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S R Ojeda

Publications and source records attributed to S R Ojeda.

At least 73 records · Page 4Linked to original sources
PubMed1992

Transforming growth factor-alpha gene expression in the hypothalamus is developmentally regulated and linked to sexual maturation.

Hypothalamic injury causes female sexual precocity by activating luteinizing hormone-releasing hormone (LHRH) neurons, which control sexual development. Transforming growth factor-alpha (TGF-alpha) has been implicated in this process, but its involvement in normal sexual maturation is unknown. The present study addresses this issue. TGF-alpha mRNA and protein were found mostly in astroglia, in regions of the hypothalamus concerned with LHRH control. Hypothalamic TGF-alpha mRNA levels increased at times when secretion of pituitary gonadotropins--an LHRH-dependent event--was elevated, particularly at the time of puberty. Gonadal steroids involved in the control of LHRH secretion increased TGF-alpha mRNA levels. Blockade of TGF-alpha action in the median eminence, a site of glial-LHRH nerve terminal association, delayed puberty. These results suggest that TGF-alpha of glial origin is a component of the developmental program by which the brain controls mammalian sexual maturation.

Animals↗
PubMed1992

Postnatal development of sympathetic and sensory innervation of the rhesus monkey ovary.

We have used immunofluorescence to study the postnatal development of the sympathetic and sensory innervation to the rhesus monkey (Macaca mulatta) ovary. Sympathetic nerves were identified as adrenergic by their content of tyrosine hydroxylase (TH)-like immunoreactivity and as peptidergic by the presence of neuropeptide Y (NPY). Fibers containing substance P (SP) or calcitonin gene-related peptide (CGRP)-like immunoreactivity were considered as sensory, whereas vasoactive intestinal peptide (VIP)-positive fibers were only defined as peptidergic because VIP may be present in both sympathetic and sensory nerves. Ovaries from neonatal (2-mo-old), juvenile (9-18-mo-old), peripubertal (3-3.5-yr-old), adult (9-14-yr-old), and senescent (20-27-yr-old) monkeys were studied. At all ages, with the exception of senescence, TH-, NPY-, and VIP-containing fibers were associated with follicles in different developmental stages. In peripubertal and adult animals, some primordial follicles were found to be selectively innervated by VIPergic fibers that almost completely encircled each follicle. Both sympathetic and VIP fibers were also detected in the interstitial tissue and associated with the ovarian vasculature at all ages. The number of sympathetic and VIP fibers increased significantly (p < 0.01) between 2 mo and 9-18 mo of age, and again increased (p < 0.01) around the age of puberty (approximately 3 yr of age). After this time, the number of NPY and TH fibers remained constant. Conversely, the number of VIP fibers decreased (p < 0.05) by 9-14 yr of age, but remained constant thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Norepinephrine release in the immature ovary is regulated by autoreceptors and neuropeptide-Y.

Experiments were undertaken to study the role that neuropeptide-Y (NPY) and adrenergic autoreceptors may play in the regulation of norepinephrine (NE) release from the rat ovary. Ovaries from 28- to 32-day-old rats were preincubated with [3H]NE, and the release of the recently taken up catecholamine in response to electric field stimulation was assessed. The release was strictly dependent on the presence of extracellular calcium and decreased when the frequency of stimulation was increased. This drop in [3H]NE release was significantly reversed by exposure of the ovaries during stimulation to yohimbine, a selective alpha 2-adrenoreceptor blocker. The existence of prejunctional alpha 2-adrenergic autoreceptors in ovarian nerves was further suggested by the ability of exogenous NE to mimic the inhibitory effect of high frequency stimulation. NPY inhibited by 40% the release of [3H]NE induced by electrical stimulation. The specificity of this effect and its prejunctional nature were demonstrated by the finding that avian pancreatic polypeptide, a structural homolog of NPY that is not recognized by prejunctional NPY receptors of the Y2 subtype, failed to alter the induced release of [3H]NE. Neither NPY, avian pancreatic polypeptide, nor peptide-YY, another member of the pancreatic polypeptide fold family, altered progesterone or estradiol secretion from whole ovaries or granulosa cells in culture, suggesting that NPY (and its structural homologs) does not directly affect ovarian steroidogenesis. The results suggest that 1) the release of NE from ovarian sympathetic nerves is subjected to a dual modulatory influence provided by NE itself and NPY; and 2) this regulatory effect is exerted via specific prejunctional receptors. Such NE/NPY actions are likely to regulate the availability of NE to its postsynaptic receptors during ovarian development and adult function. The fact that NPY is mostly released during high frequency stimulation raises the possibility of NPY involvement in ovarian dysfunctions associated with situations of enhanced sympathetic discharge, such as strenuous exercise and psychogenic amenorrhea.

Animals↗
PubMed1992

Effect of hypothalamic lesions that induce precocious puberty on the morphological and functional maturation of the luteinizing hormone-releasing hormone neuronal system.

Recent evidence has implicated the transforming growth factor-alpha (TGF alpha)/epidermal growth factor receptor (EGFR) system in the mechanism by which hypothalamic lesions accelerate female sexual development. Since acquisition and maintenance of reproductive functions depend on the secretory activity of LHRH neurons, the present studies were undertaken to characterize some of the cellular and molecular events that underlie lesion-induced activation of the LHRH neuronal network. Bilateral electrolytic lesions of the posterior portion of the preoptic region and anterior hypothalamic area (POA-AHA) in 22-day-old rats resulted in vaginal opening and ovulation within 7 days. Morphological maturation of LHRH neurons was assessed by the relative frequency of irregular and smooth neurons (the former being the predominant type in adult animals). Within 20 h after the lesion, there was a significant decrease in the proportion of LHRH neurons with spiny irregular contours, indicating reversal to a more immature morphological type. This change was followed by accelerated spine reformation, so that at the time of precocious proestrus, the incidence of irregular LHRH neurons was similar in lesioned and age-matched control rats. A striking increase in c-fos mRNA levels occurred within 1 h after the lesion in the area neighboring the site of injury, reflecting the immediate cell response to trauma. Immunohistochemical localization of the c-fos protein, used to estimate changes in cellular activity at the single cell level, demonstrated c-fos induction in unidentified cells near the lesion and astrocytes, but not in LHRH neurons 20 h after injury. In contrast, a selective increase in c-fos expression was observed in LHRH neurons during the initiation of precocious puberty 5-7 days later at the time of the first proestrus. An increase in plasma LH associated with a drop in LHRH content in the median eminence and an increase in pro-LHRH precursor in the POA-AHA, with no changes in LHRH mRNA, was found to antedate the first preovulatory surge of gonadotropins in lesioned rats. Assessment of the changes in PC2 mRNA, which encodes a novel dibasic endoprotease presumptively involved in tissue-specific processing of a class of prohormones that includes pro-LHRH, showed that the content of PC2 mRNA in the AHA-POA increases during normal puberty, but not in lesioned animals, thus providing a potential explanation for the divergent changes in pro-LHRH and mature decapeptide found in lesioned rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Neurotrophic factors and female sexual development.

The concept is proposed that polypeptide neurotrophic factors contribute to the developmental regulation of ovarian and hypothalamic function in mammals. Nerve growth factor (NGF) and neurotrophin-3, two members of the neurotrophin family, have been identified in the rat ovary and one of its receptors has been localized to the innervation and thecal cells of developing follicles. Although NGF supports the sympathetic innervation of the gland, the extent to which follicles are innervated appears to be defined by the differential expression of NGF receptors in the theca of developing follicles. The presence of NGF receptors in steroid-producing cells suggests a direct involvement of neurotrophins in the regulation of gonadal endocrine function. Evidence is beginning to emerge suggesting that development of the reproductive hypothalamus is affected by insulin-like growth factor 1 secreted by peripheral tissues, and transforming growth factor alpha (TGF alpha) produced locally. In the rat hypothalamus, TGF alpha appears to be synthesized in both neurons and glial cells. In glial cells it may interact with epidermal growth factor (EGF) receptors to further enhance TGF alpha synthesis and to, perhaps, stimulate eicosanoid formation. In turn, one of these eicosanoids, prostaglandin E2, may act on luteinizing hormone-releasing hormone (LHRH) neurons to stimulate the release of LHRH in a genomic-independent manner. This provides the basis for the notion that during development LHRH secretion is regulated by a dual mechanism, one that involves transsynaptic effects exerted by neurotransmitters, the other that requires a glial-neuronal interaction and that may predominantly regulate release of the neuropeptide. An increased expression of the TGF alpha and EGF receptor genes in reactive astrocytes is postulated to contribute to the process by which hypothalamic injury causes sexual precocity. Morphological maturation of the reproductive hypothalamus is thought to occur during sexual development. The process is accelerated by estradiol, which exerts its neurotrophic effects by enhancing the expression of genes encoding cytoskeletal proteins involved in neuronal development and regeneration. It is suggested that acquisition of functional competence by both the ovaries and the reproductive hypothalamus requires the participation of specific, but not similar, neurotrophic factors. The relevance of these concepts to the process of sexual development in other species, particularly primates, remains to be defined.

Animals↗
PubMed1991

Transforming growth factor alpha contributes to the mechanism by which hypothalamic injury induces precocious puberty.

It has long been known that lesions of the hypothalamus lead to female sexual precocity. While an increased production of luteinizing hormone-releasing hormone (LHRH), the neurohormone that controls sexual development, appears to mediate the advancement of puberty induced by these lesions, little is known about the mechanism(s) by which hypothalamic injury activates LHRH secretion. Since brain lesions result in accumulation of neurotrophic/mitogenic activities in the injured area, we tested the hypothesis that transforming growth factor alpha (TGF-alpha), a mitogenic polypeptide recently shown to stimulate LHRH release, is produced in response to hypothalamic injury and mediates the effect of the lesion on puberty. Radiofrequency lesions of the preoptic area-anterior hypothalamic area (POA-AHA) of 22-day-old female rats resulted in precocious puberty within 7 days after the operation. RNA blot hybridization revealed that lesion-induced puberty was preceded by an increase in TGF-alpha mRNA levels in the POA-AHA. Epidermal growth factor (EGF) mRNA was undetectable in both intact and lesioned hypothalami. TGF-alpha mRNA levels, quantitated by RNase protection assays, were 3.5-fold greater in lesioned animals approaching puberty than in age-matched controls. Immunohistochemical studies, utilizing single- and double-staining procedures, demonstrated the presence of TGF-alpha precursor-like immunoreactivity in reactive astrocytes surrounding the lesion site. Hybridization histochemistry showed increased TGF-alpha mRNA expression in cells of the same area, further implicating reactive astrocytes as a site of TGF-alpha synthesis. The actions of TGF-alpha are mediated by its interaction with EGF receptors. Continuous infusion of RG-50864, an inhibitor of EGF receptor kinase activity, at the site of injury prevented the advancement of puberty induced by the lesion. These results suggest that TGF-alpha acting via EGF-like receptors contributes to the acceleration of puberty induced by anterior hypothalamic lesions. They also indicate that activation of TGF-alpha gene expression in glial cells is a component of the hypothalamic response to injury.

Animals↗
PubMed1991

The genes encoding nerve growth factor and its receptor are expressed in the developing female rat hypothalamus.

Nerve growth factor (NGF), its messenger RNA (mRNA) and its receptor protein and mRNA are found in several brain regions. Little attention has been given to the possibility that the hypothalamus, which controls the endocrine system, may produce NGF and/or express NGF receptors. This would indicate the existence in this brain area of neuronal populations which are either target for NGF-responsive cells or sensitive to NGF, respectively. Blot hybridization of polyadenylated (poly(A)+) RNA to a mouse NGF cRNA probe revealed the presence of NGF mRNA in both the suprachiasmatic region (henceforth, called preoptic area [POA]) and medial basal hypothalamus (MBH) of developing female rats. The mRNA was already detectable on fetal day 18 and reached maximal levels around postnatal day 3 (MBH) and 12 (POA), declining thereafter. This pattern was temporally different than that of areas known to produce NGF, i.e., the neocortex (Cc) and hippocampus (Hc). In agreement with previous reports, NGF mRNA levels in these areas were negligible before birth, became maximal between the second and third week of postnatal life and decreased moderately thereafter. The concentration of NGF protein, measured by a two-site enzyme immunoassay, was 3 times higher in the POA than in the MBH at an infantile age (day 12), increasing 2-fold in the POA of juvenile animals (day 28) but not in the MBH. This developmental pattern was similar to that seen in the Hc, though the NGF concentrations were significantly lower in the POA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Insulin-like growth factor I: a possible metabolic signal involved in the regulation of female puberty.

In both rats and primates, including humans, serum levels of insulin-like growth factor I (IGF-I) increase during the onset of puberty, suggesting a role for IGF-I in this process. We examined the ability of IGF-I to affect the release of hypothalamic luteinizing hormone releasing hormone (LHRH) in prepubertal female rats. Our results indicate that IGF-I acts on the median eminence, which contains the highest density of type 1 IGF receptors in the brain, to elicit a dose-related increase in LHRH release. In this regard, a minimal effective dose of 10 ng/ml (p less than 0.05) and a maximal effective dose of 100 ng/ml (p less than 0.01) was observed. IGF-II and insulin were one order of magnitude less effective. The results demonstrate that IGF-I has the capability to act directly upon the median eminence to effect release of LHRH, thereby suggesting a role for IGF-I in facilitating peripubertal changes in LHRH release. Thus, IGF-I may represent one of the 'metabolic signals' thought to be involved in the initiation of puberty.

Animals↗
PubMed1991

Functional recovery of the developing rat ovary after transplantation: contribution of the extrinsic innervation.

These experiments were undertaken to define the neuroendocrine mechanisms underlying the recovery of ovarian function after transplantation to an ectopic site. Both ovaries from 23-day-old rats were transplanted to the region of the neck, next to the jugular vein. Serum gonadotropin and plasma immunoreactive inhibin-alpha levels were determined at several intervals thereafter. Serum estradiol (E2) was measured during the first week posttransplantation. Reinnervation of the ovary by sympathetic and sensory nerves was monitored by immunohistochemistry. Sympathetic nerves were identified as adrenergic by the presence of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, and as peptidergic, by their neuropeptide-Y (NPY) or vasoactive intestinal peptide (VIP) immunoreactivity. Sensory nerves were identified by the presence of substance P (SP) and calcitonin-gene related peptide (CGRP) immunoreactivity. Serum LH and FSH increased, and plasma inhibin levels decreased, within 48 h after transplantation. Serum LH reached maximum levels on day 4, decreasing rapidly thereafter to basal values by day 6. These changes were functionally correlated with the posttransplantation fluctuations in serum E2, which decreased at 48 h, rebounded by day 4, and returned to basal values on day 7. Removal of the transplanted ovaries on day 3 resulted in the disappearance of serum E2 levels on day 4, thus confirming the ovarian graft as the source of E2. In contrast to LH, serum FSH remained significantly elevated for at least 3 weeks after transplantation, then decreased to basal levels after day 21, coinciding with the rise in inhibin secretion. Although a substantial loss of follicles was noted 48 h after transplantation, quantitative examination of the changes on day 4 revealed that approximately 40% of antral follicles were not necrotic. Ovulation and formation of corpora lutea were noted 21 days after transplantation. Reinnervation of the transplanted ovary by TH-, VIP-, NPY-, SP-, and CGRP-containing fibers was first detected 7 days after transplantation. Although VIP reinnervation was sparse and only transiently detected (days 7-21), the density of sympathetic (TH, NPY) and sensory (SP, CGRP) fibers increased 2- to 3-fold between days 7-28, remaining unchanged thereafter. Since apparent completion of this reinnervation coincided with reestablishment of normal levels of both LH and FSH, an additional experiment was performed to determine if the two events were causally related.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Nerve growth factor receptors in the peripubertal rat ovary.

We previously demonstrated that the immature rat ovary synthesizes nerve growth factor (NGF), and that interference of NGF actions by immunoneutralization during neonatal life prevents development of the ovarian sympathetic innervation and delays follicular maturation. Since the actions of NGF are exerted via binding to specific cell surface receptors, the present study was undertaken to define and characterize the presence of NGF receptors (NGFrec) in the developing rat ovary. NGF interacts with two classes of NGFrec. The most abundant is a low affinity form expressed in the central nervous system and peripheral tissues. This receptor is encoded by a single 3.8-kilobase mRNA species. Cross-linking of [125I]NGF to ovarian membranes followed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography showed the presence of a approximately 90-kilodalton molecular species which corresponds in size to the predominant NGF receptor species cross-linked to its ligand. While ovarian NGFrec may be of neuronal origin and reach the gland exclusively by anterograde axonal transport, RNA blot hybridization demonstrated that the ovary expresses the NGFrec mRNA species that encodes the low affinity NGF receptor and, thus, implicated the ovary itself as a site of NGFrec synthesis. NGFrec mRNA levels decreased abruptly after the first ovulation, suggesting that NGFrec may be synthesized in growing follicles and that this capacity is lost after follicular rupture and luteinization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Expression of beta-nerve growth factor in cultured cells derived from the hypothalamus and cerebral cortex.

Although the synthesis of nerve growth factor (NGF) in brain regions innervated by magnocellular cholinergic neurons of the basal forebrain is well documented, the cell type(s) able to produce NGF in the central nervous system (CNS) remain only partially characterized. Moreover, little is known regarding the ability of brain areas not innervated by magnocellular cholinergic neurons to express NGF protein. The hypothalamus, which controls the endocrine system, is one of such regions. Primary culture of mixed populations of cells from the fetal hypothalamus were used to identify the presence of NGF in this brain area. Immunocytochemistry revealed that hypothalamic oligodendrocytes and a subpopulation of neurons expressed the NGF protein. In contrast, astrocytes were either immunonegative or equivocally stained. To define whether synthesis of NGF is restricted to a particular cell type, cultures of purified astrocytes, oligodendrocyte progenitor (oligoP) cells and neurons were utilized. They were obtained from the neonatal cerebral cortex to ensure an adequate yield of glial cells. Virtually the entire population of cerebral oligoP cells were found to express NGF protein. In contrast, and similar to hypothalamic astrocytes, cerebral type I astrocytes isolated at the same time as oligoP cells exhibited little or no NGF staining. When type I astrocytes were induced to differentiate in the presence of a serumless, chemically defined medium, a subpopulation of the culture became more robustly positive for the NGF protein. Contrasting with these differences in NGF immunoreactivity, Northern analysis of RNA isolated from purified cerebral type I astrocytes, oligoP cells and neurons demonstrated that NGF mRNA was expressed in each of these cell types at approximately the same levels. The results indicate that: (a) when placed in culture, each of the major cell types within the CNS has the capability of transcribing the NGF gene, and (b) despite similar NGF mRNA levels the cellular content of NGF protein is greater in a subpopulation of neurons and in oligodendrocytes than in astrocytes, suggesting differences in NGF post-transcriptional regulation between these cell types. In addition, the presence of NGF in hypothalamic cells suggests that NGF may be involved in the regulation of specific hypothalamic neuronal systems.

Animals↗
PubMed1990

Involvement of transforming growth factor alpha in the release of luteinizing hormone-releasing hormone from the developing female hypothalamus.

Little is known about the presence of trophic factors in the hypothalamus and the role they may play in regulating the functional development of hypothalamic neurons. We have investigated the ability of epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) to affect the release of luteinizing hormone-releasing hormone (LHRH), the neuropeptide that controls reproductive development. We have also determined whether the genes encoding EGF and TGF-alpha are expressed in the prepubertal female hypothalamus. Northern blot analysis of poly(A)+ RNA utilizing a single-stranded EGF cDNA probe failed to reveal the presence of EGF mRNA in either the hypothalamus or the cerebral cortex at any age studied (fetal day 18 to postnatal day 36). In contrast, both a complementary RNA probe and a double-stranded TGF-alpha cDNA recognized in these regions a 4.5-kilobase (kb) mRNA species identical to TGF-alpha mRNA. The abundance of TGF-alpha mRNA was 3-4 times greater in the hypothalamus than in the cerebral cortex. Both EGF and TGF-alpha (2-100 ng/ml) elicited a dose-related increase in LHRH release from the median eminence of juvenile rats in vitro. They also enhanced prostaglandin E2 (PGE2) release. The transforming growth factors TGF-beta 1 and -beta 2 were ineffective. Only a high dose of basic fibroblast growth factor was able to increase LHRH and PGE2 release. Blockade of the EGF receptor transduction mechanism with RG 50864, a selective inhibitor of EGF receptor tyrosine kinase activity, prevented the effect of both EGF and TGF-alpha on LHRH and PGE2 release but failed to inhibit the stimulatory effect of PGE2 on LHRH release. Inhibition of prostaglandin synthesis abolished the effect of TGF-alpha on LHRH, indicating that PGE2 mediates TGF-alpha-induced LHRH release. The results indicate that the effect of EGF and TGF-alpha on LHRH release is mediated by the EGF/TGF-alpha receptor and suggest that TGF-alpha rather than EGF may be the physiological ligand for this interaction. Since in the central nervous system most EGF/TGF-alpha receptors are located on glial cells, the results also raise the possibility that--at the median eminence--TGF-alpha action may involve a glial-neuronal interaction, a mechanism by which the trophic factor first stimulates PGE2 release from glial cells, and then PGE2 elicits LHRH from the neuronal terminals.

Aging↗
PubMed1990

Hypothalamic aromatase activity in male and female rats during juvenile peripubertal development.

Evidence exists that testosterone (T) regulates brain aromatase activity in adult rats. It is not known, however, whether the activity and/or its regulation by androgens change during the time of puberty. In the present study, we examined the change in basal aromatase activity associated with puberty in both male and female rats. We also assessed the influence of castration and treatment with a nonaromatizable androgen, dihydrotestosterone (DHT), on the hypothalamic aromatase system during juvenile and peripubertal development of male rats. Aromatase activity was estimated by both quantifying the 3H2O released from [1 beta-3H]T and by isolating the estrogen product(s) by thin-layer chromatography (TLC) after incubations with [1,2,6,7-3H]T. 5 alpha-Reductase activity was determined simultaneously in the male hypothalamus by TLC using [1 alpha-3H]T as the substrate. Aromatase activity was linear with time of incubation and amount of tissue used. It was detected at similar levels in both tissue fragments and acutely dispersed cell preparations. Expression in the latter, but not the former required the addition of NADPH. Intracellular rates of both aromatase and 5 alpha-reductase activities were highest in the mitochondrial-microsomal fraction. In both males and females the time of puberty was associated with a decrease in hypothalamic aromatase activity. In females, this drop was found to occur between the days of first proestrus and first estrus. In males, it occurred between 48 and 68 days of age (i.e., after the animals had reached puberty, as assessed by the presence of free sperm in the seminiferous tubules).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The gene encoding nerve growth factor is expressed in the immature rat ovary: effect of denervation and hormonal treatment.

The rat ovary is innervated by sympathetic nerve fibers. Since the development and survival of peripheral sympathetic neurons innervating nonreproductive organs have been shown to depend on the production of nerve growth factor (NGF) by the innervated tissues, the present experiments were undertaken to determine if the immature rat ovary has the capability of synthesizing NGF. Blot hybridization of ovarian polyadenylated RNA (A+-RNA) to a NGF cRNA probe revealed the presence of a 1.3- to 1.4-kilobase (kb) mRNA species similar to mature NGF mRNA detected in mouse submaxillary gland, a source rich in NGF. Quantitation of NGF protein by a sensitive and specific two-site enzyme immunoassay demonstrated the presence of NGF in juvenile ovaries at levels comparable to those found in other sympathetically innervated tissues. Neither denervation of the ovary nor treatment with gonadotropins (hCG and FSH) or somatomammotropins (PRL and GH) affected the levels of NGF mRNA. However, denervation significantly increased NGF levels, suggesting that, as in other target tissues, denervation prevents the retrograde transport of NGF by the sympathetic terminals and leads to accumulation of the protein at its site of production. It is concluded that 1) the developing ovary is able to both transcribe the NGF gene and translate its mRNA into NGF protein; and 2) the NGF content in the ovary is regulated by its innervation. The results provide the biochemical basis for the concept, elaborated in the companion paper, that NGF through its trophic actions on ovarian sympathetic neurons contributes to the regulation of ovarian development and, hence, to the acquisition of female reproductive capacity.

Animals↗
PubMed1990

Involvement of nerve growth factor in female sexual development.

The ovary is innervated by noradrenergic and peptidergic fibers. Treatment of neonatal rats with antibodies to nerve growth factor (NGF Ab) resulted in failure of the sympathetic (noradrenergic and neuropeptide-Y) nerves to develop. Partial loss of sensory innervation, represented by calcitonin gene-related peptide fibers, was also observed. Follicular growth was stunted, and production of androgens and estradiol was reduced. The timing of first ovulation was delayed, estrous cyclicity was disrupted, and fertility was compromised. Plasma LH levels were elevated, and LH pulsatility was enhanced, suggesting primary ovarian failure. A normal appearance of tyrosine hydroxylase-, LHRH-, and neuropeptide-Y-immunoreactive neurons in the hypothalamus, as determined by immunocytochemistry, suggested that neonatal immunosympathectomy did not directly affect hypothalamic reproductive function. In vitro release of LHRH from median eminence nerve terminals in response to prostaglandin E2 was, however, reduced in NGF Ab-treated rats. Normalization of the response by prior in vivo exposure of the animals to physiological estradiol levels, suggested that the diminished LHRH output was due at least in part to estrogen deficiency. Although ovarian dysfunction induced by immunosympathectomy may be related to alterations in vascular tone, the striking loss of perifollicular noradrenergic innervation caused by NGF Ab suggests that the absence of the nonvascular norepinephrine stimulus to follicular steroidogenesis is a primary factor responsible for the alterations observed. The results indicate that development of the sympathetic innervation of the ovary is NGF dependent and that NGF, by supporting the differentiation and survival of the innervating neurons, contributes to the acquisition of mature ovarian function.

Animals↗
PubMed1990

Epoxygenase products of arachidonic acid are endogenous constituents of the hypothalamus involved in D2 receptor-mediated, dopamine-induced release of somatostatin.

The epoxyeicosatrienoic acids (EETs) were discovered as products of a cyclooxygenase/lipoxygenase-independent, cytochrome P-450 catalyzed metabolism of arachidonic acid (AA) termed the "epoxygenase" pathway. The rat hypothalamus is able to synthesize EETs from exogenous AA, and 5,6-EET has been found to release the neuropeptide somatostatin (SRIF) from hypothalamic nerve terminals of the median eminence (ME). In the present study, hypothalami from male rats were examined for the presence of endogenous EETs, using chemical, chromatographic, and mass spectral analysis procedures. The samples were initially separated in a C18 Sepralyte column, fractionated on TLC plates, and purified by reverse phase HPLC. Thereafter, they were esterified (pentafluorobenzyl esters) and subjected to negative ion chemical ionization/gas chromatography (GC)/mass spectral (MS) analysis. The GC retention time and the MS fragmentation patterns revealed the presence of a mixture of 8,9-, 11,12- and 14,15-EETs; instability of 5,6-EET during the isolation protocol precluded its identification. Total hypothalamic EET concentration was estimated to be 120 ng/g wet tissue. The 8,9-regiosomer released SRIF from ME nerve terminals with an ED50 of 5 x 10(-12) M; Dopamine (DA) and the D2 receptor agonist PPHT, but not the D1 receptor agonist SKF-38393, induced SRIF release from the ME. This effect was blocked by clotrimazole and ketoconazole, two inhibitors of microsomal cytochrome P-450 function and AA epoxygenase in particular. In contrast, the inhibitors failed to affect the increase in SRIF release induced by 8,9-EET. These results indicate that: 1) in addition to cyclooxygenase and lipoxygenase products, epoxygenase metabolites of AA are endogenous compounds of the hypothalamus, and 2) EETs may mediate the increase in SRIF release from hypothalamic neurons induced by the interaction of DA with D2 receptors.

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