Integrated Knowledge Translation Guiding Principles for Conducting and Disseminating Spinal Cord Injury Research in Partnership.

OBJECTIVE: To address a gap between spinal cord injury (SCI) research and practice by rigorously and systematically co-developing integrated knowledge translation (IKT) guiding principles for conducting and disseminating SCI research in partnership with research users. DESIGN: The process was guided by the internationally accepted The Appraisal of Guidelines for REsearch & Evaluation (AGREE) II Instrument for evaluating the development of clinical practice guidelines. SETTING: North American SCI research system (ie, SCI researchers, research users, funders). PARTICIPANTS: The multidisciplinary expert panel (n=17) and end users (n=35) included individuals from a North American partnership of SCI researchers, research users, and funders who have expertise in research partnerships. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Clarity, usefulness, and appropriateness of the principles. RESULTS: Data regarding 125 principles of partnered research were systematically collected from 4 sources (review of reviews, scoping review, interviews, Delphi consensus exercise). A multidisciplinary expert panel held a 2-day meeting to establish consensus, select guiding principles, and draft the guidance. The panel reached 100% consensus on the principles and guidance document. The final document includes a preamble, 8 guiding principles, and a glossary. Survey data showed that the principles and guidance document were perceived by potential end users as clear, useful, and appropriate. CONCLUSIONS: The IKT Guiding Principles represent the first rigorously co-developed, consensus-based guidance to support meaningful SCI research partnerships. The principles are a foundational tool with the potential to improve the relevance and impact of SCI research, mitigate tokenism, and advance the science of IKT.

Supporting meaningful research partnerships: an interview study applying behavior change theory to develop relevant recommendations for researchers.

Research partnerships, while promising for ensuring translation of relevant and useable findings, are challenging and need support. This study aimed to apply behavior change theory to understand and support researchers' adoption of a research partnership approach and the Integrated Knowledge Translation (IKT) Guiding Principles for conducting and disseminating spinal cord injury (SCI) research in partnership. Using an IKT approach, SCI researchers across Canada and the USA completed a survey (n = 22) and were interviewed (n = 13) to discuss barriers and facilitators to deciding to partner and follow the IKT Guiding Principles. The Behaviour Change Wheel, Theoretical Domains Framework (TDF), and Mode of Delivery Ontology were used to develop the survey, interview questions, and guided analyses of interview data. COM-B and TDF factors were examined using descriptive statistics and abductive analyses of barriers and facilitators of decisions to partner and/or use the IKT Guiding Principles. TDF domains from the interview transcripts were then used to identify intervention, content, and implementation options. 142 factors (79 barriers, 63 facilitators) related to deciding to partner, and 292 factors (187 barriers, 105 facilitators) related to deciding to follow the IKT Guiding Principles were identified. Barriers to partnering or use the IKT Guiding Principles were primarily related to capability and opportunity and relevant intervention options were recommended. Interventions must support researchers in understanding how to partner and use the IKT Guiding Principles while navigating a research system, which is not always supportive of the necessary time and costs required for meaningful research partnerships.

Research partnerships, which expand beyond researchers solely working with other researchers, are said to be promising for helping to move research into practice. However, there is a lack in understanding of how to support meaningful research partnerships with those who are not part of academia. This study interviewed spinal cord injury researchers to understand what helps and prevents them from deciding to partner when conducting research projects. Results suggest that researchers do not lack motivation to partner; however, their ability and opportunity to do so is lacking. Overall, support is needed to help researchers understand how to work in partnership within the research system.

Endogenous TrkB ligands suppress functional mechanosensory plasticity in the deafferented spinal cord.

Dorsal root injury (DRI) disrupts the flow of sensory information to the spinal cord. Although primary afferents do not regenerate to their original targets, spontaneous recovery can, by unknown mechanisms, occur after DRI. Here, we show that brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), but not nerve growth factor or neurotrophin-4, are upregulated in the spinal gray matter after DRI. Because endogenous BDNF and NT-3 have well established roles in synaptic and axonal plasticity, we hypothesized that they contributed to spontaneous recovery after DRI. We first developed a model of DRI-induced mechanosensory dysfunction: rat C7/8 DRI produced a deficit in low-threshold cutaneous mechanosensation that spontaneously improved within 10 d but did not recover completely. To determine the effects of endogenous BDNF and NT-3, we administered TrkB-Fc or TrkC-Fc fusion proteins throughout the recovery period. To our surprise, TrkB-Fc stimulated complete recovery of mechanosensation by 6 d after DRI. It also stimulated mechanosensory axon sprouting but prevented deafferentation-induced serotonergic sprouting. TrkC-Fc had no effect on low-threshold mechanosensory behavior or axonal plasticity. There was no mechanosensory improvement with single-bolus TrkB-Fc infusions at 10 d after DRI (despite significantly reducing rhizotomy-induced cold pain), indicating that neuromodulatory effects of BDNF did not underlie mechanosensory recovery. Continuous infusion of the pan-neurotrophin antagonist K252a also stimulated behavioral and anatomical plasticity, indicating that these effects of TrkB-Fc treatment occurred independent of signaling by other neurotrophins. These results illustrate a novel, plasticity-suppressing effect of endogenous TrkB ligands on mechanosensation and mechanosensory primary afferent axons after spinal deafferentation.

Expression of Semaphorin3C in axotomized rodent facial and rubrospinal neurons.

Semaphorins are a family of axonal guidance molecules that, by virtue of their chemorepulsive or chemoattractive actions, may be the important factors in determining the success or failure of axonal regeneration in the mature nervous system after injury. Here, we have used two adult mouse models of nervous system injury to evaluate the neuronal expression of Semaphorin3C (Sema3C) in regenerating (facial motoneurons) and non-regenerating (rubrospinal) neurons following axonal injury. Using in situ hybridization (ISH), we observed that uninjured facial motoneurons express Sema3C mRNA and, following axonal injury, there is a transient up-regulation in Sema3C mRNA expression in injured motoneurons. In contrast, Sema3C mRNA was not detected in uninjured rubrospinal neurons; however, following axotomy, injured rubrospinal neurons significantly up-regulate Sema3C mRNA expression. The increase in Sema3C mRNA expression in axotomized rubrospinal neurons was not limited to the mouse nervous system: serial dilution RT-PCR analysis revealed a similar increase in Sema3C mRNA expression in the axotomized rat rubrospinal nucleus, 3 days following a rubrospinal tract lesion. This demonstrates that increased Sema3C mRNA levels in axotomized rubrospinal neurons is common to both mouse and rat injury models.

Differential RIP antigen (CNPase) expression in peripheral ensheathing glia.

The RIP monoclonal antibody is commonly used to identify oligodendrocytes. Recently, the RIP antigen was identified as 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), a known non-compact myelin protein [Watanabe, M., Sakurai, Y., Ichinose, T., Aikawa, Y., Kotani, M., Itoh, K., 2006. Monoclonal antibody Rip specifically recognizes 2',3'-cyclic nucleotide 3'-phosphodiesterase in oligodendrocytes. J. Neurosci. Res. 84, 525-533]. In the present study we characterize normal and axotomy-induced changes in RIP immunoreactivity in peripheral glia. In myelinating Schwann cells, RIP demarcated paranodal regions of myelinated axons and clearly defined Schmidt-Lantermann incisures. Surprisingly, RIP immunoreactivity was not confined to myelinating glia. Robust RIP immunoreactivity was present in Remak bundles in mixed nerves and in sympathetic ganglia and grey rami. Following peripheral nerve injury, RIP immunoreactivity was redistributed diffusely throughout de-differentiating Schwann cell cytoplasm. In uninjured rats, low levels of RIP immunoreactivity were detectable in satellite cells surrounding dorsal root ganglion (DRG) neurons and in terminal Schwann cells at neuromuscular junctions. This pattern suggested a correlation between RIP immunoreactivity and the amount of axon-glial contact. We therefore injured the L5 spinal nerve to induce sympathetic sprouting and pericellular basket formation in the DRG, and asked whether relatively RIP-negative satellite glia, which normally contact only neuronal somata, would upregulate the RIP antigen upon contact with sprouting sympathetic axons. All perineuronal sympathetic sprouts infiltrated heavily RIP-immunoreactive satellite cell sheaths. RIP immunoreactivity was absent from placode-derived olfactory ensheathing glia, indicating that the relationship between axon-glial contact and RIP-immunoreactivity is restricted to peripheral ensheathing glia of the neural crest-derived Schwann cell lineage.

Protracted myelin clearance hinders central primary afferent regeneration following dorsal rhizotomy and delayed neurotrophin-3 treatment.

Regeneration within or into the CNS is thwarted by glial inhibition at the site of a spinal cord injury and at the dorsal root entry zone (DREZ), respectively. At the DREZ, injured axons and their distal targets are separated by degenerating myelin and an astrocytic glia limitans. The different glial barriers to regeneration following dorsal rhizotomy are temporally and spatially distinct. The more peripheral astrocytic barrier develops first, and is surmountable by neurotrophin-3 (NT-3) treatment; the more central myelin-derived barrier, which prevents dorsal horn re-innervation by NT-3-treated axons, becomes significant only after the onset of myelin degeneration. Here we test the hypothesis that in the presence of NT-3, axonal regeneration is hindered by myelin degeneration products. To do so, we used the Long Evans Shaker (LES) rat, in which oligodendrocytes do not make CNS myelin, but do produce myelin-derived inhibitory proteins. We show that delaying NT-3 treatment for 1 week in normal (LE) rats, while allowing axonal penetration of the glia limitans and growth within degenerating myelin, results in misdirected regeneration with axons curling around presumptive degenerating myelin ovoids within the CNS compartment of the dorsal root. In contrast, delaying NT-3 treatment in LES rats resulted in straighter, centrally-directed regenerating axons. These results indicate that regeneration may be best optimized through a combination of neurotrophin treatment plus complete clearance of myelin debris.

Dynamic wheelchair seating positions impact cardiovascular function after spinal cord injury.

BACKGROUND: Innovative wheelchairs allow individuals to change position easily for comfort and social situations. While these wheelchairs are beneficial in multiple ways, the effects of position changes on blood pressure might exacerbate hypotension and cerebral hypoperfusion, particularly in those with spinal cord injury (SCI) who can have injury to autonomic nerves that regulate cardiovascular control. Conversely, cardiovascular benefits may be obtained with lowered seating. Here we investigate the effect of moderate changes in wheelchair position on orthostatic cardiovascular and cerebrovascular reflex control. METHODS: Nineteen individuals with SCI and ten neurologically-intact controls were tested in supine and seated positions (neutral, lowered, and elevated) in the Elevation™ wheelchair. Participants with SCI were stratified into two groups by the severity of injury to cardiovascular autonomic pathways. Beat-to-beat blood pressure, heart rate and middle cerebral artery blood flow velocity (MCAv) were recorded non-invasively. RESULTS: Supine blood pressure and MCAv were reduced in individuals with lesions to autonomic pathways, and declined further with standard seating compared to those with preserved autonomic control. Movement to the elevated position triggered pronounced blood pressure and MCAv falls in those with autonomic lesions, with minimum values significantly reduced compared to the seated and lowered positions. The cumulative duration spent below supine blood pressure was greatest in this group. Lowered seating bolstered blood pressure in those with lesions to autonomic pathways. CONCLUSIONS: Integrity of the autonomic nervous system is an important variable that affects cardiovascular responses to orthostatic stress and should be considered when individuals with SCI or autonomic dysfunction are selecting wheelchairs. SPONSORSHIP: This work was supported in part by the Heart and Stroke Foundation of British Columbia and the Yukon (V.E.C).

Comparative postnatal development of spinal, trigeminal and vagal sensory root entry zones.

Somatic and visceral sensory information enters the central nervous system (CNS) via root entry zones where sensory axons span an environment consisting of Schwann cells in the peripheral nervous system (PNS) and astrocytes and oligodendrocytes in the CNS. While the embryonic extension of these sensory axons into the CNS has been well-characterized, little is known about the subsequent, largely postnatal development of the glial elements of the root entry zones. Here we sought to establish a comparative developmental timecourse of the glial elements in the postnatal (P0, P3, P7, P14) and adult rat of three root entry zones: the spinal nerve dorsal root entry zone, the trigeminal root entry zone, and the vagal dorsal root entry zone. We compared entry zone development based on the expression of antigens known to be expressed in astrocytes, oligodendrocytes, oligodendrocyte precursor cells, Schwann cells, radial glial fibres and the PNS extracellular matrix. These studies revealed an unexpected distribution among glial cells of several antigens. In particular, antibodies used to label mature oligodendrocytes (RIP) transiently labelled immature Schwann cell cytoplasm, and a radial glial antigen (recognized by the 3CB2 antibody) initially decreased, and then increased in postnatal astrocytes. While all three root entry zones had reached morphological and antigenic maturity by P14, the glial elements comprising the PNS-CNS interface of cranial root entry zones (the trigeminal root entry zone and the vagal dorsal root entry zone) matured earlier than those of the spinal nerve dorsal root entry zone.

Detection and classification of sensory information from acute spinal cord recordings.

One avenue of research for partial restoration of function following spinal cord injury is the use of neural prostheses, an example of which is functional electrical stimulation (FES) devices for motor functions. Neural prostheses may also be useful for the extraction of sensory information directly from the nervous system. We suggest the spinal cord as a possible site for the detection of peripheral sensory information from neural activity alone. Acute multichannel extracellular recordings were used to extract neural spike activity elicited from peripheral sensations from the spinal cords of rats. To test the recording method and classification potential, eight classes of sensory events were recorded consisting of electrical stimulation of seven locations on rat forepaws, and another class of data during which no stimulus was present. A dual-stage classification scheme using principal component analysis and k-Means clustering was devised to classify the sensory events during single trials. The eight tasks were correctly identified at a mean accuracy of 96%. Thus, we have shown the methodology to detect and classify peripheral sensory information from multichannel recordings of the spinal cord. These methods may be useful, for example, in a closed-loop FES for restoration of hand grasp.

Minocycline treatment reduces delayed oligodendrocyte death, attenuates axonal dieback, and improves functional outcome after spinal cord injury.

Minocycline has been demonstrated to be neuroprotective after spinal cord injury (SCI). However, the cellular consequences of minocycline treatment on the secondary injury response are poorly understood. We examined the ability of minocycline to reduce oligodendrocyte apoptosis, microglial/macrophage activation, corticospinal tract (CST) dieback, and lesion size and to improve functional outcome after SCI. Adult rats were subjected to a C7-C8 dorsal column transection, and the presence of apoptotic oligodendrocytes was assessed within the ascending sensory tract (AST) and descending CST in segments (3-7 mm) both proximal and distal to the injury site. Surprisingly, the numbers of dying oligodendrocytes in the proximal and distal segments were comparable, suggesting more than the lack of axon-cell body contiguity played a role in their demise. Minocycline or vehicle control was injected into the intraperitoneal cavity 30 min and 8 hr after SCI and thereafter twice daily for 2 d. We report a reduction of apoptotic oligodendrocytes and microglia within both proximal and distal segments of the AST after minocycline treatment, using immunostaining for active caspase-3 and Hoechst 33258 staining in combination with cell-specific markers. Activated microglial/macrophage density was reduced remote to the lesion as well as at the lesion site. Both CST dieback and lesion size were diminished after minocycline treatment. Footprint analysis revealed improved functional outcome after minocycline treatment. Thus, minocycline ameliorates multiple secondary events after SCI, rendering this clinically used drug an attractive candidate for SCI treatment trials.

Spinal brain-derived neurotrophic factor governs neuroplasticity and recovery from cold-hypersensitivity following dorsal rhizotomy.

Brain-derived neurotrophic factor (BDNF) has multiple effects on tropomyosin-related receptor kinase B--(TrkB) expressing neurons, including potentiation of spinal nociceptive transmission and stimulation of axon outgrowth. BDNF is upregulated in the spinal cord following dorsal root injury (DRI), a manipulation which elicits both pain and collateral sprouting. Transection of the C7 and C8 dorsal roots (C7/8 DRI) generates cold pain in the ipsilateral forepaw which peaks at 10 days, and resolves within three weeks after injury. In the present study, we investigated the influence of chronic BDNF sequestration, by intrathecal delivery of TrkB-Fc, on the plasticity of nociceptive circuitry and resultant cold pain behaviour following spinal deafferentation. C7/8 DRI resulted in a pronounced deafferentation of the C7 dorsal horn and significant depletion of both peptidergic- and non-peptidergic nociceptive projections. While changes in GAP-43 expression revealed that endogenous BDNF was exerting an overall plasticity-promoting influence on intraspinal axons after DRI, continuous TrkB-Fc treatment stimulated sprouting of nociceptive terminals. DRI stimulated a BDNF-dependent increase in the density of GABAergic interneuronal processes, as indicated by increased vesicular GABA transporter--(VGAT) and neuropeptide Y--(NPY) positive terminal densities. Finally, chronic TrkB-Fc treatment prevented cold pain resolution. These findings demonstrate that endogenous BDNF has both plasticity-promoting and plasticity-suppressing effects on the intrinsic spinal components of nociceptive circuitry, which are likely to underlie cold pain behaviour following C7/8 DRI.

A novel diketopiperazine stimulates sprouting of spinally projecting axons.

Following spinal cord injury, spared axonal projections undergo spontaneous compensatory sprouting in an attempt to reinnervate synaptic targets that were deinnervated as a result of injury. However, compensatory sprouting is hindered by the expression of a myriad of inhibitory molecules throughout the adult central nervous system, including chondroitin sulfate proteoglycans (CSPGs) and myelin associated inhibitory proteins (MAIPs). In this study, we have identified a diketopiperazine designated DKP101516 that can overcome the inhibitory effects of MAIPs and CSPGs on neurite outgrowth and branching. In vivo analysis demonstrates that DKP101516 enhances the plasticity of various axonal populations following septuple dorsal rhizotomy by overcoming the inhibitory effects of CSPGs and MAIPs. Our results suggest that DKP101516 may encourage spinal cord repair by stimulating compensatory sprouting of intact axonal projections.

The astrocytic barrier to axonal regeneration at the dorsal root entry zone is induced by rhizotomy.

After dorsal rhizotomy, sensory axons fail to regenerate beyond the astrocytic glia limitans at the dorsal root entry zone (DREZ) but this inhibition can be overcome with the delivery of exogenous neurotrophin-3. We investigated whether axonal inhibition at the DREZ is constitutive or induced after dorsal rhizotomy. Primary afferent neurones from enhanced green fluorescent protein-expressing mice were transplanted into adult rat dorsal root ganglia in the presence or absence of dorsal rhizotomy. In the absence of dorsal rhizotomy mouse axons freely extended into the rat central nervous system. After host dorsal rhizotomy, mouse axons were unable to cross the DREZ. However, in rats that received a dorsal rhizotomy concomitant with intrathecal neurotrophin-3, the mouse axons were able to cross the DREZ. These results indicate that, under normal circumstances, the adult DREZ is permissive to the regeneration of adult sensory axons and that it only becomes inhibitory once dorsal root axons have been injured and astrocytes at the DREZ have become reactive.

Both positive and negative factors regulate gene expression following chronic facial nerve resection.

Previously, we reported that following a chronic nerve resection, removal of the neuroma reversed the atrophy, increased the number of countable motoneurons and resulted in the re-expression of GAP-43 and alpha tubulin mRNA. In the present study, we questioned whether this response was due to the removal of the neuroma, or a result of factors such as neurotrophins, produced at the injury site. To test this hypothesis, 10 weeks after axotomy, the axonal transport blocker colchicine or, glial derived neurotrophic factor (GDNF) was injected proximal to the neuroma. The injection of GDNF or colchicine elicited an increase in motoneuron size and in GAP-43, but not alpha tubulin, mRNA. These data suggest that in addition to factors produced at the injury site, the neuroma acts as a source of target-like repressive signals that when removed results in an increase in gene expression and motoneuron size. To analyze the regenerative potential of chronically resected motoneurons, mice without a previous nerve injury and mice with a chronic resection received a pre-degenerated segment of sciatic nerve attached to the proximal facial nerve stump. Axons from both the chronic and acute groups grew into the grafts, however, significantly more retrogradely labeled motoneurons were counted in the acute group compared to the chronic resection group. No difference in motoneuron cell size was observed between the two groups of regenerated neurons. Therefore, despite severe atrophy, many of the surviving mouse facial motoneurons retain the propensity to extend their axons when provided with the appropriate environment.

The contribution of activated phagocytes and myelin degeneration to axonal retraction/dieback following spinal cord injury.

Myelin-derived molecules inhibit axonal regeneration in the CNS. The Long-Evans Shaker rat is a naturally occurring dysmyelinated mutant, which although able to express the components of myelin lacks functional myelin in adulthood. Given that myelin breakdown exposes axons to molecules that are inhibitory to regeneration, we sought to determine whether injured dorsal column axons in a Shaker rat would exhibit a regenerative response absent in normally myelinated Long-Evans (control) rats. Although Shaker rat axons did not regenerate beyond the lesion, they remained at the caudal end of the crush site. Control rat axons, in contrast, retracted and died back from the edge of the crush. The absence of retraction/dieback in Shaker rats was associated with a reduced phagocytic reaction to dorsal column crush around the caudal edge of the lesion. Systemic injection of minocycline, a tetracycline derivative, in control rats reduced both the macrophage response and axonal retraction/dieback following dorsal column injury. In contrast, increasing macrophage activation by spinal injection of the yeast particulate zymosan had no effect on axonal retraction/dieback in Shaker rats. Schwann cell invasion was reduced in minocycline-treated control rats compared with untreated control rats, and was almost undetectable in Shaker rats, suggesting that like axonal retraction/dieback, spinal Schwann cell infiltration is dependent upon macrophage-mediated myelin degeneration. These results indicate that following spinal cord injury the phagocyte-mediated degeneration of myelin and subsequent exposure of inhibitory molecules to the injured axons contributes to their retraction/dieback.

Axotomy abolishes NeuN expression in facial but not rubrospinal neurons.

The neuronal nuclei (NeuN) antibody, which binds to a poorly characterized antigen/antigens, is increasingly being used in several areas of study as a specific marker to identify neuronal populations. Despite the increasing reliance on NeuN as a panneuronal marker, changes of NeuN expression following axonal injury have not yet been examined. In the present study, NeuN immunoreactivity was analyzed in adult rodent facial motoneurons [peripheral nervous system (PNS) model] following nerve resection or crush and in rubrospinal neurons [central nervous system (CNS) model] after lesion of the dorsal lateral funiculus at the cervical level of the spinal cord. Peripheral nerve resection in the rat and mouse resulted in an almost complete loss of NeuN immunoreactivity in facial motoneurons by 3 days postinjury and remained absent at 28 days post-resection despite the survival of the neurons as evidenced by neuronal tracing. These results were confirmed with Western blot. In the peripheral nerve crush model of injury, there was an initial decline in NeuN immunoreactivity in facial motoneurons, but unlike the resection model, NeuN immunoreactivity began to return within 7 days postinjury and returned to the uninjured level of expression by 28 days. In contrast, axotomy in the CNS model resulted in little decline in NeuN immunoreactivity in the rubrospinal neurons, even after 28 days postaxotomy. These results indicate that NeuN expression in response to axonal injury is different in separate neuronal populations (PNS and CNS), and that care must be taken when addressing cell survival based on NeuN staining alone.

Caspase inhibition attenuates transection-induced oligodendrocyte apoptosis in the developing chick spinal cord.

A developmental model of spinal cord injury in the embryonic chick was specifically developed to characterize the involvement of caspases in injury-induced oligodendrocyte apoptosis remote from the lesion and the ability of caspase inhibitors to attenuate this process. Developmental apoptosis in the cervical spinal cord increased within the white matter between embryonic days 13 and 18, the period of myelination of this region. Spinal cord transection during this period induced a rapid increase in apoptotic cells in the ventral and lateral white matter over several millimeters caudal to the injury. Immunostaining identified large numbers of these cells as oligodendrocytes. Catalytic activity assays and immunostaining demonstrated caspase-3-like but not caspase-1-like activity to be involved in this apoptotic response. In vivo application of specific caspase inhibitors significantly attenuated transection-induced apoptosis. Thus, we describe a developmental period during which spinal oligodendrocytes exhibited a heightened, caspase-dependent sensitivity to transection-induced apoptosis that is attenuated by caspase inhibition.

Axonal reinjury reveals the survival and re-expression of regeneration-associated genes in chronically axotomized adult mouse motoneurons.

Recently, we reported that chronically axotomized rubrospinal neurons survive for up to 1 year in an atrophied state. This finding contrasted previous work suggesting the death of up to 50% of the neurons over time. In the adult mouse, the majority of facial motoneurons appear to be lost as a result of chronic nerve resection. Here, we sought to determine if chronically resected adult mouse facial motoneurons, like rubrospinal neurons, survive in an atrophied state. To test this hypothesis, we asked whether a second nerve injury, 10 weeks after an initial nerve resection, could stimulate a regenerative cell body response. After chronic resection (10 weeks), mouse facial motoneurons underwent atrophy resulting in a loss of countable neuronal cell bodies. In addition, the motoneurons failed to maintain their initial increase in expression of GAP-43 and alpha-tubulin mRNA. Reinjury of 10-week chronically resected facial motoneurons by the removal of the neuroma reversed the atrophy of the cell bodies and increased the percentage of identifiable cell bodies from 36% of contralateral to 79% in C57BL/6-C3H mice and from 28% of contralateral to 40% in Balb/c mice. Moreover, the reinjured motoneurons displayed an increase in GAP-43 and alpha-tubulin mRNA expression. The results of this study indicate that a second axon injury stimulates regenerative cell body responses in chronically resected mouse facial motoneurons and suggest previous studies using this model may have overestimated the number of dying motoneurons.