Desensitization of 5-HT1A receptors by 5-HT2A receptors in neuroendocrine neurons in vivo

An imbalance between serotonin-2A (5-HT2A) and 5-HT1A receptors may underlie several mood disorders. The present studies determined whether 5-HT2A receptors interact with 5-HT1A receptors in the rat hypothalamic paraventricular nucleus (PVN). The sensitivity of the hypothalamic 5-HT1A receptors was measured as oxytocin and adrenocorticotropic hormone (ACTH) responses to the 5-HT1A receptor agonist (+)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide [(+)8-OH-DPAT] (40 microg/kg s.c.). The 5-HT(2A/2C) receptor agonist (-)DOI [(-)-1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane HCl] (1 mg/kg s.c.) injected 2 h prior to (+)8-OH-DPAT significantly reduced the oxytocin and ACTH responses to (+)8-OH-DPAT, producing a heterologous desensitization of the 5-HT1A receptors. Microinjection of the 5-HT2A receptor antagonist MDL100,907 [(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol; 0, 10, or 20 nmol, 15 min prior to (-)DOI] into the PVN dose-dependently prevented the desensitization of 5-HT1A receptors induced by the 5-HT2A receptor agonist (-)DOI. Double-label immunocytochemistry revealed a high degree of colocalization of 5-HT1A and 5-HT2A receptors in the oxytocin and corticotropin-releasing factor neurons of the PVN. Thus, activation of 5-HT2A receptors in the PVN may directly induce a heterologous desensitization of 5-HT1A receptors within individual neuroendocrine cells. These findings may provide insight into the long-term adaptation of 5-HT1A receptor signaling after changes in function of 5-HT2A receptors; for example, during pharmacotherapy of mood disorders.     

Serotonin 5-HT2A receptors underlie increased motor behaviors induced in dopamine-depleted rats by intrastriatal 5-HT2A/2C agonism

Gene expression studies have suggested that dopamine (DA) depletion increases the sensitivity of striatal direct pathway neurons to the effects of serotonin (5-HT) via the 5-HT(2) receptor. The present study examined the possible influence(s) of 5-HT(2A) or 5-HT(2C) receptor-mediated signaling locally within the striatum on motor behavior triggered by 5-HT(2) receptor agonism in the neonatal DA-depleted rat. Male Sprague-Dawley rats were treated with 6-hydroxydopamine (6-OHDA; 60 microg in 5 microl per lateral ventricle) on postnatal day 3 to achieve near-total DA depletion bilaterally. Sixty days later, sham-operated (saline-injected) or 6-OHDA-treated rats were challenged with the 5-HT(2A/2C) agonist DOI [(+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane] or saline either by systemic treatment or bilateral intrastriatal infusion. Motor behavior was quantified for 60 min after agonist injection using computerized activity monitors. Systemic DOI treatment (0.2 or 2.0 mg/kg i.p.) was more effective in inducing motor activity in the DA-depleted group compared with intact controls. Intrastriatal DOI infusion (1.0 or 10.0 microg/side) also produced a significant rise in motor activity in the DA-depleted group during the 30- to 60-min period of behavioral analysis but did not influence behavior in intact animals. The effects of intrastriatal DOI infusion were blocked by intrastriatal coinfusion of the 5-HT(2) antagonist ketanserin (1.0 microg) and the 5-HT(2A)-preferring antagonist M100907 [(R)(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol; 1.0 microg] but not the 5-HT(2C)-preferring antagonist RS102221 [8-[5-(2,4-dimethoxy-5-(4-trifluoromethylsulfo-amido)phenyl-5-oxopentyl]-1,3,8-triazaspiro[4.5]decane-2,4-dione; 1.0 microg]. Such results support the hypothesis that 5-HT(2A) receptor-mediated signaling events are strengthened within the striatum under conditions of DA depletion to provide a more potent regulation of motor activity.     

Regulation of extracellular concentrations of 5-hydroxytryptamine (5-HT) in mouse striatum by 5-HT(1A) and 5-HT(1B) receptors

The ability of selective serotonin (5-HT) receptor agonists to reduce the extracellular concentration of 5-HT was examined in the striatum of awake, unrestrained mice by in vivo microdialysis. Systemic administration of either 8-OH-PIPAT (R-(+)-trans-8-hydroxy-2-[N-n-propyl-N-(3'-iodo-2'-propenyl)] aminotetralin), a novel 5-HT(1A) receptor agonist, or CP 94,253, a selective 5-HT(1B) receptor agonist, resulted in significant dose-related reductions of striatal 5-HT. The effect of 8-OH-PIPAT (1.0 mg/kg) was blocked by pretreatment with WAY 100635 (0.1 mg/kg), a selective 5-HT(1A) receptor antagonist, but it was not blocked by pretreatment with GR 127935 (0.056 mg/kg), a selective 5-HT(1B/1D) receptor antagonist. The effect of CP 94,253 (1.0 mg/kg) was blocked by pretreatment with GR 127935 (0.056 mg/kg) but was not blocked by pretreatment with WAY 100635 (0.1 mg/kg). Neither WAY 100635 nor GR 127935 altered extracellular 5-HT levels at the doses that were able to completely block the effects of either 8-OH-PIPAT or CP 94,253. The present findings suggest that, on systemic administration, both 8-OH-PIPAT and CP 94,253 are potent and selective agonists at the somatodendritic 5-HT(1A) autoreceptor and terminal 5-HT(1B/1D) autoreceptor, respectively, and are each able to cause decreases in extracellular levels of 5-HT in the mouse striatum by activating a distinct set of receptors.     

5-Hydroxytryptamine 5-HT2A receptor and 5-hydroxytryptamine transporter polymorphisms in acute myocardial infarction

This study was designed to analyse possible associations between DNA polymorphisms in the 5-hydroxytryptamine (5-HT; serotonin) 5-HT(2A) receptor and the 5-HT transporter (5-HTT) genes, and myocardial infarction (MI). 5-HT has been shown to be involved in cardiovascular pathophysiology. In addition to platelet aggregation and vascular contraction, 5-HT induces hyperplasia of artery smooth muscle cells. Recently, a 5-HT transporter gene polymorphism has been associated with MI. To determine the influence of genetic variation at the 5-HT(2A) receptor (T102C polymorphism) and the 5-HTT (insertion/deletion polymorphism) on the risk of developing early MI, we genotyped 210 MI patients of < 55 years old and 238 healthy control subjects for DNA polymorphisms in these genes. In addition, we genotyped 95 patients with late-onset MI (> 60 years old) to analyse the effects of these polymorphisms on the age at which the first MI episode occurred. The 5-HT(2A) receptor polymorphism was not associated with MI in our population. In addition, since the 5-HT(2A) receptor gene and genotype frequencies did not differ between patients with early and late onset of MI, this polymorphism does not appear to have an effect on age at the first MI episode. Gene and genotype frequencies for the 5-HTT promoter did not differ between patients < 55 years old and healthy controls (independent of smoking status). However, homozygotes for the deletion (the ss genotype, where s denotes the short allele) were present at a significantly higher frequency in patients >60 years old compared with patients < 55 years old (P = 0.009; P = 0.004 when only smokers were compared). According to our data, the ss genotype would seem to have a protective role against MI, delaying the age of onset of the first episode, especially among smokers. This could be a consequence of the lower 5-HTT levels linked to the s allele, so that individuals homozygous for the ss genotype may have lower 5-HT re-uptake by platelets.     

Spinal 5-HT(2) and 5-HT(3) receptors mediate low, but not high, frequency TENS-induced antihyperalgesia in rats

Transcutaneous electrical nerve stimulation (TENS) is a form of non-pharmacological treatment for pain. Involvement of descending inhibitory systems is implicated in TENS-induced analgesia. In the present study, the roles of spinal 5-HT and alpha(2)-adrenoceptors in TENS analgesia were investigated in rats. Hyperalgesia was induced by inflaming the knee joint with 3% kaolin-carrageenan mixture and assessed by measuring paw withdrawal latency (PWL) to heat before and 4 h after injection. The (1). alpha(2)-adrenergic antagonist yohimbine (30 microg), (2). 5-HT antagonist methysergide (5-HT(1). and 5-HT(2). 30 microg), one of the 5-HT receptor subtype antagonists, (3). NAN-190 (5-HT(1A), 15 microg), (4). ketanserin (5-HT(2A), 30 microg), (5). MDL-72222 (5-HT(3), 12 microg), or (6). vehicle was administered intrathecally prior to TENS treatment. Low (4 Hz) or high (100 Hz) frequency TENS at sensory intensity was then applied to the inflamed knee for 20 min and PWL was determined. Selectivity of the antagonists used was confirmed using respective agonists administered intrathecally. Yohimbine had no effect on the antihyperalgesia produced by low or high frequency TENS. Methysergide and MDL-72222 prevented the antihyperalgesia produced by low, but not high, frequency TENS. Ketanserin attenuated the antihyperalgesic effects of low frequency TENS whereas NAN-190 had no effect. The results from the present study show that spinal 5-HT receptors mediate low, but not high, frequency TENS-induced antihyperalgesia through activation of 5-HT(2A) and 5-HT(3) receptors in rats. Furthermore, spinal noradrenergic receptors are not involved in either low or high frequency TENS antihyperalgesia.     

Relationship between receptors mediating serotonin (5-HT) contractions in the canine basilar artery to 5-HT1, 5-HT2 and rat stomach fundus 5-HT receptors

The receptors responsible for contraction to serotonin (5-HT) in the canine basilar artery have not been definitively established to date. Several selective 5-HT2 receptor antagonists (spiperone, ketanserin and LY53857) did not inhibit markedly 5-HT-induced contractions in the canine basilar artery in doses higher than required for substantial inhibition of 5-HT2 receptor-mediated responses. These data suggest that the receptors mediating 5-HT-induced contractions in the basilar artery are not 5-HT2 receptors. Using a series of 5-HT antagonists with relatively high affinity at 5-HT1 sites, over a 1000-fold difference occurred in their ability to block 5-HT receptors in the canine basilar artery, in spite of the similar and high affinity of the antagonists at 5-HT1 binding sites. These data support the contention that 5-HT receptors in the canine basilar artery are not 5-HT1 receptors as defined by ligand binding studies in brain cortical membranes. Similarity of the contractile effects of 5-HT in the rat stomach fundus and in the basilar artery coupled to the previous observations that receptors mediating 5-HT-induced contractions in the fundus were not 5-HT1, 5-HT1A, 5-HT1B or 5-HT2 led us to consider the possibility that 5-HT receptors in the canine basilar artery may resemble those in the rat stomach fundus. The affinity of several 5-HT antagonists determined in the canine basilar artery correlated extremely well (correlation coefficient = 0.96) with the affinities obtained for the same antagonists in the rat stomach fundus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of serotonin2 (5-HT2) receptors by quipazine increases arterial pressure and renin secretion in conscious rats

Quipazine, a nonselective serotonin (5-HT) agonist, has been shown to increase plasma renin activity (PRA). The present study examined the effects of quipazine on mean arterial pressure (MAP), heart rate (HR) and PRA in conscious, chronically catheterized male rats. Quipazine caused dose (0.3-3.0 mg/kg i.v.)-and time (up to 30 min)-dependent increases in MAP and PRA. The maximum increases in MAP (control = 94 +/- 2 mm Hg, 3 mg/kg = 155 +/- 1 mm Hg) and PRA (nanograms of angiotensin 1 per milliliter per hour; control = 2.5 +/- 0.2, 3 mg/kg = 25.2 +/- 5.9) were observed 5 min after quipazine. HR tended to decrease, but a significant bradycardia was observed only 15 min after 3 mg/kg. The selective 5-HT2 antagonist LY 53857 (1 mg/kg i.v.) did not affect MAP, HR or PRA per se, but at 0.03 to 1.0 mg/kg totally abolished the pressor response to quipazine (3 mg/kg). At 0.01 mg/kg, LY 53857 attenuated quipazine-induced hypertension, whereas 0.003 mg/kg was ineffective. Total blockade of quipazine-induced renin secretion was produced by LY 53857 at 0.003 mg/kg, and the response was still reduced by 50% at 0.001 mg/kg. In summary, although quipazine increases arterial pressure and renin secretion, endogenous 5-HT does not tonically control MAP or PRA in conscious, unrestrained, normotensive rats through 5-HT2 receptors. The 10-fold difference in the dose of LY 53857 necessary to block the pressor and renin responses may be due to subtle differences in receptor subtypes, or to pharmacokinetic properties favoring antagonism of quipazine-induced renin secretion.     

Functional selectivity of hallucinogenic phenethylamine and phenylisopropylamine derivatives at human 5-hydroxytryptamine (5-HT)2A and 5-HT2C receptors

2,5-Dimethoxy-4-substituted phenylisopropylamines and phenethylamines are 5-hydroxytryptamine (serotonin) (5-HT)(2A/2C) agonists. The former are partial to full agonists, whereas the latter are partial to weak agonists. However, most data come from studies analyzing phospholipase C (PLC)-mediated responses, although additional effectors [e.g., phospholipase A(2) (PLA(2))] are associated with these receptors. We compared two homologous series of phenylisopropylamines and phenethylamines measuring both PLA(2) and PLC responses in Chinese hamster ovary-K1 cells expressing human 5-HT(2A) or 5-HT(2C) receptors. In addition, we assayed both groups of compounds as head shake inducers in rats. At the 5-HT(2C) receptor, most compounds were partial agonists for both pathways. Relative efficacy of some phenylisopropylamines was higher for both responses compared with their phenethylamine counterparts, whereas for others, no differences were found. At the 5-HT(2A) receptor, most compounds behaved as partial agonists, but unlike findings at 5-HT(2C) receptors, all phenylisopropylamines were more efficacious than their phenethylamine counterparts. 2,5-Dimethoxyphenylisopropylamine activated only the PLC pathway at both receptor subtypes, 2,5-dimethoxyphenethylamine was selective for PLC at the 5-HT(2C) receptor, and 2,5-dimethoxy-4-nitrophenethylamine was PLA(2)-specific at the 5-HT(2A) receptor. For both receptors, the rank order of efficacy of compounds differed depending upon which response was measured. The phenylisopropylamines were strong head shake inducers, whereas their phenethylamine congeners were not, in agreement with in vitro results and the involvement of 5-HT(2A) receptors in the head shake response. Our results support the concept of functional selectivity and indicate that subtle changes in ligand structure can result in significant differences in the cellular signaling profile.     

Role of spinal 5-HT(1A) receptors in morphine analgesia and tolerance in rats.

We here studied the involvement of spinally located 5-HT(1A) and opioid receptors, in the paradoxical effects that their activation can produce on nociception. Intrathecal (i.t.) injection of the 5-HT(1A) receptor agonist 8-hydroxy-2-[di-n-propylamino] tetralin (8-OH-DPAT) (1-10 microg) induced analgesic effects in the formalin model of tonic pain whereas in the paw pressure test, it decreased the vocalization threshold. In this latter test, i.t. 8-OH-DPAT also markedly reduced the analgesic effect of systemic morphine (5-10 mg/kg, s.c.). At 10 microg, 8-OH-DPAT totally abolished the effect of 5 mg/kg of morphine; this inhibitory effect was antagonized by pre-treatment with 0.63 mg/kg of the 5-HT(1A) antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl)-cyclohexanecarboxamide-trihydrochloride). In contrast, the i.t. injection of WAY-100635 (1-10 microg) dose-dependently potentiated the antinociceptive activity of a dose of morphine (2.5 mg/kg, s.c.). Furthermore, WAY-100635 (10 microg, i.t.) potentiated morphine analgesia in morphine-tolerant rats. These findings demonstrate that 5-HT(1A) receptor agonists can act in the spinal cord to produce both hyper- and hypo-algesic effects and play a major role in the opioid analgesia and tolerance.     

Selective and divergent regulation of cortical 5-HT(2A) receptors in rabbit.

It is well established that repeated administration of both 5-hydroxytryptamine(2) (5-HT(2)) receptor agonists and antagonists decreases the density of 5-HT(2A) and 5-HT(2C) receptors. However, the regulation of these two receptors has not been studied in the same tissue. Therefore, we examined the effects of repeated daily injections of the 5-HT(2) receptor agonists (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) and D-lysergic acid diethylamide (LSD) and the antagonists d-2-bromolysergic acid diethylamide hydrogen tartrate (BOL) and alpha-phenyl-2-(2-phenylethyl)-4-piperidinemethanol (MDL 11,939) on rabbit cortical 5-HT(2A) and 5-HT(2C) receptors. Repeated administration of DOI, LSD, or BOL decreased cortical 5-HT(2A) receptor density but had no effect on the density of cortical 5-HT(2C) receptors. Repeated administration of the selective 5-HT(2A) receptor antagonist MDL 11,939 significantly increased 5-HT(2A) receptor density. This unexpected outcome also occurred without any change in cortical 5-HT(2C) receptor density. The down-regulation of 5-HT(2A) receptors produced by chronic administration of BOL was associated with a decrease in DOI-elicited head bobs, whereas 5-HT(2A) receptor up-regulation produced by MDL 11,939 was associated with an increase in DOI-elicited head bobs compared with controls. These studies demonstrate that 5-HT(2A) receptor antagonists can both down- and up-regulate the density of cortical 5-HT(2A) receptors and these changes in receptor density have functional consequences for 5-HT(2A) receptor-mediated behaviors. Furthermore, because DOI, LSD, and BOL have approximately equal affinities for the 5-HT(2A) and 5-HT(2C) receptors, these results suggest that different mechanisms regulate 5-HT(2A) and 5-HT(2C) receptor density, in that chronic occupation of 5-HT(2C) receptors does not modulate their density in rabbit frontal cortex.     

Selective blockade of A(2A) receptor protects against neurotoxicity induced by kainic acid in young rats

The aim of this study was to investigate the effect of SCH 58261, a selective adenosine A(2A) receptor (A(2A)R) antagonist, on kainic acid (KA)-induced seizures in 21-day-old rats. Rats were pretreated with SCH 58261 (1 or 3 mg/kg) by intraperitoneal (i.p.) route 30 min before KA (10 mg/kg, i.p.) administration. The appearance of clonic seizures, the latency for the onset of the first clonic seizure episode, and the number of deaths induced by KA were evaluated. To test the hypothesis of the oxidative imbalance induced by KA exposure, reactive species (RS) levels, catalase (CAT), glutathione peroxidase (GPx), and glutathione S-transferase (GST) activities in the brains of rats were measured. Both doses of SCH 58261 prolonged the latency for the onset of the first clonic seizure episode. SCH 58261, at the highest dose, decreased the appearance of clonic seizures as well as the mortality rate induced by KA administration. SCH 58261, at the dose of 3 mg/kg, was also effective in protecting against alterations in oxidative stress parameters (RS levels, CAT, GPx, and GST activities) in the brains of young rats exposed to KA. Our data reveal that SCH 58261 was protective against the neurotoxicity induced by KA. Therefore, the blockade of A(2A)R might represent a novel approach for the treatment of seizures.     

Temporal regulation of agonist efficacy at 5-hydroxytryptamine (5-HT)1A and 5-HT 1B receptors

Coactivation of purinergic (P 2Y) receptors reduces agonist efficacy at serotonin 1B (5-HT 1B), but not 5-HT 1A receptors. Herein, we report that pretreatment for 5 min with the P 2Y receptor agonist ATP reduced agonist responsiveness at the 5-HT 1A, but not at the 5-HT 1B, receptor. The effect of ATP pretreatment on the 5-HT 1A receptor response rapidly reversed within a 10 min time frame between P 2Y receptor and 5-HT 1A receptor activation. ATP pretreatment effects on 5-HT 1A agonist responsiveness were blocked by the protein kinase inhibitors staurosporine and bisindolylmaleimide, suggesting that the ATP-mediated temporal regulation involves activation of protein kinase C (PKC). Moreover, the temporal effect of ATP was blocked by incubation with 1% ethanol, suggesting that consequences of phospholipase D (PLD) activation play a role. ATP pretreatment blocked the inhibitory effect produced by 5-HT 2C receptor activation on the 5-HT 1A, but not the 5-HT 1B, receptor response, suggesting that the 5-HT 1A receptor itself was the target for PLD/PKC action. Finally, ethanol did not block the reduction in responsiveness of the 5-HT 1A receptor system produced by activation of PKC with phorbol ester treatment, suggesting that PKC activation lies downstream of PLD. Taken together, these data suggest that activation of P 2Y receptors can reduce responsiveness of the 5-HT 1A receptor system via a PLD/PKC-dependent mechanism that is highly dependent upon the temporal pattern of receptor activation. Moreover, this work underscores the importance of time as a variable in receptor signaling cross talk and serves to further illustrate differences between the 5-HT 1A and 5-HT 1B receptor systems.     

5-Hydroxytryptamine (5-HT)-induced endothelium-dependent relaxation of pig coronary arteries is mediated by 5-HT receptors similar to the 5-HT1D receptor subtype

The 5-hydroxytryptamine (5-HT) receptor mediating endothelium-dependent relaxation of pig coronary arteries was characterized using a variety of 5-HT receptor agonists and antagonists. Unrubbed (with endothelium preserved) rings precontracted by prostaglandin F2 alpha in the presence of ketanserin relaxed in an endothelium-dependent manner to 5-HT, 5-carboxamidotryptamine and 5-methoxytryptamine with about equal potency and efficacy. By comparison, bufotenine, 3-(dimethylamino)ethyl-N-methyl-1H-indole-5-methane sulfonamide, (-)-alpha-methyl-5-HT,N,N-dipropyl-5-carboxamidotryptamine and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H indole were half-efficient and other drugs [in particular the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin] were inactive as agonists up to 0.1 mM. The effect of 5-carboxamidotryptamine was antagonized in an apparently competitive manner by 15 drugs. Among the most potent antagonists (mean pKB value) were the nonselective 5-HT receptor antagonists, methiothepin (7.30) and metergoline (6.86), the 5-HT1A/5-HT1D receptor ligand, 1-[2-(4-amino-phenyl)ethyl]-4-(3-trifluoromethylphenyl)-piperazine (7.02), the 5-HT1A/5-HT1B/5-HT1D receptor ligand, 7-trifluoromethyl-4-(4-methyl-1-piperazinyl)-pyrrolo[1,2,-a]quinoxaline 1 (6.73) and yohimbine (6.37). Selective ligands for 5-HT1A receptors were either inactive [8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide] or poorly active (spiperone, 4.44). Beta-adrenoceptor antagonists with affinity for 5-HT1A and 5-HT1B receptors weakly antagonized the effect of 5-carboxamidotryptamine (pKB values less than or equal to 5.32), as did the 5-HT1c/5-HT2 receptor antagonist, mesulergine (5.30) and the yohimbine isomer, corynanthine (4.85). Methysergide was clearly a noncompetitive antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Increase of capsaicin-induced trigeminal Fos-like immunoreactivity by 5-HT(7) receptors

Objective.— To explore whether pharmacological stimulation of the 5‐hydroxytryptamine₇ (5‐HT₇) receptor modulates Fos‐like immunoreactivity in the trigeminal nucleus caudalis of rats. Background.— The serotonin 5‐HT₇ receptor was proposed to be involved in migraine pathogenesis and evidence suggests it plays a role in peripheral nociception and hyperalgesia through an action on sensory afferent neurons. Methods.— The potential activating or sensitizing role of 5‐HT₇ receptors on trigeminal sensory neurons, as visualized by Fos‐like immunoreactivity in the superficial layers of the trigeminal nucleus caudalis in rats, was investigated using the 5‐HT₇ receptor agonist, LP‐211, in the absence and the presence of intracisternal capsaicin, respectively. The agonist effect was characterized with the 5‐HT₇ receptor antagonist, SB‐656104. Male Wistar rats received a subcutaneous injection of LP‐211, SB‐656104, and SB‐656104 + LP‐211. They were then anesthetized and prepared to receive an intracisternal injection of capsaicin or its vehicle. Animals were perfused and brains removed; sections of the brain stem from the area postrema to the CI level were obtained and processed for Fos immunohistochemistry. Results.— Capsaicin but not its vehicle induced Fos‐like immunoreactivity within laminae I and II of trigeminal nucleus caudalis. Pretreatment with LP‐211 had no effect on Fos‐like immunoreactivity but strongly increased the response produced by capsaicin; this effect was abolished by SB‐656104. Interestingly, capsaicin‐induced Fos‐like immunoreactivity was abolished by SB‐656104 pretreatment thus suggesting involvement of endogenous 5‐HT. Conclusions.— Data suggest that 5‐HT₇ receptors increase activation of meningeal trigeminovascular afferents and/or transmission of nociceptive information in the brain stem. This mechanism could be relevant in migraine and its prophylactic treatment.     

Central 5-hydroxytryptamine (5-HT) receptors in blood pressure regulation.

Both intravenous and central administration of ketanserin, a 5-HT2 receptor antagonist, decrease blood pressure and sympathetic nerve activity, suggesting a central origin of its effects. However, ketanserin also possesses alpha 1-adrenoceptor blocking properties. Selective 5-HT2 receptor antagonists devoid of alpha 1-adrenoceptor blocking properties, e.g. LY 53857 and cinanserin, fail to reduce blood pressure and sympathetic nerve activity. In addition, 5-HT2 receptor agonists increase blood pressure and sympathetic nerve discharge. Therefore, it seems improbable that blockade of central 5-HT2 receptors alone could lead to a reduction in blood pressure. In contrast, the selective 5-HT1A receptor agonists 8-OH-DPAT and flesinoxan decrease blood pressure and heart rate by a centrally-mediated decrease in sympathetic tone and an increase in vagal tone. The sympatho-inhibitory effects of 5-HT1A receptor agonists result from the stimulation of postsynaptic 5-HT1A receptors within the ventrolateral pressor area. These results suggest that selective 5-HT1A receptor agonists acting in the central nervous system could be developed for the treatment of hypertension. Indeed, drugs such as flesinoxan and urapidil are effective in this setting.     

腺苷后适应对糖尿病急性心肌梗死再灌注的保护作用

目的:观察经皮冠状动脉介入治疗(PCI)术中腺苷后适应对糖尿病急性心肌梗死(AMI)再灌注的保护作用。方法:将84例AMI患者按入选条件分为非糖尿病再灌注组(IR),非糖尿病腺苷后处理组(POST),糖尿病再灌注组(DIR),糖尿病腺苷后处理组(DPOST),糖尿病组按入院时所测糖化血红蛋白(HbA1c)值再分为DIR1(HbA1c<7%)、DIR2(HbA1c≥7%)、DPOST1(HbA1c<7%)、DPOST2(HbA1c≥7%)。POST及DPOST组于支架植入前静滴腺苷,IR及DIR组于支架植入前静滴等量生理盐水。检测PCI术前及术后30min冠脉血浆中的MDA、SOD及PCI术后6、12、24及48h静脉血CM-MB水平。结果:6组患者术后MDA值均较术前升高(P﹤0.01),SOD值均较术前降低(P﹤0.01);POST及DPOST组MDA值比IR及DIR组升高较少(P﹤0.05),SOD值比IR及DIR降低较少(P﹤0.05)。术后POST及DPOST组CK-MB峰值较IR及DIR组降低(P﹤0.05)。结论:糖尿病急性心肌梗死PCI治疗时应用腺苷后处理可以减轻心肌缺血再灌注损伤,起到心肌保护的作用。     

5-hydroxytryptamine3 (5-HT3) receptors mediate spinal 5-HT antinociception: an antisense approach.

To examine the role of the 5-hydroxytryptamine(1B) (5-HT1B) and 5-HT3 receptor subtypes in the analgesia produced by 5-HT (serotonin) agonists, we assessed the effect of antisense oligodeoxynucleotides (AODNs) designed to "knock down" the number of these receptor subtypes on analgesia produced by intrathecal (i.t.) 5-HT, the 5-HT1B receptor agonist, 7-trifluoromethyl-4-(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]quinoxaline maleate (CGS-12066A), and the 5-HT3 receptor agonist, 2-methyl-5-HT. Groups of mice (n = 17-20) were injected i.t. on days 1, 3, and 5 with one of the AODNs, a mismatch oligo, or saline. On day 6, all mice were injected i.t. with 70.5 nmol of 5-HT, 44.4 nmol of CGS-12066A, or 49 nmol of 2-methyl-5-HT by lumbar puncture. Following testing, spinal cords were rapidly removed and prepared for receptor binding assays. Treatment with AODN for 5-HT1B receptors produced a 70% reduction in ligand binding to this receptor subtype. After treatment with AODN for 5-HT3 receptors, ligand binding to this receptor subtype was undetectable. In mice tested with i.t. 5-HT, tail-flick analgesia was attenuated only in mice treated with the 5-HT3 receptor AODN. Mice treated with the AODN designed to knock down 5-HT(1B) receptors or with its mismatch oligo were not significantly different from controls. In mice tested with i.t. administration of CGS-12066A, none of the oligo treatments produced a significant attenuation of analgesia. In mice tested with i.t. administration of 2-methyl-5-HT, only 5-HT3 receptor AODN attenuated analgesia. Thus, 5-HT and 2-methyl-5-HT analgesia are mediated by the 5-HT3 receptor subtype. However, spinal CGS-12066A analgesia appears not to be mediated by either the 5-HT1B or the 5-HT3 receptor subtypes.     

Activation of 5-HT1A and 5-HT7 receptors in the parafascicular nucleus suppresses the affective reaction of rats to noxious stimulation

The antinociceptive effects of the serotonin (5-HT)1A/7 receptor agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) administered into the medial thalamus were evaluated. Pain behaviors organized at spinal (spinal motor reflexes, SMRs), medullary (vocalizations during shock, VDSs), and forebrain (vocalization after discharges, VADs) levels of the neuraxis were elicited by tailshock. Administration of 8-OH-DPAT (5, 10, and 20 microg/side) into nucleus parafascicularis (nPf) produced dose-dependent increases in VDS and VAD thresholds, but failed to elevate SMR threshold. The increase in VAD threshold was significantly greater than that of VDS threshold. Similar effects were observed with administration of 8-OH-DPAT (20 microg/side) into the rostral portion of the central lateral thalamic nucleus. The bilateral or unilateral administration of 8-OH-DPAT (20 microg) into other thalamic nuclei, or into sites dorsal to nPf, did not elevate vocalization thresholds. Increases in vocalization thresholds produced by nPf-administered 8-OH-DPAT were mediated by both 5-HT1A and 5-HT7 receptors. Intra-nPf administration of the 5-HT1A receptor antagonist WAY-100635 (0.05 or 0.5 microg/side), or the 5-HT7 receptor antagonist SB-269970 (1 or 2 microg/side), but not the dopamine D2 receptor antagonist raclopride (10 microg/side), reversed 8-OH-DPAT induced elevations in vocalization thresholds. These results provide the first reported evidence of behavioral antinociception following the administration of a 5-HT agonist into the medial thalamus.     

Role of peripheral 5-HT(4), 5-HT(6), and 5-HT(7) receptors in development and maintenance of secondary mechanical allodynia and hyperalgesia

The role of 5-hydroxytryptamine (5-HT)₄, 5-HT₆, and 5-HT₇ receptors in formalin-induced secondary allodynia and hyperalgesia in rats was assessed. Formalin produced acute nociceptive behaviors (flinching and licking/lifting) followed by long-term secondary mechanical allodynia and hyperalgesia. Pretreatment (−10 min) with cromoglycate (195-1950 nmol/paw) partially inhibited acute nociceptive behaviors and completely prevented secondary allodynia and hyperalgesia on day 6 after injection. Ipsilateral peripheral pretreatment with the selective 5-HT₄ (ML-10302, 1-100 nmol/paw), 5-HT₆ (EMD-386088, 0.001-0.01 nmol/paw), and 5-HT₇ (LP-12, 0.01-100 nmol/paw) receptor agonists significantly increased secondary allodynia and hyperalgesia in both paws. In contrast, ipsilateral peripheral pretreatment with the selective 5-HT₄ (GR-125487, 1-100 nmol/paw), 5-HT₆ (SB-258585, 0.00001-0.001 nmol/paw), and 5-HT₇ (SB-269970, 0.1-10 nmol/paw) receptor antagonists significantly prevented formalin-induced secondary allodynia and hyperalgesia in both paws. The pronociceptive effect of ML-10302 (100 nmol/paw), EMD-386088 (0.01 nmol/paw), and LP-12 (100 nmol/paw) were completely prevented by GR-125487 (5-HT₄ antagonist, 1 nmol/paw), SB-258585 (5-HT₆ antagonist, 0.00001 nmol/paw), and SB-269970 (5-HT₇, antagonist, 0.01 nmol/paw), respectively. Ipsilateral peripheral posttreatment with cromoglycate or GR-125487 (1-100 nmol/paw), SB-258585 (0.001-0.1 nmol/paw), and SB-269970 (0.1-10 nmol/paw) reversed formalin-induced secondary allodynia and hyperalgesia in both paws. Results suggest that a barrage of afferent input induced by 5-HT at peripheral 5-HT₄, 5-HT₆, and 5-HT₇ receptors participate in the development and maintenance of formalin-induced long-term secondary allodynia and hyperalgesia in the rat.