Seasonal variations of Substance P in the striatum of the female rat are affected by maternal and offspring pinealectomy.

The effect of pinealectomy (PIN-X) and PIN-X+melatonin treatment during pregnancy (PIN-X+MEL) 100µg/100g body weight on Substance P (SP) in the striatum was investigated in offspring female rats. Female offspring were divided into control and PIN-X at the neonatal period, and studied at days 31 and 60. PIN-X mother/control offspring showed a positive influence on striatal SP values in winter, at both ages and in spring at day 31. However, this effect of maternal PIN-X was not observed in summer or fall. The effect of PIN-X on the offspring showed a positive effect in spring at day 31 and summer at the two ages studied. This effect was not observed in fall or winter. Two generations, PIN-X mother/PIN-X offspring, altered the effect of mother or offspring PIN-X and decreased the SP values in winter, spring and summer. Only striatal SP at day 60 in fall was increased. In two generations PIN-X, the striatal SP values were similar to those observed in control mother/control offspring. The effect of PIN-X+MEL treatment on mothers during pregnancy was inhibitory for the intact offspring and stimulatory for PIN-X offspring. In conclusion, the results indicate that maternal and offspring PIN-X seem to exert a rotative and positive seasonal influence from winter to spring to summer. Two generations PIN-X disrupted this rotative circuit and in fall a compensatory discharge of SP was observed.

Prenatal melatonin and its interaction with tachykinins in the hypothalamic-pituitary-gonadal axis.

The pineal gland, through its hormone melatonin, influences the function of the hypothalamic-pituitary-gonadal axis. Tachykinins are bioactive peptides whose presence has been demonstrated in the pineal gland, hypothalamus, anterior pituitary gland and the gonads, in addition to other central and peripheral structures. Tachykinins have been demonstrated to influence the function of the hypothalamic-pituitary-gonadal axis, acting as paracrine factors at each of these levels. In the present review, we examine the available evidence supporting a role for melatonin in the regulation of reproductive functions, the possible role of tachykinins in pineal function and the possible interactions between melatonin and tachykinins in the hypothalamic-pituitary-gonadal axis. Evidence is presented showing that melatonin, given to pregnant rats, influences the developmental pattern of tachykinins in the hypothalamus and the anterior pituitary gland of the offspring during postnatal life. In the gonads, the effects of melatonin on the tachykinin developmental pattern were rather modest. In particular, in the present review, we have included a summary of our own work performed in the past few years on the effect of melatonin on tachykinin levels in the hypothalamic-pituitary-gonadal axis.

Influence of maternal pineal gland on the developmental pattern of neurokinin A (NKA) and substance P (SP) in male-rat-offspring: relationship to the season of the year.

The present study examines the influence of maternal pineal gland on the frontal cortex, striatal and testicular concentrations of the tachykinins, neurokinin A (NKA) and substance P (SP). Control, pinealectomized (PIN-X) and PIN-X plus melatonin-treated (PIN-X + MEL) mother rats were prepared. Male offspring rats were studied at 21, 31 and 60 days of age, during the four seasons of the year. In control-offspring tachykinin concentrations in frontal cortex were found at their highest levels in 21-day-old rats with a moderate decrease up to 60 days of age. This developmental pattern was season-dependent, observed only during summer and fall. Maternal PIN-X or PIN-X + MEL resulted in alterations in the offspring, showing during spring and summer significantly higher concentrations (P < 0.01) and during fall significantly lower concentrations of tachykinins in the frontal cortex (P < 0.05, P < 0.01) as compared to control-offspring. The tachykinin concentration in the striatum of control-offspring showed no major modifications throughout the ages studied in the four seasons of the year. With very few exceptions, PIN-X- and PIN-X + MEL did not alter tachykinin concentrations in striatum. Testicular SP concentrations showed a decrease from 21 to 60 days of age. PIN-X or PIN-X + MEL only caused minor and inconsistent modifications in testicular SP levels. In conclusion, our data clearly indicate for the first time that the maternal pineal gland participates in the regulation of the postnatal tachykinin development in some areas of the central nervous system. This effect was more evident in the frontal cortex than in the striatum and testes.

Seasonal changes of SP and NKA in frontal cortex, striatum and testes in the rat. Role of maternal pineal gland.

The concentrations of neurokinin A (NKA) and substance P (SP), members of tachykinins family, have been studied in all seasons of the year in frontal cortex, striatum and testes of male offspring 21-, 31-, or 60 days old of mother Wistar rats: control, pinealectomized (PIN-X) and pinealectomized + melatonin during pregnancy (PIN- X + MEL) kept under 12h:12h L:D. Control-offspring: in spite of having been kept under constant environmental conditions throughout the year, had marked differences in tachykinin concentrations. The highest tachykinin concentrations in the frontal cortex were found in summer and fall and the lowest in winter and spring. Maternal PIN-X resulted in alterations of this developmental pattern, mainly in PIN-X- and PIN- X + MEL-offspring in which the highest tachykinin concentrations at 21 and 31 days of age were only observed during summer. The alterations were observed up to 60 days of age for both tachykinins, when at this age control-offspring showed similar NKA concentrations. Seasonal variations were still observed in PIN-X- and PIN- X + MEL-offspring. In striatum and testes no mayor modifications throughout the four seasons of the year were found, with very few exceptions. PIN-X did not alter tachykinin concentrations, neither treatment with melatonin did it. In conclusion, our data clearly indicate for the first time that NKA and SP do indeed have seasonal rhythms in frontal cortex and that the maternal pineal gland plays a role in their entrainment already during fetal life.

Developmental pattern of tachykinins during aging in several organs: effect of exogenous melatonin.

Mammalian neurokinin A (NKA) and substance P (SP) are neuropeptides widely distributed in the body; they are potential regulators of the basal blood flow and therefore of the function of many organs and tissues. In the present investigation, we studied the age-dependent changes in NKA and SP in ovary, liver, pancreas and spleen as well as the role of exogenous melatonin on these changes. Female rats of 5, 15 or 25 months of age were studied. In the ovary, NKA concentrations did not change during aging. SP concentrations in the control group were significantly higher (P<0.01) in old rats than in the other two age groups studied. Melatonin treatment resulted in reduced concentrations as compared with those of the control old rats. In the pancreas, NKA and SP concentrations increased during aging, the young rats showing significantly lower values (P<0.01) than middle-aged and old rats for NKA and significantly lower (P<0.01) than the old rats for SP. After melatonin treatment the differences in NKA concentrations disappeared and SP decreased in middle-aged as compared with those in old rats. In the liver, NKA and SP concentrations in the control and melatonin-treated groups did not differ significantly for the three age groups studied. Splenic NKA in control and melatonin-treated groups increased from young to middle-age up to old ages. SP concentrations showed similar values at all ages except in melatonin-treated old rats; in these animals there were significantly higher concentrations than in young melatonin-treated rats. The effect of melatonin was mainly observed on the ovary and pancreas in old rats, with a reduction in the concentrations as compared with those observed in the young groups.

Age differences in neurokinin A and substance P from the hypothalamus, pituitary, pineal gland, and striatum of the rat. Effect of exogenous melatonin.

Previous data showed that aging of the central nervous system (CNS) is associated with widespread changes in tachykinin gene expression. However, there are no data about the possible role of exogenous melatonin in modulating the tachykinergic system during aging. The aim of this work was to analyze the age-dependent changes on neurokinin A (NKA) and substance P (SP) levels in hypothalamus, pituitary, pineal gland and striatum and the role of exogenous melatonin on these changes. We studied female rats at three different ages: 5-month-old (cyclic), 15-month-old (preacyclic) and 25-month-old (acyclic). Hypothalamic tachykinin levels increase when female rats reached acyclicity, this increase was blunted in acyclic-melatonin-treated rats. However, melatonin treatment in young cyclic rats resulted in significantly increased values as compared to controls. Pituitary NKA concentrations did no show age-dependent changes in control rats, however, in both, preacyclic and acyclic-melatonin-treated rats significantly increased values of pituitary NKA were found compared to controls. In the pineal gland, a marked decrease of NKA levels was observed in acyclic-control rats. Melatonin treatment did not alter this decrease. In the striatum, NKA and SP concentrations were significantly reduced in preacyclic- and acyclic-control rats compared to young cyclic rats, melatonin had no effect on striatal tachykinins. Our results indicate that melatonin may regulate tachykinin stores during aging mainly on structures of the neuroendocrine-reproductive axis.

Spermatogenesis in Bclw-deficient mice.

Bclw is a death-protecting member of the Bcl2 family of apoptosis-regulating proteins. Mice that are mutant for Bclw display progressive and nearly complete testicular degeneration. We performed a morphometric evaluation of testicular histopathology in Bclw-deficient male mice between 9 days postnatal (p9) through 1 yr of age. Germ cell loss began by p22, with only few germ cells remaining beyond 7 mo of age. A complete block to elongated spermatid development at step 13 occurred during the first wave of spermatogenesis, whereas other types of germ cells were lost sporadically. Depletion of Sertoli cells commenced between p20 and p23 and continued until 1 yr of age, when few, if any, Sertoli cells remained. Mitochondria appeared to be swollen and the cytoplasm dense by electron microscopy, but degenerating Bclw-deficient Sertoli cells failed to display classical features of apoptosis, such as chromatin condensation and nuclear fragmentation. Macrophages entered seminiferous tubules and formed foreign-body giant cells that engulfed and phagocytosed the degenerated Sertoli cells. Leydig cell hyperplasia was evident between 3 and 5 mo of age. However, beginning at 7 mo of age, Leydig cells underwent apoptosis, with dead cells being phagocytosed by macrophages. The aforementioned cell losses culminated in a testis-containing vasculature, intertubular phagocytic cells, and peritubular cell "ghosts." An RNA in situ hybridization study indicates that Bclw is expressed in Sertoli cells in the adult mouse testis. Consequently, the diploid germ cell death may be an indirect effect of defective Sertoli cell function. Western analysis was used to confirm that Bclw is not expressed in spermatids; thus, loss of this cell type most likely results from defective Sertoli cell function. Because Bclw does not appear to be expressed in Leydig cells, loss of Leydig cells in Bclw-deficient mice may result from depletion of Sertoli cells. Bclw-deficient mice serve as a unique model to study homeostasis of cell populations in the testis.

Cell proliferation and hormonal changes during postnatal development of the testis in the pig.

Histometrical evaluation of the testis was performed in 36 Piau pigs from birth to 16 mo of age to investigate Sertoli cell, Leydig cell, and germ cell proliferation. In addition, blood samples were taken in seven animals from 1 wk of age to adulthood to measure plasma levels of FSH and testosterone. Sertoli cell proliferation in pigs shows two distinct phases. The first occurs between birth and 1 mo of age, when the number of Sertoli cells per testis increases approximately sixfold. The second occurs between 3 and 4 mo of age, or just before puberty, which occurs between 4 to 5 mo of age, when Sertoli cells almost double their numbers per testis. The periods of Sertoli cell proliferation were concomitant with high FSH plasma levels and prominent elongation in the length of seminiferous cord/tubule per testis. Leydig cell volume increased markedly from birth to 1 mo of age and just before puberty. In general, during the first 5 mo after birth, Leydig cell volume growth showed a similar pattern as that observed for testosterone plasma levels. Also, the proliferation of Leydig cells per testis before puberty showed a pattern similar to that observed for Sertoli cells. However, Leydig cell number per testis increased up to 16 mo of age. Substantial changes in Leydig cell size were also observed after the pubertal period. From birth to 4 mo of age, germ cells proliferated continuously, increasing their number approximately two- to fourfold at each monthly interval. A dramatic increase in germ cells per cross-section of seminiferous tubule was observed from 4 to 5 mo of age; their number per tubule cross-section stabilized after 8 mo. To our knowledge, this is the first longitudinal study reporting the pattern of Sertoli cell, germ cell, and Leydig cell proliferative activity in pigs from birth to adulthood and the first study to correlate these events with plasma levels of FSH and testosterone.

Cimetidine (Tagamet) is a reproductive toxicant in male rats affecting peritubular cells.

Cimetidine (Tagamet) is a potent histaminic H2-receptor antagonist, extensively prescribed for ulcers and now available without prescription. Cimetidine is a known testicular toxicant, but its mechanism of action remains uncertain. Rats were treated i.p. with cimetidine either at 50 mg/kg or 250 mg/kg body weight for 59 days. Accessory sex organ weights, but not testis weight, were significantly reduced in the high dose treated groups. FSH levels were significantly elevated in both treated groups, but testosterone levels were unchanged. A high degree of variability characterized testis histology, with most tubules appearing normal and some tubules (15-17%) partially lacking or devoid of germ cells. Morphometry showed that although seminiferous tubule volume was not significantly changed, the volume of peritubular tissue was reduced in the high dose group. There was extensive duplication of the basal lamina, lamina densa in both apparently normal spermatogenic tubules and severely damaged tubules. Apoptotic peritubular myoid cells were also found. TUNEL labeling confirmed extensive apoptotic cell death in peritubular cells, but revealed apoptosis of vascular smooth muscle. Given that 1) peritubular myoid cell apoptosis occurs in apparently normal tubules, that 2) basal lamina disorders are found, and that 3) peritubular cells are lost from the testis, it is suggested that the primary event in cimetidine-related damage is targeted to testicular smooth muscle cells. This is the first in vivo-administered toxicant to be described that targets myoid cells, resulting in abnormal spermatogenesis.

Prenatal melatonin exposure affects luteinizing hormone and hypothalamic and striatal neuropeptide Y in the male rat offspring.

The present study examines the influence of prenatal melatonin on the hypothalamic and striatal neuropeptide Y (NPY) concentrations as well as on luteinizing hormone (LH) levels. Male rat offspring of control and melatonin treated mother rats were studied at different ages of the sexual development: infantile, prepubertal, pubertal and adult ages. Hypothalamic NPY levels were much higher during the juvenile than throughout the infantile period. After prenatal melatonin treatment significantly higher values since day 15 up to 35, also at 60 days of age were found, as compared with controls. Striatal NPY levels were lower than in hypothalamus. Again, NPY in the striatum from offspring of melatonin treated mother rats showed significantly higher values than the respective controls at most of the ages studied. However, prenatal melatonin exerted an inhibitory influence upon LH secretion pattern, since decreased concentrations up to 25 days of age and delayed peak values at pubertal age were observed. The present study also suggest that the effect of NPY upon LH secretion is related to sexual development, since NPY exerted opposite effect in infantile than in pubertal period and melatonin administration during intrauterine life prevented this effect.

Intracellular distribution of GABA in the rat anterior pituitary. An electron microscopic autoradiographic study.

We studied the internalization and intracellular distribution of [3H] GABA in rat anterior pituitary cells. Electron microscopic autoradiography of anterior pituitary fragments or dispersed pituitary cells incubated with [3H] GABA showed that lactotrophs and, to a lesser extent, somatotrophs were the only cells that contained radioactive grains. Grain density analysis performed on dispersed pituitary cells after a pulse-chase experiment (10 min pulse and then change to a medium without radioactive GABA for various periods up to 2 h) revealed that GABA internalized by lactotrophs was distributed in various intracellular membranous organelles. Of the cell compartments examined, plasma membrane, Golgi apparatus, mitochondria and secretory granules had different time-dependent labeling patterns. The highest grain density values were associated with plasma membrane (at the first chase time) and the Golgi apparatus. Mitochondria and secretory granules also showed significant grain density values. A similar pattern of distribution was observed when fragments of prolactin-secreting pituitary adenomas were incubated with [3H] GABA. These results provide morphological data on the cellular specificity and intracellular distribution of GABA in anterior pituitary cells.

Effects of growth hormone overexpression and growth hormone resistance on neuroendocrine and reproductive functions in transgenic and knock-out mice.

Transgenic mice overexpressing growth hormone (GH) exhibit alterations in the function of the hypothalamic-pituitary-gonadal (HPG) axis and the H-P-adrenal axis. Alterations in the turnover of hypothalamic neurotransmitters, in plasma hormone levels, and in regulation of their release are associated with reproductive deficits, particularly in females. Results reported after publication of our minireview on this subject provided evidence that GH-transgenic mice have increased binding of GH to GH binding proteins in plasma, are hyperinsulinemic and insulin resistant, and have major alterations in energy budgets with increased allocation to growth. Reduced life span and fertility of these animals may be related to insufficient allocation of energy to reproduction and maintenance. Growth hormone resistance induced by transgenic expression of an antagonistic bGH analog or by targeted disruption (knock-out, KO) of the GH receptor (GH-R) gene leads to dramatic suppression of plasma levels of insulin-like growth factor-1 (IGF-1), and dwarf phenotype due to reduced growth and increased adiposity. In both models of GH resistance, there are marked reproductive deficits in females, decline of breeding performance of males, and alterations in the function of the HPG axis. In GH-R-KO females, puberty is delayed, and litter size is reduced. Fetal weights are reduced whereas placental weights are increased, and the weight of newborn pups is reduced despite an increase in the length of gestation. In GH-R-KO males, copulatory behavior and fertility are reduced, plasma PRL is elevated, and responses to luteinizing hormone releasing hormone (LHRH) in vivo and to LH in vitro are suppressed. However, reproductive deficits in GH-R-KO mice are very mild when compared to those described previously in IGF-KO animals. Apparently, the amounts of IGF-1 that may be produced locally in the absence of GH stimulation are sufficient for sexual maturation and fertility in both sexes, whereas quantitative deficits in reproductive function reflect absence of GH-dependent IGF-1 production and other consequences of eliminating GH signaling. The reproduction phenotype of the GH-R-KO mice is also mild when compared to dwarf mice that lack GH, prolactin (PRL), and thyroid stimulating hormone (TSH). This is presumably related to the presence of redundant mechanisms in the stimulatory control of the gonads by the pituitary and the ability of animals capable of producing PRL and TSH to compensate partially for the absence of GH signaling.

Exposure to constant light during testis development increases daily sperm production in adult Wistar rats.

Testis histometry and daily sperm production (DSP) were evaluated in adult (160-day-old) Wistar rats exposed to constant light for the first 25 days after birth, and compared with control animals which were exposed to a 12 h-light-12 h-dark light regimen. Significantly greater (P < 0.05) numbers of Sertoli cell nucleoli and round spermatids per cross-section of seminiferous tubule were found in animals exposed to constant light. In addition, epididymis weight, DSP per testis and per gram of testis, as well as Leydig cell compartment volume, were significantly increased in treated animals. Although there was a clear trend toward an increased Sertoli cell population per testis in animals exposed to constant light, this difference was not statistically significant (P < 0.05). The number of round spermatids as expressed per Sertoli cell was the same in both groups. Surprisingly, the diameter and volume of round spermatid nucleus at stages I and VII of the cycle of seminiferous epithelium were significantly lower (P < 0.05) in treated animals. In conclusion, constant illumination during neonatal testis development increased sperm production and Leydig cell compartment volume in adult rats probably through a mechanism involving elevated follicle stimulating hormone and luteinizing hormone during the prepubertal period. To our knowledge, this is the first study showing that altering the light regimen can affect sperm production in non-seasonal breeders.

Effect of progesterone on tachykinin concentrations in the hypothalamus and anterior pituitary of female siberian hamsters.

The effect of progesterone on SP- and NKA-like immunoreactive substances in the hypothalamus and anterior pituitary was studied in ovariectomized and in ovariectomized, estrogen treated Siberian hamsters. Neither ovariectomy nor progesterone or estradiol treatment resulted in apparent changes in the tachykinin concentration in the hypothalamus. No effect of the treatments was seen on the release of tachykinins by hypothalami incubated in vitro in presence of high KCl concentrations. Ovariectomy resulted in a significant increase in the concentrations of both tachykinins in the anterior pituitary, as compared with intact animals. Progesterone (5 mg/animal) significantly reduced tachykinin concentrations in the anterior pituitary, as compared with the values found in ovariectomized animals. Estradiol completely suppressed the post-ovariectomy increase in anterior pituitary tachykinins, and progesterone did not significantly modify the response to estradiol. Lower doses of progesterone (250 microg or 1 mg/animal) significantly reduced NKA concentrations in the anterior pituitary of ovariectomized Siberian hamsters, but SP concentrations, although showing a similar tendency, were not significantly different in progesterone-treated as compared with ovariectomized, control animals. These results suggest that progesterone may modulate tachykinin stores in the anterior pituitary gland of Siberian hamsters.

Transgenic mice overexpressing the growth-hormone-releasing hormone gene have high concentrations of tachykinins in the anterior pituitary gland.

According to recent reports, substance P (SP) is localized in the anterior pituitary gland within subsets of thyrotropes and somatotropes, although earlier electron-microscopic studies described the presence of this tachykinin in mammotropes and gonadotropes. Transgenic mice overexpressing the growth-hormone-releasing hormone (GHRH) gene have markedly enlarged pituitary glands, due to hyperstimulation of the somatotropes. Therefore, we speculated that if somatotropes are able to synthesize tachykinins, these peptides should be greatly increased in the anterior pituitary of transgenic GHRH mice. We found that, in accordance with our working hypothesis, both SP and neurokinin A (NKA) were markedly increased in the anterior pituitary gland of male and female transgenic mice, compared with their respective normal controls. In male transgenic mice, NKA was 13.6- and SP 20.2-fold higher than in the anterior pituitary from normal mice. In female transgenic mice, NKA was 40- and SP 100-fold higher than in the anterior pituitary from normal female mice. In male transgenic mice, NKA and neuropeptide K (NPK) contents in the anterior pituitary showed no significant changes between 26 and 50 days of age but significantly increased between 50 days and 5 months of age. The concentration of NKA in the anterior pituitary did not show significant differences between 26 days and 5 months of age, but NPK concentrations in the anterior pituitary significantly decreased with age. In female transgenic mice, NKA content and concentration in the anterior pituitary increased after 35 days of age, but NPK concentrations significantly decreased after 26 days of age. Triiodothyronine markedly decreased anterior pituitary tachykinins, but ovariectomy and estrogen administration failed to significantly affect tachykinin concentrations in the anterior pituitary of transgenic mice. Tachykinin immunostaining was detected in some somatotropes, but tachykinins were also present in cells that were not GH positive. These findings indicate that hyperstimulated somatotropes contain increased stores of tachykinins and that these cells are a source of tachykinins in the anterior pituitary. Tachykinin stores in the anterior pituitary of transgenic mice were affected by thyroid hormones but seem to be insensitive to estrogens. The GHRH transgenic mice may be an interesting model to study the regulation of tachykinin stores in the anterior pituitary gland.

Developmental changes of hypothalamic, pituitary and striatal tachykinins in response to testosterone: influence of prenatal melatonin.

Substance P (SP) and neurokinin A (NKA), members of the family of mammalian tachykinins, are involved in the regulation of many physiological functions and are widely distributed in mammalian tissues. In this report, the effects of prenatal melatonin on the postnatal developmental pattern of NKA, and SP, and on testosterone secretion were investigated. Also, tachykinin response to the administration of testosterone propionate (TP) was studied. The brain areas studied were medio-basal-hypothalamus, pituitary gland and striatum. Male rat offspring of control or melatonin treated mother rats were studied at different ages of the sexual development: infantile, juvenile or prepubertal periods, and pubertal period. Both groups received exogenous TP (control-offspring+TP and MEL-offspring+TP), or the vehicle (control-offspring+placebo and MEL-offspring+placebo). Hypothalamic concentrations of all peptides studied in control-offspring+placebo remained at low levels until the juvenile period, days 30-31 of age. After this age, increasing concentrations of these peptides were found, with peak values at puberty, 40-41 days of age, then declining until adulthood. In the MEL-offspring+placebo a different pattern of development was observed; hypothalamic concentrations of NKA and SP from the infantile period until the end of juvenile period were significantly higher than in control-offspring+placebo. TP administration exerted a more marked influence on MEL-offspring than on control-offspring and prevented the elevation in tachykinin concentrations associated with prenatal melatonin treatment. TP administration to control-offspring resulted in significantly reduced (P < 0.05) tachykinin concentration only at 40-41 days of age, and increased (P < 0.01) during infantile period as compared to control-offspring+placebo. Pituitary NKA concentrations were lower than in the hypothalamus. In control-offspring+placebo pituitary NKA levels did not show significant changes throughout sexual development. A different developmental pattern was observed in MEL-offspring+placebo, with significantly increased (P < 0.05) pituitary NKA concentrations at 35-36 days of age than in control-offspring+placebo. TP administration to control-offspring influenced pituitary NKA levels at the end of the infantile and pubertal periods, showing at both stages significantly higher (P < 0.05) NKA levels as compared to control-offspring+placebo. NKA levels in MEL-offspring+TP were only affected at 21-22 days of age, showing significantly increased (P < 0.01) values as compared to MEL-offspring+placebo. Striatal tachykinin concentrations in control-offspring did not undergo important modifications throughout sexual development, but during the prepubertal period they started to increase. Maternal melatonin and TP injections produced short-lived alterations during the infantile period. The results showed that prenatal melatonin delayed the postnatal testosterone secretion pattern until the end of the pubertal period and postnatal peptide secretion in brain structures. Consequently, all functions depending of the affected areas will in turn, be affected.

Modulation of the hypothalamo-pituitary-gonadal axis and the pineal gland by neurokinin A, neuropeptide K and neuropeptide gamma.

Modulation of the hypothalamo-pituitary-gonadal axis and the pineal gland by neurokinin A, neuropeptide K, and neuropeptide gamma. PEPTIDES 1999. Neurokinin A (NKA), neuropeptide K (NPK) and neuropeptide gamma (NPG) are members of the family of tachykinins, and act preferentially on NK-2 tachykinin receptors. These peptides are widely distributed and are potent stimulators of smooth muscle contraction, especially in the respiratory and gastrointestinal tract. They also induce vasodilatation and plasma extravasation. Through their effects on the vascular tone, they are also potential regulators of the blood flow and therefore of the function of many organs and tissues. Tachykinins have been demonstrated to influence the secretory activity of endocrine cells, and they may have a physiological role as regulators of endocrine functions. A number of reports have indicated that NPK, NKA and NPG act on the hypothalamo-pituitary gonadal axis to regulate functions related to reproduction. Therefore, we thought that, at this point, it was important to review the available evidence suggesting the role of these tachykinins on reproductive functions by effects exerted at 3 different levels of regulation: the hypothalamus, the anterior pituitary and the gonads. These 3 tachykinin peptides were reported to have effects on reproductive functions, acting on the control of the secretion of gonadotropin and prolactin at the level of the hypothalamo-pituitary axis, and on the steroid secretion by the testes and the ovaries. Acting on the hypothalamus, tachykinins, mainly NPK, were reported to inhibit LH secretion, but this effect is dependent on the presence of gonadal steroids. On the anterior pituitary gland, however, tachykinins were shown to stimulate LH and prolactin secretion, and this effect is also dependent on the presence of gonadal steroids. Tachykinin concentrations in the hypothalamus and pituitary are regulated by steroid hormones. In the hypothalamus, estrogens and testosterone increase tachykinin concentration. In the anterior pituitary gland, estradiol and thyroid hormones markedly depress tachykinin concentrations. Ovariectomy and exposure to short photoperiods significantly increase anterior pituitary tachykinins in the Siberian hamster. In the pineal gland, SP and NK-1 receptors are present and, more recently, the presence of NKA and probably also NPK was demonstrated. Castration and steroid replacement modified the content of tachykinins in the pineal gland. The removal of the superior cervical ganglia was followed by an increase in NKA content in the pineal gland. These results suggest that gonadal steroids may influence tachykinins in the pineal gland. In the gonads, tachykinins stimulated the secretory activity of Sertoli cells, but inhibited testosterone secretion by Leydig cells. There are very few reports on the role of tachykinins in the ovary, but some of them indicated that these peptides are present in some of the ovarian structures, and they may affect the secretion of ovarian steroids. Thus, NKA, NPK and NPG appear to have a modulatory role, mainly acting as paracrine factors, on the hypothalamo-pituitary-gonadal axis.

Prenatal melatonin influences developmental changes of tachykinins in response to estradiol benzoate.

The developmental changes of hypothalamic, pituitary, striatum and pineal gland tachykinin concentrations, as well as the response to estradiol-benzoate (EB) administration, were studied in offspring of control and melatonin (MEL) treated mother rats. Female rats were studied throughout different phases of the sexual development: infantile, prepubertal and pubertal periods, in the four following groups; control-offspring+vehicle; control-offspring+EB; MEL-offspring+vehicle; MEL-offspring+EB. Hypothalamic NKA in control-offspring+ vehicle was significantly increased only at 27 days of age and in control-offspring+EB at 27 days of age and during the infantile period. Hypothalamic SP levels increased similarly in control-offspring+EB during the infantile period but the EB influence was more pronounced with significantly increased concentrations at 32 days of age. Prenatal melatonin treatment produced major alterations in these patterns of postnatal development. In MEL-offspring+EB tachykinins concentrations in the hypothalamus during infantile and prepubertal periods did not increase, however at 37 days of age, they showed significantly higher values than in control-offspring+EB groups. The developmental pattern of pituitary NKA and SP concentrations in both; control-offspring+vehicle and control-offspring+EB groups, showed similar values from the infantile period to puberty, indicating that NKA and SP concentrations remained at similar levels independently of the sexual stage, only at 27 days of age in control-offspring+EB significantly increased values were found as compared to MEL-offspring+EB. Prenatal melatonin did not produce marked modifications, only significantly lower NKA and SP concentrations in MEL-offspring+EB group were observed at 25 days of age in comparison to control-offspring+EB group. Striatal NKA and SP concentrations showed a similar developmental pattern. In control-offspring, EB treatment produced NKA and SP decreased concentrations at the infantile period than in control-offspring+vehicle and significantly increased concentrations during the prepubertal period, then during the pubertal period NKA and SP concentrations decreased in control-group+EB. However, prenatal melatonin treatment reduced the levels of striatal NKA and SP during the prepubertal period after EB treatment and delayed until pubertal period the increase previously observed in control group during the prepubertal period. In MEL-offspring+vehicle group striatal concentrations of both tachykinins remained at low levels from infantile period until pubertal period. Prenatal melatonin and EB did not produce major alterations in SP pineal concentrations throughout sexual development. Plasma estradiol concentrations were significantly higher in the groups that received EB treatment than in those that received vehicle during prepubertal and juvenile periods in control-offspring+EB group and during the pubertal period in MEL-offspring+EB group. These data indicate that prenatal MEL treatment may influence NKA and SP developmental pattern from the infantile period until adulthood in the female rat.