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We report the presence of variations in the rate and direction of re-entrainment to acute simulated jet lag in wild-caught North Indian palm squirrels (Funambulus pennanti). Adult laboratory and wheel-acclimated (Lafayette, USA) males (N = 30) were entrained to a 12:12 h light/dark (LD) schedule, followed by a 9 h advance of the LD schedule to simulate acute jet lag. The direction and rate of re-entrainment, i.e. the number of orthodromic (advancing) and antidromic (delaying) transients, the acrophases of daily rhythms in each case, duration of activity (α) and phase angle relationship (ψ) were noted using Clocklab (Coulbourn, USA). The squirrels exhibited distinct variations in their response to simulated acute jet lag, re-entraining either slowly (14/30) or rapidly (10/30) by advancing transients, or undergoing antidromic re-entrainment slowly (5/30), and, in only one individual, rapidly. Acrophases re-entrained slower than onsets.αunderwent compression during re-entrainment, particularly during fast orthodromic responses.ψwas not significantly different in any of the groups before or after re-entrainment. This phenomenon has scope for further investigation and highlights the need for individual assessment of re-entrainment patterns before taking preventive measures for jet lag. [ABSTRACT FROM AUTHOR]

Photic phase response curves (PRCs) have been extensively studied in many laboratory-bred diurnal and nocturnal rodents. However, comparatively fewer studies have addressed the effects of photic cues on wild diurnal mammals. Hence, we studied the effects of short durations of light pulses on the circadian systems of the diurnal Indian Palm squirrel, Funambulus pennanti. Adult males entrained to a light-dark cycle (12 h-12 h) were transferred to constant darkness (DD). Free-running animals were exposed to brief light pulses (250 lux) of 15 min, 3 circadian hours (CT) apart (CT 0, 3, 6, 9, 12, 15, 18 and 21). Phase shifts evoked at different phases were plotted against CT and a PRC was constructed. F. pennanti exhibited phase-dependent phase shifts at all the CTs studied, and the PRC obtained was of type 1 at the intensity of light used. Phase advances were evoked during the early subjective day and late subjective night, while phase delays occurred during the late subjective day and early subjective night, with maximum phase delay at CT 15 (−2.04 ± 0.23 h), and maximum phase advance at CT 21 (1.88 ± 0.31 h). No dead zone was seen at this resolution. The free-running period of the rhythm was concurrently lengthened (deceleration) during the late subjective day and early subjective night, while period shortening (acceleration) occurred during the late subjective night. The maximum deceleration was noticed at CT 15 (−0.40 ± 0.09 h) and the maximum acceleration at CT 21 (0.39 ± 0.07 h). A significant positive correlation exists between the phase shifts and the period changes ( r = 0.684, p = 0.001). The shapes of both the PRC and period response curve (τRC) qualitatively resemble each other. This suggests that the palm squirrel's circadian system is entrained both by phase and period responses to light. Thus, F. pennanti exhibits robust clock-resetting in response to light pulses. [ABSTRACT FROM AUTHOR]

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.