An ultrastructural study of dynorphin-immunoreactive nerve fibers and terminals in the celiac-superior mesenteric ganglion of the guinea pig

Dynorphin-immunoreactive nerve fibers and terminals were identified in the celiac-superior mesenteric ganglion of the guinea pig at the ultrastructural level with the peroxidase-antiperoxidase technique. The immunostained material was localized in the large dense core vesicles of the terminals but was also present diffusely in the axoplasm. The terminals formed numerous axodendritic and a few axosomatic contacts, interpreted as synapses, with the principal ganglion cells. These findings suggest that dynorphin plays a role as a neurotransmitter or neuromodulator in the ganglion and, taken together with earlier findings, indicate an involvement of dynorphin neurons in the intestino-intestinal inhibitory reflex.     

Intranigral injection of dynorphin in combination with substance P on striatal dopamine metabolism in the rat

The effects of intranigral injection of dynorphin(1-13), substance P and their combination on striatal dopamine (DA) metabolism as well as circling behavior were studied in rats. Dynorphin(1-13) produced a significant dose-dependent increase of dihydroxyphenyl acetic acid (DOPAC) concentration as well as the number of contralateral circling. No change in dopamine (DA) concentration was observed. Substance P caused a dose-dependent increase of DOPAC concentration. At large doses it also produced an increase in DA concentration. Combined intranigral dynorphin(1-13) and substance P brought about an additive effect for the increase of DOPAC and the number of contralateral circling. No additive effect was found when dynorphin(1-13) and neurokinin A were injected together intranigrally.     

Effect of Acute Ethanol Administration on the Release of Opioid Peptides From the Midbrain Including the Ventral Tegmental Area

Background:  Experimental evidence suggests that ethanol alters the activity of the endogenous opioid peptide systems in a dose and brain-region dependent manner. These alterations may influence the processes of ethanol reward and reinforcement. Thus, it was the objective of this study to investigate the response of the 3 major opioid peptide systems (endorphins, enkephalins, and dynorphins) to acute ethanol administration, at the level of the midbrain including the ventral tegmental area (midbrain/VTA), a region important for drug, including ethanol reinforcement.
Methods:  Using the in vivo microdialysis technique coupled with specific solid-phase radioimmunoassay for β-endorphin, met-enkephalin, and dynorphin A_1–8, changes in the extracellular concentration of theses peptides at the level of midbrain/VTA were determined at distinct time points following the administration of 0.0 (saline), 0.8, 1.2, 1.6, 2.0, and 2.4 g ethanol/kg B.Wt.
Results:  A biphasic effect of ethanol on β-endorphin release was found, with low to medium (1.2, 1.6, and 2.0 g) but not high (2.4 g) doses of ethanol, inducing a significant increase in the dialysate content of β-endorphin. A late increase in the dialysate content of dynorphin A_1–8 was observed in response to the 1.2 g ethanol dose. However, none of the ethanol doses tested significantly altered the content of met-enkephalin in the dialysate.
Conclusions:  The present findings suggest that the ethanol-induced increase of β-endorphin release at the level of midbrain/VTA may influence alcohol reinforcement.     

Dynorphin B and spinal analgesia: induction of antinociception by the cannabinoids CP55,940, Δ-THC and anandamide

The endogenous opioid dynorphin B was evaluated for its role in cannabinoid-induced antinociception. Previous work in our laboratory has shown that the synthetic, bicyclic cannabinoid, CP55,940, induces the release of dynorphin B whilst the naturally occurring cannabinoid, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), releases dynorphin A. The dynorphins contribute in part to the antinociceptive effects of both cannabinoids at the level of the spinal cord. The present study compares dynorphin B released from perfused rat spinal cord in response to acute administration of anandamide (AEA), Δ⁹-THC and CP55,940 at two time points, 10 min and 30 min post administration, and attempts to correlate such release with antinociceptive effects of the drugs. Dynorphin B was collected from spinal perfusates of rats pretreated with Δ⁹-THC, CP55,940 or AEA. The supernatant was lyophilized and the concentrations of dynorphin B were measured via radioimmunoassay. At a peak time of antinociception (10 min), CP55,940 and Δ⁹-THC induced significant two-fold increases in the release of dynorphin B. AEA did not significantly release dynorphin B. Upon a 30-min pretreatment with the drugs, no significant dynorphin B release was observed, although antinociceptive effects persisted for CP55,940 and Δ⁹-THC. Previous work indicates that Δ⁹-THC releases dynorphin A while AEA releases no dynorphin A. This study confirms that although all three test drugs produced significant antinociception at 10 min, the endocannabinoid, AEA, does not induce antinociception via dynorphin release. Thus, our data indicate a distinct mechanism which underlies AEA-induced antinociception.     

A strychnine-sensitive site is involved in dynorphin-induced paralysis and loss of the tail-flick reflex

Dynorphin A(1-13) administered intrathecally to rats induces a reversible hindlimb paralysis and permanent loss of the tail-flick reflex in a dose-dependent and all-or-none manner. The loss of the tail-flick reflex has been determined to result from neurotoxicity linked to the N-methyl-D-aspartate (NMDA) receptor. Recently, it has been reported that NMDA antagonists attenuate irreversible paralysis induced by dynorphin A(1-17) and dynorphin A(2-17). In the present studies, we examined whether repeated injections of dynorphin A(1-13) acetate salt could change the characteristics of the reversible paralysis. Injections repeated every 48 h resulted in hindlimb paralysis upon each injection which was not different in terms of magnitude or duration (P greater than 0.60). Injections repeated at 2 h intervals resulted in desensitization of the paralytic effects (P less than 0.05). We also examined if strychnine sulfate, a glycine antagonist would alter the paralytic response to dynorphin. Strychnine protected rats from paralysis (P less than 0.01) and loss of the tail-flick reflex with an ED50 of 7 nmol. We conclude that the reversible paralysis induced by dynorphin A(1-13) is repeatable which suggests that the paralysis results from nontoxic or subtoxic actions of dynorphin. Desensitization to the paralytic effects occurs with closely spaced injections by some unknown mechanism. In addition, we conclude that the spinal glycinergic inhibitory system may participate in the induction of the paralysis because strychnine antagonizes dynorphin-induced paralysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Elevation of guinea pig brain preprodynorphin mRNA expression and hypothalamic-pituitary-adrenal axis activity by “binge” pattern cocaine administration

The endogenous opioid system and the hypothalamic-pituitary-adrenal (HPA) axis have been implicated in many of the neurobiological effects of cocaine. Previous studies in our laboratory showed that “binge” pattern cocaine administration increases preprodynorphin (ppDyn) mRNA levels in the caudate putamen and circulating levels of corticosterone in the rat. The present study extended these findings to guinea pigs, a species known to have a κ opioid receptor profile similar to that of humans. Male guinea pigs were treated with: (a) “binge” pattern cocaine for 7 days (subchronic) (3 × 15 mg/kg/day, hourly, intraperitoneal); (b) “binge” pattern saline for 5 days followed by “binge” pattern cocaine for 2 days (subacute); or (c) “binge” pattern saline for 7 days. Thirty minutes after the final injection, levels of ppDyn mRNA were quantitated in the nucleus accumbens, caudate putamen, frontal cortex, amygdala, hippocampus, and hypothalamus using a solution hybridization RNase protection assay. Regional distribution of ppDyn mRNA levels in the guinea pig brain was similar to that found in rat, with highest levels in the nucleus accumbens and caudate putamen. In the caudate putamen, ppDyn mRNA was significantly increased following either 2 days (38% increase) or 7 days (32% increase) of “binge” pattern cocaine administration as compared to saline-treated controls. No significant changes in ppDyn mRNA levels were found in any other brain region. Both subacute and subchronic “binge” cocaine administration significantly elevated plasma levels of adrenocorticotropin hormone (ACTH) and cortisol. However, the ACTH and cortisol increases were significantly blunted following 7 days of “binge” cocaine administration as compared to 2 days of drug treatment, reflecting the development of HPA tolerance or adaptation to repeated cocaine administration. Thus, the ppDyn mRNA and HPA responses to cocaine in guinea pigs are similar to those observed in rats.     

Neuropeptides in epilepsy

Neuropeptides play an important role in modulating seizures and epilepsy. Unlike neurotransmitters which operate on a millisecond time-scale, neuropeptides have longer half lives; this leads to modulation of neuronal and network activity over prolonged periods, so contributing to setting the seizure threshold. Most neuropeptides are stored in large dense vesicles and co-localize with inhibitory interneurons. They are released upon high frequency stimulation making them attractive targets for modulation of seizures, during which high frequency discharges occur. Numerous neuropeptides have been implicated in epilepsy; one, ACTH, is already used in clinical practice to suppress seizures. Here, we concentrate on neuropeptides that have a direct effect on seizures, and for which therapeutic interventions are being developed. We have thus reviewed the abundant reports that support a role for neuropeptide Y (NPY), galanin, ghrelin, somatostatin and dynorphin in suppressing seizures and epileptogenesis, and for tachykinins having pro-epileptic effects. Most in vitro and in vivo studies are performed in hippocampal tissue in which receptor expression is usually high, making translation to other brain areas less clear. We highlight recent therapeutic strategies to treat epilepsy with neuropeptides, which are based on viral vector technology, and outline how such interventions need to be refined in order to address human disease.     

N-硝基-L-精氨酸抑制大鼠吗啡身体依赖的强啡肽机制

目的　研究N 硝基 L 精氨酸 (NO2 Arg)在抑制吗啡身体依赖形成中的作用及探讨强啡肽在该过程中的可能作用。方法　采用剂量递增皮下注射吗啡法建立大鼠吗啡身体依赖模型 ;身体依赖程度采用皮下注射 5mg·kg-1 纳洛酮激发戒断症状并对大鼠 6 0min内可数和不可数的戒断症状评分的方法进行 ;采用放射免疫法分别测定大鼠脑各分区、垂体、脊髓和血浆内免疫活性强啡肽A(ir-Dyn)的含量。结果　NO2 Arg可剂量相关性地抑制吗啡身体依赖的形成 ,其中 5mg·kg-1 NO2 Arg可显著抑制吗啡依赖大鼠大多数戒断症状 ;NO2 Arg处理可显著升高吗啡依赖大鼠脊髓、纹状体、垂体及血浆内ir-Dyn的水平。该作用可被特异性κ -受体阻滞剂norbinaltorphimine (nor-BNI)所拮抗。结论　NO2 Arg剂量相关性地抑制吗啡身体依赖的形成 ,该抑制作用可能与其调节机体内源性强啡肽的水平显著相关     

舒芬太尼镇痛途径对家兔外周血强啡肽和前列腺素E2的影响

目的:研究舒芬太尼两种镇痛给药方法对家兔外周血强啡肽和前列腺素E2的影响。方法:实验分3组,每组6只。建立福尔马林致痛兔模型后,A、B组分别经静脉和硬膜外注射舒芬太尼,C组静脉注射等容量生理盐水作为对照。根据行为判断标准进行疼痛反应评分,并检测致痛前（T₀）,致痛后10min（T₁）、20min（T₂）、40min（T₃）、2h（T₄）、8h（T₅）、24h（T₆）和48h（T₇）时家兔血清中强啡肽和前列腺素E₂的水平。结果:舒芬太尼能有效降低福尔马林致痛兔疼痛反应。与T₀比较,致痛后C组各观察时间点强啡肽水平明显升高（P<0.05）;A组强啡肽水平T₀～T₃保持稳定,于T₄升高;B组T₀～T₄保持稳定,于T₅升高。致痛后C组前列腺素E₂水平均高于A组和B组（P<0.05）,A、B组分别于T₆和T₅降至致痛前水平,C组T₇仍高于致痛前水平。结论:舒芬太尼镇痛有助于保持强啡肽的稳定并抑制前列腺素E₂的升高,硬膜外镇痛途径疗效优于静脉镇痛。