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G H Jacobs

Publications and source records attributed to G H Jacobs.

At least 73 records · Page 4Linked to original sources
PubMed1988

Temporal properties of the short-wavelength cone mechanism: comparison of receptor and postreceptor signals in the ground squirrel.

Temporal properties of the short-wavelength cone mechanism of the California ground squirrel (Spermophilus beecheyi), a dichromat, were explored with single light pulses and pulse trains. Both the electroretinogram (ERG) and the isolated PIII component of the retinal gross response were recorded under chromatic adaptation conditions that favored the detection of test lights by either the middle-wavelength mechanism or the short-wavelength mechanism. The ERG b-wave generated by the short-wavelength mechanism was significantly slower than that of the middle-wavelength mechanism, but there was no such difference in the PIII components of the two mechanisms. Analysis of PIII revealed that both cone types respond equally well to flicker at rates at least as high as 46 Hz. Differences in the temporal response properties of these two cone mechanisms must arise largely from post-receptoral interactions.

Action Potentials↗
PubMed1988

Ultrastructural study of the effects of chloroquine and verapamil on Plasmodium falciparum.

Verapamil, a calcium antagonist, has recently been shown to reverse chloroquine resistance in malarial parasites in vitro. We report the first ultrastructural morphological changes associated with this phenomenon using chloroquine-sensitive and -resistant clones of Plasmodium falciparum. While the administration of 6.3 x 10(-8) M chloroquine had little morphological effect on the chloroquine-resistant strain, the combination of chloroquine and verapamil resulted in typical chloroquine-related food vacuolar swelling with increased amounts of granular matrix. Secondary morphological changes included degeneration of nuclei, mitochondria, and other organelles. These effects appeared similar to those in the chloroquine-sensitive strain of P. falciparum treated with chloroquine alone or with the chloroquine/verapamil combination. Furthermore mild food vacuolar changes were seen in a small number of parasites (from both chloroquine-sensitive and -resistant groups) exposed to high concentrations (1 x 10(-4) M) of verapamil alone.

Animals↗
PubMed1987

Polymorphism of photopigments in the squirrel monkey: a sixth phenotype.

We describe here a trichromatic type of squirrel monkey that resembles Old World monkeys in having two well-separated photopigments in the red-green part of the spectrum; the cones of this phenotype have peak sensitivities close to 430, 536 and 564 nm. The existence of such animals is predicted by a genetic model that postulates three alleles for a single locus on the X-chromosome of the squirrel monkey. The three alleles correspond to three different photopigments in the red-green spectral range. A male monkey, or a homozygous female, will be dichromatic, combining short-wave cones with just one of the cone types in the red-green range. But a female monkey, if heterozygous at the locus, draws any two of the three alleles from the set. X-chromosome inactivation ensures that the two alleles are expressed in different subpopulations of retinal cone, giving the monkey the basis for trichromatic colour vision. This model requires three trichromatic types of female squirrel monkey. The photopigment complements of two types have previously been reported and microspectrophotometric data are now given for the third type. Behaviourally, this third type of trichromat gives precise Rayleigh matches that are intermediate between those of the other two types of trichromat. The polymorphism of photopigments in the squirrel monkey may be maintained by the heterozygous advantage enjoyed by the trichromatic females. This would be an instructive instance of heterozygous advantage because it is a case where X-chromosome inactivation plays a crucial role in segregating the two different gene-products into different cells.

Animals↗
PubMed1987

Action spectrum of the retinal mechanism mediating nocturnal light-induced suppression of rat pineal gland N-acetyltransferase.

The spectral properties of the retinal mechanism mediating the inhibitory effects of nocturnal light on pineal gland N-acetyltransferase (NAT) activity were determined. Pineal gland NAT activity declined linearly in albino rats exposed to different irradiances of a 460 or 580 nm monochromatic light during the middle of the dark phase of the cycle. The difference in sensitivity to the test lights is that predicted for a photopigment having peak absorbance at 495 nm, suggesting the inhibition of pineal gland N-acetyltransferase activity is mediated by the photopigment found in rat rods.

Acetyltransferases↗
PubMed1987

Increment thresholds of the three spectral mechanisms in the retina of the California ground squirrel (Spermophilus beecheyi).

Increment threshold (IT) functions were obtained for the electroretinogram (ERG) and for single units in the optic nerve of the California ground squirrel. The three spectral mechanisms providing input to ganglion cells in this retina were isolated and their increment thresholds to large field, long-duration stimuli were examined. Mean IT functions for the 519 nm mechanism (irrespective of unit class), the 500 nm mechanism, and the ERG all showed shallow log-log slopes between 0.52 and 0.63. The slope of the mean IT function for the 440 nm mechanism depended on the spectral character of the adapting light. When the dominant wavelength of this light was close to the peak sensitivity of the 440 nm mechanism, the mean IT function was steep (0.92), but when the dominant wavelength of the adapting light was at the cross-point of the opponent cells, the slope of the function was shallow (0.49). The difference in IT slope under these two conditions may be attributed to an additional sensitivity loss occuring at a spectrally-opponent site.

Animals↗
PubMed1987

Early color deprivation and subsequent color vision in a dichromatic monkey.

A squirrel monkey (Saimiri sciureus) was reared for the first 4 months of life in a dim, colorless environment. Following an additional 10 months of normal visual experience, tests of color vision and spectral sensitivity were run on this animal and a control subject. The results suggest that the adult expression of dichromatic color vision does not depend on color experience during the first 4 months of life.

Animals↗
PubMed1987

Color vision polymorphism and its photopigment basis in a callitrichid monkey (Saguinus fuscicollis).

The color vision of five saddle-backed tamarins (Saguinus fuscicollis) was studied. Behavioral tests of color discrimination and spectral sensitivity indicate that this species has a color vision polymorphism. Individual monkeys have either dichromatic or trichromatic color vision. Measurements of the spectral sensitivity of cones on this species were made on nine animals with the technique of electroretinogram (ERG) flicker photometry. Both the electrophysiological and the behavioral results suggest that there are four classes of cone pigment in this species. In addition to a short wavelength sensitive cone, apparently common to all tamarins, there are three classes of middle to long wavelength cone (lambda max = 545, 557 and 562 nm). Individual animals have either one or two of the latter types. The color vision variation in this species differs for males and females.

Adaptation, Ocular↗
PubMed1987

Polymorphism of the middle wavelength cone in two species of South American monkey: Cebus apella and Callicebus moloch.

The spectral sensitivity of the middle wavelength cone was measured in two species of South American monkey, Cebus apella and Callicebus moloch, using electroretinogram (ERG) flicker photometry. Both of these species were found to have a polymorphism of the middle wavelength cone. Eight male Cebus monkeys each had only a single type of middle wavelength cone having lambda max values of either 550 or 562 nm. Eight Callicebus monkeys (7 male, 1 female) showed a similar polymorphism of the middle wavelength cone (lambda max = 549 or 561 nm). A single female of this latter species had two types of middle wavelength cone. The cone polymorphisms of these species appear very similar to that previously described for the squirrel monkey (Saimiri sciureus).

Adaptation, Ocular↗
PubMed1987

Inheritance of color vision in a New World monkey (Saimiri sciureus).

Squirrel monkeys (Saimiri sciureus) have a striking color-vision polymorphism; each animal has one of six different types of color vision. These arise from individual variation in the presence of three different middle- to long-wavelength cone pigments. The distribution of cone phenotypes was established for a large sample of squirrel monkeys, including several families, through analysis of a retinal gross potential. The results indicate that the inheritance of color vision in the squirrel monkey can be explained by assuming that the three middle- to long-wavelength cone pigments are specified by three alleles at a single locus on the X chromosome. This arrangement is discretely different from that found in Old World monkeys and humans.

Animals↗
PubMed1987

Molluscum contagiosum and the acquired immunodeficiency syndrome: clinical and immunological details of two cases.

We report here the clinical and immunological findings in two patients with molluscum contagiosum poxvirus infection and the acquired immunodeficiency syndrome (AIDS). These cases support earlier evidence that the molluscum contagiosum virus may act as cases support earlier evidence that the molluscum contagiosum virus may act as an opportunistic pathogen. There is now evidence that members of all five families of double stranded DNA-containing human viruses have been associated with unusual clinical manifestations in AIDS patients, and the significance of DNA virus infections in patients with AIDS is discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1987

An ultrastructural study of the effects of mefloquine on malaria parasites.

The ultrastructural changes induced by the administration of a recently developed antimalarial drug, mefloquine, were studied in mice infected with Plasmodium berghei and human erythrocytes infected with P. falciparum in vitro. Pronounced changes which occurred in both experiments comprised swelling of the parasites' food vacuoles with gradual loss of pigment granules, which did not form clumps as occurs with chloroquine. These findings suggest that the malarial parasites' food vacuole is the target of this drug.

Animals↗
PubMed1987

Hamartomatous malformation in the mitral valve's anterior leaflet.

We report a previously undescribed (to our knowledge) anomaly of the mitral valve's anterior leaflet: a cystic lesion that protruded from the atrial surface in the midportion near the base. The lesion consisted of large, irregularly shaped, endothelial-lined spaces separated by trabeculae of tissue containing atrial myocardial fibers. The endothelial-lined spaces communicated with the left ventricular cavity through an opening on the ventricular surface of the leaflet. Inasmuch as the anterior mitral leaflet arises embryologically by fusion of the endocardial cushions, the location of the lesion suggests that an anomaly in the fusion process might have been involved.

Hamartoma↗
PubMed1986

Spectral sensitivity of cat cones to rapid flicker.

Records obtained from the flicker photometric electroretinogram indicate that only a single spectral mechanism (lambda MAX = 555 nm) in the cat eye contributes to the response to 50 Hz flicker. A photopic mechanism (lambda MAX = 500-510 nm) detected in earlier studies does not respond to high frequency flicker.

Adaptation, Physiological↗
PubMed1986

Spectral mechanisms and color vision in the tree shrew (Tupaia belangeri).

The retina of the tree shrew (Tupaia belangeri) is heavily cone dominated, rods comprising less than 4% of the total photoreceptors. Spectral mechanisms and color vision were investigated in this species in both behavioral and electrophysiological experiments. In confirmation of an earlier investigation, the tree shrew was found to have a clear spectral neutral point (at ca 505 nm) and is thus a dichromat. Spectral sensitivity functions determined in an increment threshold discrimination task show two clear peaks (at ca 440 and 550-560 nm) with an intermediate region of lowered sensitivity centered at about 500 nm. Spectral sensitivity of the two cone types in this animal were determined using ERG flicker photometry. One of these cone classes has a peak at 556 nm; the other has a 444 nm peak.

Animals↗
PubMed1986

Reexamination of spectral mechanisms in the rat (Rattus norvegicus).

The spectral mechanisms of the rat were studied in electrophysiological and behavioral experiments. The photopic electroretinogram (ERG) was recorded (a) to rapidly flickering lights, (b) during the cone phase of dark adaptation, and (c) with a flicker photometric procedure. Each procedure indicated the presence of a single cone mechanism having a lambda max of about 510 nm. Increment-threshold spectral sensitivity functions measured in a behavioral test situation yielded the same conclusion. A behavioral experiment failed to produce any evidence for the presence of color vision in this rodent. The consistent conclusion from both behavioral and electrophysiological experiments is that the rat retina contains only a single photopic spectral mechanism.

Animals↗
PubMed1986

Retinoid-binding proteins in cone-dominant retinas.

We identified and localized interphotoreceptor (or interstitial) retinoid-binding protein (IRBP) and cellular retinaldehyde-binding protein (CRALBP) in the cone-dominant retinas of diurnal squirrels. Western blots were prepared from sodium dodecyl sulfate polyacrylamide gels (SDS-PAGE) from whole retina, and from retina proximal and distal to the photoreceptor nuclei. Blots were incubated with purified rabbit IgG's specific for the bovine retinal antigens, and the labeled components were visualized using immunoperoxidase techniques. Anti-bovine IRBP and anti-bovine CRALBP recognized single components on gels of retinal supernatants that corresponded to the electrophoretic migration of the bovine antigens. The component recognized by anti-bovine IRBP on blots of outer retinal proteins (Mr 146,000) was absent on blots of inner retinal proteins. Twelve and 24 hr after intravitreal injection of 3H-L-fucose, electropherograms showed one major peak of radioactivity that coincided with the component recognized by anti-bovine IRBP. By immunoelectron microscopy, anti-bovine CRALBP labeling was restricted to the cytoplasm of both RPE and Muller cells, with light labeling of nuclear euchromatin in both cell types. In contrast, anti-bovine IRBP recognized antigenic sites primarily in the interphotoreceptor space (IPS). Intracellular labeling was limited to occasional granules in the photoreceptor myoids and the apical RPE cytoplasm. Extracellular labeling with anti-bovine IRBP was strongly associated with patches or small clumps of amorphous, electron opaque material distributed throughout the IPS. This material was particularly prominent near the cone outer segment plasma membranes, and was tentatively identified as the residual interphotoreceptor matrix that remained after exposure to the solvents used during tissue processing. In general, the results are consistent with those obtained in rod-dominant species. In addition, they imply that cones as well as rods are responsible for IRBP synthesis in the ground squirrel.

Animals↗