Recommendation on Orbiting Sample Cleanliness

The National Aeronautics and Space Administration-European Space Agency (NASA-ESA) Mars Sample Return (MSR) campaign involves the collection of samples on Mars by the Perseverance (Mars 2020) rover and their return to Earth. To accomplish this, the Orbiting Sample container (OS) will be sent to Mars to accommodate the collected samples then launched from Mars and returned to Earth, where the samples will be removed for examination in the Sample Return Facility (SRF). Crucial to this entire sequence will be establishment of the required level of cleanliness inside the OS. In February 2021, the NASA Headquarters' Mars Sample Return Program and Office of Planetary Protection assembled an MSR OS Tiger Team (OSTT) to discuss the appropriate cleanliness level options of the interior of the OS. The team's remit was primarily focused on evaluating the trade-offs between Planetary Protection cleanliness levels 4a and 4b. These cleanliness levels are determined by the Committee on Space Research (COSPAR) planetary protection regulations, where 4a requires <300 bacterial spores/m² and <3 x 10⁵ bacterial spores on the spacecraft (in this case, the interior of the OS) and 4b mandates the more stringent requirement of <30 bacterial spores on the spacecraft. This report documents the consensus opinion submitted by the OSTT that recommended the interior of the OS be cleaned to a 4a requirement with any feasible added effort toward 4b. This report provides, as well, the rationale for that decision.

Reappraisal of hydrocarbon biomarkers in Archean rocks

Hopanes and steranes found in Archean rocks have been presented as key evidence supporting the early rise of oxygenic photosynthesis and eukaryotes, but the syngeneity of these hydrocarbon biomarkers is controversial. To resolve this debate, we performed a multilaboratory study of new cores from the Pilbara Craton, Australia, that were drilled and sampled using unprecedented hydrocarbon-clean protocols. Hopanes and steranes in rock extracts and hydropyrolysates from these new cores were typically at or below our femtogram detection limit, but when they were detectable, they had total hopane (<37.9 pg per gram of rock) and total sterane (<32.9 pg per gram of rock) concentrations comparable to those measured in blanks and negative control samples. In contrast, hopanes and steranes measured in the exteriors of conventionally drilled and curated rocks of stratigraphic equivalence reach concentrations of 389.5 pg per gram of rock and 1,039 pg per gram of rock, respectively. Polycyclic aromatic hydrocarbons and diamondoids, which exceed blank concentrations, exhibit individual concentrations up to 80 ng per gram of rock in rock extracts and up to 1,000 ng per gram of rock in hydropyrolysates from the ultraclean cores. These results demonstrate that previously studied Archean samples host mixtures of biomarker contaminants and indigenous overmature hydrocarbons. Therefore, existing lipid biomarker evidence cannot be invoked to support the emergence of oxygenic photosynthesis and eukaryotes by ∼ 2.7 billion years ago. Although suitable Proterozoic rocks exist, no currently known Archean strata lie within the appropriate thermal maturity window for syngenetic hydrocarbon biomarker preservation, so future exploration for Archean biomarkers should screen for rocks with milder thermal histories.

Assessing the distribution of sedimentary C40 carotenoids through time

A comprehensive marine biomarker record of green and purple sulfur bacteria (GSB and PSB, respectively) is required to test whether anoxygenic photosynthesis represented a greater fraction of marine primary productivity during the Precambrian than the Phanerozoic, as current models of ocean redox evolution suggest. For this purpose, we analyzed marine rock extracts and oils from the Proterozoic to the Paleogene for C40 diagenetic products of carotenoid pigments using new analytical methods. Gas chromatography coupled with tandem mass spectrometry provides a new perspective on the temporal distributions of carotenoid biomarkers for phototrophic sulfur bacteria, specifically okenane, chlorobactane, and paleorenieratane. According to conventional paleoredox interpretations, this revised stratigraphic distribution of the GSB and PSB biomarkers implies that the shallow sunlit surface ocean (<24 m) became sulfidic more frequently in the geologic past than was previously thought. We reexamine whether there is evidence supporting a planktonic source of GSB and PSB pigments in marine systems or whether additional factors are required to explain the marine phototrophic sulfur bacteria record. To date, planktonic GSB and PSB and their pigments have been identified in restricted basins and lakes, but they have yet to be detected in the unrestricted, transiently sulfidic, marine systems. Based on modern observations, additional environmental factors, including basin restriction, microbial mats, or sediment transport, may be required to fully explain GSB and PSB carotenoids in the geologic record.

Galantamine effects on memory, spatial cue utilization, and neurotrophic factors in aged female rats

Galantamine is an acetylcholine esterase inhibitor that has been approved for use in Alzheimer's disease. However, even though clinical studies indicate efficacy in attenuating some of the symptoms associated with the disease, there are a paucity of studies evaluating the effects of galantamine administration on cognitive performance and brain parameters in aged rats. Further, because all previous animal studies using galantamine have been performed in male rats, there is no information on how females respond to galantamine treatment. Therefore, we studied the effects of 0.3, 0.6, and 1.2 mg/kg/day galantamine in 20-month-old female rats in terms of performance on the working and reference memory water radial arm maze task. Galantamine did not influence maze performance. Furthermore, a probe trial procedure to determine extra-maze cue utilization while solving the water radial arm maze established that aged female rats utilized extramaze cues, and that they did not rely on a nonspatial chaining strategy to locate hidden platforms. Galantamine treatment had no effect on use of extramaze cues or chaining. In addition, there were no significant changes in neurotrophin levels in the frontal cortex, entorhinal cortex, hippocampus, or basal forebrain after galantamine administration. Therefore, the data reported here suggest that aged animals do utilize spatial strategies for solving a working memory task, but galantamine has no appreciable effects on this task, at least not at the doses tested.

11beta-Hydroxysteroid dehydrogenase type 2 protects the neonatal cerebellum from deleterious effects of glucocorticoids

11beta-Hydroxysteroid dehydrogenase type 2 is a glucocorticoid metabolizing enzyme that catalyzes rapid inactivation of corticosterone and cortisol to inert 11-keto derivatives. As 11beta-hydroxysteroid dehydrogenase type 2 is highly expressed in the developing brain, but not in the adult CNS, we hypothesized that it may represent a protective barrier to the deleterious actions of corticosteroids on proliferating cells. To test this hypothesis we have investigated the development and growth of the cerebellum in neonatal C57BL/6 mice and mice lacking 11beta-hydroxysteroid dehydrogenase type 2 (-/-). 11beta-Hydroxysteroid dehydrogenase type 2-/- mice had consistently lower body weight throughout the neonatal period, coupled with a smaller brain size although this was normalized when corrected for body weight. The cerebellar size was smaller in 11beta-hydroxysteroid dehydrogenase type 2-/- mice, due to decreases in size of both the molecular and internal granule layers. When exogenous corticosterone was administered to the pups between postnatal days 4 and 13, 11beta-hydroxysteroid dehydrogenase type 2(-/-) mice were more sensitive, showing further inhibition of cerebellar growth while the wildtype mice were not affected. Upon withdrawal of exogenous steroid, there was a rebound growth spurt so that at day 21 postnatally, the cerebellar size in 11beta-hydroxysteroid dehydrogenase type 2-/- mice was similar to untreated mice of the same genotype. Furthermore, 11beta-hydroxysteroid dehydrogenase type 2-/- mice had a delay in the attainment of neurodevelopmental landmarks such as negative geotaxis and eye opening. We therefore suggest that 11beta-hydroxysteroid dehydrogenase type 2 acts as to protect the developing nervous system from the deleterious consequences of glucocorticoid overexposure.

Transport of genistein-7-glucoside by human intestinal CACO-2 cells: potential role for MRP2

This study demonstrated rapid apical to basolateral absorption of genistein across Caco-2 cell monolayers with a P(app) of 20.0+/-0.8 x 10(-6)cm/sec. In contrast, genistein's main dietary source, genistein-7-glucoside (genistin), was not absorbed. In fact, genistin demonstrated basolateral to apical efflux of 1.28+/-0.10 x 10(-6) cm/sec, which exceeded the flux of the paracellular transport marker mannitol by 6-fold. Although genistin hydrolysis to genistein occurred in the preparation, it did not contribute significantly to these observations. In experiments trying to define the efflux mechanism for genistin, MK-571 reduced the efflux by 87% to 0.19+/-0.02 x 10(-6) cm/sec, implying transport by the polarized efflux pump MRP2.

Dysregulation of diurnal rhythms of serotonin 5-HT2C and corticosteroid receptor gene expression in the hippocampus with food restriction and glucocorticoids

Both serotonergic dysfunction and glucocorticoid hypersecretion are implicated in affective and eating disorders. The adverse effects of serotonergic (5-HT)2C receptor activation on mood and food intake, the antidepressant efficacy of 5-HT2 receptor antagonists, and the hyperphagia observed in 5-HT2C receptor knockout mice all suggest a key role for increased 5-HT2C receptor-mediated neurotransmission. Glucocorticoids, however, downregulate 5-HT2C receptor mRNA in the hippocampus, and it is unclear how increased 5-HT2C receptor sensitivity is achieved in the presence of elevated glucocorticoid levels in depression. Here we show a monophasic diurnal rhythm of 5-HT2C receptor mRNA expression in the rat hippocampus that parallels time-dependent variations in 5-HT2C receptor agonist-induced behaviors in open field tests. Rats entrained to chronic food restriction show marked but intermittent corticosterone hypersecretion and maintain an unaltered 5-HT2C receptor mRNA rhythm. The 5-HT2C receptor mRNA rhythm, however, is suppressed by even modest constant elevations of corticosterone (adrenalectomy + pellet) or with elevated corticosterone during the daytime (8 A.M.), whereas a normal rhythm exists in animals that have the same dose of corticosterone in the evening (6 P.M.). Thus, animals showing even a transient daytime corticosterone nadir exhibit normal hippocampal 5-HT2C receptor mRNA rhythms, even in the presence of overt corticosterone hypersecretion. Chronic food restriction also abolishes the normal diurnal variation in hippocampal glucocorticoid receptor (GR) and mineralocorticoid receptor mRNAs and produces, unusually, both elevated corticosterone and increased GR. The mismatch between elevated glucocorticoids and maintained 5-HT2C receptor and increased GR gene expression in the hippocampus provides a new model to dissect mechanisms that may underlie affective and eating disorders.

Modulation of serotonin and corticosteroid receptor gene expression in the rat hippocampus with circadian rhythm and stress

Glucocorticoids and serotonin (5-HT) modulate behaviour and hypothalamic-pituitary-adrenal (HPA) axis responses. The two systems interact prominently in the hippocampus, where these effects may occur. We have previously shown that hippocampal 5-HT2C receptor mRNA expression is increased by adrenalectomy or central 5-HT lesions. We have now determined expression of corticosteroid and 5-HT receptor subtype genes in the hippocampus across the diurnal cycle, when there are changes both in plasma corticosterone and hippocampal 5-HT levels, as well as the responses of these transcripts to acute and chronic stress, using in situ hybridisation histochemistry. Expression of both glucocorticoid (GR) and mineralocorticoid (MR) receptor mRNAs was significantly higher (131-153%) in the hippocampus at 08.00 h (corticosterone nadir) than at 20.00 h (corticosterone peak). 5-HT2C receptor mRNA expression also showed circadian variation (106-184% higher in CA1-CA3 in the morning). Hippocampal 5-HT1A and 5-HT2A receptor mRNA expression had no diurnal variation. Chronic (15 day) adjuvant arthritis stress, abolished the circadian corticosterone nadir, maintaining plasma corticosterone around diurnal peak values. Chronic arthritis stress suppressed hippocampal 5-HT2C receptor mRNA expression at 08.00 h to levels comparable to 20.00 h controls. By contrast to chronic stress, 6 h after acute laparotomy stress, plasma corticosterone was elevated above control (20.00 h) and 5-HT2C receptor mRNA expression was increased (CA2). Neither acute nor chronic stress altered MR, GR, 5-HT1A or 5-HT2A receptor mRNA expression in any hippocampal subfield. These results show that hippocampal expression of the 5-HT2C receptor gene, but not other subtypes, is sensitive to a variety of manipulations.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of adrenalectomy on 5-hydroxytryptamine and corticosteroid receptor subtype messenger RNA expression in rat hippocampus

Both central serotonergic dysfunction and glucocorticoid hypersecretion have been separately implicated in the aetiology of affective disorders. The hippocampus highly expresses receptors for 5-hydroxytryptamine and glucocorticoids, and adrenalectomy alters the responsivity of hippocampal neurons to 5-hydroxytryptamine. The hippocampus thus represents a prime locus for interactions between the two systems. In this study we examined the effects of glucocorticoid manipulations on neuronal expression of messenger RNA encoding corticosteroid receptor and 5-hydroxytryptamine receptor subtypes in the hippocampus and 5-hydroxytryptamine1A messenger RNA expression in the dorsal raphe, in the rat. Interestingly, there was no effect of adrenalectomy on 5-hydroxytryptamine1A or 5-hydroxytryptamine2A receptor messenger RNA expression in the dorsal or ventral hippocampus at any time point measured. Furthermore, no changes in 5-hydroxytryptamine1A receptor gene expression were seen in the dorsal raphe (encoding autoreceptors) after adrenalectomy. However, 5-hydroxytryptamine2C (5-hydroxytryptamine1C) receptor messenger RNA expression was increased specifically in posterior CA1 and CA3 neurons following adrenalectomy, an effect that was reversed by glucocorticoid replacement. Following adrenalectomy, glucocorticoid and mineralocorticoid receptor messenger RNA expression increased in the dentate gyrus, CA1 and CA3 subfields of the hippocampus. These increases were apparent 6 h after adrenalectomy, were maintained at two days, but 14 days after adrenalectomy hippocampal glucocorticoid receptor and mineralocorticoid receptor gene expression had returned to control levels. These effects of adrenalectomy were abolished by dexamethasone, but not aldosterone administration, suggesting mediation by autoregulatory glucocorticoid receptors. Our results show that adrenalectomy only transiently increases corticosteroid receptor gene expression in the hippocampus, and selectively increases hippocampal 5-hydroxytryptamine2C receptor messenger RNA expression. The resulting change in 5-hydroxytryptamine2C receptor-mediated responses may produce the alterations in hippocampal neuronal activity in response to 5-hydroxytryptamine observed after adrenalectomy.

Glucocorticoid receptor gene expression is unaltered in hippocampal neurons in Alzheimer's disease

Excessive glucocorticoid levels increase the metabolic vulnerability of hippocampal neurons to a wide variety of insults. Since glucocorticoid hypersecretion occurs in Alzheimer's-type dementia it has been proposed that a primary reduction in hippocampal glucocorticoid receptor expression leads to failure of feedback, hypercortisolemia and hence further neuronal loss. However, we have recently found that lesions of the cholinergic innervation of the hippocampus--known to be severely affected in Alzheimer's disease--increase corticosteroid receptor gene expression in the rat hippocampus. We have now examined both glucocorticoid (GR) and mineralocorticoid (MR) receptor gene expression in individual neurons in human postmortem hippocampus, using in situ hybridization histochemistry in 5 patients with Alzheimer's disease (81 +/- 3 years) and 7 controls (81 +/- 7 years) without neurological disease. The distribution and intensity of MR and GR mRNA expression in the hippocampus of Alzheimer's disease were similar to that in control tissue, with high expression in dentate gyrus and CA2-4, but significantly lower expression in CA1. In a separate group of patients with Alzheimer's disease we found significantly increased 24 h integrated plasma cortisol levels (59% greater than age-matched controls) and reduced cortisol-binding globulin (21% lower). These data do not suggest a primary deficiency of biosynthesis of hippocampal corticosteroid receptors in Alzheimer's disease. The maintenance of hippocampal GR and MR gene expression, in the face of an increased glucocorticoid feedback signal, may reflect loss of the cholinergic innervation.