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Biomedical subjects

D L Meyer

Publications and source records attributed to D L Meyer.

At least 37 records · Page 2Linked to original sources
PubMed1997

Antibody to keyhole limpet hemocyanin labels retinal horizontal cells in some amphibians, but not in others.

Antibody to keyhole limpet hemocyanin (KLH) reacts with putative horizontal cells in anuran amphibians of the superfamily Bufonoidea. The reactive epitope appears to be located on the cell membrane. No KLH-like immunoreactivity was observed in the outer plexiform layer (OPL) of anurans not members of this superfamily, nor in the OPL of urodeles or other vertebrates. Thus KLH-like immunoreactivity in the OPL provides a tool for assessing phylogenetic relationships within anurans.

Amphibians↗
PubMed1996

Bulbar representation of the 'water-nose' during Xenopus ontogeny.

Olfactory epithelium that is specialized for the detection of water-borne odors is located in different cranial cavities in larval and postmetamorphic Xenopus. Soybean agglutinin histochemistry reveals that both "water-noses' innervate only the ventral olfactory bulb (OB). This is evidence for a parcellation of the OB into a ventral portion mediating information on water-soluble odorants and a dorsal part that processes information on volatile substances.

Animals↗
PubMed1996

Nervus terminalis projection to the retina in the 'four-eyed' fish, Anableps anableps.

The eye of the surface dwelling 'four-eyed' fish, Anableps possesses an aquatic and an aerial optical system. The aerial system is strongly hyperopic when the animal dives, i.e. during mating, and the dorsal pupil is submerged. We studied the retino-petal nervus terminals projection to the aerial and to the aquatic retina by Phe-Met-Arg-Phe-NH2 (FMRF) immunocytochemistry and found both to be equally innervated. This finding sheds doubt on the proposed functional significance of this projection for reproductive behaviour.

Animals↗
PubMed1996

Soybean agglutinin binding by primary olfactory and primary accessory olfactory projections in different frogs.

Comparing eight species of frogs adapted to habitats ranging from aquatic to arboreal, we observed differences in the affinity of primary olfactory projections to the lectin 'soybean agglutinin'. Particularly pronounced differences exist between Pipa, a frog that rarely leaves the water, and Eleutherodactylus, an arboreal species that does not even utilize aquatic environments for reproduction. We interpret these differences as reflecting specializations to the perception of air-borne vs. water-borne odors.

Animals↗
PubMed1995

Expression of S100 protein in the vestibular nuclei during compensation of unilateral labyrinthectomy symptoms.

In adult guinea pigs, unilateral labyrinthine lesions were inflicted by chloroform injections into the middle ear. Immunoreactivity for S100 protein (S100) in the vestibular nuclei was studied during compensation of lesion-induced postural asymmetry symptoms, i.e., nystagmus, asymmetrical head position. 1 h after unilateral labyrinthectomy, increased levels of astroglial S100 immunoreactivity were found in the superior vestibular nucleus and in the medial/lateral vestibular nucleus border region on the side contralateral to the deafferentation. Bilaterally, the astrocytic S100 immunoreaction increased in the lateral vestibular nuclei around Deiters neurons. Maximal expression of S100 was noted 3 h after the lesion. Subsequently, it diminished. Our data reveal that transsynaptically altered neuronal activity induces an astrocytic reaction which provides increased levels of S100 to the local neuropil. Calcium and zinc binding S100 proteins may play a functional role for the neuroplasticity during vestibular compensation.

Animals↗
PubMed1995

The extrabulbar olfactory pathway: primary olfactory fibers bypassing the olfactory bulb in bony fishes?

Recent evidence has revealed that some primary olfactory fibers bypass the olfactory bulb and terminate in tel- and/or diencephalic areas (extrabulbar olfactory pathway, EBOP). We investigated the projections of this system in different fishes by means of soybean agglutinin binding studies. In all species in which primary olfactory fibers were labelled, fiber bundles can be traced beyond the olfactory bulb. These run with the medial forebrain bundle and terminate at different targets, depending on the species. In the teleosts Macrognathus, Mogurnda, and Hemichromis, EBOP fibers can be traced into the ventral telencephalon, pars ventralis, pars supracommissuralis and/or into the preoptic nucleus. In most nonteleosts studied (Polypterus, Chalamoichthys, Amia), the EBOP also innervates diencephalic targets. An exception is Acipenser, which displays an innervation pattern similar to that in teleosts. Comparison with results obtained by other techniques suggests that the EBOP consists of primary olfactory fibers, which project not only to the olfactory bulb but also to various other targets in the prosencephalon of anamniotic vertebrates.

Animals↗
PubMed1995

Screening for disease, cost-effectiveness, and guidelines.

This article provides a brief overview of issues involved in selecting prevention maneuvers for primary care practitioners. Screening diseases, the screening tests themselves, patient characteristics, and cost-effectiveness are discussed.

Cost-Benefit Analysis↗
PubMed1994

Birds that feed-on-the-wing have few isthmo-optic neurons.

The isthmo-optic system is less developed in birds feeding-on-the-wing, than in pecking avians. This was suggested previously. By intraocular horseradish peroxidase applications, we studied the central origin of this retino-petal system in thrush, haw finch, swift and swallow. Our data support the assumption on a correlation between feeding habits and the development of the isthmo-optic nucleus in adult avians as this brainstem region is more highly developed in thrush and finch than in swift and swallow. This is particularly relevant since the latter species is taxonomically related to the two pecking birds whereas it is unrelated to the swift that also feeds-on-the-wing.

Animals↗
PubMed1994

Central projections of the nervus terminalis and the nervus praeopticus in the lungfish brain revealed by nitric oxide synthase.

Lungfishes possess two cranial nerves that are associated with the olfactory system: the nervus terminalis enters the telencephalon with the olfactory nerve, and the nervus praeopticus enters the diencephalon at the level of the optic nerve. We investigated the central projections of the nervus terminalis and the nervus praeopticus in the Australian lungfish (Neoceratodus forsteri) and in the African lungfish (Protopterus dolloi) by NADPH-diaphorase histochemistry (nitric oxide synthase; NOS) and compared them with the projections of the nervus terminalis of the frog (Xenopus laevis). In Neoceratodus, NOS-positive fascicles of the nervus terminalis divide and project with a ventral component through the septum and with a dorsal component through the pallium; fibers of both trajectories extend caudally beyond the anterior commissure and join the lateral forebrain bundle. In the nervus praeopticus, about 300 fibers contain NOS; they innervate the preoptic nucleus and continue their course through the diencephalon; many fibers cross in the commissure of the posterior tuberculum. In Protopterus, ganglion cells of the nervus terminalis and of the nervus praeopticus contain NOS. NOS-positive fibers of the nervus terminalis project through the septal region but not through the pallium. Several major fascicles cross in the rostral part of the anterior commissure, where they are joined by a small number of NOS-containing fibers of the nervus praeopticus. Both nerves innervate the preoptic nucleus. The number and pathways of the fascicles of the nervus terminalis are not always symmetric between the two sides. The nervus terminalis fascicles remain in a ventral position, whereas the nervus praeopticus gives rise to the more dorsal fascicles. Many fibers of the two nerves extend throughout the diencephalon and cross in the commissure of the posterior tuberculum. These findings demonstrate many similarities but also significant differences between the contributions of the nervus terminalis and the nervus praeopticus to forebrain projections in the two lungfishes. They support the view that the nervus praeopticus is part of a nervus terminalis system comparable to that in frogs and other nonmammalian vertebrates.

Amino Acid Oxidoreductases↗
PubMed1994

Interspecific variation of isthmo-optic projections in poikilothermic vertebrates.

Retinopetal projections from isthmic and caudal mesencephalic regions were studied in a number of poikilothermic vertebrates. The tested animals were elasmobranchs, bony fishes, amphibians, and reptiles. Isthmo-optic projections were absent in elasmobranchs, sturgeons, most teleosts, all anuran and urodel amphibians, and in anolis lizards. Tegmental projections to the retina were found in a few fishes and in most reptiles. Interspecific variations regarding three morphological parameters were as follows: (i) isthmic projections to the contralateral eye originate from one or from two distinct nuclei; (ii) major interspecific differences exist regarding numbers and aggregation densities of cells in the nuclei of origin; (iii) the percentage of retinopetal fibres that innervate the ipsilateral retina varies significantly between species.

Amphibians↗
PubMed1994

NADPH-diaphorase in the central nervous system of the larval lamprey (Lampetra planeri).

The distribution of nitric oxide synthase (NOS) in the lamprey brain was studied by using reduced nicotinamide-adenine-dinucleotide phosphate (NADPH)-diaphorase histochemistry to further elucidate the evolution of neurons synthesizing nitric oxide. Intense labeling of fibers and/or neurons was found in portions of the lamprey central nervous system, such as the olfactory system, the pineal organ, the habenular region, the nervus stato-acousticus (N. VIII), the brainstem, and the spinal cord, and also in the adenohypophysis. Labeled giant cells located at the floor of the 3rd and 4th ventricle were recognized as reticulospinal neurons. Mauthner and Müller cells were identified according to morphological criteria. Eight pairs of Müller cells and one pair of Mauthner cells were labeled by NADPH histochemistry. None of these cells had, as yet, been described to display NOS activity in any vertebrate. The massive staining of these cells and the apparent lack of labeling, e.g., in teleost fishes, may be a histochemical correlate to already known differences of functions served by these cells in different species. In addition, our results suggest that the nitric oxide (NO) system has appeared early in vertebrate evolution.

Animals↗
PubMed1993

Retinopetal projections from diencephalic neurons in a primitive actinopterygian fish, the sterlet Acipenser ruthenus.

Horseradish peroxidase (HRP) injections into the sterlet (Acipenser ruthenus) retina retrogradely label neurons in the dorso-medial thalamus, bilaterally. On the contralateral side, 5-7 cells were labelled, whereas ipsilaterally, only 2-3 cells were backfilled. Such diencephalic retinopetal cells have, so far, only been found in teleosts and in tetrapods. It has, therefore, been suggested that they evolved independently in these two vertebrate groups. Our findings on a primitive actinopterygian fish, suggest a more ancient origin of diencephalic projections to the retina.

Animals↗
PubMed1993

Site-specific prodrug activation by antibody-beta-lactamase conjugates: regression and long-term growth inhibition of human colon carcinoma xenograft models.

Antibody-directed catalysis (ADC) is a two-step method for the delivery of chemotherapeutic agents in which enzyme-antibody conjugate, prelocalized to antigen-bearing tumor cells, catalyzes the site-specific conversion of prodrug to drug. An ADC system consisting of F(ab')-beta-lactamase conjugates and a cephalosporin derivative of the oncolytic agent 4-desacetylvinblastine-3-carboxhydrazide was investigated. The ability of the system to mediate antitumor activity was compared with that of free drug given alone and with covalent drug-antibody conjugates in LS174T and T380 colon carcinoma xenografts in nude mice. Efficacy increased from moderate tumor growth inhibition by using free 4-desacetylvinblastine-3-carboxhydrazide to tumor regression and long-term stabilization with the ADC system. Labile covalent drug-antibody conjugates prepared from the same antibodies were less effective than ADC and required much higher antibody doses. The antigens KS1/4, carcinoembryonic antigen, and tumor-associated glycoprotein-72, TAG-72, present on the model cell lines, were chosen to investigate the effect of differences in subcellular location and expression heterogeneity on the efficacy of ADC delivery. Response was equivalent with the three tumor antigens. Hence, heterogeneous expression and membrane shedding of carcinoembryonic antigen and TAG-72, did not diminish the suitability of these antigens as targets for ADC therapy. In contrast, drug-antibody conjugate efficacy was more sensitive to subcellular location and heterogeneity. Thus, ADC is a highly effective form of immunochemotherapy in preclinical models, with applicability toward a variety of antigen targets.

Animals↗
PubMed1993

Visual-evoked responses in the salmon telencephalon change during smolt transformation.

During smolt transformation, salmon behaviour changes dramatically and the fish are imprinted to their natal stream. This brief episode is accompanied by changes in neurochemistry and connectivity of the brain. Comparing visual-evoked potentials, recorded from optic tectum and telencephalon by glass microcapillaries, we found pronounced differences before and after smolt transformation in the telencephalon. In the forebrain of presmolts, only small short-latency responses are present whereas postsmolts display large long-latency waves which characteristic dynamic properties in addition. These findings suggest changes in the functional role of the telencephalon during smolt transformation.

Animals↗
PubMed1993

Enzymehistochemical demonstration of nitric oxide synthase in the diencephalon of the rainbow trout (Oncorhynchus mickiss).

Nitric oxide, a free radical, has recently been shown to exert major influences on CNS functions in mammals. It is synthesized by NO-synthase. For the first time, this study reveals this enzyme's existence in the CNS of a teleost fish and describes its distribution in the diencephalon, where the paraventricular organ displays an extraordinarily high activity. The study contributes to an evolutionary perspective of the biological role played by nitric oxide in the vertebrate CNS, and raises questions regarding the significance of this gas in cerebrospinal fluid-contacting neurons.

Amino Acid Oxidoreductases↗
PubMed1993

Optic tectum in congenitally monophthalmic fishes and chicks.

Morphometry of optic tectum layers was performed in fishes and birds that were congenitally monophthalmic (or had one very small or malformed eye). The optic chiasm was studied with regard to possible anomalies of the fiber distribution. In two very young fish larvae with only one ocular rudiment, no differences were found between the two tecta. In fishes and chicks with one normal and one eye of reduced size, the volume of superficial tectal layers contralateral to the small eye was significantly more affected (reduction by 40 to 70%) than that of the deep layers (reduction by 10 to 30%). Particularly pronounced differences between the superficial tectal layers of both sides were found in a fish where a thin optic nerve, originating in an unusually small eye, projected to the ipsilateral side of the brain. It is concluded that (1) the development of superficial tectal layers depends more strongly on optic innervation than that of deep layers; (2) obvious differences between tecta with and without optic innervation develop rather late in ontogeny; (3) there seems to be no measurable difference between effects of a poor (less than 25%) innervation of the tectum and a complete lack of this projection.

Anguilla↗