Tidal and diel influence on zooplankton occurrence in the Mandovi estuary, Goa

Distribution and abundance of zooplankton over the tidal cycle were studied in the Mandovi estuary, Goa, during August and December 1971 and May 1972. Tide induced salinity fluctuations were obvious with high values during spring tides. Salinity was low during August, apparently due to precipitation and land run off but increased subsequently. The mean biomass values for the day and night collections were 13.6 and 19.8 ml/100 m super(3) respectively. Occurrence of most of the zooplankton taxa and species was related to diel rhythm and tidal oscillations. However, overall mean zooplankton standing stock at both the stations were same (16.3 ml/100 m super(3)) indicating that estuarine zooplankton maintained their position during tidal exchanges. Variations in occurrence of common groups and species of zooplankton over the tidal cycle are discussed.

Tidal and sea level changes at Jeddah, Red Sea

Tidal and sea level changes during 1991 at a coastal station (Jeddah) in the central part of the Red Sea are investigated. Analysis shows higher sea levels in winter and lower in summer. The amplitude of change at Jeddah is above 50cm. Analysis of wind stress at Jeddah indicates an insignificant contribution of the cross-shore component, while a major part of the changes in the sea level can be accounted for by the long-shore component.

Lunar, diurnal and tidal periodicity in relation to the prawn abundance and migration in the Godavari estuarine systems

Preliminary investigations to study the lunar, diurnal and tidal periodicity in abundance and migrations of prawns were made in the Bairavapalam distributary of the Goutami branch of the Godavari estuary during the period of November 1961 to July 1962. The study was based on observation of the catches of a stake net (bag net) operated near the mouth of the estuary. Records of the catches were maintained tidewise daily. Comparative estimates of abundance were made on the basis of catch per hour's operation. It was generally observed that the catches were higher during the darker half of the month than in the brighter fortnight. The landings during low tides were generally higher than those during high tides and usually heavier catches were made during nocturnal low tides than during the day low tides. A continuous inward and outward (immigration and emigration) movement of prawns of all size groups was observed in the estuary from November to July. In general, more penaeid prawns were found to be immigrating at dawn than at dusk. Similarly, the number of emigrants was also found to be generally higher during the new moon period than during the full moon. Metapenaeus monoceros showed an almost distinct nocturnal periodicity in migration, while no such periodicity was observed, distinctly, in other species. In the case of Penaeus indicus the movement of migrants was prolonged. In M. brevicornis the migrants were scarce till March and thereafter increased numerically. The migrant forms of Metapenaeus dobsoni continued to be abundant till May with peak periods in January and February. The migratory pattern of Metapenaeus affinis was similar to that of Metapenaeus brevicornis, though the migrants of the former species appeared a month earlier than the latter. Intensive studies over extended areas for longer periods are required to understand clearly the migratory pattern of the various species. The phenomenon of immigration of prawns can be clearly understood only by vital staining or tagging studies. Perhaps the emigrants might be returning with the succeeding changing life. To verify this, laboratory experiments, by vital stains, were conducted. The marked specimens, if released during the low tides on a large scale, may be recaptured during the subsequent high tides and the duration also may be calculated. At least some percentage of the emigrants remains in the sea for maturity and breeding.

Emigration dynamics of three species of penaeid prawn from backwaters and tidal ponds of Cochin, India

Emigration of three species of penaeid prawn from backwaters and tidal ponds were studied. Considerable diel, tidal, lunar and seasonal fluctuations were observed in emigration process, which was almost nocturnal. Rate of emigration and composition of emigrants varied with time of migration. Large pulses of emigration always coincided with spring tides with major peak during new moon. Seasonal variation was observed with peak emigration of Penaeus indicus during monsoon months and that of Metapenaeus dobsoni and Metapenaeus monoceros during pre-monsoon. Rate of emigration was relatively large from shallow tidal ponds. It correlated directly with the prevailing environmental conditions and juvenile density. Instantaneous rate of emigration was also large in seasonal ponds. The basic stimulus for emigration is the urge for sexual maturation. Coupled with it ecological changes in the habitat have been causing various patterns in migration.

Observation on the lunar and tidal influence on gill netting in the Bay of Bengal

The effect of lunar and tidal influence on the landing of pelagic fish with drift gill nets has been studied for the first time from Bay of Bengal along the Orissa coast. The catchability of the gear was highest during the first quarter and lowest in the fourth quarter of the moon. The variation in catch rates during the four different quarters was not statistically significant. Contrary to the earlier belief, landing with gill net was not poor during the moonlit nights. The extensive use of bluish grey nylon twine matching with seawater in place of indigenous hemp or cotton twine, has largely eliminated the visibility of gear during the brighter phase of the moon. The rate of exploitation was found to be significantly higher during the nights of neap tide, compared to those of spring tide. A plausible explanation for this phenomenon has been offered.

Preliminary observations on the lunar and tidal influences on the catches of seer by gill nets

The paper deals with the lunar and tidal influences on the catches of seer by gill nets. The landings during full moon and new moon nights, during low and high tides and during different quarters of the lunar month for three fishing seasons are discussed.

Ingression, abundance and settlement dynamics of Penaeid chrimp postlarvae in backwaters and adjacent tidal ponds in Cochin, India

Dynamics of penaeid postlarval ingression and settlement in the backwaters of Cochin were studied. Postlarval recruits were constituted by Metapenaeus dobsoni (70.8-78.4%), Penaeus indicus (17.5-24.6%), M. monoceros (3.8-4.6%) and P. monodon (0.3-0.4%). Their composition varied with location and season. Postlarval abundance and ingression were influenced by diel, tidal, lunar and seasonal factors. Ingression is mainly nocturnal in all species with nearly 84% of the activity during night hours. Abundance and ingression peaked up during high tides at night with major peaks coinciding with spring tides of full and new moon. It also followed a generalized seasonal pattern with two well-defined peaks for all species. It was pre-monsoon followed by post-monsoon for P. indicus and M. monoceros and post-monsoon followed by pre-monsoon for M. dobsoni. Sizes of the recruits were relatively small during pre-monsoon and post-monsoon and large during monsoon.

Enhancement of GABAA Receptor-Mediated Inhibitory Postsynaptic Currents Induced by "Partial Oxygen-Glucose Deprivation

下载PDF阅读器"氧糖剥夺"模型作为研究脑缺血的离体模型被广泛使用,该模型模拟了局灶性脑缺血的主要病理变化.然而在缺血病灶核心区与正常脑组织之间称为缺血半暗带的区域,脑血流也有程度不一的降低.为了模拟这种病理变化,发展了一种"不完全氧糖剥夺"的离体脑片模型,该模型满足两个条件,灌流液里氧气部分剥夺而葡萄糖含量降低;"氧糖剥夺"可以导致谷氨酸介导的兴奋性毒性,从而引起神经细胞的坏死.而A型γ-氨基丁酸受体(GABAAR)介导的神经元抑制性活动可以对抗谷氨酸引起的兴奋性毒性,因此近年来引起广泛的研究兴趣.而谷氨酸受体和γ-氨基丁酸受体功能在缺血半暗带是否有改变尚不得而知.因此本文采用海马脑片全细胞膜片钳的记录方法,研究"不完全氧糖剥夺"对海马CA1区神经元的A型γ-氨基丁酸受体介导的抑制性突触后膜电流(IPSCs)的影响.研究发现"不完全氧糖剥夺"使GABAAR介导的IPSCs的峰值增加而衰减时程延长.进一步研究发现该电流的峰值增加是由于GABAAR-氯离子通道的电导增加所致,而与氯离子的反转电位变化无关.这些发现提示在脑缺血的缺血半暗带区域GABAAR介导的神经元抑制性活动可能是增强的,这可能是神经元面对缺血状态产生自我保护的一种内稳态机制.

Properties of the proton-evoked currents and their modulation by Ca2+ and Zn2+ in the acutely dissociated hippocampus CA1 neurons

The characterization of acid-sensing ion channel (ASIC)-like currents has been reported in hippocampal neurons in primary culture. However, it is suggested that the profile of expression of ASICs changes in culture. In this study, we investigated the properties of proton-activated current and its modulation by extracellular Ca2+ and Zn2+ in neurons acutely dissociated from the rat hippocampal CA1 using conventional whole-cell patch-clamp recording. A rapidly decaying inward current and membrane depolarization was induced by exogenous application of acidic solution. The current was sensitive to the extracellular proton with a response threshold of pH 7.0-6.8 and the pH(50) Of 6.1, the reversal potential close to the Na+ equilibrium potential. It had a characteristic of acid-sensing ion channels (ASICs) as demonstrated by its sensitivity to amiloride (IC50 = 19.6 +/- 2.1 muM). Either low [Ca2+](0) or high [Zn2+](0) increased the amplitude of the current. All these characteristics are consistent with a current mediated through a mixture of homomeric ASIC1a and heteromeric ASIC1a + 2a channels and closely replicate many of the characteristics that have been previously reported for hippocampal neurons cultured for a week or more, indicating that culture artifacts do not necessarily flaw the properties of ASICs. Interestingly, we found that high [Zn2+] (>10(-4) M) slowed the decay time constant of the ASIC-like current significantly in both acutely dissociated and cultured hippocampal neurons. In addition, the facilitating effects of low [Ca2+](0) and high [Zn2+](0) on the ASIC-like current were not additive. Since tissue acidosis, extracellular Zn elevation and/or Ca2+ reduction occur concurrently under some physiological and/or pathological conditions, the present observations suggest that hippocampal ASICs may offer a novel pharmacological target for therapeutic invention. (C) 2004 Elsevier B.V. All rights reserved.

Effects of ginkgo biloba extract on cation currents in rat ventricular myocytes

Ginkgo biloba extract (GBE), a valuable natural product for cerebral and cardiovascular diseases, is mainly composed of two classes of constituents: terpene lactones (e.g., ginkgolide A and B, bilobalide) and flavone glycosides (e.g., quercetin and kaempferol). Its electrophysiological action in heart is yet unclear. In the present study, using whole-cell patch clamp technique, we investigated electrophysiological effects of GBE on cation channel currents in ventricular myocytes isolated from rat hearts. We found that GBE 0.01-0.1% inhibited significantly the sodium current (I-Na), L-type calcium current (I-Ca) and transient outward potassium current (IKto) in a concentration-dependent manner. Surprisingly, its main ingredients, ginkgolide A (GB A), ginkgolide B (GB B) and bilobalide (GB BA) at 0.1 mM did not exhibit any significant effect on these cation channel currents. These results suggested that GBE is a potent non-selective cation channel modulator in cardiaomyocytes. Other constituents (rather than GB A, GB B and GB BA) might be responsible for the observed inhibitory effects of GBE on cation channels. (C) 2004 Elsevier Inc. All rights reserved.