Anterior Optic Tract Research Articles

Chromatic processing and receptive-field structure in neurons of the anterior optic tract of the honeybee brain.

Color vision in honeybees is a well-documented perceptual phenomenon including multiple behavioral tests of trichromaticity and color opponency. Data on the combined color/space properties of high order visual neurons in the bee brain is however limited. Here we fill this gap by analyzing the activity of neurons in the anterior optic tract (AOT), a high order brain region suggested to be involved in chromatic processing. The spectral response properties of 72 units were measured using UV, blue and green light stimuli presented in 266 positions of the visual field. The majority of these units comprise combined chromatic-spatial processing properties. We found eight different neuron categories in terms of their spectral, spatial and temporal response properties. Color-opponent neurons, the most abundant neural category in the AOT, present large receptive fields and activity patterns that were typically opponent between UV and blue or green, particularly during the on-tonic response phase. Receptive field shapes and activity patterns of these color processing neurons are more similar between blue and green, than between UV and blue or green. We also identified intricate spatial antagonism and double spectral opponency in some receptive fields of color-opponent units. Stimulation protocols with different color combinations applied to 21 AOT units allowed us to uncover additional levels of spectral antagonism and hidden inhibitory inputs, even in some units that were initially classified as broad-band neurons based in their responses to single spectral lights. The results are discussed in the context of floral color discrimination and celestial spectral gradients.

Evidence for the possible existence of a second polarization-vision pathway in the locust brain

For spatial orientation and navigation, many insects derive compass information from the polarization pattern of the blue sky. The desert locust Schistocerca gregaria detects polarized light with a specialized dorsal rim area of its compound eye. In the locust brain, polarized-light signals are passed through the anterior optic tract and tubercle to the central complex which most likely serves as an internal sky compass. Here, we suggest that neurons of a second visual pathway, via the accessory medulla and posterior optic tubercle, also provide polarization information to the central complex. Intracellular recordings show that two types of neuron in this posterior pathway are sensitive to polarized light. One cell type connects the dorsal rim area of the medulla with the medulla and accessory medulla, and a second type connects the bilaterally paired posterior optic tubercles. Given the evidence for a role of the accessory medulla as the master clock controlling circadian changes in behavioral activity in flies and cockroaches, our data open the possibility that time-compensated polarized-light signals may reach the central complex via this pathway for time-compensated sky-compass navigation.

Histopathologic Features of Multiple Myeloma Involving the Optic Nerves

We report a case of optic nerve involvement by multiple myeloma in which progressive visual loss heralded leukemic transformation and intracranial involvement. Imaging showed enhancing nodules in the intracranial segments of both optic nerves posterior to the optic canals and in the anterior optic tract, optic chiasm, and basal leptomeninges. Postmortem histopathologic examination disclosed malignant plasma cells in the subarachnoid spaces around the optic nerves and in the optic nerves. Infarctions were present in both optic nerves near their junction with the globes. Microscopic examination also showed malignant plasma cell infiltration of the leptomeninges of the cerebrum, brain stem, optic chiasm, pituitary gland, cranial bone marrow, and subarachnoid blood vessels. This is the first reported histopathologic examination in conjunction with MRI of multiple myeloma involving the anterior visual pathway. The mechanism of optic neuropathy in this case is probably related to infiltration of the optic nerve meninges by malignant plasma cells and impaired vascular supply caused by aggregated intraluminal plasma cells and monoclonal hypergammaglobulinemia.

Characterization of NADPH-diaphorase-positive glial cells of the tench optic nerve after axotomy.

NADPH-diaphorase (ND) positive cell types were characterized throughout the optic nerve of the tench in normal conditions and after optic nerve transection with survival periods of 1, 3, 7, 14, 30, 60, 120 and 180 days. Astrocytic markers (S100 and glutamine synthetase) and the microglial marker tomato lectin were employed. In the control prechiasmatic optic nerve two types (types I and II) of ND-positive glial cells appeared. All type I cells showed S100 immunoreactivity, whereas only a subpopulation of them were positive to glutamine synthetase. Type II cells only presented S100 immunoreactivity. In the control anterior optic tract, all ND-positive glial cells (type III) presented immunolabeling to S100 and glutamine synthetase. After transection, types I and II did not show any changes in the staining patterns for the glial markers when observed. Two new types of ND-positive glial cells (types IV and V) were observed after axotomy. All type IV cells were S100-immunopositive, and a subpopulation presented glutamine synthetase immunolabeling. Only a subpopulation of type V cells showed glutamine synthetase immunostaining. The presence of type IV or V cells in the lesioned optic nerve occurred simultaneously with significant decreases or absence of type I cells. These data suggest that type I and III cells are astrocytes and type II cells are oligodendrocytes. Types IV and V cells are the result of the activation of type I cells after optic nerve section. The polymorphism observed in ND-positive cells may reflect different cell functions during degenerative and regenerative processes.

Surgical lesion of the anterior optic tract abolishes polarotaxis in tethered flying locusts, Schistocerca gregaria

Many insects can detect the polarization pattern of the blue sky and rely on polarization vision for sky compass orientation. In laboratory experiments, tethered flying locusts perform periodic changes in flight behavior under a slowly rotating polarizer even if one eye is painted black. Anatomical tracing studies and intracellular recordings have suggested that the polarization vision pathway in the locust brain involves the anterior optic tract and tubercle, the lateral accessory lobe, and the central complex of the brain. To investigate whether visual pathways through the anterior optic tract mediate polarotaxis in the desert locust, we transected the tract on one side and tested polarotaxis (1) with both eyes unoccluded and (2) with the eye of the intact hemisphere painted black. In the second group of animals, but not in the first group, polarotaxis was abolished. Sham operations did not impair polarotaxis. The experiments show that the anterior optic tract is an indispensable part of visual pathways mediating polarotaxis in the desert locust.

Additive gene actions on the fiber number in the anterior optic tract of Drosophila melanogaster.

The influence of mutations in seven neurological genes on the number of fibers in the anterior optic tract (AOT) of Drosophila melanogaster has been investigated. It is shown that the number of fibers in the AOT can be drastically reduced in single and especially in multiple mutants. However, no evidence for synergistic interactions between the sample of mutations used in the sine oculis (so), reduced optic lobes (rol), minibrain (mnb), and small optic lobes (sol) genes was obtained at the level of the AOT. The rolKS222 and so mutations eliminate similar fiber sets in the AOT, which are distinctly different from those eliminated by solKS58 and mnb1.

Structural organization of the brain and subesophageal ganglion of male Aedes aegypti (L.) (Diptera : Culicidae)

The brain and subesophageal ganglion of male Aedes aegypti (L.) (Diptera : Culicidae) are described from cryofractures and silver-stained, semithin (0.5 μm) serial sections of whole heads observed in the scanning and light microscopes. The brain and subesophageal ganglion of male A. aegypti are fused. The major structures of the brain include the protocerebral lobes and bridge, the mushroom bodies, central complex of the protocerebrum, the mechanosensory regions and olfactory loves of the deutocerebrum, and the tritocerebrum. Major commissures of the brain are the anterior optic tract, central commissure, posterior dorsal commissure, and subesophageal commissure. The structural associations of brain components with each other and the subesophageal ganglion, as well as the paths of the major nerve tracts in male A. aegypti are described and compared with those in other Diptera.

Genetic dissection of the anterior optic tract of Drosophila melanogaster

Electron microscopy shows that in wild-type Drosophila melanogaster the anterior optic tract (AOT) is formed by about 1260 fibers in males and slightly fewer in females. Golgi staining suggests that most AOT fibers connect the lobula with different regions of the central brain. In the sine oculis (so) and small optic lobes (sol) mutants the number of axons is drastically reduced, by 58% in sol and by 35% in so. In the double mutant sol:so there is a loss of up to 83% of the fibers in the AOT. Approximately half of the remaining 220 fibers form a well defined subbundle of very thin axons which is identifiable in wild type as well as in both single mutants. The fibers of this subbundle neither originate nor terminate in the visual ganglia: instead, they connect two different central brain regions. It is concluded that the combined action of the sol and so mutations abolishes more than 90% of the fibers of visual origin or destination in the AOT. Quantitative analysis of electron micrographs shows that the so and sol mutations act independently on nearly exclusive subsets of axons in the AOT.

Horizontal movement detectors of honeybees: Directionally-selective visual neurons in the lobula and brain

1. Intracellular recordings have been made from both input (ipsilateral) and output (contralateral) ends of directionally-selective optomotor neurons in the left lobulae of worker honeybees. Optical stimuli were two, monocular, horizontally-moving vertical gratings placed on opposite sides of the bee's head. The eyes could be stimulated separately or together. 2. Horizontal regressive motion-sensitive (HR) cells are strongly excited (and depolarized) by ipsilateral regressive motion. They are moderately excited by contralateral progressive motion but are inhibited by contralateral regressive motion. Ipsilateral progressive motion has little effect (Figs. 1 and 2). The HR cells (HRLeft and HRRight cells) are bilateral, reciprocal neurons which run from one lobula to the other via the anterior optic tracts, the optic tubercles, and the intertubicular tract. They have co-extensive dendrites and terminals in the distal lamellae of the lobulae (Figs. 4–6). HR cells are the bees' optomotor neurons, known hitherto from extracellular recordings. 3. Horizontal progressive-motion sensitive (HP) cells (HPRight and HPLeft cells) are excited and depolarized by ipsilateral progressive motion but are inhibited and hyperpolarized by ipsilateral regressive motion. It is uncertain if there are bilateral influences on HP cells (Figs. 7 and 8). No stained HP cells have been recovered. 4. Other directionally-selective cells with and without spikes have also been stained and reconstructed (Figs. 9 and 10). 5. A model network is proposed between HR and HP cells in which a) HR cells mutually inhibit each other; b) the ipsilateral, input end of each HR cell inhibits the HP cell originating in the same lobula; and c) the contralateral, output terminals of each HP cell excite the HR cell originating in the opposite lobula (Fig. 11 A). It is discussed how the model could explain the observed directional selectivities of cells (Figs. 11B, C and 12). Additionally, the possible role of such a model network in optomotor behavior is considered.

Brain of the black blowfly, Phormia regina Meigen (Diptera: Calliphoridae)

The objective of this work is to describe the structural associations and the courses of major nerve tracts in Phormia regina. Where possible, comparisons are made of similar structures in other insects. The prominent components of the Phormia brain are the: accessory protocerebral lobes, antennal glomeruli, corpora pedunculata, central complex, olfactorio globularis, optic lobes, protocerebral lobe and bridge, and the suboesophageal area. Large commissures are the: anterior accessory commissure, anterior optic tract, central commissure, dorsal posterior commissure of the protocerebrum, and the commissure of fine fibers for antennal glomeruli. The major tracts and association centers in Phormia are similar to those in other insects studied. Differences, where observed, have been described. A previously unnamed nerve fiber originating in the chiasmic region of the optic lobe and entering the ellipsoid body is also noted.

Diencephalic vasodepressor responses independent of heart rate changes

The purpose of this study was to probe selected regions of the diencephalon of the rat and identify sites that respond to electrical stimulation by changes in blood pressure. In experiments utilizing anesthetized and awake adult male Wistar rats a vasodepressor area was identified in the antero-lateral diencephalon. It is located between the hypothalamus and the medial forebrain bundle at the level of the anterior optic tracts. Electrical stimulation in this region resulted in a transient depressor response without alterations in either heart rate, pulse pressure or respiration rate. A region adjacent to the anterior commissure also was found to have vasodepressor activity similar to that observed in the cat and the dog. In contrast, the intervening columns of the fornix appear unresponsive. Biphasic pressor-depressor responses were seen at some stimulation points and have also been presented.

Visual neurones in the anterior optic tract of the privet hawk moth

Three classes of visual neurones were recorded in the right anterior optic tract (AOT) of the privet hawk moth. All classes are output cells from the optic lobe with ipsilateral visual fields (30° or more in diameter) within which they respond to small moving stimuli. The responses are altered in a variety of ways by gratings travelling over the rest of the binocular field, but surround movement on its own does not evoke a response.