A disynaptic sensorimotor pathway in the lobster stomatogastric system

1. In the lobster Homarus, muscle gm 1 that causes protraction of the medial tooth of the gastric mill system is innervated via a dorsal branch of the anterior gastric nerve by motoneurons (GM) arising in the stomatogastric ganglion (STG) (Fig. 1). 2. A ventral branch of the anterior gastric nerve (VAGN) contains a single unit that is mechanosensitive, responds to gentle pressure on the stomach wall in the vicinity of gm 1, and evokes reflex activation of GM motoneurons (Fig. 2). 3. This mechanoreceptor neuron (called anterior gastric receptor, AGR) has been identified morphologically (Fig. 3) and electrophysiologically (Figs. 4 and 5). The bipolar cell body is located in the dorsal ventricular nerve immediately posterior to the STG. It sends out long peripheral processes in the left and right VAGNs to ramify bilaterally in the epidermis of the stomach wall underlying muscle gm 1. The axon of the AGR runs anteriorly through the STG and projects to the left and right commissural ganglia (CoGs) via the stomatogastric (STN) and inferior esophageal nerves. 4. AGR activation of GM motoneurons disappears after cutting the STN, indicating that the reflex is mediated by an axonal pathway involving rostral ganglia (Fig. 6). 5. Electrophysiological (Fig. 7) and morphological (Fig. 8) methods were used to identify an interneuron (commissural gastric neuron, CG) located in each CoG and intercalated between AGR and GM. Axons of the two CGs project to the STG via the superior esophageal nerves and the STN. 6. Simultaneous intracellular recordings from the three cell types demonstrate that AGR excites CG, which in turn excites GM; in each case excitatory postsynaptic potentials follow presynaptic impulses one for one and at constant latency (Fig. 9). Raising the threshold for spiking with saline containing high divalent cation concentrations further indicates that both excitatory connections are monosynaptic and confirms that AGR does not directly excite GM motoneurons (Fig. 10). 7. The input/output properties of AGR in this disynaptic excitatory pathway (Fig. 11) are discussed as also are the functional implications of such a long-loop pathway for sensorimotor integration.     

The effect of abnormal fixational eye movements upon visual acuity in congenital nystagmus.

PURPOSE: The purpose of this study was to investigate the role that abnormal eye movements play in the degradation of visual acuity. METHODS: Visual acuity was measured monocularly in 10 normal subjects (26.7+/-4.3 years) and 5 subjects with congenital nystagmus (34.9+/-8.8 years), using Regan Repeat Letter charts (RRL) and a logMAR based test (LogMAR Crowded Acuity Test (CAT)) while eye movements were continuously recorded using a commercially available infrared limbal eye tracker (Type 54, Optoelectronic Developments, UK). The eye tracker was controlled via a virtual oscilloscope (Viewdac, Keighly Instruments, UK) on an IBM PC clone (Opus Technology 486). RESULTS: The mean visual acuity obtained with RRL was significantly higher than that obtained by CAT in the subjects with congenital nystagmus. A significant correlation was found between the root mean square value of the nystagmus waveform and the angular extent of CAT. Linear regression analysis revealed a correlation between the duration of the foveation periods and the linear acuity of the subjects with congential nystagmus. The nystagmus waveforms also demonstrated increased amounts of high frequency components (HFC: >3.0 Hz) when compared to the normal eyes. CONCLUSIONS: The results of this study reveal 1) RRL charts provide a measure of a subjects resolution limit which is less dependent on eye movements; 2) the duration of foveation periods has a significant effect on visual acuity measurements obtained using a linear test chart format; 3) the predominance of high frequency components in the congenital nystagmus waveforms lead to short foveation periods adding to the degree of fixation instability.     

空间与时间对比敏感度是你看到一个模糊世界的关键衡量尺度吗?

目标:一直都有所记录的事实是:弱视者的视力和对比敏感度在高空间频率下都被削弱,这就显示了弱视者看东西应该是模糊的。因为他们没有反映足够清晰边角所必需的高空间频率的资料。在我们的研究中,我们用模糊辨别和模糊配对的任务来探索弱视者的模糊视觉表现。方法:我们测量了单眼模糊辨别的阈值,受试者要求辨别那一边的边界(左或右)没那么模糊。他们同时用两眼分视的方法用好眼把边界调整到与差眼看的视标(目标图)相同的模糊度。结果:弱视眼和健眼的模糊辨别阈值都有所升高,但两眼配对的阈值就在正常范围内。总结:结果显示弱视者视觉系统里的不确切视觉表现有模糊的现象。但令人惊讶的是所有弱视者,甚至那些重度患者,都能正确配对所有的模糊边界,包括最清晰的边界。这就暗示了弱视者能正确反映一定程度的模糊,并定义这一模糊程度的空间结构是超出他们的辨别能力的。     

Snakes and ladders: the role of temporal modulation in visual contour integration.

We investigated temporal aspects of the cortical mechanisms supporting visual contour integration by measuring observers' efficiency at detecting fragmented contours, composed of Gabor micropatterns, embedded in a field of distractor elements. Gabors consisted of a static Gaussian enveloping a sinusoidal carrier which was temporally modulated by motion or counter-phase flicker. The elements forming the path could be oriented either parallel ('snakes') or perpendicular to the contour orientation ('ladders'). Sensitivity to contour structure (estimated by measuring the maximum tolerable element orientation jitter supporting contour detection) was increased when the elements were drifting or flickering. Snakes were more detectable than ladders under all conditions. The increase in sensitivity conferred by drifting carriers was present even when the elements in the same stimulus were drifting at a range of speeds spanning almost three octaves. These results lend further support to the notion that the contour integration system receives separate transient and sustained input.     

Grouping local directional signals into moving contours

We consider how local motion signals are combined to represent the movements of spatially extensive objects. A series of band-pass target dots, whose collective motion defined a moving contour, was positioned within a field of randomly moving noise dots. The visibility of the contours did not depend on the direction of movement relative to local contour orientation unless the contour was constrained to pass through fixation, suggesting that a previously reported advantage for collinear motion trajectories depends on the probability of detecting any of the target elements rather than the integrated contour. Contour visibility was invariant of the spatial frequency of the elements, but it did depend on the speed, number and spacing of elements defining it, as well as the angle and spatial frequency difference between adjacent elements. Local averaging of directional signals is not sufficient to explain these results. The visibility of these moving contours identifies narrow-band grouping processes that are sensitive to the shape defined by the directions of the elements forming the contour.     

The extent of the dorsal extra-striate deficit in amblyopia

Previously, we have shown that humans with amblyopia exhibit deficits for global motion discrimination that cannot be simply ascribed to a reduction in visibility or contrast sensitivity. Deficits exist in the processing of global motion in the fronto-parallel plane that suggest reduced extra-striate function (i.e., MT) in amblyopia. Here, we ask whether such a deficit also exists for rotation and radial components of optic flow that are first processed at higher sites along the dorsal pathway (i.e., MSTd). We show that similar motion processing deficits occur in our amblyopic group as a whole for translation, rotation, and radial components of optic flow and that none of these can be solely accounted for by the reduced visibility of the stimuli. Furthermore, on a subject-by-subject basis there is no significant correlation between the motion deficits for radial and rotational motion and those for translation, consistent with independent deficits in dorsal pathway function up to and including MSTd.     

Therapeutic implications of nanomedicine for ocular drug delivery

Delivering therapeutics to the eye is challenging on multiple levels: rapid clearance of eyedrops from the ocular surface requires frequent instillation, which is difficult for patients; transport of drugs across the blood–retinal barrier when drugs are administered systemically, and the cornea when drugs are administered topically, is difficult to achieve; limited drug penetration to the back of the eye owing to the cornea, conjunctiva, sclera and vitreous barriers. Nanomedicine offers many advantages over conventional ophthalmic medications for effective ocular drug delivery because nanomedicine can increase the therapeutic index by overcoming ocular barriers, improving drug-release profiles and reducing potential drug toxicity. In this review, we highlight the therapeutic implications of nanomedicine for ocular drug delivery.     

Localization of the G-CSF gene on chromosome 17 proximal to the breakpoint in the t(15;17) in acute promyelocytic leukemia

The human granulocyte-colony stimulating factor gene (G-CSF) is localized at 17q11.2-q21, the region of one of the breakpoints in the 15;17 chromosome translocation specific for acute promyelocytic leukemia (APL). As G-CSF induces differentiation and loss of tumorigenicity in myeloid leukemic cells or cell lines, it was possible that the translocation in APL involved the DNA of the G-CSF coding region or its regulatory region. In situ hybridization to chromosomes with the t(15;17) from patients with the APL translocation using a G- CSF cDNA clone revealed that the coding region of this gene is proximal to the t(15;17) breakpoint on chromosome 17. Southern analysis of DNA from patients with the APL translocation showed no differences in hybridization between normal and leukemic cells. These results indicate that the G-CSF coding sequence is not disrupted by the chromosomal rearrangement characteristic of APL.