Norepinephrine turnover in pineal gland and superior cervical ganglia. Changes after gonadotrophin administration to castrated rats

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

The temporal relationship between melatonin and prolactin in women

The relationship between the concentrations of melatonin and prolactin (PRL) over 24 hours has been investigated. Two peaks in PRL concentrations were distinguished: an evening peak (at 8:00 P.M.) and a nocturnal peak (at 6:00 A.M.). Melatonin concentrations showed a single peak (at 2:00 A.M.). In both the follicular and luteal phases of the menstrual cycle, melatonin increased 2 to 3 hours after the evening increase in PRL and 4 hours before the nocturnal rise in PRL concentrations. Oral administration of melatonin stimulated PRL release. The PRL response varied with menstrual cycle stage being significantly greater in the ovulatory (P less than 0.001) and luteal (P less than 0.01) phases than in the follicular phase. The results suggest that melatonin may be involved in control of the nocturnal PRL increase.

Sex-related differences in pineal gland N-acetyltransferase induction by d-amphetamine

The activity of the rat pineal gland enzyme, N-acetyltransferase (NAT), was measured to determine if amphetamine stimulation of norepinephrine release from sympathetic fibers innervating the gland varies according to sex-dependent mechanisms. Pineal gland NAT activity was increased following amphetamine treatment to a greater extent and for a longer duration in adult female rats compared to male animals. The greater in vivo stimulation of adult female pineal gland NAT activity by the drug developed after puberty, depended upon intact gonads, and apparently was not due to sex differences in the amount of norepinephrine released by the drug from sympathetic nerves when tested under in vitro conditions. The in vivo sex dependent effects of amphetamine may be related to the lesser rate at which the drug is metabolized and/or excreted by female rats compared to males.

Molecular mechanisms of neuroendocrine integration in the central nervous system: an approach through the study of the pineal gland and its innervating sympathetic pathway

In the brain specialized cells known as 'neuroendocrine transducers' translate an input of neural activity into a hormonal output, e.g. oxytocin released into the blood stream. Other, more typical neurons make the reverse conversion constituting chemoreceptors which transform the hormonal 'language' into changes in their firing rate ('endocrine-neural' transduction). 'Endocrine-endocrine' transducing events occur at the level of the neurosecretory cells that translate a hormonal signal into another, different, hormone output. This article reviews the molecular aspects of several neuroendocrine integrative processes in the hypothalamus, the pineal gland and the cervical sympathetic pathway. The discussed results indicate that the pineal gland and its innervating sympathetic neurons located in the superior cervical ganglia constitute an easy-to-manipulate model system for the study of basic neuroendocrine mechanisms because: (i) receptors for various hormones exist in the mammalian pineal and sympathetic ganglia; (ii) the pattern of pineal steroid metabolism resembles that of the neuroendocrine hypothalamus; (iii) pineal estrophilic and androphilic receptors as well as the pattern of steroid metabolism are modulated by the sympathetic nerves; (iv) neuronal activity in the cervical sympathetic pathway is modified by hormone treatment at preganglionic, ganglionic and postganglionic sites.

Sex-differences in catecholamine metabolites in human urine during development and at adulthood

Adrenergic amines (dopamine [DA], norepinephrine [NE], epinephrine [E] and related compounds (DOPA, 3-methoxytyramine [MT], normetanephrine [NMN], metanephrine [MN], 3-5-dihydroxyphenylacetic acid [DOPAC], vanilmandelic acid [VMA] were analyzed in urine of human from one day to 40 years of age, in view to investigate the sex influence on catecholamine metabolism during life. In neonatal life (1 day to 3.5 months), the total amounts of urinary (E + MN) and (NE + NMN + VMA) were lower in girls than in boys, the former two compounds being mainly of adrenal medullary origin and the latter three coming largely from the sympathetic neurons. In adulthood, women excreted epinephrine (12.5 +/- 2.2 micrograms/24 hours) at lower levels then men (22.8 +/- 4.5 micrograms/24 hours) but no sex related differences occurred in the total amounts of urinary E + MN and NE + NMN + VMA. It is concluded from our study that, during the neonatal life, girls exhibit a lesser adreno-sympathetic maturity than boys, but full maturation of peripheral adrenergic sites is reached near to the fifth year of age in both sexes. The role of testosterone has been discussed. In adults, the lower epinephrine levels found in women urine do not seem to result from a sex difference in the degree of adrenergic maturity, but perhaps partly from an increased rate of epinephrine inactivation by catechol-O-methyltransferase.

Testosterone decreases beta-adrenoceptor sites in rat pineal gland and brain

Testosterone administration to orchidectomized rats brought about a significant, 55% decrease of beta-adrenoceptor sites in the pineal gland, assessed from the specific binding of radioactive dihydroalprenolol (DHA). The changes in density of binding sites were not accompanied by significant modifications of the Kd. FSH or LH treatment of acutely castrated animals did not affect pineal beta-adrenoceptor binding. The depressive effects of testosterone in beta-adrenergic receptors were also observed in crude membrane fractions of medial basal hypothalamus and cerebral cortex. Sympathetic denervation of the pineal gland by superior cervical ganglionectomy did not abolish the changes in pineal beta-adrenoceptor density caused by testosterone. Hormone effects did not depend on a direct effect of the hormone on beta-adrenoceptor sites because testosterone did not compete with [3H]-DHA for the binding sites, in vitro. These results suggest that testosterone depresses pineal beta-adrenergic sites by acting mainly on postsynaptic sites.

The sympathetic superior cervical ganglia as peripheral neuroendocrine centers

The superior cervical ganglia (SCG) provide sympathetic innervation to the pineal gland, cephalic blood vessels, the choroid plexus, the eye, carotid body and the salivary and thyroid glands. Removal of the ganglia brings about several neuroendocrine changes in mammals, including the disruption of water balance in pituitary stalk-sectioned rats, and the alteration of normal photoperiodic control of reproduction in hamsters, ferrets, voles, rams and goats. These effects are commonly attributed to pineal denervation. However pinealectomy does not always mimic ganglionectomy in its neuroendocrine sequelae. This paper discusses several examples illustrating the lack of homology of ganglia and pineal removal, including the prolactin release brought about by gonadal steroids in spayed rats, the changes in drinking behaviour caused by ganglionectomy and the control of goitrogenic response to methylmercaptoimidazole in rats. All these examples indicate that SCG removal, at least as far as for neuroendocrinologists and pineal experimenters are concerned, should not be considered simply as "pineal denervation". A functionally relevant link between SCG and the hypothalamus may occur in rats inasmuch as ganglionectomy depresses norepinephrine uptake and increases the number and responses of alpha-adrenoceptors in medial basal hypothalamus. Lastly the SCG are active points of concurrency for hormone signals, as revealed by the metabolic changes induced by steroid and anterior pituitary hormones in these structures even in the absence of intact preganglionic connections, as well as by the existence of putative receptors for some of the hormones, namely, estradiol, testosterone and corticosteroids. The SCG appear to constitute a peripheral neuroendocrine center.