Nelumbinis Semen reverses a decrease in 5-HT1A receptor binding induced by chronic mild stress, a depression-like symptom

Depression is associated with a dysfunctional serotonin (5-hydroxytryptamine; 5-HT) system. More recently, several lines of evidence suggest that an important factor in the development of depression may be a deficit in the function and expression of 5-HT1A receptors. The present study assessed if Nelumbinis Semen (N.s.) had an anti-depression effect through reversing a decrease in 5-HT1A receptor binding in rats with depression-like symptoms induced by chronic mild stress. Using a 5-HT1A receptor binding assay, with a specific 5-HT1A receptor agonist, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino) tetralin), the mechanism of the anti-depression effect of N.s. on rats was investigated, and the effects compared with two well-known antidepressants, Hyperium Perforatum (St. Johns Wort) and fluoxetine (Prozac). Animals were divided into five groups: the normal (N) group without chronic mild stress (CMS), the control (C) group under CMS for 8 weeks, the Nelumbinis Semen (N.s.) treatment group under CMS for 8 weeks, the Hyperium Perforatum (H.p.) treatment group under CMS for 8 weeks and finally, the fluoxetine (F) treatment group under CMS for 8 weeks. Each treatment was administered to rats during the last 4 weeks of the 8-week CMS. A sucrose intake test was performed to test the anti-depression effect of N.s. The N.s. treatment significantly reversed the decreased sucrose intake under CMS (P < 0.05 compared to control group under CMS). In the CA2 and CA3 regions of the hippocampus, both N.s. and H.p. reversed the CMS-induced decrease in 5-HT1A receptor binding. In the I to II regions of the frontal cortex, N.s. and H.p. also reversed the CMS-induced decrease in 5-HT1A receptor binding, and even showed a significant increase in 5-HT1A receptor binding compared to the F treatment group (N.s. vs. P, p < 0.05, H.p. vs. P, p < 0.05). However, in the hypothalamus, all treatments reversed the CMS-induced decrease in 5-HT1A receptor binding. This reversal effect of N.s. on the decrease in 5-HT1A receptor binding in the frontal cortex, hippocampus and hypothalamus of rat brains was very similar to that of H.p, but different from that of F. It is concluded that N.s. presents an anti-depression effect through enhancing 5-HT1A receptor binding.     

Repeated paroxetine treatment reverses anhedonia induced in rats by chronic mild stress or dexamethasone.

The present study was designed to assess the effect of dexamethasone, a synthetic glucocorticoid receptor agonist, in the sucrose preference test in rats. Rats treated acutely with dexamethasone (5-10 mg/kg) showed a significant decrease in sucrose preference (anhedonia) in comparison to vehicle treated rats, although 1 mg/kg dexamethasone did not alter the sucrose preference. Daily paroxetine treatment (10 g/kg, i.p., 14 days) reversed the anhedonic effect of acute dexamethasone (5 mg/kg), while causing no increased sucrose preference in rats that received dexamethasone vehicle. The paroxetine vehicle treated rats showed anhedonia even 14 days after acute dexamethasone administration. Paroxetine (10 mk/kg, i.p. for 28 days) also reversed anhedonia induced by chronic mild stress (8 weeks). In conclusion, acute dexamethasone induced an enduring anhedonic state that was reversed by repeated paroxetine treatment. Thus, the present study adds new data to the evidence supporting an important role for glucocorticoid in depression.     

Electroconvulsive stimulation reverses anhedonia and cognitive impairments in rats exposed to chronic mild stress

Electroconvulsive therapy remains the most effective treatment for depression including a fast onset of action. However, this therapeutic approach suffers from some potential drawbacks. In the acute phase this includes amnesia. Electroconvulsive stimulation (ECS) has previously been shown to reverse a depression-like state in the chronic mild stress model of depression (CMS), but the effect of ECS on cognition has not previously been investigated. In this study the CMS model was used to induce a depressive-like condition in rats. The study was designed to investigate the acute effect of ECS treatment on working memory and the chronic effect of repeated ECS treatments on depression-like behavior and working memory. The results indicated that, in the acute phase, ECS treatment induced a working memory deficit in healthy controls unexposed to stress, while repeated treatments reversed stress-induced decline in working memory, as well as recovering rats submitted to the CMS paradigm from the anhedonic-like state. Like in the clinical setting, a single ECS exposure was ineffective in inducing remission from a depression-like state.     

咖啡酸对慢性应激大鼠的抗抑郁作用

目的探讨咖啡酸对慢性应激大鼠的抗抑郁作用。方法采用各种慢性不可预见轻微刺激建立大鼠抑郁模型。21 d后,ig给予大鼠咖啡酸10,30和50 mg.kg-1,连续21 d。通过旷场实验检测中央格停留时间、水平活动和垂直活动情况,通过强迫游泳实验检测大鼠静止不动行为百分比(PI);检测海马超氧化物歧化酶(SOD)活性与丙二醛(MDA)含量。结果与正常对照组相比,模型组大鼠在旷场实验中央格停留时间增长,水平活动和垂直活动减少,强迫游泳静止不动状态增加,SOD活性显著降低,MDA含量显著升高(P<0.01)。与模型组相比,咖啡酸10～50 mg.kg-1组能够显著缩短停留时间(P<0.05)、增加垂直活动(P<0.01),但对水平活动无明显影响。模型组PI为(79.69±15.84)%,咖啡酸10～50 mg.kg-1组PI显著降低,分别为(16.00±2.11)%,(10.33±2.92)%和(7.33±2.63)%。与正常对照组相比,模型组SOD酶活性显著降低,MDA含量显著增加(P<0.01),与模型组相比,咖啡酸10～50 mg.kg-1能够显著增加SOD酶活性,分别为模型组的1.50,2.46和2.59倍(r=0.915,P<0.01);MDA含量显著降低,分别为模型组的18.64%,11.37%和6.35%(P<0.01),且呈剂量依赖性(r=0.982,P<0.01)。咖啡酸与舍曲林5 mg.kg-1的作用相似。结论咖啡酸对慢性应激大鼠有一定的抗抑郁作用。     

Modulation of hippocampal serotonin (5-HT) release by endogenous adenosine

Slices of rabbit hippocampus were preincubated with [3H]serotonin then superfused continuously and stimulated twice electrically. The stimulation-evoked overflow of tritium was Ca2+-dependent, tetrodotoxin-sensitive and subject to modulation by serotonin autoreceptors. It was decreased by various adenosine receptor agonists in an order of potency that was typical for A1-(Ri-) receptors: N6-cyclohexyladenosine greater than (-)N6-phenylisopropyladenosine greater than 5'-N-ethylcarboxamideadenosine greater than (+)N6-phenylisopropyladenosine = adenosine. The effects of the agonists were antagonized by 8-phenyltheophylline. The hypothesis that endogenous adenosine influences hippocampal serotonin release is supported by the following findings: both the adenosine receptor antagonists (theophylline or 8-phenyltheophylline (10 microM, each)) and the enzyme adenosine deaminase (10 micrograms/ml) increased, whereas R-E 244 (3 microM), an inhibitor of adenosine uptake, significantly decreased the evoked tritium overflow. When 8-phenyltheophylline was present throughout superfusion the effects of both R-E 244 and exogenous adenosine deaminase were abolished. It is concluded that serotonin release in the rabbit hippocampus is depressed by endogenous adenosine via A1-(Ri-) receptors.     

阿魏酸钠对慢性不可预知温和刺激抑郁症大鼠抑郁行为的影响及其机制

目的：研究阿魏酸钠能否改善慢性不可预知温和刺激（chronic unpredicted mild stress,CUMS）抑郁大鼠的抑郁样行为并探讨其机制。方法：将SD大鼠随机分为正常对照组、CUMS模型组、CUMS+氟西汀（10 mg· kg^-1）组、CUMS+阿魏酸钠（50,100,150 mg· kg^-1）组。采用慢性温和不可预知应激方法建立大鼠抑郁模型,造模完成后,连续灌胃给药21 d。旷场实验、糖水偏爱实验、强迫游泳实验检测大鼠的行为学变化;生物化学方法检测大鼠海马超氧化物歧化酶（superoxide dismutase,SOD）和过氧化氢酶（catalase,CAT）活性及活性氧（reactive oxygen species,ROS）含量。实时荧光定量PCR（q-PCR）法检测海马炎症因子IL-1β、TNF-α、PGE₂及IL-10基因的mRNA转录水平;酶联免疫吸附试验检测海马炎症因子IL-1β、TNF-α、PGE₂及IL-10含量的变化。结果：行为学检测结果显示,与正常对照组相比,旷场实验中模型组大鼠水平运动和垂直运动得分降低（P<0.01）,糖水偏爱实验中糖水偏爱度显著下降（P<0.01）,强迫游泳实验中不动时间明显延长（P<0.01）;分子生物学检测结果显示,模型组大鼠海马内ROS含量显著升高（P<0.01）,SOD和CAT的活性显著降低（P<0.01）,海马IL-1β、TNF-α、PGE₂和IL-10 mRNA和蛋白水平明显升高（P<0.05,P<0.01）。阿魏酸钠和氟西汀均能不同程度地改善CUMS诱导的上述改变。结论：阿魏酸钠能明显改善CUMS所致的大鼠抑郁样行为,其机制可能与降低海马氧化应激水平和改善炎症反应相关。     

Reversal by flunarizine of the decrease in hippocampal acetylcholine release in pentylenetetrazole-kindled rats.

The aim of our study was to evaluate the effect of the non-selective calcium antagonist flunarizine on hippocampal acetylcholine (ACh) release with the microdialysis technique in freely moving rats after long-term concomitant administration of pentylenetetrazole (PTZ) in comparison with rats treated long-term with PTZ (kindled animals). The basal extracellular concentration of ACh in the hippocampus of rats treated with PTZ alone was significantly reduced relative to that of vehicle-treated rats (2.04+/-0.2 vs 3.94+/-0.3 pmol per 20-min sample; P < 0.01). Administration of flunarizine (7.5 mg/kg i.p.) before each PTZ injection prevented this decrease in basal ACh output (3.75+/-0.4 pmol per 20-min sample). On the contrary, the expression of PTZ-induced kindling was not prevented by administration of flunarizine. The specific antagonistic effect of flunarizine on the kindling-induced decrease in hippocampal ACh release is shared by the selective antagonist of the L-type calcium channel, nifedipine, but not by the dopamine D2 antagonist, (-)-sulpiride, suggesting that the decrease in Ca2+ overload by a blockade of the L-type calcium channel may be responsible for the protective action on cholinergic neurons exerted by flunarizine. These data also suggest a potential therapeutic role for flunarizine in counteracting impairment of hippocampal cholinergic activity.     

金丝桃苷对慢性不可预知温和刺激大鼠抑郁行为的影响

目的研究金丝桃苷对慢性温和不可预知应激(CUMS)大鼠抑郁样行为的影响。方法大鼠随机分空白组,模型组,金丝桃苷低(5 mg·kg~(-1))、中(10 mg·kg~(-1))、高(15 mg·kg~(-1))剂量组和氟西汀(10 mg·kg~(-1))对照组,每组10只。采用慢性温和不可预知应激进行为期6周的造模,在造模第3周后给药,持续给药3周。采用糖水偏爱实验、旷场实验和强迫游泳实验观察金丝桃苷的抗抑郁样作用;通过检测海马活性氧(ROS)、丙二醛(MDA)含量和超氧化物歧化酶(SOD)活性观察金丝桃苷的抗氧化应激作用;通过检测血清促肾上腺皮质激素释放激素(CRH)、促肾上腺皮质激素(ACTH)和皮质酮(CORT)水平以及海马糖皮质激素受体(GR)蛋白表达水平观察金丝桃苷对下丘脑-垂体-肾上腺(HPA)轴的影响。结果与空白组相比,糖水偏爱实验中模型组大鼠糖水偏爱度明显降低、旷场实验中穿越格子数以及直立次数明显减少、强迫游泳试验中不动时间明显增加(均P<0.01),而在给予金丝桃苷中、高剂量以及氟西汀后均能得到不同程度的逆转(P<0.05,或P<0.01);模型组大鼠的海马ROS和MDA含量以及血清CRH、ACTH和CORT水平明显升高、海马SOD活性与GR蛋白表达明显降低(均P<0.01),而在给予金丝桃苷中、高剂量以及氟西汀后均能得到不同程度的逆转(P<0.05,或P<0.01)。结论金丝桃苷能够改善CUMS大鼠的抑郁样作用,其作用与降低海马氧化应激水平及对HPA轴的调节作用相关。     

Curcumin reverses impaired cognition and neuronal plasticity induced by chronic stress

Chronic stress occurs in everyday life and induces impaired spatial cognition, neuroendocrine and plasticity abnormalities. A potential therapeutic for these stress related disturbances is curcumin, derived from the curry spice turmeric. Previously we demonstrated that curcumin reversed the chronic stress-induced behavioral deficits in escape from an aversive stimulus, however the mechanism behind its beneficial effects on stress-induced learning defects and associated pathologies are unknown. This study investigated the effects of curcumin on restraint stress-induced spatial learning and memory dysfunction in a water maze task and on measures related neuroendocrine and plasticity changes. The results showed that memory deficits were reversed with curcumin in a dose dependent manner, as were stress-induced increases in serum corticosterone levels. These effects were similar to positive antidepressant imipramine. Additionally, curcumin prevented adverse changes in the dendritic morphology of CA3 pyramidal neurons in the hippocampus, as assessed by the changes in branch points and dendritic length. In primary hippocampal neurons it was shown that curcumin or imipramine protected hippocampal neurons against corticosterone-induced toxicity. Furthermore, the portion of calcium/calmodulin kinase II (CaMKII) that is activated (phosphorylated CaMKII, pCaMKII), and the glutamate receptor sub-type (NMDA_2B) expressions were increased in the presence of corticosterone. These effects were also blocked by curcumin or imipramine treatment. Thus, curcumin may be an effective therapeutic for learning and memory disturbances as was seen within these stress models, and its neuroprotective effect was mediated in part by normalizing the corticosterone response, resulting in down-regulating of the pCaMKII and glutamate receptor levels.     

Vortioxetine,but not escitalopram or duloxetine,reverses memory impairment induced by central 5-HT depletion in rats: Evidence for direct 5-HT receptor modulation

Depressed patients suffer from cognitive dysfunction, including memory deficits. Acute serotonin (5-HT) depletion impairs memory and mood in vulnerable patients. The investigational multimodal acting antidepressant vortioxetine is a 5-HT₃, 5-HT₇ and 5-HT_1D receptor antagonist, 5-HT_1B receptor partial agonist, 5-HT_1A receptor agonist and 5-HT transporter (SERT) inhibitor that enhances memory in normal rats in novel object recognition (NOR) and conditioned fear (Mørk et al., 2013). We hypothesized that vortioxetine's 5-HT receptor mechanisms are involved in its memory effects, and therefore investigated these effects in 5-HT depleted rats. Four injections of the irreversible tryptophan hydroxylase inhibitor 4-chloro-dl-phenylalanine methyl ester hydrochloride (PCPA, 86 mg/kg, s.c.) induced 5-HT depletion, as measured in hippocampal homogenate and microdialysate. The effects of acute challenge with vortioxetine or the 5-HT releaser fenfluramine on extracellular 5-HT were measured in PCPA-treated and control rats. PCPA's effects on NOR and spontaneous alternation (SA) performance were assessed along with the effects of acute treatment with 5-hydroxy-l-tryptophan (5-HTP), vortioxetine, the selective 5-HT reuptake inhibitor escitalopram, or the 5-HT norepinephrine reuptake inhibitor duloxetine. SERT occupancies were estimated by ex vivo autoradiography. PCPA depleted central 5-HT by >90% in tissue and microdialysate, and impaired NOR and SA performance. Restoring central 5-HT with 5-HTP reversed these deficits. At similar SERT occupancies (>90%) vortioxetine, but not escitalopram or duloxetine, restored memory performance. Acute fenfluramine significantly increased extracellular 5-HT in control and PCPA-treated rats, while vortioxetine did so only in control rats. Thus, vortioxetine restores 5-HT depletion impaired memory performance in rats through one or more of its receptor activities.     

消郁安神胶囊对慢性轻度不可预见应激大鼠抑郁模型的影响

目的:观察消郁安神胶囊对慢性轻度不可预见应激抑郁大鼠模型的影响。方法:以慢性轻度不可预见应激建立大鼠抑郁模型,灌胃给予消郁安神胶囊(3.3,10,30 mg.kg-1)和舍曲林(5 mg.kg-1)。通过旷场实验、强迫游泳实验测定大鼠行为学变化情况。生化酶学方法测定大鼠海马中超氧化物歧化酶(SOD)与丙二醛(MDA)的含量变化。结果:旷场实验结果显示慢性轻度不可预见应激抑郁大鼠在中央格停留时间明显延长、垂直运动次数明显减少;抑郁大鼠在强迫游泳实验中静止时间所占百分比明显超过正常组;抑郁大鼠海马MDA含量明显升高,SOD活性明显降低。消郁安神胶囊给予能剂量依赖性缩短抑郁大鼠在中央格停留时间、增加垂直运动次数,并能明显减少大鼠在强迫游泳实验中静止时间。消郁安神胶囊能明显下调抑郁大鼠海马MDA含量并提高SOD活性。结论:消郁安神胶囊能明显改善慢性轻度不可预见应激大鼠的抑郁行为,其机制可能与抗氧化应激、减少炎症反应有关。     

Paradoxical decrease of brain 5-HT turnover by metergoline,a central 5-HT receptor blocker

Summary Since metergoline (1-methyl-8-beta-carbobenzyloxy-aminomethyl-10-alpha-ergoline) is a potent 5-HT antagonist in peripheral organs, its possible blocking effects on 5-HT receptors in the rat brain were investigated. In vitro, metergoline inhibited both the specific high affinity binding of ³H-5-HT onto synaptosomal membranes (IC 50=18 nM) and the stimulating effect of 10 M 5-HT on the adenylate cyclase activity in colliculi homogenates from newborn rats (IC 50=12 M). In vivo, the administration of metergoline (10 mg/kg i.p., 60 min before death) resulted in a significant decrease in the ³H-5-HT binding capacity of synaptosomal membranes from the forebrain of adult rats. Taken together, these data clearly indicated that metergoline is a potent blocker of some serotoninergic receptors in the rat brain. Surprisingly, the changes in 5-HT turnover occurring in the brainstem and in the forebrain 1 h after metergoline (2–10 mg/kg) treatment were similar to those normally induced by a central 5-HT agonist: both the rate of 5-HT utilisation and that of 5-HT synthesis were significantly decreased. These changes were in contrast to the acceleration of 5-HT turnover induced by the administration of another potent central 5-HT antagonist, methiothepin. These results are discussed in relation to the possible existence of several types of serotoninergic receptors in the rat brain. It is possible that the positive feedback regulation of 5-HT turnover is triggered by the blockade of serotoninergic receptors sensitive to methiothepin, but not to metergoline.     

Regulatory role of nitric oxide over hippocampal 5-HT release in vivo

Previous work has shown that N-methyl-D-aspartate (NMDA) receptor activation decreases 5-hydroxytryptamine (5-HT) release in the hippocampus of freely moving rats. Given the association between NMDA receptor function and nitric oxide (NO) production with the regulation of 5-HT release in other brain regions, we have studied this in rat hippocampus. NMDA (100 microM) decreased hippocampal 5-HT release by approximately 70% and this was reversed by the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5; 10 microM). The NO donor S-nitroso-N-acetylpenicillamine (SNAP) had an inverse concentration-dependent effect on 5-HT release. At 500 microM, SNAP elevated dialysate 5-HT by 55% over basal, while at 5 mM a 70% decrease was seen. The non-selective nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) at 1 mM increased extracellular 5-HT, although a return to basal levels occurred despite the continued presence of the drug. At 1 mM L-NAME prevented the decrease in 5-HT elicited by NMDA (100 microM) infusion. 7-Nitroindazole (7-NI), a relatively selective neuronal NOS (nNOS) inhibitor, decreased extracellular 5-HT at 100 microM and 1 mM. When 100 microM 7-NI was infused for 60 min prior to NMDA, 5-HT levels were transiently increased above basal before returning to control levels. Following combined application of the two drugs, no decrease in dialysate 5-HT was seen. Our data support a role for NO in modulating both basal and NMDA-evoked changes in 5-HT release in the hippocampus, however, the association appears to be complex. It may be that the recorded changes in 5-HT release are secondary to changes in the release of amino acid transmitters which we have previously found to be dependent on the prevailing extracellular NO concentration.     

ICP—MS法测定莲子中重金属元素含量

目的建立电感耦合等离子体质谱法（ICP—MS）测定莲子中砷（As）、镉（cd）、铅（Pb）、汞（Hg）等重金属含量的方法。方法样品经微波消解处理后,以铟（In）为内标,采用ICP—MS同时测定上述4种元素的含量。结果各测定元素线性关系良好（相关系数r〉0．9995）,回收率在97．5％-107．8％之间。结论该方法准确、简便、快速、灵敏,可用于莲子中这4种重金属元素的测定。     

Characterization of the discriminative stimulus properties induced by 5-HT1 and 5-HT2 agonists in rats

The effect of different serotonin (5-HT) agonists and antagonists on the discriminative stimulus properties (cue) induced by 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OHDPAT), 1-(m-trifluoromethylphenyl)piperazine (TFMPP) and d-LSD (d-lysergic acid diethylamide) has been investigated. The 8-OHDPAT cue was mimicked by the 5-HT1A agonists ipsapirone, buspirone, gepirone and partially by 5-methoxy-N,N-dimethyltryptamine and d-LSD. 5-HT1B (TFMPP and RU 24969) and 5-HT2 agonists (DOM, DOI and quipazine) were ineffective and induced disruption of responding. The 8-OHDPAT cue was antagonized by spiroxatrine and partially by (-)-alprenolol, whereas selective antagonists of 5-HT2 (ketanserin and ritanserin), 5-HT3 (ICS 205-930), alpha 1-adrenergic (prazosin) and beta-adrenergic receptors (ICI 118.551) were ineffective. The TFMPP cue was mimicked by RU 24969 and partially by quipazine. Other compounds were ineffective. Only (-)-alprenolol antagonized the effect of TFMPP. The d-LSD cue was mimicked by DOM, DOI, quipazine, 5-methoxy-N,N-dimethyltryptamine and partially by ipsapirone, TFMPP and RU 24969. The 3 latter compounds and 5-HT1A agonists induced disruption of responding. The d-LSD cue was antagonized by ketanserin and ritanserin, but not by the other antagonists mentioned above. The specific inhibitor of 5-HT uptake citalopram was not able to substitute for any of the 3 agonists. It is concluded that the drug discrimination technique can be used to identify selective agonists and antagonists of 5-HT receptor subtypes. Compounds with mixed effects on 5-HT receptor subtypes can also be identified. These show additional effects on reaction time and often disrupt responding at higher dosages.     

Estrogen enhances a 5-HT1A response in hippocampal slices from female rats

The interaction of threshold doses of bradykinin (BK) and substance P (SP) with acetylcholine (ACh)-induced bronchospasm was investigated in anaesthetized guinea-pigs. The two peptides potentiated the ACh-induced bronchospasm, an effect which did not seem to depend on prostaglandin release. On the other hand, vagotomy abolished the capacity of BK and SP to potentiate the ACh-induced bronchospasm. The present data suggest a possible involvement of BK and SP in the genesis of airway hyperreactivity.     

Ejaculatory response induced by a 5-HT2 receptor agonist m-CPP in rats: differential roles of 5-HT2 receptor subtypes

It has been reported that systemic administration of m-CPP (1-[3-chlorophenyl] piperazine hydrochloride), a 5-HT(2) receptor agonist, produces a 5-HT(2C) receptor-mediated penile erections and self-grooming in rats. In the present study, we examined the ability of m-CPP to induce ejaculation in rats and determined which 5-HT(2) receptor subtypes may be involved in the m-CPP-induced ejaculation. The ejaculatory response was assessed by weighing the seminal materials accumulated over 30 min. In Experiment 1, systemic administration of m-CPP (0.1-3.0 mg/kg, i.p.) produced a dose-dependent increase in both the incidence of ejaculation and the weight of the seminal materials. The inverted U-shaped dose-response effects of m-CPP on penile erection and genital grooming were also observed, with maximum effects at 0.6 mg/kg. Pretreatment with SB242084 (0.1 and 0.3 mg/kg, i.p.), a selective 5-HT(2C) receptor antagonist, dose-dependently attenuated the ejaculatory response induced by m-CPP (3.0 mg/kg). The proejaculatory effect of m-CPP was also attenuated by ketanserin (0.3 and 1.0 mg/kg, i.p.), a 5-HT(2A) receptor antagonist, whereas SB204741 (0.1 and 0.3 mg/kg, i.p.), a selective 5-HT(2B) receptor antagonist, significantly potentiated the m-CPP-induced ejaculatory response. Penile erection and genital grooming induced by m-CPP (0.3 mg/kg, i.p.) was only blocked by SB242084. In Experiment 2 (termed as corset test), in rats fitted with a corset at the thoracic level to prevent the loss of seminal materials by genital grooming, the proejaculatory effect of m-CPP was more efficiently detected than in the non-fitted animals: the ED(50) value for inducing ejaculation was reduced to less than 50% of the ED(50) in non-fitted animals. In this test, the proejaculatory effect of m-CPP (0.6 mg/kg, i.p.) was completely blocked by SB242084 (0.3 mg/kg, i.p.), whereas ketanserin (0.3 mg/kg, i.p.) or SB204741 (0.3 mg/kg, i.p.) did not affect the m-CPP -induced ejaculation. From these observations, it is suggested that the 5-HT(2) receptor agonist m-CPP at low doses (0.3-1.0 mg/kg) possesses the proejaculatory as well as proerectile effects in rats that are primarily associated with the activation of 5-HT(2C) receptors, and that the activation of 5-HT2B receptors may produce an inhibitory effect on ejaculation induced by a high dose (3.0 mg/kg) of m-CPP. Furthermore, the results of the present study also indicate that the corset test employed in this study may be useful for detecting the proejaculatory effect of the compounds.     

An investigation of amphetamine-induced release of 5-HT from rat hippocampal slices

The spontaneous release of [3H]5-HT from hippocampal slices, preincubated with [3H]5-HT, was increased by dopamine (P less than 0.001) and d-amphetamine (P less than 0.001) in a dose-dependent way. d-Amphetamine (10(-5) M) also increased (P less than 0.05) the release evoked by KCl (26 mM) whereas dopamine did not. The effects of dopamine and d-amphetamine on spontaneous [3H]5-HT release were antagonised by haloperidol and cis-flupenthixol. The release of [3H]HT evoked by KCl (26 mM) was reduced by noradrenaline (P less than 0.001) for conc. of 10(-5) M. It is concluded that the effects of d-amphetamine on [3H]5-HT release are probably mediated, in part by presynaptic dopamine receptors located on the 5-HT nerve terminals and that this response may depend upon the release of dopamine from adjacent terminals.