Method of Attenuating Physical Damage to the Spinal Cord

1. Field of the Invention

This invention relates to the attenuation of nervous system damage after injury produced externally or by processes occurring within the organism itself. More particularly, the invention relates to the prevention of sequelae of nervous system injury by the coadministration of steroid hormones or steroid precursors such as pregnenolone, pregnenolone sulfate, and structurally similar organic compounds together with substances such as bacterial lipopolysaccharides (hereinafter referred to by the abbreviation LPS), ImuVert, muramyl dipeptide, and pyran or dextran polymers that stimulate secretion of cytokines by glia, monocytes, macrophages, and Schwann cells and with non-steroidal antiinflammatory substances or drugs (hereinafter referred to by the abbreviation NSAIDs) such as aspirin, indomethacin, ibuprofen, acetaminophen, sodium salicylate, BW755c, diclofenac, naproxen, and BF389 that suppress the inflammatory effects of enhanced activation of the above-mentioned non-neural cells while not diminishing the recovery-promoting effects of the cytokines secreted by them.

2. Description of the Prior Art

Externally initiated injuries to the nervous system are exemplified by contusions or compressions produced by direct blows to the head or spinal cord or by injuries to brain or spinal cord as a result of falls or other accidents; by penetrating wounds caused by knife blades, bullets, or other types of foreign objects or by complete severance of the spinal cord caused by such wounds; by X-rays, electromagnetic radiation, or exposure to radioactive fallout; by infections caused by bacteria, protozoa, yeast, fungi, or viruses. Indigenous modes of injury are exemplified by partial or complete occlusions of blood vessels by immune complexes, platelet aggregations, arteriosclerotic plaques, or sickle cell erythrocytes; by aneurysms, strokes, vascular spasms; by deposition of lipofuscin and/or amyloid; by autoimmune processes in allergic reactions, lupus erythematosus, and demyelinating disorders; by variously produced irritative inflammatory processes in endothelial cells of capillaries of blood vessels which result in permeabilization of blood vessels and the consequent edematous swelling in regions of the brain and spinal cord; or by invasive lesions caused by benign or malignant tumors.

Both regionally and globally, the whole functional terrain in the nervous system is disturbed after injury occurs. There is damage to microvasculature and there are losses of neuronal cells, decreases in neuronal processes in surviving cells, and increases in various glial elements and/or changes in their proportions and functions. Accelerated degeneration of neural, endothelial, neuroendocrine, and endocrine elements together with incoordination of the networks of relations among the cellular components of the immune system with coincident disruption of neurovascular relations and breakdown of the blood-brain barrier in the affected regions predispose to development of circulating and cellular autoantibodies to various polymeric cellular components of cellular and extracellular components in the disrupted regions. This leads to enhanced cellular destruction and deposition of the relatively indigestible debris of immune complexes in capillaries and extracellular sites. A further consequence of perturbation of the immune system is immunosuppression, with resultant activation of latent viruses destructive to the nervous system.

In view of the great complexity of the biological situations touched upon above and the ripple-like, radiating effects of injury, it is not surprising that there are changes in a myriad of measured parameters. A primary therapeutic task has been to identify key therapeutically-accessible, rate-limiting processes and to facilitate their relief. The remarkable self-organizing properties of biological systems often enable them to begin to function adaptively once effective communications among their relevant subunits are reinstituted.

Injuries to the nervous system have been treated in the past using supportive and surgical procedures. For example, many injuries have been treated simply by immobilizing the head and neck for a period of time. The recent advances in nursing and acute medical and rehabilitational care are largely responsible for the improved longevity of patients with spinal-cord injuries, but there have not been accompanying improvements in neurologic outcome. Only recently have advances been made that show medication can enhance recovery from nervous system damage. Specifically, Bracken et al. in The New England Journal of Medicine, 322:1405-1412 (May 17, 1990), reported that in patients with acute spinal-cord injury, treatment with methylprednisolone can improve neurologic recovery when the medication is given within the first eight hours after injury, however, treatment with naloxone does not improve neurologic recovery. The Bracken et al. study shows that methylprednisolone had no effect at low doses and was only effective at high, receptor saturating levels.

It is an object of this invention to provide a method and compositions for attenuating progression of damage to the nervous system once injury has occurred.

It is another object of this invention to provide a combination drug treatment for attenuating nervous system damage such as may occur with spinal cord injuries and the like.

According to the invention, a treatment has been developed for attenuation of nervous system damage after injury wherever in the nervous system it occurs and by whatever means it is produced. It consists of coadministration soon after injury of steroid hormones or steroid hormone precursors such as PREG, PREG-S, or PREG esters that readily give rise to PREG and/or PREG-S, together with one of several substances that stimulate secretion of cytokines by glia, monocytes, macrophages, and Schwann cells and with a NSAID to suppress inflammatory effects of enhanced activation of the above-mentioned non-neural cells while not diminishing the recovery promoting effects of the cytokines secreted by them. Similarities in nervous system function in various mammals, including human beings, as well as much previous experience in the field, indicate that such treatment will be effective in attenuation of nervous system damage in men as well as in rats.

Although cytokine secretory stimulants and antiinflammatory substances, alone and together, show modest degrees of attenuation of nervous system damage, never before have such substances been proposed to be used in conjunction with steroid hormones or steroid hormone precursors such as PREG or PREG-S for this purpose. The combination of the three compounds produces remarkably superior results.

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of the preferred embodiments of the invention with reference to the drawings, in which:

FIG. 1 is a skeletal outline of steroid metabolism;

FIGS. 2a and 2b are line graphs illustrating motor function in rats receiving different treatments as a function of time after spinal cord compression; and

FIGS. 3a-h are photographs showing histological results showing the injury attenuating effects of PREG+LPS+IM.

Research on spinal cord injury largely has focused on glial proliferation and scarring, neuronal sprouting and regeneration, and the phagocytic activity of macrophages. Macrophages synthesize and secrete a variety of macromolecules that contribute to the healing of wounds (1). Some of the secretory products, such as tumor necrosis factor (2), prostaglandins (3), and oxygen free radicals (4) cause necrosis of foreign or invading cells; others aid wound healing by stimulating mitosis (5), angiogenesis (6) and reactive gliosis (7,8). Other cytokines, such as the interleukins, coordinate immune responses (9). Microglia and astrocytes also show comparable secretory activity (10-12) in response to macrophage-released cytokines (7-10) or when stimulated directly by LPS (10-12).

Often conditions in injured nervous tissue are not sufficiently stimulatory, by themselves, to cause non-neural cells such as mentioned above to express fully their secretory capabilities. They must be activated by specific exogenously supplied agents. After having been primed by exposure to lymphokines released by lymphocytes, neutrophils or other cells at the site of inflammation, the macrophages must be made fully competent for secretion of cytokines by exposure to LPS or other activating molecules (13). Microglia and astrocytes must be activated similarly in order to fully express their secretory capabilities (10,11).

However, the consequences of full secretory activation of the above cell types often cannot be adequately controlled by the organism without external intervention, and the macrophages often are aroused to a feeding frenzy following over-secretion of excess cytotoxic factors, resulting in cystic degeneration and cavitation and consequentially irreversible damage. The key to attenuation of injury to the nervous tissue and possibly to successful neural regeneration lies in adjusting the relationships between the injured tissue and overzealous non-neural defenders (14,15).

In order to achieve attenuation of damage as a result of injury, it is necessary to facilitate adaptive coupling among relevant cellular components. The various steroids that abound in tissues and tissue fluids play key multifactorial roles in facilitating such coupling. Although mechanisms of effects in particular instances largely have not yet been defined at the molecular level, the overall experimental results and clinical observations suggest the roles of steroids to be those of pleiotropic facilitators of coordinative processes that enable immune, neural, and metabolic systems, separately and together, to cycle freely through their operational modes in achieving rebalancing when malfunctioning occurs (16).

Non-genomic and genomic effects are exerted by the non-covalent association of steroids with sites on macromolecular entities, affecting their conformations and, therefore, their functional states. Individual substances to which steroids bind may have several potential binding sites with varying affinities for different steroids. At the genomic level, there is extensive overlap in binding site competition among substances that bind to various steroid receptors as well as promiscuity in binding of different steroid-receptor complexes to the same DNA sequence. Modulation of some genes by steroids may involve combinatorial interactions. A continuum of binding specificities may exist from virtually complete promiscuity, such as is found in induction of the mammary tumor virus, to the extreme exclusivity of the induction of some secondary sex characteristics. High degree of binding specificity of a particular steroid-receptor complex to a DNA region near a particular gene, the transcription of which it regulates in target tissues, might be conferred by the nearby binding of other transcriptional regulatory proteins, including other steroid-receptor complexes (17-23).

This invention focuses on one steroid, pregnenolone (hereinafter referred to by the abbreviation PREG), in the context of the above formulation, with full awareness that the roles that may be ascribed to PREG are played out in environments in which many steroids coexist; and that at any time it is the pattern of distribution of these substances that helps determine regional functional states and behavior of the organism as a whole and not just the level of one particular steroid. This invention particularly includes the use of esters of PREG and PREG-S in which the 3.beta. hydroxyl group is esterified to give a variety of esters that can be hydrolyzed in the gastrointestinal tract or absorbed as such and hydrolyzed to PREG or PREG-S in various tissues, including the brain and spinal cord. Such esters have the structure R.sub.1 COOR.sub.2, formed from the acids R.sub.1 COOH and the alcohols HOR.sub.2, where the latter is PREG or PREG-S. R.sub.1 is an alkyl, aryl, heterocyclic, or amino group or an H atom.

FIG. 1 shows a skeletal outline of the steroid metabolic scheme as it may occur in the human organism as a whole. If one were to homogenize the entire organism and extract the homogenate appropriately, one could expect there to be the substances shown in FIG. 1 and many others derived from them, known and still unknown, and to be able to demonstrate the activities of enzymes that catalyze the required interconversions. However, it is highly unlikely that any single tissue or tissue fluid contains all of the substances and/or enzymes; and among those tissues in which they do exist, marked differences in levels would be found. All cells in the body probably require for regulation of their functions some or all of these steroids, whose combined activities range from modulation of membrane excitability to regulation of genomic transcription.

The biosynthesis of steroid hormones begins with cholesterol, from which the sex steroids, glucocorticoids, and mineralocorticoids all derive. PREG is the major precursor for the steroid hormones. It is formed from cholesterol in mitochondria of tissues that produce steroid hormones. The rate of steroid synthesis is controlled by the delivery of cholesterol from cytoplasmic inclusion droplets to the inner mitochondrial membrane, where steroidogenesis begins by production of PREG from cholesterol by action of cytochrome P-450scc (side-chain cleavage enzyme), a reaction found in peripheral tissues as well as in brain. Formation of PREG is regulated by pituitary hormones, such as luteinizing hormone and follicle-stimulating hormone in ovaries and testes, ACTH and one or more non-ACTH pituitary peptides in adrenals, and possibly hypothalamic hormones at the latter and other sites. PREG can go directly to progesterone and thence to aldosterone (route A, FIG. 1) or to 17.alpha.-OH PREG, which is a precursor for cortisol formation (route B, FIG. 1) and for sex-related steroids (route C, FIG. 1). Route A can contribute to route B and route B to route C, as shown. Dehydroepiandrosterone, the first product in route C, can inhibit the flow through routes B and C by inhibiting conversion of PREG to 17.alpha.-OH PREG. PREG is of major interest because it lies at the branchpoint at which decisions are made as to how the subsequent metabolic flow is fractionated between the mineralocorticoid, androgen.fwdarw.estrogen, and glucocorticoid pathways. Further discussion of steroid metabolism is eschewed since reviews, books, and symposia on all aspects of the subject abound (see ref 24-31 and literature citations therein).

Since PREG is the precursor of all of the known steroid hormones, it is not surprising that under special experimental circumstances it exhibits effects of every hormone formed from it. It also has its own relatively specific effects, e.g. on GABA.sub.A and NMDA receptors (32-39) and serves as precursor for the formation of a panoply of different steroids and steroid derivatives. PREG, the parent steroid, also can play synergic roles with other steroids at genomic and non-genomic sites, facilitating their actions in helper-like fashion through allosteric effects exerted by binding at different loci to the same entities. An adequate supply of locally synthesized and/or externally supplied PREG could ensure near-optimal modulation of non-genomic and genomic processes at sites at which enzyme activities exist for the subsequent conversion of PREG to tissue-specific patterns of steroids.

With aging, continued stress, injury or disease, decreases in amounts or incoordination in rates of formation of PREG and steroids arising from it can occur globally throughout the organism or locally at specific tissue sites, which may lead to failure of maintenance of optimal steroid patterns and, therefore, to decreased capacity to respond adaptively to demands of injury (40). In normal individuals mean blood serum levels of PREG and PREG sulfate (herein referred to by the abbreviation PREG-S) decrease with age, those of PREG-S showing a 60% reduction at a mean age of 75 yr by comparison with the values observed at a mean age of 35 yr (unpublished results).

Levels of PREG many times higher than in plasma are found in human brain and in cranial and peripheral nerves (41,42), at which sites PREG is present in oligodendrocytes and Schwann cells, respectively, and in which cells it is formed independently of the peripheral endocrine system and from which it can be released during nerve activity. Cholesterol that is used for PREG synthesis may come either from preformed cholesterol delivered to sites of synthesis of PREG or may be furnished by indigenous synthesis of cholesterol from acetyl coenzyme A (43-49). Ordinarily, facile alterations can be made in rates of flow of cholesterol to sites of PREG synthesis through adjustments in rates of transport and biosynthetic pathways so that an adequate supply of precursor is maintained. However, upon injury, either one or both sources of precursor supply may become rate-limiting, and the ability to form and release PREG and substances formed from it could become compromised. If both lines of supply of cholesterol were constricted, inability or decreased ability to synthesize PREG and its derivatives in nerve tissue and to release them at a sufficiently rapid rate could seriously handicap the many functions they regulate or modulate, and adverse effects would occur, limiting extent of self-repair at all stages after injury occurs. Administration of PREG would prevent such undesirable effects from occurring.

Restoration of normal steroid patterns by administration of PREG alone or together with much smaller than currently employed amounts of other steroids is less physiologically disturbing than is administration of arbitrarily selected amounts of more potent substances that derive from it, e.g., cortisone, sex steroids, or aldosterone, because myriad feedback inhibitory loci exist in steroid formation beginning with the synthesis of PREG from cholesterol, which in different tissues may be under control of different pituitary hormones, and because there exists widespread competition of steroids for binding to receptor and allosteric sites. For example, administration of large amounts of dehydroepiandrosterone (DHEA), the first substance in route C (FIG. 1), retards metabolite flow through routes B and C by inhibiting conversion of PREG to 17.alpha.-OH PREG, upsetting the balances of steroid hormones in various tissues and, therefore, tending to decrease adaptability. Nonetheless, experimental results discussed below with DHEA-S, the sulfate derivative of DHEA, demonstrate that steroid hormones will be of some utility in the practice of the invention.

Thus, PREG helps maintain a balanced steroidal environment, minimizing disturbances in allosteric and transcriptional relationships that large excesses of administration of particular steroids might bring about by competing with other steroids. In those instances in which desired therapeutic goals cannot be attained without actual administration of particular specialized steroids, themselves, co-administration of PREG with relatively small amounts of such steroids might give the same physiological effects as would administration of larger amounts of the latter alone. This would also explain why slight improvement in function after spinal cord injury could be obtained only with super-high doses of methylprednisolone (Bracken et al., ibid.). This would minimize risk of feedback inhibition of formation and/or release of pituitary factors that play a role in steroid hormone synthesis and thus attenuate the consequent homeostatic disturbance that would occur upon cessation of administration of steroid or a reduction in dosage.

Importantly, no toxic effects were observed in experimental animals following large doses of PREG by oral, subcutaneous, or intraperitoneal routes (51). PREG also was found to be without observable toxicity in man when given parentally or orally in a number of older studies (e.g. see ref. 52-61). The lack of toxicity in man has been confirmed in a current study with Alzheimer patients on daily oral intake of 525 mg for 3 months; and orally administered PREG has been shown to be readily absorbed (in preparation). That even low oral doses of PREG can exert CNS effects in man was shown in a study in which 1 mg of PREG given orally before sleep to male volunteers significantly increased the amount of time spent in slow wave sleep and depressed EEG sigma (62).

The use of the naturally-occurring non-toxic PREG therapeutically, alone or together with other substances as suggested in the foregoing, is most advantageous and its efficacy documented experimentally in the following pages. The metabolic machinery for managing its disposition is in place at various tissue sites. Its administration in appropriate amounts in situations in which its availability is insufficient for normal function to take place does not create serious problems of physiological reorganization.

We have chosen controlled injury to the rat spinal cord as the paradigm by which to represent central nervous system injury in general, and to develop agents that significantly reduce adverse histopathological changes, enhance axonal regeneration and improve functional recovery. Similarity in nervous system function in various mammals, including human beings, as well as much previous experience in the field indicate that such therapeutic agents also will be damage-attenuators and repair-enhancers in human beings as well as in rats.

Test Animals and Surgical Procedures. Random-bred Sprague-Dawley female rats (170-200 grams) were anesthetized with 4% chloral hydrate (400 mg/kg, intraperitoneally), shaved, and the dorsal skin scrubbed with benzalkonium chloride (0.13% aqueous). Using aseptic surgical technique, a laminectomy was performed at T8, while taking care to leave the dura intact. A #5 Dumont jewelers forceps then was introduced between the dura mater and the bone, and the spinal cord was compressed for two seconds. Hemostasis was secured by topical application of Avitene (Med Chem Products, Inc., Woburn Mass. 01801). Drug or control pellets were implanted subcutaneously into a pocket prepared by lateral extension of the rostral margin of the incision or into a second incision made just lateral to the rostral margin of the first one. Care was taken to eliminate any accumulation of tissue fluid prior to implanting the pellets. If more than one pellet was implanted, separate sites were chosen for each. The wounds were closed by suturing the underlying muscle with 6-0 silk and the skin incisions with wound clips. Each animal was housed individually and urine expressed by manual compression of the abdomen twice daily until bladder control was restored (7-10 days).

Substances Tested. All pellets were obtained from Innovative Research of America (Toledo, Ohio 43606) and contained matrix alone for controls, 50 mg of PREG, or 25 mg of acetylsalicylic acid (hereinafter referred to by the abbreviation ASP). The matrix provided continual release of the drug for 21 days (i.e., 2.38 mg PREG or 1.19 mg ASP per day). The pellets were disc-shaped and were approximately 6 mm in diameter and 2 mm thick. Rats receiving LPS were given daily intraperitoneal injections of 0.2 mg LPS from Salmonella enteritidis (Sigma) in 0.1 ml sterile, pyrogen-free water. Those receiving indomethacin (hereinafter referred to by the abbreviation IM) were given daily intraperitoneal injections of 0.2 mg IM sodium trihydrate (Indocin, iv., Merck Sharp & Dohme).

Histological Procedures. On the 21st experimental postoperative day, the rats were anesthetized and euthanized by intracardial perfusion with 15 ml saline followed by 250 ml of Bouin's fixative. The vertebral column was removed immediately and immersed for 24 hours in fixative and 48 hours in 70% ethanol. The spinal cord then was dissected from the vertebral column, dehydrated, and embedded in Paraplast (Fisher Scientific Co., Pittsburgh, Pa.). Serial longitudinal sections were cut at 10 .mu.m thickness in either the horizontal or vertical plane. Every tenth slide was stained with H&E for examination of cellular detail and for image analysis, and adjacent slides were impregnated with protargol for visualization of nerve fibers.

Image analysis was performed with appropriate illumination and background correction using the BioQuant system (BQ Meg IV, Biometrics Inc.). Only those sections containing a portion of central canal in proximity to the lesion were studied, in order to ensure that observations were made at the same level in all samples. The selected slides were then coded and randomized. A 4X objective was used so that the entire lesion could be included in one microscope field. The area of the lesion was estimated by drawing a line around the entire lesion and measuring the area within the perimeter. The area of the cavities within the lesion was determined by using a threshold setting that allowed measurement of areas devoid of cells. The number of cells within the lesion was obtained by using a threshold setting that counted only the cell nuclei within the lesion. This value was divided by the area of the lesion to obtain the number of cells per mm.sup.2 of lesion.

Functional Assessment. The walking ability of all operated rats was evaluated daily in double-blind fashion independently by two investigators. Evaluations were made without knowledge of the treatment group or of the previous day's ratings. The rating system used was the modification of the Tarlov scale recommended by Wrathall et al. (63): 0, complete hindlimb paralysis; 1, barely perceptible hindlimb movements; 2, clearcut hindlimb movements which do not result in weight bearing or locomotion; 3, hindlimbs are used to crawl but do not support the weight of the body; 4, hindlimbs are used for support of the body and walking but with clearcut disability; 5, posture and walking ability is nearly normal.

Statistical Analysis. The locomotor function was analyzed statistically by the analysis of variance (ANOVA) with multiple comparisons made by the Student-Newman-Keuls procedure. The scale of 1-5 consists of an ordered metric level of measurement where the relative ordering of the intercategory distances is known even though their absolute magnitude cannot be measured (64). Such data can be treated as though it had been measured at equal intervals, and the ANOVA is an appropriate and sensitive method of statistical analysis of such data (64). Nonparametric ANOVA (Dunn's procedure) was performed in those instances when the parametric procedure was inappropriate (e.g., when the Bartlett test revealed statistically significant differences in the variance between the treatment groups).

In the first set of experiments (Table 1, FIG. 2A), a group of rats implanted with control pellets immediately after injury was compared with 5 other groups treated with IM, LPS, or PREG alone or with LPS+IM or PREG+LPS+IM, as described under Methods. The only experimental group showing statistically significant attenuation of decrement in motor function by comparison with the controls was that receiving PREG+LPS+IM (Table 1; FIG. 2A). The results were remarkable in that 4 of 6 animals in the PREG+LPS+IM group walked almost normally at 21 days (Table 1) and the mean daily Tarlov scores were higher than those of all of the other groups between the 7th and 21st postoperative days, although all treatment groups improved in walking ability to some extent (FIG. 2A). Such a result as that with PREG+LPS+IM group has not been observed by us in the many years we have employed the same experimental paradigm for study of the therapeutic potential of various test substances.

Table 1 shows the total area occupied by the lesion was significantly smaller in the PREG+LPS+IM group than in the controls, while the other experimental groups did not show a statistically significant difference from the controls.

The proportions of the areas of the lesions occupied by cavities were least in the case of the PREG+LPS+IM group. The mean ratios of cavity to lesion also were significantly smaller in the LPS and LSP+IM groups than in the controls. The fact that the cavitation ratios were not significantly redused in the case of the groups receiving IM or PREG alone is consistent with the interpretation that stimulation of release and exchange of cytokines, as by LPS, is a requirement for the attenuation of damage resulting from the injury. In some instances, the combination of LPS+IM gives a somewhat better histological result than LPS alone. This is consistent with the idea that a decrease in inflammatory processes, such as results from administration of IM, is important in attenuating subsequent damage. The remarkable additional attenuative effect observed when PREG is present in the therapeutic regimen is attributable to its pleiotropic effects, among which are effects on gene transcription (17-23), maintenance of neuronal excitability (32-39), antiinflammatory action (52-61), and formation of other steroidal substances from it, as shown in FIG. 1, that exert specific hormonal effects.

A second experiment (Table 2; FIG. 2B) was performed with 4 groups of rats: control, PREG+LPS, PREG+LPS+IM, and PREG+LPS+ASP. In the latter group ASP replaced IM as an antiinflammatory agent. In each of the above three experimental groups there was a decrement in damage to motor function by comparison with controls at all times through the 21st postoperative day, which was calculated to be statistically significant at days 10 and 21.

The remarkable effect of PREG is illustrated by the fact that 6 of 10 animals of the PREG+LPS+IM group were able to walk in almost normal fashion at the end of the experiment. One of the 10 rats in the PREG+LPS+ASP group also could walk almost normally but none of the animals in the PREG+LPS or control groups could walk. The relative degrees of cavitation of the lesion area and the cellularity of the lesion were significantly decreased and increased, respectively, only in the PREG+LPS+IM group, although the respective mean values for the PREG+LPS+ASP group also were in the same direction. The somewhat lesser attenuative effect observed in the Latter group may be related to the relatively low dose of ASP used.

The results at the cellular tissue level obtained with the PREG+LPS+IM combination are illustrated in FIG. 3 and described in the legend to the individual panels in FIG. 3. To our knowledge, no previously proposed treatment for attenuation of nervous system damage has given an effect comparable to that which has been observed with PREG+LPS+IM. There were remarkable histological differences between the controls (FIG. 3 panels A and B) and the PREG+LPS+IM group (FIG. 3 panels E and F).

FIGS. 3A-H. Midsagittal sections of spinal cord through site of lesion; 21 days postoperative. In each photomicrograph, the dorsal part of cord is at the top and the ventral part is at the bottom. A. Vehicle treatment (control); H&E, X40. In the center of the lesion, a large cavity occupies the dorsal part of the cord and smaller areas of cavitation are seen ventrally. The central canal, seen in the undamaged tissue at the right side of the photograph, shows a characteristic dilatation (*) near the lesion. B. Vehicle-treatment (control); H&E, X100. Higher magnification shows the lesion site to be heavily infiltrated by large macrophages. C. PREG +LPS treatment; H&E, X40. Cavitation is most notable at the margins of the lesion bordering the dark-staining intact spinal tissue. The largest cavities are dorsal to the level of the central canal, which is indicated by an asterisk (*), while smaller areas of cavitation are seen ventrally. There is a thin rim of residual spinal tissue at the ventral margin of the lesion (arrow). D. PREG +LPS treatment; H&E, X100. Higher magnification reveals a loose arrangement of macrophages at the ventral region of the lesion and the cellularity of the spared ventral tissue (arrows) lying subjacent to the pia-arachnoid, subdural space and dura mater. E. PREG+LPS+IM treatment; H&E, X36. In this photograph, the lesion is to the right and the undamaged cord to the left. The dorsal region of the lesion contains less cavitation and is more densely cellular than in the animals treated with vehicle or PREG+LPS (compare with panels A and C). The tissue ventral to the central canal (*) is characterized by sparing of the white matter (arrow) and ingrowth of blood vessels (arrowheads). From the central canal emerges a stream of cells that enter the lesion. F. PREG+LPS+IM treatment; H&E, X90. This higher magnification photograph of a portion of panel E illustrates that the cells migrating into the lesion from the central canal (*) are ependymal cells. The staining properties of the spared ventral white matter (arrows) is consistent with that of myelinated nerve fibers. The blood vessels entering the ventral gray matter include large capillaries (left arrowhead) and arterioles (right arrowhead). G. PREG+LPS+IM treatment; Protargol, X180. A modest number of nerve fibers course within the lesion. These have the characteristics of regenerating axons. They vary from fine to medium in diameter, are varicose in appearance, and are oriented by the cellular environment. Note especially how they tend to avoid regions of cystic degeneration. H. PREG+LPS+IM treatment; Protargol, X90. This section, which is serial to that of panel F, shows that the spared tissue in the ventral white matter (arrows) consists of normal-appearing, longitudinally-oriented, nonvaricose nerve fibers. A small number of extremely fine nerve fibers are present in the lesion dorsal to the spared tissue.

Similar experiments conducted with dehydroepiandrosterone sulfate (DHEA-S) showed that significant reduction in lesion size can be achieved provided the steroid is administered in combination with LPS and IM. This effect was identical to that obtained with PREG+LPS+IM. However, treatment with DHEA-S+LPS+IM was significantly less effective in restoring locomotor function than was the treatment with PREG+LPS+IM. Taken together, these observations further support the hypotheses (a) that protocols involving combinations of therapeutic agents provide a more effective means of treating spinal cord injury than do treatments with single agents alone and (b) that the pharmacological actions of the recommended therapeutic agents are highly effective.

While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.

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