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PubMed1976

Morphology of the gills of larval and parasitic adult sea lamprey, Petromyzon marinus L.

The general morphology of the gills is similar in larval (ammocoetes) and parasitic adult sea lampreys, Petromyzon marinus, despite different methods of ventilation necessitated by their feeding habits. The gill lamellae are supported by randomly-distributed pillar cells which enclose blood spaces and collagen columns. The distribution of these cells in lampreys is different from that of higher fishes and it may be inefficient for respiratory exchange. The presence of cytoplasmic microfilaments suggests that these cells have the ability to reduce the lamellar blood spaces through contraction. Marginal channels at the tips of the lamellae are lined only by endothelial cells. The thickness of the water-blood pathway in lampreys falls within the range described for higher fishes, with the most efficient gas exchange likely occuring at the lamellar tips where only a single layer of epithelial cells is present. The abrupt increase in height of the epithelium near the lamellar bases in adults, compared to the gradual transition in height along the lamellae in ammocoetes, is perhaps reflective of higher oxygen requirements during the parasitic stage. The consistent appearance of wide, lateral intercellular spaces within the respiratory epithelium of lampreys indicates possible involvement of these spaces in transport. Mucous secretion appears to be an important function of the superficial platelet cells in ammocoetes. "Mitochondria-rich" and "mitochondria-poor" superficial cells are observed in both ammocoetes and adults, with the mitochondria-rich cells more prevalent toward the lamellar bases. The possibility that at least some of these cells may be involved in absorption is discussed. Mitochondria-rich cells in the interlamellar region are morphologically different in ammocoetes and adults but all possess an abundance of smooth endoplasmic reticulum and hence resemble "chloride cells" of higher fishes. The similarity of these cells in the parasitic adult lamprey to chloride cells of marine fishes may reflect the potential of the adult lamprey to osmoregulate in salt water. A scarcity of these cells in ammocoetes and their resemblance to chloride cells in freshwater fishes may reflect the restriction of larval lampreys to a freshwater habitat.

Animals↗
PubMed1995

In vivo effects of lamprey GnRH-I and cyclized analogs: a structure-activity study.

Lamprey GnRH-I and lamprey GnRH-III are the only two members of the GnRH family to have substitutions in the sixth position, Glu6 and Asp6, respectively; all other GnRH peptides have Gly in the sixth position suggesting a different conformational structure. Thus, a structure-activity study of lamprey GnRH-I or analogs that were cyclized or with sixth position substitutions were determined in vivo in adult female sea lamprey, Petromyzon marinus. The following analogs which were tested, ([D-Glu6]-GnRH-I; cyclo-[D-Glu6-Trp7-Lys8]-GnRH-I; or cyclo-[Glu6-Trp7-Lys8]-GnRH-I), significantly elevated plasma estradiol compared to controls. However, [D-Glu6]-lamprey GnRH-I was the only analog to significantly stimulate ovulation while another analog [Gly6]-lamprey GnRH-I significantly delayed ovulation. These data suggest that the sixth position of lamprey GnRH is critical for function.

Amino Acid Sequence↗
PubMed2005

Calbindin and calretinin immunoreactivity in the retina of adult and larval sea lamprey.

The presence of calretinin and calbindin immunoreactivity is studied in the retina of larval and adult lamprey and their respective distributions are compared. Calretinin distribution is also studied in the retina of transforming stages. Western blot analysis in brain extracts showed a 29-kDa band with both polyclonal anti-calbindin and anti-calretinin antibodies. Calbindin and calretinin immunoreactivity has shown a partially different distribution. In the adult retina large and small bipolar cells, with respectively stratified or diffuse axons, the inner row of horizontal cells and ganglion cells and/or some amacrine cells were labeled with anti-calretinin antibody. The anti-calbindin antibody labels the same cell types except most of ganglion cells, but the label was less conspicuous. Therefore, the possible existence of these two calcium-binding proteins in the central nervous system of the sea lamprey could be discussed. In the differentiated central retina of larval lampreys, numerous calretinin immunoreactive bipolar and ganglion cells were observed, while, in the lateral retina, only ganglion cells were labeled, accordingly with the lack of differentiation of other neural cell types. CR-ir bipolar cells appeared in the retina by the stage 5 of transformation, i.e. about the time when differentiation of photoreceptors occurs. The comparison of the distribution of calretinin and calbindin between adult and larval central retina of lampreys shows striking differences that could be related to the different functionality of eyes in these two stages of the life cycle of lampreys. In addition, this is the first report on the presence of calcium-binding proteins in the larval and transforming lamprey retina, on the presence of calretinin- and calbindin-immunoreactive horizontal cells in adult lamprey retinas and on the differential stratification of bipolar cell terminals.

Animals↗
PubMed2004

Lamprey parasitism of sharks and teleosts: high capacity urea excretion in an extant vertebrate relic.

We observed 10 sea lampreys (Petromyzon marinus) parasitizing basking sharks (Cetorhinus maximus), the world's second largest fish, in the Bay of Fundy. Due to the high concentrations of urea in the blood and tissues of ureosmotic elasmobranchs, we hypothesized that sea lampreys would have mechanisms to eliminate co-ingested urea while feeding on basking sharks. Post-removal urea excretion rates (J(Urea)) in two lampreys, removed from separate sharks by divers, were initially 450 ( approximately 9000 micromol N kg-1 h-1) and 75 times ( approximately 1500 micromol N kg-1 h-1) greater than basal (non-feeding) rates ( approximately 20 micromol N kg-1 h-1). In contrast, J(Urea) increased by 15-fold after parasitic lampreys were removed from non-ureosmotic rainbow trout (Oncorhynchus mykiss). Since activities of the ornithine urea cycle (OUC) enzymes, carbamoyl phosphate synthetase III (CPSase III) and ornithine carbamoyl transferase (OCT) were relatively low in liver and below detection in intestine and muscle, it is unlikely that the excreted urea arose from de novo urea synthesis. Measurements of arginase activity suggested that hydrolysis of dietary arginine made a minor contribution to J(Urea.). Post-feeding ammonia excretion rates (J(Amm)) were 15- to 25-fold greater than basal rates in lampreys removed from both basking sharks and rainbow trout, suggesting that parasitic lampreys have a high capacity to deaminate amino acids. We conclude that the sea lamprey's ability to penetrate the dermal denticle armor of sharks, to rapidly excrete large volumes of urea and a high capacity to deaminate amino acids, represent adaptations that have contributed to the evolutionary success of these phylogenetically ancient vertebrates.

Ammonia↗
PubMed2001

Theory on the evolutionary history of lamprey metamorphosis: role of reproductive and thyroid axes.

Metamorphosis is a developmental strategy used by only a small number of extant fishes and little is known about its phylogenetic development during the evolution history of this large group of vertebrates. The present report provides a putative evolutionary history of metamorphosis in the lamprey, an extant agnathan with direct descendancy from some of the oldest known vertebrates. The study reviews recent data on the role of the thyroid gland and its hormones in metamorphosis, summarizes some recent views on the evolution of the endostyle/follicular thyroid in lampreys, and provides new data on the content of two gonadotropin-releasing hormones (GnRH-I and -III) in brain during goitrogen-stimulated, precocious metamorphosis. These new data support an earlier viewpoint of a relationship between thyroid and reproductive axes during metamorphosis. It is proposed that the earliest lampreys were paedomorphic larvae and they lived in a marine environment; as such, they resembled in many ways the larvae from which the ancient protochordates, Larvacea, are derived. The iodide-concentrating efficiency of the endostyle was a critical factor in the evolution of metamorphosis and this gland was replaced by a follicular thyroid, for postmetamorphic animals needed to store iodine following their invasion of freshwater. Larval growth and postmetamorphic reproduction in freshwater became fixtures in the lamprey life cycle; a non-parasitic adult life-history type appeared later. The presence among extant lampreys of two different adult life-history types, and examples of the lability of the timing of sexual maturation in some species, imply that there has been a complex interplay between the thyroid and reproductive axes during the evolution of metamorphosis in lampreys. This proposal is consistent with what we know of interplay of these axes in extant adult lampreys and with the long-held viewpoint that thyroid function and sexual maturation are an association with an ancient history.

Animals↗
PubMed2006

A lamprey from the Devonian period of South Africa.

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.

Animals↗
PubMed1992

Evolutionary implications of the cDNA sequence of the single lactate dehydrogenase of a lamprey.

All vertebrates other than lampreys exhibit multiple loci encoding lactate dehydrogenase +ADL-LDH; (S)-lactate:NAD+ oxidoreductase, EC 1.1.1.27+BD. Of these loci, Ldh-A is expressed predominantly in muscle, Ldh-B is expressed predominantly in heart, and Ldh-C (where present) exhibits different tissue-restricted patterns of expression depending on the taxon. To examine the relationship of the single LDH of lampreys to other vertebrate LDHs, we have determined the cDNA sequence of the LDH of the sea lamprey Petromyzon marinus and compared it to previously published sequences from bacteria, plants, and vertebrates. The lamprey sequence exhibits a mixture of features of both LDH-A and LDH-B at the amino acid level that may account for its intermediate kinetic properties. Both distance and maximum parsimony analyses strongly reject a relationship of lamprey LDH with mammalian LDH-C but do not significantly distinguish among remaining alternative phylogenetic hypotheses. Evolutionary parsimony analyses suggest that the lamprey LDH is related to Ldh-A and that the single locus condition has arisen as a result of the loss of Ldh-B (prior to the appearance of Ldh-C). The collection of LDH sequences for further studies of the evolution of the vertebrate LDH gene family will be facilitated by the PCR approach that we have used to obtain the lamprey sequence.

Amino Acid Sequence↗
PubMed1995

The olfactory system of migratory adult sea lamprey (Petromyzon marinus) is specifically and acutely sensitive to unique bile acids released by conspecific larvae.

Larval sea lamprey inhabit freshwater streams and migrate to oceans or lakes to feed after a radical metamorphosis; subsequently, mature adults return to streams to spawn. Previous observations suggested that lamprey utilize the odor of conspecific larvae to select streams for spawning. Here we report biochemical and electrophysiological evidence that this odor is comprised of two unique bile acids released by larvae. High performance liquid chromatography and mass spectrometry demonstrated that larval sea lamprey produce and release two unique bile acids, allocholic acid (ACA) and petromyzonol sulfate (PS). Electro-olfactogram (EOG) recording also demonstrated that the olfactory system of migratory adult sea lamprey is acutely and specifically sensitive to ACA and PS; detection thresholds for these compounds were approximately 10(-12) M. ACA and PS were the most potent of 38 bile acids tested and cross-adaptation experiments suggested that adult sea lamprey have specific olfactory receptor sites associated with independent signal transduction pathways for these bile acids. These receptor sites specifically recognize the key substituents of ACA and PS such as a 5 alpha-hydrogen, three axial hydroxyls, and a C-24 sulfate ester or carboxyl. In conclusion, the unique lamprey bile acids, ACA and PS, are potent and specific stimulants of the adult olfactory system, strongly supporting the hypothesis that these unique bile acids function as migratory pheromones in lamprey.

Animals↗
PubMed1996

Feeding and breathing in lampreys.

A basic problem faced by the agnathans in evolution was how to feed and breathe without jaws. Three solutions are represented by lampreys and their ammocoete larvae, reviewed here, and hagfishes. Lampreys feed upon fish with their suckers and breathe in and out of their branchial gill sacs. Parasitic species of lampreys can be flesh-feeders or blood-feeders, depending primarily on the structure of their teeth. Feeding behavior is characterized by rhythmic rasping, negative pressure pulses in the sucker, and swallowing of fluid into the gut. Ammocoete larvae use a velar pump for unidirectional ventilation and suspension feeding. In both lampreys and ammocoetes the branchial basket is actively compressed for exhalation; branchial expansion and inhalation is by passive elastic recoil, but in ammocoetes water is drawn from the mouth. Central pattern generators for respiration are distributed in the medulla, particularly lateral to Vm, and drive branchial motoneurons in VIIm-IXm-Xm. Trigeminal pattern generators in lampreys may be a holdover from the ammocoete stage, in which they drive nearby velar motoneurons as the primary pump for ventilation. Respiration in lampreys and ammocoetes is stimulated by hypoxia and modulated by reflexes. Metamorphosis from ammocoete to adult lamprey involves extensive remodeling of the head with regression and replacement of most muscles. Trigeminal motoneurons are probably preserved during metamorphosis, as inferred from constant maps of motoneurons in Vm. This hypothesis is supported by analogy with anuran metamorphosis in which V motoneurons are retained and remodeled. In Mallatt's current models, the earliest vertebrates breathed by branchial contractions and valves; jaws initially evolved for better ventilation and later were used for feeding.

Animals↗
PubMed1988

Immunocytochemical studies on the islet and the gut of the arctic lamprey, Lampetra japonica.

The endocrine cells and nerves in the islet and the gut of the arctic lamprey Lampetra japonica were examined immunocytochemically by using antisera against brain-gut peptides and amine. The cellular composition of the islets as reported by previous researchers in European species of the lamprey was confirmed in the present study. The islet consisted exclusively of insulin immunoreactive cells in the larvae (ammocoetes), whereas in the adult somatostatin immunoreactive cells were added to the insulin immunoreactive cells; the gut epithelium in the adult was now devoid of somatostatin cells. In the gut of the lamprey, the endocrine cells--which were flask-shaped with a cytoplasmic process extended to the lumen--were classified into three types in the larvae, but were represented by a single type in the adult. In the larval lamprey, the first type was immunoreactive for somatostatin, the second one for gastrin/cholecystokinin (CCK) and the third cell type was immunoreactive for glucagon, pancreatic polypeptide and FMRFamide, simultaneously. In the gut of the adult lamprey, the single type of endocrine cell reacted simultaneously to C-terminal specific anti-glucagon serum, N-terminal specific anti-glucagon serum, anti-bovine PP serum, anti-neuropeptide Y serum and anti-FMRFamide serum. These cells occurred most frequently in the upper intestine, their distribution decreasing from the middle to the lower intestine. Two types of peptide containing nerves were identified in the islet and the gut of the larval and adult lamprey. The first type of neurons (perikarya and fibers) was immunoreactive for serotonin and calcitonin gene-related peptide (CGRP), and was located in the mucous and muscular layer of the intestine and in the islet. The second type of neurons contained both serotonin- and gastrin releasing peptide (GRP)-like immunoreactivities and was scattered exclusively in the muscular layer of the gut. In larval and adult lampreys, a few serotonin/CGRP immunoreactive nerve cell bodies and beaded fibers were found in the connective tissue around the islet cell cords. These nerve fibers were sometimes closely apposed to the blood capillaries and to the islet cells. These findings indicate that a neuroendocrine correlation comparable with that in mammals may have been established in the islet of this most primitive vertebrate.

Aging↗
PubMed1988

Fibril-forming collagens in lamprey.

Five types of collagen with triple-helical regions approximately 300 nm in length were found in lamprey tissues which show characteristic D-periodic collagen fibrils. These collagens are members of the fibril forming family of this primitive vertebrate. Lamprey collagens were characterized with respect to solubility, mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, carboxylmethyl-cellulose chromatography, peptide digestion patterns, composition, susceptibility to vertebrate collagenase, thermal stability, and segment long spacing-banding pattern. Comparison with fibril-forming collagens in higher vertebrates (types I, II, III, V, and XI) identified three lamprey collagens as types II, V, and XI. Both lamprey dermis and major body wall collagens had properties similar to type I but not the typical heterotrimer composition. Dermis molecules had only alpha 1(I)-like chains, while body wall molecules had alpha 2(I)-like chains combined with chains resembling lamprey type II. Neither collagen exhibited the interchain disulfide linkages or solubility properties of type III. The conservation of fibril organization in type II/type XI tissues in contrast to the major developments in type I and type III tissues after the divergence of lamprey and higher vertebrates is consistent with these results. The presence of type II and type I-like molecules as major collagens and types V and XI as minor collagens in the lamprey, and the differential susceptibility of these molecules to vertebrate collagenase is analogous to the findings in higher vertebrates.

Amino Acids↗
PubMed1976

The haematopoietic supraneural organ of adult, sexually immature river lampreys (Lampetra fluviatilis [L.] Gray) with particular reference to azurophil leucocytes.

The haematopoietic tissue in the supraneural organ of the freshwater river lamprey (Lampetra fluviatilis L. Gray) was studied in sexually immature animals. Besides erythro- and granulopoietic elements, macrophages, reticular cells, fibroblasts and glycogen-rich fat cells were seen. Developing granulocytes of the lamprey contain one type of azurophil granules originating from small cytoplasmic (Golgi) vesicles. The lamprey's azurophil granulocytes seem to be homologous with those of fishes. However, the granulocytes of fishes, studied thus far, show granules with only one type of inclusion, whereas in lamprey the granulocyte inclusions are variable in size and shape. Thus, lamprey granulocytes are, in this respect, reminiscent of similar cells of higher vertebrates. The PAS and alkaline phosphatase reactions, common markers of vertebrate neutrophil leucocytes, are very weak in the haematopoietic tissue granulocytes of the lamprey, and intense in the blood cells of the same animal. Lamprey granulocytes, similarly to the granulocytes of Chondrostei and Elasmobranchiata, do not stain with peroxidase, naphthol-AS-D-chloroacetate esterase and sudan black B. The haematopoietic tissue contains a relatively high number of degenerated granulocytes.

Animals↗
PubMed1995

Interactions between muscle activation, body curvature and the water in the swimming lamprey.

The travelling wave of curvature which propels a fish forward arises from the interaction of the patterns of motoneurone activity generated by the spinal cord with the mechanical properties of (1) the muscle, (2) the skin, bone and connective tissues of the body, and (3) the water in which it is swimming. Furthermore, in the lamprey, a powerful feedback system has been demonstrated which allows local body curvature to influence the timing of the activity pattern generated by the spinal cord. The relative timing between activation and curvature are illustrated for both closed- and open-loop conditions, using data from intact swimming lampreys and from an in vitro preparation of lamprey spinal cord and notochord. The mechanical behaviour of a lamprey has been simulated with a mathematical model based on springs, dashpots, light rods, point masses and power units incorporating properties of lamprey muscle. Results are presented which illustrate the behaviour of a lamprey out of water. To anticipate the inclusion of the lamprey body model in the computation of the fluid dynamics, a hydrodynamical model has been developed in which the body motion and the forward swimming have been prescribed by mathematical functions. Results are presented to illustrate the hydrodynamic vortex structure as predicted by a two-dimensional, time-dependent numerical solution of the Navier-Stokes equations, including both viscous and inertial terms.

Animals↗
PubMed1999

Lack of glomerular intermittency in the river lamprey lampetra fluviatilis acclimated to sea water and following acute transfer to iso-osmotic brackish water

Previous studies have suggested that in the lamprey Lampetra fluviatilis, in contrast to teleost fish, all glomeruli are actively filtering. In the present study, we have applied the ferrocyanide technique to obtain more definitive values for the population of filtering nephrons in the lamprey under conditions of high (in fresh water) and low (in sea water) glomerular filtration rate (GFR) and when the branchial osmotic gradient was eliminated by acute transfer of freshwater lampreys to iso-osmotic brackish water. These studies demonstrated that the renal antidiuresis in lampreys acclimated to full-strength sea water does not involve any reduction in the filtering population of glomeruli. Transfer to brackish water significantly reduced GFR and thereby urine flow rate (287+/-23 ml kg-1 24 h-1 in fresh water; 6.9+/-2.5 ml kg-1 24 h-1 in brackish water). In four of the eight fish examined, 100 % of glomeruli remained filtering; in the other four fish, non-filtering glomeruli occurred in patches along the kidney, always associated with an absence of vascular perfusion, which implies possible endocrine/neural control of vascular tone. The numbers of non-filtering glomeruli were always small, and these glomeruli do not appear to make a major contribution to the overall decline in urine output. The results provide firm evidence that although lampreys, like teleosts, show considerable variations in urine output, the renal mechanisms by which lampreys and the teleosts achieve this differ fundamentally, with glomerular intermittency playing little or no part in the lamprey.

Journal Article↗
PubMed2000

Chondrogenesis of the branchial skeleton in embryonic sea lamprey, Petromyzon marinus.

This study provides concise temporal and spatial characteristics of branchial chondrogenesis in embryonic sea lamprey, Petromyzon marinus, using high resolution light microscopy, transmission electron, and immunoelectron microscopy. Prechondrogenic condensations representing the first branchial arch appeared first in the mid-region of the third pharyngeal arch at 13 days post-fertilization (pf). Cartilage differentiation, defined by the presence of the unique, fibrillar, non-collagenous matrix protein characteristic of branchial cartilage, was first observed at 14 days pf. Development of lamprey branchial cartilage appeared unusual compared to that in jawed fishes, in that precartilage condensations appear as a one-cell wide orderly stack of flattened cells that extend by the addition of one dorsal and one ventral condensation. Development of lamprey gill arches from three condensations that fuse to form a single skeletal element differs from the developing gill arches of jawed fishes, where more than one skeletal element forms from a single condensation. The initial orderly arrangement of cells in the lamprey branchial prechondrogenic condensations remains throughout development. Once chondrification of the condensations begins, the branchial arches start to grow. Initially, growth occurs as a result of matrix secretion and cell migration. Later in development, the arches grow mainly by cell proliferation and enlargement. This study defines the morphology and timing of lamprey branchial chondrogenesis. Studies of lamprey chondrogenesis provide not only insight into the developmental biology of a unique non-collagenous cartilage in a primitive vertebrate but also into the general evolution of the skeletal system in vertebrates.

Animals↗
PubMed1989

Ultrastructural cytochemistry of aortic microfibrils in the Arctic lamprey, Lampetra japonica.

In the ventral aorta of lamprey, microfibrils are major components of the extracellular matrix. With special reference to these microfibrils, we have cytochemically examined the lamprey ventral aorta, utilizing the tannic acid (pH 7.0)-uranyl acetate (TA-UA) method, elastase en bloc digestion, Thiéry's periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method, and ferritin- or horseradish peroxidase-labeled concanavalin A (Con A) methods. The lamprey microfibrils were strongly stained with PA-TCH-SP and both Con A methods, but did not show TA-UA staining nor elastase sensitivity. These cytochemical properties of lamprey microfibrils are identical with those of mammalian elastin-associated microfibrils. On the other hand, in spite of extensive examination, TA-UA positive and elastase-sensitive extracellular components were not found, so that lamprey ventral aorta does not appear to contain elastin. These results indicate that lamprey aortic connective tissue contains microfibrils as elastic components, but deposition of amorphous elastin does not occur.

Actin Cytoskeleton↗
PubMed2002

Increase in descending brain-spinal cord projections with age in larval lamprey: implications for spinal cord injury.

The purpose of this study was to determine whether new descending brain-spinal cord projections are added with age in larval lamprey and might contribute substantially to restoration of these projections following spinal cord injury. Retrograde horseradish peroxidase (HRP) labeling of descending brain neurons was performed in "young" and "old" larval lamprey that differed in age by at least one year. In old larval lamprey, significantly more descending brain neurons projected to specific rostral levels of the spinal cord than in young animals. Furthermore, in young and old lamprey, the main morphological change in Müller and Mauthner cells was an increase in soma size. The major conclusion from the present study is that in larval lamprey, some new brain-spinal cord projections are added with age that could be due to axonal elongation by preexisting brain neurons and/or descending projections from new neurons (i.e., neurogenesis or maturation of incompletely differentiated neurons). Following spinal cord transections, the numbers of descending projections were not significantly different than those in normal, unlesioned animals. Thus, some new descending projections are added with age, but at a relatively slow rate, and the rate does not appear to be affected significantly by spinal cord transections. Together, the present results and those from our recent double-labeling study suggest that following spinal cord transection in larval lamprey, axonal regeneration by descending brain neurons, rather than the relatively slow addition of new brain-spinal cord projections with age, probably accounts for the majority of restored projections and recovery of locomotor function

Aging↗
PubMed1976

An electron microscopic study of the neuromuscular junction in the myotomes of larval lamprey, Lampetra japonica.

The neuromuscular junction in the myotomes of larval and adult lampreys, Lampetra japonica, was studied with the electron microscope. In larval lampreys of 26 days after artificial insemination, the myotome consists of triangular lamellae of muscle cell with their bases laterally and apexes medially oriented and placed one on the other. The lateral aspect of the myotome is covered by a layer of flattened cell, and the other aspect is covered by an external lamina which does not extend into the intercellular space between adjacent cells within a myotome. A bundle of thin axons was found in a depression at the middle of medial edge (apex) of each muscle lamella of the myotome and neuromuscular junction was formed here. No nerve endings were found at the myoseptal ends or at the lateral borders of the muscle lamellae. Enlarged axon terminals contained numerous clear vesicles with a few cored vesicles, mitochondria and neurofilaments. The presynaptic axolemma was separated from the postsynaptic sarcolemma by an interspace (50-55 mmu wide) with an interposed external lamina. In the trunk musculature of adult lampreys, nerve endings were found on the surface of the parietal fibers whereas they were seen on both the myoseptal ends near the myotendinous junction along the medial border of each central fiber. Thickening and enhancement in the electron density and accumulation of filamentous material on the sarcoplasmic surface of the postsynaptic sarcolemma were noted in both the larval and adult lampreys. Any other specific alterations were not found on both the pre- and postsynaptic membrane in the neuromuscular junctions of larval and adult lampreys. A brief comment was made on the relationship in development of the characteristic muscle units and patterns of the motor innervation in the larval and adult lampreys. The significance of the neuromuscular junction in the very young larvae reported here was also discussed in respect to the evolution of the neuromuscular junction, particularly in lower chordates, and it was presumed to be the most primitive pattern of innervation in the vertebrate skeletal muscle.

Animals↗