Limits...
Ultrastructural characterization of noradrenergic axons and Beta-adrenergic receptors in the lateral nucleus of the amygdala.

Farb CR, Chang W, Ledoux JE - Front Behav Neurosci (2010)

Bottom Line: The lateral nucleus of the amygdala (LA) is a critical brain region for fear learning and regulating the effects of stress on memory.These astrocytic processes were frequently interposed between unlabeled terminals or ensheathed asymmetric synapses.Our findings provide a morphological basis for understanding ways in which NE may modulate transmission by acting via synaptic or non-synaptic mechanisms in the LA.

View Article: PubMed Central - PubMed

Affiliation: Center for Neural Science, New York University New York, NY, USA.

ABSTRACT
Norepinephrine (NE) is thought to play a key role in fear and anxiety, but its role in amygdala-dependent Pavlovian fear conditioning, a major model for understanding the neural basis of fear, is poorly understood. The lateral nucleus of the amygdala (LA) is a critical brain region for fear learning and regulating the effects of stress on memory. To understand better the cellular mechanisms of NE and its adrenergic receptors in the LA, we used antibodies directed against dopamine beta-hydroxylase (DβH), the synthetic enzyme for NE, or against two different isoforms of the beta-adrenergic receptors (βARs), one that predominately recognizes neurons (βAR 248) and the other astrocytes (βAR 404), to characterize the microenvironments of DβH and βAR. By electron microscopy, most DβH terminals did not make synapses, but when they did, they formed both asymmetric and symmetric synapses. By light microscopy, βARs were present in both neurons and astrocytes. Confocal microscopy revealed that both excitatory and inhibitory neurons express βAR248. By electron microscopy, βAR 248 was present in neuronal cell bodies, dendritic shafts and spines, and some axon terminals and astrocytes. When in dendrites and spines, βAR 248 was frequently concentrated along plasma membranes and at post-synaptic densities of asymmetric (excitatory) synapses. βAR 404 was expressed predominately in astrocytic cell bodies and processes. These astrocytic processes were frequently interposed between unlabeled terminals or ensheathed asymmetric synapses. Our findings provide a morphological basis for understanding ways in which NE may modulate transmission by acting via synaptic or non-synaptic mechanisms in the LA.

No MeSH data available.


Related in: MedlinePlus

Electron micrographs show DβH-terminals in LA. (A) A DβH – terminal (DBH) apposes a dendritic spine (sp) and an unlabeled terminal (ut) forming an asymmetric synapse (asterisks) onto a spine (sp). (B) A DβH-terminal forms a symmetric synapse (arrows) with a dendrite (d). (C) A DβH-terminal forms a synapse (arrowheads) onto a dendrite (d) that also receives a synapse (arrows) from an unlabeled terminal (ut). Glial processes (g and asterisk) are also shown. (D) A DBH-terminal forms a symmetric synapse (arrows) onto a dendritic (d) whose spine (sp) receives a synapse (arrowheads) from an unlabeled terminal (ut). Also shown is a glial process (g). (E) A DβH-terminal is apposed to an unlabeled terminal (ut1) that forms a symmetric synapse (arrows) on a dendrite (d). An unlabeled terminal (ut2) forms an asymmetric synapse (arrowheads) on the dendrite's spine (sp). Unlabeled glial processes (g and *) are also shown. (F) A DβH-terminal (DBH1) forms a synapse (arrows) onto a dendritic shaft (d1), whose spine (sp) receives an asymmetric synapse (arrowheads) from a second DβH-terminal (DBH2). DβH2 apposes unlabeled terminals (ut1–2) forming asymmetric synapses (arrowheads) with a spine (sp) and a dendrite (d2). Scale bars = 0.500 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2967335&req=5

Figure 3: Electron micrographs show DβH-terminals in LA. (A) A DβH – terminal (DBH) apposes a dendritic spine (sp) and an unlabeled terminal (ut) forming an asymmetric synapse (asterisks) onto a spine (sp). (B) A DβH-terminal forms a symmetric synapse (arrows) with a dendrite (d). (C) A DβH-terminal forms a synapse (arrowheads) onto a dendrite (d) that also receives a synapse (arrows) from an unlabeled terminal (ut). Glial processes (g and asterisk) are also shown. (D) A DBH-terminal forms a symmetric synapse (arrows) onto a dendritic (d) whose spine (sp) receives a synapse (arrowheads) from an unlabeled terminal (ut). Also shown is a glial process (g). (E) A DβH-terminal is apposed to an unlabeled terminal (ut1) that forms a symmetric synapse (arrows) on a dendrite (d). An unlabeled terminal (ut2) forms an asymmetric synapse (arrowheads) on the dendrite's spine (sp). Unlabeled glial processes (g and *) are also shown. (F) A DβH-terminal (DBH1) forms a synapse (arrows) onto a dendritic shaft (d1), whose spine (sp) receives an asymmetric synapse (arrowheads) from a second DβH-terminal (DBH2). DβH2 apposes unlabeled terminals (ut1–2) forming asymmetric synapses (arrowheads) with a spine (sp) and a dendrite (d2). Scale bars = 0.500 μm.

Mentions: Most of our EM analysis was performed on tissue fixed with acrolein since both the ultrastructure and membrane preservation were superior to tissue fixed with low levels of glutaraldehyde. Four hundred and ten DβH-labeled terminals were analyzed from tissue taken from the four animals with the best morphology. Analysis was performed on three animals perfused with acrolein and one animal perfused with glutaraldehyde. Ultrathin sections were collected from 3–4 vibratome sections from each animal for a total of 14 samples. DβH-labeled terminals were unmyelinated and varied in size from 0.4–1.5 μm. DβH terminals contained small, clear vesicles, though many terminals also contained 1–5 dense-core vesicles (Figures 3A–F). DβH terminals frequently contained mitochondria and some DβH-labeled axons appeared to follow the contours of blood vessels (Figure 4A). Frequently, the reaction product filled the axoplasm and obscured the morphological features of the terminal. Those terminals whose membranes were not intact due to the use of detergent were not included in the analysis. The vast majority of DβH terminals did not form synapses in a single plane of section (282/410 or 69%) (Figures 3A,E). About half the DβH terminals (223/410, or 54%) were directly apposed to unlabeled terminals (Figures 3B,C,E,F). In some instances (9/410 or 2%) possible axo–axonic contacts were observed: the plasma membranes of DβH terminals showed close and parallel alignment with the plasma membrane of unlabeled terminals and some intercleft density was present (Figure 4A). When DβH terminals did form synapses, most formed symmetric synapses (90/128 or 70%) (Figure 5A) and the vast majority of these (75/90, 83%) occurred on dendrites (Figures 3B,D) though some symmetric synapses were made on spines (13/90, 14%) and two occurred on somata (2/90, 2%). DβH symmetric synapses on spines usually occurred on the spine neck. When DβH terminals formed junctions on spines, almost one-quarter (9/37 or 24%) of these spines received another synapse from an unlabeled terminal. Most of these second synapses were asymmetric (8/9 or 89%) and were formed on the spine head. Almost one-third of synapse-forming DβH terminals made asymmetric synapses (38/128 or 30%). The majority of asymmetric synapses occurred on spines (24/38, or 63%) (Figures 3F and 5B), though many were formed on dendrites (14/38 or 37%) (Figures 3C and 5B).


Ultrastructural characterization of noradrenergic axons and Beta-adrenergic receptors in the lateral nucleus of the amygdala.

Farb CR, Chang W, Ledoux JE - Front Behav Neurosci (2010)

Electron micrographs show DβH-terminals in LA. (A) A DβH – terminal (DBH) apposes a dendritic spine (sp) and an unlabeled terminal (ut) forming an asymmetric synapse (asterisks) onto a spine (sp). (B) A DβH-terminal forms a symmetric synapse (arrows) with a dendrite (d). (C) A DβH-terminal forms a synapse (arrowheads) onto a dendrite (d) that also receives a synapse (arrows) from an unlabeled terminal (ut). Glial processes (g and asterisk) are also shown. (D) A DBH-terminal forms a symmetric synapse (arrows) onto a dendritic (d) whose spine (sp) receives a synapse (arrowheads) from an unlabeled terminal (ut). Also shown is a glial process (g). (E) A DβH-terminal is apposed to an unlabeled terminal (ut1) that forms a symmetric synapse (arrows) on a dendrite (d). An unlabeled terminal (ut2) forms an asymmetric synapse (arrowheads) on the dendrite's spine (sp). Unlabeled glial processes (g and *) are also shown. (F) A DβH-terminal (DBH1) forms a synapse (arrows) onto a dendritic shaft (d1), whose spine (sp) receives an asymmetric synapse (arrowheads) from a second DβH-terminal (DBH2). DβH2 apposes unlabeled terminals (ut1–2) forming asymmetric synapses (arrowheads) with a spine (sp) and a dendrite (d2). Scale bars = 0.500 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2967335&req=5

Figure 3: Electron micrographs show DβH-terminals in LA. (A) A DβH – terminal (DBH) apposes a dendritic spine (sp) and an unlabeled terminal (ut) forming an asymmetric synapse (asterisks) onto a spine (sp). (B) A DβH-terminal forms a symmetric synapse (arrows) with a dendrite (d). (C) A DβH-terminal forms a synapse (arrowheads) onto a dendrite (d) that also receives a synapse (arrows) from an unlabeled terminal (ut). Glial processes (g and asterisk) are also shown. (D) A DBH-terminal forms a symmetric synapse (arrows) onto a dendritic (d) whose spine (sp) receives a synapse (arrowheads) from an unlabeled terminal (ut). Also shown is a glial process (g). (E) A DβH-terminal is apposed to an unlabeled terminal (ut1) that forms a symmetric synapse (arrows) on a dendrite (d). An unlabeled terminal (ut2) forms an asymmetric synapse (arrowheads) on the dendrite's spine (sp). Unlabeled glial processes (g and *) are also shown. (F) A DβH-terminal (DBH1) forms a synapse (arrows) onto a dendritic shaft (d1), whose spine (sp) receives an asymmetric synapse (arrowheads) from a second DβH-terminal (DBH2). DβH2 apposes unlabeled terminals (ut1–2) forming asymmetric synapses (arrowheads) with a spine (sp) and a dendrite (d2). Scale bars = 0.500 μm.
Mentions: Most of our EM analysis was performed on tissue fixed with acrolein since both the ultrastructure and membrane preservation were superior to tissue fixed with low levels of glutaraldehyde. Four hundred and ten DβH-labeled terminals were analyzed from tissue taken from the four animals with the best morphology. Analysis was performed on three animals perfused with acrolein and one animal perfused with glutaraldehyde. Ultrathin sections were collected from 3–4 vibratome sections from each animal for a total of 14 samples. DβH-labeled terminals were unmyelinated and varied in size from 0.4–1.5 μm. DβH terminals contained small, clear vesicles, though many terminals also contained 1–5 dense-core vesicles (Figures 3A–F). DβH terminals frequently contained mitochondria and some DβH-labeled axons appeared to follow the contours of blood vessels (Figure 4A). Frequently, the reaction product filled the axoplasm and obscured the morphological features of the terminal. Those terminals whose membranes were not intact due to the use of detergent were not included in the analysis. The vast majority of DβH terminals did not form synapses in a single plane of section (282/410 or 69%) (Figures 3A,E). About half the DβH terminals (223/410, or 54%) were directly apposed to unlabeled terminals (Figures 3B,C,E,F). In some instances (9/410 or 2%) possible axo–axonic contacts were observed: the plasma membranes of DβH terminals showed close and parallel alignment with the plasma membrane of unlabeled terminals and some intercleft density was present (Figure 4A). When DβH terminals did form synapses, most formed symmetric synapses (90/128 or 70%) (Figure 5A) and the vast majority of these (75/90, 83%) occurred on dendrites (Figures 3B,D) though some symmetric synapses were made on spines (13/90, 14%) and two occurred on somata (2/90, 2%). DβH symmetric synapses on spines usually occurred on the spine neck. When DβH terminals formed junctions on spines, almost one-quarter (9/37 or 24%) of these spines received another synapse from an unlabeled terminal. Most of these second synapses were asymmetric (8/9 or 89%) and were formed on the spine head. Almost one-third of synapse-forming DβH terminals made asymmetric synapses (38/128 or 30%). The majority of asymmetric synapses occurred on spines (24/38, or 63%) (Figures 3F and 5B), though many were formed on dendrites (14/38 or 37%) (Figures 3C and 5B).

Bottom Line: The lateral nucleus of the amygdala (LA) is a critical brain region for fear learning and regulating the effects of stress on memory.These astrocytic processes were frequently interposed between unlabeled terminals or ensheathed asymmetric synapses.Our findings provide a morphological basis for understanding ways in which NE may modulate transmission by acting via synaptic or non-synaptic mechanisms in the LA.

View Article: PubMed Central - PubMed

Affiliation: Center for Neural Science, New York University New York, NY, USA.

ABSTRACT
Norepinephrine (NE) is thought to play a key role in fear and anxiety, but its role in amygdala-dependent Pavlovian fear conditioning, a major model for understanding the neural basis of fear, is poorly understood. The lateral nucleus of the amygdala (LA) is a critical brain region for fear learning and regulating the effects of stress on memory. To understand better the cellular mechanisms of NE and its adrenergic receptors in the LA, we used antibodies directed against dopamine beta-hydroxylase (DβH), the synthetic enzyme for NE, or against two different isoforms of the beta-adrenergic receptors (βARs), one that predominately recognizes neurons (βAR 248) and the other astrocytes (βAR 404), to characterize the microenvironments of DβH and βAR. By electron microscopy, most DβH terminals did not make synapses, but when they did, they formed both asymmetric and symmetric synapses. By light microscopy, βARs were present in both neurons and astrocytes. Confocal microscopy revealed that both excitatory and inhibitory neurons express βAR248. By electron microscopy, βAR 248 was present in neuronal cell bodies, dendritic shafts and spines, and some axon terminals and astrocytes. When in dendrites and spines, βAR 248 was frequently concentrated along plasma membranes and at post-synaptic densities of asymmetric (excitatory) synapses. βAR 404 was expressed predominately in astrocytic cell bodies and processes. These astrocytic processes were frequently interposed between unlabeled terminals or ensheathed asymmetric synapses. Our findings provide a morphological basis for understanding ways in which NE may modulate transmission by acting via synaptic or non-synaptic mechanisms in the LA.

No MeSH data available.


Related in: MedlinePlus