Limits...
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 SPON axons in the TLC. (A–F, A′–F′) Digital micrographs of six coronal sections taken from different rostrocaudal levels of the midbrain tectum of case 97084, whose injection site is depicted in Figure 1B. Sections have been ordered from caudal to rostral. The number at the bottom of each panel indicates the distance in millimeters between the depicted plane and the interaural coronal plane (I.A.). Micrographs in the right column show higher magnification views of the corresponding micrograph in the left column. Vertical dashed lines indicate the midline. Scale bars in (F,F′) apply to all six micrographs within the corresponding column. Abbreviations of SC layers as in Figure 2. Other abbreviations: CoIC, commissure of the IC; CoSC, commissure of the SC; PAG, periaqueductal gray matter.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3045713&req=5

Figure 3: Labeled SPON axons in the TLC. (A–F, A′–F′) Digital micrographs of six coronal sections taken from different rostrocaudal levels of the midbrain tectum of case 97084, whose injection site is depicted in Figure 1B. Sections have been ordered from caudal to rostral. The number at the bottom of each panel indicates the distance in millimeters between the depicted plane and the interaural coronal plane (I.A.). Micrographs in the right column show higher magnification views of the corresponding micrograph in the left column. Vertical dashed lines indicate the midline. Scale bars in (F,F′) apply to all six micrographs within the corresponding column. Abbreviations of SC layers as in Figure 2. Other abbreviations: CoIC, commissure of the IC; CoSC, commissure of the SC; PAG, periaqueductal gray matter.

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 SPON axons in the TLC. (A–F, A′–F′) Digital micrographs of six coronal sections taken from different rostrocaudal levels of the midbrain tectum of case 97084, whose injection site is depicted in Figure 1B. Sections have been ordered from caudal to rostral. The number at the bottom of each panel indicates the distance in millimeters between the depicted plane and the interaural coronal plane (I.A.). Micrographs in the right column show higher magnification views of the corresponding micrograph in the left column. Vertical dashed lines indicate the midline. Scale bars in (F,F′) apply to all six micrographs within the corresponding column. Abbreviations of SC layers as in Figure 2. Other abbreviations: CoIC, commissure of the IC; CoSC, commissure of the SC; PAG, periaqueductal gray matter.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Labeled SPON axons in the TLC. (A–F, A′–F′) Digital micrographs of six coronal sections taken from different rostrocaudal levels of the midbrain tectum of case 97084, whose injection site is depicted in Figure 1B. Sections have been ordered from caudal to rostral. The number at the bottom of each panel indicates the distance in millimeters between the depicted plane and the interaural coronal plane (I.A.). Micrographs in the right column show higher magnification views of the corresponding micrograph in the left column. Vertical dashed lines indicate the midline. Scale bars in (F,F′) apply to all six micrographs within the corresponding column. Abbreviations of SC layers as in Figure 2. Other abbreviations: CoIC, commissure of the IC; CoSC, commissure of the SC; PAG, periaqueductal gray matter.
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