Effect of constant light on rhythmic gastric functions in fasting rats

Abstract

The effects of four weeks of continuous illumination (LL), a subacute stress, on gastric mucosal endogenous aggressive and defensive factors were studied. Young male Sprague-Dawley rats were used with two different illumination regimens: LL and 12 hr light/12 hr dark (LD). At the end of three to four weeks of either regimen of illumination, gastric acid secretion, pepsin secretion, mucus secretion, and potential difference (PD) were studied. All gastric parameters, except mucus secretion, were significantly reduced by LL. The reduction in acid secretion (13.3%) was not significant after Bonferroni correction for the four t tests Pepsin secretion and PD were 27.9% and 24.6% less, respectively. These differences were significant after Bonferroni correction. The LD rats showed significant circadian rhythms for acid, mucus, and pepsin secretion. The LL rats showed significant rhythmicity for these same parameters with period lengths different from 24 hr. Gross inspection of the gastric mucosa indicated that 69.8% of the LL rats had lesion scores of 1.0 or higher, while none of the LD rats had scores above 0.5.

Relationship of work schedules to gastrointestinal diagnoses, symptoms, and medication use in auto factory workers

“…Previous research and theory concerning gastric and intestinal circadian rhythms provide some support for this interpretation [Tarquini et al, 1986;Vener et al, 1989;Larsen et al, 1994;Moore et al, 1994]. Evening shift phase delays the timing of sleep (go to bed later and get up later), which can change the relationship between the external light/ dark cycle cues and circadian system.…”

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

“…Pineal dependence of innate immunity has been inferred from a study which maintained hamsters in constant light, suppressing endogenous melatonin secretion (Yellon et al, 2005); pineal dependence of adaptive immunity has been inferred from an experiment which exposed pinealectomized hamsters to short days for 1 week prior to antigenic challenge (Yellon et al, 1999b). The interpretation of these studies is not straightforward, given that: (1) daily melatonin injections also render the circadian system in a SD-typical state (Puchalski and Lynch, 1988;Margraf and Lynch, 1993), (2) little is known regarding the significance of the amplitude of melatonin signals on immune function, and (3) constant light renders circadian rhythms in a free-running state, functions as a stressor, and can be immunosuppressive (Morimoto et al, 1975;Ramaley, 1977;Larsen et al, 1994;Liebmann et al, 1996). An alternative, and definitive, approach is to determine whether photoperiodic responses in the immune system endure following removal of the endogenous pineal melatonin signal (via surgical pinealectomy) and exposure to longer seasonal intervals of short days (>6 weeks).…”

Time-dependent exacerbation of amphetamine-induced taste aversions following exposure to footshock

“…Constant light has also been shown to decrease saccharin intake and sac charin preference (Rusak and Zucker 1974). In addition, constant light blocks the development of LiCl-induced CTA (Rusak and Zucker 1974), an effect possibly medi ated by alterations in intestinal acid secretion among ani mals housed under constant light (Larsen et al 1994). Because dexamethasone injections can alter the cortico sterone response to stressors depending upon the time in the light/davk cycle (Dunn and Carrillo 1978), it is diffi cult to interpret the meaning of Revusky and Reilly's (1989) data indicating that dexamethasone attenuated both morphine and cisplatin CTA.…”

“…This contrasts with earlier reports that dexamethasone attenuates both LiCl-and radiation-in duced CTA (Cairnie and Leach 1982;Smotherman 1986). More importantly, their animals were maintained on a constant light cycle, a treatment employed as a stressors itself (Larsen et al 1994). Constant light has also been shown to decrease saccharin intake and sac charin preference (Rusak and Zucker 1974).…”