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Serotonin Activates Presynaptic and Postsynaptic Receptors in Rat Globus Pallidus

Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis, Tennessee

Submitted 17 October 2007; accepted in final form 26 January 2008

Although recent histological, behavioral, and clinical studies suggest that serotonin (5-HT) plays significant roles in the control of pallidal activity, only little is known about the physiological action of 5-HT in the pallidum. Our recent unit recording study in monkeys suggested that 5-HT provides both presynaptic and postsynaptic modulations of pallidal neurons. The present study using rat brain slice preparations further explored these presynaptic and postsynaptic actions of 5-HT. Bath application of 5-HT or the 5-HT_1A/1B/1D/5/7 receptor (R) agonist 5-carboxamidotryptamine maleate (5-CT) depolarized some and hyperpolarized other pallidal neurons. Pretreatments of slices with blockers of the hyperpolarization–cyclic nucleotide-activated current or with the 5-HT_2/7R–selective antagonist mesulergine occluded 5-CT–induced depolarization. The 5-HT_1AR–selective blocker N-[2[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohex- anecarboxamide maleate occluded the 5-CT–induced hyperpolarization. These results suggested involvement of 5-HT₇R and 5-HT_1AR in the postsynaptic depolarization and hyperpolarization, respectively. 5-CT presynaptically suppressed both internal capsule stimulation–induced excitatory postsynaptic currents (EPSCs) and striatal stimulation–induced inhibitory postsynaptic currents (IPSCs). The potencies of 5-CT on the presynaptic effects were 20- to 25-fold higher than on postsynaptic effects, suggesting that 5-HT mainly modulates presynaptic sites in the globus pallidus. Experiments with several antagonists suggested involvement of 5-HT_1B/DR in the presynaptic suppression of EPSCs. However, the receptor type involved in the presynaptic suppression of IPSCs was inconclusive. The present results provided evidence that 5-HT exerts significant control over the synaptic inputs and the autonomous activity of pallidal neurons.

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				C. Gunay, J. R. Edgerton, and D. Jaeger Channel Density Distributions Explain Spiking Variability in the Globus Pallidus: A Combined Physiology and Computer Simulation Database Approach J. Neurosci., July 23, 2008; 28(30): 7476 - 7491. [Abstract] [Full Text] [PDF]