Peter Görner

The area octavo-lateralis in Xenopus laevis

SummaryCentral projections of afferents from the lateral line nerves and from the individual branches of the VIIIth cranial nerve in Xenopus laevis and Xenopus mülleri were studied by the application of HRP to the cut end of the nerves.Upon entering the rhombencephalon, the lateral line afferents form a longitudinal fascicle of ascending and descending branches in the ventro-lateral part of the lateral line neuropile. The fascicle exhibits a topographic organization, that is not reflected in the terminal field of the side branches. The terminal field can be subdivided into a rostral, a medial and a caudal part, each of which shows specific branching and terminal pattern of the lateral line afferents. These different patterns within the terminal field are interpreted as the reflection of functional subdivisions of the lateral line area. The study did not reveal a simple topographic relationship between peripheral neuromasts and their central projections.Two nuclei of the alar plate with significant lateral line input were delineated: the lateral line nucleus (LLN) and the medial part of the anterior nucleus (AN). An additional cell group, the intermediate nucleus (IN), is a zone of lateral line and eighth nerve overlap, although such zones also exist within the ventral part of the LLN and the dorsal part of the caudal nucleus (CN). Six nuclei which receive significant VIIIth nerve input are recognized: the cerebellar nucleus (CbN), the lateral part of the anterior nucleus, the dorsal medullary nucleus (DMN), the lateral octavus nucleus (LON), the medial vestibular nucleus (MVN) and the caudal nucleus (CN).All inner ear organs have more than one projection field. All organs project to the dorsal part of the LON and the lateral part of the AN. Lagena, amphibian papilla and basilar papilla project to separate regions of the dorsal medullary nucleus (DMN). There is evidence for a topographic relation between the hair cells of the amphibian papilla (AP) and the central projections of AP fibers. The sacculus projects extensively to a region between the DMN and the LON. Fibers from the sacculus and the lagena project directly to the superior olive. Fibers from the utriculus and the three crista organs terminate predominantly in the medial vestibular nucleus (MVN) and in the adjacent parts of the reticular formation, and their terminal structures appear to be organotopically organised. Octavus fiber projections to the cerebellum and to the spinal cord are also described.

Homing Behavior and Orientation in the Funnel-Web Spider, Agelena labyrinthica Clerck

This paper reviews what is known to date about the homing abilities of the funnel-web spider and discusses recent research in this field based on new and partly unpublished data. To provide a more comprehensive overview of the ability of spiders in general to orientate, research on other species will also be considered. A theory of the optical and idiothetic navigation of the funnel web spider will be presented in Chapter XV by H. Mittelstaedt, this Volume.

Innervation Patterns of the Lateral Line Stitches of the Clawed Frog, Xenopus laevis, and Their Reorganization during Metamorphosis

We quantitatively examined the afferent innervation pattern of the lateral line stitches of both larval and postmetamorphotic clawed frogs, Xenopus laevis, using a silver staining technique. We also studied the relevance of the number of neuromasts in a stitch to physiological properties, recording afferent activity with an electrode inserted directly into the neuromast. The innervation pattern changed during early metamorphosis, the fiber thickness increasing after the reorganization. We found three different innervation patterns: in type A stitches, the same two afferent fibers innervate all neuromasts; in type B stitches, one or two fibers innervate more than one stitch; in type C stitches, three to six fibers innervate a stitch. The distribution of the different types of stitches varied in different parts of the body. The frequency of type A stitches differed between larval trunk and larval head. For both larvae and juveniles, type B stitches were more frequent on ventral than dorsal areas, while type C stitches were more frequent on the head than on the trunk. Electrophysiological experiments indicated that the sensitivity of an afferent fiber increases with the number of neuromasts it innervates. This increase and the variation in innervation patterns shows that the single afferent fiber, not the stitch, is the functional unit of the lateral line periphery.

Reaction to surface waves by Xenopus laevis Daudin. Are sensory systems other than the lateral line involved

The turning response to surface waves of clawed toads (Xenopus laevis) with an inactivated lateral line was reinvestigated to examine whether sensory systems other than the lateral line (“second systems”) are involved. Two methods were used to block the lateral line input: selective and reversible inactivation of the lateral line periphery using CoCl2 or chronic destruction with thermocautery. The time-course of the response recovery (response frequency, turning accuracy and reaction time) was recorded. Following CoCl2 inactivation 10 out of 13 animals did not respond to surface waves for at least 2 days. The remaining 3 animals gave sporadic turning responses. It is assumed that in these individuals a “second system” is permanently involved in the detection of surface waves parallel to the lateral line. Five days after the chronic destruction of the lateral line all animals again turned to the centre of surface waves. It is suggested that by this time the “second system” had become capable of substituting for the missing lateral line input. The response frequency and the accuracy of the turning response of lesioned animals varied considerably among individuals but was always lower than in untreated animals (tested up to 120 days).

Multisensory interaction in the torus semicircularis of the clawed toad Xenopus laevis

Interactions between the lateral-line, general somatosensory and auditory system were studied using field potential analysis and single unit recordings in the torus semicircularis of the clawed toad Xenopus laevis. As a response to paired stimuli (electric shocks applied to the peripheral nerves or acoustic clicks), in all systems a reduction of the second evoked potential occurred for intervals of up to 5 s. Following consecutive stimulation of two different systems, the amplitude of the second evoked potential was also reduced, indicating mutual interaction of different systems. Single unit recordings revealed the existence of both inhibitory and excitatory interaction between different modalities.

Stimulus discrimination and wave source localization in fishing spiders (Dolomedes triton and D. okefinokensis)

We have studied the behavioral responses of fishing spiders (Dolomedes triton and Dolomedes okefinokensis) to water surface wave stimuli. D.okefinokensis responded to click-like wave stimuli (Fig. 3C) in less than 15% of the cases. Responsiveness did not increase if up to 20 clicks were elicited in quick succession from the same spot (Fig. 5). If longer lasting concentric stimuli were offered, the spiders determined the direction (Fig. 6) and the distance (Fig. 8) to the wave source. This was true for monofrequency stimuli and for narrow-band and broadband noise stimuli. If concentric multifrequency surface waves were offered, even a fivefold decrease in stimulus amplitude did not significantly change the mean running distance of D.triton. However, if multifrequency wave stimuli with a flat wave front were presented, the spiders (D.triton) no longer determined the source distance precisely (Figs. 11, 12). Our results indicate that fishing spiders of the genus Dolomedes mainly use the curvature of a concentric wave stimulus for distance determination.

A Brief Overview of the Mechanosensory Lateral Line System and the Contributions to This Volume

The mechanosensory lateral line system can be most easily distinguished from its electrosensory counterpart by the morphology of its end organ, the neuromast, which consists of hair cells and associated support cells (see Jorgensen, Chapter 6, for further details). Historically, at least four classes of end organs, distinguished primarily by surrounding support structures, have been classified as mechanosensory lateral line organs: (1) superficial neuromasts found on the skin surface in cartilaginous and bony fishes and some aquatic and semiterrestrial amphibians; (2) canal neuromasts enclosed in tubes formed by cartilage in elasmobranch fishes and by bone or scale in most bony fishes; (3) spiracular organs housed in diverticula of the hyoid pouch and found in most nonteleost bony fishes; and (4) vesicles of Savi, enclosed pouches containing a cluster of neuromasts and found in some elasmobranchs. The majority of the work contained in this book focuses on what is known about the first two classes of neuromasts (see Dijkgraaf 1963 and Coombs et al. 1988 for further reviews on morphological variation within these classes), but the chapter by Barry and Bennett is devoted exclusively to spiracular organs and the vesicles of Savi.