Similarity between the effects of suprachiasmatic nuclei lesions and of pinealectomy on gonadotropin release in ovariectomized, sulpiride-treated and melatonin-replaced rats.

The aim of this study was to compare the effects of pineal indole treatments on LH and FSH release in pinealectomized and suprachiasmatic lesioned and ovariectomized rats rendered hyperprolactinemic by acute sulpiride treatment. Pinealectomy or suprachiasmatic nuclei lesions in female rats both decreased plasma LH and FHS at 10, but not at 20 d after surgery, whereas the daily afternoon administration of melatonin effectively restored levels of both gonadotropins to control values. In ovariectomized rats, pinealectomy or suprachiasmatic nuclei lesions were ineffective in counteracting the high plasma levels of LH and FSH.

Absence of plasma melatonin circadian rhythm during the first 72 hours of life in human infants.

To assess whether the circadian rhythm of melatonin (MT) described in umbilical cord blood of term babies is due to an active pineal in the newborn, we analyzed 119 normal neonates during the first 72 h of life. Plasma MT was measured by RIA in different neonates at different hours of the day. Statistical analysis consisted of comparison of the means of MT values grouped in two time periods of 12 h each [day period, 0900-2100 h (77 neonates); night period, 2100-0900 h (42 neonates)] and cosinor analyses to determine the existence of a circadian rhythm of MT.

Intracerebroventricular injection of naloxone blocks melatonin-dependent brain [3H]flunitrazepam binding.

The pineal hormone melatonin modulates the brain benzodiazepine binding sites and its circadian rhythm. In the present study the effects of intracerebroventricular (i.c.

Melatonin concentration in the umbilical artery and vein in human preterm and term neonates and neonates with acute fetal distress.

In order to assess the existence of a rhythmic secretion of melatonin (aMT) in newborns and whether this rhythm is affected by neonatal stress, we studied 112 newborns classified in three groups: normal babies delivered at term, preterm infants born before the 38th week, and babies with fetal distress. Melatonin was measured by RIA in the umbilical artery and vein at the time of birth. Melatonin levels in umbilical arterial and venous blood showed a diurnal rhythm in all groups.

Characterization of ouabain high-affinity binding to rat cerebral cortex. Modulation by melatonin.

High-affinity [3H]ouabain binding to membrane preparations of rat cerebral cortex was examined using a rapid filtration procedure. At 37 degrees C, binding reached equilibrium in about 60 min. Scatchard analyses of the data at equilibrium revealed a single population of binding sites with a dissociation constant of KD = 3.

Paradoxical effects of melatonin on spontaneous neuronal activity in the striatum of sham-operated and pinealectomized rats.

The acute effects of intravenous melatonin on spontaneously active striatal neurons in sham-operated and pinealectomized rats were studied. Extracellular recordings in a total of 76 neurons showed that only 19 did not modify their spontaneous activity after melatonin injection. In sham-pinealectomized rats, neural firing decreased in most cells (80% of neurons), and increased in only 5.

Modulation by pineal gland of ouabain high-affinity binding sites in rat cerebral cortex.

To investigate the participation of the pineal gland and its hormone melatonin on Na(+)-K(+)-ATPase (the sodium pump) in rat brain, we used Scatchard plots to analyze the changes in rat cerebral cortex of [3H]ouabain high-affinity binding in groups of intact, pinealectomized (PX), and sham-PX rats. Only one type of binding site, with a dissociation constant of approximately 3 nM and site number (Bmax) of approximately 250 fmol/mg protein, was apparent with our assay conditions. PX or sham-PX rats (subjected to surgery 15 days earlier) were killed at six different time intervals during the 24-h cycle.

Pinealectomy increases ouabain high-affinity binding sites and dissociation constant in rat cerebral cortex.

The effect of the pineal gland on the ouabain high-affinity binding sites (Kd = 3.1 +/- 0.4 nM, Bmax = 246.

Changes in gamma-aminobutyric acid high affinity binding to cerebral cortex membranes after pinealectomy or melatonin administration to rats.

In order to assess the effect of pinealectomy (Px) on the diurnal rhythmicity of gamma-aminobutyric acid (GABA) high affinity binding to cerebral cortex membranes, groups of intact, Px or sham Px rats (subjected to surgery 15 days earlier) were killed at six different time intervals during the 24-hour cycle. GABA binding was estimated by Scatchard analysis of 3H-GABA binding to cerebral cortex membranes prepared from individual brains; only one type of binding site with dissociation constant (KD) about 20-50 nM and site number (Bmax) about 200-500 fmol/mg protein was apparent in the assay conditions employed. In intact and sham Px rats Bmax attained minimal values at night and increased during daylight.

Diurnal variations of benzodiazepine binding in rat cerebral cortex: disruption by pinealectomy.

In a previous work, pinealectomy was found to depress benzodiazepine (BZP) receptor binding in cerebral cortex membranes of rats killed at noon. In order to assess the effect of pineal removal on diurnal variations of BZP binding site concentration and affinity, groups of intact, pinealectomized, or sham-pinealectomized rats (subjected to surgery 2 wk earlier) were killed at six different time intervals during the 24-h cycle. BZP binding was assessed by Scatchard analysis of 3H-flunitrazepam high-affinity binding to cerebral cortex membranes.