Figure 2. Light evokes aversive but not pain-associated vocalizations in neonatal mice.

(A) Raster plots of the 62-kHz USVs from six wild type (WT) and six melanopsin-knockout (KO) pups during one-minute periods before, during and after light exposure. Each tick represents a 62-kHz USV of an individual pup. (B) Percent responders to one-minute light were qualitatively assessed during the experiments. Locomotor response was considered positive if a pup turned around or produced vigorous head pivoting in response to light. No or very little movement was present in either WT or KO pups during one minute prior to light onset. Vocalization response was positive if a pup noticeably increased the number of 62-kHz USVs during exposure to light as compared to baseline. (C) Average number of 62-kHz USVs in the minute prior to turning light on (Dark) and during 1 minute of light (Light) in WT (n = 22) and KO (n = 13,) pups. The asterisk (*) indicates p<10⁻⁵. (D) Average number of 5-kHz squeals in the minute before and 1 minute after the onset of light or tail pinch in WT (n = 8) and KO (n = 10) pups. No 5-kHz squeals were present at any time during isolation, acclimation and light stimulation. Data are presented as mean values ± SEM.