María Jesús Delgado

Inhibitory Effect of Serotonin on Feeding Behavior in Goldfish: Involvement of CRF

The possible action of 5-HT on feeding behavior in goldfish has been studied. Food intake was significantly reduced by intracerebroventricular (ICV) injection of serotonin (5-HT, 10 microg) at 2 h postinjection. After peripheral (intraperitoneal) administration of 5-HT (1 and 10 microg/g bw), no significant modifications in food intake were detected. Thus, it can be concluded that there is a central anoretic action of 5-HT in teleost fish. Taking in mind the inhibitory effect of corticotropin releasing factor (CRF) on feeding in teleosts and the interactions between 5-HT and CRF described in mammals, we investigated the possible involvement of CRF as mediator of the 5-HT anoretic action in goldfish. The ICV pretreatment with alpha-Helical CRF[9-41](20 microg) partially blocked the inhibitory effect of 5-HT on food consumption in goldfish. These results show that CRF mediates, at least in part, the 5-HT-induced feeding inhibition in goldfish. On the other hand, the alterations in hypothalamic indoleamines content evoked by ICV treatments would suggest that the activation of CRF neurons by 5-HT appears to inhibit hypothalamic serotoninergic transmission, supporting the intermediate role of this neuropeptide in the central anoretic effect of 5-HT in goldfish.

Role of corticotropin-releasing factor (CRF) as a food intake regulator in goldfish

The effect of intraperitoneal or intracerebroventricular corticotropin-releasing factor (CRF) administration on food intake has been studied in goldfish after 24 h of food deprivation. Food intake was evaluated at different time periods after injection, 0-2, 2-8, and 0-8 h. The 1 and 2 micrograms doses of CRF intracerebroventricularly administered induced a reduction in food intake during the first 2 h, although an increased feeding was observed in the next 6 h. The higher dose of CRF used in this study (3.3 micrograms) increased cumulative food intake at 8 h postinjection. However, intraperitoneal injection of 1 microgram CRF did not modify food intake in any of the studied intervals. These results suggest that CRF may play a role in central regulation of feeding behavior intake in goldfish, and show that CRF effects are time- and dose-dependent.

Effect of environmental temperature and photoperiod on the melatonin levels in the pineal, lateral eye, and plasma of the frog, Rana perezi: Importance of ocular melatonin

Day-night melatonin concentrations were studied in the pineal body, lateral eye, and plasma of the frog Rana perezi in animals maintained in February and July under long (18L:6D) or short (6L:18D) photoperiod and high (25 +/- 1 degree) or low (6 +/- 1 degree) temperature in order to evaluate the influence of these environmental factors. When frogs were kept under short photoperiod and low temperature in February, no melatonin rhythm was observed in the pineal, ocular tissue, and plasma. High temperature at this period of the year induced a day-night rhythm of melatonin levels in the lateral eye and plasma. In July, under long photoperiod and high temperature, animals showed pronounced rhythms of melatonin in the pineal, eye, and plasma. A decrease of environmental temperature in this season abolished the melatonin rhythm. When animals were maintained in August under high (25 +/- 1 degree) temperature and long (18L:6D) or short (6L:18D) photoperiod, the duration of high night time ocular melatonin levels was correlated to the length of the dark phase. In all experiments the high ocular melatonin concentrations and the close parallelism observed between ocular and circulating melatonin profiles suggest that in this species melatonin could be released from the eyes in the general circulation.

Circadian Clock Genes of Goldfish, Carassius auratus: cDNA Cloning and Rhythmic Expression of Period and Cryptochrome Transcripts in Retina, Liver, and Gut:

Clock genes are known to be the molecular core of biological clocks of vertebrates. They are expressed not only in those tissues considered central pacemakers, but also in peripheral tissues. In the present study, partial cDNAs for 6 of the principal clock genes (Period 1-3 and Cryptochrome 1-3) were cloned from a teleost fish, the goldfish (Carassius auratus ). These genes showed high homology (approximately 90%) with the respective cDNAs of zebrafish (Danio rerio), the only other teleost from which clock genes have been cloned. The daily expression pattern of each gene in retina, gut, and liver of goldfish was investigated using quantitative RT-PCR and cosinor analysis. All clock genes analyzed in the retina showed circadian rhythmicity; however, only Per 2-3 and Cry 2-3 were rhythmic in goldfish liver and gut. The amplitude and phase of the expression in liver and gut were different from those found in goldfish retina. Such differences suggest that other cues, such as feeding time, may contribute to the entrainment of oscillators in goldfish liver and gut. Our results support the use of goldfish as a teleost model to investigate the location and functioning of the circadian oscillators.

Leptins and leptin receptor expression in the goldfish (Carassius auratus). Regulation by food intake and fasting/overfeeding conditions

Leptin is a hormone involved in feeding and body weight regulation in vertebrates, but the relationship between energy status and leptin has not been clearly established in fish. The aim of this study was to investigate in a teleost, the goldfish (Carassius auratus), the tissue expression pattern of two leptins (gLep-aI and gLep-aII) and leptin receptor (gLepR); and the effect of feeding on expression of these genes. Leptin system expression in goldfish was firstly analyzed in fish under overfeeding (2 weeks) or fasting (1 week), and secondly, at different postfeeding times (0, 3, 6, 9 and 12h). Goldfish has two Lep-a paralog genes, gLep-aI was widely expressed in central and peripheral tissues, whereas gLep-aII was preferentially expressed in brain. This different distribution pattern of leptins suggests that they can play different physiological roles in goldfish. The gLepR mRNA was ubiquitous expressed, with the highest expression in the telencephalon and hypothalamus. No significant differences in the leptin system expression were found among control, overfed and fasting groups, suggesting an apparent lack of correlation between nutritional status and leptin system in goldfish. Hepatic expression of gLep-aI significantly increased 9h after feeding time, while hypothalamic leptin system expression did not change after feeding. In summary, leptin in goldfish could signal short-term changes in food intake, as postprandial satiety, but seems to be independent of fasting/overfeeding conditions in this teleost. The widespread distribution of leptins and leptin receptor in goldfish strongly supports that this hormone may have pleitropic actions in fish.

Corticotropin-releasing factor stimulates metamorphosis and increases thyroid hormone concentration in prometamorphic Rana perezi larvae

Attempts to identify a hypothalamic molecule that stimulates thyrotropin (TSH) secretion from amphibian pituitary have been unsuccessful to date. The effects of mammalian (ovine and human) corticotropin-releasing factor (CRF) on the thyroid function of prometamorphic (Taylor & Kollros stages XI-XVII) (Taylor and Kollros, 1946) Rana perezi larvae were studied. Chronic treatments with both ovine and human CRF (oCRF, hCRF) stimulated metamorphosis while delaying larval growth. Chronic hCRF (1 microgram) administration induced 3.2- and 5.3-fold increases in whole body concentration of thyroxine (T4) and triiodothyronine (T3), respectively. In contrast, the 0.5-microgram dose of hCRF stimulated a significant (3.4-fold) increase in whole body concentration of T4 but not of T3. Histological studies of the thyroid gland revealed a 22% increase in the number of follicles per section as a result of the chronic treatment with oCRF (1 microgram). Acute oCRF (2 micrograms) treatment induced a significant increase in T4 concentration at 4 hr (1.3-fold) and 8 hr (2.3-fold) postinjection. T3 concentration was not altered. These results support previous reports and lead us to conclude that a CRF-like peptide, and not TRH, is involved in the regulation of thyroid activity in anuran amphibians during metamorphosis.

The galanin-induced feeding stimulation is mediated via α2-adrenergic receptors in goldfish

In the present study we examined the effects of intracerebroventricular (ICV) or intraperitoneal (IP) galanin administration on food intake in satiated goldfish, at different time intervals after injections, 0-2, 2-8 and 0-8 h. We found that food intake was increased by ICV administered galanin (1 and 3.33 micrograms) at 2 and 8 h postinjection, while no modifications on feeding were observed after intraperitoneal injection in any of the studied time intervals. The galanin receptor antagonist, galantide, blocked the galanin-induced feeding increase. Pretreatment with yohimbine (alpha 2-adrenergic receptor antagonist), but not with prazosin (alpha 1-adrenergic receptor antagonist) antagonized the stimulatory effect of galanin on ingestive behavior. These results suggest that galanin is involved in the central regulation of feeding in goldfish, being the food intake stimulatory effect mediated by the alpha 2-adrenergic system.

Central administration of β-endorphin increases food intake in goldfish: pretreatment with the opioid antagonist naloxone

The effect of intraperitoneal or intracerebroventricular beta-endorphin administration on food intake has been studied in satiated goldfish. Food intake was evaluated at different time intervals after injections, 0-2, 2-8 and 0-8 h. The 0.1 and 1 micrograms doses of beta-endorphin intracerebroventricularly administered induced an increase in food intake during the first 2 h postinjection, while no modifications on feeding were observed in the next 6 h. These same doses of beta-endorphin used increased cumulative food intake at 8 h postinjection. In contrast, intraperitoneal injection of 1 micrograms of beta-endorphin did not modify food intake in any of the studied time intervals. Naloxone, an opioid antagonist, attenuated the beta-endorphin-induced feeding increase. These results suggest that opioids may play a role in modulation of feeding central regulation, acting via opioid receptors in goldfish.

Seasonal variation of gonadal development, sexual steroids, and lipid reserves in a population of the lizard Psammodromus algirus

We studied the seasonal variations of reproductive characteristics in a wild population of the lacertid lizard Psammodromus algirus by measuring gonadal weight, germinal epithelium height, sexual steroids (testosterone, estradiol, and progesterone), and lipid reserves (in fat bodies and liver) in three phases of the reproductive cycle: early breeding (late April), late breeding (mid-June), and post-breeding season (late July). In males, testis size, germinal epithelium, and testosterone plasma levels were high in the breeding season and decreased dramatically in July. However, spermatogenesis (maximum in June) was slightly delayed with respect to testosterone secretion (peak in April), suggesting that a previous increase in testosterone levels could be necessary to stimulate the initial stages of spermatogenesis

Seasonal cycles in testicular activity in the frog, Rana perezi

Studies of seasonal testicular cycle based on spermatogenetic activity and direct measurement of plasma testosterone were made in male frog Rana perezi obtained from its natural biotope in the Iberian Peninsula. Testosterone plasma level was determined by radioimmunoassay and exhibited notable differences according to season: plasma testosterone was lowest (less than 0.5 ng/ml) in summer and then increased progressively to reach a peak in spring (3-4 ng/ml), coincident with mating. After spermiation, when an increase in temperature and photoperiod in the natural habitat occurs, levels decline. Fat bodies also show a pronounced seasonal cycle with total regression following breeding and maximal development in winter. However, testicular weight was independent of seasons, and no significant change was observed throughout the year. Histological evidence indicates that although cell nests of different types are present every month of the year, the most important spermatogenetic activity is initiated in summer. The possible relationship between spermatogenetic activity and testosterone production and the importance of environmental factors as synchronizers of seasonal reproduction are discussed.