Molecular neuroscienceEarly and transient increase in spontaneous synaptic inputs to the rat facial motoneurons after axotomy in isolated brainstem slices of rats
Section snippets
Unilateral facial nerve axotomy
Our manipulation of animals conformed to the Guiding Principles for the Care and Use of Animals in the Field of Physiological Sciences of the Physiological Society of Japan (1988) and International guiding principles for biomedical research involving animals by the Council for International Organizations of Medical Sciences (1984). Experimental protocol was approved by the Animal Experiments Committee of the Jikei University School of Medicine. All possible efforts were made to minimize the
Identification of facial motoneurons after axotomy in the brain slice
We made unilateral axotomy in 50 rats (P1–P6, n=17; P7–P14, n=33). The brainstem slices were prepared on D1 (68 slices from 36 rats; P1–P6, n=10; P7–P14, n=26), D3 (10 slices from six rats; P1–P6, n=2; P7–P14, n=4), D5 (eight slices from five rats; P1–P6, n=3; P7–P14, n=2) and D7 (three slices from three rats; P1–P6, n=2; P7–P14, n=1). We first confirmed that surviving motoneurons after axotomy could be successfully visualized with IR-DIC optics and were healthy enough that they could undergo
Discussion
The axonal injury of the motoneurons leads to a variety of post-injury morphofunctional events. This is the first study that has analyzed the changes in the synaptic inputs of the motoneurons following section of their axons. The main novel finding of this study is that the amount of excitatory synaptic inputs to the surviving axotomized motoneurons is increased to ∼three-fold of that of the non-axotomized motoneurons at the first day following axotomy, whereas after the fifth day post-injury,
Conclusion
Axonal injury of the motoneurons is likely to result in the synaptic re-organization of the premotor-to-motoneuron synapses. This re-organization might modify the fate of the axotomized motoneurons through modifying excitability of these surviving motoneurons.
Acknowledgments
This work was supported in part by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Nos. 13680902, 15650071, 17023042, 17650116 and 17300123) and Grants for the Research on Health Sciences focusing on Drug Innovation from the Japan Health Sciences Foundation (KH21014) to F.K. The authors thank Dr. Frank Scott Howell (the Sophia University) for scientific and linguistic comments. The expert assistance in the experiments and during preparation of the
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2014, NeuroscienceCitation Excerpt :In agreement with the same principle, but suggesting a pre-synaptic locus of early change, another study reported that synaptic stripping in axotomized motoneurons is preceded by a period of reduced release probability from afferent terminals (Yamada et al., 2008). The notion of a Hebbian model of synapse removal following axotomy is, however, inconsistent with other findings indicating a robust increase in the strength of synaptic inputs from Ia afferents to spinal motoneurons shortly after peripheral nerve injury (Miyata and Yasuda, 1988; Bichler et al., 2007b) or the presence of postsynaptic glutamatergic currents of high frequency and large amplitude in facial motoneurons at an early postaxotomy stage (Ikeda and Kato, 2005). Even with all this information, it is still difficult to define with precision the temporal sequence of changes that occur at both sides of the synapse preceding its elimination in axotomized motoneurons.
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