Complementary Roles of the Hippocampus and the Dorsomedial Striatum during Spatial and Sequence-Based Navigation Behavior

We investigated the neural bases of navigation based on spatial or sequential egocentric representation during the completion of the starmaze, a complex goal-directed navigation task. In this maze, mice had to swim along a path composed of three choice points to find a hidden platform. As reported previously, this task can be solved by using two hippocampal-dependent strategies encoded in parallel i) the allocentric strategy requiring encoding of the contextual information, and ii) the sequential egocentric strategy requiring temporal encoding of a sequence of successive body movements associated to specific choice points. Mice were trained during one day and tested the following day in a single probe trial to reveal which of the two strategies was spontaneously preferred by each animal. Imaging of the activity-dependent gene c-fos revealed that both strategies are supported by an overlapping network involving the dorsal hippocampus, the dorsomedial striatum (DMS) and the medial prefrontal cortex. A significant higher activation of the ventral CA1 subregion was observed when mice used the sequential egocentric strategy. To investigate the potential different roles of the dorsal hippocampus and the DMS in both types of navigation, we performed region-specific excitotoxic lesions of each of these two structures. Dorsal hippocampus lesioned mice were unable to optimally learn the sequence but improved their performances by developing a serial strategy instead. DMS lesioned mice were severely impaired, failing to learn the task. Our data support the view that the hippocampus organizes information into a spatio-temporal representation, which can then be used by the DMS to perform goal-directed navigation.     

Deep-sea squat lobster biogeography (Munidopsidae: Leiogalathea) unveils Tethyan vicariance and evolutionary patterns shared by shallow-water relatives

The ecology, abundance and diversity of galatheoid squat lobsters make them an ideal group to study deep-sea diversification processes. Here, we reconstructed the evolutionary and biogeographic history of Leiogalathea, a genus of circum-tropical deep-sea squat lobsters, in order to compare patterns and processes that have affected shallow-water and deep-sea squat lobster species. We first built a multilocus phylogeny and a calibrated species tree with a relaxed clock using StarBEAST2 to reconstruct evolutionary relationships and divergence times among Leiogalathea species. We used BioGeoBEARS and a DEC model, implemented in RevBayes, to reconstruct ancestral distribution ranges and the biogeographic history of the genus. Our results showed that Leiogalathea is monophyletic and comprises four main lineages; morphological homogeneity is common within and between clades, except in one; the reconstructed ancestral range of the genus is in the Atlantic and Indian oceans (Tethys). They also revealed the divergence of the Atlantic species around 25 million years ago (Ma), intense cladogenesis 15–25 Ma and low levels of speciation over the last 5 million years (Myr). The four Leiogalathea lineages showed similar patterns of speciation: allopatric speciation followed by range expansion and subsequent stasis. Leiogalathea started diversifying during the Oligocene, likely in the Tethyan. The Atlantic lineage then split from its Indo-Pacific sister group due to vicariance driven by closure of the Tethys Seaway. The Atlantic lineage is less speciose compared with the Indo-Pacific lineages, with the Tropical Southwestern Pacific being the current centre of diversity. Leiogalathea diversification coincided with cladogenetic peaks in shallow-water genera, indicating that historical biogeographic events similarly shaped the diversification and distribution of both deep-sea and shallow-water squat lobsters.     

Effects of starvation,chilling, and injury on endocrine gland function in Galleria mellonella

Starvation, chilling, and injury of last instar Galleria mellonella larvae typically elicit extra larval molts or a delay in pupation. The primary sites of action and the nature of the signals by which these treatments affect development are not known. However, since the connections of the brain to the nerve cord are crucial for the effects of starvation and chilling, these signals apparently affect the brain-centered program of developmental regulation via the nerve cord. Chilling, and occasionally starvation, cause extra larval molts in last instar larvae treated prior to the nervous inhibition of their corpora allata; release of a cerebral allatotropin, which stimulates the production of juvenile hormone, appears to be involved in this effect. After this time, a delay in pupation is the principal effect of starvation and chilling, and is apparently due to a temporal inhibition of the release of the prothoracicotropic hormone. Chilling also appears to inhibit unstimulated ecdysteroid production by the prothoracic glands. The effect of injury is not mediated by the nerve cord, but appears to involve an inhibitory humoral factor that affects either the brain or the prothoracic glands themselves. Injury also stimulates juvenile hormone production, an effect which is enhanced when the brain is separated from the nerve cord and which is evidenced by a delay of ecdysis and the occasional retention of some larval features in the ecdysed insects. None of the effects of these various treatments on the brain and the endocrine glands persist when the brains or glands are implanted into untreated hosts.     

Regulation of sodium excretion by renal interstitial hydrostatic pressure

Renal interstitial hydrostatic pressure (RIHP) appears to play a crucial role in linking the renal circulation to the rate of tubular reabsorption of sodium and water. Various physiological and pharmacological maneuvers that increase RIHP are associated with increases in sodium excretion. Renal vasodilators that increase RIHP also increase sodium excretion, whereas the vasodilators that do not alter RIHP do not affect sodium excretion. Preventing increases in RIHP during intrarenal infusion of vasodilators markedly attenuates the normal increase in sodium and water excretion. Techniques that directly increase RIHP by renal interstitial volume expansion increase urinary excretion of sodium and water. RIHP may be an important mediator of renal perfusion pressure (RPP) natriuresis. Experimental evidence suggests that the proximal tubule of deep nephrons may be an important nephron site that is sensitive to changes in RPP.     

Macrophage-mediated fungistasis: requirement for a macromolecular component in serum

Peritoneal macrophages from Mycobacterium bovis- or Toxoplasma gondii-infected mice cultured in vitro in Dulbecco's medium containing 10% fetal bovine serum (FBS) and endotoxin stopped replication of Cryptococcus neoformans for 30 hr, whereas yeast cells cultured alone reproduced with a 3.0-hr doubling time. Without at least 5% FBS, macrophage fungistasis was poor. FBS without macrophages enhanced the growth rate of cryptococci. Macrophages preincubated in vitro for 24 hr without serum became fungistatic when challenged with cryptococci in medium with FBS but were not fungistatic without FBS. Macrophages preincubated in medium with FBS were never subsequently fungistatic. Dialyzed, heated (56 degrees C, 30 min), or delipidated FBS supported macrophage fungistasis, whereas FBS heated at 70 degrees C for 30 min did not. FBS contained no measurable opsonic activity for C. neoformans. Inclusion of endotoxin and/or murine IFN-gamma over wide concentration ranges did not substitute for FBS. Ultrafiltration estimation of FBS activity localized to 50 to 150 Kd. By gel filtration chromatography, FBS activity ran in the 25 to 100 Kd range. Dye-ligand affinity chromatography on Cibacron blue agarose gel dissociated the FBS activity from the albumin and lipoprotein fractions. Anion-exchange chromatography on DEAE-Sephacel revealed activity in the first fraction eluting at low ionic strength, pointing to a protein(s) with an isoelectric point toward neutral. Activated macrophages can prevent microbial replication within host tissues; the local environment is critical for fulfillment of this important physiologic function. These results point to a macromolecular factor(s) present in serum that is essential for full fungistatic capability of activated macrophages.     

Lymphocyte in vitro cytotoxicity: mechanism of human lymphotoxin-induced target cell destruction

These in vitro studies were conducted in an attempt to elucidate the mechanism of how cell-free supernatant fluids obtained from PHA-stimulated human lymphocytes cause destruction of cells. The undiluted supernatant fluids with high activity exerted a nonspecific cytotoxic effect on many different continuous cell lines. However, upon dilution, a wide spectrum of cell sensitivities was observed. These studies suggest human lymphotoxin acts by first absorbing to receptors on the target cell plasma membrane. The next effect is shut-down of cellular DNA synthesis, followed later by a decrease in cell numbers and finally, cellular destruction. Once sufficient LT has bound to the target cell surface, the cytopathic effect is irreversible. A role for LT in lymphocyte-mediated tissue destruction is discussed.     

Atriopeptin does not augment the transvascular flux of macromolecules in the hamster cheek pouch.

Natriuretic peptides elaborated by atrial myocytes promote marked renal sodium and water excretion as a mechanism for fluid and electrolyte balance. Recent evidence suggests that atriopeptin (ANP) also targets the non-renal vasculature as a site for enhanced fluid exchange. It remains unclear whether ANP alters microvascular integrity to facilitate the efflux of both plasma and proteins across the endothelial barrier, or if fluid exchange is selectively enhanced. This study evaluated the influence of ANP on macromolecular transport through the direct observation of microvessels in the hamster cheek pouch using fluorescent intravital microscopy. Fluorescein isothiocyanate conjugated to either bovine serum albumin or dextran 150,000 Mw was utilized as a permeability probe. Macromolecular efflux was quantified as fluorochrome clearance. The clearance of fluorescein-conjugated bovine serum albumin (57.94 +/- 7.03) or fluorescein-conjugated dextran 150 (4.09 +/- 1.35) remained unaltered by intravascular injection of 1 microgram/kg ANP. Topical application of 40 ng to cheek pouch microvessels produced similar results. All pouches demonstrated positive leakage response to histamine 2.5 x 10(-6) M, increasing fluorochrome clearance approximately 2- to 11-fold. Bolus injection of 1 microgram/kg ANP reduced mean arterial pressure, increased urine flow from 6.63 +/- 2.59 microliters/min to 8.20 +/- 6.13 microliters/min, and elevated sodium excretion from 1.37 +/- 0.49 microEq/min to 2.54 +/- 0.99 microEq/min. These results suggest that ANP fails to significantly alter the integrity of the protein-transporting channels in the microvascular exchange barrier.     

Effect of sodium intake on fasting and postprandial levels of atrial natriuretic factor in humans

The effect of chronic dietary sodium intake on fasting and postprandial plasma atrial natriuretic factor (ANF) levels was examined in 2 studies of normal humans. In Study I, 3 separate groups of normals (n = 8 for each) received diets of either low (L), normal (N) or high (H) daily sodium intake for 7 days. Twenty-four h urines for sodium were obtained on days 6 and 7. Urine sodium excretion for each group was (L) 13.1 +/- 3.7, (N) 150.1 +/- 19.4 and (H) 271.3 +/- 33.6 mEq/day. On the completion of day 7, fasting plasma ANF showed no change with alteration in sodium intake. In contrast, when blood samples were obtained postprandially, significant increases in plasma ANF were observed in the group maintained on high sodium diet. In Study II, a continuous group of normals (n = 8) received the 3 sodium controlled diets for 7 days sequentially (L/N/H). No significant changes in fasting levels of ANF were detected between L/N/H sodium diets. In conclusion, these studies show that the maintenance of sodium balance during chronic changes in sodium intake can occur despite no significant increase in plasma ANF under normal steady state conditions. However, plasma ANF is significantly elevated during chronic high sodium intake, when measured postprandially.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.