NEURONAL SUPERNUMERARY AND DENDRITIC SPROUTING OF THE NUCLEUS AMBIGUUS AFTER CHRONIC ALTERATION OF PERIPHERAL TARGETS IN CATS

Anatomic changes of neuronal profiles in response to chronic alteratio n of peripheral targets were investigated in the nucleus ambiguus (NA) of cats. Unilateral vagal-hypoglossal nerve anastomosis was performed by suturing the transected proximal stump of the vague nerve to the t ransected distal stump of the hypoglossal nerve. After comparing horse radish peroxidase (HRP)-labeled neurons on the ipsilateral operated si de of the NA with the contralateral unoperated NA and the NA following transection and reuniting to the vagus itself, a remarkable ramificat ion and elongation of the dendritic trees was observed in the HRP-posi tive neurons on the ipsilateral NA. Quantitative analysis of neuronal profiles revealed that the number of the medium and large neurons on t he ipsilateral NA was greater than the contralateral NA and the NA fol lowing autologous suturing of the vague. Comparisons of variable dendr itic lengths of the medium and large neurons on the ipsilateral NA rev ealed longer distances and more branches of the tertiary and perisomat ic dendrites than those of the contralateral NA and the NA ipsilateral to autologous reunion. Our results suggest that remarkable sprouting and elongation of the dendritic trees as well as cell supernumerary oc curred in the dominant NA motoneurons ipsilateral to the nerve anastom osis. In conclusion, there Is a trophic influence in the tongue muscul ature, which was retrogradely transported to the NA neurons via the re generating axons and caused the morphological changes in the NA in res ponse to the rerouting of efferents from the vagus nerve to the hypogl ossal nerve to innervate intimate tongue musculature. (C) 1998 Elsevie r Science B.V. All rights reserved.