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Synaptic connectivity of the cholinergic axons in the olfactory bulb of the cynomolgus monkey.

Liberia T, Blasco-Ibáñez JM, Nácher J, Varea E, Lanciego JL, Crespo C - Front Neuroanat (2015)

Bottom Line: Our results demonstrate that the cholinergic axons form synaptic contacts on interneurons.Although the cholinergic boutons were frequently found in close vicinity of the dendrites of principal cells, we have not found synaptic contacts on them.From a comparative perspective, our data indicate that the synaptic connectivity of the cholinergic circuits is highly preserved in the OB of macrosmatic and microsmatic mammals.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Biology, Department of Cell Biology, University of Valencia Burjassot, Valencia, Spain.

ABSTRACT
The olfactory bulb (OB) of mammals receives cholinergic afferents from the horizontal limb of the diagonal band of Broca (HDB). At present, the synaptic connectivity of the cholinergic axons on the circuits of the OB has only been investigated in the rat. In this report, we analyze the synaptic connectivity of the cholinergic axons in the OB of the cynomolgus monkey (Macaca fascicularis). Our aim is to investigate whether the cholinergic innervation of the bulbar circuits is phylogenetically conserved between macrosmatic and microsmatic mammals. Our results demonstrate that the cholinergic axons form synaptic contacts on interneurons. In the glomerular layer, their main targets are the periglomerular cells, which receive axo-somatic and axo-dendritic synapses. In the inframitral region, their main targets are the granule cells, which receive synaptic contacts on their dendritic shafts and spines. Although the cholinergic boutons were frequently found in close vicinity of the dendrites of principal cells, we have not found synaptic contacts on them. From a comparative perspective, our data indicate that the synaptic connectivity of the cholinergic circuits is highly preserved in the OB of macrosmatic and microsmatic mammals.

No MeSH data available.


VAChT-staining in the glomerular layer under light microscopy. (A) Low-magnification view of the glomerular layer (GL) showing VAChT-containing puncta. Note the low density of staining found in the external plexiform layer (EPL). (B) Detailed view of an olfactory glomerulus (g). The VAChT-containing fibers run throughout the periglomerular region and also innervate the glomerular neuropil. (C) High-magnification view of the neuropil of an olfactory glomerulus revealing that the VAChT-containing puncta appear restricted to strands surrounding neuropil compartments where no VAChT-containing puncta are found (asterisks). (D) High-magnification photomicrograph taken from the periglomerular region of the glomerular layer showing the somata of immunonegative neurons (asterisks) surrounded by VAChT-containing puncta. Scale bars: 30 μm in (A) and (B); 15 μm in (C) and (D).
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Figure 1: VAChT-staining in the glomerular layer under light microscopy. (A) Low-magnification view of the glomerular layer (GL) showing VAChT-containing puncta. Note the low density of staining found in the external plexiform layer (EPL). (B) Detailed view of an olfactory glomerulus (g). The VAChT-containing fibers run throughout the periglomerular region and also innervate the glomerular neuropil. (C) High-magnification view of the neuropil of an olfactory glomerulus revealing that the VAChT-containing puncta appear restricted to strands surrounding neuropil compartments where no VAChT-containing puncta are found (asterisks). (D) High-magnification photomicrograph taken from the periglomerular region of the glomerular layer showing the somata of immunonegative neurons (asterisks) surrounded by VAChT-containing puncta. Scale bars: 30 μm in (A) and (B); 15 μm in (C) and (D).

Mentions: All the bulbar layers contained VAChT-positive axons, with the exception of the olfactory nerve layer. The highest density of VAChT-positive fibers was found in the glomerular layer (Figure 1). Here, the cholinergic fibers spread throughout the periglomerular region surrounding the olfactory glomeruli. Axon collaterals arose from these fibers and innervated the glomerular neuropil (Figures 1A,B). The distribution of the cholinergic axons inside the glomeruli was not homogeneous: They were restricted to some strands of neuropil and were never found in other neuropil compartments (Figure 1C). The neuropil of the olfactory glomeruli is divided into two separate compartments as previously described (Kosaka et al., 1997; Liberia et al., 2013): The “olfactory nerve zone”, which contains the axons of the olfactory nerve, and the “non-olfactory nerve zone”, which does not contain axons of the olfactory nerve. The analysis of the glomerular neuropil under electron microscopy demonstrated that the distribution of the VAChT-containing axons was restricted to the “non-olfactory nerve zone” and they did not innervate the “olfactory nerve zone” (data not shown).


Synaptic connectivity of the cholinergic axons in the olfactory bulb of the cynomolgus monkey.

Liberia T, Blasco-Ibáñez JM, Nácher J, Varea E, Lanciego JL, Crespo C - Front Neuroanat (2015)

VAChT-staining in the glomerular layer under light microscopy. (A) Low-magnification view of the glomerular layer (GL) showing VAChT-containing puncta. Note the low density of staining found in the external plexiform layer (EPL). (B) Detailed view of an olfactory glomerulus (g). The VAChT-containing fibers run throughout the periglomerular region and also innervate the glomerular neuropil. (C) High-magnification view of the neuropil of an olfactory glomerulus revealing that the VAChT-containing puncta appear restricted to strands surrounding neuropil compartments where no VAChT-containing puncta are found (asterisks). (D) High-magnification photomicrograph taken from the periglomerular region of the glomerular layer showing the somata of immunonegative neurons (asterisks) surrounded by VAChT-containing puncta. Scale bars: 30 μm in (A) and (B); 15 μm in (C) and (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4362316&req=5

Figure 1: VAChT-staining in the glomerular layer under light microscopy. (A) Low-magnification view of the glomerular layer (GL) showing VAChT-containing puncta. Note the low density of staining found in the external plexiform layer (EPL). (B) Detailed view of an olfactory glomerulus (g). The VAChT-containing fibers run throughout the periglomerular region and also innervate the glomerular neuropil. (C) High-magnification view of the neuropil of an olfactory glomerulus revealing that the VAChT-containing puncta appear restricted to strands surrounding neuropil compartments where no VAChT-containing puncta are found (asterisks). (D) High-magnification photomicrograph taken from the periglomerular region of the glomerular layer showing the somata of immunonegative neurons (asterisks) surrounded by VAChT-containing puncta. Scale bars: 30 μm in (A) and (B); 15 μm in (C) and (D).
Mentions: All the bulbar layers contained VAChT-positive axons, with the exception of the olfactory nerve layer. The highest density of VAChT-positive fibers was found in the glomerular layer (Figure 1). Here, the cholinergic fibers spread throughout the periglomerular region surrounding the olfactory glomeruli. Axon collaterals arose from these fibers and innervated the glomerular neuropil (Figures 1A,B). The distribution of the cholinergic axons inside the glomeruli was not homogeneous: They were restricted to some strands of neuropil and were never found in other neuropil compartments (Figure 1C). The neuropil of the olfactory glomeruli is divided into two separate compartments as previously described (Kosaka et al., 1997; Liberia et al., 2013): The “olfactory nerve zone”, which contains the axons of the olfactory nerve, and the “non-olfactory nerve zone”, which does not contain axons of the olfactory nerve. The analysis of the glomerular neuropil under electron microscopy demonstrated that the distribution of the VAChT-containing axons was restricted to the “non-olfactory nerve zone” and they did not innervate the “olfactory nerve zone” (data not shown).

Bottom Line: Our results demonstrate that the cholinergic axons form synaptic contacts on interneurons.Although the cholinergic boutons were frequently found in close vicinity of the dendrites of principal cells, we have not found synaptic contacts on them.From a comparative perspective, our data indicate that the synaptic connectivity of the cholinergic circuits is highly preserved in the OB of macrosmatic and microsmatic mammals.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Biology, Department of Cell Biology, University of Valencia Burjassot, Valencia, Spain.

ABSTRACT
The olfactory bulb (OB) of mammals receives cholinergic afferents from the horizontal limb of the diagonal band of Broca (HDB). At present, the synaptic connectivity of the cholinergic axons on the circuits of the OB has only been investigated in the rat. In this report, we analyze the synaptic connectivity of the cholinergic axons in the OB of the cynomolgus monkey (Macaca fascicularis). Our aim is to investigate whether the cholinergic innervation of the bulbar circuits is phylogenetically conserved between macrosmatic and microsmatic mammals. Our results demonstrate that the cholinergic axons form synaptic contacts on interneurons. In the glomerular layer, their main targets are the periglomerular cells, which receive axo-somatic and axo-dendritic synapses. In the inframitral region, their main targets are the granule cells, which receive synaptic contacts on their dendritic shafts and spines. Although the cholinergic boutons were frequently found in close vicinity of the dendrites of principal cells, we have not found synaptic contacts on them. From a comparative perspective, our data indicate that the synaptic connectivity of the cholinergic circuits is highly preserved in the OB of macrosmatic and microsmatic mammals.

No MeSH data available.