Surgical removal of the olfactory bulbs increases sensitivity of the reproductive system of female rats to the inhibitory effects of late afternoon melatonin injections (original) (raw)
Related papers
Journal of Neuroendocrinology, 1990
The effects of castration and testosterone treatment on pineal day-night rhythms were studied in male rats. Bilateral gonadectomy was performed at 21 days of age. Testosterone propionate was given subcutaneously to castrated animals in a dose of 10 μg/100 g body weight during two consecutive days before sacrifice. Animals were killed 40 days after gonadectomy at four different times of a 12:12 h light-dark cycle (1600, 2400, 0400 and 0800h). Tyrosine hydroxylase activity was measured in individual pineals by means of high-performance liquid chromatography determination of L-DOPA formed. Pineal levels of norepinephrine, dopamine, 5-hydroxytryptamine and 5-hydroxyindole acetic acid were determined by high-performance liquid chromatography with amperometric detection, while pineal melatonin content was measured by radioimmunoassay. Castration abolished the day-night rhythms of pineal tyrosine hydroxylase activity and norepinephrine content, both by elevating their daytime levels and by blocking their nocturnal rise. In addition, gonadectomy drastically modified pineal indoleamine metabolism by increasing daytime levels of both 5-hydroxytryptamine and 5-hydroxyindole acetic acid, and by reducing the nocturnal elevation of pineal melatonin content. Testosterone treatment was unable to prevent the effect of orchidectomy on pineal rhythms of tyrosine hydroxylase activity, 5-hydroxytryptamine or 5-hydroxyindole acetic acid content, however it partially restored the day-night pineal rhythms of both norepinephrine and melatonin content. These results are indicative of a possible participation of reproductive hormones in the control of pineal rhythmic activity in the male rat. Apparently, since gonadectomy abolished the nocturnal rise of both pineal tyrosine hydroxylase activity and norepinephrine content, the primary site of action of reproductive hormones could be at the level of the superior cervical ganglion.
Canadian Journal of Physiology and Pharmacology, 1977
Adrenocol.tica1 function was studied in rats after shampineaIectorny, pinealectomy, or immunization against melatonin and IV-acetylserotonin (NAS). Pineais were stimulated to increase melatonin synthesis by blinding or exposure to 23 h of darkness daily. Blintfing elevated morning corticosterone levels without altering the corticosterone response to novelty stirnulation. Among blinded animals, pinealectomy partially reversed and immunization completely reversed the elevations in morning steroid levels. Exposure to short daily photoperiods flattened the diurnal corticosterone rhythm. Pineaiectomy did not affect morning corticosterone levels but reduced evening corticosterone levels. More importantly, ira~naunization resulted in reduced corticosterone levels throughout the diurnal cycle. These findings suggest that melatonita and (or) NAS may be involved in the regulation of resting diurnal adrenocortical function.
Brazilian Journal of Medical and Biological Research, 2004
The current study was conducted to investigate the relationship between melatonin and chronic anovulation. Adult (3-4 months old) female Wistar rats were submitted to pinealectomy: group I: pinealectomized ovariectomized melatonin-treated (N = 10); group II: pinealectomized ovariectomized placebo-treated (N = 12); group III: pinealectomized light-treated placebo-treated (N = 10) or maintained under continuous light; group IV: maintained under continuous light, ovariectomized melatonin-treated (N = 22); group V: maintained under continuous light, ovariectomized placebo-treated (N = 10); group VI: maintained under continuous light placebo-treated (N = 10). In order to assess ovarian modifications, unilateral ovariectomy was performed during the fourth month in groups I, II, IV, V and the other ovary was removed after 8 months. Ovariectomy was performed in groups III and VI only after eight months. Melatonin (200 µg/100 g body weight) dissolved in 0.02 ml absolute ethanol was injected intramuscularly daily during the last 4 months into groups I and IV. The other groups were treated with placebo (NaCl). The ovarian cysts were analyzed and their area, perimeter and maximum diameter, as well as the thickness of the ovarian capsule were measured. Daily colpocytological smears were performed throughout the study. Persistent estrous condition and ovarian cysts were observed in all groups. In pinealectomized rats the ovarian and vaginal alterations disappeared at the end of the study and in rats maintained under continuous light the vaginal and ovarian polycystic aspect was reversed only in those treated with melatonin. We conclude that melatonin may act on the ovarian response reverting chronic anovulation induced by pinealectomy or continuous light.
The ontogeny of pineal and serum melatonin in male rats at mid-light and mid-dark
Journal of Neural Transmission, 1988
The levels of pineal and serum melatonin at mid-light and mid-dark of male rats under a photoperiod of 12 h light: 12 h darkness with age ranging from day 1 to day 42 postpartum were determined. At mide-dark, pineal melatonin levels were found to increase with age; when the body weight was considered, an early developmental rise (1-to-9-day old), an active period (11to 17-day old), and a period of lower levels (after 21-day-old) were noted. Serum melatonin levels at mid-dark showed similar changes to the latter. At mid-light, this pattern of change was also present in pineal melatonin contents relative to body weight but was absent in serum melatonin levels. Our study indicated that weaning was not responsible for the pre-pubertal decline in pineal melatonin secretion. It was suggested that these changes in the secretory pattern of pineal melatonin may play a role in the development of the reproductive system in rats.
Steroids, 1996
M) were looked .fi~r upon isoproterenol-stimulated melatonin release by perifused pineal gland~" removed from male rats and female rats in diestrus. Two different times of a 12/12 hour light~dark cycle, i.e., 7 and 19 hours after light onset, were documented in order to look for the existence of a circadian stage-dependence of the hormone effects. Both testosterone (45~50%) and estradiol (60-80%) markedly increased melatonin release by glands removed during the dark span and not during the light span. These results show a direct effect of gonadal hormones on pineal melatonin release and strongly suggest a time-related effect ~[ these hormones on pineal function.
Biology of Reproduction, 1993
The aims of this study were to validate the use of a timed infusion protocol for restoring physiologically appropriate rhythms of melatonin in the circulation of pinealectomized hamsters and, using such infusions, to compare the relative importance of the parameters of the nocturnal melatonin signal-frequency, phase, and duration of the interval between signals-in the photoperiodic control of testicular function in male Syrian hamsters. Hamsters were pinealectomized and fitted with a chronic s.c. cannula enabling them to receive timed infusions of melatonin (50 ng/h) or saline vehicle (50 jl/h). In experiment 1, RIA of serum samples confirmed that s.c. infusions produced a pattern of melatonin in the blood equivalent in amplitude and duration to that observed previously in pineal-intact animals exposed to a short photoperiod. In experiment 2, we investigated the relative importance of the frequency of the melatonin signal and the duration of the interval between signals. Pinealectomized animals that received infusions of saline for 6 wk had large testes and high concentrations of LH in the serum. Animals that received a series of short-day-like infusions of melatonin of 14-h duration, separated by an interval of either 10 h or 6 h, underwent gonadal regression and had low serum concentrations of LH. Animals that received infusions of melatonin of 8-h duration, separated by intervals of 12 h, also exhibited full gonadal collapse. However, animals that received the same 8-h infusions separated by intervals of 8 h (i.e., once every 16 h) did not undergo gonadal regression and their circulating levels of LH remained high. These results demonstrate that the frequency at which melatonin signals are received, rather than the duration of the interval between them, is critical to interpretation of photoperiodic information. To confirm that the continuous duration of a melatonin signal is also important, another group of animals received two daily infusions of melatonin of 5-h duration, separated by a break of 4 h, giving an overall signal of 14 h. These infusions were ineffective, there being no difference in testicular size or serum LH titers between animals receiving melatonin and those receiving saline. In experiment 3, we tested whether the phase at which a signal is presented is important in order for animals to recognize a series of long signals and engage a short-day-like response. Controls receiving infusions of melatonin of 8-h duration at the same phase every day (infusions terminated 1 h before lights-off) for 6 wk exhibited gonadal regression. Experimental animals received the same number of infusions, but these were delivered at one of three phases of the light:dark (L:D) cycle, in an irregular order such that no infusion was predicted by the phase of its predecessor. After 6 wk, these animals exhibited significant gonadal atrophy, demonstrating that the phase of the L:D cycle at which a melatonin signal is encountered does not matter and that a series of signals need not be encountered in an ordered fashion for a photoperiodic response to occur.
Journal of Neural Transmission, 1985
Pineal levels of tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindoleacetic acid and the activities of the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase were determined in male albino rats and Syrian hamsters that were implanted with the appropriate corticosteroid or adrenalectomized two weeks earlier. Melatonin content and NAT activity were increased at 4 hours (during darkness) in adrenalectomized hamsters; conversely, no alterations in melatonin levels were observed in either adrenalectomized or implanted rats. It is suggested that the changes in adrenal function probably have a minor influence on pineal melatonin production.
Journal of Neuroendocrinology, 1996
Using quantitative autoradiography, melatonin receptors have been studied during post-natal and pubertal development of the rat in 2 brain and 2 pituitary structures. In the pars distalis of anterior pituitary, melatonin receptors decrease gradually in density after birth and disappear in 30 day-old animals. In contrast melatonin binding is only expressed in the paraventricular nuclei of the thalamus at the age of 21-23 days and is always present in adult animals. In the suprachiasmatic nuclei and in the pars tuberalis of the pituitary, melatonin receptor density decreases after birth, remains stable for approximately 1 month and increases again at puberty to reach the birth values in the adult. This increase was absent in pinealectomized and in castrated animals but present in castrated animals receiving testosterone suggesting that it depends upon circulating testosterone and melatonin levels. These results show that melatonin receptors are differentially regulated during post-natal development in each of the 4 structures studied, and that melatonin and testosterone are 2 factors which could be involved in the regulation of melatonin receptor density in the suprachiasmatic nuclei and pars tuberalis.