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Characterization of genetically targeted neuron types in the zebrafish optic tectum.

Robles E, Smith SJ, Baier H - Front Neural Circuits (2011)

Bottom Line: The second type, a GABAergic non-stratified periventricular interneuron, extends a bushy arbor containing both dendrites and axons into the SGC and the deepest sublayers of the SFGS.Interestingly, the same axons form en passant synapses within the deepest neuropil layer of the tectum, the stratum album centrale.These observations establish a framework for studying the morphological and functional differentiation of neural circuits in the zebrafish visual system.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California San Francisco San Francisco, CA, USA.

ABSTRACT
The optically transparent larval zebrafish is ideally suited for in vivo analyses of neural circuitry controlling visually guided behaviors. However, there is a lack of information regarding specific cell types in the major retinorecipient brain region of the fish, the optic tectum. Here we report the characterization of three previously unidentified tectal cell types that are specifically labeled by dlx5/6 enhancer elements. In vivo laser-scanning microscopy in conjunction with ex vivo array tomography revealed that these neurons differ in their morphologies, synaptic connectivity, and neurotransmitter phenotypes. The first type is an excitatory bistratified periventricular interneuron that forms a dendritic arbor in the retinorecipient stratum fibrosum et griseum superficiale (SFGS) and an axonal arbor in the stratum griseum centrale (SGC). The second type, a GABAergic non-stratified periventricular interneuron, extends a bushy arbor containing both dendrites and axons into the SGC and the deepest sublayers of the SFGS. The third type is a GABAergic periventricular projection neuron that extends a dendritic arbor into the SGC and a long axon to the torus semicircularis, medulla oblongata, and anterior hindbrain. Interestingly, the same axons form en passant synapses within the deepest neuropil layer of the tectum, the stratum album centrale. This approach revealed several novel aspects of tectal circuitry, including: (1) a glutamatergic mode of transmission from the superficial, retinorecipient neuropil layers to the deeper, output layers, (2) the presence of interneurons with mixed dendrite/axon arbors likely involved in local processing, and (3) a heretofore unknown GABAergic tectofugal projection to midbrain and hindbrain. These observations establish a framework for studying the morphological and functional differentiation of neural circuits in the zebrafish visual system.

No MeSH data available.


Related in: MedlinePlus

The non-stratified periventricular interneuron cell type. (A) Dorsal view of a two-photon image volume containing a single labeled nsPVIN imaged at 5 dpf. Note the long apical neurite extended into the neuropil. (B) Forty-five degree rotation of image volume in (A). Note the absence of any stratification within the arbor. (C) Merged confocal image volume of a single 4 dpf nsPVIN expressing both dsRed (red) and Syp–GFP (green). Arrow depicts orientation of neuropil layers from superficial (S) to deep (D). (D) 2.5× magnification of boxed region in (C). Note the bright Syp–GFP puncta contained within a subset of neurite branches (arrows). (E) Schematic depiction of nsPVIN cell body distribution throughout the SPV layer. Cell traced in black corresponds to neuron in (A) and (B). Note the deep SPV location of cell body. (F) Manual tracing of the neurite arbor in (D). Green lines indicate branches containing Syp–GFP puncta, whereas branches devoid of Syp–GFP labeling are in red. Scale bar, 20 μm in (A–C), 8 μm in (D,F).
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Figure 7: The non-stratified periventricular interneuron cell type. (A) Dorsal view of a two-photon image volume containing a single labeled nsPVIN imaged at 5 dpf. Note the long apical neurite extended into the neuropil. (B) Forty-five degree rotation of image volume in (A). Note the absence of any stratification within the arbor. (C) Merged confocal image volume of a single 4 dpf nsPVIN expressing both dsRed (red) and Syp–GFP (green). Arrow depicts orientation of neuropil layers from superficial (S) to deep (D). (D) 2.5× magnification of boxed region in (C). Note the bright Syp–GFP puncta contained within a subset of neurite branches (arrows). (E) Schematic depiction of nsPVIN cell body distribution throughout the SPV layer. Cell traced in black corresponds to neuron in (A) and (B). Note the deep SPV location of cell body. (F) Manual tracing of the neurite arbor in (D). Green lines indicate branches containing Syp–GFP puncta, whereas branches devoid of Syp–GFP labeling are in red. Scale bar, 20 μm in (A–C), 8 μm in (D,F).

Mentions: Of the 92 cells labeled by the dg4ii plasmid 13 were non-stratified periventricular interneurons (nsPVINs). The low frequency at which these neurons were observed suggests that this cell type may be a small tectal subpopulation. The majority of nsPVINs imaged had cell bodies deep in the SPV layer and were positioned near the medial or posterior edges of the SPV (Figure 7E). Like bsPVINs, nsPVIN cell bodies extend an apical primary process into the neuropil and lack an efferent projection. Unlike bsPVINs, these neurons typically possessed a single arborization that lacked laminar specificity (Figures 7A,B). Rotation of 3D image volumes confirmed that the neuronal arbors of nsPVINs are not stratified along any plane and neurite branchpoints are distributed throughout the arbor volume (Figures 7A,B). Based on the average location and thickness of this arbor these neurons primarily target the deeper layer of the SFGS and the SGC. To determine if the axonal and dendritic compartments are spatially segregated in nsPVIN cells we examined the distribution of presynaptic boutons by DsRed/Syp–GFP expression. In five nsPVIN cells examined there was a clear segregation of Syp–GFP puncta, such that the majority of branches containing Syp–GFP puncta had a deeper position with respect to the neuropil layers, whereas those devoid of Syp–GFP labeling were located more superficially (Figures 7C,D). Detailed analysis of the location of Syp–GFP puncta within these arbors revealed that branches either contained multiple Syp–GFP puncta along their length or were completely devoid of puncta, suggesting that during nsPVIN arbor growth individual branches are specified as either presynaptic or postsynaptic compartments. This possibility is strengthened by the fact that higher order branches retained the synaptic identity of parent branches such that primary axonal branches only gave rise to secondary axonal branches. This can be seen in the traced arbor in Figure 7F, where the axonal and dendritic arbors each arise from two primary branches of the primary apical process.


Characterization of genetically targeted neuron types in the zebrafish optic tectum.

Robles E, Smith SJ, Baier H - Front Neural Circuits (2011)

The non-stratified periventricular interneuron cell type. (A) Dorsal view of a two-photon image volume containing a single labeled nsPVIN imaged at 5 dpf. Note the long apical neurite extended into the neuropil. (B) Forty-five degree rotation of image volume in (A). Note the absence of any stratification within the arbor. (C) Merged confocal image volume of a single 4 dpf nsPVIN expressing both dsRed (red) and Syp–GFP (green). Arrow depicts orientation of neuropil layers from superficial (S) to deep (D). (D) 2.5× magnification of boxed region in (C). Note the bright Syp–GFP puncta contained within a subset of neurite branches (arrows). (E) Schematic depiction of nsPVIN cell body distribution throughout the SPV layer. Cell traced in black corresponds to neuron in (A) and (B). Note the deep SPV location of cell body. (F) Manual tracing of the neurite arbor in (D). Green lines indicate branches containing Syp–GFP puncta, whereas branches devoid of Syp–GFP labeling are in red. Scale bar, 20 μm in (A–C), 8 μm in (D,F).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 7: The non-stratified periventricular interneuron cell type. (A) Dorsal view of a two-photon image volume containing a single labeled nsPVIN imaged at 5 dpf. Note the long apical neurite extended into the neuropil. (B) Forty-five degree rotation of image volume in (A). Note the absence of any stratification within the arbor. (C) Merged confocal image volume of a single 4 dpf nsPVIN expressing both dsRed (red) and Syp–GFP (green). Arrow depicts orientation of neuropil layers from superficial (S) to deep (D). (D) 2.5× magnification of boxed region in (C). Note the bright Syp–GFP puncta contained within a subset of neurite branches (arrows). (E) Schematic depiction of nsPVIN cell body distribution throughout the SPV layer. Cell traced in black corresponds to neuron in (A) and (B). Note the deep SPV location of cell body. (F) Manual tracing of the neurite arbor in (D). Green lines indicate branches containing Syp–GFP puncta, whereas branches devoid of Syp–GFP labeling are in red. Scale bar, 20 μm in (A–C), 8 μm in (D,F).
Mentions: Of the 92 cells labeled by the dg4ii plasmid 13 were non-stratified periventricular interneurons (nsPVINs). The low frequency at which these neurons were observed suggests that this cell type may be a small tectal subpopulation. The majority of nsPVINs imaged had cell bodies deep in the SPV layer and were positioned near the medial or posterior edges of the SPV (Figure 7E). Like bsPVINs, nsPVIN cell bodies extend an apical primary process into the neuropil and lack an efferent projection. Unlike bsPVINs, these neurons typically possessed a single arborization that lacked laminar specificity (Figures 7A,B). Rotation of 3D image volumes confirmed that the neuronal arbors of nsPVINs are not stratified along any plane and neurite branchpoints are distributed throughout the arbor volume (Figures 7A,B). Based on the average location and thickness of this arbor these neurons primarily target the deeper layer of the SFGS and the SGC. To determine if the axonal and dendritic compartments are spatially segregated in nsPVIN cells we examined the distribution of presynaptic boutons by DsRed/Syp–GFP expression. In five nsPVIN cells examined there was a clear segregation of Syp–GFP puncta, such that the majority of branches containing Syp–GFP puncta had a deeper position with respect to the neuropil layers, whereas those devoid of Syp–GFP labeling were located more superficially (Figures 7C,D). Detailed analysis of the location of Syp–GFP puncta within these arbors revealed that branches either contained multiple Syp–GFP puncta along their length or were completely devoid of puncta, suggesting that during nsPVIN arbor growth individual branches are specified as either presynaptic or postsynaptic compartments. This possibility is strengthened by the fact that higher order branches retained the synaptic identity of parent branches such that primary axonal branches only gave rise to secondary axonal branches. This can be seen in the traced arbor in Figure 7F, where the axonal and dendritic arbors each arise from two primary branches of the primary apical process.

Bottom Line: The second type, a GABAergic non-stratified periventricular interneuron, extends a bushy arbor containing both dendrites and axons into the SGC and the deepest sublayers of the SFGS.Interestingly, the same axons form en passant synapses within the deepest neuropil layer of the tectum, the stratum album centrale.These observations establish a framework for studying the morphological and functional differentiation of neural circuits in the zebrafish visual system.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of California San Francisco San Francisco, CA, USA.

ABSTRACT
The optically transparent larval zebrafish is ideally suited for in vivo analyses of neural circuitry controlling visually guided behaviors. However, there is a lack of information regarding specific cell types in the major retinorecipient brain region of the fish, the optic tectum. Here we report the characterization of three previously unidentified tectal cell types that are specifically labeled by dlx5/6 enhancer elements. In vivo laser-scanning microscopy in conjunction with ex vivo array tomography revealed that these neurons differ in their morphologies, synaptic connectivity, and neurotransmitter phenotypes. The first type is an excitatory bistratified periventricular interneuron that forms a dendritic arbor in the retinorecipient stratum fibrosum et griseum superficiale (SFGS) and an axonal arbor in the stratum griseum centrale (SGC). The second type, a GABAergic non-stratified periventricular interneuron, extends a bushy arbor containing both dendrites and axons into the SGC and the deepest sublayers of the SFGS. The third type is a GABAergic periventricular projection neuron that extends a dendritic arbor into the SGC and a long axon to the torus semicircularis, medulla oblongata, and anterior hindbrain. Interestingly, the same axons form en passant synapses within the deepest neuropil layer of the tectum, the stratum album centrale. This approach revealed several novel aspects of tectal circuitry, including: (1) a glutamatergic mode of transmission from the superficial, retinorecipient neuropil layers to the deeper, output layers, (2) the presence of interneurons with mixed dendrite/axon arbors likely involved in local processing, and (3) a heretofore unknown GABAergic tectofugal projection to midbrain and hindbrain. These observations establish a framework for studying the morphological and functional differentiation of neural circuits in the zebrafish visual system.

No MeSH data available.


Related in: MedlinePlus