Abnormalities in whisking behaviour are associated with lesions in brain stem nuclei in a mouse model of amyotrophic lateral sclerosis (original) (raw)
Title : Dynamic neuromuscular remodeling precedes motor-unit loss in a mouse 1 model of ALS 2
Affiliations: 4 1 Département de neurosciences, Université de Montréal, PO box 6128, Station centre-ville, 5 Montréal, Québec, Canada, H3C 3J7. 6 2 Groupe de recherche sur le système nerveux central, Université de Montréal. 7 3 Centre de recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), 900 Saint 8 Denis Street, Montréal, Québec, Canada, H2X 0A9. 9 *To whom correspondence should be addressed: richard.robitaille@umontreal.ca; Phone 10 number: 1-514-343-6111 ext 1946; Fax: 1-514-343-7972. 11 12
Morphological and functional changes in innervation of a fast forelimb muscle in SOD1-G85R mice
Neurobiology of Disease, 2012
Muscle endplates become denervated in mice that express mutations of human superoxide dismutase 1 (hSOD1), models of familial amyotrophic lateral sclerosis. This denervation is especially marked in fast limb muscles, and precedes death of motor neuron somata. This study used mice that expressed yellow fluorescent protein (YFP) in neurons to investigate changes in the morphology and function of axons and motor terminals innervating a fast forelimb muscle (epitrochleoanconeus, ETA) in presymptomatic and symptomatic hSOD1-G85R mice, compared to those in mice that express wild-type (wt) hSOD1. The percentage of endplates (identified using fluorescently-labeled α-bungarotoxin) innervated by motor terminals remained high in presymptomatic SOD1-G85R mice, but fell to~50% in symptomatic mice. The number of large diameter (≥ 4 μm) axons in the ETA nerve also decreased as mice became symptomatic, and endplate innervation correlated best with the number of large diameter axons. Motor terminal function was assessed using changes in terminal YFP fluorescence evoked by trains of action potentials; different components of the pH-dependent YFP signals reflect stimulation-induced Ca 2+ entry and vesicular exo/endocytosis. Most visible motor terminals (>90%) remained capable of responding to nerve stimulation in both pre-and symptomatic hSOD1-G85R mice, but with functional alterations. Responses in presymptomatic terminals suggested reduced acidification and increased vesicular release, whereas symptomatic terminals exhibited increased acidification and reduced vesicular release. The fact that most remaining terminals were able to respond to nerve stimulation suggests that motor terminal-protective therapies might contribute to preserving neuromuscular function in fALS mice.
Preferential motor unit loss in the SOD1G93A transgenic mouse model of amyotrophic lateral sclerosis
The Journal of Physiology, 2008
The present study investigated motor unit (MU) loss in a murine model of familial amyotrophic lateral sclerosis (ALS). The fast-twitch tibialis anterior (TA) and medial gastrocnemius (MG) muscles of transgenic SOD1 G93A and SOD1 WT mice were studied during the presymptomatic phase of disease progression at 60 days of age. Whole muscle maximum isometric twitch and tetanic forces were 80% lower (P < 0.01) in the TA muscles of SOD1 G93A compared to SOD1 WT mice. Enumeration of total MU numbers within TA muscles showed a 60% reduction (P < 0.01) within SOD1 G93A mice (38 ± 7) compared with SOD1 WT controls (95 ± 12); this was attributed to a lower proportion of the most forceful fast-fatigable (FF) MU in SOD1 G93A mice, as seen by a significant (P < 0.01) leftward shift in the cumulative frequency histogram of single MU forces. Similar patterns of MU loss and corresponding decreases in isometric twitch force were observed in the MG. Immunocytochemical analyses of the entire cross-sectional area (CSA) of serial sections of TA muscles stained with anti-neural cell adhesion molecule (NCAM) and various monoclonal antibodies for myosin heavy chain (MHC) isoforms showed respective 65% (P < 0.01) and 28% (P < 0.05) decreases in the number of innervated IIB and IID/X muscle fibres in SOD1 G93A , which paralleled the 60% decrease (P < 0.01) in the force generating capacity of individual fibres. The loss of fast MUs was partially compensated by activity-dependent fast-to-slower fibre type transitions, as determined by increases (P < 0.04) in the CSA and proportion of IIA fibres (from 4% to 14%) and IID/X fibres (from 31% to 39%), and decreases (P < 0.001) in the CSA and proportion of type IIB fibres (from 65% to 44%). We conclude that preferential loss of IIB fibres is incomplete at 60 days of age, and is consistent with a selective albeit gradual loss of FF MUs that is not fully compensated by sprouting of the remaining motoneurons that innervate type IIA or IID/X muscle fibres. Our findings indicate that disease progression in fast-twitch muscles of SOD1 G93A mice involves parallel processes: (1) gradual selective motor axon die-back of the FF motor units that contain large type IIB muscle fibres, and of fatigue-intermediate motor units that innervate type IID/X muscle fibres, and (2) activity-dependent conversion of motor units to those innervated by smaller motor axons innervating type IIA fatigue-resistant muscle fibres.
Muscle & Nerve, 2012
Introduction-Rodent whisking behavior is supported by the buccal and mandibular branches of the facial nerve, a description of how these branches converge and contribute to whisker movement is lacking. Methods-Eight rats underwent isolated transection of either the buccal or mandibular branch and subsequent opposite branch transection. Whisking function was analyzed following both transections. Anatomical measurements, and video recording of stimulation to individual branches, were taken from both facial nerves in 10 rats. Results-Normal to near-normal whisking was demonstrated after isolated branch transection. Following transection of both branches whisking was eliminated. The buccal and mandibular branches form a convergence just proximal to the whisker-pad, named the "distal pes." Distal to this convergence, we identified consistent anatomy that demonstrated cross-innervation. Conclusion-The overlap of efferent supply to the whisker pad must be considered when studying facial nerve regeneration in the rat facial nerve model.
Frontiers in Molecular Neuroscience, 2023
Introduction: The ultimate deficit in amyotrophic lateral sclerosis (ALS) is neuromuscular junction (NMJ) loss, producing permanent paralysis, ultimately in respiratory muscles. However, understanding the functional and structural deficits at NMJs prior to this loss is crucial for therapeutic strategy design. Should early interventions focus on reversing denervation, or supporting largely intact NMJs that are functionally impaired? We therefore determined when functional and structural deficits appeared in diaphragmatic NMJs relative to the onset of hindlimb tremor (the first overt motor symptoms) in vivo in the SOD1-G93A mouse model of ALS. Materials and methods: We employed electrophysiological recording of NMJ postsynaptic potentials for spontaneous and nerve stimulation-evoked responses. This was correlated with fluorescent imaging microscopy of the postsynaptic acetylcholine receptor (AChR) distribution throughout the postnatal developmental timecourse from 2 weeks to early symptomatic ages. Results: Significant reduction in the amplitudes of spontaneous miniature endplate potentials (mEPPs) and evoked EPPs emerged only at early symptomatic ages (in our colony, 18-22 weeks). Reductions in mEPP frequency, number of vesicles per EPP, and EPP rise time were seen earlier, at 16weeks, but this reversed by early symptomatic ages. However, the earliest and most striking impairment was an inability to maintain EPP amplitude during a 20 Hz stimulus train, which appeared 6 weeks before overt in vivo motor symptoms. Despite this, fluorescent α-bungarotoxin labelling revealed no systematic, progressive changes in 11 comprehensive NMJ morphological parameters (area, shape, compactness, number of acetylcholine receptor, AChR, regions, etc.) with disease progression. Rather, while NMJs were largely normally-shaped, from 16 weeks there was a progressive and substantial disruption in AChR concentration and distribution within the NMJ footprint. Discussion: Thus, NMJ functional deficits appear at least 6 weeks before motor symptoms in vivo, while structural deficits occur 4 weeks later, and predominantly within NMJs. These data suggest initial therapies focused on rectifying suboptimal NMJ function could produce effective relief of symptoms of weakness.
Whisker Movements Evoked by Stimulation of Single Motor Neurons in the Facial Nucleus of the Rat
Journal of Neurophysiology, 2008
The lateral facial nucleus is the sole output structure whose neuronal activity leads to whisker movements. To understand how single facial nucleus neurons contribute to whisker movement we combined single-cell stimulation and high-precision whisker tracking. Half of the 44 stimulated neurons gave rise to fast whisker protraction or retraction movement, whereas no stimulation-evoked movements could be detected for the remainder. Direction, speed, and amplitude of evoked movements varied across neurons. Protraction movements were more common than retraction movements ( n = 16 vs. n = 4), had larger amplitudes (1.8 vs. 0.3° for single spike events), and most protraction movements involved only a single whisker, whereas most retraction movements involved multiple whiskers. We found a large range in the amplitude of single spike-evoked whisker movements (0.06–5.6°). Onset of the movement occurred at 7.6 (SD 2.5) ms after the spike and the time to peak deflection was 18.2 (SD 4.3) ms. Ea...
Neurobiology of Disease, 2007
Many patients suffer lifelong disabilities after peripheral nerve injury. Insufficient recovery has been attributed to excessive axonal branching, axonal regrowth to improper targets and polyneuronal reinnervation of motor endplates. We used the rat facial nerve transection/suture model to quantify the effects of mechanical stimulation on the paralyzed whisker musculature. "Manual" stimulation involved briskly stroking the whiskers by hand in a manner that specifically mimicked normal whisker movement. "Environmental" stimulation involved enhanced whisker use as rats encountered objects in an enriched environment. Manual and environmental stimulation were also combined. Videobased motion analysis of vibrissal motor performance showed that daily manual, but not environmental, stimulation for 2 months resulted in full recovery of whisking. Polyneuronal reinnervation of motor endplates was reduced but not misdirected axonal regrowth. Our findings indicate the potential of use-specific training to enhance appropriate functional outcome after peripheral nerve injury and may be useful in a clinical rehabilitation setting.
Partial denervation of the whiskerpad in adult mice: pattern and origin of reinnervation
European Journal of Neuroscience, 1999
We studied sensory organ reinnervation after nerve transection in the mouse whisker-to-barrel pathway. In one set of adult mice, we determined at light microscopy level the number of ®bres reaching the caudal whisker follicles 5, 15, 20, 60, 100 days and 1 year after transection of the sensory nerve of row C. Regenerated ®bres were ®rst detected 15 days post lesionem (p.l.) and myelin ®rst observed at 20 days. Between 60 and 100 days, the number of ®bres stayed at » 80% of the values obtained in control animals. At that time, myelinated ®bres reached only 58% of their number in controls. At the electron microscopy level, these ®bres differ from control ones by a smaller ®bre diameter. The innervation of follicles of adjacent rows was not modi®ed, indicating that follicular reinnervation is row speci®c. We checked this feature by injecting in another set of mice the denervated follicles and the adjacent ones with distinct retrograde tracers 45 days and 1 year after nerve transection. The percentage of double-labelled neurons in the Gasserian ganglion did not increase in experimental animals. This con®rms the absence of colonization of intact follicles by regenerating ®bres and indicates that reinnervation of the whisker follicles takes place by regeneration of the degenerated axons without collateral reinnervation. The companion paper describes the pattern of activation of the barrel cortex relative to the present ®ndings.
Development
The relationship between neuronal death and the formation of patterned connections was studied in the facial neuromuscular system of foetal, neonatal, and adult mice. The facial neuromuscular system was selected because two large, widely separated, facial muscles (the nasolabial and posterior auricular muscles) are innervated by clearly separated partsof the the facial motor nucleus in the adult mouse. The number of motorneurones in the facial nucleus was counted in Nissl-stained sections at different stages of development. Over 6400 neurones were present in the facial nucleus at day 17 p.c. (post-coitum). After day 17 p.c. the number of neurones fell rapidly and only 2000 cells remain in the adult nucleus. This represents a loss of 68%, most of which occurs between days 18 and 20 p.c. Neurones with pyknotic nuclei are seen on day 17 p.c. and are most numerous on day 18 p. c. This leads us to believe that the fall in neurone numbers is due to cell death. Indirect evidence provided b...