Ciliated Sensory Cells in Amphioxus (Branchiostoma)

Abstract

Various workers during the past century have figured sensory cells bearing cilia amongst the ordinary non-ciliated epidermal cells of the body surface. Similar sensory cells were also found on the buccal cirrhi, and on the velar tentacles at the entry to the atrium. This earlier work at the light microscope level was summarized by Franz (1923) in his excellent review. More recently Schulte & Riehl (1977) have re-examined the innervation of the oral region and buccal cirrhi at the ultrastructural level, and observed two types of sensory cell in these regions, distinguished by their apical structure. They suggest that these are both secondary sensory neurons (as Franz had previously surmised), but their figures hardly make this suggestion convincing. In this note we show that there is probably only a single type of sensory cell amongst the epidermal cells of the body surface and buccal cirrhi; that it synapses at its base with incoming axons of central cells, and that a different type is indeed found in amphioxus, but only in the velar tentacles.

Distribution of GABA immunoreactivity in the central and peripheral nervous system of amphioxus (Branchiostoma lanceolatum pallas)

“…The presence of ciliated cells in the epidermis and atrial cavity of amphioxus has been described previously (Bone, 1960b;Bone and Best, 1978;Baatrup, 1981), although they have been interpreted in very different ways. In the atrial region the ciliated cells lack an axon and are contacted at their basal pole by a nerve fiber (Bone and Best, 1978), whereas those of the rostral epidermis bear an axon-like process (Baatrup, 1981). Our immunocytochemical results confirm that ciliated cells of the rostral epidermis have an axon, as suggested by Baatrup (1981), and indicate that many of them are GABA-ir and that their distribution is similar at the two ends of the body.…”

“…Our immunocytochemical results confirm that ciliated cells of the rostral epidermis have an axon, as suggested by Baatrup (1981), and indicate that many of them are GABA-ir and that their distribution is similar at the two ends of the body. It has been suggested that ciliated cells are either mechanoreceptors (Bone and Best, 1978) or chemoreceptors (Schulte and Riehl, 1977;Baatrup, 1981). Since some amphioxus apical receptors are GABAergic, they might inhibit locomotion.…”

“…The remarkable simplicity of arrangement of the amphioxus nervous system is thought to be primitive (Bone, 1960a). Most of our knowledge of the morphology of the amphioxus nervous system is based on light microscopic studies with classical neurohistological methods (Rohde, 1888;Retzius, 1891;Hesse, 1898;Joseph, 1904;Stendell, 1914;Bone, 1960a), although some authors have investigated the ultrastructure of the brain vesicle (Welsch, 1968;Meves, 1973;Anadón, 1976;Obermü ller-Wilén, 1976, 1979Obermü ller-Wilén and van Veen, 1981;Watanabe and Yoshida, 1986;Ruiz and Anadón, 1991b,c;Lacalli et al, 1994;Lacalli, 1996a), the spinal cord (Eakin and Westfall, 1962;Flood, 1966Flood, , 1968Guthrie, 1975;Vigh-Teichmann and Vigh, 1983;Anadón, 1989, 1991a,c), and peripheral nerves and sensory cells (Peters, 1963;Bone and Best, 1978;Baatrup, 1981Baatrup, , 1982. Recent ultrastructural studies performed in early larvae (Lacalli et al, 1994;Lacalli, 1996a,b), together with studies of the expression in the neural tube of genes implicated in the control of the axial patterning during embryonic development (Holland et al, 1992Holland, 1996;Holland and García-Ferná ndez, 1996), have provided new landmarks that facilitate comparison of the regions of the rostral nerve cord of amphioxus with the main regions of the vertebrate brain (Lacalli, 1996b).…”

Characterization of novel GPCR gene coding locus in amphioxus genome: Gene structure, expression, and phylogenetic analysis with implications for its involvement in chemoreception

“…Although the sensory cells of the peripheral nervous system of amphioxus have been studied extensively by microscopy (Frantz, 1923;Schulte and Riehl, 1977;Bone and Best, 1978;Baatrup, 1981Baatrup, , 1982Lacalli and Hou, 1999;, immunostaining (Yasui et al, 1998;Kaji et al, 2001), cell labeling and axon tracing by DiI (Holland and Yu, 2002), and gene expression Mazet et al, 2004), it is not known conclusively whether they are mechanosensory or chemosensory cells.…”

Novel, secondary sensory cell organ in ascidians: In search of the ancestor of the vertebrate lateral line

“…In the cephalochordate Amphioxus, considered to be the closest living relative of vertebrates, different sensory cells, type I cells and type II cells, are found scattered in the rostral epithelium. Type I cells are primary sensory cells, while type II cells are secondary sensory cells, with synaptic terminals borne out on short extensions of the cell body (Bone and Best, 1978;Lacalli and Hou, 1999;Holland and Holland 2001;Holland and Yu, 2002). For both types of cells, neither their embryological origin nor their functional properties are known, although they are generally assumed to be either mechano-or chemoreceptors on the basis of their morphology.…”