GM1 ganglioside treatment reduces visual deficits after graded crush of the rat optic nerve

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

Neurosteroid allopregnanolone reduces ipsilateral visual cortex potentiation following unilateral optic nerve injury

In adult mice with unilateral optic nerve crush injury (ONC), we studied visual response plasticity in the visual cortex following stimulation with sinusoidal grating. We examined visually evoked potentials (VEP) in the primary visual cortex ipsilateral and contralateral to the crushed nerve. We found that unilateral ONC induces enhancement of visual response on the side ipsilateral to the injury that is evoked by visual stimulation to the intact eye. This enhancement was associated with supranormal spatial frequency thresholds in the intact eye when tested using optomotor response. To probe whether injury-induced disinhibition caused the potentiation, we treated animals with the neurosteroid allopregnanolone, a potent agonist of the GABA_A receptor, one hour after crush and on post-injury days 3, 8, 13, and 18. Allopregnanolone diminished enhancement of the VEP and this effect was associated with the upregulated synthesis of the δ-subunit of the GABA_A receptor. Our study shows a new aspect of experience-dependent plasticity following unilateral ONC. This hyper-activity in the ipsilateral visual cortex is prevented by upregulation of GABA inhibition with allopregnanolone. Our findings suggest the therapeutic potential of allopregnanolone for modulation of plasticity in certain eye and brain disorders and a possible role for disinhibition in ipsilateral hyper-activity following unilateral ONC.

Cholinergic Potentiation of Restoration of Visual Function after Optic Nerve Damage in Rats

Enhancing cortical plasticity and brain connectivity may improve residual vision following a visual impairment. Since acetylcholine plays an important role in attention and neuronal plasticity, we explored whether potentiation of the cholinergic transmission has an effect on the visual function restoration. To this end, we evaluated for 4 weeks the effect of the acetylcholinesterase inhibitor donepezil on brightness discrimination, visually evoked potentials, and visual cortex reactivity after a bilateral and partial optic nerve crush in adult rats. Donepezil administration enhanced brightness discrimination capacity after optic nerve crush compared to nontreated animals. The visually evoked activation of the primary visual cortex was not restored, as measured by evoked potentials, but the cortical neuronal activity measured by thallium autometallography was not significantly affected four weeks after the optic nerve crush. Altogether, the results suggest a role of the cholinergic system in postlesion cortical plasticity. This finding agrees with the view that restoration of visual function may involve mechanisms beyond the area of primary damage and opens a new perspective for improving visual rehabilitation in humans.

Repetitive Transcorneal Alternating Current Stimulation Reduces Brain Idling State After Long-term Vision Loss

BACKGROUND

Deafferentation of visual system structures following brain or optic nerve injury leaves cortical areas deprived of visual input. Deprived cortical areas have a reduced sensory information processing and are characterized with localized enhanced or synchronized rhythms believed to represent an "idling state".

OBJECTIVE/HYPOTHESIS

We hypothesized that cortical idling can be modified with transcorneal alternating current stimulation (tACS) known to modulate cortical oscillations and thus change the functional state of the deafferented areas.

METHODS

tACS was applied in rat model of severe optic nerve crush using a protocol similar to our clinical studies (200 μA, 2-8 Hz) for 5 treatment days right after the lesion and at the chronic stage (3 months later). EEG and VEP were recorded over the visual cortices. In vivo confocal neuroimaging of the retina and histology of the optic nerves were performed.

RESULTS

Morphological investigations showed massive retinal ganglion cells death and degeneration of the optic nerves after crush. Visual loss was associated with increased EEG spectral power and lower coherence, indicating an "idling state". Stimulation induced a significant decrease of EEG power towards normal values. These effects were especially pronounced in the chronic stage.

CONCLUSION

Our results suggest that alternating current injected via the eye is able to modulate visually deprived brain areas and thus reduce cortical idling.

Calibration and standardisation of graded optic nerve injuries in rats

OBJECTIVES

To calibrate and standardise an animal model of graded optic nerve injury (ONI) in rats to facilitate future inter-laboratory data comparisons, focussing on quantification of injury intensity, injury severity, and the correlation between them.

METHODS

A pair of cross-action forceps or a pair of artery clips was used to induce optic nerve (ON) crush injuries. A lever principle and a simplified method were used to measure the crushing force. The simplified method directly measured weights as an external force exerted on the tip of the forceps or clips, which was just sufficient to maintain a gap and was equivalent to the closing (crush) force. The impulse and averaged impulse were explored as physical quantities to compare injury intensities. Graded ONIs were made by crushing the ON for 3, 6, 12, 30 or 60 seconds by the cross-action forceps, or 5, 10 or 15 seconds by the artery clips. The injury severity was evaluated by counting surviving retinal ganglion cell (RGC) through applied FluoroGold to the superior colliculus and lateral geniculate body before ON crush, intact RGC counting by applied FluoroGold after ON crush, and ON axon counting.

RESULTS

Similar results were obtained by the lever principle method and the simplified method. The crushing force of the cross-action forceps and the artery clips was 148.0 gram force (gf) and 32.4 gf, respectively. The graded ONI animal models were successfully created in rats without retinal ischaemia post-trauma. The averaged impulse produced by the artery clips for 15 seconds was equal to that produced by a 3-second crush of the cross-action forceps. The correlation between injury intensity and injury severity was fitted for a power function.

DISCUSSION

Our results provide a simplified and effective means to quantify and analyse data from ON crush studies compared with previously reported animal models.

Toxicity of polymeric nanoparticles in vivo and in vitro

Polybutylcyanoacrylate nanoparticles (PBCA NPs) are candidates for a drug delivery system, which can cross the blood-brain barrier (BBB). Because little is known about their toxicity, we exposed cells to PBCA NPs in vitro and in vivo and monitored their life and death assays. PBCA NPs were fabricated with different surfactants according to the mini-emulsion technique. Viabilities of HeLa and HEK293 cells after NP incubation were quantified by analysing cellular metabolic activity (MTT-test). We then repetitively injected i.v. rhodamine-labelled PBCA NP variations into rats and monitored the survival and morphology of retrogradely labelled neurons by in vivo confocal neuroimaging (ICON) for five weeks. To test for carrier-efficacy and safety, PBCA NPs loaded with Kyotorphin were injected in rats, and a hot plate test was used to quantify analgesic effects. In vitro, we found dose-dependent cell death which was, however, only detectable at very high doses and mainly seen in the cultures incubated with NPs fabricated with the tensids SDS and Tween. However, the in vivo experiments did not show any NP-induced neuronal death, even with particles which were toxic at high dose in vitro, i.e. NPs with Tween and SDS. The increased pain threshold at the hot plate test demonstrated that PBCA NPs are able to cross the BBB and thus comprise a useful tool for drug delivery into the central nervous system (CNS). Our findings showing that different nanoparticle formulations are non-toxic have important implications for the value of NP engineering approaches in medicine.

Optic nerve inflammation and demyelination in a rodent model of nonarteritic anterior ischemic optic neuropathy

PURPOSE

Optic nerve (ON) ischemia associated with nonarteric anterior ischemic optic neuropathy (NAION) results in axon and myelin damage. Myelin damage activates the intraneural Ras homolog A (RhoA), contributing to axonal regeneration failure. We hypothesized that increasing extrinsic macrophage activity after ON infarct would scavenge degenerate myelin and improve postischemic ON recovery. We used the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) to upregulate ON macrophage activity, and evaluated GM-CSF's effects after ON ischemia in the NAION rodent model (rAION).

METHODS

Following rAION induction, GM-CSF was administered via intraventricular injection. Retinal ganglion cell (RGC) stereologic analysis was performed 1 month postinduction. The retinae and optic nerve laminae of vehicle- and GM-CSF-treated animals were examined immunohistochemically and ultrastructurally using transmission electron microscopy (TEM). RhoA activity was analyzed using a rhotekin affinity immunoanalysis and densitometry. Isolated ONs were analyzed functionally ex vivo by compound action potential (CAP) analysis.

RESULTS

Rodent NAION produces ON postinfarct demyelination and myelin damage, functionally demonstrable by CAP analysis and ultrastructurally by TEM. Granulocyte-macrophage colony-stimulating factor increased intraneural inflammation, activating and recruiting endogenous microglia, with only a moderate amount of exogenous macrophage recruitment. Treatment with GM-CSF reduced postinfarct intraneural RhoA activity, but did not neuroprotect RGCs after rAION.

CONCLUSIONS

Sudden ON ischemia results in previously unrecognized axonal demyelination, which may have a clinically important role in NAION-related functional defects and recovery. Granulocyte-macrophage colony-stimulating factor is not neuroprotective when administered directly to the optic nerve following ON ischemia, and does not improve axonal regeneration. It dramatically increases ON-microglial activation and recruitment.

Transcorneal electrical stimulation alters morphology and survival of retinal ganglion cells after optic nerve damage

Traumatic optic nerve injury leads to retrograde death of retinal ganglion cells (RGCs), but transcorneal electrical stimulation (TES) can increase the cell survival rate. To understand the mechanisms and to further define the TES-induced effects we monitored in living animals RGC morphology and survival after optic nerve crush (ONC) in real time by using in vivo confocal neuroimaging (ICON) of the retina. ONC was performed in rats and ICON was performed before crush and on post-lesion days 3, 7 and 15 which allowed us to repeatedly record RGC number and size. TES or sham-stimulation were performed immediately after the crush and on post-injury day 11. Three days after ONC we detected a higher percentage of surviving RGCs in the TES group as compared to sham-treated controls. However, the difference was below significance level on day 7 and disappeared completely by day 15. The death rate was more variable amongst the TES-treated rats than in the control group. Morphological analysis revealed that average cell size changed significantly in the control group but not in stimulated animals and the morphological alterations of surviving neurons were smaller in TES-treated compared to control cells. In conclusion, TES delays post-traumatic cell death significantly. Moreover, we found "responder animals" which also benefited in the long-term from the treatment. Our in vivo cellular imaging results provide evidence that TES reduces ONC-associated neuronal swelling and shrinkage especially in RGCs which survived long-term. Further studies are now needed to determine the differences of responders vs. non-responders.

Transcorneal alternating current stimulation induces EEG "aftereffects" only in rats with an intact visual system but not after severe optic nerve damage

Noninvasive alternating current stimulation can induce vision restoration in patients with chronic optic nerve damage and results in electroencephalogram (EEG) aftereffects. To better understand the mechanisms of action, we studied such EEG "aftereffects" of transcorneal alternating current stimulation (tACS) at the chronic posttraumatic state in rats. EEG baseline was recorded from visual cortex under ketamine/xylazine narcosis of healthy rats and rats with chronic severe optic nerve crush. One week later, both groups were again anesthetized and stimulated transcorneally twice for 12 min each time. tACS-induced changes were compared with baseline EEG. Over the course of 65 min narcosis baseline EEG revealed a shift from a dominant delta power to theta. This shift was significantly delayed in lesioned animals compared with healthy controls. tACS applied during the late narcosis stage in normal rats led to significantly increased theta power with a parallel shift of the dominating peak to higher frequency which outlasted the stimulation period by 15 min (aftereffects). EEG in lesioned rats was not significantly changed. In rodents, tACS can induce neuroplasticity as shown by EEG aftereffects that outlast the stimulation period. But this requires a minimal level of brain activation because aftereffects are not seen when tACS is applied during deep anesthesia and not when applied to animals after severe optic nerve damage. We conclude that tACS is only effective to induce cortical plasticity when the the retina can be excited.

Vision restoration after brain and retina damage: the "residual vision activation theory"

Vision loss after retinal or cerebral visual injury (CVI) was long considered to be irreversible. However, there is considerable potential for vision restoration and recovery even in adulthood. Here, we propose the "residual vision activation theory" of how visual functions can be reactivated and restored. CVI is usually not complete, but some structures are typically spared by the damage. They include (i) areas of partial damage at the visual field border, (ii) "islands" of surviving tissue inside the blind field, (iii) extrastriate pathways unaffected by the damage, and (iv) downstream, higher-level neuronal networks. However, residual structures have a triple handicap to be fully functional: (i) fewer neurons, (ii) lack of sufficient attentional resources because of the dominant intact hemisphere caused by excitation/inhibition dysbalance, and (iii) disturbance in their temporal processing. Because of this resulting activation loss, residual structures are unable to contribute much to everyday vision, and their "non-use" further impairs synaptic strength. However, residual structures can be reactivated by engaging them in repetitive stimulation by different means: (i) visual experience, (ii) visual training, or (iii) noninvasive electrical brain current stimulation. These methods lead to strengthening of synaptic transmission and synchronization of partially damaged structures (within-systems plasticity) and downstream neuronal networks (network plasticity). Just as in normal perceptual learning, synaptic plasticity can improve vision and lead to vision restoration. This can be induced at any time after the lesion, at all ages and in all types of visual field impairments after retinal or brain damage (stroke, neurotrauma, glaucoma, amblyopia, age-related macular degeneration). If and to what extent vision restoration can be achieved is a function of the amount of residual tissue and its activation state. However, sustained improvements require repetitive stimulation which, depending on the method, may take days (noninvasive brain stimulation) or months (behavioral training). By becoming again engaged in everyday vision, (re)activation of areas of residual vision outlasts the stimulation period, thus contributing to lasting vision restoration and improvements in quality of life.

Two faces of calcium activation after optic nerve trauma: life or death of retinal ganglion cells in vivo depends on calcium dynamics

Calcium elevations after neurotrauma are not only implicated in cell death but may contribute to adaptive plasticity. We now wished to resolve this contradiction by following calcium dynamics after optic nerve crush in vivo. Adult rats received no injury (n = 5), unilateral mild (n = 10) or moderate optic nerve crush (n = 10) (ONC), or axotomy (n = 5). Before surgery, retinal ganglion cells (RGCs) were retrogradely labelled with Oregon Green BAPTA-dextran, a fluorescent calcium marker. Calcium-related fluorescence intensity (FI) was repeatedly measured in individual RGCs in vivo using the in vivo confocal neuroimaging (ICON) method. Four different RGC types were found. Normal RGCs without FI change were found in sham rats and also in both ONC groups. RGCs with mild damage were seen only after mild ONC, showing an initial calcium depression of 26% at day 4 followed by a 169% increase 15 days after ONC. RGCs with moderate damage were found only after moderate ONC and showed calcium hypoactivation followed by a slower return toward baseline and a delayed calcium increase of 72% above baseline. Sixty to sixty-five per cent of the RGCs in both ONC groups and all RGCs in the axotomy group died within 6 days following a fast and massive calcium increase of 316% with a concomitant 156% soma size increase. In conclusion rapid calcium elevation leads to cell death, while an initial calcium depression followed by a delayed and moderate calcium hyperactivation is associated with cell survival. We propose that immediate, massive calcium activation is maladaptive whereas delayed and moderate hyperactivation of surviving cells is adaptive. Implications for pharmacotherapy are discussed.

A standardized method to create optic nerve crush: Yasargil aneurysm clip

It is often difficult to compare results obtained by different investigators on nerve compression injuries, owing to differences in method of pressure application and noncomparable pressure levels. In the present study, we described a new method to crush the optic nerve by using a specially designed and commercially available device. We think that standardization of the compression methods is necessary to compare interlaboratory results.

Visual performance in monosodium glutamate-treated rats

The purpose of this study was to examine the effect of monosodium glutamate on the visual performance in rats. The Wistar strain of neonatal rats were injected subcutaneously with a solution of the glutamate at doses of 1 or 2 or 4 mg/gm body weight on days 2, 4, 6, 8 and 10 postnatally. Control rats received an injection of physiological saline. At 1, 2 and 3 months of age, the rats were tested for visual performance (brightness discrimination, pattern discrimination and visual acuity). As a result, the 4 mg/gm glutamate treatment was observed to impair brightness discrimination performance at 1 month of age as compared to the control animals. This impairment was also observed in animals at 2 and 3 months as compared, in addition, to the values in other doses of glutamate treatment. Pattern discrimination performance in every group of animals was at the same level at 1 month of age. However, at 2 months of age, the performance in the 2- and 4 mg/gm glutamate-treated groups was lower than those in the control group. This comparison was more pronounced at 3 months of age. Visual acuity performance results were quite the same as the pattern discrimination performance at all ages of animals. In conclusion, glutamate treatment was shown to cause dose-dependent deficit in visual performance and this may reflect impairment of visual organs and brain function.

R-esp1, a rat homologue of drosophila groucho, is differentially expressed after optic nerve crush and mediates NGF-induced survival of PC12 cells

The differential display reverse transcription polymerase chain reaction method was used to detect alterations in gene expression in the superior colliculus after optic nerve crush in adult rats. One of the most prominent changes observed was the selective induction of R-esp1, a homologue of the Drosophila enhancer of split locus (Groucho). Therefore, we studied the influence of R-esp1 on nerve growth factor (NGF)-induced cell survival of PC12 cells. Overexpression of R-esp1 promotes cell survival even in the absence of NGF and, conversely, it is reduced by antisense-mediated inhibition of R-esp1 expression. In conclusion, we propose a novel model in which R-esp1 protein mediates the NGF-signaling pathway.

Growth factors and gangliosides as neuroprotective agents in excitotoxicity and ischemia

1. At least two different groups of molecules can be considered neurotrophic factors because they exert a variety of effects upon neural cells. The first consists of the numerous families of polypeptide growth factors known to take part in almost all stages of neural cell growth and functioning, including development, differentiation, survival and pathology. The second group also is characterized by extensive complexity of multiple forms, and consists of the sialic acid-containing glycosphingolipids or gangliosides. These molecules also take part in the transfer of information from the extracellular milieu to the cell interior, and, similarly to growth factors, are participants in such aspects as development, differentiation and functioning. 2. In this short overview, we consider the existing data on the neuroprotective effects of growth factors [e.g., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and brain-derived neurotrophic factor] and one species of ganglioside (GM1) against retinal ischemia in vivo and cerebral excitotoxicity in vitro. 3. We used three different experimental models to investigate their relevance to ischemic and excitotoxic conditions in the retina and have shown that: (a) both bFGF and EGF show highly effective neuroprotection for rat retinal neurons exposed to toxic levels of glutamate or its nonphysiological agonist kainate in vitro (b) retinal glial cells suffer morphological perturbations after glutamate or kainate treatment, and this effect depends on neuron-glial interactions; (c) these glial changes can also be corrected by posttreatment with either bFGF or EGF in vitro; (d) with the use of an in vivo animal model involving anterior chamber pressure-induced ischemia in adult rats, either pretreatment by intraperitoneal injection of GM1 or posttreatment by intraocular injection of the same ganglioside significantly reduces histological damage to inner nuclear regions. 4. Hence both groups of trophic molecules show interesting features for retinal ischemic treatment.

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.

Intravitreal injection of ganglioside GM1 after ischemia reduces retinal damage in rats

BACKGROUND AND PURPOSE

Gangliosides are normal components of cell membranes and contribute to structural rigidity and membrane function. They have been shown to protect against various insults in the brain. We have shown previously that GM1 administered intraperitoneally before the induction of retinal ischemia provides a protective effect. This study evaluates the protective effect of GM1 administered intravitreally after ischemia on retinal lesions.

METHODS

We induced retinal ischemia unilaterally in Long-Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (20 microL x 10(-5) mol/L) or saline (20 microL) was injected into the vitreous 15 minutes after ischemia, and the postischemic survival time was either 8 or 15 days. The degree of retinal damage was assessed by histopathological study.

RESULTS

Retinal ischemia led to reductions in thickness and cell number, principally in the inner retinal layers (39% to 80%) and to a lesser extent in the outer retinal layers (26% to 45%). Postischemic treatment with intravitreally injected GM1 conferred significant protection against retinal ischemic damage after both 8 and 15 days of survival time. After 8 days of reperfusion, the ischemia-induced loss in overall retinal thickness was reduced by 15% and those of the inner nuclear and plexiform layers by 44% and 17%, respectively. Ischemic-induced ganglion cell and inner nuclear cell density losses were reduced by 37% and 27%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day saline-injected group.

CONCLUSIONS

GM1 protects the rat retina from pressure-induced ischemic injury when given intravitreally after the insult. The protection provided by GM1 after initiation of retinal damage could be of therapeutic interest.

MK-801 reduces retinal ganglion cell survival but improves visual performance after controlled optic nerve crush

Excitotoxicity is implicated in secondary cell death after ischemic or traumatic brain injury. We therefore evaluated the role of excitotoxicity mediated by the NMDA glutamate receptor subtype on retinal ganglion cell (RGC) survival and visual performance after optic nerve injury in adult rats. To monitor visual deficits after mild optic nerve crush, rats were trained in a two-choice pattern discrimination task. Immediately after the crush and on postoperative day 1, MK-801 (1 nmol), a noncompetitive open channel blocker of the NMDA-receptor, was injected intraocularly. Within the first few days after crush, all rats showed a loss of their discrimination ability that was followed by a significant recovery within a 3-week testing period. Although animals treated with MK-801 had a significantly smaller initial deficit compared with PBS-injected controls, anatomic investigations using retrograde HRP tracing revealed a significant retrograde loss of RGC in lesioned rats that was significantly exacerbated by MK-801. These results confirm our earlier studies suggesting that neuronal damage does not uniformly match behavioral defects in CNS injury paradigms and that near-normal visual performance occurs in rats with only about 10% of RGC being connected to their target. The observation that after traumatic injury MK-801 is neuroprotective functionally while being neurotoxic anatomically is a structural-functional paradox that needs to be explored further.

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.

Cytoskeletal derangements following central nervous system injury: modulation by neurotrophic gene transfection

This paper reviews important new evidence indicating that traumatic brain injury can produce more widespread derangements to the neuronal cytoskeleton than previously recognized. Although cytoskeletal derangements in axons have long been documented, recent data suggest that traumatic brain injury can produce structural derangements to dendrites and cell bodies as well. Many of these investigations have employed in vivo models to provide important insights into mechanisms possibly mediating the acute loss of cytoskeletal proteins, including disturbances in calcium homeostasis and activation of calcium-dependent proteolytic enzymes. However, we have little understanding of processes mediating the recovery of cytoskeletal proteins following injury. This paper provides recent evidence from in vitro models of central nervous system injury that neurotrophic proteins can enhance the recovery of the neuronal cytoskeleton. Neurotrophin-based therapy could employ either administration of exogenous neurotrophic proteins and/or transfection of cDNA for appropriate neurotrophins.

A behavioral model of excitotoxicity: retinal degeneration, loss of vision, and subsequent recovery after intraocular NMDA administration in adult rats

To establish a new behavioral animal model of excitotoxicity, we injected adult rats intraocularly with a single dose of 2, 20, or 100 nmol of N-methyl-D-aspartate (NMDA). We quantified visual impairment by plotting the size of the visual field in which the rats successfully oriented towards a small, moving target. In comparison to the saline-injected (contralateral) control side, the side injected with 2 nmol of NMDA was not significantly impaired. When injected with higher doses, the rats were nearly blind immediately after surgery, with only about 20% (20 nmol NMDA) or 10% (100 nmol NMDA) of residual vision. Within about 3 weeks, however, visual performance returned to near-normal levels. Simultaneous intraocular administration of a non-competitive NMDA-antagonist, MK-801 (1 nmol), resulted in complete behavioral protection. NMDA administration led to a dose-dependent loss of cells within the ganglion cell layer, as assessed in whole-mounted retinae which were retrogradely labelled with horseradish peroxidase (HRP). Whereas 2 nmol of NMDA led to the loss of about 30% of retinal ganglion cells (RGCs), at higher NMDA doses only 13% of the RGCs survived. After the injection of 20 nmol of NMDA, large-diameter RGCs (> 22 microns) survived the lesion to a greater extent than small diameter cells (8-21 microns); at 100 nmol cells of all diameters were equally affected. The number of Nissl-stained cells with small diameters (< 11 microns), presumed to be displaced amacrine cells, was also affected by NMDA, although to a lesser degree. Analysis of behavioral performance (vision score) and the number of cells in the retina revealed a correlation of r = 0.76 between visual performance and the number of HRP-filled RGCs immediately after surgery. Lower correlations were found between visual performance and cells stained with Nissl of diameters smaller than 11 microns (presumed RGCs without retinofugal connections; r = 0.55 and r = 0.58, respectively). Because of the spontaneous recovery of vision, all correlations declined to values near 0 after 3 weeks. Thus, despite a dramatic loss of RGCs following NMDA administration, visual deficits recover significantly in adult rats within 2-3 weeks.

Topical GM1 ganglioside to promote crushed rat sciatic nerve regeneration

The effects of topical GM1 ganglioside on crushed rat sciatic nerve regeneration were studied in this presentation. Thirty-four rats, with 68 bilateral sciatic nerves, were divided into seven groups: one group of four rats for measurement of normal motor nerve conduction velocity (MNCV), three as controls, and another three in the GM1-treated groups. Sciatic nerves were exposed and crushed at a site 6 mm distal to the sciatic notch by the standard technique. In this manner, 3 mm wide crush injuries were created. Then 2.1 microliters of normal saline was injected into the crush site in the control groups and an equal volume of GM1 solution (containing 10 micrograms GM1) was injected into the GM1-treated groups. Electrophysiological, histological, and morphometric evaluations were carried out at 12, 28, and 56 days. A significantly higher muscle action potential (MAP) rate was found in the GM1-treated group (70%) vs. the controls (none) at 12 days (P < 0.005), and increased MNCV was found in the GM1-treated groups at both 28 and 56 days, especially at 56 days, when it was 39.59 +/- 9.23 m/sec vs. 31.42 +/- 4.07 m/sec in controls (P < 0.05). Morphometrically, there were more regenerated myelinated fibers (RMFs) at 12 days, and larger diameter of RMFs were observed at 12, 28, and 56 days in the GM1-treated groups.

Neurofilament 68 and neurofilament 200 protein levels decrease after traumatic brain injury

We have examined the effect of lateral cortical impact injury on the levels of axonal cytoskeletal proteins in adult rats. Traumatic brain injury (TBI) causes a significant decrease in the protein levels of two prominent neurofilament (NF) proteins, NF68 and NF200. We employed quantitative immunoreactivity measurements on Western blots to examine NF68 and NF200 levels in homogenates of hippocampal and cortical tissue taken at several intervals postinjury. Sham injury had no effect on NF protein levels. However, injury was associated with a significant loss of NF68, restricted to the cortex ipsilateral to the injury site. NF68 loss was detectable as early as 3 h and lasted at least 2 weeks postinjury. Similarly, TBI induced a decrease in NF200 protein, although losses were observed both ipsilateral and contralateral to the injury site. No loss of NF68 or NF200 protein was detected in hippocampal samples obtained from the same injured animals. An increase in the presence of lower molecular weight (MW) NF68 immunopositive bands was associated with the decrease of NF68 in the ipsilateral cortex. This NF68 antigenicity pattern suggests the production of NF68 breakdown products caused by the pathologic activation of neuronal proteases, such as calpain. Putative NF68 breakdown products increase significantly until 1 day postinjury, suggesting that NF degradation may be ongoing until that time and indicating that a potential therapeutic window may exist within the first 24 h postinjury. In summary, these data identify specific biochemical alterations of the neuronal cytoskeleton following TBI and lay a foundation for further investigation of postinjury cytoskeletal changes in neuronal processes.

Increased anticholinergic sensitivity following closed skull impact and controlled cortical impact traumatic brain injury in the rat

Evidence suggests that prolonged memory deficits in several neurodegenerative diseases are attributable to deficits in central cholinergic neurotransmission. In traumatic brain injury (TBI), such cholinergic deficits also may contribute to prolonged memory disturbances. This study determined whether moderate magnitudes of TBI produced by controlled cortical impact and mild magnitudes of experimental TBI produced by a new closed head impact technique in rats would produce an enhanced vulnerability to the memory disruptive effects of scopolamine, a muscarinic cholinergic receptor antagonist. Water maze performance was used to determine changes in cholinergic hippocampal function following TBI. In the first experiment, rats received a moderate level of TBI by means of a controlled cortical impact. A Morris water maze task assessed spatial memory function on days 30-34 postinjury. During the 5 day assessment period, statistical analyses showed a group main effect for swim latency. Subsequent post hoc analyses indicated that injured rats had significantly longer latencies on days 30 and 31 (p < 0.05, injury vs sham controls). By days 32-35, injured rats showed no statistically significant deficits in spatial memory performance. On day 35, scopolamine (1 mg/kg, IP) was injected into injured rats and sham-injured rats 15 min prior to being retested in the maze. Results showed that although the scopolamine had no effects on the performance of the sham-injured rats, the same dose significantly (p < 0.05) increased the latency to find the hidden platform in the injured group. In the second experiment, rats received a mild concussive closed head impact. Water maze performance was assessed on days 8-12 postinjury. No significant water maze performance deficits were observed. On day 13, injured and uninjured rats were pharmacologically challenged with scopolamine (1 mg/kg) and retested. Similar to the first experiment, injured rats manifested a significantly greater (p < 0.05) sensitivity to scopolamine than sham controls. The results from both experiments suggest that concussive and more severe levels of TBI can produce an enhanced vulnerability to disruption of cholinergically mediated memory function, even when memory function appears normal in the absence of secondary challenges. These data demonstrate that covert deficits can persist after the recovery of normal function. These deficits may be attributable to a decrease in the ability of cholinergic neurons to function properly. These data also provide important insights into features of receptor-coupled disturbances that could contribute to the maintenance of enduring cognitive deficits following TBI.

Traumatic optic neuropathy

Knowledge concerning the pathophysiologic mechanisms of traumatic optic neuropathy is limited. The optic nerve is a tract of the brain. Therefore, the cellular and biochemical pathophysiology of brain and spinal cord trauma and ischemia provide insight into mechanisms that may operate in traumatic optic neuropathy. The dosage of methylprednisolone (30 mg/kg/6 hours) which was successful in the National Acute Spinal Cord Injury Study 2 (NASCIS 2) evolved from the unique pharmacology of corticosteroids as antioxidants. The management of traumatic optic neuropathy rests on an accurate diagnosis which begins with a comprehensive clinical assessment and appropriate neuroimaging. The results of medical and surgical strategies for treating this injury have not been demonstrated to be better than those achieved without treatment. The spinal cord is a mixed grey and white matter tract of the brain in contrast to the optic nerve which is a pure white matter tract. The treatment success seen with methylprednisolone in the NASCIS 2 study may not generalize to the treatment of traumatic optic neuropathy. Conversely, if the treatment does generalize to the optic nerve, NASCIS 2 data suggests that treatment must be started within eight hours of injury, making traumatic optic neuropathy one of the true ophthalmic emergencies. Given the uncertainties in the treatment, ophthalmologists involved in the management of traumatic optic neuropathy are encouraged to participate in the collaborative study of traumatic optic neuropathy.

Recovery of brightness discrimination in adult rats despite progressive loss of retrogradely labelled retinal ganglion cells after controlled optic nerve crush

Restoration of brightness discrimination was studied in adult rats after controlled crush of the optic nerve in order to further characterize a recently introduced experimental brain injury model. Mild, moderate or severe crush of the optic nerve produced partial or complete loss of the ability to perform a brightness discrimination task. Two to three weeks following mild injury we observed nearly complete spontaneous behavioural recovery whereas recovery was more limited after moderate and totally absent after severe crush. Horseradish peroxidase (HRP) injected into the superior colliculus was transported retrogradely across the lesion site and accumulated in retinal ganglion cells (RGCs). Two days following mild, moderate or severe crush, 28, 23 and 8% respectively of RGCs were found to be labelled with HRP, indicating that they are still connected with their target and are therefore presumably intact. RGC loss affected all areas of the retina homogeneously. At postoperative day 14, the number of morphologically 'intact' RGCs declined even further to 11% in the mild injury group, despite our observation of recovery of vision to near-normal levels. The mechanism whereby such impressive neuronal plasticity is achieved despite the rather small number of intact RGCs is still unknown. However, further studies of the crush model using additional behavioural, morphological and electrophysiological techniques may allow us to determine more clearly the biological basis of recovery of function after central nervous system injury.

Kinetics and organ distribution of [14C]-sialic acid-GM3 and [3H]-sphingosine-GM1 after intravenous injection in rats

Serum kinetics and organ distribution of [14C]-sialic acid-GM3 and [3H]-sphingosine-GM1, administered as an intravenous bolus, were analysed in Wistar rats. [3H]-GM1 and [14C]-GM3 had serum half-lives of 1.4 hours and 1.8 hours, respectively. Three hours after injection 75% of the GM1- and 38% of the GM3-associated label were present in the liver. Smaller yet significant amounts of label were present in the central nervous system, kidneys and lung. In vitro studies showed that [14C]-GM3 and [3H]-GM1 incubated with serum were predominantly bound to the High Density Lipoprotein and the Low Density Lipoprotein fractions. These results suggest a rapid serum clearance of exogenous gangliosides by the liver in rats.