Embryonic and paralarval development of the central nervous system of the loliginid squid Sepioteuthis lessoniana

Abstract

The embryonic development of the central nervous system (CNS) in the oval squid Sepioteuthis lessoniana is described. It has three distinct phases: (1) The ganglionic accumulation phase: Ganglionic cell clusters develop by ingression, migration, and accumulation of neuroblasts. (2) The lobe differentiation phase: Ganglia differentiate into lobes. The phase is identified by the beginning of an axogenesis. During this phase, neuropils are first formed in the suboesophageal mass, then in the basal lobe system, and finally in the inferior frontal lobes and the superior frontal-vertical lobe systems. (3) The neuropil increment phase: After the shape of the lobes reached its typical form, neuropil growth occurs, specifically in the vertical lobe. The paralarval central nervous system (CNS) is characterized by neuronal gigantism of the giant fibers and some suboesophageal commissures and connectives. The neuropil formation in the CNS of S. lessoniana occurs somewhat earlier than in Octopus vulgaris, although the principal developmental plan is quite conservative among the other coleoids investigated. Some phylogenetic aspects are discussed based on the similarities in the morphologic organization of their brains.

Expression of serotonin (5-HT) during CNS development of the cephalopod mollusk, Idiosepius notoides

“…These spatiotemporal expression patterns mirror the general trend in cephalopod neurogenesis that the neuropils of the subesophageal mass develop more rapidly than the ones of the supraesophageal mass (Marquis 1989;Shigeno et al 2001aShigeno et al , b, c, 2008Yamamoto et al 2003;Shigeno and Yamamoto 2005;Wollesen et al 2009Wollesen et al , 2010. Besides phylogenetic constraints, this might be due to functional aspects such as increased growth rate of the mantle muscles, which are innervated by the subesophageal mass (Shigeno et al 2001a).…”

FaRP cell distribution in the developing CNS suggests the involvement of FaRPs in all parts of the chromatophore control pathway in Sepia officinalis (Cephalopoda)

“…Embryonic neural territories are first identified as paired structures, either ganglia or cords, which evolve during the development to form the CNS and PNS. Cerebroid, pedal, brachial and visceral ganglia migrate and fuse, forming the complex brain that, together with the optic lobes, constitutes the CNS (Shigeno et al, 2001;Yamamoto et al, 2003;Navet et al, 2009). The PNS is composed of all peripheral ganglia (stellate, buccal, and brachial ganglia) and nerve networks.…”

Mollusca

“…Thus, a signifi cant number of studies, mainly concerned with the analysis of gangliogenesis based on histological sections, exist (e.g., Kölliker 1844 ;Faussek 1901 ;Martin 1965 ;Raven 1966 ;Meister 1972 ;Demian and Yousif 1975 ;Kriegstein 1977 ;Marquis 1989 ;Page 1992a , b ;Lin and Leise 1996 ;Page and Parries 2001 ;Shigeno et al 2001 ). In the gastropods, the ganglia form already in the larva from invaginating or delaminating ectodermal cells (Raven 1966 ;Kandel et al 1981 ;Mescheryakov 1990 ; see Croll 2000 for brief review).…”