Effects of calcium ion on neurite outgrowth of rat spinal cord neurons in vitro: The role of non-neuronal cells in regulating neurite sprouting

The interactions of nerve cells with their environment and other cells are specific to different stages of cellular differentiation. Neurite outgrowth was measured from cultured spinal cord neurons under the influence of different Ca²⁺ concentrations. We used fluorodeoxyuridine (FuDr), an antimitotic agent which reduces significantly the proportion of non-neuronal cells in spinal cord cell cultures, to examine the effects of non-neuronal cells on neurite outgrowth. Spinal cord neurons responded to changes in their environment by means of two types of neurite outgrowth: sprouting and elongation. The concurrent presence of non-neuronal cells led to increased sprouting of neurites in certain ionic environments, thus lending support to the idea that non-neuronal cells release diffusible factors which influence sprouting and guide neurite outgrowth.     

蛋白激酶C调节脊髓神经元突起的生长(英文)

目的关于蛋白激酶C(PKC)在神经元突起生长和神经再生中的作用,目前仍存有争议。本研究主要观察PKC对离体培养的脊髓神经元生长的调节作用,旨在阐明PKC对突起生长的调节作用。方法分离纯化胎龄14天(E14)的SD胎鼠的脊髓前角神经元,进行原代培养,并检测不同时相点膜/浆PKC活性(m/c-PKCactivity)的比值。结果神经元培养3-11d期间,神经元内m/c-PKC比值以及PKC-βII在突起中的表达水平均与突起生长呈显著相关关系(r=0.95,P<0.01;r=0.73,P<0.01)。此外,PKC激动剂PMA能显著提高m/c-PKC比值,且与神经突起的生长一致(r=0.99,P<0.01)。而PKC抑制剂GF109203X则能显著抑制突起生长,且不被PMA作用所逆转。结论PKC的活性在脊髓神经元突起生长调节中具有重要作用,其中βII亚型可能扮演重要角色。     

The development of a rat in vitro model of spinal cord injury demonstrating the additive effects of Rho and ROCK inhibitors on neurite outgrowth and myelination

It is currently thought that treatment for spinal cord injury (SCI) will involve a combined pharmacological and biological approach; however, testing their efficacy in animal models of SCI is time-consuming and requires large animal cohorts. For this reason we have modified our myelinating cultures as an in vitro model of SCI and studied its potential as a prescreen for combined therapeutics. This culture comprises dissociated rat embryonic spinal cord cells plated onto a monolayer of astrocytes, which form myelinated axons interspaced with nodes of Ranvier. After cutting the culture, an initial cell-free area appears persistently devoid of neurites, accompanied over time by many features of SCI, including demyelination and reduced neurite density adjacent to the lesion, and infiltration of microglia and reactive astrocytes into the lesioned area. We tested a range of concentrations of the Rho inhibitor C3 transferase (C3) and ROCK inhibitor Y27632 that have been shown to promote SCI repair in vivo. C3 promoted neurite extension into the lesion and enhanced neurite density in surrounding areas but failed to induce remyelination. In contrast, while Y27632 did not induce significant neurite outgrowth, myelination adjacent to the lesion was dramatically enhanced. The effects of the inhibitors were concentration-dependent. Combined treatment with C3 and Y27632 had additive affects with an enhancement of neurite outgrowth and increased myelination adjacent to the lesion, demonstrating neither conflicting nor synergistic effects when coadministered. Overall, these results demonstrate that this culture serves as a useful tool to study combined strategies that promote CNS repair.     

Acidic and basic fibroblast growth factors enhance neurite outgrowth in cultured rat spinal cord neurons

Abstract

We have studied neurotrophic effects of acidic fibroblast growth factor (aFCF) and basic fibroblast growth factor (bFGF) on explanted ventral and dorsal spinal cord cultures from 13- and 14-day-old rat embryos. Cultures treated with aFCF and bFGF significantly enhanced neurite outgrowth with cultures of ventral spinal cord, but not with cultures of dorsal spinal cord. Our data suggest that aFCF and bFGF are potent neurotrophic factors on rat ventral spinal cord neurons in vitro. [Neurol Res 1995; 17: 70-72]     

Adult human spinal cord harbors neural precursor cells that generate neurons and glial cells in vitro

Adult human and rodent brains contain neural stem and progenitor cells, and the presence of neural stem cells in the adult rodent spinal cord has also been described. Here, using electron microscopy, expression of neural precursor cell markers, and cell culture, we investigated whether neural precursor cells are also present in adult human spinal cord. In well-preserved nonpathological post-mortem human adult spinal cord, nestin, Sox2, GFAP, CD15, Nkx6.1, and PSA-NCAM were found to be expressed heterogeneously by cells located around the central canal. Ultrastructural analysis revealed the existence of immature cells close to the ependymal cells, which display characteristics of type B and C cells found in the adult rodent brain subventricular region, which are considered to be stem and progenitor cells, respectively. Completely dissociated spinal cord cells reproducibly formed Sox2(+) nestin(+) neurospheres containing proliferative precursor cells. On differentiation, these generate glial cells and gamma-aminobutyric acid (GABA)-ergic neurons. These results provide the first evidence for the existence in the adult human spinal cord of neural precursors with the potential to differentiate into neurons and glia. They represent a major interest for endogenous regeneration of spinal cord after trauma and in degenerative diseases.     

ROCK inhibition enhances neurite outgrowth in neural stem cells by upregulating YAP expressionin vitro

Spontaneous axonal regeneration of neurons does not occur after spinal cord injury because of inhibition by myelin and other inhibitory factors. Studies have demonstrated that blocking the Rho/Rho-kinase (ROCK) pathway can promote neurite outgrowth in spinal cord injury models. In the present study, we investigated neurite outgrowth and neuronal differentiation in neural stem cells from the mouse subventricular zone after inhibition of ROCK in vitro. Inhibition of ROCK with Y-27632 increased neurite length, enhanced neuronal differentiation, and upregulated the expression of two major signaling pathway effectors, phospho-Akt and phospho-mitogen-activated protein kinase, and the Hippo pathway effector YAP. These results suggest that inhibition of ROCK mediates neurite outgrowth in neural stem cells by activating the Hippo signaling pathway.     

Extracellular calcium ionic activity in experimental spinal cord contusion

Entry of calcium ions (Ca²⁺) into axons has been hypothesized by several investigators to play a major role in myelopathy of spinal trauma. Although some evidence supports this hypothesis, a rapid and large influx of Ca²⁺ into cells prior to development of necrotic changes has not been demonstrated in spinal injury. Because large influxes of Ca²⁺ into cells are manifested by decreases in extracellular Ca²⁺, we measured extracellular Ca²⁺ activity in contused cat spinal cords, using ion-selective microelectrodes and relating the Ca²⁺ changes to local blood flow and evoked potentials.Within 5 min of 400 g·cm contusion, we found decreases of spinal extracellular Ca²⁺ from normal pre-injury levels (1.0–1.3 mM) to < 0.1 mM at or within 5 mm of the impact site. The time course of extracellular Ca²⁺ recovery depended on distance from the contusion. In gray matter at the impact site, extracellular Ca²⁺ did not recover above 0.1 mM for up to 4 h after injury. In white matter at the impact site, extracellular Ca²⁺ recovered to 0.35 mM but fell to <0.1 mM at 2–3 h after injury. In white matter at the edge of the impact site, extracellular Ca²⁺ returned slowly to 0.6 mM by 4 h. In white matter 5 mm from the impact site, extracellular Ca²⁺ normalized by 3 hours.The initial extracellular Ca²⁺ fall preceded the onset of significant blood flow changes in spinal cord white matter. Thus, the Ca²⁺ change was related to the trauma and not to subsequent blood flow alterations. Evoked potentials often recovered transiently at 1–2 h after injury, suggesting that some axons were not immediately destroyed by the contusion and their subsequent survival or function was influenced by factors other than the initial Ca²⁺ derangement. Neither blood flow changes nor action potential conduction recovery depended on specific levels of extracellular Ca²⁺. In conclusion, our data support the hypothesis of Ca²⁺-mediated injury of spinal tracts but additional work is required to define the role of Ca²⁺ in the later phases of spinal injury.     

Calpain inhibitors block Ca2+-induced suppression of neurite outgrowth in isolated hippocampal pyramidal neurons

Ca²⁺ is an important regulator of neurite elongation and growth cone movements but the mechanism(s) mediating these Ca²⁺-dependent effects is nuclear. Since cytoskeletal proteins are rapidly degraded by Ca²⁺-dependent proteinases (calpains) in vitro and in vivo, we investigated whether Ca²⁺-induced pruning or regression of neuronal processes is mediated by calpains. Isolated hippocampal pyramidal-like neurons were cultured and the ability of the membrane-permeable calpain inhibitors ethyl(+)-(2S,3S)-3-[(S)-methyl-1-(3-methylbutylcarbamoyl)-butylcarbamoyl]-2- oxiranecarboxylate (EST) and carbobenzoxyl-valyl-phenylalanyl-H (MDL 28170) to block the Ca²⁺ ionophore A23187-induced suppression in neurite outgrowth was investigated. Addition of 100 nM A23187 to the culture medium resulted in a retraction of dendrites without altering axonal elongation. The addition of 300 nM A23187 to the culture medium resulted in a significant decrease in the rate of axonal elongation as well as a retraction of dendritic processes. Administration of EST (5 or 20 m?M) to the culture medium completely blocked the pruning effect of 100 nM A23187 on dendrites and of 300 nM A23187 on axons, while EST alone did not significantly affect neurite outgrowth rate. MDL 28170 (20 m?M) showed the same effect as EST in preventing ionophore-induced pruning of dendrites and axons at 100 and 300 nM concentrations, respectively, of A23187. EST (20 m?M) did not block the A23187-induced rise of [Ca²⁺]_i as measured with fura-2. These results suggest that calpains play a role in Ca²⁺-induced pruning of neurites in isolated hippocampal pyramidal neurons. © 1994 Wiley-Liss, Inc.     

Observation of cultured peripheral non-neuronal cells implanted into the transected spinal cord

Summary We have previously reported that cultured peripheral non-neuronal cells could be used as an adjunct to spinal cord reconstruction with the delayed nerve graft technique. The cultured cells appeared to enhance axonal regeneration and with their use the time it took for axons from the spinal cord stumps to reach the nerve graft was reduced. To gain insight into the possible mechanisms through which peripheral nonneuronal cells can foster CNS regeneration, we have now investigated the behaviour of the peripheral nonneuronal cells after implantation into the spinal cord. Autologous mixed non-neuronal cell cultures were prepared from cat sciatic nerve biopsies and labeled in culture with tritiated thymidine. The labeled cells were implanted so as to completely fill the gap in the spinal cord produced by a narrow slit transection. Light-and electron-microscopic autoradiography was used to identify the cells 3 and 7 days after implantation and to determine their proximity to, and possible interaction with, axons in the spinal cord stumps. The implanted peripheral cells were frequently found near spinal cord axons and axon terminals. Some of the labeled cells ensheathed axons in which case they displayed morphological characteristics of Schwann cells. Other labeled cells had characteristics of fibroblasts and were surrounded by an extracellular matrix rich in collagen fibrils. Many of the labeled cells contained phagocytosed myelin debris. These observations are consistent with the implanted cells acting to enhance regeneration in the spinal cord either by direct interaction with axons (ensheathment) or indirectly via the production of soluble neuronotrophic factors or a favorable extracellular matrix. The ability of the implanted cells to rapidly move into the spinal cord stumps and attain positions close to spinal cord axons would be an important factor for any of these mechanisms.Supported by grants from the Veterans Administration and the National Institutes of Health (NS-14413)     

Development of commissural neurons in the embryonic rat spinal cord.

Little is known about the development of the various populations of interneurons in the mammalian spinal cord. We have utilized the lipid-soluble tracer DiI in fixed tissue to study the migration and dendritic arborization of spinal neurons with axons in the ventral commissure in embryonic rats. Crystals of DiI were placed in various locations in the thoracic spinal cord in order to label commissural neurons within the dorsal horn, intermediate zone, and ventral horn at E13.5, E15, E17, and E19. Seven different groups of commissural interneurons are present in the spinal cord by E13.5. Migration is relatively simple with groups occupying a position along the dorsoventral axis roughly corresponding to their position of origin along the neuroepithelium. By E15, commissural cells are near their final locations and exhibit characteristic morphology. One striking feature is the tendency of cells with similar morphology to cluster in distinct groups. By E19, at least 18 different types of commissural interneurons can be identified on morphological grounds. Although the situation is complex, some generalities about dendritic morphology are apparent. Commissural neurons located in the dorsal horn are small and have highly branched dendrites oriented along the dorsoventral axis. In more ventral regions, commissural neurons are larger and possess dendritic arbors oriented obliquely or parallel to the mediolateral axis with long dendrites extending toward the lateral and ventral funiculi. The number of primary dendrites of most groups is set by E15 and dendritic growth occurs in the transverse plane by lengthening and branching of these primary processes. This study demonstrates that a large number of classes of commissural interneurons can be recognized on the basis of characteristic morphologies and locations within the dorsal horn, intermediate zone and ventral horn of the embryonic rat spinal cord. This finding is consistent with the fact that commissural neurons project to many different targets and mediate a variety of different functions. The demonstration that dendritic arbors of spinal interneurons with characteristic morphologies can be conveniently labelled with DiI should prove useful in future studies on the development of specific circuits in the mammalian spinal cord.     

Review: Manipulating the extracellular matrix and its role in brain and spinal cord plasticity and repair

Brain and spinal cord injury can result in permanent cognitive, motor, sensory and autonomic deficits. The central nervous system (CNS) has a poor intrinsic capacity for regeneration, although some functional recovery does occur. This is mainly in the form of sprouting, dendritic remodelling and changes in neuronal coding, firing and synaptic properties; elements collectively known as plasticity. An important approach to repair the injured CNS is therefore to harness, promote and refine plasticity. In the adult, this is partly limited by the extracellular matrix (ECM). While the ECM typically provides a supportive framework to CNS neurones, its role is not only structural; the ECM is homeostatic, actively regulatory and of great signalling importance, both directly via receptor or coreceptor‐mediated action and via spatially and temporally relevant localization of other signalling molecules. In an injury or disease state, the ECM represents a key environment to support a healing and/or regenerative response. However, there are aspects of its composition which prove suboptimal for recovery: some molecules present in the ECM restrict plasticity and limit repair. An important therapeutic concept is therefore to render the ECM environment more permissive by manipulating key components, such as inhibitory chondroitin sulphate proteoglycans. In this review we discuss the major components of the ECM and the role they play during development and following brain or spinal cord injury and we consider a number of experimental strategies which involve manipulations of the ECM, with the aim of promoting functional recovery to the injured brain and spinal cord.     

Ionic mechanisms of 3 types of functionally different neurons in the lamprey spinal cord

Action potentials and afterpotentials were compared in giant interneurons, sensory dorsal cells and large intraspinal axons in the lamprey spinal cord. Afterpotentials of giant interneurons and dorsal cells consisted of two hyperpolarizing phases, an early and a late one, which were separated by a delayed depolarization. The afterpotentials of axons had a single hyperpolarizing phase also followed by a delayed depolarization. Tetraethyl ammonium chloride (TEA+) eliminated the early phase of the afterhyperpolarization in giant interneurons, only partially reduced the early phase in dorsal cells and did not affect the single phase of axons. The delayed depolarization of dorsal cells was attenuated by TEA+ but in axons it was unaltered. The heavy metal ions Mn2+ and Co2+ (2 mM) eliminated the late phase in giant interneurons but did not reduce the late phase in dorsal cells. The delayed depolarization remained in both types of cell in the presence of these ions. Action potentials of giant interneurons and dorsal cells, but not those of axons, were broadened by TEA+. The TEA-prolonged action potentials were narrowed by Mn2+ applied in combination with TEA+. The afterhyperpolarizations of all 3 cells were reduced by injection of negative current and enhanced by positive current. Repetitive stimulation resulted in summation of the afterhyperpolarization in giant interneurons and dorsal cells. The results suggest that different sets of potassium channels are responsible for the afterhyperpolarizations in each type of cell. In giant interneurons fast channels which are sensitive to TEA+ may underlie the early phase and slow channels activated by calcium entry may underlie the slow phase. The early phase of dorsal cells may be caused by two types of fast channel, one similar to that in giant interneurons and another less sensitive to external TEA+. This latter type may also cause the afterhyperpolarization in axons. Although calcium channels appear to contribute to the action potentials of giant interneurons and dorsal cells, the late phase of the latter neurons does not seem to be activated by calcium entry. The delayed depolarizations of the neurons appear to be due to an inward current which is not carried by calcium.     

Nerve growth factor (NGF) induces motoneuron apoptosis in rat embryonic spinal cord in vitro

Recent studies have demonstrated that nerve growth factor (NGF) induces apoptosis of several cell types in the central nervous system through its low-affinity p75 neurotrophin receptor (p75NTR). To test the effect of NGF on embryonic motoneuron survival, we developed an organotypic culture system which allowed the in vitro development of intact embryonic rat spinal cords. In our system, neural tubes were taken and cultured at E13, just before the onset of physiological motoneuron death. After 2 days in vitro (DIV), motoneurons underwent apoptosis over a time-course similar to that in vivo. In this system, the addition of NGF (200 ng/mL) for 2 days enhanced the number of apoptotic motoneurons by 37%. This pro-apoptotic effect was completely reversed by the blocking anti-p75NTR (REX) antibody which inhibits NGF binding to p75NTR. Other neurotrophins, e.g. brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and neurotrophin 4/5 (NT4/5) did not have any effect, while glial cell-derived neurotrophic factor (GDNF) promoted motoneuron survival. Anti-BDNF blocking antibodies enhanced motoneuron death indicating that endogenous BDNF promotes motoneuron survival in explants. Our results demonstrate, for the first time, that NGF can induce embryonic motoneuron apoptosis through its receptor p75NTR.     

体外培养大鼠脊髓前角神经元：脑源性神经生长因子对突触蛋白表达的影响

探讨BDNF对体外培养的大鼠脊髓前角神经元内突触素I与突触囊泡素(SYN)表达的影响。取孕14 d大鼠子宫内胎鼠的脊髓腹侧部分神经元,体外有血清培养。在培养7 d后．随机分成对照组、BDNF组和抗BDNF组。BDNF组培养液中加入BDNF(20 ng/ml),抗BDNF组培养液中加入BDNF抗体(20цg/ml),对照组加入等量Hanks液。3 d后在倒置显微镜下计数三组神经元成活数,并用NF-200、MAP-2、NSE的免疫组化反应对神经细胞进行鉴定。行突触素I与SYN免疫组化反应,对部分细胞行突触素I mRNA原位杂交反应,运用图像分析系统对突触素I与SYN免疫反应阳性产物以及突触素I原位杂交反应阳性产物作光密度分析。结果发现有血清培养时各组脊髓前角神经元的存活数差异无显著性 (P>0.05);BDNF组突触素I与SYN免疫反应阳性产物的平均光密度值高于其它两组,抗BDNF组最低（P<0.01）。BDNP组突触素I mRNA阳性产物的平均光密度值明显高于其它两组,抗BDNF组突触素I mRNA阳性产物的平均光密度值最低（P<0.01）。本研究结果提示BDNF对有血清培养时脊髓前角神经元的存活没有明显影响,但BDNF可明显上调培养的脊髓前角神经元内突触素I与SYN的表达     

Impact of chemokines on the properties of spinal cord‐derived neural progenitor cells in a rat spinal cord lesion model

The existence of endogenous neural progenitor cells (NPCs) in the adult spinal cord (sc) provides the potential for tailored repair therapies after spinal cord injury (SCI). This study investigates the impact of inflammatory mediators on properties of NPC cultures derived from adult rats after SCI. The Infinite Horizon impactor was used to apply 200‐kdyn thoracic sc lesions in adult rats. Control groups received laminectomies to equivalent sc regions. Thoracic sc segments were taken for neurosphere cell cultures. Cell proliferation was found to be significantly higher in lesion groups. Neurosphere‐derived cells differentiated into neurons, oligodendroglia, and astroglia. Lesion cultures exhibited significantly higher amounts of glial fibrillary acidic protein (GFAP) mRNA (P < 0.0005) and β‐III‐tubulin mRNA (P < 0.05) compared with sham animals. Neurospheres from different treatment groups exhibited the same amounts of tumor necrosis factor‐α, interleukin (IL)−1β, and IL‐6 mRNA. C‐C chemokine receptor (CCR) expression on neurospheres was examined by real‐time RT‐PCR. CCR1 was expressed most consistently in mRNA levels in neurospheres from both treatment groups. After cell differentiation, CCR1 mRNA amounts decreased. CCR1 was detectable by immunohistochemistry in neurospheres and differentiated cells of both groups. Application of CCL3 during differentiation cycles led to significantly higher GFAP mRNA amounts in sham animals compared with CCL3‐free cultures; in contrast, CCL3 had no impact on cell differentiation in the lesion group. In conclusion, impact SCI alters differentiation tendencies and proliferation rates of adult‐derived sc NPCs. Thereby, CCR1/CCL3 promotes specifically astroglial differentiation of NPCs, which provides a potential target for future neurorestorative approaches. © 2014 Wiley Periodicals, Inc.     

Interactions between intraspinal Schwann cells and the cellular constituents normally occurring in the spinal cord: an ultrastructural study in the irradiated rat

Relationships between intraspinal Schwann cells and neuroglia, particularly, astrocytes, were studied following X-irradiation of the spinal cord in 3-day-old rats. Initially, this exposure results in a depletion of the neuroglial population. By 10 days post-irradiation (P-I), gaps occur in the glia limitans, although the overlying basal lamina remains intact. Development of and myelination by intraspinal Schwann cells is well underway by 15 days P-I. These Schwann cell-occupied regions have a paucity of astrocyte processes, a finding which persists throughout the study (60 days P-I), and several types of Schwann cell-neuroglial interfaces are observed, including: (1) astrocyte separation of Schwann cells from oligodendrocyte-myelinated regions; (2) intermingling of Schwann cell-myelinated axons and oligodendrocyte-myelinated axons in the absence of astrocyte processes; and (3) ensheathment of unmyelinated axons by astrocyte processes which separate these axons from the Schwann cells. The gaps in the glia limitans widen as the P-I interval increases. At 45 and 60 days P-I, the basal lamina no longer forms a singular, continuous covering over the spinal cord surface, but follows instead a rather tortuous course over the disrupted glia limitans and the intraspinal Schwann cells. Although the mode of initial occurrence of Schwann cells within the spinal cord is not yet understood, the data indicate that the astrocyte population is involved in that process, as well as in limiting the further development of Schwann cells within the substance of the spinal cord.     

Stimulatory effect of opioid peptides and naloxone on rat spinal cord cells in primary dissociated culture

Opioid peptides leu-enkephalin, a synthetic analog of enkephalin dalargin and an opiate receptor blocker naloxone were studied for their morphological effect on the cells of dissociated cultures of rat spinal cord.Low density seeding of cells (3.10⁵; 6.10⁵ cells/ml) on collagen substrate was performed to document that opioid peptides increase the number of cultured cells and neurite outgrowth and lead to the activation of the initiated processes of aggregate formation. Upon higher density of plating (5.10⁶ cells/ml) with poly-l-lysine as a substrate, activation of the aggregate formation process was demonstrated, both opioid peptides and naloxone leading to an increase in the size of aggregates. Statistical treatment of the results obtained in this set of experiments documented that leu-enkephalin, dalargin and naloxone increased 2.2-, 2.2–2.6-, 2.4-fold, respectively, the size of aggregates compared to the control, i.e. the reaction of spinal cord cells to opioid peptides and opiate receptor blocker naloxon was unidirected. The total effect of opioid peptides and naloxon resulted in a 3.6-fold increase in the size of the aggregates compared to the control. The data obtained in this study allow the assumption that opioid peptides and naloxone, while activating spinal cord cells via receptors of a different type, manifest the properties of factors thus increasing survival and adhesion of spinal cord cells in culture.     

Collateral sprouting of the central terminals of cutaneous primary afferent neurons in the rat spinal cord: pattern, morphology, and influence of targets

The capacity of the central terminals of primary afferents to sprout into denervated areas of neonatal spinal cord and the morphology of any novel terminals has been investigated. In rats which had undergone sciatic nerve section on the day of birth, 12 of 18 physiologically characterized intact saphenous hair follicle afferents (HFAs) were labelled intra-axonally with horseradish peroxidase (HRP) were shown to sprout up to 2,000 microns into the deafferented sciatic terminal field. The morphology of these sprouts depended on which area of the sciatic nerve territory was invaded by the afferent sprouts. Six HFAs sprouted into areas normally innervated by glabrous skin afferents and the morphology of the collateral sprouts in this region resembled that of rapidly adapting (RA) afferents. The other six saphenous HFAs had sprouted into sciatic "hairy" skin areas and the morphology of these sprouts, although abnormal, was flame shaped. In rats whose sural, saphenous, and superficial peroneal nerves were cut at birth, 4 of 7 single HRP labelled RA afferents had central terminals that had sprouted into regions of cord normally devoted to "hairy" input. These showed clear signs of HFA morphology despite their peripheral receptive fields remaining in the glabrous skin. The results show collateral sprouting of single cutaneous sensory afferent axons into adjacent inappropriate central target regions following neonatal deafferentation. Such plasticity may provide some compensation following neonatal injury. The morphology of the sprouted terminals is appropriate to the new target area rather than to its functional class and is also independent of the peripheral receptive field location providing an example of central rather than peripheral control over afferent growth patterns.