Differential innervation of the goldfish tonic red muscles and twitch white muscles by neuropeptide-immunoreactive motoneurons

Molecular characterization of calcitonin gene-related peptide (CGRP) related peptides (CGRP, amylin, adrenomedullin and adrenomedullin-2/intermedin) in goldfish (Carassius auratus): cloning and distribution

To further characterize the structure and function of calcitonin gene-related peptide (CGRP) related peptides in fish, we have cloned cDNA sequences for CGRP, amylin, adrenomedullin (AM) and adrenomedullin-2/intermedin (IMD) in goldfish (Carassius auratus) and examined their tissue distribution. CGRP, amylin, AM and IMD cDNAs were isolated by reverse transcription (RT) and rapid amplification of cDNA ends (RACE). The cloned sequences contain the complete four mature peptides, which present a high degree of identity with mature peptide sequences from other fish. Phylogenetic analyses show that goldfish AM and IMD form a sub-family within the CGRP-related peptides that is distinct from the CGRP/amylin sub-family. The distribution of goldfish CGRP-like peptides mRNA expression in different tissues and within the brain was studied by RT-PCR. CGRP, IMD and AM are detected throughout the brain, in pituitary and in most peripheral tissues examined. Amylin mRNA is mostly expressed in the brain, in particular posterior brain, optic tectum and hypothalamus, but is also present in pituitary, gonad, kidney and muscle. Our results suggest that goldfish CGRP, amylin, AM and IMD are conserved peptides that show the typical structure characteristics present in their mammalian counterparts. The widespread distributions of CGRP, AM and IMD suggest that these peptides could be involved in the regulation of many diverse physiological functions in fish. Amylin mRNA distribution suggests possible new roles for this peptide in teleosts, including the control of reproduction.

Regeneration of descending projections to the spinal motor neurons after spinal hemisection in the goldfish

Following spinal transection, descending spinal projections from goldfish brainstem neurons spontaneously regenerate beyond the lesion site. The nucleus of the medial longitudinal fasciculus (nFLM), which has a critical role in swimming, also sends regenerated axons over a long distance to the ipsilateral spinal cord. To examine whether regenerated axons re-innervate the appropriate targets, we injected rhodamine dextran amine (RDA) into the nFLM of spinally transected goldfish and examined anterogradely labeled axons in the spinal cord. In intact controls, there were many RDA-labeled boutons or varicosities in the spinal cord in close apposition to both neurons positive for calcitonin gene-related peptide (CGRP), and those negative for CGRP. This suggests that the nFLM neurons project axons directly to the motoneurons and interneurons in the spinal cord. Four days after hemisection 1 mm caudal to the rostral end of the spinal cord, the number of RDA-labeled boutons in close apposition to the spinal neurons was significantly decreased on the side ipsilateral to the injection. Six to twelve weeks after spinal hemisection, regenerated axons ran through the repaired lesion site, and the number of RDA-labeled boutons or varicosities in close apposition to the ipsilateral spinal neurons had returned to the control level. These findings suggest that the midbrain-spinal pathway, critical for locomotion in fish, spontaneously regenerates beyond the lesion site to re-innervate the appropriately innervated targets after spinal lesion.

Somatostatin-, calcitonin gene-related peptide, and γ-aminobutyric acid-like immunoreactivitity in the frog lumbosacral spinal cord: distribution and effects of sciatic nerve transection

Using immunohistochemistry and optical densitometry, somatostatin (SOM), calcitonin gene-related peptide (CGRP), and gamma-aminobutyric acid (GABA) were investigated in the lumbosacral spinal cord of the frog Rana catesbeiana after sciatic nerve transection. In control animals, the densest network of the SOM-, CGRP- and GABA-like immunoreactive fibers was located in the dorsal part of the lateral funiculus. SOM and GABA-like fibers were found in the dorsal terminal field and in the mediolateral band. The latter region showed CGRP and SOM-like immunoreactive cell bodies. SOM- and GABA-like immunoreactive neurons also occurred around the cavity of the central canal, and other GABA-like fibers were found in the ventral terminal field. While the ventral horn showed scarce somatostatin-like fibers, the putative motoneurons were immunoreactive for the two peptides investigated and GABA, but only a few SOM- and GABA-like fibers occurred in the ventral funiculus. After axotomy, GABA-like immunoreactivity decreased in the dorsal part of the lateral funiculus on the same side of the lesion. The other regions remained labeled. These changes were observed at 3 days following axonal injury and persisted at 5, 8 and 15 days. There was no significant difference in the pattern of CGRP- and SOM- immunoreactivity between the axotomized and the control sides. These results are discussed in relation to the effects of the peripheral axotomy on GABA, SOM, and CGRP expression in vertebrates, emphasizing the use of frogs as a model to study the effects of peripheral nerve injury.

Monoaminergic and peptidergic axonal projections to the vagal motor cell column of a teleost, the filefish Stephanolepis cirrhifer

In an immunohistochemical study, the vagal motor nucleus of a teleost, the filefish Stephanolepis cirrhifer, could be divided into a rostral part and a caudal part, and the former into a dorsolateral group and a ventromedial group. The dorsolateral group consisted of neurons immunoreactive for calcitonin gene-related peptide, whereas the ventrolateral-caudal group was negative for calcitonin gene-related peptide. The latter group was retrogradely labeled after dextran amine injection to the visceral ramus of the vagus nerve, suggesting that it is a general visceral efferent column, made up of parasympathetic preganglionic neurons, whereas the dorsolateral rostral group is a special visceral efferent column. In the general visceral efferent column, a dense concentration of nerve fibers immunoreactive for serotonin, tyrosine hydroxylase, cholecystokinin-8, and substance P, and a small number of fibers immunoreactive for neuropeptide Y was observed. Perikarya in contact with varicose terminals immunoreactive for these substances were frequently seen. In contrast, in the special visceral efferent column, only a moderate concentration of neuropeptide Y-immunoreactive nerve fibers and a sparse distribution of fibers immunoreactive for tyrosine hydroxylase were observed. Perikarya in contact with varicose terminals immunoreactive for these substances were rare. These results suggest that the vagal parasympathetic preganglionic neurons might receive multiple inputs of monoaminergic and peptidergic fibers involved in the regulation of the visceral organs. On the other hand, monoaminergic and peptidergic afferent fibers might be of much less significance in the activity of the special visceral efferent component of the vagus nerve.