Gene therapy restores the transcriptional program of hematopoietic stem cells in Fanconi anemia

Clinical trials have shown that lentiviral-mediated gene therapy can ameliorate bone marrow failure (BMF) in nonconditioned Fanconi anemia (FA) patients resulting from the proliferative advantage of corrected FA hematopoietic stem and progenitor cells (HSPC). However, it is not yet known if gene therapy can revert affected molecular pathways in diseased HSPC. Single-cell RNA sequencing was performed in chimeric populations of corrected and uncorrected HSPC co-existing in the BM of gene therapy-treated FA patients. Our study demonstrates that gene therapy reverts the transcriptional signature of FA HSPC, which then resemble the transcriptional program of healthy donor HSPC. This includes a down-regulated expression of TGF-β and p21, typically up-regulated in FA HSPC, and upregulation of DNA damage response and telomere maintenance pathways. Our results show for the first time the potential of gene therapy to rescue defects in the HSPC transcriptional program from patients with inherited diseases; in this case, in FA characterized by BMF and cancer predisposition.

Preclinical models for prediction of immunotherapy outcomes and immune evasion mechanisms in genetically heterogeneous multiple myeloma

The historical lack of preclinical models reflecting the genetic heterogeneity of multiple myeloma (MM) hampers the advance of therapeutic discoveries. To circumvent this limitation, we screened mice engineered to carry eight MM lesions (NF-κB, KRAS, MYC, TP53, BCL2, cyclin D1, MMSET/NSD2 and c-MAF) combinatorially activated in B lymphocytes following T cell-driven immunization. Fifteen genetically diverse models developed bone marrow (BM) tumors fulfilling MM pathogenesis. Integrative analyses of ∼500 mice and ∼1,000 patients revealed a common MAPK-MYC genetic pathway that accelerated time to progression from precursor states across genetically heterogeneous MM. MYC-dependent time to progression conditioned immune evasion mechanisms that remodeled the BM microenvironment differently. Rapid MYC-driven progressors exhibited a high number of activated/exhausted CD8⁺ T cells with reduced immunosuppressive regulatory T (T_reg) cells, while late MYC acquisition in slow progressors was associated with lower CD8⁺ T cell infiltration and more abundant T_reg cells. Single-cell transcriptomics and functional assays defined a high ratio of CD8⁺ T cells versus T_reg cells as a predictor of response to immune checkpoint blockade (ICB). In clinical series, high CD8⁺ T/T_reg cell ratios underlie early progression in untreated smoldering MM, and correlated with early relapse in newly diagnosed patients with MM under Len/Dex therapy. In ICB-refractory MM models, increasing CD8⁺ T cell cytotoxicity or depleting T_reg cells reversed immunotherapy resistance and yielded prolonged MM control. Our experimental models enable the correlation of MM genetic and immunological traits with preclinical therapy responses, which may inform the next-generation immunotherapy trials.

Uncovering perturbations in human hematopoiesis associated with healthy aging and myeloid malignancies at single-cell resolution

Early hematopoiesis is a continuous process in which hematopoietic stem and progenitor cells (HSPCs) gradually differentiate toward specific lineages. Aging and myeloid malignant transformation are characterized by changes in the composition and regulation of HSPCs. In this study, we used single-cell RNA sequencing (scRNA-seq) to characterize an enriched population of human HSPCs obtained from young and elderly healthy individuals.

Based on their transcriptional profile, we identified changes in the proportions of progenitor compartments during aging, and differences in their functionality, as evidenced by gene set enrichment analysis. Trajectory inference revealed that altered gene expression dynamics accompanied cell differentiation, which could explain aging-associated changes in hematopoiesis. Next, we focused on key regulators of transcription by constructing gene regulatory networks (GRNs) and detected regulons that were specifically active in elderly individuals. Using previous findings in healthy cells as a reference, we analyzed scRNA-seq data obtained from patients with myelodysplastic syndrome (MDS) and detected specific alterations of the expression dynamics of genes involved in erythroid differentiation in all patients with MDS such as TRIB2. In addition, the comparison between transcriptional programs and GRNs regulating normal HSPCs and MDS HSPCs allowed identification of regulons that were specifically active in MDS cases such as SMAD1, HOXA6, POU2F2, and RUNX1 suggesting a role of these transcription factors (TFs) in the pathogenesis of the disease.

In summary, we demonstrate that the combination of single-cell technologies with computational analysis tools enable the study of a variety of cellular mechanisms involved in complex biological systems such as early hematopoiesis and can be used to dissect perturbed differentiation trajectories associated with perturbations such as aging and malignant transformation. Furthermore, the identification of abnormal regulatory mechanisms associated with myeloid malignancies could be exploited for personalized therapeutic approaches in individual patients.

Deconvolution of the hematopoietic stem cell microenvironment reveals a high degree of specialization and conservation

Understanding the regulation of normal and malignant human hematopoiesis requires comprehensive cell atlas of the hematopoietic stem cell (HSC) regulatory microenvironment. Here, we develop a tailored bioinformatic pipeline to integrate public and proprietary single-cell RNA sequencing (scRNA-seq) datasets. As a result, we robustly identify for the first time 14 intermediate cell states and 11 stages of differentiation in the endothelial and mesenchymal BM compartments, respectively. Our data provide the most comprehensive description to date of the murine HSC-regulatory microenvironment and suggest a higher level of specialization of the cellular circuits than previously anticipated. Furthermore, this deep characterization allows inferring conserved features in human, suggesting that the layers of microenvironmental regulation of hematopoiesis may also be shared between species. Our resource and methodology is a stepping-stone toward a comprehensive cell atlas of the BM microenvironment.

Single-Cell RNA Sequencing Analysis Reveals a Crucial Role for CTHRC1 (Collagen Triple Helix Repeat Containing 1) Cardiac Fibroblasts After Myocardial Infarction

BACKGROUND

Cardiac fibroblasts (CFs) have a central role in the ventricular remodeling process associated with different types of fibrosis. Recent studies have shown that fibroblasts do not respond homogeneously to heart injury. Because of the limited set of bona fide fibroblast markers, a proper characterization of fibroblast population heterogeneity in response to cardiac damage is lacking. The purpose of this study was to define CF heterogeneity during ventricular remodeling and the underlying mechanisms that regulate CF function.

METHODS

Collagen1α1-GFP (green fluorescent protein)-positive CFs were characterized after myocardial infarction (MI) by single-cell and bulk RNA sequencing, assay for transposase-accessible chromatin sequencing, and functional assays. Swine and patient samples were studied using bulk RNA sequencing.

RESULTS

We identified and characterized a unique CF subpopulation that emerges after MI in mice. These activated fibroblasts exhibit a clear profibrotic signature, express high levels of Cthrc1 (collagen triple helix repeat containing 1), and localize into the scar. Noncanonical transforming growth factor-β signaling and different transcription factors including SOX9 are important regulators mediating their response to cardiac injury. Absence of CTHRC1 results in pronounced lethality attributable to ventricular rupture. A population of CFs with a similar transcriptome was identified in a swine model of MI and in heart tissue from patients with MI and dilated cardiomyopathy.

CONCLUSIONS

We report CF heterogeneity and their dynamics during the course of MI and redefine the CFs that respond to cardiac injury and participate in myocardial remodeling. Our study identifies CTHRC1 as a novel regulator of the healing scar process and a target for future translational studies.

Melanocortin 4 receptor activates ERK-cFos pathway to increase brain-derived neurotrophic factor expression in rat astrocytes and hypothalamus

Melanocortins are neuropeptides with well recognized anti-inflammatory and anti-apoptotic effects in the brain. Of the five melanocortin receptors (MCR), MC4R is abundantly expressed in the brain and is the only MCR present in astrocytes. We have previously shown that MC4R activation by the α-melanocyte stimulating hormone (α-MSH) analog, NDP-MSH, increased brain-derived neurotrophic factor (BDNF) expression through the classic cAMP-Protein kinase A-cAMP responsive element binding protein pathway in rat astrocytes. Now, we examined the participation of the mitogen activated protein kinases pathway in MC4R signaling. Rat cultured astrocytes treated with NDP-MSH 1 µM for 1 h showed increased BDNF expression. Inhibition of extracellular signal-regulated kinase (ERK) and ribosomal p90 S6 kinase (RSK), an ERK substrate, but not of p38 or JNK, prevented the increase in BDNF expression induced by NDP-MSH. Activation of MC4R increased cFos expression, a target of both ERK and RSK. ERK activation by MC4R involves cAMP, phosphoinositide-3 kinase (PI3K) and the non receptor tyrosine kinase, Src. Both PI3K and Src inhibition abolished NDP-MSH-induced BDNF expression. Moreover, we found that intraperitoneal injection of α-MSH induces BDNF and MC4R expression and activates ERK and cFos in male rat hypothalamus. Our results show for the first time that MC4R-induced BDNF expression in astrocytes involves ERK-RSK-cFos pathway which is dependent on PI3K and Src, and that melanocortins induce BDNF expression and ERK-cFos activation in rat hypothalamus.

Molecular mechanisms involved in interleukin 1-beta (IL-1β)-induced memory impairment. Modulation by alpha-melanocyte-stimulating hormone (α-MSH)

Pro-inflammatory cytokines can affect cognitive processes such as learning and memory. Particularly, interleukin-1β (IL-1β) influences the consolidation of hippocampus-dependent memories. We previously reported that administration of IL-1β in dorsal hippocampus impaired contextual fear memory consolidation. Different mechanisms have been implicated in the action of IL-1β on long-term potentiation (LTP), but the processes by which this inhibition occurs in vivo remain to be elucidated. We herein report that intrahippocampal injection of IL-1β induced a significant increase in p38 phosphorylation after contextual fear conditioning. Also, treatment with SB203580, an inhibitor of p38, reversed impairment induced by IL-1β on conditioned fear behavior, indicating that this MAPK would be involved in the effect of the cytokine. We also showed that IL-1β administration produced a decrease in glutamate release from dorsal hippocampus synaptosomes and that treatment with SB203580 partially reversed this effect. Our results indicated that IL-1β-induced impairment in memory consolidation could be mediated by a decrease in glutamate release. This hypothesis is sustained by the fact that treatment with d-cycloserine (DCS), a partial agonist of the NMDA receptor, reversed the effect of IL-1β on contextual fear memory. Furthermore, we demonstrated that IL-1β produced a temporal delay in ERK phosphorylation and that DCS administration reversed this effect. We also observed that intrahippocampal injection of IL-1β decreased BDNF expression after contextual fear conditioning. We previously demonstrated that α-MSH reversed the detrimental effect of IL-1β on memory consolidation. The present results demonstrate that α-MSH administration did not modify the decrease in glutamate release induced by IL-1β. However, intrahippocampal injection of α-MSH prevented the effect on ERK phosphorylation and BDNF expression induced by IL-1β after contextual fear conditioning. Therefore, in the present study we determine possible molecular mechanisms involved in the impairment induced by IL-1β on fear memory consolidation. We also established how this effect could be modulated by α-MSH.

Glutamate induces apoptosis in anterior pituitary cells through group II metabotropic glutamate receptor activation

Glutamate can induce neuronal cell death by activating ionotropic glutamate receptors (iGluRs) as well as metabotropic glutamate receptors (mGluRs). In the present study, we investigated whether glutamate induces apoptosis of cultured anterior pituitary cells from female rats. Glutamate (1 mm) significantly reduced the metabolic activity of viable cells and increased the percentage of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells and caspase-3 activity in anterior pituitary cells. The inhibitory effect of glutamate on the viability of anterior pituitary cells was not observed in the presence of [2S]-alpha-ethylglutamic acid (0.75 mm), a specific group II mGluR antagonist. Also, (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (LCCG-I; 0.75 mm), a specific group II mGluR agonist, reduced viability and increased the percentage of TUNEL-positive anterior pituitary cells. Group I and III mGluRs and iGluRs agonists failed to modify the metabolic activity of anterior pituitary cells. Glutamate and LCCG-I increased the percentage of TUNEL-positive lactotropes and somatotropes. The subunit mGluR2/3, belonging to group II mGluR, was localized in these cell types. Glutamate increased nitric oxide (NO) synthase (NOS) activity and inducible NOS expression in anterior pituitary cells. N-methyl-l-arginine (NMMA, 0.5 mm), a NOS inhibitor, potentiated the apoptotic effect of glutamate in anterior pituitary cells, indicating that NO may restrain glutamate-induced apoptosis. Incubation of anterior pituitary cells with a cAMP analog (N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate; 1 mm) attenuated the apoptosis induced by glutamate. Glutamate and LCCG-I decreased prolactin release from anterior pituitary cells. N6, 2'-o-dibutyryladenosine 3', 5'-cyclic monophosphate reversed the inhibitory effect of glutamate on prolactin release, but NMMA failed to modify it. Our data show that glutamate induces apoptosis of lactotropes and somatotropes through group II mGluR activation, probably by decreasing cAMP synthesis.

Effect of ionotropic and metabotropic glutamate agonists and D-aspartate on prolactin release from anterior pituitary cells

Although the presence of ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors has been demonstrated in the anterior pituitary, recent reports on the direct effect of glutamate on prolactin (PRL) secretion by anterior pituitary cells have presented contradictory results. Hence, the aim of this study was to determine the effect of ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptor agonists on prolactin (PRL) release. In addition, since D-Aspartate (D-Asp) is found in the pituitary and is involved in neuroendocrine regulation, we also studied the direct action of D-Asp on PRL secretion. Finally, since the posterior pituitary participates in the regulation of PRL secretion, we examined the influence of the posterior pituitary on the effects of NMDA and D-Asp on PRL release. Glutamate (1000 microM) increased PRL secretion from cultured anterior pituitary cells. Both NMDA (100 microM) and kainate (100 microM) increased PRL secretion and these effects were blocked by a specific NMDA receptor antagonist. AMPA did not modify PRL release in these cultures. The group I and II mGluR agonist, trans-ACPD (1000 microM), and a specific group II mGluR agonist, L-CCG-I (100-1000 microM), inhibited whereas specific group I and III mGluR agonists, 3-HPG and L-AP4 respectively, had no effect on PRL release. Finally, D-Asp (100-1000 microM) stimulated PRL secretion and this effect was reduced by a NMDA receptor antagonist. When anterior pituitary cells were cultured in the presence of posterior pituitary cells, NMDA did not modify PRL or GABA release, while D-Asp increased PRL secretion and decreased GABA release in these cocultures. In conclusion, our results show that L-glutamate has a differential direct effect on PRL release: it exerts a stimulatory action via iGluRs and an inhibitory effect via mGluRs. D-Asp could directly stimulate PRL release through NMDA receptors. D-Asp may also stimulate PRL release by decreasing GABA release from the posterior pituitary.

Differential effects of glutamate agonists and D-aspartate on oxytocin release from hypothalamus and posterior pituitary of male rats

In order to determine whether ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptor activation modulates oxytocin release in male rats, we investigated the effect of agonists of both types of glutamate receptors on oxytocin release from hypothalamus and posterior pituitary. Kainate and quisqualate (1 mM) increased hypothalamic oxytocin release. Their effects were prevented by selective AMPA/kainate receptor antagonists. NMDA (0.01-1 mM) did not modify hypothalamic oxytocin release. Group I mGluR agonists, such as quisqualate and 3-HPG, significantly increased hypothalamic oxytocin release. These effects were blocked by AIDA (a selective antagonist of group I mGluRs). In the posterior pituitary, oxytocin release was not modified by kainate, quisqualate, trans-ACPD (a broad-spectrum mGluR agonist) and L-SOP (a group III mGluR agonist). However, NMDA (0.1 mM) significantly decreased oxytocin release from posterior pituitary. D-Aspartate significantly increased oxytocin release from the hypothalamus, while it decreased oxytocin release from posterior pituitary. AP-5 (a specific NMDA receptor antagonist) reduced the D-Aspartate effect in the hypothalamus, but not in the posterior pituitary. Our data indicate that the activation of non-NMDA receptors and group I mGluRs stimulates oxytocin release from hypothalamic nuclei, whereas NMDA inhibits oxytocinergic terminals in the posterior pituitary. D-Aspartate also has a dual effect on oxytocin release: stimulatory at the hypothalamus and inhibitory at the posterior pituitary. These results suggest that excitatory amino acids differentially modulate the secretion of oxytocin at the hypothalamic and posterior pituitary levels.

Neurokinin A inhibits oxytocin and GABA release from the posterior pituitary by stimulating nitric oxide synthase

Neurokinin A (NKA) is a tachykinin that participates in the control of neuroendocrine functions. The posterior pituitary lobe (PP) contains abundant nitric oxide synthase (NOS), suggesting that nitric oxide (NO) may play a role in controlling the release of neuropeptides and neurotransmitters. In the present project, we investigated the in vitro effect of NKA on oxytocin release from hypothalamic explants and PP of male rats and the possible involvement of NO in the action of NKA. Since NKA inhibits gamma-aminobutyric acid (GABA) release from PP, we also examined the role of NO in the effect of NKA on basal and K(+)-evoked GABA release. NKA (10(-7)-10(-5) M) significantly decreased oxytocin release from PP, whereas it did not affect its release from hypothalamic explants. The inhibitory effect of NKA on oxytocin release from PP was completely blocked by the NOS inhibitors N(G)-monomethyl-L-arginine (L-NMMA, 0.5 mM) or N(G)-nitro-L-arginine-methyl-ester (L-NAME, 1 mM). Sodium nitroprusside (0.5 mM), an NO releaser, had no effect on basal GABA release but significantly decreased K(+)-evoked GABA release. L-NMMA (0.3 mM) and L-NAME (0.5 mM) increased K(+)-evoked GABA release, indicating that NO plays an inhibitory role in GABA release from PP. The inhibition in both basal and K(+)-evoked GABA release induced by NKA (10(-7) M) was reduced by L-NAME (1 mM). Also, NKA (10(-7) M) increased NO synthesis as measured by [(14)C] citrulline production. Considered all together, our data indicate that NO may mediate the inhibitory effect of NKA on the release of both oxytocin and GABA from PP.

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.

Role of phosphodiesterase and protein kinase G on nitric oxide-induced inhibition of prolactin release from the rat anterior pituitary

OBJECTIVE

In order to determine the mechanism by which nitric oxide (NO) inhibits prolactin release, we investigated the participation of cGMP-dependent cAMP-phosphodiesterases (PDEs) and protein kinase G (PKG) in this effect of NO.

METHODS

Anterior pituitary glands of male rats were incubated with inhibitors of PDE and PKG with or without sodium nitroprusside (NP). Prolactin release, and cAMP and cGMP concentrations were determined by RIA.

RESULTS AND CONCLUSIONS

The inhibitory effect of NP (0.5 mmol/l) on prolactin release and cAMP concentration was blocked by EHNA (10(-4)mol/l) and HL-725 (10(-4)mol/l), inhibitors of cGMP-stimulated cAMP-PDE (PDE2). 8-Br-cGMP (10(-4) and 10(-3)mol/l), which mimics cGMP as a mediator of NP effects on prolactin release, also decreased cAMP concentration. Zaprinast (10(-4)mol/l), a selective inhibitor of specific cGMP-PDE (PDE5), potentiated the NP effect on cAMP concentration. Rp-8-[(4-chlorophenyl)thio]-cGMP triethylamine (Rp-8-cGMP, 10(-7)-10(-6)mol/l), an inhibitor of PKG, reversed the effect of NP on prolactin release. The present study suggests that several mechanisms are involved in the inhibitory effect of NO on prolactin release. The activation of PDE2 by cGMP may mediate the inhibitory effect of NO on cAMP concentration and therefore on prolactin release. NO-activated PKG may also be participating in the inhibitory effect of NO on prolactin release.

Interaction between substance P and TRH in the control of prolactin release

Substance P (SP) may participate as a paracrine and/or autocrine factor in the regulation of anterior pituitary function. This project studied the effect of TRH on SP content and release from anterior pituitary and the role of SP in TRH-induced prolactin release. TRH (10(-7) M), but not vasoactive intestinal polypeptide (VIP), increased immunoreactive-SP (ir-SP) content and release from male rat anterior pituitary in vitro. An anti-prolactin serum also increased ir-SP release and content. In order to determine whether intrapituitary SP participates in TRH-induced prolactin release, anterior pituitaries were incubated with TRH (10(-7) M) and either WIN 62,577, a specific antagonist of the NK1 receptor, or a specific anti-SP serum. Both WIN 62,577 (10(-8) and 10(-7) M) and the anti-SP serum (1:250) blocked TRH-induced prolactin release. In order to study the interaction between TRH and SP on prolactin release, anterior pituitaries were incubated with either TRH (10(-7) M) or SP, or with both peptides. SP (10(-7) and 10(-6) M) by itself stimulated prolactin release. While 10(-7) M SP did not modify the TRH effect, 10(-6) M SP reduced TRH-stimulated prolactin release. SP (10(-5) M) alone failed to stimulate prolactin release and markedly decreased TRH-induced prolactin release. The present study shows that TRH stimulates ir-SP release and increases ir-SP content in the anterior pituitary. Our data also suggest that SP may act as a modulator of TRH effect on prolactin secretion by a paracrine mechanism.

Estrogens modulate the inhibitory effect of tumor necrosis factor-alpha on anterior pituitary cell proliferation and prolactin release

Considering that tumor necrosis factor-alpha (TNF-alpha) is involved in normal tissue homeostasis and that its receptors are expressed in the anterior pituitary, we examined the effect of this cytokine on pituitary cell growth. Because anterior pituitary function depends on hormonal environment, we also investigated the influence of gonadal steroids in the effects of TNF-alpha on cell proliferation and the release of PRL from anterior pituitary cells. In addition, the release of TNF-alpha and its action on the release of PRL from anterior pituitary cells of rats at different stages of the estrous cycle was evaluated. In minimum essential medium D-valine, a medium that restricts fibroblastic proliferation, TNF-alpha (10 and 50 ng/mL) reduced 3H-Thymidine incorporation, DNA content, and active cell number. TNF-alpha failed to affect proliferation of cells from ovariectomized (OVX) rats. However, it significantly inhibited growth of cells from OVX rats cultured with 17beta-estradiol (E2) (10(-9) M) and from chronically estrogenized rats. TNF-alpha decreased the release of PRL from cells of intact rats, especially in proestrous, OVX rats cultured with E2 and chronically estrogenized rats. The release of anterior pituitary TNF-alpha was higher in proestrous rats. These results indicate that TNF-alpha plays an inhibitory role in anterior pituitary cell growth and the release of PRL in an estrogen-dependent manner.

Effect of interleukin-6 and tumor necrosis factor-alpha on GABA release from mediobasal hypothalamus and posterior pituitary

The release of cytokines during infection, inflammation and stress induces brain-mediated responses, including alterations of neuroendocrine functions. We examined the effect of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on release of gamma-aminobutyric acid (GABA) from mediobasal hypothalamic (MBH) explants and posterior pituitaries (PP) of male rats. IL-6 (10 ng/ml) did not modify basal GABA release from MBH and PP, but significantly increased GABA release under depolarizing conditions (40 mM K(+)). This effect was abolished by incubation of the tissue with indomethacin, an inhibitor of cyclooxygenase activity, indicating that prostaglandins could mediate the stimulation of GABA release induced by IL-6. On the contrary, TNF-alpha (50 ng/ml) significantly decreased K(+)-evoked GABA release from both MBH and PP. This inhibitory effect was not modified by indomethacin. Neither IL-6 nor TNF-alpha affected nitric oxide synthesis, as measured by [(14)C]citrulline production. The current results indicate that IL-6 stimulates GABA release from both hypothalamus and posterior pituitary by a mechanism mediated by prostaglandins. On the contrary, TNF-alpha inhibits GABA release from both tissues. These results suggest the possibility that GABAergic activity in the hypothalamic-pituitary axis could be involved in neuroendocrine responses to cytokines.

NMDA receptor-mediated control of GABA release from neurointermediate lobes of female and male rats

The effect of glutamate (GLUT) and its ionotropic receptor agonists on K(+)-evoked GABA release from the neurointermediate lobe (NIL) was investigated in diestrus, ovariectomized, ovariectomized-estrogenized female rats and intact male rats. GLUT and N-methyl-D-aspartate (NMDA) increased K(+)-evoked GABA release from the NIL in all the experimental groups. This stimulatory effect of NMDA was blocked by specific NMDA receptor antagonists but not by non-NMDA receptor antagonists. However, kainate did not modify evoked GABA release from the NIL in any of these groups. Neither GLUT nor NMDA modified nitric oxide synthase activity. These results indicate that GLUT, acting through NMDA receptors, stimulates evoked GABA release from the NIL of female and male rats. This effect is not influenced by gonadal status and does not appear to be mediated by nitric oxide production.

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.

The hormonal status modulates the effect of neurokinin A on prolactin secretion in female rats

We have previously reported that neurokinin A (NKA), a tachykinin closely related to substance P, increases the release of prolactin (PRL) from the anterior pituitary gland of male rats, but not from pituitaries of ovariectomized (OVX) female rats. In this study, we evaluated the influence of estrogens in the action of NKA on PRL secretion in female rats. NKA stimulated the in vitro release of PRL from pituitary glands of OVX-chronically estrogenized rats, and of proestrus and estrus rats, but had no effect in anterior pituitaries of diestrus rats. In addition, we observed that cultured anterior pituitary cells of OVX rats responded to NKA only when they were incubated for 3 days in the presence of estradiol 10(-9) M. This effect was blocked by L-659,877, an NK-2 receptor antagonist. We also studied the action of NKA on PRL release during lactation. The response of anterior pituitary cells to NKA was variable over this period. The maximal sensitivity to NKA was observed at day 10 of lactation. Furthermore, the blockade of endogenous NKA by the administration of an anti-NKA serum to lactating rats reduced the PRL surge induced by the suckling stimulus. These results show that the responsiveness of the anterior pituitary gland of female rats to NKA is modulated by the endocrine environment, and suggest that NKA may participate in the control of PRL secretion during the estrus cycle and lactation.

Effect of lipopolysaccharide on tumor necrosis factor and prolactin release from rat anterior pituitary cells

TNF-alpha plays a critical role in the cascade of neuroendocrine events during inflammation and septic shock. It also affects the release of pituitary hormones and acts as a growth factor in immune and nonimmune cells. The aim of the present study was to investigate the release of TNF-alpha from rat anterior pituitary cells and the effect of the steroid medium on its release. Cultured anterior pituitary cells from lactating rats spontaneously released TNF-alpha. The presence of lipopolysaccharide (LPS, 0.1 microg/mL) in the culture medium significantly increased TNF-alpha release and inhibited prolactin release. Chronic estrogenization of ovariectomized rats or the presence of 17 beta-estradiol in the culture medium also increased TNF-alpha release. LPS significantly stimulated TNF-alpha release in all groups and abrogated the estrogen-induced prolactin release. We also investigated the effect of TNF-alpha on prolactin release. The presence of TNF-alpha (50 ng/mL) in the culture medium inhibited prolactin release from anterior pituitary cells. These data show that anterior pituitary cells in culture release TNF-alpha and that this release is stimulated by estrogens. Our results also indicate that LPS inhibits prolactin release in an estrogenic environment, suggesting that TNF-alpha could affect pituitary hormone release during endotoxemia.

The effect of excitatory aminoacids on GABA release from mediobasal hypothalamus of female rats

The purpose of the present study was to examine the in vitro effect of L-glutamate and its agonists on basal and potassium-evoked GABA release from incubated mediobasal hypothalamus (MBH) of intact, ovariectomized (OVX) and OVX-estrogenized female rats. L-glutamate (100 microM) decreased evoked GABA release from MBH of intact female rats in diestrus. NMDA and quisqualate (10 and 100 microM) modified neither basal nor evoked hypothalamic GABA release of intact rats. However, kainate (10 and 100 microM) decreased hypothalamic basal and evoked GABA release of intact rats. Kainate induced no changes in basal or in evoked GABA release from hypothalami of OVX rats, but decreased GABA release in chronically estrogenized rats. DNQX (6,7-dinitroquinoxaline-2,3-dione), a non-NMDA receptor antagonist, failed to affect GABA release but blocked the inhibitory effect of kainate. The kainate effect was not Mg2+-sensitive and was not inhibited by D-AP5 (D(-)-2-amino-5-phosphonopentanoic acid), an NMDA-specific receptor antagonist. Kainate induced no changes in nitric oxide synthase activity in MBH of either intact or estrogenized rats. These data indicate that kainate decreases GABA release from MBH of female rats through a non-NMDA receptor subtype, and provide evidence to support the view that kainate-mediated decrease of the hypothalamic GABAergic tone is affected by estrogens.

Vasoactive intestinal peptide (VIP) mediates the effect of estrogens on the dopaminergic tone in the hypothalamic-pituitary axis of ovariectomized (OVX) rats

The role of vasoactive intestinal peptide (VIP) in the regulation of dopamine (DA) concentration in mediobasal hypothalamus (MBH), posterior and anterior pituitary of ovariectomized (OVX) estrogenized rats was studied using passive immunization against VIP with a specific antiserum (a-VIP). Chronic estradiol administration decreased DA concentration in MBH, and in posterior and anterior pituitary, compared to OVX control rats. DA tissue concentration increased following a-VIP administration to control and estrogenized OVX rats. In vitro study of VIP and a-VIP on DA release from MBH in chronically estrogenized OVX rats showed that estrogens decreased DA evoked-release from MBH;a-VIP increased DA evoked-release from MBH of control OVX and estrogenized rats. VIP decreased DA evoked-release from MBH of OVX rats, but had no effect on estrogenized rats. VIP decreased DA tissue concentration in MBH of OVX control but not of estrogenized rats. It is suggested that VIP decreases DA synthesis and release from hypothalamic neurons in female rats, and that VIP partially mediates the inhibitory effect of long-term estrogen administration on DA release from MBH.

Role of nitric oxide/cyclic GMP pathway in the inhibitory effect of GABA and dopamine on prolactin release

The anterior pituitary gland is a site of nitric oxide (NO) production and action, suggesting a local regulatory function. We recently reported that NO inhibits in vitro prolactin release. The aim of the present study was to establish the mechanism of action of NO on prolactin release and to determine whether NO is involved in the inhibitory effect of GABA on prolactin release. Since NO exerts its action through cGMP by activating guanylate cyclase in different tissues, we examined the effect of sodium nitroprusside (NP), a NO releaser, on intrapituitary cGMP levels. Incubation of anterior pituitary glands with 0.5 mM NP 4-fold increased intrapituitary cGMP content, but decreased intrapituitary cAMP levels. In addition, we studied the effect of NP on prolactin release in the presence of LY 83583, an inhibitor of guanylate cyclase activity and 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of phosphodiesterase activity. 10 microM LY 83583 and 0.5 mM IBMX blocked the inhibitory effect of NP on prolactin release. (10(-3) M) 8Br-cGMP, an analogue of cGMP, mimicked the effect of NP on prolactin release. On the other hand, NO seems to be involved in the inhibitory effect of GABA on prolactin release since hemoglobin, a scavenger of NO, and Nw-nitro-L-arginine methyl ester, an inhibitor of NO synthase (NOS), blocked the pituitary response to GABA. Moreover, GABA (10(-6) M) stimulated NOS activity by almost 50%. GABA increased intrapituitary cGMP levels and decreased cAMP. Dopamine stimulated NOS activity weakly. These observations suggest that NO, acting through the guanylate cyclase-cGMP pathway, inhibits prolactin secretion. In addition, NO may be involved in the inhibitory effect of GABA and dopamine on prolactin release.

Neurokinin A affects the tubero-hypophyseal gabaergic system

We have studied the in vitro effects of neurokinin A (NKA) on anterior pituitary GABA concentration and GABA release from the mediobasal hypothalamus and the neurointermediate lobe of male and ovariectomized female (OVX) rats. NKA significantly decreased the anterior pituitary GABA concentration, while the presence of a specific anti-NKA serum in the incubation medium increased the GABA concentration in this gland. By contrast, NKA did not modify basal or K(+)-evoked GABA release from the mediobasal hypothalamus of male or OVX rats. However, NKA decreased basal and K(+)-evoked GABA release from the neurointermediate lobe. Since GABA inhibits both prolactin (PRL) secretion from the anterior pituitary and the release of several putative PRL-releasing factors from the neurointermediate lobe, the decrease in anterior pituitary GABA concentration and the reduction in tubero-hypophyseal GABAergic activity induced by NKA may contribute to the stimulatory effect of this peptide on PRL secretion.

Nitric oxide inhibits the release of norepinephrine and dopamine from the medial basal hypothalamus of the rat

Previous research indicates that norepinephrine and dopamine stimulate release of luteinizing hormone (LH)-releasing hormone (LHRH), which then reaches the adenohypophysis via the hypophyseal portal vessels to release LH. Norepinephrine exerts its effect via alpha 1-adrenergic receptors, which stimulate the release of nitric oxide (NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback. MBH explants were incubated in the presence of sodium nitroprusside (NP), a releaser of NO, and the effect on release of catecholamines was determined. NP inhibited release of norepinephrine. Basal release was increased by incubation of the tissue with the NO scavenger hemoglobin (20 micrograms/ml). Hemoglobin also blocked the inhibitory effect of NP. In the presence of high-potassium (40 mM) medium to depolarize cell membranes, norepinephrine release was increased by a factor of 3, and this was significantly inhibited by NP. Hemoglobin again produced a further increase in norepinephrine release and also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitor NG-monomethyl-L-arginine (NMMA) at 300 microM, basal release of norepinephrine was increased, as was potassium-evoked release, and this was associated in the latter instance with a decrease in tissue concentration, presumably because synthesis did not keep up with the increased release in the presence of NMMA. The results were very similar with dopamine, except that reduction of potassium-evoked dopamine release by NP was not significant. However, the increase following incubation with hemoglobin was significant, and hemoglobin, when incubated with NP, caused a significant elevation in dopamine release above that with NP alone. In this case, NP increased tissue concentration of dopamine along with inhibiting release, suggesting that synthesis continued, thereby raising the tissue concentration in the face of diminished release. When the tissue was incubated with NP plus hemoglobin, which caused an increase in release above that obtained with NP alone, the tissue concentration decreased significantly compared with that in the absence of hemoglobin, indicating that, with increased release, release exceeded synthesis, causing a fall in tissue concentration. When NO synthase was blocked by NMMA, the release of dopamine, under either basal or potassium-evoked conditions, was increased. Again, in the latter instance the tissue concentration declined significantly, presumably because synthesis did not match release. Therefore, the results were very similar with both catecholamines and indicate that NO acts to suppress release of both amines. Since both catecholamines activate the release of LHRH, the inhibition of their release by NO serves as an ultra-short-loop negative feedback by which NO inhibits the release of the catecholamines, thereby reducing the activation of the NOergic neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.

Role of nitric oxide in control of prolactin release by the adenohypophysis

Nitric oxide synthase-containing cells were visualized in the anterior pituitary gland by immunocytochemistry. Consequently, we began an evaluation of the possible role of NO in the control of anterior pituitary function. Prolactin is normally under inhibitory hypothalamic control, and in vitro the gland secretes large quantities of the hormone. When hemipituitaries were incubated for 30 min in the presence of sodium nitroprusside, a releaser of NO, prolactin release was inhibited. This suppression was completely blocked by the scavenger of NO, hemoglobin. Analogs of arginine, such as NG-monomethyl-L-arginine (NMMA, where NG is the terminal guanidino nitrogen) and nitroarginine methyl ester, inhibit NO synthase. Incubation of hemipituitaries with either of these compounds significantly increased prolactin release. Since in other tissues most of the actions of NO are mediated by activation of soluble guanylate cyclase with the formation of cyclic GMP, we evaluated the effects of cyclic GMP on prolactin release. Cyclic GMP (10 mM) produced an approximately 40% reduction in prolactin release. Prolactin release in vivo and in vitro can be stimulated by several peptides, which include vasoactive intestinal polypeptide and substance P. Consequently, we evaluated the possible role of NO in these stimulations by incubating the glands in the presence of either of these peptides alone or in combination with NMMA. In the case of vasoactive intestinal polypeptide, the significant stimulation of prolactin release was augmented by NMMA to give an additive effect. In the case of substance P, there was a smaller but significant release of prolactin that was not significantly augmented by NMMA. We conclude that NO has little effect on the stimulatory action of these two peptides on prolactin release. Dopamine (0.1 microM), an inhibitor of prolactin release, reduced prolactin release, and this inhibitory action was significantly blocked by either hemoglobin (20 micrograms/ml) or NMMA and was completely blocked by 1 mM nitroarginine methyl ester. Atrial natriuretic factor at 1 microM also reduced prolactin release, and its action was completely blocked by NMMA. In contrast to these results with prolactin, luteinizing hormone (LH) was measured in the same medium in which the effect of nitroprusside was tested on prolactin release, there was no effect of nitroprusside, hemoglobin, or the combination of nitroprusside and hemoglobin on luteinizing hormone release. Therefore, in contrast to its inhibitory action on prolactin release NO had no effect on luteinizing hormone release. Immunocytochemical studies by others have shown that NO synthase is present in the folliculostellate cells and also the gonadotrophs of the pituitary gland. We conclude that NO produced by either of these cell types may diffuse to the lactotropes, where it can inhibit prolactin release. NO appears to play little role in the prolactin-releasing action of vasoactive intestinal polypeptide and substance P, but mediates the prolactin-inhibiting activity of dopamine and atrial natriuretic factor.

Involvement of hypothalamic substance P in the effect of prolactin on dopamine release

In order to examine the role of hypothalamic SP in the feedback regulation of prolactin, we studied the effect of prolactin and dopamine on SP concentration and release, and the effect of SP on dopamine release. Hypothalamic fragments from male Wistar rats were incubated in the presence of prolactin, dopamine or SP under basal and K(+)-stimulated conditions. SP (10(-7) M) stimulated dopamine release, while dopamine (10(-7) M) decreased SP content and release. Prolactin (100 ng ml-1) increased SP content and release. An increase in hypothalamic SP content was also found during suckling. In addition, a specific antagonist for SP, Win 62,577, blocked the effect of prolactin and dopamine release. These results show an interaction between SP and dopamine at the hypothalamic level and suggest that SP could mediate the feedback action of prolactin on dopamine release.

GABA transport and subcellular distribution in the rat anterior pituitary gland

In this investigation we have studied the uptake of gamma aminobutyric acid (GABA) into anterior pituitary slices. Tissue:medium ratios of about 45:1 were obtained after a 30-min incubation. The process responsible for 3H-GABA uptake was temperature-sensitive and sodium-dependent. The kinetic constants of saturable GABA transport were: Km 4.141 microM and Vmax 0.973 pmol/min/mg protein, at 25 degrees C. The incorporation of GABA into anterior pituitary was inhibited by specific inhibitors of neuronal and/or glial uptake. The subcellular distribution of GABA was investigated by continuous sucrose density gradients and differential centrifugation. Most of the endogenous and labelled GABA was present in the soluble fraction. However, a small part of GABA was found in the particulate fraction. These observations indicate that the anterior pituitary gland is able to concentrate GABA which interacts with intracellular particles.

Possible role of neurokinin a in the control of prolactin secretion in rats and hamsters

Abstract The possible role of neurokinin A (NKA) in the control of prolactin secretion was studied in vivo, by injecting anti-NKA serum to ovariectomized rats treated with estrogens and to proestrous rats and hamsters. Injections of an anti-NKA serum to ovariectomized rats treated with two doses of 80 mug 17ss-estradiol 24 h apart, or treated chronically with estradiol implants induced a significant decrease of serum prolactin levels as compared with those of similarly treated rats injected with normal rabbit serum. In proestrous rats, the anti-NKA serum did not modify the afternoon surge of prolactin or luteinizing hormone, but when the antiserum was injected the day before, on diestrus II, it significantly reduced the prolactin surge during the afternoon of proestrus. As in these results obtained in the rat, injections of anti-NKA serum to golden hamsters on diestrus II also significantly decreased the prolactin surge in the afternoon of proestrus. These results suggest a possible physiological role of NKA on prolactin secretion, exerting a stimulatory influence on the release of this hormone.

Possible role of vasoactive intestinal peptide in the hyperprolactinemia induced by ethanol

The effect of the blockade of endogenous VIP by injecting a specific rabbit anti-VIP serum (A-VIP) was studied in rats receiving an acute injection of ethanol. A-VIP administration decreased serum prolactin levels and reduced the hyperprolactinemia induced by ethanol. We also investigated the effect of the acute administration of ethanol on the concentration and release of VIP from the mediobasal hypothalamus. Ethanol decreased VIP concentration in the mediobasal hypothalamus, whereas it stimulated the in vitro K(+)-evoked release of VIP from this tissue. Conversely, ethanol increased VIP concentration in the anterior pituitary gland. The data indicate that VIP may be involved in the pituitary response to ethanol. The increased anterior pituitary VIP after ethanol may be due to an augmented release from the mediobasal hypothalamus.

The effect of gonadal steroids on vasoactive intestinal Peptide concentration and release from mediobasal hypothalamus and the anterior pituitary gland

Abstract The effects of chronic administration of sex steroids on the content of vasoactive intestinal peptide (VIP) in the mediobasal hypothalamus and anterior pituitary were studied in adult rats. Gonadectomy had no effect on VIP concentration in the mediobasal hypothalamus or anterior pituitary gland. Estradiol benzoate (1 mug/100 g body wt/day) administered for 10 days decreased mediobasal hypothalamus VIP concentration of ovariectomized rats whereas it produced no change in mediobasal hypothalamus VIP content of orchidectomized rats. Testosterone propionate (100 mug/100 g body wt/day) administration decreased mediobasal hypothalamus VIP content in both sexes. Estradiol administration caused an increase whereas testosterone treatment resulted in a decrease in anterior pituitary VIP levels in both sexes. The effect of chronic administration of the sex steroids on VIP release from the mediobasal hypothalamus and anterior pituitary was also investigated. Estradiol increased evoked VIP release from the mediobasal hypothalamus and decreased mediobasal hypothalamus VIP content whereas testosterone decreased both mediobasal hypothalamus release and content. Chronic treatment with estradiol enhanced anterior pituitary VIP release and content while testosterone decreased both parameters studied. The data indicate that anterior pituitary VIP content is under the control of gonadal hormones and that the increased anterior pituitary VIP found after estradiol administration may be due to an augmented release from the mediobasal hypothalamus and probably an increase in anterior pituitary VIP synthesis.

Ethanol-related changes in substance P in the hypothalamus and anterior pituitary

The effect of the administration of a rabbit anti-substance P serum (ASPS) was studied in rats receiving an acute injection of ethanol. ASPS lowered serum prolactin levels and reduced the hyperprolactinemia induced by ethanol. ASPS also decreased LH serum levels in both saline- and ethanol-treated rats. The effect of ethanol on the concentration of substance P-like immunoreactivity (SP-LI) in the mediobasal hypothalamus and the anterior pituitary gland was also investigated. Ethanol reduced SP-LI in the mediobasal hypothalamus but increased it in the anterior pituitary gland. The presence of ethanol (50 mM) did not affect the K(+)-evoked release of SP-LI from either mediobasal hypothalamus or anterior pituitary gland, though it increased the SP-LI concentration remaining in this gland. These results indicate that ethanol increases the content of SP-LI in the anterior pituitary gland and suggest that substance P may be involved in the prolactin release induced by the acute administration of ethanol.

Substance P affects the GABAergic system in the hypothalamo-pituitary axis

In the present work we examined the effect of the neutralization of endogenous substance P by the administration of an anti-substance P serum (ASPS) on GABA concentration in the anterior pituitary in hyperprolactinemic conditions induced by 5-hydroxytryptophan or by grafting anterior pituitaries. ASPS reduced the increase in the anterior pituitary GABA concentration induced by hyperprolactinemia. In vitro experiments showed that substance P inhibited K(+)-evoked GABA efflux from hypothalamic fragments and decreased GABA concentration in the anterior pituitary but ASPS increased it. Our results demonstrate that substance P modifies hypothalamic GABA release and anterior pituitary GABA concentration and suggest that an interaction exists between substance P and GABA.

Effects of serotonin on the hypothalamic-pituitary GABAergic system

The effects of serotonin (5-HT) and its precursor, 5-hydroxytryptophan (5-HTP) on the GABAergic system in the mediobasal hypothalamus (MBH) and the anterior pituitary were studied. The IP administration of 5-HTP produced a transient increase (only at 45 min after the injection) in glutamate decarboxylase activity (GAD) of MBH and in GABA concentration in anterior pituitary. Besides, 5-HTP administration increased the in vitro evoked GABA release from MBH. The administration of 5-HTP to hypophysectomized rats partially reversed the inhibitory effects of hypophysectomy on GABA concentration in MBH. We also examined the direct effect of 5-HT on some parameters on the hypothalamic GABAergic system. The presence of 5-HT in the incubation medium increased GAD activity and evoked GABA release from MBH. These observations indicate that the serotoninergic stimulation of the hypothalamic GABAergic system could be a direct effect which may, at least partially, be independent of the feedback mechanism induced by prolactin on the GABAergic neurons. The serotoninergic increase of prolactin secretion could be accomplished through stimulation of the hypothalamic GABAergic transmission.

Vasoactive intestinal peptide affects the GABAergic system in the hypothalamic-pituitary axis

The effect of a specific antiserum against vasoactive intestinal peptide (VIP) on GABA in the hypothalamic-pituitary axis was studied. The administration of anti-VIP serum (A-VIP) increased anterior pituitary GABA concentration in control rats, but decreased this neurotransmitter in rats with hyperprolactinemia induced by acute or chronic treatments with estrogens, or by the implanting of anterior pituitary glands under the kidney capsule. Besides, the injection of the A-VIP serum in the morning in proestrous rats causes a decrease in anterior pituitary GABA concentration, measured in the afternoon of the same day. The in vitro effect of A-VIP and VIP on endogenous GABA release from hypothalamic fragments and on anterior pituitary GABA concentration was studied. A-VIP increased both basal and high K(+)-evoked GABA effluxes whereas VIP produced a decrease in evoked GABA efflux from hypothalamic fragments. Furthermore, A-VIP inhibited the normal degradation of GABA that occurs in the isolated gland whereas VIP increased it. These results suggest that VIP modifies hypothalamic GABA release and anterior pituitary GABA concentration.

Effects of passive immunization against vasoactive intestinal peptide on serum prolactin and LH levels

Recent findings suggest that vasoactive intestinal peptide (VIP) may be a physiological regulator of prolactin secretion and may also be involved in the control of LH secretion. In the present work we have studied the effect of the blockade of endogenous VIP by means of the injection of a specific rabbit anti-VIP serum, in male and female rats with hyperprolactinemia. The administration of 0.5 ml of the VIP antiserum in ovariectomized rats given an acute or chronic treatment with 17 beta-estradiol induced a significant decrease in serum prolactin and LH levels as compared with estrogenized-control rats injected with normal rabbit serum. Anti-VIP serum also reduced serum LH levels in ovariectomized rats not treated with estrogens. The administration of the same antiserum decreased serum prolactin levels in male rats implanted with 2 anterior pituitary glands under the kidney capsule. On the other hand, the injection of the anti-VIP serum in the morning in proestrus rats brought about an increase in serum prolactin and LH levels in the afternoon of the same day. These results confirm previous data showing that VIP is a stimulator of prolactin release, and may also participate in the control of LH secretion in ovariectomized rats acting as a facilitatory factor. During proestrus however, VIP may act in an opposite way, inhibiting, rather than stimulating, prolactin and LH release.

Estriol affects prolactin and LH secretion in rats

The effects of estriol on serum prolactin (PRL) and LH levels, on the pituitary response to TRH and LHRH and on the synthesis and release of PRL from the anterior pituitary gland were investigated in female rats. The increase of serum PRL levels after estradiol administration was found to be associated with an increase of glutamic acid decarboxylase (GAD) and GABA-transaminase (GABA-T) in the hypothalamus. Thus, a study was carried out on the effects of estradiol and estriol on PRL secretion and on GAD, GABA-T and gamma-amino butyric acid (GABA) in the hypothalamus and the anterior pituitary. Under basal and TRH-stimulated conditions, estriol increased serum PRL levels, decreased basal serum LH levels, and increased the response to LHRH, in terms of LH release. Estradiol and estriol increased the synthesis and release of 3H-PRL from hemipituitary glands in incubations of pretreated animals. Both estrogens induced hyperprolactinemia, concomitantly with an increase of hypothalamic GAD and GABA-T activity. Estriol increased hypothalamic GABA concentration, but did not modify GABA concentration in the pituitary glands. Our results show that estriol, at relatively high doses, seems to be active in increasing PRL synthesis and release and in decreasing serum LH levels; it can also modify pituitary response to TRH and LHRH stimulation.

Effect of sex steroids on GABA receptors in the rat hypothalamus and anterior pituitary gland

Our data indicate that sex steroids modify the number of GABA receptors, as detected by a [3H]muscimol binding assay, in the tuberoinfundibular GABAergic system. GABA binding was affected by chronic hormonal treatments in different ways depending on the sex of the rats and the steroids administered. Estradiol increased GABA binding in ovariectomized female rats while testosterone decreased the number of GABA binding sites in gonadectomized male rats. These results suggest a sex difference in the regulation of hypothalamic GABA receptors.

Possible mechanisms of action of ethanol-induced release of prolactin from rat anterior pituitary

We have demonstrated previously that ethanol increases the in vitro synthesis and release of prolactin by the anterior pituitary gland. In the present study we have examined the possible role of calcium and calmodulin in the ethanol-stimulation of in vitro prolactin release from hemipituitary glands. We also investigated the effect of inhibitors of arachidonic acid metabolism on the release of prolactin induced by ethanol. In addition we studied the effect of ethanol on the release of prostaglandins and the conversion of arachidonic acid to hydroperoxides. Basal and ethanol-stimulated prolactin release was almost blocked completely by omitting calcium from the incubation medium. In vitro addition of calmodulin-blocking agents such as pimozide and trifluoperazine reduced basal and ethanol-induced prolactin release. Acetylsalicylic acid, an inhibitor of the cycloxygenase pathway, had no effect on prolactin release. Nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway, blocked completely the release of prolactin induced by ethanol. Ethanol (5 and 10 mM) significantly increased the release of prostaglandin E2 and prostaglandin F2 alpha and the conversion of [14C]arachidonic acid to 5-hydroxyeicosatetraenoic acid. The results of this study show that ethanol increases prolactin release by a calcium-dependent mechanism. Besides, our data suggest that arachidonic acid metabolism is involved in ethanol-stimulated prolactin secretion and that lipoxygenase pathway metabolites are at least partially responsible for this effect.

Effect of passive immunization against substance P in rats with hyperprolactinemia

Substance P, an undecapeptide isolated from gut and brain tissues, was reported to stimulate prolactin release. It was suggested that substance P may play a role in the control of prolactin secretion. In this investigation we studied the effects of the blockade of endogenous substance P by the administration of a specific anti-substance P serum on serum prolactin levels in rats in the evening of proestrus, in lactating rats after suckling, and in male rats with hyperprolactinemia induced by grafting 2 anterior pituitary glands under the kidney capsule. The injection of the anti-substance P serum was followed by a significant decrease of the prolactin surge induced by 30 min suckling in lactating rats, when the antiserum was administered 24 hr but not 5.30 hr earlier. Anti-substance P serum also induced a significant decrease in serum prolactin levels in pituitary grafted rats, but induced no change in the proestrous surge of prolactin and LH. These results show that substance P may be involved in the release of prolactin induced by suckling and that this peptide may have an intrapituitary role in the process of prolactin release. On the other hand, substance P does not seem to play a significant role in the proestrous peak of prolactin and LH.

Effect of ethanol on GABA uptake and release from hypothalamic fragments

A study was performed on the effect of ethanol on the basal and K+-evoked efflux of endogenous GABA from rat hypothalamic fragments. The amount of GABA present in the medium and in the tissue was measured by radioreceptor assay. In vitro addition of ethanol (50 and 100 mM) enhanced the K+-evoked efflux of GABA in a Ca++-dependent manner, and increased tissue GABA content. Since K+-evoked outflow induced by ethanol was not affected by the presence of nipecotic acid, ethanol appears to alter the uptake of endogenous GABA. An inhibitory effect of ethanol on 3H-GABA uptake was observed under K+ depolarization. On the other hand, acute ethanol administration produced a decrease in basal and K+-evoked efflux from hypothalamic fragments and in tissue GABA concentration. Changes in GABA efflux may lie behind some of the neuropharmacological effects of ethanol.

Mechanisms of endogenous GABA release from hypothalamic fragments. Effect of prolactin

The efflux of endogenous gamma-aminobutyric acid (GABA) has been studied using small hypothalamic fragments containing arcuate-paraventricular nuclei and median eminence from the rat brain. The amount of GABA present in the medium and the tissue GABA content were quantified by radioreceptor assay. The endogenous GABA efflux was found to be dependent upon the Ca2+ and K+ concentrations in the incubation medium, and it required synthesis of GABA, indicating neuronal origin of the released neurotransmitter. Nipecotic acid, an inhibitor of neuronal and glial uptake, prevented reuptake of released GABA. Prolactin in concentrations of 250 and 1,000 ng/ml augmented the K+-evoked efflux of GABA. The effect of prolactin was dependent on the presence of Ca2+ and on the synthesis of GABA. In addition, prolactin seems to alter the reuptake of endogenous GABA and the uptake of [3H]-GABA. In conclusion, these results suggest that prolactin may influence its own secretion by stimulating the release of hypothalamic GABA, both through an increase of its synthesis and a modification of its reuptake.

Effect of an anti-substance P serum on prolactin and gonadotropins in hyperprolactinemic rats

The effects of the acute injection of a rabbit anti-substance P serum (ASPS) were studied in normal rats and rats with hyperprolactinemia induced by 5-hydroxytryptophan and estradiol given as a short or chronic treatment. The anti-substance P serum decreased the release of prolactin induced by 5-hydroxytryptophan when this serotonin precursor was injected 24 h, but not 1 h, after the administration of the antiserum. ASPS reduced the hyperprolactinemia induced by short and chronic treatment with estradiol in castrated rats. This effect was observed 24 h after the injection of the antiserum. On the other hand, the injection of ASPS induced a significant decrease in LH levels in serum of intact male rats injected with 5-hydroxytryptophan 24 h after ASPS, and in castrated rats treated with short-term and chronic administration of estradiol, 24 h after the injection of the antiserum. These results suggest that substance P may have a role in the control of prolactin secretion and could play a part in the hyperprolactinemic effects of estradiol. On the other hand, substance P, under certain circumstances, may stimulate LH release.

The effect of prolactin on glutamate decarboxylase activity and GABA concentration in hypothalamic slices

The effect of prolactin on the activity of GABA-related enzymes and GABA concentrations were studied in hypothalamic slices incubated in vitro. After short periods of incubation (up to 40 min), prolactin (0.25 micrograms/ml) added to the incubation medium produced a significant increase (21% at 20 min of incubation) in glutamic acid decarboxylase (GAD) activity in the hypothalamic slices. A higher concentration of prolactin (1.0 micrograms/ml) produced a slight but significant decrease (8% at 20 min of incubation) in hypothalamic GAD activity. However, after longer periods of incubation (over 8 hr), both doses of prolactin induced a sustained increase in hypothalmic GAD activity, a response which depends upon protein synthesis. No changes were observed in GABA-transaminase (GABA-T) activity of hypothalamic slices incubated in the presence of prolactin. Prolactin decreased GABA concentration in the hypothalami incubated for 10 hr and, at the same time, increased GABA release into the medium. These results indicate that prolactin modifies the synthesis and release of hypothalmic GABA and suggest the existence of a feedback mechanism that prolactin may exert directly at the hypothalamic level.

Effect of GABA-T inhibitors on prolactin secretion in vitro

A study was made of the effect of GABA-transaminase (GABA-T) inhibitors on the in vitro release of prolactin by pituitaries of male and female rats. Aminooxyacetic acid (AOAA) and gamma-acetylenic GABA (GAG) added to the incubation medium decreased prolactin release from both male and female rat pituitaries. Additive effects on prolactin release were only observed when male rat pituitaries were incubated with AOAA plus GABA. Prolactin concentration in the pituitary gland was also decreased by AOAA in both sexes. The present results lend support to the idea of an inhibitory action of GABA on prolactin release by the pituitary gland.