Aging induces a range of physiological effects on the body, which includes gastrointestinal function and its microbiota. Studies of aged individuals and animals frequently reveal decreased transit and motility, which may contribute to the increased incidence of constipation in old age. The purpose of this study was to test whether the neuroactive microbe Lactobacillus rhamnosus (JB-1™) might reverse age-related hypomotility when added to the colon lumen. Our previous research with JB-1 has shown therapeutic effects in the treatment of stress-related dysmotility in adult mice (West et al. 2016), and we hypothesized that JB-1 might also have beneficial effects on motility in the aged colon. Ex-vivo colonic motility experiments were performed in an organ bath perfusion chamber using 4-cm colon segments from 18-month old CD1 male mice. The colon was cannulated at both the oral and anal ends and perfused luminally with a 34oC oxygenated Krebs buffer control, followed by intraluminal addition of 10E8 cfu/mL JB-1 in Krebs buffer applied for 30 min followed by Krebs only washout. Video recordings were converted to spatiotemporal maps (Dmaps), for which propagating contractile cluster (PCC) velocity, frequency, and amplitudes were measured and analyzed using paired t-tests for control and treatment groups. Previous research in our lab showed that for 1-year old mice PPC velocity, frequency, and amplitude were reduced by 47%, 54%, and 46% respectively in comparison to 2-month old mice (Kunze et al. 2014). JB-1 treatment of old-age mice increased PCC colonic velocity by 69% (N = 12, P = 0.002). PCC colonic frequency was increased by 22% (N= 12, P = 0.244) all within 15 min of application. PCC amplitude was increased by 16% (N= 12, P = 0.493) from controls. The results suggest that luminal Lactobacillus rhamnosus JB-1 application may help to reverse colon hypomotility dysfunction in old mice. Oral administration of JB-1 bacteria may have translational potential to improve constipation or hypomotility in old age. Kunze, W.A., Yan R.M., Min, K.K., Pasyk, M., Stanisz, A.M., & Zasloff, M. (2014). Squalamine reverses age and loperamide associated dysmotility in a mouse biomarker model of constipation. Gastroenterology146, S356. West, C., Wu, R.Y., Wong, A., Stanisz, A.M., Yan, R., Min, K.K., Pasyk, M., McVey-Neufield, K.A., Karamat, M.I., Foster, J.A., Bienenstock, J., Forsythe, P., & Kunze, W.A. (2016). Lactobacillus rhamnosus strain JB-1 reverses restraint stress-induced gut motility. Neurogastroenterol. Motil. Epub ahead of print: 1–11 [PMID: 27381257 DOI: 10.1111/nmo.12903] Natural Sciences and Engineering Research Council of Canada Discovery Grant (2014–05517)