Inactivation by 6-hydroxydopamine of the cerebral factor(s) responsible for the inhibition of the autoxidation of norepinephrine in vitro

The effect of extracts from rat cerebral cortex was examined on the stability of norepinephrine-HC1 (NE) in 16 mM Na-phosphate buffer, pH 7.4, at 37 degrees C. The autoxidation products of NE were detected spectrophotometrically at 480 nm. Dialysed samples from a synaptosomal preparation and from the 100,000 g supernatant of a crude homogenate were tested. Aliquots from these preparations, in the range of 0.005-5.0 or 0.01-10.0 micrograms protein/ml, respectively, produced up to 80-85% inhibition of the autoxidation of 100 microM NE for a period of at least 3 h. Similar results were obtained with albumin and ovalbumin at 10- and 10(3)-times higher concentrations, respectively. After the preparations were exposed to 0.1-1.0 mg 6-hydroxydopamine-HC1/mg protein for 5 min at 25 degrees C followed by rapid dialysis, the maximal inhibitory effect was reduced to between 95% to less than 5% of control values. The percent inactivation by a given quantity of 6-hydroxydopamine (6-OHDA) was inversely related to the potency of the untreated sample. Additional observations are presented which suggest that the destruction of the antioxidant activity is caused by breakdown products of 6-OHDA reacting with nucleophilic sites of the preparation. Similar inactivating substances are expected to be formed from other autoxidizing catecholamines, although at a slower rate.     

Mechanism of action of baclofen on myocardial and vascular contractility

Department of Anatomy and Physiology of Man and Animals, A. I. Gertsen Leningrad Pedagogic Institute. Department of Pharmacology, Academician I. P. Pavlov First Leningrad Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. V. Val'dman.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 106, No. 10, pp. 436–438, October, 1988.     

Excitatory amino acids and potassium release in the frog spinal cord

Synaptic release of excitatory amino acids such as L-glutamate and/or L-aspartate and subsequent activation of specific receptors by these putative transmitters appears necessary for the release of K+ by afferent stimulation in the isolated frog spinal cord. This conclusion is based on the findings that (-)baclofen, which is thought to reduce the presynaptic release of putative excitatory amino acid transmitters, and some amino dicarboxylic amino acids (D, L-alpha-aminoadipic acid, 2-amino-4-phosphonobutyric acid, and D, L-alpha, epsilon-diaminopimelic acid), which are believed to interfere with the activation of receptors by these same excitatory amino acids, significantly attenuate the increment in extracellular K+ evoked by tetanic dorsal root stimulation.     

Stereoselectivity of L-baclofen in hippocampal slices of the rat

Extra- and intracellular recording from hippocampal slices of the rat revealed the following effects when baclofen (BF) (0.1-10 microM) was added to the perfusion fluid: a block of synaptic potentials evoked by stimulation of stratum radiatum; a direct hyperpolarization and a conductance increase (for potassium ions) of CA1 pyramidal cells. All this activity was found in the L- none in the D-enantiomer. D-BF did not antagonize the action of L-BF.     

Effects of GABAergic drugs on the GABA turnover in the substantia nigra and the corpus striatum of the rat

Summary Changes in the endogenous GABA concentration and in GABA turnover following GABA receptor stimulation or blockade were studied in the substantia nigra and the corpus striatum of the rat. The GABA agonists, muscimol, baclofen and THIP decreased the accumulation of GABA following inhibition of GABA--ketoglutaric acid aminotransferase by-acetylenic GABA (GAG) in both structures investigated. Only the effect of muscimol in the substantia nigra was inhibited by the GABA antagonist, bicuculline. Muscimol, baclofen and progabide reduced the disappearance rate of GABA in the substantia nigra following inhibition of the glutamate decarboxylase by 4-deoxypyridoxine. The endogenous GABA concentration was decreased in the corpus striatum following muscimol, THIP or baclofen, probably due to a decreased synthesis of GABA. Smaller effects were seen on the endogenous GABA concentration in the substantia nigra, since both the synthesis and the utilization of GABA were decreased by muscimol and baclofen. Thus, the turnover of brain GABA might be regulated by changes in receptor activity.     

GABAB receptor protein and mRNA distribution in rat spinal cord and dorsal root ganglia

The presence of metabotropic receptors for GABA, GABAB, on primary afferent terminals in mammalian spinal cord has been previously reported. In this study we provide further evidence to support this in the rat and show that the GABAB receptor subunits GABAB1 and GABAB2 mRNA and the corresponding subunit proteins are present in the spinal cord and dorsal root ganglion. We also show that the predominant GABAB1 receptor subunit mRNA present in the afferent fibre cell body appears to be the 1a form. In frozen sections of lumbar spinal cord and dorsal root ganglia (DRG) GABAB receptors were labelled with [3H]CGP 62349 or the sections postfixed with paraformaldehyde and subjected to in situ hybridization using oligonucleotides designed to selectively hybridize with the mRNA for GABAB(1a), GABAB(1b) or GABAB2. For immunocytochemistry (ICC), sections were obtained from rats anaesthetized and perfused-fixed with paraformaldehyde. The distribution of binding sites for [3H]CGP 62349 mirrored that previously observed with [3H]GABA at GABAB sites. The density of binding sites was high in the dorsal horn but much lower in the ventral regions. By contrast, the density of mRNA (pan) was more evenly distributed across the laminae of the spinal cord. The density of mRNA detected with the pan probe was high in the DRG and distributed over the neuron cell bodies. This would accord with GABAB receptor protein being formed in the sensory neurons and transported to the primary afferent terminals. Of the GABAB1 mRNA in the DRG, approximately 90% was of the GABAB(1a) form and approximately 10% in the GABAB(1b) form. This would suggest that GABAB(1a) mRNA may be responsible for encoding presynaptic GABAB receptors on primary afferent terminals in a manner similar to that we have previously observed in the cerebellar cortex. GABAB2 mRNA was also evenly distributed across the spinal cord laminae at densities equivalent to those of GABAB1 in the dorsal horn. GABAB2 mRNA was also detected to the same degree within the DRG. Immunocytochemical analysis revealed that GABAB(1a), GABAB(1b) and GABAB2 were all present in the spinal cord. GABAB(1a) labelling appeared to be more dense than GABAB(1b) and within the superficial dorsal horn GABAB(1a) was present in the neuropil whereas GABAB(1b) was associated with cell bodies in this region. Both 1a and 1b immunoreactivity was expressed in motor neurons in lamina IX. GABAB2 immunoreactivity was expressed throughout the spinal cord and was evident within the neuropil of the superficial laminae.     

氯苯氨丁酸抑制脊髓背角神经元谷氨酸量子释放的机制

目的　研究GABAB 受体特异性激动剂氯苯氨丁酸(baclofen)在脊髓背角神经元抑制谷氨酸量子释放的机制。方法　在脊髓薄片标本上 ,采用全细胞电压钳法记录脊髓背角神经元谷氨酸能的微兴奋性突触后电流 (miniatureexcita torypostsynapticcurrents;mEPSCs) ,通过分析这些电流的变化来研究baclofen影响谷氨酸量子释放的机制。结果　ba clofen抑制mEPSCs的发放频率 ,但对平均幅度无明显影响 ,表明baclofen抑制谷氨酸释放的作用部位在突触前。在无钙溶液或者K+ 通道阻滞剂 4 AP存在的条件下 ,baclofen对mEPSCs发放频率的抑制作用不受影响 ,但腺苷酸环化酶激动剂foskolin (可使cAMP保持在较高水平 )能降低其抑制作用。而蛋白激酶C (PKC)激动剂PDBu对baclofen的抑制作用无影响。用NEM破坏G蛋白 ,则可取消baclofen的抑制效果。结论　baclofen不是通过影响突触前Ca2 + 通道或K+通道 ,或PKC途径 ,而是通过作用于G蛋白和 (或 )cAMP途径抑制谷氨酸的释放 ;这种抑制作用可能参与baclofen在脊髓水平的镇痛     

全身体积描记法在大鼠呼吸系统试验中的应用

目的 应用全身体积描记法观察药物对大鼠呼吸指标的影响,对动物肺功能检测系统进行性能验证,为该技术用于药物安全药理学评价提供依据。方法 SD大鼠30只,雌雄各半,分为溶媒对照组、巴氯芬（30 mg/kg）组、茶碱（30 mg/kg）组,溶媒对照组给予等体积的0.5%羧甲基纤维素钠溶液。实验时将动物放入体积描记箱中,动物肺功能检测系统连续获取给药前至少60 min及给药后6 h内的数据,药后24 h至少连续采集60 min的数据,将每只动物给药前、给药后1、2、4、6、24 h均选取连续平稳的30个呼吸波,检测潮气量（TV）、每分钟通气量（MV）、呼吸频率（F）。结果 与溶媒对照组比较,巴氯芬组TV在给药后1、2、4、6、24 h显著增大（P<0.05）,呈先上升后下降趋势;F在药后2、4、6 h显著减慢（P<0.05）,呈先下降后上升趋势。大鼠给予30 mg/kg的茶碱后呼吸急促,药后1、2、4 h F明显加快、MV显著增加,均呈先上升后下降趋势,与溶媒对照组比较,药后1、2 h出现统计学差异（P<0.05）。结论 SD大鼠给予巴氯芬和茶碱后呼吸指标具有良好时间-反应趋势,可作为阳性药用于仪器的性能验证;肺功能检测系统能够准确记录清醒无束缚大鼠呼吸指标的变化情况,可用于呼吸系统安全药理学研究。