5-hydroxytryptamine 1A (5-HT1A) but not 5-HT3 receptor is involved in mediating the nucleus submedius 5-HT-evoked antinociception in the rat.
Our previous studies have indicated that the thalamic nucleus submedius (Sm) is involved in modulation of nociception as part of an ascending component of an endogenous analgesic system consisting of spinal cord-Sm-ventrolateral orbital cortex (VLO)-periaqueductal gray (PAG)-spinal cord loop. Microinjection of 5-hydroxytryptamine (5-HT) into Sm produces antinociception and this effect is blocked by 5-HT(2) receptor antagonist. The aim of the present study was to examine whether the 5-HT(1) and 5-HT(3) receptors were also involved in the Sm 5-HT-evoked antinociception. Nociception was assessed in lightly anesthetized rats with radiant-heat-evoked tail flick (TF). 5-HT(1A) and 5-HT(3) receptor antagonists were microinjected into the Sm alone or in combination with a microinjection of 5-HT into the same Sm site. 5-HT(1A) receptor antagonist p-MPPI (0.87 nmol) facilitated the TF reflex; a lower dose (0.43 nmol) of p-MPPI significantly attenuated the Sm 5-HT-evoked inhibition of TF reflex. Microinjection of the 5-HT(3) receptor antagonist LY-278,584 (12 nmol) had no effect either on the TF reflex or on the Sm 5-HT-evoked inhibition. These results suggest that 5-HT(1A) receptor but not 5-HT(3) receptor is involved in mediating the 5-HT-evoked antinociception. Possible mechanisms of Sm 5-HT-induced descending antinociception are discussed.
Xiao
Dan-Qin
DQ
Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Department of Physiology, School of Medicine, Xi'an Jiaotong University, Shaanxi, People's Republic of China.
Zhu
Juan-Xia
JX
Tang
Jing-Shi
JS
Jia
Hong
H
D000698:Analgesia; D000818:Animals; D008845:Microinjections; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D020656:Posterior Thalamic Nuclei / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044282:Receptor, Serotonin, 5-HT1A / Q000187:drug effects / Q000502:physiology*; D044406:Receptors, Serotonin, 5-HT3 / Q000187:drug effects / Q000502:physiology*; D012016:Reference Values; D012018:Reflex / Q000187:drug effects / Q000502:physiology; D012702:Serotonin Antagonists / Q000008:administration & dosage
D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; D044282:Receptor, Serotonin, 5-HT1A