- Worms on the spectrum - C. elegans models in autism research. [Review]
- ENExp Neurol 2017 Apr 20
- The small non-parasitic nematode Caenorhabditis elegans is widely used in neuroscience thanks to its well-understood development and lineage of the nervous system. Furthermore, C. elegans has been us...
The small non-parasitic nematode Caenorhabditis elegans is widely used in neuroscience thanks to its well-understood development and lineage of the nervous system. Furthermore, C. elegans has been used to model many human developmental and neurological conditions to better understand disease mechanisms and identify potential therapeutic strategies. Autism spectrum disorder (ASD) is the most prevalent of all neurodevelopmental disorders, and the C. elegans system may provide opportunities to learn more about this complex disorder. Along with a repertoire of behaviours, since basic cell biology and biochemistry of the C. elegans nervous system is generally very similar to mammals, cellular or molecular phenotypes can be investigated. For instance, worms have contributed greatly to the understanding of mechanisms underlying mutations in genes coding for synaptic proteins such as neuroligin and neurexin. However, using worms to model neurodevelopmental disorders like ASD, is still an emerging topic that harbours great, untapped potential. This review summarizes the numerous contributions of C. elegans to the field of biology and introduces the nematode system as a potential research tool to study essential roles of genes associated with ASD.
- Supraspinal respiratory plasticity following acute cervical spinal cord injury. [Journal Article]
- ENExp Neurol 2017 Apr 19; 293:181-189
- Impaired breathing is a devastating result of high cervical spinal cord injuries (SCI) due to partial or full denervation of phrenic motoneurons, which innervate the diaphragm - a primary muscle of r...
Impaired breathing is a devastating result of high cervical spinal cord injuries (SCI) due to partial or full denervation of phrenic motoneurons, which innervate the diaphragm - a primary muscle of respiration. Consequently, people with cervical level injuries often become dependent on assisted ventilation and are susceptible to secondary complications. However, there is mounting evidence for limited spontaneous recovery of respiratory function following injury, demonstrating the neuroplastic potential of respiratory networks. Although many studies have shown such plasticity at the level of the spinal cord, much less is known about the changes occurring at supraspinal levels post-SCI. The goal of this study was to determine functional reorganization of respiratory neurons in the medulla acutely (>4h) following high cervical SCI. Experiments were conducted in decerebrate, unanesthetized, vagus intact and artificially ventilated rats. In this preparation, spontaneous recovery of ipsilateral phrenic nerve activity was observed within 4 to 6h following an incomplete, C2 hemisection (C2Hx). Electrophysiological mapping of the ventrolateral medulla showed a reorganization of inspiratory and expiratory sites ipsilateral to injury. These changes included i) decreased respiratory activity within the caudal ventral respiratory group (cVRG; location of bulbospinal expiratory neurons); ii) increased proportion of expiratory phase activity within the rostral ventral respiratory group (rVRG; location of inspiratory bulbo-spinal neurons); iii) increased respiratory activity within ventral reticular nuclei, including lateral reticular (LRN) and paragigantocellular (LPGi) nuclei. We conclude that disruption of descending and ascending connections between the medulla and spinal cord leads to immediate functional reorganization within the supraspinal respiratory network, including neurons within the ventral respiratory column and adjacent reticular nuclei.
- Role of the locus coeruleus catecholaminergic neurons in the chemosensory control of breathing in a Parkinson's disease model. [Journal Article]
- ENExp Neurol 2017 Apr 19; 293:172-180
- A previous study has demonstrated that in the 6-hydroxydopamine (6-OHDA)-model of Parkinson's disease (PD) there is a reduction in the number of Phox2b neurons in the retrotrapezoid nucleus (RTN) and...
A previous study has demonstrated that in the 6-hydroxydopamine (6-OHDA)-model of Parkinson's disease (PD) there is a reduction in the number of Phox2b neurons in the retrotrapezoid nucleus (RTN) and a decrease in the respiratory response to hypercapnia 40days after PD-induction. The functional deficiency is restored 60days after 6-OHDA injection and here we tested the hypothesis that the locus coeruleus (LC) could be a candidate to restore the breathing deficiency. Minute Ventilation (VE) in response to hypercapnia (7% CO2) was assessed one day before, and then 40 and 60days after bilateral 6-OHDA (24μg/μL) or vehicle injections into the LC in control or PD-induced male Wistar rats. Bilateral injections of 6-OHDA decreased catecholaminergic neurons by 86% and 83% in the substantia nigra pars compacta (SNpc) and LC, respectively. As already described, in animals with lesions to the SNpc (N=6/group), the reduction in the ventilatory response to hypercapnia was restored 60days after PD (1257±81 vs. vehicle: 1185±49mL/kg/min). However, in animals with PD and lesion in the LC, the ventilation was blunted (674±39mL/kg/min). In another group of PD rats, we observed a reduction in the number of hypercapnia-induced-fos(+) cells in the RTN region (40days: 38±3 and 60days: 8.5±0.9 vs. vehicle 78±3 cells) and an increase in the LC (40days: 46±4 and 60days: 94±22 vs. vehicle 1±1 cells). Our data suggest that LC catecholaminergic neurons can be a candidate structure mediating chemoreceptor function in a model of PD.
- Mice with conditional NeuroD1 knockout display reduced aberrant hippocampal neurogenesis but no change in epileptic seizures. [Journal Article]
- ENExp Neurol 2017 Apr 18
- Adult neurogenesis is significantly increased in the hippocampus of rodent models of temporal lobe epilepsy (TLE). These adult-generated neurons have recently been shown to play a contributing role i...
Adult neurogenesis is significantly increased in the hippocampus of rodent models of temporal lobe epilepsy (TLE). These adult-generated neurons have recently been shown to play a contributing role in the development of spontaneous recurrent seizures (SRS). In order to eventually target pro-epileptic adult neurogenesis in the clinical setting, it will be important to identify molecular players involved in the control of aberrant neurogenesis after seizures. Here, we focused on NeuroD1 (ND1), a member of the bHLH family of transcription factors previously shown to play an essential role in the differentiation and maturation of adult-generated neurons in the hippocampus. Wild-type mice treated with pilocarpine to induce status epilepticus (SE) showed a significant up-regulation of NeuroD1+ immature neuroblasts located in both the granule cell layer (GCL), and ectopically localized to the hilar region of the hippocampus. As expected, conditional knockout (cKO) of NeuroD1 in Nestin-expressing stem/progenitors and their progeny led to a reduction in the number of NeuroD1+ adult-generated neurons after pilocarpine treatment compared to WT littermates. Surprisingly, there was no change in SRS in NeuroD1 cKO mice, suggesting that NeuroD1 cKO fails to reduce aberrant neurogenesis below the threshold needed to impact SRS. Consistent with this conclusion, the total number of adult-generated neurons in the pilocarpine model, especially the total number of Prox1+ hilar ectopic granule cells were unchanged after NeuroD1 cKO, suggesting strategies to reduce SRS will need to achieve a greater removal of aberrant adult-generated neurons.
- Inflammation-induced GluA1 trafficking and membrane insertion of Ca(2+) permeable AMPA receptors in dorsal horn neurons is dependent on spinal tumor necrosis factor, PI3 kinase and protein kinase A. [Journal Article]
- ENExp Neurol 2017 Apr 12; 293:144-158
- Peripheral inflammation induces sensitization of nociceptive spinal cord neurons. Both spinal tumor necrosis factor (TNF) and neuronal membrane insertion of Ca(2+) permeable AMPA receptor (AMPAr) con...
Peripheral inflammation induces sensitization of nociceptive spinal cord neurons. Both spinal tumor necrosis factor (TNF) and neuronal membrane insertion of Ca(2+) permeable AMPA receptor (AMPAr) contribute to spinal sensitization and resultant pain behavior, molecular mechanisms connecting these two events have not been studied in detail. Intrathecal (i.t.) injection of TNF-blockers attenuated paw carrageenan-induced mechanical and thermal hypersensitivity. Levels of GluA1 and GluA4 from dorsal spinal membrane fractions increased in carrageenan-injected rats compared to controls. In the same tissue, GluA2 levels were not altered. Inflammation-induced increases in membrane GluA1 were prevented by i.t. pre-treatment with antagonists to TNF, PI3K, PKA and NMDA. Interestingly, administration of TNF or PI3K inhibitors followed by carrageenan caused a marked reduction in plasma membrane GluA2 levels, despite the fact that membrane GluA2 levels were stable following inhibitor administration in the absence of carrageenan. TNF pre-incubation induced increased numbers of Co(2+) labeled dorsal horn neurons, indicating more neurons with Ca(2+) permeable AMPAr. In parallel to Western blot results, this increase was blocked by antagonism of PI3K and PKA. In addition, spinal slices from GluA1 transgenic mice, which had a single alanine replacement at GluA1 ser 845 or ser 831 that prevented phosphorylation, were resistant to TNF-induced increases in Co(2+) labeling. However, behavioral responses following intraplantar carrageenan and formalin in the mutant mice were no different from littermate controls, suggesting a more complex regulation of nociception. Co-localization of GluA1, GluA2 and GluA4 with synaptophysin on identified spinoparabrachial neurons and their relative ratios were used to assess inflammation-induced trafficking of AMPAr to synapses. Inflammation induced an increase in synaptic GluA1, but not GluA2. Although total GluA4 also increased with inflammation, co-localization of GluA4 with synaptophysin, fell short of significance. Taken together these data suggest that peripheral inflammation induces a PI3K and PKA dependent TNFR1 activated pathway that culminates with trafficking of calcium permeable AMPAr into synapses of nociceptive dorsal horn projection neurons.
- Hypersociability in the Angelman syndrome mouse model. [Journal Article]
- ENExp Neurol 2017 Apr 11; 293:137-143
- Deletions and reciprocal triplications of the human chromosomal 15q11-13 region cause two distinct neurodevelopmental disorders. Maternally-derived deletions or inactivating mutations of UBE3A, a 15q...
Deletions and reciprocal triplications of the human chromosomal 15q11-13 region cause two distinct neurodevelopmental disorders. Maternally-derived deletions or inactivating mutations of UBE3A, a 15q11-13 gene expressed exclusively from the maternal allele in neurons, cause Angelman syndrome, characterized by intellectual disability, motor deficits, seizures, and a characteristic increased social smiling, laughing, and eye contact. Conversely, maternally-derived triplications of 15q11-13 cause a behavioral disorder on the autism spectrum with clinical features that include decreased sociability that we recently reconstituted in mice with Ube3a alone. Based on the unique sociability features reported in Angelman syndrome and the repressed sociability observed when Ube3a gene dosage is increased, we hypothesized that mice with neuronal UBE3A loss that models Angelman syndrome would display evidence of hypersocial behavior. We report that mice with maternally-inherited Ube3a gene deletion (Ube3a(mKO)) have a prolonged preference for, and interaction with, social stimuli in the three chamber social approach task. By contrast, interactions with a novel object are reduced. Further, ultrasonic vocalizations and physical contacts are increased in male and female Ube3a(mKO) mice paired with an unfamiliar genotype-matched female. Single housing wild type mice increased these same social behavior parameters to levels observed in Ube3a(mKO) mice where this effect was partially occluded. These results indicate sociability is repressed by social experience and the endogenous levels of UBE3A protein and suggest some social behavioral features observed in Angelman syndrome may reflect an increased social motivation.
- Human stem cell modeling in neurofibromatosis type 1 (NF1). [Review]
- ENExp Neurol 2017 Apr 06
- The future of precision medicine is heavily reliant on the use of human tissues to identify the key determinants that account for differences between individuals with the same disorder. This need is ...
The future of precision medicine is heavily reliant on the use of human tissues to identify the key determinants that account for differences between individuals with the same disorder. This need is exemplified by the neurofibromatosis type 1 (NF1) neurogenetic condition. As such, individuals with NF1 are born with a germline mutation in the NF1 gene, but may develop numerous distinct neurological problems, ranging from autism and attention deficit to brain and peripheral nerve sheath tumors. Coupled with accurate preclinical mouse models, the availability of NF1 patient-derived induced pluripotent stem cells (iPSCs) provides new opportunities to define the critical factors that underlie NF1-associated nervous system disease pathogenesis and progression. In this review, we discuss the generation and potential applications of iPSC technology to the study of NF1.
- Early-life febrile seizures worsen adult phenotypes in Scn1a mutants. [Journal Article]
- ENExp Neurol 2017 Apr 01; 293:159-171
- Mutations in the voltage-gated sodium channel (VGSC) gene SCN1A, encoding the Nav1.1 channel, are responsible for a number of epilepsy disorders including genetic epilepsy with febrile seizures plus ...
Mutations in the voltage-gated sodium channel (VGSC) gene SCN1A, encoding the Nav1.1 channel, are responsible for a number of epilepsy disorders including genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS). Patients with SCN1A mutations often experience prolonged early-life febrile seizures (FSs), raising the possibility that these events may influence epileptogenesis and lead to more severe adult phenotypes. To test this hypothesis, we subjected 21-23-day-old mice expressing the human SCN1A GEFS+ mutation R1648H to prolonged hyperthermia, and then examined seizure and behavioral phenotypes during adulthood. We found that early-life FSs resulted in lower latencies to induced seizures, increased severity of spontaneous seizures, hyperactivity, and impairments in social behavior and recognition memory during adulthood. Biophysical analysis of brain slice preparations revealed an increase in epileptiform activity in CA3 pyramidal neurons along with increased action potential firing, providing a mechanistic basis for the observed worsening of adult phenotypes. These findings demonstrate the long-term negative impact of early-life FSs on disease outcomes. This has important implications for the clinical management of this patient population and highlights the need for therapeutic interventions that could ameliorate disease progression.
- A rapid chemical-genetic screen utilizing impaired movement phenotypes in C. elegans: Input into genetics of neurodevelopmental disorders. [Journal Article]
- ENExp Neurol 2017 Apr 01; 293:101-114
- Autism spectrum disorder (ASD) is the most common neurodevelopmental disorder with a constantly increasing prevalence. Model organisms may be tools to identify underlying cellular and molecular mecha...
Autism spectrum disorder (ASD) is the most common neurodevelopmental disorder with a constantly increasing prevalence. Model organisms may be tools to identify underlying cellular and molecular mechanisms, as well as aid the discovery and development of novel therapeutic approaches. A simple animal such as the nematode Caenorhabditis elegans may provide insights into the extreme complexity of ASD genetics. Despite its potential, using C. elegans in ASD research is a controversial approach and has not yet been used extensively in this context. In this study, we present a screening approach of potential C. elegans mutants as potential ASD models. We screened these mutants for motor-deficiency phenotypes, which can be exploited to study underlying mechanisms of the disorder. Selected motor-deficient mutants were then used in a comprehensive drug screen of over 3900 compounds, including many FDA-approved and natural molecules, that were analyzed for their ability to suppress motility defects caused by ASD-associated gene orthologues. This genetic-chemical approach, i.e. establishing C. elegans models for ASD and screening of a well-characterized compound library, might be a promising first step to understand the mechanisms of how gene variations cause neuronal dysfunction, leading to ASD and other neurological disorders. Positively acting compounds could also be promising candidates for preclinical studies.
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- Phosphodiesterase-4 inhibition restored hippocampal long term potentiation after primary blast. [Journal Article]
- ENExp Neurol 2017 Mar 31; 293:91-100
- Due to recent military conflicts and terrorist attacks, blast-induced traumatic brain injury (bTBI) presents a health concern for military and civilian personnel alike. Although secondary blast (pene...
Due to recent military conflicts and terrorist attacks, blast-induced traumatic brain injury (bTBI) presents a health concern for military and civilian personnel alike. Although secondary blast (penetrating injury) and tertiary blast (inertia-driven brain deformation) are known to be injurious, the effects of primary blast caused by the supersonic shock wave interacting with the skull and brain remain debated. Our group previously reported that in vitro primary blast exposure reduced long-term potentiation (LTP), the electrophysiological correlate of learning and memory, in rat organotypic hippocampal slice cultures (OHSCs) and that primary blast affects key proteins governing LTP. Recent studies have investigated phosphodiesterase-4 (PDE4) inhibition as a therapeutic strategy for reducing LTP deficits following inertia-driven TBI. We investigated the therapeutic potential of PDE4 inhibitors, specifically roflumilast, to ameliorate primary blast-induced deficits in LTP. We found that roflumilast at concentrations of 1nM or greater prevented deficits in neuronal plasticity measured 24h post-injury. We also observed a therapeutic window of at least 6h, but <23h. Additionally, we investigated molecular mechanisms that could elucidate this therapeutic effect. Roflumilast treatment (1nM delivered 6h post-injury) significantly increased total AMPA glutamate receptor 1 (GluR1) subunit expression, phosphorylation of the GluR1 subunit at the serine-831 site, and phosphorylation of stargazin at the serine-239/240 site upon LTP induction, measured 24h following injury. Roflumilast treatment significantly increased PSD-95 regardless of LTP induction. These findings indicate that further investigation into the translation of PDE4 inhibition as a therapy following bTBI is warranted.