Bridging the gap: large animal models in neurodegenerative research

The world health organisation has declared neurological disorders as one of the greatest public health risks in the world today. Yet, despite this growing concern, the mechanisms underpinning many of these conditions are still poorly understood. This may in part be due to the seemingly diverse nature of the initiating insults ranging from genetic (such as the Ataxia's and Lysosomal storage disorders) through to protein misfolding and aggregation (i.e. Prions), and those of a predominantly unknown aetiology (i.e. Alzheimer's and Parkinson's disease). However, efforts to elucidate mechanistic regulation are also likely to be hampered because of the complexity of the human nervous system, the apparent selective regional vulnerability and differential degenerative progression. The key to elucidating these aetiologies is determining the regional molecular cascades, which are occurring from the early through to terminal stages of disease progression. Whilst much molecular data have been captured at the end stage of disease from post-mortem analysis in humans, the very early stages of disease are often conspicuously asymptomatic, and even if they were not, repeated sampling from multiple brain regions of "affected" patients and "controls" is neither ethical nor possible. Model systems therefore become fundamental for elucidating the mechanisms governing these complex neurodegenerative conditions. However, finding a model that precisely mimics the human condition can be challenging and expensive. Whilst cellular and invertebrate models are frequently used in neurodegenerative research and have undoubtedly yielded much useful data, the comparatively simplistic nature of these systems makes insights gained from such a stand alone model limited when it comes to translation. Given the recent advances in gene editing technology, the options for novel model generation in higher order species have opened up new and exciting possibilities for the field. In this review, we therefore explain some of the reasons why larger animal models often appear to give a more robust recapitulation of human neurological disorders and why they may be a critical stepping stone for effective therapeutic translation.

Equine grass sickness, but not botulism, causes autonomic and enteric neurodegeneration and increases soluble N-ethylmaleimide-sensitive factor attachment receptor protein expression within neuronal perikarya

REASONS FOR PERFORMING STUDY

Equine grass sickness (EGS) is of unknown aetiology. Despite some evidence suggesting that it represents a toxico-infection with Clostridium botulinum types C and/or D, the effect of EGS on the functional targets of botulinum neurotoxins, namely the soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, is unknown. Further, while it is commonly stated that, unlike EGS, equine botulism is not associated with autonomic and enteric neurodegeneration, this has not been definitively assessed.

OBJECTIVES

To determine: 1) whether botulism causes autonomic and enteric neurodegeneration; and 2) the effect of EGS on the expression of SNARE proteins within cranial cervical ganglion (CCG) and enteric neuronal perikarya.

STUDY DESIGN

Descriptive study.

METHODS

Light microscopy was used to compare the morphology of neurons in haematoxylin-eosin stained sections of CCG and ileum from 6 EGS horses, 5 botulism horses and 6 control horses. Immunohistochemistry was used to compare the expression of synaptosomal-associated protein-25, synaptobrevin (Syb) and syntaxin within CCG neurons, and of Syb in enteric neurons, from horses with EGS, horses with botulism and control horses. The concentrations of these SNARE proteins in extracts of CCG from EGS and control horses were compared using quantitative fluorescent western blotting.

RESULTS

EGS, but not botulism, was associated with autonomic and enteric neurodegeneration and with increased immunoreactivity for SNARE proteins within neuronal perikarya. Quantitative fluorescent western blotting confirmed increased concentrations of synaptosomal-associated protein-25, Syb and syntaxin within CCG extracts from EGS vs. control horses, with the increases in the latter 2 proteins being statistically significant.

CONCLUSIONS

The occurrence of autonomic and enteric neurodegeneration, and increased expression of SNARE proteins within neuronal perikarya, in EGS but not botulism, suggests that EGS may not be caused by botulinum neurotoxins. Further investigation of the aetiology of EGS is therefore warranted.

Pathogenesis of scrapie in ARQ/ARQ sheep after subcutaneous infection: effect of lymphadenectomy and immune cell subset changes in relation to prion protein accumulation

It is well established that the infectious agent of scrapie can replicate in the lymphoreticular system (LRS). However, the effects of removal of LRS target tissues on the pathogenesis of the infection and the accumulation of disease-associated prion protein (PrP(d)) in LRS tissues on specific immune cell subsets are poorly understood aspects. To address these questions 16 ARQ/ARQ sheep were subcutaneously inoculated in the drainage area of the prefemoral lymph node with brain homogenate derived from Suffolk sheep naturally infected with scrapie. Fourteen sheep were then subjected to either early (14-17 days post-inoculation [dpi]) or late (175-201 dpi) lymphadenectomy and culled at preclinical or clinical stages of infection. Neither late nor even early lymphadenectomy prevented infection or had any effect on the accumulation of PrP(d) in the LRS or CNS suggesting a rapid organic dissemination of the infectious agent after inoculation. Lymph nodes from eight scrapie inoculated sheep selected on the basis of the amount of PrP(d) in their LRS tissues (negative, low or high) were examined for six different immune cell markers. The PrP(d) negative lymph nodes from two sheep with no evidence of scrapie infection showed lower numbers of cluster of determination (CD) 21 positive cells than PrP(d) positive nodes, irrespective of their location (hind leg or head). However, quantitative differences in the expression of this marker were not detected when comparing lymph nodes with low and high levels of PrP(d) accumulation, suggesting that proliferation of CD21 positive cells is related to scrapie infection, but not directly linked to the magnitude of PrP(d) accumulation. An additional observation of the study was that sheep that were methionin-threonine at codon 112 of the prion protein gene showed lower attack rates than methionine homozygotes (67% and 100%, respectively) and also generally lower levels of PrP(d) accumulation in the LRS and brain and increased survival times, suggesting an influence of such polymorphism in the susceptibility to scrapie.

Immunophenotype of cells within cervine rectoanal mucosa-associated lymphoid tissue and mesenteric lymph nodes

Rectoanal mucosa-associated lymphoid tissue (RAMALT) is a part of the lymphoid system that can be sampled easily in live animals, especially ruminants. RAMALT biopsy is useful for the diagnosis of transmissible spongiform encephalopathies, including scrapie in sheep and goats and chronic wasting disease (CWD) in cervids. Diagnosis is reliant on detection of abnormal prion protein (PrP(d)), which is associated with lymphoid follicles. For enzyme linked immunosorbent assays (ELISAs) detecting PrP(d) it is necessary to ensure that lymphoid follicles are present in biopsy samples to avoid false-negative results. Monoclonal antibodies known to recognize specific immune cell subsets present in lymphoid tissues of sheep were tested for cross-reactivity with cervine RAMALT and mesenteric lymph nodes (MLNs) preserved in zinc salts fixative. The distribution of cells expressing CD3, CD4, CD79, CD21 and class II molecules of the major histocompatibility complex was determined in these tissues. Cells of each immunophenotype had similar distributions in RAMALT and MLNs and these distributions were similar to those reported previously for sheep and cattle. The identification and validation of cervine lymphoid follicle cell markers (CD79 and CD21) may allow reduction in false-negative results during diagnosis of CWD by ELISA.

Immunological differences between susceptible and resistant sheep during the preclinical phase of scrapie infection

In order to investigate the relationship between the immune response to scrapie infection and genetic susceptibility to the disease in sheep, immune cell subsets and prion protein (PrP) expression were determined in susceptible and resistant Suffolk sheep in the preclinical phase of infection. At 6 months of age, 12 ARQ/ARQ (susceptible) and nine ARR/ARR (resistant) scrapie-free Suffolk lambs were challenged subcutaneously with scrapie inoculum. Prefemoral lymphadenectomies were carried out at 14 and 180 days post-inoculation (p.i.) and serial bleeds were collected at monthly intervals for up to 1 year p.i. An indirect double-labelling procedure was carried out on peripheral blood mononuclear cells (PBMCs) and lymph node cell preparations and analysed using flow cytometry. Prior to scrapie challenge, significantly more PrP+cells were detected in PBMCs from the susceptible sheep. Furthermore, following challenge, significantly more CD8+andγΔ+T cells were detected in the PBMCs of the resistant sheep. However, at both 14 and 180 days p.i, CD21+cell expression was significantly higher in the lymph node preparations of the susceptible sheep. In contrast, more CD4+cells were detected in the lymph nodes of the resistant sheep at both time points. It was concluded that significant differences in immune cell subsets and PrP expression occur between ARQ/ARQ and ARR/ARR Suffolk sheep in the preclinical phase of infection.

Initial reactions in the oxidation of 1,2-dihydronaphthalene by Sphingomonas yanoikuyae strains

The substrate oxidation profiles of Sphingomonas yanoikuyae B1 biphenyl-2,3-dioxygenase and cis-biphenyl dihydrodiol dehydrogenase activities were examined with 1,2-dihydronaphthalene and various cis-diols as substrates. m-Xylene-induced cells of strain B1 oxidized 1,2-dihydronaphthalene to (-)-(1R,2S)-cis-1,2-dihydroxy-1,2-3,4-tetrahydronaphthalene as the major product (73% relative yield). Small amounts of (+)-(R)-2-hydroxy-1,2-dihydronaphthalene (15%), naphthalene (6%), and alpha-tetralone (6%) were also formed. Strain B8/36, which lacks an active cis-biphenyl dihydrodiol dehydrogenase, formed (+)-(1R,2S)-cis-1,2-dihydroxy-1,2-dihydronaphthalene (51%), in addition to (-)-(1R,2S)-cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene (44%) and (+)-(R)-2-hydroxy-1,2-dihydronaphthalene (5%). The cis-biphenyl dihydrodiol dehydrogenase of strain B1 oxidized both enantiomers of cis-1,2-dihydroxy-1,2-dihydronaphthalene, but only the (+)-(1S,2R)-enantiomers of cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene and cis-1,2-dihydroxy-3-phenylcyclohexa-3,5-diene. The results show that biphenyl dioxygenase expressed by S. yanoikuyae catalyzes dioxygenation, monooxygenation, and desaturation reactions with 1,2-dihydronaphthalene as the substrate, and cis-biphenyl dihydrodiol dehydrogenase catalyzes the enantioselective dehydrogenation of (+)-(1S,2R)-cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene and (+)-(1S,2R)-cis-1,2-dihydroxy-3-phenylcyclohexa-3,5-diene.

The Effect of Nonspecific Imaging Practice on the Mental Imagery Ability of Nursing Students

Mental imagery practice has assisted in the acquisition of psychomotor skills in several fields. Nursing education programs include many psychomotor skills which students need to learn quickly and efficiently. Examining imagery ability might be the first step in improving methods of teaching psychomotor nursing skills. This study hypothesized that subjects with low imagery who were exposed to non-specific imaging practice could have their imagery ability enhanced through the use of imaging exercises. A within subjects experimental design was used. Sixty sophomore nursing students were divided into high and low imagers based on scores on the shortened form of the Betts' QMI Vividness of Imagery Scale. Each group received one of two treatments--nonspecific imaging practice sessions or relaxation practice sessions; all subjects were posttested on the Betts'. A one-way analysis of variance with followup planned comparison tests using power analysis showed a highly significant main effect for low imagers.