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.     

强啡肽A对烫伤大鼠免疫功能与cAMP、cGMP含量变化的影响

采用放射免疫分析技术测定了强啡肽 A(DynA)对烫伤大鼠淋巴细胞内 cAMP 和 cGMP 含量的影响,并观察了其与免疫功能的关系,旨在探讨 DynA 调节烫伤大鼠免疫功能的机制。结果表明,烫伤大鼠脾淋巴细胞转化与白细胞介素2(IL-2)的生成明显降低,脾淋巴细胞内 cAMP 的含量明显升高,而 cGMP 的含量无明显变化。烫伤大鼠血清可抑制正常大鼠淋巴细胞转化功能和 IL-2的生成,并使淋巴细胞内 cAMP 含量升高。DynA 可增强烫伤大鼠淋巴细胞转化和 IL-2的生成,降低细胞内 cAMP 含量,钠洛酮可翻转 DynA 的这种作用。DynA 还可改善烫伤大鼠血清对淋巴细胞转化功能的抑制作用,降低烫伤大鼠血清引起的淋巴细胞内 cAMP 含量升高。提示 DynA 可增强烫伤大鼠的免疫功能,且这种作用与淋巴细胞内第二信使 cAMP 改变有关。     

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     

Dynorphin-(1–13)-Like Immunoreactivity in Central Nervous System and Pituitary Gland of Spontaneously Hypertensive Rats

We determined by radioimmunoassay concentrations of dynorphin-(1–13)-like immunoreactivity in the central nervous system and pituitary gland of spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto rats (WKYs). Compared to WKYs, SHRs had significantly lower levels of dynorphin-(1–13)-like immunoreactivity in the hypothalamus and pituitary gland. However, such immunoreactivity in the cerebral cortex, caudate nucleus, diencephalon, brainstem and spinal cord of SHRs and WKYs were similar.     

Agmatine inhibits morphine-induced locomotion sensitization and morphine-induced changes in striatal dopamine and metabolites in rats

The effects of agmatine on morphine-induced locomotion sensitization and morphine-induced changes in extracellular striatal dopamine (DA) and DA metabolites were studied. The locomotor response to morphine challenge (3 mg/kg, s.c.) was enhanced in rats 3 days after repeated morphine administration, indicating development of locomotion sensitization. In vivo microdialysis demonstrated a significant increase in striatal basal levels of the DA metabolites DOPAC and HVA, but not in DA itself, and an increase in DA response to morphine challenge in rats 3 days after withdrawal. Agmatine (1, 10, 80 mg/kg) inhibited morphine-induced locomotion sensitization and the changes in DA noted above. Idazoxan attenuated the effects of agmatine on locomotion, suggesting that the effects are mediated by imidazoline receptors. In addition, repeated morphine also increased the expression of tyrosine hydroxylase mRNA in the VTA after 4 days of morphine pretreatment, while decreasing the expression of dynorphin mRNA at 3 days after withdrawal. Agmatine inhibited morphine-induced changes in dynorphin, but not in tyrosine hydroxylase mRNA expression. These data suggest that agmatine, likely by activating imidazoline receptors, inhibits morphine-induced locomotion sensitization and morphine-induced changes in extracellular DA and in dynorphin expression. Thus, agmatine deserves further study as an anti-opioid medication.     

The effect on opioid peptides in the rat brain, after chronic treatment with the anabolic androgenic steroid, nandrolone decanoate

In recent years, an increase in abuse of anabolic androgenic steroids (AAS) has been seen among individuals not directly connected to sports. Clinical evidence suggests that abuse of these steroids may result in profound changes in personality, expressed by depressive symptoms, irritability and increased aggression. It is still unknown whether these alterations are related to changes in any particular transmitter system or whether they are persistent or reversible. In this study we focused on AAS effect on the endogenous dynorphin and enkephalin system in the brain. Male rats were given intramuscular injections of the AAS nandrolone decanoate (15 mg/kg), once daily for 2 weeks. The levels of the opioid peptide immunoreactivities (ir) were assessed by radioimmunoassay in two groups immediately after the treatment and in two other groups after additional 3 weeks without any drug treatment (recovery period). The result indicates that chronic AAS treatment increased the activity in the dynorphin B- and Met-enkephalin-Arg(6)Phe(7)-ir in the hypothalamus, striatum and periaqueductal gray (PAG) compared to controls. In addition, the steroid induced an imbalance between the dynorphin and the enkephalin opioid system in the nucleus accumbens, hypothalamus and PAG. This imbalance remained after the recovery period. Since increased peptide activity was found in brain regions regulating emotions, dependence, defensive reactions and aggression, it was suggested that the actual endogenous opioid systems are involved in previously reported AAS-induced changes in these behaviours.     

The nature of conditioned anti-analgesia: spinal cord opiate and anti-opiate neurochemistry

The central nervous system contains circuitry that inhibits pain sensitivity (analgesia), as well as circuitry that opposes pain inhibition (anti-analgesia). Activation of analgesia systems and anti-analgesia systems can each be brought under environmental control using classical conditioning procedures. Analgesia can be produced by cues present before and during aversive events such as electric shock, while active inhibition of analgesia comes to be produced by cues never present immediately before or during shock and therefore signal safety. We have recently reported that these analgesia and anti-analgesia systems interact at the level of the spinal cord. A series of 3 experiments were performed to examine how such interactions occur. First, potential opioid mediation of conditioned analgesia was investigated using systemic and intrathecal (i.t.) delivery of opiate antagonists. Conditioned analgesia was found to be mediated by activation of spinal μ and δ opiate receptors. Second, analgesia produced by each of these receptor subtypes was challenged by environmental signals for safety. Analgesias produced by μ and δ opiate agonists were each abolished by safety signals. Third, antagonists/antisera directed against several putative anti-opiate neurotransmitters were tested i.t. to identify which mediate conditioned anti-analgesia at the level of the spinal cord. A cholecystokinin antagonist abolished conditioned anti-analgesia. In contrast, neuropeptide FF antiserum and a κ opiate antagonist were without effect.     

Hypothalamic opioids and the acute-phase glycoprotein response in guinea pigs

Endogenous opioids (EO) probably do not modulate endotoxin (LPS)- or interleukin 1 (IL1)-induced fever because naloxone does not prevent its development. Yet, increases in CSF and hypothalamic levels of beta-endorphin have been reported during LPS-and IL1-induced fevers. Since IL1 also reduces the specific binding of opioids to their receptors in guinea pig brain, the opioids could be involved in modulating nonfebrile effects of IL1. To determine whether EO might have a role in the IL1-induced acute-phase glycoprotein response of guinea pigs, (1) naloxone (5 and 10 mg/kg, SC) was injected prior to LPS (S. enteritidis 2 micrograms/kg, IV; N = 5), and (2) morphine (MOR, 10 micrograms/microliter), [D-ala2]-met-enkephalinamide (DAME, 5 micrograms/microliter), or dynorphin A (DYN, 5 micrograms/microliter) was injected into the preoptic area (1 microliter, bilaterally; N = 8/treatment) or into the 3rd ventricle (N = 4/treatment); pyrogen-free saline was the control injection. Measurements were: core temperature (Tco) and, as indices of acute-phase glycoproteins, plasma levels of copper (Cu) and N-acetylneuraminic acid (NANA). Naloxone did not prevent the fever or the increases in plasma Cu and NANA levels evoked by LPS. The intracerebral administration of opioid agonists by either route induced variable rises in Tco, each with a different pattern, but no increases in plasma Cu and NANA levels. Thus, EO do not participate in the central modulation of acute-phase glycoprotein synthesis, but may have a role in influencing other nonthermal IL1 effects in the CNS.     

Increased release of immunoreactive dynorphin A1-17 from the spinal cord after intrathecal treatment with endomorphin-2 in anesthetized rats

We previously demonstrated pretreatment with antiserum against dynorphin A1-17 attenuates endomorphin-2-induced analgesia and antianalgesia, suggesting that these endomorphin-2 effects are mediated by the release of dynorphin A1-17. Lumbar-cisternal spinal perfusion was used to measure the release of immunoreactive dynorphin A1-17 into spinal perfusates from urethane-anesthetized rats following endomorphin-2 or endomorphin-1 treatment within the perfusion solution. Treatment with endomorphin-2 (5-50 nmol) for 3 min caused a dose-dependent increase of immunoreactive dynorphin A1-17 in spinal perfusates, with a maximal increase detected between 24 and 48 min after endomorphin-2 treatment, while levels returned to baseline within 60 min. Endomorphin-2-induced release of immunoreactive dynorphin A1-17 was attenuated by pretreatment with mu-opioid receptor antagonist naloxone or 3-methoxynaltrexone. Endomorphin-1 induced a slight increase in immunoreactive dynorphin1-17 as well, but only at the highest dose used (50 nmol). Our results suggest that endomorphin-2 stimulated a specific subtype of mu-opioid receptor to induce the release of immunoreactive dynorphin A1-17 in spinal cords of rats.     

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.