Biomedical subjects

A Lerant

Publications and source records attributed to A Lerant.

8 recordsLinked to original sources

PubMed2001

Nuclear translocation of STAT5 and increased expression of Fos related antigens (FRAs) in hypothalamic dopaminergic neurons after prolactin administration.

Ample evidence indicates feedback relationships between pituitary prolactin and hypothalamic dopaminergic neurons. Since the presence of prolactin receptors was earlier demonstrated in hypothalamic dopaminergic neurons, our working hypothesis was that prolactin induced activation of prolactin receptor coupled signaling leads to increased neuronal activity in these neurons. The aim of this study was to correlate prolactin receptor mediated signaling and prolactin induced activation in hypothalamic dopaminergic neurons. We used nuclear translocation of STAT5 as a marker of prolactin receptor induced signaling and expression of Fos related antigens (FRAs) as an indicator of neuronal activation. We performed double label immunocytochemical studies to determine the time course of the presence of FRAs and STAT5 in the nuclei of hypothalamic dopaminergic neurons after ovine prolactin treatment. Exogenous ovine prolactin treatment of ovariectomized rats resulted in an increase in serum ovine prolactin levels and a decrease in endogenous serum prolactin levels, indicating that ovine prolactin activated mechanisms inhibited pituitary prolactin secretion. Indeed, ovine prolactin activated the prolactin receptors in most subpopulations of hypothalamic dopaminergic neurons, resulting in nuclear translocation of STAT5. Also, increased neuronal activity, indicated by expression of FRAs, was observed in the same neuron populations after ovine prolactin treatment. These results suggest that signal transduction mechanisms coupled to prolactin receptors in hypothalamic dopaminergic neurons resemble those observed in other tissues; and nuclear translocation of STAT5 can be used as a marker of prolactin receptor activation in hypothalamic dopaminergic neurons.

Active Transport, Cell Nucleus↗

PubMed2001

Endothelin-like immunoreactivity in lactotrophs, gonadotrophs, and somatotrophs of rat anterior pituitary gland are affected differentially by ovarian steroid hormones.

It has been previously found that all hormone-producing phenotypes of the anterior lobe of the pituitary gland are capable of producing endothelin (ET)-like substances. The aim of this study was to determine whether the expression of ET-1-like peptides in lactotrophs, gonadotrophs, and somatotrophs is influenced by different in vivo ovarian hormonal conditions. Anterior lobes of the pituitary gland were harvested from ovariectomized and ovarian steroid-replaced adult female rats 10-12 d after surgery. Quantitative immunocytochemistry was performed on enzymatically dispersed pituitary cells. The presence of ET-1-like immunoreactivity in prolactin-, luteinizing hormone-, or growth hormone-producing cells was demonstrated by double-label immunocytochemistry. The incidence of ET-1 immunopositive pituitary cells was unaffected by progesterone treatment alone. Estradiol replacement caused a modest decrease in the number of lactotrophs and somatotrophs expressing ET-1 but increased the incidence of ET-1 immunopositive cells among gonadotrophs. Combined treatment with estradiol and progesterone robustly increased the incidence of ET-1 immunopositive lactotrophs and gonadotrophs but had no effect on somatotrophs. These data reveal that the synthesis of ET-1-like peptides in lactotrophs and gonadotrophs (and, to a lesser extent, in somatotrophs) is sensitive to ovarian steroids. Furthermore, these findings predict that ovarian steroids modulate ET-1 biosynthesis during the estrous cycle, suggesting a possible mechanism by which the ovarian steroid milieu may regulate the responsiveness of lactotrophs and gonadotrophs to their hypothalamic secretagogues.

Animals↗

PubMed2000

Prolactin: structure, function, and regulation of secretion.

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Alternative Splicing↗

PubMed1998

Ovarian steroids differentially regulate the expression of PRL-R in neuroendocrine dopaminergic neuron populations: a double label confocal microscopic study.

The aims of this study were (1) to identify the possible hypothalamic targets for a short prolactin (PRL) feedback in the adult female rat by identifying DAergic neuron populations expressing PRL receptor (PRL-R); (2) to describe the effect of ovarian steroids on the expression of PRL-R and (3) to compare the distribution of both the extracellular (EC) and ligand binding (LB) domains of the PRL-R on the hypothalamic dopaminergic neurons by applying double label immunocytochemistry for the different domains of PRL-R and for tyrosine hydroxylase (TH). Five- to six-month-old female rats were ovariectomized (OVX) and implanted with either 17 beta-estradiol (E2), progesterone (P4) or received an E2 and a P4 implant (E2 + P4) at the same time. In the periventricular nucleus and in the dorsomedial portion of the middle arcuate nucleus, a dramatic increase in PRL-REC immunoreactivity was observed in E2 implanted rats. This increase was attenuated in E2 + P4 rats, but P4 treatment alone had no effect. Changes in PRL-REC expression were paralleled by changes in serum PRL levels. Interestingly, PRL-REC expression in the rostral arcuate nucleus decreased in P4 implanted rats, however, P4 did not attenuate the E2-induced increase in PRL-REC density. PRL-REC immunostaining was observed on the membrane, in the cytoplasm and in the nucleus. PRL-RLB immunoreactivity was also detectable in the TH positive neurons, but no nuclear staining was observed with this antibody. However, we found a strong PRL-RLB immunostaining in the ependymal lining of the 3rd ventricle and in the processes of tanycytes projecting to the median eminence. These data indicate that (1) all neuroendocrine DAergic cells can be targets for PRL, (2) expression of PRL-R is differentially affected by ovarian steroids in the different TH cell populations, (3) PRL-RLB domain may be involved in trafficking PRL in the median eminence.

Animals↗

PubMed1998

Ovarian steroids modulate responsiveness to dopamine and expression of G-proteins in lactotropes.

The effects of chronic ovarian steroid treatment on the secretory activity of individual lactotropes and the mechanisms modulating their responsiveness to dopamine (DA) were studied. Female rats were ovariectomized (OVX) and implanted with Silastic capsules containing progesterone (P4), 17beta), 17beta-estradiol (E2) or both E2 (E2+P4). Ten days after surgery, anterior pituitaries were enzymatically dispersed and the reverse hemolytic plaque assay (RHPA) was performed to assess the release of prolactin (PRL) from individual lactotropes. RHPA was combined with immunocytochemistry (ICC) for PRL, Galphas or Gialpha3/Galphao proteins. E2 treatment alone or in combination with P4 increased the percentage of immunoreactive lactotropes among anterior pituitary cells. Incidence of active (plaque-forming) lactotropes, however, was increased both in P4-, and E2-treated rats and E2+P4 treatment increased it even further. While P4 treatment did not affect the frequency distribution of lactotropes, both E2 and E2+P4 treatments increased the large plaque-forming lactotrope population. This increase was reflected by the significantly greater mean plaque areas of lactotropes from E2- and E2+P4-treated rats compared to OVX or P4-treated animals. The responsiveness of lactotropes to DA from P4-treated rats did not differ from that of OVX rats: thus challenge with 1 microM DA inhibited the release of PRL, while 100 pM DA had no effect. E2 and E2+P4 treatments, however, profoundly changed the lactotrope's responsiveness: challenge with 1 microM DA had no effect and 100 pM DA resulted in moderate stimulation of PRL release in E2+P4 rats. Double-label ICC revealed that ovarian steroid treatments did not affect the expression of Galphas in lactotropes. The incidence of Gialpha3/Galphao-immunoreactive lactotropes, however, decreased after E2 treatment, alone or in combination with P4. Although expression of Galphas was similar in all plaque-forming cells regardless of plaque size, lactotropes expressing Gialpha3/Galphao were more likely to form small plaques in all treatment groups. These data suggest: (1) ovarian steroid treatment recruits quiescent lactotropes to release PRL; (2) E2 treatment alone or in combination with P4 increases the amount of PRL rleased by individual lactotropes; (3) E2-induced alterations in the frequency distribution and lactotrope responsiveness to DA may be due in part to a decreased expression of Gialpha3/Galphao.

Animals↗

PubMed1998

Endothelin is an autocrine regulator of prolactin secretion.

The aim of this study was to establish the cellular source of ET-like peptides affecting PRL secretion. Fluorescence double label immunocytochemistry and confocal laser scanning microscopy were used to demonstrate cellular colocalization for PRL and endothelin-1 (ET1)-like immunoreactivities in the anterior lobe of the pituitary gland of rats. An ET-specific reverse hemolytic plaque assay was applied to demonstrate that lactotrophs are capable of releasing ET-like peptides. A PRL-specific reverse hemolytic plaque assay was used to assess the influence of the released endogenous ETs on PRL secretion. ET(A)-specific receptor antagonists BQ123 and BQ610, and endothelin convertase enzyme inhibitory peptide, [22Val]big ET1-(16-38), increased PRL secretion, whereas the ET(B) receptor-specific antagonist BQ788 was ineffective. The ET(A) antagonist BQ123-induced increase in PRL secretion followed a bell-shaped dose-response curve in cells obtained from female rats, whereas it followed a sigmoid curve in males. Frequency distribution of PRL plaque sizes using logarithmically binned data revealed two subpopulations of lactotrophs with differential responsiveness to endogenous ETs. These data demonstrate that a large proportion of lactotrophs is capable of expressing and secreting ET-like peptides in biologically significant quantities. As low pituitary cell density in reverse hemolytic plaque assay minimizes cell to cell communications, these findings constitute direct proof of autocrine regulation of PRL secretion by ET-like peptides.

Animals↗

PubMed1997

Dopaminergic neurons in periventricular and arcuate nuclei of proestrous and ovariectomized rats: endogenous diurnal rhythm of Fos-related antigens expression.

The expression of Fos-related antigens (FRAs) in the A12 and the A14 hypothalamic dopaminergic neurons was compared throughout the day in proestrous (PRO) and ovariectomized (OVX) rats to establish the relationship between secretion of prolactin (PRL) and dopaminergic neuronal activation. Animals with intact ovaries were sacrificed at 11:00, 13:00, 15:00, 17:00 and 21:00 h on the day of proestrus and 06:00 and 09:00 h in the morning of estrus. OVX animals were sacrificed at the same time points on the 12th day after surgery. Double-label immunocytochemistry was performed by using antibodies against FRAs as markers of tonic neuronal activity and tyrosine hydroxylase to identify dopaminergic neurons. Serum PRL levels were determined by radioimmunoassay. A pattern of FRAs expression was present in the A14 and A12 neurons of PRO rats. The incidence of FRAs expressing neurons was the highest in the first half of the day when the PRL levels were low, and decreased prior to the surge of serum PRL during the afternoon. This pattern was present in the dopaminergic neurons of the periventricular nucleus (A14), and in all portions of the arcuate nucleus (A12) except the ventrolateral portion of the middle arcuate nucleus. A similar pattern of FRAs expression existed in the A14 and A12 neurons of OVX rats in spite of that there were no detectable changes in serum PRL levels. However, the amplitude of decrease in the incidence of FRAs-labeled neurons was lower in OVX than in PRO rats. These data suggested that similar to the control of hypothalamic PRL releasing factors, the activation/deactivation pattern of the A12 and the A14 neurons is governed by a seemingly endogenous rhythmic input. The incidence of this rhythm is independent of the reproductive state, but its amplitude is enhanced by ovarian steroids. The disparity between the FRAs expression and serum PRL levels in OVX rats indicated that the effect of this endogenous dopaminergic rhythm upon PRL secretion is dependent on the ovarian steroid background.

Animals↗

PubMed1996

Dopaminergic neurons of periventricular and arcuate nuclei of pseudopregnant rats: semicircadian rhythm in Fos-related antigens immunoreactivities and in dopamine concentration.

The activity of the A14 and A12 hypothalamic dopaminergic (DAergic) neurons were characterized throughout a day of pseudopregnancy to establish their relationship to the generation of PRL surges during that time. Double-label immunocytochemistry was performed using fos-related antigens as markers of neuronal activity, and tyrosine hydroxylase antibody to identify DAergic neurons of the periventricular nucleus and the arcuate nucleus (ARN). Dopamine concentrations were measured with HPLC with electrochemical detection from micropunched samples to approximate synthetic activities of A14 and A12 neurons. Serum PRL levels were determined by RIA. On the fifth and sixth day of pseudopregnancy, five rats/time point were killed at 1100 h, 1300 h, 1500 h, 1800 h, 2100 h, 2400 h, 0300 h, and 0600 h. When the serum PRL was low, the incidence of fos-related antigens/tyrosine hydroxylase double-labeled neurons was high, and it decreased twice a day by 1500 and 0300 h in the periventricular nucleus, rostral ARN, dorsomedial subpopulation of the middle ARN, and in the caudal ARN, corresponding to the initiation of PRL surges. Concentrations of DA were high in these areas, and decreased before PRL surges in agreement with the immunocytochemical data. These findings suggest a semicircadian rhythm in the activities of A14 and A12 neurons which, in concert with PRL releasing factors, contribute to the generation of PRL surges in pseudopregnant animals.

Animals↗