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Biomedical subjects

B B Lee

Publications and source records attributed to B B Lee.

153 records · Page 9Linked to original sources
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A comparison of the 40-Hz response in man, and the properties of macaque ganglion cells.

Visually evoked field potentials in human subjects and single-cell responses from retinal ganglion cells in the macaque monkey were compared in closely similar stimulus situations. The classical heterochromatic flicker photometry (HFP) technique was used to measure spectral sensitivity in man, both psychophysically and by recording the 40-Hz response, and to measure the spectral sensitivity of magnocellular (MC-) pathway cells of the macaque. The three measures gave closely similar spectral-sensitivity curves. Close agreement between the three measures was also found when the variable-modulation HFP technique was used to measure spectral sensitivity. When the relative phase between red and green lights was varied, the point of minimum subjective flicker for human observers was close to a sharp minimum found in the amplitude of the 40-Hz response in human and was also close to a minimum in the response of MC-pathway neurons in the monkey. The human 40-Hz response saturated at between 10 and 30% modulation depth, and so did the response of MC-pathway cells in the monkey. The 16-Hz response in human showed none of the above correlations with MC-pathway properties. On the other hand, parvocellular (PC-) pathway cells responded vigorously to constant-luminance, chromatic modulation, at frequencies higher than can be detected by human observers. The human 16-Hz response also was strong in that stimulus situation. In addition, the response of PC-pathway cells on increasing modulation depth showed little saturation, and this behaviour was paralleled by the human 16-Hz response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
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Topography of ganglion cells and photoreceptors in the retina of a New World monkey: the marmoset Callithrix jacchus.

We studied the anatomical substrates of spatial vision in a New World monkey, the marmoset Callithrix jacchus. This species has good visual acuity and a foveal specialization which is qualitatively similar to that of humans and other Old World primates. We measured the spatial density of retinal ganglion cells and photoreceptors, and calculated the relative numbers of these cell populations. We find that ganglion cells outnumber photoreceptors by between 2.4:1 and 4.2:1 in the fovea. The peak sampling density of ganglion cells is close to 550,000 cells/mm2. This value falls by almost 1000-fold between the fovea and peripheral retina; a value which approaches recent estimates of the centroperipheral ganglion cell gradient for human and macaque monkey retina and primary visual cortex. The marmoset shows a sex-linked polymorphism of color vision: all male and some female marmosets are dichromats. Six of the retinas used in the present study came from animals whose chromatic phenotype was identified in electrophysiological experiments and confirmed by polymerase chain reaction (PCR) amplification of cone opsin encoding genes. One animal was a trichromat and the others were dichromats. Antibodies against short wavelength-sensitive (SWS) cones labeled close to 8% of all cones near the fovea of one dichromat animal, consistent with electrophysiological evidence that the SWS system is present in all marmosets. The topography and spatial density of cone photoreceptors and ganglion cells was similar to that reported for macaque retina, and we found no obvious difference between dichromatic and trichromatic marmoset retinas. These results reinforce the view that the main determinate of primate foveal topography is the requirement for maximal spatial resolution.

Animals↗
PubMedDate not supplied

Steady discharges of macaque retinal ganglion cells.

Steady discharges were collected from ganglion cells of the magnocellular (MC) and parvocellular (PC) pathways of the macaque while their receptive fields were uniformly illuminated with a 4.7-deg steady yellow light of photopic illuminance. The mean rates, coefficients of variation, interval distributions, serial correlation coefficients, and power spectra of these discharges were determined. The results presented permit one to estimate the noise power in the discharges of macaque ganglion cells and hence determine how visual signals of different amplitudes will be affected by the noise resident in their discharges. Although there was some small serial correlation in the discharges of both MC- and PC-pathway cells, their discharges can be considered to result from renewal processes with reasonable accuracy. As with the discharges of cat ganglion cells, macaque ganglion cell discharges can be considered to have approximately gamma-distributed intervals. Steady discharges of MC- and PC-pathway cells show considerable overlap in their statistics, although small but significant differences are present.

Action Potentials↗
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Receptive fields of primate retinal ganglion cells studied with a novel technique.

We have reinvestigated receptive-field structure of ganglion cells of the macaque parafovea using counterphase modulation of a bipartite field. Receptive fields were mapped with luminance, chromatic, and cone-isolating stimuli. Center sizes of middle (M) and long (L) wavelength cone opponent cells of the parvocellular (PC) pathway were consistent with previous estimates (Gaussian radii of 2-4 min of arc, corresponding to center diameters of 6-12 min of arc). We calculate that a large factor of the enlargement relative to cone radius could be blur due to the eye's natural optics. Maps were consistent with cone selectivity in surround mechanisms, which had radii of 5-8 min of arc. For magnocellular (MC) cells, center size estimates were also consistent with grating measurements from the literature (also Gaussian radii of 2-4 min of arc). The surround mechanism contributing the MC-cell frequency-doubled response to chromatic modulation appears to possess a subunit structure, and we speculate it derives from nonlinear summation of signals from M,L-cone opponent subunits, such as midget bipolar cells.

Animals↗
PubMedDate not supplied

Ganglion cells of a short-wavelength-sensitive cone pathway in New World monkeys: morphology and physiology.

We have studied the morphology and physiology of retinal ganglion cells of a short-wavelength-sensitive cone (SWS-cone) pathway in dichromatic and trichromatic New World anthropoids, the capuchin monkey (Cebus apella) and tufted-ear marmoset (Callithrix jacchus). In Old World anthropoids, in which males and females are both trichromats, blue-ON/yellow-OFF retinal ganglion cells have excitatory SWS-cone and inhibitory middle- and long-wavelength-sensitive (MWS- and LWS-) cone inputs, and have been anatomically identified as small-field bistratified ganglion cells (SB-cells) (Dacey & Lee, 1994). Among retinal ganglion cells of New World monkeys, we find SB-cells which have very similar morphology to such cells in macaque and human; for example, the inner dendritic tree is larger and denser than the outer dendritic tree. We also find blue-on retinal ganglion cells of the capuchin to have physiological responses strongly resembling such cells of the macaque monkey retina; for example, responses were more sustained, with a gentler low frequency roll-off than MC-cells, and no evidence of contrast gain control. There was no difference between dichromatic and trichromatic individuals. The results support the view that SWS-cone pathways are similarly organized in New and Old World primates, consistent with the hypothesis that these pathways form a phylogenetically ancient color system.

Animals↗
PubMedDate not supplied

Current concepts in lymphatic malformation.

A lymphatic malformation (LM) is the most common form of congenital vascular malformation (CVM). The new Hamburg classification of CVM distinguishes the truncular (T) form from the extratruncular (ET) form of LMs. Both are consequences of a developmental arrest at the different stages of lymphangiogenesis as a result of defective genes. The purpose of this review was to evaluate the current management results of both forms of LMs. A retrospective review of the clinical data of 315 patients with a diagnosis of LMs treated between September 1994 and December 2001 was performed. Lymphoscintigraphy was the most frequent diagnostic test. The patients with the ET form were treated with sclerotherapy with OK-432 and/or ethanol. Combinations of CDP (complex decongestive physiotherapy) and/or compressotherapy were used to treat all the T-form patients. In addition, surgery, either reconstructive or ablative, was offered to patients with the T form who failed to respond to the proper CDP. A multidisciplinary team performed the management of LM, and the results were evaluated every 6 months. Among 797 patients with CVM, 315 were confirmed to have LMs, either as the T form (226) or the ET form (89). Another 66 LMs were diagnosed with hemolymphatic malformations (HLM). Most of the ET forms (89/315) were the cystic type (70/89), while the T forms included aplasia and/or an obstruction (204/226). The ET form was most frequent in the head, neck, and thorax (69/89). The T form was located most frequently to the extremities (202/226), mostly to the lower limb (180/202). Two hundred and twenty-six T forms belonged to the various clinical stages: stages I-32, II-104, III-48, IV-18, and an unclear stage-24. The ET form was treated with sclerotherapy using OK-432 (108/120) and absolute ethanol (12/120). Among the 11 patients with the multiple ET form, 7 patients underwent perioperative sclerotherapy with OK-432 and a subsequent surgical excision. The clinical response of the T form at the extremity to CDP was excellent to good in a majority of clinical stages I to II (121/136) but decreased to a good to fair degree in stages III to IV (31/66). The additional surgical therapy, either reconstructive (10/19) or ablative (9/19), provided limited success in improving CDP efficacy, owing mainly to poor compliance. The long-term outcome of the initial success through self-motivated home-maintenance care during the follow-up period of up to 48 months was totally dependent on patient compliance. OK-432 sclerotherapy to 51 ET forms has shown excellent results on 88.9% of the cystic type (40/45) and 50% (3/6) of the cavernous type (minimum follow-up for 24 months). Seventeen ET forms in 7 patients were treated with a preoperative OK-432 sclerotherapy and a subsequent surgical excision, which provided good to excellent results in 14 for a minimum of 24 months. Primary lymphedema, which is the T form of LMs, can be managed safely by a combination of CDP with compressotherapy. Patients with good compliance can benefit from additional surgical therapy, either reconstructive or ablative. The ET form, particularly the cystic type, can be treated with various scleroagents that are preferably less toxic as the primary therapy. A surgical excision with or without perioperative sclerotherapy provides good results for patients with the localized cavernous type of the ET form. A multidisciplinary team approach is essential for the proper care of LM.

Adolescent↗