Pituitary and gonadal effects of GnRH (gonadotropin releasing hormone) analogues in two peripubertal female rat models.

Central precocious puberty is commonly treated by gonadotropin releasing hormone (GnRH) agonists. To compare modes of action and effectiveness of GnRH analogues and assess treatment combinations of agonistic (triptorelin) and antagonistic (cetrorelix acetate) GnRH analogues with established treatment, we used prepubertal 31-d-old ovariectomized female rats. Strongest inhibition of LH and FSH occurred after 2-d treatment with antagonist alone (LH 0.

Recent progress in understanding the temporal behavior of unicellular organisms.

This survey summarizes the findings concerning endogenous oscillations of three unicellular organisms: the dinophyte Gonyaulax polyedra, the ciliate Tetrahymena thermophila and the euglenophyte Euglena gracilis. All of them behave rhythmically and show the common features of zeitgeber action, differential sensitivity and temperature compensation; however, they exhibit some species-specific peculiarities that make each of them suitable for addressing particular chronobiological questions. Although ultradian rhythms have been described for Tetrahymena thermophila and Euglena gracilis, they appear under different conditions: in the first case, a modulation of the period in relation to the concentration of nutrients is observed, whereas Euglena oscillates in an ultradian and circadian fashion simultaneously.

On the primary functions of melatonin in evolution: mediation of photoperiodic signals in a unicell, photooxidation, and scavenging of free radicals.

Melatonin is widely abundant in many eukaryotic taxa, including various animal phyla, angiosperms, and unicells. In the bioluminescent dinoflagellate Gonyaulax polyedra, melatonin is produced in concentrations sometimes exceeding those found in the pineal gland, exhibits a circadian rhythm with a pronounced nocturnal maximum, and mimics the short-day response of asexual encystment. Even more efficient as a cyst inducer is 5-methoxyptryptamine (5MT), which is also periodically formed in Gonyaulax.

Effects of indoleamines and short photoperiods on the encystment of Gonyaulax polyedra.

At a temperature of 15 degrees C, Gonyaulax polyedra responds to short days (light less than or equal to 10 h) by transition to the stage of a resting cyst. At 20 degrees C, even an light:dark (LD) cycle of 6:18 is incapable of inducing this process. In otherwise cyst-inducing conditions (15 degrees C; 10 h of light per day), an interruption of the scotophase by 2 h of light (LDLD 8:2:2:12 or 2:2:8:12) prevented encystment.

Photoperiodism and effects of indoleamines in a unicellular alga, Gonyaulax polyedra.

Mediation of photoperiodic effects by indoleamines, especially melatonin, is known in higher vertebrates. A similar mechanism may occur in a unicellular alga, the dinoflagellate Gonyaulax polyedra. This organism entered the dormant stage of a cyst upon short-day treatment at lowered temperatures.