ISN Newsletter - July 1997

Newsletter - July 1997

Section 2

Material for Future Newsletters
The Danish Centre for Sound Communication
Comparative Sensory Physiology and Neurobiology at the University of Bonn, Poppelsdorfer Schloss
Neuroethological Viewpoints - Is There a Role for Comparative Genetics in Neuroethology?

MATERIAL FOR FUTURE NEWSLETTERS

Send news, job advertisements, meeting announcements, and other related information for the next Newsletter (to be published in November) to Arthur Popper at: popper@zool.umd.edu. All material should be sent via E-mail.

THE DANISH CENTRE FOR SOUND COMMUNICATION

The Centre for Sound Communication, CSC, is an inter-institutional research group funded by the Danish National Research Foundation for the period 1994-1998. It is located at Odense University (OU), Denmark, but research is also performed at the universities in Aarhus (AU) and Copenhagen (CU). CSC uses several animal species in the study of a wide spectrum of problems concerned with sound communication (generation, emission, propagation, reception, processing, and perception of sound signals). An important part of CSC's contribution to international research is the introduction of new methods and research at the borderline between behavioral physiology, physics, and signal analysis. All research projects involve intensive international co-operation with leading research groups in Europe and North America (e.g. Würzburg, Hawaii, Maryland, and Cologne). In 1996 CSC gave an international graduate course on methods in acoustic communication which we plan to repeat in 1998.

Dr. Axel Michelsen (OU) is the director of CSC and heads the INSECT GROUP (like the other groups, it includes graduate students and postdocs). Laboratory and field research focuses on problems concerned with sound communication in insects. Current studies are concerned with, e.g., the biophysics of directional hearing in natural habitats and an investigation of how honeybees perceive communication dances in the darkness of the hive. In the latter case, follower bees may detect strong, local air currents produced by the dancing bee and we are trying to measure and model the air currents and to find the functional sense organs. In the BIOSONAR GROUP Drs. Lee A. Miller (OU), Bertel Mhl (AU), and Annemarie Surlykke (OU) study numerous aspects of the echolocation systems of bats and toothed whales, plus the audition and avoidance reactions of prey animals (fishes and moths). An exciting new development is the establishment of the harbor porpoise facility at the "Fjord- og Baeltcenter" in Kerteminde 20 km from Odense and the procurement of a vessel to facilitate studies of whale biosonar both in captivity and in the field.

In the BIRD GROUP Drs. Torben Dabelsteen (CU) and Ole Naesbye Larsen (OU) study biotope constraints on songbird communication. The structure of songbird communication networks and the signal value of interactions between their members are investigated with acoustic location systems and computer aided interactive playback techniques. In the laboratory we focus on visualizing the biomechanics of the avian syrinx with endoscopic techniques and investigating middle ear mechanics in relation to directional hearing.

In the FROG GROUP Drs. Jakob Christensen- Dalsgaard (OU) and Morten Buhl Jrgensen (OU) study the neural processing of directional information in frogs both in the auditory nerve and at higher auditory centers and supplement the studies with behavioral and biophysical investigations. We also investigate frog vibratory sensitivity at neural and behavioral levels.

Development of new methods heavily depends on skilled and continuous TECHNICAL SUPPORT. CSC benefits enormously from the ingenuity of competent workshops (electronics and mechanical) headed by Mr. Bent Bach Andersen (OU) and from the equally competent advice on signal analysis and creative software development by Mr. Simon Boel Pedersen (DSP-Consultant). For further information see: http://www.ou.dk./Nat/biology/neuro/csc-eng.html.

Ole Naesbye Larsen

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COMPARATIVE SENSORY PHYSIOLOGY AND NEUROBIOLOGY AT THE UNIVERSITY OF BONN, POPPELSDORFER SCHLOSS

The Zoological Institute of the Univ. of Bonn is situated in the middle of the Botanical garden in an old castle called Poppelsdorfer Schloss. Our research focuses on the biological significance and the physiology of sensory systems. The experimental approaches we are using includes electrophysiology, neuroanatomy, and behavioral physiology. The members of my group and their research interests are briefly described:

The research of Joachim Mogdans (E-mail: unb305@uni-bonn.de) is directed towards an understanding of the behavioral capabilities and the neurobiology of the mechanosensory lateral line of fishes. At the behavioral level, Joachim studies the ability of fish to analyze amplitude and frequency modulated dipole stimuli as well as complex water movements such as those generated by an object moving in the water. At the physiological level he records neural responses from primary afferents as well as from medullary, midbrain, and forebrain lateral line areas.

Gerhard von der Emde (unb308@uni-bonn.de) works on sensory processing and neuronal computation in weakly electric fish. He investigates the sensory capabilities of mormyrid and gymnotid fish during active electrolocation. One of Gerhard’s goals is to uncover the neuronal processes which enable weakly electric fish to detect, identify and localize animate and inanimate objects with aid of the electric sense. Gerhard also studies the 'novelty response' in weakly electric fish, i.e. an unspecific orienting response which only occurs if the fish is confronted with a new stimulus of any modality. Because of it's nature, the novelty response can serve as a model system for the study of arousal, sensory memory and attention.

Guido Dehnhard (guido.dehnhardt@muenster.de) specializes in animal psychophysics and cognition with his main emphasis on functional aspects of the vibrissal system of pinnipeds and other aquatic mammals. Studies in this field of research contribute to a new concept of underwater foraging and orientation in this animal group. In addition, Guido studies audition in small cetaceans and chemoreception in pinnipeds. Comparative studies on animal cognition concentrate on mental representations. Based on the concept of mental rotation the question is addressed to which degree animals possess image-like representations of visual information.

Michael Hofmann (unb316@uni-bonn.de) investigates eye movements and their neuronal control in fishes. One important function of eye movements is to stabilize the image on the retina during locomotion. In many fishes, this seems to be the most important, if not sole function of the oculomotor system. Michael’s primary interest is on spontaneous eye movements which occur to a variable degree in many fish species, although their functional significance is not known. Key questions are: Why do some fish move their eyes spontaneously and how does the brain control these movements?

Helmut Schmitz (hschmitz.zoology@t-online.de) is the first to provide physiological evidence that some insects have infrared receptors. Helmut is especially interested in uncovering the mechanism which enables the buprestid beetle Melanophila acuminata to detect and localize forest fires. In addition Helmut has started to study thermoreception (infrared-reception) in blood-sucking insects like Chaggas bugs and Tsetse-flies.

Horst Bleckmann (Bleckmann@uni-bonn.de)

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NEUROETHOLOGICAL VIEWPOINTS

With this issue of the Newsletter we introduce Neuroethological Viewpoints. These articles, as in the following piece by David King, provide thoughtful ideas on a particular issue that should be of interest to a large number of neuroethologists. See the article about changes in the Newsletter for submission information.

IS THERE A ROLE FOR COMPARATIVE GENETICS IN NEUROETHOLOGY?

Flies comprise a wonderfully diverse group for neuroethology, exhibiting some extraordinary behavioral differences. Some years ago I began a survey of axonal size distributions in the cervical connectives of various fly species. On the basis of previous experience, I expected to find identifiable individual neurons with similar characteristics in related species. But I was astonished by the wide variation in axonal diameter that appeared in different flies. (Details remain unpublished, although they have been presented at several meetings; e.g., King 1988.) These observations suggested, perhaps unsurprisingly, that evolution had exerted exquisite control over the shape of many individually identifiable neurons. John Edwards once quipped that my slides of flies' necks displayed coded "ideograms" of each species' behavior, with the sizes of various axons representing the adaptive importance of particular pathways.

Neuronal function depends on numerous anatomical and physiological parameters, including axon diameter. Since a limited genome could not possibly permit so many variables to be "concatenated without limitations" (Bullock 1976), I began to wonder whether any simplifying generalizations might arise from an evolutionary perspective.

Perhaps some general rules govern the translation of genetic mutations into changes in neuronal organization. How could gradual evolution, based on specific mutations within a limited set of genes and preceding in small steps from an ancestral state, yield such diverse adaptive design at the level of individually identifiable neurons?

If only genes had "tuning knobs" for manipulating the parameters most critical for neuronal function! Finding those knobs could then tell us what neuronal features were adaptively important. The idea of a tuning knob offers a familiar metaphor for a modular mechanism that enables graded and reversible adjustment of a parameter. A small set of tuning knobs can permit a gradual approach toward any one of a vast array of possible configurations, just as a few knobs on a microscope can be used to frame and focus images of any region, large or small, anywhere on a specimen.

At the time, I had never heard of adjustable genes. Nevertheless, consideration of how useful adjustable neuronal parameters could be led me to imagine a way to make tuning knobs from repetitive DNA. Repetitive DNA experiences frequent, small and reversible alterations in repeat number. If the number of repeats could somehow affect the regulation of some genetic trait, then spontaneous mutations could "twiddle the knob", providing genetic variation for efficient evolutionary transformation from one parameter state to another. For several years this scenario seemed wildly speculative. There was scant evidence (none of it known to me) that repetitive DNA did anything at all, let alone regulate genetic traits as a function of repeat number.

Then came the discovery that several human neurological disorders are caused by excessive expansion of repeated CAG triplets, a phenomenon which was widely reported as "unexpected" and "puzzling". Remarkably, disease severity and latency to onset are linked to the number of repeats. I couldn't overlook the parallel between these mutation-prone, disease-causing genes and my hypothetical "tuning knobs". I proposed (King 1994) that such odd DNA sequences might function normally as quantitative gene regulators with an advantageous evolutionary role. By now there is clear evidence that CAG triplets, as well as microsatellite sequences with other motifs, do indeed occur within many normal regulatory genes where they can influence gene transcription activity. Such repetitive sequences appear to equip the genome with adjustable "tuning knobs" that can facilitate evolution (King et al. 1997).

Following separate paths, both comparative neurobiology and clinical neurology have led to a novel mechanism that permits small, reversible mutations in regulatory genes. I would invite ISN colleagues to consider the following hypothesis. Regulatory genes that contain microsatellite sequences may help implement evolutionary flexibility. When expressed in nervous tissue, such loci may indicate genetically variable parameters that have neuroethological significance. Conversely, behavioral differences among related species may point to the existence of adjustable genes for regulating relevant parameters of neural organization. Excessive expansion of certain triplet repeats may cause neurological disease, but normal variation at the same loci may have been an important source of variability during the evolution of the human nervous system.

References

King DG 1988 On the evolution of specialized neuronal form: Phylogenetic variation in cervical giant axons of flies (Diptera). Proc. XVIII Int. Congress of Entomology, p. 70.

Bullock TH 1976 In search of principles in neural integration. In: Simpler Networks and Behavior, John C. Fentress, editor. Sinauer Associates, Inc., Sunderland, Massachusetts.

King DG 1994 Triplet repeat DNA as a highly mutable regulatory mechanism. Science 263:595-596. King DG, Soller M, and Kashi Y 1997 Evolutionary Tuning Knobs. Endeavor 21:36-40. David G. King, E-mail: dgking@siu.edu