Limits...
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.

Show MeSH

Related in: MedlinePlus

Effect of Trolox and DTT treatment on ramp-evoked currents when mitochondrial membrane potential was impaired with CCCP. (a) and (b), Mean differential I-V plots (i.e., Antioxidants-control) demonstrating the impact of 100 μM Trolox (a) and 1 mM DTT (b) cotreatments with 1 μM CCCP. Graph shows mean ± SEM with n = 13 for (a) and n = 6 for (b).
© Copyright Policy - open-access
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3345253&req=5

fig5: Effect of Trolox and DTT treatment on ramp-evoked currents when mitochondrial membrane potential was impaired with CCCP. (a) and (b), Mean differential I-V plots (i.e., Antioxidants-control) demonstrating the impact of 100 μM Trolox (a) and 1 mM DTT (b) cotreatments with 1 μM CCCP. Graph shows mean ± SEM with n = 13 for (a) and n = 6 for (b).

Mentions: Ramp protocols were used as they can reveal voltage-dependent currents, including those that flow during the interspike interval [16]. CCCP (1 μM) induced an initial differential outward (up to ~−20 mV) followed by an inward current during the ramp depolarization (Figure 5). Cotreatment with Trolox (100 μM) caused a small reduction in the CCCP-induced differential outward current between membrane potentials ~−40 mV to ~−30 mV (Figure 5(a)). DTT cotreatment in contrast had a more profound impact on the CCCP-induced differential outward current. It partially reversed the outward current and reduced it to less than half at its peak (Figure 5(b)). DTT co-treatment also shifted the reversal potential from ~80 mV to ~−60 mV, suggesting recruitment of different channels and/or modulation of the channel's selectivity to ions. These results suggest that the antioxidants Trolox and DTT can affect mitochondrial function either directly or by altering existing neuronal free radicals.


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)

Effect of Trolox and DTT treatment on ramp-evoked currents when mitochondrial membrane potential was impaired with CCCP. (a) and (b), Mean differential I-V plots (i.e., Antioxidants-control) demonstrating the impact of 100 μM Trolox (a) and 1 mM DTT (b) cotreatments with 1 μM CCCP. Graph shows mean ± SEM with n = 13 for (a) and n = 6 for (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Effect of Trolox and DTT treatment on ramp-evoked currents when mitochondrial membrane potential was impaired with CCCP. (a) and (b), Mean differential I-V plots (i.e., Antioxidants-control) demonstrating the impact of 100 μM Trolox (a) and 1 mM DTT (b) cotreatments with 1 μM CCCP. Graph shows mean ± SEM with n = 13 for (a) and n = 6 for (b).
Mentions: Ramp protocols were used as they can reveal voltage-dependent currents, including those that flow during the interspike interval [16]. CCCP (1 μM) induced an initial differential outward (up to ~−20 mV) followed by an inward current during the ramp depolarization (Figure 5). Cotreatment with Trolox (100 μM) caused a small reduction in the CCCP-induced differential outward current between membrane potentials ~−40 mV to ~−30 mV (Figure 5(a)). DTT cotreatment in contrast had a more profound impact on the CCCP-induced differential outward current. It partially reversed the outward current and reduced it to less than half at its peak (Figure 5(b)). DTT co-treatment also shifted the reversal potential from ~80 mV to ~−60 mV, suggesting recruitment of different channels and/or modulation of the channel's selectivity to ions. These results suggest that the antioxidants Trolox and DTT can affect mitochondrial function either directly or by altering existing neuronal free radicals.

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