Diagnostic occlusion test in cases of unilateral strabismus sursoadductorius.

PURPOSE: To investigate the diagnostic occlusion test (OT) according to Marlow in strabismus sursoadductorius (StS; also known as 'unilateral superior oblique palsy') and its implications for surgical treatment. METHODS: In 67 cases of StS, angles of strabismus were measured before and after patching the affected eye for three days. Horizontal, vertical and torsional deviations were measured in front of the tangent screen of Harms in nine directions of gaze. RESULTS: After OT, most cases of StS showed the following distribution of vertical deviation (VD) on horizontal versions: setting the VD in 30 degrees adduction to 100%, VD in primary position (PP) was 50%, VD in abduction 14%, excyclotropia in PP about 40% of the amount of VD. Those StS-cases showing the same distribution of VD on horizontal versions before and after OT were called 'typical' ones (27% of the patients). However, 73% of the patients showed a different distribution before OT: 68% VD in PP, 36% VD in abduction, excyclotropia of 20% in PP. After OT these cases converted to the normal pattern described above: VD in PP was 53 % and VD in 30 degrees abduction was 19%, excyclotropia in PP was 36%. CONCLUSION: In 'typical' StS-cases, OT is not necessary. 'Atypical' cases, however, can be converted into 'typical' ones: they get more incomitant VD on horizontal versions and greater excyclotropia in PP. As VD in adduction remains almost the same in both groups after OT, surgery can be based on the angle in adduction. In individual 'atypical' patients the amount of oblique muscle surgery has to be modified after OT.

Staging of middle and late embryonic development in the medicinal leech, Hirudo medicinalis.

We present a description of the last half of embryonic development in the European medicinal leech, Hirudo medicinalis, based entirely on externally visible morphological features, and establish reliably observable stages during that development. Embryogenesis, from the time fertilized eggs are deposited in an eggcase (called a cocoon) to the emergence of juveniles from the cocoon, takes approximately 4 weeks at room temperature. The stages described in this paper extend from the completion of segmentation to the appearance of the final bands of pigmentation. Developmental stages are expressed as percentages of total embryonic developmental time. This staging table was constructed for embryos kept at 20 degrees C. In addition, the development of animals kept at 17 degrees C or at 24 degrees C was compared with those held at 20 degrees C. Development proceeds more quickly at higher temperatures. Because development in embryos held at higher or lower temperatures was linearly related to the stages determined for embryos held at 20 degrees C, the rate of development at any intermediate temperature can be predicted from the staging table at 20 degrees C by simple multiplication.

Development of spontaneous and evoked behaviors in the medicinal leech.

ABSTRACT The ontogeny of behavior in an organism must reflect developmental events in the nervous system, and it thus provides a noninvasive measure of neuronal development. This approach may be particularly fruitful in the medicinal leech because the neuronal basis of several behaviors has been characterized in adult leeches, providing a rich background against which behavioral development can be interpreted. We have investigated the order in which behaviors arise during the period of embryonic development and have determined the time at which each behavior is first expressed. Some behaviors, such as lateral ridge formation, germinal plate bending, spiral twisting, and sidewinding, were produced spontaneously by embryos. Others, such as shortening, circumferential indentation, local bending, and elongation, occurred only when they were elicited by weak mechanical stimulation. Such stimulation rarely evoked a behavioral response in young embryos (at 45% of the time required for complete embryonic development, 45% ED), but by 80% ED embryos responded to nearly 100% of the stimuli presented. In embryos older than 50% ED, the behavior most frequently evoked by stimulation of the anterior end, the posterior end, or the rear sucker was shortening. Stimulation of the midbody usually evoked behavior other than shortening, illustrating that the body was behaviorally compartmentalized, at least in part. Some behaviors observed during embryogenesis are never seen in adult leeches. For example, in response to stimulation of the midbody, young embryos produced a behavior that we have called "circumferential indentation," whereas older embryos produced local bending, a response previously described for adults. The switch from circumferential indentation to local bending may signal the formation of new synaptic connections.

Interneuronal and motor patterns during crawling behavior of semi-intact leeches.

Semi-intact tethered preparations were used to characterize neuronal activity patterns in midbody ganglia of the medicinal leech during crawling. Extra- and intracellular recordings were obtained from identified interneurons and from motor neurons of the longitudinal and circular muscles during crawling episodes. Coordinated activities of nine excitatory and inhibitory motor neurons of the longitudinal and circular muscles were recorded during the appropriate phases of crawling. Thus, during crawling, the leech uses motor output components known to contribute to other types of behavior, such as swimming or the shortening/local bending reflex. Interneurons with identified functions in these other types of behavior exhibit membrane potential oscillations that are in phase with the behavior pattern. Therefore, the recruitment of neuronal network elements during several types of behavior occurs not only at the motor neuron level but also involves interneurons. This applies even to some interneurons that were previously thought to have dedicated functions (such as cells 204 and 208 and the S cell). The function of neuronal circuitries in producing different types of behavior with a limited number of neurons is discussed.

Temporal correlation between neuronal tail ganglion activity and locomotion in the leech, Hirudo medicinalis.

Intracellular and extracellular recordings were performed in the posterior ventral nerve cord of restrained crawling preparations of the medicinal leech, Hirudo medicinalis. Short-latency neuronal activities in the tail ganglion nerves correlated with different phases of crawling behavior. Eight neurons with characteristic activation patterns during crawling were identified morphologically and physiologically in the tail ganglia of 23 preparations. The axons of four of these neurons projected through posterior tail brain nerves; four ascending interneurons had projections in the connectives or in Faivre's nerve. These interneurons are suitable candidates for carrying information between the front end and the tail end of the animal to coordinate the behavioral components during a crawling step.

Parallel pathways coordinate crawling in the medicinal leech, Hirudo medicinalis.

Changes in the behavior of crawling leeches were investigated after various kinds of manipulations, including selective transection or inactivation of body parts, as well as partial or complete transection of the central nerve cord, using a frame-by-frame analysis of video tapes of the crawling animals. From these studies, we found that: 1. Leeches made rhythmic crawling cycles even after their suckers were prevented from contacting the substrate by covering them over with glue. Hence, engagement and disengagement of the suckers are not necessary links in the crawling cycle. 2. Cutting the small, medial connective (Faivre's nerve) had no influence on crawling, but contraction during the whole-body shortening reflex was interrupted. Thus two behaviors which use the same motor output (i.e., whole-body shortening and the contraction phase of crawling) are mediated by two different pathways. 3. Cutting all the connectives between two ganglia in the middle of the leech resulted in a loss of coordination between the parts of the animal on either side of the cut. Therefore, temporally coordinated sucker activity must be mediated through these connectives. 4. Pieces of leech bodies produced by complete transection produced rhythmic crawling cycles as long as the pieces included the head or tail plus 2-4 adjacent midbody segments. In all cases, the crawling movements progressed without delays as the movements reached the cut ends. Pieces of animals that included only midbody segments did not produce crawling movements. 5. These results can be explained by a model composed of intersegmental pathways for both elongation and contraction, circuits in the head and tail brains that switch between elongation and contraction, and both ascending and descending inhibitory influences that determine when the cycle switches from elongation to contraction and back again.

Monitoring neuronal activity during discrete behaviors: a crawling, swimming and shortening device for tethered leeches.

An apparatus is described which facilities continuous electrophysiological recordings in segmental ganglia of leeches while the animal performs different behavioral patterns: crawling, swimming or shortening. Both the behaviors and neuronal recordings are monitored by a video camera system and can be evaluated simultaneously. The device is well suited to investigate questions of behavioral choice and neuronal decision-making mechanisms in these animals. It can also be modified to study the neural control of behavior in other aquatic animals, such as snails.

Simulation of self-motion in tethered flying insects: an optical flow field for locusts.

A low-cost solution for a visual flow field device is described. The apparatus generates progressive and regressive patterns of motion with variable angular speeds and intensities. Additionally, rotational stimuli can be applied. First results show the efficiency of the flow field in producing flight behavior and steering responses in visual interneurons of locusts.

Sensitivity of ocellar interneurons of the honeybee to constant and temporally modulated light.

Sinusoidally modulated and discrete light pulses, the parameters of which approximated natural light conditions, were used to determine the response characteristics of ocellar first-order interneurons of the worker honeybee (Apis mellifera carnica). Large ocellar interneurons which terminate within the brain (LB neurons) were recorded from intracellularly and were identified visually after dye injection. Absolute sensitivity of LB neurons to light flashes ranges from 4 X 10(9) quanta/cm2s (Q) for MOC1,7 neurons to 1 X 10(12) Q for MOC3,4. The slope of the response-intensity (R/I) functions, which were calculated for intensities between 2 X 10(9) and 4 X 10(13) Q, varies in different types of LB neurons. The strongest response is given by one group of median ocellar neurons. With constant light around 10(13) Q, most LB neurons exhibit oscillatory hyperpolarizations which, upon increasing the stimulus to even higher intensities (10(14)-10(15) Q), gradually evolve to a hyperpolarized plateau. The frequency of these oscillatory voltage fluctuations increases with the rate of modulation of the stimulating light and reaches maximum values at 5-15 Hz modulation frequency. Two groups of MOC neurons follow sinusoidally modulated light up to 32 +/- 8 Hz (n = 5) and 29 +/- 6 Hz (n = 3), respectively, whereas lateral ocellar neurons cut off at 17 +/- 5 Hz (n = 4). The possible role of LB neurons is discussed. They may be inactivated when the bee is flying in bright sunlight.