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<em>In Vitro</em> Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats

Dysfunction of the colonic sensory nerves has been implicated in the pathophysiology of several common conditions, including functional and inflammatory ...

Shanghai Jiaotong University School of Medicine

Oculomotor nerve injury is a common complication of cranial trauma and craniotomy. For a long time, it has been generally considered that the oculomotor nerve is unable to regenerate and recover functionally after injury. With the development of neuroradiology, microsurgery and neurohistology, it has been reported that the injured oculomotor nerve could be repaired by operation. However, the mechanisms of neural regeneration of the injured oculomotor nerve remain obscure. Therefore, by investigating the differentiation of the newborn nerve cells in oculomotor nuclear after oculomotor nerve injury, the mechanisms of the neural regeneration of the injured oculomotor nerve was studied in the present paper. After animal model establishment, we found that the function of the injured oculomotor nerve could recover at some degree without treatment, at fourth week after the nerve injury. This result confirms that the injured oculomotor nerve per se has the potential to regenerate and repair. At the present study, by BredU stain, BrdU labeling cells were observed in oculomotor nuclear at the fourth week post-operatively. It indicated that the oculomotor nuclear per se has the ability of generating the cells, which will regenerate and differentiate after the nerve injury, without stimulation by exogenous agents. Immunofluorescence double staining was used in this study to show the differentiation of the newborn cells in oculomotor nuclear after oculomotor nerve injury. It is found that they could differentiate into neural progenitor cells, neuronal cells and neuroglial cells. It is suggested that the different differentiation of cells may play a role in the nerve regeneration procedure.

The differentiation of the newborn nerve cells in oculomotor nuclear after oculomotor nerve injury.

Technical developments have extensively promoted experimental and clinical studies on cranial nerve regeneration, but intracranial nerve recovery is still an unexplored research area compared to peripheral nerve repair. In this study, we researched whether neurogenesis occurs in adult oculomotor (OMN) and Edinger-Westphal nucleus (EWN) or not after oculomotor nerve injury. To assess cell proliferation in response to unilateral oculomotor nerve crush (ONC) in adult beagle dog, repetitive 5-bromo-2'-deoxyuridine (BrdU) intravenous injections were performed during 3 or 7 days before the dogs were euthanized 2 h after the last injection on days 3, 7, 14, and 28 post-ONC. The proliferating cell types were investigated with three cell phenotypic markers and confocal microscopy on serial sections throughout the whole extent of OMN and EWN. BrdU-positive nuclei were detected in bilateral OMNs and EWNs from 3 to 28 days after ONC with the peak value at 3 days. Confocal analysis revealed that partial BrdU-positive cells colocalized with nestin or βIII-tubulin or GFAP, and the number of every kind of double-labeled cell maintained an increased tendency from 3 to 28 days post-ONC. Neither single-labeled BrdU-positive nuclei nor double-labeled cells were detected in the subependymal layer of cerebral aqueduct (SELCA) of all unilateral ONC dogs; also, they were not observed in the OMNs, EWNs, and SELCA of intact and sham-operated dog. These findings demonstrate that ONC can trigger continual mitotic activity, proliferation of NSCs, neurogenesis, and astrogliogenesis in the OMN and EWN of adult dogs.

Oculomotor nerve injury induces nuerogenesis in the oculomotor and Edinger-Westphal nucleus of adult dog.

The oculomotor nerve can regenerate anatomically and histologically after injury; however, the degree of functional recovery of extraocular muscles and the pupil sphincter muscle was not satisfactory. Electrostimulation was one potential intervention that was increasingly being studied for use in nerve injury settings. However, the effect of electrostimulation on regeneration of the injured oculomotor nerve was still obscure. In this study, we studied the effects of electrostimulation on neural regeneration in terms of neurofunction, myoelectrophysiology, neuroanatomy, and neurohistology after oculomotor nerve injury and found that electrostimulation on the injured oculomotor nerve enhanced the speed and final level of its functional and electrophysiological recovery, promoted neural regeneration, and enhanced the selectivity and specificity of reinnervation of the regenerated neuron, the conformity among the electrophysiological and functional recovery of extraocular muscles, and neural regeneration, and that the function of extraocular muscles recovered slower than electrophysiology. Thus, we speculated that electrostimulation on the injured oculomotor nerve produced a marked effect on all phases of neural regeneration including neuronal survival, sprout formation, axonal elongation, target reconnection, and synaptogenesis. We think that neural electrostimulation can be used in oculomotor nerve injury.

Experimental study on the effect of electrostimulation on neural regeneration after oculomotor nerve injury.

This study describes a method that not only generates an automatic and standardized crush injury in the skull base, but also provides investigators with the option to choose from a range of varying pressure levels. We designed an automatic, non-serrated forceps that exerts a varying force of 0 to 100 g and lasts for a defined period of 0 to 60 seconds. This device was then used to generate a crush injury to the right oculomotor nerve of dogs with a force of 10 g for 15 seconds, resulting in a deficit in the pupil-light reflex and ptosis. Further testing of our model with Toluidine-blue staining demonstrated that, at 2 weeks post-surgery disordered oculomotor nerve fibers, axonal loss, and a thinner than normal myelin sheath were visible. Electrophysiological examination showed occasional spontaneous potentials. Together, these data verified that the model for oculomotor nerve injury was successful, and that the forceps we designed can be used to establish standard mechanical injury models of peripheral nerves.

Youqiang Meng

Hongqiao International Institute of Medical Research,
Tongren Hospital and Department of Physiology,
Faculty of Basic Medical Sciences,
Hongqiao International Institute of Medical Research, Tongren Hospital and Department of Physiology, Faculty of Basic Medical Sciences

Shanghai Jiaotong University School of Medicine

In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats