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Connections of the Superior Paraolivary Nucleus of the Rat: II. Reciprocal Connections with the Tectal Longitudinal Column.

Viñuela A, Aparicio MA, Berrebi AS, Saldaña E - Front Neuroanat (2011)

Bottom Line: SPON fibers reach the TLC by two routes: as collaterals of axons of the CoIC, and as axons that circumvent the ipsilateral IC before traveling in the deep layers of the superior colliculus (SC).The density of these projections identifies SPON as a significant source of input to the TLC.This observation suggests that the SPON is a significant target of TLC projections.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for the Neurobiology of Hearing, Neuroscience Institute of Castilla y León, University of Salamanca Salamanca, Spain.

ABSTRACT
The superior paraolivary nucleus (SPON), a prominent GABAergic center of the mammalian auditory brainstem, projects to the ipsilateral inferior colliculus (IC) and sends axons through the commissure of the IC (CoIC). Herein we demonstrate that the SPON is reciprocally connected with the recently discovered tectal longitudinal column (TLC). The TLC is a long and narrow structure that spans nearly the entire midbrain tectum longitudinally, immediately above the periaqueductal gray matter (PAG) and very close to the midline. Unilateral injections of biotinylated dextran into the SPON of the rat label abundant terminal fibers in the TLC of both sides, with an ipsilateral predominance. The SPON provides a dense innervation of the entire rostrocaudal extent of the ipsilateral TLC, and a relatively sparser innervation of the caudal and rostral portions of the contralateral TLC. SPON fibers reach the TLC by two routes: as collaterals of axons of the CoIC, and as axons that circumvent the ipsilateral IC before traveling in the deep layers of the superior colliculus (SC). The density of these projections identifies SPON as a significant source of input to the TLC. Other targets of the SPON discovered in this study include the deep layers of the SC and the PAG. The same experiments reveal numerous labeled cell bodies in the TLC, interspersed among the labeled SPON fibers. This observation suggests that the SPON is a significant target of TLC projections. The discovery of novel reciprocal connections between the SPON and the TLC opens unexpected avenues for investigation of sound processing in mammalian brainstem circuits.

No MeSH data available.


Related in: MedlinePlus

Trajectory and distribution of SPON axons. (A–F) Drawings of coronal sections of the midbrain illustrating axons labeled following a single injection of BDA into the left SPON. Case 97084, whose injection site is depicted in Figure 1B. The sections have been ordered from caudal to rostral and illustrate levels similar to those shown in Figure 3. The TLC is represented in light gray and the scale bar in (A) applies to all six drawings. Abbreviations of SC layers: DpG, deep gray; DpW, deep white; InG, intermediate gray; InW, intermediate white; Op, stratum opticum; SuG, superficial gray; Zo, stratum zonale. Abbreviations of periaqueductal gray matter (PAG) columns: PAGl, lateral column; PAGdl, dorsolateral column; PAGdm, dorsomedial column. Other abbreviations: Aq, cerebral aqueduct; IC, inferior colliculus; MGB, medial geniculate body; VNLL, ventral nucleus of the lateral lemniscus.
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Figure 2: Trajectory and distribution of SPON axons. (A–F) Drawings of coronal sections of the midbrain illustrating axons labeled following a single injection of BDA into the left SPON. Case 97084, whose injection site is depicted in Figure 1B. The sections have been ordered from caudal to rostral and illustrate levels similar to those shown in Figure 3. The TLC is represented in light gray and the scale bar in (A) applies to all six drawings. Abbreviations of SC layers: DpG, deep gray; DpW, deep white; InG, intermediate gray; InW, intermediate white; Op, stratum opticum; SuG, superficial gray; Zo, stratum zonale. Abbreviations of periaqueductal gray matter (PAG) columns: PAGl, lateral column; PAGdl, dorsolateral column; PAGdm, dorsomedial column. Other abbreviations: Aq, cerebral aqueduct; IC, inferior colliculus; MGB, medial geniculate body; VNLL, ventral nucleus of the lateral lemniscus.

Mentions: To generate the drawings of Figure 2, the sections were first photographed at high resolution with the 5× objective lens. At this magnification, several micrographs were needed to photograph every section. These photographs were then arranged and fitted using Adobe Photoshop software to create a large mosaic image of the section. The resulting digital image was imported into Canvas software. To increase the resolution of the final image, a new layer was created over the digital image and each labeled fiber contained within the original micrograph was redrawn digitally using Canvas’ freehand drawing tool. This digital procedure allowed us to subsequently adjust the thickness of the lines. The new digital layer, without the underlying micrograph, was finally saved as a TIFF file.


Connections of the Superior Paraolivary Nucleus of the Rat: II. Reciprocal Connections with the Tectal Longitudinal Column.

Viñuela A, Aparicio MA, Berrebi AS, Saldaña E - Front Neuroanat (2011)

Trajectory and distribution of SPON axons. (A–F) Drawings of coronal sections of the midbrain illustrating axons labeled following a single injection of BDA into the left SPON. Case 97084, whose injection site is depicted in Figure 1B. The sections have been ordered from caudal to rostral and illustrate levels similar to those shown in Figure 3. The TLC is represented in light gray and the scale bar in (A) applies to all six drawings. Abbreviations of SC layers: DpG, deep gray; DpW, deep white; InG, intermediate gray; InW, intermediate white; Op, stratum opticum; SuG, superficial gray; Zo, stratum zonale. Abbreviations of periaqueductal gray matter (PAG) columns: PAGl, lateral column; PAGdl, dorsolateral column; PAGdm, dorsomedial column. Other abbreviations: Aq, cerebral aqueduct; IC, inferior colliculus; MGB, medial geniculate body; VNLL, ventral nucleus of the lateral lemniscus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3045713&req=5

Figure 2: Trajectory and distribution of SPON axons. (A–F) Drawings of coronal sections of the midbrain illustrating axons labeled following a single injection of BDA into the left SPON. Case 97084, whose injection site is depicted in Figure 1B. The sections have been ordered from caudal to rostral and illustrate levels similar to those shown in Figure 3. The TLC is represented in light gray and the scale bar in (A) applies to all six drawings. Abbreviations of SC layers: DpG, deep gray; DpW, deep white; InG, intermediate gray; InW, intermediate white; Op, stratum opticum; SuG, superficial gray; Zo, stratum zonale. Abbreviations of periaqueductal gray matter (PAG) columns: PAGl, lateral column; PAGdl, dorsolateral column; PAGdm, dorsomedial column. Other abbreviations: Aq, cerebral aqueduct; IC, inferior colliculus; MGB, medial geniculate body; VNLL, ventral nucleus of the lateral lemniscus.
Mentions: To generate the drawings of Figure 2, the sections were first photographed at high resolution with the 5× objective lens. At this magnification, several micrographs were needed to photograph every section. These photographs were then arranged and fitted using Adobe Photoshop software to create a large mosaic image of the section. The resulting digital image was imported into Canvas software. To increase the resolution of the final image, a new layer was created over the digital image and each labeled fiber contained within the original micrograph was redrawn digitally using Canvas’ freehand drawing tool. This digital procedure allowed us to subsequently adjust the thickness of the lines. The new digital layer, without the underlying micrograph, was finally saved as a TIFF file.

Bottom Line: SPON fibers reach the TLC by two routes: as collaterals of axons of the CoIC, and as axons that circumvent the ipsilateral IC before traveling in the deep layers of the superior colliculus (SC).The density of these projections identifies SPON as a significant source of input to the TLC.This observation suggests that the SPON is a significant target of TLC projections.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for the Neurobiology of Hearing, Neuroscience Institute of Castilla y León, University of Salamanca Salamanca, Spain.

ABSTRACT
The superior paraolivary nucleus (SPON), a prominent GABAergic center of the mammalian auditory brainstem, projects to the ipsilateral inferior colliculus (IC) and sends axons through the commissure of the IC (CoIC). Herein we demonstrate that the SPON is reciprocally connected with the recently discovered tectal longitudinal column (TLC). The TLC is a long and narrow structure that spans nearly the entire midbrain tectum longitudinally, immediately above the periaqueductal gray matter (PAG) and very close to the midline. Unilateral injections of biotinylated dextran into the SPON of the rat label abundant terminal fibers in the TLC of both sides, with an ipsilateral predominance. The SPON provides a dense innervation of the entire rostrocaudal extent of the ipsilateral TLC, and a relatively sparser innervation of the caudal and rostral portions of the contralateral TLC. SPON fibers reach the TLC by two routes: as collaterals of axons of the CoIC, and as axons that circumvent the ipsilateral IC before traveling in the deep layers of the superior colliculus (SC). The density of these projections identifies SPON as a significant source of input to the TLC. Other targets of the SPON discovered in this study include the deep layers of the SC and the PAG. The same experiments reveal numerous labeled cell bodies in the TLC, interspersed among the labeled SPON fibers. This observation suggests that the SPON is a significant target of TLC projections. The discovery of novel reciprocal connections between the SPON and the TLC opens unexpected avenues for investigation of sound processing in mammalian brainstem circuits.

No MeSH data available.


Related in: MedlinePlus