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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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Properties of ensemble Na+ currents. (A) Representative recordings (top) from a PD patch showing the ensemble Na+ currents evoked by various amplitude voltage steps from a holding potential −20 mV hyperpolarized from rest. Each line is an average of >60 individual traces. The transmembrane potential is given by the gray dotted line in the bottom schematic. (B) The I-V plot of the patch shown in (A). In this graph the x-axis is the transmembrane voltage to which the patch was stepped and the y-axis is the peak single channel current. (C) Plots of normalized peak conductances as a function of steps to various transmembrane potentials for groups of patches from the PD (blue), soma (purple) and PA (green). Each dot represents the normalized conductance for a single patch. The lines are Boltzmann fits.
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Figure 3: Properties of ensemble Na+ currents. (A) Representative recordings (top) from a PD patch showing the ensemble Na+ currents evoked by various amplitude voltage steps from a holding potential −20 mV hyperpolarized from rest. Each line is an average of >60 individual traces. The transmembrane potential is given by the gray dotted line in the bottom schematic. (B) The I-V plot of the patch shown in (A). In this graph the x-axis is the transmembrane voltage to which the patch was stepped and the y-axis is the peak single channel current. (C) Plots of normalized peak conductances as a function of steps to various transmembrane potentials for groups of patches from the PD (blue), soma (purple) and PA (green). Each dot represents the normalized conductance for a single patch. The lines are Boltzmann fits.

Mentions: Next we characterized the ensemble currents produced by summing over numerous single sweeps (Figure 3A). For these experiments patches were held −40 mV below rest and a series of voltage steps 20–80 mV above rest were delivered. Even for patches with the smallest N, an ensemble current could always be observed by averaging hundreds traces following a voltage step to −20 mV. However, for constructing I-V plots we only used patches containing more than 6 channels. Figure 3B describes the I-V relationship of the ensemble current depicted in Figure 3A. We used two approaches to calculate the average half activation voltage (Vmid) for each region. First, Boltzmann fits to the normalized conductances for each patch were performed and the average Vmid was then calculated. The resultant Vmid values were not different between regions: −16.1 ± 1.11 mV, n = 6 for the PD vs. −16.4 ± 2.65 mV, n = 5 for the soma vs. 16.5 ± mV, n = 5 for the PA (F(2,14) = 0.04, p = 0.96). Second, for each region we combined the normalized conductance values from all single patches into a single plot and then performed the Boltzmann fits (Figure 3C). The obtained values of Vmid were similar to the first approach and were −16.4 ± 0.65 mV for the PD, −16.2 ± 1.04 mV for the soma and 16.14 ± 0.72 for the PA.


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)

Properties of ensemble Na+ currents. (A) Representative recordings (top) from a PD patch showing the ensemble Na+ currents evoked by various amplitude voltage steps from a holding potential −20 mV hyperpolarized from rest. Each line is an average of >60 individual traces. The transmembrane potential is given by the gray dotted line in the bottom schematic. (B) The I-V plot of the patch shown in (A). In this graph the x-axis is the transmembrane voltage to which the patch was stepped and the y-axis is the peak single channel current. (C) Plots of normalized peak conductances as a function of steps to various transmembrane potentials for groups of patches from the PD (blue), soma (purple) and PA (green). Each dot represents the normalized conductance for a single patch. The lines are Boltzmann fits.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Properties of ensemble Na+ currents. (A) Representative recordings (top) from a PD patch showing the ensemble Na+ currents evoked by various amplitude voltage steps from a holding potential −20 mV hyperpolarized from rest. Each line is an average of >60 individual traces. The transmembrane potential is given by the gray dotted line in the bottom schematic. (B) The I-V plot of the patch shown in (A). In this graph the x-axis is the transmembrane voltage to which the patch was stepped and the y-axis is the peak single channel current. (C) Plots of normalized peak conductances as a function of steps to various transmembrane potentials for groups of patches from the PD (blue), soma (purple) and PA (green). Each dot represents the normalized conductance for a single patch. The lines are Boltzmann fits.
Mentions: Next we characterized the ensemble currents produced by summing over numerous single sweeps (Figure 3A). For these experiments patches were held −40 mV below rest and a series of voltage steps 20–80 mV above rest were delivered. Even for patches with the smallest N, an ensemble current could always be observed by averaging hundreds traces following a voltage step to −20 mV. However, for constructing I-V plots we only used patches containing more than 6 channels. Figure 3B describes the I-V relationship of the ensemble current depicted in Figure 3A. We used two approaches to calculate the average half activation voltage (Vmid) for each region. First, Boltzmann fits to the normalized conductances for each patch were performed and the average Vmid was then calculated. The resultant Vmid values were not different between regions: −16.1 ± 1.11 mV, n = 6 for the PD vs. −16.4 ± 2.65 mV, n = 5 for the soma vs. 16.5 ± mV, n = 5 for the PA (F(2,14) = 0.04, p = 0.96). Second, for each region we combined the normalized conductance values from all single patches into a single plot and then performed the Boltzmann fits (Figure 3C). The obtained values of Vmid were similar to the first approach and were −16.4 ± 0.65 mV for the PD, −16.2 ± 1.04 mV for the soma and 16.14 ± 0.72 for the PA.

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