Extraocular muscles in the lamprey, Lampetra fluviatils L. II. Motor end plates

Motor innervation and particularly the structure of motor end plates (MEPs) was studied in the extraocular muscles of the lamprey, Lampetra fluviatilis L., by light and electron microscopy. Each muscle is supplied with numerous thin motor nerve fibres. Motor end plates are located at their ends or along their course. Two motor end plate types were distinguished: en grappe-like plates with a low acetylcholinesterase (AChE) activity were observed on thin muscle fibres, whilst en plaque-like plates with a high AChE activity were found on thick mitochondria-rich and thick multifibrillar muscle fibres. The postsynaptic membrane of the former MEP type does not show the presence of infoldings, MEPs located on thick mitochondria-rich fibres show occasional infoldings, whereas the postsynaptic membrane of MEPs present on thick multifibrillar fibres reveals numerous infoldings. Motor end plates present in the extraocular muscles in the lamprey possess features typical for higher vertebrates and elasmobranch fishes, as well as for Tunicata.     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The proximal neurosecretory contact region (PNCR) of the lamprey, a homologue of the median eminence of tetrapods, was studied by light, fluorescence and electron microscopy. Paraldehyde fuchsin-positive neurosecretory fibers are seen mainly in the central part of the rostral subdivision of the PNCR. The Falck-Hillarp technique reveals a weak, mainly diffuse yellow-green fluorescence in the PNCR. The ultrastructure of the tanycyte layer of the PNCR is very similar to that in the neurohypophysis of the same species, although the funnel-shaped protrusions of the third ventricle in the rostral part of the PNCR are more frequent than in the neurophypophysis. Peptidergic A1 and A2 neurosecretory fibers are characterized by neurosecretory granules of 120-200 nm and 100-150 nm in diameter, respectively. Monoaminergic B type fibers contain granules 80-100 nm in diameter. Neurosecretory terminals and the vascular endfeet of tanycytes make contact with the basement membrane of the avascular connective tissue layer separating the PNCR from the hypophysial pars distalis. It is suggested that both peptide and monoamine neurohormones diffuse through the thick connective tissue septa into the underlying blood vessels which supply the pars distalis and thus affect the function of its glandular cells.     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The distribution of monoaminergic structures was studied in the proximal neurosecretory contact region and neurohypophysis of the lamprey by light and electron microscopic radioautography. Only weak radioautographic reactions were found in the proximal neurosecretory contact region 1 h after injection of 3H-dopamine. High-resolution radioautography revealed some labeled neurosecretory terminals mainly in contact with the basement membrane of the connective tissue layer separating the proximal neurosecretory contact region from the hypophysial pars distalis. The number of silver grains as well as the number of neurosecretory terminals marked by the presence of labeled dopamine was much higher in the neurohypophysis of the same species. In the latter, labeled neurosecretory terminals were found in contact with the connective tissue layer containing blood vessels of the general circulation. Some neurosecretory terminals make synaptoid contacts with tanycyte perikarya and their basal processes. According to their ultrastructure and the size of their granules, the labeled neurosecretory terminals are identical with the B type terminals described in both neurohemal regions (transmission electron microscopy). No labeled neurosecretory terminals were observed in the proximal neurosecretory contact region and the neurohypophysis of lampreys treated with the serotonin precursor, 3H-5-hydroxytryptophan.     

Monoamines in the liquor-contacting nerve cells in the hypothalamus of the lamprey,Lampetra fluviatilis L.

Summary The hypothalamus of adult lampreys (Lampetra fluviatilis L.) was studied by means of light and fluorescence microscopy (Falck's technique). Some single liquorcontacting nerve cells (LCNC) showing a weak green fluorescence were demonstrated in the ventral part of the third ventricle, above the preoptic recess. Caudally numerous fluorescent LCNC occur in the ventral part of the third ventricle, in the infundibular and in the posterior recess. The LCNC are to be observed between or below the ependymal cells lining the ventricular wall. These cells appear to be of the bipolar type. One process with a club-like protrusion is directed into the ventricular lumen, the other one into the opposite direction. Two types of fluorescent LCNC were distinguished: yellowish green cells, containing catecholamines, and yellowish orange cells, containing 5-hydroxytryptamine. Some similarity between the hypothalamic monoaminergic LCNC in lampreys and LCNC of the paraventricular organ of the other vertebrates was found. The localization, structure and monoaminergic nature of the hypothalamic LCNC in lampreys suggest the possibility, that their monoamines are released into the cerebrospinal fluid.I am very obliged to Prof. A.L. Polenov for his continuous help and advice. The skilful technical assistance of Mrs. G.N. Yakshina is gratefully acknowledged.     

The intestinal blood circulation in the River lamprey, Lampetra fluviatilis

Serial sections, injections with india ink and latex, and observations on fresh material, have been used to determine the pattern of blood circulation within the intestine of larval and adult lampreys. Attention has also been paid to resolving the variable terms previously applied to many of the blood vessels, and to the possible functional significance of the differences found between the two life cycle stages. In the larva, the main arterial supply to the intestine consists of a typhlosolar artery, while the venous return is comprised of a posterior and a left and right anterior intestinal vein that usually unite before entering the liver. Although a typhlosolar artery is also present in the adult, the main venous return of the ammocoete is replaced at metamorphosis by a newly formed typhlosolar vein. Moreover, in the ammocoete a considerable amount of blood is discharged into the haemopoietic sponge-work of the typhlosole and the arterial supply to the intestine is poorly developed. By contrast, the typhlosolar sponge-work is lost in the adult and a more efficient arterial supply is developed within the lamina propria of the various intestinal regions. Furthermore, vascular couples are developed in the adult which facilitate the flow of blood in opposite directions in the intestinal wall. Since, during both life cycle stages, the arterial blood passes into tissue spaces, there is no true capillary network in the intestine and no evidence was found for the presence of a lymphatic system. It is suggested that the changes which take place in the intestinal blood supply and the internal structure of the gut during metamorphosis result in improvements both to the vascular system and to the assimilation efficiency.     

Cell division in the olfactory epithelium of the lamprey,Lampetra fluviatilis

Summary The turnover of cells within the olfactory epithelium of the lamprey Lampetra fluviatilis was investigated using tritiated thymidine followed by autoradiography. It was found that cell division occurred in three distinct regions of the olfactory lamellae. Two of these regions — a distal lamellar region and a proximal lamellar region occurred outside the sensory area proper, but appeared to contribute cells to the sensory area as well as giving rise to secretory or ciliated cells outside the sensory area. A third region of division occurrred at the base of the sensory area. Division of specialised basal or blastema cells in this region gives rise to cells that are confined to the sensory region of the lamellae. These findings are discussed in the light of previous studies on cell replacement within the olfactory epithelium.     

Population genetics of a cyclostome species pair, river lamprey (Lampetra fluviatilis L.) and brook lamprey (Lampetra planeri Bloch)

Horizontal agarose gel electrophoresis of 24 allozyme loci in four species of Central European lampreys (321 Lampetra planeri , 83 L. fluviatilis , 11 Eudontomyzon mariae and nine Petromyzon marinus ) was used to study the 'paired species' L. fluviatilis and L. planeri . The genetic differentiation of the anadromous river lamprey ( L. fluviatilis ) from the stationary brook lamprey ( L. planeri ) was within the range of ingroup differentiation of the latter, but L. fluviatilis exhibited much greater population cohesion over a more extended geographic range: G _ST = 0.0537 versus G _ST = 0.3398, N _em = 4.402 versus N _em = 0.4856, mean genetic among-stock distances D = 0.0047 versus D = 0.0257. L. planeri populations coexisting geographically with L. fluviatilis in the Rhine and Elbe river systems were genetically more cohesive than L. planeri stocks from the Danubian basin where L. fluviatilis is absent. Danubian L. planeri populations exhibit a lower degree of heterozygosity than brook lampreys from the Rhine river system, but comprise deeper genetic lineages ( G _ST = 0.4629 versus G _ST = 0.2434), despite being sampled from a much more restricted area. Isolation-by-distance is observed for L. planeri from the Danubian but not from the Atlantic drainage basins. Transspecific gene flow between L. planeri from Atlantic drainage basins and the long-distant migrating L. fluviatilis is inferred, raising doubt on the validity of two separate biospecies. E. mariae and P. marinus are clearly differentiated from Lampetra spp. at several allozyme loci.     

Visual cells and visual pigments of the lamprey,Lampetra fluviatilis

Summary The long and short photoreceptors in the lamprey retina possess similar cone-like outer segments where many disks are infoldings of the outer plasmic membrane. Following the treatment by the Hartwig's (1967) method, outer segments of the long receptors are stained red, and those of the short receptor are stained blue, like the cones and rods in higher vertebrates, resp. (Fig. 1). Microspectrophotometry has shown that the short cells contain P517₁ whereas the long receptors possess P555₁ (Fig. 3). Spectral sensitivity of the dark-adapted retina measured by electroretinographic b-wave and aspartate-isolated receptor potential, corresponds to P517 (Figs. 5, 8). Judging from the receptor potential, the short receptors do not saturate at high illuminances and contribute to the retinal function in photopic conditions as well (Fig. 7). Photopic ERG is of a typical cone-dominant shape (Fig. 4).It is concluded that the long photoreceptors of the lamprey retina are cones whereas the short cells should be regarded as a peculiar kind of rods which possess cone ultrastructure and can operate in scotopic as well as in photopic conditions.Abbreviation LRP late receptor potential     

Locomotor activity of river lamprey Lampetra fluviatilis (L.) during the spawning season

At high latitudes (62–64°N) the river lamprey Lampetra fluviatilis (L.) is shown to have a 24-hr locomotor activity during its spawning period just before midsummer. By keeping lampreys in cold water, the spawning was delayed about one month. Analysis of event recorder graphs indicate that the 24-hr activity is caused by addition of diurnal spawning activity to the basic nocturnal activity and is not caused by weak Zeitgeber conditions during midsummer.Water temperature might indirectly determine time of spawning of the river lamprey.     

Mitochondrial and lysosomal pathways of lamprey (Lampetra fluviatilis L.) hepatocyte death

Mechanisms of mitochondrial and lysosomal pathways of natural death of lamprey hepatocytes are described at the spring period of the prespawn migration. The mitochondrial pathway (release of cytochrome c from mitochondria into cytosol and activation of caspases) is realized by the classic scheme of apoptosis. Comparatively recently, the lysosomal pathway of cell death associated with cathepsin B activation has been revealed in cells in pathologies, specifically in obstruction of gallbladder and bile ducts. A peculiarity of lamprey hepatocytes consists in that in the adult animal liver there takes place biliary atresia (the absence of gallbladder and bile ducts. Thereby, the lamprey hepatocytes are an excellent object for study of this new pathway of cell death. We have revealed development of the mitochondrial and the lysosomal pathways of cell death of lamprey hepatocytes.     

A microdissection study of Lampetra fluviatilis lamprey nephrons]

Each of the nephrons in the lamprey L. fluviatilis consists of three distinct segments-proximal, thin, and distal ones. Proximal segments are differentiated into a convoluted and a descending parts, whereas distal ones-into a convoluted and an ascending parts. Therefore microdissection studies indicate that the anatomical composition of a single nephron in the river lamprey is identical to that of a superficial nephron in mammals. Parallel arrangement of the proximal descending, thin, and distal ascending segments, as well as of the collecting tubules, also makes the kidney of the lamprey similar to the countercurrent system in the medulla of mammalian kidney. The data obtained imply that Henle's loop is present in the kidneys not only of higher Vertebrates, but of Cyclostomes as well.