α1- and α2-Adrenoceptors in rat cerebral cortex: Effect of frontal lobotomy

Summary Surgical noradrenergic denervation of the cortex via frontal lobotomy was used to destroy the noradrenergic nerve endings and thus give some insight into the distribution of alpha-adrenoceptors. Frontal lobotomy caused a reduction in noradrenaline content in rat cerebral cortex (2.1±0.4 ng/mg protein for lesioned side, 6.0±0.3 mg/mg protein for nonlesioned side), indicating an effective noradrenergic denervation. The differences in ³H-clonidine and ³H-prazosin binding observed following surgery were a significant decrease in the number of ₂-adrenoceptors (115.0±4.5 to 91.7±3.2 fmol/mg protein, n=7, P<0.001) and a smaller but significant increase in the number of ₁-adrenoceptors (119.7±2.5 to 131.6±5.4 fmol/mg protein, n=7, P<0.05) in the lesioned cortex. Results of this study indicate that ₂-adrenoceptors located on presynaptic noradrenergic terminals represent only a small proportion of the total ₂-adrenoceptors in rat cerebral cortex.     

The Roles of Dopamine and α1-Adrenergic Receptors in Cocaine Preferences in Female and Male Rats

Cocaine dependence is characterized by compulsive drug taking and reduced involvement in social, occupational, or recreational activities. Unraveling the diverse mechanisms contributing to the loss-of-interest in these ‘non-drug'' pursuits is essential for understanding the neurobiology of addiction and could provide additional targets for treating addiction. The study objectives were to examine changes in cocaine-induced dopamine (DA) overflow in the nucleus accumbens (NAc) over the course of self-administration and determine the roles of α1- and β-adrenergic receptors (AR) in the loss-of-interest in food rewards following the development of an addicted phenotype in male and female rats. Subjects were given access to cocaine and palatable food pellets in a choice self-administration paradigm to identify ‘addicted'' cocaine-preferring (CP) individuals and resistant pellet-preferring (PP) individuals based on their patterns of self-administration over 7 weeks. Cocaine-induced DA overflow in the NAc was examined with microdialysis early and late during self-administration (weeks 2 and 7). Subjects were treated in counter-balanced order with propranolol (β-AR antagonist), terazosin (α1-AR antagonist), or vehicle for an additional 3 weeks of self-administration. CP rats displayed increased motivation for cocaine and attenuated motivation for pellets following the development of cocaine preferences. In females, the estrous cycle affected pellet, but not cocaine, self-administration. CP rats displayed attenuated cocaine-induced DA overflow in the NAc. Propranolol enhanced cocaine reinforcement and reduced pellet intake, whereas terazosin enhanced motivation for pellets and reversed preferences in a subset of CP rats. The implications of these results for the treatment of addiction are discussed.     

Synthesis and Analgesic Effects of μ-TRTX-Hhn1b on Models of Inflammatory and Neuropathic Pain

μ-TRTX-Hhn1b (HNTX-IV) is a 35-amino acid peptide isolated from the venom of the spider, Ornithoctonus hainana. It inhibits voltage-gated sodium channel Nav1.7, which has been considered as a therapeutic target for pain. The goal of the present study is to elucidate the analgesic effects of synthetic μ-TRTX-Hhn1b on animal models of pain. The peptide was first synthesized and then successfully refolded/oxidized. The synthetic peptide had the same inhibitory effect on human Nav1.7 current transiently expressed in HEK 293 cells as the native toxin. Furthermore, the analgesic potentials of the synthetic peptide were examined on models of inflammatory pain and neuropathic pain. μ-TRTX-Hhn1b produced an efficient reversal of acute nociceptive pain in the abdominal constriction model, and significantly reduced the pain scores over the 40-min period in the formalin model. The efficiency of μ-TRTX-Hhn1b on both models was equivalent to that of morphine. In the spinal nerve model, the reversal effect of μ-TRTX-Hhn1b on allodynia was longer and higher than mexiletine. These results demonstrated that μ-TRTX-Hhn1b efficiently alleviated acute inflammatory pain and chronic neuropathic pain in animals and provided an attractive template for further clinical analgesic drug design.     

Effect of α2-adrenoceptor agonists on the expression of morphine-withdrawal in rats

Summary Previous studies using clonidine indicate that ₂-adrenoceptors are involved in suppressing opiate-withdrawal symptoms. However, clonidine may act as a partial agonist at ₂-adrenoceptors and it also possesses significant ₁-receptor agonist activity.The aim of this study was to determine the role of ₂-adrenoceptors in the expression of opiate withdrawal signs using morphine-dependent rats. A range of agonists were selected for study on the basis of their differential preferences for -adrenoceptors.Hooded Wistar rats were made physically dependent on morphine (s.c. injection of an emulsion releasing a total of 250 mg/kg of morphine base over 48 h). Test drugs were injected s.c. followed by naloxone (10 mg/kg i.p.) 20 min later. The incidence of 5 selected withdrawal signs was recorded during the following 20 min. The ₂-adrenoceptor agonists displayed different profiles of activity. Azepexole (1–10 mg/kg) reduced all signs. Clonidine (80–800 g/kg) reduced all signs except paw shakes while guanfacine (25–250 g/kg) reduced all except jumping and diarrhoea. Talipexole (0.1–1 mg/kg) reduced all signs except diarrhoea which was not affected and jumping which was markedly enhanced. UK 14,304 (80–800 g/kg) reduced jumps, potentiated paw shakes but did not affect body shakes, teeth chattering or diarrhoea. The results suggest that there are subpopulations of ₂-adrenoceptors that modulate the expression of opiate withdrawal signs and/or that some of the drugs used affect receptors other than ₂-adrenoceptors.     

Effect of α-asarone on angiogenesis and matrix metalloproteinase

α-Asarone is a main component of Acorus gramineus widely known as an oriental traditional medicinal stuff. A. gramineus has been known to have a variety of medicinal efficacies such as anti-gastric ulcer and anti-allergic activities, inhibition of histamine release and antioxidant effect. However, its effect on angiogenesis remains unclear. The aim of this study was to investigate the effect of α-asarone on induction of angiogenesis through modulation of matrix metalloproteinase (MMP). First of all, MTT assay was performed to evaluate the effect of α-asarone on cell viability using MTT assay, and then tube formation assay with human umbilical vein endothelial cells (HUVEC) in vitro and rat aorta ring assay ex vivo were carried out to elucidate its effect on angiogenesis. Treatment with α-asarone below 6 μM showed no cytotoxicity in human fibrosarcoma cells (HT1080) and HUVEC. It was observed that α-asarone not only promotes tube formation of HUVEC but also induces angiogenesis of rat aorta. In addition, the effects of α-asarone on the expressions of protein and gene were evaluated using western blot analysis and RT-PCR assay. α-Asarone increased the expression levels of MMP-2 and MMP-9 stimulated by phenazine methosulfate (PMS) and phorbol 12-myristate 13-acetate (PMA) in HT1080. Especially, the expression level of antioxidant enzyme such as glutathione reductase was increased in the presence of α-asarone. Therefore, above findings suggest that α-asarone may play an important role in pathological diseases related to MMP and angiogenesis.     

Differential Roles of α6β2* and α4β2* Neuronal Nicotinic Receptors in Nicotine- and Cocaine-Conditioned Reward in Mice

Mesolimbic α6* nicotinic acetylcholine receptors (nAChRs) are thought to have an important role in nicotine behavioral effects. However, little is known about the role of the various α6*-nAChRs subtypes in the rewarding effects of nicotine. In this report, we investigated and compared the role of α6*-nAChRs subtypes and their neuro-anatomical locus in nicotine and cocaine reward-like effects in the conditioned place preference (CPP) paradigm, using pharmacological antagonism of α6β2* nAChRs and genetic deletion of the α6 or α4 subunits in mice. We found that α6 KO mice exhibited a rightward shift in the nicotine dose–response curve compared with WT littermates but that α4 KO failed to show nicotine preference, suggesting that α6α4β2*-nAChRs are involved. Furthermore, α6β2* nAChRs in nucleus accumbens were found to have an important role in nicotine-conditioned reward as the intra-accumbal injection of the selective α6β2* α-conotoxin MII [H9A; L15A], blocked nicotine CPP. In contrast to nicotine, α6 KO failed to condition to cocaine, but cocaine CPP in the α4 KO was preserved. Intriguingly, α-conotoxin MII [H9A; L15A], blocked cocaine conditioning in α4 KO mice, implicating α6β2* nAChRs in cocaine reward. Importantly, these effects did not generalize as α6 KO showed both a conditioned place aversion to lithium chloride as well as CPP to palatable food. Finally, dopamine uptake was not different between the α6 KO or WT mice. These data illustrate that the subjective rewarding effects of both nicotine and cocaine may be mediated by mesolimbic α6β2* nAChRs and that antagonists of these receptor subtypes may exhibit therapeutic potential.     

Participation of cardiac presynaptic α1-Adrenoceptors in the bradycardiac effects of clonidine and analogues

Summary The possible involvement of cardiac presynaptic ₂-adrenoceptors in the acute negative chronotropic effect of intravenous clonidine and four selected analogues was tested in pentobarbitone-anaesthetized normotensive rats by establishing the following parameters: 1) the peripheral presynaptic activity (inhibition of tachycardia to stimulation of the spinal cord in pithed rats); 2) central hypotensive potency in intact rats (decrease in mean arterial pressure); 3) overall bradycardiac activity in intact rats (decrease in cardiac frequency); 4) sympathetic bradycardia in bilaterally vagotomized rat; and 5) vagal bradycardia in -blocked rats. The lipophilicity of the imidazolidines (log P) was measure in the octanol/buffer (pH=7.4) reference system at 37°C. Central hypotensive activity as well as vagal bradycardiac potency correlated with the ability to penetrate the central nervous system, as indicated by the overall lipophilic behavior (log P) of the compounds. In contrast, brain penetration was not a prerequisite for the provocation of bradycardia in bilaterally vagotomized rats. This sympathetic bradycardia resembled peripheral presynaptic inhibition. The hydrophilic — poor brain-penetrating — substances already induced maximal sympathetic bradycardia at doses which did not induce hypotension or vagal bradycardia. The lipophilic drugs, however, only showed a preferentially sympathetic bradycardiac effect over vagal bradycardia at low doses. In intact pentobarbitone-anaesthetized rats, the log dose-bradycardiac response curves of the hydrophilic imidazolidines displayed a bisigmoidal character in contrast to their lipophlic analogues, i.e. at the lower dose-range of the hydrophilic drugs, bradycardia in intact rats resembled peripheral presynaptic inhibition, whereas a contribution of increased vagal activity only was significant after maximal sympathoinhibition was achieved. These data provide evidence for the view that the bradycardiac action of clonidine in pentobarbitone-anaesthetized normotensive rats is due, at least in part, to the functional role of cardiac presynaptic ₂-adrenoceptors. The stimulation of these receptors will inhibit the sympathetic neurotransmission in the heart.     

The Inhibitory Effect of Quercetin-3-O-��-D-Glucuronopyranoside on Gastritis and Reflux Esophagitis in Rats

It was evaluated the inhibitory action of quercetin-3-O-β-D-glucuronopyranoside (QGC) on reflux esophagitis and gastritis in rats. QGC was isolated from the herba of Rumex Aquaticus. Reflux esophagitis or gastritis was induced surgically or by administering indomethacin, respectively. Oral QGC decreased ulcer index, injury area, gastric volume, and acid output and increased gastric pH as compared with quercetin. Furthermore, QGC significantly decreased gastric lesion sizes induced by exposing the gastric mucosa to indomethacin. Malondialdehyde levels were found to increase significantly after inducing reflux esophagitis, and were reduced by QGC, but not by quercetin or omeprazole. These results show that QGC can inhibit reflux esophagitis and gastritis in rats.     

Protective Effect of Tetrandrine and Fructose-1,6-diphos phate on the Model of Focal Cerebral Ischemia in Rats

以大鼠大脑中动脉阻塞２４小时后的梗塞面积和体积为指标，试验了汉防己碱和１，６┐二磷酸果糖对大鼠局部脑缺血的保护作用。在大脑中动脉阻塞后，汉防己碱７．５，１２．０和１５．０ｍｇ·ｋｇ┐１以及１，６┐二磷酸果糖２００和３５０ｍｇ·ｋｇ┐１分别立即腹腔给药，以剂量依赖方式明显减少大鼠脑的梗塞面积和体积。ＭＫ８０１２．０ｍｇ·ｋｇ┐１亦能减少梗塞面积和体积。汉防己碱和１，６┐二磷酸果糖联合用药所产生的保护作用比任何一药物单用时的保护作用都好，提示汉防己碱和１，６┐二磷酸果糖有协同作用。在大脑中动脉阻塞后１小时和２小时给药，汉防己碱和１，６┐二磷酸果糖仍有脑缺血保护作用，但在梗塞后３小时给药则未见任何保护作用。提示中风或脑缺血后，既非５分钟即不可救药，但亦应尽早用药。实验结果表明汉防己碱和１，６┐二磷酸果糖可能是有希望的脑缺血保护剂。     

The Effect of Chronic Alcohol Ingestion on TGF-β1 and bFGF mRNA of Lung Tissues in Rats

目的:观察慢性饮酒后大鼠肺组织中转化生长因子-β1(TGF-β1)和碱性成纤维细胞生长因子(bFGF)mRNA的表达,探讨慢性饮酒对肺间质的影响.方法:健康雄性Sprague-Dawley大鼠20只随机分为无乙醇液体饲料的对照组和乙醇液体饲料的乙醇组,每组10只.喂养16周后观察所有大鼠肺泡内炎性细胞浸润程度并评分,Masson染色观察肺间质胶原沉积情况,电镜观察肺组织超微结构变化,实时荧光定量PCR检测肺组织TGF-β1和bFGF mRNA的表达量.结果:光镜下肺泡内炎性细胞浸润程度评分乙醇组高于对照组,差异有统计学意义(Z=50,P＜0.05).乙醇组电镜可见线粒体膜和嵴均有不同程度融合、模糊不清,细胞间隔均可见不同程度的胶原纤维沉积.乙醇组肺组织中TGF-β1和bFGF mRNA表达量高于对照组,差异有统计学意义(t分别为3.702和3.487,均P＜0.01).结论:慢性饮酒可增加大鼠肺组织中TGF-β1、bFGF mRNA表达量,使肺组织胶原沉积,引起肺泡炎症和肺间质疾病.     

Effect of endothelium on basal and α-adrenoceptor stimulated calcium fluxes in rat aorta

Summary The rate of unstimulated influx of Ca²⁺ into rat aorta smooth muscle, measured as uptake of ⁴⁵Ca, was inhibited in the presence of endothelium as compared to influx in the absence of endothelium. Efflux of ⁴⁵Ca from unstimulated prelabelled tissues was also reduced in the presence of endothelium. In normal physiological solution the rate of influx and efflux of Ca²⁺ stimulated by B-HT 920 (1 and 10 M), but not that stimulated by phenylephrine (30 nM and 1 M), was also reduced in the presence of endothelium. In the presence of the calcium entry blocker flunarizine (3 M), phenylephrine (1 M) stimulated efflux of Ca²⁺ was inhibited by the presence of endothelium. A correlation between inhibition of Ca²⁺ influx and modulation of -adrenoceptor agonist-induced contractions by endothelium could not be demonstrated, and methylene blue, an antagonist of endothelium mediated inhibition of B-HT 920 contractions, did not affect Ca²⁺ influx stimulated by the agonist. The effects of endothelium on Ca²⁺ influx and efflux are unlikely to be due to alterations by endothelium of diffusion of ⁴⁵Ca or the agonists in the vessel. The results demonstrate that an endothelial derived factor or factors can reduce calcium influx into smooth muscle cells and also modulate the release of calcium from cells, perhaps by affecting intracellular calcium pumping mechanisms. A reduction of calcium influx cannot be the sole explanation for the modulatory effect of endothelium on -adrenoceptor agonist-induced contractions but an effect on intracellular calcium metabolism may be important.     

Effect of α-asarone on ethanol-induced learning and memory impairment in mice and its underlying mechanism

OBJECTIVE To investigate the effect ofα-asarone on ethanol-impaired cognitive ability and explore the underlying mechanism in mice. METHODS A mouse model of impaired learning and memory was created by ethanol(2.0 g · kg~(-1), ig). α-Asarone(7.5, 15 and 30 mg·kg~(-1), ip) was delivered 10 min prior to ethanol administration. After 40 min, the locomotor activity of mice with learning and memory impairment was evaluated by the open field test and the behavioral effect of α-asarone was evaluated using the novel object recognition test.Glutamate(Glu) and γ-aminobutyric acid(GABA) levels in the hippocampus were determined by ELISA, and the proteins expression levels of hippocampal α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid(AMPA) receptor(Glu R2), N-methyl-D-aspartic acid(NMDA)receptor(NMDAR2 B), synaptophysin I(SYNΙ), glutamate transporter type 1(GLT-1) and calcium/calmodulindependent protein kinaseⅡ(Ca MKⅡ) were detected by Western blotting. RESULTS There was no significant difference in the horizontal or vertical locomotor activity between the ethanol and normal groups or the 7.5, 15 and 30 mg·kg~(-1)α-asarone groups[F(5, 48)=0.6536, P>0.05; F(5, 49)=1.995, P>0.05]. The recognition index in the ethanol group was significantly decreased as compared with that in the normal group[F(5, 46) =6.739, P<0.05]and was markedly increased in the α-asarone groups as compared with that in the ethanol group(P<0.05), with the exception of the 7.5 mg · kg~(-1)α-asarone group(P>0.05). The hippocampal Glu: GABA ratio in mice was significantly elevated in the ethanol group as compared with that in the normal group(33.42±0.8972 vs 30.79±0.2102, P<0.05) and significantly lower in the α-asarone groups(31.99±0.4986 vs. 33.42±0.8972; 30.97±0.1757 vs. 33.42±0.8972; 30.83 0.1723 vs. 33.42±0.8972, P<0.05). The expression levels of GluR2, NMDAR2B, pSYNⅠand p Ca MKII were significantly higher in the ethanol group as compared with those in the normal group(P<0.05) and obviously lower in the α-asarone groups(P<0.05), with the exception of GluR2, NMDAR2B and pCaMKⅡ in the 7.5 mg·kg~(-1)α-asarone group(P>0.05).And the expression level of GLT-1 was significantly lower in the ethanol group as compared with that in the normal group(P<0.05) and obviously higher in the α-asarone groups(P<0.05). CONCLUSION Pretreatment with α-asarone significantly improved the learning and memory impairment. A possible underlying mechanism is regulation of the calcium signaling cascade to correct functioning of related proteins, and thus, maintain the level of Glu.     

Roles of phosphoinositide-dependent kinase-1 in α1B-adrenoceptor phosphorylation and desensitization

The role of phosphoinositide-dependent protein kinase-1 (PDK-1) activity on α(1B)-adrenoceptor phosphorylation and function was explored using pharmacological inhibitors and expression of a dominant-negative mutant of this enzyme. Noradrenaline-, phorbol myristate acetate-, lysophosphatidic acid- and epidermal growth factor-mediated α(1B)-adrenoceptor phosphorylation were markedly reduced by the two inhibitors used: UCN-01 [(7-hydroxystaurosporine; (3R*,8S*, 9R*, 10R*,12R*)-2,3,9,10,11,12-hexahydro-3-hydroxy-9-methoxy-8-methyl-10-(methylamino)-8,12-epoxy-1H, 8H-2,7b,12a-triazadibenzo[a,g]-cyclonona[cde]triden-1-one)] and OSU-03012 [(2-amino-N-[4-[5-(2-phenanthrenyl)-3-trifluoromethyl)-1H-pyrazol-1-yl]phenyl]-acetamide)]. A similar effect was observed in cells expressing a PDK-1 dominant-negative mutant. Phosphorylated PDK-1 (S241) and protein kinase C α (T497) were associated with cell membranes in the basal state which increased in response to the hormonal stimuli mentioned previously. UCN-01 essentially abolished phospho-PDK-1 membrane-association and markedly attenuated that of protein kinase C α. Consistent with the findings, UCN-01 reduced lysophosphatidic acid- and epidermal growth factor-induced α(1B-)adrenoceptor desensitization. Our data suggest that PDK-1 plays a permissive role in α(1B)-adrenoceptor desensitization and phosphorylation and participates in the formation of signaling complexes, which delicately modulate receptor function and regulation.     

Effect of catecholamic acid on detoxication and distribution of NiCl_2 in mice and rats

目的：研究双酚胺酸（ＣＢＭＩＤＡ）对氯化镍的解毒作用．方法：ＮｉＣｌ２中毒后，立即给予ＣＢＭＩＤＡ，记录动物存活数；小鼠ｉｖ６３ＮｉＣｌ２后给药，测定２４ｈ组织中６３镍；用整体放射自显影术，显示小鼠体内６３镍分布．结果：ｓｃＣＢＭＩＤＡ０５－１５ｇ·ｋｇ－１对ｉｐＮｉＣｌ２５００ｍｇ·ｋｇ－１有解毒作用；小鼠ｉｐＮｉＣｌ２ＬＤ５０为８２８ｍｇ·ｋｇ－１，给药１５或２５ｇ·ｋｇ－１，ＬＤ５０分别为７８９和８２０ｍｇ·ｋｇ－１；大鼠ｉｍＣＢＭＩＤＡ５００ｍｇ·ｋｇ－１使ＮｉＣｌ２的ＬＤ５０提高８倍；组织中６３镍测定和定位显示，ＣＢＭＩＤＡ减少肺和血液中６３镍，增加了骨中６３镍，２４ｈ尿、粪６３镍排出与对照组无明显差异．结论：ＣＢＭＩＤＡ有效地解除镍毒性，提高动物存活率，降低镍在肺部的滞留．     

Effect of Glyceryl Monocaprylate–Modified Chitosan on the Intranasal Absorption of Insulin in Rats

Nasal administration of insulin showed the attractive potential to improve the compliance of diabetic patients and alleviate mild cognitive impairment of Alzheimer's patients. However, the nasal absorption of insulin was not ideal, limiting its therapeutic effect in clinic. This study was to explore the potential of glyceryl monocaprylate–modified chitosan (CS-GMC) on the intranasal absorption of insulin via in vivo pharmacodynamic experiment in conscious rats. It was demonstrated that the absorption-enhancing effect of CS-GMC depended on the existing state of insulin in the formulation, substitution degree of GMC on chitosan and concentration of CS-GMC. Better insulin absorption was achieved when insulin existed in molecular form compared with that in polyelectrolyte complexes. CS-GMC with substitution degree 12% (CS-GMC 12%) was a preferred absorption enhancer, and its absorption enhancing effect increased linearly with the increment of its concentration in the range investigated. Compared with chitosan of the same concentration, CS-GMC12% showed remarkably enhanced and prolonged therapeutic effect up to at least 5 h under the concentration of 0.6% (w/v). CS-GMC12% showed almost no ciliotoxicity to the nasal cilia up to concentration 1.0% (w/v). In conclusion, CS-GMC was a promising absorption enhancer to improve the intranasal absorption of insulin.     

Effect of converting enzyme inhibition and angiotensin receptor blockade on the vasoconstriction mediated by α1 and α2 stimulation in pithed normotensive rats

Summary The effect of functional impairment of the renin-angiotensin system on the vasoconstriction mediated by postsynaptic ₁ and ₂-adrenoceptors in pithed normotensive rats was studied. Selective ₁-adrenoceptor stimulation was induced by intravenously administered cirazoline, whereas B-HT 920 was used as a selective agonists at ₂-adrenoceptors. The angiotensin converting enzyme was inhibited by intravenous treatment of the pithed rats with captopril, teprotide or enalapril. Blockade of angiotensin receptors was produced by intravenously applied [Sar¹ Ala⁸]angiotensin II (saralasin). Pretreatment with angiotensin converting enzyme inhibitors or with saralasin in doses which produced a maximal reduction in basal diastolic blood pressure, only slightly attenuated the hypertensive response to cirazoline. In contrast, these drugs provoked a most significant reduction of the ₂-adrenoceptor mediated vasoconstriction. Restoration of the basal diastolic blood pressure by intravenous infusion with angiotensin II or with vasopressin completely reversed the inhibitory effect of captopril on the vasopressor response to B-HT 920. One hour after bilateral nephrectomy, captopril still reduced the ₂-adrenoceptor mediated vasoconstriction. However, 18–24 h after bilateral nephrectomy, captopril had no additional inhibitory effect on the vasopressor response to selective ₂-adrenoceptor stimulation. It is concluded that in pithed normotensive rats the pressor response to ₂-adrenoceptor stimulation is significantly potentiated by endogenous angiotensin II, even at low circulating levels of the octapeptide. The modulatory action of angiotensin II on the -adrenoceptor mediated vasoconstriction probably represents an effect on the basal arteriolar muscular tone rather than a specific interaction.     

Effect of α7 nicotinic acetylcholine receptor agonists and antagonists on motor function in mice

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation channels found throughout the body, and serve to mediate diverse physiological functions. Muscle-type nAChRs located in the motor endplate region of muscle fibers play an integral role in muscle contraction and thus motor function. The toxicity and teratogenicity of many plants (which results in millions of dollars in losses annually to the livestock industry) are due to various toxins that bind to nAChRs including deltaline and methyllycaconitine (MLA) from larkspur (Delphinium) species, and nicotine and anabasine from tobacco (Nicotiana) species. The primary result of the actions of these alkaloids at nAChRs is neuromuscular paralysis and respiratory failure. The objective of this study was to further characterize the motor coordination deficiencies that occur upon exposure to a non-lethal dose of nAChR antagonists MLA and deltaline as well as nAChR agonists nicotine and anabasine. We evaluated the effect of nAChR agonists and antagonists on the motor function and coordination in mice using a balance beam, grip strength meter, rotarod, open field analysis and tremor monitor. These analyses demonstrated that within seconds after treatment the mice had significant loss of motor function and coordination that lasted up to 1 min, followed by a short period of quiescence. Recovery to normal muscle coordination was rapid, typically within approximately 10 min post-dosing. However, mice treated with the nAChR agonist nicotine and anabasine required a slightly longer time to recover some aspects of normal muscle function in comparison to mice treated with the nAChR antagonist MLA or deltaline.     

Subclassification of presynaptic α2-adrenoceptors: α2A-autoreceptors in rabbit atria and kidney

The study was devised to classify, by means of antagonist affinities, the presynaptic ₂-autoreceptors of rabbit atria and kidney in terms of _2A, _2B, _2C and _2D-A set of antagonists was chosen that was able to discriminate between the four subtypes. Small pieces of the left atrium and slices of the kidney cortex were preincubated with ³H-Noadrenaline and then superfused and stimulated electrically.In one series of experiments, tissue pieces were stimulated by relatively long pulse trains (1 or 2 min) leading to ₂-autoinhibition. All 11 (atria) or 10 (kidney) antagonists increased the evoked overflow of tritium. pEC_30% values (concentrations causing 30% increase) were interpolated from concentration-response curves. In a second series of experiments, tissue pieces were stimulated by brief pulse trains (0.4 s) that did not lead to ₂-autoinhibition, and concentration-inhibition curves of the ₂-selective agonist 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) were determined. Most of the 11 (atria) or 8 (kidney) antagonists shifted the concentration-inhibition curve of UK 14,304 to the right. pK_d values of the antagonists were calculated from the shifts. pEC_30% values correlated with pK_d values, both in atria (r = 0.728) and in the kidney (r = 0.930). pEC_30% values in atria correlated with pEC_30% values in the kidney (r = 0.988) and pK_d values in atria correlated with pK_d values in kidney (r = 0.923).It is concluded that the ₂-autoreceptors in atria and the kidney are the same. Comparison with antagonist affinities for prototypic native ₂ binding sites, ₂ binding sites in cells transfected with ₂ subtype genes, and previously classified presynaptic ₂-adrenoceptors — all taken from the literature — indicates that both autoreceptors are _2A. This conclusion is reached with either of the two independent estimates of autoreceptor affinity, pEC_30% and pK_d. The results are compatible with the hypothesis that at least the majority of ₂-autoreceptors belong to the _2A/D branch of the ₂-adrenoceptor tree, across mammalian or at least rodent and lagomorph species.     

Effect of nicardipine on learning and memory in mice

AIM: To study if nicardipine could improve learning and memory in mice. METHODS AND RESULTS: Nicardipine (0.5mg·kg~(-1)or 0.2 mg·kg~(-1), po) was shown to improve learning and memory in Y mize in mice, which increased passive avoidane response. Nicardipine was capable of antagonizing pentobarbital (15 mg·kg~(-1), ip)-in