Investigation of Demyelination and Remyelination Processes of the Compressed Optic Chiasm: An Experimental Model.

AIM: To demonstrated demyelination and remyelination of the optic nerve histologically by electron microscopy in an experimental model similar to the compression of pituitary adenomas on the optic chiasm. MATERIAL AND METHODS: The rats were fixed to a stereotaxic device under deep anesthesia, and a balloon catheter was placed under the optic chiasm through a burr hole which was in front of the bregma in accordance with the brain atlas of rats. The animals were divided into five groups (n=8): control, mild compression demyelination, severe compression demyelination, mild compression remyelination, severe compression remyelination. The fine structures of the tissues obtained were evaluated using electron microscopy. RESULTS: We found a significant difference in the severity of degeneration when comparing group 1 with group 5 (p < 0.001); there was no degeneration in group 1 rats and severe degeneration in all of the group 5 rats. Oligodendrocytes were found in all rats in group 1 and none of the rats in no group 2. The nuclei were preserved in the group 1 rats but damaged in all of the group 5 rats. There were no lymphocytes or erythrocytes in group 1 and all positives in group 5. CONCLUSION: This technique, which induced degeneration without causing damage to the optic nerve with toxic or chemical agents, revealed Wallerian degeneration similar to tumoral compression. After compression relief, the optic nerve remyelination process can be better understood, particularly for sellar lesions. In our opinion, this model may guide future experiments to identify protocols to induce and accelerate remyelination.

Agmatine has beneficial effect on harmaline-induced essential tremor in rat.

Essential tremor (ET) is one of the most prevalent movement disorders and the most common cause of abnormal tremors. However, it cannot be treated efficiently with the currently available pharmacotherapy options. The pathophysiology of harmaline-induced tremor, most commonly used model of ET, involves various neurotransmitter systems including glutamate as well as ion channels. Agmatine, an endogenous neuromodulator, interacts with various glutamate receptor subtypes and ion channels, which have been associated with its' beneficial effects on several neurological disorders. The current study aims to assess the effect of agmatine on the harmaline model of ET. Two separate groups of male rats were injected either with saline or agmatine (40 mg/kg) 30 min prior to single intraperitoneal injection of harmaline (20 mg/kg). The percent duration, intensity and frequency of tremor and locomotor activity were evaluated by a custom-built tremor and locomotion analysis system. Pretreatment with agmatine reduced the percent tremor duration and intensity of tremor induced by harmaline, without affecting the tremor frequency. However, it did not affect the decreased spontaneous locomotor activity due to harmaline. This pattern of ameliorating effects of agmatine on harmaline-induced tremor provide the first evidence for being considered as a treatment option for ET.

Etanercept rescues cognitive deficits, depression-like symptoms, and spike-wave discharge incidence in WAG/Rij rat model of absence epilepsy.

Pro-inflammatory cytokines have been shown to be associated with the development of seizures in the WAG/Rij rat model of absence epilepsy. Importantly, WAG/Rij rats also exhibit cognitive deficits and depression-like behaviors. It is possible that pro-inflammatory cytokines mediate these comorbid conditions of absence epilepsy given their well-established effects on cognition and affective responses. The current study investigated the potential therapeutic effect of etanercept (tumor necrosis factor inhibitor) on cognitive impairment, depression-like behavior, and spike-wave discharges (SWDs) typically observed in the WAG/Rij rats. Eight-month-old male WAG/Rij rats and Wistar controls were tested in Morris water maze (MWM), passive avoidance (PA), forced swimming, sucrose preference, and locomotor activity tests, and electroencephalogram (EEG) recordings were taken from a separate group of WAG/Rij rats after 8 weeks of etanercept or vehicle treatment. Consistent with earlier work, WAG/Rij rats exhibited cognitive deficits and depression-like behavior. From these, the cognitive deficits and despair-like behavior were rescued by etanercept administration, which also reduced the frequency of SWDs without affecting their duration. Our results support the hypothesis that pro-inflammatory cytokines mediate the absence seizures and comorbid symptoms of absence epilepsy.

Timing behavior in genetic murine models of neurological and psychiatric diseases.

How timing behavior is altered in different neurodevelopmental and neurodegenerative disorders is a contemporary research question. Genetic murine models (GMM) that offer high construct validity also serve as useful tools to investigate this question. But the literature on timing behavior of different GMMs largely remains to be consolidated. The current paper addresses this gap by reviewing studies that have been conducted with GMMs of neurodevelopmental (e.g. ADHD, schizophrenia, autism spectrum disorder), neurodegenerative disorders (e.g., Alzheimer's disease, Huntington's disease) as well as circadian and other mutant lines. The review focuses on those studies that specifically utilized the peak interval procedure to improve the comparability of findings both within and between different disease models. The reviewed studies revealed timing deficits that are characteristic of different disorders. Specifically, Huntington's disease models had weaker temporal control over the termination of their anticipatory responses, Alzheimer's disease models had earlier timed responses, schizophrenia models had weaker temporal control, circadian mutants had shifted timed responses consistent with shifts in the circadian periods. The differences in timing behavior were less consistent for other conditions such as attention deficit and hyperactivity disorder and mutations related to intellectual disability. We discuss the implications of these findings for the neural basis of an internal stopwatch. Finally, we make methodological recommendations for future research for improving the comparability of the timing behavior across different murine models.

Etanercept improves aging-induced cognitive deficits by reducing inflammation and vascular dysfunction in rats.

Normal aging may lead to cognitive deficits, which is associated with endothelial dysfunction and neuroinflammation. Dysregulation of TNFα expression contributes to vascular aging and dementia. In this study, we investigated the effects of etanercept, which is a TNFα inhibitor, on cognitive and endothelial function in aged rats. Male Wistar albino rats were divided into 3 groups: Young (4 month), aged (24 month) aged+ETA (24 month+etanercept). Etanercept (0.8 mg/kg/weekly) was given to the aged+ETA group subcutaneously for 8 weeks. Then passive avoidance test (PAT) and the Morris water maze test (MWMT) were used to evaluate cognitive functions of rats. After the behavioral tests, the rats were subjected to systolic blood pressure (SBP) measurement, and then endothelial function of thoracic aorta was evaluated by isolated organ bath system. Thoracic eNOS expression, hippocampal BDNF expression and serum and hippocampal TNF levels were also measured. In aged rats, it was shown that cognitive performances in MWMT and PAT were abolished whereas SBP unchanged. Furthermore, aging resulted in endothelial dysfunction, decreased expressions of thoracic eNOS and hippocampal BDNF, and increased level of TNF in serum and hippocampus. In contrast, ETA improved age-related cognitive deficits and endothelial dysfunction. In addition, ETA reversed changes in protein expression in aged rats. The results of this study indicate that ETA prevents cognitive deficits, endothelial dysfunction, peripheral and neuro-inflammation and decreament of neurotrophin expression in aged rats. These findings suggest that ETA may be beneficial with neuroprotective and vasculoprotective effects in elderly patients.

Aging impairs perceptual decision-making in mice: integrating computational and neurobiological approaches.

Decision-making is one of the cognitive domains which has been under-investigated in animal models of cognitive aging along with its neurobiological correlates. This study investigated the latent variables of the decision process using the hierarchical drift-diffusion model (HDDM). Neurobiological correlates of these processes were examined via immunohistochemistry. Young (n = 11, 4 months old), adult (n = 10, 10 months old), and old (n = 10, 18 months old) mice were tested in a perceptual decision-making task (i.e. two-alternative forced-choice; 2AFC). Observed data showed that there was an age-dependent decrease in the accuracy rate of old mice while response times were comparable between age groups. HDDM results revealed that age-dependent accuracy difference was a result of a decrease in the quality of evidence integration during decision-making. Significant positive correlations observed between evidence integration rate and the number of tyrosine hydroxylase positive (TH+) neurons in the ventral tegmental area (VTA) and axon terminals in dorsomedial striatum (DMS) suggest that decrease in the quality of evidence integration in aging is related to decreased function of mesocortical and nigrostriatal dopamine.

Interval timing deficits and their neurobiological correlates in aging mice.

Age-related neurobiological and cognitive alterations suggest that interval timing (as a related function) is also altered in aging, which can, in turn, disrupt timing-dependent functions. We investigated alterations in interval timing with aging and accompanying neurobiological changes. We tested 4-6, 10-12, and 18-20 month-old mice on the dual peak interval procedure. Results revealed a specific deficit in the termination of timed responses (stop-times). The decision processes contributed more to timing variability (vs. clock/memory process) in the aged mice. We observed age-dependent reductions in the number of dopaminergic neurons in the VTA and SNc, cholinergic neurons in the medial septum/diagonal band (MS/DB) complex, and density of dopaminergic axon terminals in the DLS/DMS. Negative correlations were found between the number of dopaminergic neurons in the VTA and stop times, and the number of cholinergic neurons in MS/DB complex and the acquisition of stop times. Our results point at age-dependent changes in the decisional components of interval timing and the role of dopaminergic and cholinergic functions in these behavioral alterations.

The lower expression of parvalbumin in the primary somatosensory cortex of WAG/Rij rats may facilitate the occurrence of absence seizures.

Absence epilepsy (AE) is classified as a genetic generalized epilepsies. WAG/Rij strain of rats are regarded one of the most validated models of absence epilepsy. Studies point out the existence of hyperexcitable focus in somatosensory cortex of these rats, which has been attributed to the deficits in the GABAergic system. In the current study, we studied the changes of calcium binding proteins (CaBPs) in somatosensory cortex (S1) of the 2 and 8 month-old WAG/Rij rats and their age-matched Wistar Albino controls by investigating the expression levels of CaBPs (calbindin, calretinin and parvalbumin) in western blotting. Since WAG/Rij rats showed the low expression level of parvalbumin (PV) in western blots in comparison to Wistar Albino rats, we selectively investigated the number of PV positive neurons using the immunofluorescence staining method in order to confirm this decrement in the perioral region of somatosensory cortex (S1po). The most critical finding of this study was the age- independent reduction in the expression level of PV in the somatosensory cortex of epileptic rats as demonstrating western blotting. Nevertheless, no significant difference was found among numbers of PV + neuron in the S1po region by immunofluorescence staining concerning both of age and strain dependency. These results suggest that the disruption in the activity of the PV-expressing GABAergic interneurons might be involved in the generation of rather than the age-dependent increase in the SWDs in WAG/Rij rats.

TNF-alpha inhibition prevents cognitive decline and maintains hippocampal BDNF levels in the unpredictable chronic mild stress rat model of depression.

Previous findings have shown that patients with depression express higher levels of proinflammatory cytokines such as TNF-α and IL-6. We have recently found that Infliximab (a TNF-α inhibitor) decreased anhedonia and despair-like behavior in the rat unpredictable chronic mild stress (UCMS) model of depression suggesting that inflammation might play an important role in depression. An increasing number of studies suggest that inflammation is also associated with cognitive impairments. The current study aimed to investigate the effect of UCMS on the cognitive performance of rats and their hippocampal BDNF levels and the effect of chronic Infliximab (5mg/kg/weekly, i.p.) treatment on these measures. Rats were subjected to different types of stressors daily for a period of 56 days to induce depression-like state. The UCMS resulted in impairments in spatial and emotional memory acquisition and retention with no effect on the level of locomotor activity. These behavioral effects of UCMS were accompanied by reduction in the level of BDNF in the CA1 and CA3 regions of the hippocampus. Chronic Infliximab treatment prevented the UCMS-induced cognitive impairments as well as the reduction in the levels of hippocampal brain-derived neurotrophic factor (BDNF). These results suggest that Infliximab improves the spatial and emotional memory impairments induced by chronic stress in rats likely through its effects on hippocampal function by modulating inflammation.

Etanercept improves cognitive performance and increases eNOS and BDNF expression during experimental vascular dementia in streptozotocin-induced diabetes.

Diabetes mellitus (DM) is related to an increase in the incidence of vascular dementia. Inflammation is an important cause of endothelial dysfunction and cognitive deficits. The anti -tumor necrosis factor (TNF)-α fusion protein etanercept has been reported to exhibit memory-enhancing effects and endothelial protection. We tested the effect of etanercept on the cognitive endpoints and compared it with the cognitive dysfunction in streptozotocin (STZ )- induced DM rats by using the Morris water maze test (MWMT) and passive avoidance test (PAT). Systolic blood pressure (SBP), thoracic endothelial function, endothelial nitric oxide synthase (eNOS) expression, and hippocampal brain-derived neurotrophic factor (BDNF) expression were assessed. Thirty days after the induction of DM, rats exhibited severe learning and memory deficits associated with endothelial dysfunction and decreased expression of eNOS and BDNF. Chronic treatment with etanercept (0.8 mg/kg, s.c., every week for 30 days) improved cognitive performance, endothelial function, and expression of eNOS and BDNF in DM rats. Furthermore, the memory-improving effects of etanercept were independent of hyperglycemia. These data suggest that etanercept treatment prevents changes in endothelial function, eNOS expression, and hippocampal expression of BDNF and, consequently, vascular dementia in DM rats.

Comparative proteomic approach in rat model of absence epilepsy.

The aim of this study was to investigate cellular proteins in the pathogenesis of the genetic rat model of absence epilepsy. Protein spots were identified with peptide mass fingerprinting analysis using matrix-assisted laser desorption ionization time of flight mass spectrometry. Data were gathered from the frontoparietal cortex and thalamus of Wistar Albino Glaxo/Rij (WAG/Rij) and Wistar by using two-dimensional gel electrophoresis (2D-PAGE). Six proteins (Clathrin light chain-A protein, Transmembrane EMP24 Domain-Containing Protein, Stathmin-4, Myosin Light Chain4, Rheb, phosphoserine phosphatase) were found to be differentially expressed in the frontoparietal cortex of WAG/Rij and Wistar rats in both age groups. Another set of six proteins (Protein FAM89A and Oasl1, Gemin2, NuDEL1, Pur-beta, 3-alpha HSD) were found to be differentially expressed in the thalamus of WAG/Rij and Wistar rats. Findings from the frontoparietal cortex suggest the presence of altered serine metabolism and increased vesicular trafficking in the frontoparietal cortex of WAG/Rij rats compared with Wistar rats. These differences in the protein levels might reflect the crucial role of these proteins and related pathways in the generation of absence seizures. In the thalamic specimens, age-dependent changes in protein expression were remarkable, suggesting that this phenomenon may be a precursor or a consequence of absence seizures. Our findings further highlight the potential role of the mTOR signaling pathway in absence epilepsy.

The link between unpredictable chronic mild stress model for depression and vascular inflammation?

Inflammation has been suggested to be associated with stress-induced depression and cardiovascular dysfunction. Tumor necrosis factor alpha (TNF-α) is a major cytokine in the activation of neuroendocrine, immune, and behavioral responses. In this study, we investigated the effects of infliximab (a TNF-α inhibitor) on endothelium-dependent vascular reactivity, systemic blood pressure, and endothelial nitric oxide synthase (eNOS) immunoreactivity in the unpredictable chronic mild stress (UCMS) model of depression in rats. There was no significant change between all groups in the systemic blood pressure. In UCMS, endothelium-dependent relaxation of the smooth muscle in response to carbachol was significantly decreased with 50 % maximal response (E max) and pD2 values compared with the controls. Infliximab was able to reverse this UCMS effect. Relaxation in response to the nitric oxide (NO) donor sodium nitroprusside and papaverine and KCl-induced contractile responses was similar between groups. In UCMS, decreased expression of eNOS was detected. Moreover, there was no significant change in UCMS + infliximab group with respect to control rats. Our results suggest that tumor necrosis factor-alpha (TNF-α) could be a major mediator of vascular dysfunction associated with UCMS, leading to decreased expression of eNOS.

The effects of vagal nerve stimulation in focal cerebral ischemia and reperfusion model.

AIM: This study aimed to investigate the effects of VNS in transient middle cerebral artery occlusion and reperfusion (MCAO/R) rat model of ischemia based on behavioral, morphological, and molecular approaches. MATERIAL AND METHODS: Wistar albino rats were divided into 3 groups: ischemia-reperfusion (I/R), I/R+VNS, and sham (for I/R). Each group was further divided into two subgroups for the assessment of neurological deficits and infarct area, or biochemical parameters related to oxidative stress. RESULTS: The infarct area and neurological scores were significantly lower in I/R+VNS group compared with the I/R group. MDA levels were significantly higher in I/R group compared to control and I/R+VNS groups in the cortical and subcortical specimens. There were also betweengroup differences in terms of GSH levels. GSH levels were higher in sham group compared with and I/R and I/R+VNS groups in cortical specimens whereas these levels for lower in I/R group compared to control and I/R+VNS groups in the subcortical specimens. SOD activity was higher in control group compared to I/R and I/R+VNS groups both in the cortical and subcortical specimens. There was no difference between I/R and I/R+VNS groups in neither cortical nor subcortical specimens. CONCLUSION: The neuroprotective and antioxidant properties of VNS suggest its efficacy as a potential anti-ischemic treatment.

Effects of long-term etanercept treatment on anxiety- and depression-like neurobehaviors in rats.

Growing evidence indicates that there is a correlation between depression and inflammation. Administration of anti-tumor necrosis factor (TNF) agents for treatment of chronic inflammatory diseases, such as psoriasis, was associated with decreased depressive symptoms and increased quality of life in some clinical studies. The aim of the present study was to investigate the effects of chronic etanercept, a TNF-α inhibitor, on anxiety- and depression-like neurobehaviors in rats. Male rats were treated for 8 weeks with either saline or etanercept (0.8 mg/kg/week, subcutaneously). The anxiety levels of rats were evaluated using the elevated plus maze, a classical rodent model of anxiety and depression was measured using the force swimming test, a behavioral despair task. The anxiety-like neurobehaviors of the animals were found significantly decreased after the etanercept treatment. Etanercept significantly decreased immobility time in rat model of despair test, seemed to have an antidepressive effect in rats. Compared to saline treatment, long-term etanercept treatment had no effect on the total number and pattern of locomotor activities. Findings of the study supported the hypothesis that TNF-α has a role in the modulation of emotional processes and its inhibition may represent a novel strategy for the treatment of affective disorders.

The effect of etanercept on aortic nitric oxide-dependent vasorelaxation in an unpredictable chronic, mild stress model of depression in rats.

Stress has been recognized as a risk factor for cardiovascular disease and depression, but the correlation is not well understood. However, inflammation is known to have a crucial role in both cardiovascular disease and depression. Tumor necrosis factor alpha (TNF-α) is a major cytokine for the activation of neuroendocrine, immune and behavioral responses. Therefore, we aimed to explore the effects of etanercept, an anti-TNF-α fusion protein, on endothelium-dependent vascular reactivity, blood pressure and endothelial nitric oxide synthase (eNOS) immunoreactivity in a model of unpredictable chronic mild stress (UCMS). Male rats were exposed to UCMS for 8 weeks, and etanercept (0.8 mg/kg, weekly) was administered during UCMS induction. The systolic blood pressure was recorded by the tail cuff method, and the relaxant responses of the aorta induced by carbachol, sodium nitroprusside (SNP) and papaverine were evaluated in an isolated organ bath system. UCMS rats exhibited an impaired carbachol-induced relaxant response compared to control rats, but there were no significant differences in the SNP- and papaverine-induced relaxant responses between the control and stressed rats. Etanercept treatment improved the carbachol-induced endothelium dependent relaxations observed in rats that experienced UCMS. No significant change in the systemic blood pressure was observed, but decreased expression of eNOS was detected in the UCMS group. Moreover, there were no significant changes in the etanercept treatment group compared to the control rats. Our results suggest that TNF-α could be a mediator of vascular dysfunction associated with UCMS, which leads to decreased expression of eNOS.

Chronic administration of infliximab (TNF-α inhibitor) decreases depression and anxiety-like behaviour in rat model of chronic mild stress.

Pro-inflammatory cytokines have been proposed to be associated with the pathogenesis of depression. Consistent with this notion, several clinical observations have suggested the antidepressant efficacy of TNF-α inhibitors in patients with chronic inflammatory diseases. In this study, we evaluated the antidepressant and anxiolytic effects of chronic TNF-α inhibitor (infliximab, 5 mg/kg, i.p., weekly) administration in the chronic mild stress (CMS) model of depression. Rats were divided into three groups: saline-control (no stress), saline-CMS, and infliximab-CMS. Rats in the latter two groups were exposed to CMS for 8 weeks. Saline (former two groups) or infliximab was injected weekly during this period. After CMS, total locomotor activity, anxiety-like behaviour and depression-like behaviours were evaluated using automated locomotor activity cage, elevated plus maze (EPM), and sucrose preference (SPT) and forced swimming (FS) tests, respectively. As expected, the saline-CMS group exhibited higher depression-like behaviours in FS and SPT tests compared with the saline-control group. There were no differences between these two groups in terms of the anxiety-like behaviour or total locomotor activity. Infliximab reduced the depression-like behaviour of CMS rats compared with saline-CMS group, and anxiety-like behaviour of CMS rats compared with saline-CMS and saline-control groups. Our findings suggest that chronic and systemic TNF-α inhibition reduced depression and anxiety-like behaviour in the CMS model of depression in rats.

Age-dependent decline in learning and memory performances of WAG/Rij rat model of absence epilepsy.

Recent clinical studies revealed emotional and cognitive impairments associated with absence epilepsy. Preclinical research with genetic models of absence epilepsy however have primarily focused on dysfunctional emotional processes and paid relatively less attention to cognitive impairment. In order to bridge this gap, we investigated age-dependent changes in learning and memory performance, anxiety-like behavior, and locomotor activity of WAG/Rij rats (a valid model of generalized absence epilepsy) using passive avoidance, Morris water maze, elevated plus maze, and locomotor activity cage. We tested 5 month-old and 13 month-old WAG/Rij rats and compared their performance to age-matched Wistar rats. Results revealed a decline in emotional and spatial memory of WAG/Rij rats compared to age-matched Wistar rats only at 13 months of age. Importantly, there were no significant differences between WAG/Rij and Wistar rats in terms of anxiety-like behavior and locomotor activity at either age. Results pointed at age-dependent learning and memory deficits in the WAG/Rij rat model of absence epilepsy.

The effect of memantine in harmaline-induced tremor and neurodegeneration.

Essential tremor (ET) is one of the most common and most disabling movement disorders among adults. The drug treatment of ET remains unsatisfactory. Additional therapies are required for patients with inadequate response or intolerable side effects. The current study aims to investigate the anti-tremogenic and neuroprotective effects of memantine (NMDA receptor antagonist) on the harmaline model of transient action tremor. The effects of memantine were further compared with ethanol. Three separate groups of male Wistar rats were injected either with saline, ethanol (1.5 gr/kg), or memantine (5 mg/kg) 15 min prior to a single intraperitoneal injection of harmaline (20 mg/kg). Tremor and locomotion were evaluated by a custom-built tremor and locomotion analysis system. After 24 h of harmaline injection, cellular viability, and apoptosis were assessed using crystal violet staining, and caspase-3 immunostaining, respectively. Harmaline caused neuronal cell loss and caspase-3 mediated apoptosis in cerebellar granular and purkinje cells as well as the inferior olivary neurons. Despite a reduction in tremor intensity and duration with ethanol, this compound resulted in cell loss in cerebellum and olivary nucleus. Memantine exhibited neuroprotective efficacy on cerebellar and inferior olivary neurons albeit weaker anti-tremor effect compared to ethanol. In conclusion, anti-tremogenic and neuroprotective effects do not necessarily overlap. Memantine is a potential treatment for ET particularly given its neuroprotective efficacy.

Perirhinal cortical kindling in rats with genetic absence epilepsy.

Two genetic models of absence epilepsy, GAERS and WAG/Rij rat strains, are resistant to progression of partial seizures induced by amygdaloid or hippocampal kindling. Perirhinal cortex is one of the crucial areas for the secondary generalization of partial seizures. Therefore we focused on perirhinal cortical kindling in both epileptic rat strains and examined whether the resistance to limbic epilepsy is restricted to the amygdala and hippocampus or whether it can also occur with perirhinal cortical kindling. The mean afterdischarge (AD) thresholds were significantly higher in WAG/Rij and GAERS compared to the Wistar rats. Analysis of the rate of perirhinal cortical kindling for the 3 strains indicated highly significant differences. The mean number of stimulations for the development of the first stage 2, 3, 4 or 5 seizures was significantly higher in WAG/Rij and GAERS groups than in Wistar rats. Further, the cumulative total duration and number of SWDs increased during the first epoch of the post-stimulation period at the first stage 2 and 4/5 seizures in the WAG/Rij and GAERS rats compared to the pre-stimulation period. The higher AD threshold and delays to all stages of kindling in WAG/Rij and GAERS indicate that the perirhinal cortex is a part of the circuits involved in the kindling resistance in genetic models of absence epilepsy.