Raúl Aguilar-Roblero

Persistence of metabolic rhythmicity during fasting and its entrainment by restricted feeding schedules in rats

The presence of a food-entrainable oscillator (FEO) independent from the SCN is now well established, but until now its location and characterization have been elusive. Because its expression requires priming of the animals metabolism toward a catabolic state, it is possible that metabolic rhythms may be related to FEO. The present study was designed to determine whether metabolic rhythms persist during fasting and whether such rhythms could be entrained to a restricted feeding schedule. The results indicate persistent rhythms of triacylglycerides, free fatty acids, glucose, and proteins during fasting, whereas ketone bodies and liver glycogen changed their concentration as a function of fasting. Daily food pulses of 2 h entrained the rhythms of triacylglycerides and free fatty acids and restored ketone bodies and liver glycogen to similar levels as controls. Neither glucose nor proteins were affected by the food pulse. These results indicate the relevance of lipid metabolism as a phenomenon associated with the FEO.The presence of a food-entrainable oscillator (FEO) independent from the SCN is now well established, but until now its location and characterization have been elusive. Because its expression requires priming of the animals metabolism toward a catabolic state, it is possible that metabolic rhythms may be related to FEO. The present study was designed to determine whether metabolic rhythms persist during fasting and whether such rhythms could be entrained to a restricted feeding schedule. The results indicate persistent rhythms of triacylglycerides, free fatty acids, glucose, and proteins during fasting, whereas ketone bodies and liver glycogen changed their concentration as a function of fasting. Daily food pulses of 2 h entrained the rhythms of triacylglycerides and free fatty acids and restored ketone bodies and liver glycogen to similar levels as controls. Neither glucose nor proteins were affected by the food pulse. These results indicate the relevance of lipid metabolism as a phenomenon associated with the FEO.

Fetal suprachiasmatic nucleus transplants: diurnal rhythm recovery of lesioned rats

The diurnal rhythm organization of drinking behavior was determined prior to and after suprachiasmatic nucleus (SCN) lesions. Five weeks after SCN lesions which produced total loss of the diurnal rhythm, the anterior hypothalamus including the SCN of fetal rats was transplanted into the floor of the 3rd ventricle of the lesioned rats. Eight weeks after the graft, rats recovered their rhythm. The results show that grafts allow animals to recover lost functional properties due to lesions, and further support the notion that the SCN is a pacemaker for certain behaviors.

Circadian rhythmicity in the GABAergic system in the suprachiasmatic nuclei of the rat

The participation of GABAergic mechanisms in the regulation of circadian rhythmicity by the suprachiasmatic nuclei (SCN) has been suggested from different lines of evidence. Little is known, however, whether GABA synthesis, release, uptake or content within the SCN may show a circadian pattern. The present results show that the activity of the GABAergic system within the SCN region of the rat exhibits circadian rhythmicity, which is manifested by correlative changes of the GABA content and the glutamic acid decarboxylase activity under the light/dark cycle, and by changes in the GABA content in animals kept under constant darkness.

The siesta culture concept is not supported by the sleep habits of urban Mexican students

Evidence in support for the concept of the so‐called ‘siesta culture’ is not well developed and has, to date, relied largely on qualitative anthropological data. Presumably such cultures are characterized by a strong tendency for daytime naps and daytime sleepiness, phenomena which may partially represent the effects of geographic, climatic or light conditions and/or cultural influences. In this study we surveyed the nocturnal sleep habits and daytime sleep tendencies of 577 Mexican college students residing in Mexico City (19°N latitude). Results indicated a number of parallels between the reported sleep habits of these students and those reported from other cultures at latitudes far to the north (North America, Europe), such as longer sleep at the weekends, an association between snoring and daytime sleepiness and a lack of relationship between nocturnal sleep duration and the reported tendency to nap. There was some suggestion that these Mexican students may actually nap less when compared to other college student populations. Taken together, these results call into question what is meant by the concept of a ‘siesta culture’, at least in this urban, educated, upper social economic scale (SES) population, and suggest that future studies in equatorial regions be undertaken to further appreciate the role of climate, photoperiod and/or culture in the tendency for humans to nap during the day.

Morphological Correlates of Circadian Rhythm Restoration Induced by Transplantation of the Suprachiasmatic Nucleus in Hamsters

A compelling body of evidence indicates that the suprachiasmatic nucleus (SCN) of the hypothalamus is a pacemaker in the rodent circadian timing system. Two important components of this evidence are studies showing that SCN lesions abolish circadian rhythms and others demonstrating restoration of circadian activity rhythms after transplantation of fetal SCN into the brains of arrhythmic hosts. In the present study, we evaluated what has remained a persisting issue in this transplant literature, the extent to which the exact localization and organization of the transplants is critical to their capacity to restore circadian function in the hamster. The data obtained indicate that the location of the graft in the ventricular system is not crucial to outcome. Grafts in the lateral ventricle, dorsal third ventricle, interventricular foramen, and caudal third ventricle are as capable of restoring circadian function as ones placed in the ventral third ventricle in the vicinity of the lesion. Restoration of rhythmicity does require that the grafts contain a minimum volume of SCN-like tissue as defined by cytoarchitecture and the presence of vasopressin--and vasoactive intestinal polypeptide (VIP)--immunoreactive cells and fibers. There is also an indication that VIP-immunoreactive elements are the component critical to functional recovery. Connections between graft and host are evident in the immunohistochemical material but are quite variable in extent and often very limited. Thus, the data obtained in this study are consistent with the view that restoration of circadian function by fetal grafts requires the presence of SCN, and probably VIP-containing neurons, but does not depend upon the exact location of the graft or the presence of specific connections between graft and host.

Fetal brain transplants induce recuperation of taste aversion learning.

Rats showing disrupted taste aversion due to gustatory neocortex or amygdala lesions were transplanted into the lesioned area with homologous brain tissue obtained from 17-day-old fetuses. Comparisons of taste aversions scores before and after the graft, revealed that the grafted animals significantly recuperated taste aversions, whereas cortical lesioned animals without grafts did not. Surprisingly, however, amygdala-lesioned animals without graft presented spontaneous recovery. These results not only support the hypothesis that fetal brain transplants can restore cognitive functions, but also that there are some fundamental functional differences between the gustatory neocortex and the amygdala in the regulation of the processes involved in the acquisition and retention of taste aversion.

Organization of circadian rhythmicity and suprachiasmatic nuclei in malnourished rats

The present study was aimed at characterizing the effects of low-protein malnutrition (6% casein) on the circadian rhythm of drinking behavior and on suprachiasmatic nuclei immunohistochemistry in Sprague-Dawley rats. Recordings were started at 30 days of age under a 12:12-h light-dark (LD) cycle. At age 150 days, recordings were continued under constant dim red light, and finally the latency to entrain to complete and skeleton photoperiods was established. At the end of the recordings rats were processed for histological analysis. Compared with their controls, malnournished rats exhibited 1) splitting of rhythmicity under LD that 2) condensed to one component in constant dim red light, 3) delayed entrainment to skeleton photoperiod, and 4) precocious entrainment under complete photoperiod. Immunohistochemical analysis showed mainly a decrease in the immunohistochemical detection of vasoactive intestinal polypeptide and glial fibrillar acid protein cells in malnourished animals. These results indicate that in malnourished rats there is a decrease 1) in the coupling force among the oscillators and 2) in the strength of the phase lock between the oscillators and the light-dark cycle.

Metabolic correlates of the circadian pattern of suckling-associated arousal in young rabbits

Abstract Young rabbits (Oryctolagus cuniculus) are only nursed for 3–5 min every 24 h. They show a circadian increase in activity in anticipation of this, which is entrained by suckling. Our aim was to determine whether serum and liver metabolites show diurnal fluctuations which could act to regulate this circadian pattern. Stomach weight, liver glycogen and serum metabolites were measured every 3 h in 7- to 8-day-old pups when normally nursed (up to 24 h after suckling) and fasted (up to 48 h after suckling). The results suggest:

c-fos proto-oncogene change in relation to REM sleep duration

Auditory stimulation has been shown to increase REM sleep periods in cats and humans. This effect has been attributed to an elevation of the level of excitability in a variety of brain stem neuronal groups. Fos-like immunostaining (FLI) has been useful in constructing maps of post-synaptic neuronal activity with single cell resolution, and has been suggested to be tightly correlated with ongoing neuronal activity. This study used FLI to quantify neurons from structures expressing c-fos in brain stem areas in animals with normal REMs and compared them with those showing extended REM periods. The results basically indicated that brain stem areas which in other studies have been described as having REM-ON cells, showed an increase in FLI, while no FLI changes occurred in areas described as having REM-OFF cells. These results are discussed in terms of the possibility that REM maintenance is related to a widespread increase in brain stem excitability.

Circadian modulation of the ryanodine receptor type 2 in the SCN of rodents.

We examined the temporal modulation of intracellular calcium release channels in the suprachiasmatic nucleus (SCN). We found a circadian rhythm in [3H]ryanodine binding that was specific to the SCN. The peak in the rhythm occurred at CT 7 and was due to an increase in Bmax, which correlated well with immunoblots showing an increase in RyR-2 expression in the SCN. Double immunohistochemical studies showed that RyR-2 was expressed exclusively in neurons. Ryanodine and caffeine applied around CT 7-9 advanced the clock phase in a hamster brain slice preparation. No rhythm of IP3R was seen in any of the brain areas studied. Our results indicate that RyR-2 exhibits an endogenous rhythm, which influences the intracellular calcium dynamics and thus modulates SCN activity.