Deviations of spontaneous firing in the cochlear nucleus of the frog from the renewal point process

The analysis of statistical characteristics of spontaneous activity (distribution of interpulse intervals, hazard function, autocorrelation function, autocorrelation function for a process with shifted intervals, interdependence between adjoining intervals) for 123 units located in the cochlear nucleus of the frog has been performed. In the majority of cells, this activity was distinct from the poissonic process, and in some cases firing periodicity was noticed. Besides, deviations of the spontaneous activity from the renewal process were usually observed. A reliable positive correlation of interpulse intervals was typical for the majority of the units, though in some cases a negative correlation of short adjoining intervals was revealed. The data indicate the occurrence of effects of memory in the activity of single units of the acoustical system.     

Auditory units in the medulla of the marsh frog with unusual patterns of spontaneous activity

Statistical properties of spontaneous firing were studied in 79 single auditory units located in the dorsal medullar (cochlear) nucleus of unanaesthetized curarized marsh frogs (Rana ridibunda). The great majority of these units showed irregular spontaneous activity with mean rates in the range 1–30 spikes · s^–1. In 53% of the cells the auto-renewal functions of the spontaneous activity monotonically rose to an asymptotic value, but 41% of the cells produced auto-renewal functions which showed a pronounced peak after a dead-time period. Five low-frequency auditory neurons revealed periodic firing in the absence of controlled stimuli. The preferred period did not correspond to the unit's best frequency but demonstrated a modest correlation with the best modulation frequency of the unit's response to amplitude-modulated tones and with the duration of the after-onset dip in peri-stimulus time histograms.Abbreviations AM amplitude modulation - ARF auto-renewal function - DMN dorsal medullar nucleus - PST peristimulus time - SA spontaneous activity - TID time interval distribution - RMG response modulation gain     

A point process analysis of the spontaneous activity of anterior semicircular canal units in the anesthetized pigeon

A point process analysis was performed on extracellular trains of spontaneous activity, which were recorded from anterior semicircular canal units in Scarpa's ganglion in the anesthetized pigeon. For stationary units, the mean interspike interval (ISI) varied from 4.00 to 51.22 ms, and the coefficient of variation ranged from 0.05 to 0.88. Selected tests indicated that 63.6% of units had the properties of a renewal process. The ISI histograms of these renewal-type units were fitted with several probability density functions (pdfs) including the gamma, exponential, exponential-with-delay and the pdf for the first passage times (fpts) in a Wiener-Lévy (WL) process. The WL process provided a good fit to irregular discharge patterns. Furthermore, a neurophysiological basis for this process exists within the vestibular neuroepithelium. It is conjectured that a generalization of this process would also describe regular discharge patterns which have been observed in the spontaneous activity of vestibular primary afferents.DCIEM Research Paper 76-X-58     

Circadian control of spontaneous flight activity in the blowfly, Lucilia cuprina

ABSTRACT. Under laboratory light: dark cycles, the flight activity of adult Lucilia cuprina (Wied.) was low during darkness and uniformity high during light. This pattern persisted as a rhythm both in constant darkness and in constant light of intensity up to 1lx, with a period of approximately 22 h in each. Light pulses of 15 min at l00lx applied to the free-running rhythm in constant darkness generated phase shifts of up to 60°, 12-h light pulses of the same intensity generated maximal (180°) phase shifts. The phase response curves had shapes similar to those of a number of other insect rhythms. When exposed to light periods (70 lx) of greater than 12 h followed by constant darkness, the rhythm reinitiated at the light-dark transition from a constant phase equivalent to that at the time of the light-dark transition in the LD 12:12 cycle.     

Muscarinic agonists do not alter the process of spontaneous quantum secretion of the mediator from motor nerve endings in the frog

The action of carbacholine (Cch) and muscarinic agonists--methylfurmethide, oxotremorine, metacholine, L- and D-F-2268 isomers on spontaneous quantum transmitter release was investigated in experiments on the frog sartorius muscle of R. temporaria. Cch decreased the frequency of miniature and plate potentials (mEEP) by 48%. The muscarinic agonists at a wide concentration range had no effect on mEEP frequency both in normal ionic medium and with potassium concentration increase to 10 mmol/l. The data obtained confirm the assumption that the inhibitory action of Cch on spontaneous transmitter release is unrelated to its muscarinic activity. It was concluded that muscarinic cholinoreceptors controlling spontaneous transmitter release are absent in the frog motor nerve terminals.     

on the vertical distribution of microorganisms in lake baikal during spring deep-water renewal

The vertical distribution of microorganisms during spring deep-water renewal in Lake Baikal was studied. The downward advection of trophogenic waters was found to create conditions for the extensive growth of microorganisms capable of decomposing and mineralizing organic carbon, nitrogen, and phosphorus in deep water layers. These processes occur annually at spring thermal bars near the underwater slope of Lake Baikal, whereas in its pelagic zone, the deep intrusions of waters rich in organic material are observed only in the years when enhanced deep-water renewal is accompanied by a high spring yield of phytoplankton.     

耳聋左慈丸对水杨酸耳鸣模型大鼠听中枢神经元放电的影响

目的：在慢性水杨酸（SA）耳鸣模型上,观察耳聋左慈丸对大鼠下丘外侧核（ICx）和次听皮层（AⅡ）放电的影响,探讨耳聋左慈丸防治耳鸣的神经机制。方法：健康SD大鼠30只,随机平均分成三组：正常对照组、慢性SA耳鸣模型组和耳聋左慈丸防治组。采用立体定位技术及细胞外记录方法,观察不同组别大鼠ICx和AⅡ自发放电活动,用平均自发放电率和放电间隔直方图为观察指标。结果：①慢性SA耳呜模型组与正常对照组大鼠相比,ICx神经单元平均自发放电率增高（4．57±0．54Hz vs 3．14±0．40Hz,P〈0．05）,进一步从放电间隔直方图来分析,短间隔自发放电脉冲数占总放电数比例较高（0-40ms为58％ vs 40％;0～4ms为9％vs5％）。慢性SA耳鸣模型组AⅡ神经单元平均自发放电率与正常对照组大鼠相比有增高趋势（3．844±0．36Hzvs3．17±0．34Hz）,短间隔自发放电脉冲数占总放电数比例较正常对照组增高（0-22ms：31％VS 16％;0—8ms：19％vs16％）。②耳聋左慈丸防治组大鼠与慢性SA耳鸣模型组相比,ICx和AⅡ神经单元平均自发放电率显著降低（ICx：2．41±0．21Hzvs4．57±0．54Hz,P〈0．01;AⅡ：2．24±0．24Hz vs 4．57±0．54Hz,P〈0．01）,短间隔自发放电脉冲数占总放电数比例较低（ICx 0～40 ms：50％vs58％;0-4ms：4％vs9％;AⅡ0～22ms：24％VS 31％;0—8 ms;11％ vs 19％）。结论：慢性SA耳鸣模型动物ICx和AⅡ神经元自发放电活动增加,短间隔放电脉冲数比例较正常对照组增加,耳聋左慈丸能减弱这种变化。     

Juvenile hormone drives the maturation of spontaneous mushroom body neural activity and learned behavior

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Effect of temperature on spontaneous interneuron activity in grasshoppers Tettigonia cantans and Metrioptera roeselii (Orthoptera, Tettigoniidae)

Using electrophysiological methods, effects of temperature on rhythmic impulsation of spontaneously active neurons of thoracic ganglia was studied in grasshoppers Tettigonia cantans and Metrioptera roeselii. Several types of response to temperature changes were observed. Its elevation caused an increase or decrease of the discharge dispersion and a gradual, proportional or abrupt rise of the impulse rate. On decreasing temperature, the impulsation usually returned to its original state, although sometimes at different rate. In neurons whose impulse rate was close to that of pulse repetition rate in male advertisement calls, this dependence was preserved at temperature changes. On the whole, there is reason to believe that changes of temperature in CNS are accompanied not only by a simple change of the neuronal activity level, but also by a complex readjustment in the neuronal network functioning, which allow preserving optimal level of insect metabolic processes and adequate behavior.     

Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding

Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tonepulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23–2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.Abbreviations MTF modulation transfer function - PAM pulse amplitude modulated - SAM sinusoidally amplitude modulated - SC synchronization coefficient - TW time window     

Effect of prolonged refractoriness on the forward masking of tone bursts in single units of the mouse inferior colliculus

The estimation of conditional probability was used to demonstrate the effect of the postspike changes in neuron excitability on its response to the second burst in a pair with an interval between bursts ranging from 50 to 200 ms. The responses of the neurons of the inferior colliculus to pairs of low-intensity tone bursts were recorded extracellularly in anesthetized albino mice. The probability of the response to the second burst in a pair was estimated under two conditions: the presence and the absence of a spike in the response to the first burst. If the interval between burst was 50 ms, the probability of response was decreased in most neurons where there was a spike in the response to the first burst. The opposite trend was observed in a small proportion of neurons. If the interval was increased, it weakened the dependence of the response to the second burst on the character of the response to the first one. The suppression of inhibitory inputs by bicuculline emphasized the postspike refractoriness rather than canceled it. The possible mechanisms of the interdependence between the responses to two consecutive signals are discussed.     

Regulation of dopaminergic neuron firing by heterogeneous dopamine autoreceptors in the substantia nigra pars compacta

Dopamine (DA) receptors generate many cellular signals and play various roles in locomotion, motivation, hormone production, and drug abuse. According to the location and expression types of the receptors in the brain, DA signals act in either stimulatory or inhibitory manners. Although DA autoreceptors in the substantia nigra pars compacta are known to regulate firing activity, the exact expression patterns and roles of DA autoreceptor types on the firing activity are highly debated. Therefore, we performed individual correlation studies between firing activity and receptor expression patterns using acutely isolated rat substantia nigra pars compacta DA neurons. When we performed single-cell RT-PCR experiments, D(1), D(2)S, D(2)L, D(3), and D(5) receptor mRNA were heterogeneously expressed in the order of D(2)L > D(2)S > D(3) > D(5) > D(1). Stimulation of D(2) receptors with quinpirole suppressed spontaneous firing similarly among all neurons expressing mRNA solely for D(2)S, D(2)L, or D(3) receptors. However, quinpirole most strongly suppressed spontaneous firing in the neurons expressing mRNA for both D(2) and D(3) receptors. These data suggest that D(2) S, D(2)L, and D(3) receptors are able to equally suppress firing activity, but that D(2) and D(3) receptors synergistically suppress firing. This diversity in DA autoreceptors could explain the various actions of DA in the brain.     

Epistatic interactions of spontaneous mutations in haploid strains of the yeast Saccharomyces cerevisiae

Several important biological phenomena, including genetic recombination and sexual reproduction, could have evolved to counteract genome contamination by deleterious mutations. This postulate would be especially relevant if it were shown that deleterious mutations interact in such a way that their individual negative effects are reinforced by each other. The hypothesis of synergism can be tested experimentally by crossing organisms bearing deleterious mutations and comparing the fitness of the parents and their progeny. The present study used laboratory strains of the budding yeast burdened with mutations resulting from absence of a major DNA mismatch repair function. Only in one, or possibly two, crosses out of eight did fitness of the progeny deviate from that of their parents in a direction indicating synergism. Furthermore, the distributions of progeny fitness were not skewed as would be expected if strong interactions were present. The choice of experimental material ensured that genetic recombination was extensive, all four meiotic products were available for fitness assays, and that the mutations were probably numerous. Despite this generally favourable experimental setting, synergism did not appear to be a dominating force shaping fitness of yeast containing randomly generated mutations.     

Homeostatic regulation mechanism of spontaneous firing determines glutamate responsiveness in the midbrain dopamine neurons

Autonomous tonic firing of the midbrain dopamine neuron is essential for maintenance of ambient dopamine level in the brain, in which intracellular Ca²⁺ concentration ([Ca²⁺]c) plays a complex but pivotal role. However, little is known about Ca²⁺ signals by which dopamine neurons maintain an optimum spontaneous firing rate. In the midbrain dopamine neurons, we here show that spontaneous firing evoked [Ca²⁺]c changes in a phasic manner in the dendritic region but a tonic manner in the soma. Tonic levels of somatic [Ca²⁺]c strictly tallied with spontaneous firing rates. However, manipulatory raising or lowering of [Ca²⁺]c with caged compounds from the resting firing state proportionally suppressed or raised spontaneous firing rate, respectively, suggesting presence of the homeostatic regulation mechanism for spontaneous firing rate via tonic [Ca²⁺]c changes of the soma. More importantly, abolition of this homeostatic regulation mechanism significantly exaggerated the responses of tonic firings and high-frequency phasic discharges to glutamate. Therefore, we conclude that this Ca²⁺-dependent homeostatic regulation mechanism is responsible for not only maintaining optimum rate of spontaneous firing, but also proper responses to glutamate. Perturbation of this mechanism could cause dopamine neurons to be more vulnerable to glutamate and Ca²⁺ toxicities.     

Tritiated thymidine autoradiographic study on the origin and renewal of argentaffin cells in the pyloric gland of hamsters

Summary The origin and renewal of the argentaffin cells in the pyloric glands of hamsters were studied by flash, cumulative and pulse labelling autoradiography with ³H-thymidine. The argentaffin cells were identified by the Diazo Method using Fast Red B Salt.By flash labelling autoradiography, it was shown that the argentaffin cells located from the middle to the lower level of the pyloric mucosa were not labelled with ³H-thymidine, indicating that this cell type has no proliferative activity. On the 10th and the 20th day of cumulative labelling, 31% and 63% of the argentaffin cells in the gland were found to be labelled, respectively. The labelled argentaffin cells were concentrated in the upper part of the gland (around the region of the isthmus), and no label was found over nuclei of the cells at the lowermost level of the gland. These labelled cells were shown to undergo a downward migration in the days following pulse labelling. They were replaced by unlabelled (and weakly or very weakly labelled) cells which arose at the region of the isthmus. The argentaffin cells in the pyloric gland are thought to arise from epithelial precursor cells at the region of the isthmus.The labelled argentaffin cells in the gland were found to decrease in number almost exponentially after pulse labelling. This indicates that the life span of argentaffin cells is not fixed, but their renewal conforms to the random loss system. The half time of turnover of this cell population was 15 days on average.Supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture, Japan     

用盾叶薯蓣生产薯蓣皂苷元预发酵与水解条件优化

采用RP-HPLC法检测薯蓣皂苷元,对薯蓣皂苷元提取过程中影响产率的多种因素,分预发酵、水解2部分分别用单因素和正交设计的方法进行优化.结果表明:40℃预发酵16 h,加6%浓H2SO4,料液比为1∶6,温度为121～126℃,水解5 h,产率高达3.62%,说明预发酵与水解条件优化可以提高盾叶薯蓣(Dioscorea zingiberensis C. H. Wright)生产薯蓣皂苷元的产率.