Targeting hyperphosphorylated tau with sodium selenate suppresses seizures in rodent models.

Tau hyperphosphorylation has been implicated in the pathogenesis of a variety of forms of human epilepsy. Here we investigated whether treatment with sodium selenate, a drug which reduces pathological hyperphosphorylated tau by enhancement of PP2A activity, would inhibit seizures in rodent models. In vitro, sodium selenate reduced tau phosphorylation in human neuroblastoma cells and reversed the increase in tau phosphorylation induced by the PP2A inhibitor, okadaic acid. Sodium selenate treatment was then tested against three different rodent seizure models. Firstly the propensity of 6-Hz electrical corneal stimulation to induce seizures in adult mice was assessed following acute treatment with different doses of sodium selenate. Secondly, the number of seizures induced by pentylenetetrazole (PTZ) was quantified in rats following chronic sodium selenate treatment via drinking water. Finally, amygdala kindled rats were chronically treated with sodium selenate in drinking water and the length and the severity of the seizures evoked by stimulation of the amygdala recorded. The results demonstrated a dose-dependent protection of sodium selenate against 6-Hz stimulation induced seizures, and significant reduction in the total number of seizures following PTZ injection. Amygdala kindled rats chronically treated with sodium selenate had significantly shorter seizure duration compared controls, with more pronounced effects observed as the duration of treatment increased. The results of this study indicate that targeting hyperphosphorylated tau by treatment with sodium selenate has anti-seizure effects in a broad range of rodent models, and may represent a novel approach to treatment of patients with epilepsy.

Neuroprotective properties of the non-peptidyl radical scavenger IAC in rats following transient focal cerebral ischemia.

Experimental evidence suggests that reactive free radicals are generated during brain ischemia. We investigated the effect of a novel brain penetrant, low molecular weight, non-peptidyl carbon, oxygen- and nitrogen-centered radical scavenger, IAC, on infarct volume and sensory-motor performance in a rat transient middle cerebral artery occlusion model (tMCAO). Rats received 90 min tMCAO and treated with i.p. or i.v. injections of vehicle or IAC following tMCAO. Sensory-motor performance was evaluated by neuroscore tests (NS). Cerebral infarct volume was evaluated at 72 h after tMCAO. Rats treated with IAC i.p. (1 or 6 h after the onset of tMCAO) or i.v. (1 h after the onset of tMCAO) showed significant improvement in NS during the 3 or 21 day follow-up period when compared to vehicle treated rats. Cerebral infarct volumes were significantly decreased compared to vehicle in rats receiving IAC i.p. 1 h or 6 h after occlusion, approximately 30.5% decrease compared to vehicle, or i.v. 1 h after the onset of tMCAO, 48.6% decrease compared to vehicle. These results demonstrate that IAC has neuroprotective properties with a wide therapeutic window following tMCAO in rats. IAC could therefore be a candidate for the treatment of stroke.

Tissue sparing and functional recovery following experimental traumatic brain injury is provided by treatment with an anti-myelin-associated glycoprotein antibody.

Axonal injury is a hallmark of traumatic brain injury (TBI) and is associated with a poor clinical outcome. Following central nervous system injury, axons regenerate poorly, in part due to the presence of molecules associated with myelin that inhibit axonal outgrowth, including myelin-associated glycoprotein (MAG). The involvement of MAG in neurobehavioral deficits and tissue loss following experimental TBI remains unexplored and was evaluated in the current study using an MAG-specific monoclonal antibody (mAb). Anesthetized rats (n=102) were subjected to either lateral fluid percussion brain injury (n=59) or sham injury (n=43). In surviving animals, beginning at 1 h post-injury, 8.64 microg anti-MAG mAb (n=33 injured, n=21 sham) or control IgG (n=26 injured, n=22 sham) was infused intracerebroventricularly for 72 h. One group of these rats (n=14 sham, n=11 injured) was killed at 72 h post-injury for verification of drug diffusion and MAG immunohistochemistry. All other animals were evaluated up to 8 weeks post-injury using tests for neurologic motor, sensory and cognitive function. Hemispheric tissue loss was also evaluated at 8 weeks post-injury. At 72 h post-injury, increased immunoreactivity for MAG was seen in the ipsilateral cortex, thalamus and hippocampus of brain-injured animals, and anti-MAG mAb was detectable in the hippocampus, fimbria and ventricles. Brain-injured animals receiving anti-MAG mAb showed significantly improved recovery of sensorimotor function at 6 and 8 weeks (P<0.01) post-injury when compared with brain-injured IgG-treated animals. Additionally, at 8 weeks post-injury, the anti-MAG mAb-treated brain-injured animals demonstrated significantly improved cognitive function and reduced hemispheric tissue loss (P<0.05) when compared with their brain-injured controls. These results indicate that MAG may contribute to the pathophysiology of experimental TBI and treatment strategies that target MAG may be suitable for further evaluation.

Time-dependent increase in Nogo-A expression after focal cerebral ischemia in marmoset monkeys.

Nogo-A is a myelin-associated protein that has been shown to inhibit axonal sprouting after lesions to the CNS. Several studies have demonstrated that blocking the activity or expression of this inhibitor can induce structural and functional recovery after CNS lesions. However, there are limited and contradictory data on the expression of Nogo-A after CNS lesions. In the present study, marmoset monkeys received permanent occlusion of the middle cerebral artery (MCAo). Two, 3, or 4 months after the onset of injury brain sections were stained for Nogo-A protein. Two sham operated marmosets were included as a control. Nogo-A protein expression was quantified in white matter and grey matter in the areas adjacent to the lesion (or the equivalent areas in the intact side). At 2 months after injury, but not at 3 or 4 months, there was a significant increase in the number of oligodendrocytes that were Nogo-A immunopositive. This increase was observed in white matter structures that were adjacent to the lesion (e.g. corona radiate (CR)); but not in: white matter structures distal to the lesion (e.g. corpus callosum (CC)); cortical regions adjacent to the lesion; contralateral regions or in sham operated marmosets. These data suggest that Nogo-A levels are significantly increased within oligodendrocytes in areas adjacent to the lesion up to 2 months following cerebral ischaemia. Future studies will determine whether this offers the opportunity to promote plasticity by targeting Nogo-A weeks or months following stroke.

Wavelet-based cluster analysis: data-driven grouping of voxel time courses with application to perfusion-weighted and pharmacological MRI of the rat brain.

MRI time series experiments produce a wealth of information contained in two or three spatial dimensions that evolve over time. Such experiments can, for example, localize brain response to pharmacological stimuli, but frequently the spatiotemporal characteristics of the cerebral response are unknown a priori and variable, and thus difficult to evaluate using hypothesis-based methods alone. Here we used features in the temporal dimension to group voxels with similar time courses based on a nonparametric discrete wavelet transform (DWT) representation of each time course. Applying the DWT to each voxel decomposes its temporal information into coefficients associated with both time and scale. Discarding scales in the DWT that are associated with high-frequency oscillations (noise) provided a straight-forward data reduction step and decreased the computational burden. Optimization-based clustering was then applied to the remaining wavelet coefficients in order to produce a finite number of voxel clusters. This wavelet-based cluster analysis (WCA) was evaluated using two representative classes of MRI neuroimaging experiments. In perfusion-weighted MRI, following occlusion of the middle cerebral artery (MCAO), WCA differentiated healthy tissue and different regions within the ischemic hemisphere. Following an acute cocaine challenge, WCA localized subtle differences in the pharmacokinetic profile of the cerebral response. We conclude that WCA provides a robust method for blind analysis of time series image data.

Endogenous and exogenous melanocortin antagonists induce anti-allodynic effects in a model of rat neuropathic pain.

A number of studies suggest melanocortin (MC) system involvement in nociceptive modulation. Although the mechanism through which this occurs is still unknown, experimental evidence would suggest a primary role of MC4 receptors. To further investigate the implication of this MC receptor subtype in chronic pain, we have studied the effects of several MC antagonists on spinal nerve ligation-induced nociceptive behavior in rats. The intrathecal injection of synthetic antagonists with different selectivity to MC4 receptor and of an endogenous antagonist (Agouti related protein; AgRP) reduced mechanical allodynia in neuropathic rats, as measured by von Frey hair test. Treatments produced an anti-allodynic effect at the dose of 1.5 nmol (25-30% maximum possible effect, MPE, P<0.05). To further investigate the possible physiological role of AgRP in pain modulation we studied its expression in both sham and neuropathic rat spinal cord and dorsal root ganglia (DRG) by quantitative real time PCR and immunohistochemistry. AgRP was present in both spinal cord and DRG, and its expression, was unchanged in neuropathic animals. In conclusion MC4 receptor antagonists with different selectivity profile, induce anti-allodynic effects in one of the most relevant neuropathic pain model. In addition the expression of AgRP in spinal cord and DRG suggests an endogenous tonic inhibitory control on MC system activity. In pathological conditions this steady control could be insufficient to cope with an over activated MC system leading to increase in nociception. These data suggest that targeting MC4 with synthetic antagonists could restore the balance and hence reduce nociception.

A novel behavioural registration system LABORAS and the social interaction paradigm detect long-term functional deficits following middle cerebral artery occlusion in the rat.

Following stroke, patients suffer a wide range of disabilities including motor impairment, anxiety and depression. However, to date, characterisation of rodent stroke models has concentrated mainly on the investigation of motor deficits. The aim of the present studies was therefore to investigate home cage behaviour (as assessed by a recently developed automatic behavioural classification system, LABORAS) and social behaviour (as a measure of anxiety) in rats following transient middle cerebral artery occlusion (tMCAO). Rats subjected to tMCAO (90 min) showed deficits in general home cage behaviours including locomotion, rearing, grooming and drinking for up to 7 weeks post occlusion, as compared with sham operated controls. In addition, a significant decrease in the total duration of social interaction was also observed in occluded rats compared with shams. The data shows that in addition to motor deficits, animals display changes in home cage behaviour and decreased social behaviour which, in contrast to motor function, are prolonged over time. Transient MCAO in rats may therefore provide a pre-clinical model to investigate agents offering symptomatic relief for ischaemia-induced motor deficits and anxiety over time following injury.

The therapeutic potential of the cannabinoids in neuroprotection.

After thousands of years of interest the last few decades have seen a huge increase in our knowledge of the cannabinoids and their mode of action. Their potential as medical therapeutics has long been known. However, very real concerns over their safety and efficacy have lead to caution and suspicion when applying the legislature of modern medicine to these compounds. The ability of this diverse family of compounds to modulate neurotransmission and act as anti-inflammatory and antioxidative agents has prompted researchers to investigate their potential as neuroprotective agents. Indeed, various cannabinoids rescue dying neurones in experimental forms of acute neuronal injury, such as cerebral ischaemia and traumatic brain injury. Cannabinoids also provide symptomatic relief in experimental models of chronic neurodegenerative diseases, such as multiple sclerosis and Huntington's disease. This preclinical evidence has provided the impetus for the launch of a number of clinical trials in various conditions of neurodegeneration and neuronal injury using compounds derived from the cannabis plant. Our understanding of cannabinoid neurobiology, however, must improve if we are to effectively exploit this system and take advantage of the numerous characteristics that make this group of compounds potential neuroprotective agents.

Site-specific actions of interleukin-1 on excitotoxic cell death in the rat striatum.

The pro-inflammatory cytokine interleukin-1 (IL-1) contributes to and exacerbates many forms of neurodegeneration. When co-administered with the potent glutamatergic agonist S-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (S-AMPA) in the rat striatum, IL-1 induces marked and widespread cell death throughout the ipsilateral cortex. The mechanisms underlying this action of IL-1 are not known but may involve activation of polysynaptic neuronal pathways leading from the striatum to the cortex via other brain areas such as the hypothalamus. The aims of the present study were to identify specific sites of action of IL-1 in the rat striatum, in order to further understand these pathways. Ventral regions of the caudate-putamen and the lateral shell of the nucleus accumbens (NAcc) were particularly sensitive to the effects of IL-1 on excitotoxic damage. A high percentage of co-injections in these sites induced distant cortical damage, whereas injections in more dorsal areas of the caudate-putamen or core regions of the NAcc were less likely to result in cortical cell death. The 'positive' injection sites differ from the unresponsive areas in that they have extensive connections with the limbic system and it may be that IL-1 displays specific actions on limbic pathways that, in conjunction with AMPA/kainate receptor activation, contribute to the remote cell death in the cortex. These findings enhance our understanding of the actions of IL-1, and the mechanisms by which it participates in neurodegeneration through both local and long-range effects.