Analysis Tools
mortality/aging
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• most die by P1, although a few survive into the first week
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behavior/neurological
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• do not orient toward a stimulus (stroking under the chin) and do not open mouth except for an occasional gasp
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• homozygotes inhale milk instead of swallowing it when manually fed
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• unresponsive to tactile stimuli in vibrissae area
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nervous system
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• up to 70% reduction in density of facial motor nucleus
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• at P1, homozygotes display deficient innervation in the vestibular and cochlear sensory epithelia
• in the utricular macula nerve fibers have reached the base of the hair cells, but are degenerating and retracting from their targets
• no innervation is observed in the sensory epithelia of the ampullary cristae
• at P1, vestibular nerves lack membrane vesicles and contain residual synaptic plates at their nerve endings; degenerating nerve fibers, empty perineural sheets and lack of myelination are observed
• as shown at E16.5, some vestibular and cochlear fibres initially reach their peripheral targets but fail to maintain innervation and thus degenerate
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• at P1, homozygotes fail to innervate the OHCs of the cochlea
• the sensory epithelium containing OHCs is generally devoid of nerve fibers, although retracting neurites with residual synaptic contacts are occasionally detected
• in contrast, the innervation pattern of IHCs appears normal
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• reduction in motor neuron number in lumbar region only (L2-L5)
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• at P1, cochlear ganglia display areas of reduced cell density and large extracellular spaces, albeit to a lesser extent than vestibular ganglia
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• at P1, a 11% and 15% reduction in cochlear ganglion size and neuron number is, respectively, observed
• small-sized type II neurons (innervating OHCs) are preferentially lost (77% reduction), whereas larged-sized type I neurons (innervating IHCs) remain unaffected
• no significant changes in cochlear ganglion size or neuron number are noted at E14.5 or E18.5
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• about 40% reduction in the number of ganglion neurons, with the largest decrease in the anterior half of the ganglion, however size of neurons is normal
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• at P1, vestibular ganglia display areas of reduced cell density and large extracellular spaces
• at this stage, cells with nuclei surrounded by a very small amount of cytoplasm are abundant
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• at E18.5, a 38% reduction in vestibular neuron number is observed
• by P1, a 57% reduction in vestibular ganglion size and neuron number is observed
• however, no significant changes in vestibular ganglion size or neuron number are noted at E14.5
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• about 30% reduction in the number of neurons in the dorsal root ganglia from thoracic level 12 to the lumbar level 3 regions of the spinal cord
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hearing/vestibular/ear
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• in contrast, the innervation pattern of IHCs appears normal
• at P1, homozygotes fail to innervate the OHCs of the cochlea
• the sensory epithelium containing OHCs is generally devoid of nerve fibers, although retracting neurites with residual synaptic contacts are occasionally detected
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• at P1, no innervation is observed in the sensory epithelia of the ampullary cristae
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• at P1, nerve fibers have reached the base of hair cells in the utricular maculae but appear to degenerate and retract from their targets
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