Branchiogenic motoneurons innervating facial, masticatory, and esophageal muscles show aberrant distribution in the reeler‐phenotype mutant rat, Shaking Rat Kawasaki

Abstract

Shaking Rat Kawasaki (SRK) is an autosomal recessive mutant rat that is characterized by cerebellar ataxia. Although previous studies indicated many points of similarity between this mutant rat and the reeler mouse, nonlaminated structures such as the facial nucleus have not been studied in this mutant rat. Nissl-stained sections through the brainstem showed that the cytoarchitecture of the facial, motor trigeminal, and ambiguus nuclei was abnormal in SRK, especially in the lateral cell group of the facial nucleus and the compact formation of the ambiguus nucleus. To examine whether orofacial motoneurons are also malpositioned in the SRK rat, horseradish peroxidase (HRP) was injected into the facial, masticatory, and abdominal esophageal muscles of the SRK rats and normal controls to label facial, trigeminal, and ambiguus motoneurons, respectively. HRP-labeled facial, trigeminal, and ambiguus motoneurons of the SRK rat were distributed more widely than those of their normal counterparts, as in the case of the reeler mouse, with the one exception that labeled facial motoneurons innervating the nasolabial muscle were distributed more widely in the ventrolateral-to-dorsomedial direction in comparison with those of the reeler mutant. These data demonstrate that nonlaminated structures in the brainstem of the SRK rat are affected severely, as is the case in the reeler mutant mouse.

Ambiguus motoneurons innervating laryngeal and esophageal muscles are malpositioned in the Reelin-deficient mutant rat, Shaking Rat Kawasaki

“…Our previous studies demonstrated that ambiguus motoneurons innervating the subdiaphragmatic esophagus of Reelin -deficient animals, reeler and SRK , are more widely distributed compared with their normal counterparts [11,12]. The present study has confirmed that ambiguus motoneurons innervating laryngeal and esophageal muscles of the SRK rats are not only located in the ambiguus nucleus, but also scattered more widely in an arch running between the floor of the fourth ventricle.…”

“…Of these four components, only the compact formation is recognized in the adult SRK rat [12], and the boundaries of other subnuclei were blurred in this mutant rat due to the displacement of laryngeal and esophageal motoneurons. Furthermore, these subnuclear structures of young pups could not be clearly demarcated even in the normal P21 rat.…”

“…The motor trigeminal, facial, and ambiguus nuclei form a single longitudinal column consisting of branchial motoneurons with a rostral-to-caudal cytogenetic gradient [20]. Among these three branchial motor nuclei, the cytoarchitecture of the motor trigeminal nucleus is affected the least and the cytoarchitecture of the ambiguus nucleus is affected most, implying that migration of late-forming branchial motoneurons is affected more severely than the migration of early-forming ones [12].…”

“…In the rat, the esophageal motor neurons are exclusively located in the compact formation [12,15,17,19]. The cricothyroid motoneurons are in the semi-compact formation ventral to the compact formation, and the thyroarytenoid and the posterior cricoarytenoid motoneurons are located in the loose formation [15, 17 Á19].…”

“…Previous studies using retrograde tracing methods demonstrated clearly that ambiguus motoneurons innervating the subdiaphragmatic esophageal muscle are dislocated both in the reeler [11] and SRK [12]. However, it remains obscure whether musculotopic arrangements within the ambiguus nucleus are preserved or not.…”