Relocation of an Extrasynaptic GABAA Receptor to Inhibitory Synapses Freezes Excitatory Synaptic Strength and Preserves Memory

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Developmental regulation of plasticity along neurite shafts

Although it is becoming increasingly clear that structural dynamics on neurite shafts play important roles in establishing neuronal architecture, the underlying mechanisms are unknown. The present study investigates local induction of filopodia along the shafts of neurites, a process that, by analogy to the growth cone, can represent the first stage in the generation of a new neuronal process. We show that filopodia can be induced reliably along the neurite shaft in response to a localized electric field stimulus that evokes large local intracellular calcium increases. Neither induction of filopodia nor a local rise in intracellular calcium occurred in calcium free medium. Although calcium induction of neurite filopodia is highly reliable, forming in response to more than 90% of attempts, it is developmental state-dependent, since neurite filopodia could not be induced in neurons previously defined as “stable state.” We have found two distinct changes in stable state neurons that can decrease the ability to induce new neurites. The first is a reduced calcium response: Field stimulation produced large local rises (280 nM) in stable state neurons. Second, stable state neurons change so that even when the stimulus intensity was increased to elicit a calcium response that would have been sufficient to induce filopodia in growing neurites, neurite filopodia were still not induced. Thus, intracellular calcium plays a key role in structural changes along the shafts of neurites. Furthermore, developmental changes in both calcium homeostatic components, and in calcium responsiveness (i.e., the sensitivity of cellular components that modulate neurite morphology) underlie shifts from plasticity to stability of neuronal architecture in this system. © 1995 John Wiley & Sons, Inc.     

Behavioural osmotic control in the euryhaline diamondback terrapin Malaclemys terrapin: responses to low salinity and rainfall

Diamond terrapins, Malaclemys terrapin Latreille, inhabit salt marshes and estuaries where they may encounter sustained high salinities for weeks or months. Terrapins can discriminate between salinities. When salt-loaded they avoid drinking high salinities (27.2–34.0%), drink small amounts of salinities which are a little more concentrated than the blood (13.6–20%), and drink copious quantities of lower salinities (0–10.2%). After seven days in full sea water (34%) they can rehydrate themselves in < 15 min if given access to fresh water. Terrapins are capable of drinking from the thinnest of freshwater films (1.6 mm), exploit menisci and have specific postural responses to collect small quantities of fresh water from horizontal and vertical surfaces. Specimens of Malaclemys terrapin respond to the vibration of simulated rainfall by rapid emergence followed by drinking from thin films, either on the exposed substratum or from the surface of the water column. Under simulated conditions of heavy rainfall they collect rain directly from above.     

Combining insights from quantile and ordinal regression: Child malnutrition in Guatemala

Chronic child undernutrition is a persistent problem in developing countries and has been the focus of hundreds of studies where the primary intent is to improve targeting of public health and economic development policies. In national level cross-sectional studies undernutrition is measured as child stunting and the goal is to assess differences in prevalence among population subgroups. Several types of regression modeling frameworks have been used to study childhood stunting but the literature provides little guidance in terms of statistical properties and the ease with which the results can be communicated to the policy community. We compare the results from quantile regression and ordinal regression models. The two frameworks can be linked analytically and together yield complementary insights. We find that reflecting on interpretations from both models leads to a more thorough analysis and forces the analyst to consider the policy utility of the findings. Guatemala is used as the country focus for the study.     

Severity and timing of early thyroid deficiency as factors in the induction of learning disorders in rats

In Experiment 1 (N = 277 rats), more extreme deficits in maze learning than heretofore shown appeared in the adult offspring of mothers exposed for 16 pre- and 16 postnatal days to thiouracil-treated mash diets in doses up to 0.3%; the same offspring also displayed deficits in single-alternation pattern learning and a modified operant discrimination task. Surprisingly small maze learning deficits, however, were found in the offspring of mothers which received thiouracil during the 16 postnatal days only, despite previous findings indicating that the postnatal half of the total 32-day perinatal period was the more critical in determining later learning impairments. Reconciliation was provided by Experiment 2 (N = 54), in which the manipulation of a 0.2% thiouracil diet starting at birth or 3, 6, 10, or 15 days before birth indicated a lower age boundary of the critical period for the induction of maze learning deficit by thyroid deficiency at approximately the fetal age at which thyroid tissue becomes functional-around the 18th day of gestation.     

Relationship between magnitude estimation of resistive loads, inspiratory pressures, and the RREP P(1) peak.

This study investigated the relationship among resistive load magnitude (DeltaR), the cortical evoked potential P(1) peak amplitude of the respiratory-related evoked potential (RREP), mouth pressure (Pm), esophageal pressure (Pes), transdiaphragmatic pressure (Pdi), and resistive load magnitude estimation (ME) in human subjects. The RREP, Pdi, Pes, Pm, and ME were recorded in response to three DeltaR values. The RREP was recorded from C(3) and C(4), referenced to the vertex C(Z). The group means of the Pdi, Pm, ME, and RREP P(1) amplitude increased with increases in the DeltaR. A log-log plot of the P(1) amplitudes showed a relationship with ME as did Pes, Pdi, and Pm. There were linear log-log relationships between C(Z)-C(3) P(1) amplitude, C(Z)-C(4) P(1) amplitude, and Pdi to ME. Pdi had a linear log-log relationship with C(Z)-C(3) and C(Z)-C(4). These results support the hypothesis that the estimated magnitude of the respiratory load is related to the P(1) amplitude of the RREP. Pm, Pes, and Pdi are mechanically related and correlated with the P(1) peak amplitude, suggesting that the mechanoreceptors mediating the P(1) peak of the RREP are activated by changes in mechanical forces related to the inspiratory pump.