B Hengstenberg

The number and structure of giant vertical cells (VS) in the lobula plate of the blowflyCalliphora erythrocephala

Summary1.The structure of one class of giant tangential neurons in the lobula plate ofCalliphora, the ‘Vertical System (VS)’ has been investigated by light microscopy. Different staining and reconstruction procedures were employed to ensure that all existing VS-neurons are revealed.2.There are 11 VS-cells in a characteristic, and constant arrangement (Fig. 2). Each cell covers a particular area of the lobula plate, i.e., a distinct area of the retinotopic input array (Table 2), and therefore has a distinct receptive field.3.Although VS-cells in general tend to occupy the posterior surface of the lobula plate, only three of them (VS 2-VS 5) reside exclusively in this layer. The other cells (VS1 and VS6-VS10) have bistratified dendritic arborizations (Fig. 6), whose dorsal parts are apposed to the anterior surface of the lobula plate.4.The arrangement, territory and stratification of any given VS-cell is largely invariant in different individuals, whereas the branching pattern may vary considerably (Fig. 3).5.The present results provide the framework for physiological studies of the role of individual VS-cells in movement perception, and their involvement in the control of particular locomotor behaviour.

Optomotor control of wing beat and body posture in drosophila

Continuous movement of striped patterns was presented on either side of a tethered fruitfly, Drosophila melanogaster, in order to simulate the displacement of stationary landmarks within the visual field of the freely moving fly. The horizontal components of the stimulus elicit, predominantly, yaw-torque responses during flight, or turning responses on the ground, which counteract involuntary deviations from a streight course in the corresponding mode of locomotion. The vertical components elicit, predominantly, covariant responses of lift and thrust which enable the fly to maintain a given level of flight. Monocular stimulation is sufficient to produce antagonistic responses, if the direction of the stimulus is reversed. The following constituents of the responses were derived mainly from properties of wing beat and body posture on photographs of fixed flight under visual stimulation. Wing stroke modulation (W. S. M.): The difference, and the sum, of the stroke amplitudes on either side are independently controlled by horizontal and vertical movement components, respectively. The maximum range of modulation per wing (12.3°) is equivalent to a 63% change in thrust on the corresponding side. Leg stroke modulation (L.S.M.): In the walking fly each pair of legs is under control of visual stimulation. The details of leg articulation are still unknown. Abdominal deflection (A.D.): An actively induced posture effect. Facilitates steering during free flight at increased air speed. Hind leg deflection (H.L.D.): Same as before. On most of the photographs the hind legs were deflected simultaneously and in the same direction as the abdomen. Hitch inhibition (H.I.): The term “hitch” denotes a transient reduction of stroke amplitude which seems to occur spontaneously and independently on either side of the fly. The hitch angle (12.2±3.8° S.D.) is most probably invariant to visual stimulation. Hitches are comparatively frequent in the absence of pattern movement. Their inhibition under visual stimulation is equivalent to an increase of the average thrust of the corresponding wing. The different constituents contribute to the optomotor responses according to the following tentative scheme (Fig. 7). The torque response is essentially due to the effects of W.S.M., A.D., H.L.D. and H.I., and the turning response to L.S.M. and possibly H.L.D., if the landmarks drift from anterior to posterior. So far, H.I. seems to be the only source of the torque response, and L.S.M. the only source of the turning response, if the landmarks drift in the opposite direction. The lift/thrust response results essentially from the effects of W.S.M. and H.I., no matter whether the landmarks drift from inferior to superior or in the opposite direction. The results obtained so far suggest that the optomotor control of course and altitude in Drosophila requires at least eight independent input channels or equivalent means for the separation of the descending signals from the visual centres. Further extension and refinement of the “wiring scheme” is required in order to improve the identification of the sensory inputs of the motor system and the classification of optomotor defective mutants.

Compensatory head roll in the blowfly Calliphora during flight

Video records were made of the blowfly Calliphora erythrocephala L. mainly during tethered flight in a wind-tunnel, to study its movements about the longitudinal body axis (roll). During undisturbed flight, flies hold their head on average aligned with the body but may turn it about all three body axes. Pitch and yaw turns of the head are comparatively small (20°), whereas roll turns can be large (90°), and fast (1200° s-1). When passively rolled, flies produce compensatory head movements during walking or flight; at rest this reflex is turned off. Flies perceive a static misalignment relative to the vertical, as well as roll motion up to 10000° s-1. Within this range flies counteract an imposed roll with maximal gain at about 1000° s-1. Compensatory head movements are made with very low latency (down to ∆t ≈ 5ms), and with considerable speed (up to ω = 1000° s-1). Flies may ‘disregard’ an apparent deviation from their correct orientation, and may superimpose spontaneous head movements on those elicited by a stimulus. Compensatory head movements generally undercompensate the imposed misalignment. Simultaneously, however, flies modify their wing pitch and wingbeat amplitude to produce a compensatory roll torque. Since head and body roll act simultaneously and in the same direction, the overall speed and degree of head realignment, relative to external coordinates, increase considerably. This is certainly an advantage for flight in turbulent air. In still air, without need to correct an imposed misalignment, flies nevertheless produce spontaneous fluctuations of their flight torque, and head roll movements in the opposite direction. This is to be expected if flies intend to keep their eyes aligned with the coordinates of the environment while spontaneously performing banked turns. The limits of fly vision and the advantages of compensatory head movements for different visually guided behaviour are discussed. Compensatory head roll movements give flies greater manoeuvrability when cruising than the visual system would allow, without such a stabilizing reflex.

Intracellular Staining of Insect Neurons with Procion Yellow

The principal advantages of simultaneously recording from, and staining of single neurons, buried deep in tissue, is obvious and need not be stressed. Particularly in insects, where most cell somata are electrically silent, there is so far no way to correlate neuronal activity with a particular cell other than to penetrate and to label small fibers simultaneously (Hengstenberg, 1971). Great efforts have been undertaken during the past years to develop methods that would meet the many and often conflicting demands that an ideal intracellular marking procedure has to satisfy (see Nicholson and Kater, 1973). The injection of Procion dyes (Stretton and Kravitz, 1968; Christensen, 1973), cobalt(II) ions (Pitman et al., 1972; Tyrer and Bell, 1974), and horseradish peroxidase (Muller and McMahan, 1976), followed by appropriate histochemical and histologic procedures, seem at present to approach most closely the requirements of an ideal marking method. Each of the three has distinct advantages to recommend it for a particular problem and drawbacks that may prohibit its application in other instances.

Three-Dimensional Reconstruction and Stereoscopic Display of Neurons in the Fly Visual System

Nerve cells are complicated anisomorphic bodies, intertwined amongst thousands of others. Their structural complexity is apparently crucial for their function and, therefore, the function of the nervous system as a whole. However, it is notoriously difficult to visualize the three-dimensional structure of nerve cells and their spatial relationships within different brain regions (His 1887).