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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 D1/D5 receptor antagonist blocks the effect of the D1/D5 agonist on the late Na+ channel openings. Quantification of the effects of the D1/D5 agonist (3 µM SKF81297) in the presence of the D1/D5 receptor antagonist (3 µM SCH23390) on the average number of late openings (per channel, per sweep) (left), the open probability (middle) and the average dwell time (right) of single Na+ channels recorded from the PD during a 70 mV depolarizing step. Patches were held 20 mV more negative than resting membrane potential. Each pair of connected dots represents data from the same patch.
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Figure 7: The D1/D5 receptor antagonist blocks the effect of the D1/D5 agonist on the late Na+ channel openings. Quantification of the effects of the D1/D5 agonist (3 µM SKF81297) in the presence of the D1/D5 receptor antagonist (3 µM SCH23390) on the average number of late openings (per channel, per sweep) (left), the open probability (middle) and the average dwell time (right) of single Na+ channels recorded from the PD during a 70 mV depolarizing step. Patches were held 20 mV more negative than resting membrane potential. Each pair of connected dots represents data from the same patch.

Mentions: In order to confirm that the above effect of SKF81297 on Na+ channel gating in the PD was due to D1/D5 receptor activation, we tested if the D1/D5 receptor antagonist SCH23390 could block the effect of SKF81297 by applying SCH23390 (3 µM) 10 min before application of SKF81297(3 µM). As can be seen in Figure 7, when the D1/D5 receptor agonist was applied in the presence of a D1/D5 receptor antagonist, no increase in either the number of late channel openings (0.24 ± 0.0049 in SCH23390 control vs. 0.21 ± 0.052 in SKF81297 + SCH23390, t4 = 2.23, p = 0.09), the channel open probability (0.0015 ± 0.0003 in SCH23390 control vs. 0.0014 ± 0.0003 in SKF81297 + SCH23390, t4 = 4.7, p = 0.009) or the dwell time (0.457 ± 0.037 ms in SCH23390 control vs. 0.486 ± 0.073 ms in SKF81297 + SCH23390, t4 = 0.66, p = 0.55) was observed.


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 D1/D5 receptor antagonist blocks the effect of the D1/D5 agonist on the late Na+ channel openings. Quantification of the effects of the D1/D5 agonist (3 µM SKF81297) in the presence of the D1/D5 receptor antagonist (3 µM SCH23390) on the average number of late openings (per channel, per sweep) (left), the open probability (middle) and the average dwell time (right) of single Na+ channels recorded from the PD during a 70 mV depolarizing step. Patches were held 20 mV more negative than resting membrane potential. Each pair of connected dots represents data from the same patch.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: The D1/D5 receptor antagonist blocks the effect of the D1/D5 agonist on the late Na+ channel openings. Quantification of the effects of the D1/D5 agonist (3 µM SKF81297) in the presence of the D1/D5 receptor antagonist (3 µM SCH23390) on the average number of late openings (per channel, per sweep) (left), the open probability (middle) and the average dwell time (right) of single Na+ channels recorded from the PD during a 70 mV depolarizing step. Patches were held 20 mV more negative than resting membrane potential. Each pair of connected dots represents data from the same patch.
Mentions: In order to confirm that the above effect of SKF81297 on Na+ channel gating in the PD was due to D1/D5 receptor activation, we tested if the D1/D5 receptor antagonist SCH23390 could block the effect of SKF81297 by applying SCH23390 (3 µM) 10 min before application of SKF81297(3 µM). As can be seen in Figure 7, when the D1/D5 receptor agonist was applied in the presence of a D1/D5 receptor antagonist, no increase in either the number of late channel openings (0.24 ± 0.0049 in SCH23390 control vs. 0.21 ± 0.052 in SKF81297 + SCH23390, t4 = 2.23, p = 0.09), the channel open probability (0.0015 ± 0.0003 in SCH23390 control vs. 0.0014 ± 0.0003 in SKF81297 + SCH23390, t4 = 4.7, p = 0.009) or the dwell time (0.457 ± 0.037 ms in SCH23390 control vs. 0.486 ± 0.073 ms in SKF81297 + SCH23390, t4 = 0.66, p = 0.55) was observed.

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