Development of the commissure of the superior colliculus in the hamster

Abstract

The development of the corpus callosum (CC) and the anterior commissure (CA) is well known in a wide variety of species. No study, however, has described the development of the commissure of the superior colliculus (CSC) from embryonic state to adulthood in mammals. In this study, by using the lipophylic tracer DiI, we investigated the ontogeny of this mesencephalic commissure in the hamster at various ages. The development of axonal terminals, growth cone morphologies, and axons branching were described for the superior colliculus (SC) contralateral to the tracer injection. The first CSC axons cross the midline at embryonic day 11 (E-11) and grow further into the intermediate layers of the contralateral SC between E-12 and E-14. There is little axon growth therein between E-14 and the day of birth (P-0). Growth cones at the tip of these axons adopt complex morphologies at E-12 and progressively simplify until P-0. Pioneer axons are clearly visible between E-14 and P-1. These are followed by other axons progressively more numerous between P-0 and P-5. Axons do not show any branching until P-2. Between P-3 and P-9, the axons progressively arborize in the intermediate layers. Some axons reach the superficial layers at P-5, and they become more numerous around P-11, and only a few axons remain therein by P-21. Myelinated axons appear at P11 and are very dense at P-21. Our results indicate that the CSC follows developmental schemes similar to those of the CC and the AC but that initial axon midline crossing occurs earlier.

The TLC: A Novel Auditory Nucleus of the Mammalian Brain

“…It will be particularly interesting to establish whether TLC neurons receive direct input from commissural SC neurons, most of which participate in the processing of visual information (McIlwain, 1991). The fact that the crossed projections of the SC innervate the most medial regions of the SC (Yamasaki et al, 1984;Rhoades et al, 1986;Behan and Kime, 1996;Chebat et al, 2006) lends support to this possibility. Extending our knowledge of the auditory properties of TLC neurons, determining their responses to light and other sensory modalities, and unraveling the afferent and efferent connections of the nucleus will lead to a much better understanding of its functional significance.…”

Auditory response properties of neurons in the tectal longitudinal column of the rat

“…The TLC is well placed to receive such information, as the nucleus is crossed by fibers in the commissure of the superior colliculus, a complex tract that contains axons from over forty tectal and non-tectal sources (Huerta and Harting, 1984). Although the contribution of each of these crossed projections to the innervation of the TLC remains unknown, the TLC probably receives direct input from commissural SC neurons, whose axons give off collaterals in the vicinity of the midline in both the rat (Yamasaki et al, 1984) and the hamster (Rhoades et al, 1986; Chebat et al, 2006). …”

Regenerating optic axons restore topography after incomplete optic nerve injury

“…In the context of the present study, intact RGC axons following incomplete injury might be viewed as playing an equivalent role to that of pioneer axons, for which there is considerable evidence during development (Key and St John, 2002;Nural and Mastick, 2004;Chebat et al, 2006). In zebrafish, developing RGC growth cones in the optic nerve contact more mature pioneer axons arising from adjacent RGCs (Bodick and Levinthal, 1980).…”