Localized increases in synaptic strength constitute a synaptic basis for learning and memory in CNS.

Spinal cord injury (SCI) could determine dendritic spines remodeling and can con-tribute to neuronal hyperexcitability and neuropathic pain through synaptic changes. Synaptic plasticity induced by SCI may appear in the spinal cord dorsal horn and may contribute 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 it is not studied enough. Rac1 can modulate dendritic spine morphology 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. Inhibi-tion of the Rac1 signaling cascade ameliorated the development of abnormal spine morphologies, reduced neuronal excitability, and normalized nociceptive thresholds. [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 . Cortac-tin 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 diameter after SCI) occurs after SCI in dorsal horn neurons.

Rac1 could be interpreted as critical in maintaining neuropathic pain through its regu-lation of dendritic spines. WDR (Wide-Dynamic Range ) neurons exhibit hyperexcitabil-ity 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 to-gether 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�erents. Nature 355:75–78.2. Kim BG, Dai HN, McAtee M, Vicini S, Bregman BS (2006) Remodeling of synaptic struc-tures in the motor cortex following 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 Ste-phen G. Waxman, and Bryan C. Hains, Neuropathic Pain Memory Is Maintained by Rac1-Regulated Dendritic Spine Remodeling after Spinal Cord Injury, The Journal of Neuro-science, 28(49):13173–13183 • 13173

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 den-drites. The most common morphological type is com-posed of a bulbous head and a thin neck. The head is con-nected with the dendrite through the neck. There is a po-tential relation between spine shape and synaptic func-tion, since morphological 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 uncorrelated with the spine neck length. In rat, in CA1 pyramidal cells, the volume of the spine head was reported to be proportional to the post-synaptic density (PSD) area and to the number of presyn-aptic vesicles [4]. The spine neck length is correlated to the time constant of calcium compartmentalization [3] and also proportional to the �ltering of electrical poten-tials and it may be involved in calcium dependent learn-ing 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 neocorti-cal pyramidal neurons spines that were further away from the soma were longer and had larger heads. In CA1 pyra-midal 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 corre-lated with the head volume) [5]. The PSD area is itself pro-portional to the number of postsynaptic receptors [8]. The volume of the spine head is likely to be directly propor-tional to the average reliability and strength of its syn-apse. CA1 pyramidal neurons show a larger spine size with increasing distance from the soma [7, 6], as if synap-tic weight is compensating for the dendritic electrotonic �ltering [5].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.

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Rac1 (Ras-related C3 botulinum toxin sub-strate 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.

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 guanine nucleotide exchange factors (ex:Kalirin-7) and the GTPase-activating pro-teins. 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, tran-scription, 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 hydrolyzed 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 downstream of Rac1 in lamellipodia formation are mainly the WAVE subfam-ily of the WASP proteins. POR1 may also be involved in this process [2,3,4]. 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 respon-sible for the number of dendritic 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 polym-erization [1,6] . Cdk5 and its regulator 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 formation 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 local-ized 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 medi-ated 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]. How-ever, recent data have indicated that it is the balance of Rho GTPase activities that is important in the regulation of neurite outgrowth. Too much or too little Rac1 activ-ity reduces neurite outgrowth.

1 Cheng-Gee Koh, Rho GTPases and Their Regulators in Neuronal Func-tions 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, Kirsch-ner 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 polymer-ization and dendritic spine morphology. Nature 2006;442: 814–8177 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.

Dendritic spines contain a cytoskeleton com-posed mostly of �lamentous actin (F-actin) which determines the shape and stability/motility of spines. Spines have a small amount of intermedi-ate �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 Den-dritic Spine Synapses, Physiology 21:38-47, 2006

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 Ste-phen G. Waxman, and Bryan C. Hains, Neuropathic Pain Memory Is Maintained by Rac1-Regulated Dendritic Spine Remodeling after Spinal Cord Injury, The Journal of Neuro-science, 28(49):13173–13183 • 13173

Actin regulationg pathways under the control of ionotropic glutamate receptor.

Vanessa Schubert and Carlos G. Dotti,Transmitting on actin: synaptic control of dendritic architecture, Journal of Cell Science 120, 205-212

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 proteins in spines. The actin severing activity of co�lin is dependent on the balance existing between kinases and phos-phatases. - 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 stabilizing 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.

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.

Dendritic spines are small protrusions from Dendritic spines are small protrusions from Dendritic spinesneuronal dendrites that typically receives input from the Dendritic spinesneuronal dendrites that typically receives input from the Dendritic spines

and Neuropathic Pain after Spinal Cord Injury

Dendritic Spines

These graphics are orientative and representthe 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

design & concept by C. Barsila & L. Spinumedical students

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Dendritic Spine

desi

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http://neuroscience-bucharest.blogspot.comhttp://www.thalamus.ro

http://www.thalamus.ro

This poster does not intend to be an “authoritative” article. It represents our interest in researchand also it represents our interest in medical graphic design. You are not allowed to sell or use thisposter or parts of it in any circumstances. You can use this poster for personal purposes or foreducational purposes. If you use this poster please link back or leave a comment on http://neuroscience-bucharest.blogspot.com or http://www.thalamus.ro

- more details about this subject on - http://neuroscience-bucharest.blogspot.com

Dend

ritic

spines

Localized increases in synaptic strength constitute a synaptic basis for learning and memory in CNS.

Dendritic Spines

Dendritic spines

and and Neuropathic Pain after Spinal Cord InjuryDendritic spines, Rac 1

- some interesting aspects - - some interesting aspects -

design & concept by C. Barsila & L. Spinu

TrkB

Src

Vanessa Schubert and Carlos G. Dotti,Transmitting on actin: synaptic control of dendritic architecture, Journal of Cell Science 120, 205-212

Dendritic Spines

on the stimuli [1]. This GTP-ases are under control of

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neuroscience & medicine

Localized increases in synaptic strength constitute a synaptic basis for learning and

One of the key regulators of the actin cytoskeleton is

Dendritic Spines

Dendritic spines Dendritic spines

design & concept by C. Barsila & L. Spinu

design & concept by C. Barsila & L. Spinu

design & concept by C. Barsila & L. Spinu

Neuropathic Pain after Spinal Cord InjuryNeuropathic Pain after Spinal Cord Injury

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