Development of the trochlear nucleus in quail and comparative study of the trochlear nucleus, nerve, and innervation of the superior oblique muscle in quail, chick, and duck

Abstract

The present study was undertaken to examine the development of the trochlear nucleus in quail and to compare the mature trochlear nucleus, nerve, and their sole target of innervation, the superior oblique muscle, in quail, chick, and duck. Study of the trochlear nucleus in quail from embryonic day 5 through hatching shows a maximum of 1,248 neurons on embryonic day 10 followed by spontaneous degeneration of 40% of the neurons between days 10 and 16. Previous studies have shown that although the initial and final number of neurons is different in chick and duck, the magnitude of trochlear cell loss in both species is about 40%. This study shows the average number of neurons in the nucleus of quail, chick, and duck, 2 weeks post-hatching, to be 658, 743 and 1,459, respectively. Fiber counts in the trochlear nerve from electron micrograph montages at the same period indicated a ratio of about 1:1 between neurons and axons. While a majority of the fibers in these nerves are myelinated, an average of 3-6% of the fibers are unmyelinated. The nucleus in the quail not only contains the smallest number of neurons but it also innervates the smallest muscle in terms of total number of muscle cells and endplates. However, the opposite relationship does not hold true. The nucleus in duck contains the largest number of neurons, yet the largest number of muscle cells and endplates were found in the chick. The ratios between the neurons and muscle cells as well as between neurons and endplates are about the same in quail and duck. These ratios are much higher in the chick, reflecting the relatively small neuron pool destined for a relatively large target. In spite of variations in the number of neurons, muscle fibers, and endplates the average number of endplates per muscle fiber is relatively constant among the three species.

Establishing the trochlear motor axon trajectory: role of the isthmic organiser and Fgf8

“…Trochlear motor neurons develop both within and posterior to the isthmic organiser Previous studies variously reported the location of trochlear motor neuron cell bodies as being within the midbrain, isthmus or within rhombomere 1 (r1) of the hindbrain (Altman and Bayer, 1981;Bubien-Waluszewska, 1981;Lumsden, 1990;Lumsden and Keynes, 1989;Sohal et al, 1985). Fgf8 is expressed at the isthmus and can reproduce all of its patterning activities thereby providing the most useful marker for the isthmic organiser.…”

The Cells that Fill the Bill: Neural Crest and the Evolution of Craniofacial Development

“…The domestic duck has a long history of being included in avian chimeras as a way to study those patterning mechanisms that make embryos morphologically distinct (Waddington, 1930(Waddington, , 1932Hampe, 1957;Zwilling, 1959;Dhouailly, 1967Dhouailly, , 1970Pautou, 1968;Sohal, 1976;Sohal et al, 1985Sohal et al, , 1990Sohal, 1986, 1987). But the combination of Japanese quail (Coturnix coturnix japonica) and White Pekin duck (Anas platyrhynchos) as donors and/or hosts adds value for at least four reasons (Lwigale and Schneider, 2008).…”

Analysis of spontaneous and nerve-evoked calcium transients in intact extraocular muscles in vitro

“…We focused much of our work on chicken, because the avian superior oblique muscle is easier to prepare into nerve-muscle preparations suitable for electrical stimulation and calcium imaging. Detailed information is available about muscle force, number of endplates, motor neurons, and myofibers in chicken EOMs of this age (Sohal et al, 1985; Hatton and von Bartheld, 1999; Croes and von Bartheld, 2005; Baryshnikova et al, 2007; Croes et al, 2007; Li et al, 2010, 2011). We describe two types of spontaneous and nerve-stimulation evoked calcium transients in avian EOMs, and we compare their physiological and pharmacological characteristics with the range of calcium transients previously reported in developing mammalian myotubes in culture (Flucher and Andrews, 1993; Jaimovich et al, 2000; Powell et al, 2001; Eltit et al, 2004; Campbell et al, 2006; Casas et al, 2010).…”