Use of the RatLoft™ in laboratory conditions decreases pup mortality in lactating mice
Mice in laboratory conditions are under considerable stress. Lactating dams may manifest this psychological distress through a decrease in milk yield or increase in pup mortality. The RatLoft™ is a stainless steel tube that hangs over the side of the cage with access to food, allowing the dam time away from her pups. Here, we examined the effect of the RatLoft™ on milk yield, circulating serotonin (5-HT), pup mortality, and behavioral distress as measured by the Porsolt Forced Swim Test (FST). Pregnant mice deficient for tryptophan hydroxylase-1 (TPH1-/-, n=10) and wild type mice (WT, n=10) were randomly assigned to loft (L; n=5) and no loft (NL; n=5) treatment groups. Milk yield was measured daily for 21d. The FST was performed on d10 and pup mortality was recorded throughout the experiment. Blood was collected on d1, 9, and 21. Data was analyzed using a two-way ANOVA. Milk yield increased over time in all animals (p<0.0001). Presence or absence of the RatLoft™ did not affect milk yield (p>0.05). Overall, WT mice had increased milk yield compared to TPH1-/- mice, regardless of the presence of RatLoft™ (p<0.05). The FST used to evaluate behavioral distress indicated that the presence or absence of RatLoft™ was not significant (p>0.05). Serum 5-HT concentrations were increased in WT compared to TPH1-/- mice. Presence or absence of the RatLoft™ did not affect circulating 5-HT concentrations (p>0.05, 373 vs. 309 ± 55 ng/mL), but 5-HT concentrations decreased throughout lactation (455 vs. 245 ± 65 ng/mL on d1 and 21, respectively). Serotonin concentrations were increased in TPH1-/- mice with the L (p<0.01; 33 ± 13 ng/mL vs. 13 ± 1.4 ng/mL). TPH1-/- mice with L had less 5-HT on d1 and d9 compared to d21 (p=0.005; 21 and 17 vs. 51 ± 6.5 ng/mL, respectively). 5-HT levels in TPH1-/- mice with NL did not change over time (p>0.05). Pup mortality was significantly less for dams with L as compared to mice with NL (p=0.047, 0.49 ± 0.16 pups/dam vs. 0.195 ± 0.06). Mortality rates were not different between WT and TPH1-/- mice (p>0.05). These results demonstrate that access to RatLoft™ during lactation decreases pup mortality rates in all animals, as well as increased 5-HT concentrations in TPH1-/- mice. In conclusion, use of the RatLoft™ could prove beneficial to researchers working with lactating mouse models to decrease pup mortality rates.
Keywords: serotonin, lactation, RatLoft™