Bernard Canguilhem

Seasonal variations in the daily rhythm of pineal gland and/or circulating melatonin and 5-methoxytryptophol concentrations in the European hamster, Cricetus cricetus.

Day-night variations in pineal and/or circulating melatonin and 5-methoxytryptophol (5-ML) concentrations were measured monthly throughout the year in female European hamsters, Cricetus cricetus, maintained under natural conditions. Pronounced seasonal variations in the day-night rhythm of both melatonin and 5-ML were observed. As previously reported for melatonin, the daily rhythm of both methoxyindoles disappeared in spring and early summer, while a clear day-night rhythm occurred in autumn, winter, and early spring. The amplitude of the day-night variations appeared to be maximum from October until January. An inverse relationship existed between the rhythms of melatonin and 5-ML.

Photoperiodic regulation of body mass, food intake, hibernation, and reproduction in intact and castrated male European hamsters, Cricetus cricetus.

SummaryA group of sexually active male European hamsters were raised either in short-photoperiod conditions (SP; LD 8∶16) or in long-photoperiod conditions (LP; LD 16∶8) from their capture at the end of the hibernation period. Another group of hamsters was castrated in April and gonadectomized animals were maintained in SP and cold (7 °C) or in a succession of SP and LP plus cold. Another group, castrated in May or in September and raised in LP conditions, was transferred in September to SP conditions and cold.1.Normal hamsters raised in continuous SP or LP apparently did not show signs of rhythmic behavior, except possibly in gonadal activity.2.Body weight increased continuously, plasma testosterone levels oscillated between 1.5 and 2.5 ng/ml, and animals raised in SP and in cold did not enter hibernation.3.Similar results were also found in castrated animals kept in SP conditions and cold.4.The sequence LP-SP induced a decrease in food intake and body weight and a decrease in plasma testosterone levels and triggered entry into hibernation in both intact and castrated animals.5.After 6 months continuously in SP and with exposure to cold spontaneous recrudescence in food intake and body weight occurred and hibernation ended in both intact and castrated animals.6.In normal animals a spontaneous increase in plasma testosterone levels was observed.7.In both normal and gonadectomized animals the phase of refractoriness could be broken by exposure to LP conditions.8.The critical photoperiod lies between 15 and 15.5 h. These results demonstrate that the European hamster is a photoperiodic species. Three parameters are under the control of the photoperiod: energy balance, hibernation, and gonadal function. These experiments provide evidence that in addition to having a gonadal effect the photoperiod can act directly on unknown cerebral structures involved in body weight regulation and hibernation.

Are the annual reproductive and body weight rhythms in the male European hamster (Cricetus cricetus) dependent upon a photoperiodically entrained circannual clock

Masson‐Pévet M, Naimi F, Canguilhem B, Saboureau M, Bonn D, Pévet P. Are the annual reproductive and body weight rhythms in the male European hamster (Cricetus cricetus) dependent upon a photoperodically entrained circannual clock? J. Pineal Res. 1994; 17:151–163.

The Photoperiodic Response in Syrian Hamster Depends upon a Melatonin‐Driven Circadian Rhythm of Sensitivity to Melatonin

The pineal gland, via the daily pattern of melatonin (MEL) secretion, is directly involved in the conduction of photoperiodic information. The duration of MEL secretion is proportional to the duration of the dark period and, whatever the photoperiod is, MEL synthesis occurs 3 or 4 h after the dark onset in Syrian hamsters. In order to determine the relative importance of the duration or the coincidence hypothesis, a daily infusion protocol was used in sexually active pinealectomized hamsters. Long duration of MEL infusion (10 h) completely inhibit testes whereas short duration infusion (5 h) had no effect. When the animals were infused twice within 2 h 30 min separated by 3 h, they presented a complete gonadal atrophy, similar to the one observed with the 10 h infusion. Measurement of plasma MEL during the infusion and seperation periods revealed that MEL reached physiological nighttime values during the infusion period and fell to daytime values 1 h after the end of an infusion period. Thus, the results could not be due to a time additive action of the two MEL pulses. An intermediate response was observed when the 2 signals were applied across the light/dark transition. Gonadal regression did not occur when the 2 periods of infusion were separated by 5 h 30 min. The efficiency of this type of infusion was not dependent on the ambiant photoperiod since similar results were obtained in long and short photoperiods. The infusion was also as effective during the day as well as during the night. These results suggest that there is a rhythm of sensitivity to MEL, based on the coincidence hypotheses, that are important for transmission of photoperiodic information. This rhythm of sensitivity to MEL seems to be entrained by MEL itself, since the efficiency of the two pulses of MEL is not dependent of time of application and/or of photoperiod.

Effects of different doses and durations of melatonin infusions on plasma melatonin concentrations in pinealectomized Syrian hamsters: Consequences at the level of sexual activity

Abstract: The effect of different doses and durations of melatonin infusions on plasma melatonin concentrations has been studied in pinealectomized Syrian hamsters maintained under short photoperiod at either 7°C or 18°C. The effects of the infusions on plasma melatonin concentrations and on gonadal activity were compared. The results show that the minimal effective quantity of infused melatonin that induced gonadal atrophy was 40 ng/h at 7°C and 20 ng/h at 18°C. An infusion of 8 hr duration per day is necessary to inhibit sexual activity, while an infusion of 6 hr duration was ineffective. This finding suggests that the critical duration of melatonin infusion is between 6 and 8 hr. Despite the various doses of melatonin infused, plasma melatonin concentrations measured in the middle of the infusion period did not differ significantly from concentrations measured in intact animals. This finding suggests that the metabolism of infused melatonin increases as the dose of melatonin increases. Moreover, the different physiological effects observed after the various melatonin infusions cannot be explained by variations in plasma melatonin concentrations.

Melatonin, Serotonin, 5‐Hydroxyindole‐3‐Acetic Acid and N‐Acetyltransferase in the Pineal of the European Hamster (Cricetus cricetus) Kept Under Natural Environmental Conditions: Lack of a Day/Night Rhythm in Melatonin Formation in Spring and Early Summer

In female European hamsters killed in spring and early summer, pineal melatonin content exhibited no day/night rhythm. Absolute levels measured were relatively low, being on the order of daytime levels detected in other hamster species. An absence of day/night changes in the activity of N‐acetyltransferase was also observed. However, a marked rhythm in pineal serotonin (5‐HT) was found, an abrupt large increase being observed at the beginning of the light period. The day /night rhythm of pineal 5‐HIAA content is similar to that of 5‐HT. This absence of rhythm in pineal melatonin formation might mean that in the European hamster it is not melatonin but another substance that is of importance in photoperiodism. An absence of melatonin rhythm, however, could also be simply a peculiar pattern of melatonin production observed at a given period of the year. In this case, melatonin would be able to transduce photoperiodic information in the European hamster, as in other photope riodic species.

Circannual reproductive rhythm in the European hamster (Cricetus cricetus): Demonstration of the existence of an annual phase of sensitivity to short photoperiod

Abstract: In the European hamster (Cricetus cricetus) short photoperiod (SP) is responsible for the transition between the breeding and the resting season and data obtained previously suggest that a circannual “clock” drives the annual rhythm of reproduction. This hypothesis implies the existence of a SP‐sensitive phase of the circannual system that occurs independently of the photoperiodic regime perceived by the animals after their arousal from hibernation at the end of March. In control animals kept outside, testicular atrophy occurs in August. When the animals were transferred from outdoors to controlled SP conditions (LD 10:14 and ambient temperature Ta = 18 ± 2°C), immediately (Group II) or 2, 4, 6 wk after capture (Groups IV, V, VI, respectively), sexual arrest occurs at the same time between mid‐June and mid‐July. In the other groups, transfer from outdoors to SP either after 6, 8, 10, 12 or 14 wk (Groups VI, VII, IX, X, XI, respectively) after capture, is followed directly within 4 wk by the gonadal atrophy. When SP was applied from the beginning of August (Group XII) gonadal atrophy was observed after only 2 wk. In this last group, however, the rapid involution is the consequence of the already initiated decline in sexual activity induced by the short daylengths from July. When comparing the effect of SP in two different ambient temperatures (Ta: 18 ± 2°C vs 7 ± 2°C), immediately (Groups II vs III), 8 (Groups VII vs VIII) or 16 (Groups XII vs XIII) wk after capture, it appears that low temperature does not affect the physiological process described above. In the European hamster, after the gonadal regrowth at the end of hibernation, the animals do not need to experience increasing long days to react against SP. Gonadal inhibition is induced when, following our hypothesis, SP coincides with an endogenous period of sensitivity that extends from mid‐May to at least July‐August. The present findings complement and extend earlier evidence to support the existence of an endogenous circannual control of seasonal reproduction in the European hamster.

Non-gonadal mediated effect of photoperiod on hibernation and body weight cycles of the European hamster

1. Sexually active male European hamsters raised under short photoperiod display high levels of plasma testosterone, high body weight and do not hibernate. 2. Castrated males in May, raised under the same conditions, do not hibernate and do not present the physiological body weight rhythm. 3. Normal and castrated animals under natural conditions enter hibernation and display a normal body weight rhythm. 4. Normal and castrated animals not submitted to the natural succession of long and short days do not enter hibernation. 5. Photoperiod directly controls body weight and hibernation gonadal interactions.

Chapter 24 The suprachiasmastic nucleus: the biological clock of all seasons

Publisher Summary The suprachiasmatic nucleus (SCN) plays an essential role in the generation and maintenance of circadian rhythms in mammals. The intrinsic pacemaker activity of the SCN is autonomous in nature and is entrained to the daily 24-hour period primarily by the light/dark cycle. Due to its connections with the pineal gland, the SCN is also known to be indirectly involved in the control of seasonal rhythms. The data presented in this chapter demonstrates that SCN activity is not only cued by the light/dark cycle but also strongly influenced by the photoperiod. Moreover, it appears that integration of the photoperiodic message through the rhythmic secretion of Mel implicates a Mel driven circadian rhythm of sensitivity to Mel. This clearly indicates that the SCN is a biological clock for all seasons regulating photoperiodic changes observed at the physiological and behavioral level. It also indicates that the currently accepted separation between the circadian and seasonal photo-timing system is perhaps not justified on the physiological grounds.

Seasonal variation of the composition of membrane lipids in liver mitochondria of the hibernator cricetus cricetus relation to intramitochondrial intermembranal protein movement

Abstract 1. 1. European hamster ( Cricetus cricetus ) raised under constant temperature conditions show a seasonal variation in the profiles of the structural fatty acids of the liver mitochondrial membrane. In these animals there are but small differences between sleeping and aroused animals in winter. 2. 2. The most important variation in lipid composition occurs in the prehibernating phase—at the end of summer and the beginning of autumn. 3. 3. However, there is no apparent coordinated relation between the seasonal variation of the composition of the fatty acids and the membrane “fluidity” as expressed by the break in the Arrhenius curve for protein release in intermembranal space of the liver mitochondria. 4. 4. This break occurred at a higher temperature in active animals in winter (arousedl than in summer. 5. 5. No general correlation could be found between the breaks in the Arrhenius curves and the variations of the different fatty acid species during the seasonal cycle, except for the most polyunsaturated fatty acid (docosahexanoic acid) where an excellent inverse correlation was observed. 6. 6. Our results suggest that the more fluid parts of the lipidic leaflet of the mitochondrial membrane are those more specifically involved in such phenomena as succinate induced intramitochondrial protein movement and that the changes in composition of the mitochondrial lipids are a possible adaptative advantages for the hibernator.