Behavior-driven arc expression is reduced in all ventral hippocampal subfields compared to CA1, CA3, and dentate gyrus in rat dorsal hippocampus.

Anatomical connectivity and lesion studies reveal distinct functional heterogeneity along the dorsal-ventral axis of the hippocampus. The immediate early gene Arc is known to be involved in neural plasticity and memory and can be used as a marker for cell activity that occurs, for example, when hippocampal place cells fire. We report here, that Arc is expressed in a greater proportion of cells in dorsal CA1, CA3, and dentate gyrus (DG), following spatial behavioral experiences compared to ventral hippocampal subregions (dorsal CA1 = 33%; ventral CA1 = 13%; dorsal CA3 = 23%; ventral CA3 = 8%; and dorsal DG = 2.5%; ventral DG = 1.2%). The technique used here to obtain estimates of numbers of behavior-driven cells across the dorsal-ventral axis, however, corresponds quite well with samples from available single unit recording studies. Several explanations for the two- to-threefold reduction in spatial behavior-driven cell activity in the ventral hippocampus can be offered. These include anatomical connectivity differences, differential gain of the self-motion signals that appear to alter the scale of place fields and the proportion of active cells, and possibly variations in the neuronal responses to non-spatial information within the hippocampus along its dorso-ventral axis.

Nonuniform allocation of hippocampal neurons to place fields across all hippocampal subfields.

The mechanisms governing how the hippocampus selects neurons to exhibit place fields are not well understood. A default assumption in some previous studies was the uniform random draw with replacement (URDWR) model, which, theoretically, maximizes spatial "pattern separation", and predicts a Poisson distribution of the numbers of place fields expressed by a given cell per unit area. The actual distribution of mean firing rates exhibited by a population of hippocampal neurons, however, is approximately exponential or log-normal in a given environment and these rates are somewhat correlated across multiple places, at least under some conditions. The advantage of neural activity-dependent immediate-early gene (IEG) analysis, as a proxy for electrophysiological recording, is the ability to obtain much larger samples of cells, even those whose activity is so sparse that they are overlooked in recording studies. Thus, a more accurate representation of the activation statistics can potentially be achieved. Some previous IEG studies that examined behavior-driven IEG expression in CA1 appear to support URDWR. There was, however, in some of the same studies, an under-recruitment of dentate gyrus granule cells, indicating a highly skewed excitability distribution, which is inconsistent with URDWR. Although it was suggested that this skewness might be related to increased excitability of recently generated granule cells, we show here that CA1, CA3, and subiculum also exhibit cumulative under-recruitment of neurons. Thus, a highly skewed excitability distribution is a general principle common to all major hippocampal subfields. Finally, a more detailed analysis of the frequency distributions of IEG intranuclear transcription foci suggests that a large fraction of hippocampal neurons is virtually silent, even during sleep. Whether the skewing of the excitability distribution is cell-intrinsic or a network phenomenon, and the degree to which this excitability is fixed or possibly time-varying are open questions for future studies. © 2016 Wiley Periodicals, Inc.

Age-related changes in Arc transcription and DNA methylation within the hippocampus.

The transcription of genes that support memory processes are likely to be impacted by the normal aging process. Because Arc is necessary for memory consolidation and enduring synaptic plasticity, we examined Arc transcription within the aged hippocampus. Here, we report that Arc transcription is reduced within the aged hippocampus compared to the adult hippocampus during both "off line" periods of rest, and following spatial behavior. This reduction is observed within ensembles of CA1 "place cells", which make less mRNA per cell, and in the dentate gyrus (DG) where fewer granule cells are activated by behavior. In addition, we present data suggesting that aberrant changes in methylation of the Arc gene may be responsible for age-related decreases in Arc transcription within CA1 and the DG. Given that Arc is necessary for normal memory function, these subregion-specific epigenetic and transcriptional changes may result in less efficient memory storage and retrieval during aging.

Hippocampal granule cells opt for early retirement.

Increased excitability and plasticity of adult-generated hippocampal granule cells during a critical period suggests that they may "orthogonalize" memories according to time. One version of this "temporal tag" hypothesis suggests that young granule cells are particularly responsive during a specific time period after their genesis, allowing them to play a significant role in sculpting CA3 representations, after which they become much less responsive to any input. An alternative possibility is that the granule cells active during their window of increased plasticity, and excitability become selectively tuned to events that occurred during that time and participate in later reinstatement of those experiences, to the exclusion of other cells. To discriminate between these possibilities, rats were exposed to different environments at different times over many weeks, and cell activation was subsequently assessed during a single session in which all environments were revisited. Dispersing the initial experiences in time did not lead to the increase in total recruitment at reinstatement time predicted by the selective tuning hypothesis. The data indicate that, during a given time frame, only a very small number of granule cells participate in many experiences, with most not participating significantly in any. Based on these and previous data, the small excitable population of granule cells probably correspond to the most recently generated cells. It appears that, rather than contributing to the recollection of long past events, most granule cells, possibly 90-95%, are effectively "retired." If granule cells indeed sculpt CA3 representations (which remains to be shown), then a possible consequence of having a new set of granule cells participate when old memories are reinstated is that new representations of these experiences might be generated in CA3. Whatever the case, the present data may be interpreted to undermine the standard "orthogonalizer" theory of the role of the dentate gyrus in memory.

Sparse, environmentally selective expression of Arc RNA in the upper blade of the rodent fascia dentata by brief spatial experience.

After a spatial behavioral experience, hippocampal CA1 pyramidal cells express the activity-regulated, immediate early gene Arc in an environment-specific manner, and in similar proportions ( 40%) to cells exhibiting electrophysiologically recorded place fields under similar conditions. Theoretical accounts of the function of the fascia dentata suggest that it plays a role in pattern separation during encoding. The hypothesis that the dentate gyrus (DG) uses a sparse, and thus more orthogonal, coding scheme has been supported by the observation that, while granule cells do exhibit place fields, most are silent in a given environment. To quantify the degree of sparsity of DG coding and its corresponding ability to generate distinct environmental representations, behaviorally induced Arc expression was assessed using in situ hybridization coupled with confocal microscopy. The proportion of Arc(+) cells in the "upper blade" of the fascia dentata (i.e., the portion that abuts CA1) increased in an environment-specific fashion, approximately 4-fold above cage-control activity, after behavioral exploration. Surprisingly, cells in the lower blade of the fascia dentata, which are capable of expressing Arc following electrical stimulation, exhibited virtually no behaviorally-induced Arc expression. This difference was confirmed using "line scan" analyses, which also revealed no patterns or gradients of activity along the upper blade of the DG. The expression of Arc in the upper blade was quantitatively similar after exploring familiar or novel environments. When animals explored two different environments, separated by 20 min, a new group of cells responded to the second environment, whereas two separated experiences in the same environment did not activate a new set of granular cells. Thus, granule cells generate distinct codes for different environments. These findings suggest differential contribution of upper and lower blade neurons to plastic networks and confirm the hypothesis that the DG uses sparse coding that may facilitate orthogonalization of information.

Echocardiographic imaging of technically difficult patients in the intensive care unit: use of optison in combination with fundamental and harmonic imaging.

Previous studies of intravenous contrast agents have excluded patients in the intensive care unit. These patients remain among the most technically difficult to image with ultrasound. We studied the effect of different imaging modalities with and without intravenous contrast (Optison) on endocardial border visualization during echocardiography. Fifty patients in the intensive care unit (32 men, 24 on mechanical ventilator, 10 with chest bandages; mean age, 59 years; mean weight, 91.7 kg; mean height, 67.6 inches) were considered to have technically difficult images when the endocardium could not be visualized in at least 2 of the 6 segments in either apical view. Each patient was studied with the use of fundamental (F), harmonic (H), fundamental + Optison (F + O), and H + O techniques, with standard long-axis, short-axis, and apical 4- and 2-chamber views. Intravenous Optison (0.5 to 1.5 mL) was given before F + O and H + O imaging. There were no contrast-related side effects noted. All images were stored digitally in a quad-screen format. For each set of images, segments (n = 22) were given an endocardial border visualization score of 0 if not visualized, 1 if visualized in either systole or diastole, and 2 if visualized in both. There was stepwise improvement in endocardial border visualization, with mean endocardial border visualization score of 1.09 +/- 0.83 (F), 1.33 +/- 0.81 (H), 1.64 +/- 0.62 (F + O), and 1.90 +/- 0.35 (H + O). There was a statistically significant difference between each group (P <.001). The incremental benefit of Optison was greater with harmonic imaging than with fundamental (P <.001). The use of Optison is safe and effective in the intensive care unit. In combination with harmonic imaging, contrast provides maximal endocardial border delineation during echocardiographic imaging of technically difficult patients in the intensive care unit.

Independence of firing correlates of anatomically proximate hippocampal pyramidal cells.

In neocortex, neighboring neurons frequently exhibit correlated encoding properties. There is conflicting evidence whether a similar phenomenon occurs in hippocampus. To assess this quantitatively, a comparison was made of the spatial and temporal firing correlations within and between local groups of hippocampal cells, spaced 350-1400 microm apart. No evidence of clustering was found in a sample of >3000 neurons. Moreover, cells active in two environments were uniformly interspersed at a scale of <100 microm, as assessed by the activity-induced gene Arc. Independence of encoding characteristics implies uncorrelated inputs, which could enhance the capacity of the hippocampus to store arbitrary associations.

Identification and characterization of calcifying valve cells from human and canine aortic valves.

BACKGROUND AND AIM OF THE STUDY: Cardiac valve calcification is the predominant pathology in patients needing valve replacement. The aim of this study was to determine if aortic valve cells calcify spontaneously and, if so, to characterize the nodular complex and response to growth factors. METHODS: Aortic valves were obtained from humans undergoing surgical valve replacement, and from female dogs. The valvular endothelium was removed and explants cultured in medium. RESULTS: A population of valvular interstitial cells spontaneously formed distinct calcified nodules containing hydroxyapatite within two to three weeks in canine and within six weeks in human aortic valves. The nodules contained an inner ring of dead cells surrounded by an outer ring of living cells. Cells associated with nodules had osteoblast-like characteristics and stained positively for extracellular bone matrix proteins. Incubating canine cells with potential calcifying stimuli tested the stimulus for calcification. The rate of nodule formation was increased with transforming growth factor beta-1 (+25 nodules), 25-hydroxycholesterol (+9 nodules) and bone morphogenetic protein 2 (+4 nodules) as compared with vehicle control (+3 nodules) over 25 days. CONCLUSIONS: We identified a population of valvular interstitial cells with osteoblast-like characteristics that spontaneously form calcific nodules in cell culture. In addition, the rate of calcific nodule formation was increased with transforming growth factor beta-1 and 25-hydroxycholesterol. Further study of these 'calcifying valve cells' may yield a new in vitro model for testing therapy aimed at preventing calcific valve stenosis.

Localization of neurons expressing substance P and neurokinin B gene transcripts in the human hypothalamus and basal forebrain.

In situ hybridization histochemistry was used to map the distribution of neurons expressing the substance P (SP) or neurokinin B (NKB) genes in the human hypothalamus and basal forebrain. Hypothalami from five adult males were frozen in isopentane at -30 degrees C and serially sectioned at 20 jm thickness. Every 20th section was hybridized with [35S]-labeled, 48-base synthetic cDNA probes that were complementary to either SP or NKB mRNAs. Slides were dipped into nuclear emulsion for visualization of mRNAs at the single-cell level. The location of labeled neurons (greater than x 5 background) was mapped by using an image-combining computer microscope system. A distinct and complementary distribution pattern of SP and NKB neurons was observed in the human hypothalamus and basal forebrain. NKB was the predominant tachykinin in the rostral hypothalamus, whereas SP mRNA predominated in the posterior hypothalamus. Numerous NKB neurons were identified in the magnocellular basal forebrain, the bed nucleus of stria terminalis, and the anterior hypothalamic area. Scattered NKB neurons were present in the infundibular and paraventricular nuclei, paraolfactory gyrus, posterior hypothalamic area, lateral division of the medial mammillary nucleus, and amygdala. Numerous neurons expressing SP mRNAs were identified in the premammillary, supramammillary, and medial mammillary nuclei; the posterior hypothalamic area; and the corpus striatum. Scattered SP neurons were also observed in the preoptic area; the infundibular, intermediate, dorsomedial, and ventromedial nuclei; the infundibular stalk; the amygdala; the bed nucleus of stria terminalis; and the paraolfactory gyrus. These studies provide the first description of the location of neurons that express tachykinin gene transcripts in the human hypothalamus.

Acute viral hepatitis types E, A, and B singly and in combination in acute liver failure in children in north India.

The aetiological agents responsible for, and the outcome of, acute liver failure were investigated prospectively in 44 children (29 males, 15 females) attending a tertiary health care facility in India. The children were between the ages of 2 months and 13 years. Studies for viral infections and other etiologies could be carried out in 40 patients. Specific aetiological labels were possible in 35 (87.5%) patients. Thirty (75%) had evidence of acute viral hepatitis. Acute hepatitis E virus (HEV) infection was found in a total of 18 children, with hepatitis A (HAV) in 16, hepatitis B in 5, and C in 1. Seven had isolated infection with hepatitis E, five with A, and four with B. Nine had both E and A infection. Superinfection of HEV was observed in a child with Indian childhood cirrhosis (ICC). Acute HEV infection was confirmed by immunoblot assay in all the patients and in eight of these, HEV-RNA was also detected in the serum. HAV was involved in 37.5% of cases with isolated infection in 10% (4 of 40). The aetiological factors associated with acute liver failure, apart from HAV and HEV, were other hepatotropic viruses (22.5%), Wilson's disease (5%), ICC (5%), and hepatotoxic drugs (7.5%). In five patients, no serological evidence of acute viral hepatitis could be found, neither did the metabolic screen yield any result. It was observed that enterically transmitted hepatitis viruses (HAV and HEV) were associated with 60% of acute hepatic failure in children. Mixed infection of HAV and HEV formed the single largest aetiological subgroup. In developing countries, where hepatitis A and E infections are endemic, severe complications can arise in the case of mixed infection. This may contribute to most of the mortality from acute liver failure during childhood.