Early Development of the Cranial Nerves in a Primitive Vertebrate, the Sea Lamprey, Petromyzon Marinus L.~!2008-08-19~!2008-09-30~!2008-10-24~!

Abstract

The early development of the cranial nerves of the sea lamprey, Petromyzon marinus L., was studied in embryos and early prolarvae by immunocytochemical techniques with the marker for post-mitotic neurons acetylatedtubulin. The trigeminal and facial nerves were first observed in embryos 9 days post fertilisation. The glossopharyngeal and vagal nerves appeared later, which indicates a rostrocaudal gradient in differentiation of branchiomeric nerves. The anterior and posterior lateral line, octaval and hypoglossal nerves also appeared in early developmental stages, but the ocular motor nerves were not observed in prolarvae. The present results indicate that, in comparison with cranial nerves and ganglia organisation reported in larval and adult lampreys, organisational changes occur in the cranial nerves between the prolarval and larval stages. One important change is the disappearance of the pharyngeal branch of the facial nerve, which was not previously reported to be present in larval and adult lampreys, whereas it had been observed in earlier developmental stages. Comparison of the present results with those from studies carried out in other vertebrate species, including the Japanese lamprey, suggests that the developmental pattern of the cranial nerves is conserved in agnathans and differs from that reported in other vertebrate groups. As maturation of lamprey eyes and extraocular muscles is completed at metamorphosis, there appears to be a correlation between the late development of eye-related cranial nerves in lampreys and the anatomical structures that they innervate.

A vesicular glutamate transporter in lampreys: cDNA cloning and early expression in the nervous system

“…Fertilization was conducted in the laboratory and embryos kept in fresh oxygenated water at 15 8C, until the desired stages were obtained. Embryos were staged according to the table established by Tahara (1988) for Lampetra reissneri [see Barreiro-Iglesias et al (2008b) for a table of equivalences with the stages of Piavis (1971) for P. marinus]. Embryos and prolarvae were fixed in 4% paraformaldehyde in phosphate-buffered saline during 12-36 h at 4 8C, dehydrated in methanol and stored in 100% methanol at À20 8C before use.…”

“…Both also led to strictly superimposable patterns at each stage studied. We identified the anatomical regions of the brain and the cranial ganglia of the sea lamprey using the nomenclature of previous studies on the development of the first tracts (Barreiro-Iglesias et al, 2008a) and cranial ganglia (Barreiro-Iglesias et al, 2008b).…”

“…In these embryos, two transverse ventricular sulci, the anterior and posterior intraencephalic sulci separate the diencephalic/mesencephalic primordium from the primordia of the telencephalon and rhombencephalon, respectively. The first neuronal populations (Villar-Cheda et al, 2006;Barreiro-Iglesias et al, 2008a) and cranial nerve ganglia (Barreiro-Iglesias et al, 2008b) become recognizable during late embryonic periods.…”

Doublecortin is expressed in trigeminal motoneurons that innervate the velar musculature of lampreys: considerations on the evolution and development of the trigeminal system

“…The topography of motoneuron subgroups innervating different jaw-closing and jaw-opening muscles is well known from experimental studies in mammals (Mizuno et al 1975(Mizuno et al , 1981Limwongse and DeSantis 1977;Lynch 1985), but there are no known molecular markers that allow differentiation among subgroups of trigeminal motoneurons. The lamprey trigeminal nerve is also comprised of three principal branches: the ophthalmic, maxillary, and mandibular (or velar) nerves (Kuratani et al 1997;Barreiro-Iglesias et al 2008a). The ophthalmic nerve is sensory and has a separate ganglion similar to the profundal ganglion found in some gnathostomes.…”

“…The ophthalmic nerve is sensory and has a separate ganglion similar to the profundal ganglion found in some gnathostomes. However, the maxillary and mandibular (velar) branches are mixed in lamprey, and the motor nucleus innervates the prebranchial muscles of the upper and lower lip and the velum in ammocoetes and their derivatives in adults (Johnston 1905;Hardisty and Rovainen 1982;Koyama et al 1987;Kuratani et al 1997;Barreiro-Iglesias et al 2008a). The homology of the maxillary branch of lampreys in relation to that of gnathostomes is not clear because it contains motor fibers, whereas in gnathostomes trigeminal motor fibers are restricted to the mandibular branch (Song and Boord 1993).…”