5-HT2 receptors promote plateau potentials in turtle spinal motoneurons by facilitating an L-type calcium current.
The effects of serotonin (5-HT) on intrinsic properties of spinal motoneurons were investigated with intracellular recordings in a slice preparation from adult turtles. In 55% of the cells that were recorded, addition of 5-HT to the extracellular medium promoted plateau potentials as revealed by the response to depolarizing current pulses applied through the intracellular electrode. In the remaining 45% of cells, 5-HT had an inhibitory effect. However, when tested with an applied electric field that preferentially polarizes distal dendrites, 5-HT facilitated plateau potentials in 100% of the cells. Plateau potentials were also promoted by 5-HT focally applied on a dendrite by iontophoresis. Applied near the soma, 5-HT either promoted plateau potentials or inhibited spike generation. The latter effect was accompanied by a decrease in input resistance. Voltage-clamp recordings showed that the facilitation of plateau potentials mediated by L-type Ca(2+) channels was due to activation of 5-HT(2) receptors. These findings show that 5-HT regulates intrinsic properties of motoneurons in opposite ways: activation of 5-HT receptors in the soma region inhibits spike generation and plateau potentials, while activation of 5-HT(2) receptors in the dendrites and the soma region promotes spiking by facilitation of plateau potentials mediated by L-type Ca(2+) channels.
Perrier
Jean-François
JF
Department of Medical Physiology, Panum Institute, University of Copenhagen, DK 2200 Copenhagen N, Denmark. perrier@mfi.ku.dk
Hounsgaard
Jørn
J
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002451:Cell Compartmentation / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*; D014426:Turtles
D020746:Calcium Channels, L-Type; D011985:Receptors, Serotonin; D012701:Serotonin