Browsing by Author "Leonard, R.B."

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    The descending and intrinsic serotoninergic innervation of an Elasmobranch spinal cord.
    (1984) Ritchie, T.C.; Roos, L.J.; Williams, B.J.; Leonard, R.B.; Journal of Comparative Neurology.
    The descending and the intrinsic components of the serotoninergic (5HT) innervation of the Atlantic stingray spinal cord were described by comparing the distributions of neuronal elements exhibiting 5HT-like immunoreactivity (peroxidase-antiperoxidase method) in sections caudal and rostral to spinal transections. The cells of origin of the descending 5HT system were located with a double labeling method for both retrogradely transported horseradish peroxidase (HRP) and 5HT staining. The descending system provides virtually the entire 5HT innervation of the dorsal horn, the intermediate zone, and the dorsal and lateral portions of the ventral horn. Fibers of the descending 5HT system course in the lateral funiculus, the dorsal portion of the ventral funiculus, and in the submeningeal zones of the dorsal and lateral aspects of the spinal cord. This projection primarily originates from the 5HT cell groups of the caudal rhombencephalon (groups II and III; Ritchie et al., '83), with a minor contribution from group IV in the rostral rhombencephalon. The organization of the descending 5HT system in stingrays is remarkably similar to that of mammals. The intrinsic spinal 5HT system consists of cells distributed in the ventromedial spinal cord that have processes extending longitudinally in a ventral submeningeal fiber network. Fibers were traced from the submeningeal system to the ventral horn, where varicose processes were restricted largely to the neuropil ventral to the somata of the fin motoneurons. The existence of a well-defined intrinsic 5HT system in stingrays supports the hypothesis that such a system exists in the spinal cords of a variety of vertebrates.
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    The distribution of serotonin in the CNS of an Elasmobranch fish: immunocytochemical and biochemical studies in the Atlantic Stingray, Dasyatis sabina.
    (1983) Ritchie, T.C.; Livingston, C.A.; Hughes, M.G.; McAdoo, D.J.; Leonard, R.B.; Journal of Comparative Neurology.
    The distribution of serotonin (5 HT) in the brain of the Atlantic stingray was studied with peroxidase-antiperoxidase immunocytochemistry and high-pressure liquid chromatography. The regional concentrations of 5HT determined for this stingray fell within the range of values previously reported for fishes. A consistent trend in vertebrates for the hypothalamus and midbrain to have the highest concentrations and the cerebellum the lowest was confirmed in stingrays. Neuronal cell bodies and processes exhibiting 5HT like immunoreactivity were distributed in variable densities throughout the neuroaxis system in the Atlantic stingray: (I) spinal cord, (II-IV) rhombencephalon, (V,VI) mesencephalon, (VII, VIII) prosencephalon, (IX) pituitary, and (X) retina. There were three noteworthy features of the 5HT system in the Atlantic stingray: (1) 5HT cells were demonstrated in virtually every location in which 5HT-containing cells have been described or alluded to in the previous literature. The demonstration of immunopositive cells in the spinal cord, the retina, and the pars distalis of the pituitary suggests that 5HT may be an intrinsic neurotransmitter (or hormone) in these regions. (2) The distribution of 5HT cells in the brainstem shared many similarities with that in other vertebrates. However, there were many 5HT cells outside of the raphe nuclei, in the lateral tegmentum. It appears that the hypothesis that lateralization of the 5HT system is an advanced evolutionary trend cannot be supported. (3) 5HT fibers and terminals were more widely distributed in the Atlantic stingray brain than has been reported for other nonmammalian vertebrates on the basis of histofluorescence. It appears that this feature of the 5HT system arose early in phylogeny, and that the use of immunohistochemistry might reveal a more general occurrence of widespread 5HT fibers and terminals.
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    A documentation of an age related increase in neuronal and axonal numbers in the stingray, Dasyatis sabina, Leseuer
    (1978) Leonard, R.B.; Coggeshall, R.E.; Willis, W.D.; Journal of Comparative Neurology.
    The present study documents that in the stingray Dasyatis sabina the numbers of (1) dorsal root ganglion cells, (2) dorsal root axons, (3) ventral root axons, and (4) motor cells in the ventral horn increase steadily as the animals increase in size. This increase in axonal and neuronal numbers persists much further into adult life than is the case for other vertebrates that have been studied from this point of view. We hypothesize this steady increase in axonal numbers may be related to the ability of fish to regenerate parts of their central and/or peripheral nervous systems.
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    Evidence for two pharmacologically distinct populations of glutamate-activated first order interneurons in a vertebrate spinal cord.
    (Alan R. Liss, Incorporated, 1987) Gannon, R.L.; Leonard, R.B.; Excitatory amino acid transmission.
    The Atlantic stingray, Dasyatis sabina, is being employed as a simple vertebrate model for studying spinal cord circuitry. Current investigations are aimed at determining the role of excitatory amino acids in the production of spinal reflexes. It is generally believed that primary afferents in vertebrates release a transmitter, probably glutamate, onto first order interneurons which act on non-N-methyl-D-aspartate (NMDA) receptors (Davies and Watkins, 1983). In this communication we sought to test this hypothesis by assessing the pharmacological profile of glutamate-activated first order interneurons in the stingray spinal cord in vivo. Glutamate has been shown to be a mixed agonist on mammalian spinal neurons, capable of activating both NMDA and non-NMDA receptors (Mayer and Westbrook, 1985). By using the selective NMDA antagonist DL-2-amino-5-phosphonovaleric acid (APV) (Davies et al, 1981), and the nonselective excitatory amino acid antagonist kynurenate (Perkins and Stone, 1982) we are able to determine if glutamate is acting primarily on NMDA or non-NMDA receptors.
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    Immunocytochemical demonstration of serotonergic cells, terminals and axons in the spinal cord of the stingray, Dasyatis sabina.
    (1982) Ritchie, T.C.; Leonard, R.B.; Brain Research
    Serotonin-like immunoreactivity, as demonstrated by the PAP dorsal funiculi.
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    Immunocytochemical demonstration of serotonergic neurons and processes in the retina and optic nerve of the stingray, Dasyatis sabina.
    (1983) Ritchie, T.C.; Leonard, R.B.; Brain Research
    Neurons and processes in the stingray retina can be stained using PAP immunohistochemistry and an antibody to serotonin, without pharmacological pretreatment. Most of the cell bodies are in the inner nuclear layer while the processes ramify in the inner plexiform layer suggesting the presence of a population of serotonin containing amacrine cells in this species. Scattered immunopositive axons were observed in the optic nerve from the optic chiasm to the optic nerve head.
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    Immunohistochemical studies on the distribution and origin of candidate peptidergic primary afferent neurotransmitters in the spinal cord of an elasmobranch fish, the Atlantic Stingray (Dasyatis sabina).
    (1983) Ritchie, T.C.; Leonard, R.B.; Journal of Comparative Neurology.
    The distribution and origin of four peptide neurotransmitter candidates of primary afferents (substance P, SP; somatostatin, SS; cholecystokinin, CCK; and vasoactive intestinal polypeptide, VIP) were studied in the stingray with peroxidase-antiperoxidase(PAP) immunohistochemistry. This elasmobranch has virtually no unmyelinated primary afferents, having instead only large and small myelinated afferents. SP-like immunoreactivity was distributed densely in the superficial aspect of the substantia gelatinosa (SG), particularly laterally, and was ventral horn. The distributions of SS-, CCK-,and VIP-like immunoreactivities were similar to each other, but different from that of SP. Stained fibers appeared to issue from a prominent tract in the dorsolateral funiculus to form a plexus at the lateral margin of the nucleus proprius. The fibers spread dorsally and medially through the SG to terminate in a thin band at the superficial margin of the SG. Both SS and CCK were more dense within this structure. The remaining regions of the spinal gray matter contained immunoreactive fibers and terminals in variable densities. Many SS-positive cell bodies were observed in the ventral horn, in the deep dorsal horn, and in the ependymal latyer. CCK-positive cells were observed in the medial ventral horn, and VIP-positive cells were observed subjacent to the SG and within the dorsolateral funiculus. After unilateral SP appears to be a candidate primary afferent transmitter.
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    Induction of swimming in the high spinal stingray by L-DOPA.
    (1981) Williams, B.J.; Droge, M.H.; Hester, K.; Leonard, R.B.; Brain Research
    Stingrays with high spinal transections, which do not spontaneously locomote, can be induced to swim by intravenous injection of L-DOPA. The L- DOPA-induced swim of the spinal animal is associated with patterns of EMG activity that appear similar to those of the spontaneous swim of the decerebrate preparation. However, in contrast to the decerebrate condition, the L-DOPA-induced cycles of swimming are slower and less vigorous. Furthermore, secondary periodicities and altered intersegmental timing relationships are also evident.
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    Intracellular recording from pectoral fin motoneurons of the stingray, Dasyatis sabina, an elasmobranch fish.
    (1984) Williams, B.J.; Droge, M.H.; Leonard, R.B.; Journal of Neurophysiology.
    No abstract available
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    Locomotion evoked by stimulation of the brain stem in the Atlantic Stingray, Dasyatis sabina.
    (1990) Livingston, C.A.; Leonard, R.B.; Journal of Neuroscience.
    The primary pathway descending to the spinal cord to initiate locomotion in the stingray is located in the intermediate to ventral portion of the lateral funiculus; a second pathway is located in the dorsolateral funiculus. The goal of this study was to identify the origins of these pathways in the rhombencephalic reticular formation (RF). To do this we used microstimulation of the RF in conjunction with selective lesions of the brain stem and spinal cord. In some animals microinjections of excitatory amino acids were used to avoid stimulating axons of passage. Locomotion in the contralateral pectoral fin was evoked by microstimulation of the dorsal and ventral reticular nuclei, the middle and superior RF, and the ventral portion of the lateral RF. The regions from which locomotion was evoked by chemical stimulation were more restricted and included the rostral dorsal reticular nucleus, the middle RF, and the adjacent ventral lateral RF. This area incompasses the magnocellular RF and coincides with the distribution of numerous reticulospinal cells that project ipsilaterally into the ventral half of the lateral funiculus. Our results indicate, then , that locomotion in the stingray is mediated primarily by a pathway originating in the magnocellular RF that descends ipsilaterally in the ventral half of the lateral funiculus to elicit swimming in the contralateral pectoral fin. We suggest that this primary pathway is specifically associated with the control of locomotion. We also demonstrated that locomotion can be evoked independently from the lateral RF, but is probably mediated by an indirect pathway relaying near the spinomedullary junction or in the rostral spinal cord.
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    Organization of peripheral nerves and spinal roots of the Atlantic stingray, Dasyatis sabina.
    (1978) Coggeshall, R.E.; Leonard, R.B.; Applebaum, M.L.; Willis, W.D.; Journal of Neurophysiology.
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    Organization of spinal motor nuclei in the stingray, Dasyatis sabina.
    (1983) Droge, M.H.; Leonard, R.B.; Brain Research
    The Atlantic stingray, Dasystis sabina, has enlarged pectoral fins consisting of a series of antagonist dorsal (elevator) and ventral (depressor) muscles. Each muscle is divided into superficial and deep components. The retrograde transport of horseradish peroxidase (HRP) was used to determine the organization of motoneuron pools innervating fin and epaxial muscles. HRP applied to a single peripherial nerve labeled motoneurons within a single spinal segment. Following intramuscular injection of HRP, 3 distinct cell groups were identified in the transverse plane. Motoneurons innervating elevator muscles were lateral in the ventral horn, while motoneurons innervating depressor muscles were dorsomedial. The epaxial muscles were found to be innervated by a distinct cell column along the ventral border of the ventral horn. Separate injections of the superficial and deep bundles of the elevator muscle resulted in considerable overlap in the distribution of labeled motoneurons. Some areas for both elevator and depressor motoneurons were unimodally distributed. The mean cell diameters were 33.6 and 31.8 micrometers respectively. Motoneurons innervating the superficial and deep bundles of elevator muscle also had similar size distributions. The location of motoneurons innervating elevator and depressor fin muscles in the stingray supports the hypothesis that motoneurons innervating muscle derived from the dorsal premuscle mass are located laterally in the ventral horn while motoneurons innervating muscle derived from the ventral premuscle mass are located medially.
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    The organization of the electromotor nucleus and extraocular motor nuclei in the stargazer (Astroscopus y-graecum).
    (1979) Leonard, R.B.; Willis, W.D.; Journal of Comparative Neurology.
    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, the 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.
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    The organization of the extraocular motor nuclei in the Atlantic stingray, Dasyatis sabina.
    (1980) Rosiles, J.R.; Leonard, R.B.; Journal of Comparative Neurology.
    Retrograde transport of HRP was used to determine the location and organization of the motor nuclei innervating the extrinsic eye muscles of the stingray, and elasmobrach fish. Oculomotor neurons are located both medial to and immediately ventrolateral to the MLF in the rostral midbrain. A ventral oculomotor nucleus was found among the IIIrd nerve rootlets close to the base of the midbrain. The dendrites of cells in the dorsal nucleus appear to be preferentially oriented in the transverse plane penetrating the MLF. Motorneuron pools innervating individual muscles are incompletely segregated in the dorsal group. However, the ventral nucleus innervates only the inferior oblique muscle. Dorsally, motorneurons innervating a single muscle are found on both sides of the MLF. In the caudal midbrain, the majority of trochlear motorneurons are scattered in the medulla from a ventrolateral position resembling the location of the nucleus in teleost fish to a dorsomedial position close to the MLF as in most other vertebrates. In contrast to other vertebrates, the medial rectus muscle is innervated by the contralateral oculomotor nucleus. Motorneurons innervating the other muscles have the same laterality as found in other vertebrates.
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    Spinal cord pathways involved in initiation of swimming in the stingray, Dasyatis sabina: spinal cord stimulation and lesions.
    (1984) Williams, B.J.; Livingston, C.A.; Leonard, R.B.; Journal of Neurophysiology.
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    Swimming pattern in intact and decerebrated stingrays.
    (1983) Droge, M.H.; Leonard, R.B.; Journal of Neurophysiology.
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    Swimming rhythm in decerebrated, paralyzed stingrays: normal and abnormal coupling.
    (1983) Droge, M.H.; Leonard, R.B.; Journal of Neurophysiology.
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    Tonic descending inhibition in the stingray's spinal cord.
    (1985) Livingston, C.A.; Leonard, R.B.; Brain Research
    Reflexes elicited by peripheral nerve stimulation were compared in decerebrated stingrays with the spinal cord intact, after a lesion of the dorsal spinal cord and after spinal transection. Reflexes elicited in decerebrated stingrays are tonically inhibited. Lesions of the dorsal spinal cord release this tonic descending inhibiton. The tonic descending inhibitory system in stingrays is comparable to that of mammals.