Limits...
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.

Show MeSH

Related in: MedlinePlus

The effect of a D1/D5 agonist on Na+ channel gating. (A) Traces from a representative PD patch where isolated Na+ channel openings were evoked by 70 mV voltage steps from −100 mV to −30 mV (see bottom schematic). The resting potential is given by the dotted line in the bottom schematic. Control traces are shown at the left and traces from the same patch following bath application of SKF81297(3 µM) are given at the right. (B) Quantification of the effects of the D1/D5 agonist on the late openings of Na+ channels recorded from the PD: the number of late openings (per channel, per 80 ms) (left), the open probability (middle) or the average dwell time (right). The late channel openings were counted starting 20 ms after the beginning of the depolarizing step. Each pair of connected dots is from a single patch. (C) Same as (B) but for patches recorded from the soma. (D) Same as (B) but for patches recorded from the PA. ***represents significance at p < 0.001, **represents significance at p < 0.01 and *represents significance at p < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4325928&req=5

Figure 6: The effect of a D1/D5 agonist on Na+ channel gating. (A) Traces from a representative PD patch where isolated Na+ channel openings were evoked by 70 mV voltage steps from −100 mV to −30 mV (see bottom schematic). The resting potential is given by the dotted line in the bottom schematic. Control traces are shown at the left and traces from the same patch following bath application of SKF81297(3 µM) are given at the right. (B) Quantification of the effects of the D1/D5 agonist on the late openings of Na+ channels recorded from the PD: the number of late openings (per channel, per 80 ms) (left), the open probability (middle) or the average dwell time (right). The late channel openings were counted starting 20 ms after the beginning of the depolarizing step. Each pair of connected dots is from a single patch. (C) Same as (B) but for patches recorded from the soma. (D) Same as (B) but for patches recorded from the PA. ***represents significance at p < 0.001, **represents significance at p < 0.01 and *represents significance at p < 0.05.

Mentions: Next we investigated the effects of SKF81297 on multiple late single channel openings. In these experiments we utilized 100 ms and 550 ms depolarizing voltage steps. Since we didn’t find any difference in the late Na+ channel openings between these two groups, they were pooled. The number of late openings was calculated by dividing the number of all late openings by the number of channels in the patch and by the number of depolarizing sweeps and then scaled to a 80 ms length of sweep. Figure 6A shows example traces from a dendritic patch under baseline conditions and following the activation of D1 receptors by SKF81297. Across the population of patches recorded at voltage steps to transmembrane potentials of −40 to −50 mV, SKF81297 significantly increased the number of openings in the PD (0.17 ± 0.036 in control vs. 0.24 ± 0.042 in SKF81297, t9 = 5.96, p = 0.0001), but not the soma (0.24 ± 0.04 in control vs. 0.29 ± 0.051 in SKF81297, t8 = 1.15, p = 0.14) or PA (0.148 ± 0.021 in control vs. 0.18 ± 0.035 in SKF81297, t6 = 1.84, p = 0.057) (Figure 6B). SKF81297 also significantly increased Po in the PD (0.00165 ± 0.00054 in control vs. 0.00217 ± 0.00068 in SKF81297, t9 = 3.75, p < 0.002) the soma (0.00155 ± 0.0003 in control vs. 0.00217 ± 0.00053 in SKF81297, t8 = 2.41, p = 0.045) but not the PA (0.00168 ± 0.00044 in control vs. 0.00160 ± 0.00028 in SKF81297, t6 = −0.33, p = 0.37) (Figures 6B,C). The overall dwell time did not differ under baseline vs. SKF81297 (Figures 6B–D) in the PD (0.663 ± 0.081 ms in control vs. 0.656 ± 0.068 ms in SKF81297, t9 = 0.31, p = 0.38), the soma (0.519 ± 0.058 ms in control vs. 0.621 ± 0.072 ms in SKF81297, t8 = 2.52, p = 0.05) or the PA (0.944 ± 0.158 ms in control vs. 0.982 ± 0.119 ms in SKF81297, t6 = −1.27, p = 0.12). Therefore, D1/D5 receptor stimulation mainly increased the probability that Na+ channels open in the PD and to a lesser extent in the soma.


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 effect of a D1/D5 agonist on Na+ channel gating. (A) Traces from a representative PD patch where isolated Na+ channel openings were evoked by 70 mV voltage steps from −100 mV to −30 mV (see bottom schematic). The resting potential is given by the dotted line in the bottom schematic. Control traces are shown at the left and traces from the same patch following bath application of SKF81297(3 µM) are given at the right. (B) Quantification of the effects of the D1/D5 agonist on the late openings of Na+ channels recorded from the PD: the number of late openings (per channel, per 80 ms) (left), the open probability (middle) or the average dwell time (right). The late channel openings were counted starting 20 ms after the beginning of the depolarizing step. Each pair of connected dots is from a single patch. (C) Same as (B) but for patches recorded from the soma. (D) Same as (B) but for patches recorded from the PA. ***represents significance at p < 0.001, **represents significance at p < 0.01 and *represents significance at p < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: The effect of a D1/D5 agonist on Na+ channel gating. (A) Traces from a representative PD patch where isolated Na+ channel openings were evoked by 70 mV voltage steps from −100 mV to −30 mV (see bottom schematic). The resting potential is given by the dotted line in the bottom schematic. Control traces are shown at the left and traces from the same patch following bath application of SKF81297(3 µM) are given at the right. (B) Quantification of the effects of the D1/D5 agonist on the late openings of Na+ channels recorded from the PD: the number of late openings (per channel, per 80 ms) (left), the open probability (middle) or the average dwell time (right). The late channel openings were counted starting 20 ms after the beginning of the depolarizing step. Each pair of connected dots is from a single patch. (C) Same as (B) but for patches recorded from the soma. (D) Same as (B) but for patches recorded from the PA. ***represents significance at p < 0.001, **represents significance at p < 0.01 and *represents significance at p < 0.05.
Mentions: Next we investigated the effects of SKF81297 on multiple late single channel openings. In these experiments we utilized 100 ms and 550 ms depolarizing voltage steps. Since we didn’t find any difference in the late Na+ channel openings between these two groups, they were pooled. The number of late openings was calculated by dividing the number of all late openings by the number of channels in the patch and by the number of depolarizing sweeps and then scaled to a 80 ms length of sweep. Figure 6A shows example traces from a dendritic patch under baseline conditions and following the activation of D1 receptors by SKF81297. Across the population of patches recorded at voltage steps to transmembrane potentials of −40 to −50 mV, SKF81297 significantly increased the number of openings in the PD (0.17 ± 0.036 in control vs. 0.24 ± 0.042 in SKF81297, t9 = 5.96, p = 0.0001), but not the soma (0.24 ± 0.04 in control vs. 0.29 ± 0.051 in SKF81297, t8 = 1.15, p = 0.14) or PA (0.148 ± 0.021 in control vs. 0.18 ± 0.035 in SKF81297, t6 = 1.84, p = 0.057) (Figure 6B). SKF81297 also significantly increased Po in the PD (0.00165 ± 0.00054 in control vs. 0.00217 ± 0.00068 in SKF81297, t9 = 3.75, p < 0.002) the soma (0.00155 ± 0.0003 in control vs. 0.00217 ± 0.00053 in SKF81297, t8 = 2.41, p = 0.045) but not the PA (0.00168 ± 0.00044 in control vs. 0.00160 ± 0.00028 in SKF81297, t6 = −0.33, p = 0.37) (Figures 6B,C). The overall dwell time did not differ under baseline vs. SKF81297 (Figures 6B–D) in the PD (0.663 ± 0.081 ms in control vs. 0.656 ± 0.068 ms in SKF81297, t9 = 0.31, p = 0.38), the soma (0.519 ± 0.058 ms in control vs. 0.621 ± 0.072 ms in SKF81297, t8 = 2.52, p = 0.05) or the PA (0.944 ± 0.158 ms in control vs. 0.982 ± 0.119 ms in SKF81297, t6 = −1.27, p = 0.12). Therefore, D1/D5 receptor stimulation mainly increased the probability that Na+ channels open in the PD and to a lesser extent in the soma.

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