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In the early 1990s, ecological and fishery data from the Gulf of Nicoya (Pacific Ocean) were holistically analyzed, and a trophic model was constructed using the Ecopath modeling approach. The results indicated that this tropical estuary, which is a Costa Rican fishery hot spot, was already overexploited by shrimp trawlers and the longline fleet, and recent observations suggest further deteriorations in this system. To evaluate the ecosystem and socioeconomic changes in the Gulf of Nicoya over the last 20 years, the 1993 model was reconstructed with data from 2013 to compare both system states. Although the summary statistics of both states (i.e., 1993 and 2013) suggested that the system maintained its general functionality and even enabled the total harvest to increase by approximately 20%, a more detailed analysis of the levels of the functional groups suggested that the system was further degraded as follows: (1) most shrimp, eel, and catfish species decreased their share in the catches, with severe economic losses for the fishery; (2) of the species that substantially increased their share in the catches, most were short‐lived, low‐value species, such as small pelagic and small demersal fishes; and (3) catches of long‐lived, high‐trophic‐level fish, such as rays, sharks, mackerels, and barracudas, decreased. A picture emerged in which the advancing fishery of low‐trophic‐level species with low economic value enabled the total harvest to increase, while valuable shrimp resources and higher‐trophic‐level species were depleted. These developments caused a tremendous economic loss of approximately 50%.

The South Pacific bay scallop Argopecten purpuratus represents a high-value species harvested along the Peruvian and Chilean coastline for more than 60 years. Following the strong El Nino event of 1983/84, both countries experienced a boom in scallop fisheries, but catches dropped as soon as environmental conditions normalized. Aquaculture production began in Chile, which dominated the Latin American scallop market in the 1990s. Peruvian production remained small until the early 2000s, but has increased dramatically ever since, with a single location in northern Peru, Sechura Bay, contributing most (50%) to the Latin American scallop production. We review the historical trends of this species’ production and analyse the ecological and socio-economic factors that have favoured Sechura Bay's progress, and largely displaced Chilean production through dominance of the market. Advantageous environmental conditions in Sechura Bay (e.g. low water depths, higher temperatures, high natural seed supply) result in improved scallop growth and production, and the socio-economic factors, causing lower operational costs than those of the Chilean production favoured this development. The bottom-up initiation of aquaculture operations by small-scale producers likely created a personal incentive for the long-term sustainable use, which differs from the more industrialized aquaculture activities in Chile.

Ketamine shows, besides its general anaesthetic effect, a potent analgesic effect after spinal administration. We investigated the local anaesthetic-like action of ketamine and its enantiomers in Na+ and K+ channels and their functional consequences in dorsal horn neurones of laminae I–III, which are important neuronal structures for pain transmission receiving most of their primary sensory input from Aδ and C fibres. Combining the patch-clamp recordings in slice preparation with the ‘entire soma isolation’ method, we studied action of ketamine on Na+ and voltage-activated K+ currents. The changes in repetitive firing behaviour of tonically firing neurones were investigated in current-clamp mode after application of ketamine. Concentration–effect curves for the Na+ peak current revealed for tonic block half-maximal inhibiting concentrations (IC50) of 128 μM and 269 μM for S(+) and R(−)-ketamine, respectively, showing a weak stereoselectivity. The block of Na+ current was use-dependent. The voltage-dependent K+ current (KDR) was also sensitive to ketamine with IC50 values of 266 μM and 196 μM for S(+) and R(−)-ketamine, respectively. Rapidly inactivating K+ currents (KA) were less sensitive to ketamine. The block of KDR channels led to an increase in action potential duration and, as a consequence, to lowering of the discharge frequency in the neurones. We conclude that ketamine blocks Na+ and KDR channels in superficial dorsal horn neurones of the lumbar spinal cord at clinically relevant concentrations for local, intrathecal application. Ketamine reduces the excitability of the neurones, which may play an important role in the complex mechanism of its action during spinal anaesthesia. British Journal of Pharmacology (2005) 146, 826–833. doi:10.1038/sj.bjp.0706385

Combining the patch-clamp recordings in slice preparation with the ‘entire soma isolation' method we studied action of several local anaesthetics on delayed-rectifier K+ currents in spinal dorsal horn neurones. Bupivacaine, lidocaine and mepivacaine at low concentrations (1–100 μM) enhanced delayed-rectifier K+ current in intact neurones within the spinal cord slice, while exhibiting a partial blocking effect at higher concentrations (>100 μM). In isolated somata 0.1–10 μM bupivacaine enhanced delayed-rectifier K+ current by shifting its steady-state activation characteristic and the voltage-dependence of the activation time constant to more negative potentials by 10–20 mV. Detailed analysis has revealed that bupivacaine also increased the maximum delayed-rectifier K+ conductance by changing the open probability, rather than the unitary conductance, of the channel. It is concluded that local anaesthetics show a dual effect on delayed-rectifier K+ currents by potentiating them at low concentrations and partially suppressing at high concentrations. The phenomenon observed demonstrated the complex action of local anaesthetics during spinal and epidural anaesthesia, which is not restricted to a suppression of Na+ conductance only. Keywords: Patch-clamp, spinal cord, local anaesthetics, delayed rectifier potassium channel, single channel Introduction Different types of local anaesthetics are widely used in clinical practice for spinal, epidural and local anaesthesia. Although their principal action is usually explained through a suppression of voltage-gated Na+ conductance, there is a continuously increasing number of reports showing that the block of some other systems of ionic channels (Ca2+, K+ or transmitter-activated) can be also involved (Aracava et al., 1984; Ikeda et al., 1984; Castle, 1990; Barann et al., 1993; Valenzuela et al., 1995; Hirota et al., 1997; Rossner & Freese, 1997; Nilsson et al., 1998; Brau et al., 1995; 1998; Kindler et al., 1999; Nau et al., 1999). Among them, K+ channels represent the most diverse family of ionic channels with multiple physiological functions. Since different types of K+ channels influence the resting potential, firing threshold, spike depolarization and repetitive firing frequency (Connor & Stevens, 1971; Llinas, 1988; Koh et al., 1992; Safronov et al., 1996; Hille, 2001), their block or modulation by local anaesthetics may considerably affect the generation of simple spikes as well as complex patterns of activity in the neurone. As a consequence, this can modify the pattern of the entire afferent input and its processing in the spinal cord. Dorsal horn neurones from superficial laminae of the spinal cord are involved in processing of nociception (Light & Perl, 1979; Light et al., 1979). During epidural and spinal anaesthesia they are exposed to local anaesthetics, which directly diffuse into the spinal cord (Bromage et al., 1963). In our previous study performed on intact dorsal horn neurones in the spinal cord slice (Olschewski et al., 1998) it was shown that bupivacaine, lidocaine, and mepivacaine at concentrations between 1 μM and 1 mM suppress a fast inactivating A-type K+ current, whereas delayed-rectifier currents were not remarkably affected. However, a more elaborate analysis of those data has unexpectedly revealed that low concentrations of local anaesthetics enhanced, rather than blocked, the delayed-rectifier K+ currents, so that their activation was seen at more negative potentials. The present study was undertaken to describe this phenomenon in more detail. For this purpose, we used the ‘entire soma isolation' (ESI) method (Safronov et al., 1997; Safronov, 1999) which enabled the study of channel pharmacology in isolated somata of visually identified dorsal horn neurones under conditions where diffusion of the blocker molecules toward the cell membrane was not impeded by connective tissue within the slice and the quality of current recording was not affected by insufficient space clamp (Olschewski et al., 2000). This study shows that low concentrations of local anaesthetics indeed potentiate delayed-rectifier K+ current by shifting its activation to more negative potentials and increasing its maximum conductance. Local anaesthetics interact with the activation gates of the channel and increase its open probability without affecting the unitary conductance. At high concentrations, the local anaesthetics additionally blocked the current. It is concluded that bupivacaine, lidocaine and mepivacaine exert a dual effect on delayed-rectifier K+ channels.

1.This study is the first attempt using Levins's Theory (loop analysis) in order to develop a sustainable management for the scallop, Argopecten purpuratus, fishery in Peru during El Nino-Southern Oscillation events (ENSO) and upwelling conditions. Based on this theoretical framework, it was possible to estimate the local stability for each of these model systems and to follow the qualitative changes of the variables in response to external factors. 2.Based on our results, we suggest the following management policies to be implemented: (1) during ENSO events the size at the first capture of the scallops should be >70 mm and (2) the increase in the number of fishermen during ENSO events must be prevented. Both measures increase the sustainability of fishery under ENSO and upwelling conditions. The ecological models predict that during ENSO and upwelling events, any management strategy to increase the recruitment of the scallop would not have a positive impact on the adult stock. 3.Finally, we suggest that more efforts must be focused on the development of extended eco-social models, which incorporate further social and economic variables, increasing realism of the abstractions for this fishery activity. Copyright © 2002 John Wiley & Sons, Ltd.

1. A dynamical and spatial simulation model of a harvested benthic ecosystem of central northern Chile (Tongoy Bay) was constructed using the ECOSPACE software package. 2. In this system the red alga (Chondrocanthus chamissoi), the scallop (Argopecten pupuratus), the gastropod (Xanthochorus cassidiformis) and the crab (Cancer polyodon) are harvested intensively. The impacts of harvesting these resources exclusively in the seagrass, sand-gravel, and in the sand habitats, as well as, in the seagrass and sand-gravel and in all habitats were assessed. The goal was to explore policies of sustainable exploitation of the benthic systems. 3. The most important findings were: (a) Fishing exclusively in either the seagrass or sand habitats produces a population increase in the sea star Luidia magallanica, in the seagrass Heterozostera tasmanica, and in the crab Paraxanthus barbiger. (b) Exclusive fishing in the sand-gravel habitat causes only small effects on the species and groups, which suggests that this habitat is the most resistant to harvest. (c) The simultaneous fishing on two or three habitats would produce the largest negative effect on the entire system. Therefore, a habitat rotation fishery is recommended. 4. Our study suggests that trophic-spatially explicit models offer great possibilities for the screening and planning of effective interventions or manipulations of natural systems. Copyright © 2002 John Wiley & Sons, Ltd.

1. This paper sets out to: (1) review previous ecological studies and analyse recent trends of the Peruvian bay scallop fishery in order to better understand and to model the species’ temporal and spatial (meta) population dynamics along the South Pacific coast; (2) develop a fisheries model to protect the stock from overexploitation and optimize the annual yield of the pulse fishery in Independence Bay, the centre of the scallop diving fishery in Peru. 2. Natural stock fluctuations are very pronounced in this species and are positively correlated with the El Nino–Southern Oscillation (ENSO). During such an event, habitat conditions for the Peruvian bay scallop are improved either regionally or locally, such that populations proliferate and larval production and dispersal are greatly increased. Extinct beds and new habitats are recolonized during these periods (producing a strong pulse of metapopulation biomass), although most become extinct very shortly thereafter. 3. For management purposes, two considerations are fundamental: (1) heavy overfishing or extinction of the main scallop source populations would endanger the metapopulation as a whole; (2) rates of growth and survival greatly increase (and with them the potential yield of the scallop stock) locally over an El Nino cycle in a way that can be roughly estimated from past experience, including the most recent El Nino event (1997–1998). 4. We suggest a fisheries management regime capable of adapting to natural changes and propose a procedure for calculating both the optimal yield and the respective fishing effort under normal upwelling and El Nino scenarios, considering changes in the size at first capture (Lc) and fishery mortality (F). Copyright © 2000 John Wiley & Sons, Ltd.

1. A novel method of 'entire soma isolation' was used to describe the distribution of voltage-gated K+ channels between soma, axon and dendrites of dorsal horn neurones identified in spinal cord slices of newborn rat. 2. The soma contained 36 % of total inactivating (KA) current but only 15 % of delayed rectifier (KDR) current. The axon initial segment possessed almost half (47 %) of the total KA current and 38 % of KDR current. In contrast, dendrites contained a small portion (17 %) of KA but 47 % of KDR current. 3. Under current-clamp conditions, the soma isolated from axon and dendrites was not able to generate action potentials. It passively conducted weak (/= -50 mV) and amplified pronounced (-50 to 0 mV) depolarizations but inhibited strong (/= 0 mV) depolarizations. 4. It is concluded that the soma plays a complex role in the excitability of spinal dorsal horn neurones. It conducts passively or amplifies excitatory postsynaptic potentials on their way from dendrites and soma to the axon initial segment but it inhibits back-propagation of the action potential from the axon to the dendrites.

1. Voltage-gated Na+ channels and their distribution were studied by the patch-clamp technique in intact dorsal horn neurones in slices of newborn rat spinal cord and in neurones isolated from the slice by slow withdrawal of the recording pipette. This new method of neurone isolation was further used to study the roles of soma and axon in generation of action potentials. 2. Tetrodotoxin (TTX)-sensitive Na+ currents in intact neurones consisted of three components. A fast component with an inactivation time constant (tau f) of 0.6-2.0 ms formed the major part (80-90%) of the total Na+ current. The remaining parts consisted of a slowly inactivating component (tau s of 5-20 ms) and a steady-state component. 3. Single fast and slow inactivating Na+ channels with conductances of 11.6 and 15.5 pS, respectively, were identified in the soma of intact neurones in the slice. Steady-state Na+ channels were not found in the soma, suggesting an axonal or dendritic localization of these channels. 4. In the whole-cell recording mode, the entire soma of a dorsal horn neurone could be isolated from the slice by slow withdrawal of the recording pipette, leaving all or nearly all of its processes in the slice. The isolated structure was classified as: (1) 'soma' if it lost all of its processes, (2) 'soma+axon' complex if it preserved one process and at least 85% of its original peak Na+ current or (3) 'soma+dendrite' complex if it preserved one process but the remaining Na+ current did not exceed those observed in the isolated 'somata'. 5. The spatial distribution of Na+ channels in the neurone was studied by comparing Na+ currents recorded before and after isolation. The isolated 'soma' contained 13.8 +/- 1.3% of inactivating Na+ current but no steady-state Na+ current. 'Soma+axon' complexes contained 93.6 +/- 1.4% of inactivating and 46% of steady-state Na+ current. 6. In current-clamp experiments, the intact neurones and isolated 'soma+axon' complexes responded with 'all-or-nothing' action potentials to current injections. In contrast, isolated 'somata' showed only passive or local responses and were unable to generate action potentials. 7. It is concluded that dorsal horn neurones of the spinal cord possess three types of TTX-sensitive voltage-gated Na+ channels. The method of entire soma isolation described here shows that the majority of inactivating Na+ channels are localized in the axon hillock and only a small proportion (ca 1/7) are distributed in the soma. Steady-state Na+ channels are most probably expressed in the axonal and dendritic membranes. The soma itself is not able to generate action potentials. The axon or its initial segment plays a crucial role in the generation of action potentials.