Orphanin FQ stimulates prolactin and growth hormone release in male and female rats

Intracerebroventricular administration of Orphanin FQ (5.5, 55 or 550 pmol) caused a dose-related increase in prolactin secretion in both male and female rats and stimulated GH secretion in males. The magnitude of the prolactin secretory response was greater in females than in males. These effects of OFQ on prolactin and growth hormone release are the same as the stimulatory effects of the endogenous opioid peptides.     

Alterations in the level of OFQ/N-IR in rat brain regions by cocaine

We have previously shown that administration of orphanin FQ/nociceptin (OFQ/N), the endogenous ligand of the opioid receptor-like (ORL-1) receptor, into the lateral ventricles or VTA blocked cocaine sensitization. In the present study, we determined the effect of acute and chronic cocaine treatment on the level of endogenous OFQ/N in rat brain regions. Male Sprague Dawley rats were tested for motor activity in response to saline or cocaine (20 mg/kg) injection once daily for three consecutive days. To determine the effect of single or repeated cocaine administration on the level of OFQ/N, rats were sacrificed 1 h following saline or cocaine injection either on day 1 or 3, respectively. Additional groups of rats were treated similarly with saline or cocaine on days 1-3 and sacrificed or tested for locomotor sensitization on day 8. Consistent with previous studies, repeated cocaine administration induced locomotor sensitization to a challenge dose of cocaine (7.5 mg/kg) given on day 8. Measurements of tissue content of OFQ/N-IR using radioimmunoassay indicated that the rat hypothalamus and striatum, respectively, contained the highest and lowest levels of the peptide among the brain regions tested. Acute cocaine decreased the level of OFQ-IR in the rat midbrain and to a lesser extent in the striatum. On the other hand, the level of OFQ/N was higher in rats treated with cocaine on days 1-3 and sacrificed on day 8. These findings suggest that endogenous OFQ/N may be involved in the actions of cocaine and possibly in cocaine-induced motor stimulation and locomotor sensitization.     

Expression of morphine-conditioned place preference is more vulnerable than naloxone-conditioned place aversion to disruption by nociceptin in mice

The opioid peptide nociceptin (orphanin FQ) suppresses the incentive and rewarding properties of drugs. Thus, targeting the nociceptin system may be beneficial in treating drug addiction. The effects of nociceptin (0–1.5 nmol intracerebroventricular) on the expression of morphine- (6 mg/kg subcutaneous) and naloxone-(6 mg/kg subcutaneous) induced place conditioning were examined in mice. Whereas doses of 0.5 nmol nociceptin and above disrupted expression of morphine-conditioned place preference (CPP), naloxone-conditioned place aversion (CPA) remained intact at all doses of nociceptin tested. Doses of 0.5 nmol nociceptin and above suppressed locomotion, though this appeared unrelated to the expression of place conditioning. These results suggest that nociceptin more potently blocks the ability of reward-associated cues than aversion-associated cues to influence behavioral biases.     

Modification of acetylcholine release by nociceptin in conscious rat striatum

Nociceptin (NOC), an endogenous ligand for the orphan opioid receptor ORL1 (ORL1), has recently been recognized as a neuropeptide. We used brain microdialysis and on-line high performance liquid chromatography (HPLC) to examine the effect of NOC on the basal outflow of acetylcholine (ACh) in the freely moving rat striatum in vivo. ACh release was reduced by nociceptin at a concentration of 10(-5) M to 79% of control release. This effect of NOC was attenuated by [Phe1Psi(CH2-NH)Gly2]nociceptin-(1-13)-NH2 (PhePsi), suggesting that NOC activates the ORL1 receptor and (PhePsi) acts as an antagonist on ORL1 in rat striatum in vivo. These findings indicate that NOC may act as a neuropeptide which inhibits ACh release in the striatum via ORL1.     

心理应激对大鼠肠道敏感性及血浆孤啡肽含量的影响

目的 探讨慢性心理应激对大鼠肠道敏感性及血浆孤啡肽(OFQ)含量的影响.方法 80只SD雌性大鼠分为实验组和对照组,实验组大鼠采用束缚应激的方法制作肠易激综合征(IBS)动物模型,并鉴定模型.2组分别于实验0、1、2、3、4周时随机取出8只,用球囊扩张的方法测定肠道敏感性,用放射免疫方法测定血浆OFQ含量.结果 IBS模型经鉴定符合其病理特征,结肠组织学观察显示各组均无明显炎症表现.实验组大鼠各时点肠道敏感性均高于相应对照组(P均<0.01);应激1周时肠道敏感性最高(P均<0.01);应激2周时,肠道敏感性高于3、4周组(P均<0.01);应激3、4周肠道敏感性差异无统计学意义(P>0.05).实验组大鼠血浆OFQ含量与相应对照组比较均明显升高(P均<0.01),应激1周时最高(P<0.05或P<0.01),2～4周逐渐下降,3、4周时差异无统计学意义(P>0.05),但仍高于应激前水平(P均<0.05).肠道敏感性与血浆OFQ含量变化趋势一致,二者呈显著正相关(r=0.660,P<0.01).结论 慢性心理应激引起大鼠肠道敏感性及血浆OFQ含量增高;血浆OFQ含量与肠道敏感性变化趋势一致,可能与慢性心理应激大鼠肠道敏感性变化有关.     

阻断孤啡肽受体对大鼠局灶性脑缺血损伤的保护作用

目的 研究侧脑室给予孤啡肽受体(ORL-1)阻断药对大鼠脑缺血-再灌注损伤的影响.方法 雄性SD大鼠55只,随机分为三个不同剂量的给药组(T_1、T_2、T_3组)和假手术组(S组)、对照组(C组),每组11只.给药组和C组都采用线栓法阻断大脑中动脉模型(MCAO),缺血2 h后恢复再灌注.给药组于手术前45 min右侧脑室分别给予ORL-1阻断药Nphel 0.03、0.3、3 nmol,剂量10μl.每组大鼠随机分为两部分,其中8只在恢复再灌后24 h行行为学评分(NDS),后断头取脑行TTC染色,计算脑梗死容积.3只在恢复冉灌注后24 h断头分离右侧海马组织,Western blot法分析Caspase-3蛋白表达.结果 与C组相比,T_3组的NDS明显提高(P<0.05),T_2、T_3组的脑梗死容积明显减小(P<0.05);T_2、T_3组在缺血-再灌注后24 h Caspase-3蛋白表达明显降低.结论 阻断ORL-1能剂量依赖性减轻脑缺血-再灌注损伤.其机制可能与阻断神经元凋亡有关.     

The novel neuropeptide orphanin FQ fails to produce conditioned place preference or aversion

An unbiased conditioned place preference procedure was used to determine whether the newly-identified neuropeptide orphanin FQ produced motivational effects after intracerebroventricular microinjections. Microinjections of orphanin FQ (0.1–100 nmol) failed to produce conditioned place preference or aversion, but a pronounced motor impairment was observed during conditioning sessions with the two highest doses. Thus, it appears that orphanin FQ lacks motivational effects when administered at behaviourally active doses.     

Spinal analgesic activity of orphanin FQ/nociceptin and its fragments

Previous work reveals that orphanin FQ/nociceptin (OFQ/N) administered supraspinally produces an initial hyperalgesic response followed by analgesia. Spinally, OFQ/N elicits a rapidly appearing, naltrexone-reversible, dose-dependent analgesia in the tailflick assay without any indication of hyperalgesia. Two OFQ/N fragments, OFQ/N (1–7) and OFQ/N (1–11), are active, but far weaker. Blockade of sigma receptors with haloperidol enhances the analgesic potency of spinal OFQ/N, OFQ/N (1–7) and OFQ/N (1–11), but not as dramatically as supraspinal OFQ. Antisense probes targeting the second and third coding exons, but not the first exon, of the cloned mouse OFQ/N receptor (KOR-3) partially block OFQ/N analgesia.     

Involvement of local orphanin FQ in the development of analgesic tolerance induced by morphine microinjections into the dorsal raphe nucleus of rats

It is well known that dorsal raphe nucleus (DRN) is one of the key structures for the development of opioid analgesia and tolerance. An increased activity of ‘antiopioids’ like orphanin-FQ (OFQ) has been proposed as a possible mechanism for opioid tolerance. The present study evaluates the role of DRN-located OFQ in the opioid analgesic tolerance induced by repeated microinjections of morphine (MOR) into DRN. Male rats were implanted with chronic guide cannulae aimed at the DRN. Microinjection of MOR (0.5 μg in 0.5 μl) into DRN caused antinociception as quantified with the tail flick and the hot plate tests. When MOR microinjection was repeated twice daily, the antinociceptive effect disappeared within 2 days (tolerance). However, if each MOR microinjection was preceded (within 15 min) by a microinjection of the OFQ receptor antagonist nocistatin (NST) (1 ng in 0.5 μl) into the same DRN site, the microinjections of MOR always produced antinociception and did not induce tolerance. If NST microinjections were suspended, subsequent MOR microinjections induced tolerance. In MOR-tolerant rats, a single NST microinjection into the same DRN site was enough to restore the antinociceptive effect of MOR. On the other hand, if OFQ (1 ng in 0.5 μl) was microinjected into DRN, then MOR microinjection administered 15 min later into the same DRN site did not elicit antinociception. Finally, opioid tolerance induced by repeated systemic MOR injections (5 mg/kg, ip) was reversed by a single microinjection of NST into DRN. This emphasizes the central importance of DRN-located OFQ in the MOR analgesic tolerance.     

Analgesia elicited by OFQ/nociceptin and its fragments from the amygdala in rats

The heptadecapeptide, orphanin FQ/nociceptin (OFQ/N), binds with high affinity to the ORL-1/KOR-3 opioid receptor clone, yet binds poorly with traditional opioid receptors. OFQ/N has a complex functional profile with relation to nociceptive processing, displaying pro-nociceptive properties in some studies, acting as an inhibitor of stress-induced analgesia in others, yet producing both spinal and supraspinal antinociceptive actions in other studies. Among the intracerebral sites at which OFQ/N might produce one or more of these actions is the amygdala which has been intimately implicated in both antinociceptive and stress-related responses. Therefore, the present study assessed whether microinjections into the amygdala of equimolar doses of OFQ/N_1–17 or its shorter-chained active fragments, OFQ/N_1–11 or OFQ/N_1–7, would produce analgesia as measured by either reactivity to high-intensity radiant heat or reactivity to electric shock, and produce hyperalgesia as measured by reactivity to lower-intensity radiant heat. OFQ/N_1–17 in the amygdala produced a dose-dependent and time-dependent increase in high-intensity tail-flick latencies with maximal effects observed at a dose range of 0.75–3 nmol, and lesser effects at lower (0.015–0.15 nmol) and higher (5.5–30 nmol) doses. Both OFQ/N_1–11 and OFQ/N_1–7 in the amygdala displayed lower magnitudes of analgesia than OFQ/N_1–17 on this measure, with OFQ/N_1–11 displaying maximal effects at higher (15–30 nmol) doses and OFQ/N_1–7 displaying maximal effects at lower (0.15–1.5 nmol) doses. In contrast to traditional μ and κ opioids and β-endorphin, none of the OFQ/N fragments in the amygdala exhibited any analgesic responses on the jump test. Finally, using a low-intensity radiant heat assay capable of detecting hyperalgesic responses, each of the OFQ/N fragments in the amygdala increased tail-flick latencies on this measure. Therefore, OFQ/N fragments appear to exert only analgesic responses in the amygdala with quantitative and qualitative differences relative to traditional opioid agonists.