Morphology Of Experimentally Denervated And Reinnervated Guinea Pigs Facial Nerve And Facial Muscles

IntroductionA motor neuron and the skeletal muscles controled by the neuron constitute a motor unit . Each part of the motor unit is important for the unit and the integrality of the motor unit's structure is the foundation of its physical function . When the integrality of the motor unit has been destroyed , function of the motor unit will be obstructed or losed .Trauma to a peripheral nerve is one of the reasons that the integrality of the motor unit has been destroyed . Facial nerve is one of the easiest destroyed cranial nerve for the reason of anatomy . Clinical doctors are concerned about the recovery of facial nerve function following injury . The experimental research of the facial nerve injury and recovery develops abroad which provide theory foundation for repairing the injuried facial nerve in clinic .Contrary to denervating processes in peripheral neuropathies of the limb muscles , which mostly start insidiously and are generally not recognized at their beginning , the precise time of onset in facial palsy is usually known within a few hours . This occurrence renders facial muscle useful when investigating den-ervation and reinnercation .Motor end plate ( MEP) is a special area in the middle of motor neuron end axon and the skeletal muscle , or we call it neuromuscular junction , is the key part of skeletal muscle contract brought by nerve system . It is useful for the diagnosis of neuromuscular disease and the selection of treatment occasion and the prognosis of the muscle in clinic , to study the morphology and structure of the MEP .We set up the animal model that its facial nerve injuried in different degree, observe the eye - branch and mouth - branch of facial nerve and facial muscle and their neuromuscular junction by transmissional electron microscope . We discuss the pathology of muscle and neuromuscular junction by succinate dehy-drogenase (SDH) and acetylcholinesterase(AchE) histocytochemistry methods when the facial nerve was injured. We want to obtain the useful information to help facial nerve reconstruction of the change of pathology of different nerve and muscle and MEP when the facial nerve was injured in different degree . We want to provide the experimental evidence for the rationality of part evaluating system of facial palsy .Materials and methodsThe animal model was set up in three groups that the right facial nerve was resected and compressed for 15 seconds and 30 seconds respectively in 30 guinea - pigs . At two sequential intervals of 1 week and 1 month , the eye - branch and mouth - branch of facial nerve and orbicularis oculi muscle (M. oculi) and orbicularis oscular muscle( M. oscular) were excised on both sides and tested as follows :1. we discuss the pathological changes on both branches of facial nerve and the difference between them by light microscope (LM) in half-thin section and by electron miproscope (EM) in ultrathin section when the facial nerve were in-juried .2. we analyse the pathological changes of M. oculi and M. oscular by SDH staining in LM and EM , discuss the relationship among SDH activity , muscular types and devervation .3. we analyse the pathological changes of MEP in M. oculi and M. oscular by AchE staining in LM and EM , discuss the relationship among AchE activity , muscular species and types .Results1. To calculate the diameter and observe the morphology of the eye - branchand mouth - branch of facial nerve byLM in half - thin section.In normal , the diameter of the eye - branch is bigger than that of mouth -branch . When the facial nerve is injuried for 1 week , the diameter of facial nerve become smaller , the diameter of the eye - branch is bigger than that of mouth - branch always . When the facial nerve is injuried for 1 month , in the group of 15s the diameter of mouth - branch of facial nerve become bigger and near normal , but the eye - branch recover badly . In the group of 1 month 30s , neither eye - branch nor mouth - branch of facial nerve recover apparently .2. To compare the ultrastructure of eye - branch of facial nerve with mouth - branch in EM in different degree of compression .When the facial nerve is injuried for 1 week , the ultrastructure damage of eye - branch and mouth - branch of facial nerve is badly in EM , 15s <30s < excision group . When the facial nerve is injuried for 1 month , the function of facial nerve recover in certain extent , the ultrastructure damage of eye - branch and mouth - branch of facial nerve is alleviated in EM , 15s lweek > 15si month , 30slweek >30s 1 month , eye -branch > mouth -branch , mouth -branch is easier to recover than eye - branch . In the group of excision , the terminal of nerval axon hasnt recover a little , the damage degree becomes worse .3. To measure the ratio of type I and type II in M. oculi and M. oscular In normal mimic muscles , the ratio of type I is 29.51% and the type II is70.49% in M. oculi , there has type II 100% only in M. oscular . When the facial nerve is injuried for 1 week , type I becomes fewer and type II becomes more . When the facial nerve is injuried for 1 month , following the function of facial nerve recover in certain extent , type I becomes mroe and type II becomes fewer .4. To measure the SDH activity of type I and type II in M. oculi and M. oscularWhen the facial nerve is injuried for 1 week , the SDH activity decreases of M. oculi and M. oscular , excision group < 30s < 15s , both type I and type II myofiber become atrophy , and type II myofiber become severer atrophy , type I and type II myofiber can be distinguished apparently . When the facial nerve is injuried for 1 month , the SDH activity recover gradually , the type of excisiongroup becomes faintness , the type of 15s and 30s group can be distinguished on the whole .5. To compare the ultrastructure change of M. oculi and M. oscularIn EM , in normal group , SDH positive outcome is high electronic dense granule which locate in inner and outer membrane and middle cavity of the membrane of the mitochondria . When the facial nerve is injuried for 1 week , the mitochondria ultrastructure has been destroyed , SDH positive granule become sparseness , the degree of injury : excision group >30s > 15s . When the facial nerve is injuried for 1 month , following the function of facial nerve recover in certain extent , the mitochondria ultrastructure and SDH positive granule become recovered partially , 15s > 30s .6. To observe the MEP morphology and analyse the AchE activityIn normal group , the AchE activity in M. oculi and M. oscular is similar , When the facial nerve is injuried for 1 week , the AchE activity in M. oculi and M. oscular hasnt changed apparently . When the facial nerve is injuried for 1 month , the AchE activity in M. oscular hasnl changed apparently all the same , however , it has changed in M. oculi , excision group <30s < 15s .7. To observe the MEP ultrastructure in EMIn EM , in normal group , the junctional fold is expanse , AchE positive outcome is high electronic dense granule which locate in anterior and posterior membrane of the synapse . When the facial nerve is injuried for 1 week , posterior membrane of the synapse and motor nerve ending become atrophy , primary synaptic fold and secondary synaptic fold become shallow , the MEP structure of M. oculi and M. oscular is similar . When the facial nerve is injuried for 1 month , in excision group , M. oscular primary synaptic, fold and secondary synaptic fold become shallower continually . In group of 15s and 30s , M. oscular primary synaptic cleft is similar to normal . In the group of 30s and excision , M. oculi primary synaptic fold and secondary synaptic fold become shallower continually , a number of the secondary synaptic fold disappear .