Biomedical subjects

J M Hopkins

Publications and source records attributed to J M Hopkins.

At least 19 recordsLinked to original sources

PubMed1997

The cone synapses of cone bipolar cells of primate retina.

One each of bipolar cell types DB2 and DB4, together with a flat and an invaginating midget bipolar cell, were taken from a Golgi-stained rhesus macaque retina; then serially sectioned for EM examination of their synapses with cone pedicles. The cone input to the dendrites of the DB2 cell was exclusively at basal junctions; it had a characteristic distribution. Fifty per cent of the basal synapses were with cone pedicle membrane immediately adjacent to the dendrite of a bipolar cell invaginating to end opposite the ribbon of a cone triad (this, therefore, is called triad-associated). The remainder were one or more synapses distant from the triad-associated position (and, therefore, non-triad associated). The DB4 cell had both basal (predominantly in the triad-associated position) and ribbon-related synaptic input. But the basal to invaginating ratio differed from that of our previously published cell; 56% basal, 43% invaginating, as compared with 31% basal and 69% invaginating. Like foveal IMB cells the synapses of the mid-peripheral invaginating midget bipolar cell were exclusively invaginating; but were about 25% more numerous. The flat midget bipolar cell made exclusively basal synapses. These were 2.5 times more numerous than those of foveal flat midget bipolar cells, and 3.5 times the number of invaginating midget bipolar synapses at equivalent eccentricity. The synapses between cones and diffuse and midget bipolar cells are characteristic for each particular bipolar cell type, but the details depend on a cell's distance from the fovea (eccentricity). A rather constant number of cone pedicle synaptic ribbons 38.6 +/- 2.5 (n = 60) was found across mid-peripheral macaque and vervet monkey retinae. The smaller mean number for vervet monkey, 27.4 +/- 3.5 (n = 23), suggests there can also be generic differences in synaptic detail at cone bipolar cell synapses.

Animals↗

PubMed1996

The cone synapses of DB1 diffuse, DB6 diffuse and invaginating midget, bipolar cells of a primate retina.

The distribution of synapses between cones and two types of diffuse cone bipolar cell in a rhesus monkey retina is described. The dendrites of representative Golgi-stained cells of each of the diffuse cone bipolar cell types DB1 and DB6 were serially sectioned for EM examination. Bipolar cells of the DB1 type have axons terminating in the outer half of the inner plexiform layer. The dendrites of the cell examined were postsynaptic to seven cones at 71 basal synapses; in addition, they had two ribbon synapses with one cone, and one with another. A DB6 type of bipolar cell has axons ending in the inner half of the inner plexiform layer. The dendrites of the cell examined received input from seven cones at 30 ribbon synapses; in addition there were 13 basal junctions distributed between five of the seven cones contacted. Two invaginating midget bipolar cells were found to be postsynaptic at 25 and 26 ribbon synapses of cone pedicles containing 44 and 40 ribbons respectively. These results combined with our previously published work, show that the position and number of synapses is characteristic for each category of cell. Those bipolar cells (flat) making basal synapses have more sites of synaptic contact with the cones than those bipolar cells (invaginating) with predominantly ribbon synaptic input. Over 95% of the cone junctions of the three types of diffuse bipolar cell, DB1, DB2 and DB3, are basal; and their axons always end in the a- (Off-) layer of the inner plexiform layer. All three types of diffuse invaginating cone bipolar cell, DB4, DB5 & DB6, have axons terminating in the b- (On-) layer of the inner plexiform layer; their dendrites are predominantly postsynaptic as central elements invaginating at the cone triads. However, unlike invaginating midget bipolar cells, whose dendrites are exclusively postsynaptic at ribbon synapses, between 10% (DB5) and 40% (DB4 and DB6) of the cone input to diffuse invaginating bipolar cells is through basal junctions. These data are discussed in the context of recent work on the synapses between foveal cones and their bipolar cells.

Animals↗

PubMed1995

Synapses between cones and diffuse bipolar cells of a primate retina.

The photoreceptor synapses of three representative cells of the six types of diffuse bipolar cell of the rhesus macaque monkey's retina are described at 3.5-4.0 mm eccentricity. Bipolar cell DB3 was found to be postsynaptic to 11 cones at 155 basal synapses; about 70% of these were triad associated. Bipolar cell DB4 as postsynaptic to eight cones at 52 ribbon synapses; in addition it was found also to make an average of two or three basal (non-ribbon) synapses per cone (total 23). The DB5 bipolar cell type had 57 invaginating synapses with seven cones. It too had basal synapses, but only two with each of three cones. The diffuse invaginating bipolar cell described by Mariani (1981) is identified as a member of the DB5 category. Dendrites of cone bipolar cell types which have axons ending in the a-layer of the inner plexiform layer make only basal synapses with the cone pedicle. Those so far investigated are the flat midget bipolar cell and the DB2 and DB3 flat diffuse bipolar cells. All bipolar cells whose axons terminate in the b-layer of the inner plexiform layer are postsynaptic at the ribbon synapses of the cone pedicles. They now appear to fall into two groups. Those whose dendrites are exclusively postsynaptic at the ribbons; these are the blue cone and invaginating midget bipolar cells. And the diffuse bipolar cell DB4, that has both ribbon and basal synapses in a ratio of about 2.3:1. It is uncertain into which category cell DB5 should be placed; its basal synapses are so few the cell could be anomalous. It now seems that at least one primate bipolar cell type may be like those of other vertebrates in having, as defined ultrastructurally, two different kinds of synaptic connection with its cones. The results are discussed in the context of a brief review of the photoreceptor synapses of other mammalian bipolar cells.

Animals↗

PubMed1995

Expression of fibroblast growth factors in thyroid cancer.

We have examined immunoreactive fibroblast growth factor-1 (FGF-1) and FGF-2 in thyroid sections from normal tissue, follicular adenoma, differentiated follicular and papillary carcinoma, and anaplastic carcinoma. Polyclonal primary antibodies (Dr. A. Baird, Whittier Institute, La Jolla, CA) to FGF-1 and FGF-2 and fluorescein-conjugated secondary antibodies were used with confocal microscopy to allow quantitation and subcellular localization of the antigens. Staining for FGF-1 and FGF-2 was intense in the differentiated malignant tumor specimens, whereas staining in the normal thyroid tissue controls was not detectable above background fluorescence. Staining for FGF-1 and FGF-2 was intracellular and was not found in the nucleus. Staining using either antibody was enhanced in follicular adenomas, but was less intense than that in the malignant tumors. Sections from anaplastic carcinomas also stained positively. In primary cultures of thyroid cells derived from a papillary carcinoma, staining for FGF-2 was 10-fold greater than that from normal thyroid cells from the same patient. The data suggest a possible role for FGFs in the etiology of thyroid carcinoma.

Adenocarcinoma, Follicular↗

PubMed1993

Cone synapses of a flat diffuse cone bipolar cell in the primate retina.

A Golgi-stained flat diffuse cone bipolar cell from a vervet monkey's retina (Cercopithecus aethiops), contacting six cones, was serially sectioned for electron microscopy (EM) to determine the types of synapses it made with the cone pedicles. All the synapses were basal (flat) contacts. Their distribution and ultrastructural type were similar at each pedicle. Approximately half the synapses were definable as triad-associated and the rest were elsewhere on the cone pedicle base. Their ultrastructure is the same regardless of those positions. About 25 synapses were made with each cone. Thus this type (DB2 of Boycott & Wässle, 1991) of flat diffuse cone bipolar cell is in contact with six cones through about 150 synapses. At the eccentricity studied each cone pedicle probably makes 90-100 basal synapses with between three and four DB2 bipolar cells. This is between two and three times the number that are made with all the types of invaginating bipolar cells. A brief review of cone photoreceptor synapses with bipolar cells shows that, for those so far examined in the primate retina, the dichotomy into two types of bipolar cell invaginating (ribbon-related), with axons ending in the b-layer of the inner plexiform layer (IPL) (hence presumptive On-bipolars) and flat (basal synapses), with axons ending in the a-layer of the inner plexiform layer (hence presumptive Off-bipolars) is the rule. But other vertebrate retinae, including that of the cat, also have bipolar cells which vary from this pattern.

Animals↗

PubMed1992

Synaptic contacts of a two-cone flat bipolar cell in a primate retina.

The Golgi-stained dendrites of a two-cone bipolar cell of a vervet monkey were serially sectioned for electron microscopy and shown to make basal synapses with two neighboring cones. The synapses were all on the cone pedicle membrane adjacent to the bipolar processes invaginating to form the triads. This is the characteristic position for flat midget bipolar cells. The numbers of triads in nine adjacent cone pedicles were not significantly different from those in the cones contacted by the bipolar. Based on this measure the two-cone bipolar does not contact a special population of cones. The advantages and disadvantages of using vertical or horizontal sections for the determination by electron microscopy of the connectivity of the dendrites of Golgi-stained flat bipolar cells are discussed.

Animals↗

PubMed1991

Regeneration of axons from adult rat retinal ganglion cells on cultured Schwann cells is not dependent on basal lamina.

The ability of sciatic nerve grafts to support in vivo regeneration of retinal ganglion cell axons in the adult rat raises the question of which peripheral nerve constituents may be required to promote this unexpected central regenerative response. Prime candidates for this role include the surface of the Schwann cell and components of extracellular matrix present in peripheral nerve trunks. To determine the relative importance of Schwann cells and their basal lamina in promoting retinal ganglion cell axon regeneration in the mammalian visual system, we have used an in vitro model. This approach allowed analysis of the abilities of defined peripheral nerve constituents to promote in vitro outgrowth of neurites from explants of adult rat retina harvested 7 to 10 days after in vivo optic nerve crush. Neurite outgrowth was assessed by neurofilament immunofluorescence after 3 to 20 days in vitro. Culture substrata, consisting of isolated Schwann cells (SC), Schwann cells with their assembled extracellular matrix (SC + ECM), or isolated extracellular matrix from which the Schwann cells had been removed (ECM), were prepared by first co-culturing rat Schwann cells with embryonic dorsal root ganglion neurites on a layer of type I collagen, and then manipulating the cultures to produce the desired substrata. Type I collagen alone did not support neurite growth from adult rat retina. SC and SC + ECM supported regeneration of axons from retinal explants at average growth rates of 18 and 30 microns/h, respectively. Isolated ECM was a poor substrate for retinal neurite growth; the few neurites that gained access to this material grew at rates averaging less than 3 microns/h. These observations suggest that regeneration of adult mammalian retinal ganglion cell axons through peripheral nerve grafts (in vivo) is primarily dependent on neurite-promoting factors present on the surface of Schwann cells and does not require organized extracellular matrix.

Animals↗

PubMed1991

In vitro myelination of regenerating adult rat retinal ganglion cell axons by Schwann cells.

Schwann cell cultures provide a highly favorable substrate for retinal ganglion cell (RGC) survival and axon growth in vitro (Bähr and Bunge, Exp Neurol 106:27, 1989; Hopkins and Bunge, Glia 4:46, 1991). In this report we have extended former studies to obtain axon regeneration, long-term survival, and myelination of adult rat RGC axons in co-cultures of retinal explants with purified Schwann cells. By using modified co-culture conditions, we observed myelination of regenerating adult RGC axons by Schwann cells after 3-4 weeks in vitro. Myelination was associated with a one-to-one Schwann cell-axon relationship, characteristic of the formation of peripheral myelin. Under culture conditions that supported myelination, long-term survival (more than 12 weeks) of a small population of RGCs was observed. These findings highlight the remarkable ability of Schwann cells to support long-term survival of adult rat RGCs in the absence of either central nervous system (CNS) target tissue or other peripheral nervous system (PNS) components. This tissue culture system may serve as a model for the systematic study of the molecular mechanisms which are involved in axon regeneration and myelination of adult CNS neurons.

Animals↗

PubMed1991

Regeneration of axons from adult human retina in vitro.

In an effort to establish an in vitro model of regenerating adult human central nervous system (CNS) neurons, we have investigated the potential for neurite growth from explants prepared from normal adult human retina. Eyes (donated for corneal transplantation) were removed within 2.0 h postmortem and stored on ice for 1.5 to 7.0 days. Retinal explants (1 mm2) were prepared and cultured at 37 degrees C on cellular or acellular substrata in an oxygen-rich, humidified atmosphere. Neurite outgrowth, visualized by neurofilament immunofluorescence, was observed only in the presence of Schwann cells, after a quiescent period of approximately 6 days in vitro. Of 50 explants cultured for 7 days or more on substantia containing Schwann cells, 43 showed evidence of viability in vitro and 28 extended neurites onto Schwann cell surfaces. Estimated rates of neurite growth on Schwann cell substrata reached a maximum of 0.22 mm/day. Neurites did not grow beyond the explant border onto culture substrata composed of either polylysine, laminin, type-I collagen, or monolayers of adult human retinal glia. These results demonstrate that under selected conditions, explants prepared from adult human retina harbor viable neurons and that Schwann cells promote and support regeneration of neurites from these neurons in vitro, allowing systematic analysis of conditions favorable to axonal regeneration from adult human CNS neurons.

Axons↗

PubMed1990

Enhanced resistance to cefotaxime and imipenem associated with outer membrane protein alterations in Enterobacter aerogenes.

Mutants exhibiting enhanced resistance to cefotaxime and imipenem were selected by plating a strain of Enterobacter aerogenes, which already produced chromosomal beta-lactamase constitutively, on to varying concentrations of different beta-lactam antibiotics. Frequencies of mutation varied from 10(-5) to 10(-8), depending upon the particular antibiotic and concentration used for selection. Only minor variations in beta-lactamase specific activities were observed and these could not be directly correlated with changes in resistance when compared with the original strain. In the majority of mutants, the selection of an enhanced level of resistance to cefotaxime was associated with a significant increase in resistance to imipenem, but no increase in resistance to the non-beta-lactam antibiotics tested was observed. Examination of outer membrane protein profiles revealed a number of complex changes in the mutants when directly compared to the original strain. In one mutant imipenem/cefotaxime resistance was directly associated with almost total loss of a 42K protein which was non-covalently associated with peptidoglycan and therefore possibly a porin protein.

Cefotaxime↗

PubMed1988

Long-term analysis of organelle translocation in isolated axoplasm of Myxicola infundibulum.

Moving intra-axonal organelles demonstrate frequent variations in speed when viewed over several seconds. To evaluate these and other motion variations, a long-term analysis of organelle motion in isolated axoplasm of Myxicola infundibulum was carried out using differential interference contrast optics and analog and digital image enhancement techniques. Motion characteristics of individual organelles were analyzed for periods of up to 58 minutes. Three principle observations on organelle motion were made: 1) Classes of organelles of the same size demonstrated a 5- to 25-fold variation of speed, with the slowest speeds occurring most frequently; 2) organelle speeds over individual translocations (motion without stopping) are inversely proportional to their size, but the speeds calculated for the long-term analysis of organelle motion (total distance travelled/total observation time, including pauses) did not reflect this observation; and 3) organelles displayed variable trip lengths, durations, mean speeds, and pause durations, and the relationships between these variations showed no repetitive patterns. In contrast to reported observations of uniform velocities of organelles moving on isolated microtubule preparations, these observations suggest that a variety of factors must play a role in organelle translocation in Myxicola axoplasm.

Animals↗

PubMed1987

Cone connections of the horizontal cells of the rhesus monkey's retina.

The presence in the rhesus monkey's retina of a second morphological type of horizontal cell (H2), described by Kolb et al. (1980), is confirmed. Both types of cell are here further described. Their cone connections are quantified and compared with those of mammals and other vertebrates. The dendrites and axons of the H2 type of cell contact only cones as do the dendrites of the H1 cell (originally described by Polyak (1941)) which has an axon contacting only rods. The dendrites of foveal H2 cells contact between 11 and 14 cones; those of H1 contact 7. The number of cones that each type of cell contacts increases with increasing distance from the fovea, so that, by 5-6 mm eccentricity, H2-type cells synapse with between 20 and 30 cones, and the H1 cells with 12-15. The qualitatively estimated coverage factors of each are 3 or 4; every cone synapses with more than one of both types. Neither type of horizontal cell makes chromatically specific connections that are anatomically recognizable, unlike the situation in some teleostean and turtle retinae. Individual horizontal cells, particularly those connected to foveal cones, may have different ratios of chromatic input. At equivalent eccentricities, up to about 6 mm from the fovea, the dendritic fields of H2 horizontal cells are about twice the size of H1 cells and contact about twice the number of cones. These relative differences are closely similar to those of the cat's horizontal cells and it is suggested that they are a basic feature of most placental mammals. The organization of foveal cone fibres within Henle's layer is described. The distribution of primate cone telodendria, gap junctions and synapses in the outer plexiform layer are briefly reviewed and compared with those of other vertebrate retinae.

Animals↗

PubMed1987

Selection of enhanced cefotaxime resistance in Enterobacter spp.

Four strains of Enterobacter spp. with different chromosomal beta-lactamase expression (inducible, constitutive or negligible) were grown in broth containing either cefoxitin or cefotaxime, then plated on to agar containing 20 mg cefotaxime per litre to quantitate the cefotaxime-resistant mutants present in the population. Spontaneous resistant mutants were initially isolated from each strain at frequencies of 10(-4) to 10(-5). These high frequencies of spontaneous mutation suggested that more than one type of mutational event could yield cefotaxime resistance. Induction of a high level of beta-lactamase in broth cultures was not in itself sufficient to confer a high level of cefotaxime resistance on the population, and increased resistance following selection of resistant mutants did not necessarily correlate with any significant increase in beta-lactamase activity.

Cefotaxime↗

PubMed1986

The social behavior of autistic children with younger and same-age nonhandicapped peers.

Results of a study observing autistic children's interactions with nonhandicapped and autistic peers are reported. Six 8- to 12-year-old autistic children played in dyads with younger, normally developing kindergarten children and with nonhandicapped peers matched on chronological age for 10 15-minute sessions spaced over 3 weeks and then with a playmate of the alternate age for another 10 sessions. After intervention, all subjects showed gains in proximity, orientation, and responsiveness when playing with nonhandicapped peers and with autistic classmates. Same-age nonhandicapped playmates initiated more frequently than did younger nonhandicapped playmates and were better able to modify their initiations in ways that increased the likelihood of response from the autistic children.

Age Factors↗

PubMed1986

Laminin supports neurite outgrowth from explants of axotomized adult rat retinal neurons.

The influence of laminin on neurite outgrowth from explants of adult rat retina and its distribution in normal and lesioned rat optic nerves were examined. Neurite outgrowth required the presence of laminin in the substratum, and as with a goldfish retinal explant system, was markedly stimulated by prior axotomy. Except for blood vessels and the nerve sheath, normal rat optic nerve was devoid of laminin immunoreactivity. Unlike results seen in the goldfish optic nerve, injury to the rat optic nerve induced no observable increase in laminin content or change in its distribution. The differences in the in vivo regenerative capacities of these two species may in part be related to the differences in their abilities to provide a proper substratum for axon regrowth.

Animals↗

PubMed1985

Laminin and optic nerve regeneration in the goldfish.

Previous work from our laboratory had shown that goldfish retinal fragments explanted onto a polylysine substratum 1 to 2 weeks following optic nerve crush exhibit a striking clockwise pattern of neuritic outgrowth. In the present study, however, when the basal lamina component laminin was used as a substratum, neurites grew out as uncurved spokes, were less fasciculated, and had an increased rate of elongation. When laminin was combined with polylysine in the substratum, the degree of fasciculation and rate of elongation were similar to those seen on laminin alone, whereas the tendency for clockwise outgrowth was even more pronounced than that observed with polylysine alone. These results suggest that regenerating neurites have an affinity for laminin. Using an antibody to murine Engelbreth-Holm-Swarm sarcoma laminin, which cross-reacted with basal lamina in goldfish tissue sections, we studied the histochemical distribution of laminin in the goldfish visual system. Immunoperoxidase staining for laminin showed a characteristic scalloped pattern of staining in cross-sections of optic nerve bundles. Following optic nerve crush, the reaction product became much more diffuse and intense, especially distal to the crush site. When the retinal ganglion cell bodies were eliminated by removing the eye, the degenerating optic nerve stump still showed the intensive staining. We interpret these results to indicate that optic nerve glia are responsible in large part for the formation of laminin. Taken together, these in vivo and in vitro findings suggest that laminin plays a role in nerve regeneration in the goldfish central nervous system.

Animals↗

PubMed1984

Assessment of right ventricular function using two-dimensional echocardiography.

With the use of two-dimensional echocardiography (2DE), we analyzed apical and subcostal four-chamber views for evaluation of right ventricular (RV) function in 30 individuals as compared to RV ejection fraction (RVEF) obtained by radionuclide angiography. In addition to previously reported parameters of changes in areas and chords, a new simple measurement of tricuspid annular excursion was correlated with RVEF. A close correlation was noted between tricuspid annular plane systolic excursion (TAPSE) and RVEF (r = 0.92). The RV end-diastolic area (RVEDA) and percentage of systolic change in area in the apical four-chamber view also showed close correlation with RVEF (r = -0.76 and 0.81); however, the entire RV endocardium could only be traced in about half of our patients. The end-diastolic transverse chord length and the percentage of systolic change in chord length in the apical view showed a poor correlation with RVEF. The correlation between RVEF and both areas and chords measured in the subcostal view was poor. It is concluded that the measurement of TAPSE offers a simple echocardiographic parameter which reflects RVEF. This measurement is not dependent on either geometric assumptions or traceable endocardial edges. When the endocardial outlines could be traced, the apical four-chamber view was superior to the subcostal view in assessment of RV function.

Adult↗

PubMed1984

A neurofibrillar method stains solitary (primary) cilia in the mammalian retina: their distribution and age-related changes.

Richardson's reduced silver method, developed for the staining of autonomic nerve fibres in the mammalian intestine, is shown consistently to stain solitary (primary) cilia and diplosomes of the cells of the retinae of cats and rabbits. The cilia comprise a centriole, a basal body and an axoneme with a 9 + 0 complement of microtubules. Probably all retinal cells possess a cilium during their development but, contrary to previous reports, not all retain the axoneme after birth. Axonemes are absent from horizontal, bipolar, microglia, Müllerian, and probably some other glial, cells; all of which showed paired centrioles (diplosomes) after staining. Photoreceptor, amacrine, interplexiform, displaced amacrine and ganglion cells have each one cilium. These differences between cell types persist, without significant change, in the retina of adult rabbits up to the age of 2 years, and in the cat up to 5 years. The alpha-type ganglion cells of the cat are an exception. In 4 to 8-week-old kittens they are all ciliated, like other types of ganglion cells. But by two years about 30% of central area alpha-cells lack an axoneme. Individual cells may have only diplosomes, unusual dispositions of the centrioles in the perikaryal cytoplasm, or even show complete loss of the whole ciliary apparatus. By 5 years of age the proportion of those alpha-cells showing unusual arrangements has increased to approximately 70%, while less than 5% of the other types of ganglion cells are so affected. Cilia of peripheral alpha-cells change at a different rate and by 5 years of age are approximately like the 2-year-old central area population.

Aging↗