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GABA Signaling and Neuroactive Steroids in Adrenal Medullary Chromaffin Cells.

Harada K, Matsuoka H, Fujihara H, Ueta Y, Yanagawa Y, Inoue M - Front Cell Neurosci (2016)

Bottom Line: GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect.This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs).In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Systems Physiology, University of Occupational and Environmental Health School of Medicine Kitakyushu, Japan.

ABSTRACT
Gamma-aminobutyric acid (GABA) is produced not only in the brain, but also in endocrine cells by the two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67. In rat adrenal medullary chromaffin cells only GAD67 is expressed, and GABA is stored in large dense core vesicles (LDCVs), but not synaptic-like microvesicles (SLMVs). The α3β2/3γ2 complex represents the majority of GABAA receptors expressed in rat and guinea pig chromaffin cells, whereas PC12 cells, an immortalized rat chromaffin cell line, express the α1 subunit as well as the α3. The expression of α3, but not α1, in PC12 cells is enhanced by glucocorticoid activity, which may be mediated by both the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect. Allopregnanolone, a neuroactive steroid which is secreted from the adrenal cortex, produces a marked facilitation of GABAA receptor channel activity. Since there are no GABAergic nerve fibers in the adrenal medulla, GABA may function as a para/autocrine factor in the chromaffin cells. This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs). In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.

No MeSH data available.


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Immunostaining for glutamic acid decarboxylase (GAD) and vesicular GABA transporter (VGAT) in rat adrenal medullary chromaffin cells. (A) Immunohistochemistry for GAD in rat adrenal gland. Sections were incubated overnight in PBS with (GAD) or without (PBS) rabbit anti-GAD antibody (Ab). The bound Ab was detected with the indirect immunoperoxidase method. The middle panel represents an enlargement of the area indicated by the square in the left panel. (B) Immunocytochemistry for VGAT in a dissociated rat adrenal medullary cell. The adrenal medulla was treated with collagenase and then cells were mechanically dissociated with needles. The cells were treated overnight with rabbit anti-VGAT Ab and goat anti-chromogranin A (CgA) Ab and then with secondary Abs conjugated with Alexa 488 and Alexa 546. Images from left to right represent differential interference contrast (DIC), rhodamine-like, FITC-like, and merge of the second and the third. (A,B) Are reproduced from Matsuoka et al. (2008).
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Figure 1: Immunostaining for glutamic acid decarboxylase (GAD) and vesicular GABA transporter (VGAT) in rat adrenal medullary chromaffin cells. (A) Immunohistochemistry for GAD in rat adrenal gland. Sections were incubated overnight in PBS with (GAD) or without (PBS) rabbit anti-GAD antibody (Ab). The bound Ab was detected with the indirect immunoperoxidase method. The middle panel represents an enlargement of the area indicated by the square in the left panel. (B) Immunocytochemistry for VGAT in a dissociated rat adrenal medullary cell. The adrenal medulla was treated with collagenase and then cells were mechanically dissociated with needles. The cells were treated overnight with rabbit anti-VGAT Ab and goat anti-chromogranin A (CgA) Ab and then with secondary Abs conjugated with Alexa 488 and Alexa 546. Images from left to right represent differential interference contrast (DIC), rhodamine-like, FITC-like, and merge of the second and the third. (A,B) Are reproduced from Matsuoka et al. (2008).

Mentions: When the localization of GABA was examined in bovine, dog and mouse adrenal medullae with immune-labeling approaches, GAD- and/or GABA-like immunoreactivities (IRs) were detected in chromaffin cells and nerve fiber-like structures (Kataoka et al., 1984, 1986; Iwasa et al., 1998). Previously, retrograde tracing had revealed that several areas in the brain and the spinal cord had materials that were retrogradely transported from the rat adrenal medulla (Mohamed et al., 1988; Coupland et al., 1989). Thus, it is possible that neurons in such areas send GABAergic nerve fibers to adrenal chromaffin cells. However, this idea has not been supported by pharmacological analyses of neuronal transmission. Fast synaptic currents evoked in slices of the rat adrenal medulla by field stimulation were completely suppressed by application of hexamethonium, a nicotinic ACh receptor blocker (Barbara and Takeda, 1996; Kajiwara et al., 1997). These electrophysiological findings would negate the possible innervation by GABAergic fibers in the adrenal medulla. This notion is further supported by immunostaining for GAD and vesicular GABA transporter (VGAT), which is involved in the uptake of GABA into vesicles. GAD proteins were recognized in the rat adrenal medulla by immunoblotting, and GAD-like IR was present in rat adrenal chromaffin cells but not in fiber-like structures (Figure 1). Furthermore, the mRNA for GAD67, but not GAD65, was detected in rat adrenal medullae by RT-PCR analysis (Matsuoka et al., 2008; Inoue et al., 2010), suggesting that the GAD activity was not in nerve terminals. VGAT was also detected in rat adrenal chromaffin cells at the mRNA and protein levels (Matsuoka et al., 2008). The immunostaining for GAD and VGAT unambiguously indicate that GABA is synthesized in chromaffin cells, but not nerve fibers, in the adrenal medulla of at least rats.


GABA Signaling and Neuroactive Steroids in Adrenal Medullary Chromaffin Cells.

Harada K, Matsuoka H, Fujihara H, Ueta Y, Yanagawa Y, Inoue M - Front Cell Neurosci (2016)

Immunostaining for glutamic acid decarboxylase (GAD) and vesicular GABA transporter (VGAT) in rat adrenal medullary chromaffin cells. (A) Immunohistochemistry for GAD in rat adrenal gland. Sections were incubated overnight in PBS with (GAD) or without (PBS) rabbit anti-GAD antibody (Ab). The bound Ab was detected with the indirect immunoperoxidase method. The middle panel represents an enlargement of the area indicated by the square in the left panel. (B) Immunocytochemistry for VGAT in a dissociated rat adrenal medullary cell. The adrenal medulla was treated with collagenase and then cells were mechanically dissociated with needles. The cells were treated overnight with rabbit anti-VGAT Ab and goat anti-chromogranin A (CgA) Ab and then with secondary Abs conjugated with Alexa 488 and Alexa 546. Images from left to right represent differential interference contrast (DIC), rhodamine-like, FITC-like, and merge of the second and the third. (A,B) Are reproduced from Matsuoka et al. (2008).
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Related In: Results  -  Collection

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Figure 1: Immunostaining for glutamic acid decarboxylase (GAD) and vesicular GABA transporter (VGAT) in rat adrenal medullary chromaffin cells. (A) Immunohistochemistry for GAD in rat adrenal gland. Sections were incubated overnight in PBS with (GAD) or without (PBS) rabbit anti-GAD antibody (Ab). The bound Ab was detected with the indirect immunoperoxidase method. The middle panel represents an enlargement of the area indicated by the square in the left panel. (B) Immunocytochemistry for VGAT in a dissociated rat adrenal medullary cell. The adrenal medulla was treated with collagenase and then cells were mechanically dissociated with needles. The cells were treated overnight with rabbit anti-VGAT Ab and goat anti-chromogranin A (CgA) Ab and then with secondary Abs conjugated with Alexa 488 and Alexa 546. Images from left to right represent differential interference contrast (DIC), rhodamine-like, FITC-like, and merge of the second and the third. (A,B) Are reproduced from Matsuoka et al. (2008).
Mentions: When the localization of GABA was examined in bovine, dog and mouse adrenal medullae with immune-labeling approaches, GAD- and/or GABA-like immunoreactivities (IRs) were detected in chromaffin cells and nerve fiber-like structures (Kataoka et al., 1984, 1986; Iwasa et al., 1998). Previously, retrograde tracing had revealed that several areas in the brain and the spinal cord had materials that were retrogradely transported from the rat adrenal medulla (Mohamed et al., 1988; Coupland et al., 1989). Thus, it is possible that neurons in such areas send GABAergic nerve fibers to adrenal chromaffin cells. However, this idea has not been supported by pharmacological analyses of neuronal transmission. Fast synaptic currents evoked in slices of the rat adrenal medulla by field stimulation were completely suppressed by application of hexamethonium, a nicotinic ACh receptor blocker (Barbara and Takeda, 1996; Kajiwara et al., 1997). These electrophysiological findings would negate the possible innervation by GABAergic fibers in the adrenal medulla. This notion is further supported by immunostaining for GAD and vesicular GABA transporter (VGAT), which is involved in the uptake of GABA into vesicles. GAD proteins were recognized in the rat adrenal medulla by immunoblotting, and GAD-like IR was present in rat adrenal chromaffin cells but not in fiber-like structures (Figure 1). Furthermore, the mRNA for GAD67, but not GAD65, was detected in rat adrenal medullae by RT-PCR analysis (Matsuoka et al., 2008; Inoue et al., 2010), suggesting that the GAD activity was not in nerve terminals. VGAT was also detected in rat adrenal chromaffin cells at the mRNA and protein levels (Matsuoka et al., 2008). The immunostaining for GAD and VGAT unambiguously indicate that GABA is synthesized in chromaffin cells, but not nerve fibers, in the adrenal medulla of at least rats.

Bottom Line: GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect.This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs).In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Systems Physiology, University of Occupational and Environmental Health School of Medicine Kitakyushu, Japan.

ABSTRACT
Gamma-aminobutyric acid (GABA) is produced not only in the brain, but also in endocrine cells by the two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67. In rat adrenal medullary chromaffin cells only GAD67 is expressed, and GABA is stored in large dense core vesicles (LDCVs), but not synaptic-like microvesicles (SLMVs). The α3β2/3γ2 complex represents the majority of GABAA receptors expressed in rat and guinea pig chromaffin cells, whereas PC12 cells, an immortalized rat chromaffin cell line, express the α1 subunit as well as the α3. The expression of α3, but not α1, in PC12 cells is enhanced by glucocorticoid activity, which may be mediated by both the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect. Allopregnanolone, a neuroactive steroid which is secreted from the adrenal cortex, produces a marked facilitation of GABAA receptor channel activity. Since there are no GABAergic nerve fibers in the adrenal medulla, GABA may function as a para/autocrine factor in the chromaffin cells. This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs). In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.

No MeSH data available.


Related in: MedlinePlus