A new hypertonic saline assay for analgesic screening in mice: effects of animal strain, sex, and diurnal phase

There exists a pressing need for the identification of novel analgesics. We recently reported on new preclinical assay rapid analgesic screening based intraplantar (i.pl.) injection 10% hypertonic saline (HS) in female outbred (CD-1) mice. Herein, we characterized HS assay’s performance inbred (C57BL/6) mice, sensitivity to sex differences, and effects diurnal rhythm phase. In randomized, controlled, blinded vivo animal experiments, studied nociceptive responses induced by i.pl. C57BL/6 (vs CD-1) mice both sexes (n = 240) determined phase animals. established morphine constructing dose-response curves calculating half-maximal inhibitory doses (ID50s). The produced (licking biting) all tested. CD-1 mean (95% confidence interval [CI]) response magnitudes were greater females vs males (C57BL/6: 87 sec [64 110] 45 [29 61]; difference means, 42 sec; 95% CI, 17 68; P < 0.001; n 10/group; CD-1: 110 [95 126] 53 [32 74]; 57 34 79; 10/group). CI) at 24:00 hr than 12:00 (64 [40 88] 37 [24 51]; 27 7 47; 0.007; 10/group), but not (P 0.97). Intravenous dose-dependently attenuated (ID50, 0.6 2.5 mg·kg−1, respectively; 0.41). These findings solidify utility as an effective, rapid, robust, versatile tool screening.