Mechanical, thermal and formalin-induced nociception is differentially altered in 5-HT1A-/-, 5-HT1B-/-, 5-HT2A-/-, 5-HT3A-/- and 5-HTT-/- knock-out male mice

Extensive studies in rodents suggest that serotonin (5-HT) modulates nociceptive responses through the stimulation of several receptor types. However, it remains to demonstrate that these receptors participate in the control of nociception under physiological conditions. Pain behaviors of mutants which do not express 5-HT_1A, 5-HT_1B, 5-HT_2A or 5-HT_3A receptors, or lacking the 5-HT transporter, compared to paired wild-type mice of the same genetic background, were examined using validated tests based on different sensory modalities. Mechanical (von Frey filaments, tail pressure, tail clip tests), thermal (radiant heat, 46 °C water bath, hot-plate test) and formalin-induced nociception were determined in 2- to 3-month-old males. 5-HT_1A knock-out mice differed from wild-types by higher thermal sensitivity (hot-plate test only), and 5-HT_1B knock-out mice by higher thermal and formalin sensitivity. Both 5-HT_2A and 5-HT_3A knock-out mice differed from wild-types by a dramatic decrease in the formalin-induced nociceptive responses for phase II (16–45 min after injection/inflammatory phase). In contrast, neither mechanical, thermal nor formalin-induced nociception differed between mutants lacking the 5-HT transporter and paired wild-type mice. Although differences in spontaneous locomotor activity in 5-HT_1B−/− (increase) and 5-HT_3A−/− (decrease) knock-out mice versus paired wild-types might have confounded differences in nociception, acute 5-HT receptor blockade by selective antagonists was found to replicate in wild-type mice the effects on pain behavior, but not on locomotor activity, of the respective gene knock-out in mutants. These results support the conclusion that the complex control of pain mechanisms by 5-HT, acting at multiple receptors, is physiologically relevant in mice.     

Plasticity of 5-HT serotonin receptor in patients with analgesic-induced transformed migraine

Chronic drug exposure can induce a significant change in neurotransmitter receptor systems and is possibly involved in the pathogenesis of drug-induced neurological disorders. Abuse of analgesics is known to induce deterioration in headache status in patients with primary headaches, especially migraine. To assess the possibility of 5-HT2A serotonin receptor plasticity in this condition, we investigated receptor binding on the platelet membrane in patients with analgesic-induced transformed migraine, patients with migraine, and nonheadache controls. Various concentrations of [3H]-spiperone (0.4 to 12 nmol) was used as a radioligand, and ketanserin was used to determine nonspecific binding. A lower maximal number of receptors (Bmax) was observed in patients with migraine as compared to patients with transformed migraine, and controls (467 +/- 58, 708 +/- 36, and 786 +/- 64 fmol/mg protein, respectively, P<0.01); whereas the value of the dissociation equilibrium constant (Kd) remained unchanged (1.72 +/- 0.16, 1.41 +/- 0.13, and 1.25 +/- 0.21 nmol for patients with migraine, patients with transformed migraine, and nonheadache controls, respectively). A significant decrease in Bmax value was observed in patients with transformed migraine after 4 weeks of analgesic withdrawal (770 +/- 25 and 345 +/- 31 fmol/mg protein, P<0.001), whilst no significant change in Kd value was observed (1.95 +/- 0.12 and 2.47 +/- 0.30 nmol, respectively). These findings indicate that 5-HT2A serotonin receptor system is altered in patients with transformed migraine with analgesic overuse. Such receptor plasticity may be an important step in the pathogenic mechanism of transformed migraine.     

Pharmacological analysis of the cardiac effects of 5-HT and some 5-HT receptor agonists in the pithed rat

Summary— A pharmacological analysis of the effects of 5-HT on heart rate has been performed in the pithed rat. 5-HT induced a dose-dependent increase in heart rate whereas 5-HT, receptor agonists — 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 5-methoxy-N,N-dimethyl-tryptamine (5-MeODMT), 5-methoxy 3-(1,2,3,6-tetrahydro-4-piridinyl) 1H indole (RU 24969) and 1-(m-trifluoromethylphenyl)-piperazine (TFMPP) — failed to increase heart rate. The increase in heart rate induced by the selective 5-HT₂ receptor agonist 1-(2,5-dimethoxy-4-iodo-phenyl)-2-aminopropane (DOI) was not significant. The dose-response curve to 5-HT for its tachycardic effects was shifted two-fold to the right by ketanserin and LY 53857 and nine-fold to the right by methiothepin. The effects of high doses of 5-HT (higher than 100 μg/kg iv) were antagonized by methiothepin, (-)propranolol, 2-{2-[4(O-methoxyphenyl)-piperazine-1-yl]-ethyl}4,4-dimethyl-1,3 (2H-4H) isoquinoline-dione (AR-C 239) and by pretreatment with reserpine. The 5-HT₁ receptor antagonists, pindolol and spiroxatrine, the 5-HT₃ receptor antagonist MDL 72222 and the α₂-adrenoceptor blocking agent idazoxan failed to antagonize the tachycardia induced by 5-HT. It is concluded that in the pithed rat, the tachycardia induced by 5-HT remained unexplained (implication of 5-HT₂ receptors probably different from the classical vascular 5-HT₂ receptor, or implication of 5-HT_1C receptors?). Moreover, at high doses (higher than 100 μ/kg iv), 5-HT may increase heart rate by releasing catecholamines.     

Lack of efficacy of 5-HT2A receptor antagonists to reduce brain damage after 3 minutes of transient global cerebral ischaemia in gerbils

Summary— Stimulation of the 5-HT_2A receptors by serotonin has been reported to exert an excitatory effect on neocortical neurons in rats and mice, to facilitate ischaemia-induced release of excitatory amino acids and to mediate the vasomotor constrictor component of the response of blood vessels to 5-HT. 5-HT_2A receptor antagonists have, therefore, been proposed as potential protectants against the effects of cerebral ischaemia. The aim of this study was to evaluate the effects of two relatively selective 5-HT_2A receptor antagonists, ketanserin and ritanserin, on delayed hyperactivity and the ensuing neuronal degeneration induced by 3 minutes of bilateral carotid artery ligation in Mongolian gerbils. Effects were compared to that of flunarizine, which blocks calcium overload and served as a positive control in this paradigm. Temporal and/or rectal temperatures were measured and strictly controlled during the ischaemia and the early reperfusion phase. Locomotor activity was measured one day after the ischaemia and neuronal degeneration quantified 7 days later using an image analysis system (Quantimet 570, Leica). Global ischaemia in gerbils elicits hyperactivity associated with a delayed neuronal degeneration predominantly in the CA1 zone of the hippocampus. Ketanserin and ritanserin (3 and 10 mg/kg ip, twice daily for 3 days, pre- and postischaemia) did not protect the CA1 neurons against ischaemic damage. The postischaemic hyperactivity was inhibited only with the higher dose of ketanserin. As previously reported, flunarizine (30 mg/kg po) markedly reduced neuronal degeneration (-44.2%, p < 0.01) and totally abolished the ischaemia-induced hyperactivity. These data demonstrate that ketanserin and ritanserin are not effective protectants of the gerbil hippocampus against ischaemic damage when the body temperature of the animals is controlled, thus suggesting that 5-HT_2A receptors are not directly implicated in the pathogenesis of global cerebral ischaemia in this model.     

正中神经电刺激脑外伤昏迷大鼠前额叶皮质5-HT 2A受体表达的实验研究

目的:研究正中神经电刺激对脑外伤昏迷大鼠前额叶皮质5-羟色胺(5-HT)2A受体表达的影响。方法:将72只SD大鼠随机分为空白组、假刺激组、刺激组和拮抗剂组共4组。采用经典的自由落体模型建立脑外伤昏迷模型及大鼠意识状态6级评定标准评估四组大鼠行为学变化,并于实验完成后6、12、24h用免疫组化技术检测各组大鼠前额叶皮质组织的5-HT 2A受体表达。结果:刺激组13只大鼠(72.22%)出现翻正反射,拮抗剂组9只(50%)、假刺激组5只(27.78%)出现翻正反射。空白对照组意识状态分级秩均值为9.50级,假刺激组为52.75级,刺激组为37.61级,拮抗剂为46.14级,四组的意识状态分级呈"空刺拮假"递增趋势,组间比较差异有显著性意义(P0.01)。免疫组化结果显示组间比较前额叶5-HT 2A受体表达呈"空假拮刺"递增趋势(P0.05),组内比较呈"6h24h12h"趋势(P0.05)。结论:正中神经电刺激可作为脑外伤后昏迷的一种有效促醒手段,其机制可能与前额叶皮质5-HT 2A受体水平上调有关,且Orexin-A可能在其中发挥调节作用。     

Spinal 5-HT receptors that contribute to the pain-relieving effects of spinal cord stimulation in a rat model of neuropathy

Spinal cord stimulation (SCS) is extensively employed in the management of neuropathic pain, but the underlying mechanisms are only partially understood. Recently, we demonstrated that the pain-relieving effect of SCS appears to involve the spinal serotonin system, and the present study aimed at identifying the types of the spinal serotonin receptors involved. Experiments were performed on rats with neuropathy produced by partial ligation of the sciatic nerve. Tactile sensitivity was assessed using von Frey filaments, and cold and heat sensitivity with cold spray and radiant heat, respectively. Selective 5-HT receptor antagonists, methiothepin (5-HT₁,₆,₇), ketanserin tartrate (5-HT_2A), TICM (5-HT₃), SDZ-205,557 (5-HT₄), as well as receptor agonists, α-m-5-HT (5-HT₂), m-CPBG (5-HT₃) in per se ineffective doses, or vehicle, were administrated intrathecally 5 minutes prior to the application of SCS. Ketanserin and SDZ-205,557 significantly attenuated the suppressive effect of SCS on tactile hypersensitivity, while methiothepin and TICM were ineffective. The suppressive effect on cold hypersensitivity of SCS was counteracted by ketanserin only. None of the 5-HT receptor antagonists attenuated the suppressive effect on heat hyperalgesia of SCS. Subeffective doses of α-m-5-HT and m-CPBG enhanced the suppressive effect of SCS on tactile hypersensitivity. The enhancing effect of m-CPBG was abolished by a γ-aminobutyric acid (GABA)_A or GABA_B antagonist intrathecally. These results suggest that the activation of 5-HT_2A, 5-HT₃, and 5-HT₄ receptors plays an important role in SCS-induced relief of neuropathic pain. The activation of 5-HT₃ receptors appears to operate via spinal GABAergic interneurons.     

5-羟色胺1/2受体拮抗剂米安色林对大鼠睡眠呼吸暂停的影响

目的 中枢5-羟色胺(5-HT)及其受体在呼吸调控中发挥着重要作用.呼吸调控不稳定可以导致不规则的呼吸以及呼吸暂停的发生.本研究的目的 在于探讨5-HT1/2受体在大鼠睡眠呼吸暂停中的作用.方法 成年SD大鼠10只,手术埋置脑电、肌电电极和微注射套管.通过体描箱和多导生理仪,监测大鼠脑电、肌电和呼吸.通过微量泵,向第四脑室匀速泵入5-HT1/2受体的拮抗剂米安色林(mianserin)(100 μmol/L)40 μl,观察大鼠给药前后呼吸暂停的变化.结果大鼠呈现两种呼吸暂停的类型:自发呼吸暂停(spontaneous apnea)和叹息后呼吸暂停(post-sigh apnea).中枢微注射5-HT1/2受体拮抗剂米安色林减小了慢速眼球运动睡眠(non-rapid eye movements,NREM) 和快速眼球运动睡眠(REM)期的叹息后睡眠呼吸暂停(P<0.05),而对NREM 和 REM 期的自发呼吸暂停无影响(P>0.05),对总睡眠呼吸暂停指数也无显著影响(P>0.05).在睡眠结构方面,米安色林对睡眠效率及睡眠结构无显著影响(P>0.05).结论 5-HT 和5-HT1/2受体在呼吸调控网络中扮演重要角色,并与大鼠中枢型呼吸暂停的发生密切相关.5-HT1/2受体的不同亚型既有兴奋性受体,又有抑制性受体.米安色林对5-HT1/2受体的双向调节作用可能导致呼吸暂停减轻.     

Exclusion of 5-HT2A and 5-HT2C Receptor Genes as Candidate Genes for Migraine

Several lines of investigation suggest that the serotonergic system may be involved in the pathogenesis of migraine. In particular, drugs which block 5-HT₂ receptor subtypes appear to be effective migraine prophylactic agents. Therefore, chromosomal DNA regions overlapping the 5-HT_2A (13q14-q22) and 5-HT_2c (Xq22-25) receptor loci were analyzed for possible linkage to the clinical diagnosis of migraine. No evidence for linkage to either chromosomal region was found, although a small subset of migrainous families showed positive likelihood of odds (LOD) scores. However, a homogeneity (HOMOG) analysis provided no statistical evidence for locus heterogeneity. The coding region of the 5-HT_2A and 5-HT_2c receptor genes was also analyzed in migraine patients and unaffected controls using polmerase chain reaction and direct sequencing. No mutations were found in the deduced amino acid sequence of either receptor in the sample of migraineurs tested. These results indicate that DNA-based mutations in the 5-HT_2A and 5-HT_2c receptors are not generally involved in the pathogenesis of migraine.     

按经选穴针刺对失眠大鼠下丘脑5-HT 1a、5-HT 2a受体mRNA表达的影响

目的:观察按经选穴针刺对失眠大鼠下丘脑5-HT 1a、5-HT 2a受体mRNA表达的影响,探讨针刺治疗失眠症的疗效机制及按经选穴针刺对腧穴配伍效应的影响。方法:将60只SD大鼠随机分为5组,即:空白组、模型组、百会+神门穴组、百会+三阴交穴组、百会+非经非穴组,每组12只,通过腹腔注射DL-4-氯苯基丙氨酸混悬液建立失眠模型大鼠,各治疗组针刺相应腧穴,每次30min,治疗7d。运用实时荧光定量方法检测大鼠下丘脑5-HT1a、5-HT 2a受体mRNA表达量。结果:与模型组比较,各针刺组大鼠下丘脑5-HT 1a受体mRNA表达量均有一定程度的升高,5-HT 2a受体mRNA表达量均有一定程度的降低,且以百会+神门穴组调节效果最明显,百会+三阴交穴组及百会+非经非穴组次之。结论:针刺治疗可能通过调节失眠大鼠下丘脑5-HT 1a、5-HT 2a受体mRNA的表达发挥治疗作用,且按经选穴针刺可能是影响腧穴配伍效应的影响因素之一。     

Inhibition of 5-hydroxytryptamine2A receptor prevents occlusive thrombus formation on neointima of the rabbit femoral artery

BACKGROUND: Thrombus propagation on disrupted plaque is a major cause of acute coronary events and serious complication after coronary intervention. 5-Hydroxytryptamine (5-HT) is a potent vasoactive and platelet-aggregating substance that is predominantly mediated by 5-HT2A receptor. However, the roles of 5-HT2A receptor in occlusive thrombus formation on disrupted plaque remain obscure. OBJECTIVE: We investigated the role of 5-HT2A receptor in thrombus formation using a rabbit model of repeated balloon-injury. METHODS: Three weeks after a first balloon-injury of the femoral arteries, luminal diameter, neointimal growth, and vasoconstriction by 5-HT in vitro were examined. Thrombus propagation and the role of 5-HT2A receptor after a second balloon-injury were evaluated using sarpogrelate, a selective 5-HT2A receptor antagonist. RESULTS: Three weeks after the first balloon-injury, luminal stenosis was evident in the femoral arteries, where the neointima expressed tissue factor and 5-HT2A receptor. The hypercontractile response of the stenotic arteries to 5-HT was significantly reduced by sarpogrelate. Balloon-injury of the neointima with substantially reduced blood flow promoted the formation of occlusive thrombus that was immunoreactive against glycoprotein IIb-IIIa, 5-HT2A receptor and fibrin. Intravenous injection of sarpogrelate significantly inhibited ex vivo platelet aggregation induced by adenosine 5'-diphosphate, thrombin and collagen alone as well as with 5-HT, and significantly prevented occlusive thrombus formation in vivo. CONCLUSIONS: The 5-HT2A receptor appears to play a crucial role in occlusive thrombus formation in diseased arteries via platelet aggregation and vasoconstriction. Inhibition of 5-HT2A receptor might help reduce the onset of acute coronary events and of acute coronary occlusion after the intervention.     

Biochemical and electrophysiological properties of SR 57746A, a new, potent 5-HT1A receptor agonist

Summary— SR 57746A (1-[2-(naphth-2-yl) ethyl]-4-(3-trifluoromethylphenyl)-1, 2, 5, 6 tetra-hydropyridine hydrochloride) binds competitively, and with high affinity (K_i = 2.0 ± 0.7 nM) to 5-HT_1A receptors from rat hippocampus in vitro , but has much less affinity for other 5-HT receptor subtypes (IC₅₀ > 650 nM). SR 57746A produces a concentration-dependent inhibition of forskolin-stimulated adenylate cyclase activity in rat hippocampal homogenates, with a maximal effect identical to that of 8-OH-DPAT, suggesting that SR 57746A behaves as a full agonist in tthis experimental model. SR 57746A potently displaces [³H]8-OH-DPAT binding to rat hippocampal membranes ex vivo , with an ID₅₀ of 11.1 mg/kg po, 30 min after administration, and 2.8 mg/kg po, 2 h after administration. This effect of SR 57746A is long-lasting (at least 24 hours at 10 mg/kg po). SR 57746A does not modify the levels of 5-HT or DA in various brain areas, but decreases the concentrations of 5-HIAA, and increases those of DOPAC, HVA and 3-MT. Following iv administration, SR 57746A (0.095 to 0.25 mg/kg) inhibits the spontaneous firing of dorsal raphe neurones, but does not modify the activity of DA neurones in the substantia nigra or ventral tegmental area. Thus, SR 57746A is a potent, selective and full agonist at 5-HT_1A receptors in vitro and vivo.     

5‐HT2C receptor agonists attenuate pain‐related behaviour in a rat model of trigeminal neuropathic pain

Peripheral branches of the trigeminal nerve may be damaged during maxillofacial injury or surgical procedures and trigeminal trauma may induce severe pain that is very challenging to treat. Chronic constriction injury to the infraorbital nerve (ION‐CCI) by loose ligatures has proven a useful model for some types of trigeminal neuropathic pain disorder. Using ION‐CCI rats, we examined the antiallodynic effects of intrathecally administered agents which are selective for 5‐HT2C receptors. Allodynia was evaluated by applying von Frey filaments to skin innervated by the injured ION. Dose‐dependent antiallodynic effects followed administration of three 5‐HT2C receptor agonists, 6‐chloro‐2‐(1‐piperazinyl)‐pyrazine (MK212: 10, 30, and 100 μg); (S)‐2‐(chloro‐5‐fluoro‐indol‐l‐yl)‐1‐methyamine fumarate (RO 60‐0175: 10, 30, and 100 μg); (AaR)‐8,9‐dichloro‐2,3,4,4a‐tetrahydro‐1H‐pyrazino[1,2‐a]quinoxalin‐5(6H)‐one (WAY‐161503: 10, 30, and 100 μg). ED50 values for antiallodynic effects of MK212, RO 60‐0175, and WAY‐161503 were 39.62, 46.67, and 51.22 μg, respectively. Intrathecal administration of the 5‐HT2C receptor antagonist, 8‐[5‐2,4‐dimethoxy‐5‐(4‐trifluoromethylphenylsulphonamido)phenyl‐5‐oxopentyl]‐1,3,8‐triazaspiro[4,5]decane‐2,4‐dione (RS‐102221: 30 μg) did not alter the mechanical threshold. Intrathecal pretreatment with RS‐102221 (10 and 30 μg) reduced the antiallodynic effects of the highest dose of 5‐HT2C agonists. These results indicated that, in this rat model, the 5‐HT2C receptor plays a role in spinal inhibition of trigeminal neuropathic pain.     

Effects of chronic sumatriptan and zolmitriptan treatment on 5-HT receptor expression and function in rats

Triptans are commonly used anti-migraine drugs and show agonist action mainly at serotonin 5-HT(1B/1D/1F) receptors. It is not known whether frequent or long-term treatment with these drugs would alter 5-HT receptor function. We investigated the effects of protracted (14-18 days) sumatriptan and zolmitriptan treatment in rats on 5-HT(1) receptor mRNA expression and function in tissues related to migraine pathophysiology. RT-PCR analysis revealed that 5-HT(1B/1D/1F) receptor mRNA was reduced in the trigeminal ganglion after treatment with either triptan (reduction by: sumatriptan 39% and zolmitriptan 61% for 5-HT(1B); 60%vs 41% for 5-HT(1D); 32%vs 68% for 5-HT(1F)). Sumatriptan attenuated 5-HT(1D) receptor mRNA by 49% in the basilar artery, whereas zolmitriptan reduced 5-HT(1B) mRNA in this tissue by 70%. No change in 5-HT(1) receptor mRNA expression was observed in coronary artery and dura mater. Chronic triptan treatment had no effect in two functional assays [sumatriptan mediated inhibition (50 mg/kg, i.p.) of electrically induced plasma protein extravasation in dura mater and 5-nonyloxytryptamine-stimulated [(35)S]guanosine-5'-O-(3-thio)triphosphate binding in substantia nigra]. Furthermore, vasoconstriction to 5-HT in isolated basilar artery was not affected by chronic triptan treatment, while it was slightly reduced in coronary artery. We conclude that, although our treatment protocol altered mRNA receptor expression in several tissues relevant to migraine pathophysiology, it did not attenuate 5-HT(1) receptor-dependent functions in rats.     

Selective impairment of spinal mu-opioid receptor mechanism by plasticity of serotonergic facilitation mediated by 5-HT2A and 5-HT2B receptors

Opioid analgesia is compromised by intracellular mediators such as protein kinase C (PKC). The phosphatidylinositol hydrolysis-coupled serotonin receptor 5-HT2 is ideally suited to promote PKC activation. We test the hypothesis that 5-HT2A and 5-HT2B receptors, which have been previously shown to become pro-excitatory after spinal nerve ligation (SNL), can negatively influence the ability of opioids to depress spinal excitation evoked by noxious input. Spinal superfusion with (100 nM) mu-opioid receptor (MOR)-agonist DAMGO significantly depressed C fiber-evoked spinal field potentials. Simultaneous administration of subclinical 5-HT2AR antagonist 4F 4PP (100 nM) or 5-HT2BR antagonist SB 204741 (100 nM) significantly reduced the IC50 value for DAMGO in nerve-ligated rats (97.56 nM ± 1.51 and 1.20 nM ± 1.28 respectively, relative to 104 nM ± 1.08 at the baseline condition), but not in sham-operated rats. Both antagonists failed to alter depression induced by delta-opioid receptor (DOR)-agonist D-ala2-deltorphin II after SNL as well as in the sham condition. Western blot analysis of dorsal horn homogenates revealed bilateral upregulation of 5-HT2AR and 5-HT2BR protein band densities after SNL. As assessed from double immunofluorescence labeling for confocal laser scanning microscopy, scarce dorsal horn cell processes showed co-localization color overlay for 5-HT2AR/MOR, 5-HT2BR/MOR, 5-HT2AR/DOR, or 5-HT2BR/DOR in sham-operated rats. Intensity correlation-based analyses showed significant increases in 5-HT2AR/MOR and 5-HT2BR/MOR co-localizations after SNL. These results indicate that plasticity of spinal serotonergic neurotransmission can selectively reduce spinal MOR mechanisms via 5-HT2A and 5-HT2B receptors, including upregulation of the latter and increased expression in dorsal horn neurons containing MOR.     

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

Summary.  Background:  Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents. Objective:  The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction. Methods:  We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin. Results:  Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT_2A receptor, and sarpogrelate, a selective 5-HT_2A receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries. Conclusions:  These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT_2A receptor and the Rho-kinase pathway.     

Lasmiditan and 5-Hydroxytryptamine in the rat trigeminal system; expression,release and interactions with 5-HT1 receptors

Background5-Hydroxytryptamine (5-HT) receptors 1B, 1D and 1F have key roles in migraine pharmacotherapy. Selective agonists targeting these receptors, such as triptans and ditans, are effective in aborting acute migraine attacks and inhibit the in vivo release of calcitonin gene-related peptide (CGRP) in human and animal models. The study aimed to examine the localization, genetic expression and functional aspects of 5- HT_1B/1D/1F receptors in the trigeminal system in order to further understand the molecular sites of action of triptans (5-HT_1B/1D) and ditans (5-HT_1F).MethodsUtilizing immunohistochemistry, the localization of 5-HT and of 5-HT_1B/1D/1F receptors was examined in rat trigeminal ganglion (TG) and combined with quantitative polymerase chain reaction to quantify the level of expression for 5-HT_1B/1D/1F receptors in the TG. The functional role of these receptors was examined ex vivo with a capsaicin/potassium induced 5-HT and CGRP release.Results5-HT immunoreactivity (ir) was observed in a minority of CGRP negative C-fibres, most neuron somas and faintly in A-fibres and Schwann cell neurolemma. 5-HT_1B/1D receptors were expressed in the TG, while the 5-HT_1F receptor displayed a weak ir. The 5-HT_1D receptor co-localized with receptor activity-modifying protein 1 (RAMP1) in Aδ-fibres in the TG, while 5-HT_1B-ir was weakly expressed and 5-HT_1F-ir was not detected in these fibres. None of the 5-HT₁ receptors co-localized with CGRP-ir in C-fibres.5-HT_1D receptor mRNA was the most prominently expressed, followed by the 5-HT_1B receptor and lastly the 5-HT_1F receptor. The 5-HT_1B and 5-HT_1D receptor antagonist, {"type":"entrez-nucleotide","attrs":{"text":"GR127935","term_id":"238377770"}}GR127935, could reverse the inhibitory effect of Lasmiditan (a selective 5-HT_1F receptor agonist) on CGRP release in the soma-rich TG but not in soma-poor TG or dura mater. 5-HT release in the soma-rich TG, and 5-HT content in the baseline samples, negatively correlated with CGRP levels, showing for the first time a physiological role for 5-HT induced inhibition.ConclusionThis study reveals the presence of a subgroup of C-fibres that store 5-HT. The data shows high expression of 5-HT_1B/1D receptors and suggests that the 5-HT_1F receptor is a relatively unlikely target in the rat TG. Furthermore, Lasmiditan works as a partial agonist on 5-HT_1B/1D receptors in clinically relevant dose regiments.Supplementary InformationThe online version contains supplementary material available at 10.1186/s10194-022-01394-z.     

Effect of MKC-733, a 5-HT receptor partial agonist, on bowel motility and symptoms in subjects with constipation: an exploratory study

BACKGROUND: MKC-733, a 5-HT(3) receptor partial agonist, is a novel enteroprokinetic compound. OBJECTIVE: The aim of this study was to explore the effects of MKC-733 on bowel motility and symptoms in a small group of subjects with constipation. Tolerability was also examined. METHODS: The study was conducted in a single-blind and dose-escalation manner on 14 male and female subjects with constipation aged 22-67 years. After a 1 week run-in period, subjects were treated with placebo (b.i.d.) for 1 week, and 0.2 and 0.5 mg of MKC-733 (b.i.d.) for 2 weeks sequentially. Geometric mean and per cent elimination of surrogate markers of bowel motility were measured by a radio-opaque marker technique at the end of each treatment period. They were analysed on the whole group and subgroups with low (n = 6) and high (n = 8) bowel motility based upon the geometric mean value after placebo treatment. Subjects kept diaries of their bowel habits and gastrointestinal symptoms. RESULTS: Percent elimination increased after treatment with 0.5 mg MKC-733 compared with placebo treatment in the whole group (70.4 +/- 33.5% vs. 47.1 +/- 36.6%, mean +/- SD, P < 0.05). In the low bowel motility group, both geometric mean and percent elimination increased after treatment with 0.5 mg MKC-733 compared with placebo (7.1 +/- 0.9 vs. 5.9 +/- 0.5, P < 0.05; 60.0 +/- 35.8% vs. 13.3 +/- 19.4%, P < 0.05). Stool frequency increased after the first-week treatment with MKC-733 compared with placebo (P < 0.05). Numbers of sensation of incomplete evacuation and gastrointestinal symptoms decreased to half and less after the treatment with MKC-733. No serious adverse effect was noted. CONCLUSION: Multiple doses of 0.5 mg MKC-733 improve bowel motility, which was clearly demonstrated in the subjects with decreased bowel motility. MKC-733 at the doses studied might be effective in increasing stool frequency and reduce gastrointestinal symptoms related to constipation. MKC-733 was well tolerated. Further studies will be needed to clarify efficacy and safety of MKC-733 on a larger population.     

Efficacy of the 5-HT1A agonist, buspirone hydrochloride, in migraineurs with anxiety: a randomized, prospective, parallel group, double-blind, placebo-controlled study

OBJECTIVE: To examine the efficacy of buspirone, a 5-HT1A agonist, for migraine combined with anxiety disorder. BACKGROUND: Modulation of the 5-hydroxytryptamine (5-HT) system is used for the neuropharmacology of migraine treatment; however, the involvement of the 5-HT1A system in migraine is not fully understood. METHODS: Seventy-four outpatients aged 20 to 70 years (mean, 46.4; SD, 12.8) were analyzed. All subjects were diagnosed to have migraine according to the International Headache Society criteria and anxiety disorder according to DSM-IV. Subjects were randomly assigned to treatment with either buspirone (10 mg/day) or placebo for 6 weeks. Efficacy variables included changes in headache frequency, headache intensity, Hamilton Anxiety Rating Scale (HAM-A), Headache Self-Efficacy Scale (HMSE), and Headache Disability Inventory (HDI). The correlation between the headache improvement and the anxiolytic effect was analyzed. RESULTS: Headache frequency showed a 43.3% reduction in the buspirone-treated group, but by only 10.3% in the placebo group. HAM-A and HDI were also significantly more lowered in buspirone-treated patients than in placebo-treated patients. However, headache intensity and HMSE score were unchanged. Correlation analysis of the relation between headache frequency reduction and HAM-A improvement, revealed no significant association. CONCLUSIONS: In this study, buspirone showed a prophylactic effect in migraine with anxiety disorder, which was not secondary to its anxiolytic effect. This suggests that the agonistic action for 5-HT1A can be directly effective in migraine prophylaxis. However, more long-term study is warranted before concluding the efficacy.     

阻断炎症局部5-HT2A受体对大鼠脊髓背角一氧化氮合酶表达的影响

目的:研究阻断局部炎症组织中的5-HT2A受体后,脊髓背角一氧化氮合酶的变化,以了解外周5-HT2A受体在慢性炎症维持中的作用。方法:给大鼠足掌皮下注射2%角叉菜胶(carrageenan),1h后注射5-HT2A受体拮抗剂酮舍林(ketanserin)20μg。24h于大鼠同一位点注射1%福尔马林(formalin)。25h灌流、取材,进行NADPH-d组织化学实验。结果:注射角叉菜胶和福尔马林后,双侧脊髓背角浅层的NADPH-d阳性神经元数目均增多,以同侧更为显著。给予酮舍林后明显抑制这种增加。外周阿片受体拮抗剂纳洛酮(naloxone methiodide)可使酮舍林对炎症引起NADPH-d阳性神经元的抑制作用完全消失。结论:阻断外周5-HT2A受体能抑制角叉菜胶和福尔马林炎性痛刺激引起脊髓背角神经元的活化,这种抑制作用可能是通过激活阿片镇痛机制,继而抑制一氧化氮信号通路实现的。