Localization of serotonin receptors in the rat thalamus by electrophysiology and the action of 5-HTP-DP-hex.
This study was designed to pinpoint the site at which N-hexanoyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP-hex) exerts its previously reported effect on thalamic neurons in rats. The animals were prepared under chloralose-urethane anesthesia for a stereotaxic approach to either the nucleus ventralis posterolateralis (nVPL) or the centrum medianum-parafascicularis complex (CM-Pf) of the thalamus. Individual neurons in these nuclei were separately activated by single-pulse stimulation of the sciatic nerve or the thalamic fibers that form reciprocal connections between the CM-Pf and the second somatosensory (SII) region of the nVPL. Poststimulus time histograms were constructed from computer readouts of the stimulus-evoked responses of a neuron during a 500-ms period accumulated in a digital computer 100X. In addition, the number of spikes accumulated in each histogram was compared to the number of spikes accumulated under identical conditions on the same neuron after intracarotid infusion of 5-HTP-DP-hex. The effect of the drug was reversed by the infusion of 5-HTP. Statistical evaluation of the accumulated spike counts indicated that 5-HTP-DP-hex suppressed only the excitation of CM-Pf neurons from the SII of the nVPL; the input of the sciatic nerve into the CM-Pf remained unaltered. Furthermore, no effect was exerted by this dipeptide on the afferent excitation of neurons in the SII of the nVPL.(ABSTRACT TRUNCATED AT 250 WORDS)
Emmers
R
R
Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Tamir
H
H
Wilchek
M
M
D006916:5-Hydroxytryptophan / Q000031:analogs & derivatives*; D000818:Animals; D002339:Carotid Arteries; D004558:Electric Stimulation; D004594:Electrophysiology; D007269:Injections, Intra-Arterial; D008297:Male; D009474:Neurons / Q000502:physiology; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism*; D012584:Sciatic Nerve / Q000502:physiology; D013788:Thalamus / Q000166:cytology / Q000378:metabolism*; D014018:Tissue Distribution
D011985:Receptors, Serotonin; C052636:N-hexanoyl-5-hydroxytryptophyl-5-hydroxytryptophanamide; D006916:5-Hydroxytryptophan