Kontakt

Johann H. Bollmann
Telefon: +49 6221 486-282
Fax: +49 6221 486-325

Publikationen

1.
Preuss, S. J.; Trivedi, C.; vom Berg-Maurer, C.; Ryu, S.; Bollmann, J. H.: Classification of object size in retinotectal microcircuits. Current Biology 24 (20), S. 2376 - 2385 (2014)
2.
Trivedi, C.; Bollmann, J. H.: Visually driven chaining of elementary swim patterns into a goal-directed motor sequence: a virtual reality study of zebrafish prey capture. Frontiers in Neural Circuits 7, 2013.00086, S. 1 - 18 (2013)
3.
Jens Peter Gabriel, Chintan Trivedi, Colette Maurer, Soojin Ryu, and Johann H. Bollmann, "Layer-specific targeting of direction-selective neurons in the zebrafish optic tectum," Neuron 76 (6), 1147-1160 (2012).

Gruppe Johann Bollmann

Johann Bollmann Group -Neural Circuits and Behavior

+++++ Please note: The Bollmann group has moved to Freiburg.
Heisenberg Research Group "Neural Circuits and Behavior"
University of Freiburg, Faculty of Biology, Institute for Biology I, Hauptstr. 1, 79104 Freiburg

For contact: johann.bollmann@bio.uni-freiburg.de+++++

<p><strong>Fig. 1: Imaging structure and function in the zebrafish visual system</strong><br />(A) Eye and retino-tectal projection in a 3-day-old zebrafish (labeled with antibody against ath5-GFP). (B) Larval zebrafish retina, double-labeled with DiO (green, temporal retina) and DiI (red, nasal retina). (C) GFP expression in optic tectum in 6-day-old zebrafish (anterior is towards bottom). (D) Magnified view shows fine structure of tectal lamination (same preparation as in C).</p> Bild vergrößern

Fig. 1: Imaging structure and function in the zebrafish visual system
(A) Eye and retino-tectal projection in a 3-day-old zebrafish (labeled with antibody against ath5-GFP). (B) Larval zebrafish retina, double-labeled with DiO (green, temporal retina) and DiI (red, nasal retina). (C) GFP expression in optic tectum in 6-day-old zebrafish (anterior is towards bottom). (D) Magnified view shows fine structure of tectal lamination (same preparation as in C).

[weniger]

Despite the dynamic nature of early neuronal connections in a developing network, the early nervous system is capable of processing complex sensory stimuli, which controls behaviors critical for the survival of the organism. While neural circuits form, sensory inputs have a defining influence on neuronal structure and the formation of appropriate connections between neurons. Our research aims at understanding the functional role of visually responsive neurons in the developing brain, and the molecular and cellular mechanisms that guide a neuron towards assuming its functional role. The visual system of zebrafish larvae offers unique experimental avenues to address these questions because the structure and function of individual neurons and small networks can be imaged in the intact animal, and molecular and genetic tools are available to observe and interfere with neuronal function in the intact nervous system.

Methods comprise custom-built, functional multi-photon imaging and in vivo electrophysiology at the sub-cellular, cellular and population scale. Functional studies are aided by the availability of genetic reporters of neuronal class, structure and function in the zebrafish. Thus, functional imaging of cellular activity in combination with the unsurpassed resolution of patch-clamp electrophysiology in genetically defined sets of neurons is used to elucidate the maturation and function of neural circuits in the zebrafish central nervous system. Another focus is on the analysis of the central nervous system at the connec­tomic level, using se­rial block-face electron microscopy.

Virtual prey capture sequences in a closed-loop visual environment

<p><strong>Fig. 2: Virtual prey capture assay</strong></p>
<p>(A) Single frames of a prey capture sequence. (B) Measurement of eye and tail movements. (C) Kinematic analysis of orienting swims (left) and forward swims (right). (D) Time course of fish orientation and tail movements during a prey capture sequence. (E) Virtual prey capture behavior: larva partially embedded in center of arena. Stimulus location and direction indicated by curved arrows. (F) The virtual prey as seen by the larva.</p> Bild vergrößern

Fig. 2: Virtual prey capture assay

(A) Single frames of a prey capture sequence. (B) Measurement of eye and tail movements. (C) Kinematic analysis of orienting swims (left) and forward swims (right). (D) Time course of fish orientation and tail movements during a prey capture sequence. (E) Virtual prey capture behavior: larva partially embedded in center of arena. Stimulus location and direction indicated by curved arrows. (F) The virtual prey as seen by the larva.

[weniger]

Larval zebrafish perform rapid prey capture sequences, in which discrete swim bouts are chained into a sequence, predominantly controlled by the visual system. To better understand the relation between vision and action during this important behavior, we set out to obtain a detailed picture of what the fish sees when freely swimming and hunting small ciliates, its natural prey. From high-speed recordings of freely swimming larvae, body kinematics are automatically parameterized and spectrally analyzed. This way we observed that prey capture sequences are composed of versions of a basic motor pattern, which are superimposed with a graded turning component that allows the larva to adjust its heading direction on a fine, continuous scale towards the target (Trivedi and Bollmann, 2013).

Furthermore, we developed closed-loop visual stimulation methods, which allow us to elicit multi-step prey capture sequences in larvae embedded in a virtual environment. These methodological advances allow us to test the role of visual feedback during prey capture. For example, we observed that small spatio-temporal shifts in stimulus updates result in significantly longer reaction times. We hypothesize that visual feedback-driven activity interacts with residual activity from previous motor steps, which could lead to accelerated programming of subsequent motor commands. We now combine these methods with two-photon Ca2+ imaging and patch-clamp recordings in order to investigate the spatio-temporal patterns of activity underlying these visually driven motor sequences. 

<p><strong>Fig. 3: Zebrafish larva performing virtual prey capture behavior<br /></strong>The partly embedded larva observes the virtual prey on a small screen. As soon as it swims in a particular direction, a rotation is simulated by shifting the projected visual environment.</p> Bild vergrößern

Fig. 3: Zebrafish larva performing virtual prey capture behavior
The partly embedded larva observes the virtual prey on a small screen. As soon as it swims in a particular direction, a rotation is simulated by shifting the projected visual environment.

[weniger]

Layer-specific processing of stimulus motion in tectal microcircuits

<p><strong>Figure 4: Direction-selective cell types in the optic tectum</strong></p>
<p>(A) Expression of GFP in a specific cell type highlights laminar organization of tectal neuropil. (B) Expression of GCaMP3 in the same cell type. (C) Calcium signals exhibit directional selectivity: the neuron marked in B prefers stimulus motion to anterior. (D) <em>Bottom</em>: Two structurally different neurons (type 1 and type 2, red) exhibit opposite preferred directions. <em>Top</em>: Firing rates in response to different stimulus directions (indicated by arrows) reveal directional preference.</p> Bild vergrößern

Figure 4: Direction-selective cell types in the optic tectum

(A) Expression of GFP in a specific cell type highlights laminar organization of tectal neuropil. (B) Expression of GCaMP3 in the same cell type. (C) Calcium signals exhibit directional selectivity: the neuron marked in B prefers stimulus motion to anterior. (D) Bottom: Two structurally different neurons (type 1 and type 2, red) exhibit opposite preferred directions. Top: Firing rates in response to different stimulus directions (indicated by arrows) reveal directional preference.

[weniger]

Neurons sensitive to the direction of a moving stimulus have been observed at all levels of the visual system, but the underlying mechanisms remain controversial, especially in visual centers beyond the retina. A critical question is whether direction selectivity is coded in retinal ganglion cell activity and relayed to downstream targets, or whether direction selectivity emerges de novo in higher visual circuits from basic, topographically organized input maps. We could address this question for two morphologically distinct cell types in the zebrafish optic tectum (Gabriel et al, 2012). Using the Gal4-UAS-expression system, distinct neuronal cell types in the tectum were labeled with the genetically encoded Ca2+ indicator GCaMP-3. Multi-photon Ca2+ imaging showed that cell types with directional preference for opposing directions were morphologically distinct and exhibited dendritic arborizations in different layers of the tectal neuropil. The dendritic profiles colocalized with presynaptic retinal ganglion cell terminals in sublayers with corresponding directional tuning. Furthermore, multi-photon targeted patch clamp recordings show that these cell-types receive directionally tuned excitatory inputs in the preferred direction and weaker, tuned inhibitory inputs. These findings demonstrate a remarkable correspondence between the functional and structural profile of morphologically distinct cell types, which indicates that the central principle of lamina-specific feature extraction applies not only to the retina but also to higher visual centers.

Classification of object size during visually guided prey capture

<p><strong>Fig. 5: Fast perceptual decision making in the zebrafish visual system.<br /></strong>Small and large objects activate distinct circuits in the visual system of zebrafish larvae. This separation begins in the eye and determines the direction of swimming behavior.</p> Bild vergrößern

Fig. 5: Fast perceptual decision making in the zebrafish visual system.
Small and large objects activate distinct circuits in the visual system of zebrafish larvae. This separation begins in the eye and determines the direction of swimming behavior.

[weniger]

Zebrafish larvae perform orienting swims towards a prey-like target or away from a threatening object depending on the size of a visual stimulus. Using high-speed kinematic analysis of swimming behavior, multi-photon calcium imaging, in vivo electrophysiology and closed-loop visual stimulation methods, we find that object size is classified in the activity of different neural populations throughout the retinotectal system (Preuss et al., 2014). First, we devised visual stimuli that closely mimic salient visual features of a prey-like object. In response to these ethologically relevant stimuli, we observed that object size is encoded in the activity of different retinal ganglion cell types (RGC) projecting to the optic tectum. Then, using multi-photon targeted patch clamp recordings, we find that a class of horizontal cells called superficial interneurons (SINs) exhibit distinct, size-dependent synaptic inputs, depending on the tectal layer in which their dendrites arborize. SINs fall into different response types, with a distinct class of SINs preferentially tuned to small, prey-like stimuli. These SINs arborize in the most superficial neuropil, where RGCs are predominantly tuned to small moving objects. At the next processing stage, tectal cells in the periventricular zone exhibit differential size selectivities, with approximately equal fractions of cells tuned either to small or large moving objects. We conclude that behaviorally relevant size classification begins in the retina, and that parallel, size-selective channels activate distinct, size-processing subnetworks in the tectum. These distinct subnetworks may represent a bifurcation point for behavioral decision making during visually controlled motor behavior.

The wiring diagram of the zebrafish spinal cord

A wiring diagram of the central nervous system (CNS) would represent a valuable structural basis for understanding information processing in this vertebrate model system. In collaboration with W. Denk, we aim to analyze the CNS of the larval zebrafish at the connectomic level, using serial block-face electron microscopy (SBEM). We have acquired a high-contrast SBEM data set comprising several segments of the zebrafish spinal cord, which yields information on how the reticulo-spinal system connects to spinal motor circuits. This allows us to map the synaptic contacts between descending hindbrain neurons, spinal interneurons and different pools of motor neurons in order to address the question whether recruitment patterns of motor neurons may be implemented in specific connectivity rules between these cell types.

References

Preuss, S.J., Trivedi, C.A., vom Berg-Maurer, C.M., Ryu, S, and Bollmann, J.H. (2014). Classification of object size in retinotectal microcircuits. Current Biology 24, 2376-2385.

Trivedi, C. A. and Bollmann, J. H. (2013). Visually driven chaining of elementary swim patterns into a goal-directed motor sequence: a virtual reality study of zebrafish prey capture. Frontiers in Neural Circuits 7 (86): 1-18.

Gabriel, J. P., Trivedi, C. A., Maurer, C. M., Ryu, S., and Bollmann, J. H. (2012). Layer-specific targeting of direction-selective neurons in the zebrafish optic tectum. Neuron 76 (6): 1147-60.

Bollmann, J. H. and Engert. F. (2009). Sub-cellular topography of visually driven dendritic activity in the vertebrate visual system. Neuron. 61 (6): 895-905.

Bollmann, J. H. and Sakmann, B. (2005). Control of synaptic strength and timing by the release-site Ca2+ signal. Nat. Neurosci. 8: 426-434.

 

Links to current press releases:

1.)   http://www.mpg.de/8416636/zebrafish-eye

2.)   http://www.mpg.de/7259556/hunting-behaviour-zebrafish-larvae?filter_order=LT&research_topic=BM-NB

3.)   http://www.bio-pro.de/magazin/index.html?lang=de&artikelid=/artikel/09567/index.html

 
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