Palaeoclimatic changes resulted in range expansion and subsequent divergence in brown fur seals, Arctocephalus pusillus

Past climatic change as a driving force of marine diversification is still largely unclear, particularly for Southern Hemisphere species. Here, we present a case using the brown fur seal, Arctocephalus pusillus, assessing the geographical structure and demographic history using mitochondrial and nuclear data. Results show the two previously defined subspecies (one from Australia and the other from southern Africa) are phylogeographically distinct. Migration analyses based on nuclear data suggest the absence of migrants among the two genetically close assemblages. The demographic history of A. pusillus is characterized by a glacial population expansion (approx. 18 kya) in the southern African lineage, which coincides with time estimates of population expansion of prey species of seals. Approximate Bayesian calculations support an eastward dispersal event during the Last Glacial Maximum when sea levels were lower, followed by a postglacial divergence event, approximately 13 kya. The demographic history of the brown fur seal in the Southern Oceans provides support that recent palaeoclimatic changes could have facilitated expansions in some marine species and that postglacial sea-level rise may have acted as a dispersal barrier for species mostly confined to continental shelves.

South African cardiovascular risk stratification guideline for non-cardiac surgery

Executive summary The South African (SA) guidelines for cardiac patients for non-cardiac surgery were developed to address the need for cardiac risk assessment and risk stratification for elective non-cardiac surgical patients in SA, and more broadly in Africa.The guidelines were developed by updating the Canadian Cardiovascular Society Guidelines on Perioperative Cardiac Risk Assessment and Management for Patients Who Undergo Non-cardiac Surgery, with a search of literature from African countries and recent publications. The updated proposed guidelines were then evaluated in a Delphi consensus process by SA anaesthesia and vascular surgical experts. The recommendations in these guidelines are:1. We suggest that elective non-cardiac surgical patients who are 45 years and older with either a history of coronary artery disease, congestive cardiac failure, stroke or transient ischaemic attack, or vascular surgical patients 18 years or older with peripheral vascular disease require further preoperative risk stratification as their predicted 30-day major adverse cardiac event (MACE) risk exceeds 5% (conditional recommendation: moderate-quality evidence).2. We do not recommend routine non-invasive testing for cardiovascular risk stratification prior to elective non-cardiac surgery in adults (strong recommendation: low-to-moderate-quality evidence).3. We recommend that elective non-cardiac surgical patients who are 45 years and older with a history of coronary artery disease, or stroke or transient ischaemic attack, or congestive cardiac failure or vascular surgical patients 18 years or older with peripheral vascular disease should have preoperative natriuretic peptide (NP) screening (strong recommendation: high-quality evidence).4. We recommend daily postoperative troponin measurements for 48 - 72 hours for non-cardiac surgical patients who are 45 years and older with a history of coronary artery disease, or stroke or transient ischaemic attack, or congestive cardiac failure or vascular surgical patients 18 years or older with peripheral vascular disease, i.e. (i) a baseline risk >5% for MACE 30 days after elective surgery (if no preoperative NP screening), or (ii) an elevated B-type natriuretic peptide (BNP)/N-terminal-prohormone B-type natriuretic peptide (NT-proBNP) measurement before elective surgery (defined as BNP >99 pg/mL or a NT-proBNP >300 pg/mL) (conditional recommendation: moderate-quality evidence).Additional recommendations are given for the management of myocardial injury after non-cardiac surgery (MINS) and medications for comorbidities.

Photoperiod differentially regulates clock genes' expression in the suprachiasmatic nucleus of Syrian hamster

The suprachiasmatic nuclei (SCN) contain the master circadian pacemaker in mammals. Generation and maintenance of circadian oscillations involve clock genes which interact to form transcriptional/translational loops and constitute the molecular basis of the clock. There is some evidence that the SCN clock can integrate variations in day length, i.e. photoperiod. However, the effects of photoperiod on clock-gene expression remain largely unknown. We here report the expression pattern of Period (Per) 1, Per2, Per3, Cryptochrome (Cry) 1, Cry2, Bmal1 and Clock genes in the SCN of Syrian hamsters when kept under long (LP) and short (SP) photoperiods. Our data show that photoperiod differentially affects the expression of all clock genes studied. Among the components of the negative limb of the feedback loop, Per1, Per2, Per3, Cry2 but not Cry1 genes show a shortened duration of their peak expression under SP compared with LP. Moreover, mRNA expression of Per1, Per3 and Cry1 are phase advanced in SP compared with LP. Per3 shows an mRNA peak of higher amplitude under SP conditions whereas Per1 and Per2 peak amplitudes are unaffected by photoperiod changes. Bmal1 expression is phase advanced without a change of duration in SP compared with LP. Furthermore, the expression of Clock is rhythmic under SP whereas no rhythm is observed under LP. These results, which provide further evidence that the core clock mechanisms of the SCN integrate photoperiod, are discussed in the context of the existing molecular model.

The circadian clock, light/dark cycle and melatonin are differentially involved in the expression of daily and photoperiodic variations in mt(1) melatonin receptors in the Siberian and Syrian hamsters

Mechanisms underlying the daily and photoperiodic variations in mt(1) melatonin receptors were investigated in the pars tuberalis (PT) and suprachiasmatic nuclei (SCN) of Siberian and Syrian hamsters. Whatever its daily profile, melatonin receptor density was strongly increased in both structures and species after constant light exposure or pinealectomy, and decreased after a single melatonin injection, indicating melatonin involvement in the daily regulation of the receptor protein. This was confirmed by a strong inverse correlation between melatonin binding capacity and plasma melatonin concentration. In contrast, regulation of mt(1) mRNA appeared more complex. The circadian clock, the light/dark cycle and melatonin are all implicated in mt(1) gene daily fluctuations, but the extent of their involvement depends upon the structure and the species studied. The photoperiodic decrease in melatonin receptor density observed in short photoperiod (PT of the two hamster species and Syrian hamster SCN) seems to be the consequence of a long-term mt(1) gene repression induced by the lengthening of the melatonin peak. Altogether, these results show that during daily variations, mt(1) melatonin receptor mRNA and protein are differentially regulated, while at the photoperiodic level, the mt(1) protein status depends on mRNA transcription.

Day-night pattern of energy expenditure and body temperature in cachectic tumour-bearing rats

The implication of an increase in energy expenditure in cancer cachexia, which seems to be related to the type of tumour, remains unclear. We therefore investigated the energy metabolism and body temperature in anorectic and cachectic rats bearing the Yoshida sarcoma (TB), in comparison with pair-fed (PF) and ad-libitum fed (AL) control rats. The resting energy expenditure was higher in the TB than in the two control groups when corrected for the modifications of body composition. However, the total energy expenditure did not differ between the TB and the AL, presumably because of the drop of activity in TB. There was a temporal distribution of differences in energy expenditure with higher energy expenditure in TB than in AL during the diurnal phase and a lack of difference during the nocturnal phase. The TB presented a fever, which was limited to the diurnal period. Moreover, the acrophase of the body temperature rhythm was delayed in the TB. These results highlight the circadian effects of tumour development on the energy metabolism of the host and hint to the possible implication of cytokines.

Potentiation effect of vasopressin on melatonin secretion as determined by trans-pineal microdialysis in the Rat

The mammalian pineal gland is known to receive a noradrenergic innervation originating from the superior cervical ganglion which corresponds to the primary regulatory input for melatonin synthesis. However, many peptidergic fibers containing peptides such as vasopressin and oxytocin have also been found in the rat pineal gland. The present study was performed to investigate the possible role of vasopressin and oxytocin on melatonin secretion in vivo. Therefore, both neuropeptides were delivered for 2 h through a trans-pineal microdialysis probe directly into the gland at different times during the nocturnal phase of the light:dark cycle. At the same time pineal dialysates were collected continuously. Melatonin concentrations were measured by radioimmunoassay. Melatonin synthesis potentiation was achieved when vasopressin was infused locally in the pineal, during the onset of nocturnal melatonin secretion. In order to assess the possible role of a physiological increase of endogenous circulating vasopressin on pineal metabolism, melatonin synthesis was recorded in the same animals before and after a prolonged dehydration period. Night time melatonin concentration was increased after the water deprivation vs control conditions. Contrary to that, oxytocin seems not to affect pineal metabolism in the rat since no significant change was observed on melatonin secretion in response to a local oxytocin infusion. These results show that vasopressin can modulate melatonin synthesis in the rat pineal whereas no effect was obtained with oxytocin, at least under the present experimental conditions.

Interindividual differences in the pattern of melatonin secretion of the Wistar rat

In vivo trans-pineal microdialysis was performed in male Wistar rats maintained under a 12 hr light:12 hr dark (LD 12:12) cycle. Collected dialysates were assayed by radioimmunoassay for melatonin concentrations. A non-linear regression was fitted through the obtained datapoints to determine the time points at which a 50% increase (IT50) and decrease (DT50) of the nocturnal melatonin peak were reached. In a first experiment, the nocturnal melatonin profiles of four animals were determined throughout 5 consecutive days. In a second experiment, we analysed the melatonin profiles during the night in rats originating from three different breeding colonies (Dépré Harlan, and Iffa-Cŕedo). A low intraindividual variability was found on the phase markers IT50 and DT50, as on peak duration of melatonin rhythms estimated over 5 subsequent days in the same animal. In contrast, animals showed a large interindividual variability in their profile phase markers and the values were dependent on the origin of the breeding colony. Each rat colony was characterized by early or late IT50 and DT50 as long or short peak length. It is concluded from experiment 1 that the melatonin rhythm is a very stable circadian marker. Nevertheless, great caution must be taken in the choice of animal groups while studying circadian rhythms due to the large interindividual variability observed in experiment 2. Therefore, as the technique allows the use of the animal as its own control, the present study demonstrated that the use of the microdialysis technique is of interest in studies on the circadian system.

Organization of rat circadian rhythms during daily infusion of melatonin or S20098, a melatonin agonist

Daily administration of melatonin or S20098, a melatonin agonist, is known to entrain the free-running circadian rhythms of rats. The effects of the duration of administration on entrainment were studied. The animals demonstrated free-running circadian rhythms (running-wheel activity, body temperature, general activity) in constant darkness. Daily infusions of melatonin or S20098 for 1, 8, or 16 h entrained the circadian rhythms to 24 h. Two daily infusions of 1 h (separated by 8 h) entrained the activity peak within the shorter time interval. The entraining properties of melatonin and S20098 were similar and were affected neither by pinealectomy nor by infusion of 1- or 8-h duration. However, with 16-h infusion, less than half of the animals became entrained. Once entrained, the phase angle between the onset of infusion and the rhythms (onset of activity or acrophase of body temperature) increased with the duration of infusion. Before entrainment, the free-running period increased with the duration of infusion, an effect that was not predictable from the phase response curve.

Photoperiodic control of the rat pineal arylalkylamine-N-acetyltransferase and hydroxyindole-O-methyltransferase gene expression and its effect on melatonin synthesis

Photoperiodic changes of pineal melatonin (MEL) profile are accompanied by parallel changes of arylalkylamine-N-acetyltransferase (AA-NAT) activity. In the present study, the authors investigated, for the first time, whether two other important variables of pineal metabolism, AA-NAT and hydroxyindole-O-methyltransferase (HIOMT) gene expression, also may be affected by the photoperiod. Evening rises in AA-NAT and HIOMT mRNA and in circulating MEL occurred concomitantly with an increased delay from dark onset as scotophase shortened. On the opposite, the morning declines of all three variables occurred with different kinetics but were locked to light onset. These observations demonstrate that the daily rhythms in AA-NAT and HIOMT gene expression are modulated by the photoperiod and bring further evidence in favor of nor adrenaline as the possible link between the endogenous clock and MEL. Interestingly, the duration of the nocturnal peak in HIOMT mRNA was positively correlated with HIOMT activity. In conclusion, this study adds two important links to the chain of mechanisms involved in the photoperiodic control of pineal metabolism. First, photoperiodic modulation of the MEL rhythm primarily results from changes in the AA-NAT gene expression. Second, the photoperiodic regulation of HIOMT activity occurs at the transcriptional level.

Daily variations in pineal melatonin concentrations in inbred and outbred mice

Melatonin was measured using a specific radioimmunoassay in 1 strain of outbred mice (OF1 Swiss) and 4 strains of inbred mice, 2 of them being known to synthesize melatonin (CBA and C3H) and the 2 others being controversial (BALB/c and C57BL/6). In this study, the 5 mouse strains were able to synthesize melatonin, but the basal levels as well as the diurnal variations were very different from one strain to another. CBA and C3H strains showed a clear-cut day-night rhythm of pineal melatonin concentration, with peak levels of 276 +/- 22 pg/pineal in CBA and 135 +/- 12 pg/pineal in C3H. In BALB/c, the authors confirmed the presence of a very short melatonin peak (15 min) in the middle of the dark period. In C57BL/6 and OF1 Swiss, a very small but significant peak was observed in the middle of the darkness. In the former, another small peak was also observed at light onset. Whether these very small peaks, which may be related to the deficience of N-acetyl transferase activity reported by others, have a physiological meaning remains to be determined.

Determination of vitamin A in milk and flour consumed by one- to four-year-old children in Côte d'Ivoire

As part of a United Nations Children's Found (UNICEF) study, an analytical method is proposed for routine analysis of vitamin A in milk and flour consumed by 1- to 4-year-old children in Côte d'Ivoire. The method involves liquid-liquid extraction of sample followed by reversed-phase liquid chromatography (LC). The method has been validated and used to analyze various samples collected at different locations and stored under unfavorable conditions. Average vitamin A content was 575 micrograms/100 g for milk powder and 1350 micrograms/100 g for millet flour. Lower contents were found in corn flour (40-240 micrograms/100 g), and no vitamin A could be detected in rice flour.

Brown fat thermogenesis in rats fed high-fat diets enriched with n-3 polyunsaturated fatty acids

OBJECTIVE

To examine the possible involvement of an increase in diet-induced thermogenesis from brown adipose tissue (BAT) in the n-3 polyunsaturated fatty acids (n-3 PUFA) induced limitation of the development of white fat pads during high-fat feeding.

DESIGN

Rats fed for four weeks on a low-fat/high-carbohydrate diet (C group) or high-fat diet without n-3 PUFA (REF group), with eicosapentaenoic acid (EPA group), with docosahexaenoic acid (DHA group) or with a mixture of these two fatty acids (MIX group).

MEASUREMENTS

Epididymal and retroperitoneal fat pad mass, BAT composition, Guanosine 5'-diphosphate (GDP) binding and uncoupling protein (UCP) content were measured in the five groups of rats.

RESULTS

The masses of retroperitoneal and epididymal white fat pads were lower in the groups fed n-3 PUFA than in the C and REF groups. The total BAT GDP binding was 1.6 times higher in the MIX and EPA groups than in the REF group. The BAT from the EPA group presented an enrichment in mitochondria compared to the C and REF groups whereas the BAT from the DHA and REF groups presented a hyperplasia and an increase in thermogenic activity of the mitochondria compared to the C group. The higher thermogenic activity of BAT was observed in the MIX group and is due to hyperplasia and to an increase in thermogenic activity of mitochondria.

CONCLUSIONS

n-3 PUFA induce a marked stimulation of BAT thermogenic activity without changes in the UCP content compared to a high-fat diet without n-3 PUFA. The mixture of EPA and DHA has the more pronounced effect while EPA and DHA seem to act in synergy on BAT thermogenesis via different mechanisms.

Fos-like immunoreactivity in the circadian timing system of calorie-restricted rats fed at dawn: daily rhythms and light pulse-induced changes

Daily rhythms of pineal melatonin, body temperature, and locomotor activity are synchronized to the light-dark cycle (LD) via a circadian clock located in the suprachiasmatic nuclei (SCN). A timed caloric restriction in rats fed at dawn induces phase-advances and further phase-stabilization of these rhythms, suggesting that the circadian clock can integrate conflicting daily photic and non-photic cues. The present study investigated the daily expression of Fos-like immunoreactivity (Fos-ir) and light pulse-induced Fos-ir in the SCN, the intergeniculate leaflet (IGL) and the paraventricular thalamic nucleus (PVT) in calorie-restricted rats fed 2 h after the onset of light and in controls fed ad libitum. A daily rhythm of Fos-ir in the SCN was confirmed in control rats, with a peak approximately 2 h after lights on. At this time point (i.e. just prior to the feeding time), the level of SCN Fos-ir was lowered in calorie-restricted rats. Concomitantly, IGL Fos-ir was higher in calorie-restricted vs. control rats. In response to a light pulse during darkness, Fos-ir induction was found to be specifically (i.e. phase-dependently) lowered in the SCN and IGL of calorie-restricted rats. Observed changes of Fos-ir in the PVT were possibly related to the wake state of the animals. This study shows that repetitive non-photic cues presented in addition to a LD cycle affect the Fos expression in the circadian timing system.

Lesion of the serotonergic terminals in the suprachiasmatic nuclei limits the phase advance of body temperature rhythm in food-restricted rats fed during daytime

The daily rhythm of body temperature was recorded in control rats fed ad libitum and subsequently fed during daytime 50% of ad libitum food intake. Aside from the expression of a feeding-associated component, body temperature rhythm was phase advanced (7 h) by a timed caloric restriction; the new plateau of the acrophase of the nocturnal peak was close to the light-dark transition. A lesion of serotonergic (5-HTergic) terminals in the suprachiasmatic nuclei (SCN)-the endogenous circadian clock(s)-was performed by microinjection of the 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). During the ad libitum-fed state, the acrophase of body temperature rhythm was not modified by the 5,7-DHT treatment. In response to a timed caloric restriction, however, the phase advance of the nocturnal peak of body temperature rhythm was reduced by 2 h in rats with 5,7-DHT lesions as compared to that of sham-operated rats. Magnitude and day-night pattern of wheel-running activity between the two groups of rats also were analyzed. No intergroup difference was found in the amount of wheel-running activity prior to the time of feeding. Moreover, the phase advance of nocturnal component of locomotor activity rhythm observed toward the time of feeding in sham-operated rats was limited by 5,7-DHT treatment. It is concluded that the photic synchronization of body temperature rhythm does not depend on the 5-HTergic projection to SCN under ad libitum conditions. By contrast, the phase-advancing property of a timed caloric restriction on the daily rhythm of body temperature is mediated by a neuronal circuit involving the 5-HTergic projection to SCN. That the phase advance was not fully eliminated by 5,7-DHT treatment suggests that other pathways participate in this mediation.

Environmental control of the seasonal variations in the daily pattern of melatonin synthesis in the European hamster, Cricetus cricetus

Nocturnal patterns of pineal melatonin concentrations were measured at hourly intervals in the European hamster, Cricetus cricetus, maintained under different natural or experimental environmental conditions. There were pronounced variations in the night peak of pineal melatonin both in the duration and the amplitude of the melatonin peak and in the onset and decline of melatonin synthesis. The duration of the melatonin peak increased proportionally with increased dark period. The amplitude increased abruptly from LD 16/8 to LD 15/9 and remained constant in all other photoperiods. The onset of synthesis started 6:00 hours after the onset of darkness in LD 16/8, 15/9, and 14/10, while it started 4:00 hours after dark onset in shorter photoperiods (LD 12/12 and 10/14). This result is opposite to that observed in the rat. The decline of synthesis was delayed as darkness increased and was directly related to lights on in long photoperiods, while it was endogenous in short photoperiods. Temperature, under a long photoperiod, also seems to be implicated in the regulation of the amplitude of the melatonin peak.

Effect of prolonged fasting and subsequent refeeding on free-running rhythms of temperature and locomotor activity in rats

This study investigated the possible effect(s) of prolonged fasting and subsequent ad lib refeeding on the circadian organization of rats kept in constant darkness. Free-running rhythms of wheel-running activity and body temperature were studied in rats fasted during a 7-day interval followed with ad lib refeeding started either at subjective midday, i.e., CT6 (circadian time 6) or subjective midnight, i.e., CT18. Phase-shifts of temperature acrophases were similar to those of activity acrophases. During fasting, phase-shifts were phase-advanced (1 circadian h on the average) in most cases. During refeeding, they were mostly phase-delays (2 circadian h on the average) independently of the circadian time of refeeding, i.e., ad lib refeeding did not act as a Zeitgeber. In conclusion, prolonged fasting and subsequent refeeding induce opposite effects on the circadian organization.

Phase-advanced daily rhythms of melatonin, body temperature, and locomotor activity in food-restricted rats fed during daytime

This study was performed to investigate possible effects of a timed caloric restriction on the light-dark (LD) synchronization of four biological rhythms pair-studied in the same animals. In Experiment 1, food-restricted rats kept under a photoperiod of 12 h light:12 h dark received 50% of previous ad libitum food 2 h after the onset of light. Their daily rhythm of pineal melatonin and rhythms of plasma melatonin and corticosterone were examined and compared to those of ad libitum control rats after 1 or 2 months of food restriction. A significant phase advance (about 2 h) was found for the pineal melatonin rhythm and for the daily onset of plasma melatonin. Timing of nocturnal peak of circulating corticosterone was unchanged, and a diurnal peak anticipated food presentation by about 2 h. In Experiment 2, effects of a timed caloric restriction under 12L:12D were studied on the expression of daily rhythms of body temperature and locomotor activity. To discriminate between the effects of timed meal feeding and those of the added caloric restriction, these rhythms were analyzed in food-restricted rats, as in Experiment 1, and were compared to those in sham-restricted rats, concomitantly fed twice more than food-restricted rats (i.e., a timed meal feeding without caloric restriction). Acrophase of the nocturnal peak of body temperature rhythm reached the greatest phase advance (7 h) in food-restricted rats, in which it was close to LD transition. The nocturnal component of locomotor activity rhythm also was markedly phase advanced (6 h) by caloric restriction, as indicated by wheel-running and general activity occurring form early afternoon to midnight. A smaller 4-h phase advance of the nocturnal peak of body temperature also was observed in sham-restricted rats, although the onset of locomotor activity rhythm apparently was unaffected by meal feeding and the end of activity rhythm was phase advanced by 2 h. These results indicate that timed caloric restriction is a potent phase-shifting agent that interacts with the LD cycle zeitgeber. This nonphotic stimulus phase advances melatonin, corticosterone, body temperature, and activity rhythms to different extents and thus suggests a change in the internal synchronization of the circadian system.

Single-dose benzathine penicillin in infants at risk of congenital syphilis--results of a randomised study

OBJECTIVE

To determine the efficacy of single-dose benzathine penicillin G in infants at high risk of congenital syphilis.

DESIGN

Randomised study comparing benzathine penicillin with no therapy.

SETTING

Peninsula Maternal and Neonatal Service, Cape Town.

SUBJECTS

Asymptomatic infants born to mothers with untreated syphilis whose VDRL titre was 32 or more.

OUTCOME MEASURES

The number of cases of congenital syphilis was determined by results of IgM Western blots and follow-up VDRL titres.

RESULTS AND CONCLUSIONS

Of 8 patients followed up in the non-treatment group, 4 had congenital syphilis while 0/11 had the disease (P = 0.035) in the group receiving benzathine penicillin. Although the exact failure rate is unknown, benzathine penicillin is effective in preventing symptomatic congenital syphilis when administered to high-risk newborns.

Ventromedial nuclei of the hypothalamus are involved in the phase advance of temperature and activity rhythms in food-restricted rats fed during daytime

Daily rhythms are synchronized to the light-dark cycle (LD) via a circadian clock located in the suprachiasmatic nuclei. A timed caloric restriction phase advances daily rhythms of body temperature and wheel-running activity in rats kept under LD. Because lesions of the ventromedial hypothalamic nuclei (VMH) prevent the fasting-induced changes in the day-night pattern of activity, it was hypothesized that the VMH might participate in the caloric restriction-induced phase changes. To test this hypothesis, rats with electrolytic or ibotenic acid lesions of VMH and control rats were fed 2 h after lights on 50% of ad lib food intake. During the preceding fed state, rats with electrolytic lesions of VMH displayed a less marked day-night difference in locomotor activity and a phase-advanced acrophase of temperature rhythm (2 h) compared to those of sham-operated rats. These effects were not found in fed rats with ibotenic lesions of VMH, suggesting that these effects of electrolytic lesions were due to disruption of undetermined fibers of passage. In response to a timed caloric restriction, the nocturnal peak of temperature rhythm was phase advanced by 7 h in sham-operated rats. Their day-night pattern of activity was also phase advanced towards the time of feeding. In both groups of food-restricted VMH-lesioned rats, the acrophase of temperature rhythm plateaued 3 h later than in sham-operated group. The phase advance of body temperature was, therefore, reduced to 4 h by ibotenic lesions of VMH and to 2 h by electrolytic lesions. Except for a feeding-associated component of activity expressed in control and VMH-lesioned rats, no significant change in day-night pattern of activity was detected in VMH-lesioned rats, either by electrolytic or ibotenic lesions. These results indicate that neuronal damage of the VMH limits the phase-advancing properties of a timed caloric restriction on the daily rhythms of temperature and locomotor activity.

Intergeniculate leaflet lesion and daily rhythms in food-restricted rats fed during daytime

In control rats kept under light/dark cycle (LD) and fed during daytime 50% of ad lib food intake, the acrophase of temperature rhythm was 5 h phase-advanced, and plateaued close to the light/dark transition. The nocturnal pattern of locomotor activity rhythm was 6 h phase-advanced. By contrast, in food-restricted rats with electrolytic lesion of intergeniculate leaflet (IGL: IGLX group), there was only a 1 h phase-advance of the acrophase of temperature rhythm. Furthermore, except for a feeding-associated activity, the nocturnal pattern of activity of food-restricted IGLX rats remained unchanged. This demonstrates the involvement of IGL in the phase-advancing properties of a timed caloric restriction in LD.

Daily hypocaloric feeding entrains circadian rhythms of wheel-running and body temperature in rats kept in constant darkness

Since high levels of physical activity are known to interact with the circadian system, we tested whether hyperactivity induced by hypocaloric feeding may facilitate the synchronizing effect of periodic feeding in rats in constant darkness. Wheel-running (WRR) and body temperature (BTR) rhythms were analyzed in rats fed daily 50% of ad libitum food intake. In addition to a feeding-associated component (FAC) expressed for both rhythms, WRR and BTR were phase-shifted towards the feeding time by 12.1 +/- 0.4 and 12.4 +/- 0.4 h, respectively. BTR and FAC of temperature merged into a single cosine-wave food-entrained rhythm (FER) of temperature. Similarly, WRR and FAC of activity merged into a unimodal FER of wheel-running. This indicates that daily hypocaloric feeding may synchronize circadian rhythms in rats.

Ventromedial hypothalamic lesions prevent the fasting-induced changes in day-night pattern of locomotor activity

The time-course of day-night organization of running wheel activity during prolonged fasting was studied in rats, with or without electrolytic lesions in the ventromedial hypothalamus (VMH). For each individual, dates were referenced to the metabolic transition from lipid to protein utilization in late fasting; this was estimated by daily weighing. In fasted sham-operated controls, daytime activity increased progressively over the fast. This fasting-induced rise in diurnal activity was not due to daily handling, since it was observed also in non-handled (fasted) controls. The pattern of the increase in sham-operated rats differed between 2-hour periods (8-10 h to 18-20 h). The distribution of nocturnal activity was also modified during food deprivation: nocturnal activity in late fasting increased in the 20-22 h period and concomitantly decreased in the two 4-6 h and 6-8 h periods. By contrast, VMH lesions markedly limited and delayed the rise in diurnal running activity, irrespective of the 2-hour period. They prevented any significant change in nocturnal activity pattern over the fast. In fasted sham-operated rats, the data may be interpreted as a phase-advance of the nocturnal pattern of locomotor activity, concomitant with the increase of activity during daytime. These changes were suppressed by the VMH lesions. This suggests that the fasting-induced changes in the day-night pattern of locomotor activity are centrally mediated by a neuronal circuit involving the ventromedial hypothalamus.

Stimulation of brown adipose tissue activity in tumor-bearing rats

Despite anorexia, cancer development is frequently accompanied by an increase of energy expenditure. Considering the pivotal role played by brown adipose tissue (BAT) in the energy metabolism of small mammals, we investigated the functional and compositional modification in BAT of anorexic tumor-bearing (Yoshida sarcoma) and pair-fed control rats. BAT thermogenic activity (assessed by maximal mitochondrial GDP binding) was 1.8-fold greater in tumor-bearing rats than in controls, while the thermogenic capacity (assessed by measurement of uncoupling protein) was unchanged. This suggests that tumor bearing had induced an unmasking of uncoupling protein sites. BAT hypertrophy and hyperplasia, characteristic of full-fledged BAT activation, did not occur. The mitochondrial oxidative capacity of BAT (assessed by cytochrome c oxidase activity) was 1.6-fold lower in tumor-bearing than in control rats. The main compositional modification observed in BAT of tumor-bearing rats was an increase in the saturation of cardiolipin fatty acids. These results suggest that the BAT stimulation induced by tumor bearing after 10 days is almost exclusively functional and that the tissue development is limited, probably by anorexia. However, a suppressive effect of anorexia inhibition by tumor bearing cannot be excluded.

Locomotor activity and utilization of energy reserves during fasting after ventromedial hypothalamic lesions

The ventromedial hypothalamus (VMH) is known to be involved in the regulation of energy metabolism but it may also modulate locomotor activity. Since prolonged fasting is marked by a succession of changes in energy utilization and locomotor activity, it was hypothesized that VMH may be a critical link controlling mobilization of energy stores and/or behavioral changes in response to fasting. To test this, the changes in rate of body mass loss, body content in lipid and protein, and wheel-running activity were studied in fasted nonobese rats with VMH electrolytic lesions. Secondary effects of VMH obesity were ruled out by postoperative restricted feeding. During fasting, VMH lesions impaired neither the overall lipid mobilization nor the late rise in daily body mass loss, concomitant with the increase in net proteolysis. Despite that the onset of this late stage of fasting was significantly delayed in VMH vs. sham-operated rats (13 +/- 1 vs. 8 +/- 1 days, respectively), the final amount of reserve lipids (3 g) was closely similar in both groups: this is the first experimental evidence of the hypothesis of a lipidic set-point. These results indicate that VMH is not a critical link controlling the time-course of utilization of energy reserves. The increase in diurnal (and total) daily wheel-running observed in fasted sham-operated rats still occurred in fasted VMH rats but was significantly reduced and delayed. VMH nuclei and/or associated fibers are therefore involved in the fasting-induced rise in diurnal activity.

Involvement of corticosterone in the fasting-induced rise in protein utilization and locomotor activity

During fasting, most of the energy is derived from lipids whereas proteins are efficiently spared. However, there is a late rise in net protein utilization. Fasting is also associated with an increase in locomotor activity. Because the plasma corticosterone level increases concomitantly with these metabolic and behavioral changes, the involvement of corticosterone has been hypothesized. To test this, the net protein utilization and locomotor activity were investigated in fasted adrenalectomized (Adx) rats, with or without replacement with corticosterone, and in fasted intact rats treated with RU486, an antagonist of type II glucocorticoid receptors. During the phase of fasting characterized by protein sparing, urine nitrogen loss was further reduced in Adx rats and in RU486-treated controls compared with intact rats and with Adx rats with corticosterone replacement: this indicates a catabolic effect of corticosterone through type II receptors. In the last phase of fasting, the rise in net protein breakdown was suppressed in Adx rats and restored by corticosterone replacement. The increase in locomotor activity induced by fasting in controls was suppressed in Adx and restored by corticosterone replacement. This rise in running activity was still present in RU486-treated rats. In conclusion, this study shows that corticosterone plays a critical role in the changes of both protein catabolism and locomotor activity during prolonged fasting.

Search for rhythmicity during hibernation in the European hamster

Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000-0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P < 0.01), either below 24 h (21.8 +/- 0.5 h, n = 4) or above (27.3 +/- 0.5 h, n = 7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.

Body protein and lipid deficit in tumour-bearing rats in relation to age

Cancer cachexia is among the most dramatic situations of depletion in body energy reserves. To ascertain whether the pattern of body composition alteration during tumour development is influenced by aging as in uncomplicated starvation, we compared the difference of body composition between Yoshida sarcoma bearing rats and young (200 g, 7 weeks) and adult (400 g, 13 weeks) control rats. After the same duration of tumour bearing, mass and composition of tumours were similar in adult and young rats, indicating that they are independent of host age. Food intake decreased to a remarkably similar value in both young and adults. Body water content was elevated in hosts of both ages. The relative deficit of body lipid vs controls was similar for both, the absolute lipid deficit being therefore larger in adult than in young tumour-bearing rats (14.3 +/- 4.4 g vs 6.8 +/- 0.9 g; P < 0.01). In contrast, there was a relatively larger deficit of body protein in young rats. Paradoxically, these rats still maintained a positive nitrogen balance whereas this balance was negative in adult tumour-bearing rats. In conclusion, as previously shown in uncomplicated undernutrition, the anorexia induced by Yoshida sarcoma development is still associated with some protein accretion in young rats whereas cachexia develops in adults.

Early insulin response after food intake in geese

Plasma glucose and insulin levels were measured in chronically catheterized, freely moving, undisturbed geese, which were offered a free standard meal after an overnight fast. The insulin level markedly rose within the first minute after the start of food ingestion, whereas plasma glucose did not increase. This early insulin response was not correlated with the size of the meal. In contrast, both postabsorptive insulin response and plasma glucose changes were dependent on meal size. When a small amount of food (2-6 g) was eaten, insulin returned to basal level within 30 min, whereas plasma glucose remained unchanged. Larger meals (15-20 g) maintained plasma insulin at a higher level and induced a sustained rise of plasma glucose. These results indicate that there is a cephalic phase of insulin secretion at the beginning of the meal in birds as previously described in mammals.

pH and hypometabolism in mammalian hibernation

In mammalian hibernation, the reduction of metabolic rate occurs by three processes: inhibition of cold-induced thermogenesis, temperature effect on metabolic reaction rates (Q10), and a further inhibition. Concomitantly, the animal undergoes a marked respiratory acidosis (CO2 retention). At the intracellular level, a respiratory acidosis occurs in brain and muscles, suggesting that intracellular pH regulation is depressed. The hyperventilation of early arousal provides evidence for the hypothesis that acidosis exerts an inhibition in hibernation, and should be removed to permit thermogenesis. Muscle glycolysis and brown adipose tissue thermogenesis are depressed by acidosis in vitro, but a decrease in pH probably also affects other systems, especially the preoptic area of the hypothalamus.

pH-temperature interactions on protein function and hibernation: GDP binding to brown adipose tissue mitochondria

1. [3H]GDP binding to the uncoupling protein of brown adipose tissue was determined on mitochondria isolated from hibernating European hamsters, at two temperatures, 35 and 15 degrees C, and four values of 25pH (pH corrected to 25 degrees C): 6.4, 6.8, 7.2 and 7.6, encompassing the physiological range of pH. Buffer composition was adjusted to get the same pH-temperature relationship as for mammalian blood, in which this relationship is mainly determined by protein imidazole buffers. 2. The maximal binding capacity was independent both of temperature and pH. The dissociation constant KD was highly pH-dependent, but was independent of temperature when 25pH was held constant. Under these conditions, the uncoupling protein thus fully conserves its regulatory properties over the temperature range studied (eurythermal adaptation). 3. The temperature coefficient of the apparent pK' for the pH effect (-0.012 +/- 0.004) differed significantly from that of GDP terminal phosphoryl group, but not from that of blood protein imidazole buffer groups, in good agreement with the imidazole alphastat theory. 4. The results indicate that GDP reaction with the protein involves an electrostatic binding with a titratable group of the protein, probably a sulfhydryl. 5. pH modulation of the uncoupling of brown adipose tissue mitochondria probably permits a reversible control of thermogenesis in the hibernation cycle, heat dissipation being inhibited by respiratory acidosis in deep hibernation, but facilitated by the hyperventilation of arousal.

Time-course of blood acid-base state during arousal from hibernation in the European hamster

1. Arterial blood was sampled at 15 min-intervals in European hamsters Cricetus cricetus fitted with indwelling catheters, from deep hibernation to full arousal. Temperature-corrected pH and PCO2, respectively pH* and P*CO2, were directly measured at 37 degrees C. 2. Deep hibernation corresponded to a respiratory acidosis: pH* = 7.01 +/- 0.01 (mean +/- SE), P*CO2 = 160 +/- 4 Torr (n = 9 animals). 3. Three periods could be distinguished in the arousal: (i) a period of hyperventilation (28 +/- 5 min), in which P*CO2 was reduced to 79 +/- 4 Torr, while cheek pouch temperature increased only by 0.9 +/- 0.2 degrees C; (ii) a period of metabolic acidification by lactate accumulation (84 +/- 6 min), corresponding to the period of peak thermogenesis; (iii) a progressive return to euthermic conditions (104 +/- 10 min), by simultaneous respiratory and metabolic alkalinization. 4. Over 60% of the blood CO2 stores accumulated at the beginning of the hibernation bout were released by hyperventilation during the first period, prior to the full development of thermogenesis. This is in agreement with the hypothesis of an inhibitory role of the respiratory acidosis in hibernation.

Intracellular pH in hibernation and respiratory acidosis in the European hamster

Intracellular pH was determined (DMO method) in European hamsters, in the spontaneously-occurring respiratory acidosis of hibernation, in hypercapnia due to breathing 12% CO2 in air in euthermy in spring, and in euthermicnormocapnic controls. From euthermy to hibernation, the temperature coefficient of pH was lowest in blood plasma and brain, intermediate in striated muscles (thigh muscles and diaphragm), and highest in heart and liver (Fig. 1). Correspondingly, the estimated dissociation ratio of the protein imidazole buffer groups, alpha Im, decreased markedly in plasma and brain, denoting an acid titration, but varied little in liver and heart. Striated muscles were intermediate (Fig. 2). Like in other mammals, intracellular responses to short-term euthermic respiratory acidosis were characterized by a partial metabolic compensation in the brain and a small metabolic acidification in striated muscles. In hibernation, a powerful metabolic compensation took place in liver and heart, nearly restoring alpha Im, but none occurred in brain (Figs. 3 to 5). The existence of an intracellular acidosis in brain and striated muscles during hibernation is in keeping with an inhibitory role of acidosis, whereas the homeostasis of intracellular alpha Im in liver and heart would subserve the eurythermal functioning of metabolic regulations in these organs, like in most organs of ectotherms.

An O2-CO2 mixing system for studies on water-breathing animals

A simple system based on single-stage gas-stream mixing produces accurate O2-CO2 mixtures suitable for studies on water-breath-ing animals. CO2 fractions as low as 0.05% can be obtained, with an output pressure up to 25 kPa and a full range accuracy of +/- 1%.

Exchanges between plasma and red cells at a variable temperature

When blood temperature is varied in closed ('anaerobic') conditions, the difference between plasma pH and red cell pH stays remarkably constant. Model studies show that this constancy results from diffusive CO2 equilibration and Donnan equilibrium of HCO3- and Cl- ions, more than from a strictly defined buffer composition.

A two-compartment model of blood acid-base state at constant or variable temperature

Information available in the literature on the acid-base properties of oxygenated mammalian blood at a constant or variable temperature was put together into a synthetic model; this also aimed at reconciling the single compartment descriptions of acid-base vs temperature relationships in closed ('anaerobic') conditions with the standard dual compartment analysis of isothermal titrations. Experimental values for the concentrations of blood constituents, buffer dissociation constants, etc. were introduced into the set of physicochemical equations governing the steady-state distribution of CO2, electrolytes and water between plasma and red cells. Design of the model was such as to permit monitoring of all variables (e.g. concentrations) throughout any simulated acid-base transformation. A fairly good fit was obtained between model predictions and experimentally-determined relationships or quantities not introduced into the model from the start. Applications to variable temperature titration and to the effects of changes in blood composition or osmolality are presented. The latter underline the implicit assumptions made by neglecting such variables in current presentations of blood acid-base state.

Intracellular acid-base state at a variable temperature in air-breathing vertebrates and its representation

When temperature changes are superimposed on changes in the control variables of acid-base state (PCO2, strong ion difference), the understanding of acid-base changes becomes difficult. A solution has recently been proposed for blood (Malan, 1977); it was based on the assumption that closed system conditions correspond to a minimal change in the overall acid-base state when temperature varies. The feasibility of extending these concepts to muscle intracellular acid-base vs temperature relationships is evaluated on the basis of a model study; the errors made by replacing closed conditions (which require knowledge of chemical composition) by more convenient approximations are estimated. A representation of both extracellular and intracellular acid-base data on a temperature-corrected bicarbonate-pH diagram is derived. It allows the interpretation of variable-temperature intracellular acid-base changes in terms of changes in control variables, 'respiratory (PCO2) or 'metabolic' (strong ion difference).

Hibernation as a model for studies on thermogenesis and its control

Mammalian hibernation is characterized by the alternation of prolonged periods of hypothermia and spontaneous arousals with a temporary return to euthermia. Of special interest to the physiology of effectors of thermogenesis are the following points: a) In the second part of the arousal process, the metabolic rate reaches 6 to 8 times BMR, with a body temperature about 10 degrees C lower. Enzymatic adaptations provide for the maintenance of normal reaction rates and regulatory potentials at low temperatures, but how very high thermogenetic rates can be achieved still remains largely unexplained. b) Entrance into hibernation involves a resetting of the hypothalamic thermostat to a lower level, but this is probably not the only intervening regulation. Evidence is presented in favor of a control of thermogenesis at the effector level, in terms both of baseline levels and of loop gains. One likely control factor is acid-base state, which can be changed rapidly and reversibly by ventilation and is characterized by a strong acidosis in hibernation.