| Abstract No.: | A-D1157 |
| Country: | Canada |
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| Title: | DIFFERENTIAL EFFECTS OF D1-LIKE AND D2-LIKE DOPAMINERGIC RECEPTORS ON AMPA CURRENTS IN SPINAL MOTONEURONS |
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| Authors/Affiliations: | 1 Pengcheng Han*; 1 Patrick Whelan;
1 Hotchkiss Brain Institute, Calgary, AB, Canada
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| Content: | Objectives: It is well recognized that dopamine (DA) can modulate spinal networks and reflexes. Our previous study showed that DA can boost excitability in spinal motoneurons by increasing glutamatergic transmission onto motoneurons (Han et al, Journal of Neuroscience 27:13192). In this study, we examined the effects of different dopaminergic receptors on AMPA currents.
Materials and Methods: Experiments were performed on Swiss Webster mice (P3-8). The spinal cord was dissected free in ice-cold, oxygenated sucrose-ACSF solution (concentrations in mM: 25 NaCl, 188 sucrose, 1.9 KCl, 10 MgSO4, 1.2 Na2HPO4, 26 NaHCO3, 25 D -glucose), and immediately transferred to a pre-cooled (4oC) slicing chamber and stabilized in an upright position onto an agar block using 20% gelatin. Transverse sections (350 µm) were cut (Leica Vibrotome VT1000S), and the slices were collected in a chamber containing pre-warmed (36oC), oxygenated recovery ACSF (concentrations in mM: 119 NaCl, 1.9 KCl, 1 CaCl2, 10 MgSO4, 1.2 Na2HPO4, 26 NaHCO3,10 D-glucose), and equilibrated for at least 45 minutes before being placed into the recording chamber for IR-DIC visually guided patch clamp recordings. The external oxygenated ACSF solution contains (in mM): 128 NaCl, 4 KCl, 1.5 CaCl2, 1 MgSO4, 0.5 Na2HPO4, 21 NaHCO3, 30 D-glucose and 1 µM TTX. The internal pipette solution contains (in mM): 150 CsCl, 1 EGTA, 10 HEPES, 0.1 CaCl2, 4.6 MgCl2, 2 ATP, and 0.5 GTP. AMPA (100 µM) was puffed onto the targeted cells using a Clampex protocol to trigger the Picospritzer.
Results: The D1 receptor agonist SKF 38393 (20 µM) increased the amplitude of the evoked AMPA currents (the maximal increment was 44.7 ± 8.9%, N=3). SKF 38393 (20 µM) also increased the decay time constant (the maximal increment was 52.4 ± 10.3%, N=2). In addition, the cell-attached single channel recording suggested that SKF 38393 (20 µM) increased the open probability and open time of AMPA conductance. In contrast, the D2-like receptor agonist quinpirole (50 µm) reduced the AMPA current amplitude (the maximal suppression was 20.3 ± 3.1%, N=5), and shortened the decay time constant (the maximal suppression was 14.7 ± 3.5%, N=5). In the presence of the D1 receptor antagonist LE 300 (10 nM), DA was not able to increase AMPA current amplitude or prolong the decay time constant as we observed previously (Han et al, Journal of Neuroscience 27:13192). On the other hand, in the presence of D2 receptor antagonist L-741626 (20 nM), DA remained capable of increasing the amplitude and decay time constant of AMPA currents.
Conclusion: Activation of D1-like and D2-like receptors result in opposite effects on AMPA conductance on spinal motoneurons. Thus, the modulation of AMPA conductance by DA is likely a net combination of multiple receptor effects, which balance with one another to ensure that dopaminergic modulation is constrained in an appropriate range.
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