Histochemistry of cholinesterase in amphioxus (Branchiostoma lanceolatum, pallas)

Abstract

Biochemical and histochemical experiments showed that the cholinesterase activity in amphioxus is due to specific acetylcholinesterase. Light and electron microscopic histochemical staining methods demonstrated that the acetylcholinesterase activity is localized to the junctions between processes of the trunk muscle fibres and the lateral surface of the spinal cord (the central motor end plate), to the junction between processes of the muscular notochordal lamellae and the ventral surface of the spinal cord (the neuro-chordal junction), and to the junctions between the pterygeal axon plexus and processes of the pterygeal muscle fibres. In the central motor end plate the dorsal and the ventral compartments, innervating superficial "red" and deep "white" trunk muscle fibres respectively, were equally intensely stained. Lower activities were seen in the spinal cord,trunk muscle, pterygeal muscle and notochord. It is concluded that most of the specific acetylcholinesterase found in amphioxus tissues is related to various kinds of neuro-muscular junction and accordingly that these probably are cholinergicThe histochemical localization of cholinesterase in amphioxus has previously been mentioned by Mackay and Peters ('61) p. 183. They stated that "cholinesterase appears as diffuse streaks which are parallel to the muscle fibres of the myotomes and there is no evidence of staining in the vicinity of the myosepta, except where nerve bundles occur."Later it was shown that two or three different kinds of muscle fibre or lamella are present in the trunk muscle of amphioxus, and that these lamellae are motorically innervated in an unusual way by so-called central motor end plates (Flood, '66, '68a). Each muscle lamella sends a sarcoplasmic process, the so-called ventral root fibres, towards the surface of the spinal cord to receive its innervation. The processes from the sarcoplasma-rich superficial muscle lamella are apposed to boutons containing small syqaptic vesicles (mean diameter about 700 A) and those from the sarcoplasma-poor deep lamellae to boutons with Isrge vesicles (mean diameter about 1170 A).The superficial type of muscle lamella are probably homologous to the red or slow type of muscle fibre, and the deep lamellae to the white or fast type of muscle fibre present in other chordates (Andersen et J. COMP. NEUR., 157: 407438.al., '63; Bone, '66; Guthrie, '67; Teravainen, '71).All the boutons that innervate the muscle lamellae of a single segment of the trunk are gathered in a large plaque at the lateral surface of the spinal cord. Within this plaque, the boutons with small vesicles are gathered in a small dorsal compartment segregated from those with large vesicles by a narrow glial barrier (Flood, '68a).It has been known since long that the lamellae of the notochord in amphioxus contain transverse filaments in a crossstriation pattern resembling muscle sarcomeres of 30 pm length (Ebner, 1895; Joseph, '02). By electron microscopy it has recently been demonstrated that some of these filament? have a pe...

Somatomotor system of the adult amphioxus (Branchiostoma lanceolatum) revealed by an anticalretinin antiserum: An immunocytochemical study

“…3B,E) synaptic compartments. In amphioxus, the notochord is formed of special vacuolated muscle cells, and tails of these cells contact with the nerve cord through a paired series of pits of the notochord sheath (Flood, 1970, 1974). No CR‐ir processes were observed at the neuro‐notochordal junctions (Fig.…”