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H Luksch

Publications and source records attributed to H Luksch.

11 recordsLinked to original sources
PubMed2000

Bottlebrush dendritic endings and large dendritic fields: motion-detecting neurons in the mammalian tectum.

The widefield vertical neurons of the lower stratum griseum superficiale (SGS3) and upper stratum opticum (SO) of the superior colliculus provide an extrageniculate route for visual information to reach the pulvinar. Previous physiological studies indicate that SGS3/SO neurons have large receptive fields and respond to small moving stimuli. We sought to better characterize the dendritic morphology of SGS3/SO neurons with intracellular filling in slice preparations of the ground squirrel superior colliculus. We found that dendrites of widefield vertical cells end in monostratified arrays of spiny terminal specializations called "bottlebrush" dendritic endings. Two major subtypes of neurons are described. Type I neurons have somata restricted to the SGS3 and bottlebrush endings in the most superficial sublayer of the SGS. Type II neurons are found at the base of the SGS and in the upper SO, and have bottlebrush endings arrayed within the middle sublayers of the SGS. Bottlebrush endings may sample and integrate laminated afferents to the superior colliculus, and cellular subtypes may underlie multiple information streams within the tectopulvinar pathway. A similar dendritic morphology and projection pattern can be found in cells of the avian optic tectum that project upon the nucleus rotundus, a thalamic nucleus homologous to the mammalian caudal/inferior pulvinar. Because motion processing is a dominant feature of the avian tectorotundal pathway, the current results suggest that both dendritic morphology and motion processing are conserved features of widefield vertical cells in the tectopulvinar pathway of vertebrates.

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PubMed2000

A candidate pathway for a visual instructional signal to the barn owl's auditory system.

Many organisms use multimodal maps to generate coherent neuronal representations that allow adequate responses to stimuli that excite several sensory modalities. During ontogeny of these maps, one modality typically acts as the dominant system the other modalities are aligned to. A well studied model for the alignment of sensory maps is the calibration of the auditory space map by the visual system in the optic tectum of the barn owl. However, a projection from the optic tectum to the site of plasticity in the auditory pathway that could deliver an instructive signal has not been found so far. We have analyzed the development of the connectivity between the bimodal (visual and auditory) map of space in the barn owl's optic tectum and the auditory space map in the inferior colliculus with tracing methods and intracellular fills. Neurons in the tectal stratum griseum centrale were found to be suited to deliver an alignment signal from the visual midbrain to the auditory pathway. These neurons are presumably part of the efferent tectal projection pathway that mediates head saccades. The implications of a sensory alignment signal possibly being delivered by a (pre)motor command pathway are discussed.

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PubMed2000

Chemoarchitecture of the anuran auditory midbrain.

The anuran torus semicircularis consists of several subnuclei that are part of the ascending auditory pathway as well as audiomotor interface structures. Additionally, recent anatomical studies suggest that the midbrain tegmentum is an integral part of the audiomotor network. To describe the chemoarchitecture of these nuclei, taking into account the toral subdivisions, we investigated the distribution of serotonin, leucine-enkephalin, substance P, tyrosine-hydroxylase, dopamine D2-receptor, parvalbumin, aspartate, GABA, and estrogen-binding protein-immunoreactivity in the midbrain of Bombina orientalis, Discoglossus pictus and Xenopus laevis. In the torus semicircularis, the highest density of immunoreactive fibers and terminals for all transmitters was found in the laminar nucleus. Parvalbumin-like immunoreactivity was highest in the principal nucleus, and D2-receptor-like immunoreactivity was uniformly distributed throughout the torus. In the tegmentum, axons and/or dendrites were stained with all antibodies except estrogen-binding protein. Additionally, heavily stained enkephalin and substance P-immunopositive fiber plexus were found in the lateral and dorsal tegmentum. The immunostainings revealed no qualitative differences between the three species. Immunopositive cell bodies were labeled in several brain areas, the connectivity of which with torus and tegmentum is discussed on the background of functional questions. The putative neuromodulatory innervation of both the laminar nucleus of the torus semicircularis and the tegmentum may be the anatomical basis for the influence of the animal's endogenous state on the behavioral reaction to sensory stimuli. These data corroborate earlier anatomical and physiological findings that the neurons of these nuclei are key elements in the audio-motor interface.

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PubMed1998

Bottlebrush dendritic endings and large dendritic fields: motion-detecting neurons in the tectofugal pathway.

In avian and mammalian brains, visual information from the retina is conveyed to the telencephalon via two separate pathways: the thalamofugal and the tectofugal pathways. Recently, Karten et al. ([1997] J. Comp. Neurol. 387:449-465) examined a portion of the tectofugal pathway, the projection from the optic tectum to the nucleus rotundus thalami, in pigeons. They defined two distinct subpopulations of tectal neurons projecting from the stratum griseum centrale (SGC; tectal layer 13) to specific divisions of the rotundus. The goal of this study in chick was to verify the existence of the type I and type II SGC neurons, as defined by Karten et al., and then examine in greater detail the connectivity and morphology of these SGC neurons. Furthermore, our results suggest how the unique morphological characteristics of SGC neurons contribute to the large receptive fields (20-50 degrees) found in physiological recordings and the SGC neuronal response to extremely small (ca. 0.05 degree), fast-moving (100 degrees/second) stimuli. By injecting retrograde tracer into various divisions of the chick rotundus, we verified that, indeed, the chick did possess type I and type II SGC neurons, as well as a "new" type of SGC neuron, type III, that is not found in the pigeon. We then used intracellular cell-filling techniques to define further these three types of SGC neurons. Our examination revealed the following: Type I SGC neurons had large, circular dendritic fields (average diameter, 1,725 microns) composed of smooth dendrites and ending in spine-rich, bottlebrush endings located in retinorecipient tectal layer 5b; type II SGC neurons had elliptical dendritic fields (average 1,447 microns) and dendritic endings located never more superficially than tectal layer 8; and type III SGC neurons had large dendritic fields (average 1,800 microns) of unknown shape and bottlebrush dendritic endings located in retinorecipient tectal layer 4. We suggest that the neuronal features of the SGC neurons (i.e., bottlebrush dendritic endings and large dendritic fields) are key morphological characteristics for the detection of motion within the tectofugal pathway. Furthermore, because neurons with similar morphology have also been found in the tecta of both mammals and reptiles, we suggest that these neuronal features are fundamental components of a phylogenetically conserved system used for the "extrastriate" detection of motion in vertebrates.

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PubMed1998

Connectivity of the salamander pretectum: an in-vitro (whole-brain) intracellular tracing study.

The amphibian optic tectum and pretectum have been analyzed in detail anatomically and physiologically, and a specific model for tecto-pretectal interaction in the context of the visual guidance of behavior has been proposed. However, anatomical evidence for this model, particularly the precise pattern of pretectotectal connectivity, is lacking. Therefore, we stained pretectal neurons intracellularly in an in-vitro preparation of the salamanders Plethodon jordani and Hydromantes genei. Our results demonstrate that the projections of neurons of the nucleus praetectalis profundus are divergent and widespread. Individual neurons may project divergently to telencephalic (ipsilateral amygdala and striatum), diencephalic (ipsi-and contralateral thalamus, contralateral pretectum), and mesencephalic (ipsi- and contralateral tectum and tegmentum) centers, and to the ipsi- and contralateral medulla oblongata and rostral spinal cord. The projection of pretectal cells to the optic tectum is bilateral; axonal structures do not show discernible patterns and are present in all layers of the superficial white matter. A classification of pretectal neurons on the basis of axonal termination pattern or dendritic arborization has not been possible. Our results do not support the hypothesis that a distinct class of pretectal neurons projects to a particular subset of tectal cells. Rather, the pretectum appears to influence the tectum indirectly, acting either on retinal afferents or modulating inhibitory interneurons.

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PubMed1998

Morphology and axonal projection patterns of auditory neurons in the midbrain of the painted frog, Discoglossus pictus.

Acoustic signals are extensively used for guiding various behaviors in frogs such as vocalization and phonotaxis. While numerous studies have investigated the anatomy and physiology of the auditory system, our knowledge of intrinsic properties and connectivity of individual auditory neurons remains poor. Moreover, the neural basis of audiomotor integration still has to be elucidated. We determined basic response patterns, dendritic arborization and axonal projection patterns of auditory midbrain units with intracellular recording and staining techniques in an isolated brain preparation. The subnuclei of the torus semicircularis subserve different tasks. The principal nucleus, the main target of the ascending auditory input, has mostly intrinsic neurons, i.e., their dendrites and axons are restricted to the torus itself. In contrast, neurons of the magnocellular and the laminar nucleus project to various auditory and non-auditory processing centers. The projection targets include thalamus, tegmentum, periaqueductal gray, medulla oblongata, and in the case of laminar neurons--the spinal cord. Additionally, tegmental cells receive direct auditory input and project to various targets, including the spinal cord. Our data imply that both auditory and premotor functions are implemented in individual toral and tegmental neurons. Their axons constitute parallel descending pathways to several effector systems and might be part of the neural substrate for differential audiomotor integration.

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PubMed1996

Pretecto-tectal interactions: effects of lesioning and stimulating the pretectum on field potentials in the optic tectum of salamanders in vitro.

Interactions between pretectum and optic tectum of salamanders were analyzed by recording evoked potentials (EPs) in the optic tectum in vitro in response to stimulation of the contralateral optic nerve. Neither lesioning of the pretectum nor ablation of the medulla oblongata including the nucleus isthmi altered the shape of tectal EPs, suggesting that the tectal EP in this preparation reflects activation of tectal circuitry by retinal afferents without a major contribution from non-retinal afferents. To analyze the effect of stimulation of the pretectum on the tectal EP, we stimulated the pretectal area pharmacologically. Amplitudes of tectal EPs decreased rapidly after stimulation of the pretectum and recovered within minutes (glutamate) or hours (kainic acid). The pretectal influence on the tectal EP might act presynaptically on retinal afferents or by modulating the response of inhibitory interneurons.

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PubMed1996

The use of in vitro preparations of the isolated amphibian central nervous system in neuroanatomy and electrophysiology.

In the present study an isolated preparation of the complete anuran central nervous system (CNS) is described which can be kept alive for several days and allows tracing, immunohistochemical and electrophysiological studies. A simple perfusion chamber is being used in which the isolated CNS preparation is superfused with oxygenated Ringer. The use of an isolated CNS has many advantages including: (1) virtually all areas are easily accessible at the same time without having the problem of blood vessels that hinder access; (2) large lesions and massive tracer applications are possible without survival problems of the animal, and tracers will not be translocated by blood circulation; (3) since pulsations caused by the pressure changes of blood circulation do not occur, intracellular recordings are comparatively easy and stable; and (4) this approach offers the possibility of working on the same brain for several days by storing the preparation in a refrigerator overnight at low temperatures, thus allowing extensive utilization of a single preparation and reduction in the number of experimental animals required. Some applications to the anuran auditory system illustrate that the isolated anuran CNS is well-suited for a variety of neuroanatomical and physiological techniques.

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PubMed1994

Audio-motor interface in anurans.

Like males of many anuran species, fire-bellied toads (Bombina orientalis) call antiphonally, which demonstrates an auditory input into the call-generating network. Males produce their calls by an inspiratory airstream, which is generated exclusively by contraction of the muscles of the buccal cavity. The painted frog (Discoglossus pictus) possesses a combined inspiratory and expiratory call mechanism, and also uses only buccal muscles. These muscles are controlled by branchial motoneurons, which receive vocal premotor input mainly from the pretrigeminal nucleus. The interconnections between the auditory pathway and the vocal pathway were examined by neuroanatomical tracing and intracellular recording. Mesencephalic auditory nuclei, laminar and magnocellular nucleus of the torus semicircularis, and tegmental nuclei constitute strong descending efferents, which, in turn, form collaterals that terminate in vocal premotor nuclei. These findings imply fast audio-vocal interfacing, which is a prerequisite for the control of antiphonal calling.

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PubMedDate not supplied

Active sensing--closing multiple loops.

In this contribution, it is argued that the prevailing view of the sensory system as an intricate, but passive processor of external information does not capture the full complexity of brain performance. Instead, we try to reinforce a notion that sees the brain as a system embedded within the environment and actively exploring it. We will attempt to emphasize the bidirectional interaction between brain and environment at all levels of processing and at different scales of the system description. This modified approach to the understanding of the brain has profound consequences for experimental investigations, starting with the experimental design and extending into data analysis and interpretation.

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