Presynaptic opioid receptors on dopaminergic nerves in the rabbit caudate nucleus: coupling to pertussis toxin-sensitive G-proteins and interaction with D2 autoreceptors?

Slices of the rabbit caudate nucleus, preincubated with [³H]dopamine and subjected to electrical field stimulation, were used (1) to investigate the involvement of G-proteins in the signal transduction of presynaptic D₂ (auto)receptors and -opioid receptors on dopaminergic axon terminals in this tissue and (2) to study a possible mutual interaction of these two presynaptic receptors. Pretreatment of the slices with either pertussis toxin (8 g/ml; 18 h), or N-ethylmaleimide (30 M, 30 min) significantly reduced the inhibitory effects of both the D₂ agonist quinpirole and the -opioid receptor agonist U-50488H on the [³H]overflow evoked by 36 pulses (2 ms, 24 mA, 0.3 Hz), suggesting the coupling of both receptors to G-proteins.Experiments designed to study possible interactions of these two presynaptic receptors were carried out under stimulation conditions (only 1 pulse), which strongly diminish interference of endogenous transmitters released in the tissue with modulatory effects of exogenous drugs. For instance, due to the presence of endogenous dopamine, quinpirole was much less potent during 36-pulse-than during 1-pulse field stimulation, whereas the D₂ antagonist domperidone was almost without effect in the latter case. Using the 1-pulse stimulation paradigm, the concentration/response curve of quinpirole was unaffected in the presence of the halfmaximal inhibitory concentration of U-50,488 H (0.1 M). On the other hand, also quinpirole at its halfmaximal inhibitory concentration (0.1 M), hardly affected the concentration/response curve of U-50,488 H: only high concentrations of U-50,488 H (above 1 M) seemed to be slightly less effective in the presence than in the absence of the D₂ agonist. U-50,488 H, at these high concentrations, was also less potent under 36-pulse than under 1-pulse stimulation conditions. From these findings, we conclude that there is only a limited interaction between presynaptic D₂ autoreceptors and -opioid receptors on dopaminergic axon terminals in the rabbit caudate nucleus, despite they are both coupled to PTX/NEM-sensitive G-proteins. Correspondence to: R. Jackisch at the above address     

Presynaptic α2A-adrenoceptors inhibit the release of endogenous dopamine in rabbit caudate nucleus slices

₂-Adrenoceptors modulating the release of dopamine were identified and characterized in slices of the head of the rabbit caudate nucleus. Release of endogenous dopamine was measured by fast cyclic voltammetry as the increase in the extracellular concentration of dopamine elicited by electrical stimulation. The electrochemical signal was identified as dopamine by means of the oxidation potential, the voltammogram and the fact that the signal was not changed by desipramine, which inhibits the high affinity uptake of noradrenaline, but was greatly increased by nomifensine, which in addition inhibits the high affinity uptake of dopamine.Stimulation by 6 pulses/100 Hz increased the extracellular concentration of dopamine by about 85 nM. The selective ₂-adrenoceptor agonist 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) reduced this release with an EC₅₀ of 173 nM and by maximally 75%. The ₂-adrenoceptor agonists clonidine and oxymetazoline only tended to cause a decrease. Six drugs, including oxymetazoline, were tested as antagonists against UK 14,304. Their order of antagonist potency (pK_D values in brackets) was rauwolscine (8.0) > oxymetazoline (7.5) > 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane (WB 4101; 7.3) > phentolamine (7.1) > corynanthine (5.1) prazosin (< 6). Given alone, the antagonists did not change the release of dopamine elicited by 6 pulses/100 Hz, and the same was true for the dopamine receptor antagonist sulpiride. When caudate slices were stimulated by 10 pulses/1 Hz, sulpiride increased the release of dopamine. Desipramine and rauwolscine, in contrast, again caused no change.It is concluded that dopaminergic axons in the rabbit caudate nucleus possess release-inhibiting ₂-adrenoceptors. The antagonist affinities indicate that they belong to the _2A subtype. In this, they agree with all presynaptic ₂-autoreceptors studied so far in rabbits as well as with the ₂-heteroreceptors modulating the release of serotonin in rabbit brain cortex, suggesting that at least the majority of presynaptic ₂-adrenoceptors in the rabbit are _2A. The agonist sensitivity of the caudate presynaptic ₂-adrenoceptors is low in comparison with cerebrocortical presynaptic ₂-autoreceptors, possibly due to absence of a receptor reserve. Correspondence to: N. Limberger at the above address     

Autoradiographic localization of dopamine D2-like receptors in the rabbit pulmonary vascular tree

In the present study, the pharmacological characteristics and the anatomical localization of dopamine D₂-like receptor sites in the extraparenchymal and in the intraparenchymal portion of the rabbit pulmonary artery were investigated using combined radioligand binding and light microscope autoradiography with [³H]-spiroperidol (spiperone) as a ligand. The ligand was bound to sections of the pulmonary artery in a manner consistent with the labelling of dopamine D₂-like receptors with an equilibrium dissociation constant (K _d) of about 2.4±0.07 nmol/l and a maximum density of binding sites of 65±4.5 fmol/mg tissue. In contrast, binding experiments made with sections of rabbit lung did not allow the evaluation of specific binding. Light microscope autoradiography showed the development of specific silver grains within the tunica adventitia of extraparenchymal branches of rabbit pulmonary artery and of large and, to a lesser extent, of medium-sized intraparenchymal branches of the pulmonary artery. No silver grains were found within small branches of the pulmonary artery or of the pulmonary vein. Development of adventitial silver grains was inhibited by compounds active at dopamine receptors. The greater sensitivity to displacement by domperidone, haloperidol, (–)-sulpiride and bromocriptine than to displacement byN-propyl-norapomorphine, quinpirole or clozapine suggests that the [³H]-spiroperidol binding sites observed in extraparenchymal, large and medium-sized branches of the pulmonary artery belong, probably, to the dopamine D₂ receptor subtype. The possible pre-junctional localization of these sites is discussed. Correspondence to: R Amenta     

Biotransformation of locally applied l-dopa in the corpus striatum of the hemi-Parkinsonian rat studied with microdialysis

Microdialysis was used to study the biotransformation of l-dopa in intact and denervated striata of rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the substantia nigra. Microdialysis probes were placed in the intact and in the denervated striatum. Observations were then made on freely moving rats. Extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and 4-hydroxy-3-methoxyphenylacetic acid (homovanillic acid; HVA) were monitored before, during and after the local administration of l-dopa via the microdialysis probe for 20 min.A dose-dependent increase in extracellular dopamine levels was seen in intact striatum after application of l-dopa in concentrations ranging between 100 nmol/l and 10 mol/l. In the denervated striatum, the severity of the lesion influenced dopamine formation, so that no dose-effect relation could be established.The effects of the continuous intra striatal infusion of nomifensine, tetrodotoxin or benserazide on the l-dopa-induced dopamine outflow revealed that in the intact striatum this dopamine release is mainly voltage dependent. It was concluded that in the denervated striatum other cells of non-neuronal origin and containing aromatic l-amino acid decarboxylase make a major contribution to the increase in extracellular dopamine levels. Furthermore, l-dopa itself shows no dopamine-releasing properties, at least under the present experimental conditions. Correspondence to: S. Sarre at the above address     

A cyclic adenosine monophosphate agonist elevates the b- and c-waves of the rabbit direct-current electroretinogram

The effects of the stable cyclic adenosine monophosphate analogue adenosine 3, 5-cyclic monophosphorothioate Sp-isomer (Sp-cAMPS) on the direct-current electroretinogram and the standing potential of the eye were studied. Corneal recordings were obtained from unilaterally vitrectomized albino rabbit eyes during alternating intravitreal perfusions with Sp-cAMPS and a control solution (Pharmacia eye irrigating solution). The contralateral eye was used as a control. To evaluate further the effects on the c-wave,in vivo intraretinal microelectrode measurements were made during simultaneous intravitreal perfusion of Sp-cAMPS and irrigating solution, respectively. Sp-cAMPS in concentrations of 1, 10 and 100µM was tested by corneal direct-current electroretinography. There was no significant effect on the a-wave amplitude. The b-wave amplitude was reversibly elevated at an Sp-cAMPS concentration of 100µM (p<0.01, n=7). The c-wave amplitude was reversibly elevated at a concentration of 10µM (p<0.001, n=8), and this effect was more pronounced at 100µM (p<0.001, n=7). The SP increased reversibly at a concentration of 100µM (p<0.001, n=7). Microelectrode recordings were performed with Sp-cAMPS at a concentration of 100µM. The recordings showed significant increases in both the transepithelial potential (p<0.01, n=3) and the slow PIII (p<0.01, n=3). The effects of Sp-cAMPS on the b-wave as well as on the two components of the c-wave suggest influences on both the inner retina and the retinal pigment epithelium of the rabbit eye.Abbreviations PHS Pharmacia eye irrigating solution - AMP adenosine monophosphate - Sp-cAMPS adenosine 3, 5 - cyclic monophosphorothioate Sp-isomer     

Inhibitory presynaptic imidazoline receptors on sympathetic nerves in the rabbit aorta differ from I1- and I2-imidazoline binding sites

The involvement of imidazoline receptors in modulation of noradrenaline release was investigated in the rabbit aorta preincubated with [³H]noradrenaline and superfused with physiological salt solution containing cocaine, corticosterone and propranolol.After blockade of ₂-autoreceptors by rauwolscine, the electrically evoked tritium overflow was inhibited by various imidazolines and guanidines. The rank order of potency was BDF 7579 (4-chloro-2-isoindolinyl) guanidine) BDF 6143 (4-chloro-2-(2-imidazolin-2-ylamino)-isoindoline] > BDF 6100 [2-(2-imidazolin2-y-lamino)-isoindoline] > clonidine > ST587 (2-(2-chloro-5-trifluoromethylphenylimino) imidazolidine nitrate) cirazoline > tolazoline > idazoxan > phentolamine. Comparison of the potencies of these drugs with those previously found for the presynaptic imidazoline receptors in the rabbit pulmonary artery revealed a very good correlation. In contrast, no positive correlation was found with their affinities for the I₁-and I₂-imidazoline binding sites in bovine adrenal medullary membranes and with their lipophilicity (log P values). The electrically evoked tritium overflow was also inhibited by the recently identified endogenous imidazoline receptor ligand agmatine, but was not affected by amiloride. In further series of experiments, the ability of putative antagonist at presynaptic imidazoline receptors to counteract the inhibitory effect of imidazoline derivatives was determined. Amiloride, imidazole-4-acetic acid and 1-benzylimidazole did not attenuate the inhibitory effect of BDF 6143 on the electrically evoked tritium overflow. In contrast, rauwolscine antagonized the inhibitory effect of various imidazolines; rauwolscine was clearly less potent in antagonizing the effect of clonidine, BDF 6143 and cirazoline (apparent pA₂ 6.48–7.32) than in antagonizing that of oxymetazoline and moxonidine (apparent pA₂ 8.33 and 8.12, respectively). In a final series of experiments, BDF 6143 (under the conditions applied a selective agonist at presynaptic imidazoline receptors) proved to be considerably less potent in inhibiting tritium overflow evoked by high K⁺ than by electrical stimulation, whereas moxonidine (in rabbit aorta a selective agonist at presynaptic ₂-adrenoceptors) exhibited similar potency in inhibiting the overflow evoked by both methods of stimulation.It is concluded that noradrenaline release in the rabbit aorta is inhibited via both ₂-autoceptors and presynaptic imidazoline receptors which can be activated by the endogenous imidazoline receptor ligand agmatine. The occurrence of such an ₂-adrenoceptor-independent mechanism is compatible with the ability of K⁺ ions to attenuate the inhibitory effect of an imidazoline receptor agonist but not of an ₂-adrenoceptor agonist, since susceptibility to K⁺ ions has been suggested to be a typical feature of imidazoline recognition sites. The presynaptic imidazoline receptor in rabbit aorta appears to be identical with the previously characterized presynaptic imidazoline receptor in rabbit pulmonary artery, but differs clearly from the I₁ and I₂ binding sites in the bovine adrenal medulla.     

引导组织再生术屏障膜放置时间的研究

在 ３０ 只成年兔的下颌两切牙唇侧牙槽骨制备 １０ｍ ｍ ×５ｍ ｍ 的开窗骨缺损,其表面覆盖 Ｇｏｒｅ Ｔｅｘ 膜。该膜分别于术后 １、２、３、５ 周取出,以不放膜组为空白对照。所有动物５ 周处死,标本作组织学分析。结果表明,２ 周取膜组较空白对照组有更多的新骨形成,而 ３ 周或 ５ 周取膜组织的再生量无进一步增加。提示在引导兔开窗骨缺损的牙周再生中,屏障膜放置所需要的最适宜时间是 ２ 周。     

兔胆囊结石成石过程中脂代谢的变化及高密度脂蛋白制剂对其影响的研究

为研究高胆固醇膳食诱发兔胆囊胆固醇结石模型的脂代谢变化,以及高密度脂蛋白（ＨＤＬ）对其脂代谢及成石的影响,将动物随机分为对照组、高胆固醇膳食组及高胆固醇膳食＋ＨＤＬ注射组,观察各组血浆脂质、胆汁中胆固醇、血卵磷脂胆固醇酰基转移酶（ＬＣＡＴ）活性及血和胆汁中胆汁酸及成石率的变化。结果显示：动物体内胆固醇等脂质的消除障碍导致体内脂质的大量堆积以及清除紊乱,是高胆固醇膳食诱发兔胆囊结石脂代谢变化的主要特点,胆汁中胆固醇与胆汁酸的清除比例失调可能导致成石性胆汁形成;尽管外源性ＨＤＬ制剂能够升高血浆ＨＤＬ２－Ｃ／ＨＤＬ３－Ｃ的比值,增加ＬＣＡＴ的活性从而促使ＨＤＬ成熟,并能降低肝脏的胆固醇含量,但未能降低成石率。结果表明外源性ＨＤＬ制剂对兔胆囊结石形成中脂代谢有一定的影响,但抗成石作用不明显     

Moyamoya病发生、发展及转归实验研究

目的研究Ｍｏｙａｍｏｙａ病的发生、发展及转归过程。方法建立Ｍｏｙａｍｏｙａ病的实验动物模型。结果颈动脉逐渐狭窄或闭塞的过程是内弹力纤维变性、断裂后,中膜平滑肌细胞沿断裂处向内膜游走、深入增生的过程。早期,因侧支循环血管建立不完善,脑组织缺血、缺氧出现多灶性脑软化坏死。随时间延长,脑内大量小动脉及毛细血管代偿性增生,其血管壁腔大壁薄,形成异网。同时５个粟粒状或囊状动脉瘤．蛛网膜下腔、脑室内及脑实质内有小的出血灶。结论Ｍｏｙａｍｏｙａ病临床表现早期以缺血性脑血管病为主,后期以出血性脑血管病为主,是由Ｍｏｙａｍｏｙａ病理的演变过程所决定的,是疾病的发展规律。     

香附水提剂对离体兔肠管活动的影响

目的：探讨香附水提剂对离体兔肠平滑肌的作用。方法：采用Magnus实验装置,使用二道仪描记离体兔肠平滑肌收缩曲线5min作为对照,然后观察药物对其作用25min后曲线变化,并与对照组比较。结果：给香附水提剂后5min离体平滑肌收缩频率及幅度降低较阿托品对照组明显;5-15min二者接近;25min后降低幅度为阿托品组1.3倍,二者比较差异显著（P＜0.01）。结论：香阳水提剂能明显抑制离体兔肠平滑肌的收缩幅度与频率,同时也能拮抗乙酰胆碱和氯化钡所致离体肠管平滑肌的兴奋作用。