Photic and nonphotic effects on the circadian activity rhythm in the diurnal rodent Arvicanthis ansorgei.

The main purpose of the study was to compare behavioural properties of entrainment to photic (30 min; 200lx) and nonphotic (melatonin: 1 h; 100 microg) stimuli in the diurnal rodent Arvicanthis ansorgei. Male animals (n=38) were used, and running wheel activity was recorded. Following entrainment to 12:12 h LD the animals were transferred to DD (dim red light) to freerun before treatment started. A phase response curve (PRC) to light was determined showing a phase delay region in the early subjective night (CT 8-16) and a phase advance region in the late subjective night (CT 18-4). Activity onset defined CT=0. Entrainment to daily phase advance and phase delay light pulses occurred at circadian phases corresponding to the respective phase shift regions of the PRC. Similarly, also entrainment to daily melatonin pulses occurred in two narrow time windows located near the beginning (CT 0) and the end of the subjective day (CT 10), but where light had a phase advance effect melatonin had a phase delay effect and vice versa. These results are consistent with the neurobiological model of Hastings et al. (Chronobiol Int 1998;15:425-445) on the differential effects of photic and nonphotic resetting cues on the circadian pacemaker.

Maternal nutritional knowledge and child nutritional status in the Volta region of Ghana.

The relationship between mother's nutritional knowledge, maternal education, and child nutritional status (weight-for-age) was the subject of investigation in this study. The data were collected in Ghana on 55 well nourished and 55 malnourished mother-child pairs. A questionnaire designed to collect data on mother's knowledge and practices related to child care and nutrition was administered to the mothers. Data on mother's demographic and socio-economic characteristics as well as child anthropometric data were also collected. A nutrition knowledge score was calculated based on mother's responses to the nutrition related items. Bivariate analysis gave significant associations between child nutritional status and the following variables: time of initiating of breastfeeding, mother's knowledge of importance of colostrum and whether colostrum was given to child, age of introduction of supplementary food, and mother's knowledge about causes of kwashiorkor. The two groups also showed significant differences in their nutrition knowledge scores. Maternal formal education, and marital status were also found to be associated with child nutritional status in bivariate analyses. Further analysis with logistic regression revealed that maternal nutrition knowledge was independently associated with nutritional status after the effects of other significant variables were controlled for. Maternal education on the other hand was not found to be independently associated with nutritional status. These results imply that mother's practical knowledge about nutrition may be more important than formal maternal education for child nutrition outcome.

Daily infusion of melatonin entrains circadian activity rhythms in the diurnal rodent Arvicanthis ansorgei.

The effect of exogenous melatonin (MEL) on the circadian system in nocturnal species has been extensively studied, but little is known about its chronobiotic effect in diurnal mammals. The present study investigated the effect of exogenous MEL on the circadian locomotor activity rhythm in the diurnal rodent Arvicanthis ansorgei. Male animals (n=34) were fitted with a subcutaneous catheter for daily infusion of MEL (1 h; 100 microg) and their running wheel activity was recorded. The results showed that administration of MEL to animals free-running in DD entrained their activity rhythm by phase advances at circadian time (CT) 10.62, and by phase delays at CT -0.40 (CT 0, activity onset). The range of entrainment was 17 and 11.5 min for advance and delay stimuli, respectively. Interestingly, in the nocturnal rat and the A. ansorgei, entrainment of the activity rhythm to exogenous MEL by phase advances occurs at exactly the same phase of the circadian cycle. In both nocturnal and diurnal species, the sensitivity window for exogenous MEL is located near the activity/rest transition points. It is concluded that the functional properties of entrainment to exogenous MEL are similar to those of other nonphotic stimuli. Furthermore, A. ansorgei might be an interesting animal model for studies on the chronobiotic effects of exogenous MEL in diurnal mammals including humans.

Entrainment of circadian activity rhythms in rats to melatonin administered at T cycles different from 24 hours.

Entrainment of running wheel activity in DD was studied in adult male Long Evans rats exposed to cycles of a constant dose of melatonin (MEL; 100 microg/h) infused subcutaneously. The period (T) of the MEL cycle was initially kept at 24 h until stable entrainment was established; T was then changed in a stepwise manner, and each new T value was maintained for at least 20 cycles. Entrainment by phase advance occurred near circadian time 12 (activity onset), and the range of entrainment was between 30 and 35 min. The negative phase angle difference between activity onset and MEL onset increased as T values approached the entrainment limit, whereas no change in the duration of daily activity periods was found. No difference was observed between pre- and posttreatment values of the endogenous circadian period; hence, no aftereffects were found for any T value. These results indicate that the functional properties of entrainment to MEL are similar to those of entrainment to light, suggesting that both zeitgebers share a common timing mechanism.