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Barkan CL, Zornik E. Feedback to the future: motor neuron contributions to central pattern generator function. ACTA ACUST UNITED AC 2019; 222:222/16/jeb193318. [PMID: 31420449 DOI: 10.1242/jeb.193318] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Motor behaviors depend on neural signals in the brain. Regardless of where in the brain behavior patterns arise, the central nervous system sends projections to motor neurons, which in turn project to and control temporally appropriate muscle contractions; thus, motor neurons are traditionally considered the last relay from the central nervous system to muscles. However, in an array of species and motor systems, an accumulating body of evidence supports a more complex role of motor neurons in pattern generation. These studies suggest that motor neurons not only relay motor patterns to the periphery, but directly contribute to pattern generation by providing feedback to upstream circuitry. In spinal and hindbrain circuits in a variety of animals - including flies, worms, leeches, crustaceans, rodents, birds, fish, amphibians and mammals - studies have indicated a crucial role for motor neuron feedback in maintaining normal behavior patterns dictated by the activity of a central pattern generator. Hence, in this Review, we discuss literature examining the role of motor neuron feedback across many taxa and behaviors, and set out to determine the prevalence of motor neuron participation in motor circuits.
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Affiliation(s)
| | - Erik Zornik
- Biology Department, Reed College, Portland, OR 97202, USA
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2
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Deardorff AS, Romer SH, Sonner PM, Fyffe REW. Swimming against the tide: investigations of the C-bouton synapse. Front Neural Circuits 2014; 8:106. [PMID: 25278842 PMCID: PMC4167003 DOI: 10.3389/fncir.2014.00106] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 08/17/2014] [Indexed: 11/19/2022] Open
Abstract
C-boutons are important cholinergic modulatory loci for state-dependent alterations in motoneuron firing rate. m2 receptors are concentrated postsynaptic to C-boutons, and m2 receptor activation increases motoneuron excitability by reducing the action potential afterhyperpolarization. Here, using an intensive review of the current literature as well as data from our laboratory, we illustrate that C-bouton postsynaptic sites comprise a unique structural/functional domain containing appropriate cellular machinery (a “signaling ensemble”) for cholinergic regulation of outward K+ currents. Moreover, synaptic reorganization at these critical sites has been observed in a variety of pathologic states. Yet despite recent advances, there are still great challenges for understanding the role of C-bouton regulation and dysregulation in human health and disease. The development of new therapeutic interventions for devastating neurological conditions will rely on a complete understanding of the molecular mechanisms that underlie these complex synapses. Therefore, to close this review, we propose a comprehensive hypothetical mechanism for the cholinergic modification of α-MN excitability at C-bouton synapses, based on findings in several well-characterized neuronal systems.
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Affiliation(s)
- Adam S Deardorff
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Shannon H Romer
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Patrick M Sonner
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Robert E W Fyffe
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
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3
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Saywell SA, Ford TW, Kirkwood PA. Axonal projections of Renshaw cells in the thoracic spinal cord. Physiol Rep 2013; 1:e00161. [PMID: 24400162 PMCID: PMC3871475 DOI: 10.1002/phy2.161] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2013] [Revised: 10/17/2013] [Accepted: 10/18/2013] [Indexed: 02/01/2023] Open
Abstract
Renshaw cells are widely distributed in all segments of the spinal cord, but detailed morphological studies of these cells and their axonal branching patterns have only been made for lumbosacral segments. For these, a characteristic distribution of terminals was reported, including extensive collateralization within 1-2 mm of the soma, but then more restricted collaterals given off at intervals from the funicular axon. Previous authors have suggested that the projections close to the soma serve inhibition of motoneurons (known to be greatest for the motor nuclei providing the Renshaw cell excitation) but that the distant projections serve mainly the inhibition of other neurons. However, in thoracic segments, inhibition of motoneurons is known to occur over two to three segments (20-40 mm) from the presumed somatic locations of the Renshaw cells. Here, we report the first detailed morphological study of Renshaw cell axons outside the lumbosacral segments, which investigated whether this different distribution of motoneuron inhibition is reflected in a different pattern of Renshaw cell terminations. Four Renshaw cells in T7 or T8 segments were intracellularly labeled with neurobiotin in anesthetized cats and their axons traced for distances ≥6 mm from the somata. The only morphological difference detected within this distance in comparison with Renshaw cells in the lumbosacral cord was a minimal taper in the funicular axons, where in the lumbosacral cord this is pronounced. Patterns of termination were virtually identical to those in the lumbosacral segments, so we conclude that these patterns are unrelated to the pattern of motoneuronal inhibition.
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Affiliation(s)
- Shane A Saywell
- School of Health Sciences, Queen's Medical Centre, University of Nottingham Nottingham, NG7 2HA, U.K
| | - Timothy W Ford
- School of Health Sciences, Queen's Medical Centre, University of Nottingham Nottingham, NG7 2HA, U.K
| | - Peter A Kirkwood
- Sobell Department for Motor Neuroscience and Movement Disorders, UCL Institute of Neurology Queen Square, London, WC1N 3BG, U.K
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4
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Pullen AH, Athanasiou D. Increase in presynaptic territory of C-terminals on lumbar motoneurons of G93A SOD1 mice during disease progression. Eur J Neurosci 2009; 29:551-61. [DOI: 10.1111/j.1460-9568.2008.06602.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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5
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Abstract
Renshaw cell properties have been studied extensively for over 50 years, making them a uniquely well-defined class of spinal interneuron. Recent work has revealed novel ways to identify Renshaw cells in situ and this in turn has promoted a range of studies that have determined their ontogeny and organization of synaptic inputs in unprecedented detail. In this review we illustrate how mature Renshaw cell properties and connectivity arise through a combination of activity-dependent and genetically specified mechanisms. These new insights should aid the development of experimental strategies to manipulate Renshaw cells in spinal circuits and clarify their role in modulating motor output.
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Affiliation(s)
- Francisco J Alvarez
- Department of Neuroscience, Cell Biology & Physiology, Boonshoft School of Medicine, Wright State University, 3640 Col. Glenn Hwy, Dayton, OH 45435, USA.
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Mentis GZ, Siembab VC, Zerda R, O'Donovan MJ, Alvarez FJ. Primary afferent synapses on developing and adult Renshaw cells. J Neurosci 2007; 26:13297-310. [PMID: 17182780 PMCID: PMC3008340 DOI: 10.1523/jneurosci.2945-06.2006] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The mechanisms that diversify adult interneurons from a few pools of embryonic neurons are unknown. Renshaw cells, Ia inhibitory interneurons (IaINs), and possibly other types of mammalian spinal interneurons have common embryonic origins within the V1 group. However, in contrast to IaINs and other V1-derived interneurons, adult Renshaw cells receive motor axon synapses and lack proprioceptive inputs. Here, we investigated how this specific pattern of connectivity emerges during the development of Renshaw cells. Tract tracing and immunocytochemical markers [parvalbumin and vesicular glutamate transporter 1 (VGLUT1)] showed that most embryonic (embryonic day 18) Renshaw cells lack dorsal root inputs, but more than half received dorsal root synapses by postnatal day 0 (P0) and this input spread to all Renshaw cells by P10-P15. Electrophysiological recordings in neonates indicated that this input is functional and evokes Renshaw cell firing. VGLUT1-IR bouton density on Renshaw cells increased until P15 but thereafter decreased because of limited synapse proliferation coupled with the enlargement of Renshaw cell dendrites. In parallel, Renshaw cell postsynaptic densities apposed to VGLUT1-IR synapses became smaller in adult compared with P15. In contrast, vesicular acetylcholine transporter-IR motor axon synapses contact embryonic Renshaw cells and proliferate postnatally matching Renshaw cell growth. Like other V1 neurons, Renshaw cells are thus competent to receive sensory synapses. However, after P15, these sensory inputs appear deselected through arrested proliferation and synapse weakening. Thus, Renshaw cells shift from integrating sensory and motor inputs in neonates to predominantly motor inputs in adult. Similar synaptic weight shifts on interneurons may be involved in the maturation of motor reflexes and locomotor circuitry.
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Affiliation(s)
- George Z. Mentis
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Valerie C. Siembab
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
| | - Ricardo Zerda
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
| | - Michael J. O'Donovan
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Francisco J. Alvarez
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
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7
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Pullen AH, Tucker D, Martin JE. Morphological and morphometric characterisation of Onuf's nucleus in the spinal cord in man. J Anat 1997; 191 ( Pt 2):201-13. [PMID: 9306197 PMCID: PMC1467673 DOI: 10.1046/j.1469-7580.1997.19120201.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In the absence of a systematic morphometric study of Onuf's nucleus in man, this investigation defines the limits of variation of segmental position and the range of length and volume of Onuf's nucleus in 6 normal humans displaying no neurological disease (2 males, 4 females). Serial section reconstruction methods in conjunction with the disector method provided information on the numbers, sizes and shapes of the constituent motor neurons of Onuf's nucleus. In contrast to previous descriptions, the cranial origin of Onuf's nucleus occurred in rostral S1 in 50% of subjects, and midcaudal S1 in the remaining subjects. Onuf's nucleus varied in length between 4 and 7 mm, and was 0.2-0.37 mm3 in volume. Differences in length or volume between males or females, or between the left and right side of the cord were not statistically significant. Neurons in Onuf's nucleus varied in diameter between 10 microns and 60 microns (mean 26 microns) and their mean number was 625 +/- 137. A higher density of neurons occurred at the cranial and caudal ends of the nucleus relative to the middle. While 37% of neurons were approximately spherical (shape index approximately 1), 44% were ellipsoid and 19% fusiform (shape indices varying between 0.26 and 0.8). These findings are compared with previous studies of Onuf's nucleus in man and animals. The results form a basis for further studies on Onuf's nucleus in normality and neurodegenerative diseases.
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Affiliation(s)
- A H Pullen
- Sobell Department of Neurophysiology, Institute of Neurology, London, UK.
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8
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Ramírez-León V, Ulfhake B, Arvidsson U, Verhofstad AA, Visser TJ, Hökfelt T. Serotoninergic, peptidergic and GABAergic innervation of the ventrolateral and dorsolateral motor nuclei in the cat S1/S2 segments: an immunofluorescence study. J Chem Neuroanat 1994; 7:87-103. [PMID: 7528512 DOI: 10.1016/0891-0618(94)90010-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Indirect single- and double-staining immunofluorescence techniques were used to study the serotoninergic, peptidergic and GABAergic innervation of the ventrolateral (Onuf's nucleus) and dorsolateral (innervating intrinsic foot sole muscles) nuclei, located in the S1/S2 segments of the cat spinal cord. The relative density of 5-hydroxytryptamine-, thyrotropin-releasing hormone-, substance P- and gamma-aminobutyric acid-immunoreactive axonal varicosities was similar in both nuclei. The highest relative density was recorded for varicosities immunoreactive to gamma-aminobutyric acid, while those immunoreactive to 5-hydroxytryptamine or thyrotropin-releasing hormone yielded the lowest values. The density of enkephalin-immunoreactive varicosities was higher in the ventrolateral than in the dorsolateral nucleus. Calcitonin gene-related peptide-like immunoreactivity could be seen in neurons of the ventrolateral and dorsolateral nuclei. Occasionally, calcitonin gene-related peptide-immunoreactive axonal fibers were also encountered in these nuclei. Virtually all thyrotropin-releasing hormone-immunoreactive varicosities in the ventrolateral and dorsolateral nuclei also contained 5-hydroxytryptamine-like immunoreactivity, while a somewhat smaller number of them were co-localized with substance P. About 5-10% of the 5-hydroxytryptamine-immunoreactive varicosities were devoid of peptide-like immunoreactivity, and the number of 5-hydroxytryptamine-immunoreactive varicosities lacking thyrotropin-releasing hormone-like immunoreactivity was higher in the dorsolateral than in the ventrolateral nucleus. Finally, the free fraction of substance P-immunoreactive varicosities, i.e., those lacking both 5-hydroxytryptamine and thyrotropin-releasing hormone, was about 39% in the ventrolateral and 26% in the dorsolateral nucleus. Spinal cord transection at the lower thoracic level induced a depletion of 5-hydroxytryptamine and thyrotropin-releasing hormone-immunoreactive fibers from the ventrolateral and dorsolateral nuclei, indicating an exclusive supraspinal origin for these fibers. A reduction in substance P-like immunoreactivity following spinal cord transection alone or spinal cord transection combined with unilateral dorsal rhizotomy was also detected in both nuclei, suggesting a dual origin for substance P-immunoreactive fibers, i.e., both supra- and intraspinal. The decrease in number of substance P-immunoreactive fibers was however smaller than expected from the analysis of the fraction of substance P-immunoreactive fibers co-localized with 5-hydroxytryptamine, indicating thus that the experimental lesions may have triggered a sprouting of substance P-immunoreactive axons originating from spinal cord sources. The distribution of gamma-aminobutyric acid in the ventrolateral and dorsolateral nuclei was not affected by the different lesion paradigms. It is therefore assumed that these inputs are intrinsic to the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- V Ramírez-León
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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9
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Pullen AH, Martin JE, Swash M. Ultrastructure of pre-synaptic input to motor neurons in Onuf's nucleus: controls and motor neuron disease. Neuropathol Appl Neurobiol 1992; 18:213-31. [PMID: 1630576 DOI: 10.1111/j.1365-2990.1992.tb00784.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Ultrastructural analyses of sphincteric motoneurons in Onuf's nucleus at S2 were undertaken in human spinal cord obtained 3-6 h post-mortem from three subjects with no neurological disease ('controls') and five in which death was due to motor neuron disease (MND). Neurons in specified locations within Onuf's nucleus of control subjects ranged between 17.8 and 71.7 microns diameter (mean 38.6 microns). Analyses of synaptology revealed five ultrastructural classes of presynaptic terminal synapsing with the neuronal surface membrane. When classified by size, vesicle morphology, and synaptic site structure these conformed to the S, F, T, M and C-terminals defining somatic motoneurons. No terminals characteristic of autonomic motoneurons were found. In MND subjects, neurons in Onuf's nucleus at S2 were preserved despite a paucity of neurons in medial and lateral motor nuclei and were of similar size range to those in control subjects. The morphological classes of pre-synaptic terminal found in controls, also characterized sphincteric motoneurons in MND subjects, including the C-type terminal. The presence of C-terminals indicates (i) that sphincteric motoneurons are somatic alpha-motoneurons, and (ii) that hypotheses explaining the survival of sphincteric motoneurons in MND on the basis of Onuf's nucleus being an extension of the pre-ganglionic parasympathetic nucleus, or having intrinsic autonomic properties are incorrect.
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Affiliation(s)
- A H Pullen
- Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, London
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10
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Affiliation(s)
- U Windhorst
- Zentrum Physiologie und Pathophysiologie der Universität Göttingen, Abteilung Neuro- und Sinnesphysiologie, F.R.G
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11
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Fung SJ, Pompeiano O, Barnes CD. Coerulospinal influence on recurrent inhibition of spinal motonuclei innervating antagonistic hindleg muscles of the cat. Pflugers Arch 1988; 412:346-53. [PMID: 3174390 DOI: 10.1007/bf01907550] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The locus coeruleus's (LC's) effect on recurrent inhibition of gastrocnemius-soleus (GS) and common peroneal (CP) monosynaptic reflexes (MSRs) was demonstrated to exceed the concomitant facilitation, indicating the independency of LC's disinhibition and facilitation measures in this study. In contrast, the disinhibition effect correlated closely with the recurrently inhibited MSRs. The disinhibition phenomenon was also accompanied by progressive delay and diminution in the Renshaw cell field potential. Hence, the recovery of recurrently inhibited MSRs was probably due, in part at least, to the LC's inhibition of the related Renshaw cell activity. Furthermore, the site-specific, discordant changes in the disinhibition of GS, compared with CP MSRs, as revealed by tracking studies imply that representations of these antagonistic motonuclei may occupy different LC loci. Accordingly, the nonuniform disinhibition may be due to the activation of discrete aggregates of LC neurons which are responsible predominantly in controlling the recurrent inhibitory pathway belonging to one or the other of the antagonistic motonuclei. These findings support a differential LC inhibitory control of Renshaw cell activity, releasing the related motoneurones for the Ia synaptic transmission - a disinhibitory process that is crucial for the LC's independent control of the recurrent circuit of antagonistics extensor and flexor motoneurons.
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Affiliation(s)
- S J Fung
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, College of Veterinary Medicine, Washington State University, Pullman 99164-6520
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12
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Pullen AH. Quantitative synaptology of feline motoneurones to external anal sphincter muscle. J Comp Neurol 1988; 269:414-24. [PMID: 3372721 DOI: 10.1002/cne.902690308] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Motoneurones innervating the cat external anal sphincter muscle were labelled retrogradely following intramuscular injections with horseradish peroxidase (HRP). Labelled motoneurones were examined by correlative light and electron microscopy (LM and EM) with special regard to a qualitative and morphometric analysis of the axon terminals resident on the neuronal membrane. By LM, labelled motoneurones were (1) ipsilateral to the injections; (2) all in S1-S2; (3) found only in the superior dorsomedial region of Onuf's nucleus; and (4) exhibited a broad spectrum of diameters (25-72 micron, mean 47.4 +/- 11.3 micron). By EM, axon terminals on the neuronal membrane when classified according to size, vesicle shape, and synaptic complex ultrastructure conformed to the S-, F-, T-, M-, and C-type terminals previously described for cat lumbosacral motoneurones. C-terminals confirmed these sphincteric motoneurones to be skeletomotor. Pooled data from midnuclear sections through 15 random labelled motoneurones (20-64-micron diameter) revealed that S- and F-type terminals predominated, with numerically few M and C types. Notwithstanding their low frequency (0.3/100 micron membrane) C-terminals contributed 1% of the mean areal coverage by terminals, which implies a potentially larger synaptic influence relative to other terminal types. Linear relationships occurred between terminal frequency (or cover) and motoneurone diameter. While motoneurones greater than 40 micron in diameter exhibited all five terminal types, labelled motoneurones less than or equal to 30 micron generally possessed only S-, F-, and occasional T-type terminals, and in this respect resembled gamma motoneurones.
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Affiliation(s)
- A H Pullen
- Sobell Department of Neurophysiology, Institute of Neurology, London, England
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13
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Takasu N, Nakatani T, Arikuni T, Kimura H. Immunocytochemical localization of gamma-aminobutyric acid in the hypoglossal nucleus of the macaque monkey, Macaca fuscata: a light and electron microscopic study. J Comp Neurol 1987; 263:42-53. [PMID: 3667970 DOI: 10.1002/cne.902630104] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The hypoglossal nucleus of the macaque monkey Macaca fuscata was investigated with light and electron microscopic immunocytochemistry with an antibody directed against gamma-aminobutyric acid (GABA). At the light microscopic level, GABA immunoreactivity was present in small neurons, punctate structures, and thin, fiberlike structures. These GABA-positive elements were distributed throughout the hypoglossal nucleus at rostrocaudal levels. There was no immunoreactivity in the hypoglossal motoneurons. The GABA-positive small neurons were fusiform or ovoid (15 X 9 micron) and extended a few proximal dendrites from both poles. At the ultrastructural level, these small neurons were characterized by a markedly invaginated nucleus and a scanty cytoplasm in which cisternae of rough endoplasmic reticulum were not organized into extensive lamellar arrays as seen in the motorneurons. The GABA-positive punctate structures at the light microscopic level were identified as vesicle-containing axon boutons at the electron microscopic level. These GABA-positive axon terminals made synaptic contacts mainly with the dendrites of the motoneurons and infrequently with the somata. The majority of them made symmetric synapses and they contained pleomorphic synaptic vesicles. However, a small number of GABA-positive terminals (7%) formed asymmetric synapses with the dendrites of motoneurons, and these contacts exhibited postsynaptic dense bars or Taxi bodies lying beneath the postsynaptic membranes. There were no GABA-positive boutons that contacted the cell bodies of the small neurons. Although GABA-positive myelinated and unmyelinated axons were seen as thin, fiberlike structures, these myelinated and unmyelinated axons rarely gave rise to boutons on the motoneurons. The present study suggests that GABAergic inhibition in the monkey hypoglossal nucleus occurs mainly on the dendrites of the motoneurons and to some extent on the somata.
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Affiliation(s)
- N Takasu
- Department of Anatomy, Osaka University Medical School, Japan
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14
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Lagerbäck PA, Kellerth JO. Light microscopic observations on cat Renshaw cells after intracellular staining with horseradish peroxidase. I. The axonal systems. J Comp Neurol 1985; 240:359-67. [PMID: 3880355 DOI: 10.1002/cne.902400404] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Five intracellularly HRP-stained Renshaw cells were subjected to light microscopic analysis of the trajectories, branching patterns, and projections of the axonal systems. The cell bodies were located ventrally in lamina VII. In three neurons the axon originated from the cell body and in the remaining two cells from a dendrite. After a 600-870-microns distance the axons entered the ventral funiculus, where all of them continued rostrally. Two axons also gave off a caudal branch in the funiculus. The diameters of the main axons varied between 2.1 and 10.0 microns. The main axons gave off one to four first-order collaterals before entering the ventral funiculus and up to three collaterals could be seen to originate from the same node of Ranvier. In the ventral funiculus up to five first-order collaterals could be traced from the same main axon. The axon collateral trees were often very extensive and daughter branches up to the 22nd order were observed. The distance between two successive branching points varied between 4 and 410 microns. A large number of boutonlike swellings were found along (59%) or at the ends of the collateral branches. At the most, 1,278 swellings originated from a single axon collateral tree. Most of the swellings were located in lamina IX, but they also appeared ventrally and dorsolaterally in lamina VII.
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Affiliation(s)
- P A Lagerbäck
- Department of Anatomy, Karolinska Institutet, Stockholm, Sweden
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15
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Lagerbäck PA, Kellerth JO. Light microscopic observations on cat Renshaw cells after intracellular staining with horseradish peroxidase. II. The cell bodies and dendrites. J Comp Neurol 1985; 240:368-76. [PMID: 3880356 DOI: 10.1002/cne.902400405] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The cell bodies and dendritic trees of five lumbosacral Renshaw cells of adult cats were studied in the light microscope (LM) after intracellular injection with horseradish peroxidase (HRP). The cell bodies were all located in the ventral part of lamina VII. The dendrites extended up to 0.7 mm from the cell body into the neighbouring parts of laminae VIII and IX as well as into more dorsal parts of lamina VII. The dendritic branching was sparse and about half the dendrites were unbranched. The mean diameter of the cell body was positively correlated to both the combined and mean diameters of the first-order dendrites. Between four and eight dendrites originated from the cell bodies. The number of dendritic end-branches, the combined dendritic length, the mean dendritic length from the cell body to the termination of the end branches, the distance from the cell body to the termination of the most remote end-branch, the dendritic surface area, and the dendritic volume all correlated positively with the diameter of the parent first-order dendrite. The dendritic tapering was somewhat more pronounced in the Renshaw cells than previously observed in alpha- and gamma-motoneurons. The present data are discussed in relation to previous morphological observations on Renshaw cells and alpha- and gamma-motoneurons.
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Affiliation(s)
- P A Lagerbäck
- Department of Anatomy, Karolinska Institutet, Stockholm, Sweden
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16
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Lagerbäck PA. An ultrastructural study of cat lumbosacral gamma-motoneurons after retrograde labelling with horseradish peroxidase. J Comp Neurol 1985; 240:256-64. [PMID: 4067010 DOI: 10.1002/cne.902400304] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Twelve retrogradely horseradish peroxidase (HRP)-labelled triceps surae motoneurons of gamma size (mean cell body diameter less than 38 micron) were studied ultrastructurally. The contours of the cell bodies, as observed in the transverse midnucleolus plane, were elongated to rounded. The axons identified all originated from the cell body. The mean diameter of the stem dendrites was 4.5 micron. A substantial part of the cell membrane was covered by glial extensions. The boutons and synaptic contacts apposing the gamma-motoneurons could be classified into two categories on the basis of the type of synaptic vesicles: S-type boutons with spherical synaptic vesicles and F-type boutons with flattened vesicles. In each neuron, the values for mean length and mean area of apposition, percentage synaptic covering, and packing density of S-type, F-type, and S+F-type boutons were estimated on the cell body and in two dendritic compartments. In comparison with alpha-motoneurons and Renshaw cells, the cell bodies of the gamma-motoneurons were covered by smaller and strikingly fewer boutons of both the S- and F-types. The values for percentage synaptic covering and packing density of boutons on the proximal dendrites were also lower for gamma-motoneurons than for both alpha-motoneurons and Renshaw cells, although the differences were less pronounced than on the cell body. No boutons of the C-, M-, and T-types described for alpha-motoneurons were found on the gamma-motoneurons.
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17
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Lagerbäck PA. An ultrastructural study of serially sectioned Renshaw cells. III. Quantitative distribution of synaptic boutons. Brain Res 1983; 264:215-23. [PMID: 6850294 DOI: 10.1016/0006-8993(83)90819-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The quantitative distribution of synaptic boutons on 17 presumed Renshaw cells has been studied ultrastructurally. All 17 neurons were postsynaptic to axon collateral boutons of intracellularly HRP-stained triceps surae alpha-motoneurons and were located in lamina VII, ventromedially to the main motor nuclei. In each of the presumed Renshaw cells, the values for mean length and mean area of apposition, percentage synaptic covering, and packing density of S-type, F-type, and S + F-type boutons were estimated on the cell body and in two dendritic compartments. The F/S percentage synaptic covering ratio was also calculated. The previously demonstrated differences within the present group of neurons, with respect to the site of axonal origin, were not accompanied by any corresponding differences in the quantitative distribution of synaptic boutons. However, it is suggested that the presumed Renshaw cells may possibly fall into two categories with respect to the F/S percentage synaptic covering ratio. The results are discussed in relation to previous studies on the neuronal architecture and synaptic types on the same presumed Renshaw cells, as well as in relation to earlier observations on the quantitative distribution of boutons on central neurons, particularly spinal alpha-motoneurons.
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