The Adaptor Protein CD2AP Is a Coordinator of Neurotrophin Signaling-Mediated Axon Arbor Plasticity.

Unlabelled: Growth of intact axons of noninjured neurons, often termed collateral sprouting, contributes to both adaptive and pathological plasticity in the adult nervous system, but the intracellular factors controlling this growth are largely unknown. An automated functional assay of genes regulated in sensory neurons from the rat in vivo spared dermatome model of collateral sprouting identified the adaptor protein CD2-associated protein (CD2AP; human CMS) as a positive regulator of axon growth. In non-neuronal cells, CD2AP, like other adaptor proteins, functions to selectively control the spatial/temporal assembly of multiprotein complexes that transmit intracellular signals.

Transcriptional changes in sensory ganglia associated with primary afferent axon collateral sprouting in spared dermatome model.

Primary afferent collateral sprouting is a process whereby non-injured primary afferent neurons respond to some stimulus and extend new branches from existing axons. Neurons of both the central and peripheral nervous systems undergo this process, which contributes to both adaptive and maladaptive plasticity (e.g.

Neurotrophins and spinal circuit function.

Work early in the last century emphasized the stereotyped activity of spinal circuits based on studies of reflexes. However, the last several decades have focused on the plasticity of these spinal circuits. These considerations began with studies of the effects of monoamines on descending and reflex circuits.

Neurotrophic factors in spinal cord injury.

A major challenge in repairing the injured spinal cord is to assure survival of damaged cells and to encourage regrowth of severed axons. Because neurotrophins are known to affect these processes during development, many experimental approaches to improving function of the injured spinal cord have made use of these agents, particularly Brain derived neurotrophic factor (BDNF) and Neurotrophin-3 (NT-3). More recently, neurotrophins have also been shown to affect the physiology of cells and synapses in the spinal cord.

Constructing and deconstructing the gate theory of pain.

The gate theory of pain, published by Ronald Melzack and Patrick Wall in Science in 1965, was formulated to provide a mechanism for coding the nociceptive component of cutaneous sensory input. The theory dealt explicitly with the apparent conflict in the 1960s between the paucity of sensory neurons that responded selectively to intense stimuli and the well-established finding that stimulation of the small fibers in peripheral nerves is required for the stimulus to be described as painful. It incorporated recently discovered mechanisms of presynaptic control of synaptic transmission from large and small sensory afferents, which was suggested to "gate" incoming information depending on the balance between these inputs.

Organization of sensory input to the nociceptive-specific cutaneous trunk muscle reflex in rat, an effective experimental system for examining nociception and plasticity.

Detailed characterization of neural circuitries furthers our understanding of how nervous systems perform specific functions and allows the use of those systems to test hypotheses. We have characterized the sensory input to the cutaneous trunk muscle (CTM; also cutaneus trunci [rat] or cutaneus maximus [mouse]) reflex (CTMR), which manifests as a puckering of the dorsal thoracolumbar skin and is selectively driven by noxious stimuli. CTM electromyography and neurogram recordings in naïve rats revealed that CTMR responses were elicited by natural stimuli and electrical stimulation of all segments from C4 to L6, a much greater extent of segmental drive to the CTMR than previously described.

Bilateral transient changes in thalamic nucleus ventroposterior lateralis after thoracic hemisection in the rat.

We made simultaneous bilateral recordings of unit activity in the nucleus ventroposterior lateralis (VPL) in intact rats and after acute and chronic left thoracic hemisection. We observed an immediate bilateral decline in multireceptive units, reflecting a loss of nociceptive input on the lesion side and a loss of low-threshold inputs contralaterally. Unit properties were restored to normal by 6 wk.

Differential effects of brain-derived neurotrophic factor and neurotrophin-3 on hindlimb function in paraplegic rats.

We compared the effect of viral administration of brain-derived neurotrophic factor (BDNF) or neurotrophin 3 (NT-3) on locomotor recovery in adult rats with complete thoracic (T10) spinal cord transection injuries, in order to determine the effect of chronic neurotrophin expression on spinal plasticity. At the time of injury, BDNF, NT-3 or green fluorescent protein (GFP) (control) was delivered to the lesion via adeno-associated virus (AAV) constructs. AAV-BDNF was significantly more effective than AAV-NT-3 in eliciting locomotion.

Chondroitinase ABC combined with neurotrophin NT-3 secretion and NR2D expression promotes axonal plasticity and functional recovery in rats with lateral hemisection of the spinal cord.

Elevating spinal levels of neurotrophin NT-3 (NT3) while increasing expression of the NR2D subunit of the NMDA receptor using a HSV viral construct promotes formation of novel multisynaptic projections from lateral white matter (LWM) axons to motoneurons in neonates. However, this treatment is ineffective after postnatal day 10. Because chondroitinase ABC (ChABC) treatment restores plasticity in the adult CNS, we have added ChABC to this treatment and applied the combination to adult rats receiving a left lateral hemisection (Hx) at T8.

Combined delivery of Nogo-A antibody, neurotrophin-3 and the NMDA-NR2d subunit establishes a functional 'detour' in the hemisected spinal cord.

To encourage re-establishment of functional innervation of ipsilateral lumbar motoneurons by descending fibers after an intervening lateral thoracic (T10) hemisection (Hx), we treated adult rats with the following agents: (i) anti-Nogo-A antibodies to neutralize the growth-inhibitor Nogo-A; (ii) neurotrophin-3 (NT-3) via engineered fibroblasts to promote neuron survival and plasticity; and (iii) the NMDA-receptor 2d (NR2d) subunit via an HSV-1 amplicon vector to elevate NMDA receptor function by reversing the Mg(2+) block, thereby enhancing synaptic plasticity and promoting the effects of NT-3. Synaptic responses evoked by stimulation of the ventrolateral funiculus ipsilateral and rostral to the Hx were recorded intracellularly from ipsilateral lumbar motoneurons. In uninjured adult rats short-latency (1.

Antagonism of nerve growth factor-TrkA signaling and the relief of pain.

Nerve growth factor (NGF) was originally discovered as a neurotrophic factor essential for the survival of sensory and sympathetic neurons during development. However, in the adult NGF has been found to play an important role in nociceptor sensitization after tissue injury. The authors outline mechanisms by which NGF activation of its cognate receptor, tropomyosin-related kinase A receptor, regulates a host of ion channels, receptors, and signaling molecules to enhance acute and chronic pain.

Computational functions of neurons and circuits signaling injury: relationship to pain behavior.

The basic circuitry of the "pain pathway" mediating transmission of information from the periphery to the brain is well known, consisting of specialized sensory fibers known as nociceptors projecting to specific spinal cord neurons, which in turn project on to the thalamus and cerebral cortex. Here we survey some of the unique properties of these circuits, such as peripheral and central sensitization, and the segmental and descending modulatory control of synaptic transmission. We also review evidence indicating dissociation between nociceptor activity and behavioral indications of pain.

Intramuscular AAV delivery of NT-3 alters synaptic transmission to motoneurons in adult rats.

We examined whether elevating levels of neurotrophin-3 (NT-3) in the spinal cord and dorsal root ganglion (DRG) would alter connections made by muscle spindle afferent fibers on motoneurons. Adeno-associated virus (AAV) serotypes AAV1, AAV2 and AAV5, selected for their tropism profile, were engineered with the NT-3 gene and administered to the medial gastrocnemius muscle in adult rats. ELISA studies in muscle, DRG and spinal cord revealed that NT-3 concentration in all tissues peaked about 3 months after a single viral injection; after 6 months NT-3 concentration returned to normal values.

Skin incision induces expression of axonal regeneration-related genes in adult rat spinal sensory neurons.

Unlabelled: Skin incision and nerve injury both induce painful conditions. Incisional and postsurgical pain is believed to arise primarily from inflammation of tissue and the subsequent sensitization of peripheral and central neurons. The role of axonal regeneration-related processes in development of pain has only been considered when there has been injury to the peripheral nerve itself, even though tissue damage likely induces injury of resident axons.

Role of chondroitin sulfate proteoglycans in axonal conduction in Mammalian spinal cord.

Chronic unilateral hemisection (HX) of the adult rat spinal cord diminishes conduction through intact fibers in the ventrolateral funiculus (VLF) contralateral to HX. This is associated with a partial loss of myelination from fibers in the VLF (Arvanian et al., 2009).

Differential NR2B subunit expression at dorsal root and ventrolateral funiculus synapses on lumbar motoneurons of neonatal rat.

Synapse specific differences in NR2 subunit expression exist in several systems within the mammalian CNS. Here we have studied such differences on motoneurons in the neonatal rat cord using ifenprodil known to inhibit voltage-, use- and glycine-independent responses mediated by NR2B-containing N-methyl-d-aspartate receptors (NMDARs) with high specificity. In neonatal rats (P1-P9), the synapses made by the dorsal root (DR) fibres were more sensitive to ifenprodil than ventrolateral funiculus (VLF) connections on the same motoneuron.

Input-specific plasticity of N-methyl-D-aspartate receptor-mediated synaptic responses in neonatal rat motoneurons.

Lumbar motoneurons can be activated monosynaptically by two glutamatergic synaptic inputs: the segmental dorsal root (DR) and the descending ventrolateral funiculus (VLF). To determine whether their N-methyl-d-aspartate (NMDA) receptors are independent, we used (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine-hydrogen-maleate (MK-801), known to induce a use-dependent irreversible block of NMDA receptors (NMDARs). In the presence of MK-801 (in bath) and non-NMDA antagonists (in bath, to isolate NMDARs pharmacologically), we first stimulated the DR.

Chronic spinal hemisection in rats induces a progressive decline in transmission in uninjured fibers to motoneurons.

Although most spinal cord injuries are anatomically incomplete, only limited functional recovery has been observed in people and rats with partial lesions. To address why surviving fibers cannot mediate more complete recovery, we evaluated the physiological and anatomical status of spared fibers after unilateral hemisection (HX) of thoracic spinal cord in adult rats. We made intracellular and extracellular recordings at L5 (below HX) in response to electrical stimulation of contralateral white matter above (T6) and below (L1) HX.

Sensory afferents regenerated into dorsal columns after spinal cord injury remain in a chronic pathophysiological state.

Axon regeneration after experimental spinal cord injury (SCI) can be promoted by combinatorial treatments that increase the intrinsic growth capacity of the damaged neurons and reduce environmental factors that inhibit axon growth. A prior peripheral nerve conditioning lesion is a well-established means of increasing the intrinsic growth state of sensory neurons whose axons project within the dorsal columns of the spinal cord. Combining such a prior peripheral nerve conditioning lesion with the infusion of antibodies that neutralize the growth inhibitory effects of the NG2 chondroitin sulfate proteoglycan promotes sensory axon growth through the glial scar and into the white matter of the dorsal columns.

Changes in motoneuron properties and synaptic inputs related to step training after spinal cord transection in rats.

Although recovery from spinal cord injury is generally meager, evidence suggests that step training can improve stepping performance, particularly after neonatal spinal injury. The location and nature of the changes in neural substrates underlying the behavioral improvements are not well understood. We examined the kinematics of stepping performance and cellular and synaptic electrophysiological parameters in ankle extensor motoneurons in nontrained and treadmill-trained rats, all receiving a complete spinal transection as neonates.

Spinal cord transection enhances afferent-evoked inhibition in lamina II neurons and abolishes BDNF-induced facilitation of their sensory input.

We previously reported that the pronociceptive neurotrophin brain-derived neurotrophic factor (BDNF) induces facilitation of C-fiber evoked EPSCs and NMDA currents in lamina II neurons of rats up to P40. Here, patch-clamp recording was used to study BDNF-induced modification of synaptic and NMDA-evoked responses in transverse spinal slices from lumbar (L2-L5) spinal cord of rats from P3 to P21 following complete spinal cord transection at P2. After transection injury at either T13/L1 or L6/S1, BDNF failed to facilitate synaptic AMPA-kainate currents or agonist-induced NMDA currents.

Combined treatment with neurotrophin-3 and LSD facilitates behavioral recovery from double-hemisection spinal injury in neonatal rats.

We explored functional recovery in two spinal cord injury models following a novel combination treatment (NT-3 + LSD). One group of rats received a staggered double hemisection (DH) at postnatal day 2 (P2) of the left hemicord at T11 and the right hemicord at T12. Another group received complete transection (CT) at T11 on P2.

Combined delivery of neurotrophin-3 and NMDA receptors 2D subunit strengthens synaptic transmission in contused and staggered double hemisected spinal cord of neonatal rat.

We investigated whether administration of neurotrophin-3 (NT-3) and NMDA-2D-expressing units, found previously to enhance transmission in neonatal rat spinal cord, strengthens synaptic connections in the injured neonatal cord. We employed electrophysiological methods to evaluate the strength of synaptic transmission to individual motoneurons in the contusion and staggered double hemisection spinal cord injury (SCI) models. SCI at caudal thoracic levels (T11-T12) was carried out at postnatal day 2 (P2).