Effects of acute ethanol on opioid peptide release in the central amygdala: an in vivo microdialysis study

Rationale  There is experimental evidence that indicates that the endogenous opioid system of the central nucleus of the amygdala (CeA) may mediate some of the reinforcing effects of ethanol. However, the precise interactions of ethanol with the endogenous opioid system at the level of the CeA have not been investigated. Objectives  The aim of the current study was to investigate the hypothesis that acute systemic ethanol administration will increase the release of endogenous opioid peptides at the level of the CeA in a time- and dose-dependent manner. Materials and methods  Rats were implanted with a unilateral guide cannula to aim microdialysis probes at the CeA. Intraperitoneal injections of saline and various doses of ethanol (0.8, 1.6, 2.0, 2.4, and 2.8 g ethanol/kg body weight) were administered to the rats. Dialysate samples were collected at 30-min intervals at distinct time points prior to and following treatment. Radioimmunoassays specific for β-endorphin, met-enkephalin, and dynorphin A1–8 were used to determine the effect of ethanol on the content of the opioid peptides in the dialysate. Results  We report that the 2.8-g/kg dose of ethanol induced a long-lasting increase in β-endorphin release from 60 min onwards following administration and, later, an ongoing increase in dynorphin A1–8 release. None of the ethanol doses tested elicited significant changes in dialysate met-enkephalin content compared to the saline treatment. Conclusions  Acute systemic ethanol administration induced a dose- and time-dependent increase in β-endorphin and dynorphin A1–8 release at the level of the CeA, which may be involved in ethanol consumption.     

Stress-induced reinstatement of cocaine seeking is mediated by the kappa opioid system

INTRODUCTION: Prior activation of the kappa opioid system by repeated stress or agonist administration has been previously shown to potentiate the rewarding properties of subsequently administered cocaine. In the present study, intermittent and uncontrollable footshock, a single session of forced swim, or acute administration of the kappa agonist U50,488 (5 mg/kg) were found to reinstate place preference in mice previously conditioned with cocaine (15 mg/kg) and subsequently extinguished by repeated training sessions without drug. RESULTS AND DISCUSSION: Stress-induced reinstatement did not occur for mice pretreated with the kappa opioid receptor antagonist norbinaltorphimine (10 mg/kg) and did not occur in mice lacking either kappa opioid receptors (KOR -/-) or prodynorphin (Dyn -/-). In contrast, the initial cocaine conditioning and extinction rates were not significantly affected by disruption of the kappa opioid system. Cocaine-injection also reinstated conditioned place preference in extinguished mice; however, cocaine-primed reinstatement was not blocked by kappa opioid system disruption. CONCLUSION: The results suggest that stress-induced drug craving in mice may require activation of the dynorphin/kappa opioid system.     

中枢去甲肾上腺素和强啡肽A（1—17）在痛觉调制中的相互作用

大鼠以辐射热甩尾法测痛。应用脊髓蛛网膜下腔（ｉ．ｔ．）连续累加注射法观察药物的镇痛作用。（１）ｉ．ｔ．单独注射强啡肽Ａ（１－１７）２．５μｇ本身无镇痛作用，但与去甲肾上腺素（ＮＥ）合用时却能产生协同镇痛作用；该作用即能被ｉ．ｔ．注射α受体拮抗剂酚妥拉明３０μｇ所对抗，也能被κ阿片受体拮抗剂Ｎｏｒ－ＢＮＩＯ９μｇ所对抗。（２）强啡肽Ａ和ＮＥ的协同镇痛揭示在两种受体激动剂协同作用时，阻断其中一种受体，     

Localized overexpression of FGF-2 and BDNF in hippocampus reduces mossy fiber sprouting and spontaneous seizures up to 4 weeks after pilocarpine-induced status epilepticus

Purpose: We have recently reported that viral vector–mediated supplementation of fibroblast growth factor‐2 (FGF‐2) and brain‐derived neurotrophic factor (BDNF) in a lesioned, epileptogenic rat hippocampus limits neuronal damage, favors neurogenesis, and reduces spontaneous recurrent seizures. To test if this treatment can also prevent hippocampal circuit reorganization, we examined here its effect on mossy fiber sprouting, the best studied form of axonal plasticity in epilepsy. Methods: A herpes‐based vector expressing FGF‐2 and BDNF was injected into the rat hippocampus 3 days after an epileptogenic insult (pilocarpine‐induced status epilepticus). Continuous video–electroencephalography (EEG) monitoring was initiated 7 days after status epilepticus, and animals were sacrificed at 28 days for analysis of cell loss (measured using NeuN immunofluorescence) and mossy fiber sprouting (measured using dynorphin A immunohistochemistry). Key Findings: The vector expressing FGF‐2 and BDNF decreased both mossy fiber sprouting and the frequency and severity of spontaneous seizures. The effect on sprouting correlated strictly with the cell loss in the terminal fields of physiologic mossy fiber innervation (mossy cells in the dentate gyrus hilus and CA3 pyramidal neurons). Significance: These data suggest that the supplementation of FGF‐2 and BDNF in an epileptogenic hippocampus may prevent epileptogenesis by decreasing neuronal loss and mossy fiber sprouting, that is, reducing some forms of circuit reorganization.     

Inhibitory effects of processed Aconiti tuber on morphine-induced conditioned place preference in rats

Aim of the study

Our previous studies indicated that processed Aconiti tuber (PAT), a traditional Chinese herbal medicine, had antinociceptive effects and inhibitory effects on morphine tolerance by activation of kappa-opioid receptor (KOR). Preclinical studies also demonstrated that KOR agonists functionally attenuate addictive behaviors of morphine, such as conditioned place preference (CPP). Therefore, we hypothesize that PAT may inhibit morphine-induced CPP in rats.

Materials and methods

(1) Five groups of rats (n = 8 for each group) were alternately subcutaneous (s.c.) injected with morphine 10 mg/kg (one group receive normal saline as a control) and normal saline for 8 days and oral co-administrated with distilled water or PAT 0.3, 1.0, or 3.0 g/kg daily on days 2-9 during CPP training, respectively. (2) Other four groups of rats were randomly s.c. injected with nor-binaltorphimine (nor-BNI; 5 mg/kg) or normal saline (as a control) 120 min before alternately s.c. with morphine and normal saline and oral co-administrated with distilled water or PAT 3.0 g/kg daily. Each rat was acquired pre-conditioning and post-conditioning CPP data and assayed dynorphin concentrations by radioimmunoassay in rat's nucleus accumbens (NAc) after CPP training.

Results

(1) PAT 1.0 or 3.0 g/kg dose-dependently decreased the morphine-induced increase of CPP scores. (2) Nor-BNI completely antagonized the inhibition of PAT on morphine-induced CPP. (3) PAT dose-dependently increased dynorphin content in rats’ NAc after CPP training.

Conclusions

(1) PAT dose-dependently inhibited morphine-induced CPP. (2) The inhibition of PAT on morphine-induced CPP was probably due to activation of KOR by increasing dynorphin release in rats’ NAc.     

Formalin-induced long-term secondary allodynia and hyperalgesia are maintained by descending facilitation

This work analyzes the role of cholecystokinin (CCK) receptors, dynorphin A_1-17 and descending facilitation originated in the rostral ventromedial medulla (RVM) on secondary allodynia and hyperalgesia in formalin-injected rats. Formalin injection (50 μL, 1%, s.c.) produced acute nociception (lasting 1 h) and long-term secondary allodynia and hyperalgesia in ipsilateral and contralateral hind paws (lasting 1-12 days). Once established, intra-RVM administration of lidocaine at day 6, but not at 2, reversed secondary allodynia and hyperalgesia in rats. The injection of YM022 (CCK₂ receptor antagonist), but not lorglumide (CCK₁ receptor antagonist), into the RVM or spinal cord reversed both nociceptive behaviors. Pre-treatment with lidocaine, lorglumide or YM022 did not prevent the development of secondary allodynia or hyperalgesia regardless of the administration route. Formalin injection increased dynorphin content in the dorsal, but not the ventral, spinal cord sections at day 6. Moreover, intrathecal administration of dynorphin antiserum reversed, but was unable to prevent, secondary allodynia and hyperalgesia in both hind paws. These results suggest that formalin-induced secondary allodynia and hyperalgesia are maintained by activation of descending facilitatory mechanisms which are dependent on CCK₂ receptors located in the RVM and spinal cord. In addition, data suggest that spinal dynorphin A_1-17 and CCK play an important role in formalin-induced secondary allodynia and hyperalgesia.     

术前应用地佐辛对瑞芬太尼诱发早期痛觉过敏大鼠模型的抑制效应

目的在瑞芬太尼诱发术后2h痛觉过敏大鼠模型中,探讨术前应用地佐辛抑制痛觉过敏的效果及机理。方法制备瑞芬太尼痛觉过敏模型：将大鼠分为切口组（I）和切口加瑞芬太尼组（IR）,分别泵人生理盐水和瑞芬太尼（1．3μg·kg。·min-1）,同时行切口手术。模型成功后将大鼠随机分为A、B、C、D、E5组,分别给予生理盐水、x受体激动剂U50488、小剂量”受体拮抗剂CTOP、U50488加小剂量CTOP和地佐辛,建立痛觉过敏模型。于术前、术后2h测量各组大鼠热缩足反射潜伏期（PWTL）,检测脊髓强啡肽表达。结果（1）PWTL：与I组相比,IR组明显缩短（P〈0．05）;与A组相比,B、C、D、E组延长（P〈0．05）;与B、C组相比,D、E组延长（P〈0．05）;D、E组无统计学差异（P〉0．05）。（2）强啡肽：与A、C组相比,B、D、E组均增加（P〈0．05）;I、IR组之间,A、c组之间,B、D、E组之间比较差异均无统计学意义（P〉0．05）。结论持续泵人瑞芬太尼在术后2h诱发了痛觉过敏;地佐辛通过两方面协同抑制痛觉过敏：一方面拮抗部分”受体,另一方面激动x受体促进内源性强啡肽表达增加。     

刺激迷走神经向中端对大鼠中枢β-内啡肽和强啡肽含量的影响

我们利用放射免疫的方法,研究了刺激迷走神经向中端对大鼠中枢内β-内啡肽和强啡肽B样免疫活性物质含量的影响.结果表明:脊髓、丘脑和垂体内β-内啡肽样免疫活性物质的含量显著下降(P<0.05);而在海马、中脑、桥延和皮层则显著增高(P<0.05).强啡肽B样免疫活性物质的含量,在海马显著增高(P<0.05),而在脊髓则下降非常明显(P<0.01).     

Effect of intranigral injections of dynorphin, dynorphin fragments and alpha-neoendorphin on rotational behaviour in the rat

Peptides deriving from the proenkephalin B precursor were studied in the Ungerstedt rotational model after their unilateral injection into the substantia nigra. Dynorphin (DYN)-(1-17), DYN-(1-13) and DYN-(1-8) in 0.1-10 micrograms doses induced marked contralateral rotation. This effect was enhanced by subsequent systemic administration of D-amphetamine and blocked by previous treatment with naloxone. alpha-Neoendorphin produced similar effects although there was no evidence for dose-dependency. DYN-(6-17) which lacks opioid activity also produced contralateral rotation, which, however, was not naloxone reversible and D-amphetamine given subsequently did not induce asymmetric activation. Methionine enkephalin and leucine enkephalin, deriving from the proenkephalin A precursor were tested for comparison. Only the former produced weak contralateral rotation. GABA injected at the same site as DYN-(1-17) also induced contralateral rotation which was mimicked by nanogram doses of the gabaergic agonist muscimol. These findings suggest an interaction between peptides from the proenkephalin B precursor and nigro-striatal dopamine neurons as well as gabaergic striato-nigral efferents and/or interneurons.     

Stimulation of hypothalamic β-endorphin and dynorphin release by corticotropin-releasing factor (in vitro)

Corticotropin-releasing factor (CRF) at doses of 10⁻¹²–10⁻⁸ M significantly stimulated the release of β-endorphin and dynorphin from superfused rat hypothalamic slices. These effects were shown to be mediated by the CRF receptor since they were antagonized by the CRF receptor antagonist α-helical CRF_9–41 (10⁻⁶ M). The two opioid peptides showed different time courses of response and in the case of β-endorphin, an attenuation of the response upon continued exposure to CRF was observed.