Localization of motoneurons innervating the extraocular muscles in salamandra salamandra L. (amphibia, urodela)

Abstract

The central innervation patterns of the extraocular muscles were investigated in the European fire salamander Salamandra salamandra L. by means of the horseradish peroxidase method. The ipsilateral portion of the nucleus nervi oculomotorii, which is located in the rostral ventral tegmentum mesencephali, supplies the musculi recti inferior and medialis and the musculus obliquus inferior without a clear somatotopic representation of the motoneurons. The musculus rectus superior is innervated mainly by a contralateral portion of this nucleus. A definite nucleus Edinger-Westphal could not be recognized. The nucleus nervi trochlearis, which rostrally joins the nucleus nervi oculomotorii with a gap of only about 40 micron between the nuclei, is situated completely contralateral to the musculus obliquus superior supplied by it. The nucleus nervi abducentis, innervating the musculus rectus lateralis, and the nucleus accessorius nervi abducentis, supplying the musculus retractor bulbi, are found in the ipsilateral medulla oblongata and exhibit a large rostrocaudal extension from the eighth cranial nerve to the first root of the vagus nerve. Dendrites of the nucleus nervi oculumotorii and of the nucleus accessorius nervi abducentis extend into neuropil areas receiving primary sensory afferents.

Innervation of the medial rectus muscle in the ratfish,Hydrolagus colliei

“…The distribution of oculomotor and trochlear motoneurons in ratfish is similar to what has been described for elasmobranchs (Rosiles and Leonard, 1980;Graf and Brunken, 1984) and other jawed-vertebrates (Matesz and Székely, 1977;Luiten and Dijkstra-de Vlieger, 1978;Heaton and Wayne, 1983;Porter et al, 1983;Graf and McGurk, 1985;Naujoks-Manteuffel et al, 1986;Szabo et al, 1987). The oculomotor and trochlear motoneurons are, for the most part, closely associated with the MLF.…”

“…In contrast, in ratfish, as in dogfish sharks (Graf and Brunken, 1984) and other jawed-vertebrates (Leonard and Willis, 1979;Glicksman, 1980;Porter et al, 1983;Graf and McGurk, 1985;Naujoks-Manteuffel et al, 1986), the trochlear motoneurons are distributed within the periventricular gray, dorso-medial to the MLF. Furthermore, the trochlear motoneurons in ratfish project exclusively to the contralateral side.…”

“…In contrast to the condition in cartilaginous fishes, the medial rectus muscle in osteichthyans (bony fishes and tetrapods) is innervated by an ipsilateral motoneuron pool (Luiten and Dijkstra-de Vlieger, 1978;Porter et al, 1983;Heaton and Wayne, 1983;Graf and McGurk, 1985;Naujoks-Manteuffel et al, 1986;Szabo et al, 1987;Evinger et al, 1987). The medial rectus muscles in these two lineages also differ in their peripheral innervation pattern (Nishi, 1938;Isomura, 1981), and in the developmental anlage from which they originate (Neal, 1918;Jacob et al, 1984).…”

“…In lamprey (Finger and Rovainen, 1979;Fritzsch et al, 1990), carp (Luiten and Dijkstra-de Vlieger, 1978), goldfish (Graf and McGurk, 1985), lungfish (von Bartheld, 1992), some amphibians (Fritzsch and Sonntag, 1987), and mammals (Gacek, 1974;Labandeira Garcia et al, 1983;Miyazaki, 1985;Murphy et al, 1986), the trochlear nucleus is composed of both ipsiand contralaterally projecting neurons. However, in salamanders (Naujoks-Manteuffel et al, 1986), stargazers (Leonard and Willis, 1979), the weakly electric fish Gnathonemus petersii (Szabo et al, 1987), and cartilaginous fish, the trochlear motoneurons are reported to innervate only the contralateral superior oblique muscle. Whether this variation is real or merely reflects differences in experimental techniques is unclear.…”

“…The innervation pattern of these muscles has been studied by using modern neuroanatomical methods in representatives of the major jawedvertebrate lineages (Matesz and Székely, 1977;Luiten and Dijkstra-de Vlieger, 1978;Rosiles and Leonard, 1980;Heaton and Wayne, 1983;Labandeira et al, 1983;Porter et al, 1983;Graf and Brunken, 1984;Graf and McGurk, 1985;Graf and Baker, 1985;Naujoks-Manteuffel et al, 1986;Evinger et al, 1987;Szabo et al, 1987;BarbasHenry and Lohman, 1988;von Bartheld, 1992). These studies have shown that the six eye muscles are innervated by motoneurons distributed in three motonuclei: The oculomotor nucleus innervates the superior, inferior, and medial recti, as well as the inferior oblique.…”