Barbara Claas

Centrifugal innervation of the retina in cichlid and poecilid fishes. A horseradish peroxidase study

Abstract After injecting horseradish peroxidase (HRP) solution into the eye or optic nerve in cichlid or poecilid fishes, neurons in the olfactory bulb, ventral telencephalon and pretectal area of the diencephalon contain retrogradely transported HRP. The dendrites of the telencephalic neurons project into the olfactory bulb. The dendrites of the pretectal neurons project into the ventricular gray on the border between ventral and dorsal thalamus and are detectable up to the caudal end of the nucleus glomerulosus. We consider these neurons to be the origin of centrifugal innervation of the retina.

Directional sensitivity of lateral line units in the clawed toadXenopus laevis Daudin

SummaryFollowing lateral line stimulation with surface waves single unit activity was recorded from the periphery, torus semicircularis, and tecturn opticum ofXenopus laevis. The reaction of units to varying stimulus directions was examined.The directional specificity (DS) was calculated on the basis of spike counts per stimulus using circular statistics. It was expressed as the length of the mean vector.Discharges of primary afferents of the ramus supraorbitalis and ramus infraorbitalis were phase locked to the stimulus to a varying degree depending on the location of the corresponding groups of neuromasts. Their DS was not better than 0.26.Lemniscal fibers, representing the ascending output of the medulla and units of the torus semicircularis reached a DS of 0.10–0.24 and 0.11–0.36 respectively. Neurons in the tectum opticum were the most sharply tuned with DS ranging between 0.81 and 0.96.The surroundings were represented by the best directions of two arrays of tectal units forming a map which is in register with the representation of the corresponding visual field of the animal.

Electroreceptive and mechanoreceptive units in the lateral line of the axolotlAmbystoma mexicanum

SummaryThe properties of electroreceptive units (ampullary organs) and mechanoreceptive units (neuromasts) in the head lateral line system of the axolotlAmbystoma mexicanum were compared by recording single unit activity in the afferent fibers:1.Electroreceptive units respond with excitation to cathodal (outward) and with inhibition to anodal (inward) current. Ordinary lateral line units react in the opposite way: they are excited by anodal and inhibited by cathodal current.2.Electroreceptive units react to electric field stimuli (square pulses) down to a voltage gradient parallel to the skin of 10 μV cm−1 with 10% change of the mean resting activity. Mechanoreceptive lateral line units show this response at a stimulus strength of about 10 mV cm−1. Sinusoidal stimulation of electroreceptive units in the best frequency range with amplitudes down to 5 μV cm−1 resulted in 10% modulation response.3.Electroreceptive units respond only to rough mechanical stimulation with water jets, while mechanoreceptive lateral line units have thresholds to local water displacement below 1 μm and show direction sensitivity.4.The statistical distribution of the resting activity impulse intervals in electroreceptive units has a median between 5 and 25 imp s−1. The value of the median of mechanoreceptive units resting activity is between 5 and 80 imp s−1. Electroreceptive units have a more symmetrical interspike interval distribution (modus — median: ca. 5 imp s−1) than mechanoreceptive units (modus — median: 0–80 imp s−1) under present experimental conditions.5.Electroreceptive units reduce their resting activity after application of 200 μl aliquots of 10 mmol/l MgCl2 solution to the receptor sites. However, in mechanoreceptive lateral line units, the same stimulus elicits either a weak increase in activity or no reaction at all.6.The electroreceptive units were tested with sinusoidal electric field stimuli from 0.05 to 100 Hz. The gain curve has its maximum around 10 Hz. At the low frequency end the slope of the curve is 2.7 dB/oct. Above 20 Hz the gain decreases with a slope of 3–4 dB/oct. The mechanoreceptive lateral line units are most sensitive to local sinusoidal water displacements of 20–50 Hz. The gain curve increases with a slope of 12 dB/oct.

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.

Common efferents to lateral line and labyrinthine hair cells in aquatic vertebrates

Abstract The axonal arborization of lateral line efferent neurones of fishes and urodeles is demonstrated using retrogradely transported horseradish peroxidase. Axon collaterals can be traced into the lateral line nerve and the sensory epithelia of the labyrinth. In fishes efferent somata and axon collaterals are restricted to the ipsilateral side, but they are bilaterally distributed in urodeles. Because of the widespread axonal branching the efferents are considered to have a more general effect, rather than to influence single maculae selectively.

Representation of lateral line and electrosensory systems in the midbrain of the axolotl, Ambystoma mexicanum

SummaryThe study focussed on the representation of the electrosensory and lateral line units in the midbrain of the axolotl Ambystoma mexicanum. In addition, the responses to photic and acoustic/vibrational stimuli were determined. Unit properties were characterized with respect to baseline activity, sensitivity, latency, directional specificity and number of input modalities. The anatomical arrangement of the units was determined using stereotactic and histological measurements of the electrode positions.Of 106 units recorded, 29 units were unimodal, 77 units responded to more than one modality. Most units discharged only in response to stimuli. Thresholds of electrosensory units were about 100 μV/cm field strength; lateral line units had thresholds below 5 μm pp amplitude. The shortest latencies (8–17 ms) were found for responses to visual stimuli. Lateral line and vestibular units responded after 35–58 ms, electroreceptive units after 79–150 ms. All electrosensory and about 50% of the lateral line units were sharply tuned to definite stimulus directions.Electrosensory and lateral line units formed topographical maps in the tectum. The map in each tectal hemisphere contained information about the contralateral surroundings. The electrosensory, lateral line and visual representations were only partly in register; especially in the caudal areas of the midbrain the alignment was poor.

The Terminal Nerve and Its Development in the Teleost Fishes

The name “nervus terminalis” ( N T ) ’ was given at the turn of the century to a cranial nerve first identified in sharks by Fritsch’ and in lungfish by Pinkus.’ Since then, this “supernumerary” cranial nerve has been found in nearly all vertebrate classes.” In recent years several studies demonstrated that N T neurons in different species or even in the same species are of heterogeneous morphology and arrangement.8.9 The course and the targets of their peripheral and central processes and their neuropeptide content also show considerable differences.6.’.1° In summary, the published anatomical data indicated that the N T system is more complex than a typical cranial nerve. In cartilagenous fish, lungfish and some reptiles the N T can be easily identified on the basis of its extracerebral fiber tract which is completely separated from the olfactory nerve. In teleosts as in higher vertebrates, the most rostral N T fibers are closely associated with the fila olfactoria and the central parts of the olfactory system proper.”-” The heterogeneity of the N T in different teleostean species and the proximity to the olfactory system proper sometimes makes it difficult to distinguish the central projections of the two systems with classical histologic methods. In the past the presence of projections to areas rostral to the olfactory bulb and the termination of fibers caudal to the olfactory bulb were used as criteria for identifying a neuron as belonging to the NT. But, since phylogenetic development of the NT may be accompanied by variation in these characters, a clear distinction between NT and secondary olfactory neurons is almost impossible in many cases. More recently, fiber tracing techniques have revealed additional characters of NT neurons. These include the projection of teleostean NT neurons to the retina”” and to hypothalamic and mesencephalic centers.” Furthermore, the presence of gonadotropin hormone-releasing hormone (GnRH) and other neuropeptide-like s u b ~ t a n c e s ~ ~ ’ ~ ~ ’ ’ ~ ’ ~ in NT was found. In the present study the reactivity of NT neurons to GnRH antibodies was used to reinvestigate the distribution of cell bodies and fibers making up the teleostean NT. The data provide a basis to discuss the development of the NT during the phylogeny of teleostean fishes.

Projection of lateral line afferents in a teleost's brain.

After injection of horseradish peroxidase solution into the lateral line nerves of a poeciliid fish the afferent fibres can be followed up to their termination fields in the medulla, lobus vestibulolateralis, corpus cerebelli and valvula cerebelli. Labelling of all fibres innervating individual neuromasts reveals a well-ordered branching pattern of afferents in the CNS and a projection to all termination areas.

Horseradish Peroxidase Study of Tectal Afferents in Xenopus laevis with Special Emphasis on Their Relationship to the Lateral-Line System

Afferent projections to the tectum opticum of the clawed toad Xenopus laevis were studied by injections of horseradish peroxidase (HRP) into the tectum. Cells were labelled in the following nuclei, listed from rostral to caudal: nucleus entopeduncularis anterior, nucleus anterior thalami, nucleus posterior thalami, nucleus ventromedialis thalami, nucleus ventrolateralis thalami pars dorsalis, nucleus lateralis thalami pars posterodorsalis, nucleus neuropilis postthalamici, nucleus lentiformis mesencephali, nucleus praetectalis, nucleus laminaris tori semicircularis, nucleus principalis tori semicircularis, nucleus magnocellularis tori semicircularis, nucleus profundus mesencephali, nucleus anterodorsalis tegmenti, nucleus posterodorsalis tegmenti, nucleus posteroventralis tegmenti, nucleus isthmi, nucleus lineae lateralis pars rostralis, nucleus lineae lateralis pars caudalis, nucleus intermedius, nucleus lateralis nervi octavi, nucleus descendens nervi trigemini, nucleus reticularis superior, nucleus reticularis medius, nucleus reticularis inferior, nucleus reticularis lateralis, nucleus cuneatus and area dorsalis medullae spinalis. Four of these nuclei can be associated with lateral-line processing: the nuclei lineae lateralis rostralis and caudalis of the medulla and the centrolateral nuclei magnocellularis and principalis of the torus semicircularis. The toric input is particularly prominent; it is topologically organized in that central parts of the torus project to the medial tectum, and lateral parts of the torus project to the rostrolateral tectum. For comparison, the torotectal connection was also examined in several anuran species that lose their lateral line at metamorphosis. In these animals, this projection is less well developed than in Xenopus. Therefore, it is argued that the torotectal connection primarily conveys lateral-line information.

Electrophysiological evidence of electroreception in the axoloyl Siredon mexicanum

Abstract Single unit recordings from a branch of the anterior lateral line nerve of the axolotl Siredon mexicanum , reveal the existence of two types of afferents. One type reacts to electric field square pulses below 100 μV/cm and is insensitive to weak mechanical stimuli. The other type is very sensitive to water displacements and can only be excited by electric square pulses above 3 mV/cm. We consider the fiber population with low electric thresholds to originate from electrosensitive receptors and the second population to represent fibers from ordinary mechanosensitive lateral line organs.