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Biomedical subjects

M Lemire

Publications and source records attributed to M Lemire.

35 records · Page 2Linked to original sources
PubMed1979

[Ultrastructure of the secretory parenchyma of the postanal gland of the coelacanth, Latimeria chalumnae Smith].

Latimeria chalumnae Smith, the only surviving crossopterygian, possesses a well-developed, unpaired, postanal gland whose function is as yet undocumented. The availability of tissues suitable for ultrastructural and histochemical studies from the recent International Comores Expedition has permitted a reappraisal of the comparative morphology and functional hypotheses relating to the postanal gland. The richly vascularized tubuloacinar postanal gland is composed of cells which show the characteristic specializations of active ion transport. These include complex and extensive development of basal and lateral cell membrane infolding (cisternae) which are closely associated with numerous large, dense mitochondria. Histochemical studies have shown a high level of ATPase activity within the gland cells. These features of the postanal gland correlate well with those of the rectal glands of elasmobranchs and suggest a similar role in ion excretion and osmoregulation.

Animals↗
PubMed1978

A radioautographic study of retinal projections in type I and type II lizards.

The retinofugal projections of 5 species (Acanthodactylus boskianus, Scincus scincus, Tarentola mauritanica, Uromastix acanthinurus and Zonosaurus ornatus) belonging to 5 different families of Type I and Type II lizards have been examined by means of the radioautographic method. In the 5 species the retinal ganglion cells project to the contralateral hypothalamus (nucleus suprachiasmaticus), thalamus (nucleus geniculatus lateralis pars ventralis, nucleus geniculatus lateralis pars dorsalis), pretectum (nuclei lentiformis mesencephali, geniculatus pretectalis, postero-dorsalis griseus tectalis), tectum opticum (layer 2 to layer 6 of the stratum griseum et fibrosum superficiale) and tegmentum mesencephali (nucleus opticus tegmenti). Ipsilateral optic fibers were never observed in Uromastix acanthinurus, whereas an uncrossed quota was visible in both nucleus geniculatus lateralis pars dorsalis and nucleus postero-dorsalis in the other species. An ipsilateral retinotectal projection was observed only in Tarentola mauritanica. With the exception of the nucleus griseus tectalis the contralateral optic centers identified in this material have to a large extent been observed in other reptiles belonging to the different orders. The presence in reptiles of a general pattern of contralateral visual projections indicates that these were established very clearly in the course of evolution. Similarities become apparent when this plan is compared with that observed in birds. In marked contrast the ipsilateral component in reptiles is unstable and mutable in nature. This ipsilateral retinotectal projections do not appear to be a feature restricted to Type I lizards. On the other hand, the presence of this optic component cannot be linked solely to nocturnal habits.

Animals↗
PubMed1976

[Utrastructure of acinar cells of the post anal gland of Latimeria chalumnae Smith (Crossopterygii, Coelancathidae)].

The acinar-cells of the post-anal gland of Latimeria possess the same singular ultrastructural pattern. The cell outline shows remarkable complexity by extensive infoldings and interdigitations of lateral and basal plasma membranes. Mitochondria are large and very numerous. This cellular morphology correlates well with that seen in "secreting (ion-transporting) cells" of the rectal gland of Elasmobranchs. This differentiation leads to the hypothesis of a post-anal (salt-excreting) gland in Latimeria.

Animals↗
PubMed1976

Retinal projections in cyprinid fishes: a degeneration and radioautographic study.

The retinal projections of three species of cyprinid fish (Cyprinus macrolepidotus, Cyprinus carpio, Rutilus rutilus) were examined with Nauta and Fink-Heimer methods following enucleation and with radioautography following intraocular injection of [3H]-L-proline. Optic tract axons cross completely in the optic chiasma and are distributed to the hypothalamus (nucleus opticus hypothalamicus pars magnocellularis), the thalamo-pretectal region (11 distinct primary optic centers), and the tectum opticum (stratum fibrosum et griseum superficiale, stratum griseum centrale and stratum album centrale). No accessory optic tract was found. The experimental studies on visual projection of various teleosts are reviewed and discussed.

Animals↗
PubMedDate not supplied

Overlapping visual fields and ipsilateral retinal projections in turtles.

The possible relationship between overlap of the visual fields and the importance of ipsilateral retinal projections was investigated in the two Chelonian genera Chinemys and Trionyx. Of these two species, Trionyx has more frontally located eyes, yet ipsilateral retinal projections could not be demonstrated by radioautography. In Chinemys, on the other hand, the ipsilateral retinothalamic projections are extensive. It is suggested that, in contrast to Trionyx, the anatomic substrate of stereoscopic vision in Chinemys may be similar to that in mammals.

Animals↗
PubMedDate not supplied

Sequential events of degeneration and synaptic remodelling in the viper optic tectum following retinal ablation. A degeneration, radioautographic and immunocytochemical study.

The ultrastructural changes taking place in the retino-recipient layers of the viper optic tectum were examined between 5 and 122 days after retinal ablation. The initial degeneration of retinotectal terminals proceeds at widely different rates and is characterized by a marked degree of polymorphism in which a number of different patterns can be discerned. In the final stages of degeneration, either both the degenerating bouton and the distal portion of the postsynaptic element are engulfed by reactive glia, or, more frequently, only the degenerating terminal is eliminated and the postsynaptic differentiation remains. The free postsynaptic differentiations are reoccupied predominantly by boutons containing pleiomorphic vesicles and which are for the most part gamma-aminobutyric acid (GABA)ergic, thus forming heterologous synapses; less frequently these sites are occupied by boutons of the ipsilateral visual contingent to form homologous synapses. These two processes, both of which depend on terminal axonal sprouting, take place within the first 3 postoperative months. They are followed by a decrease in the number of heterologous synapses and a concurrent increase in the number of homologous synapses newly formed by optic boutons generated by collateral preterminal sprouting of ipsilateral retinotectal fibres. The data suggest that partial deafferentation of the optic tectum induces a transitory GABAergic innervation of free postsynaptic sites prior to the restoration of new retinal synaptic contacts.

Afferent Pathways↗
PubMedDate not supplied

Ultrastructural study of the optic nerve in blind mole-rats (Spalacidae, Spalax).

The optic nerve in two species of subterranean mole-rats (Spalacidae) has been examined at the ultrastructural level. The axial length of the eye and the diameter of the optic nerve are 1.9 mm and 52.5 microns in Spalax leucodon, and 0.7 mm and 80.8 microns in Spalax ehrenbergi, respectively. An anti-glial fibrillary acidic protein postembedding procedure was used to distinguish glial cell processes from axons. In both species, the optic nerve is composed exclusively of unmyelinated axons and a spatial distribution gradient according to the size or the density of fibers is lacking. The optic nerve of S. leucodon contains 1790 fibers ranging in diameter from 0.07-2.30 microns (mean = 0.57 microns), whereas in S. ehrenbergi, only 928 fibers, with diameters of 0.04-1.77 microns (mean = 0.53 microns) are observed. In S. ehrenbergi, a higher proportion of glial tissue is present and the fascicular organization of optic fibers is less obvious. Distribution gradients according to size frequency or density of fibers in the optic nerve are absent in both species. Comparison with other mammals suggests that although ocular regression in microphthalmic species is correlated with a significant decrease in the total number of optic fibers and the relative proportion of myelinated fibers, no difference in the absolute size range of unmyelinated axons is observed. The total absence of myelinated fibers in Spalax may be related to the subcutaneous location of the eyes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[The diagnosis of mental retardation in fragile X syndrome is revolutionized by molecular genetics].

The fragile X syndrome is the most common cause of inherited mental retardation. Clinical signs, which are neither specific to the syndrome nor constant, become apparent late in childhood or after puberty, making early diagnosis difficult on a clinical basis alone. The inheritance of the syndrome is peculiar for an X linked disease, since a high proportion of female carriers show a certain degree of mental retardation and "normal transmitting males" do exist. Affected males can be diagnosed by cytogenetic demonstration of the typical fragile X site but only a minority of female carriers can be identified. This makes genetic counseling difficult. In 1991, the cloning and sequencing of the target site of the mutation marked an important step towards full understanding of the peculiarities of inheritance of the fragile X syndrome. A new type of mutation has been revealed: a multistep "expansion" of a small part of a gene that takes place over several generations. A new diagnostic technique by direct genotypic analysis has been developed. With a very high sensitivity and specificity, this analysis detects affected individuals with a "full mutation" (a large "expansion" associated with abnormal methylation of the surrounding region) and individuals with a "premutation" (smaller "expansion") who do not show mental retardation but are at risk of having affected children or grand children. With the direct DNA analysis at the fragile X locus, it is now possible to diagnose easily those children affected with the syndrome and to offer adequate genetic counseling and prenatal diagnosis to female carriers in affected families.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosome Mapping↗