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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 agonist on the ensemble Na+ current. (A) Representative traces showing the ensemble current evoked by the voltage step shown in the bottom schematic under control conditions (left, blue) and following bath application of SKF81297 (3 µM) (right, red). The resting membrane potential for this patch recorded after break-in is given by the dotted line in the bottom schematic. (B) Change in the average ensemble Na+ current amplitude evoked by a 50 mV voltage step above rest in single patches by SKF81297. Each dot represents the averaged ensemble Na+ current amplitude recorded for a single patch. Patches were stepped to a single voltage under control conditions and following bath application of SKF81297 (3 µM). * represents significance at p < 0.05. (C) Plots of the normalized peak conductances as a function of steps to various transmembrane potentials for PD, somatic and PA patches. Each dot represents the normalized peak conductance for a single patch. Lines represent Boltzmann fits under control conditions (blue) and in SKF81297 (red). Average half activation is given in the insets.
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Figure 5: The effects of the D1/D5 agonist on the ensemble Na+ current. (A) Representative traces showing the ensemble current evoked by the voltage step shown in the bottom schematic under control conditions (left, blue) and following bath application of SKF81297 (3 µM) (right, red). The resting membrane potential for this patch recorded after break-in is given by the dotted line in the bottom schematic. (B) Change in the average ensemble Na+ current amplitude evoked by a 50 mV voltage step above rest in single patches by SKF81297. Each dot represents the averaged ensemble Na+ current amplitude recorded for a single patch. Patches were stepped to a single voltage under control conditions and following bath application of SKF81297 (3 µM). * represents significance at p < 0.05. (C) Plots of the normalized peak conductances as a function of steps to various transmembrane potentials for PD, somatic and PA patches. Each dot represents the normalized peak conductance for a single patch. Lines represent Boltzmann fits under control conditions (blue) and in SKF81297 (red). Average half activation is given in the insets.

Mentions: The average ensemble response from a single PD patch under baseline and SKF81297 conditions is shown in Figure 5A for a voltage step to a transmembrane potential of −20 mV. It shows a moderate increase in the ensemble current in response to D1/D5 receptor stimulation. Figure 5B represents group data for the patches from the three regions. The amplitudes of the ensemble currents were increased by SKF81297 in PD patches by 28 ± 8 %, n = 6, in somatic patches by 23 ± 17 %, n = 6 and in PA patches by 25 ± 7 %, n = 5.


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 agonist on the ensemble Na+ current. (A) Representative traces showing the ensemble current evoked by the voltage step shown in the bottom schematic under control conditions (left, blue) and following bath application of SKF81297 (3 µM) (right, red). The resting membrane potential for this patch recorded after break-in is given by the dotted line in the bottom schematic. (B) Change in the average ensemble Na+ current amplitude evoked by a 50 mV voltage step above rest in single patches by SKF81297. Each dot represents the averaged ensemble Na+ current amplitude recorded for a single patch. Patches were stepped to a single voltage under control conditions and following bath application of SKF81297 (3 µM). * represents significance at p < 0.05. (C) Plots of the normalized peak conductances as a function of steps to various transmembrane potentials for PD, somatic and PA patches. Each dot represents the normalized peak conductance for a single patch. Lines represent Boltzmann fits under control conditions (blue) and in SKF81297 (red). Average half activation is given in the insets.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: The effects of the D1/D5 agonist on the ensemble Na+ current. (A) Representative traces showing the ensemble current evoked by the voltage step shown in the bottom schematic under control conditions (left, blue) and following bath application of SKF81297 (3 µM) (right, red). The resting membrane potential for this patch recorded after break-in is given by the dotted line in the bottom schematic. (B) Change in the average ensemble Na+ current amplitude evoked by a 50 mV voltage step above rest in single patches by SKF81297. Each dot represents the averaged ensemble Na+ current amplitude recorded for a single patch. Patches were stepped to a single voltage under control conditions and following bath application of SKF81297 (3 µM). * represents significance at p < 0.05. (C) Plots of the normalized peak conductances as a function of steps to various transmembrane potentials for PD, somatic and PA patches. Each dot represents the normalized peak conductance for a single patch. Lines represent Boltzmann fits under control conditions (blue) and in SKF81297 (red). Average half activation is given in the insets.
Mentions: The average ensemble response from a single PD patch under baseline and SKF81297 conditions is shown in Figure 5A for a voltage step to a transmembrane potential of −20 mV. It shows a moderate increase in the ensemble current in response to D1/D5 receptor stimulation. Figure 5B represents group data for the patches from the three regions. The amplitudes of the ensemble currents were increased by SKF81297 in PD patches by 28 ± 8 %, n = 6, in somatic patches by 23 ± 17 %, n = 6 and in PA patches by 25 ± 7 %, n = 5.

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