NOTE: End date changed to 12/30/2018 per H. Paul/JSC HRP (Ed., 12/22/17)

NOTE: End date changed to 12/31/2017 per NSSC information (Ed., 4/20/2016)

NOTE: End date will be 6/30/2017 per R. Brady/JSC HRP (Ed., 11/3/15)

No innovative technologies have been developed during this period.

Hind-limb unloading (HLU) has been an established technique modeling microgravity for over 40 years. Recent observations showed that astronauts on long-duration spaceflight missions develop visual defects. This program examined whether these could be duplicated in the rat HLS (hindlimb suspension) model. Also of interest were any effects on intracranial pressure and their possible connection to the observed visual changes. Overall, the project proved successful; within limits, the rat continues to be a useful translational animal model for spaceflight research. The use of the rat allows continuous recording of physiological measurements using indwelling technology leading to the collection of large amounts of data from freely behaving subjects.

In summary, the rats evidenced

• some, but not all, of the visual changes seen in long-duration astronauts.

• a small, but sustained increase in intracranial pressure (ICP) that appears to be time of day dependent in that differences between HLS and baseline ICP were greater during the animals’ rest period, leading to a decrease in the circadian rhythm amplitude of ICP.

• alterations in circadian timing. The reduction in the amplitude of the rhythm of ICP is consistent with results from the rhythms of Tb and EEG. Changes were also seen in the circadian mean and phasing of these rhythms. This type of circadian dysfunction is known to occur during spaceflight, and can lead to overall physiological and behavioral deficits.

There was a gender and also an age factor in the responses. Comparison of the responses between Young male and Young female rats showed that the effects were much smaller in female rats. Comparison between Old and Young male rats revealed larger effects in the older animals.

These observations are of interest because the increase in ICP during the rest period may also have led to a decreased turnover of CSF (cerebrospinal fluid) and/or other CNS (central nervous sytem) fluid exchanges. Such decreases over extended periods of time may have resulted in CNS inflammatory responses.

DECEMBER 2018 ANNUAL REPORT:

During this period of performance, the research team has concluded the collection of data from all cohorts. These included young males, young females (to examine possible gender differences), older males (to examine possible age effects) and, finally, older males exposed to a hypercapnic environment similar to that present on International Space Station (ISS). Older males were chosen for hypercapnic exposure as this group presented the most significant response to HLS. Analysis of the data from this group will allow us to determine if there is a role of increased CO2 exposure in the etiology of these visual changes.

Intracranial pressure, body temperature, and EEG were recorded via biotelemetry. Biotelemetry data have been collected from the young male, young female, older male, and older male hypercapnic cohorts. Data analysis is underway.

Additional measurements of visual system function including complete ophthalmic clinical exams and measurement of intraocular pressure by tonometry have been performed. The retinal imaging performed during this program included both fundus imaging with fluorescein angiography and optical coherence tomography (OCT). The tissue histology studies that will complement these data are underway.

NOTE: End date changed to 12/31/2017 per NSSC information (Ed., 4/20/2016)

NOTE: End date will be 6/30/2017 per R. Brady/JSC HRP (Ed., 11/3/15)

No innovative technologies have been developed during this period.

Data are collected from animals in long-term HLS and controls. In order to measure intracranial pressure, animals are chronically instrumented with biotelemetry. The biotelemetry transmitter also allows for the collection of body temperature and activity data. Additional data collected include intraocular pressure measured by tonometry and MRI images encompassing brain and visual system morphology. Retinal morphology and ultrastructure are also being examined at specified intervals both during HLS and post-HLS recovery by both ophthalmic examinations and tissue histology evaluation.

Both male and female subjects are studied in order to examine possible gender differences in these responses. Additionally, we are examining the possible contributory factors of aging and elevated (1%) atmospheric carbon dioxide (hypercapnia) on to these responses of the visual system. Further, in addition to mimicking the effects of long duration exposure to microgravity through the use of the HLS model, we are examining the responses of our measured outcomes during long-term recovery in the post-HLS period. Collectively, these data will help allow us to develop a model to both understand and predict the etiology of changes in visual structure and function in astronauts exposed to the microgravity of spaceflight and during postflight recovery. In summary, our ultimate goal is the development of a translational mammalian model; the data generated using this model would be used to facilitate the development of countermeasures to alleviate any visual system decrements arising from exposure to the microgravity spaceflight environment.

We utilized biotelemetry to record intracranial pressure. This required the review and testing of three biotelemetry systems, all of which claimed to allow continuous recording of biological pressure. To improve the ease and accuracy of data collection as well as to tailor the system to meet the needs of this research program, we have extensively revised the data acquisition software. Biotelemetry data have been collected from the young male, young female, and older male cohorts and is currently being collected from the older male hypercapnic cohort.

Additional measurements of visual system function including complete ophthalmic clinical exams and measurement of intraocular pressure by tonometry have been performed. These will be complemented by tissue histology studies. The retinal imaging performed during this program included both fundus imaging with fluorescein angiography and OCT.

During this period of performance, the research team has concluded the collection of data from cohorts of: young males, young females (to examine possible gender differences), and older males (to examine possible age effects). The older male cohort currently presents the most significant response to HLS and is currently under study in a hypercapnic environment (similar to that experienced on the ISS-International Space Station). This will allow us to determine if there is a role of increased CO2 exposure in the etiology of these visual changes.

This program is aimed at determining if long-term cephalic fluid shift can cause the effects seen on visual system structure and function during and after long-duration spaceflight. As such, animals were exposed to HDT (head down tilt) for a longer period of time than is utilized in most studies. We will continue to work with the Biospecimen Sharing Program at Ames Research Center to ensure that tissues not utilized in our analyses are available for other researchers, thus increasing the science yielded by this program.

NOTE: End date will be 6/30/2017 per R. Brady/JSC HRP (Ed., 11/3/15)

No innovative technologies have been developed during this period.

Animals are chronically instrumented with biotelemetry to continuously measure intracranial pressure. Additionally, regular intraocular pressure measurements are made by tonometry during long-term exposure to cephalic fluid shifts induced by suspension. MRI images visualizing the visual system morphology have also been collected from HLS and control animals at regular intervals. Retinal morphology and ultrastructure are being examined at specified intervals both during HLS and post-HLS recovery by both ophthalmic examinations and tissue histology evaluation.

This program utilizes both male and female subjects in order to examine possible gender differences in these responses. We are examining the possible contributory factors of aging and elevated atmospheric carbon dioxide (hypercapnia) on to these responses of the visual system. Further, in addition to mimicking the effects of long duration exposure to microgravity through the use of the HLS model, we are examining the responses of our measured outcomes during long-term recovery in the post-HLS period. Collectively, these data will help allow us to develop a model to both understand and predict the etiology of changes in visual structure and function in astronauts exposed to the microgravity of spaceflight and during postflight recovery. In summary, our ultimate goal is the development of a translational mammalian model; the data generated using this model would be used to facilitate the development of countermeasures to alleviate any visual system decrements arising from exposure to the microgravity spaceflight environment.

During this period of performance, the research team has expanded the study of cohorts of young males, young females (to examine possible gender differences) and older males (to examine possible age effects). The older male cohort currently presents the most significant response to HLS and will be studied in a hypercapnic environment (similar to that experienced on the International Space Station--ISS). This will allow us to determine if there is a role of increased CO2 exposure in the etiology of these visual changes.

We are utilizing biotelemetry to record intracranial pressure. We have reviewed and tested three biotelemetry systems, all of which claim to allow continuous recording of biological presssure. We have extensively revised the data acquisition software, which has been necessary to both improve the ease and accuracy of data collection, as well as to tailor the system to meet the needs of this research program. Biotelemetry data have been collected from both male cohorts and we are currently expanding this to the female cohort.

Additional measurements of visual system function include complete ophthalmic clinical exams, measurement of intraocular pressure by tonometry, and, ultimately, tissue histology. The retinal imaging performed during this program include both fundus imaging with fluorescein angiography and OCT.

This program is aimed at determining if long-term cephalic fluid shift can cause the effects seen on visual system structure and function during and after long-duration spaceflight. As such, animals are exposed to HDT (head down tilt) for a longer period of time than is utilized in most studies. We are working with the Biospecimen Sharing Program at Ames Research Center to ensure that tissues not utilized in our analyses are available for other researchers, thus increasing the science yielded by this program.

NOTE: End date will be 6/30/2017 per R. Brady/JSC HRP (Ed., 11/3/15)

No innovative technologies have been developed during this period.

During this period of performance, the research team has been hired and trained, major equipment purchased, and facilities set-up. We have put into place the core techniques and capabilities that will be necessary for the successful execution and completion of this program. This has included establishing a flow for the employment of the tail suspension model using the pigmented Long-Evans rat. While our initial subjects were young males, we are also studying cohorts of young females (to examine possible gender differences) and older males (to examine possible age effects). The cohort that presents the most significant response to HLS will be studied in a hypercapnic environment (similar to that experienced on the International Space Station (ISS)). This will allow us to determine if there is a role of increased CO2 exposure in the etiology of these visual changes. The subjects currently proposed for use in the hypercapnic study are older males.

We are utilizing biotelemetry to record intracranial pressure. We have extensively revised the data acquisition software, which has been necessary to both improve the ease and accuracy of data collection, as well as to tailor the system to meet the needs of this research program. The first cohort from which the biotelemetry data were collected were older males.

Additional measurements of visual system function include complete ophthalmic clinical exams, measurement of intraocular pressure by tonometry, and, ultimately, tissue histology. The retinal imaging performed during this program include both fundus imaging with fluorescein angiography and OCT.

NOTE: End date will be 6/30/2017 per R. Brady/JSC HRP (Ed., 11/3/15)

No innovative technologies have been developed during this period.

The use of biotelemetry allows continuous measurement of intracranial pressure from freely moving animals. Additionally, regular intraocular pressure measurements are made by tonometry. MRI images visualizing visual system morphology will also be collected from HLS and control animals at regular intervals. Retinal morphology and ultrastructure are being examined at specified intervals both during HLS and post-HLS recovery by both ophthalmic examinations and tissue histology evaluation. Changes in retinal/visual function will be regularly assessed electrophysiologically by measuring visual evoked potentials and electroretinograms.

This program utilizes both male and female subjects in order to examine possible gender differences in these responses. We are also examining the possible contributory factors of aging and elevated atmospheric carbon dioxide (hypercapnia) on these responses of the visual system. Further, in addition to mimicking the effects of long duration exposure to microgravity through the use of the HLS model, we will examine the responses of our measured outcomes during long-term recovery in the post-HLS period. Collectively, these data will allow us to develop a model to both understand and predict the etiology of changes in visual structure and function in astronauts exposed to the microgravity of spaceflight and during postflight recovery. In summary, our ultimate goal is to develop a translational mammalian model that can facilitate the development of countermeasures to alleviate any visual system decrements arising from exposure to the microgravity spaceflight environment.

We have successfully completed a 90-day HLS study and a 90-day HLS with 28 days of recovery study in young males as well as all the shorter-term HLS studies (7, 14, and 28 days) on both young males and young females. Fundus imaging, fluorescein angiography, and OCT were completed from HLS and age-matched control animals at baseline and at the end of HLS. Additionally, complete ophthalmic exams and measurement of intraocular pressure using tonometry were performed. The integration of the Zanello proposal into this program added histological and genetic examination of the eye to this study; these tissues were harvested from control and HLS animals.

This program is aimed at determining if long-term cephalic fluid shift can cause the effects seen on visual system structure and function during and after long-duration spaceflight. As such, animals are exposed to HLS for a longer period of time than is utilized in most studies. At the completion of each HLS study, tissues not utilized in our analyses were harvested and preserved by the Biospecimen Sharing Program at Ames Research Center; they will be available for other researchers, thus increasing the science yielded by this program.

No innovative technologies have been developed during this period.

This ground-based program is intended to address the etiology of visual system structural and functional changes observed in astronauts during both inflight and postflight periods. Using the well-documented rat hindlimb suspension (HLS) model, functionally equivalent to human head-down bedrest, we will examine the relationship between cephalic fluid shifts resulting from long-duration G-unloading and the regulation of intracranial and intraocular pressures, as well as the effects these same cephalic fluid shifts have on visual system structure and function. A proposal examining additional histological and genetic effects was integrated into our protocol, adding these measures.

Animals will be chronically instrumented with biotelemetry to continuously measure intracranial pressure. Additionally, regular intraocular pressure measurements will be made by tonometry during long-term exposure to cephalic fluid shifts induced by suspension. MRI images visualizing the visual system morphology will also be collected from HLS and control animals at regular intervals. Retinal morphology and ultrastructure will be examined at specified intervals both during HLS and post-HLS recovery by both ophthalmic examinations and tissue histology evaluation. Changes in retinal/visual function will be regularly assessed electrophysiologically by measuring visual evoked potentials and electroretinograms.

This program will utilize both male and female subjects in order to examine possible gender differences in these responses. We will also examine the possible contributory factors of aging and elevated atmospheric carbon dioxide (hypercapnia) on to these responses of the visual system. Further, in addition to mimicking the effects of long duration exposure to microgravity through the use of the HLS model, we will examine the responses of our measured outcomes during long-term recovery in the post-HLS period. Collectively, these data will help allow us to develop a model to both understand and predict the etiology of changes in visual structure and function in astronauts exposed to the microgravity of spaceflight and during postflight recovery. In summary, our ultimate goal is to develop a translational mammalian model by which the data generated using this model can facilitate the development of countermeasures to alleviate any visual system decrements arising from exposure to the microgravity spaceflight environment.

During this initial period of performance, the research team has been hired and trained, major equipment purchased, and facilities set-up. We have put into place the core techniques and capabilities that will be necessary for the successful execution and completion of this program. This has included establishing a flow for the employment of the tail suspension model using the pigmented Long-Evans rat. While our initial subjects will be young males, we will also study cohorts of young females (to examine possible gender differences) and older males (to examine possible age effects). The cohort that presents the most significant response to HLS will be studied in a hypercapnic environment (similar to that experienced on the ISS). This will allow us to determine if there is a role of increased CO2 exposure in the etiology of these visual changes.

We are utilizing biotelemetry to record intracranial pressure. This has required working with the vendor to develop a custom redesign of the transmitters. The successful redesign is currently being evaluated and confirmed. We have taken this opportunity to refine our surgical implant technique. Additionally, we have extensively revised the data acquisition software, which has been necessary to both improve the ease and accuracy of data collection, as well as to tailor the system to meet the needs of this research program. The biotelemetry system will also be used to record evoked visual potentials. Having in situ leads will ensure the accuracy and reproducibility of measurements taken over the entire study (up to 180 days).

Additional measurements of visual system function will include complete ophthalmic clinical exams, measurement of intraocular pressure by tonometry, and, ultimately, tissue histology. The retinal imaging that will be performed during this program includes both fundus imaging with fluorescein angiography and OCT. The manufacturers of the equipment used to provide these images have both provided training sessions for team personnel. Additional practice sessions have been continued to ensure successful capture of images and a second training session has been scheduled with the OCT manufacturer.

This program is aimed at determining if long-term cephalic fluid shift can cause the effects seen on visual system structure and function during and after long-duration spaceflight. As such, animals will be exposed to HDT for a longer period of time than is utilized in most studies. We are working with the Biospecimen Sharing Program at Ames Research Center to ensure that tissues not utilized in our analyses will be available for other researchers, thus increasing the science yielded by this program.