CHALLENGES TO ASTRONAUT HEALTH CAUSED BY SPACEFLIGHT-RELEVANT STRESSORS WILL IMPACT SIGNALING PATHWAYS BETWEEN SYSTEMS ULTIMATELY LEADING TO DEGENERATIVE CHANGES AS HOMEOSTASIS IS IMPAIRED. FOR EXAMPLE CHANGES IN THE MICROBIAL ENVIRONMENT CAN RESULT IN DRAMATIC CHANGES IN VARIOUS INTERNAL AND EXTERNAL MICROBIOMES. BOTH PSYCHOLOGICAL AND PHYSIOLOGICAL STRESS ACTIVATES THE SYMPATHETIC NERVOUS SYSTEM (SNS) AND INITIATES WIDE-RANGING PHYSIOLOGIC CHANGES. THESE CHANGES HAVE SERIOUS IMPLICATIONS ON IMMUNE FUNCTION AND THE ACTIVATION OF INFLAMMATORY PATHWAYS. WE PROPOSE TO USE CENTRIFUGATION TO CHARACTERIZE THE IMPACT OF CHRONIC CHANGES IN THE GRAVITATIONAL ENVIRONMENT ON CROSS-SYSTEM COMMUNICATION. .WE HYPOTHESIZE THAT HYPER-GRAVITY INDUCED CHANGES IN GUT MICROBIOME SNS FUNCTION AND INFLAMMATORY ACTIVITY LEAD TO A BREAKDOWN IN THE COMMUNICATION BETWEEN DISTINCT PHYSIOLOGICAL SYSTEMS (AS MEASURED BY CHANGES IN CARDIOPULMONARY CONTROL); AND THAT THESE RESPONSES DEPEND ON THE GRAVITATIONAL ENVIRONMENT. FURTHERMORE WE PROPOSE THAT THESE GRAVITY-DEPENDENT DEFICITS CAN BE COUNTERED BY A COMBINATION OF PREBIOTIC NUTRITIONAL SUPPLEMENTS THAT ARE KNOWN TO PREFERENTIALLY EXPAND STRESS PROTECTIVE BACTERIAL SPECIES..SPECIFIC AIMS .SPECIFIC AIM 1. CONFIRM THAT CENTRIFUGATION RESULTS IN DETECTABLE CHANGES IN GUT MICROBIOME AS WELL AS IN SYMPATHETIC AND INFLAMMATORY ACTIVITY INDICATIVE OF INCREASED HEALTH RISK. MICE WILL BE PLACED ON THE 8 FT DIAMETER CENTRIFUGE AT AMES RESEARCH CENTER AND EXPOSED TO 1.5 OR 2 G FOR 4 WEEKS. AFTER CENTRIFUGATION ADRENAL GLANDS BLOOD LIVER SPLEEN AND INTESTINES WILL BE COLLECTED AND ASSESSED FOR CHANGES IN SYMPATHETIC AND INFLAMMATORY ACTIVITY AS WELL AS FOR CHANGES IN MICROBIOME AS COMPARED TO MATCHED 1 G CONTROLS. .SPECIFIC AIM 2. CONFIRM THAT PROLONGED EXPOSURE TO HYPER-GRAVITY LEADS TO A BREAKDOWN IN COMMUNICATION BETWEEN DISTINCT PHYSIOLOGICAL SYSTEMS CAUSING DECREMENTS IN FUNCTION. THE SAME MICE USED IN AIM 1 WILL BE USED HERE. OUR MODEL FOCUSES ON BRAINSTEM CONTROL OF CARDIOPULMONARY FUNCTION DRIVEN PRIMARILY BY SYMPATHETIC/VAGAL INNERVATION. THE BRAINSTEM SPINAL CORD HEART AND LUNGS WILL BE COLLECTED. ANALYSIS WILL FOCUS SPECIFICALLY ON THE NUCLEUS TRACTUS SOLITARII (NTS) THE FIRST-ORDER INTEGRATIVE SITE FOR VAGAL AFFERENTS PROJECTING FROM THE GUT HEART AND LUNGS TO THE CENTRAL NERVOUS SYSTEM. THE NTS COORDINATES EFFERENT OUTPUT TO TARGETS THAT ARE CRITICAL FOR THE CONTROL OF BREATHING HEART/VASCULATURE AND GUT. IN VIVO AND IN VITRO ELECTROPHYSIOLOGY WILL BE USED TO QUANTIFY CHANGES IN SYMPATHETIC TONE AND CONFIRM THAT SYNAPTIC ACTIVITY WITHIN THE NTS IS ALTERED BY CHANGES IN MICROBIOME. IMMUNOHISTOCHEMISTRY AND RNASEQ WILL BE USED TO ASSESS CHANGES IN INFLAMMATION AND STRESS-RELATED MESSAGE ALLOWING US TO DETERMINE THE ROLE CYTOKINES AND DOWNSTREAM EFFECTORS PLAY IN MODULATING NTS NEURONAL ACTIVITY CORRELATED WITH CARDIORESPIRATORY CONTROL. .SPECIFIC AIM 3. DETERMINE THAT CENTRIFUGATION-INDUCED CHANGES IN HEALTH STATUS SIGNALING ARE LINKED TO CHANGES IN MICROBIOME. BASED ON OUR PREVIOUS FINDINGS WE HYPOTHESIZE THAT INGESTION OF A PREBIOTIC SUPPLEMENT BLEND [GALACTOOLIGOSACCHARIDES (GOS) + POLYDEXTROSE (PDX) + LACTOFERRIN + MILK FAT GLOBULE MEMBRANE PROTEIN (MFGMP)] WILL BOTH PREVENT GUT MICROBIAL DYSBIOSIS PRODUCED BY CENTRIFUGATION AND INCREASE SELECTIVE STRESS PROTECTIVE GUT BACTERIA (I.E. LACTOBACILLUS AND BIFIDOBACTERIA). PREBIOTIC-ENRICHED CHOW OR CALORICALLY MATCHED CHOW WILL BE AVAILABLE AD LIBITUM THROUGHOUT THE EXPERIMENT STARTING 1 WEEK PRIOR TO CENTRIFUGATION. MICE WILL BE PLACED ON THE 8 FT DIAMETER CENTRIFUGE AT AMES RESEARCH CENTER AND EXPOSED TO 2 G FOR 4 WEEKS. PARAMETERS DESCRIBED IN AIMS 1&2 WILL BE ASSESSED AS DESCRIBED. .