Quantitative evaluation of orofacial motor function in mice: The pasta gnawing test, a voluntary and stress-free behavior test

Long-term changes in oral feeding behaviors of growing rats

Oral feeding is critical for survival in both humans and animals. However, few studies have reported quantitative behavioral measures associated with the development of oral feeding behaviors. Therefore, the present study investigated developmental changes in the oral feeding behaviors of rats by quantitatively assessing pasta eating and licking behaviors. In the pasta eating test, the time to finish pasta sticks of three different thicknesses (Φ = 0.9, 1.4, and 1.9 mm, 4 cm long) was recorded between postnatal day 29 (P29) and P49, because all rats were able to finish eating these pasta sticks on P29. A developmental decrease in the time to finish pasta sticks of all thicknesses was observed during the initial period of recordings and plateaued before P35. The extent of this decrease was dependent on the thickness of pasta sticks. In the licking test, the number of licks per 10 s and the total intake volume during the test were recorded between P19 and P49, because all rats were able to access and lick the solution on P19. The time courses of developmental increases in the number of licks and the total intake volume were similar to the results obtained in the pasta eating test. Collectively, these results suggest that developmental changes in pasta eating and licking behaviors markedly differed between the weanling and periadolescent periods. The present study also demonstrated the applicability of the pasta eating and licking tests to the quantification of developmental changes in the oral feeding behaviors of rats.

Long-term administration of CU06-1004 ameliorates cerebrovascular aging and BBB injury in aging mouse model

BACKGROUND

Age-related changes in the cerebrovasculature, including blood-brain barrier (BBB) disruption and vascular dementia, are emerging as potential risks for many neurodegenerative diseases. Therefore, the endothelial cells that constitute the cerebrovasculature may play key roles in preventing brain injury. Our previous study showed that CU06-1004, an endothelial cell dysfunction blocker, prevented vascular leakage, enhanced vascular integrity in ischemic reperfusion injury, and promoted the normalization of tumor vasculature. Here, we evaluated the effects of CU06-1004 on age-related cerebrovascular functional decline in the aged mouse brain.

RESULTS

In this study, we investigated the protective effects of CU06-1004 against oxidative stress-induced damage in human brain microvascular endothelial cells (HBMECs). HBMECs were treated with hydrogen peroxide (H₂O₂) to establish an oxidative stress-induced model of cellular injury. Compared with H₂O₂ treatment alone, pretreatment of HBMECs with CU06-1004 considerably reduced oxidative stress-induced cytotoxicity, reactive oxygen species generation, senescence-associated β-galactosidase activity, senescence marker expression, and the expression levels of inflammatory proteins. Based on the observed cytoprotective effects of CU06-1004 in HBMECs, we examined whether CU06-1004 displayed protective effects against cerebrovascular aging in mice. Long-term administration of CU06-1004 alleviated age-associated cerebral microvascular rarefaction and cerebrovascular senescence in the aged mouse brain. CU06-1004 supplementation also reduced the extravasation of plasma IgG by improving BBB integrity in the aged mouse brain, associated with reductions in neuronal injury. A series of behavioral tests also revealed improved motor and cognitive functions in aged mice that received long-term CU06-1004 administration.

CONCLUSIONS

These findings suggest that CU06-1004 may represent a promising therapeutic approach for delaying age-related cerebrovascular impairment and improving cognitive function in old age.

Evaluation of Functional Recovery in Rats After Median Nerve Resection and Autograft Repair Using Computerized Gait Analysis

Computerized gait analysis is a common evaluation method in rat models of hind limb nerve injuries, but its use remains unpublished in models of segmental nerve injury of the forelimb. It was the aim of this work to investigate if computerized gait analysis is a feasible evaluation method in a rat model of segmental median nerve injury and autograft repair. Ten male Lewis rats underwent 7-mm resection of the right median nerve with immediate autograft repair. The left median nerve was resected without repair and served as an internal control. Animals were assessed for 12 weeks after surgery via CatWalk (CW) gait analysis every 2 weeks. Evaluation of motor recovery by means of the grasping test was performed weekly while electrophysiological measurements were performed at the end of the observation period. CW data were correlated with grasping strength at each post-operative time point. CW data were also correlated with electrophysiology using linear regression analysis. Principal component analysis was performed to identify clusters of outcome metrics. Recovery of motor function was observable 4 weeks after surgery, but grasping strength was significantly reduced (p < 0.01) compared to baseline values until post-operative week 6. In terms of sensory recovery, the pain-related parameter Duty Cycle showed significant (p < 0.05) recovery starting from post-operative week 8. The Print Area of the right paw was significantly (p < 0.05) increased compared to the left side starting from post-operative week 10. Various parameters of gait correlated significantly (p < 0.05) with mean and maximum grasping strength. However, only Stand Index showed a significant correlation with compound muscle action potential (CMAP) amplitude (p < 0.05). With this work, we prove that computerized gait analysis is a valid and feasible method to evaluate functional recovery after autograft repair of the rat median nerve. We were able to identify parameters such as Print Area, Duty Cycle, and Stand Index, which allow assessment of nerve regeneration. The course of these parameters following nerve resection without repair was also assessed. Additionally, external paw rotation was identified as a valid parameter to evaluate motor reinnervation. In summary, computerized gait analysis is a valuable additional tool to study nerve regeneration in rats with median nerve injury.

Castanospermine reduces Zika virus infection-associated seizure by inhibiting both the viral load and inflammation in mouse models

Zika virus (ZIKV) outbreaks have been reported worldwide, including a recent occurrence in Brazil where it spread rapidly, and an association with increased cases of microcephaly was observed in addition to neurological issues such as GBS that were reported during previous outbreaks. Following infection of neuronal tissues, ZIKV can cause inflammation, which may lead to neuronal abnormalities, including seizures and paralysis. Therefore, a drug containing both anti-viral and immunosuppressive properties would be of great importance in combating ZIKV related neurological abnormalities. Castanospermine (CST) is potentially a right candidate drug as it reduced viral load and brain inflammation with the resulting appearance of delayed neuronal disorders, including seizures and paralysis in an Ifnar1^−/− mouse.

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Anti-ZIKV activity of castanospermine (CST) In vivo and in vitro.

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CST reduces ZIKV induced inflammation of brain.

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CST delays the ZIKV induced seizure and improves neuronal disorders such as motor function.

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CST gives marginal improvement in survivability in Ifnar1−/− mice.

Acute motor deficit and subsequent remyelination-associated recovery following internal capsule demyelination in mice

Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system (CNS), characterized by accumulated motor disability. However, whether remyelination promotes motor recovery following demyelinating injury remains unclear. Damage to the internal capsule (IC) is known to result in motor impairment in multiple sclerosis and stroke. Here, we induced focal IC demyelination in mice by lysophosphatidylcholine (LPC) injection, and examined its effect on motor behavior. We also compared the effect of LPC-induced IC damage to that produced by endothelin-1 (ET1), a potent vasoconstrictor used in experimental stroke lesions. We found that LPC or ET1 injections induced asymmetric motor deficit at 7 days post-lesion (dpl), and that both lesion types displayed increased microglia/macrophage density, myelin loss, and axonal dystrophy. The motor deficit and lesion pathology remained in ET1-injected mice at 28 dpl. In contrast, LPC-injected mice regained motor function by 28 dpl, with corresponding reduction in activated microglia/macrophage density, and recovery of myelin staining and axonal integrity in lesions. These results suggest that LPC-induced IC demyelination results in acute motor deficit and subsequent recovery through remyelination, and may be used to complement future drug screens to identify drugs for promoting remyelination.

Characterization of the visceral and neuronal phenotype of 4L/PS-NA mice modeling Gaucher disease

Gaucher disease is caused by a deficiency in glucocerebrosidase that can result in non-neuronal as well as neuronal symptoms. Common visceral symptoms are an increased organ size, specifically of the spleen, and glucosylceramide as well as glucosylsphingosine substrate accumulations as a direct result of the glucocerebrosidase deficiency. Neuronal symptoms include motor deficits and strong alterations in the cerebellum. To evaluate the effect of new compounds for the treatment of this devastating disease, animal models are needed that closely mimic the human phenotype. The 4L/PS-NA mouse as model of Gaucher disease is shown to present reduced glucocerebrosidase activity similar to human cases but an in-depth characterization of the model was still not performed. We therefore analyzed 4L/PS-NA mice for visceral alterations, motor deficits and also neuronal changes like glucocerebrosidase activity, substrate levels and neuroinflammation. A special focus was set at pathological changes of the cerebellum. Our results show that 4L/PS-NA mice have strongly enlarged visceral organs that are infiltrated by enlarged leukocytes and macrophages. Furthermore, animals present strong motor deficits that are accompanied by increased glucosylceramide and glucosylsphingosine levels in the brain, astrocytosis and activated microglia in the cortex and hippocampus as well as reduced calbindin levels in the cerebellum. The latter was directly related to a strong Purkinje cell loss. Our results thus provide a detailed characterization of the 4L/PS-NA mouse model over age showing the translational value of the model and validating its usefulness for preclinical efficiency studies to evaluate new compounds against Gaucher disease.

Hepatic and neuronal phenotype of NPC1-/- mice

Niemann-Pick type C disease (NPC) is a fatal autosomal recessive disorder characterized by a defect in the intracellular transport of lipoproteins leading to the accumulation of lipids in diverse tissues. A visceral and neuronal phenotype mimicking human NPC1 disease has been described in NPC1 mutant mice. These mice are by now the most widely used NPC1 rodent model to study NPC and developmental compounds against this devastating disease. Here we characterized NPC1^−/− mice for their hepatic and neuronal phenotype to confirm the stability of the phenotype, provide a characterization of disease progression and pinpoint the age of robust phenotype onset. Animals of 4–10 weeks of age were analyzed for general health, motor deficits as well as hepatic and neuronal alterations with a special focus on cerebellar pathology.

Our results show that NPC1^−/− mice have a reduced general health at the age of 9–10 weeks. Robust motor deficits can be observed even earlier at 8 weeks of age. Hepatic changes included increased organ weight and cholesterol levels at 6 weeks of age accompanied by severely increased liver enzyme levels. Analysis of NPC1^−/− brain pathology showed decreased cholesterol and increased Aβ levels in the hippocampus at the age of 6 weeks. Further analysis revealed a decrease of the cytokine IL-12p70 in the cerebellum along with a very early increase of astrocytosis. Hippocampal IL-12p70 levels were increased at the age of 6 weeks followed by increased activated microglia levels. By the age of 10 weeks, also cerebellar Aβ levels were increased along with strongly reduced Calbindin D-28k levels.

Our results validate and summarize the progressive development of the hepatic and neuronal phenotype of NPC1^−/− mice that starts with cerebellar astrocytosis, making this mouse model a valuable tool for the development of new compounds against NPC.

Voluntary biting behavior as a functional measure of orofacial pain in mice

INTRODUCTION

Pain-related behavior secondary to masticatory function can be assessed with the rodent bite force model. A reduction of the bite force has been shown to be related to pain associated with the masseter muscle and jaw activity, while an increase in bite force suggests improvement of muscle function and less pain. To evaluate the usefulness of the bite force measure in studying long-lasting orofacial pain we analyzed biting parameters during prolonged myofascial pain induced by ligation injury of the masseter muscle tendon (TL) in mice.

METHODS

C57Bl/6 mice were habituated to bite at a pair of aluminum plates attached to a force displacement transducer. The transduced voltage signals were amplified and converted to force through calibration with a standard weight set. Voluntary biting behavior was recorded for 100 s/session and those with bite forces ≥980 mN were analyzed. Nociception was also verified with von Frey, conditioned place avoidance (CPA) tests and mouse grimace scale. Persistent orofacial pain was induced with unilateral ligation of one tendon of the masseter muscle (TL).

RESULTS

To reduce interference of random bites of smaller forces, the top 5 or 15 bite forces (BF5/15) were chosen as a measure of masticatory function and related to pain behavior. Both male and female mice exhibited similar BF5/15. For the first nascent test of all mice, mean bite force was significantly and positively correlated with the body weight. However, this correlation was less clear in the latter tests (2-8 w). TL induced a reduction of BF5/15 that peaked at 1 w and returned to the baseline within 3 w. The von Frey and CPA tests indicated that mechanical allodynia/hyperalgesia persisted at the time when the BF had returned to the pre-injury level. Infusion of pain-relieving bone marrow stromal cells improved biting behavior in both male and female mice as shown by significantly increased BF5/15, compared to vehicle-treated mice.

CONCLUSIONS

Mouse voluntary biting behavior can be reliably measured and quantified with a simplified setup. The bite force showed an inverse relationship with the level of pain after TL and was improved by pain-relieving manipulations. However, the injury-induced reduction of bite force peaked early and did not parallel with other measures of nociception in the later phase of hyperalgesia. The results suggest that multiple factors such as the level of habituation, cognitive motive, physical status, and feeding drive may affect random voluntary biting and confound the biting parameters related to maintained hyperalgesia.

Animal models of early-stage Parkinson's disease and acute dopamine deficiency to study compensatory neurodegenerative mechanisms

Parkinson's disease is a common neurodegenerative disease characterized by a widely variety of motor and non-motor symptoms. While the motor deficits are only visible following a severe dopamine depletion, neurodegenerative process and some non-motor symptoms are manifested years before the motor deficits. Importantly, chronic degeneration of dopaminergic neurons leads to the development of compensatory mechanisms that play roles in the progression of the disease and the response to anti-parkinsonian therapies. The identification of these mechanisms will be of great importance for improving our understanding of factors with important contributions to the disease course and the underlying adaptive process. To date, most of the data obtained from animal models reflect the late, chronic, dopamine-depleted states, when compensatory mechanisms have already been established. Thus, adequate animal models with which researchers are able to dissect early- and late-phase mechanisms are necessary. Here, we reviewed the literature related to animal models of early-stage PD and pharmacological treatments capable of inducing acute dopamine impairments and/or depletion, such as reserpine, haloperidol and tetrodotoxin. We highlighted the advantages, limitations and the future prospective uses of these models, as well as their applications in the identification of novel agents for treating this neurological disorder.

mTh1 driven expression of hTDP-43 results in typical ALS/FTLD neuropathological symptoms

Transgenic mouse models are indispensable tools to mimic human diseases and analyze the effectiveness of related new drugs. For a long time amyotrophic lateral sclerosis (ALS) research depended on only a few mouse models that exhibit a very strong and early phenotype, e.g. SOD1 mice, resulting in a short treatment time window. By now, several models are available that need to be characterized to highlight characteristics of each model. Here we further characterized the mThy1-hTDP-43 transgenic mouse model TAR6/6 that overexpresses wild type human TARDBP, also called TDP-43, under control of the neuronal Thy-1 promoter presented by Wils and colleagues, 2010, by using biochemical, histological and behavioral readouts. Our results show that TAR6/6 mice exhibit a strong TDP-43 expression in the hippocampus, spinal cord, hypothalamus and medulla oblongata. Apart from prominent protein expression in the nucleus, TDP-43 protein was found at lower levels in the cytosol of transgenic mice. Additionally, we detected insoluble TDP-43 in the cortex, motoneuron loss, and increased neuroinflammation in the central nervous system of TAR6/6 animals. Behavioral analyses revealed early motor deficits in the clasping- and wire suspension test as well as decreased anxiety in the elevated plus maze. Further motor tests showed differences at later time points compared to non-transgenic littermates, thus allowing the observation of onset and severity of such deficits. Together, TAR6/6 mice are a valuable tool to test new ALS/FTLD drugs that target TDP-43 expression and insolubility, neuroinflammation, motoneuron loss or other TDP-43 related downstream signaling pathways since these mice exhibit a later pathology as previously used ALS/FTLD mouse models.

Early start of progressive motor deficits in Line 61 α-synuclein transgenic mice

BACKGROUND

Synucleinopathies such as Parkinson's disease or multiple system atrophy are characterized by Lewy bodies in distinct brain areas. These aggregates are mainly formed by α-synuclein inclusions, a protein crucial for synaptic functions in the healthy brain. Transgenic animal models of synucleinopathies are frequently based on over-expression of human wild type or mutated α-synuclein under the regulatory control of different promoters. A promising model is the Line 61 α-synuclein transgenic mouse that expresses the transgene under control of the Thy-1 promoter.

RESULTS

Here, we show an extended characterization of this mouse model over age. To this end, we analyzed animals for the progression of human and mouse protein expression levels in different brain areas as well as motor and memory deficits. Our results show, that Line 61 mice exhibited an age dependent increase of α-synuclein protein levels in the hippocampus but not the striatum. While murine α-synuclein was also increased with age, it was lower expressed in Line 61 mice than in non-transgenic littermates. At the age of 9 months animals exhibited increased neuroinflammation. Furthermore, we found that Line 61 mice showed severe motor deficits as early as 1 month of age as assessed by the wire hanging and nest building tests. At later ages, initial motor deficits were validated with the RotaRod, pasta gnawing and beam walk tests. At 8 months of age animals exhibited emotional memory deficits as validated with the contextual fear conditioning test.

CONCLUSION

In summary, our results strengthen and further expand our knowledge about the Line 61 mouse model, emphasizing this mouse model as a valuable in vivo tool to test new compounds directed against synucleinopathies.