Effects of stationary textured backgrounds on the initiation of pursuit eye movements in monkeys

1. The initial ocular pursuit of small target spots (0.25 degrees diam) that suddenly start to move at constant speed (ramps) was recorded in four rhesus monkeys with the electromagnetic search coil technique. All target motions were horizontal, and both eyes were monitored. 2. In agreement with the observations of Keller and Khan, stationary textured backgrounds substantially reduced the initial eye acceleration achieved during pursuit but did not affect its latency. Correlation techniques were used to assess the changes in the eye speed profiles and indicated that the reduction in eye acceleration due to the background was a linear function of the logarithm of target speed over the range investigated (5-40 degrees/s), averaging 60% with the fastest targets. 3. Selectively excluding the background texture from the path of the target with a horizontal strip of card (vertical width, 4 degrees) reduced the impact of the background only slightly, and, even when the vertical width of the card was increased to 60 degrees, the effect of the background was not entirely eliminated. Thus the effect involves regions of the visual field well beyond the target and is not due simply to the reduced physical salience (contrast) of the target spot. Such spatially remote interactions suggest that the neurons decoding the target's motion have very extensive visual receptive fields. 4. Textured backgrounds also caused similar reductions in the eye acceleration during initial pursuit when, before the ramps, the fixated target spots stepped forward, i.e., stepped in the direction of the subsequent ramps (step ramps). In this situation, as with no steps, initial target ramps were foveofugal. When the fixated target spots were stepped back before moving forward so that initial target ramps were foveopetal, textured backgrounds now also delayed the onset of pursuit, and the reductions in eye acceleration were not seen until some time later when tracking resulted from foveofugal target-ramp motion. Selectively excluding the texture from the path of the target with a narrow strip of card eliminated any delays in the onset of pursuit to step ramps, but the later reductions in eye acceleration were still evident. These step-ramp data indicate that the mechanisms decoding foveofugal and foveopetal target ramps differ markedly in their sensitivity to textured backgrounds. That backgrounds can influence the latency and the initial eye acceleration independently is consistent with the idea that there are independent trigger and drive mechanisms for the decoding of target motions.(ABSTRACT TRUNCATED AT 400 WORDS)

Two cellular single-strand-specific DNA-binding proteins interact with two regions of the bovine papillomavirus type 1 genome, including the origin of DNA replication

We have identified and purified to near homogeneity two specific single-stranded DNA-binding factors (SPSF I and II) with molecular masses of 42 and 39 kDa, respectively, from calf thymus. Gel retention analysis and competition experiments demonstrate that the ubiquitous proteins SPSF I and II specifically interact with single-stranded DNA derived from the minimal in vitro origin of replication of bovine papillomavirus type 1 and a region of the viral genome proposed to be involved in plasmid maintenance. Bovine papillomavirus type 1 proteins do not interfere with DNA binding of SPSF I and II. The exact location of the binding domains of SPSF I and II on the DNA has been determined by methylation interference and T4 DNA polymerase footprinting. A potential cellular binding site for SPSF I and II is the major promoter (P2) of the human c-myc gene.

Bravo/Nr-CAM is closely related to the cell adhesion molecules L1 and Ng-CAM and has a similar heterodimer structure

Diverse cell-surface molecules of the nervous system play an important role in specifying cell interactions during development. Using a method designed to generate mAbs against neural surface molecules of defined molecular weight, we have previously reported on the surface protein, Bravo, found in the developing avian retinotectal system. Bravo is immunologically detected on developing optic fibers in the retina, but absent from distal regions of the same fibers in the tectum. We have isolated cDNA clones encompassing the entire coding region of Bravo, including clones containing five alternative sequences of cDNA. These putative alternatively spliced sequences encode stretches of polypeptide ranging in length from 10-93 amino acids and are predicted to be both extra- and intracellular. The deduced primary structure of Bravo reveals that, like the cell adhesion molecules (CAMs) chicken Ng-CAM and mouse L1, Bravo is composed of six Ig-like domains, five fibronectin type III repeats, a transmembrane domain, and a short cytoplasmic region. Recently, the cDNA sequence of a related molecule, Nr-CAM, was reported and its possible identity with Bravo discussed (Grumet, M., V. Mauro, M. P. Burgoon, G. E. Edelman, and B. A. Cunningham. 1991. J. Cell Biol. 113:1399-1412). Here we confirm this identity and moreover show that Bravo is found on Müller glial processes and end-feet in the developing retina. In contrast to the single polypeptide chain structure of Nr-CAM reported previously, we show that Bravo has a heterodimer structure composed of an alpha chain of M(r) 140/130 and a beta chain of 60-80 kD. As with L1 and Ng-CAM, the two chains of Bravo are generated from an intact polypeptide by cleavage at identical locations and conserved sites within all three molecules (Ser-Arg/Lys-Arg). The similar domain composition and heterodimer structure, as well as the 40% amino acid sequence identity of these molecules, defines them as an evolutionarily related subgroup of CAMs. The relationship of Bravo to molecules known to be involved in cell adhesion and process outgrowth, combined with its pattern of expression and numerous potential isoforms, suggests a complex role for this molecule in cell interactions during neural development.

A method for the generation of monoclonal antibodies against rare cell-surface molecules

Monoclonal antibodies provide a powerful tool for the identification and analysis of novel cell-surface molecules. We present here a method for antigen preparation and an immunization protocol that facilitates generation of mAb reactive with cell-surface molecules of low abundance and/or low antigenicity. The procedure involves isolation and extensive fractionation of cell-surface and detergent-soluble extracellular-matrix molecules prior to immunization. Cell-surface proteins on intact tissue are biotin-labeled using a reagent that does not penetrate cells. Avidin affinity chromatography is then used to purify these biotinylated molecules. Size-exclusion HPLC is used to separate these surface molecules on the basis of apparent molecular mass. Finally, immunization with antigen coupled to keyhole-limpet hemocyanin is combined with long-term booster immunizations to generate a hyperimmune response resulting in high-affinity IgG. A test application of this approach was aimed at the generation of mAb against cell-surface molecules of approximately 135 kDa in the developing chicken retinotectal system. Immunochemical analyses using antibodies produced by this approach which showed restricted patterns of tissue staining reveal that mAb were generated against all previously identified immunoglobulin superfamily molecules of this size in this system. Furthermore, we produced many additional antibodies that labeled retinotectal tissue in novel staining patterns. In the two cases analyzed in detail, these new patterns reflect the distributions of previously uncharacterized members of the immunoglobulin superfamily. The success of this initial study suggests that this method may represent a broadly applicable approach towards the preparation of extensive libraries of antibodies against cell-surface molecules expressed on cells from numerous sources.

Firing characteristics of vestibular nuclei neurons in the alert monkey after bilateral vestibular neurectomy

After destruction of the peripheral vestibular system which is not activated by moving large-field visual stimulation, not only labyrinthine-ocular reflexes but also optokinetic-ocular responses related to the "velocity storage" mechanism are abolished. In the normal monkey optokinetic-ocular responses are reflected in sustained activity changes of central vestibular neurons within the vestibular nuclei. To account for the loss of optokinetic responses after labyrinthectomy, inactivation of central vestibular neurons consequent on the loss of primary vestibular activity is assumed to be of major importance. To test this hypothesis we recorded the neural activity within the vestibular nuclear complex in two chronically prepared Rhesus monkeys during a period from one up to 9 and 12 months after both vestibular nerves had been cut. The discharge characteristics of 829 cells were studied in relation to eye fixation, and to a moving small and large (optokinetic) visual stimulus producing smooth pursuit (SP) eye movements and optokinetic nystagmus (OKN). Units were grouped into different subclasses. After chronic bilateral vestibular neurectomy (BVN) we have found: (1) a rich variety of spontaneously active cells within the vestibular nuclear complex, which--as far as comparison before and after BVN is possible--belong to all subclasses of neurons functionally defined in normal monkey; and (2) no sustained activity changes which are related to the activation of the "velocity storage" mechanism; this is especially true for "pure-vestibular", "vestibular-pause" and "tonic-vestibular-pause" cells in normal monkey which show a "pure", "pause" and "tonic-pause" firing pattern after BVN. Neurons which are modulated by eye position are, however, modulated with the velocity of slow eye movements with comparable sensitivity during SP and OKN. Retinal slip is extremely rarely encoded. The results of the present study do not directly answer the question why the "velocity storage" mechanism is abolished after BVN but they suggest that only a small number of central vestibular cells may be inactivated by neurectomy.

The interaction of oculomotor cues and stimulus size in stereoscopic death constancy

In the natural world, observers perceive an object to have a relatively fixed size and depth over a wide range of distances. Retinal image size and binocular disparity are to some extent scaled with distance to give observers a measure of size constancy. The angle of convergence of the two eyes and their accommodative states are one source of scaling information, but even at close range this must be supplemented by other cues. We have investigated how angular size and oculomotor state interact in the perception of size and depth at different distances. Computer-generated images of planar and stereoscopically simulated 3-D surfaces covered with an irregular blobby texture were viewed on a computer monitor. The monitor rested on a movable sled running on rails within a darkened tunnel. An observer looking into the tunnel could see nothing but the simulated surface so that oculomotor signals provided the major potential cues to the distance of the image. Observers estimated the height of the surface, their distance from it, or the stereoscopically simulated depth within it over viewing distances which ranged from 45 cm to 130 cm. The angular width of the images lay between 2 deg and 10 deg. Estimates of the magnitude of a constant simulated depth dropped with increasing viewing distance when surfaces were of constant angular size. But with surfaces of constant physical size, estimates were more nearly independent of viewing distance. At any one distance, depths appeared to be greater, the smaller the angular size of the image. With most observers, the influence of angular size on perceived depth grew with increasing viewing distance. These findings suggest that there are two components to scaling. One is independent of angular size and related to viewing distance. The second component is related to angular size, and the weighting accorded to it grows with viewing distance. Control experiments indicate that in the tunnel, oculomotor state provides the principal cue to viewing distance. Thus, the contribution of oculomotor signals to depth scaling is gradually supplanted by other cues as viewing distance grows. Binocular estimates of the heights and distances of planar surfaces of different sizes revealed that angular size and viewing distance interact in a similar way to determine perceived size and perceived distance.

Ocular responses to translation and their dependence on viewing distance. I. Motion of the observer

1. The horizontal eye movements induced by acceleration along the interaural axis were recorded from five monkeys (Macaca mulatta) by the use of the electromagnetic search-coil technique. Animals sat on a sled that was moved briefly in darkness along a linear track (bell-shaped acceleration profile: peak, 400 mm/s2; duration, 200 ms). Immediately before acceleration, animals fixated one of five target lights located at distances ranging from 16 to 150 cm. During fixation, the horizontal positions of both eyes were used to check vergence, while accommodation was monitored with an infrared optometer. 2. Sled motion induced eye movements that were generally smooth and compensatory, e.g., rightward sled motion elicited leftward eye movement. We attribute these responses to a translational vestibuloocular reflex (TVOR) that senses the sled motion through the otolith organs. However, in three animals, these responses were preceded by weak anticompensatory movements (duration, less than 40 ms; amplitude, less than 10% of the maximum compensatory response). 3. Geometry indicates that, during brief sled motion, the eye movements required to keep gaze aligned on a particular location ("full" compensation) are inversely proportional to the viewing distance. Response measures based on the computed eye velocity profiles, such as the velocity achieved at specific times ("time slices") or the peak values of the estimated covariance functions, all indicated that compensatory responses were a linear function of the inverse of the prior viewing distance. Cross-correlation analyses indicated that the effect of the prior viewing distance was to scale responses, although detailed spectral analyses revealed that high-frequency components (greater than 10 Hz) tended to scale less vigorously than lower ones. 4. The adequacy of the compensatory eye movements was assessed by calculating the gain (response recorded/response required for full compensation). Regardless of the response measure used, gains varied considerably from one animal to another and, in some particular animals, from one direction to another but showed a general tendency to increase with viewing distance. For example, on the basis of the peak eye velocity achieved within 250 ms of the onset of sled motion, mean gain at 16 cm was 0.74 (range, 0.48-1.01), whereas at 150 cm it was 1.25 (range, 0.67-1.73). 5. Using wedge prisms to dissociate vergence and accommodation indicated that ocular responses to sled motion were sensitive to selective increases in either vergence (base-out prism with the most distant target) or accommodation (base-in prism with the nearest target). However, the magnitude of the effects showed considerable variability from one animal to another and, in some particular animals, from one direction to another.(ABSTRACT TRUNCATED AT 400 WORDS)

Ocular responses to translation and their dependence on viewing distance. II. Motion of the scene

1. The ocular following responses induced by brief (100-ms) movements of the visual scene were examined for their dependence on viewing distance in 5 monkeys (Macaca mulatta). The horizontal positions of both eyes and the vertical position of one eye were recorded using the electromagnetic search-coil technique. Accommodation was monitored in selected experiments by use of an infrared optometer. Test patterns (random dots) were back-projected onto a translucent tangent screen facing the animal. Six viewing distances were used (range, 20-150 cm), the size and speed of the image on the screen being adjusted for each so as to preserve a constant retinal image. 2. Response measures based on the amplitude of the first peak in the eye acceleration profile or the eye velocity achieved at specific times all indicated that ocular following responses were inversely related to viewing distance, the relationship being linear for the earliest measures. On average, the sensitivity to viewing distance was comparable with that reported for the translational vestibuloocular reflex (TVOR) in the preceding paper: as viewing distance increased from 20 cm, ocular following decremented at a mean rate (+/- SD) of 17 +/- 3% per m-1, while the TVOR decremented at a mean rate (+/- SD) of 18 +/- 1% per m-1. 3. Ocular following responses showed the postsaccadic enhancement described by Kawano and Miles regardless of viewing distance. To a first approximation, the effects of postsaccadic enhancement and viewing distance summed linearly. 4. The dependence of ocular following on speed showed the progressive saturation previously described by Miles et al. at all viewing distances, the peak eye velocity achieved being inversely related to the viewing distance, indicating that the saturation must originate upstream of the dependence on viewing distance. Under normal viewing conditions, this speed saturation will tend to offset the dependence on viewing distance because the retinal slip speeds experienced by the moving observer will tend to vary inversely with viewing distance, resulting in greater saturation with nearer viewing. 5. Wedge prisms were used to dissociate vergence and accommodation and indicated that ocular following responses were sensitive to selective increases in either vergence (base-out prism with the screen at 100 cm) or accommodation (base-in prism with the screen at 20 cm). However, as with the TVOR, the magnitude of the effects showed considerable variability from one animal to another and, in some particular animals, from one direction to another.(ABSTRACT TRUNCATED AT 400 WORDS)

Isoprenaline cannot act on pancreatic beta cells without hyperglycemia or alpha-block

During long-term increase in isoprenaline (pronounced beta-effect) and isoprenaline plus regitine (pure beta-effect) pancreatic insulin-secretion still depended mostly on blood glucose levels. This means that increased beta-effect during normo- or hypoglycemia could not cause a higher insulin-secretion. Only during additional alpha-receptor blockade insulin-secretion was slightly but insufficiently increased. Catecholamines seem to be more regulator than originator of the insulin secretory process.

Topologically restricted appearance in the developing chick retinotectal system of Bravo, a neural surface protein: experimental modulation by environmental cues

A novel neural surface protein, Bravo, shows a pattern of topological restriction in the embryonic chick retinotectal system. Bravo is present on the developing optic fibers in the retina; however, retinal axons in the tectum do not display Bravo. The appearance of Bravo in vitro is modulated by environmental cues. Axons growing out from retinal explants on retinal basal lamina, their natural substrate, express Bravo, whereas such axons growing on collagen do not. Retinal explants provide a valuable system to characterize the mechanism of Bravo restriction, as well as the cellular signals controlling it. Bravo was identified with monoclonal antibodies from a collection generated against exposed molecules isolated by using a selective cell surface biotinylation procedure. The NH2-terminal sequence of Bravo shows similarity with L1, a neural surface molecule which is a member of the immunoglobulin superfamily. This possible relationship to L1, together with its restricted appearance, suggests an involvement of Bravo in axonal growth and guidance.

The avian tectobulbar tract: development, explant culture, and effects of antibodies on the pattern of neurite outgrowth

The tectobulbar tract is the first long-distance projecting fiber pathway to appear during the development of the avian optic tectum (dorsal half of the mesencephalon). Immunologically stained wholemounts of the E3 mesencephalon reveal that the early tectobulbar axons course in a dorsal-to-ventral direction and abruptly turn in a caudal direction shortly before reaching the ventral midline. During subsequent development, more tectobulbar axons are generated that form a parallel array of thick fascicles coursing ventrally within the mesencephalon. At this later stage of development, the tectobulbar tract bifurcates into an ipsilateral and contralateral pathway, both growing in a caudal direction near the mesencephalic ventral midline. Bifurcation and change in direction of growth is accompanied by a complete loss of the fasciculated growth pattern. Each tectobulbar axon is thus divided into a proximal fasciculated and a distal unfasciculated segment. Tectobulbar fascicles occupy the most superficial surface layer of the mesencephalon at early stages and are displaced deeper into the tissue beginning at embryonic day 5. In both of these locations, tectobulbar axons express molecules involved in axon-axon and axon-substrate interactions like the G4 antigen, neural cell adhesion molecule (N-CAM), neurofascin, and T61 antigen as revealed by immunohistochemistry and immunoblotting. Stripes of the mesencephalon explanted onto a basal lamina substratum show vigorous outgrowth of neurites. These processes grow in fascicles at a growth rate of 40 microns/h. Staining of the neurites with specific antibodies, as well as the position of the retrogradely labeled cell bodies, is in agreement with these processes being tectobulbar axons. This in vitro explant system was used to investigate the expression and possible functional involvement of N-CAM, neurofascin, G4 protein, and T61 antigen in the growth of these axons. The presence of antigen-binding fragments of polyclonal anti-G4 antibodies completely blocks fasciculation of the neurites but has no influence on their rate of elongation. Antibodies against N-CAM and neurofascin have no detectable effects. The number and length of the in vitro growing axons are reduced by the monoclonal T61 antibody. This effect is reversible. The elucidation of the exact course in vivo and the accessibility to the axons growing in vitro make the tectobulbar tract an excellent model system for the investigation of the role of these and other proteins in axonal growth and guidance during the development of the CNS.

Use of the biotin-avidin system for labelling, isolation and characterization of neural cell-surface proteins

We describe a method for the selective labelling, isolation and electrophoretic analysis of cell-surface molecules and extracellular matrix components. Intact tissues are reacted with activated esters of biotin and the labelled surface molecules identified on Western blots with horseradish-peroxidase-coupled or 35S-labelled streptavidin. Alternatively, the biotinylated proteins can be purified from tissue homogenates by affinity chromatography on an avidin-agarose column. Evidence is presented to show that this method is indeed specific for membrane and matrix components. Its practical application to embryonic neural tissues is demonstrated.

[AIDS and females. Change in problems for the gynecologist]

We report on our experience with 47 HIV-positive women, died in the meantime. 32% stated, that they had never taken i.v. drugs. Their clinical pattern varies greatly. Psychosocial problems and infections, such as genital herpes and candidosis and others predominate. Long-term controls of 12 couples with HIV-negative male partner only showed one case of HIV-transmission. Since 1980 21 children were born by these patients, 7 of them are seropositive 2 years after birth, and one of them has meanwhile died of AIDS.

Ocular responses to linear motion are inversely proportional to viewing distance

Eye movements exist to improve vision, in part by preventing excessive retinal image slip. A major threat to the stability of the retinal image comes from the observer's own movement, and there are visual and vestibular reflexes that operate to meet this challenge by generating compensatory eye movements. The ocular responses to translational disturbances of the observer and of the scene were recorded from monkeys. The associated vestibular and visual responses were both linearly dependent on the inverse of the viewing distance. Such dependence on proximity is appropriate for the vestibular reflex, which must transform signals from Cartesian to polar coordinates, but not for the visual reflex, which operates entirely in polar coordinates. However, such shared proximity effects in the visual reflex could compensate for known intrinsic limitations that would otherwise compromise performance at near viewing.

Vestibular habituation in student pilots

The dynamics of vestibular nystagmus were measured in 42 military student pilots (age 19 to 21). Their responses were compared with 40 non-flying subjects of similar age who were also fulfilling requirements for the mandatory Swiss military service. The following differences emerged: the time constant of the nystagmus response after vestibular stimulation was shorter (p less than 0.001; t-test) in student pilots, whereas the gain tended to be higher (p less than 0.025). These changes in the response dynamics are attributed to habituation. Student pilots were additionally tested with conflicting visual-vestibular stimulation. Nystagmus response was delayed and attenuated when compared to stimulation in darkness. Under these conditions motion sickness occurred in one third of the subjects. We found no relation between the occurrence of motion sickness and the value of the time constant or gain of vestibular nystagmus. Results show that there is no single "normal" value of vestibular nystagmus. This becomes important when defining "normal" values as opposed to pathological values in vestibular testing.

[The physiologic and anatomic principles of rapid eye movements (saccades) and their clinical significance]

Our understanding of the organisation of eye movements has been greatly expanded in recent years, mainly due to studies in animals. A review of the clinically important neurophysiological and anatomical aspects of the generation of rapid eye movements (saccades) will be presented. A knowledge of these basic aspects will assist the clinician's investigation and understanding of pathological eye movements in patients.

On the generation of vertical and torsional rapid eye movements in the monkey

The role of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in generating the vertical and torsional components of rapid eye movements was examined. The on-directions of burst neurons in the riMLF of alert Rhesus monkeys were obtained during quick phase nystagmus in three dimensions. The distinguishing feature of these burst neurons was the torsional component of their on-directions; neurons on the right side exhibited a clockwise component, from the point of view of the subject, while those on the left had a counterclockwise component. Vertical components could have up or down directions. This organization was verified by means of unilateral reversible inactivation of the riMLF using Muscimol. An injection in the right riMLF impaired the generation of quick phases with clockwise components while one on the left impaired counterclockwise components.

Oculomotor functions of the flocculus and the vestibular nuclei after bilateral vestibular neurectomy

Ito's hypothesis of an important role of the flocculus of the vestibulocerebellum in the immediate visual control of the VOR during visual-vestibular interaction has received substantial support. Nevertheless, several parts in this hypothesis are unclear, at least in primates. In normal monkey, vestibularly driven neurones in the vestibular nuclei do not carry signals which are adequate to account for the full range of eye movement responses during optokinetic tracking (OKN) and different situations of visual-vestibular interaction (especially VOR-suppression). Thus these neurones seem not to be located at the final stage where floccular "gaze-velocity" Purkinje cells (PCs) exert their control function on the three-neurone-reflex arc. The signals of these "central" vestibular neurones (if relevant for the oculomotor output) must further be processed. After bilateral vestibular neurectomy (BVN) only a small number of vestibular nuclei neurones were found with eye velocity sensitivities during smooth pursuit tracking (SP) and OKN in the range of those of floccular PCs (also after BVN), and with the appropriate polarity of modulation. Our difficulties in finding neurones in the vestibular nuclei which, according to their neurophysiological behaviour, could be main target cells of floccular PCs, either in normal or in BVN monkeys, are discussed.

The composition of the murein of Escherichia coli

Escherichia coli murein, the polymer from which the shape-maintaining structure of the cell envelope is made, shows unexpected complexity. The separation of murein building blocks with high performance liquid chromatography reveals about 80 different types of muropeptides. Their behavior in high performance liquid chromatography and their chemical structure are described. The complexity of E. coli murein is due to the free combination of seven different types of side chains (L-Ala-D-Glu-R with R = -OH, -m-A2pm, -m-A2pm-D-Ala, -m-A2 pm-Gly, -m-A2pm-D-Ala-D-Ala, -m-A2pm-D-Ala-Gly, -m-A2pm-Lys-Arg) with two types of cross-bridges (D-Ala-m-A2pm, -m-A2pm-m-A2pm). The novel type of cross-bridge, A2pm-A2pm, contains an L,D-peptide bond, as shown by Edman degradation and chemical analysis of the reaction products. The A2pm-A2pm cross-bridge is assumed to play a role in the adaptation of the cross-linkage of murein to different growth conditions of the cell. The structural data of E. coli murein agree best with a model of a thin, however multilayered, murein sacculus.

[Rapid eye movements (saccades): review of their physiological and anatomical basis and their clinical significance]

Our understanding of the organization of eye movements has been greatly expanded in recent years, mainly due to studies in animals. A review of the clinically important neurophysiological and anatomical aspects of the organization of rapid eye movements (saccades) is presented. A knowledge of these basic aspects will assist the clinician's investigation and understanding of pathologic eye movements in patients.