Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Up- and down-regulation of synaptic strength (i.e., long-term potentiation, LTP, long-term depression) is thought to be the primary mechanism mediating experience-dependent plasticity of cortical networks. Recent evidence indicates that the expression of plastic changes at synapses itself is dynamic and regulated, at least in part, by the recent history of synaptic activity, a concept termed metaplasticity. Here, adult, urethane-anesthetized rats were exposed to light or dark conditions for various durations (1, 2, and 5 h) to influence activity levels in the retinal-dorsal lateral geniculate nucleus (dLGN)-primary visual cortex (V1) pathway. Field potentials, recorded in layer IV of V1, were evoked by light flashes to the retina or single pulse electrical stimulation of the dLGN. Brief (60 s) periods of high frequency (50 Hz) retinal light stimulation results in an increase in visual evoked potential (VEP) amplitude in animals exposed to complete darkness for 2 h, while VEP amplitude failed to show potentiation in animals maintained in darkness for shorter periods. Similarly, weak theta burst stimulation of the dLGN failed to induce LTP in animals maintained under continuous light, but elicited robust LTP after 5 h of dark exposure. These data demonstrate that induction thresholds for sensory- and electrically-induced LTP in the retino-geniculo-cortical pathway of adult rats are dynamically regulated by levels of preceding sensory stimulation. Importantly, such metaplastic adjustments of plasticity in V1 can occur over time-scales significantly shorter than previously recognized.
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PMID:Short-term (2 to 5 h) dark exposure lowers long-term potentiation (LTP) induction threshold in rat primary visual cortex. 1940 76

The fundus reflexes reveal, in a manner not yet completely understood, the texture and contour of the reflecting surfaces and the condition of the underlying tissues. In this way they may play an important part in the biomicroscopy of the eye.The physiological reflexes are seen at their best in the eyes of young subjects, in well-pigmented eyes, with undilated pupils and with emmetropic refraction. Their absence during the first two decades, or their presence after the forties, their occurrence in one eye only, their appearance, disappearance or change of character should suggest the possibility of some pathological state.The investigation and interpretation of the reflexes are notably assisted by comparing the appearances seen with long and short wave lights such as those of the sodium and mercury vapour lamps, in addition to the usual ophthalmoscopic lights. Most of the surface reflexes disappear in the light of the sodium lamp, sometimes revealing important changes in the deeper layers of the retina and choroid.The physiological reflexes, chiefly formed on the surface of the internal limiting membrane, take the forms of the familiar watered silk or patchy reflexes, the peri-macular halo, the fan reflex in the macular depression and the reflex from the foveal pit. The watered silk or patchy reflexes often show a delicate striation which follows the pattern of the nerve-fibre layer, or there may be a granular or criss-cross texture. Reflexes which entirely lack these indications of "texture" should be considered as possibly pathological. This applies to the "beaten metal" reflexes and to those formed on the so-called hyaloid membrane.The occurrence of physiological reflexes in linear form is doubtful, and the only admittedly physiological punctate reflexes are the so-called Gunn's dots.Surface reflexes which are broken up into small points or flakes are pathological, and are most frequently seen in the central area of the fundus in cases of pigmentary degeneration of the retina or after the subsidence of severe retinitis or retino-choroiditis.A mirror reflex from the layer of pigmented epithelium or from the external limiting membrane is sometimes recognizable in normal eyes, especially in the brunette fundus. In such, it forms the background to a striking picture of the fine circumfoveal vessels.Pathological reflexes from the level of the pigmented epithelium or of the external limiting membrane are also observed, and these often present a granular, frosted or crystalline appearance. They may indicate a senile change, or result from trauma or from retino-choroidal degeneraion. Somewhat similar reflexes may sometimes be present as small frosted patches anterior to the retinal vessels.Linear sinuous, whether appearing in annular form, as straight needles, as broader single sinuous lines, as the tapering, branched double reflexes of Vogt, or in association with traction or pressure folds, in the retina, are probably always pathological.By the use of selected light of long and short wave lengths, it can be shown that intraretinal or true retinal folds may exist with or without the surface reflexes which indicate a corresponding folding of the internal limiting membrane. On the other hand, superficial linear reflexes of various types may occur without evidence of retinal folding.Annular reflexes usually accompany a rounded elevation of the retina due to tumour, haemorrhage or exudate, but may indicate the presence of rounded depressions; traction folds occur where there is choroido-retinal scarring, or in association with macular hole or cystic degeneraion at the macula; pressure folds in cases of orbital cyst, abscess or neoplasm; and the other linear reflexes in association with papillo-retinal oedema, for example, in retrobulbar neuritis, in hypertensive neuro-retinitis, in contusio bulbi and in anterior uveitis.Punctate reflexes, other than Gunn's dots, are also pathological. They may occur as one variety of "fragmented" surface reflexes, or as evidence of the presence of some highly refractile substance, such as cholesterin or calcium carbonate, in a retinal exudate or other lesion.It is characteristic of the pathological reflexes that they come and go and change their character according to the progress of the pathological condition. The linear reflexes in particular may change from one from to another, and may be finally transformed into surface reflexes of physiological character.
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PMID:The Reflexes of the Fundus Oculi: (Section of Ophthalmology). 1999 7

Light is a powerful modulator of higher-order cognitive processes such as mood but it remains unclear which neural circuits mediate the impact of light on affective behavior. We found that light deprivation produces a depressive-like behavioral state that is reversed by activation of direct retinal signals to the serotonergic dorsal raphe nucleus (DRN) in a manner equivalent to treatment with the selective serotonin reuptake inhibitor fluoxetine. Surprisingly, the DRN-projecting retinal ganglion cells (RGCs) are indistinguishable from the classic alpha/Y-like RGC type that contributes to image-forming visual pathways. Silencing RGC firing or specific immunotoxin ablation of DRN-projecting RGCs increased depressive-like behavior and reduced serotonin levels in the DRN. Serotonin has a key role in the pathophysiology of depression, and these results demonstrate that retino-raphe signals modulate DRN serotonergic tone and affective behavior.
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PMID:Direct retino-raphe projection alters serotonergic tone and affective behavior. 2337 Jan 56

A significant number of depressed people are resistant to drug therapy. Promising alternative therapy may be brain stimulation achievable by diverse methods. In a mouse model of depression, we previously investigated the mechanisms by which repetitive transcranial magnetic stimulation (rTMS) reverses depression-like behavior, and found an essential involvement of the immediate early gene product Homer1a. Home1a is known to be expressed not just by rTMS but also by photic stimulation (PS) via activation of the retino-geniculo-cortical pathway, suggesting that PS may have an antidepressant effect. This was tested by using a two-phase version of forced swimming (FS), in which the first phase consists of a 10-min swimming for 5 consecutive days and the second phase takes place at a 4-week interval for testing behavior. During the 4-week period, PS was applied everyday (300lx, 2Hz for 6h daily). After the last swimming, the brains were removed and subjected to quantitative RT-PCR and electrophysiological analysis. The 4-week-long PS alleviated depression-like behavior to the extent comparable to that obtained with rTMS previously. Homer1a expression was drastically reduced by FS and recovered by PS. Consistently with our previous studies, activity of the large conductance calcium-activated potassium (BK) channel was facilitated by PS in a Homer1a-dependent manner. PS may thus have a potential utility for depression therapy. Furthermore, given that Homer1a is implicated in various neuropsychiatric disorders, brain stimulations that induce Homer1a expression, such as rTMS or PS, may have a wider applicability than currently thought.
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PMID:Homer1a-dependent recovery from depression-like behavior by photic stimulation in mice. 2598 87

Observations from clinical trials have frequently demonstrated that light therapy can be an effective therapy for seasonal and non-seasonal major depression. Despite the fact that light therapy is known to have several advantages over antidepressant drugs like a low cost, minimal side-effects, and fast onset of therapeutic effect, the mechanism underlying light therapy remains unclear. So far, it is known that light therapy modulates mood states and cognitive functions, involving circadian and non-circadian pathways from retinas into brain. In this review, we discuss the therapeutic effect of light on major depression and its relationship to direct retinal projections in the brain. We finally emphasize the function of the retino-raphe projection in modulating serotonin activity, which probably underlies the antidepressant effect of light therapy for depression.
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PMID:The Antidepressant Effect of Light Therapy from Retinal Projections. 2943 May 86

Synaptic short-term plasticity (STP) regulates synaptic transmission in an activity-dependent manner and thereby has important roles in the signal processing in the brain. In some synapses, a presynaptic train of action potentials elicits post-synaptic potentials that gradually increase during the train (facilitation), but in other synapses, these potentials gradually decrease (depression). We studied STP in neurons in the visual thalamic relay, the dorsal lateral geniculate nucleus (dLGN). The dLGN contains two types of neurons: excitatory thalamocortical (TC) neurons, which transfer signals from retinal afferents to visual cortex, and local inhibitory interneurons, which form an inhibitory feedforward loop that regulates the thalamocortical signal transmission. The overall STP in the retino-thalamic relay is short-term depression, but the distinct kind and characteristics of the plasticity at the different types of synapses are unknown. We studied STP in the excitatory responses of interneurons to stimulation of retinal afferents, in the inhibitory responses of TC neurons to stimulation of afferents from interneurons, and in the disynaptic inhibitory responses of TC neurons to stimulation of retinal afferents. Moreover, we studied STP at the direct excitatory input to TC neurons from retinal afferents. The STP at all types of the synapses showed short-term depression. This depression can accentuate rapid changes in the stream of signals and thereby promote detectability of significant features in the sensory input. In vision, detection of edges and contours is essential for object perception, and the synaptic short-term depression in the early visual pathway provides important contributions to this detection process.
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PMID:Short-term Synaptic Depression in the Feedforward Inhibitory Circuit in the Dorsal Lateral Geniculate Nucleus. 2980 82


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