Neuronal Stability, Volumetric Changes, and Decrease in GFAP Expression of Marmoset (Callithrix jacchus) Subcortical Visual Nuclei During Aging.

The physiological aging process is well known for functional decline in visual abilities. Among the components of the visual system, the dorsal lateral geniculate nucleus (DLG) and superior colliculus (SC) provide a good model for aging investigations, as these structures constitute the main visual pathways for retinal inputs reaching the visual cortex. However, there are limited data available on quantitative morphological and neurochemical aspects in DLG and SC across lifespan. Here, we used optical density to determine immunoexpression of glial fibrillary acidic protein (GFAP) and design-based stereological probes to estimate the neuronal number, total volume, and layer volume of the DLG and SC in marmosets (Callithrix jacchus), ranging from 36 to 143 months of age. Our results revealed an age-related increase in total volume and layer volume of the DLG, with an overall stability in SC volume. Furthermore, a stable neuronal number was demonstrated in DLG and superficial layers of SC (SCv). A decrease in GFAP immunoexpression was observed in both visual centers. The results indicate region-specific variability in volumetric parameter, possibly attributed to structural plastic events in response to inflammation and compensatory mechanisms at the cellular and subcellular level. Additionally, the DLG and SCv seem to be less vulnerable to aging effects in terms of neuronal number. The neuropeptidergic data suggest that reduced GFAP expression may reflect morphological atrophy in the astroglial cells. This study contributes to updating the current understanding of aging effects in the visual system and stablishes a crucial foundation for future research on visual perception throughout the aging process.

On the Functional Role of Gamma Synchronization in the Retinogeniculate System of the Cat.

Fast gamma oscillations, generated within the retina, and transmitted to the cortex via the lateral geniculate nucleus (LGN), are thought to carry information about stimulus size and continuity. This hypothesis relies mainly on studies conducted under anesthesia and the extent to which it holds under more naturalistic conditions remains unclear. Using multielectrode recordings of spiking activity in the retina and the LGN of both male and female cats, we show that visually driven gamma oscillations are absent for awake states and are highly dependent on halothane (or isoflurane). Under ketamine, responses were nonoscillatory, as in the awake condition. Response entrainment to the monitor refresh was commonly observed up to 120 Hz and was superseded by the gamma oscillatory responses induced by halothane. Given that retinal gamma oscillations are contingent on halothane anesthesia and absent in the awake cat, such oscillations should be considered artifactual, thus playing no functional role in vision.SIGNIFICANCE STATEMENT Gamma rhythms have been proposed to be a robust encoding mechanism critical for visual processing. In the retinogeniculate system of the cat, many studies have shown gamma oscillations associated with responses to static stimuli. Here, we extend these observations to dynamic stimuli. An unexpected finding was that retinal gamma responses strongly depend on halothane concentration levels and are absent in the awake cat. These results weaken the notion that gamma in the retina is relevant for vision. Notably, retinal gamma shares many of the properties of cortical gamma. In this respect, oscillations induced by halothane in the retina may serve as a valuable preparation, although artificial, for studying oscillatory dynamics.

Reorganization of thalamocortical connections in congenitally blind humans.

Cross-modal plasticity in blind individuals has been reported over the past decades showing that nonvisual information is carried and processed by "visual" brain structures. However, despite multiple efforts, the structural underpinnings of cross-modal plasticity in congenitally blind individuals remain unclear. We mapped thalamocortical connectivity and assessed the integrity of white matter of 10 congenitally blind individuals and 10 sighted controls. We hypothesized an aberrant thalamocortical pattern of connectivity taking place in the absence of visual stimuli from birth as a potential mechanism of cross-modal plasticity. In addition to the impaired microstructure of visual white matter bundles, we observed structural connectivity changes between the thalamus and occipital and temporal cortices. Specifically, the thalamic territory dedicated to connections with the occipital cortex was smaller and displayed weaker connectivity in congenitally blind individuals, whereas those connecting with the temporal cortex showed greater volume and increased connectivity. The abnormal pattern of thalamocortical connectivity included the lateral and medial geniculate nuclei and the pulvinar nucleus. For the first time in humans, a remapping of structural thalamocortical connections involving both unimodal and multimodal thalamic nuclei has been demonstrated, shedding light on the possible mechanisms of cross-modal plasticity in humans. The present findings may help understand the functional adaptations commonly observed in congenitally blind individuals.

Time course of dorsolateral geniculate nucleus plasticity in adult monkeys with laser-induced retinal lesions.

We studied changes in the expression of growth-associated protein 43 (GAP43), glial fibrillary acidic protein (GFAP), and calcium-binding proteins (calbindin [Cb] and parvalbumin [Pv]) in the dorsal lateral geniculate nucleus (dLGN) of four capuchin monkeys with laser-induced retinal lesions. The lesions were generated with the aid of a neodymium-YAG dual-frequency laser with shots of different intensity and at different survival time in each animal. The expression of these proteins in the layers of the dLGN was evaluated by performing histodensitometry of coronal sections throughout the nucleus. High-power laser shots administered at the border of the optic disc (OD)-injured fibers resulted in large scotomas. These lesions produced a devastating effect on fibers in this passage, resulting in large deafferentation of the dLGN. The time course of plasticity expressed in this nucleus varied with the degree of the retinal lesion. Topographically, corresponding portions of the dLGN were inferred by the extent of the ocular dominance column revealed by cytochrome oxidase histochemistry in flattened preparations of V1. In the region representing the retinal lesion, the expression of GFAP, GAP43, Pv, and Cb increased and decreased in the corresponding dLGN layers shortly after lesion induction and returned to their original values with different time courses. Synaptogenesis (indicated by GAP43 expression) appeared to be increased in all layers, while "cleansing" of the glial-damaged region (indicated by GFAP expression) was markedly greater in the parvocellular layers, followed by the magnocellular layers. Schematic drawings of optic discs laser lesions and of series of coronal sections of the dLGN, in three monkeys, depicting the areas of the nucleus deafferented by the lesions.

Arterial Supply of the Thalamus: A Comprehensive Review.

The thalamus is a deep cerebral structure that is crucial for proper neurological functioning as it transmits signals from nearly all pathways in the body. Insult to the thalamus can, therefore, result in complex syndromes involving sensation, cognition, executive function, fine motor control, emotion, and arousal, to name a few. Specific territories in the thalamus that are supplied by deep cerebral arteries have been shown to correlate with clinical symptoms. The aim of this review is to enhance our understanding of the arterial anatomy of the thalamus and the complications that can arise from lesions to it by considering the functions of known thalamic nuclei supplied by each vascular territory.

On Synchronizing Coupled Retinogeniculocortical Pathways: A Toy Model.

A Newman-Watts graph is formed by including random links in a regular lattice. Here, the emergence of synchronization in coupled Newman-Watts graphs is studied. The whole neural network is considered as a toy model of mammalian visual pathways. It is composed by four coupled graphs, in which a coupled pair represents the lateral geniculate nucleus and the visual cortex of a cerebral hemisphere. The hemispheres communicate with each other through a coupling between the graphs representing the visual cortices. This coupling makes the role of the corpus callosum. The state transition of neurons, supposed to be the nodes of the graphs, occurs in discrete time and it follows a set of deterministic rules. From periodic stimuli coming from the retina, the neuronal activity of the whole network is numerically computed. The goal is to find out how the values of the parameters related to the network topology affect the synchronization among the four graphs.

Structural and functional analyses of the optic nerve and lateral geniculate nucleus in glaucoma.

PURPOSE: To analyze the correlation between structural characteristics of intraorbital optic nerve (ION) and lateral geniculate nucleus (LGN) measured by 3-Tesla magnetic resonance imaging (3T MRI), and the severity of glaucomatous damage. METHODS: In this cross-sectional study, 41 glaucoma patients and 12 age- and sex-matched controls underwent standard automated perimetry (SAP) and frequency doubling technology (FDT) as functional evaluation; optic disc stereophotograph, spectral-domain optical coherence tomography (OCT) and confocal scanning laser tomography as ocular structural evaluation; and 3T MRI. Structure-structure and structure-function correlation were performed using bootstrap resampling method for clustered data. RESULTS: The ION mean diameter and cross-sectional area were different between glaucoma and control groups at 5mm and 10mm (all, p≤0.011) from the globe, but not at 15mm (both, p≥0.067). LGN height was significantly lower in glaucoma group (p = 0.005). OCT rim area and functional parameters (SAP and FDT) correlated significantly with all ION segments, showing stronger correlations at 10 and 15 mm. ION parameters at 10 and 15 mm presented mild-to-moderate correlation with OCT peripapillary nerve fiber layer thickness, and ION at 15mm had mild association with the neuroretinal rim area on stereophotographs. Although LGN height was significantly smaller in glaucoma group (p = 0.005), LGN parameters were not associated with any ocular structural or functional parameter. CONCLUSION: Assessment of central and peripheral nervous systems using 3T MRI confirmed that glaucoma patients had smaller ION dimensions and LGN height compared to the control group. In general, ION dimensions presented mild to moderate correlations with functional and ocular structural parameters. Although ION had significant correlations at any distance from the eye, the ION distal locations correlated better with OCT results and functional parameters. However, LGN parameters were not associated with functional or ocular structural parameters.

Distribution of nitric oxide synthase in the rock cavy (Kerodon rupestris) brain I: The diencephalon.

Nitric oxide (NO) is a highly soluble and membrane-permeable neurotransmitter, so it does not need to be packed in vesicles or have a membrane receptor. In the nervous system, NO is synthesized by the neuronal form of the nitric oxide synthase (NOS) enzyme and has been considered as a local neurotransmitter. NOS distribution is widespread in the nervous system of various vertebrate species, which may explain its participation in many functions such as memory, blood pressure regulation and sexual behavior. Here we used immunohistochemistry against NOS and NADPH diaphorase histochemistry to map the distribution of NO in the diencephalon of the rock cavy (Kerodon rupestris), a rodent endemic to the Brazilian Northeast. Rock cavy has crepuscular habits and is adapted to ecological conditions such as heat and scarcity of water and food. This study found that NOS distribution was more concentrated in the hypothalamus of this animal. Among the hypothalamic nuclei, the median preoptic, supraoptic, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, ventral and dorsal premammillary nucleus, supramammillary nucleus, lateral mammillary nucleus and dorsal hypothalamic nucleus had the largest collections of NOS immunoreactive (NOS-ir) neurons. Some nuclei of the thalamus and epithalamus such as the paraventricular nucleus of the thalamus, the ventral lateral geniculate nucleus, the medial geniculate nucleus and the lateral habenula showed NOS-ir neurons. This distribution is similar to that described in other rodents, indicating that NO also has an important role in rock cavy's physiology.

L-/M-cone opponency in visual evoked potentials of human cortex.

L and M cones send their signals to the cortex using two chromatic (parvocellular and blue-yellow koniocellular) and one luminance (magnocellular) pathways. These pathways contain ON and OFF subpathways that respond to excitation increments and decrements respectively. Here, we report on visually evoked potentials (VEP) recordings that reflect L- and M-cone driven increment (LI and MI) and decrement (LD and MD) activity. VEP recordings were performed on 12 trichromats and four dichromats (two protanopes and two deuteranopes). We found that the responses to LI strongly resembled those to MD, and that LD and MI responses were very similar. Moreover, the lack of a photoreceptor type (L or M) in the dichromats led to a dominance of the ON pathway of the remaining photoreceptor type. These results provide electrophysiological evidence that antagonistic L/M signal processing, already present in the retina and the lateral geniculate nucleus (LGN), is also observed at the visual cortex. These data are in agreement with results from human psychophysics where MI stimuli lead to a perceived brightness decrease whereas LI stimuli resulted in perceived brightness increases. VEP recording is a noninvasive tool that can be easily and painlessly applied. We propose that the technique may provide information in the diagnosis of color vision deficiencies.

Involvement of microglia in early axoglial alterations of the optic nerve induced by experimental glaucoma.

Glaucoma is a leading cause of blindness, characterized by retinal ganglion cell (RGC) loss and optic nerve (ON) damage. Cumulative evidence suggests glial cell involvement in the degeneration of the ON and RGCs. We analyzed the contribution of microglial reactivity to early axoglial alterations of the ON in an induced model of ocular hypertension. For this purpose, vehicle or chondroitin sulfate (CS) were weekly injected into the eye anterior chamber from Wistar rats for different intervals. The amount of Brn3a(+) RGC significantly decreased in CS-injected eyes for 10 and 15 (but not 6) weeks. A reduction in anterograde transport of ß-subunit cholera toxin was observed in the superior colliculus and the lateral geniculate nucleus contralateral to CS-injected eyes for 6 and 15 weeks. A disruption of cholera toxin ß-subunit transport was observed at the proximal myelinated ON. A significant decrease in phosphorylated neurofilament heavy chain immunoreactivity, an increase in ionized calcium-binding adaptor molecule 1(+), ED1(+) (microglial markers), and glial fibrillary acidic protein (astrocytes) (+) area, and decreased luxol fast blue staining were observed in the ON at 6 and 15 weeks of ocular hypertension. Microglial reactivity involvement was examined through a daily treatment with minocycline (30 mg/kg, i.p.) for 2 weeks, after 4 weeks of ocular hypertension. Minocycline prevented the increase in ionized calcium-binding adaptor molecule 1(+), ED-1(+), and glial fibrillary acidic protein(+) area, the decrease in phosphorylated neurofilament heavy-chain immunoreactivity and luxol fast blue staining, and the deficit in anterograde transport induced by 6 weeks of ocular hypertension. Thus, targeting microglial reactivity might prevent early axoglial alterations in the glaucomatous ON. Cover Image for this issue: doi: 10.1111/jnc.13807.

Temporal changes in calcium-binding proteins in the medial geniculate nucleus of the monkey Sapajus apella.

The subdivisions of the medial geniculate complex can be distinguished based on the immunostaining of calcium-binding proteins and by the properties of the neurons within each subdivision. The possibility of changes in neurochemistry in this and other central auditory areas are important aspects to understand the basis that contributing to functional variations determined by environmental cycles or the animal's cycles of activity and rest. This study investigated, for the first time, day/night differences in the amounts of parvalbumin-, calretinin- and calbindin-containing neurons in the thalamic auditory center of a non-human primate, Sapajus apella. The immunoreactivity of the PV-IR, CB-IR and CR-IR neurons demonstrated different distribution patterns among the subdivisions of the medial geniculate. Moreover, a high number of CB- and CR-IR neurons were found during day, whereas PV-IR was predominant at night. We conclude that in addition to the chemical heterogeneity of the medial geniculate nucleus with respect to the expression of calcium-binding proteins, expression also varied relative to periods of light and darkness, which may be important for a possible functional adaptation of central auditory areas to environmental changes and thus ensure the survival and development of several related functions.

Effect of retinal ischemia on the non-image forming visual system.

Retinal ischemic injury is an important cause of visual impairment. The loss of retinal ganglion cells (RGCs) is a key sign of retinal ischemic damage. A subset of RGCs expressing the photopigment melanopsin (mRGCs) regulates non-image-forming visual functions such as the pupillary light reflex (PLR), and circadian rhythms. We studied the effect of retinal ischemia on mRGCs and the non-image-forming visual system function. For this purpose, transient ischemia was induced by raising intraocular pressure to 120 mm Hg for 40 min followed by retinal reperfusion by restoring normal pressure. At 4 weeks post-treatment, animals were subjected to electroretinography and histological analysis. Ischemia induced a significant retinal dysfunction and histological alterations. At this time point, a significant decrease in the number of Brn3a(+) RGCs and in the anterograde transport from the retina to the superior colliculus and lateral geniculate nucleus was observed, whereas no differences in the number of mRGCs, melanopsin levels, and retinal projections to the suprachiasmatic nuclei and the olivary pretectal nucleus were detected. At low light intensity, a decrease in pupil constriction was observed in intact eyes contralateral to ischemic eyes, whereas at high light intensity, retinal ischemia did not affect the consensual PLR. Animals with ischemia in both eyes showed a conserved locomotor activity rhythm and a photoentrainment rate which did not differ from control animals. These results suggest that the non-image forming visual system was protected against retinal ischemic damage.

An unusual cause of blindness: infarction in the bilateral lateral geniculate bodies.

A 10-year-old girl presented with acute blindness after a severe episode of febrile diarrhea. Magnetic resonance images were consistent with the diagnosis of infarction in the bilateral lateral geniculate bodies.

Color signals in retina and lateral geniculate nucleus of marmoset monkeys

Marmosets show sex-linked polymorphism of color vision, whereby all males and some females show dichromatic ("red-green color-blind") vision based on two classes of photoreceptor sensitive to short or medium wavelength bands. Most female marmosets by contrast express three photoreceptor classes, one sensitive to short wavelengths and two classes in the medium-long wavelength sensitivity band. We used this 'natural knock-out' to study the organization of color vision pathways in primates. We review here results from our and other laboratories showing how the primordial dichromatic blue-yellow pathway is characterized by selective connections to short wavelength sensitive cones in the retina and that signals for blue-yellow color vision travel through an ancient part of the subcortical visual pathway called the koniocellular system. Signals serving red-green color vision by contrast are tightly linked to retinal circuits serving high-resolution spatial vision at the fovea and show little sign of specific patterns of connections with medium- and long-wavelength sensitive cones. Routine trichromatic color vision thus is based on converging signals from two quite distinct retinal and subcortical pathways...

Evaluation of magnocellular pathway abnormalities in schizophrenia: a frequency doubling technology study and clinical implications.

BACKGROUND: Visual processing deficits have been reported for patients with schizophrenia. Previous studies demonstrated differences in early-stage processing of schizophrenics, although the nature, extent, and localization of the disturbance are unknown. The magnocellular and parvocellular visual pathways are associated with transient and sustained channels, but their respective contributions to schizophrenia-related visual deficits remains controversial. PURPOSE: The aim of this study was to evaluate magnocellular dysfunction in schizophrenia using frequency doubling technology. METHODS: Thirty-one patients with schizophrenia and 34 healthy volunteers were examined. Frequency doubling technology testing was performed in one session, consisting of a 15-minute screening strategy followed by the C-20 program for frequency doubling technology. RESULTS: Schizophrenic patients showed lower global mean sensitivity (30,97 ± 2,25 dB) compared with controls (32,17 ± 3,08 dB), p<0.009. Although there was no difference in the delta sensitivity of hemispheres, there was a difference in sensitivity analysis of the fibers crossing the optic chiasm, with lower mean sensitivity in the patient group (28,80 dB) versus controls (30,66 dB). The difference was higher in fibers that do not cross the optic chiasm, with lower mean sensitivity in patients (27,61 dB) versus controls (30,26 dB), p<0.005. CONCLUSIONS: Our results suggest that there are differences between global sensitivity and fiber sensitivity measured by frequency doubling technology. The different sensitivity of fibers that do not cross the optic chiasm is consistent with most current etiological hypotheses for schizophrenia. The decreased sensitivity responses in the optic radiations may significantly contribute to research assessing early-stage visual processing deficits for patients with schizophrenia.

The NPY intergeniculate leaflet projections to the suprachiasmatic nucleus transmit metabolic conditions.

The intergeniculate leaflet (IGL) is classically known as the area of the Thalamic Lateral Geniculate Complex providing the suprachiasmatic nucleus (SCN) non-photic information. In the present study we investigated whether this information might be related to the metabolic state of the animal. The following groups of male Wistar rats were used for analysis of neuropeptide Y (NPY) and c-Fos in the IGL and SCN. (1) Fed ad libitum. (2) Fasted for 48 h. (3) Fasted for 48 h followed by refeeding for 3 h. (4) Monosodium glutamate-lesioned and 48 h fasted. (5) Electrolytic lesion in the IGL and 48 h fasted. The results were quantified by optical densitometry. Neuronal tracers were injected in two brain areas that receive metabolic information from the periphery, the arcuate nucleus (ARC) and Nucleus of the Tractus Solitarius to investigate whether there is an anatomical relationship with the IGL. Lesion studies showed the IGL, and not the ARC, as origin of most NPY projections to the SCN. Fasting induced important changes in the NPY expression in the IGL, coinciding with similar changes of NPY/glutamate decarboxylase projections of the IGL to the SCN. These changes revealed that the IGL is involved in the transmission of metabolic information to the SCN. In fasted animals IGL lesion resulted in a significant increase of c-Fos in the SCN as compared to intact fasted animals demonstrating the inhibitory influence of the IGL to the SCN in fasting conditions. When the animal after fasting was refed, an increase of c-Fos in the SCN indicated a removal of this inhibitory input. Together these observations show that in addition to increased inhibitory IGL input during fasting, the negative metabolic condition also results in increased excitatory input to the SCN via other pathways. Consequently the present observations show that at least part of the non-photic input to the SCN, arising from the IGL contains information about metabolic conditions.

Evaluation of magnocellular pathway abnormalities in schizophrenia: a frequency doubling technology study and clinical implications / Avaliação das alterações da via magnocelular na esquizofrenia usando FDT e suas implicações clínicas

BACKGROUND: Visual processing deficits have been reported for patients with schizophrenia. Previous studies demonstrated differences in early-stage processing of schizophrenics, although the nature, extent, and localization of the disturbance are unknown. The magnocellular and parvocellular visual pathways are associated with transient and sustained channels, but their respective contributions to schizophrenia-related visual deficits remains controversial. PURPOSE: The aim of this study was to evaluate magnocellular dysfunction in schizophrenia using frequency doubling technology. METHODS: Thirty-one patients with schizophrenia and 34 healthy volunteers were examined. Frequency doubling technology testing was performed in one session, consisting of a 15-minute screening strategy followed by the C-20 program for frequency doubling technology. RESULTS: Schizophrenic patients showed lower global mean sensitivity (30,97 ± 2,25 dB) compared with controls (32,17 ± 3,08 dB), p<0.009. Although there was no difference in the delta sensitivity of hemispheres, there was a difference in sensitivity analysis of the fibers crossing the optic chiasm, with lower mean sensitivity in the patient group (28,80 dB) versus controls (30,66 dB). The difference was higher in fibers that do not cross the optic chiasm, with lower mean sensitivity in patients (27,61 dB) versus controls (30,26 dB), p<0.005. CONCLUSIONS: Our results suggest that there are differences between global sensitivity and fiber sensitivity measured by frequency doubling technology. The different sensitivity of fibers that do not cross the optic chiasm is consistent with most current etiological hypotheses for schizophrenia. The decreased sensitivity responses in the optic radiations may significantly contribute to research assessing early-stage visual processing deficits for patients with schizophrenia.

HISTÓRICO: Déficits de processamento visual foram relatados em pacientes com esquizofrenia. Estudos anteriores demonstraram diferenças no estágio inicial de processamento de esquizofrênicos, embora a natureza, extensão e localização do distúrbio são desconhecidas. As vias magnocelulares e parvocelular visuais são associados com canais transitórios e sustentado, mas suas respectivas contribuições para a esquizofrenia relacionados com déficits visuais permanece controverso. OBJETIVO: Avaliar a disfunção magnocelular na esquizofrenia usando a tecnologia de frequência dupla. MÉTODOS: Trinta e um pacientes com esquizofrenia e 34 voluntários saudáveis ​​foram examinados. Tecnologia de frequência dupla foi realizada em uma sessão, consistindo de uma estratégia de rastreio de 15 minutos, seguido do programa de C-20 para tecnologia de frequência dupla. RESULTADOS: Os pacientes esquizofrênicos apresentaram sensibilidade média inferior global (30,97 ± 2,25 dB), em comparação com os controles (32,17 ± 3,08 dB), p<0,009. Embora não tenha ocorrido diferença na sensibilidade do delta de hemisférios, houve uma diferença na análise de sensibilidade das fibras que atravessam a quiasma, com menor sensibilidade média no grupo de pacientes (28,80 dB) versus controlos (30,66 dB). A diferença foi maior em fibras que não cruzam o quiasma óptico, com menor sensibilidade média em pacientes (27,61 dB) versus controles (30,26 dB), p<0,005. CONCLUSÕES: Nossos resultados sugerem que há diferenças entre a sensibilidade global e sensibilidade da fibra medida pela tecnologia de frequência dupla. A sensibilidade diferente de fibras que não cruzam o quiasma óptico é compatível com a maioria das atuais hipóteses etiológicas para a esquizofrenia. As respostas diminuição da sensibilidade nas radiações ópticas podem contribuir significativamente para pesquisar a avaliação em estágio inicial déficits de processamento visual em pacientes com esquizofrenia.

Color signals in retina and lateral geniculate nucleus of marmoset monkeys

Marmosets show sex-linked polymorphism of color vision, whereby all males and some females show dichromatic ("red-green color-blind") vision based on two classes of photoreceptor sensitive to short or medium wavelength bands. Most female marmosets by contrast express three photoreceptor classes, one sensitive to short wavelengths and two classes in the medium-long wavelength sensitivity band. We used this 'natural knock-out' to study the organization of color vision pathways in primates. We review here results from our and other laboratories showing how the primordial dichromatic blue-yellow pathway is characterized by selective connections to short wavelength sensitive cones in the retina and that signals for blue-yellow color vision travel through an ancient part of the subcortical visual pathway called the koniocellular system. Signals serving red-green color vision by contrast are tightly linked to retinal circuits serving high-resolution spatial vision at the fovea and show little sign of specific patterns of connections with medium- and long-wavelength sensitive cones. Routine trichromatic color vision thus is based on converging signals from two quite distinct retinal and subcortical pathways.(AU)

Effects of chronic administration of efavirenz on the chromatophilic substance of the intracranial auditory relay centres of adult Wistar rats / Efectos de la administración crónica de efavirenz sobre la sustancia cromatofílica de los centros de relevo auditivos intracraneales de ratas Wistar adultas

The effects of chronic administration of efavirenz commonly used as part of highly active antiretroviral therapy (HAART) for the treatment of Human Immunodeficiency Virus (HIV) type-1 therapy on the chromatophilic substance of the intracranial auditory relay centre namely the inferior colliculus and medial geniculate body of adult wistar rats were carefully studied. The rats of both sexes (n=20), with an average weight of 200g were randomly assigned into treatment (n=10) and control (n=10) groups. The rats in the treatment group received 600 mg/70kg body weight of efavirenz dissolved in distilled water daily for 30 days through the orogastric tube. The control group received equal volume of distilled water daily for 30 days through the same route. The rats were fed with grower's mash obtained from Edo Feeds and Flour Mill Limited, Ewu, Edo state, Nigeria and given water liberally. The rats were sacrificed by cervical dislocation method on the thirty-first day of the experiment. The inferior colliculus and medial geniculate body were carefully dissected out and quickly fixed in 10 percent formal saline for histological study. The histological findings indicated that the treated sections of the inferior colliculus and medial geniculate body showed that the chromatophilics substances were less intensely stained as compared to the control. The parenchyme was vacuolated and with evidence of hypertrophy and more spaces between the axonal mesh around the sparsely distributed neurons as compared to the control group. The treated section of the inferior colliculus showed neurons with faintly stained chromatophilics substances in large, medium and small sized neurons while that of the medial geniculate body showed less intense and enlarge chromatophilics substances with some vacuolations. Chronic administration of efavirenz may therefore have an adverse effect on the chromatophilics substances of the inferior colliculus and medial geniculate body of adult wistar rats...

Fueron estudiados los efectos de la administración crónica del efavirenz, comúnmente utilizado como parte del tratamiento antirretroviral de gran actividad para el VIH tipo 1, sobre la sustancia cromatofílica del centro de relevo auditivo intracraneal, el colículo inferior y cuerpo geniculado medial, en ratas Wistar adultas. Ratas de ambos sexos (n = 20), con un peso promedio de 200g fueron asignadas aleatoriamente a tratamiento (n = 10) y control (n = 10). Las ratas del grupo tratado recibieron 600mg/70kg peso corporal de efavirenz disuelto en agua destilada durante 30 días a través de sonda orogástrica. El grupo de control recibió un volumen igual de agua destilada durante 30 días por la misma vía. Las ratas fueron alimentadas con puré agricultor obtenido de Edo Feeds and Flour Mill Limited, Ewu, estado de Edo, Nigeria y agua ad-libitum. Las ratas se sacrificaron por dislocación cervical el día 31. El colículo inferior y el cuerpo geniculado medial fueron disecados cuidadosamente y se fijaron en solución de formalina salina al 10 por ciento. Los hallazgos histológicos indicaron que en las secciones tratadas del colículo inferior y el cuerpo geniculado medial la sustancia cromatofílica fue menos intensamente teñidas en comparación con el control. El parénquima se vacuoló, con evidencia de hipertrofia y más espacios entre la red axonal alrededor de neuronas escasamente distribuidas en comparación con el grupo control. La sección tratada del colículo inferior mostró neuronas con sustancia cromatofílica débilmente teñida en las neuronas de tamaño grande, mediano y pequeño, mientras que las del cuerpo geniculado medial mostraron sustancia cromatofílica menos intensa, con algunas vacuolaciones amplias. La administración crónica de efavirenz puede tener un efecto adverso sobre las sustancias cromatofílica del colículo inferior y del cuerpo geniculado medial de ratas Wistar adultas. Se recomienda realizar estudios adicionales...

Contrast sensitivity mediated by inferred magno- and parvocellular pathways in type 2 diabetics with and without nonproliferative retinopathy.

PURPOSE: To evaluate achromatic contrast sensitivity (CS) with magnocellular- (M) and parvocellular- (P) probing stimuli in type 2 diabetics, with (DR) or without (NDR) nonproliferative retinopathy. METHODS: Inferred M- and P-dominated responses were assessed with a modified version of the steady-/pulsed-pedestal paradigm (SP/PP) applied in 26 NDR (11 male; mean age, 55 ± 9 years; disease duration, 5 ± 4 years); 19 DR (6 male; mean age, 58 ± 7 years; disease duration = 9 ± 6 years); and 18 controls (CTRL; 12 male; mean age, 55 ± 10 years). Thresholds were measured with pedestals at 7, 12, and 19 cd/m(2), and increment durations of 17 and 133 ms. The thresholds from the two stimulus durations were used to estimate critical durations (Tc) for each data set. RESULTS: Both DR and NDR patients had significant reduction in CS in both SP and PP paradigms in relation to CTRL (Kruskal-Wallis, P < 0.01). Patients' critical duration estimates for either paradigm were not significantly different from CTRL. CONCLUSIONS: The significant reduction of CS in both paradigms is consistent with losses of CS in both M and P pathways. The CS losses were not accompanied by losses in temporal processing speed in either diabetic group. Significant CS loss in the group without retinopathy reinforces the notion that neural changes associated with the cellular and functional visual loss may play an important role in the etiology of diabetic visual impairment. In addition, the results show that the SP/PP paradigm provides an additional tool for detection and characterization of the early functional damage due to diabetes.