Monitoring macroplastics in aquatic and terrestrial ecosystems: Expert survey reveals visual and drone-based census as most effective techniques.

Anthropogenic litter, such as plastic, is investigated by the global scientific community from various fields employing diverse techniques. The goal is to assess and finally mitigate the pollutants' impacts on the natural environment. Plastic litter can accumulate in different matrices of aquatic and terrestrial ecosystems, impacting both biota and ecosystem functioning. Detection and quantification of macroplastics, and other litter, can be realized by jointly using visual census and remote sensing techniques. The primary objective of this research was to identify the most effective approach for monitoring macroplastic litter in riverine and marine environments through a comprehensive survey based on the experiences of the scientific community. Researchers involved in plastic pollution evaluated four litter occurrence and flux investigation methods (visual census, drone-based surveys, satellite imagery, and GPS/GNSS trackers) through a questionnaire. Traditional visual census and drone deployment were deemed as the most popular approaches among the 46 surveyed researchers, while satellite imagery and GPS/GNSS trackers received lower scores due to limited field validation and short performance ranges, respectively. On a scale from 0 to 5, visual census and drone-based surveys obtained 3.5 and 2.0, respectively, whereas satellite imagery and alternative solutions received scores lower than 1.2. Visual and drone censuses were used in high, medium and low-income countries, while satellite census and GPS/GNSS trackers were mostly used in high-income countries. This work provides an overview of the advantages and drawbacks of litter investigation techniques, contributing i) to the global harmonization of macroplastic litter monitoring and ii) providing a starting point for researchers and water managers approaching this topic. This work supports the selection and design of reliable and cost-effective monitoring approaches to mitigate the ambiguity in macroplastic data collection, contributing to the global harmonization of macroplastic litter monitoring protocols.

Simulating drifting fish aggregating device trajectories to identify potential interactions with endangered sea turtles.

Purse-seine fishers using drifting fish aggregating devices (dFADs), mainly built with bamboo, plastic buoys, and plastic netting, to aggregate and catch tropical tuna, deploy 46,000-65,000 dFADs per year in the Pacific Ocean. Some of the major concerns associated with this widespread fishing device are potential entanglement of sea turtles and other marine fauna in dFAD netting; marine debris and pollution; and potential ecological damage via stranding on coral reefs, beaches, and other essential habitats for marine fauna. To assess and quantify the potential connectivity (number of dFADs deployed in an area and arriving in another area) between dFAD deployment areas and important oceanic or coastal habitat of critically endangered leatherback (Dermochelys coriacea) and hawksbill (Eretmochelys imbricata) sea turtles in the Pacific Ocean, we conducted passive-drift Lagrangian experiments with simulated dFAD drift profiles and compared them with known important sea turtle areas. Up to 60% of dFADs from equatorial areas were arriving in essential sea turtle habitats. Connectivity was less when only areas where dFADs are currently deployed were used. Our simulations identified potential regions of dFAD interactions with migration and feeding habitats of the east Pacific leatherback turtle in the tropical southeastern Pacific Ocean; coastal habitats of leatherback and hawksbill in the western Pacific (e.g., archipelagic zones of Indonesia, Papua New Guinea, and Solomon Islands); and foraging habitat of leatherback in a large equatorial area south of Hawaii. Additional research is needed to estimate entanglements of sea turtles with dFADs at sea and to quantify the likely changes in connectivity and distribution of dFADs under new management measures, such as use of alternative nonentangling dFAD designs that biodegrade, or changes in deployment strategies, such as shifting locations.

Simulación de las trayectorias de dispositivos de concentración de peces a la deriva para identificar las interacciones potenciales con las tortugas marinas en peligro de extinción Resumen Los pescadores que usan redes de cerco con dispositivos de concentración de peces a la deriva (dFADs), hechos principalmente con bambú, boyas de plástico y redes de plástico, para concentrar y capturar atún, instalan entre 46,000 y 65,000 dFADs al año en el Océano Pacífico. Algunas de las problemáticas principales asociadas con este dispositivo de pesca de uso extenso son el enredamiento potencial de tortugas marinas y otras especies marinas en las redes de los dFADs; los desechos marinos y la contaminación; y el potencial daño ecológico por el varamiento en los arrecifes de coral, playas y otros hábitats esenciales para la fauna marina. Realizamos experimentos lagrangianos de deriva pasiva con la simulación de perfiles de deriva de los dFADs y los comparamos con áreas conocidas de importancia para las tortugas marinas. Esto fue con el objetivo de evaluar y cuantificar la conectividad potencial (número de dFADs instalados en un área que llegan a otra área) entre las áreas de instalación de dFADs y los hábitats oceánicos o costeros importantes para la tortuga laúd (Dermochelys coriacea) y la tortuga de carey (Eretmochelys imbricata), ambas en peligro crítico de extinción, en el Océano Pacífico. Hasta el 60% de los dFADs de las áreas ecuatoriales llegaron a los hábitats esenciales para las tortugas marinas. La conectividad fue menor sólo cuando se usaron áreas en donde actualmente hay dFADs instalados. Nuestras simulaciones identificaron regiones potenciales de interacción entre los dFADs y los hábitats de migración y alimentación de la tortuga laúd en el sureste tropical del Océano Pacífico; los hábitats costeros de ambas especies en el Pacífico occidental (p. ej.: zonas de archipiélagos en Indonesia, Papúa Nueva Guinea y en las Islas Salomón); y en el hábitat de forrajeo de la tortuga laúd en una gran área ecuatorial al sur de Hawái. Se requiere de mayor investigación para estimar el enredamiento de las tortugas marinas con los dFADs en el mar y para cuantificar los cambios probables en la conectividad y la distribución de los dFADs bajo nuevas medidas de manejo, como el uso alternativo de diseños que eviten el enredamiento y sean biodegradables, o cambios en las estrategias de instalación, como la reubicación.

[Early satisfaction with care among outpatients with substance dependence]. / Satisfaction précoce vis-à-vis des soins ambulatoires chez des patients dépendants aux substances psychoactives.

BACKGROUND: Patient satisfaction with health care is an important indicator of health care quality. The main objective was to identify factors associated with early outpatient satisfaction with care 45 days after study inclusion for alcohol and opioid dependence. The secondary objective was to study the reproducibility of the satisfaction during the care. METHODS: A longitudinal study was conducted. Satisfaction was assessed during the early care process 15 and 45 days after study inclusion using the quality of care satisfaction questionnaire in outpatient consultation EQS-C. Multiple linear regression was performed to identify the variables associated with satisfaction level. The reproducibility of the questionnaire between the two measurements (15 and 45 days after inclusion) was tested by intraclass correlation coefficient. RESULTS: A total of 189 outpatients were included, and 90 patients completed the satisfaction questionnaire both at 15 and 45 days after inclusion. The level of early satisfaction with care was high. If patients without a history of previous care for substance dependence were at first more satisfied at 45 days (ß=6.8; P=0.05) than those who had received care previously, only the total score of the satisfaction with care at 15 days is associated with satisfaction with care at 45 days when taken into account in the model (ß=0,7; P<0.0001). The results indicated good total satisfaction reproducibility with an intraclass correlation coefficient ICC=0.68. CONCLUSION: We recommend an early measure of satisfaction with care among outpatients with substance dependence.

Outbreaks of colistin-resistant and colistin-susceptible KPC-producing Klebsiella pneumoniae in a Brazilian intensive care unit.

BACKGROUND: Carbapenem-resistant Enterobacteriaceae (CRE), especially those that produce Klebsiella pneumoniae carbapenemase (KPC) and are associated with colistin resistance, pose a severe health threat due to the limited treatment options. AIM: To describe two outbreaks of KPC-producing K. pneumoniae in an adult intensive care unit (AICU) in Brazil. In May 2015, 14 patients had colistin-susceptible KPC-producing strains (ColS-KPC), and in July 2015, nine patients had colistin-resistant KPC-producing strains (ColR-KPC). METHODS: Between September 2014 and August 2015, we performed surveillance at a university hospital and all CRE were tested for blaKPC genes. Clonality was investigated by pulsed-field gel electrophoresis. Resistance to colistin was confirmed by broth microdilution method. Consumption of carbapenems and colistin was expressed as defined daily doses. FINDINGS: In all, 111 patients with CRE were identified during the surveillance period; K. pneumoniae was the major isolate (77.13%). The two outbreaks were identified when infection rates (KPC per 1000 patient-days) exceeded the background level. Rates of carbapenem and colistin consumption were high. Control measures (bedside alcohol gel, contact precautions, regular rectal swabs) did not curtail the outbreaks. Mortality rates were 42.9% and 44.4% for ColS-KPC- and ColR-KPC-infected patients, respectively. After the death of four infected patients with ColR-KPC, the unit was closed to new admissions. CONCLUSION: Our experience demonstrates the serious risks presented by KPC, and especially ColR-KPC, in Brazilian AICUs. Selective pressure from excessive antibiotic use and transmission on healthcare workers' hands were likely the major factors in transmission.

A high-resolution time-depth view of dimethylsulphide cycling in the surface sea.

Emission of the trace gas dimethylsulphide (DMS) from the ocean influences the chemical and optical properties of the atmosphere, and the olfactory landscape for foraging marine birds, turtles and mammals. DMS concentration has been seen to vary across seasons and latitudes with plankton taxonomy and activity, and following the seascape of ocean's physics. However, whether and how does it vary at the time scales of meteorology and day-night cycles is largely unknown. Here we used high-resolution measurements over time and depth within coherent water patches in the open sea to show that DMS concentration responded rapidly but resiliently to mesoscale meteorological perturbation. Further, it varied over diel cycles in conjunction with rhythmic photobiological indicators in phytoplankton. Combining data and modelling, we show that sunlight switches and tunes the balance between net biological production and abiotic losses. This is an outstanding example of how biological diel rhythms affect biogeochemical processes.

Importance of salt fingering for new nitrogen supply in the oligotrophic ocean.

The input of new nitrogen into the euphotic zone constrains the export of organic carbon to the deep ocean and thereby the biologically mediated long-term CO2 exchange between the ocean and atmosphere. In low-latitude open-ocean regions, turbulence-driven nitrate diffusion from the ocean's interior and biological fixation of atmospheric N2 are the main sources of new nitrogen for phytoplankton productivity. With measurements across the tropical and subtropical Atlantic, Pacific and Indian oceans, we show that nitrate diffusion (171±190 µmol m(-2) d(-1)) dominates over N2 fixation (9.0±9.4 µmol m(-2) d(-1)) at the time of sampling. Nitrate diffusion mediated by salt fingers is responsible for ca. 20% of the new nitrogen supply in several provinces of the Atlantic and Indian Oceans. Our results indicate that salt finger diffusion should be considered in present and future ocean nitrogen budgets, as it could supply globally 0.23-1.00 Tmol N yr(-1) to the euphotic zone.

Differential rescue of spatial memory deficits in aged rats by L-type voltage-dependent calcium channel and ryanodine receptor antagonism.

Age-associated memory impairments may result as a consequence of neuroinflammatory induction of intracellular calcium (Ca(+2)) dysregulation. Altered L-type voltage-dependent calcium channel (L-VDCC) and ryanodine receptor (RyR) activity may underlie age-associated learning and memory impairments. Various neuroinflammatory markers are associated with increased activity of both L-VDCCs and RyRs, and increased neuroinflammation is associated with normal aging. In vitro, pharmacological blockade of L-VDCCs and RyRs has been shown to be anti-inflammatory. Here, we examined whether pharmacological blockade of L-VDCCs or RyRs with the drugs nimodipine and dantrolene, respectively, could improve spatial memory and reduce age-associated increases in microglia activation. Dantrolene and nimodipine differentially attenuated age-associated spatial memory deficits but were not anti-inflammatory in vivo. Furthermore, RyR gene expression was inversely correlated with spatial memory, highlighting the central role of Ca(+2) dysregulation in age-associated memory deficits.

Blending anaerobic co-digestates: synergism and economics.

Co-digestion is the process in which wastes from various sources are treated together. Therefore, more organic carbon is added to make efficient use of existing digesters. The objectives of this study were to compare potential co-digestates, determine synergistic and antagonistic co-digestion outcomes and estimate economic benefits for preliminary screening. Over 80 wastes were identified from 54 facilities within 160 km of an existing municipal digester. Synergistic, antagonistic and neutral co-digestion outcomes were observed for the various wastes. A simple economic comparison resulted in the greatest potential benefits for four co-digestates: yeast flavorings production waste, meat production dissolved air flotation float, acid whey from cheese production and thin stillage from corn ethanol production. Performance was investigated using bench-scale digesters receiving primary sludge with and without co-digestates. Methane production rates were 105 and 66% higher when co-digestates were present, but were anticipated to increase only 57 and 23% due to the additional chemical oxygen demand. Therefore, significant synergistic outcomes were observed during co-digestion. Co-digestion of the most promising wastes with primary sludge in full scale was estimated to generate enough electricity to power more than 2,500 houses.

Evaluation of heterogeneous photo-Fenton oxidation of Orange II using response surface methodology.

A mesoporous SBA-15 doped iron oxide (Fe2O3/SBA-15) was synthesized by co-condensation, characterized and used as heterogeneous catalysts for the photo-Fenton decolorization of azo dye Orange II under UV irradiation. Response surface methodology (RSM) was used to investigate operating condition effects, such as hydrogen peroxide concentration, initial pH and catalyst loadings, on the decolorization rate. UV irradiation is found to enhance the activity of the catalyst in the process. RSM analysis evidenced the influence of the initial pH value and H2O2 concentration on the dye degradation rate. The coupled UV/Fe2O3/SBA-15/H2O2 process at room temperature is revealed as a promising friendly process for wastewater treatment. Indeed, the use of a heterogeneous catalyst allows an easy active phase recycling without multi-step recovering while the heterogeneous catalyst used here exhibits high catalytic activity for the reaction considered.

Properties of iron-based mesoporous silica for the CWPO of phenol: a comparison between impregnation and co-condensation routes.

Iron-based mesoporous silica materials were prepared according to different impregnation and co-condensation procedures. Several complementary techniques, including XRD, TEM/EDX and nitrogen sorption isotherms were used to evaluate the final structural and textural properties of the calcined Fe/SBA-15 materials. While Fe(2)O(3) isolated particles of which the size is close to the silica pore diameter ( approximately 7-8 nm) were obtained using classical wet impregnation procedure, smaller iron oxide particles ( approximately 2-4 nm) homogeneously dispersed within the hexagonal pore structure of the SBA15 host support were generated by self-combustion of an impregnated iron-glycinic complex. By contrast, the various co-condensation routes used in this work were less efficient to generate iron oxide nanoparticles inside the silica mesopores. Catalytic performances of the materials were evaluated in the case of total phenol oxidation by H(2)O(2) in aqueous solution at ambient conditions. Large differences in terms of catalytic activity and iron species stability were observed. While the impregnated solids proved to be the most active catalysts (highest Fe(2)O(3) nanoparticles dispersion), iron leaching was observed in aqueous solution, accounting for a homogeneous catalytic contribution. In contrast, the co-condensed samples exhibiting larger iron oxide clusters stabilized over the silica surface proved more efficient as active sites in Fenton catalysis.

Role of fluorescence in situ hybridization in sequencing the tomato genome.

The tomato (Solanum lycopersicum L.) genome is being sequenced by a consortium of laboratories in 10 countries. Seventy-seven percent of the tomato genome (DNA) is located in repeat-rich, gene-poor, pericentric heterochromatin, while 23% of the genome is located in repeat-poor, gene-rich, distal euchromatin. It is estimated that approximately 90% of tomato's nuclear genes can be characterized by limiting the sequencing effort to euchromatin while avoiding the problems involved in sequencing the repetitive DNA in heterochromatin. Sequencing is being performed on tomato nuclear DNA cloned into bacterial artificial chromosome (BAC) vectors. Fluorescence in situ hybridization (FISH) is used to help direct the sequencing effort by cytologically demonstrating the location of selected BACs on tomato chromosomes. While mitotic metaphase chromosomes are too short and compact for this purpose, long pachytene chromosomes are ideal. BACs localized in euchromatin can be used confidently as anchors for the assembly of BAC contigs that extend through the euchromatic length of each chromosome arm. Another important role for FISH is identification of BACs near telomeres and near borders with pericentric heterochromatin to indicate that sequencing should not extend much further. This role of FISH is enhanced by our ability to estimate base pair distances between localized BACs and these chromosomal features. Finally, it is noteworthy that when BAC-FISH is combined with chromosomal in situ suppression (CISS) hybridization to block repeats and localize single/low copy sequences, the great majority of BACs localize to single sites. This observation is consistent with tomato being an ancient diploid.

Effect of palladium on the reducibility of Mn based materials: correlation with methane oxidation activity.

Mn-based oxide supports were synthesized using different procedures: (i) carbonate co-precipitation method, leading to the formation of a hexaaluminate crystallized solid (La(0.2)Sr(0.3)Ba(0.5)MnAl(11)O(19)) and (ii) solid-solid diffusion method, leading to the formation of a doped theta-Al(2)O(3) crystallized solid (nominal composition: 60 wt% La(0.2)Sr(0.3)Ba(0.5)MnAl(11)O(19) + 40 wt% Al(2)O(3)). Impregnation of 1.0 wt%Pd was carried out on both oxides. The solids were tested for the catalytic methane combustion up to 700 degrees C. It was observed that adding palladium resulted in an important increase in the catalytic activity. The combined use of H(2)-TPR and XPS techniques reveals that only Mn(3+)/Mn(2+) redox "couple" is present in the solids, whatever the synthesis procedure used. The fraction Mn(3+)/Mn is proportional to the total Mn content in the solid support, whatever the sample structure (hexaaluminate or doped theta-Al(2)O(3)) and its morphology (large crystals or aggregates of small particles, respectively). Pd impregnation and further calcination at 650 degrees C has no significant effect on the Mn(3+)/Mn fraction. However, some changes in Mn(3+) reduction profile are observed, depending on the solid structure. Indeed, palladium addition strongly affects the manganese reducibility with an important shift of the reduction process to lower temperatures (approximately 100 degrees C). On the basis of redox properties observed for the different catalysts, a Mars-van-Krevelen redox mechanism, with oxygen transfer from support oxides to palladium particles, is proposed to explain the difference in terms of catalytic conversion and stability with respect to a 1.0 wt%Pd/Al(2)O(3) reference sample.

Connexin36 vs. connexin32, "miniature" neuronal gap junctions, and limited electrotonic coupling in rodent suprachiasmatic nucleus.

Suprachiasmatic nucleus (SCN) neurons generate circadian rhythms, and these neurons normally exhibit loosely-synchronized action potentials. Although electrotonic coupling has long been proposed to mediate this neuronal synchrony, ultrastructural studies have failed to detect gap junctions between SCN neurons. Nevertheless, it has been proposed that neuronal gap junctions exist in the SCN; that they consist of connexin32 or, alternatively, connexin36; and that connexin36 knockout eliminates neuronal coupling between SCN neurons and disrupts circadian rhythms. We used confocal immunofluorescence microscopy and freeze-fracture replica immunogold labeling to examine the distributions of connexin30, connexin32, connexin36, and connexin43 in rat and mouse SCN and used whole-cell recordings to re-assess electrotonic and tracer coupling. Connexin32-immunofluorescent puncta were essentially absent in SCN but connexin36 was relatively abundant. Fifteen neuronal gap junctions were identified ultrastructurally, all of which contained connexin36 but not connexin32, whereas nearby oligodendrocyte gap junctions contained connexin32. In adult SCN, one neuronal gap junction was >600 connexons, whereas 75% were smaller than 50 connexons, which may be below the limit of detectability by fluorescence microscopy and thin-section electron microscopy. Whole-cell recordings in hypothalamic slices revealed tracer coupling with neurobiotin in <5% of SCN neurons, and paired recordings (>40 pairs) did not reveal obvious electrotonic coupling or synchronized action potentials, consistent with few neurons possessing large gap junctions. However, most neurons had partial spikes or spikelets (often <1 mV), which remained after QX-314 [N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium bromide] had blocked sodium-mediated action potentials within the recorded neuron, consistent with spikelet transmission via small gap junctions. Thus, a few "miniature" gap junctions on most SCN neurons appear to mediate weak electrotonic coupling between limited numbers of neuron pairs, thus accounting for frequent detection of partial spikes and hypothetically providing the basis for "loose" electrical or metabolic synchronization of electrical activity commonly observed in SCN neuronal populations during circadian rhythms.

Culture medium and protein supplementation in the generation and maturation of dendritic cells.

Dendritic cells (DC) are powerful antigen-presenting cells that have drawn many attentions due to the recent development of anti-cancer vaccines. Clinical grade production of monocyte-derived DC (Mo-DC) is extensively studied, and many efforts are made to develop and improve clinical standard operating procedures. Most of the parameters involved, such as the cytokines and maturation agents, have been widely assessed. However, very few are investigated about how culture medium and additional protein components affect DC yield, viability and maturation. Thus, our study aimed to compare the impact of standard culture medium on Mo-DC differentiation and maturation. Commercially available media for hematopoietic cell culture as well as different protein supplementations, that is foetal calf serum (FCS), autologous plasma (AP), human serum (HS) and human serum albumin (HSA) were tested. Culture yields, cell viability and DC maturation were investigated. Differentiation yields were similar between the conditions used. However, we evidenced significant differences in terms of cytotoxicity and DC maturation (phenotypic and functional). This underscores the importance of defining culture medium composition in clinical standard operating procedures to insure quality control, and also when preparing DC for experimental uses.

Bidirectional synaptic plasticity in intercalated amygdala neurons and the extinction of conditioned fear responses.

Classical fear conditioning is believed to result from potentiation of conditioned synaptic inputs in the basolateral amygdala. That is, the conditioned stimulus would excite more neurons in the central nucleus and, via their projections to the brainstem and hypothalamus, evoke fear responses. However, much data suggests that extinction of fear responses does not depend on the reversal of these changes but on a parallel NMDA-dependent learning that competes with the first one. Because they control impulse traffic from the basolateral amygdala to the central nucleus, GABAergic neurons of the intercalated cell masses are ideally located to implement this second learning. Consistent with this hypothesis, the present study shows that low- and high-frequency stimulation of basolateral afferents respectively induce long-term depression (LTD) and potentiation (LTP) of responses in intercalated cells. Moreover, induction of LTP and LTD is prevented by application of an NMDA antagonist. To determine how these activity-dependent changes are expressed, we tested whether LTD and LTP induction are associated with modifications in paired-pulse facilitation, an index of transmitter release probability. Only LTP induction was associated with a change in paired-pulse facilitation. Depotentiation of previously potentiated synapses did not revert the modification in paired pulse facilitation, suggesting that LTP is associated with presynaptic alterations, but that LTD and depotentiation depend on postsynaptic changes. Taken together, our results suggest that basolateral synapses onto intercalated neurons can express NMDA-dependent LTP and LTD, consistent with the possibility that intercalated neurons are a critical locus of plasticity for the extinction of conditioned fear responses. Ultimately, these plastic events may prevent conditioned amygdala responses from exciting neurons of the central nucleus, and thus from evoking conditioned fear responses.

Cell-type-specific GABA responses and chloride homeostasis in the cortex and amygdala.

The GABA responses of fast-spiking (FS) interneurons and regular-spiking (RS) principal cells were studied using whole cell and perforated-patch recordings in slices of the basolateral amygdala, neo-, and perirhinal cortex. In these three areas, responses to exogenous and synaptically released GABA were abolished by GABA(A) receptor antagonists in FS cells but also included a GABA(B) component in RS cells. Moreover, E(GABA(A)) of FS and RS cells differed from the calculated E(Cl) (-61 mV), but in opposite direction (FS, -54 mV; RS, -72 mV). This was not due to a differential dialysis of FS and RS cells by the pipette solution because the discrepancy persisted when recordings were obtained with the perforated-patch-clamp technique, using the cation-selective ionophore gramicidin. Moreover, pharmacological inhibition of cation-chloride cotransporters revealed that the differing E(GABA(A)) of FS and RS neurons arises from cell-type-specific chloride homeostatic mechanisms. Indeed, the prevalent regulators of the intracellular chloride concentration are cotransporters that accumulate chloride in FS cells and extrude chloride in RS neurons. Thus, our results suggest that in the basolateral amygdala as well as in the parietal and perirhinal cortices, FS interneurons are more excitable than principal cells not only by virtue of their dissimilar electroresponsive properties but also because they express a different complement of GABA receptors and chloride homeostatic mechanisms.

Propagation of neocortical inputs in the perirhinal cortex.

The perirhinal area is a rostrocaudally oriented strip of cortex in which lesions produce memory and perceptual impairments. It receives topographically organized transverse projections from associative neocortical areas and is endowed with intrinsic longitudinal connections that could distribute neocortical inputs in the rostrocaudal axis. In search of distinguishing network properties that might support perirhinal involvement in memory, we have performed whole-cell recordings in horizontal perirhinal slices with preserved transverse neocortical links and intrinsic longitudinal connections. Neocortical stimulation sites in rostrocaudal register with regular spiking perirhinal neurons elicited a sequence of excitatory and inhibitory synaptic potentials. In contrast, apparently pure excitatory responses were observed when the stimulating and recording sites were separated by >/=1 mm in the rostrocaudal axis. This suggested that adjacent and distant neocortical stimuli influence regular spiking perirhinal neurons by pathways that respectively form and do not form synapses with inhibitory interneurons. In keeping with this, presumed interneurons did not respond to distant neocortical stimuli. These results suggest that neocortical inputs recruit perirhinal inhibitory interneurons located at the same transverse level, limiting the depolarization of principal perirhinal cells. In contrast, distant neocortical inputs only evoke excitation because longitudinal perirhinal pathways do not engage inhibitory interneurons. This leads us to suggest that the perirhinal network is biased to favor Hebbian-like associative interactions between coincident and spatially distributed inputs.

Polarized synaptic interactions between intercalated neurons of the amygdala.

The intercalated (ITC) cell masses are small GABAergic cell clusters interposed between the basolateral (BL) complex and central (CE) nucleus of the amygdala. ITC cells receive excitatory afferents from the BL complex and generate feed-forward inhibition in the CE nucleus. Recently it was shown that ITC cells could gate impulse traffic between the BL complex and CE nucleus in a spatiotemporally differentiated manner. In addition, it was hypothesized that lateromedial inhibitory interactions between different ITC cell clusters played a critical role in this respect. Given the potential importance of such conditional computations, the present study aimed to characterize the connectivity existing among ITC cells. To this end, whole cell recordings of ITC neurons were obtained under visual guidance in coronal slices of the guinea pig amygdala. Electrical stimuli applied in the BL complex primarily elicited excitatory responses when they were applied at the same lateromedial level or more medially than the recorded ITC cells. As the stimulation site was moved laterally, the character of the response shifted toward inhibition. Both bicuculline and non-N-methyl-D-aspartate receptor antagonists abolished this BL-evoked inhibition, suggesting that it was not mediated by BL inhibitory cells projecting to ITC neurons. In keeping with this, local glutamate injections in and around the ITC clusters revealed that the most effective site to inhibit ITC cells were ITC clusters located laterally with respect to the recorded one. The activation of more medial ITC clusters evoked much smaller responses. Thus, connections between ITC clusters tend to run in a lateromedial direction. To identify the source of these directionally polarized synaptic interactions, the morphological features of ITC cells were analyzed by intracellular injection of Neurobiotin. This analysis revealed that the dendritic tree and axonal arbor of ITC cells are asymmetric in the lateromedial plane. In particular, their laterally directed dendrites were longer than the medial ones, whereas their laterally directed axon collaterals were shorter than the medial ones. It is concluded that the morphological asymmetry of ITC cells accounts for the directional polarization of inter-ITC connections. The significance of these findings for the gating of information transfer from the BL complex to the CE nucleus is discussed.

Glutamate dependence of GABA levels in neurons of hypoxic and hypoglycemic rat hippocampal slices.

Hypoxia may increase GABA levels in neurons by ATP depletion-induced activation of glutamate decarboxylase and by inhibiting GABA transaminase. Hypoglycemia, which also depletes ATP, reduces neuronal levels of GABA and its precursor glutamate. We examined whether differences in glutamate levels may contribute to these altered GABA levels in hippocampal slices. GABA levels were highly correlated with endogenous glutamate levels during both hypoxia and hypoglycemia (R=0.93 for combined data). Hypoxia maximally increased GABA levels (146+/-6.3% of control, S.E.M.) when glutamate remained above 90% of control levels and ATP was at 30% of control levels. Hypoglycemia with similar ATP levels and glutamate levels at 40% of control decreased GABA levels to 55% of control. Effects of inhibitors of glutamate decarboxylase and GABA transaminase suggested that increased synthesis and decreased catabolism may both contribute to increased hypoxic GABA levels. Immunocytochemical studies suggested that hypoxia increased GABA concentrations primarily in neurons and their processes, but not in glial cells. Severe hypoxic ATP depletion increased the release of both GABA and glutamate. Hypoxia increased GABA levels in neurons, while hypoglycemia with a similar severity of ATP depletion decreased GABA levels. Much of the difference may be related to lower levels of precursor glutamate during hypoglycemia. The twofold higher levels of neuroprotective GABA available for release during hypoxia may contribute to differences in the pathophysiology of these metabolic insults.