The cortical reaction in pig oocytes during in vivo and in vitro fertilization

The structure of pig oocytes after in vivo and in vitro fertilization and following treatment with the ionophore A23187 with differing levels of calcium are described, with particular reference to the cortical granules. Fertilization in vivo and in vitro resulted in cortical granule exocytosis. Sperm penetration in vivo was more rapid than in vitro and resulted in the dispersal of the cortical granules' contents in the perivitelline space following exocytosis. The contents of the granules remained adjacent to the plasmalemma after in vitro fertilization and suboolemmar vesicles were less numerous than after in vivo fertilization. High calcium levels were necessary to induce the dispersal of the cortical granule contents following treatment with ionophore. The observations are discussed regarding their relevance to the blockage to polyspermy.     

Modulation of Phosphoinositide Hydrolysis by NaF and Aluminum in Rat Cortical Slices

NaF stimulated phosphoinositide hydrolysis in rat cortical slices. The production of [3H]inositol monophosphate was rapid for the first 15 min of incubation with NaF, followed by a plateau. The major product detected was [3H]inositol monophosphate, although significant amounts of [3H]inositol bisphosphate and [3H]inositol trisphosphate were also produced. The stimulation of [3H]inositol monophosphate production by NaF was concentration dependent between 2 and 20 mM NaF. Addition of 10 or 100 microM AlCl3 or aluminum maltol did not alter the effect of NaF, whereas at 500 microM, these aluminum preparations resulted in significant inhibition. Increasing the concentration of K+ from 5 to 20 mM potentiated [3H]inositol monophosphate production induced by carbachol but not by NaF. Incubation with 1 microM phorbol 12-myristate 13-acetate, a phorbol ester, inhibited carbachol-induced, but not NaF-induced, [3H]inositol monophosphate production. These results further support the hypothesis that a guanine nucleotide binding protein that can be activated by NaF is involved in phosphoinositide hydrolysis in brain. The use of NaF provides a means to bypass receptors to study intracellular regulatory sites of phosphoinositide metabolism without disrupting cells.     

Subtypes of dorsal root ganglion neurons based on different inward currents as measured by whole-cell voltage clamp

Summary Electrophysiological and pharmacological properties distinguished subtypes of adult mammalian dorsal root ganglion neurons (DRGn) in monolayer dissociated cell culture. By analogy of action potential waveform and duration, neurons with short duration (SDn) and long duration (LDn) action potentials resembled functionally distinct subtypes of DRGn in intact ganglia. Patch clamp and conventional intracellular recording techniques were combined here to elucidate differences in the ionic basis of excitability of subtypes of DRGn in vitro. Both SDn and LDn were quiescent at the resting potential. Action potentials of SDn were brief (< 2 msec), sensitive to tetrodotoxin (TTX, 5–10 nM), exhibited damped firing during long depolarizations, and did not respond to algesic agents applied by pressure ejection. Action potentials of LDn were 2–6 msec in duration, persisted in 30 µM TTX, and fired repetitively during depolarizing current pulses or exposure to algesic agents (e.g., capsaicin, histamine and bradykinin). Whole-cell recordings from freshly dissociated neurons revealed two inward sodium currents (I_Na; variable with changes in sodium but not calcium concentration in the superfusate) in various proportions: a rapidly activating and inactivating, TTX-sensitive current; and, a slower, TTX (30 M)-resistant I_Na. Large neurons, presumable SDn, had predominantly TTX-sensitive current and little TTX-resistant current. The predominent inward current of small neurons, presumably LDn, was TTX-resistant with a smaller TTX-sensitive component. By analogy to findings from intact ganglia, these results suggest that fundamentally different ionic currents controlling excitability of subtypes of DRGn in vitro may contribute to functional differences between subtyes of neurons in situ.     

Photosensing and Processing of Sensory Signals in Halobacterim halobium

Halobacteria detect changes in light intensity by retinal proteins, the number and identity of which are not yet unequivocally established. The sensory receptors are different from those for light energy conversion. The cells having no preferred swimming direction spontaneously reverse about every 10 s. An oscillator model has been proposed to explain this periodicity. Depending on wavelength and sign, a stimulus leads either to one prolonged interval between two reversals, the attractant response, or to a shortened interval, the repellent response. Sensory signals generated by stimulation of P-565 and of P-370 are integrated at a common link. Signals from other receptors may be processed by separate links. The nature of the sensory signals is not known, but the membrane potential can be excluded as a candidate. On the basis of the oscillator hypothesis the output signals of the integration links act on the oscillator and thus shift the time at which it triggers a reversal of the flagellar motor. Experiments indicate that cGMP and calcium play antagonistic roles in the oscillatory activity. Reversible methylation of specific membrane proteins influences the time during which successive signals are integrated. This reaction is assumed to terminate the lifetime of the excitatory signals and thus to allow the system to adapt.     

重复短声调频在豚鼠诱发的皮层慢反应及反应阈

重复短声调频在豚鼠诱发的皮层慢反应的基本特征与其他声刺激诱发者相似,它为一正负正三相波,第一正峰的潜伏期约50ms。以调频深度表示的反应阈△f_r较易测定,可以作为动物频率辨别能力的定量表达。对从250至4000pps的复频,豚鼠△fr的均值只在2.0至2.6pps间波动,因此对需要比较不同状况时△fr的变化,一般只取复频1000pps的△f_r便可代表,不必取整个△f_r曲线。听觉系统对重复短声的频率变化比纯音的容易检别,本文对可能的机理进行了讨论。     

Electrophysiological properties of cellular and paracellular conductive pathways of the rabbit cortical collecting duct

Summary Microelectrode techniques were applied to the rabbit isolated perfused cortical collecting duct to provide an initial quantitation and characterization of the cell membrane and tight junction conductances. Initial studies demonstrated that the fractional resistance (ratio of the resistance of the apical cell membrane to the sum of the resistances of the apical and basolateral membranes) was usually independent of the point along the tubule of microelectrode impalement—implicating little cell-to-cell coupling—supporting the application of quantitative techniques to the cortical collecting duct. It was demonstrated that in the presence of amiloride, either reduction in the luminal pH or the addition of barium to the perfusate selectively reduced the apical membrane potassium conductance. From the changes inG ^te and fractional resistance upon reducing the luminal pH or addition of barium to the perfusate, the transepithelial, apical membrane, basolateral membrane and tight junction conductances were estimated to be 9.3, 6.7, 8.1 and 6.0 mS cm^–2, respectively. Ninety to ninety-five percent of the apical membrane conductance reflected the barium-sensitive potassium conductance in the presence of amiloride with an estimated potassium permeability of 1.1×10^–4 cm sec^–1. Reduction in the perfusate pH to 4.0 caused a 70% decrease in the apical membrane potassium conductance, implying a blocking site with an acidic group having a pK _a near 4.4. It is concluded that both the transcellular and paracellular pathways of the cortical collecting tubule have high ionic conductances, and that the apical membrane conductance primarily reffects a high potassium conductance. Furthermore, both reduction in the perfusate pH and addition of barium to the perfusate selectively block the apical potassium channels, although the site of inhibition likely differs since the two ions display markedly different voltage-dependent blocks of the channel.     

Demography of the Juang tribal population of Orissa

Demographic analysis of genealogical data collected in 1954 for 23 Juang villages was undertaken employing indirect estimation techniques and computer projection methodology. Results indicated that this group did not feature the historically high fertility levels associated with Indian tribal groups, although fertility was higher than previously reported for the Juang. The population did feature a mortality differential, with worse mortality conditions than the Indian national population at this time. Reversed sexual mortality differentials, common in South Asian populations, were also present for the Juang. Computer projection investigation revealed a steadily growing population, in contrast to some Indian tribal groups faced with extinction.     

Demography and sustainable management of two fiber‐producing Astrocaryum palms in Colombia

The spear leaves of the palms Astrocaryum chambira and A. standleyanum have been traditionally used by Colombian indigenous communities as a source of fiber for handicraft production. Traditional management practices, including destructive harvest, have reduced population sizes of both species. We monitored a population of A. chambira in the Amazon, and one of A. standleyanum at the Pacific lowlands of Colombia. We then constructed integral projection models (IPM) to evaluate the transient population dynamics of populations under different exploitation regimes. Our results show that during the next 50 years the population of A. standleyanum will grow at an annual rate of 2.0 percent, and that of A. chambira at a rate of 0.8 percent. However, projected population growth is highly sensitive to harvest in both species: a destructive harvest of 5 percent of all usable individuals (subadults and adults) would cease population growth, while a 10 percent harvest intensity would cause populations to decrease by 0.5–0.6 percent annually. Our simulations further indicate that management practices associated with indigenous slash‐and‐burn agriculture would reduce fiber production, whereas caring for seedlings would increase population growth and fiber production in the coming decades. In order to sustain viable populations of both species and maintain a steady fiber supply, it is vital to prevent destructive harvest practices, and to leave some forest areas untouched, where populations can regenerate and act as a source of seedlings for intervened areas.     

Demography of Oenocarpus bataua and implications for sustainable harvest of its fruit in western Amazon

Oenocarpus bataua is the seventh most abundant tree in the Amazon and one of the most used palms in the region. The main resource obtained from the species is the fruits that are harvested from wild populations for human consumption. Across its distribution area adults are most frequently felled to obtain the racemes, which may affect the palm's populations. In this paper we studied the demography of two populations of Oenocarpus bataua to assess the harvest potential of its fruits and the density variation in different habitats in the western Amazon to estimate fruit yields in different forest types. Non-inundated lands held the greatest densities with an average of 11 adults ha⁻¹ (0–132 adults ha⁻¹). The population finite growth rate (λ) in Amacayacu, Colombia, was 0.9103 because of slow growth and low survival of stemless individuals and low recruitment. On the contrary, in Yasuní, Ecuador, we found a growing population with λ = 1.0368. According to our simulations, adult felling reduced transient population growth (λ_t) in both populations, especially when harvest was frequent even at low intensities. In Amacayacu a simulated harvest of 60 % year⁻¹ of the fruits by climbing did not modify λ_t substantially, while in Yasuní, a regime of 80 % of annual harvest did not diminish λ_t below one and the initial number of adults. The results help to understand the demography of useful palms and to address sustainable management. For instance high yields can be obtained by shifting to non-destructive harvest techniques that can meet the increasing demand and maintain the populations.