Effects of melatonin administration on oxidative stress and daily locomotor activity patterns in goldfish

Melatonin has a number of physiological functions in addition to light-dark transduction. In recent years, many in vivo and in vitro studies in rodents have revealed an important antioxidant activity of melatonin, both directly and indirectly. Nevertheless, the potential effects of melatonin as an antioxidant in fish remain unknown. The aim of this research was to evaluate the capacity of melatonin injections (3 mg/kg) to attenuate oxidative damage after submitting goldfish to oxidative stress caused directly by hydrogen peroxide (H2O2) baths and indirectly by hypoxia and subsequent reoxygenation, as well as the locomotor activity. The results revealed that melatonin decreased lipid damage in muscle after hypoxia/reoxygenation (1.22 vs. 2.27 nmoles lipid peroxides/g tissue), but not in liver. Mortality caused by oxidative stress was not attenuated by melatonin. Surprisingly, melatonin caused an increase of mortality (50 vs. 95%) when administered before hypoxia. Locomotor activity was also affected by melatonin but not by the administration of the vehicle, suggesting a sedative effect of melatonin in goldfish. In conclusion, melatonin administration provoked slight effects on lipid peroxidation and mortality resulting from oxidative stress, with reduction of locomotor activity in relation to the vehicle.

How to engage medical students in chronobiology: an example on autorhythmometry

This contribution describes a new laboratory experience that improves medical students' learning of chronobiology by introducing them to basic chronobiology concepts as well as to methods and statistical analysis tools specific for circadian rhythms. We designed an autorhythmometry laboratory session where students simultaneously played the role of researchers and experimental subjects. During this session, which lasted 24 h, students recorded their own arterial pressure, heart rate, oral temperature, forced expiratory flow, glucose tolerance, muscular strength, reaction time, and sensorimotor coordination at regular intervals and also took the Horne and Ostberg test, after which they analyzed their own data. Furthermore, to gather information from subjects under normal sleep and eating schedules, some students acquired data at home. To guide and help students with their work, a dedicated web page was implemented with scientific references, cosinor analysis software, and other valuable information. All these "raw" data were combined into a single database that students could use to evaluate whatever aspect of the data they seemed fit. A number of suggestions were offered to them as guidance. Students were then instructed to write a scientific article on the subject they had chosen. The experience was highly rewarding for both instructors and students alike. In view of the high level of absenteeism in Spanish universities and the fact that 93% of the students attended the exam and 95% of these passed, the experience was considered a great success.

Daily locomotor activity and melatonin rhythms in Senegal sole (Solea senegalensis)

The daily locomotor and melatonin rhythms of the Senegal sole, a benthonic species of increasing interest in aquaculture, are still unknown, despite the fact that such knowledge is of prime importance for optimising its production. The aim of the present research was therefore to investigate the daily rhythms of locomotor activity and melatonin in the Senegal sole. For this purpose, the individual locomotor activity rhythms of fish were registered using a photocell. Plasma and ocular melatonin rhythms were studied in animals reared in circular tanks placed in earth under an LD 12:12 light regime and 16-18 degrees C temperature range (spring equinox). Blood and eye samples were taken every 3 h during a complete 24-h cycle. The impact of a light pulse in the middle of the dark period (MD) on plasma melatonin was also studied. Locomotor activity was mainly nocturnal, with 84.3% of the total activity occurring during darkness. The levels of plasma melatonin were higher at night (55 pg/ml) than during the day (2 pg/ml), while ocular melatonin levels appeared to be arrhythmic. Both weight and melatonin content were found to be significantly higher in the left eye in relation to the right eye. A light pulse in MD provoked a significant decrease in plasma melatonin levels. In summary, photoperiod is a key factor in synchronizing locomotor activity and melatonin rhythms in the Senegal sole, whose nocturnal habits should be taken into account for their rearing by aquaculture.

Effect of long-term GHRH and somatostatin administration on GH release and body weight in prepubertal female rats

In order to find a chronic GHRH administration capable of stimulating growth rate without depleting pituitary GH content, prepubertal female rats were subcutaneously (sc) treated with GHRH (1-29)-NH2 and somatostatin (SS). In experiment 1, the rats received sc injections of GHRH and cyclic natural SS for 19 days. In the second study, female rats were continuously treated during 21 days with GHRH, using a slow release pellet, alone or combined with one daily injection of long acting SS (octreotide). In experiment 1, body weight was significantly increased when GHRH was administered at the highest daily dosage (1200 microg/day), accompanied by an slight increment in pituitary GH content. Hypothalamic SS concentrations decreased when GHRH or SS were administered alone whereas the combined treatment with both peptides did not modify this parameter, which suggests the existence of a balance between the chronic actions of both peptides on hypothalamus. In experiment 2, the continuous infusion of GHRH increased plasma GH levels and tended to enhance pituitary GH content. Nevertheless, GHRH effect was not effective enough to increase body weight. By adding one daily injection of SS both GHRH effects on the pituitary gland were abolished. Our study indicates that female rats retain responsiveness to chronic GHRH and SS treatments at both pituitary and hypothalamic levels.

Periodic growth in rats

Microknemometry, a novel non-invasive technique, allows the accurate measurements of the lower leg length in the conscious rat, not only daily but even in periods smaller than 24 hours. Its use revealed the presence of nonlinear growth increments (mini-growth spurts) with periods between 4 and 5 days, that presented a gradual decline in amplitude when the animals were getting older, and a maximal growth rate between 0600h and 0900h. A sexual dimorphic growth pattern could be established with females growing less and presenting spurts of lower amplitude and smaller duration than males. High doses of recombinant human Growth Hormone (rhGH) stimulated growth velocity in female rates, but did not show any effect on males. Neonatal Monosodium Glutamate (MSG) treatment reduced growth both in males and females. Growth hormone (GH) replacement therapy in MSG treated animals was capable of increasing growth velocity, from day 30 onwards. The recovery was partial in males and complete in females. In intact male rats growth blockade induced by fasting was not followed by a catch up effect after refeeding, although growth velocity tended to increase and a clear catch up effect on weight was detected. Male rats seemed to grow at a maximal speed over at least the first 60 days of life, that cannot be accelerated with GH treatment, whereas female rats did respond to exogenous GH.

Sexual dimorphism in growth as measured by microknemometry: different responses to GH deficiency and exogenous GH administration

To monitor growth, a novel noninvasive leg length measurement technique, called microknemometry, which allows daily observation of tibial growth rate, was used. The rat exhibits a striking sex-related difference in postpubertal growth. Exogenous GH administration results in a sexually dimorphic response, affecting growth in normal young female rats but not in males. Here we investigated how chronic GH deficiency affects male and female rat growth patterns. The degree of growth rate recovery was investigated after exogenous GH administration to chronically deficient males and females. The deficiency was induced by neonatal monosodium glutamate (MSG) treatment. Since the neonatal gonadal environment plays an important role in the dimorphic growth pattern, neonatal androgenization of female rats with testosterone or neonatal feminization of male rats by castration was performed and the growth pattern monitored. MSG treatment decreased pituitary GH content and plasma IGF I levels in both sexes, but caused a less marked reduction of female rat tibial growth and body weight gain than in males. Additionally, only MSG-treated males showed decreased pituitary LH content, so that the dimorphic action of MSG on the gonadal axis may contribute to the observed differences in growth rate. GH administration was able to increase leg length in all MSG-treated rats but was more effective in females, despite a similar restoration of plasma IGF I levels in both sexes. Although neonatal castration of male rats resulted in a reduction of tibial growth rate and body weight, and neonatal testosterone administration to female rats caused a slight increase in body weight, a complete modification of the gender-dependent growth pattern was not achieved, indicating that appropriate steroid environment is also needed in puberty and adulthood.

Micro and macro perspectives in auxology: findings and considerations upon the variability of short term and individual growth and the stability of population derived parameters

The present paper links the two most contrasting aspects of auxology, and addresses the apparent discrepancy between the variability and pulsatility of short term individual growth, and the stability of population derived parameters. When body stature is measured at monthly intervals, an irregular incremental pattern becomes obvious, with a number of large scale components such as series of prepubertal and pubertal growth spurts, seasonal influences on height gain, and influences of the psychosocial and economic background. When measurement intervals decrease, the patterns of stature increment appear even more irregular, and a number of short scale components become apparent, that are distinct from measurement error. Observations are presented that suggest growth being a pulsatile, a periodic, a saltatory, respectively a chaotic event as suggested by some recent studies in animals and in human newborns. Accurate measurements of the lower leg at intervals of 24 hours support the idea of short term growth being characterized by chaotic series of 'mini growth spurts' that occur at intervals of approximately 4-9 days. The amplitude of mini growth spurts ranges between 2 and some 10 mm, and also growth velocity of each spurt varies considerably so that one spurt needs between less than one and up to several days for completion. The very opposite of the variability of individual growth was found in populations. A meta-analysis of 40 male and 51 female European and US American growth studies revealed an almost uniform general pattern of average stature increment during the last 100 years. An additional analysis of stature variation of very large Japanese and Czechoslovakian growth surveys, with all together more than 23000000 measurements, and more than 500000 German preschool and school measurements, suggested similar uniformity in the standard deviation of stature.

Short-term growth: evidence for chaotic series of mini growth spurts in rat growth

Five thousand and eighteen quadruplet daily measurements of lower-leg length of 62 female and 81 male rats, were performed in order to characterize short-term growth. Within a short time, growth proceeds irregularly and consists of multiple incremental bursts (mini growth spurts) with no evidence for strict periodic behavior. Mini growth spurts are S-shaped incremental patterns that can be characterized by double-exponential functions (Gompertz's functions). Gompertz's functions are S-shaped, and can be defined by three parameters that identify amplitude, inflection point (age at peak growth velocity), and slope. The latter not only refers to the rapidity of each incremental burst, but also alludes to the duration that one incremental burst needs for completion. In regard to these characteristics, mini growth spurts differ significantly between the sexes in rats. Mean amplitude of mini growth spurts was 2153 microm (SD 1034 microm) in female rats and 2958 microm (SD 1614 microm) in male rats. Peak growth velocity of mini growth spurts appeared lower in male rats than in female rats. Female rats showed mean gamma of -1.23 (SD 0.72), whereas male rats showed mean y of -0.96 (SD 0.72). Partial growth hormone deficiency led to a modification in rats that was reversed when exogenous growth hormone was administered. Mean intervals between subsequent mini growth spurts ranged between 4.2 and 4.6 days, but the large variation of these intervals (SD between 1.6 and 2.3 days) and the fact that neither spurt-spurt interval nor spurt amplitude appeared predictable, strongly suggest chaotic behavior of mini growth spurts.

Serum levels of GH, IGF-I, LH and ovarian steroids in cyclic and RU486-treated rats

Rats lacking progesterone action due to RU486 treatment have been reported to show numerous endocrine and morphological similarities with respect to human polycystic ovary syndrome (PCO). Nevertheless, abnormalities on insulin or insulin-like growth factor I (IGF-I) production, a frequent finding in the polycystic disease, have not been studied in such rats yet. The aim of these experiments was to evaluate the serum concentrations of IGF-I in rats treated with 4 mg of the antiprogestagen RU486 over 4 or 8 consecutive days starting on estrus (day 1) and decapitated on the morning of day 5 and 9. Serum levels of growth hormone (GH), luteinizing hormone (LH), testosterone (T) and 17 beta estradiol (E2) were determined and correlated with those of IGF-I. Controls were rats injected with oil and killed in the morning of metestrus, diestrus, proestrus and estrus. Rats treated with RU486 had increased serum concentrations of IGF-I, LH, T and E2 with respect to control rats on estrus, while no differences were found in the serum concentrations of GH. Parallel estrous cycle related changes were observed in the serum concentrations of IGF-I, T and E2 with the highest values at proestrus. However, changes on serum concentrations of GH were not associated with those of IGF-I in control rats through the estrous cycle. The present results are consistent with the idea that beside on GH, serum concentrations of IGF-I in the rat depend also on LH or LH-dependent ovarian steroid production. Moreover, the results indicate that IGF-I production increased in RU486-treated rats, which may have a role in the ovarian abnormalities induced by RU486 treatment in the rat.

Differential catch-up in body weight and bone growth after short-term starvation in rats

Catch-up or compensatory growth is known as a physiological phenomenon. However, most studies of catch-up growth were based on measurements of body weight, whereas changes in longitudinal bone growth remained largely undescribed. The present study describes the dynamics of both weight and longitudinal bone growth using mikro-knemometry, during normal feeding, severe food restriction (starvation), and refeeding of 14 intact and 28 GH-deficient male rats. Starvation induced rapid weight loss (P < 0.001), and stunted leg growth (P < 0.001). Refeeding led to rapid catch-up in weight of up to 4 times above normal daily weight gain, both in intact and GH-deficient animals, whereas an equivalent compensation of lower leg growth remained undetectable. Intact and GH-deficient animals show a circaseptan spontaneous variation of growth velocity (mini growth spurts). During starvation, mini growth spurts disappear, and return to normal after refeeding with no evidence of catch-up. In GH-deficient animals, GH (1 IU/rat, administered twice daily s.c. at 10:00 hand 16:00 h) was capable of augmenting catch-up in weight and, to a lesser extent, in leg length increment.