脑啡肽对大鼠海马神经细胞IL-6基因表达的影响

本文研究了大鼠海马内微量注射甲硫－脑啡肽（Ｍ－ＥＮＫ）对海马细胞的白细胞介素－６（Ｉｎｔｅｒｌｅｕｋｉｎ－６,ＩＬ－６）基因表达的影响。大鼠双侧海马内微量注射细菌内毒素脂多糖各１μｌ（ＬＰＳ,浓度：５０ｎｇ／ｍｌ）,于９０ｍｉｎ后用原位杂交技术检测到海马结构ＩＬ－６的基因表达,以齿状回颗粒细胞层显著。当海马内预先注射Ｍ－ＥＮＫ（每侧１μｌ,浓度：１０μｇ／μｌ）,３０ｍｉｎ后再给予脂多糖则未见ＩＬ－６基因表达。结果表明Ｍ－ＥＮＫ及ＬＰＳ可影响脑内ＩＬ－６的基因表达,在中枢调节机体免疫功能中,ＩＬ－６可能具有重要作用。     

海马内注射脑啡肽对细胞免疫功能及脑内IL－1α基因表达的影响

本文研究了海马内微量注射脑啡肽对大鼠细胞免疫功能及海马内白细胞介素－１α（ＩＬ－１α）基因表达的影响。结果发现：（１）双侧海马内微量注射甲硫－脑啡肽或亮－脑啡肽各１μｌ（１８ｍｍｏｌ／Ｌ）能明显增强ＣｏｎＡ刺激的脾淋巴细胞增殖活性,而双侧海马内微注射脂多糖各１μｌ（５０ｎｇ／μｌ）则起抑制作用。切除双侧肾上腺后,海马内注射脑啡肽仍可增强脾淋巴细胞增殖反应。低浓度亮－及甲硫－脑啡肽（１０￣（－１０）,１０￣（－１１）ｍｏｌ／Ｌ）直接作用于体外培养的大鼠脾淋巴细胞,也明显增强ＣｏｎＡ刺激的细胞增殖活性。（２）双侧海马内微量注射脂多糖各１μｌ（５０ｎｇ／μｌ）,于９０ｍｉｎ后用逆转录－聚合酶链反应技术检测到海马结构内ＩＬ－１α基因表达,而海马内甲硫或亮脑啡肽注射３０ｍｉｎ后再给予脂多糖,则未检测到ＩＬ－１αｃＤＮＡ的扩增条带。上述结果表明,海马结构对机体免疫功能的调节中脑啡肽起着重要作用,其机制可能与抑制海马结构ＩＬ－１α基因表达有关。     

中缝隐核投射至中脑导水管周围灰质腹侧部的递质分析

实验在戊巴比妥钠麻醉大鼠上进行。双侧中脑导水管周围灰质腹侧部（ｖＰＡＧ）微量注射１μｇ／μｌ肾上腺素（每侧０．１μｌ）,刺激中缝隐核（ＮＲＯ）引起的降压反应明显增强,但该效应可被ｖＰＡＧ预先注射心得安所阻断,而注射酚妥拉明对上述效应无明显影响;ｖＰＡＧ内单独微量注射１μｇ／μｌ心得安（每侧０．１μｌ）,可部分阻断ＮＲＯ降压反应,而注射１μｇ／μｌ酚妥拉明（每侧０．１μｌ）无明显影响;双侧ｖＰＡＧ微量注射１０μｇ／μｌ吗啡或０．１ｍｏｌ／Ｌ５－ＨＴ（每侧０．１μｌ）,基础血压无明显变化,ＮＫＯ的降压反应幅度减小（Ｐ＜０．０５）。提示,ＮＫＯ对ｖＰＡＧ的兴奋作用的可能递质为肾上腺素,通过β受体介导;吗啡或５－ＨＴ则可减弱ＮＲＯ对ｖＰＡＧ的兴奋性投射作用。     

纳洛酮和阿托品翻转电针抑制关节炎大鼠束旁核神经元伤害性反应的作用

用急性佐剂性关节炎大鼠作为病理性疼痛的实验模型,以丘脑束旁核中对伤害性刺激发生兴奋反应的单位放电作为指标,观察电针的影响,并分析其机制。实验发现电针能明显抑制伤害性反应;脑室注射阿片受体阻断剂纳洛酮（４μｇ／１０μｌ）或Ｍ受体阻断剂阿托品（５μｇ／１０μｌ）均能翻转电针的这种抑制作用。实验还发现脑室注射纳洛酮或阿托品对关节炎大鼠束旁核神经元自发放电有增频作用。实验结果提示：电针对关节炎大鼠丘脑束旁核神经元伤害性反应的抑制,可能是通过脑内阿片系统和胆碱能系统而发挥作用的;这两个系统对关节炎大鼠丘脑束旁核神经元自发放电可能有紧张性抑制作用。     

中枢注射U－50，488H对肾水钠钾的排出及PVH内TH－IR神经元活性的影啊

本工作用１２％乙醇麻醉的大鼠,观察了下丘脑室旁核（ＰＶＨ）微量注射Ｋ型阿片受体激动剂Ｕ－５０,４８８Ｈ对大鼠肾水钠钾排出的影响,以及第三脑室注射Ｕ－５０,４８８Ｈ对ＰＶＨ中多巴胺神经元活性的影响。结果如下：（１）ＰＶＨ微量注射Ｕ－５０,４８８Ｈ（５μｎ／ｕｌ）后２０ｍｉｎ内大鼠尿量开始增加（Ｐ＜０．０１）,持续约１００ｍｉｎ,４１—６０ｍｉｎ尿量增加达峰值（Ｐ＜０．００１）。（２）ＰＶＨ预先（１０ｍｉｎ）注射Ｋ型阿片受体阻断剂ＮＢＴ（Ｎｏｒ－ＢｉｎａｌｔｏｒｐｈｉｍｉｎｅＴｅｔｒａｈｙｄｒａｔｅ）（５μｇ／ｐｌ）可以阻断Ｕ－５０,４８８Ｈ所产生的利尿效应（Ｐ＜０．０１）。（３）第三脑室注射Ｕ－５０,４８８Ｈ（１０μｇ／１０ｕｌ）２０ｍｉｎ后,ＰＶＨ中酪氨酸羟化酶免疫反应阳性（Ｔｙｒｏｓｉｎｅｈｙｄｒｏｘｙｌａｓｅ－ｉｍｍｕｎｏｒｅａｃｔｉｖｉｔｙ,ＴＨ－ＩＲ）神经元数量减少,染色强度减弱,于注药后５０ｍｉｎ变化最为显著,１００ｍｉｎ时已恢复正常。上述结果表明：ＰＶＨ微量注射Ｕ－５０,４８８Ｈ可作用于Ｋ型阿片受体引起利尿效应;第三脑室微量注射Ｕ－５０,４８８Ｈ可抑制ＰＶＨ中ＴＨ－ＩＲ神经元的免疫活性。     

中脑导水管周围灰质内注射抗阿片肽血清对神经降压素增强电针镇痛的影响

本工作以钾离子透入引起大鼠甩尾反应作为痛反应指标,观察纳洛酮（ＮＸ）和抗阿片肽血清对大鼠中脑导水管周围灰质（ＰＡＧ）内微量注射神经降压素（ＮＴ）增强电针镇痛作用的影响。结果显示：（１）ＰＡＧ内微量注射ＮＴ后,大鼠电针镇痛效应明显提高;（２）ＰＡＧ内注射大剂量ＮＸ,可以显著减弱ＮＴ增强电针镇痛效应;（３）ＰＡＧ内微量注射抗甲脑啡肽血清和抗β内啡肽血清后,ＮＴ增强电针镇痛的作用明显降低;而ＰＡＧ内微量注射抗强啡肽Ａ１１３血清,对于ＮＴ增强电针镇痛的作用并无明显影响。提示：ＰＡＧ内ＮＴ在针刺镇痛过程中发挥重要作用,ＮＴ增强电针镇痛的作用与甲脑啡肽和β内啡肽有较密切的关系。     

弓状核中阿片受体在细胞介素所致发热效应中的作用

本研究旨在了解弓状核内的阿片受体在体温调节中的作用。研究使用细胞介素ＩＬ１β做致热源。以自动推进器向ＳＤ雄性大鼠弓状核微量注射１μ１ＩＬ１β。在给药前３０ｍｉｎ分别向弓状核微量注射通常阿片受体拮抗剂纳洛酮（Ｎａｌ）、阿片受体μ、δ和κ各自特异性拮抗剂ＣＴＡＰ、ＮＴＩ和ｎｏｒＢＮＩ做预处理,用生理盐水（Ｓａｌ）做对照。结果表明：ＩＬ１β所致的升体温效应能被Ｎａｌ和ＣＴＡＰ阻断,提示弓状核中的阿片受体（主要是μ受体）参与或介导了ＩＬ１β的致热效应;δ和κ受体特异性拮抗剂阻断ＩＬ１β所致的体温升高效应不明显。提示δ和κ阿片受体参与体温调节的可能性较小。对照ＡＲＨ和ＰＯＡＨ中阿片受体在ＩＬ１β所致发热中的作用可发现：二者作用极为相似,这一结果有力地支持了弓状核是体温调节中枢重要组成部分的观点。     

大鼠,兔肺动脉壁亮氨酸脑啡肽的分布,含量及其作用途径

用ＡＢＣ免疫组化法对ＳＤ大鼠肺动脉全层漂染,结果显示有亮氨酸脑啡肽（Ｌ－ＥＮＫ）阳性纤维走行于动脉壁外膜中。放免法测得大鼠、兔肺动脉壁合Ｌ－ＥＮＫ,含量（ｐｇ／ｍｇ组织湿重）分别为４３９．１８±３０．５２,２９．９±１．４。离体灌流的兔肺动脉螺旋条,经参数Ⅰ电场刺激可引起收缩反应,α受体阻断剂酚妥拉明可阻断之;α２受体阻断剂育亨宾小剂量增强收缩反应,大剂量则抑制,阿片受体阻断剂纳洛酮可使收缩反应增强。应用酚妥拉明后,参数Ⅱ电场仍能引起较高的收缩反应,纳洛酮对此收缩无影响。外源性ＮＥ引起肺动脉条收缩,Ｌ－ＥＮＫ对之没有抑制效应。结果提示,肺动脉壁含有内源性Ｌ－ＥＮＫ,可因电场刺激而释放,由阿片受体介导抑制动脉壁神经末梢ＮＥ释放,进而抑制血管收缩,对血管平滑肌本身活动及已释放ＮＥ均无抑制效应。关键词：     

杏仁核内注射CCK—8抑制胃运动的机制

应用脑核团内微量注射和核团电刺激方法,观察杏仁基底内侧（ＢＭＡ）对胃运动的影响,分析ＢＭＡ与下丘脑腹内侧核（ＶＭＨ）的机能联系。结果如下：（１）双侧ＢＭＡ内注射八肽胆囊收缩素（ＣＣＫ－８）（５０ｎｇ／ｌμｌ）,出现胃内压（ＩＧＰ）和胃运动频率（ＧＭＦ）显著下降（Ｐ〈０．０１）。（２）ＢＭＡ内注射ＣＣＫ－Ａ受体阻断剂［Ｌ３６４,７１８］（１００ｎｇ／ｌμｌ）或ＣＣＫ－Ｂ受体阻断剂［Ｌ３６５,２６０］     

中枢注射U—50,488H对肾水钠钾的排出及PVH内TH —IR神经元活性的影响

本工作１２％乙醇麻醉的大鼠,观察了下丘脑室旁核（ＰＶＨ）微量注射Ｋ型阿片受体激动剂Ｕ－５０,４８８Ｈ对大鼠肾水钠钾排出的影响,以及第三脑室注射Ｕ－５０,４８８Ｈ对ＰＶＨ中多马上胺神经元活性的影响。结果如下（１）ＰＶＨ微量注射Ｕ－５０,４８８Ｈ（５μｇ／ｌ）后２０ｍｉｎ内大量尿量开始增（Ｐ＜０．０１）,持续约１００ｍｉｎ,,４１－６０ｍｉｎ尿量增加达峰值（Ｐ＜０．００１）。（２）,ＰＶＨ预先（１０ｍ     

Effects of deprolorphin, a casomorphin analog, on hippocampal CA1 field potentials in vitro

The effects of infusion of low concentrations of the synthetic opioid peptide D-Pro4-beta-casomorphin-5(deprolorphin) on electrical field responses in the in vitro hippocampal slice preparation of mice were investigated. Deprolorphin (0.01-10 microM) causes a large enhancement of the population spike (PS) and appearance of additional spikes of CA1 pyramidal cells to Schaffer-commissural stimulation, which were partially antagonized by the opiate receptor antagonist naloxone. It is likely that this analgesic peptide in the hippocampus acts through mu-receptors and neuronal mechanisms already described for morphine and enkephalin analogs.     

Regulation of the rat brain endothelin system by endogenous beta-endorphin

Several lines of evidence indicate that the central endogenous opioid and endothelin (ET) system regulate each other. To explore this idea further, we determined the effect of intracerebroventricular (i.c.v.) administration of anti-beta-endorphin IgG (rabbit) on the expression level of the opioid, corticotropin-releasing hormone and endothelin receptors, and tissue concentration of ET-1. Three days after implanting cannula into the lateral ventricle, male Sprague-Dawley rats were administered 10 microl (i.c.v.) of either control rabbit IgG (2.5 microg/microl) or anti-beta-endorphin IgG (2.5 microg/microl) on days 1, 3 and 5. On day 6, animals were euthanized and caudate, cortex and hippocampus collected for Western blot analysis. Anti-beta-endorphin IgG down-regulated ET-A receptor protein expression in the caudate (51%), but had no effect on the expression of mu, delta, kappa opioid, ET-B, CRH-1 and CRH-2 receptors in any brain region. Anti-beta-endorphin IgG increased tissue ET-1 levels in the caudate by 30.3%. [35S]GTP-gamma-S binding assays demonstrated that anti-beta-endorphin IgG increased the efficacy of [D-Ala2-MePhe4, Gly-ol5]enkephalin without altering its potency in caudate. Control experiments showed that there was no detectable rabbit IgG in caudate, cortex and hippocampus samples. These results suggest that beta-endorphin in the CSF coordinately regulates ET-1 levels and the ET-A receptor in rat caudate. These findings support the hypothesis that CSF neuropeptides have regulatory effects and further demonstrate a link between opioid and ET system.     

Peripheral effect of a kappa opioid receptor antagonist on nociception evoked by formalin injected in TMJ of pregnant rats

The effect of sex hormones on orofacial pain modulation is poorly understood. Therefore, this study aimed to investigate the effect of hormonal changes as a result of pregnancy, as well as that of the kappa (kappa) opioid receptor antagonist on female rats' sensitivity to the temporomandibular joint (TMJ) formalin test. Initially, female rats at estrus and pregnant females on day 19 of pregnancy received a 50 microl formalin (1.5%) injection in the right TMJ. The pregnant females showed a reduction in nociceptive responses to the TMJ formalin test when compared with those at estrus. Then, the selective kappa-opioid receptor antagonist nor-Binaltorphimine (nor-BNI), was co-administered with the formalin. Next, additional groups received the kappa (200 microg) receptor antagonist or 0.9% NaCl 24 hours prior to the periarticular injection of formalin. Co-administration of nor-BNI with formalin into the TMJ region had no significant effect. The pre-injection of selective kappa-opioid receptor antagonist, nor-BNI, significantly enhanced the nociceptive behavioral responses in pregnant females. When applied in the contralateral TMJ, nor-BNI did not affect the magnitude of the nociceptive response induced by formalin. It can be concluded that: 1) The increase of the sex hormone levels, as result of pregnancy, induces a reduction of nociceptive behavioral responses to the TMJ formalin test; 2) the peripheral kappa opioid receptor activation, by endogenous opioid agonists release, is involved in the antinociception to TMJ formalin test, induced by pregnancy.     

Nociceptin in rVLM mediates electroacupuncture inhibition of cardiovascular reflex excitatory response in rats.

Electroacupuncture (EA) at Neiguan-Jianshi acupoints through an opioid mechanism inhibits the cardiovascular pressor response induced by mechanical stimulation of the stomach. Because nociceptin also may regulate cardiovascular activity through its action in the brain stem, we hypothesized that this neuromodulator serves a role in the EA-related inhibitory effect. Blood pressure in ventilated male Sprague-Dawley rats (400-600 g) anesthetized by ketamine and alpha-chloralose was measured during balloon inflation of the stomach. Gastric distension with 6-8 ml of air induced consistent pressor reflexes of 26 +/- 1 mmHg that could be repeated every 10 min for 100 min. When nociceptin (10 nM) was microinjected into the rostral ventrolateral medulla (rVLM), the pressor response induced by gastric distension was inhibited by 68 +/- 6%. Thirty minutes of EA also decreased the reflex response by 75 +/- 11%; microinjection of saline into the rVLM did not alter the inhibitory effect of EA. In contrast, microinjection of a nociceptin receptor antagonist into the rVLM promptly reversed the EA response. Pretreatment with the opioid receptor antagonist naloxone did not influence the EA-like inhibitory effect of nociceptin on the distension-induced pressor reflex (22 +/- 1 to 8 +/- 2 mmHg). Furthermore, a mu-opioid receptor agonist microinjected into the rVLM after microinjection of a nociceptin receptor antagonist during EA promptly reversed the nociceptin receptor antagonist-related inhibition of the EA effect. Thus, in addition to the classical opioid system, nociceptin, through opioid receptor-like-1 receptor stimulation in the rVLM, participates in the modulatory influence of EA on reflex-induced increases in blood pressure.     

中缝隐核对兔奥迪氏括约肌肌电活动的影响

实验用电生理学和微量注射法观察了兔中缝隐核（NRO）对奥迪氏括约肌肌电活动的影响,动物禁食但自由饭水,18－24h手用乌拉坦（1.0g/kg)静脉麻醉,用双极康铜丝电极引导奥迪氏括约肌肌电,发现NRO内微注射谷氨酸（340mmol/L,0.4ul)可使奥迪氏括约肌肌电活动加强,与在NRO内微量注射生理盐水或者将谷氨酸（340mmol/L,0.4ul)注射到NRO以外的地方相比,具有显著差异（P＜0．01）,NRO 微量注射N-methy-D-aspartate(NM-DA)受体阻断剂氯胺酮（180mmol/L,0.1ul),可消除谷氨酸的效应,而将微量非NMDA受体阻断剂CNQX（2mmol/L,0.1ul)注入NRO,可使奥迪氏括约肌肌电加强,外周应用M－受体阻断剂阿托品（0.2mg/kg)或双侧颈部迷走神经切断,可阻断微量谷氨酸注射到NRO内所引起的效应,静脉注射α－受体阻断剂酚妥拉明（1.5mg/kg),心得安（1.5mg/kg)或自T3－4处切断脊髓,对NRO内微量注射谷氨酸的效应没有影响,结果提示,NRO对奥迪氏括约肌运行有调节作用,其中谷氨酸主要通过NMDA受体兴雷奥迪氏括约肌肌电活动,其传出途径是迷走神经和外周M受体。     

Effect of a mu-opioid receptor-selective antagonist on interleukin-6 fever

The endogenous opioid system has been found to be involved in fever caused by pyrogens. Recent work in our laboratory has demonstrated that the mu-opioid receptor is involved in interleukin-1beta (IL-1beta)- and in lipopolysaccharide (LPS)-induced fevers. In the present study, we have investigated the role of the mu-opioid receptor in the preoptic anterior hypothalamus (POAH) in fever induced by interleukin-6 (IL-6). Following stereotaxic implantation of a guide cannula into the POAH for microinjection, radio transmitters to monitor body temperature (Tb) continuously were inserted intraperitoneally. Adult male Sprague-Dawley rats were microinjected with 0.5 microg of the selective mu-opioid receptor antagonist, cyclic D-phe-Cys-Try-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP), into the POAH. Thirty min later, IL-6 (100 ng) was injected into the POAH. CTAP significantly blocked the IL-6 fever. CTAP alone had no effect on Tb during the 390-min recording period. These data indicate that mu-opioid receptors within the POAH mediate IL-6 fever and add to the increasing evidence that the opioid system is involved in the pathogenesis of fever in rats.     

Cholinergic and glutamatergic activation reverses working memory failure by hippocampal histamine H1 receptor blockade in rats

Intrahippocampal administration of the histamine H1 receptor antagonist pyrilamine (3.2-32 ug/ side) but not the histamine H2 receptor antagonist cimetidine (1.0-10 microg/side) increased the number of errors in the working memory task with a three-panel runway setup. The increase in working memory errors induced by intrahippocampal 32 microg/side pyrilamine was significantly reduced by concurrent infusion of the histamine H1 receptor agonist 2-pyridylethylamine (3.2 and 10 microg/side). The cholinesterase inhibitor physostigmine ( 1.0 and 3.2 microg/side) and D-cycloserine (0.32 and 1.0 microg/side), the partial agonist at the glycine binding site on the NMDA receptor/channel complex, reduced the increase in working memory errors induced by intrahippocampal 32 microg/side pyrilamine. These results suggest that the hippocampal histaminergic activity via histamine H1 receptor is necessary for normal working memory processes and that the septohippocampal cholinergic activation and positive modulation of the NMDA receptor/channel through activation of the glycine site can alleviate dysfunction of hippocampal histamine H1 receptor-mediated neurotransmission involved in working memory function.     

Dexamethasone reverses the memory impairment induced by antagonism of hippocampal gastrin-releasing peptide receptors

Storage of emotionally influenced memory is regulated by activation of glucocorticoid receptors (GRs) as well as of gastrin-releasing peptide receptors (GRPRs) in the dorsal hippocampus. In the present study, male Wistar rats were given a bilateral infusion of saline or the GRPR antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) (1.0 microg/side) into the dorsal hippocampus 10 min before training on an inhibitory avoidance task, followed by an immediate post-training i.p. injection of vehicle or the GR agonist dexamethasone (0.3 mg/kg). A retention test trial, carried out 24 h after training, indicated that intrahippocampal infusion of RC-3095 impaired inhibitory avoidance retention. Post-training administration of dexamethasone induced an enhancement of retention regardless of whether the animals had received saline or RC-3095 into the hippocampus before training. The findings indicate that hippocampal GRPR blockade does not prevent memory enhancement induced by dexamethasone. Together with previous results, these findings suggest that endogenous activation of GRPRs in the hippocampus modulates the consolidation of emotional memory, but is not a critical receptor system mediating memory formation.     

Inhibition of EGF-induced ERK/MAP kinase-mediated astrocyte proliferation by μ opioids: integration of G protein and β-arrestin 2-dependent pathways

Although μ, κ, and δ opioids activate extracellular signal‐regulated kinase (ERK)/mitogen‐activated protein (MAP) kinase, the mechanisms involved in their signaling pathways and the cellular responses that ensue differ. Here we focused on the mechanisms by which μ opioids rapidly (min) activate ERK and their slower (h) actions to inhibit epidermal growth factor (EGF)‐induced ERK‐mediated astrocyte proliferation. The μ‐opioid agonists ([d‐ ala², mephe⁴, gly‐ol⁵] enkephalin and morphine) promoted the phosphorylation of ERK/MAP kinase within 5 min via G_i/o protein, calmodulin (CaM), and β‐arrestin2‐dependent signaling pathways in immortalized and primary astrocytes. This was based on the attenuation of the μ‐opioid activation of ERK by pertussis toxin (PTX), the CaM antagonist, W‐7, and siRNA silencing of β‐arrestin2. All three pathways were shown to activate ERK via an EGF receptor transactivation‐mediated mechanism. This was disclosed by abolishment of μ‐opioid‐induced ERK phosphorylation with the EGF receptor‐specific tyrosine phosphorylation inhibitor, AG1478, and μ‐opioid‐induced reduction of EGF receptor tyrosine phosphorylation by PTX, and β‐arrestin2 targeting siRNA in the present studies and formerly by CaM antisense. Long‐term (h) treatment of primary astrocytes with [d ‐ala²,mephe⁴,gly‐ol⁵] enkephalin or morphine, attenuated EGF‐induced ERK phosphorylation and proliferation (as measured by 5′‐bromo‐2′‐deoxy‐uridine labeling). PTX and β‐arrestin2 siRNA but not W‐7 reversed the μ‐opioid inhibition. Unexpectedly, β‐arrestin‐2 siRNA diminished both EGF‐induced ERK activation and primary astrocyte proliferation suggesting that this adaptor protein plays a novel role in EGF signaling as well as in the opioid receptor phase of this pathway. The results lend insight into the integration of the different μ‐opioid signaling pathways to ERK and their cellular responses.     

Involvement of opioidergic system of the ventral hippocampus, the nucleus accumbens or the central amygdala in anxiety-related behavior

In the present study, the influence of opioidergic system of the ventral hippocampus, the nucleus accumbens or the central amygdala on anxiety-related behaviour was investigated in rats. As a model of anxiety, the elevated plus maze which is a useful test to investigate the effects of anxiogenic or anxiolytic drugs in rodents was used. Bilateral microinjection of different doses of morphine (2.5, 5 and 7.5 microg/rat) into the ventral hippocampus or the nucleus accumbens increased the percentage of open arm time (%OAT) and open arm entries (%OAE) but not locomotor activity, indicating an anxiolytic response. However, intra-central amygdala administration of the opioid did not show any response. On the other hand, microinjection of a dose of naloxone into the ventral hippocampus (2 microg/rat) or the nucleus accumbens (1 microg/rat) increased open arm time (%OAT), but not open arm entry (%OAE) which may indicate an anxiolytic effect. Pre-treatment administration of naloxone (0.5, 1 and 2 microg/rat) reversed the anxiolytic effect of morphine (7.5 microg/rat) injected into the ventral hippocampus in a dose-dependent manner. A dose of the antagonist (1 microg/rat) also reduced the morphine response (2.5 microg/rat) when injected in the nucleus accumbens. In conclusion, it seems that the opioidergic system in the ventral hippocampus and the nucleus accumbens are involved in anxiety-related behaviors and the ventral hippocampus may be the main site of action of the anxiolytic properties of morphine.