Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry.

UNLABELLED: Thousands of exoplanets are known to orbit nearby stars. Plans for the next generation of space-based and ground-based telescopes are fueling the anticipation that a precious few habitable planets can be identified in the coming decade. Even more highly anticipated is the chance to find signs of life on these habitable planets by way of biosignature gases. But which gases should we search for? Although a few biosignature gases are prominent in Earth's atmospheric spectrum (O2, CH4, N2O), others have been considered as being produced at or able to accumulate to higher levels on exo-Earths (e.g., dimethyl sulfide and CH3Cl). Life on Earth produces thousands of different gases (although most in very small quantities). Some might be produced and/or accumulate in an exo-Earth atmosphere to high levels, depending on the exo-Earth ecology and surface and atmospheric chemistry. To maximize our chances of recognizing biosignature gases, we promote the concept that all stable and potentially volatile molecules should initially be considered as viable biosignature gases. We present a new approach to the subject of biosignature gases by systematically constructing lists of volatile molecules in different categories. An exhaustive list up to six non-H atoms is presented, totaling about 14,000 molecules. About 2500 of these are CNOPSH compounds. An approach for extending the list to larger molecules is described. We further show that about one-fourth of CNOPSH molecules (again, up to N = 6 non-H atoms) are known to be produced by life on Earth. The list can be used to study classes of chemicals that might be potential biosignature gases, considering their accumulation and possible false positives on exoplanets with atmospheres and surface environments different from Earth's. The list can also be used for terrestrial biochemistry applications, some examples of which are provided. We provide an online community usage database to serve as a registry for volatile molecules including biogenic compounds. KEY WORDS: Astrobiology-Atmospheric gases-Biosignatures-Exoplanets. Astrobiology 16, 465-485.

Vegetation's red edge: a possible spectroscopic biosignature of extraterrestrial plants.

Earth's deciduous plants have a sharp order-of-magnitude increase in leaf reflectance between approximately 700 and 750 nm wavelength. This strong reflectance of Earth's vegetation suggests that surface biosignatures with sharp spectral features might be detectable in the spectrum of scattered light from a spatially unresolved extrasolar terrestrial planet. We assess the potential of Earth's step-function-like spectroscopic feature, referred to as the "red edge," as a tool for astrobiology. We review the basic characteristics and physical origin of the red edge and summarize its use in astronomy: early spectroscopic efforts to search for vegetation on Mars and recent reports of detection of the red edge in the spectrum of Earthshine (i.e., the spatially integrated scattered light spectrum of Earth). We present Earthshine observations from Apache Point Observatory (New Mexico) to emphasize that time variability is key to detecting weak surface biosignatures such as the vegetation red edge. We briefly discuss the evolutionary advantages of vegetation's red edge reflectance, and speculate that while extraterrestrial "light-harvesting organisms" have no compelling reason to display the exact same red edge feature as terrestrial vegetation, they might have similar spectroscopic features at different wavelengths than terrestrial vegetation. This implies that future terrestrial-planet-characterizing space missions should obtain data that allow time-varying, sharp spectral features at unknown wavelengths to be identified. We caution that some mineral reflectance edges are similar in slope and strength to vegetation's red edge (albeit at different wavelengths); if an extrasolar planet reflectance edge is detected care must be taken with its interpretation.

Characterization of extrasolar terrestrial planets from diurnal photometric variability.

The detection of massive planets orbiting nearby stars has become almost routine, but current techniques are as yet unable to detect terrestrial planets with masses comparable to the Earth's. Future space-based observatories to detect Earth-like planets are being planned. Terrestrial planets orbiting in the habitable zones of stars-where planetary surface conditions are compatible with the presence of liquid water-are of enormous interest because they might have global environments similar to Earth's and even harbour life. The light scattered by such a planet will vary in intensity and colour as the planet rotates; the resulting light curve will contain information about the planet's surface and atmospheric properties. Here we report a model that predicts features that should be discernible in the light curve obtained by low-precision photometry. For extrasolar planets similar to Earth, we expect daily flux variations of up to hundreds of per cent, depending sensitively on ice and cloud cover as well as seasonal variations. This suggests that the meteorological variability, composition of the surface (for example, ocean versus land fraction) and rotation period of an Earth-like planet could be derived from photometric observations. Even signatures of Earth-like plant life could be constrained or possibly, with further study, even uniquely determined.

Electroejaculation does not impair sperm motility in the beagle dog: a comparative study of electroejaculation and collection by artificial vagina.

Sperm samples obtained by electroejaculation (EEJ) in men with anejaculatory infertility have a markedly lower quality than those obtained by normal ejaculation. An electrical effect of the EEJ procedure has been implicated by some investigators as a direct cause of low sperm quality. To determine whether the EEJ procedure causes direct sperm damage, we compared ejaculates obtained from dogs by EEJ and by artificial vagina (AV). In seven adult beagle dogs, semen was collected weekly, alternating between the two procedures. The average (antegrade) sample from AV had a volume of 2.6 ml., sperm concentration of 150.1 x 10(6) per ml., total sperm count of 381.7 x 10(6) and motility of of 26.3%. The average antegrade sample from EEJ had a volume of 1.8 ml., a concentration of 129.6 x 10(6) per ml., a total sperm count of 166.8 x 10(6) and a motility of 30.1%. Of these differences only the total sperm counts and the total motile sperm counts were statistically significant (p < 0.05). There were no significant differences between the antegrade motilities, total sperm counts (antegrade plus retrograde-381.7 versus 243.4 x 10(6), for AV and EEJ, respectively) or the total motile sperm counts from the two procedures (103.9 versus 78.0 x 10(6)). There were no differences in the average curvilinear velocity (VCL) measured by computer-assisted sperm motion analysis (56.9 mu. per second for AV, 47.4 mu. per second for antegrade EEJ specimens and 41.7 mu. per second for retrograde EEJ specimens). Since routine semen parameters between artificial vagina and electroejaculation did not differ in dogs, we conclude that the electroejaculation procedure is not responsible for the gross semen abnormalities reported in electroejaculation of anejaculatory men.

Relief of spasticity in SCI men and women using rectal probe electrostimulation.

Although there are numerous approaches to the treatment of spasticity, many patients are still unable to find a satisfactory method of managing their spasms with acceptable side effects. In the course of our fertility studies using rectal probe electrostimulation (RPES) in SCI men to produce ejaculation, we observed that a majority of the men experienced significant relief of their spasticity for many hours. This report describes a prospective, single-blinded study of this phenomenon in six SCI men and three SCI women who underwent RPES a total of 71 times. The mean age of the subjects was 28.2 years (21-41), the mean time from injury was 6.0 years (0.5-15); there were three paraplegic and six quadriplegic persons: four were Frankel class A and five were class B. Although all subjects had moderate to severe spasticity, only four took antispasm medications; one had undergone surgery for implantation of an epidural stimulator. The effectiveness of RPES on spasticity was evaluated by each subject for frequency of spasms and interference of daily activities and by independent, blinded assessors for tone, frequency of spasms and DTRs; four patients underwent quantitative videotape analysis of the pendulum test and two underwent somatosensory evoked potentials (SSEPs) to evaluate electrical activity in the central nervous system. Treatment variables included varying probe sizes and number of stimulations. All subjects experienced good to excellent decrease in tone, frequency of spasms and interference with ADL from 3 to 24 hours depending on treatment variables used. Mean duration of relief was 8.2 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Fertility options and success after spinal cord injury.

Over the past 9 years, the fertility potential for men with spinal cord injury and other neurological impairments has improved. Approximately 80% of men with spinal cord injury have semen (collected either by vibration or by electroejaculation using rectal probe) of sufficient quality to use in intrauterine insemination or in vitro fertilization. Assuming that other factors are equal, it would seem that length or level of injury are not dominating factors that control the quality of semen from these men.

[Ejaculation induced by electrostimulation in men with spinal cord injuries]. / Elektrostimulation til frembringelse af ejakulation hos rygmarvsskadede maend.

Five men (aged 29-43 years) with ejaculatory dysfunction and spinal cord injuries for 10-41 years and level of complete lesions from C6 to T10 underwent electrostimulation. Antegrade ejaculate was obtained in all five participants and simultaneous retrograde ejaculation in four. In general, the total number of spermatozoa was greatest in the retrograde ejaculates and highly variable between the subjects both in the antegrade (0.2-5330 mill.) and in the retrograde ejaculates (0.4-5690 mill.). The percentage of immobile and morphologically abnormal spermatozoa was increased compared with normal values. In connection with the electrostimulation procedures no cases of autonomous hyperreflexia or rectal mucosal injury were observed.

Sperm retrieval by electro-ejaculation. Preliminary experience in patients with secondary anejaculation.

Twelve patients with spinal cord injury and 2 diabetics with secondary anejaculation underwent 26 sessions of electro-ejaculation, using a technique which has previously been popular only in veterinary medicine. Ejaculate was obtained on 21 occasions. Semen quality was adequate for cryostorage on 9 occasions (8 patients); on 8 occasions (5 patients) it was used for immediate artificial insemination of the partner. To date, there has been 1 pregnancy resulting in a live birth.

The effects of rectal probe electrostimulation on spinal cord injury spasticity.

Spasticity is a common sequel of spinal cord injury (SCI) with well documented effects on daily activities and increased morbidity. In the course of our fertility studies using rectal probe electrostimulation (RPES) and SCI men to produce ejaculation, we observed that a majority of the men experienced significant improvement in their spasticity for many hours. This paper describes a preliminary effort to quantitate this phenomenon in 14 consecutive subjects treated for anejaculation on 65 occasions in our SCI Fertility Clinic. The effectiveness of RPES on spasticity was evaluated by pre- and post-RPES subject assessment and neurological examinations and follow-up self reports via telephone interviews. Six of the 14 patients (42%) experienced excellent relief following 30 of 33 RPES treatments; 4 (29%) had good to fair relief following 14 of 15 RPES treatments and 4 (29%) had no effect on all 17 RPES trials. The mean duration of relief was 9 hours (3-24). There was no relation between subject age, age of injury, level or completeness of injury or ejaculatory response with relief of spasticity. All men taking medications felt RPES was more effective than drugs in relieving spasms. No untoward effects were reported and 7 (50%) said they would use a home model for daily RPES, if available.

Reproductive laparoscopy.

Reproductive laparoscopy can be used to examine, photograph, and perform surgery on the internal reproductive organs of both the male and female of many species of animals. The equipment and teaching have been adapted from human medicine. This article discusses laparoscopy's use in this context in small and large animals and non-domestic species both in captivity and in the wild.

Electroejaculatory stimulation of a quadriplegic man resulting in pregnancy.

Reproductive rehabilitation of men after spinal cord injury has been made possible by the application of assisted ejaculatory techniques such as electroejaculation. Although this technique may predictably overcome the barrier of semen recovery, the problem of seminal dysfunction still remains. This report describes one of the few pregnancies established by a quadriplegic man using electroejaculatory stimulation for semen acquisition and standard in vitro semen preparation methods for intrauterine insemination.

Diagnostic aids for the detection of urine in the equine ejaculate.

An experiment was conducted to evaluate three commercially available test kits, the Azostix, Multistix and Uric-acid test, for the detection of urine in the equine ejaculate. Azostix, which tests for urea nitrogen, consistently detected urine in the equine ejaculate. Urine contamination was evident when a color change occurred in the reagent pad, going from yellow to green after 10 sec of exposure. The sensitivity of Azostix to urea nitrogen in contaminated samples was 39 mg/dl. The Multistix test kit also successfully detected urine in semen. In the Multistix nitrite pad the color changed from yellow to organge after 3.5 min of exposure to urine-contaminated semen. The Uricacid test kit did not accurately detect urine-contaminated samples. It constantly elicited false positive results in all the control trials. The results of this study show that Azostix and Multistix are cost effective ($1.25 per analysis) and accurate diagnostic aids for detecting urine in the stallion ejaculate.

A method of artificial insemination in captive White-tailed deer (Odocoileus virginianus ).

Production of fawns by artificial insemination in captive White-tailed deer (Odocoileus virginianus ) has been accomplished by using frozen-thawed spermatozoa. The purpose of this study was to determine if frozen-thawed semen deposited at the posterior face of the os cervix could produce conception. Five hand-raised female White-tailed deer and one hand-raised male White-tailed deer were used over two breeding seasons 1984-1985 and 1985-1986. The vasectomized buck was ued to detect estrus in the does. The does were inseminated with frozen-thawed semen containing at least 100 million live normal cells with a 60% or higher motility. The artificial insemination catheters used in this study worked well, but due to the small size of the cervix, the catheter could only be passed up to the first cervical ring, the site at which the semen was deposited. Over two breeding seasons, nine does were inseminated with frozen-thawed spermatozoa; each doe was inseminated once each estrous cycle at one of the following times: 0, 6, 12, 18, 24 or 30 h. after detection of estrus. Of the nine does inseminated with frozen-thawed spermatozoa, six conceived and carried to term 11 healthy normal fawns, yielding an overall conception rate of 67%.

Seasonal variation in serum testosterone, testicular measurements and semen characteristics in the collared peccary (Tayassu tajacu).

Blood samples and testicular measurements were obtained from 4-8 captive adult collared peccaries monthly for 18 months and from wild adult males during summer (N = 16) and winter (N = 22) seasons. Serum concentrations of testosterone were determined by radioimmunoassay. Semen samples were collected monthly by electroejaculation from captive males for 1 year. Serum testosterone concentrations and testicular measurements varied in a low-amplitude circannual pattern, with maximum mean testosterone concentrations in fall and winter (1150-1400 pg/ml) and minimum values in summer (500-700 pg/ml). Circannual rhythms appeared to be related to dominance. Serum testosterone levels in wild males generally were lower than in captive males, although this difference was not significant (P greater than 0.05). Semen characteristics did not exhibit a circannual rhythm. These results suggest that the male peccary remains reproductively fertile throughout the year, yet may undergo a facultative summer quiescence influenced by ambient temperature and social factors.

Clinical electroejaculation.

Anejaculation is a disorder that occurs infrequently in the general population, but it occurs in some cases of spinal cord injury and dissection of retroperitoneal lymph nodes for testicular cancer. It is associated with multiple sclerosis, transverse myelitis, and diabetes mellitus. Electroejaculation, which involves electrodes in a probe placed in the rectum, electrically stimulates emission of seminal fluid. Semen thus obtained can be used for artificial insemination if a patient and his spouse wish to become natural parents.

Electroejaculation of paraplegic males followed by pregnancies.

Semen obtained by electroejaculation was used to achieve pregnancies in the spouses of T5-6 and T4-5 paraplegics. Viable semen was recovered in both an antegrade and retrograde fashion. In both cases, the SPA test was positive. Semen recovered for AIH IUI was washed and swum up prior to insemination.

Rectal probe electrostimulation in the treatment of anejaculatory spinal cord injured men.

This paper reviews our experience with rectal probe electroejaculation (RPE) which is part of a larger effort to determine the correlates of successful ejaculation and fertility in SCI men. RPE is performed in the outpatient clinic using specially designed rectal probes. Over the past 18 months, we have attempted RPE on 38 occasions in 12 subjects (eight paraplegics and four quadriplegics) with an age range of 23-38 years and 0.5-18 years since onset of injury. Anterograde ejaculation occurred in nine subjects with improvement in percent motility and total live sperm count on repeated stimulations in five subjects. Significant retrograde ejaculation occurred in one person and sperm acceptable for artificial insemination (AI) was obtained from four subjects. The major side effects were mild dysreflexia (three subjects) and disruption of a normal bowel program (one subject). We conclude that RPE is a safe, relatively brief outpatient procedure and, with repeated stimulations, has a good potential for producing sperm acceptable for AI in selected patients.

Electroejaculation for recovery of semen after retroperitoneal lymph node dissection: case report.

Electroejaculation with a rectal probe was used successfully for semen recovery 8 years after bilateral suprarenal hilar lymph node dissection for stage IIB embryonal cell cancer. An adequate ejaculate was obtained in relation to total sperm count, motility and normal morphology. Prior use of sympathomimetic drugs, including imipramine and ephedrine, was unsuccessful in producing an ejaculation. Electrostimulation via a rectal probe seems to be a useful technique for semen recovery in the patient with anejaculation after retroperitoneal lymph node dissection.