Regeneration of monoamine-containing axons in the developing and adult spinal cord of the rat following intraspinal 6-OH-dopamine injections or transections

Summary Growth of descending noradrenaline (NA) and 5-hydroxytryptamine (5-HT) axons in the rat spinal cord during ontogenesis and following mechanical or chemical, 6-hydroxydopamine (6-OH-DA) induced, axotomy, was studied with the Falck-Hillarp histochemical fluorescence method for monoamines.The major NA and 5-HT axon bundles and terminal innervation areas are present already at birth and an essentially mature pattern of innervation is reached after two weeks.Complete degeneration of both 5-HT and NA nerves in the distal segment is obtained by a transection of the spinal cord. Sprouting of the cut monoamine fibers into the necrotic zone and scar tissue is vigorous in both immature and mature animals, but regeneration into the distal segment is very poor.Selective degeneration of the descending NA axons and terminals is obtained by a localized intraspinal 6-OH-DA injection. Thus, the 5-HT fiber systems as well as all other parts of the spinal cord are left intact. The method should therefore prove useful for evaluating the exact functional role of the NA and 5-HT neuron systems in the spinal cord.Reinnervation of the distal part of the spinal cord by new NA fibers following 6-OH-DA induced denervation is described. This process is faster in younger animals but takes place also in adult animals. The present evidence suggests that reinnervation mainly is the result of downgrowth of the axotomized fibers, but growth in the form of collateral sprouting from a few possibly surviving fibers in the distal region may also contribute. Reinnervation lead to a normal innervation pattern within 1–2 months in the various age groups.It is suggested that the poor regeneration of many spinal nerve tracts often reported in the literature following transection of the spinal cord is due to extraneuronal factors such as scar tissue and impaired circulation rather than to the nerves per se since reinnervation by NA nerves was very poor following mechanical transection but good following chemical, 6-OH-DA-induced axotomy.     

The growth of motor axons in the spinal cord of Xenopus embryos

The innervation of the myotomal muscles in the trunk region of Xenopus embryos has been examined to see how the path taken by motoneurons within the spinal cord is formed. The growth of motor axons has been studied by retrograde labeling with horseradish peroxidase and the growth of the spinal cord and myotomes has been studied by labeling with fluorescent beads. Results show that motoneurons initially innervate the nearest muscles. Then through a process of differential growth whereby the muscles elongate more than the spinal cord, the axonal terminals in the muscles become displaced caudally relative to their cell bodies. In this manner the central pathway taken by the motor axons develops after initial innervation of their peripheral targets.     

Changes of Neurotransmitter Systems in Chronic Relapsing Experimental Allergic Encephalomyelitis in Rat Brain and Spinal Cord

Catecholamine and indoleamine neurotransmitters, together with some of their precursors and metabolites, were determined using HPLC in three brain and two spinal cord regions of Lewis rats with chronic relapsing allergic encephalomyelitis and of control rats injected with complete Freund's adjuvant. Three attacks and two recovery phases were investigated. Changes are found mainly in the spinal cord. In the lumbosacral region both 5-hydroxytryptamine and noradrenaline are reduced during the entire course of the disease, whereas in the craniothoracal region 5-hydroxytryptamine is unchanged and only noradrenaline is reduced during the attacks, returning to normal during the first recovery. The precursors tyrosine and tryptophan are greatly elevated during the first two attacks in both regions. The 5-hydroxytryptamine turnover marker 5-hydroxyindoleacetic acid is increased in the first attack in both regions, then it decreases in the later stages, indicating destruction of nerve fibers. On the fourth and seventh days after inoculation values are generally not significantly different from controls in all regions. The possible correlation of neurochemical results with neurological signs is discussed.     

Ultrastructural study of neurotensin immunoreactivity in the superficial laminae of the dorsal horn of the rat

Neurotensin immunoreactivity was identified in cell bodies, dendrites, spines, axons, terminals and varicosities in superficial laminae of rat spinal cord with the electron microscope. Unlabeled terminals synapsed with neurotensin-immunoreactive cell bodies, dendrites and spines. Presynaptic terminals contained round or pleomorphic vesicles and generally made symmetrical contacts with medium-sized neurotensin-containing dendrites in outer lamina II, and asymmetrical or symmetrical contacts with large and small dendrites and spines in inner lamina II. Neurotensin immunoreactive axons were unmyelinated, and their terminals were presynaptic to unlabeled dendrites and spines in laminae I and II. Terminals contained small, round, clear vesciles (31 nm) and occasional large granular vesicles (78 nm). Contacts in outer lamina II were evenly distributed among dendrites of various sizes and spines, whereas the majority of labeled terminals in inner lamina II made contacts onto small dendrites and spines. These findings indicate that neurotensin effects in rat spinal cord are mediated by axodendritic synapses, and that neurotensin cells at the inner and outer borders of lamina II contact dendrites of efferent neurons or other interneurons in the dorsal horn.     

DIFFERENTIATION OF DOPAMINERGIC AND NORADRENERGIC NEURONS IN RAT SPINAL CORD

Abstract— Norepinephrine (NE), dopamine (DM) and 3-methoxy-4-hydroxyphenylacetic acid (HVA) content have been measured in different parts of rat spinal cord and cerebellum by a gas chromatographic mass spectrometric method. In cerebellum, which does not contain dopaminergic neurons, the ratio of NE to DA content was 47, whereas in parts of the spinal cord this ratio varied between 11 and 19. In the cord after desipramine (25 mg/kg, i.p.) plus 6-hydroxydopamine (6-HDA, 100/jg intracisternally), there was a significant depletion of DM but not of NE. Conversely, after benztropine (25 mg/kg, i.p.) plus 6-HDA there was a significant depletion of NE but not of DM. Chlorpromazine (10 mg/kg, i.p.) or clozapine (25 mg/kg, i.p.) caused a significant increase in spinal cord HVA concentration 1 h after treatment. Evidence is presented which suggests that the increased HVA measured in the cord did not originate in the brain. After electrolytic lesion of the locus coeruleus there was a significant reduction of NE but not of DM. Spinal cord DM and NE were depleted by reserpine in a dose-dependent manner, the threshold dose for DM depletion being less than that for NE depletion. Seven days after cord transection at T₁₀ spinal cord DM was significantly reduced in the lumbar region. These results suggest that dopaminergic neurons exist in rat spinal cord independently of noradrenergic neurons and that the DM is likely to be present in the terminals of descending axons.     

Immunohistochemical demonstration of calbindin-D 28K (CABP28K) in the spinal cord motoneurons of teleost fish

Summary The distribution and localization of the calciumbinding protein, calbindin-D 28K (CaBP28K), in the spinal cord motoneurons of larvae of the teleost fish, Apteronotus leptorhynchus (Gymnotidae) and Pollimyrus isidori (Mormyridae), and in the adult goldfish, Carassius auratus (Cyprinidae), were determined by means of immunohistochemistry. Sections of whole larvae and goldfish spinal cord were reacted with a polyclonal antibody to rat renal CaBP28K. CaBP28K was located by the PAP technique (Sternberger). It was found in the soma, dendrites, axons and axon terminals of spinal motoneurons but not in those of electromotoneurons of Apteronotus leptorhynchus, whereas it occurred in both motoneurons and electromotoneurons of the larval electric organ of Pollimyrus isidori. In these species CaBP28K was also present in the electromotoneuron axon terminals that make synaptic contacts with the pedicles of the electrocytes. In adult Carassius auratus, CaBP28K was found in the soma, dendrites and axons of certain spinal motoneurons. The results indicate that, in teleosts, the motoneurons containing CaBP28K may represent a well-defined population within the spinal cord; the role of this protein in these cells remains to be determined.     

Anatomical Studies of the Spinocervical Tract of the Rat

The retrograde transport of horseradish peroxidase (HRP) was used to identify and examine the cells of origin of the spinocervical tract (SCt) in the rat. Initially, precise data on the boundaries of the rat lateral cervical nucleus (LCn) were gathered after injecting HRP into the ventrobasal thalamus. These data indicated that the LCn of the rat is restricted to a region on the extreme lateral edge of the dorsalmost portion of the lateral funiculus (DLf) within spinal segment C₂ Following small iontophoretic injections of HRP that were restricted to this area, labeled SCt neurons were found in the ipsilateral nucleus proprius at all levels of the spinal cord but were most numerous in the cervical enlargement. Lesion studies indicated that the overwhelming majority of SCt axons ascend to the LCn within the DLf. In an attempt to determine whether our injection techniques labeled a significant number of cells through axons of passage, HRP injections were made in the DLf ventral to the LCn. Such injections labeled, presumably through axons of passage, cells in several areas of the spinal cord gray matter, including a large number in the contralateral marginal zone Injections in areas immediately rostral to the LCn labeled 20% or less of the total number of cells within the enlargements that were labeled by injections into the LCn. Thus, the majority of cells labeled by injections of HRP into the LCn were labeled through preterminal fibers or terminals themselves. The cells of origin of the SCt in the rat are similar in location to those in the cat but far fewer in number.     

Target-derived astroglia regulate axonal outgrowth in a region-specific manner.

The potential neuroanatomical specificity of astrocyte influence on neurite outgrowth was studied using an in vitro coculture system in which neurons from embryonic rat spinal cord or hippocampus were grown for 4 days in the presence of, but not in direct contact with, astrocytes derived either from the same region (homotopic coculture) or from different regions (heterotopic coculture) of the rat central nervous system. The results showed that axonal outgrowth was greatly enhanced in heterotopic cocultures in which spinal cord or hippocampal neurons were grown with astrocytes derived from their appropriate CNS target regions. This effect was remarkably specific, because the astroglia harvested from spinal or hippocampal target regions were not effective in promoting axon growth of nonafferent neuronal populations. Dendritic outgrowth was similar under all coculture conditions. These data suggest that diffusible signals, produced by astrocytes, can regulate neurite extension in vitro in a neuroanatomically specific manner and that axons are more sensitive than dendrites to the regional astrocyte environment.     

Effect of Rabbit Anti-Asialo-GM1 (GA1) Polyclonal Antibodies on Neuromuscular Transmission and Acetylcholine-Induced Action Potentials: Neurophysiological and Immunohistochemical Studies

We produced anti-asialo-GM1 (GA1) polyclonal antibodies by sensitizing New Zealand rabbits with GA1 and investigated the epitopes and pathogenic role of anti-GA1 antibodies that appeared in serum. The serum blocked neuromuscular transmission, but not acetylcholine (ACh)-induced potentials, in muscle-spinal cord cocultured cells. The effect was complement independent. The antibodies inhibited voltage-gated Ca2+ channel (VGCC). The epitopes recognized by the antibodies were located in the outer membrane of Schwann cells and motor axons of Wistar rat ventral roots and on motor axons extended from spinal cord to muscle cells in muscle-spinal cocultured cells. The ACh-induced potential was not reduced by the addition of sera, suggesting the blockade is presynaptic. Thus, anti-GA1 antibodies may block neuromuscular transmission by suppressing VGCC on axonal terminals of motor nerves.     

Constitutive Expression of Calmodulin-Binding Phosphoprotein GAP-43 in Rat Serotonergic and Noradrenergic Cell Groups Which Project to the Spinal Cord

In situ hybridization was combined with serotonin (5-hydroxytryptamine, 5-HT) or tyrosine hydroxylase immunocytochemistry and with Fluoro-Gold retrograde labeling of bulbo-spinal pathways in order to investigate the expression of GAP-43 mRNA in monoamine cell groups of the adult rat brain stem. Consistent with previous reports, GAP-43 mRNA was observed in serotonin and dopamine cell groups in the pons. In addition, GAP-43 expressing cells were observed in all the major monoamine cell groups in the medulla. Thus the B1, B2 and B3 serotonin cell groups all showed high GAP-43 expression and all contained many GAP-43 expressing serotonin cells with spinal cord projections. The A1, A2, A5 and A6 noradrenalin cell groups also showed high GAP-43 expression, although cells with spinal cord projections were largely restricted to the A5 group and A6 subcoeruleus region. In all areas, GAP-43 expressing cells with spinal cord projections were also observed which were not serotonergic or noradrenergic.     

Development of the caudal neurosecretory system of the nile tilapia Oreochromis niloticus: an immunohistochemical and electron microscopic study

The development of the caudal neurosecretory system (CNSS) of the Nile tilapia, Oreochromis niloticus, has been investigated by means of UI/oCRF (urotensin I/ovine corticotropin-releasing factor) immunohistochemistry and transmission electron microscopy. UI-like immunoreactive perikarya and fibers are first detected in the caudal spinal cord of larval fish about 4 days after hatching (stage 21). In the region of the future urophysis two bundles of strongly immunoreactive neurosecretory fibers are observed. At this stage, neurosecretory axons terminate on the meninx sheath of the spinal cord with immature neurosecretory terminals. The histogenesis of the urophysis begins at stage 24. The future neurohemal organ consists of a small ventral swelling of the spinal cord, which is associated with dilated vessels. At this stage, neurosecretory axons terminate on the basal lamina of the ingrowing blood vessels. Further development occurs by means of progressive branching of vessels and the concomitant increase in the number of neurosecretory terminals. In the caudal spinal cord, immunoreactive neurons also increase in number and progressively differentiate morphologically. Typical features of the mature CNSS are recognizable in 4-month-old juveniles. Data suggest that in tilapia both the synthesis and the release of urophysial hormones begin before morphogenesis of the neurohemal organ takes place.     

Effects of L-Tryptophan on Indoleamines and Catecholamines in Discrete Brain Regions of Wild Type and Lurcher Mutant Mice

The biochemical parameters of the serotoninergic system were examined in wild type mice and Lurcher mutants after chronic treatment (40 days) with the serotonin (5-HT) precursor L-tryptophan (50 mg/kg; i.p.). Tissue contents in 5-HT, dopamine and noradrenaline, as well as some of their metabolites, were measured in frontal cortex, neostriatum, thalamus, brainstem, cerebellum and spinal cord by high-performance liquid chromatography. The tissue levels were used as a biochemical index of the function of the monoamine innervations in this animal model of cerebellar ataxia. The results show that Lurcher mutants retain higher concentrations of L-tryptophan and total indoleamines, but that 5-HT is probably stored in a non-releasable compartment. In the particular case of the hypoplastic cerebellum, the reorganization of 5-HT nerve terminals leads to an accrued indoleamine synthesis, indicating that the Lurcher mutants can accumulate 5-HT, but do not utilize it efficiently in synaptic transmission.     

Fine structure of growth cones in the upper dorsal horn of the adult primate spinal cord in the course of reactive synapto-neogenesis

Summary Following transganglionic degenerative atrophy of primary afferent terminals induced by a crush-injury of the sciatic nerve, a regenerative process takes places in the upper dorsal horn of the lumbar spinal cord in the primate Macacus rhesus. Axonal growth cones are characterized by cisterns of axoplasmic reticulum; filopodia emanating from growth cones are electron-optically translucent sheet-like expansions, often containing growth-cone vesicles. Axoplasmic reticulum appears also in preterminal portions of regenerating axons. Dendritic growth cones contain a fine, filamentous matrix; electron-dense membrane specializations can be seen in well-defined areas of their surfaces. Immature synapses are formed between filopodia of axonal growth cones and dendritic growth cones. Electron-microscopic structures of this unique CNS regeneration are similar to those seen in the course of embryonic development of the spinal cord.     

Expression and ultrastructural localization of Mint2 in the spinal cord of rats

Mint protein family, as adaptor molecules, contains three members, Mint1, Mint2 and Mint3. Although Mint3 is ubiquitously expressed, Mint1 and Mint2 have been reported to express specifically in neuron. Here we demonstrated Mint1 and Mint2 expression pattern in rat spinal cord. The protein level of Mint2 was found to be higher than that of Mint1 in rat spinal by western blot. In an attempt to know Mint2 distribution in the spinal cord of rat, in situ hybridization was carried out, Mint2 mRNA was showed to be ubiquitously distributed in cervical, thoracic and lumbar sections of rat spinal cord, and high intensive signal was detected in motor neurons. These were further confirmed by fluorescent immunohistochemistry, Mint2 was also found to exist throughout gray matter especially motor neurons where Mint2 was mainly located in perikaryon, however, Mint1 was showed to be relatively lower. By electron microscope, Mint2 was found to be mainly located in vesicles in perikaryon in motor neuron of lumbar section, and at the same time Mint2 was located in axons in myelin and presynaptic terminals. These data suggest that Mint2 may play more important role in spinal cord than the other two family members.     

Axonal transport: a quantitative study of retained and transported protein fraction in the cat

The fast axonal transport of proteins was studied in the cat sciatic nerve after injection of [3H]leucine into the spinal ganglion or the ventral horn of the seventh lumbar segment. The amount of transported proteins after ganglion injection was linearly related to the amount of label present at the ganglion. At variable intervals after ganglion or spinal cord injection, the sciatic nerves were sectioned in some experiments. The transport of proteins continued in the peripheral nerve stump in a wavelike manner, but the advancing wave leaves a labeled trail behind. A fraction of this trail corresponds to proteins moving at slower velocities than the velocity of proteins in the wave front. Another fraction of the trail corresponds to molecules retained by the axons. Each nerve segment of 5 mm in length retains 1.5% of the transported proteins, and the profile of retained proteins along the sciatic nerves follows a single exponential function. From the proportion of retained proteins, the concentration of transported proteins at the terminals of branching axons as a function of the branching ratio was estimated. In the case of motor axons innervating the soleus muscle of the cat, the concentration of recently transported proteins at the nerve terminals would be approximately 0.83% of the proteins leaving the spinal cord. This low concentration of transported proteins at the nerve terminals may explain the lability of neuromuscular synapses when axonal transport is decreased or interrupted.     

Bridging Schwann cell transplants promote axonal regeneration from both the rostral and caudal stumps of transected adult rat spinal cord

Transplantation of cellular components of the permissive peripheral nerve environment in some types of spinal cord injury holds great promise to support regrowth of axons through the site of injury. In the present study, Schwann cell grafts were positioned between transected stumps of adult rat thoracic spinal cord to test their efficacy to serve as bridges for axonal regeneration. Schwann cells were purified in culture from adult rat sciatic nerve, suspended in Matrigel:DMEM (30:70), and drawn into polymeric guidance channels 8mm long at a density of 120×106 cells ml-1. Adult Fischer rat spinal cords were transected at the T8 cord level and the next caudal segment was removed. Each cut stump was inserted 1mm into the channel. One month later, a bridge between the severed stumps had been formed, as determined by the gross and histological appearance and the ingrowth of propriospinal axons from both stumps. Propriospinal neurons (mean, 1064±145 SEM) situated as far away as levels C3 and S4 were labelled by retrograde tracing with Fast Blue injected into the bridge. Near the bridge midpoint there was a mean of 1990±594 myelinated axons and eight times as many nonmyelinated, ensheathed axons. Essentially no myelinated or unmyelinated axons were observed in control Matrigel-only grafts. Brainstem neurons were not retrogradely labelled from the graft, consistent with growth of immunoreactive serotonergic and noradrenergic axons only a short distance into the rostral end of the graft, not far enough to reach the tracer placed at the graft midpoint. Anterograde tracing with PHA-L introduced rostral to the graft demonstrated that axons extended the length of the graft but essentially did not leave the graft. This study demonstrates that Schwann cell grafts serve as bridges that support (1) regrowth of both ascending and descending axons across a gap in the adult rat spinal cord and (2) limited regrowth of serotonergic and noradrenergic fibres from the rostral stump. Regrowth of monoaminergic fibres into grafts was not seen in an earlier study of similar grafts placed inside distally capped rather than open-ended channels. Additional intervention will be required to foster growth of the regenerated axons from the graft into the distal cord tissue.     

Fine observation on nerves colonizing the regenerating tail of the lizard Podarcis sicula

During the regeneration of lizard tail, nerves sprouting from ganglia and the spinal cord invade the blastema as far as the apical epidermis. Electron microscopical observations reveal axons storing dense granules (dg) and dense core vesicles (dcv) which are concentrated in nerve terminals or in axoplasmatic regions. In the regenerating spinal cord (SC) these terminals resemble aminergic-peptidergic endings and grow as far as the distal portion of the SC, which is made up of irregularly arranged ependymal cells. Some axons storing dcv contact blastematic cells and other nerve terminals show a plasma membrane incomplete or broken. Whether this latter aspect is due to fixation artifacts or physiological rupture is unknown. Nerves containing dcv and a few dg also originate from spinal ganglia innervating the regenerating tail. The accumulation of material into these endings is probably slow and a possible trophic influence on the regeneration of lizard tail is discussed.     

Poliovirus induces indoleamine-2,3-dioxygenase and quinolinic acid synthesis in macaque brain.

Accumulation of the neurotoxin quinolinic acid within the brain occurs in a broad spectrum of patients with inflammatory neurologic disease and may be of neuropathologic significance. The production of quinolinic acid was postulated to reflect local induction of indoleamine 2,3-dioxygenase by cytokines in reactive cells and inflammatory cell infiltrates within the central nervous system. To test this hypothesis, macaques received an intraspinal injection of poliovirus as a model of localized inflammatory neurologic disease. Seventeen days later, spinal cord indoleamine 2,3-dioxygenase activity and quinolinic acid concentrations in spinal cord and cerebrospinal fluid were both increased in proportion to the degree of inflammatory responses and neurologic damage in the spinal cord, as well as the severity of motor paralysis. The absolute concentrations of quinolinic acid achieved in spinal cord and cerebrospinal fluid exceeded levels reported to kill spinal cord neurons in vitro. Smaller increases in indoleamine 2,3-dioxygenase activity and quinolinic acid concentrations also occurred in parietal cortex, a poliovirus target area. In frontal cortex, which is not a target for poliovirus, indoleamine 2,3-dioxygenase was not affected. A monoclonal antibody to human indoleamine 2,3-dioxygenase was used to visualize indoleamine 2,3-dioxygenase predominantly in grey matter of poliovirus-infected spinal cord, in conjunction with local inflammatory lesions. Macrophage/monocytes in vitro synthesized [13C6]quinolinic acid from [13C6]L-tryptophan, particularly when stimulated by interferon-gamma. Spinal cord slices from poliovirus-inoculated macaques in vitro also converted [13C6]L-tryptophan to [13C6]quinolinic acid. We conclude that local synthesis of quinolinic acid from L-tryptophan within the central nervous system follows the induction of indoleamine-2,3-dioxygenase, particularly within macrophage/microglia. In view of this link between immune stimulation and the synthesis of neurotoxic amounts of quinolinic acid, we propose that attenuation of local inflammation, strategies to reduce the synthesis of neuroactive kynurenine pathway metabolites, or drugs that interfere with the neurotoxicity of quinolinic acid offer new approaches to therapy in inflammatory neurologic disease.     

Recovery of brain noradrenaline after 5,7-dihydroxytryptamine-induced axonal lesions in the rat

Time-dependent changes in regional CNS noradrenaline (NA) concentration, 3H-NA uptake and fluorescence morphology of CNS NA neurons were analysed in the adult rat up to 6 months after intraventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), and compared with the time-course of changes in brain and spinal cord indolamine neurons. Following a substantial depletion of both amines in all CNS regions (telodiencephalon, brainstem and spinal cord) at 10 days after 150 mug 5,7-DHT, brain NA--but not 5-HT--levels recovered to near-normal values in brainstem and forebrain (35% below the age-matched controls) within 4 months. This was accompanied by a total restoration of the initially decreased capacity of the brain tissue to accumulate 3H-NA in vitro. Within 10 days after 5,7-DHT, there was a disappearance of NA terminals from many telencephalic, diencephalic and lower brain stem nuclei, from the cerebral and cerebellar cortices, and the grey matter of the spinal cord, concomitant with the appearance of numerous distorted, highly fluorescent swellings along the non-terminal axons of the major noradrenergic projection pathways. The recovery of the NA levels was paralleled by a re-appearance of fluorescent fibres, signifying an intense sprouting and regrowth of the drug-lesioned axons, which eventually re-innervated some of the previously denervated telodiencephalic regions. Except for a permanent loss of some surface-near perikarya in group A1 (the main source of the bulbospinal projections) there was no evidence of a retrograde degeneration of noradrenergic cell bodies in the rat CNS. The results are compatible with the idea that 5,7-DHT mainly causes a lesion of NA axons at a distance from the cell bodies, and this is followed by sprouting and regrowth of axons from the lisioned neurites, and formation of new terminal-like fibres in some previously denervated telodiencephalic regions. These findings indicate that chemical axotomy of central NA neurons induced by 5,7-DHT is--in contrast to that induced by 6-hydroxydopamine--followed by extensive axonal regeneration.     

Is Remodelling of Corticospinal Tract Terminations Originating in the Intact Hemisphere Associated with Recovery following Transient Ischaemic Stroke in the Rat?

Following large strokes that encompass the cerebral cortex, it has been suggested that the corticospinal tract originating from the non-ischaemic hemisphere reorganises its pattern of terminal arborisation within the spinal cord to compensate for loss of function. However many strokes in humans predominantly affect subcortical structures with minimal involvement of the cerebral cortex. The aim of the present study was to determine whether remodelling of corticospinal terminals arising from the non-ischaemic hemisphere was associated with spontaneous recovery in rats with subcortical infarcts. Rats were subjected to transient middle cerebral artery occlusion or sham surgery and 28 days later, when animals exhibited functional recovery, cholera toxin b subunit was injected into the contralesional, intact forelimb motor cortex in order to anterogradely label terminals within cervical spinal cord segments. Infarcts were limited to subcortical structures and resulted in partial loss of corticospinal tract axons from the ischaemic hemisphere. Quantitative analysis revealed there was no significant difference in the numbers of terminals on the contralesional side of the spinal grey matter between ischaemic and sham rats. The results indicate that significant remodelling of the corticospinal tract from the non-ischaemic hemisphere is not associated with functional recovery in animals with subcortical infarcts.