Organization of the six motor nuclei innervating the ocular muscles in lamprey

Abstract

The topography of motoneurons supplying each of the six ocular muscles of the lamprey, Lampetra fluviatilis, was studied by selective application of HRP to the cut nerves of identified muscles. In addition, the distributions of motoneuron populations to both eyes were studied simultaneously with fluorescein and rhodamine coupled dextran-amines (FDA and RDA) applied to cut ocular muscle nerves of either side. The motoneuron pool of the caudal oblique muscle is represented bilaterally in the trochlear (N IV) motor nucleus. The dorsal rectus muscle is innervated from a contralateral group of oculomotor (N III) motoneurons and the remaining four muscles exclusively from the ipsilateral side (N III and N VI). The inferior and posterior rectus muscles are both innervated by the abducens nerve. In contrast to all jawed vertebrates, only three eye muscles (the dorsal rectus, rostral rectus, and rostral oblique) are innervated by the oculomotor nerve in lampreys (N III). Lampreys have a motor nucleus similar to the accessory abducens nucleus previously described only in tetrapods. They lack the muscle homologous to the nasal rectus muscle of elasmobranchs and the medial rectus muscle of osteognathostomes. The distribution of the dendrites of different groups of motoneurons was studied and is considered in relation to inputs from tectum and the different cranial nerves.

Number and arrangement of extraocular muscles in primitive gnathostomes: evidence from extinct placoderm fishes

“…The innervation pattern by three cranial nerves is also consistent among extant vertebrates ( Fritzsch et al 1990). Nerve 4 (trochlearis) innervates one extraocular muscle (superior or posterior oblique; table 1).…”

“…Nerve 6 (abducens) innervates one muscle (external rectus) in chondrichthyan and osteichthyan fishes, but two muscles in the lamprey, and in most tetrapods (in the latter assumed secondary; see below). Possible partial homologies between agnathans and gnathostomes ( Fritzsch et al 1990) make direct correspondence uncertain. The remaining extraocular muscles (three in the lamprey and four in gnathostomes) are innervated by nerve 3 (oculomotorius).…”

Tectal Control of Locomotion, Steering, and Eye Movements in Lamprey

“…Little is known about tectal efferents regarding eye movements in lamprey, but eye muscles and their motor nuclei are organized in a similar way to that of other vertebrates (Fritzsch et al 1990). In goldfish, the output from optic tectum is channeled to the different eye and trunk motor nuclei by a horizontal and a vertical gaze center located in the mesencephalic reticular formation [Á ngeles Luque et al 2005;Fig. 14, blue arrow (1)].…”

Development of vestibular afferent projections into the hindbrain and their central targets

“…Overall, the wiring of the vestibular-ocular and vestibular-spinal projections seems to be extraordinarily conserved among vertebrates. However, some additional new tracts may have formed in jawed vertebrates and elasmobranches may have a reduction of second order projections owing to the simpler wiring diagram of vestibulo-ocular interactions [29,45,49].…”