Detection of chronic sensorimotor impairments in the ladder rung walking task in rats with endothelin-1-induced mild focal ischemia

Methods for evaluating gait associated dynamic balance and coordination in rodents

Balance is the dynamic and unconscious control of the body's centre of mass to maintain postural equilibrium. Regulated by the vestibular system, head movement and acceleration are processed by the brain to adjust joints. Several conditions result in a loss of balance, including Alzheimer's Disease, Parkinson's Disease, Menière's Disease and cervical spondylosis, all of which are caused by damage to certain parts of the vestibular pathways. Studies about the impairment of the vestibular system are challenging to carry out in human trials due to smaller study sizes limiting applications of the results and a lacking understanding of the human balance control mechanism. In contrast, more controlled research can be performed in animal studies which have fewer confounding factors than human models and allow specific conditions that affect balance to be replicated. Balance control can be studied using rodent balance-related behavioural tests after spinal or brain lesions, such as the Basso, Beattie and Bresnahan (BBB) Locomotor Scale, Foot Fault Scoring System, Ledged Beam Test, Beam Walking Test, and Ladder Beam Test, which are discussed in this review article along with their advantages and disadvantages. These tests can be performed in preclinical rodent models of femoral nerve injury, stroke, spinal cord injury and neurodegenerative diseases.

Analysis of Effect of Intensity of Aerobic Exercise on Cognitive and Motor Functions and Neurotrophic Factor Expression Patterns in an Alzheimer's Disease Rat Model

The effect of aerobic exercise at different intensities on Alzheimer's disease (AD) still remains unclear. We investigated the effect of aerobic exercise at different intensities on cognitive and motor functions and neurotrophic factor expression. Thirty-two AD-induced rats were randomly assigned to control (CG), low-intensity (Group I), medium-intensity (Group II), and high-intensity (Group III) exercise groups. Each group, except for the CG, performed aerobic exercise for 20 min a day five times a week. After performing aerobic exercise for 4 weeks, their cognitive and motor functions and neurotrophic factor expression patterns were analyzed and compared between the groups. All variables of cognitive and motor functions and neurotrophic factor expression were significantly improved in Groups I, II, and III compared to those in the CG (p < 0.05). Among the neurotrophic factors, brain-derived neurotrophic factor (BDNF) expression was significantly improved in Group III compared to that in Groups I and II (p < 0.05). In the intra-group comparison of cognitive and motor functions, no significant difference was observed in CG, but the aerobic exercise groups showed improvements. Only Group III showed a significant improvement in the time it took to find eight food items accurately (p < 0.05). Aerobic exercise improved the cognitive and motor functions and neurotrophic factor expression patterns in the AD-induced rat model, with high-intensity aerobic exercise having greater effects on cognitive function and BDNF expression.

The Foot Fault Scoring System to Assess Skilled Walking in Rodents: A Reliability Study

The foot fault scoring system of the ladder rung walking test (LRWT) is used to assess skilled walking in rodents. However, the reliability of the LRWT foot fault score has not been properly addressed. This study was designed to address this issue. Two independent and blinded raters analyzed 20 rats and 20 mice videos. Each video was analyzed twice by the same rater (80 analyses per rater). The intraclass correlation coefficient (ICC) and the Kappa coefficient were employed to check the accuracy of agreement and reliability in the intra- and inter-rater analyses of the LRWT outcomes. Excellent intra- and inter-rater agreements were found for the forelimb, hindlimb, and both limbs combined in rats and mice. The agreement level was also excellent for total crossing time, total time stopped, and the number of stops during the walking path. Rating individual scores in the foot fault score system (0–6) ranged from satisfactory to excellent, in terms of the intraclass correlation indexes. Moreover, we showed that experienced and inexperienced raters can obtain reliable results if supervised training is provided. We concluded that the LRWT is a reliable and useful tool to study skilled walking in rodents and can help researchers address walking-related neurobiological questions.

Clinical relevance of chronic neuropathic pain phenotypes in mice: A comprehensive behavioral analysis

Despite a large number of preclinical studies performed each year, the safe and effective therapeutic interventions for chronic pain are scant. Therefore, it appears that pre-clinical modeling requires a systematically organized behavioral test paradigm to quantify the response of animals for a specific pain state. The present study, therefore, conceptualized a test battery to evaluate the behavioral changes in mice following neuropathic pain. We employed sciatic nerve chronic constriction injury (CCI) in C57BL/6 J mice to model chronic pain state. Mice were monitored for thermal hyperalgesia and grip strength for 30 days. Subsequently, mice underwent a behavioral test battery consisting of the nociceptive threshold, the affective and cognitive functions and motor coordination, and strength. Our results showed that CCI mice are insensitive to thermal stimuli. However, nerve-injured mice showed significant changes in neuromuscular coordination, basal anxiety, and hedonic state. Such impaired neuromuscular coordination is indicative of disability rather than the actual pain phenotype. While using the digital gait analysis, our study revealed rationales for the insensitivity of CCI mice to thermal stimuli. Our results suggest that the predictive validity of the CCI model necessitates a comprehensive behavioral test battery to select the clinically relevant and measurable phenotype to quantify chronic neuropathic pain.

Comparative Therapeutic Effects of Minocycline Treatment and Bone Marrow Mononuclear Cell Transplantation following Striatal Stroke

We explored the comparative effects of minocycline treatment and intrastriatal BMMC transplantation after experimental striatal stroke in adult rats. Male Wistar adult rats were divided as follows: saline-treated (N = 5), minocycline-treated (N = 5), and BMMC-transplanted (N = 5) animals. Animals received intrastriatal microinjections of 80 pmol of endothelin-1 (ET-1). Behavioral tests were performed at 1, 3, and 7 days postischemia. Animals were treated with minocycline (50 mg/kg, i.p.) or intrastriatal transplants of 106 BMMCs at 24 h postischemia. Animals were perfused at 7 days after ischemic induction. Coronal sections were stained with cresyl violet for gross histopathological analysis and immunolabeled for the identification of neuronal bodies (NeuN), activated microglia/macrophages (ED1), and apoptotic cells (active caspase-3). BMMC transplantation and minocycline reduced the number of ED1+ cells (p < 0.05, ANOVA-Tukey), but BMMC afforded better results. Both treatments afforded comparable levels of neuronal preservation compared to control (p > 0.05). BMMC transplantation induced a higher decrease in the number of apoptotic cells compared to control and minocycline treatment. Both therapeutic approaches improved functional recovery in ischemic animals. The results suggest that BMMC transplantation is more effective in modulating microglial activation and reducing apoptotic cell death than minocycline, although both treatments are equally efficacious on improving neuronal preservation.

Lickometry: A novel and sensitive method for assessing functional deficits in rats after stroke

The need for sensitive, easy to administer assessments of long-term functional deficits is crucial in pre-clinical stroke research. In the present study, we introduce lickometry (lick microstructure analysis) as a precise method to assess sensorimotor deficits up to 40 days after middle cerebral artery occlusion in rats. Impairments in drinking efficiency compared to controls, and a compensatory increase in the number of drinking clusters were observed. This highlights the utility of this easy to administer task in assessing subtle, long-term deficits, which could be likened to oral deficits in patients.

Lesion size and behavioral deficits after endothelin-1-induced ischemia are not dependent on time of day

BACKGROUND

The occurrence of stroke exhibits a strong circadian pattern with a peak in the morning hours after waking. The factors that influence this pattern of stroke prevalence may confer varying degrees of neuroprotection and therefore influence stroke severity. This question is difficult to address in clinical cases because of the variability in the location and duration of the ischemic event.

METHODS

The purpose of this study was to determine if time of day affected the severity of stroke targeting the motor cortex in rats. Strokes were produced using topical application of the vasoconstrictor endothelin-1 to motor cortex of unanesthetized animals at 2 time points: early day and early night. Behavioral deficits were measured using reaching, cylinder, and horizontal ladder tasks, and the volume of the lesion was quantified.

RESULTS

Behavior on reaching and horizontal ladder tasks were both severely impaired by endothelin-1 treatment compared to vehicle-treated animals, but deficits did not differ according to time of treatment. Similarly, while endothelin-1 produced larger lesions of the motor cortex than did vehicle treatment, the size of the lesion did not differ according to time of treatment.

CONCLUSIONS

These results suggest that while many factors under circadian control can influence the prevalence of stroke, the magnitude of lesion and behavioral deficit resulting from an ischemic event may not be influenced by time of day.

Conditionally immortalised neural stem cells promote functional recovery and brain plasticity after transient focal cerebral ischaemia in mice

Cell therapy has enormous potential to restore neurological function after stroke. The present study investigated effects of conditionally immortalised neural stem cells (ciNSCs), the Maudsley hippocampal murine neural stem cell line clone 36 (MHP36), on sensorimotor and histological outcome in mice subjected to transient middle cerebral artery occlusion (MCAO). Adult male C57BL/6 mice underwent MCAO by intraluminal thread or sham surgery and MHP36 cells or vehicle were implanted into ipsilateral cortex and caudate 2 days later. Functional recovery was assessed for 28 days using cylinder and ladder rung tests and tissue analysed for plasticity, differentiation and infarct size. MHP36-implanted animals showed accelerated and augmented functional recovery and an increase in neurons (MAP-2), synaptic plasticity (synaptophysin) and axonal projections (GAP-43) but no difference in astrocytes (GFAP), oligodendrocytes (CNPase), microglia (IBA-1) or lesion volumes when compared to vehicle group. This is the first study showing a potential functional benefit of the ciNSCs, MHP36, after focal MCAO in mice, which is probably mediated by promoting neuronal differentiation, synaptic plasticity and axonal projections and opens up opportunities for future exploitation of genetically altered mice for dissection of mechanisms of stem cell based therapy.

ENDOTHELIN-1-INDUCED CEREBRAL ISCHEMIA: EFFECTS OF KETANSERIN AND MK-801 ON LIMB PLACING IN RATS

The long-term effects of the 5-HT(2A) receptor antagonist ketanserin on deficits in sensorimotor integration (limb placing tests) following transient focal cerebral ischemia in rats were compared to the effects of the NMDA antagonist MK-801. Middle cerebral artery occlusion was induced in conscious rats by microinjection of endothelin-1 in the vicinity of the artery (EMCAO model). The EMCAO/vehicle rats exhibited impaired tactile and proprioceptive limb placing. In contrast to ketanserin, MK-801 exerted severe early behavioral disturbances, but both drugs significantly improved the neurological scores much earlier than the spontaneous recovery of function occurred. The present results suggest that pharmacotherapy by means of ketanserin lacking the severe side effects of the NMDA antagonists can be used to enhance functional recovery after stroke.

The ladder rung walking task: a scoring system and its practical application

Progress in the development of animal models for/stroke, spinal cord injury, and other neurodegenerative disease requires tests of high sensitivity to elaborate distinct aspects of motor function and to determine even subtle loss of movement capacity. To enhance efficacy and resolution of testing, tests should permit qualitative and quantitative measures of motor function and be sensitive to changes in performance during recovery periods. The present study describes a new task to assess skilled walking in the rat to measure both forelimb and hindlimb function at the same time. Animals are required to walk along a horizontal ladder on which the spacing of the rungs is variable and is periodically changed. Changes in rung spacing prevent animals from learning the absolute and relative location of the rungs and so minimize the ability of the animals to compensate for impairments through learning. In addition, changing the spacing between the rungs allows the test to be used repeatedly in long-term studies. Methods are described for both quantitative and qualitative description of both fore- and hindlimb performance, including limb placing, stepping, co-ordination. Furthermore, use of compensatory strategies is indicated by missteps or compensatory steps in response to another limb’s misplacement.

Sensorimotor behavioral effects of endothelin-1 induced small cortical infarcts in C57BL/6 mice

Mouse models have not paralleled rat models of stroke in advances in sensitive, species appropriate measures of neurological and behavioral recovery. Most available tests of mouse sensorimotor function are adaptations of those originally developed in rats and may not be as sensitive in detecting behavioral deficits after small cortical lesions in mice. Our purpose was to test the use of a vasoconstricting peptide, endothelin-1 (ET-1), to produce focal infarcts of the mouse sensorimotor cortex and to establish a behavioral test battery sensitive to resulting sensorimotor deficits. Young adult (3-5-month-old) male C57BL/6 mice received intracortical infusions of ET-1 that produced unilateral lesions of the forelimb region of the sensorimotor cortex, intracortical infusions of sterile saline, or sham surgeries. Pre-operatively and at various time points over 3 weeks post-surgery, they were administered a test battery that included measures of sensorimotor asymmetry (Corner and Bilateral Tactile Stimulation Tests), coordinated forepaw use (Cylinder and Ladder Rung Tests), and dexterous forepaw function (Pasta Matrix Reaching Test). ET-1 infusions resulted in consistently placed, focal cortical infarcts and forelimb impairments as measured with the Ladder Rung, Bilateral Tactile Stimulation, and Pasta Matrix Reaching Tests. On the Bilateral Tactile Stimulation and Pasta Matrix Reaching Tests, impairments persisted throughout the time span of observation (26 days). These results support ET-1 as a viable option for creating small, reproducible lesions of anatomical subregions in the mouse neocortex that result in lasting functional impairments in the forelimb, as observed with sufficiently sensitive measures.

Ketanserin reduces the postischemic EEG and behavioural changes following Endothelin-1-induced occlusion of the middle cerebral artery in conscious rats

We modeled the common clinical conditions of human stroke in fully conscious rats through an occlusion of the middle cerebral artery (MCAO) by means of unilateral microinjection of Endothelin-1 (ET1) in the vicinity of the artery (EMCAO model). Since the role of serotonin (5-HT) system in the regulation of the cerebral blood flow has been known for long time and no data are available at present for the effects of 5-HT antagonists in focal ischemia models, we further tested whether a blockade of the serotonin-2A (5-HT2A) receptors by ketanserin (20 min post-ET1) would diminish the late EMCAO-induced functional and morphological changes. The long-term neurological (postural reflex) and electroencephalogram (EEG) changes in the somatosensory cortical region (S1FL) were used to assess the effects of ketanserin on the post-ischemic changes. The study was supplemented by a histopathological examination of S1FL area and striatum of both hemispheres. The EMCAO/ ketanserin-treated rats showed much smaller neurological deficits than the EMCAO rats treated with vehicle. This effect was observed on day 3 and lasted until the end of experiments-14 days after EMCAO. The depression of alpha and beta EEG frequencies found after EMCAO was significantly and earlier restored following ketanserin. Notably, there was not augmentation of the pathological slow EEG waves at day 3 post-ET1 in the EMCAO ketanserin-treated rats compared with that observed in the EMCAO vehicle-treated rats. Although there were mild morphological changes in the penumbral S1FL cortical region after EMCAO, ketanserin reduced the histopathological difference between the ipsilateral and contralateral cortical S1FL regions, but did not change the difference between striatum of both sides. Ketanserin reduced the infarct size in ipsilateral hemisphere (mainly cortex). In conclusion, the results showed that treatment with ketanserin at the early stage of stroke may reduce the consequences of ischemia by improvement of functional and morphological recovery at later stages. Ketanserin appears to be a promising candidate for mitigating the consequences of stroke.

Rat Models of Upper Extremity Impairment in Stroke

Stroke remains the leading cause of adult disability, with upper extremity motor impairments being the most prominent functional deficit in surviving stroke victims. The development of animal models of upper extremity dysfunction after stroke has enabled investigators to examine the neural mechanisms underlying rehabilitation-dependent motor recovery as well as the efficacy of various adjuvant therapies for enhancing recovery. Much of this research has focused on rat models of forelimb motor function after experimentally induced ischemic or hemorrhagic stroke. This article provides a review of several different methods for inducing stroke, including devascularization, photothrombosis, chemical vasoconstriction, and hemorrhagia. We also describe a battery of sensorimotor tasks for assessing forelimb motor function after stroke. The tasks range from measures of gross motor performance to fine object manipulation and kinematic movement analysis, and we offer a comparison of the sensitivity for revealing motor deficits and the amount of time required to administer each motor test. In addition, we discuss several important methodological issues, including the importance of testing on multiple tasks to characterize the nature of the impairments, establishing stable baseline prestroke motor performance measures, dissociating the effects of acute versus chronic testing, and verifying lesion location and size. Finally, we outline general considerations for conducting research using rat models of stroke and the role that these models should play in guiding clinical trials.

No improvement of functional and histological outcome after application of the metabotropic glutamate receptor 5 agonist CHPG in a model of endothelin-1-induced focal ischemia in rats

The role of group I metabotropic glutamate receptors (mGluRs) in neurodegeneration is as yet unclear as mGluR1/5 antagonists and agonists yielded contradictory effects in different disease models. In the present study, we examined the neuroprotective potency of the selective mGluR5 agonist, (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG), in endothelin-1(ET-1)-induced focal ischemia in rats. In addition to the effect of CHPG on the histologically defined infarct size, we studied its influence on sensorimotor impairments in the ladder rung walking test at late time points up to 4 weeks after the ischemic insult. Rats were treated i.c.v. with an injection of 1mM CHPG beginning 10min after the application of ET-1. Histological analyses 4 weeks after ET-1-induced ischemia demonstrated only a small, insignificant reduction in infarct size after CHPG application. In accordance with this result, there were no significant effects of the used CHPG concentration on sensorimotor impairments in the ladder rung walking test. In conclusion, our data point to the restricted value of CHPG as a neuroprotectant after transient focal ischemia and to the importance of evaluating neuroprotective effects at late post-ischemic time points.

Focal cerebral ischemia alters the spatio-temporal properties, but not the amount of activity in mice

Cerebral ischemia induces sensorimotor and cognitive dysfunctions in rodents; however, little is known about the changes in the spatio-temporal organization of locomotor activity after ischemia. In this study, we continuously assessed the spatio-temporal properties of locomotor activity in an enclosure (40 cm x 40 cm x 65 cm, arbitrarily divided into 16 zones) with feeding and drinking supplies, and observed the spatio-temporal changes in mice with focal cerebral ischemia. Locomotor tracks were recorded from 3rd to 24th h (total 22 h) after middle cerebral artery occlusion (MCAO) or sham operation. The absolute and relative distance traveled or time spent in different regions was analyzed. We found that there was no significant difference in total traveled distances over 22 h between the two groups. Control mice moved and stayed primarily in feeding and drinking zones, frequently in peripheral but rarely in central zones. However, ischemic mice lost such a property, almost evenly moved and stayed in 16 zones. Mice in both groups were more active (traveled more distances) shortly after they entered the enclosure, while ischemic mice returned to stable levels slower. The traveled distance had a remarkable circadian variation with more locomotion in the night in control mice, but not in ischemic mice. Most of the spatial parameters (ratios) of locomotor activity were closely correlated with the ischemic infarction, neuron densities (in cortex, hippocampal CA1 region and striatum), and typical behavioral assessments (neurological scores and inclined board test). Thus, these findings indicate that focal cerebral ischemia does not alter the amount of locomotor activity in mice, but impairs the spatio-temporal properties-prolonging the initial hyperactivity and losing regionally special distribution of the activity.