Optic Nerve Degeneration and Potential Neuroprotection: Implications for Glaucoma

In order to study the course of optic nerve degeneration and devise possible ways to achieve neuroprotection, a well-controlled, animal model of partial crush injury of the optic nerve was used. Following the controlled partial crush injury of the rat optic nerve, quantitative morphological and electrophysiological measurements were made of primary and secondary neuronal losses. The neuroprotective effects of NMDA-receptor antagonists and α2-adrenoreceptor agonists were also studied. The results suggested that the ongoing progression of the optic nerve degeneration in glaucoma might be a consequence of the toxic extracellular environment produced by neurons that degenerate as a result of the primary cause of the disease (such as increased IOP).

Some electrophysiological properties of developing rat skeletal myotubes grown in serum-free, chemically defined medium

Serum-free, chemically defined media have been reported to provide suitable conditions for growth and proliferation of mammalian skeletal muscle, but there is no information regarding the ability of myotubes to develop normal electrophysiological properties in these media. We have recorded transmembrane resting and action potentials from rat skeletal myotubes grown in both serum-containing (GM) and serum-free chemically defined (CDM) growth media. Muscle cells in CDM do not develop as high resting Em as their counterparts in conventional growth media. CDM myotubes also had a lower incidence and frequency of spontaneously occurring action potentials. Treatment with ouabain or decrease in temperature of the recording medium reduced resting Em of both GM and CDM cells to the same level. We found that the sensitivity of CDM cells to ouabain was about 10-fold higher than that of GM cells. An increase in temperature of the recording medium increased Em of GM myotubes but not of CDM myotubes. The change in resting Em in response to a 10-fold change in extracellular K(+)-ion concentration was the same for both groups of cells thus indicating that there was no difference in membrane permeability to K(+)-ion. We conclude that the difference in Em can be accounted for largely, if not entirely, by differences in activity or amount of electrogenic Na(+)-K(+) ATPase.

Macrophages and dendritic cells treatment of spinal cord injury: from the bench to the clinic

The failure of the spinal cord to recover after injury has been associated with the immune privilege mechanism that suppresses immune activity throughout the central nervous system. Primed macrophages and dendritic cells were shown to promote neurological recovery in preclinical models of spinal cord injury. A cell therapy consisting of autologous incubated macrophages is now being tested on spinal cord injury patients in clinical trials.

Therapeutic vaccine for acute and chronic motor neuron diseases: implications for amyotrophic lateral sclerosis

Therapeutic vaccination with Copaxone (glatiramer acetate, Cop-1) protects motor neurons against acute and chronic degenerative conditions. In acute degeneration after facial nerve axotomy, the number of surviving motor neurons was almost two times higher in Cop-1-vaccinated mice than in nonvaccinated mice, or in mice injected with PBS emulsified in complete Freund's adjuvant (P < 0.05). In mice that express the mutant human gene Cu/Zn superoxide dismutase G93A (SOD1), and therefore simulate the chronic human motor neuron disease amyotrophic lateral sclerosis, Cop-1 vaccination prolonged life span compared to untreated matched controls, from 211 +/- 7 days (n = 15) to 263 +/- 8 days (n = 14; P < 0.0001). Our studies show that vaccination significantly improved motor activity. In line with the experimentally based concept of protective autoimmunity, these findings suggest that Cop-1 vaccination boosts the local immune response needed to combat destructive self-compounds associated with motor neuron death. Its differential action in CNS autoimmune diseases and neurodegenerative disorders, depending on the regimen used, allows its use as a therapy for either condition. Daily administration of Cop-1 is an approved treatment for multiple sclerosis. The protocol for non-autoimmune neurodegenerative diseases such as amyotrophic lateral sclerosis, remains to be established by future studies.

T cell-mediated neuroprotection involves antithrombin activity

Functional loss after injury to the mammalian central nervous system (CNS) has been attributed not only to the immediate loss of neurons but also to secondary neuronal degeneration caused by the toxicity of physiological compounds present in abnormally high amounts as a result of the injury. One such compound appears to be the protease thrombin. Here we show that the beneficial effect of T cells directed against myelin self-antigens can be attributed, at least in part, to the ability of these 'autoimmune' T cells to produce antithrombin III. Using transgenic mice lacking the thrombin receptor PAR-1, we also present molecular evidence indicating that down-regulation of PAR-1 by genetic manipulation leads to increased post-traumatic survival of CNS neurons. We further show that the ability of autoimmune T cells to produce thrombin inhibitors and to exert post-traumatic neuroprotection are both independent of their PAR-1 expression. These findings suggest that thrombin plays a key role in post-injury neuronal survival, and that its post-traumatic toxicity can be down-regulated by appropriate alteration of the amounts of PAR-1 receptors or of antithrombin III, the latter achieved by T cell-mediated autoimmunity.

T-cell-based immunity counteracts the potential toxicity of glutamate in the central nervous system

Injuries to the central nervous system (CNS) evoke self-destructive processes, which eventually lead to a much greater loss of tissue than that caused by the trauma itself. The agents of self-destruction include physiological compounds, such as glutamate, which are essential for the proper functioning of the CNS, but become cytotoxic when their normal concentrations are exceeded. The CNS is equipped with buffering mechanisms that are specific for each compound. Here we show, using Balb/c mice (a strain resistant to induction of experimental autoimmune encephalomyelitis), that after intravitreal injection of any concentration of glutamate (a neurotransmitter that becomes toxic when in excess) or ammonium-ferrous sulfate hexahydrate (which increases the formation of toxic oxygen species), the loss of retinal ganglion cells in mice devoid of mature T cells (nude mice) is significantly greater than in matched wild-type controls. We further show that this outcome can be partially reversed by supplying the T cell-defective mice with splenocytes derived from the wild-type mice. The results suggest that potentially toxic physiological compounds, when present in excessive amounts, can recruit and activate a T-cell-dependent self-protective immune mechanism. This may represent a prototype mechanism for the physiological regulation of potentially destructive CNS events by T-cell-mediated immune activity, when the local buffering mechanisms cannot adequately cope with them.

Increased post-traumatic survival of neurons in IL-6-knockout mice on a background of EAE susceptibility

Axonal injury initiates a process of neuronal degeneration, with resulting death of neuronal cell bodies. We show here that in C57BL/6J mice, previously shown to have a limited ability to manifest a post-traumatic protective immunity, the rate of neuronal survival is increased if IL-6 is deficient during the first 24 hours after optic nerve injury. Immunocytochemical staining preformed 7 days after the injury revealed an increased number of activated microglia in the IL-6-deficient mice compared to the wild-type mice. In addition, IL-6-deficient mice showed an increased resistance to glutamate toxicity. These findings suggest that the presence of IL-6 during the early post-traumatic phase, at least in mice that are susceptible to autoimmune disease development, has a negative effect on neuronal survival. This further substantiates the contention that whether immune-derived factors are beneficial or harmful for nerve recovery after injury depends on the phenotype of the immune cells and the timing and nature of their dialog with the damaged neural tissue.

Neuronal survival after CNS insult is determined by a genetically encoded autoimmune response

Injury to the CNS is often followed by a spread of damage (secondary degeneration), resulting in neuronal losses that are substantially greater than might have been predicted from the severity of the primary insult. Studies in our laboratory have shown that injured CNS neurons can benefit from active or passive immunization with CNS myelin-associated antigens. The fact that autoimmune T-cells can be both beneficial and destructive, taken together with the established phenomenon of genetic predisposition to autoimmune diseases, raises the question: will genetic predisposition to autoimmune diseases affect the outcome of traumatic insult to the CNS? Here we show that the survival rate of retinal ganglion cells in adult mice or rats after crush injury of the optic nerve or intravitreal injection of a toxic dosage of glutamate is up to twofold higher in strains that are resistant to the CNS autoimmune disease experimental autoimmune encephalomyelitis (EAE) than in susceptible strains. The difference was found to be attributed, at least in part, to a beneficial T-cell response that was spontaneously evoked after CNS insult in the resistant but not in the susceptible strains. In animals of EAE-resistant but not of EAE-susceptible strains devoid of mature T-cells (as a result of having undergone thymectomy at birth), the numbers of surviving neurons after optic nerve injury were significantly lower (by 60%) than in the corresponding normal animals. Moreover, the rate of retinal ganglion cell survival was higher when the optic nerve injury was preceded by an unrelated CNS (spinal cord) injury in the resistant strains but not in the susceptible strains. It thus seems that, in normal animals of EAE-resistant strains (but not of susceptible strains), the injury evokes an endogenous protective response that is T-cell dependent. These findings imply that a protective T-cell-dependent response and resistance to autoimmune disease are regulated by a common mechanism. The results of this study compel us to modify our understanding of autoimmunity and autoimmune diseases, as well as the role of autoimmunity in non-autoimmune CNS disorders. They also obviously have far-reaching clinical implications in terms of prognosis and individual therapy.

Protective autoimmunity is a physiological response to CNS trauma

Primary damage caused by injury to the CNS is often followed by delayed degeneration of initially spared neurons. Studies in our laboratory have shown that active or passive immunization with CNS myelin-associated self-antigens can reduce this secondary loss. Here we show, using four experimental paradigms in rodents, that CNS trauma spontaneously evokes a beneficial T cell-dependent immune response, which reduces neuronal loss. (1) Survival of retinal ganglion cells in rats was significantly higher when optic nerve injury was preceded by an unrelated CNS (spinal cord) injury. (2) Locomotor activity of rat hindlimbs (measured in an open field using a locomotor rating scale) after contusive injury of the spinal cord (T8) was significantly better (by three to four score grades) after passive transfer of myelin basic protein (MBP)-activated splenocytes derived from spinally injured rats than in untreated injured control rats or rats similarly treated with splenocytes from naive animals or with splenocytes from spinally injured rats activated ex vivo with ovalbumin or without any ex vivo activation. (3) Neuronal survival after optic nerve injury was 40% lower in adult rats devoid of mature T cells (caused by thymectomy at birth) than in normal rats. (4) Retinal ganglion cell survival after optic nerve injury was higher (119 +/- 3.7%) in transgenic mice overexpressing a T cell receptor (TcR) for MBP and lower (85 +/- 1.3%) in mice overexpressing a T cell receptor for the non-self antigen ovalbumin than in matched wild types. Taken together, the results imply that CNS injury evokes a T cell-dependent neuroprotective response.

Vaccination for protection of retinal ganglion cells against death from glutamate cytotoxicity and ocular hypertension: implications for glaucoma

Our group recently demonstrated that autoimmune T cells directed against central nervous system-associated myelin antigens protect neurons from secondary degeneration. We further showed that the synthetic peptide copolymer 1 (Cop-1), known to suppress experimental autoimmune encephalomyelitis, can be safely substituted for the natural myelin antigen in both passive and active immunization for neuroprotection of the injured optic nerve. Here we attempted to determine whether similar immunizations are protective from retinal ganglion cell loss resulting from a direct biochemical insult caused, for example, by glutamate (a major mediator of degeneration in acute and chronic optic nerve insults) and in a rat model of ocular hypertension. Passive immunization with T cells reactive to myelin basic protein or active immunization with myelin oligodendrocyte glycoprotein-derived peptide, although neuroprotective after optic nerve injury, was ineffective against glutamate toxicity in mice and rats. In contrast, the number of surviving retinal ganglion cells per square millimeter in glutamate-injected retinas was significantly larger in mice immunized 10 days previously with Cop-1 emulsified in complete Freund's adjuvant than in mice injected with PBS in the same adjuvant (2,133 +/- 270 and 1,329 +/- 121, respectively, mean +/- SEM; P < 0.02). A similar pattern was observed when mice were immunized on the day of glutamate injection (1,777 +/- 101 compared with 1,414 +/- 36; P < 0.05), but not when they were immunized 48 h later. These findings suggest that protection from glutamate toxicity requires reinforcement of the immune system by antigens that are different from those associated with myelin. The use of Cop-1 apparently circumvents this antigen specificity barrier. In the rat ocular hypertension model, which simulates glaucoma, immunization with Cop-1 significantly reduced the retinal ganglion cell loss from 27.8% +/- 6.8% to 4.3% +/- 1.6%, without affecting the intraocular pressure. This study may point the way to a therapy for glaucoma, a neurodegenerative disease of the optic nerve often associated with increased intraocular pressure, as well as for acute and chronic degenerative disorders in which glutamate is a prominent participant.

Self-Protective mechanism awakened by glutamate in retinal ganglion cells

The progression of degeneration in chronic optic neuropathies or in animal models of optic nerve injury is thought to be caused, at least in part, by an increase in glutamate to abnormally high concentrations. We show here that glutamate, when injected in subtoxic amounts into the vitreal body of the rat eye, transduces a self-protecting signal that renders the retinal ganglion cells resistant to further toxicity, whether glutamate-derived or not. This neuroprotective effect is attained within 24 h and lasts at least 4 days. Western blot analysis of rat retinas revealed increased amounts of bcl-2 four days after injection of glutamate in either subtoxic or toxic (120 nmol) amounts, but not after saline injection. The effects of intravitreal glutamate or saline injection on the secretion of neurotrophins by retinal ganglion cells was evaluated in rat aqueous humor 6 h, 1 day, and 4 days after injection. Nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 showed similar kinetic patterns in all of the eyes; that is, they increased to a peak 1 day after the injection and returned to normal by day 4. However, increased amounts the neurotrophin receptor TrkA within the retinal ganglion cell layer and nerve fiber layer were detected 1 day after injection of glutamate in either toxic or subtoxic amounts, but not after saline injection. This finding points to the possible involvement of neurotrophin receptors in regulation of the cellular responses to glutamate challenge. Identification of the intracellular signals that trigger the glutamate-induced self-protective mechanism would shed light on the genetic balance needed for survival, and guide the development of drugs for the up-regulation of desired genes and their products.

Thrombin attenuation is neuroprotective in the injured rat optic nerve

The functional loss that often follows injury of the mammalian CNS has been attributed not only to the immediate neural loss, but also to secondary neuronal degeneration caused by toxic biochemical mediators in the environment of the injured nerve. We report here that a high thrombin content, produced as a result of injury-induced activation of prothrombin, appears to be an important mediator of secondary damage. Measurement of post-traumatic neuronal survival in vivo revealed that post-traumatic local application of the thrombin inhibitor N-alpha-(2-naphthylsulphonylglycyl)-4-(D,L)-amidinophenylalanine piperidide acetate in the rat optic nerve subjected to mild partial crush injury left twice as many retinal ganglion cells with functioning axons as in controls. Thus, by readjusting thrombin activity, thereby possibly obtaining a moderate post-traumatic increase and thus gaining the benefit of thrombin without its toxic effects, it may be possible to create an environment that is more favourable for post-traumatic survival.

Vaccination for neuroprotection in the mouse optic nerve: implications for optic neuropathies

T-cell autoimmunity to myelin basic protein was recently shown to be neuroprotective in injured rat optic nerves. In the present study, using the mouse optic nerve, we examined whether active immunization rather than passive transfer of T-cells can be beneficial in protecting retinal ganglion cells (RGCs) from post-traumatic death. Before severe crush injury of the optic nerve, SJL/J and C3H.SW mice were actively immunized with encephalitogenic or nonencephalitogenic peptides of proteolipid protein (PLP) or myelin oligodendrocyte glycoprotein (MOG), respectively. At different times after the injury, the numbers of surviving RGCs in both strains immunized with the nonencephalitogenic peptides pPLP 190-209 or pMOG 1-22 were significantly higher than in injured controls treated with the non-self-antigen ovalbumin or with a peptide derived from beta-amyloid, a non-myelin-associated protein. Immunization with the encephalitogenic myelin peptide pPLP 139-151 was beneficial only when the disease it induced, experimental autoimmune encephalomyelitis, was mild. The results of this study show that survival of RGCs after axonal injury can be enhanced by vaccination with an appropriate self-antigen. Furthermore, the use of nonencephalitogenic myelin peptides for immunization apparently allows neuroprotection without incurring the risk of an autoimmune disease. Application of these findings might lead to a promising new approach for treating optic neuropathies such as glaucoma.

Diffusion anisotropy MRI for quantitative assessment of recovery in injured rat spinal cord

Spinal cord injury and its devastating consequences are the subject of intensive research aimed at reversing or at least minimizing functional loss. Research efforts focus on either attenuating the post-injury spread of damage (secondary degeneration) or inducing some regeneration. In most of these studies, as well as in clinical situations, evaluation of the state of the injured spinal cord poses a serious difficulty. To address this problem, we carried out a diffusion-weighted MRI experiment and developed an objective routine for quantifying anisotropy in injured rat spinal cords. Rats were subjected to a contusive injury of the spinal cord caused by a controlled weight drop. Untreated control rats were compared with rats treated with T cells specific to the central nervous system self-antigen myelin basic protein, a form of therapy recently shown to be neuroprotective. After the rats were killed their excised spinal cords were fixed in formalin and imaged by multislice spin echo MRI, using two orthogonal diffusion gradients. Apparent diffusion coefficient (ADC) values and anisotropy ratio (AI) maps were extracted on a pixel-by-pixel basis. The calculated sum of AI values (SAI) for each slice was defined as a parameter representing the total amount of anisotropy. The mean-AI and SAI values increased gradually with the distance from the site of the lesion. At the site itself, the mean-AI and SAI values were significantly higher in the spinal cords of the treated animals than in the controls (P = 0.047, P = 0.028, respectively). These values were consistent with the score of functional locomotion. The difference was also manifested in the AI maps, which revealed well-organized neural structure in the treated rats but not in the controls. The SAI values, AI histograms, and AI maps proved to be useful parameters for quantifying injury and recovery in an injured spinal cord. These results encourage the development of diffusion anisotropy MRI as a helpful approach for quantifying the extent of secondary degeneration and measuring recovery after spinal cord injury. Magn Reson Med 45:1-9, 2001.

RGC death in mice after optic nerve crush injury: oxidative stress and neuroprotection

PURPOSE

To establish a method for morphometric analysis of retrogradely labeled retinal ganglion cells (RGCs) of the mouse retina, to be used for the study of molecular aspects of RGC survival and neuroprotection in this model; to evaluate the effect of overexpression of Cu-Zn-superoxide dismutase (CuZnSOD) on RGC survival after severe crush injury to the optic nerve, and to assess the effect of the alpha2-adrenoreceptor agonist brimonidine, recently shown to be neuroprotective, on RGC survival.

METHODS

A severe crush injury was inflicted unilaterally in the orbital portion of the optic nerves of wild-type and transgenic (Tg-SOD) mice expressing three to four times more human CuZnSOD than the wild type. In each mouse all RGCs were labeled 72 hours before crush injury by stereotactic injection of the neurotracer dye FluoroGold (Fluorochrome, Denver, CO) into the superior colliculus. Survival of RGCs was then assessed morphometrically, with and without systemic injection of brimonidine.

RESULTS

Two weeks after crush injury, the number of surviving RGCs was significantly lower in the Tg-SOD mice (596.6 +/- 71.9 cells/mm(2)) than in the wild-type control mice (863. 5 +/- 68 cells/mm(2)). There was no difference between the numbers of surviving RGCs in the uninjured retinas of the two strains (3708 +/- 231.3 cells/mm(2) and 3904 +/- 120 cells/mm(2), respectively). Systemic injections of brimonidine significantly reduced cell death in the Tg-SOD mice, but not in the wild type.

CONCLUSIONS

Overexpression of CuZnSOD accelerates RGC death after optic nerve injury in mice. Activation of the alpha2-adrenoreceptor pathway by brimonidine enhances survival of RGCs in an in vivo transgenic model of excessive oxidative stress.

Passive or active immunization with myelin basic protein promotes recovery from spinal cord contusion

Partial injury to the spinal cord can propagate itself, sometimes leading to paralysis attributable to degeneration of initially undamaged neurons. We demonstrated recently that autoimmune T cells directed against the CNS antigen myelin basic protein (MBP) reduce degeneration after optic nerve crush injury in rats. Here we show that not only transfer of T cells but also active immunization with MBP promotes recovery from spinal cord injury. Anesthetized adult Lewis rats subjected to spinal cord contusion at T7 or T9, using the New York University impactor, were injected systemically with anti-MBP T cells at the time of contusion or 1 week later. Another group of rats was immunized, 1 week before contusion, with MBP emulsified in incomplete Freund's adjuvant (IFA). Functional recovery was assessed in a randomized, double-blinded manner, using the open-field behavioral test of Basso, Beattie, and Bresnahan. The functional outcome of contusion at T7 differed from that at T9 (2.9+/-0.4, n = 25, compared with 8.3+/-0.4, n = 12; p<0.003). In both cases, a single T cell treatment resulted in significantly better recovery than that observed in control rats treated with T cells directed against the nonself antigen ovalbumin. Delayed treatment with T cells (1 week after contusion) resulted in significantly better recovery (7.0+/-1; n = 6) than that observed in control rats treated with PBS (2.0+/-0.8; n = 6; p<0.01; nonparametric ANOVA). Rats immunized with MBP obtained a recovery score of 6.1+/-0.8 (n = 6) compared with a score of 3.0+/-0.8 (n = 5; p<0.05) in control rats injected with PBS in IFA. Morphometric analysis, immunohistochemical staining, and diffusion anisotropy magnetic resonance imaging showed that the behavioral outcome was correlated with tissue preservation. The results suggest that T cell-mediated immune activity, achieved by either adoptive transfer or active immunization, enhances recovery from spinal cord injury by conferring effective neuroprotection. The autoimmune T cells, once reactivated at the lesion site through recognition of their specific antigen, are a potential source of various protective factors whose production is locally regulated.

Metabolic and ionic responses to global brain ischemia in the newborn dog in vivo: II. Post-natal age aspects

The main difference between newborn and adult brains is expressed in the relative resistance of the newborn brain to oxygen deprivation. The aim of the present study was to examine the effect of global ischemia in canine puppies of three different ages on the metabolic, ionic and electrical activity of the brain and to study the basic mechanisms underlying the relative resistance of the newborn brain in ischemic episode. The puppies were divided into three age groups. The young group included 0-6-day-old puppies (n = 16), the intermediate group included 7-19-day-old puppies (n = 21), and the 'adult' group included puppies aged 20 days or more (n = 17). Statistical analysis of the results led to the following conclusions: The younger the puppy, the longer is the time until the occurrence of the secondary reflectance increase SRI (13.0 +/- 1.9 min vs. 5.3 +/- 0.5 min). The younger the puppy, the longer the time until onset of potassium leakage from the cells (0.9 +/- 0.1 min vs. 0.35 +/- 0.05 min) and the lower the amount of potassium leakage (9.6 +/- 2.8 mM vs. 21.7 +/- 4.8 mM). The rate of pumping of the potassium ions into the cells during the recovery stage was higher in the oldest group (1.2 +/- 0.2 mM min-1 vs. 0.38 +/- 0.1 mM min-1). It was possible to speculate that in the young puppies there is uncoupling of the oxidative phosphorylation from respiration and as a result, there is a lower, if any, rate of ATP synthesis. It seems that the newborn brain is able to cope with a decrease in available energy for a longer period of time. This is apparently due to differences in membrane characteristics and an improved ability to retain ionic equilibrium across both sides of the membrane.

Brain metabolic and ionic responses to global brain ischemia in the newborn dog in vivo: 1. Methodological aspects

A variety of methods has been used in order to obtain a state of acute cerebral ischemia. Most of these methods suffered from drawbacks such as irreversible ischemia, difficult to obtain total ischemia and heart injury. The aim of this study was to develop a new method for induction of global or partial cerebral ischemia in the newborn dog at various post-natal ages. A multi-parameter monitoring system (MPA) measures the metabolic (mitochondria NADH oxidation/reduction state), hemodynamic (reflectance), ionic (extracellular potassium and calcium) and electrical changes (ECoG) continuously and simultaneously in the puppy's brain in vivo. A hole was made in the chest cavity, the two large arteries supplying blood to the brain, the brachiocephalic and the subclavian arteries (B + S) were isolated and occluded during the monitoring. In most of the animals, occlusion of these two arteries alone resulted in partial ischemia. For obtaining 100% ischemia, we occluded both the B + S arteries as well as the aortic arch. Immediately at the onset of ischemia, an increase (reduction) of NADH begins. During complete ischemia the average time until maximal increase was 4 min, compared to ischemia of up to 50% of the maximal reduction of the NADH where the average time was 1 min. After reperfusion of the brain, mitochondria recovery was very rapid and the average time until return of this parameter to its pre-ischemic level was 1.4 +/- 0.2 min. The ionic changes which occurred immediately upon the onset of ischemia were the accumulation of extracellular potassium ions was recorded. The rate of potassium ion accumulation was dependent on the severity of the ischemia (range 0.19 +/- 0.08-2.2 +/- 0.4 mM min-1). The increase in the extracellular potassium ion concentration occurs in two stages, an initial slow stage and a second rapid stage (13.0 +/- 1.8 mM). The results presented in this paper suggest and prove the usefulness of a new approach for global and partial ischemia in the newborn dogs. In addition, our results assess the brain metabolic, ionic, hemodynamic and electrical responses to brain ischemia in the puppies.

Autoimmune T cells retard the loss of function in injured rat optic nerves

We recently demonstrated that autoimmune T cells protect neurons from secondary degeneration after central nervous system (CNS) axotomy in rats. Here we show, using both morphological and electrophysiological analyses, that the neuroprotection is long-lasting and is manifested functionally. After partial crush injury of the rat optic nerve, systemic injection of autoimmune T cells specific to myelin basic protein significantly diminished the loss of retinal ganglion cells and conducting axons, and significantly retarded the loss of the visual response evoked by light stimulation. These results support our challenge to the traditional concept of autoimmunity as always harmful, and suggest that in certain situations T cell autoimmunity may actually be beneficial. It might be possible to employ T cell intervention to slow down functional loss in the injured CNS.

T cell immunity to copolymer 1 confers neuroprotection on the damaged optic nerve: possible therapy for optic neuropathies

We recently reported that the posttraumatic spread of degeneration in the damaged optic nerve can be attenuated by the adoptive transfer of autoimmune T cells specific to myelin basic protein. However, it would be desirable to obtain immune neuroprotection free of any possible autoimmune disease. In an attempt to obtain disease-free immune neuroprotection, we used the synthetic four-amino acid polymer copolymer 1 (Cop-1), which is known not to be encephalitogenic despite its cross-reactivity with myelin basic protein. We show here that active immunization with Cop-1 administered in adjuvant, as well as adoptive transfer of T cells reactive to Cop-1, can inhibit the progression of secondary degeneration after crush injury of the rat optic nerve. These results have implications for the treatment of optic neuropathies.

The effect of hyperbaric hyperoxia on brain function in the newborn dog in vivo

Age is a natural factor that has been found to significantly affect sensitivity to hyperbaric hyperoxia (HBO). Exposure to HBO may lead to damages in the energy metabolism of the brain cells. The aim of this study was to test the effect of HBO on the metabolic, hemodynamic and electrical activities in the newborn dog. The study was performed using one-day- to 70-day-old puppies. The puppies were placed in a pressure chamber. The pressure of pure O2 in the chamber was raised by 5 atmospheres (ATA, 75 psi = 6 ATA) within 10 min. The first biochemical change to take place during HBO was oxidation of mitochondrial NADH. The age of the puppy was found to affect the time to the initiation of seizures. In the puppies under the age of 24 days, the average time was 35.1 +/- 5.9 min. In the puppies of 24 days old and older, the average time was 5.1 +/- 0.8 min. In the younger puppies, there was a later occurrence of blood vessel contractions and a longer life span compared to the older puppies. The comparison between the puppies of different ages during exposure to HBO showed differences in the metabolic response, hemodynamic changes and electrical activity. These differences can partially explain the higher resistance in the younger puppies to HBO.

Neuroprotection: a new treatment modality for glaucoma?

It is now commonly accepted that glaucoma is a neurodegenerative disease of the optic nerve. Thus, at any given time, there are neurons that, though still viable, are vulnerable to the hostile extracellular milieu and are therefore amenable to neuroprotective therapy. Neuroprotection refers to any intervention, either external to the optic nerve or internally, that will lead to an intracellular change in the balance between survival and death signals in favor of survival. Several potential sites and modalities for such intervention may exist. When designing neuroprotective therapy, ways must be sought to recruit the physiologic self-repair mechanisms awakened by the primary or secondary risk factors. These mechanisms appear to be insufficiently effective when in their natural state, but they may be simulated or boosted by appropriate therapeutic compounds or cells.

Autoimmune T cells as potential neuroprotective therapy for spinal cord injury

Autoimmune T cells against central nervous system myelin associated peptide reduce the spread of damage and promote recovery in injured rat spinal cord, findings that might lead to neuroprotective cell therapy without risk of autoimmune disease.

Brain metabolic and ionic responses to systemic hypoxia in the newborn dog in vivo

Newborns are less sensitive than adults to hypoxic/ischemic injury. However, research into the mechanism of the newborn's relative resistance to reduced brain oxygen levels is relatively scarce, and the time-scale for the disappearance of resistance is not known. The multiprobe assembly (MPA) has enabled us to examine the resistance of puppies at various ages to hypoxia via continuous, simultaneous, on-line measurement of various ionic, metabolic and electrical parameters from the cerebral cortex. The parameters measured included electrocorticogram (ECoG), direct current (DC) steady state potential, extracellular potassium (Ke+) and calcium ion concentrations and intra-mitochondrial Nicotine amide adenine dinucleotide NADH redox levels. These parameters were measured under various degrees of hypoxia (fraction of inspiration oxygen was between 0-10%) in 6-h-old to 24-week-old puppies (n = 44). Sensitivity to hypoxia increased with age, being expressed in the leakage of potassium ions out of the cells (0.3 +/- 0.07 mM in the younger puppies and 3.0 +/- 1.3 mM in the older puppies) following an increase in intra-mitochondrial NADH redox levels. Potassium ion (Ke+) leakage was apparently due to depleted energy stores resulting from an impairment in the balance between oxygen supply and demand. Although the overall effect was similar, the kinetics of these changes were much faster in the older puppies. The time to initial increase of extracellular K+ was 2.5 +/- 0.1 min in the younger puppies and 0.9 +/- 0.1 min in the older puppies. The time to maximum increase of NADH was 3.2 +/- 0.2 min in the younger puppies and 1.4 +/- 0.1 min in the older puppies. Our results indicate that the older puppies utilize the existing oxygen faster than the younger puppies. It is concluded that the increased resistance of newborn puppies to hypoxia is due to intrinsic properties of the brain itself, like the ability of the membrane to maintain ionic homeostasis.

'Axogenic' and 'somagenic' neurodegenerative diseases: definitions and therapeutic implications

Neurodegenerative diseases are characterized by a relentless loss of specific groups of neuronal subtypes. Many of these diseases share similar molecular mechanisms and extracellular mediators of neuronal loss. We now suggest that neurodegeneration originating in the neuronal cell bodies (e.g. in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis) should be distinguished from that originating in the axons (e.g. in glaucoma, certain peripheral neuropathies and spinal stenosis). We propose that the former group of diseases be defined as 'somagenic' and the latter as 'axogenic'. Although axogenic disorders may share common symptoms and mediators of toxicity with somagenic disorders, they have distinct temporal, subcellular and signal-transduction features. We further suggest that, by adopting this classification of disorders based on pathophysiological processes, we will come to recognize additional diseases (in particular, those defined as axogenic) as being neurodegenerative and therefore possibly amenable to neuroprotective therapy.

The remedy may lie in ourselves: prospects for immune cell therapy in central nervous system protection and repair

The irreversible loss of function after axonal injury in the central nervous system (CNS) is a result of the lack of neurogenesis, poor regeneration, and the spread of damage caused by toxicity emanating from the degenerating axons to uninjured neurons in the vicinity. Now, 100 years after Ramon y Cajal's discovery that CNS neurons--unlike neurons of the peripheral nervous system--fail to regenerate, it has become evident that (a) CNS tissue is indeed capable of regenerating, at.least in part, provided that it acquires the appropriate conditions for growth support, and (b) that the spread of damage can be stopped and the postinjury rescue of neurons thus achieved, if ways are found to neutralize the mediators of toxicity, either by inhibiting their action or by increasing tissue resistance to them. In most physiological systems the processes of tissue maintenance and repair depend on the active assistance of immune cells. In the CNS, however, communication with the immune system is restricted. The accumulated evidence from our previous studies suggests that the poor posttraumatic repair and maintenance in the CNS is due at least in part to this restriction. Key factors in the recovery of injured tissues, but missing or deficient in the CNS, are the processes of recruitment and activation of immune cells. We therefore propose the development of immune cell therapies in which the injured CNS is exogenously provided with an adequate number of appropriately activated immune cells (macrophages for regrowth and autoimmune T cells for maintenance), controlled in such a way as to derive maximal benefit with minimal risk of disease. It is expected that these self-adjusting cells will communicate with the damaged tissue, monitor tissue needs, and control the dynamic course of CNS healing.

Injury-induced gelatinase and thrombin-like activities in regenerating and nonregenerating nervous systems

It is now widely accepted that injured nerves, like any other injured tissue, need assistance from their extracellular milieu in order to heal. We compared the postinjury activities of thrombin and gelatinases, two types of proteolytic activities known to be critically involved in tissue healing, in nonregenerative (rat optic nerve) and regenerative (fish optic nerve and rat sciatic nerve) neural tissue. Unlike gelatinases, whose induction pattern was comparable in all three nerves, thrombin-like activity differed clearly between regenerating and nonregenerating nervous systems. Postinjury levels of this latter activity seem to dictate whether it will display beneficial or detrimental effects on the capacity of the tissue for repair. The results of this study further highlight the fact that tissue repair and nerve regeneration are closely linked and that substances that are not unique to the nervous system, but participate in wound healing in general, are also crucial for regeneration or its failure in the nervous system.

Autoimmune T cells protect neurons from secondary degeneration after central nervous system axotomy

Autoimmunity to antigens of the central nervous system is usually considered detrimental. T cells specific to a central nervous system self antigen, such as myelin basic protein, can indeed induce experimental autoimmune encephalomyelitis, but such T cells may nevertheless appear in the blood of healthy individuals. We show here that autoimmune T cells specific to myelin basic protein can protect injured central nervous system neurons from secondary degeneration. After a partial crush injury of the optic nerve, rats injected with activated anti-myelin basic protein T cells retained approximately 300% more retinal ganglion cells with functionally intact axons than did rats injected with activated T cells specific for other antigens. Electrophysiological analysis confirmed this finding and suggested that the neuroprotection could result from a transient reduction in energy requirements owing to a transient reduction in nerve activity. These findings indicate that T-cell autoimmunity in the central nervous system, under certain circumstances, can exert a beneficial effect by protecting injured neurons from the spread of damage.

Alpha2-adrenoreceptor agonists are neuroprotective in a rat model of optic nerve degeneration

PURPOSE

The neurodegenerative progression of glaucoma is considered to be related not only to primary risk factors such as the elevation of intraocular pressure, but also to mediators of secondary neuronal degeneration. In the present study, the neuroprotective activity of the alpha2-adrenoreceptor agonists brimonidine, AGN 191103, and clonidine were examined in an animal model that simulates secondary neuronal degeneration of the optic nerve in a way thought to be independent of elevation of intraocular pressure. The beta-blocker timolol, currently used clinically to decrease intraocular pressure, was also examined for neuroprotective activity at dosages corresponding to the effective antihypertensive dosage.

METHODS

A single dose of each of the tested compounds was administered intraperitoneally immediately after partial crush injury of the rat optic nerve. Secondary degeneration was measured by determining injury-induced deficits with and without the drug. This was achieved electrophysiologically by measurement of compound action potential amplitude, and morphometrically by counting the retrogradely labeled retinal ganglion cells, representing viable optic nerve axons, in wholemounted retinas.

RESULTS

All three alpha2-adrenoreceptor agonists, but not timolol, exhibited neuroprotective effects. Treatment immediately after injury with each of these agonists resulted in a dose-dependent attenuation of the injury-induced decrease in compound action potential amplitude. Moreover, after treatment with 100 microg/kg brimonidine administered intraperitoneally, the loss of retinal ganglion cells 2 weeks after injury was three times lower than in saline-treated animals.

CONCLUSIONS

In addition to their known effect of lowering intraocular pressure, alpha2-adrenoreceptor agonists, unlike timolol, exert a neuroprotective effect. Use of the rat optic nerve model of partial crush injury can serve as a method of screening compounds that are potentially capable of alleviating the progression of secondary neuronal degeneration.

Degeneration of spared axons following partial white matter lesion: implications for optic nerve neuropathies

Neuroprotective therapy is a relatively new development in the approach to the treatment of acute and chronic brain damage. Though initially viewed in the framework of acute CNS injuries, the concept was recently extended to include chronic injuries, in which at any given time there are some neurons in an acute phase of degeneration coexisting with others that are healthy, marginally damaged, or dead. The healthy neurons and those that are only marginally damaged are the potential targets for neuroprotection. For the development of neuroprotective therapies, it is essential to employ an animal model in which the damage resulting from secondary degeneration can be quantitatively distinguished from primary degeneration. This is of particular relevance when the site of the damage is in the white matter (nerve fibers) rather than in the gray matter (cell bodies). In the present work we reexamine the concepts of secondary degeneration and neuroprotection in white matter lesions. Using a partial crush injury of the adult rat optic nerve as a model, we were able to assess both primary and secondary nerve damage. We show that neurons whose axons were not damaged or only marginally damaged after an acute insult will eventually degenerate as a consequence of their existence in the degenerative environment produced by the injury. This secondary degeneration does not occur in all of the neurons at once, but affects them in a stepwise fashion related to the severity of the damage inflicted. These findings, which may be applicable to the progression of acute or chronic neuropathy, imply that neuroprotective therapy may have a beneficial effect even if there is a time lag between injury and treatment.

Implantation of stimulated homologous macrophages results in partial recovery of paraplegic rats

Postinjury recovery in most tissues requires an effective dialog with macrophages; however, in the mammalian central nervous system, this dialog may be restricted (possibly due to its immune-privileged status), which probably contributes to its regeneration failure. We circumvented this by implanting macrophages, pre-exposed ex vivo to peripheral nerve segments, into transected rat spinal cord. This stimulated tissue repair and partial recovery of motor function, manifested behaviorally by movement of hind limbs, plantar placement of the paws and weight support, and electrophysiologically by cortically evoked hind-limb muscle response. We substantiated these findings immunohistochemically by demonstrating continuity of labeled nerve fibers across the transected site, and by tracing descending fibers distally to it by anterograde labeling. In recovered rats, retransection of the cord above the primary transection site led to loss of recovery, indicating the involvement of long descending spinal tracts. Injection of macrophages into the site of injury is relatively non-invasive and, as the cells are autologous, it may be developed into a clinical therapy.

Elevation of intraocular glutamate levels in rats with partial lesion of the optic nerve

BACKGROUND

Acute partial lesion of the rat optic nerve, although not a model for glaucoma, mimics some of the features of the disease.

OBJECTIVE

To learn whether degeneration of rat optic nerve fibers and death of their retinal ganglion cells induced by an acute partial lesion are associated with elevated levels of glutamate, known to occur in the eyes of humans and monkeys with glaucoma.

MATERIALS AND METHODS

Rat optic nerve was subjected to a partial crush injury. Aqueous humor samples were aspirated from the anterior and posterior aqueous chambers at specified times and their amino acid contents were determined by means of high-performance liquid chromatography.

RESULTS

Three and 7 days after injury, intraocular glutamate and aspartate levels were found to be significantly higher than in normal or sham-operated-on eyes, and returned to normal by day 14.

CONCLUSIONS

Degeneration of the optic nerve, induced by a mechanical injury of the axons, leads to intraocular elevation of glutamate and aspartate levels. These results illustrate that the model of the partial optic nerve lesion exhibits another feature typical of a long-term optic neuropathy, such as glaucoma.

Potential neuroprotective therapy for glaucomatous optic neuropathy

Accumulating evidence points to the existence of a mechanism that may explain why glaucomatous neuropathy continues to progress even after its primary cause, e.g., high intraocular pressure, has been alleviated or attenuated. We suggest that such a mechanism involves processes collectively termed secondary degeneration, an inevitable outcome of acute injury of the central nervous system. Secondary degeneration refers to the spread of degeneration to apparently healthy neurons that escaped the primary insult, but are adjacent to the injured neurons and are thus exposed to the degenerative milieu that the latter create. Neuroprotection, i.e., protection of undamaged neurons from secondary degeneration, would therefore require that the extracellular elements associated with the degeneration be neutralized, balanced off, or inhibited. In seeking an experimental framework for testing treatment modalities for neuroprotection, we have developed an animal model in which a well-calibrated, reproducible, partial lesion is inflicted on the optic nerve of the adult rat. Using this model, the extent of the primary damage can be quantified and the secondary degeneration demonstrated and assessed. Damage inflicted directly on the optic nerve fibers inevitably leads to their degeneration and the eventual death of their cell bodies. Over time, neurons that initially escaped the injury undergo self-perpetuating secondary degeneration, the extent of which is a function of the severity of the primary insult. We suggest that a similar mechanism may underlie the propagation of damage seen in glaucoma at any given time after alleviation of the primary cause of the disease, and might explain why patients with severe pre-existing damage are much more likely to deteriorate even if their intraocular pressure is the same or lower than that of patients without visual loss at the time of diagnosis. The model can be used to screen compounds for their efficacy in protecting initially spared neurons from undergoing secondary degeneration, thereby achieving a better functional outcome. The findings obtained using this model support the attempt to develop neuroprotective therapy for glaucoma. Such therapy would need to be applied in combination with treatment (e.g., antihypertensive therapy) directed against the primary cause of the neuropathy.

NMDA-receptor antagonist protects neurons from secondary degeneration after partial optic nerve crush

Damage resulting from a partial acute lesion of white matter in the central nervous system (CNS) gradually spreads also to neurons that escaped the primary injury, resulting in their degeneration. Such spreading has been referred to as secondary degeneration. In order to demonstrate that this degeneration is indeed secondary to that caused by the acute insult, as well as to investigate the mechanism underlying the spread of damage and ways in which to protect neurons from such damage, we have proposed the use of partial lesion of the rodent optic nerve as a model. In this model we examined whether an antagonist of a receptor-mediated channel, shown to be beneficial in gray matter lesions, can protect neurons from undergoing secondary degeneration following white matter lesion. A well-calibrated partial crush lesion inflicted on the optic nerve of adult rats was immediately followed by a single intraperitoneal injection of the N-methyl-D-aspartate receptor antagonist, MK-801 (1 mg/kg). Protection of neurons from secondary degeneration was assessed by retrograde labeling and by measurement of the visual evoked potential (VEP) response to light. Two weeks after the injury, the mean number of neurons that were still intact was about threefold higher in the MK-801-treated group than in the saline-treated control group, indicating a treatment-induced protection of neurons that had escaped primary injury. A positive VEP response to light was obtained in 90% of the MK-801 treated animals and in only 50% of injured controls. The questions regarding whether the secondary degeneration of initially spared neurons starts in their cell bodies or in their axons, and consequently the identity of the primary site of their protection by MK-801, are discussed in relation to the absence of N-methyl-D-aspartate receptors on nerve fibers. The present findings may have implications for both acute and chronic injuries of the CNS.

Potential treatment modalities for glaucomatous neuropathy: neuroprotection and neuroregeneration

PURPOSE

This article presents the rationale and an experimental strategy for the development of new treatment modalities for glaucomatous neuropathy. Accumulating evidence suggests that regardless of the primary trigger of the retinal and optic nerve damage in glaucoma, the disease will continue to progress even when the cause is removed. The resulting damage can be mimicked by the progression of damage secondary to an acute partial crush injury at the optic nerve head. Such secondary damage includes degeneration of the directly injured optic nerve fibers culminating in death of their cell bodies, as well as degeneration of nerve fibers that escaped acute injury but nevertheless deteriorate as a result of their exposure to injury-induced mediators of secondary degeneration released by the directly affected neurons.

CONCLUSION

We therefore propose that substances found to be effective in rescuing fibers from secondary degeneration and in increasing the survival rate or prolonging survival of retinal ganglion cells in the partially lesioned optic nerve may be useful for the treatment of glaucoma. The new approach does not replace hypotensive therapy, but addresses the glaucoma-induced damage by promoting nerve protection and neuroregeneration.

Complete transection of rat optic nerve while sparing the meninges and the vasculature: an experimental model for optic nerve neuropathy and trauma

In this study we present a method to achieve a complete transection of optic nerve axons in adult rat, while preserving the vasculature and retaining the continuity of the meninges. Under deep anesthesia, the optic nerve of adult rat is exposed. Using specially designed instruments built from disposable glass microsampling pipettes, a small opening is created in the meninges of the optic nerve, 2-3 mm behind the eye globe. A glass dissector is introduced through the opening and is used to cut all the axons through the whole width of the nerve. Complete transection of the optic nerve axons was achieved, while retaining the continuity of the meninges and avoiding damage to the nerve's vascular supply. Transection was confirmed by transillumination showing a complete gap in the continuity of the nerve axons, and by both morphological and electrophysiological criteria. Nerve transection performed by the conventional technique leads to neuroma formation and hampers regeneration. Crush injury may cause nerve ischemia, which is detrimental to axonal recovery. Both of these disadvantages are avoided by the method of transection presented here. The opening created in the 'meningeal tube' can be used to inject substances that may be of benefit in recovery, rescue and/or regeneration of the injured axons. The model is particularly suitable for in vivo studies on nerve regeneration, and especially for screening of putative therapeutic agents.

HU-211, a nonpsychotropic cannabinoid, produces short- and long-term neuroprotection after optic nerve axotomy

HU-211 is a novel synthetic analog of tetrahydrocannabinol that was recently shown in animal models to be nonpsychotropic. In this study we show that HU-211 can potentially be used as a neuroprotective compound in the CNS. Using a calibrated crush injury of adult rat optic nerve, we show that HU-211 can reduce injury-induced metabolic and electrophysiological deficits. Energy metabolism was monitored by measuring the intramitochondrial nicotine-amine adenine dinucleotide redox state hourly for 6 h after injury and treatment. Electrophysiological activity was assessed by compound action potential and visual evoked potential response. Beneficial effects were dose-dependent, being optimal at 7 mg/kg, administered intraperitoneally. The time window during which treatment was effective was found to be from the time of injury for at least 5 h, with treatment most effective at the time of injury. These results strongly suggest that HU-211, given immediately after CNS injury at the optimal dosage, may possess neuroprotective activities.

Recovery of visual response of injured adult rat optic nerves treated with transglutaminase

Failure of axons of the central nervous system in adult mammals to regenerate spontaneously after injury is attributed in part to inhibitory molecules associated with oligodendrocytes. Regeneration of central nervous system axons in fish is correlated with the presence of a transglutaminase. This enzyme dimerizes interleukin-2, and the product is cytotoxic to oligodendrocytes in vitro. Application of this nerve-derived transglutaminase to rat optic nerves, in which the injury had caused the loss of visual evoked potential response to light, promoted the recovery of that response within 6 weeks after injury. Transmission electron microscopy analysis revealed the concomitant appearance of axons in the distal stump of the optic nerve.

Inflammation after axonal injury has conflicting consequences for recovery of function: rescue of spared axons is impaired but regeneration is supported

Neural injury leads to tissue damage beyond that caused by the initial lesion, mainly as a result of a chain of autodestructive events triggered by the trauma. These events apparently include the activation of immune-derived cells and their products, as treatment with anti-inflammatory agents, such as corticosteroids, limits the damage and thus improves recovery. On the other hand, immune-derived substances, such as cytokines, are thought to play an important role in post-traumatic axonal regeneration. Thus, the need to reduce inflammation to limit the spread of damage appears to be in conflict with the need to permit inflammation to promote regeneration. Comprehension and resolution of this apparent conflict may lead to the development of treatment protocols aimed at rescuing axons spared by the initial injury, without hampering the potential regeneration of directly and indirectly injured axons. In this study, carried out on rats with crushed optic nerves, daily intraperitoneal injections of dexamethasone commencing prior to the injury significantly attenuated the injury-induced decrease in electrophysiological activity and reduced the area of tissue damage. On the other hand, dexamethasone treatment reduced the permissiveness of the injured nerves to neural adhesion and regrowth in vitro. This latter phenomenon was also observed in injured peripheral nerves. Results are discussed with respect to the possible establishment of an appropriate protocol for corticosteroid treatment of nerve injuries aimed at promoting neuronal rescue without compromising neuronal regeneration.

Gangliosides attenuate axonal loss after optic nerve injury

Gangliosides have been shown to be capable of protecting nerve tissue from mechanical and biochemical insults and promoting their repair. The present study provides morphologic evidence that monosialogangliosides attenuate the degenerative process at the distal stump of the rat optic nerve after crush injury. Injured rat optic nerves were treated for 7 days after injury with daily intraperitoneal injections of monosialogangliosides (30 mg/kg/day), and compared with untreated injured controls with respect to the number of viable axons 2 and 4 weeks after injury, as indicated by transmission electron microscopy. After 2 weeks, the mean number of viable axons in the treated optic nerves (n = 5) was slightly higher than in the controls (n = 5). Four weeks after injury, although the absolute number in both the experimental and the control groups had dropped, it was about seven-fold higher in the treated animals (1696 +/- 1149, n = 7) than in the untreated animals (216 +/- 65, n = 6); this difference was statistically significant. These findings, which offer some insight as to how monosialogangliosides affect injured nerves, may have important implications for treatment in cases of optic nerve injury.

GM1 reduces injury-induced metabolic deficits and degeneration in the rat optic nerve

This study demonstrates the earliest reported effects of GM1 treatment on crush-injured axons of the mammalian optic nerve. GM1, administered intraperitoneally immediately after injury, was found to reduce the injury-induced metabolic deficit in nerve activity within 2 hr of injury, as measured by changes in the nicotine-amine adenine dinucleotide redox state. After 4 wk, transmission electron microscopy 1 mm distal to the site of injury revealed a sevenfold increase in axonal survival in GM1-treated compared to untreated injured nerves. These results emphasize the beneficial effect of GM1 on injured optic nerves as well as the correlation between immediate and long-term consequences of the injury. Thus, these results have implications for treating damaged optic nerves.

Effects of age on the metabolic, ionic and electrical responses to anoxia in the newborn dog brain in vivo

The interrelation between brain energy metabolism, electrical activity and ion homeostasis developing under experimental anoxia in animals of different ages is of significant value in the understanding of brain damage occurring under similar conditions of clinical neuropathology. The purpose of the present study was to compare brain energy states and extracellular ion homeostasis during anoxia in newborn puppies of various ages. We have developed and used a multiparametric monitoring device by which various functions of the brain can be recorded in a real-time mode from a 5 mm diameter area on the surface of the cortex. Intracellular oxygen balance was evaluated in newborn puppies of various ages by monitoring the intramitochondrial NADH redox state using a fluorescence technique. The electrical activity was measured by recording the spontaneous ECoG (electrocorticogram) and DC (direct current) steady potential. Ion homeostasis was evaluated using surface potassium and calcium mini-electrodes. Newborn puppies were anesthetized, the dura mater was removed and the multiprobe assembly was placed on the brain and cemented to the skull. Five groups of puppies (0-1, 2-7, 8-14, 15-21 days and 3-24 weeks) were exposed to 5 minutes of complete O2 deprivation (100% nitrogen exposure) and were monitored during the recovery period until all parameters returned to baseline values. The results may be summarized as follows: 1. Resting baseline levels of extracellular K+ were in the same range as described for other young and adult mammals (2.9 +/- 0.05 mM). 2. Extracellular Ca2+ levels were higher than those published for other mammals (1.6 +/- 0.07 mM). 3. During 5 minutes of anoxia, a significant increase in K+ levels was recorded. This increase was not accompanied by measurable changes in extracellular Ca2+. 4. The effect of age on the length of time to the elevation of the extracellular K+ concentration and on the rate of K+ accumulation from the onset of the anoxic condition was significant, i.e., the younger the animal the longer the time and the lower the rate. 5. The rate of energy depletion was age dependent as indicated by the rate of NADH accumulation during anoxia. However, no significant effect of age on the basal aerobic metabolism was found as measured by the maximum percent increase of NADH during anoxia.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain mitochondrial redox state, tissue haemodynamic and extracellular ion responses to four-vessel occlusion and spreading depression in the rat

Fibre-optic surface fluorometer reflectrometry was used to monitor the NADH (nicotine adenine dinucleotide) redox state from rat brain during three- or four-vessel occlusion. To compare the completeness of the electrocauterization of the vertebral arteries and the effectiveness of the anterior cerebral arteries, two light guides were implanted above the cerebral hemispheres. The NADH level was measured and correlated with the changes in the intensity of the reflected light at the excitation wavelength (366 nm) and to the ECoG (electrocorticogram). In the present study, we used ten rats in which unilateral and bilateral carotid occlusion were performed. In a second group of rats we tested the effects of four-vessel occlusion on the metabolic and extracellular K+ and Ca2+ activities as compared with those recorded under spreading depression conditions. These experiments were done by using the multiprobe assembly (MPA) approach. The results could be summarized as follows: (1) in the four-vessel occlusion model, the level of cerebral ischaemia could be estimated quantitatively, in real-time, by monitoring the NADH redox state; (2) unilateral carotid occlusion (after vertebral coagulation) led to a variable level of ipsilateral ischaemia, depending upon the blood flow compensation between the two hemispheres; (3) fibre-optic fluorometry enabled the correlation of NADH redox state with other physiological parameters as well as during after-brain ischaemia; (4) using the MPA in rats exposed to four-vessel occlusion as well as spreading depression, we identified the differences between the two pathological states, although there were some similarities in the ion homeostasis responses.

Evidence for a functional role of acetylcholinesterase in cultured chick myotubes

This study was undertaken in order to assess the functional role of acetylcholinesterase (AChE) in cultures of chick skeletal muscle cells. Cultures of skeletal myotubes were prepared by mechanical dissociation of limb muscle removed from 11-day-old chick embryos and plating at a concentration of 0.8 X 10(6) cells/ml. Cultures incubated for 4-10 days were used for electrophysiological studies with intracellular microelectrodes. Individual myotubes differed with respect to the time course of repolarization following depolarization by acetylcholine (ACh), some cells repolarizing within 2-3 min and others only after 8-10 min. Physostigmine (10(-8)-10(-6) M) prolonged or sometimes completely prevented repolarization following ACh-induced depolarization. These results demonstrate that hydrolysis of ACh by AChE in cultured chick skeletal myotubes plays an important role in the repolarization of these cells following ACh-induced depolarization.