Decrease In Light Sensitivity Research Articles

Role of point-by-point light sensitivity in the assessment of glaucoma progression

This study analyzes changes in light sensitivity in each test point of the visual field in patients with different stages of glaucoma. The data of a prospective analytical case-control study were analyzed. All patients underwent assessment of retinal light sensitivity and its variability in 54 points corresponding to the 24-2 program. Mean light sensitivity values were calculated in each point. Intergroup analysis was performed to evaluate changes in light sensitivity in each point. The range of light sensitivity decrease in the early glaucoma group compared to the control group was from 1.5 to 3.6 dB. The range of light sensitivity decrease in the moderate glaucoma group compared to the control group was from 2.1 to 11.5 dB, and compared to the early glaucoma group - from -0.9 to 7.9 dB. The most frequent decrease in light sensitivity was detected in the nasal sector and along the horizontal line in the upper half of the visual field. This trend persisted within the central 10 degrees of the visual field. The range of light sensitivity decrease in the advanced glaucoma group compared to the control group was from 14.1 to 28.0 dB, and compared to the early glaucoma group - from 11.35 to 26.08 dB, compared to the moderate glaucoma group - from 9.1 to 23.5 dB. The most frequent and severe decrease in light sensitivity was detected in the paracentral zone in the lower half of the visual field. The study analyzed the trends in the development of glaucoma from the early to the advanced stage. The most frequent and severe defect in light sensitivity in cases of verified advanced glaucoma was found in the lower half of the visual field. Points No. 32, 33 and 40 can be indicated as the area of interest in assessing the progression of glaucoma, as they were found to have the most profound changes in light sensitivity as glaucoma progressed.

Retinal neurodegeneration induced by sodium iodate administration and visual cortex activity

Aims/Purpose: Recently investigations have shown that using sodium iodate (NaIO3) provides a promising animal model of retinal neurodegeneration. The aim of this research is to characterize the effects of this compound in the visual pathway.Methods: First, a single dose of NaIO3 (65 mg/kg) was administered intraperitoneally to mice (C57BL/6J strain) with a knock‐out mutation for the Opn4 gene (Opn4−/−). Then, behavioural tests (light avoidance assay, optomotor test, pupillary light reflex) were performed until Day 28. Electrophysiological tests (electroretinogram, ERG; visual evoked potentials, VEP), were performed weekly until Day 42. Finally, the retina was analysed histologically by immunohistochemical methods on day 57th.Results: First, the results of the behavioural test in the experimental group (NaIO3) reflected a progressive decrease in light sensitivity after 28 days, and a decrease in visual acuity and as well as a completely loss of the pupillary light reflex after 7 days since the administration. Second, the electrophysiological activity of retina and primary visual cortex (ERG, VEP) was significantly reduced in the treated group (NaIO3) with respect to the control group. Finally, histological analysis of the retina showed structural alterations in the outer segments of the photoreceptors of the treated animals (NaIO3).Conclusions: This research demonstrates the appearance of alterations in the outer retina and a decrease in the response at the level of the visual cortex after NaIO3 administration, as expected. This confirms that NaIO3‐induced retinal neurodegeneration is effective in obtaining a promising experimental model that could be used in the study of diseases associated with the visual system and in the development of novel therapeutic strategies.

Clinical and imaging characteristics of optic nerve tumors as the differencial diagnosis of optic neuritis

Objective: To investigate the clinical and imaging features of optic nerve tumors that require differential diagnosis from optic neuritis. Methods: A retrospective case series study was conducted. Clinical data of patients diagnosed with optic nerve tumors from January 2017 to December 2021 at the Second Affiliated Hospital of Zhejiang University School of Medicine were collected. A total of 29 patients (39 eyes) with clinical and magnetic resonance imaging (MRI) findings similar to optic neuritis or optic neuropathy were included. There were 15 cases of optic nerve sheath meningioma (ONSM) (17 eyes), 4 cases of optic nerve glioma (ONG) (5 eyes), and 10 cases of infiltrative optic nerve lesions (ION) (17 eyes). All patients underwent best-corrected visual acuity (BCVA), anterior and posterior segment examinations, visual field examination, and orbital or cranial MRI examination. Patient data were observed and analyzed, treatment and follow-up information were recorded, and clinical and imaging features were summarized and compared with those of optic neuritis or optic neuropathy. Results: Among the 29 patients with optic nerve tumors, 10 were male and 19 were female, with an average age of (43.3±13.8) years and a range of 11 to 72 years. The follow-up time was 6.8 (2.0, 11.0) months, with a range of 1 to 33 months. Sixteen patients (21 eyes) with optic nerve tumors were initially misdiagnosed as having acute optic neuritis and showed poor response to steroid treatment. Of these, 9 cases (11 eyes) were ONSM, 4 cases (6 eyes) were ION, and 3 cases (4 eyes) were ONG. The diagnostic delay time was 7.1 (1.5, 12.0) months, with a range of 1 to 24 months. The main clinical symptoms of all affected eyes were acute vision loss in 23 eyes, slow vision loss in 5 eyes, transient blackouts in 4 eyes, and no obvious visual symptoms in 7 eyes. The median BCVA of all affected eyes was 0.1, ranging from light perception to 1.0. Fundus examination results showed optic disc edema in 34 eyes and normal optic disc in 5 eyes among the 39 eyes with optic nerve tumors. A total of 27 patients (33 eyes) completed visual field examinations, which revealed an enlarged physiological blind spot in 11 eyes, a concentric or tubular visual field contraction in 8 eyes, a diffuse decrease in light sensitivity in 7 eyes, an arcuate scotoma in 4 eyes, and a normal visual field in 3 eyes. All affected eyes completed orbital or cranial MRI examinations, which showed mild optic nerve thickening in 22 eyes, significant thickening in 6 eyes with distortion, and no significant thickening in 6 eyes. Contrast-enhanced T1-weighted imaging (T1WI) MRI showed optic nerve parenchymal thickening in 5 eyes, all of which were ONG, and 2 of them had optic nerve parenchymal enhancement. Optic nerve sheath thickening and enhancement without optic nerve parenchymal thickening or enhancement were observed in 28 eyes, including 17 eyes of ION and 11 eyes of ONSM. There were 6 eyes with no obvious optic nerve thickening, which were all ONSM, showing mild or significant thickening and enhancement of the optic nerve sheath without optic nerve parenchymal thickening or enhancement. Conclusions: Optic nerve tumors can present with ophthalmic clinical features similar to optic neuritis, such as optic disc edema, and demonstrate MRI findings that resemble those of optic neuritis. Therefore, differentiation between the two is crucial, based on differences in their natural course and response to steroid therapy.

Multifocal analysis of the bioelectric potential and light sensitivity of the retina in thrombotic microangiopathy associated with malignant arterial hypertension

This study evaluates the function of the retina according to multifocal electroretinography (mfERG) and its light sensitivity according to microperimetry (MP) in patients with thrombotic microangiopathy (TMA) associated with malignant hypertension (MH). The study analyzed mfERG and MP data of 20 patients (40 eyes) aged 40.4±7.4 years (18 men, 2 women) with MH-associated TMA. In all patients TMA of the kidneys was verified by nephrobiopsy. The control group consisted of 20 healthy individuals (40 eyes) of the appropriate age. A statistically significant decrease in the response density of P1 mfERG (nV/deg2) of the central retinal zone (0-27.7°) was found in study patients in comparison with the control group (p<0.05), differences in the latency of P1 mfERG (ms) were statistically insignificant (p>0.05). Analysis of MP data in study patients revealed a statistically significant decrease in the mean light sensitivity (dB) of the central field of vision (30°) (p<0.05) compared to the control group. A statistically significant correlation was found between the response density of P1 mfERG (nV/deg2) and mean light sensitivity (dB) in the corresponding quadrants of the visual field (p<0.05). A number of statistically significant correlations were found between the indicators of MP and mfERG and some non-ocular clinical manifestations of TMA in MH. A statistically significant decrease in the light sensitivity of the central field of vision caused by marked decrease in retinal function, probably of an ischemic nature, is characteristic for MH-associated TMA. In this disease the response density of P1 mfERG (nV/deg2) is a sensitive indicator of impaired retinal function. With the activation of systemic TMA, increase in blood pressure and deterioration of kidney function in MH, the light sensitivity of the eye also decreases.

Features of Visual Dysfunctions in Patients with Primary Hypothyroidism and Thyrotoxicosis

Purpose: to study the prevalence and nature of visual dysfunctions in patients with primary hypothyroidism and thyrotoxicosis.Material and methods. The material for this study was the results of a survey of 54 patients (108 eyes) with thyroid dysfunctions: 32 people (64 eyes) with primary untreated hypothyroidism and 22 people (44 eyes) with primary untreated thyrotoxicosis. Static automated perimetry and dedicated shortwave infrared (blue-yellow) perimetry were performed. The average total value of the photosensitivity of each (n = 74) tested point of the field of view was analyzed, the topography of the location of focal defects was studied, and the severity of impairments to photosensitivity was assessed by aggregate signs.Results. Reliably high sensitivity (92.6 %) and specificity (50.0 %) of short-wave infrared perimetry in relation to static automated perimetry were revealed. In thyroid dysfunctions, the prevalence of optic neuropathy reaches 93 % according to the data of short-wave infrared perimetry versus 7 % of static automated perimetry. It is manifested by a diffuse decrease in light sensitivity to blue stimulus with an increase in the depth of depression from the center to the periphery in both types of thyroid dysfunction. Against this background, with primary hypothyroidism, focal defects appeared in the form of first-order scotomas, and with primary thyrotoxicosis, second-order scotomas. Scotomas were located at the periphery of the central visual field, 20–30° from the fixation point. In the analyzed groups, high average group indices of the maximum corrected visual acuity were established, which allows us to speak about the safety of the photopic (cone) component of the visual analyzer.Conclusion. The pattern of photosensitivity disorders, the topography of the location of the loci of local defects revealed by the short-wave infrared perimetry, indicate that the earliest signs of optical neuropathy are manifested at the level of photoreceptors — selectively in the S-cones. Decreased sensitivity to blue stimulus (440 nm) refers to an acquired color anomaly called tritanopia; which can be present with high visual function, is most often associated with a decrease in the number of S-cones and a deficiency of retinol (the source of cyanolab synthesis).

Удаление идиопатических эпиретинальных мембран с сохранением фовеальной внутренней пограничной мембраны

Introduction. The epiretinal membrane (ERM) is a connective tissue structure on the surface of the retina, formed as a result of proliferative and dystrophic processes in the inner layers of the retina and the cortical layers of the vitreous body. ERM has contractile properties and could cause tangential tractions, retinal folding and edema. To ensure the maximum preservation of visual functions, a method of ERM removal with the preservation of foveal inner limiting membrane (ILM) is proposed. Purpose. To present results of a new approach for ERM removal with preservation of foveal ILM on a series of clinical cases. Material and methods. The study included 3 patients with a diagnosis of ERM, with the complaints of metamorphopsia of less than 8 months. In addition to the standard ophthalmological examination, patients underwent optical coherence tomography (CirrusHD-OCT 5000; Carl Zeiss Meditec) and microperimetry (MAIA; CenterVue). Surgical intervention consisted in minimally invasive three-port vitrectomy with removal of ERM and ILM with preservation of foveal ILM. In the postoperative period, patients were examined at the time of 1, 3 and 6 months. Results. The analysis of microperimetric data showed that the degree of functional disorders corresponded to morphological changes: ectopia of the inner layers of the retina, deformation of its normal profile, a pronounced decrease in light sensitivity in the projection area of traction macular edema. In the postoperative period, the indicators of central light sensitivity improved gradually throughout the entire follow-up period. Conclusion. Thus, the proposed low-traumatic method of ERM removal with the preservation of foveal ILM, provides a stable anatomical and functional result, the restoration of both morphological and functional parameters. The data presented in this paper require confirmation in further comparative clinical trials. Key words: epiretinal membrane, surgical treatment, internal limiting membrane

Multifocal electroretinography in assessment of the functional state of the central retina in patients with retinitis pigmentosa

To evaluate the information content of multifocal electroretinography (mfERG) in the diagnostics of the functional state of the central retina in retinitis pigmentosa (RP). The study included 115 patients (228 eyes) with PR and 15 people (30 eyes) who comprised the control group. All subjects underwent standard ophthalmological examination, computer perimetry, color vision study, retinal spectral optical coherence tomography, ganzfeld electroretinography (gERG) and mfERG. The relationship between mfERG parameters and the degree of gERG changes, as well as various functional and morphological parameters of the retina was assessed. Visual acuity and perimetry indices varied over a wide range. GERG was unrecordable in 50.4% of cases. MfERG was registered in 214 (98.3%) eyes with varying degrees of change in visual acuity, visual field and gERG parameters. A medium degree positive relationship was revealed between the biopotential density of the retina in the foveal and parafoveal zones and visual acuity (rs=0.68; 0.63), a high degree - between the density of ttotal biopotential of the central retina (DValue) and the average light sensitivity (rs=0.9), a weak degree - between DValue and the thickness and volume of the peripheral retina (rs=0.37; 0.42), a medium negative correlation was found between the average defect in light sensitivity and the biopotential density in the periphery (Rings 4-5) on mfERG, DValue (rs= -0.67; -0.65; -0.69). MfERG detects retinal dysfunctions at an early stage of RP, in eyes with high visual acuity, normal parameters of the central visual field and gERG, as well as in low visual acuity, a pronounced decrease in light sensitivity, unrecordable gERG. MfERG can be informative in the selection of patients with RP for gene therapy.

Phosducin-like protein 1 is essential for G-protein assembly and signaling in retinal rod photoreceptors.

G-protein β subunits perform essential neuronal functions as part of G-protein βγ and Gβ5-regulators of G-protein signaling (RGS) complexes. Both Gβγ and Gβ5-RGS are obligate dimers that are thought to require the assistance of the cytosolic chaperonin CCT and a cochaperone, phosducin-like protein 1 (PhLP1) for dimer formation. To test this hypothesis in vivo, we deleted the Phlp1 gene in mouse (Mus musculus) retinal rod photoreceptor cells and measured the effects on G-protein biogenesis and visual signal transduction. In the PhLP1-depleted rods, Gβγ dimer formation was decreased 50-fold, resulting in a >10-fold decrease in light sensitivity. Moreover, a 20-fold reduction in Gβ5 and RGS9-1 expression was also observed, causing a 15-fold delay in the shutoff of light responses. These findings conclusively demonstrate in vivo that PhLP1 is required for the folding and assembly of both Gβγ and Gβ5-RGS9.

P.2.d.005 Comparison of agomelatine and melatonin for effects in chronically stressed tree shrews, an animal model of depression

Light therapy is an effective treatment for patients with seasonal affective disorders and is commonly used at an intensity of 10,000 lx. The aim of this study was to investigate the direct impact of light therapy on cones and rods photoreceptors using the electroretinogram (ERG) technique. Twelve healthy subjects were exposed for 60 min to three light conditions: 10,000 lx, 100 lx and 5 lx. ERG cone and rod luminance response functions were obtained immediately after exposures. Cone function was not affected by any light conditions. Maximal response achieved by the rods was significantly lower following the 100 lx and 10,000 lx conditions when compared with the 5 lx condition. Retinal rod sensitivity was significantly lower in the 10,000 lx condition when compared with the 12 lx condition. A decrease in rod function can readily be observed at 100 lx, that is, at regular indoor lighting. This decrease could be related to the triggering of retinal dopamine production, which would favour day vision over night vision. The further decrease in light sensitivity observed after 60 min at 10,000 lx may be perceived as a protective mechanism of the rod system against bright light.

Calcium-dependent regulation of rhodopsin phosphorylation.

Depending on ambient light conditions, a rod photoreceptor cell adapts to a light stimulus. For example, when it is kept in the light, its light sensitivity decreases because of light adaptation. The adaptational state is regulated by the Ca2+ concentration in the cytoplasm ([Ca2+]i). The [Ca2+]i is high in the dark and becomes low when the cell is light-adapted. The change in [Ca2+]i is detected by several Ca(2+)-binding proteins that change their conformations by binding Ca2+. S-modulin, found in frog rods, or its bovine homologue recoverin, is a 23 kDa Ca(2+)-binding protein that inhibits rhodopsin phosphorylation at high Ca2+ concentrations by inhibiting rhodopsin kinase. Since rhodopsin phosphorylation is an inactivating mechanism for light-activated rhodopsin (R*), the inhibition of this reaction will prolong the lifetime of R*. In this way, S-modulin is expected to increase the efficiency of phototransduction and therefore the light-sensitivity of rods in the dark. When rods are light-adapted, [Ca2+]i decreases so that the lifetime of the R* is expected to reduce, resulting in a decrease in light sensitivity. Even though it is generally agreed that S-modulin inhibits rhodopsin phosphorylation, its physiological function is not yet well understood.

Impact of light therapy on rod and cone functions in healthy subjects

Light therapy is an effective treatment for patients with seasonal affective disorders and is commonly used at an intensity of 10,000 lx. The aim of this study was to investigate the direct impact of light therapy on cones and rods photoreceptors using the electroretinogram (ERG) technique. Twelve healthy subjects were exposed for 60 min to three light conditions: 10,000 lx, 100 lx and 5 lx. ERG cone and rod luminance response functions were obtained immediately after exposures. Cone function was not affected by any light conditions. Maximal response achieved by the rods was significantly lower following the 100 lx and 10,000 lx conditions when compared with the 5 lx condition. Retinal rod sensitivity was significantly lower in the 10,000 lx condition when compared with the 12 lx condition. A decrease in rod function can readily be observed at 100 lx, that is, at regular indoor lighting. This decrease could be related to the triggering of retinal dopamine production, which would favour day vision over night vision. The further decrease in light sensitivity observed after 60 min at 10,000 lx may be perceived as a protective mechanism of the rod system against bright light.

Occupancy of the chromophore binding site of opsin activates visual transduction in rod photoreceptors.

The retinal analogue beta-ionone was used to investigate possible physiological effects of the noncovalent interaction between rod opsin and its chromophore 11-cis retinal. Isolated salamander rod photoreceptors were exposed to bright light that bleached a significant fraction of their pigment, were allowed to recover to a steady state, and then were exposed to beta-ionone. Our experiments show that in bleach-adapted rods beta-ionone causes a decrease in light sensitivity and dark current and an acceleration of the dim flash photoresponse and the rate constants of guanylyl cyclase and cGMP phosphodiesterase. Together, these observations indicate that in bleach-adapted rods beta-ionone activates phototransduction in the dark. Control experiments showed no effect of beta-ionone in either fully dark-adapted or background light-adapted cells, indicating direct interaction of beta-ionone with the free opsin produced by bleaching. We speculate that beta-ionone binds specifically in the chromophore pocket of opsin to produce a complex that is more catalytically potent than free opsin alone. We hypothesize that a similar reaction may occur in the intact retina during pigment regeneration. We propose a model of rod pigment regeneration in which binding of 11-cis retinal to opsin leads to activation of the complex accompanied by a decrease in light sensitivity. The subsequent covalent attachment of retinal to opsin completely inactivates opsin and leads to the recovery of sensitivity. Our findings resolve the conflict between biochemical and physiological data concerning the effect of the occupancy of the chromophore binding site on the catalytic potency of opsin. We show that binding of beta-ionone to rod opsin produces effects opposite to its previously described effects on cone opsin. We propose that this distinction is due to a fundamental difference in the interaction of rod and cone opsins with retinal, which may have implications for the different physiology of the two types of photoreceptors.

Normal values for fundus perimetry with the scanning laser ophthalmoscope

Purpose: To evaluate the normal light sensitivity values for fundus perimetry and their short time fluctuation (reliability) in normal volunteers of different ages. After the development of full-threshold static fundus perimetry, age-corrected sensitivity values for normal subjects are required to interpret results and to compare them with conventional computerized perimetry. Method: Full-threshold fundus perimetry of the central field (33 × 21 degrees) by means of the scanning laser ophthalmoscope was performed on 152 eyes of 99 healthy persons aged 16 to 77 years with normal vision and no eye disease. Fixation was simultaneously documented. Light sensitivity values were evaluated according to each subject’s age and test point location. Results: Linear regression analysis disclosed a significant ( P < .0001) decrease of the mean sensitivity of 0.275 dB per decade of increasing age, starting with 16.6 dB at age 10 years. Standard deviation around the center of fixation was 0.287 degrees in the first decade, and it increased by 2.82 minutes of arc per decade ( P < .0001). Variation in triple examinations of subjects did not differ from short time fluctuation. Conclusion: Visual fields examined with fundus perimetry show reliable measurements in a range comparable to conventional computerized perimetry. There is a significant correlation between increase of age and decrease of light sensitivity in fundus perimetry. Visual fields obtained with fundus perimetry seem to correlate well with known data from computerized static threshold perimetry. It should be recognized that even in normal subjects, the stability of fixation decreases with increasing age.

Clinical effects of organophosphorus cholinesterase inhibitors.

Nerve agents, highly toxic organophosphorus cholinesterase inhibitors, inhibit acetylcholinesterase and cause an accumulation of acetylcholine. Clinical effects depend on the route and amount of exposure and include miosis, bronchoconstriction, excessive secretions, vomiting, seizures, and cessation of respiratory and cardiac activity. Eye effects include miosis, engorgement of ocular vessels, pain, and decrease in light sensitivity. Therapy consists of atropine, a cholinesterase reactivator (pralidoxime), and ventilation as needed.

Synechocystis sp PCC 6803 strains lacking photosystem I and phycobilisome function.

To design an in vivo system allowing detailed analysis of photosystem II (PSII) complexes without significant interference from other pigment complexes, part of the psaAB operon coding for the core proteins of photosystem I (PSI) and part of the apcE gene coding for the anchor protein linking the phycobilisome to the thylakoid membrane were deleted from the genome of the cyanobacterium Synechocystis sp strain PCC 6803. Upon transformation and segregation at low light intensity (5 microE m-2 sec-1), a PSI deletion strain was obtained that is light tolerant and grows reasonably well under photoheterotrophic conditions at 5 microE m-2 sec-1 (doubling time approximately 28 hr). Subsequent inactivation of apcE by an erythromycin resistance marker led to reduction of the phycobilin-to-chlorophyll ratio and to a further decrease in light sensitivity. The resulting PSI-less/apcE- strain grew photoheterotrophically at normal light intensity (50 microE m-2 sec-1) with a doubling time of 18 hr. Deletion of apcE in the wild type resulted in slow photoautotrophic growth. The remaining phycobilins in apcE- strains were inactive in transferring light energy to PSII. Cells of both the PSI-less and PSI-less/apcE- strains had an approximately sixfold enrichment of PSII on a chlorophyll basis and were as active in oxygen evolution (on a per PSII basis) as the wild type at saturating light intensity. Both PSI-less strains described here are highly appropriate both for detailed PSII studies and as background strains to analyze site- and region-directed PSII mutants in vivo.

Incorporation of analogues of GTP and GDP into rod photoreceptors isolated from the tiger salamander.

1. Analogues of GTP and GDP were introduced into isolated rod photoreceptors using the whole-cell patch clamp technique, while simultaneously recording the photocurrent with a suction pipette. After several minutes of whole-cell recording the patch pipette was disengaged, thus trapping the analogue inside the cell. 2. During the introduction of the hydrolysis-resistant GTP analogues guanosine-5'-O-(3-thio-triphosphate) (GTP-gamma-S) and guanylyl-imidodiphosphate (GMP-PNP) the dark current progressively declined, and the duration of responses to flashes of light which had previously been just-saturating increased slightly. The form of the rising phases of the responses to dim or bright flashes was little affected. 3. Following the incorporation of these GTP analogues the response to an intense flash was prolonged by a factor of up to 300, and the circulating current remained suppressed for up to 1 h. Ultimately the circulating current recovered and the duration of the flash response returned to near its control value. 4. Superfusion of the outer segment with the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX) during the extended period of saturation resulted in a rapid increase in the circulating current, suggesting that the analogues had their major effect on the duration of phosphodiesterase activation by light. 5. Introduction of the phosphorylation-resistant GDP analogue guanosine-5'-O-(2-thio-diphosphate) (GDP-beta-S) resulted in a decrease in light sensitivity and a reduction in the slope of the rising phase of the flash response. 6. The response to an intense flash was also prolonged in cells containing GDP-beta-S, recovery becoming progressively slower on successive presentations of the flash following the withdrawal of the patch pipette. This observation suggests that GDP-beta-S may be slowly converted within the cell to form a hydrolysis-resistant product. 7. These results indicate that the presence of a hydrolysis-resistant analogue of GTP within the cell causes light activation of the transduction mechanism for an extended period. Our interpretation of this finding is that hydrolysis of the bound guanosine nucleotide is necessary for the quenching of activated GTP-binding protein.

Effect of lithium chloride on the lower range of entrainment in Syrian hamsters

The lower range of entrainment of Syrian hamster's locomotor activity rhythm is reduced by lithium chloride administration. The lithium effect can be explained as the result of a decrease in light sensitivity and a period lenghtening.

Effects of neurochemicals upon a dinoflagellate photoresponse.

Photoresponsiveness by Gymnodinium splendens Lebour was monitored quantitatively by a microscope-television system. Exposure to the catecholamines DOPA and Dopamine caused a decrease in light sensitivity, while 0.01 mM norepinephine, or isoproterenol did not affect photoresponsiveness. Classical catecholamine blocking agents, dichloroisoproterenol, propranolol, and dibenzyline, and an inhibitor of DOPA synthesis, alpha-methyl-rho-tyrosine, caused an increase in sensitivity. In addition, acetylcholine and an inhibitor of acetylcholinesterase activity, eserine, caused an increase in sensitivity, while an inhibitor of acetylcholine action atropine, had the opposite effect. These experiments suggest that G. splendens may have an antagonistic catecholamine-cholinergic system which participates in regulating photosensitivity.

Time and dosage effects of meprobamate on visual detection

In spite of the recent interest in the behavioral effects of psychoactive drugs, and the practical importance of the data, there has been little systematic exploration of drug effects on sensory thresholds (UH~, 1961). DICKES, FLAMM, COLTR:EI~A, and To~I~ (1955) report that mephenesin, a muscle relaxant, increased threshold of both neutral and emotionally charged words presented tachistoscopically. ]~YSENCK and AI~A (1957) found a lowering of visual threshold under both dexedrine and sodium amytal as compared to a placebo control group. HOLLAND and TREADWELL (reported in EYSENCK, 1959) found a general decrease in light sensitivity under meprobamate. It is known clinically that acute dosages of meprobamate occasionally produce drowsiness as a side effect, and, therefore, it might be expected that the drug would impair performance on a visual detection task demanding sustained attention and accuracy of immediate recall. But since the onset and duration of these drug effects have not been demonstrated empirically, the present study was concerned primarily with tracing out both the time and dosage response curves for meprobamate when administered in acute dosages within the therapeutic range. Response curves on a visual detection task were ascertained for three levels of meprobamate and a placebo at time intervals ranging from 15 minutes to four hours after ingestion. In order to partially control for effects of individual diurnal cycles of activity on performance, the experimental sessions were scheduled for both morning and evening hours. Method

Dependence of the Sensitivity of Unsensitized Photographic Emulsions upon Temperature*

The change in spectral sensitivity of unsensitized photographic emulsions with temperature and its connection with light-absorption are investigated.In the first part, the influence of temperature upon the shape of the spectral-sensitivity curves is considered and graphs are given showing the ratio of the sensitivities at −195°C and room temperature and the ratio of the sensitivities at +50°C and room temperature as a function of wave-length. For pure silver bromide emulsions, these curves show a minimum at about 470 mµ and a maximum at about 500 mµ. For emulsions containing chloride or iodide, the curve shape is somewhat changed but not in its essential features.In the second part, the absolute change of spectral sensitivity with temperature is discussed. The sensitivity of the basic light-sensitive material, silver bromide, is found to be comparatively little temperature-dependent. The large drop in sensitivity, on lowering the temperature, which is found in commercial emulsions, is due to the chemical sensitization becoming less effective.In the third part, a tentative explanation is given for the results of the first part. It is assumed that the maximum of the sensitivity-ratio curves at 500 mµ is due to a different temperature-dependence in the light-absorption of the silver bromide and that of the reaction product of the chemical sensitizer with the emulsion (probably silver sulfide) which, in this region, acts as an optical sensitizer. Measurements of the spectral light-absorption of a pure silver bromide emulsion show that the decrease in sensitivity with temperature of this emulsion at 400 mµ is, at least in the main, due to decreased light-absorption and only to a smaller extent to a genuine decrease in light-sensitivity.It is concluded from the experimental results that there exist two kinds of sensitivity specks: one kind being numerous and consisting of shallow traps, which are mainly responsible for the sensitivity of chemically non-sensitized grains and for that of the interior of chemically sensitized grains; the other kind being few in number and consisting of deep traps, which are responsible for the surface sensitivity of chemically sensitized grains.