Different astroglial reaction between the vagal dorsal motor nucleus and nucleus ambiguus following vagal-hypoglossal nerve anastomosis in cats

The dorsal motor nucleus of the vague (DMV) and nucleus ambiguus (NA) were both traced with horseradish peroxidase (HRP) retrograde labelling techniqu e after vagal-hypoglossal nerve anastomosis (VHA). By light microscopy, rei nnervation of the new target, viz. tongue skeletal musculature, by DMV and NA was established at 22 days postoperation (dpo) as shown by the neuronal labelling with HRP. Ultrastructurally, signs of retrograde degeneration occ urred in some DMV and NA neurons between 3 and 25 days after VHA. The incid ence of darkened dendrites. an early sign of dendritic loss, was more commo n in the DMV compared to the NA. Accompanying the neuronal alteration were drastic astrocytic reactions in the DMV. but not in the NA. Between 3 and 7 dpo, the astrocytes in the DMV showed extensively hypertrophied processes and by 22 dpo, the somata and dendrites of HRP-labelled DMV neurons, but no t NA's, appeared to be delineated by the increased lamellar astrocytic proc esses. Such a feature was sustained throughout the remaining postoperative intervals up to 500 dpo. It is concluded that the DMV motoneurons being aut onomic in nature are probably not conducive to the newly acquired target or gan. Hence, the insulation of the regenerating DMV motoneurons by the astro glial ensheathment would be vital in the neuronal remodelling and reconstru ction of the vagal-hypoglossal pathway. (C) 2000 Elsevier Science B.V. All rights reserved.