ZOOLOGICAL SCIENCE 5: 337-346 (1988) 1988 Zoological Society of Japan Fine Structure of the Iris Muscle in the Japanese Common Newt, Cynops pyrrhogaster, with Special Reference to Innervation MlTSUMASA OKAMOTO Department of Molecular Biology, Faculty of Science, Nagoya University, Nagoya 464, Japan ABSTRACT ? The localization and structure of the iridial muscles and associated nerves of the newt (Cynops pyrrhogaster) were examined by electron microscopy with some histochemical studies of catecholamine and acetylcholinesterase. The sphincter muscle, which was composed of pigmented smooth muscle cells, was located circumferentially in the pupillary margin of the iris. Sphincter muscle cells formed occasional close contacts with each other by protruding cellular processes. Numerous gap junctions and desmosomes were observed between anterior and posterior pigment epithelium of the iris, but not between muscle cells. Nerve endings formed varicosities and were composed of agranular vesicles and/or granular vesicles. There was no dilator muscle in this species. Prominent circumferential catecholamine fluorescence was observed in the pupillary margin. Acetyl- cholinesterase positive and negative muscle cells and nerve fibers were found within the sphincter muscle region. INTRODUCTION The iris sphincter and dilator muscles, known to be the iris muscle in the mammalian eye, change the size of the pupil and regulate the quantity of light. Studies on the iris muscles have been a fascinating subject from the standpoint of develop- ment and differentiation of the muscle, because these muscles are unique in that the sphincter muscle is the only vertebrate smooth muscle known to be derived from neuroectoderm [1-4] and the dilator muscle has myoepithelial charac- ters [1, 5-6]. They are innervated by an autonomic nervous system [7-10], which is advantageous, in that we can easily detect the action of nerves through miosis and mydriasis of the eye. In addition to morpholgical studies on the iris muscle [1-6, 11-13], numerous pharmacological and elec- trophysiological reports have been made on this nervous system using various kinds of animals [14- 20]. Studies on the fine structure of the iris muscle besides mammals have also been reported [21-24], Accepted September 24, 1987 Received August 7, 1987 but only a few works have been undertaken on amphibian species [25-27]. On the other hand, it has been well known that the newt has a capacity for regeneration from the mid-dorsal margin of the iris after having extir- pated an intrinsic lens. Numerous investigations at the light and electron microscopic level have been made on the process of lens regeneration (for review, see [28]). However, the iris muscle in the newt has so far received almost no attention in terms of the study of lens regeneration, although the sphincter muscle at the pupillary margin would appear to be closely relevant to lens regeneration. There have been no reports on the fine structure of the iris muscle of the Japanese common newt, Cynops pyrrhogaster and no histochemical works on amphibian iridial muscles and nerves. Thus, in the present study, detailed investigations on the fine structure of the iris muscle and some histo- chemical studies on the iridial muscles and associ- ated nerves were made in the adult Cynops pyrrhogaster. In addition, the present study also seeks to obtain basic information on the iris muscle, which presumably has some relevance to lens regeneration.
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ZOOLOGICAL SCIENCE 5: 337-346 (1988) 1988 Zoological Society of Japan Fine Structure of the Iris Muscle in the Japanese Common Newt, Cynops pyrrhogaster, with Special Reference to Innervation MlTSUMASA OKAMOTO Department of Molecular Biology, Faculty of Science, Nagoya University, Nagoya 464, Japan ABSTRACT ? The localization and structure of the iridial muscles and associated nerves of the newt (Cynops pyrrhogaster) were examined by electron microscopy with some histochemical studies of catecholamine and acetylcholinesterase. The sphincter muscle, which was composed of pigmented smooth muscle cells, was located circumferentially in the pupillary margin of the iris. Sphincter muscle cells formed occasional close contacts with each other by protruding cellular processes. Numerous gap junctions and desmosomes were observed between anterior and posterior pigment epithelium of the iris, but not between muscle cells. Nerve endings formed varicosities and were composed of agranular vesicles and/or granular vesicles. There was no dilator muscle in this species. Prominent circumferential catecholamine fluorescence was observed in the pupillary margin. Acetyl- cholinesterase positive and negative muscle cells and nerve fibers were found within the sphincter muscle region. INTRODUCTION The iris sphincter and dilator muscles, known to be the iris muscle in the mammalian eye, change the size of the pupil and regulate the quantity of light. Studies on the iris muscles have been a fascinating subject from the standpoint of develop- ment and differentiation of the muscle, because these muscles are unique in that the sphincter muscle is the only vertebrate smooth muscle known to be derived from neuroectoderm [1-4] and the dilator muscle has myoepithelial charac- ters [1, 5-6]. They are innervated by an autonomic nervous system [7-10], which is advantageous, in that we can easily detect the action of nerves through miosis and mydriasis of the eye. In addition to morpholgical studies on the iris muscle [1-6, 11-13], numerous pharmacological and elec- trophysiological reports have been made on this nervous system using various kinds of animals [14- 20]. Studies on the fine structure of the iris muscle besides mammals have also been reported [21-24], Accepted September 24, 1987 Received August 7, 1987 but only a few works have been undertaken on amphibian species [25-27]. On the other hand, it has been well known that the newt has a capacity for regeneration from the mid-dorsal margin of the iris after having extir- pated an intrinsic lens. Numerous investigations at the light and electron microscopic level have been made on the process of lens regeneration (for review, see [28]). However, the iris muscle in the newt has so far received almost no attention in terms of the study of lens regeneration, although the sphincter muscle at the pupillary margin would appear to be closely relevant to lens regeneration. There have been no reports on the fine structure of the iris muscle of the Japanese common newt, Cynops pyrrhogaster and no histochemical works on amphibian iridial muscles and nerves. Thus, in the present study, detailed investigations on the fine structure of the iris muscle and some histo- chemical studies on the iridial muscles and associ- ated nerves were made in the adult Cynops pyrrhogaster. In addition, the present study also seeks to obtain basic information on the iris muscle, which presumably has some relevance to lens regeneration.
Fine Structure of the Iris Muscle in the Japanese Common Newt, Cynops pyrrhogaster, with Special Reference to Innervation : Cell Biology
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