BACKGROUND: Spinal 5-hydroxytryptamine (5-HT) has been shown to display an antinociceptive effect, which is mediated by 5-HT receptors. Previous studies have revealed the presence of at least four types of 5-HT receptors in the spinal cord. The aim of this study was to assess the role of each spinal 5-HT receptor in the antinociception of intrathecal 5-HT using the formalin test. METHODS: Rats were implanted with lumbar intrathecal catheters. After the administration of 5-HT, formalin-induced nociceptive behavior (flinching response) was observed for 60 min. To further clarify the role of the 5-HT receptors in the antinociception of 5-HT, several antagonists of 5-HT receptors were administered intrathecally 10 min before 5-HT delivery, and formalin was injected 10 min later. RESULTS: Intrathecal 5-HT dose-dependently suppressed flinching during phase 1 and 2 in the formalin test. 5-HT1B (GR 55562), 5-HT2C (N-desmethylclozapine), 5-HT3 (LY-278,584) and 5-HT4 (SDZ-205,557) receptors antagonists reversed this antinociception by 5-HT during both phases in the formalin test. 5-HT1A receptor antagonist (WAY-100635) decreased antinociception by 5-HT in phase 2, but not in phase 1. A 5-HT1D receptor antagonist (BRL 15572) did not antagonize the antinociception of 5-HT in either phases. CONCLUSIONS: Spinal 5-HT1B, 5-HT2C, 5-HT3 and 5-HT4 receptors, but not the 5-HT1D receptor, are involved in the antinociception of serotonin in the facilitated state and in the acute pain evoked by a formalin stimulus. The 5-HT1A receptor seems to play a role in 5-HT-induced antinociception in the facilitated state.
Acute Pain ; Animals ; Catheters ; Formaldehyde ; Pain Measurement ; Rats* ; Receptor, Serotonin, 5-HT1A ; Receptor, Serotonin, 5-HT1D ; Receptors, Serotonin ; Receptors, Serotonin, 5-HT4 ; Serotonin* ; Spinal Cord*

Migraine and anxiety disorders are frequently co-morbid with balance disorders. Potential mechanisms for migrainous vertigo include sites of action of 5-HT (serotonin) 1B and 1D receptor agonists such as rizatriptan, which attenuate motion sickness in migraineurs. Selective serotonin reuptake inhibitors (SSRIs) are also known to be efficacious in the treatment of vertigo. Relative distribution of the 5-HT receptor subtypes and their functional roles in the vestibular nuclei and inner ear is still unknown. Using 5-HT1A, 1B, AND 1D receptors-specific antibody, we have demonstrated a differential distribution of these receptor subtypes within the rat vestibular nuclei and inner ear. For 5-HT receptor subtypes expression in the vestibular and auditory periphery, most ganglion cells in the vestibular ganglion showed immunoreactivity for 5-HT1A, 5-HT1B and 5-HT1D receptors. In addition, 5-HT1B and 1D receptors immunopositive reactivities were associated with endothelial cells of small blood vessels in the vestibular ganglion and nerve, endothelial cells in both the spiral ligament deep to the spiral prominence and stria vascularis and endothelial cells on blood vessels along the margins of the spiral ganglion. For 5-HT receptor subtypes expression in the vestibular nuclei (VN), the 5-HT1A, 1B and 1D receptors were expressed differentially in the VN. Fine varicose axons in the periventricular plexus showed intense 5-HT1A receptor expression in the medial VN (MVN) and extended into the superior VN (SVN). By contrast, 5-HT1B receptors were not expressed the ventricular plexus axons. Rather, 5-HT1B and 1D receptors immunopositive cell bodies and neuronal processes were dense in rostral MVN, dorsal SVN, lateral VN (LVN) and ventral aspect of nucleus prepositus hypoglossi (NPH). In the present study, inner ear and vestibular nuclei showed distinct distributions of 5- HT1A, 1B and 1D receptors expressions that are parallel to their distribution in peripheral and central nociceptive pathways. These differentially distributed 5-HT receptor subtypes are potential targets to explain the efficacy of SSRIs and triptans in treating migraine and migrainous vertigo.
Animals ; Anxiety Disorders ; Axons ; Blood Vessels ; Ear, Inner ; Endothelial Cells ; Ganglion Cysts ; Migraine Disorders ; Motion Sickness ; Neurons ; Rats ; Receptor, Serotonin, 5-HT1A ; Receptor, Serotonin, 5-HT1B ; Receptor, Serotonin, 5-HT1D ; Serotonin ; Serotonin Uptake Inhibitors ; Spiral Ganglion ; Spiral Ligament of Cochlea ; Stria Vascularis ; Triazoles ; Tryptamines ; Vertigo ; Vestibular Nuclei

Migraine is one of the common and frequently encountered diseases. The study proves that 5-hydroxytryptamine (5-HT) receptor, plays an important role in the occurrence of migraine. Rat striatum was used for preparation of the cell membrane stationary phase (CMSP) in our experiments. The cell membrane chromatography (CMC)-offline-HPLC system was applied to specifically recognize the components from the drug pair of Chuanxiong Rhizoma and Angelicae Dahuricae Radix, which interact with the receptors on CMSP. The dissociation equilibrium constant (KD) was measured in a rat striatum/CMC system, performed by continuously pumping sumatriptan, a 5-HT1D agonist, ranging from 2.42 x 10(-8) to 4.84 x 10(-7) mol · L(-1) through a CMC column, and the capacity factors (k') were recorded. The KD value obtained from the model was (4.59 ± 0.33) x 10(-6) mol · L(-1) for imperatorin, and the rat model of migraine induced by nitroglycerin was applied to validate the pharmacological effects of the drug pair. The results indicated that the CMC method could be a quick and efficient way for characterizing the drug-receptor interactions in vitro.
Angelica ; chemistry ; Animals ; Cell Membrane ; chemistry ; Chromatography, High Pressure Liquid ; methods ; Drug Evaluation, Preclinical ; methods ; Drugs, Chinese Herbal ; chemistry ; Male ; Migraine Disorders ; drug therapy ; Rats ; Rats, Sprague-Dawley ; Receptor, Serotonin, 5-HT1D ; chemistry ; Serotonin Receptor Agonists ; analysis

The intracranial blood vessels of the dura and the pia receive sensory afferent innervations from trigeminal nerve which has been believed to play a critical role in the mediation of vascular headache such as migraine. The purpose of this study was to discover the mechanism by which the interaction between trigeminal ganglion neurons and the function of cerebral blood vessels. Using electrophysiological recording, we studied the responses of trigeminal ganglion neurons to electrical stimulation of middle meningeal artery(MMA), superior sagittal sinus(SS) and transverse sinus(TS) in rats. Sumatriptan is a highly selective agonist for 5-HT1D receptor subtype which mediates vasoconstriction of cerebral blood vessels. We observed responses to electrical stimulation in trigeminal ganglion neurons and meningeal blood flow(MBF) after intravenous injection of sumatriptan. The results were as follows: 1) The presumed mean conduction velocities of the cells activated MMA, SS and TS by electrical stimulation were approximately 1.5, 2.9 and 2.9m/s, respectively. These were presumed to be nociceptive small myelinated or unmylinated sensory fibers. 2) The action potential discharges of trigeminal ganglion neurons on MMA, SS and TS in the experimental control groups were 671+/-39.49, 856+/-63.95 and 494+/-21.54microV, respectrely. The action potential discharges of sumatriptan groups on MMA, SS and TS(393+/-20.10, 562+/-32.26 and 262+/-18.94microV, respectively) were significantly decreased compared to that of the experimental control groups. 3) The mean MBF of normal control group was 63.29+/-7.54ml/100g/min. The mean MBF of the experimental control groups on MMA, SS and TS were 97.13+/-9.91, 104.28+/-12.54 and 91.82+/-6.41ml/100g/min, respectively(p<0.05). MBF of sumatriptan group before stimulation was significantly decreased(compared to normal: 37.17+/-4.76ml/100g /min vs 63.29+/-7.54ml/100g/min). The mean MBF of sumatriptan groups on MMA, SS and TS were 57.11+/-4.48, 66.56+/-6.23 and 56.07+/-5.00ml/100g/min, respectively. Compared to that of the experimental control groups, the MBF of the sumatriptan groups were significantly decreased. In conclusion, the activation of trigeminal sensory afferents by the electrical stimulation of the dural vessel may create vasodilatation and increase cerebral blood flow which may lead to vascular headaches via trigeminal ganglion to brain stem This pathway can be important for understanding the neural mechanism for the development of pharmacological and surgical approach to alleviate vascular headache.
Action Potentials ; Animals ; Blood Vessels ; Brain Stem ; Electric Stimulation ; Headache ; Injections, Intravenous ; Meningeal Arteries* ; Migraine Disorders ; Myelin Sheath ; Negotiating ; Neurons* ; Rats* ; Receptor, Serotonin, 5-HT1D ; Sumatriptan ; Superior Sagittal Sinus* ; Trigeminal Ganglion* ; Trigeminal Nerve ; Vascular Headaches ; Vasoconstriction ; Vasodilation