Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 Jul;114(1):698-706.
doi: 10.1152/jn.00209.2015. Epub 2015 May 20.

Diabetes induces GABA receptor plasticity in murine vagal motor neurons

C R Boychuk  1 , K Cs Halmos  1 , B N Smith  2
Affiliations

Diabetes induces GABA receptor plasticity in murine vagal motor neurons

C R Boychuk et al. J Neurophysiol. 2015 Jul.

Abstract

Autonomic dysregulation accompanies type-1 diabetes, and synaptic regulation of parasympathetic preganglionic motor neurons in the dorsal motor nucleus of the vagus (DMV) is altered after chronic hyperglycemia/hypoinsulinemia. Tonic gamma-aminobutyric acid A (GABAA) inhibition prominently regulates DMV neuron activity, which contributes to autonomic control of energy homeostasis. This study investigated persistent effects of chronic hyperglycemia/hypoinsulinemia on GABAA receptor-mediated inhibition in the DMV after streptozotocin-induced type-1 diabetes using electrophysiological recordings in vitro, quantitative (q)RT-PCR, and immunohistochemistry. Application of the nonspecific GABAA receptor agonist muscimol evoked an outward current of significantly larger amplitude in DMV neurons from diabetic mice than controls. Results from application of 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol hydrochloride (THIP), a δ-subunit agonist, suggested that GABAA receptors containing δ-subunits contributed to the enhanced inducible tonic GABA current in diabetic mice. Sensitivity to THIP of inhibitory postsynaptic currents in DMV neurons from diabetic mice was also increased. Results from qRT-PCR and immunohistochemical analyses indicated that the altered GABAergic inhibition may be related to increased trafficking of GABAA receptors that contain the δ-subunit, rather than an expression change. Overall these findings suggest increased sensitivity of δ-subunit containing GABAA receptors after several days of hyperglycemia/hypoinsulinemia, which dramatically alters GABAergic inhibition of DMV neurons and could contribute to diabetic autonomic dysregulation.

Keywords: GABA; diabetes; tonic current.

PubMed Disclaimer

Figures

Fig. 1.
Fig. 1.
Increased tonic currents induced by gamma-aminobutyric acid A (GABAA) receptor activation in dorsal motor nucleus of the vagus (DMV) neurons from STZ-treated mice. A: representative traces from saline (top)- and streptozotocin-treated (bottom) mice during application of muscimol (MUS; 75 nM), followed by bicuculline methiodide (BIC) application. B: pie graph illustrating the number of neurons in both saline- (6/9) and STZ-treated (5/7) animals that demonstrated significant MUS-induced tonic currents (>5.8 pA). C: mean MUS-induced tonic current density for saline- (n = 9) and STZ-treated (n = 7) mice, with overlaid points denoting individual neuronal responses. D: mean MUS-BIC tonic current density for each treatment, with overlaid points denoting individual neuronal responses. E: group statistics for current density in those neurons displaying a significant MUS-induced component (i.e., responders). Tonic currents were measured in C as the difference from baseline holding current to steady-state holding current in the presence of MUS (MUS-induced) and in D as the difference from MUS steady-state holding current to steady-state holding current after addition of BIC (MUS-BIC). Dashed lines in A represent these points. *Significant differences with a two-tailed t-test (P < 0.05); **Significant differences with a one-tailed t-test.
Fig. 2.
Fig. 2.
Dose-dependent 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol hydrochloride (THIP) sensitivity in DMV neurons. Mean inducible tonic current density evoked by THIP application for saline- and STZ-treated mice with 3 different doses of THIP (1, 3, and 10 μM).
Fig. 3.
Fig. 3.
Increased tonic currents after THIP application in DMV neurons from STZ-treated mice. A: representative tracings from saline (top)- and STZ-treated (bottom) mice during application of THIP (3 μM), followed by BIC application. B: pie graph illustrating the number of DMV neurons in saline (3/9)- and STZ-treated (7/9) mice that demonstrated significant THIP-induced tonic currents (i.e., >5.8 pA). C: mean THIP-induced tonic current density in DMV neurons from saline (n = 9)- and STZ-treated mice (n = 9); individual neuronal responses are also shown. D: mean THIP-BIC tonic current density for each treatment, with overlaid points denoting responses of individual neurons. E: group statistics for current density of only those neurons with a significant THIP-induced component. Tonic currents were measured in C as the difference from baseline holding current to steady-state holding current after THIP (THIP-Induced) and in D as the difference from THIP steady-state holding current to steady-state holding current in BIC (THIP-BIC). Dashed lines in A represent these points. *Significant differences with a two-tailed t-test (P < 0.05); **Significant differences with a one-tailed t-test.
Fig. 4.
Fig. 4.
Increased spontaneous inhibitory postsynaptic current (sIPSC) decay time constant after THIP application in DMV neurons from STZ-treated mice. A: averaged sIPSCs from saline (left)- and STZ-treated (right) mice at baseline (black lines) and after application of THIP (grey lines). Traces have been normalized for amplitude. Averages of 74 to 918 individual IPSCs are shown for each condition. B: mean percent change in sIPSC decay time constant after THIP application in neurons from saline (n = 9)- and STZ-treated (n = 9) mice. C: mean percent change in sIPSC frequency after THIP application. D: mean percent change in sIPSC amplitude after THIP application. No significant THIP-induced change in sIPSC frequency or amplitude was detected. *Significant differences with a two-tailed t-test (P < 0.05). Note: negative value denotes a decrease from baseline.
Fig. 5.
Fig. 5.
Relative mRNA abundance of 2 GABAA receptor subunits in the vagal complex. A: mean fold change of the GABAA receptor α4-subunit in the vagal complex of saline (n = 8)- and STZ-treated (n = 7) mice. B: mean fold change of the GABAA receptor δ-subunit for both groups.
Fig. 6.
Fig. 6.
Immunohistochemical labeling of δ-subunit-containing GABAA receptors in cholinergic DMV neurons. Representative images showing immunohistochemical labeling of choline acetyltransferase (ChAT; A and D) and the GABAA receptor δ-subunit (B and E) in the DMV. Neuronal nuclei are marked with asterisks in A, B, D, and E. Merged images are shown in C and F. DMV neurons from saline-treated mice (top; A-C) displayed light diffuse staining. In the DMV from diabetic mice (bottom; D-F), bright puncta, usually near the membrane, were consistently observed (arrows).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abramian AM, Comenencia-Ortiz E, Modgil A, Vien TN, Nakamura Y, Moore YE, Maguire JL, Terunuma M, Davies PA, Moss SJ. Neurosteroids promote phosphorylation and membrane insertion of extrasynaptic GABAA receptors. Proc Natl Acad Sci USA 111: 7132–7137, 2014. - PMC - PubMed
    1. Abramian AM, Comenencia-Ortiz E, Vithlani M, Tretter EV, Sieghart W, Davies PA, Moss SJ. Protein kinase C phosphorylation regulates membrane insertion of GABAA receptor subtypes that mediate tonic inhibition. J Biol Chem 285: 41795–41805, 2010. - PMC - PubMed
    1. Ahren B. Autonomic regulation of islet hormone secretion–implications for health and disease. Diabetologia 43: 393–410, 2000. - PubMed
    1. Ataka T, Gu JG. Relationship between tonic inhibitory currents and phasic inhibitory activity in the spinal cord lamina II region of adult mice. Mol Pain 2: 36, 2006. - PMC - PubMed
    1. Bach EC, Halmos KC, Smith BN. Enhanced NMDA receptor-mediated modulation of excitatory neurotransmission in the dorsal vagal complex of streptozotocin-treated, chronically hyperglycemic mice. PLoS One 10: e0121022, 2015. - PMC - PubMed

Publication types

MeSH terms

LinkOut - more resources