract. Such neurons include two cell types intrinsic to the gelatinosa, the central cells and the limitrophe cells of Cajal.

Animals↗
PubMed1978

Primary afferent depolarization and inhibory interactions in spinal cord of the stingray, Dasyatis sabina.

1. Excitability changes in primary afferents and inhibitory interactions in evoked spinal cord activity were investigated in unanesthetized stingrays (Dasyatis subina) with high cervical spinal transections. 2. Primary afferent excitability increases following a conditioning stimulus to an adjacent segmental nerve were demonstrated with the Wall (31) technique. 3. Stimulation of A-alpha,beta and A-delta afferent fibers produced excitability increases in both A-alpha,beta and delta-fibers of the adjacent segment. 4. The excitability increase had a latency of about 10 ms, it peaked around 25 ms, and the change lasted more than 100 ms. 5. The central afferent volley in A-alpha,beta fibers and the N1- and late negative waves due to postsynaptic activity of dorsal horn interneurons were reduced by conditioning volleys in adjacent afferent nerves. The time course of the inhibition paralleled that of the excitability increases in afferent terminal arborizations, suggesting that the depression of postsynaptic activity is, at least in part, due to presynaptic inhibition. 6. Reduction of evoked discharges and excitatory postsynaptic potentials was observed in recordings from interneurons with a time course similar to that of the primary afferent depolarization (PAD). 7. Conditioning volleys in afferents of adjacent peripheral nerves produced facilitation or inhibition of segmental reflexes.

Afferent Pathways↗
PubMed1978

Organization of peripheral nerves and spinal roots of the Atlantic stingray, Dasyatis sabina.

1. The sizes and numbers of axons in peripheral nerves and spinal roots were investigated in the stingray, Dasyatis sabina. 2. The axons of the dorsal and ventral roots do not mingle in peripheral nerves of this animal as they do in higher vertebrates. Thus, it was usually possible to split the peripheral nerve into two portions, one containing only dorsal root axons, the other containing only ventral root axons. This feature was useful for the analysis of certain aspects of spinal cord organization. 3. The fact that dorsal and ventral root axons were segregated in peripheral nerves enabled us to demonstrate, without experimental surgery, that the central processes of the dorsal root ganglion cells and the proximal ventral root axons were 10-20% narrower, on the average, than the distal processes of the same dorsal root ganglion cells or the distal parts of the same ventral root axons. 4. The stingray is remarkable in having very few unmyelinated axons in the dorsal roots, ventral roots, or peripheral nerves. This paucity of unmyelinated axons distinguishes the Atlantic stingrays from all other vertebrates whose roots and nerves have been examined for unmyelinated fibers. 5. Similar findings were obtained for one spotted eagle ray (Aetobatus narinari) and two cow-nose rays (Rhinoptera bonasus).

Animals↗
PubMed1977

Central connections of ventral root afferents as demonstrated by the HRP method.

To study the central connections of ventral root afferents, horseradish peroxidase was injected into the lumbosacral spinal cord of the cat and the appropriate dorsal root ganglia were examined from segments with (1) both dorsal and ventral roots intact, (2) both roots sectioned, and (3) only the dorsal root sectioned. The key finding was that a number of labeled cells (up to 133) were observed in the ganglion after dorsal rhizotomy. We interpret these findings to mean that the central processes of the labeled cells projected to the spinal cord through the ventral root. As expected, when both roots were cut, almost no cells were labeled and when both roots were intact, there were large numbers of labeled cells. Of the labeled cells observed in ganglia after dorsal rhizotomy, all were found to be within the ganglion itself. No labeled aberrant dorsal root ganglion cells could be found.

Afferent Pathways↗
PubMed1975

A cytoarchitectonic analysis of the spinal cord of the pigeon (Columba livia).

The spinal gray of the pigeon is described cytoarchitectonically to establish a foundation for anatomical and physiological studies of the pigeon spinal cord. The material includes segments from the high cervical cord through the lumbosacral enlargement, and nine cellular layers are described. In addition to this laminar organization, various distinct cell groups such as the dorsal magnocellular column, column of Terni, marginal cells and lobes of Lachi are described. Layers I-IV occupy the head of the dorsal horn, are apparent at all spinal levels examined, and represent the clearest case of laminar organization of the spinal gray of the pigeon. Layer V occupies the full extent of the neck of the dorsal horn at all segmental levels investigated. Also, the dorsal magnocellular column is situated in the central region of this layer from the rostral pole of the cervical enlargement through the lumbosacral enlargement, and arguments are advanced that this cell column is homologous to the column of Clarke. In the intermediate zone a Layer IV is defined, but it is apparent only at the enlargements. Layers VII-IX constitute the ventral horn, Layer IX being the motoneuronal cell groups. With the exception of the motoneuronal groups, the boundaries of the ventral horn layers are considerably less distinct than those of the dorsal horn, and no attempt is made to distinguish Layers VII and VIII at lumbosacral levels. At the enlargements there is a prominent lateral motoneuronal cell group consisting of large cells. It is generally concluded that the cytoarchitectonic organization of the spinal gray of the pigeon bears a rather close resemblance to that described for various mammalian species, particularly with respect to the dorsal horn.

Animals↗
PubMed1975

Spinal terminal fields of dorsal root fibers in the pigeon (Columba livia).

This paper describes the spinal pattern of brachial and lumbosacral dorsal root terminations in the pigeon. These are presented within the framework of the cytoarchitectonic analysis of the preceding report (Leonard and Cohen, '75). At the level of dorsal root section and immediately adjacent sections dense terminal fields were evident throughout the ipsilateral dorsal horn (Layers I-V), including the substantia gelatinosa. However, degeneration in the substantia gelatinosa was prominent only with short survival times. There were mediolateral differences in the density of degenerating material in the dorsal horn, as well as variations between the patterns at the cervical and lumbosacral enlargements. The general pattern of degeneration in the dorsal horn extended approximately three segments rostral and two segments caudal to the level of root section, becoming progressively less dense with distance from the level of rhizotomy. An exception to this was degeneration in the dorsal magnocellular (Clarke's) column where, following section of either brachial or lumbosacral roots, degeneration could be traced into the thoracic spinal cord. However, these ascending and descending projections upon column at thoracic levels overlap minimally if at all. Degeneration was sparse in the intermediate zone and ventral horn (Layers VI-IX). It tended to concentrate centrally in Layer VI at the enlargements, and much of the degeneration ventral to this was interpreted as fibers en passage to the motoneuronal cell groups, Layer IX. Terminal fields in Layer IX were evident at both cervical and lumbosacral enlargements. They were largely restricted to the lateral motoneuronal cell group and were more prominent at cervical levels where degeneration was commonly observed around cell bodies and their proximal dendrites. As with the cytoarchitectonic organization of the spinal gray in the pigeon, the terminal fields of brachial and lumbosacral dorsal root fibers appear to have a pattern similar to that reported in mammalian literature.

Animals↗
PubMed1975

The peripheral unconditioned stimulus pathway in a model learning system involving defensively conditioned heart rate change in the pigeon.

The peripheral pathway transmitting the unconditioned stimulus information is described in a vertebrate model system for studying learning-visually conditioned heart rate change in the pigeon. In this system footshock serves as the unconditioned stimulus, and it is shown that the effective stimulation field of this stimulus, defined with respect to the unconditioned cardioacceleratory response, includes cutaneous dermatomes 21-25 (L1-Sl). The stimulus information is then transmitted by Group III and IV fibers in portions of the femoral and sciatic nerves which enter the spinal cord over segments 21-25. Further, it is shown that interrupting this pathway by section of dorsal roots 21-25 precludes establishing conditioned heart rate change with footshock as the unconditioned stimulus.

Action Potentials↗