安定减低家兔膈神经放电幅度的机制分析

本实验室曾经报道静脉注射安定对于清醒、麻痹、人工呼吸的家兔具有减低膈神经放电幅度、加快呼吸频率,缩短吸气时程(T_I)和呼气时程(T_E),降低动脉血压等作用。本工作在35只家兔中进一步分析了某些药物对安定的这些作用的影响。GABA 降低膈神经放电幅度和动脉血压,这与安定的作用相同,但 GABA 延长T_I、T_E和减慢呼吸频率,与安定的作用相反。事先用氨基酸脱羧酶抑制剂异烟肼处理,或用 GABA 受体拮抗剂印防己毒素处理,可阻遏安定减低膈神经放电幅度的作用。在事先用印防己毒素处理的家兔中,可见安定缩短 T_IT_E的作用不受影响。异烟肼或印防己毒素还能部分对抗安定的降压效应。阿片受体拮抗剂纳洛酮和5-HT 受体拮抗剂赛庚啶都不能阻遏安定降低膈神经放电幅度和动脉血压的作用。上述结果提示安定降低膈神经放电幅度的作用可能通过 GABA 这一中间环节,而内啡肽和5-HT可能不起重要作用。安定的降压作用需要有内源性 GABA 参与才得以持续较长时间,在减少GABA 或阻断 GABA 受体后,安定只有短暂的降压作用。     

颈动脉窦内压的变化速率对反射性降压效应的影响

在成年狗身上制备右侧孤离颈动脉窦,借助灌流装置用饱和氧的任氏液对其进行灌流。灌流压为搏动性的。通过改变每搏泵出量、灌流管道的阻力和弹性来调节灌流压及其变化速率。用多导生理记录仪同步记录股动脉血压、窦内灌流压及其变化速率。本文主要观察窦内压的变化速率对降压反射的影响。在8只狗身上共进行了93次实验。结果表明,在窦内压相同的情况下,灌流压的上升速率愈快,降压效应愈明显,而其下降速率则无显著作用。已有资料证明搏动性窦内压所引起的降压效应较非搏动性压力更为明显。由此可见,狗的颈动脉窦压力感受器不仅对搏动性压力而且对其上升的变化速率也很敏感。     

In vitro alkylation of calf thymus DNA by acrylonitrile. Isolation of cyanoethyl-adducts of guanine and thymine and carboxyethyl-adducts of adenine and cytosine

Reaction of the rodent carcinogen acrylonitrile (AN) at pH 5.0 and/or pH 7.0 for 10 and/or 40 days with 2'-deoxyadenosine (dAdo), 2'-deoxycytidine (dCyd), 2'-deoxyguanosine (dGuo), 2'-deoxyinosine (dIno), N6-methyl-2'-deoxyadenosine (N6-Me-dAdo) and thymidine (dThd) resulted in the formation of cyanoethyl and carboxyethyl adducts. Adducts were not detected after 4 h. The adducts isolated were 1-(2-carboxyethyl)-dAdo (1-CE-dAdo), N6-CE-dAdo, 3-CE-dCyd, 7-(2-cyanoethyl)-Gua (7-CNE-Gua), 7,9-bis-CNE-Gua, imidazole ring-opened 7,9-bis-CNE-Gua, 1-CNE-dIno, 1-CE-N6-Me-dAdo and 3-CNE-dThd. Structures were assigned on the basis of UV spectra and electron impact (EI), chemical ionization (CI), desorption chemical ionization (DCI) and Californium-252 fission fragment ionization mass spectra. Evidence is presented which strongly suggests that N6-CE-dAdo was formed by Dimroth rearrangement of 1-CE-dAdo during the reaction between AN and dAdo. The carboxyethyl adducts resulted from initial cyanoethylation (by Michael addition) at a ring nitrogen adjacent to an exocyclic nitrogen atom followed by rapid hydrolysis of the nitrile moiety to a carboxylic acid. It was postulated that the facile hydrolysis is an autocatalyzed reaction resulting from the formation of a cyclic intermediate between nitrile carbon and exocyclic nitrogen. AN was reacted with calf thymus DNA (pH 7.0, 37 degrees C, 40 days) and the relative amounts of adducts isolated were 1-CE-Ade (26%), N6-CE-Ade (8%), 3-CE-Cyt (1%), 7-CNE-Gua (26%), 7,9-bis-CNE-Gua (4%), imidazole ring-opened 7,9-bis-CNE-Gua (19%) and 3-CNE-Thy (16%). Thus a carcinogen once adducted to a base in DNA was shown to be subsequently modified resulting in a mixed pattern of cyanoethylated and carboxyethylated AN-DNA adducts. Three of the adducts (1-CE-Ade, N6-CE-Ade and 3-CE-Cyt) were identical to adducts previously reported by us to be formed following in vitro reaction of the carcinogen beta-propiolactone (BPL) and calf thymus DNA. The results demonstrate that AN can directly alkylate DNA in vitro at a physiological pH and temperature.     

Neural mechanisms of auditory information processing by identified interneurones in Orthoptera

Three qualities of sound—the directional, the temporal and the spectral—are important for intraspecific communication in Orthoptera. The neural mechanisms employed by identified interneurones for encoding these sound qualities are illustrated by examples of physiological processes found at different levels of the CNS. Discussed are: (1) the creation of directional information by local interneurones in the thorax, and the use of time-intensity trading in sound location; (2) mechanisms for encoding the temporal parameters of sound by interneurones ascending to the brain; (3) frequency-dependent neural filtering of auditory information by local interneurones.     

Use of Avermectins for the Control of Meloidogyne incognita on tomatoes

The efficacy of avermectins B₁ and B₂ for control of Meloidogyne incognita on tomato was studied in pots and field plots for two seasons. Avermectins were applied as granules and liquid in furrows or by low pressure drip irrigation systems, at rates ranging from 0.093 to 0.34 kg a.i./ha, as single or multiple applications. Levels of control comparable to those obtained by oxamyl and aldicarb at 3.36 kg a.i./ha were achieved by the avermectin with only 1/10 the volume of chemicals applied to the environment. Avermectin protection of the roots remained constant throughout the first 5 weeks giving slightly longer protection than oxamyl or aldicarb.     

Cutaneous metabolism of benzo[a]pyrene: comparative studies in C57BL/6N and DBA/2N mice and neonatal Sprague--Dawley rats

The metabolism of the polycyclic aromatic hydrocarbon (PAH) carcinogen benzo[a]pyrene (BaP) was studied using microsomes prepared from the skin of the mouse and rat. Topical application of the polychlorinated biphenyl (PCB) Aroclor 1254 or the PAH 3-methylcholanthrene (3-MC) to the skin of the C57BL/6N and DBA/2N mouse and the Sprague-Dawley rat caused statistically significant enhancement of cutaneous microsomal aryl hydrocarbon hydroxylase (AHH) activity in each animal. PCB was a more potent inducer of the enzyme than was 3-MC. BaP metabolism by skin microsomes from the same animals was assessed using high performance liquid chromatography (HPLC). The skin of untreated animals metabolized BaP into 9,10-, 7,8- and 4,5-dihydrodiols, phenols and quinones. Skin application of PCB caused greater than 16–18-fold enhancement of BaP metabolism in the C57BL/6N mouse and the rat and 2–5-fold enhancement in the DBA/2N mouse. Skin application of 3-MC enhanced BaP metabolism 2–8-fold in the C57BL/6N mouse and 5–10-fold in the rat and had no effect in the DBA/2N mouse. The formation of procarcinogenic metabolite BaP-7, 8-diol was greatly enhanced (4–12-fold) by treatment with the PCB and 3-MC in the tumor susceptible C57BL/6N mouse and in the tumor-resistant neonatal Sprague-Dawley rat. In contrast, the formation of BaP-7,8-diol was either slightly enhanced (2-fold) or unaffected by treatment with the PCB or 3-MC in the tumor-resistant DBA/2N mouse. Our data indicate that neither the patterns of metabolism nor the amount of BaP-7,8-diol formation in the skin are reliable predictors of tumor susceptibility to the PAH in rodent skin.     

The efficacy of biobehavioral and compliance interventions in the adjunctive treatment of mild pregnancy-induced hypertension

This investigation assessed the efficacy of a biobehavioral intervention in the adjunctive treatment of mild pregnancy-induced hypertension (PIH), a potentially serious complication of pregnancy in which normotensive women develop hypertension, proteinuria, and edema of unknown etiology late in gestation. Forty-five women with symptoms of PIH were randomly assigned to one of three treatment conditions: bed rest alone (the most common obstetrical treatment), bed rest with individualized compliance enhancement training, or a four-session biobehavioral treatment consisting of bed rest, compliance enhancement training, and individualized thermal biofeedback-assisted relaxation training. Results indicated that while blood pressure for the bed rest and compliance enhancement groups continued to rise and pose an increasing health risk to maternal and fetal well-being, subjects in the biobehavioral group maintained their blood pressure at a significantly lower, and presumably safer, level. The biobehavioral treatment is hypothesized to affect blood pressure levels in subjects with mild PIH through the mediation of the sympathetic nervous system, decreasing peripheral vascular resistance and cardiac output. The results of this investigation suggest that the biobehavioral intervention may be an effective adjunct to bed rest in the treatment of mild PIH remote from term.     

Application ofVerticillium lecanii for the control ofAphis gossypii by a low-volume electrostatic rotary atomiser and a high-volume hydraulic sprayer

Verticillium lecanii (Fungi: Deuteromycete) blastospores were applied to a chrysanthemum crop by an ULV electrostatically charged rotary atomiser (APE-80). The deposition of spores and subsequent control ofAphis gossypii were compared to high volume hydraulic application. A full rate treatment (2×10¹³ blastospores per ha.) was applied by the APE-80 at week 1 and reduced spore rates of 1/6^th and 1/12^th applied by both the APE-80 and the hydraulic sprayer once and twice a week respectively for weeks 1 to 6. Untreated plots served as controls. Initial deposits of spores were higher with the electrostatic sprayer and better distributed with respect to the position of the target aphids. Significantly lower aphid populations were recorded on the electrostatically treated plots in week 4. The single full rate treatment had significantly fewer aphids than the untreated plots from week 3 and all treatments had significantly fewer aphids than the untreated plots from week 5 onwards. The proportion of the aphid population killed byV. lecanii was higher on the electrostatically treated plots until week 6.      

兔下丘脑室旁核刺激引起的肾交感神经传出活动的抑制

本实验用家兔,氯醛糖及尿酯混合静脉麻醉,制动,人工呼吸,颈部分离出三对神经——迷走、窦及主动脉神经,以备实验中切断。记录股动脉压、肾交感神经传出性放电活动(RSED)及其频率幅度直方图。借助脑立体定向仪刺激下丘脑室旁核,当刺激较强时,在交感神经放电短暂增加之后,可引起血压升高及RSED抑制。这一抑制过程可分为两个时相:血压不变期间的初期抑制时相及与血压升高同时并存的后期抑制时相。实验发现RSED总抑制时程及后期抑制时程均与血压变动具有正相关关系,而初期抑制时程与血压变动无相关关系。切断压力感受性神经前后,虽初期抑制时程的均值无显著差异,但在切断压力感受性神经后,总抑制时程及后期抑制时程的均值大大缩短。当用较弱刺激施于室旁核时,可不引起血压变化,但仍能引起RSED抑制。这个抑制亦可因切断压力感受神经而显著缩短。上述实验结果表明:(1) 在中枢内存在着一个室旁核-肾交感传出系统的抑制机制;(2) 初期抑制来源于中枢性抑制机制,而后期抑制时相主要来源于压力感受性反射,但亦有中枢抑制机制的参与;(3) RSED的中枢抑制可能并不是兴奋后压抑,而是自室旁核至脊髓交感节前神经元的主动性抑制。     

Effect of oxygen pressure on synthesis and export of nitrogenous solutes by nodules of cowpea

Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures of O₂ (pO₂; 1–80%, v/v, in N₂) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO₂ tested. In sub-ambient pO₂ (1 and 2.5%) nodules contained specific activities of uricase (urate: O₂ oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those from air. On a cell basis, uninfected cells in nodules from 1% O₂ contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in sub-ambient O₂, the activities of other enzymes of ureide synthesis were relatively unaffected by pO₂. Short-term effects of pO₂ on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO₂ (1, 2.5 or 5%, v/v in N₂) and¹⁵N₂. Despite a fall in total¹⁵N₂ fixation, ureide synthesis and export was maintained at a high level except in 1% O₂ where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules which allow the balance between O₂ supply and demand to be maintained over a wide range of pO₂, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of fixed nitrogen. This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance Bureau postgraduate fellowship (to F.D.D.).