RESUMEN
Biological clocks help organism to adapt temporally to a variety of rhythmic environmental cues. Acute changes in the rhythmicity of entraining cues causes short- to long-term physiological distress in individuals, for example, those occurring during jet-lag after long-haul transmeridial flights, or shift work. Variations in the rate of re-entrainment to a 9 h advanced schedule (simulation of acute Jet-lag/shift work) in the Indian pygmy field mouse, Mus terricolor are reported. Wheel- and lab-acclimated adult male mice were entrained to a 12:12 h light:dark (LD) cycles, followed by a 9 h advance in the LD cycle. In response, these mice either advanced or delayed their activity onsets, with individual variation in the rate and direction. Rapid orthodromic (advancing) re-entrainers exhibited a coincidence of activity onsets with the new dark onset in <=3 days, while gradually advancing re-entrainers took ~9 days or more. Delayers (antidromic) also either re-entrained very rapidly (<=2 days), or gradually (~9 days). Acrophase measurement confirmed the direction of the transients, which did not depend on the free-running period. Such different patterns might determine the differential survival of individuals under the pressure of re-entrainment schedules seen in jet-lag and shift work.