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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

Labeled terminal SPON fibers in the TLC. (A) Micrograph of a coronal section through the caudal portion of the left and right TLC after BDA was injected into the left SPON. Case 97097, whose injection site is depicted in Figure 1B. Several labeled SPON axons give off collateral branches (asterisks) within the ipsilateral and the contralateral TLC. Note the predominantly vertical orientation of the terminal axonal branches. (B) Micrograph of a coronal section through the central third of the TLC, Case 97084, whose injection site is depicted in Figure 1B. Numerous labeled fibers from the ipsilateral SPON enter the TLC from the SC and branch into thin collateral bearing abundant en passant and terminal boutons. Note terminal fibers entering the dorsomedial column of the PAG (PAGdm) from the overlying TLC. In both (A,B) the TLC has been delimited by dotted lines and the dashed vertical line indicates the midline.
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Figure 4: Labeled terminal SPON fibers in the TLC. (A) Micrograph of a coronal section through the caudal portion of the left and right TLC after BDA was injected into the left SPON. Case 97097, whose injection site is depicted in Figure 1B. Several labeled SPON axons give off collateral branches (asterisks) within the ipsilateral and the contralateral TLC. Note the predominantly vertical orientation of the terminal axonal branches. (B) Micrograph of a coronal section through the central third of the TLC, Case 97084, whose injection site is depicted in Figure 1B. Numerous labeled fibers from the ipsilateral SPON enter the TLC from the SC and branch into thin collateral bearing abundant en passant and terminal boutons. Note terminal fibers entering the dorsomedial column of the PAG (PAGdm) from the overlying TLC. In both (A,B) the TLC has been delimited by dotted lines and the dashed vertical line indicates the midline.

Mentions: Those SPON axons destined to innervate the TLC do so by two different routes. The first route is taken by some of the axons traveling in the CoIC (Figures 2A,B, 3A,B, and 4A). These fibers give off one or more collaterals within the ipsilateral TLC and/or, less frequently, within the contralateral TLC. Occasionally individual labeled SPON fibers give off collaterals to both the ipsilateral and contralateral TLCs (Figure 4A). All of these collaterals are usually thin and tend to run either vertically within the CoIC or rostrally, so that the latter course caudorostrally within the TLC.


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)

Labeled terminal SPON fibers in the TLC. (A) Micrograph of a coronal section through the caudal portion of the left and right TLC after BDA was injected into the left SPON. Case 97097, whose injection site is depicted in Figure 1B. Several labeled SPON axons give off collateral branches (asterisks) within the ipsilateral and the contralateral TLC. Note the predominantly vertical orientation of the terminal axonal branches. (B) Micrograph of a coronal section through the central third of the TLC, Case 97084, whose injection site is depicted in Figure 1B. Numerous labeled fibers from the ipsilateral SPON enter the TLC from the SC and branch into thin collateral bearing abundant en passant and terminal boutons. Note terminal fibers entering the dorsomedial column of the PAG (PAGdm) from the overlying TLC. In both (A,B) the TLC has been delimited by dotted lines and the dashed vertical line indicates the midline.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Labeled terminal SPON fibers in the TLC. (A) Micrograph of a coronal section through the caudal portion of the left and right TLC after BDA was injected into the left SPON. Case 97097, whose injection site is depicted in Figure 1B. Several labeled SPON axons give off collateral branches (asterisks) within the ipsilateral and the contralateral TLC. Note the predominantly vertical orientation of the terminal axonal branches. (B) Micrograph of a coronal section through the central third of the TLC, Case 97084, whose injection site is depicted in Figure 1B. Numerous labeled fibers from the ipsilateral SPON enter the TLC from the SC and branch into thin collateral bearing abundant en passant and terminal boutons. Note terminal fibers entering the dorsomedial column of the PAG (PAGdm) from the overlying TLC. In both (A,B) the TLC has been delimited by dotted lines and the dashed vertical line indicates the midline.
Mentions: Those SPON axons destined to innervate the TLC do so by two different routes. The first route is taken by some of the axons traveling in the CoIC (Figures 2A,B, 3A,B, and 4A). These fibers give off one or more collaterals within the ipsilateral TLC and/or, less frequently, within the contralateral TLC. Occasionally individual labeled SPON fibers give off collaterals to both the ipsilateral and contralateral TLCs (Figure 4A). All of these collaterals are usually thin and tend to run either vertically within the CoIC or rostrally, so that the latter course caudorostrally within the TLC.

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