Learning-induced enhancement of postsynaptic potentials in pyramidal neurons

We studied the effect of olfactory learning-induced modifications in piriform (olfactory) cortex pyramidal neurons on the propagation of postsynaptic potentials (PSPs). Rats were trained to distinguish between odors in pairs, in an olfactory discrimination task. Three days after training completion, PSPs were evoked in layer II pyramidal cells in piriform cortex brain slices by electrical stimulation of two pathways. Stimulation of layer Ib activated the intra-cortical fibers that terminate on the proximal region of the apical and basal dendrites. Stimulation of layer Ia activated the afferent axons that originate from the olfactory bulb and terminate on the distal apical dendrites. We have previously shown that olfactory training is accompanied by enhanced synaptic transmission in the intrinsic pathway, but not in the afferent pathway at 3 days after training. Here we show that at this stage, in both pathways PSPs evoked in neurons from trained rats had significantly faster rise time measured at the soma compared with PSPs in neurons from pseudo-trained and naive rats. Activation of the slow afterhyperpolarization (AHP), which is generated by potassium channels probably located at the proximal region of both apical and basal dendrites, reduced the amplitude measured at the soma of the proximal intrinsic pathway PSPs more effectively than PSPs that were generated distally by the afferent fibers. Thus the amount of reduction by AHP was used as a measure for the relative distance of PSP-generating sites from the soma. In neurons from trained rats, despite the previously reported reduction in AHP amplitude, AHP conductance shunted the PSPs from both synaptic pathways more efficiently compared with neurons from the control rats. We suggest that in neurons from trained rats PSPs are electrotonicly closer to the soma.     

Obstetric outcome of in vitro fertilized pregnancies complicated by severe ovarian hyperstimulation syndrome: a multicenter study

Objective: To assess the outcome of pregnancies conceived with the use of IVF that are complicated by severe ovarian hyperstimulation syndrome (OHSS).

Design: A retrospective nationwide multicenter study.

Setting: Sixteen of 19 tertiary care medical centers in Israel.

Patient(s): All patients undergoing IVF who were hospitalized for severe OHSS between January 1987 and December 1996.

Main Outcome Measure(s): Pregnancy rate (PR) and rates of multiple gestation, miscarriage, ectopic pregnancy, obstetric complications, and intervention.

Result(s): A total of 163 patients who had severe OHSS after IVF treatment were identified, of whom 142 (87.1%) had undergone ET. The clinical PR was 73.2%; 42.3% were singletons, 33.6% were twins, 17.3% were triplets, and 6.7% were quadruplets. The miscarriage rate was 29.8%, whereas the incidence of ectopic pregnancy was 1.9%. Forty-four percent of all births were premature, and 62.1% of all newborns had low birth weight. The most common antenatal complications were pregnancy-induced hypertension (13.2%), gestational diabetes (5.9%), and placental abruption (4.4%). The rate of cesarean section was 44.1%.

Conclusion(s): Among patients who have severe OHSS after IVF treatment, the pregnancy rate and the rates of multiple gestation, miscarriage, prematurity, low birth weight, pregnancy-induced hypertension, gestational diabetes, and placental abruption are significantly higher than those reported previously for pregnancies conceived with the use of assisted reproductive techniques.     

Toward Computational Identification of Multiscale “Tipping Points” in Acute Inflammation and Multiple Organ Failure

Sepsis accounts annually for nearly 10% of total U.S. deaths, costing nearly $17?billion/year. Sepsis is a manifestation of disordered systemic inflammation. Properly regulated inflammation allows for timely recognition and effective reaction to injury or infection, but inadequate or overly robust inflammation can lead to Multiple Organ Dysfunction Syndrome (MODS). There is an incongruity between the systemic nature of disordered inflammation (as the target of inflammation-modulating therapies), and the regional manifestation of organ-specific failure (as the subject of organ support), that presents a therapeutic dilemma: systemic interventions can interfere with an individual organ system’s appropriate response, yet organ-specific interventions may not help the overall system reorient itself. Based on a decade of systems and computational approaches to deciphering acute inflammation, along with translationally-motivated experimental studies in both small and large animals, we propose that MODS evolves due to the feed-forward cycle of inflammation?→?damage?→?inflammation. We hypothesize that inflammation proceeds at a given, “nested” level or scale until positive feedback exceeds a “tipping point.” Below this tipping point, inflammation is contained and manageable; when this threshold is crossed, inflammation becomes disordered, and dysfunction propagates to a higher biological scale (e.g., progressing from cellular, to tissue/organ, to multiple organs, to the organism). Finally, we suggest that a combination of computational biology approaches involving data-driven and mechanistic mathematical modeling, in close association with studies in clinically relevant paradigms of sepsis/MODS, are necessary in order to define scale-specific “tipping points” and to suggest novel therapies for sepsis.     

Fundamental limits on persistent activity in networks of noisy neurons

Neural noise limits the fidelity of representations in the brain. This limitation has been extensively analyzed for sensory coding. However, in short-term memory and integrator networks, where noise accumulates and can play an even more prominent role, much less is known about how neural noise interacts with neural and network parameters to determine the accuracy of the computation. Here we analytically derive how the stored memory in continuous attractor networks of probabilistically spiking neurons will degrade over time through diffusion. By combining statistical and dynamical approaches, we establish a fundamental limit on the network’s ability to maintain a persistent state: The noise-induced drift of the memory state over time within the network is strictly lower-bounded by the accuracy of estimation of the network’s instantaneous memory state by an ideal external observer. This result takes the form of an information-diffusion inequality. We derive some unexpected consequences: Despite the persistence time of short-term memory networks, it does not pay to accumulate spikes for longer than the cellular time-constant to read out their contents. For certain neural transfer functions, the conditions for optimal sensory coding coincide with those for optimal storage, implying that short-term memory may be co-localized with sensory representation.     

Two New Hemoglobin Variants: Hb Tallahassee [α3(A1)Ser→Tyr; HBA2: c.11C>A] and Hb Madison-NC [β119(GH2)Gly→Ser; HBB: c.358G>A]

Of the 1570 reported hemoglobin (Hb) variants detected to date, 390 are α2-globin chain (some variants have yet to be identified by DNA analyses and are therefore presumed) and 827 are the result of mutations of the β-globin chain. Due to their location on the Hb structure, only a minority of these variants result in a clinical phenotype; most are silent and are detected during routine surveillance, are found incidentally during other disease-related investigations or following newborn screening programs. In this report we discuss phenotype/genotype and molecular characteristics of two new Hb variants, both of which were clinically silent. One is an α2-globin chain variant located at codon 3 [α3(A1)Ser→Tyr; HBA2: c.11C?>?A] named Hb Tallahassee and the other is a β-globin chain variant located at codon 119 [β119(GH2)Gly→Ser; HBB: c.358G?>?A] called Hb Madison-NC.     

Quetiapine augmentation of antidepressant treatment in elderly patients suffering from depressive symptoms: A retrospective chart review

Depression in elderly patients is often characterized by poor responses to standard antidepressants. Several reports have suggested that quetiapine also may have antidepressant properties. The present study aimed to evaluate the efficacy of quetiapine augmentation in depressed elderly patients previously unresponsive to a full course of treatment. Medical charts of elderly depressed inpatients treated at a tertiary care psychiatric center during a 3-year period were reviewed. Clinical and demographic data were extracted from computerized records and analyzed. The primary outcome measure was the change on the clinical global impressions scale for improvement (CGI-I). Twenty depressed elderly inpatients received quetiapine augmentation during the study period. Prior to augmentation all had been treated with antidepressants. Baseline mean severity of depression was 6.40; severity after augmentation was significantly reduced to 3.25; the change in CGI-I was 2.10 (p < 0.03). Mean quetiapine dose was 70 mg; mean duration of augmentation was 3.9 weeks. Five patients complained of somnolence. One patient discontinued psycho-tropics and switched to electroconvulsive therapy (ECT) due to life-threatening suicidal tendencies. We tentatively conclude that quetiapine augmentation for elderly depressed patients unresponsive to standard antidepressant treatment may be a safe and efficacious option. Further prospective studies need be carried out to support our observation.     

Methimazole Slows Hepatocyte Streaming in Rats

Hepatocytes are hypothesized to continuallystream from the portal tract to the terminal hepaticvein. By this model, when a cell divides, one of itsprogeny replaces the dividing ancestor and the other is displaced into a more remote location. Thepresent experiment aims to demonstrate thathypothyroidism affects liver cell turnover. Thirty maleadult rats were divided into two groups. One receivedmethimazole for two weeks and the other served as control.Each rat was injected intraperitoneally with 18.5 KBq[³H]thymidine/g body weight. Rats were killedafter 1 hr and two and four weeks. Autoradiography was done. The distance of the labeled cells fromthe portal tract was measured. The mean TSH levels ofthe methimazole-treated group and controls were 1.45 and0.25 mM/liter, respectively (P < 0.01). Hepatocyte streaming was lower in hypothyroid (1.8m/day) than in untreated rats (2.5 m/day) (P< 0.01). The respective labeling indices 1 hr afterlabeling were 0.9% and 1.24% (P < 0.05). We concludethat hypothyroidism diminishes hepatocyte and littoral cellturnover and slows down their streaming.     

Expression of the chemokine receptor CCR2 on immature B cells negatively regulates their cytoskeletal rearrangement and migration

Immature B cells are targeted to specific areas in the spleen, where a fraction of these cells receive signals that induce them to mature and participate in the immune response. In this study, we show that the C-C chemokine receptor 2 (CCR2) is transcribed in immature B cells, while its message is dramatically down-regulated at the mature stage. CCR2-deficient cells exhibit up-regulation of chemokine-induced actin polymerization, migration, and homing to the lymph nodes of immature B cells. In addition, we demonstrate that control of homing by CCR2 is mediated by its ligand, CCL2/JE, which is secreted by B cells and down-regulates the stromal derived factor-1 (SDF-1) signaling cascade. Thus, this study describes an additional, previously uncharacterized, role for CCR2 and its ligand as negative regulators of the homing of immature B cells.