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Cell-attached single-channel recordings in intact prefrontal cortex pyramidal neurons reveal compartmentalized D1/D5 receptor modulation of the persistent sodium current.

Gorelova N, Seamans JK - Front Neural Circuits (2015)

Bottom Line: While past studies have tested the effects of dopamine on I(Nap), the results have been contradictory largely because of difficulties in measuring I(Nap) using somatic whole-cell recordings.As a result, D1/D5 receptor activation equalized the probability of prolonged burst occurrence across the proximal axosomatodendritic region.By circumventing the pitfalls of previous attempts to study the D1/D5 receptor modulation of I(Nap), we demonstrate conclusively that D1/D5 receptor activation can increase the I(Nap) generated proximally, however questions still remain as to how D1/D5 receptor modulates Na(+) currents in the more distal initial segment where most of the I Nap is normally generated.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry and Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

ABSTRACT
The persistent Na(+) current (I(Nap)) is believed to be an important target of dopamine modulation in prefrontal cortex (PFC) neurons. While past studies have tested the effects of dopamine on I(Nap), the results have been contradictory largely because of difficulties in measuring I(Nap) using somatic whole-cell recordings. To circumvent these confounds we used the cell-attached patch-clamp technique to record single Na(+) channels from the soma, proximal dendrite (PD) or proximal axon (PA) of intact prefrontal layer V pyramidal neurons. Under baseline conditions, numerous well resolved Na(+) channel openings were recorded that exhibited an extrapolated reversal potential of 73 mV, a slope conductance of 14-19 pS and were blocked by tetrodotoxin (TTX). While similar in most respects, the propensity to exhibit prolonged bursts lasting >40 ms was many fold greater in the axon than the soma or dendrite. Bath application of the D1/D5 receptor agonist SKF81297 shifted the ensemble current activation curve leftward and increased the number of late events recorded from the PD but not the soma or PA. However, the greatest effect was on prolonged bursting where the D1/D5 receptor agonist increased their occurrence 3 fold in the PD and nearly 7 fold in the soma, but not at all in the PA. As a result, D1/D5 receptor activation equalized the probability of prolonged burst occurrence across the proximal axosomatodendritic region. Therefore, D1/D5 receptor modulation appears to be targeted mainly to Na(+) channels in the PD/soma and not the PA. By circumventing the pitfalls of previous attempts to study the D1/D5 receptor modulation of I(Nap), we demonstrate conclusively that D1/D5 receptor activation can increase the I(Nap) generated proximally, however questions still remain as to how D1/D5 receptor modulates Na(+) currents in the more distal initial segment where most of the I Nap is normally generated.

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The effects of the D1/D5 receptor agonist on prolonged burst openings. Prolonged burst openings were openings of Na+ channels that lasted >40 ms. Such bursts were recorded when the patch was stepped from −20 mV below rest to 50 mV above rest under control conditions (open bars). Although the frequencies were highest in the PA under baseline conditions, SKF81297 (3 µM) increased the probability that they would occur in the soma and PD but not in the PA. ***represents significance at p < 0.001, *represents significance at p < 0.01.
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Figure 8: The effects of the D1/D5 receptor agonist on prolonged burst openings. Prolonged burst openings were openings of Na+ channels that lasted >40 ms. Such bursts were recorded when the patch was stepped from −20 mV below rest to 50 mV above rest under control conditions (open bars). Although the frequencies were highest in the PA under baseline conditions, SKF81297 (3 µM) increased the probability that they would occur in the soma and PD but not in the PA. ***represents significance at p < 0.001, *represents significance at p < 0.01.

Mentions: Finally we analyzed the effect of SKF81297 on prolonged bursts. First we analyzed the probability of channel entering the prolonged burst mode in patches subjected to 50 mV depolarizing steps in control and during D1/D5 agonist application. For each region we calculated the number of prolonged openings for all patches and divided this number by the total number of traces multiplied by the number of channels in each patch. The probability of prolonged burst were higher during D1/D5 agonist application compared to the control in the PD (0.000282 in control vs. 0.000783 in SKF81297) and the soma (0.000212 in control vs. 0.001575 in SKF81297) but not the PA (0.000562 in control vs. 0.000631 in SKF81297). The low probability of prolonged bursts prevented us from performing statistical comparisons on these data. To overcome this, we calculated the probability of prolonged openings in control patches and in a separate group of patches that were exposed to the D1/D5 receptor agonist. Each patch was subjected to a series of steps to several membrane potentials, totaling ~1000 traces for each patch. The probability of prolonged bursts was calculated for each patch. Even though prolonged bursts were many fold more prevalent in the PA than the PD or soma under baseline conditions, SKF81297 increased the mean probability of their occurrence only in the PD (t12 = 6.42, p = 0.0003) and the soma (t10 = 2.36, p = 0.01) but not the PA (t10 = −0.59, p = 0.48) (Figure 8). In fact, the D1/D5 receptor agonist brought the prevalence of prolonged bursts in the PD and soma to the level of the PA under baseline conditions (Figure 8) and therefore selectively boosted the relative impact of INap in these regions. This tendency to promote prolonged bursting was the most significant effect of the D1/D5 receptor agonist on INap overall yet is very consistent with the conclusion above, that the drug also increased the propensity of Na+ channels to open in shorter bursts.


Cell-attached single-channel recordings in intact prefrontal cortex pyramidal neurons reveal compartmentalized D1/D5 receptor modulation of the persistent sodium current.

Gorelova N, Seamans JK - Front Neural Circuits (2015)

The effects of the D1/D5 receptor agonist on prolonged burst openings. Prolonged burst openings were openings of Na+ channels that lasted >40 ms. Such bursts were recorded when the patch was stepped from −20 mV below rest to 50 mV above rest under control conditions (open bars). Although the frequencies were highest in the PA under baseline conditions, SKF81297 (3 µM) increased the probability that they would occur in the soma and PD but not in the PA. ***represents significance at p < 0.001, *represents significance at p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4325928&req=5

Figure 8: The effects of the D1/D5 receptor agonist on prolonged burst openings. Prolonged burst openings were openings of Na+ channels that lasted >40 ms. Such bursts were recorded when the patch was stepped from −20 mV below rest to 50 mV above rest under control conditions (open bars). Although the frequencies were highest in the PA under baseline conditions, SKF81297 (3 µM) increased the probability that they would occur in the soma and PD but not in the PA. ***represents significance at p < 0.001, *represents significance at p < 0.01.
Mentions: Finally we analyzed the effect of SKF81297 on prolonged bursts. First we analyzed the probability of channel entering the prolonged burst mode in patches subjected to 50 mV depolarizing steps in control and during D1/D5 agonist application. For each region we calculated the number of prolonged openings for all patches and divided this number by the total number of traces multiplied by the number of channels in each patch. The probability of prolonged burst were higher during D1/D5 agonist application compared to the control in the PD (0.000282 in control vs. 0.000783 in SKF81297) and the soma (0.000212 in control vs. 0.001575 in SKF81297) but not the PA (0.000562 in control vs. 0.000631 in SKF81297). The low probability of prolonged bursts prevented us from performing statistical comparisons on these data. To overcome this, we calculated the probability of prolonged openings in control patches and in a separate group of patches that were exposed to the D1/D5 receptor agonist. Each patch was subjected to a series of steps to several membrane potentials, totaling ~1000 traces for each patch. The probability of prolonged bursts was calculated for each patch. Even though prolonged bursts were many fold more prevalent in the PA than the PD or soma under baseline conditions, SKF81297 increased the mean probability of their occurrence only in the PD (t12 = 6.42, p = 0.0003) and the soma (t10 = 2.36, p = 0.01) but not the PA (t10 = −0.59, p = 0.48) (Figure 8). In fact, the D1/D5 receptor agonist brought the prevalence of prolonged bursts in the PD and soma to the level of the PA under baseline conditions (Figure 8) and therefore selectively boosted the relative impact of INap in these regions. This tendency to promote prolonged bursting was the most significant effect of the D1/D5 receptor agonist on INap overall yet is very consistent with the conclusion above, that the drug also increased the propensity of Na+ channels to open in shorter bursts.

Bottom Line: While past studies have tested the effects of dopamine on I(Nap), the results have been contradictory largely because of difficulties in measuring I(Nap) using somatic whole-cell recordings.As a result, D1/D5 receptor activation equalized the probability of prolonged burst occurrence across the proximal axosomatodendritic region.By circumventing the pitfalls of previous attempts to study the D1/D5 receptor modulation of I(Nap), we demonstrate conclusively that D1/D5 receptor activation can increase the I(Nap) generated proximally, however questions still remain as to how D1/D5 receptor modulates Na(+) currents in the more distal initial segment where most of the I Nap is normally generated.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry and Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

ABSTRACT
The persistent Na(+) current (I(Nap)) is believed to be an important target of dopamine modulation in prefrontal cortex (PFC) neurons. While past studies have tested the effects of dopamine on I(Nap), the results have been contradictory largely because of difficulties in measuring I(Nap) using somatic whole-cell recordings. To circumvent these confounds we used the cell-attached patch-clamp technique to record single Na(+) channels from the soma, proximal dendrite (PD) or proximal axon (PA) of intact prefrontal layer V pyramidal neurons. Under baseline conditions, numerous well resolved Na(+) channel openings were recorded that exhibited an extrapolated reversal potential of 73 mV, a slope conductance of 14-19 pS and were blocked by tetrodotoxin (TTX). While similar in most respects, the propensity to exhibit prolonged bursts lasting >40 ms was many fold greater in the axon than the soma or dendrite. Bath application of the D1/D5 receptor agonist SKF81297 shifted the ensemble current activation curve leftward and increased the number of late events recorded from the PD but not the soma or PA. However, the greatest effect was on prolonged bursting where the D1/D5 receptor agonist increased their occurrence 3 fold in the PD and nearly 7 fold in the soma, but not at all in the PA. As a result, D1/D5 receptor activation equalized the probability of prolonged burst occurrence across the proximal axosomatodendritic region. Therefore, D1/D5 receptor modulation appears to be targeted mainly to Na(+) channels in the PD/soma and not the PA. By circumventing the pitfalls of previous attempts to study the D1/D5 receptor modulation of I(Nap), we demonstrate conclusively that D1/D5 receptor activation can increase the I(Nap) generated proximally, however questions still remain as to how D1/D5 receptor modulates Na(+) currents in the more distal initial segment where most of the I Nap is normally generated.

Show MeSH
Related in: MedlinePlus