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Chemokines play a key role in inflammation. They are expressed not only in neuroinflammatory conditions, but also constitutively by different cell types, including neurons in the normal brain, suggesting that they may act as modulators of neuronal functions. Here, we investigated a possible neuroendocrine role of the chemokine stromal cell-derived factor 1 (SDF-1)/CXCL12. We demonstrated the colocalization of SDF-1 and its receptor CXCR4 with arginine vasopressin (AVP) in the magnocellular neurons of the supraoptic nucleus (SON) and the paraventricular hypothalamic nucleus and on AVP projections to the neurohypophysis. Electrophysiological recordings of SON neurons demonstrated that SDF-1 affects the electrical activity of AVP neurons through CXCR4, resulting in changes in AVP release. We observed that SDF-1 can blunt the autoregulation of AVP release in vitro and counteract angiotensin II-induced plasma AVP release in vivo. Furthermore, a short-term physiological increase in AVP release induced by enhanced plasma osmolarity, which was produced by the administration of 1 M NaCl i.p., was similarly blocked by central injection of SDF-1 through CXCR4. A change in water balance by long-term salt loading induced a decrease in both SDF-1 and CXCR4 parallel to that of AVP immunostaining in SON. From these data, we demonstrate that chemokine actions in the brain are not restricted to inflammatory processes. We propose to add to the known autoregulation of AVP on its own neurons, a second autocrine system induced by SDF-1 able to modulate central AVP neuronal activity and release.

Previous studies in our laboratory suggest that neurotensin (NT) acts centrally to modulate adrenocorticotropin hormone (ACTH) and corticosterone release. In the present studies, we examined hypothalamic-pituitary-adrenal (HPA) function under basal conditions and during restraint stress following central administration of the highly specific NT receptor antagonist, SR48692. Chronic delivery of SR48692 to the paraventricular nucleus (PVN) of the hypothalamus via indwelling central cannulae attenuated both the diurnal- and stress-induced elevations in HPA activity. Thus, SR48692 decreased the diurnal increase in plasma ACTH and corticosterone during the evening phase of the cycle, but did not affect morning levels. Restraint-induced increases in plasma ACTH and corticosterone levels were also significantly reduced in the SR48692-implanted animals. This suggests that the inhibitory effects of SR48692 were restricted to periods of stimulated HPA activity. A decrease in corticotropin-releasing hormone (CRH)-like immunoreactivity was observed within the PVN following chronic SR48692, and parallel decreases in CRH-like immunoreactivity were observed within the external zone of the median eminence. These findings suggest that endogenous NT serves to increase HPA activity during periods of enhanced stimulation.

More than two decades of research indicate that the peptide neurotensin (NT) and its cognate receptors participate to a remarkable extent in the regulation of mammalian neuroendocrine systems, potentially at multiple levels in a given system. NT-synthesizing neurons appear to exert a direct or indirect stimulatory influence on neurosecretory cells that synthesize gonadotropin-releasing hormone, dopamine (DA), somatostatin, and corticotropin-releasing hormone (CRH). In addition, context-specific synthesis of NT occurs in hypothalamic neurosecretory cells located in the arcuate nucleus and parvocellular paraventricular nucleus, including distinct subsets of cells which release DA, CRH, or growth hormone-releasing hormone into the hypophysial portal circulation. At the level of the anterior pituitary, NT stimulates secretion of prolactin and occurs in subsets of gonadotropes and thyrotropes. Moreover, circulating hormones influence NT synthesis in the hypothalamus and anterior pituitary, raising the possibility that NT mediates certain feedback effects of the hormones on neuroendocrine cells. Gonadal steroids alter NT levels in the preoptic area, arcuate nucleus, and anterior pituitary; adrenal steroids alter NT levels in the hypothalamic periventricular nucleus and arcuate nucleus; and thyroid hormones alter NT levels in the hypothalamus and anterior pituitary. Finally, clarification of the specific neuroendocrine roles subserved by NT should be greatly facilitated by the use of newly developed agonists and antagonists of the peptide.

Old rats of the WAG/Rij strain have a high incidence (50%) of medullary thyroid carcinoma, a calcitonin (CT)-secreting tumor. We have characterized and quantified the topographical distribution of [125I]salmon calcitonin (sCT) binding sites in the kidneys of this strain, as compared to Wistar CF rats (2% incidence of spontaneous medullary thyroid carcinoma). We report here that, up to 15 days of postnatal development, the distribution of CT-binding sites in the kidney of the WAG/Rij strain was quite similar to that found in developing and adult Wistar CF rats. However, from the age of 1 month, sCT-binding sites were dramatically reduced in both the medulla and the inner part of the kidney cortex, though plasma CT levels were not significantly different in both strains. Adult WAG/Rij rats bearing a transplanted tumor for 12 weeks had a high level of plasma calcitonin and exhibited an even greater reduction of both medullary and cortical sCT-binding sites. These results suggest that the modification in the CT-binding sites in WAG/Rij rats is not a consequence of a possible down regulation due to elevated circulating hormonal level but could be inherited and possibly associated with the later development of the tumor in this strain.

The photoaffinity labeling of neurotensin (NT) binding sites was carried out on rat midbrain sections using a monoiodo analogue of NT (125I-azidobenzoyl [Trp11] NT; 125IAB-NT). Autoradiographic data showed that the 125IAB-NT binding site localization was quite similar to that obtained with 125I-NT, with high densities in both substantia nigra and ventral tegmental area. Covalent specific binding was only observed when sections were irradiated with UV after the incubation, followed by various histological treatments necessary for light and electron microscopy.

This work describes the presence of glucocorticoid binding sites in human temporal cortex obtained following partial lobectomy in two epileptic patients. Using [3H]dexamethasone as radioligand and cold cortisol or RU 28362 as competitor we found an apparent Kd of approximately 2.8 nM with a Bmax of approximately 34 fmol/mg protein. The order of potency of various unlabeled steroids to compete for [3H]dexamethasone binding was as follows: RU 28362 = RU 38486 = cortisol = dexamethasone greater than progesterone greater than spironolactone greater than estradiol. These data provide evidence for an intracellular mechanism by which circulating glucocorticoids might regulate neuronal function in the human cortex.

In the present work we demonstrate by means of quantitative in vitro autoradiography that the vasoactive intestinal peptide (VIP) is able to increase the number of serotonin1 (5-HT1) binding sites in the dorsal subiculum of the rat hippocampus and to decrease them in the suprachiasmatic nucleus (SCN). Bilateral adrenalectomy (ADX) for 6 days counteracted the stimulatory effect of VIP on 5-HT1 binding sites in the dorsal subiculum, but did not modify the inhibitory effect of the peptide in the SCN. Moreover, ADX increased 5-HT1 binding sites in response to VIP in various subfields of the hippocampus as well as in the superior colliculus and in the dorsal lateral septum, but this effect was not observed in normal or in ADX rats bearing a corticosterone implant. The present data are suggestive of a possible interaction between VIP and 5-HT in the regulation of the SCN and of a modulatory role of adrenal steroids in VIP activity in the hippocampal formation.

In the present study, we describe the biochemical characteristics and the autoradiographic distribution of thyrotropin-releasing hormone (TRH) receptors in the rat central nervous system (CNS) after in vitro incubation of brain slices with 3H-TRH. Scatchard analysis showed that, in the range of concentrations tested (0.7-35 nM), 3H-TRH bound to a single-class of receptors with a dissociation constant of 6 nM and a number of binding sites of 20 fmol/mg protein. Increasing concentrations of unlabeled TRH produced a dose-dependent inhibition of 3H-TRH binding. The only analogue as potent as TRH to displace 3H-TRH binding was 3-Me-TRH, whereas 1-Me-TRH or TRH-free acid as well as pGlu-His, pGlu-Pro-NH2 or His-Pro-diketopiperazine were ineffective. Neither Luteinizing hormone-releasing hormone (LHRH), neurotensin, somatostatin, D-Ala-Met-enkephalin nor VIP showed any significant affinity for TRH binding sites. Autoradiograms obtained by apposition of LKB 3H-Ultrofilm showed that the highest concentrations of 3H-TRH binding sites were found in the ventral dentate gyrus of the hippocampal formation, the lateral amygdaloid nucleus, the nucleus accumbens, and the thalamic paraventricular nucleus. The biochemical characterization of 3H-TRH binding in brain sections is in good agreement with previous reports on membrane preparations and the autoradiographic localization of the binding sites provides anatomical support for the effects of TRH in the CNS.

In treating age-related osteoporosis and Paget disease of bone, it is of major importance to avoid an escape phenomenon that would reduce effectiveness of the treatment. The factors involved in the loss of therapeutic efficacy with administration of large pharmacological doses of the hormone require special consideration. Down-regulation of the hormone receptors could account for the escape phenomenon. Specific binding sites for salmon calcitonin (sCT) were characterized and localized by autoradiography on rat kidney sections incubated with 125I-labeled sCT. Autoradiograms demonstrated a heterogenous distribution of 125I-labeled sCT binding sites in the kidney, with high densities in both the superficial layer of the cortex and the outer medulla. Infusion of different doses of unlabeled sCT by means of Alzet minipumps for 7 days produced rapid changes in plasma calcium, phosphate, and magnesium levels, which were no longer observed after 2 or 6 days of treatment. Besides, infusion of high doses of sCT induced down-regulation of renal sCT binding sites located mainly in the medulla, where calcitonin (CT) has been shown to exert its physiological effects on water and ion reabsorption. These data suggest that the resistance to high doses of sCT often observed during long-term treatment of patients may be the consequence of not only bone-cell desensitization but also down-regulation of CT-sensitive kidney receptor sites.

Vasoactive intestinal peptide (VIP) is a major regulatory peptide in the nervous system, playing a role in normal brain activity. VIP levels change dramatically during postnatal rat brain development, raising the question of how these changes are regulated. To study VIP-gene expression, a sensitive RNA detection assay which uses in vitro-transcribed RNA hybridization probes, corresponding to 4 exons of the VIP-gene, was adapted. Results show that the major VIP-mRNA was 2000-2100 bases long in the rat. The amounts of this RNA varied markedly with development. In the frontal cortex of the rat brain, the 2000-2100-base mRNA increased by at least 5-fold from birth to 3-4 days, showing a maximal content at 14-16 days. VIP-mRNA synthesis therefore apparently precedes peptide synthesis by several days, as VIP in the rat cortex begins to increase only at about 7 days of age. Similarly, in the parietal cortex, VIP-mRNA was detected by 3 days of age. However, the increase in the mRNA content from 3 to 14 days of age was greater than in the frontal cortex, while almost no VIP-mRNA was detected in the newborn rat parietal cortex. In contrast, the hypothalamus and intestine contained significant quantities of VIP-mRNA at birth, the hypothalamic levels in newborns being much higher than anticipated from the peptide levels. In the hippocampus, the major peak in VIP-mRNA content occurred at 8 days of age. Taken together, these results indicate local controls of VIP-gene expression and a developmentally associated role for VIP-gene products. As the VIP-mRNA levels did not always parallel the peptide levels, regulation at the post-transcriptional stage may be essential for normal VIP function.

The characteristics and topographical distribution of monoiodo 125I-Tyr3-neurotensin (NT) binding sites in normal human brain tissue were studied on brain sections and by quantitative autoradiography. Sections at the level of the substantia nigra show a dissociation constant and maximal binding capacity of 4.8 +/- 0.8 nM and 70 +/- 7 fmol/mg protein, respectively. High density of 125I-NT binding sites were mainly found in dopaminergic (DA)-rich areas such as the substantia nigra, the ventral tegmental area, the striatum and the nucleus accumbens, further supporting an interaction between NT and DA neurons in human brain.

Renal binding sites for labelled salmon calcitonin (sCT) were studied using cryostat sections and autoradiography. Increasing concentrations of unlabelled sCT inhibited 125I-sCT binding. 125I-sCT bound to a single site with a Kd of 2 nM and a number of sites of 220 fmol/mg protein. Mammalian calcitonins had low affinities and peptides unrelated to CT were devoid of any significant affinity for 125I-sCT receptors. Autoradiograms disclosed a high concentration of 125I-sCT receptors mainly located in the outer medulla and heterogeneously in the renal cortex. The distribution of specific binding sites is in agreement with the current concepts of renal action of calcitonin.