Spinal Cord Injury Dendritic Spines

Dendritic spines, Rac 1 Dendritic spines, Dendritic spines, Dendritic spines Rac 1 and Neuropathic Pain after Spinal Cord Injury

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http://www.neuroscience-bucharest.blogspot.com

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Dendritic Spines, RAC 1 and Neurophatic Pain after Spinal Cord Injury

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Dendritic Spines, RAC 1 and Neurophatic Pain after Spinal Cord InjuryDendritic Spines, RAC 1 and Neurophatic Pain after Spinal Cord Injury

Spinal cord injury and Rac1 .......................... 2

Dendritic Spines and PSD...............................4

Rho family of GTPases.....................................5

Actin regulatory pathways.........................................8

Dorsal horn neuronal network ......................9

Medication in SCI......................................... 12

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Spinal cord injury (SCI) could determine dendritic spines remodeling and can contribute to neu-ronal hyperexcitability and neuropathic pain through synaptic changes. Synaptic plasticity induced by SCI may appear in the spinal cord dorsal horn and may contrib-ute to pain maintenance [1,2]. SCI increases Rac1 mRNA expression, which remains elevated for up to 3 months [3]. A role of Rac1, in neuropathic pain after SCI is not studied enough. Rac1 can modulate dendritic spine mor-phology and function [4, 5]. Andrew M. Tan et al (2008) applied the Rac1-speci�c inhibitor NSC23766 in order to study the e�ect of synaptic remodeling in neuropathic pain after SCI. Rac1-speci�c inhibitor NSC23766 blocks guanine exchange factors (GEFs), Trio and Tiam1. Inhi-bition of the Rac1 signaling cascade ameliorated the development of abnormal spine morphologies, reduced neuronal excitability, and normalized nociceptive thresh-olds. [6] PSD-95 expression is a marker of sites of synapse plasticity. Expression of PSD-95 is increased signi�cantly in injured spinal cord tissue compared with uninjured controls [6]. NSC23766 treatment reduces PSD-95 levels below that of uninjured levels . Cortactin levels did not signi�cantly change after NSC23766 treatment compared with intact animals.Dendritic spine density increases after SCI. In SCI plus veh animals (0.9% saline), the density of spines signi�cantly shift toward the cell body compared with the spine den-sity distribution in intact animals. An increase in spine density and redistribution of spine location relative to the cell body, and increases in spine length and head diam-eter after SCI) occurs after SCI in dorsal horn neurons.

Synaptic plasticity induced by SCI may appear in the spinal cord dorsal horn and may contribute to pain mainte-nance [1,2].

Inhibition of the Rac1 signaling cas-cade ameliorates the development of abnormal spine m o r p h o l o g i e s , reduced neuronal excitability, and nor-malized nociceptive thresholds. [6]

Dendritic spine density increases after experimentaly induced SCI in rats.

Rac1 (Ras-related C3 botulinum toxin substrate 1) is a small (~21 kDa) GTPase, and is a member of the Rac subfamily of the family Rho - family of GTPases. It is encoded by the gene RAC1.

Dendritic spines contain a cytoskeleton composed mostly of �lamentous actin (F-actin) which determines the shape and stability/motility of spines. Spines have a small amount of intermediate �laments and microtubules, ellements that are present in large mumber in the dendritic shaft .Barbara Calabrese, Margaret S. Wilson and Shelley Halpain Development and Regulation of Dendritic Spine Synapses, Physiology 21:38-47, 2006

Synaptic plasticity

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Rac1 could be interpreted as critical in maintaining neuro-pathic pain through its regulation of dendritic spines. WDR (Wide-Dynamic Range ) neurons exhibit hyperexcitability in response to evoked-innocuous and noxious stimulation after SCI. Also increased sensitivity to mechanical stimuli and reduced thermal nociceptive thresholds are found after SCI.NSC23766 is speci�c for Rac1 and does not interfere with cdc42 or RhoA-GEF or Rac1 binding to its e�ector PAK1. Andrew M. Tan et al (2008) conclude that a post-SCI shift in the number of mature spines may contribute to the strengthening of synaptic inputs, enhanced transmission �delity, and potentiation of electrical transduction, which together may lead to a pathological ampli�cation of sensory information after SCI [6].

1 .Woolf CJ, Shortland P, Coggeshall RE (1992) Peripheral nerve injury triggers central sprouting of myelinated a�er-ents. Nature 355:75–78.2. Kim BG, Dai HN, McAtee M, Vicini S, Bregman BS (2006) Remodeling of synaptic structures in the motor cortex follow-ing spinal cord injury. Exp Neurol 198:401– 415.3. Erschbamer MK, Hofstetter CP, Olson L (2005) RhoA, RhoB, RhoC, Rac1, Cdc42, and Tc10 mRNA levels in spinal cord, sensory ganglia, and corticospinal tract neurons and long-lasting speci�c changes following spinal cord injury. J Comp Neurol 484:224 –233.4. Nakayama AY, Harms MB, Luo L (2000) Small GTPases Rac and Rho in the maintenance of dendritic spines and branches in hippocampal pyramidal neurons. J Neurosci 20:5329 –5338.5. Wiens KM, Lin H, Liao D (2005) Rac1 induces the clustering of AMPA receptors during spinogenesis. J Neurosci 25:10627–10636.6. Andrew M. Tan, Severine Stamboulian, Yu-Wen Chang, Peng Zhao, Avis B. Hains,2 Stephen G. Waxman, and Bryan C. Hains, Neuropathic Pain Memory Is Maintained by Rac1-Regulated Dendritic Spine Remodeling after Spinal Cord Injury, The Journal of Neuroscience, 28(49):13173–13183 • 13173

Recordings were made in the lombar region of the rat spine, in the deep dorsal horn.

Andrew M. Tan et al (2008) conclude that a post-SCI shift in the number of mature spines may contribute to pathological am-pli�cation of sen-sory information after SCI [6].

Laminae I to IV comprise the dorsal horn and are concerned with somatosensory a�erent signaling. Lamina I and II (super�cial dorsal horn, SDH) receive input largely from thinly myelinated (Adelta) and unmyelinated (C) �bers of thermoreceptors and various nocicep-tors. Laminae III and IV (deep dorsal horn, DDH) receive their input from more myelinated (A) �bers that transmit vibration, touch, and pressure. B. A. Graham, A. M. Brichta, and R. J. Callister, Moving From an Averaged to Speci�c View of Spinal Cord Pain Processing Circuits, J Neurophysiol 98: 1057-1063, 2007.

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Dendritic spines are small protrusions from neuronal dendrites that typically receives input from the presynaptic component of the excitatory synapses in the central nervous system. They are located on the dendrites. The most common morphological type is composed of a bulbous head and a thin neck. The head is connected with the dendrite through the neck. There is a potential relation between spine shape and synaptic function, since mor-phological rearrangements of spines have been found in vitro and in vivo [1,2]. In samples of spines from layer 2/3 pyramidal neurons from mouse primary visual cortex, using �rst Golgi impregnations and then gold-toning and serial thin section electron microscopy, no detectable correlations between spine head volume and spine neck length were found [3]. The area of the PSD is correlated to the spine head volume and neck diameter and it is uncorre-lated with the spine neck length. In rat, in CA1 pyramidal cells, the volume of the spine head was reported to be proportional to the postsynaptic density (PSD) area and to the number of presynaptic vesicles [4]. The spine neck length is correlated to the time constant of calcium com-partmentalization [3] and also proportional to the �ltering of electrical potentials and it may be involved in calcium dependent learning rules. There is no correlation between head volume and neck length, although there is a weak correlation between head volume and neck diameter [3]. In neocortical pyramidal neurons spines that were further away from the soma were longer and had larger heads. In CA1 pyramidal neurons spines located in the distal portions of the apical dendrite had larger heads [6]. Similar e�ects were found in Golgi-impregnated CA1 pyramidal neurons, albeit not in neocortical pyramidal cells from layers 2/3, 4, 5, and 6 [7]. In spines from layer 2/3 pyramidal neurons, no signi�cant relation was found between distance from the soma and spine head volume, total spine volume and PSD area. There is correlation between spine head volume and the area of the PSD. It may be a correlation between the volume of the spine head and the synaptic strength or it may be linked to the release probability [5]. There is no clear correlation between the spine head volume and spine neck length. There is a lack of correlation between head volume and neck length (since the PSD area is correlated with the head volume) [5]. The PSD area is itself proportional to the number of postsynaptic receptors [8]. The volume of the spine head is likely to be directly proportional to the aver-age reliability and strength of its synapse. CA1 pyramidal neurons show a larger spine size with increasing distance from the soma [7, 6], as if synaptic weight is compensating for the dendritic electrotonic �ltering [5].

The PSD area is itself proportional to the number of postsynaptic recep-tors [8]. The volume of the spine head is likely to be directly proportional to the average reliability and strength of its synapse.

There is a potential relation between spine shape and synaptic function, since morphologi-cal rearrangements of spines have been found in vitro and in vivo [1,2].

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1. Dunaevsky A, Tashiro A, Majewska A, Mason C, and Yuste R. Develop-mental regulation of spine motility in the mammalian central nervous system. Proc Natl Acad Sci USA 96: 13438–13443, 19992. Fischer M, Kaech S, Knutti D, and Matus A. Rapid actin-based plasticity in dendritic spines. Neuron 20: 847–854, 1998.3. Barbara Calabrese, Margaret S. Wilson and Shelley Halpain, Develop-ment and Regulation of Dendritic Spine Synapses, Physiology 21:38-47, 20064. Harris KM and Stevens JK. Dendritic spines of CA 1 pyramidal cells in the rat hippocampus: serial electron microscopy with reference to their biophysical characteristics. J Neurosci 9: 2982–2997, 1989.5. Jon I. Arellano, Ruth Benavides-Piccione, Javier DeFelipe,and Rafael Yuste Ultrastructure of dendritic spines: correlation between synaptic and spine morphologies, Frontiers in Neuroscience. (2007) vol. 1, iss. 1,131-1436. Megias, M., Emri, Z., Freund, T. F., Gulyas, A. I. (2001). Total number and distribution of inhibitory and excitatory synapses on hippocampal CA1 pyramidal cells. Neuroscience 102, 527–540.7. Konur, S., Rabinowitz, D., Fenstermaker, V., Yuste, R. (2003). Systematic regulation of spine head diameters and densities in pyramidal neurons from juvenile mice. J. Neurobiol. 56, 95–112.8. Nusser, Z., Lujan, R., Laube, G., Roberts, J., Molnar, E., Somogyi, P. (1998). Cell type and pathway dependence of synaptic AMPA receptor number and variability in the hippocampus. Neuron 21, 545–559.

One of the key regulators of the actin cytoskeleton is the Rho family of GTPases. The Rho GTPases function as molecular switches to turn on or o� downstream biochemical pathways depending on the stimuli [1]. This GTP-ases are under control of proteins such as the gua-nine nucleotide exchange factors (e.g.Kalirin-7) and the GTPase-activating proteins. Rac and Cdc42 promote neurite outgrowth, RhoA stimulates retraction. The balance of these opposing activities of the di�erent Rho GTPases regulates some functions and the morphology of neurons.GTPases functions: cell movement and motility, transcrip-tion, cell growth and proliferation, as well as cell cycle progression. Members of the Rho Molecules in GTPase family have two states: GTP- and GDP-bound states. The GTPases are inactivated when the bound GTP is hydro-lyzed to GDP. Rho GTPases have intrinsic GTPase activity but the hydrolysis is slow. The Rho GTPases are normally present in cytoplasm, kept here by RhoGDI until a stimuli is applied to the cell. Well known members of Rho GTPases are RhoA, Cdc42 and Rac1 [1]. The e�ector proteins down-stream of Rac1 in lamellipodia formation are mainly the WAVE subfamily of the WASP proteins. POR1 may also be involved in this process [2,3,4].

Rac and Cdc42 pro-mote neurite out-growth, RhoA stimulates retrac-tion.

GTPases functions: cell movement and motility, transcrip-tion, cell growth and proliferation, as well as cell cycle progression.

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N-WASP mediates the link between Cdc42 and the Arp2/3 proteins in actin polymerization, and participates in the formation of �lopodia [2, 5] . WAVE1 is a downstream e�ector of Rac1. It is responsible for the number of den-dritic spines in the neurons. Phosphorylation of WAVE1 by the cyclin-dependent kinase 5 (Cdk5) inhibits WAVE1’s activity and thus limits its capacity to regulate Arp2/3-dependent actin polymerization [1,6] . Cdk5 and its regu-lator p35 have also been shown to interact with both Rac1 and PAK leading to downregulation of PAK activity [7]. It has long been established that the downstream e�ects of RhoA and Cdc42/Rac can be antagonistic to one another in cells [8] . Cdc42 and Rac are required for neurite forma-tion while dominant negative Cdc42 and Rac1 have been found to inhibit neurite outgrowth in N1E115 cells [9]. Strong Rac1 and Cdc42 activities have also been localized to the tips of the growin neurites in PC12 cells stimulated with nerve growth factor (NGF) [1,10] . The RhoA-induced neurite retraction was found to be mediated by the actions of ROK. Studies on primary neurons have also con�rmed the �ndings that Cdc42 and Rac1 generally enhance neurite formation and outgrowth whereas RhoA activity inhibits these activities [1]. However, recent data have indicated that it is the balance of Rho GTPase activi-ties that is important in the regulation of neurite outgrowth. Too much or too little Rac1 activity reduces neurite outgrowth.

1 Cheng-Gee Koh, Rho GTPases and Their Regulators in Neuronal Functions and Development, Neurosignals 2006–07;15:228–2372 Miki H, Suetsugu S, Takenawa T: WAVE, a novel WASP-family protein involved in actin reorganization induced by Rac. EMBO J 1998; 17: 6932-6941.3 Miki H, Yamaguchi H, Suetsugu S, Takenawa T: IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ru�ing. Nature 2000; 408: 732–735.4 Van Aelst L, Joneson T, Bar-Sagi D: Identi�cation of a novel Rac1-interacting protein involved in membrane ru�ing. EMBO J 1996; 15: 3778–3786.5 Rohatgi R, Ma L, Miki H, Lopez M, Kirchhausen T, Takenawa T, Kirschner MW: The interaction between N-WASP and the Arp2/3complex links Cdc42-dependent signals to actin assembly. Cell 1999; 97: 221–231.6 Kim Y, Sung JY, Ceglia I, Lee K-W, Ahn J-H, Halford JM, Kim AM, Kwak SP, Park JB, Ho Ryu S, Schenck A, Bardoni B, Scott JD, NairnAC, Greengard P: Phosphorylation of WAVE1 regulates actin polymeriza-tion and dendritic spine morphology. Nature 2006;442: 814–817

WAVE1 is a down-stream e�ector of Rac1. It is respon-sible for the number of den-dritic spines in the neurons.

It has long been established that the downstream e�ects of RhoA and Cdc42/Rac can be antagonistic to one another in cells .

Too much or too little Rac1 activity reduces neurite out-growth.

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7 Nikolic M, Chou MM, Lu W, Mayer BJ, Tsai LH: The p35/Cdk5 kinase is a neuron-speci�c Rac e�ector that inhibits Pak1 activity. Nature 1998; 395: 194–198.8 Kozma R, Ahmed S, Best A, Lim L: The Rasrelated protein Cdc42Hs and bradykinin promote formation of peripheral actin microspikes and �lopodia in Swiss 3T3 �broblasts. Mol Cell Biol 1995; 15: 1942–1952.9 Sarner S, Kozma R, Ahmed S, Lim L: Phosphatidylinositol 3-kinase, Cdc42, and Rac1 act downstream of Ras in integrin-dependent neurite outgrowth in N1E-115 neuroblastoma cells. Mol Cell Biol 2000; 20: 158– 172.10 Aoki K, Nakamura T, Matsuda M: Spatiotemporal regulation of Rac1 and Cdc42 activity during nerve growth factor-induced neurite outgrowth in PC12 cells. J Biol Chem2004; 279: 713–719.

These graphics are orienta-tive and represent the pattern found by Andrew M. et al 2008. For the original data see Andrew M. Tan, Severine Stamboulian, Yu-Wen Chang, Peng Zhao, Avis B. Hains,2 Stephen G. Waxman, and Bryan C. Hains, Neuropathic Pain Memory Is Maintained by Rac1-Regulated Dendritic Spine Remodeling after Spinal Cord Injury, The Journal of Neuroscience,28(49):13173-13183 • 13173

7 Nikolic M, Chou MM, Lu W, Mayer BJ, Tsai LH: The p35/Cdk5 kinase is a neuron-speci�c Rac e�ector that inhibits Pak1 activity. Nature 1998; 395:

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2009

Actin regulationg pathways under the control of ionotropic glutamate receptor. RhoA (activated) interacts with NMDARs. The e�ect is the activation of the ROCK/PII complex. The result is a stable actin after ROCK/PII activation. High levels of CA2+ induce CaMKII-dependent phos-phorylation of spinophilin. This detaches the spinophilin from the actin and sends it to the mem-brane. Here spinophilin interacts with Lcf. After this interaction Lcf activates RhoA. The actin-severing activity of co�lin is controlled by di�erent kinases and phosphatases. LIMK has a negative regulator e�ect on co�lin activity. Activation of LIMK depends on Rac-1, through its e�ector - PAK. NMDA stimuli increases Rac-1 activity (local) through Rac1 - GEFs PIX and Tiam 1 which increases the activity of co�lin, wich can lead to higher actin turnover rates.

actin regulatory pathways mediated by non-glutamate receptorsArp2/3 has actin-polymerizing activity. N-Wasp has actin-polymerizing activity. Both of them (Arp2/3 and N-Wasp) depend on cortactin phosphorylation levels. This levels are controlled in a TrkB and Src dependent manner. Kalirin is recruited and activated to spines by EphB. Kalirin through Rac and PAK leads to activation of myosin.

actin regulatory proteins in spines. The actin severing activity of co�lin is dependent on the balance existing between kinases and phosphatases. - LIMK and CN/PP2B. Co�lin binds to actin and a�ects the �lament structure. At this moment the debrin a�nty for actin is lowered. Debrin has a stabi-lizing e�ect on actin. Debrin prevents actin reorganization. The reorganization of actin is due to myosin binding to acting �laments and by interacting with gelsolin. Myosin stabilizes actin and contracts F-actine. PAK triggers myosin motor activity. Gelsolin caps the barbed ends of actin. In this way the actin polimerization is possible. This role of gelsolin is Ca2+ dependent.Vanessa Schubert and Carlos G. Dotti, Transmitting on actin: synaptic control of dendritic architecture, Journal of Cell Science 120, 205-212

integrin

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Laminae I to IV comprise the dorsal horn and are concerned with somatosensory a�erent signaling. They link the primary a�erent neurons and neurons of CNS. Lamina I and II (super�cial dorsal horn, SDH) receive input largely from thinly myelinated (A-delta ) and unmy-elinated (C) �bers of thermoreceptors and various noci-ceptors. Laminae III and IV (deep dorsal horn, DDH) receive their input from more myelinated (A) �bers that transmit vibration, touch, and pressure. [1] Connections between DDH neurons are predominantly unidirectional with a majority (69%) of these linkages being inhibitory in rat. Zheng, Lu, and Perl describe a similar proportion of inhibitory connections in mouse SDH. Safronov’s recently reported that only 10% of cell pairs were linked by inhibitory connections, concluding that excitatory interneurons dominate in rat lamina II [3]. This di�er-ences may have their roots in the methods used. Safronov used voltage-clamp recordings, suggesting that Safronov’s procedures may have underestimated week connectivity. Schneider found that GABA and glycine are co-transmitters at inhibitory connections between DDH interneurons. [1,4]

1. Yan Lu, Synaptic Wiring in the Deep Dorsal Horn. Focus on “Local Circuit Connections Between Hamster Laminae III and IV Dorsal Horn Neurons” J Neurophysiol 99: 1051–1052, 20082. Lu Y, Perl ER. A speci�c inhibitory pathway between substantia gelati-nosa neurons receiving direct C-�ber input. J Neurosci 23: 8752–8758, 2003.3. Santos SF, Rebelo S, Derkach VA, Safronov BV. Excitatory interneu-rons dominate sensory processing in the spinal substantia gelatinosa of rat. J Physiol 581: 241–254, 2007.4. Schneider SP. Local circuit connections between hamster laminae III and IV dorsal horn neurons. J Neurophysiol doi:10.1152/jn.00962.2007.

Nociceptive peripheral inputs make monosynaptic connections with projection neurons in lamina I and interneurons in laminae I and II [1,2]. Projection neurons in lamina I transmit nociceptive information at higher levels in CNS. Most SDH neurons (certainly 95%) are local circuit interneurons and not projection neurons [1,3,4,5]. These interneurons are excitatory or inhibitory and receive inputs from higher brain centers and other local interneu-rons. These interneurons play a crucial role in setting the overall excitability level [1]. GFP-labeled population of neurons in mice in the SDH were exclusively GABAergic and could be activated during noxious peripheral stimula-tion of C-�bers [1].

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GFP-positive neurons exhibited tonic �ring and were morphologically identi�ed as central neurons, but label-ing for GABA-ergic neurons and glycinergic neurons dem-onstrate more variability in �ring pattern and in morphol-ogy - islet neurons and central neurons. [6, 7]. These stud-ies indicate that, within the two major inhibitory neuron classes, subpopulations exist with potentially di�erent roles in SDH function. Inhibitory connections showed a single con�guration, linking islet to central neurons in lamina II through a monosynaptic GABAergic synapse. Both pre- and postsynaptic neurons received monosyn-aptic C-�ber primary a�erent input, although the inputs studied always arrived �rst at the presynaptic neuron. Inhibitory connections were always islet to central [1]. The central and lamina I neurons receive C-�ber primary a�er-ent input, whereas vertical neurons received A delta-�ber input. The connection pattern seems to be - central neuron to vertical neuron and vertical to projection. The central neuron is common in islet to central neuron circuit and to the excitatory circuit. [1]

1. B. A. Graham, A. M. Brichta, and R. J. Callister, Moving From an Averaged to Speci�c View of Spinal Cord Pain Processing Circuits, J Neurophysiol 98: 1057–1063, 2007.2. Light AR, Perl ER. Re-examination of the dorsal root projec-tion to the spinal dorsal horn including observations on the di�erential termination of coarse and �ne �bers. J Comp Neurol 186: 117–131, 19793. Polgar E, Hughes DI, Riddell JS, Maxwell DJ, Puskar Z, Todd AJ. Selective loss of spinal GABAergic or glycinergic neurons is not necessary for development of thermal hyperalgesia in the chronic constriction injury model of neuropathic pain. Pain 104: 229–239, 2003.4. Spike RC, Puskar Z, Andrew D, Todd AJ. A quantitative and morphological study of projection neurons in lamina I of the rat lumbar spinal cord. Eur J Neurosci 18: 2433–2448, 2003.5. Willis WD, Coggeshall RE. Sensory Mechanisms of the Spinal Cord. New York: Kluwer Academic/Plenum Publishers, 2004.6. Heinke B, Ruscheweyh R, Forsthuber L, Wunderbaldinger G, Sandkuhler J. Physiological, neurochemical and morpho-logical properties of a subgroup of GABAergic spinal lamina II neurones identi�ed by expression of green �uorescent protein in mice. J Physiol 560: 249–266, 2004.7. Zeilhofer HU, Studler B, Arabadzisz D, Schweizer C, Ahmadi S, Layh B, Bosl MR, Fritschy JM. Glycinergic neurons express-ing enhanced green �uorescent protein in bacterial arti�cial chromosome transgenic mice. J Comp Neurol 482: 123–141, 2005.

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GFP-positive neurons exhibited tonic �ring and were morphologically identi�ed as central neurons, but label-ing for GABA-ergic neurons and glycinergic neurons dem-onstrate more variability in �ring pattern and in morphol-ogy - islet neurons and central neurons. [6, 7]. These stud-ies indicate that, within the two major inhibitory neuron classes, subpopulations exist with potentially di�erent roles in SDH function. Inhibitory connections showed a single con�guration, linking islet to central neurons in lamina II through a monosynaptic GABAergic synapse. Both pre- and postsynaptic neurons received monosyn-aptic C-�ber primary a�erent input, although the inputs studied always arrived �rst at the presynaptic neuron. Inhibitory connections were always islet to central [1]. The central and lamina I neurons receive C-�ber primary a�er-ent input, whereas vertical neurons received A delta-�ber input. The connection pattern seems to be - central neuron to vertical neuron and vertical to projection. The central neuron is common in islet to central neuron circuit and to the excitatory circuit. [1]

1. B. A. Graham, A. M. Brichta, and R. J. Callister, Moving From an Averaged to Speci�c View of Spinal Cord Pain Processing Circuits, J Neurophysiol 98: 1057–1063, 2007.2. Light AR, Perl ER. Re-examination of the dorsal root projec-tion to the spinal dorsal horn including observations on the di�erential termination of coarse and �ne �bers. J Comp Neurol 186: 117–131, 19793. Polgar E, Hughes DI, Riddell JS, Maxwell DJ, Puskar Z, Todd AJ. Selective loss of spinal GABAergic or glycinergic neurons is not necessary for development of thermal hyperalgesia in the chronic constriction injury model of neuropathic pain. Pain 104: 229–239, 2003.4. Spike RC, Puskar Z, Andrew D, Todd AJ. A quantitative and morphological study of projection neurons in lamina I of the rat lumbar spinal cord. Eur J Neurosci 18: 2433–2448, 2003.5. Willis WD, Coggeshall RE. Sensory Mechanisms of the Spinal Cord. New York: Kluwer Academic/Plenum Publishers, 2004.6. Heinke B, Ruscheweyh R, Forsthuber L, Wunderbaldinger G, Sandkuhler J. Physiological, neurochemical and morpho-logical properties of a subgroup of GABAergic spinal lamina II neurones identi�ed by expression of green �uorescent protein in mice. J Physiol 560: 249–266, 2004.7. Zeilhofer HU, Studler B, Arabadzisz D, Schweizer C, Ahmadi S, Layh B, Bosl MR, Fritschy JM. Glycinergic neurons express-ing enhanced green �uorescent protein in bacterial arti�cial chromosome transgenic mice. J Comp Neurol 482: 123–141, 2005.

There is a particular inhibitory connection between two kinds of SG neurons that is related to primary a�erent C-�ber input. . Both neurons of this circuit are located near the interface between laminae IIo and IIi. The presyn-aptic element seems to be the islet type of SG neurons. These islet cells send a monosynaptic inhibitory projec-tion to a nearby neuron whose features match those of the transient type of central neuron. The �nding that both the presynaptic islet cell and postsynaptic central cell receive monosynaptic connections from di�erent segments of the primary a�erent C-�ber spectrum, is signi�cant. This circuit implies that a�erent input from one part of the C-�ber spectrum, through excitation of islet cells, inhibits neurons receiving excitatory input from a di�erent subset of primary a�erent C-�bers.

Yan Lu and Edward R. Perl, A Speci�c Inhibitory Pathway between Substantia Gelatinosa Neurons Receiving Direct C-Fiber Input, 2003 • 23(25):8752– 8758

Adelta �ber

C �ber

C �ber

large C �ber

small C �berislet cells

inhibitoryneurons

projection neuron

excitatoryneuron

vertical neuron

transientneuron

descendinginputs

excitatoryneuron

excitatoryneuron

inhibitoryneurons

vertical neuron

islet cells

transientneuron

excitatoryneuronprojection

neuron

lamina I

lamina II 0

lamina II i

islet cell

vertical cellother cellular types

Spinal lamina II (substantia gelatinosa) neurons plays an important role in process-ing of nociceptive information from primary a�erent nerves. Anatomical studies suggest that neurons in the outer (lamina IIo) and inner (lamina IIi) zone of lamina II receive distinct a�erent inputs.

The dorsal horn neuropil is a region of complex synaptic interactions that mediates convergence from many sensory inputs. The extent to which any connection speci�city betweenmechanosensory a�erent systems and central neu-rons is preserved by the intrinsic dorsal horn circuitry is unknown. An unusually high incidence of connections by inhibi-tory interneurons was found and these connec-tions involve multiple types of neurons in many combinations.

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Pregabalin, like gabapentin, was shown to be e�ective in several models of neuropathic pain [1,2,3,4], incisional injury , in�ammatory injury , and formalin-induced injury [1]. It is also e�ective in the treatment of anxiety, and is also a sleep-modulating drug [1]. Pregabalin increases the duration of nonrapid eye movement and also decreases rapid eye movement sleep in rats [5]. Its main site of action appears to be on one subunit of presynap-tic, voltagedependent calcium channels [6]. Pregabalin produce an inhibitory modulation of neuronal excitabil-ity , particularly in areas of the central nervous system dense in synaptic connections. [7,8,9]. In contrast to vera-pamil (Dihydopyridines) , pregabalin has no e�ect on arterial blood pressure or cardiac function. [1]

1.Noor M. Gajraj, Pregabalin: Its Pharmacology and Usein Pain Management,Anesth Analg 2007;105:1805–15 2.Partridge B, Chaplan S, Sakamoto E, Yaksh T. Characterization of the e�ects of gabapentin and 3-isobutyl-� -aminobutyric acid on substance P-induced thermal hyperalgesia. Anesthesiology 1998;88:196–2053. Jun J, Yaksh T. The e�ect of intrathecal gabapentin and 3-isobutyl aminobu-tyric acid on the hyperalgesia observed after thermal injury in the rat. Anesth Analg 1998;86:348–544. Nozaki-Taguchi N, Chaplan SR, Higuera ES, Ajakwe RC,Yaksh TL. Vincristine-induced allodynia in the rat. Pain2001;93:69–765.Kubota T, Fang J, Meltzer LT, Krueger JM. Pregabalin enhances nonrapid eye movement sleep. J Pharmacol Exp Ther 2001;299:1095–1056.Belliotti T, Capiris T, Ekhato I, Kinsora J, Field M, He�ner T, Meltzer L, Schwarz J, Taylor C, Thorpe A, Vartanian M, Wise L, Zhi-Su T, Weber M, Wustrow D. Structure-activity relationships of pregabalin and analogues that target the alfa(2)-delta protein. J Med Chem 2005;48:2294–3077. Chizh BA, Gohring M, Troster A, Quartey GK, Schmelz M, Koppert W. E�ects of oral pregabalin and aprepitant on pain and central sensitization in the electri-cal hyperalgesia model in human volunteers. Br J Anaesth 2007;98:246–548. McClelland D, Evans R, Barkworth L, Martin D, Scott R. A study comparing the actions of gabapentin and pregabalin on the electrophysiological properties of cultured DRG neurones from neonatal rats. BMC Pharmacology 2004;4:149. Hill D, Suman-Chauhan N, Woodru� G. Localization of[3H]gabapentin to a novel site in rat brain: autoradiographic studies. Eur J Pharmacol 1993;244:303–9

First-line Medications for Neuropathic Pain

Medication Beginning Dosage Titration Maximum Dosage Duration of Adequate Trial

Gabapentin 100-300 mg every night or100-300 mg 3 times daily

Increase by 100-300 mg3 times daily every 1-7 das tolerated

3600 mg/d (1200 mg3 times daily); reduce iflow creatinine clearance

3-8 wk for titration plus1-2 wk at maximumtolerated dosage

5% Lidocaine patch Maximum of 3 patches dailyfor a maximum of 12 h

None needed Maximum of 3 patches dailyfor a maximum of 12 h

2 wk

Opioid analgesics* 5-15 mg every 4 has needed

After 1-2 wk, convert totaldaily dosage tolong-acting opioidanalgesic and continueshort-acting medicationas needed

No maximum with carefultitration; considerevaluation by painspecialist at dosagesexceeding 120-180 mg/d

4-6 wk

Tramadol hydrochloride 50 mg once or twice daily Increase by 50-100 mg/d individed doses every 3-7 das tolerated

400 mg/d (100 mg 4 timesdaily); in patients olderthan 75 y, 300 mg/din divided doses

4 wk

Tricyclic antidepressants(eg, nortriptylinehydrochloride ordesipraminehydrochloride)

10-25 mg every night Increase by 10-25 mg/devery 3-7 d as tolerated

75-150 mg/d; if blood levelof active drug and itsmetabolite is 100ng/mL, continue titrationwith caution

6-8 wk with at least 1-2 wkat maximum tolerateddosage

*Dosages given are for morphine sulfate.

Robert H. Dworkin et al, Advances in Neuropathic Pain Diagnosis, Mechanisms, and Treatment Recommendations ,Arch Neurol. 2003;60:1524-1534

!! do not self-medicate. consult a specialist befor taking any medication. !!

Dextromethorphan may be used as a Preventive Treatment for Neuropathic Pain after SCI


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www.thalamus.ro

Protein kinase C-related kinase 1 (PRK1 or PKN) is involved in regulation of the intermediate�laments of the actin cytoskeleton, as well as having e�ects on processes as diverse as mitotictiming and apoptosis.Modha R, Campbell LJ, Nietlispach D, Buhecha HR, Owen D, Mott HRThe Rac1 polybasic region is required for interaction with its e�ector PRK1J. Biol. Chem. v283, p.1492-1500

Inhibition of Rho or Rho-kinase, downstreame�ector of Rho, promotes axon regeneration in vivo. These �ndings establish Rho and Rho-kinase as key play-ers in inhibiting the regenera-tion of the central nervous system, and launched a new wave of studies that aim to promote regeneration of injured axons by modulating this inhibi-tory pathway. Tanaka H, Yamashita T, Yachi K, Fujiwara K, Yoshikawa K, and Tohyama M (2004) Cytoplasmic p21Cip1/WAF1 enhances axonal regeneration and functional recovery after spinal cord injury in rats. Neurosci 127, 155-164.



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