Further studies on the extraneuronal uptake and metabolism of isoprenaline in the perfused rat heart

Summary To simultaneously determine the kinetics of removal, O-methylation and accumulation of ³H-isoprenaline, isolated rat hearts were perfused for 4 min with various concentrations of ³H-isoprenaline. The apparent K _m for the O-methylation of ³H-isoprenaline (3.3±0.5 M) was more than one order of magnitude lower than the corresponding value for the accumulation of unchanged amine (71.3±7.1 M). The apparent K _m for removal was very similar to that for accumulation (63.2±5.9 M). At perfusion concentrations higher than 25 M, i.e. when O-methylation was saturated, removal virtually equalled accumulation. However, at low substrate concentrations removal of ³H-isoprenaline was overwhelmingly followed by O-methylation; this led to a marked difference between rates of removal and those of accumulation.When initial rates of uptake of ³H-isoprenaline were determined after 1.5 min of perfusion of the hearts by the method of Graefe et al. (1978), the uptake of ³H-isoprenaline consisted of two components: a nonsaturable and a saturable (after subtraction of the nonsaturable component from the total uptake).The kinetic constants of the saturable component of uptake were higher than those obtained after 4 min perfusion (see above) (K _m : 110±19 M; V _max: 80±4 nmoles·g^–1·min^–1).Corticosterone competitively inhibited the saturable component of uptake of ³H-isoprenaline (K _m : 1.2 M).During wash out of accumulated ³H-isoprenaline, O-methylation took place predominantly in one of the two extraneuronal compartments. The efflux of 3-O-methyl-³H-isoprenaline (³H-OMI), the O-methylated metabolite of ³H-isoprenaline, was characterized by a half time of about 1.2 min. O-methylation accelerated the loss of radioactivity from the tissue during wash out.The extraneuronal uptake of ³H-isoprenaline was characterized as a pump and leak system by means of steady-state kinetics of accumulation of ³H-isoprenaline. Half saturation of the steady-state accumulation was observed at a concentration of 104.5 ±18.5 M ³H-isoprenaline; the leak component was characterized by a rate constant of 0.0359 min^–1.This study was supported by the Deutsche Forschungsge-meinschaftA preliminary account was presented at the 6th International Congress of Pharmacology (Graefe et al., 1975)     

Steady-state kinetics of imipramine in patients

Steady-state plasma level kinetics were studied in 76 patients given imipramine (IP) 150 to 225 mg/day for 2–5 weeks. IP was given in three divided doses at 8.00 a.m., 1.00 p.m. and 5.00 p.m. Plasma concentrations of IP and its active metabolite desipramine (DMI) were determined by quantitative in situ thin-layer chromatography. The plasma levels of IP and DMI showed pronounced flucutations throughout the day with a ratio of about 2 between highest and lowest level. Patients with steady-state levels of IP and/or DMI below 50 g/l reached this within 1 week of treatment. Patients with higher steady-state levels reached steady-state concentrations within 2–3 weeks. There were some intraindividual fluctuations in plasma levels from week to week after steady state had been reached (coefficient of variation: 10–20%). Interindividually, the steady-state levels corrected to a dose of 3.5 mg/kg per day varied considerably: IP: 6–356 g/l, DMI: 24–659 g/l and IP+DMI: 58–809 g/l. The steady-state plasma levels showed a skew distribution that became normal by logarithmic transformation. The IP/DMI ratio ranged from 0.07 to 5.5 with a median value of 0.47. Compared to data from amitriptyline treated patients the IP/DMI ratios had significantly lower median value and larger variation than the corresponding plasma level ratios of amitriptyline/nortriptyline. Several statistically significant differences in steady-state levels between age groups were found. For IP: Women aged 30–39 had lower levels than women aged 20–29, 40–49, and 50–59, and men aged 50–59 and 60–65; men aged 30–39 had lower levels than men aged 60–65. For DMI: Women aged 30–39 had lower levels than women aged 50–59.     

听力正常成年人同时多频听觉稳态诱发反应研究

目的　了解正常听力成人同时多频听觉稳态诱发反应的特性。方法　 32名受试者 (6 4耳 ) ,年龄 2 2～ 32岁 ,平均 2 8.3岁 ,男 12名 ,女 2 0名 ,双耳纯音听阈测试各频率听阈在 2 0dB以内。以载波频率为 0 .5、1、2和 4kHz的纯音 ,调制频率分别为 77、85、93和 10 1Hz(左耳 )以及 79、87、95、10 3Hz(右耳 )的调幅声作为测试信号 ,双耳 8个频率同时给声刺激 ,同时自动判定并记录反应。各载波频率的阈值、反应幅度等数据采用SPSS统计软件分析。结果　①同时多频听觉稳态诱发反应阈高于纯音听阈 7～ 19dB。②反应阈经双因素方差分析 (侧别×频率 ) ,左右耳之间无显著性差异 (F =1.94 2 ;μ 1,179;P =0 .16 5 ) ,但各频率之间有显著性差异 (F =31.2 5 4 ;μ 3,179;P =0 .0 0 0 ) ,各频率反应阈均值之间进一步的两两比较显示 0 .5kHz反应阈与其它频率之间存在显著性差异。③以 6 0dBSPL作为分析强度 ,男女受试者在各个频率的反应幅度的差异经双因素方差分析 (性别×频率 )有显著性差异 (F =2 .94 8;μ 3,175 ;P =0 .0 34) ,0 .5kHz反应幅度最低 ,4kHz最高。性别之间有显著性差异 (F =16 .4 90 ;μ 1,175 ;P=0 .0 0 0 ) ,男性反应幅度高于女性。④各频率不同状态下背景噪声的差异经双因素方差分析 ,提示清醒状     

Frequency-domain analysis of fast oddball responses to visual stimuli: A feasibility study

Event-related potential responses to oddball stimuli, including the P300 component, have been proposed as a diagnostic tool for discerning psychiatric or higher-level neural disorders from malingering, for instance in cases of unexplained visual loss. For clinical use, short recording durations and easy statistical assessment are highly desirable. With this aim, we investigated the feasibility of recording oddball responses in a fast steady-state regime. We used gratings with two possible orientations in a rapid oddball paradigm with an inter-stimulus interval of 214 ms. Six consecutive presentations of one stimulus type (frequent) were followed by a single presentation of the other (infrequent) stimulus type. Subjects were attending to the rare stimulus type. The electroencephalographic recordings were analyzed in the frequency domain. All subjects produced significant harmonic responses related to the processing of the rare stimulus, demonstrating the feasibility of the technique, with the potential of reducing recording times substantially compared to conventional slow stimulation. We furthermore found that the regularity of the occurrence of infrequent stimuli, which is necessary for frequency-domain analysis, does not per se reduce the P300 responses, as would have been expected in the framework of some hypotheses regarding the role of the P300.     

Dissociation of psychophysical and EEG steady-state response measures of cross-modal temporal correspondence for amplitude modulated acoustic and vibrotactile stimulation

Research examining multisensory integration suggests that the correspondence of stimulus characteristics across modalities (cross-modal correspondence) can have a dramatic influence on both neurophysiological and perceptual responses to multimodal stimulation. The current study extends prior research by examining the cross-modal correspondence of amplitude modulation rate for simultaneous acoustic and vibrotactile stimulation using EEG and perceptual measures of sensitivity to amplitude modulation. To achieve this, psychophysical thresholds and steady-state responses (SSRs) were measured for acoustic and vibrotactile amplitude modulated (AM) stimulation for 21 and 40 Hz AM rates as a function of the cross-modal correspondence. The study design included three primary conditions to determine whether the changes in the SSR and psychophysical thresholds were due to the cross-modal temporal correspondence of amplitude modulated stimuli: NONE (AM in one modality only), SAME (the same AM rate for each modality) and DIFF (different AM rates for each modality). The results of the psychophysical analysis showed that AM detection thresholds for the simultaneous AM conditions (i.e., SAME and DIFF) were significantly higher (i.e., lower sensitivity) than AM detection thresholds for the stimulation of a single modality (i.e., NONE). SSR results showed significant effects of SAME and DIFF conditions on SSR activity. The different pattern of results for perceptual and SSR measures of cross-modal correspondence of AM rate indicates a dissociation between entrained cortical activity (i.e., SSR) and perception.     

A combination of alleles 2 of interleukin (IL)-1A(-889) and IL-1B(+3954) is associated with lower gingival bleeding tendency in plaque-induced gingivitis in young adults of Arabic heritage

The aim of this study was to investigate the possible association of a distinct combination of polymorphisms in the interleukin (IL)-1 gene cluster on gingival bleeding tendency in young adult Arabs with plaque-induced gingivitis. Fifty otherwise healthy, nonsmoking volunteers, 19–28 years of age, participated. Clinical examinations included periodontal probing depth, bleeding on probing, and plaque index. Probing was done with a pressure-controlled probe at about 1.27 MPa. Examinations were repeated after 2 and 4 weeks. Polymorphisms in the IL-1 gene cluster were assessed using a reverse hybridization assay. A subject carrying alleles 2 at IL-1A ⁻⁸⁸⁹ and IL-1B ⁺³⁹⁵⁴ was designated genotype-positive. Twenty-six subjects were genotype-positive (52%). A repeated measures two-level (occasion, subject) model of the proportion of sites bleeding on probing, which was adjusted for gender, average plaque index, probing depth, and calculus, revealed a significantly lower proportion of bleeding sites in genotype-positive subjects (estimate −0.050, standard error 0.025, p < 0.05). Biserial correlations of bleeding proportions were high (0.71–0.78), confirming the steady-state plaque environment. It was concluded that inflammatory responses to dental plaque were considerably dampened in genotype-positive, nonsmoking young adults of Arabic heritage.     

Unwrapping of transient responses from high rate overlapping pattern electroretinograms by deconvolution

Objective

Due to overlapping, temporal information is mostly lost in high rate steady-state pattern electroretinograms (PERG_SS). This study develops a deconvolution method and a display/recording system to “unwrap” PERG_SS and obtain a transient, “per stimulus” response (PERG_tr) regardless of reversal rate.

Methods

Processing and instrumentation, including high temporal resolution display and acquisition were developed for deconvolving PERGs acquired at high rates by slight jittering of reversal onsets at a given mean rate.

Results

The system was successfully tested at eight rates from 2.2 to 78.1 rps. At medium rates (17.4–41.2 rps) recordings with conventional morphology (N35–P50–N95) but earlier peaks and higher amplitudes were extracted up to 40 rps. At higher rates, smaller triphasic responses were obtained, exhibiting similar peak latencies, but reversed polarity. Oscillating potentials (OPs) were also recorded at all rates after deconvolution.

Conclusions

Transient PERGs and OPs can be extracted from quasi steady-state PERG recordings obtained at high rates with a deconvolution algorithm using high temporal resolution display and acquisition systems.

Significance

The methodology to extract transient and oscillatory responses from steady-state PERGs could be useful in understanding high rate responses and diagnosis of various retinal diseases by revealing temporal information on waveform components which cannot be normally observed.     

Method for the deconvolution of auditory steady-state responses

The potential evoked by a ‘train’ of N equally spaced auditory clicks, with an inter-click period shorter than the duration of the response to an isolated click, is said to be a steady-state response (SSR). Extracting the individual responses evoked by the clicks of the train during steady state can be key to understanding of the neurophysiological mechanisms underlying SSR generation. In the literature, this task has been dealt with only under the (unwarranted) assumption that the response of the system does not vary during the presentation of the clicks, i.e. no neurophysiological adaptation is present. In this work, a new, non-parametric algorithm is proposed that, relaxing the time-invariance hypothesis, allows the extraction from the SSR of the N waveforms individually evoked by the N clicks of the train. The performance of the approach is evaluated on simulated SSRs and on real data recorded from the temporal cortex of awake rats. Results show that the method is able to detect and assess possible adaptation of the neurophysiological system in the generation of SSRs.     

Properties of the fast sodium channels in pyramidal neurones isolated from the CA1 and CA3 areas of the hippocampus of postnatal rats

The fast sodium (Na)current of hippocampal neurones was recorded using the intracellular perfusion method. Neurones were isolated from the CA₁ and CA₃ hippocampal subregions separately, after treatment of the tissue with trypsin. There were no differences between the current-voltage (I-V) characteristics of CA₁ and CA₃ neurones. In contrast to this, the steady-state inactivation (h_∞) of both types of neurones was significantly different. Additionally, there were two subpopulations of CA₁ neurones, which showed different courses of h_∞. Compared with CA₁ neurones, the steady-state activation and inactivation curves of CA₃ neurones overlapped much more in the potential range −80 mV to −50 mV. These results are consistent with the well-known fact that CA₃ neurones show spontaneous burst activity, while CA₁ cells do not. The time constant of activation (τ_m) depended upon the membrane potential in the same way for all CA₃ neurones investigated. However, there were two different subpopulations of CA₃ cells, showing different voltage dependence of the time constant of inactivation. We conclude that these differences reflect two types of pyramidal cells within the same subregion.     

L-型钙通道阻滞剂对心肌细胞钙稳态的影响

目的观察L-型钙通道阻滞对心肌细胞的影响。方法取SD大鼠颈部脱臼处死后浸入75%乙醇数秒,迅速开胸摘取心脏,置入盛有37℃预热的台氏液100ml的培养皿中。在超净工作台上用台式液清洗并修剪掉结缔组织,迅速行主动脉插管。将心脏悬挂于Langendroff灌流装置上,剪下心室并剪成约1mm3的组织块,放入37℃预热的含0.2mmol/L Ca2＋台氏液20ml的培养皿中,将心室在溶液中轻轻晃动以分散已解离的心室肌细胞。新分离的细胞在常温下放置1～2h后,用加样器取带少许细胞的原液放入试管中,加入指示剂,给予正常细胞外液灌流,测全细胞胞内钙瞬变作为前对照组;给予硝苯地平溶液灌流,测全细胞胞内钙瞬变作为实验组;给予正常细胞外液灌流,测全细胞胞内钙瞬变作为后对照组。结果不同浓度的硝苯地平对静息状态下心室肌细胞胞内钙信号的影响都不明显,仅10μmol/L硝苯地平可能使静息状态下心室肌细胞胞内钙水平轻微降低,更高浓度的硝苯地平的效果反而减弱。不同浓度的硝苯地平都能不同程度降低心室肌细胞胞内钙瞬变的峰值（P〈0.05）,5μmol/L硝苯地平的标准化值最低,降低心室肌细胞胞内钙瞬变峰值的效果比2μmol/L硝苯地平明显（P〈0.05）。但是10μmol/L硝苯地平、50μmol/L的硝苯地平的降低心室肌细胞胞内钙瞬变峰值的效果反而减弱。结论硝苯地平可以抑制大鼠心室肌细胞的电流。但是,硝苯地平对于静息状态下的心室肌细胞胞内钙信号的影响不明显,可能与硝苯地平只对去极化过程的ICa2＋、Ito和IK有抑制作用有关。