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The Journal of Neuroscience, August 31, 2005, 25(35):7993-7999; doi:10.1523/JNEUROSCI.1957-05.2005

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Cellular/Molecular
Synaptic Release of Serotonin Induced by Stimulation of the Raphe Nucleus Promotes Plateau Potentials in Spinal Motoneurons of the Adult Turtle

Jean-François Perrier¹ and Rodolfo Delgado-Lezama²

¹Department of Medical Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark, and ²Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, 07000-México, México

Serotonin (5-HT) is a major modulator of the CNS. In motoneurons recorded in slices of the spinal cord, 5-HT promotes plateau potentials mediated by the activity of low-threshold L-type calcium channels (Ca_V1.3). However, no direct evidence has shown that 5-HT actually promotes plateau potentials under physiological conditions. Here, we investigate how release of 5-HT induced by activation of the raphe nucleus modulates intrinsic properties of spinal motoneurons. We developed an integrated preparation of the brainstem left in continuity with the cervical segments of the spinal cord from adult turtles. Electrical stimulation of the raphe nucleus increased the excitability of motoneurons by decreasing the amplitude of the afterhyperpolarization following action potentials and by promoting plateau potentials. Antagonists of 5-HT₂ receptors applied in the vicinity of motoneurons inhibited the facilitation of plateaus. In a slice preparation in which glutamatergic, GABAergic, and glycinergic ionotropic synaptic transmission was blocked, stimulation of the dorsolateral funiculus facilitated a plateau potential by promoting a voltage-sensitive persistent inward current. This effect was inhibited by the addition of antagonists for 5-HT₂ receptors. Our study suggests that Ca_V1.3 channels are regulated by 5-HT released from raphe spinal synaptic terminals via 5-HT₂ receptors.

Key words: brainstem; spinal cord; raphe; serotonin; motoneuron; synaptic transmission

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Received May 17, 2005; revised July 19, 2005; accepted July 19, 2005.

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