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Heterogeneous responses to antioxidants in noradrenergic neurons of the Locus coeruleus indicate differing susceptibility to free radical content.

de Oliveira RB, Gravina FS, Lim R, Brichta AM, Callister RJ, van Helden DF - Oxid Med Cell Longev (2012)

Bottom Line: In current clamp experiments, most neurons (55%; 6/11) did not respond to the antioxidants.Calcium and JC-1 imaging demonstrated that these effects did not change intracellular Ca(2+) concentration but may influence mitochondrial function as both antioxidant treatments modulated mitochondrial membrane potential.If this is the case, there may be a protective role for antioxidant therapies.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Sciences and Pharmacy, The University of Newcastle and Hunter Medical Research Institute, Newcastle, NSW 2308, Australia.

ABSTRACT
The present study investigated the effects of the antioxidants trolox and dithiothreitol (DTT) on mouse Locus coeruleus (LC) neurons. Electrophysiological measurement of action potential discharge and whole cell current responses in the presence of each antioxidant suggested that there are three neuronal subpopulations within the LC. In current clamp experiments, most neurons (55%; 6/11) did not respond to the antioxidants. The remaining neurons exhibited either hyperpolarization and decreased firing rate (27%; 3/11) or depolarization and increased firing rate (18%; 2/11). Calcium and JC-1 imaging demonstrated that these effects did not change intracellular Ca(2+) concentration but may influence mitochondrial function as both antioxidant treatments modulated mitochondrial membrane potential. These suggest that the antioxidant-sensitive subpopulations of LC neurons may be more susceptible to oxidative stress (e.g., due to ATP depletion and/or overactivation of Ca(2+)-dependent pathways). Indeed it may be that this subpopulation of LC neurons is preferentially destroyed in neurological pathologies such as Parkinson's disease. If this is the case, there may be a protective role for antioxidant therapies.

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Impact of Trolox treatment on pacemaker activity in LC neurons. (a) Table demonstrating the effect of 100 μM Trolox on the spontaneous firing of LC neurons and comparison of values obtained for action potentials (APs) before (ACSF) and 180 s after 100 μM Trolox treatment (n = 11 for spontaneous firing and n = 23 for AP comparison). (b) Comparison of the waveshape of averaged APs before (ACSF) and 180 s after application of 100 μM Trolox in ACSF (n = 23). Hyperpolarizing group was excluded from comparison demonstrated in a and b due to lack of APs at 180 s treatment. (c) and (d) Recordings demonstrating opposite effects induced by 100 μM Trolox which in a small number of cases depolarized neurons and increased firing (c) or hyperpolarized neurons which led to abolition of AP firing (d) (n = 11). AP firing recommenced in response to depolarization induced by current injection (d, Arrow).
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fig1: Impact of Trolox treatment on pacemaker activity in LC neurons. (a) Table demonstrating the effect of 100 μM Trolox on the spontaneous firing of LC neurons and comparison of values obtained for action potentials (APs) before (ACSF) and 180 s after 100 μM Trolox treatment (n = 11 for spontaneous firing and n = 23 for AP comparison). (b) Comparison of the waveshape of averaged APs before (ACSF) and 180 s after application of 100 μM Trolox in ACSF (n = 23). Hyperpolarizing group was excluded from comparison demonstrated in a and b due to lack of APs at 180 s treatment. (c) and (d) Recordings demonstrating opposite effects induced by 100 μM Trolox which in a small number of cases depolarized neurons and increased firing (c) or hyperpolarized neurons which led to abolition of AP firing (d) (n = 11). AP firing recommenced in response to depolarization induced by current injection (d, Arrow).

Mentions: We first examined the effects of antioxidants on spontaneous firing in LC neurons. Application of 100 μM Trolox had no significant effect on 6 of 11 neurons (Figure 1(a)). Curiously, under the same conditions, 2 neurons increased their firing rate (Figures 1(a) and 1(c)) and 3 neurons exhibited strong hyperpolarization, which abolished spontaneous firing. In such cases firing could be reinstated by repolarizing the membrane potential via current injection (Figures 1(a) and 1(d)). Comparison of averaged action potentials (APs) from test (100 μM Trolox) and control (ACSF) neurons showed that there were no differences in AP shape after 180 s of treatment (Figures 1(a) and 1(b)). The electrophysiological properties of neurons that did not respond and those that hyperpolarized were compared to examine whether the hyperpolarizing neurons were damaged. This comparison showed there were no differences in resting membrane potential, input resistance, firing frequency, and after hyperpolarization amplitude. This indicates that the hyperpolarizing neurons were not simply damaged or unhealthy neurons (See Supplementary Table in Supplementary Material available online at doi:10.1155/2012/820285).


Heterogeneous responses to antioxidants in noradrenergic neurons of the Locus coeruleus indicate differing susceptibility to free radical content.

de Oliveira RB, Gravina FS, Lim R, Brichta AM, Callister RJ, van Helden DF - Oxid Med Cell Longev (2012)

Impact of Trolox treatment on pacemaker activity in LC neurons. (a) Table demonstrating the effect of 100 μM Trolox on the spontaneous firing of LC neurons and comparison of values obtained for action potentials (APs) before (ACSF) and 180 s after 100 μM Trolox treatment (n = 11 for spontaneous firing and n = 23 for AP comparison). (b) Comparison of the waveshape of averaged APs before (ACSF) and 180 s after application of 100 μM Trolox in ACSF (n = 23). Hyperpolarizing group was excluded from comparison demonstrated in a and b due to lack of APs at 180 s treatment. (c) and (d) Recordings demonstrating opposite effects induced by 100 μM Trolox which in a small number of cases depolarized neurons and increased firing (c) or hyperpolarized neurons which led to abolition of AP firing (d) (n = 11). AP firing recommenced in response to depolarization induced by current injection (d, Arrow).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3345253&req=5

fig1: Impact of Trolox treatment on pacemaker activity in LC neurons. (a) Table demonstrating the effect of 100 μM Trolox on the spontaneous firing of LC neurons and comparison of values obtained for action potentials (APs) before (ACSF) and 180 s after 100 μM Trolox treatment (n = 11 for spontaneous firing and n = 23 for AP comparison). (b) Comparison of the waveshape of averaged APs before (ACSF) and 180 s after application of 100 μM Trolox in ACSF (n = 23). Hyperpolarizing group was excluded from comparison demonstrated in a and b due to lack of APs at 180 s treatment. (c) and (d) Recordings demonstrating opposite effects induced by 100 μM Trolox which in a small number of cases depolarized neurons and increased firing (c) or hyperpolarized neurons which led to abolition of AP firing (d) (n = 11). AP firing recommenced in response to depolarization induced by current injection (d, Arrow).
Mentions: We first examined the effects of antioxidants on spontaneous firing in LC neurons. Application of 100 μM Trolox had no significant effect on 6 of 11 neurons (Figure 1(a)). Curiously, under the same conditions, 2 neurons increased their firing rate (Figures 1(a) and 1(c)) and 3 neurons exhibited strong hyperpolarization, which abolished spontaneous firing. In such cases firing could be reinstated by repolarizing the membrane potential via current injection (Figures 1(a) and 1(d)). Comparison of averaged action potentials (APs) from test (100 μM Trolox) and control (ACSF) neurons showed that there were no differences in AP shape after 180 s of treatment (Figures 1(a) and 1(b)). The electrophysiological properties of neurons that did not respond and those that hyperpolarized were compared to examine whether the hyperpolarizing neurons were damaged. This comparison showed there were no differences in resting membrane potential, input resistance, firing frequency, and after hyperpolarization amplitude. This indicates that the hyperpolarizing neurons were not simply damaged or unhealthy neurons (See Supplementary Table in Supplementary Material available online at doi:10.1155/2012/820285).

Bottom Line: In current clamp experiments, most neurons (55%; 6/11) did not respond to the antioxidants.Calcium and JC-1 imaging demonstrated that these effects did not change intracellular Ca(2+) concentration but may influence mitochondrial function as both antioxidant treatments modulated mitochondrial membrane potential.If this is the case, there may be a protective role for antioxidant therapies.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Sciences and Pharmacy, The University of Newcastle and Hunter Medical Research Institute, Newcastle, NSW 2308, Australia.

ABSTRACT
The present study investigated the effects of the antioxidants trolox and dithiothreitol (DTT) on mouse Locus coeruleus (LC) neurons. Electrophysiological measurement of action potential discharge and whole cell current responses in the presence of each antioxidant suggested that there are three neuronal subpopulations within the LC. In current clamp experiments, most neurons (55%; 6/11) did not respond to the antioxidants. The remaining neurons exhibited either hyperpolarization and decreased firing rate (27%; 3/11) or depolarization and increased firing rate (18%; 2/11). Calcium and JC-1 imaging demonstrated that these effects did not change intracellular Ca(2+) concentration but may influence mitochondrial function as both antioxidant treatments modulated mitochondrial membrane potential. These suggest that the antioxidant-sensitive subpopulations of LC neurons may be more susceptible to oxidative stress (e.g., due to ATP depletion and/or overactivation of Ca(2+)-dependent pathways). Indeed it may be that this subpopulation of LC neurons is preferentially destroyed in neurological pathologies such as Parkinson's disease. If this is the case, there may be a protective role for antioxidant therapies.

Show MeSH
Related in: MedlinePlus