Changes in oxytocin content in the magnocellular neurons of the rat hypothalamus following water deprivation or estrogen treatment. Quantitative immunohistological studies

The effects of long-term estradiol treatment on social behavior and gene expression in adult female rats

This study tested the effects of long-term estradiol (E₂) replacement on social behavior and gene expression in brain nuclei involved in the regulation of these social behaviors in adult female rats. We developed an ultrasonic vocalization (USV) test and a sociability test to examine communications, social interactions, and social preference, using young adult female cagemates. All rats were ovariectomized (OVX) and implanted with a Silastic capsule containing E₂ or vehicle, and housed in same-treatment pairs for a 3-month period. Then, rats were behaviorally tested, euthanized, and 5 nuclei in the brain's social decision-making circuit were selected for neuromolecular profiling by a multiplex qPCR method. Our novel USV test proved to be a robust tool to measure numbers and types of calls emitted by cagemates that had been reintroduced after a 1-week separation. Results also showed that E₂-treated OVX rats had profoundly decreased numbers of USV calls compared to vehicle-treated OVX rats. In a test of sociability, in which a female was allowed to choose between her cagemate or a same-treatment novel rat, we found few effects of E₂ compared to vehicle, although interestingly, rats chose the cagemate over an unfamiliar conspecific. Gene expression results revealed that the supraoptic nucleus had the greatest number of gene changes caused by E₂: Oxt, Oxtr and Avp were increased, and Drd2, Htr1a, Grin2b, and Gabbr1 were decreased, by E₂. No genes were affected in the prefrontal cortex, and 1-4 genes were changed in paraventricular nucleus (Pgr), bed nucleus of the stria terminalis (Oxtr, Esr2, Dnmt3a), and medial amygdala (Oxtr, Ar, Foxp1, Tac3). Thus, E₂ changes communicative interactions between adult female rats, together with selected expression of genes in the brain, especially in the supraoptic nucleus.

Testing the critical window of estradiol replacement on gene expression of vasopressin, oxytocin, and their receptors, in the hypothalamus of aging female rats

The current study tested the "critical window" hypothesis of menopause that postulates that the timing and duration of hormone treatment determine their potential outcomes. Our focus was genes in the rat hypothalamus involved in social and affiliative behaviors that change with aging and/or estradiol (E2): Avp, Avpr1a, Oxt, Oxtr, and Esr2 in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Rats were reproductively mature or aging adults, ovariectomized, given E2 or vehicle treatment of different durations, with or without a post-ovariectomy delay. Our hypothesis was that age-related changes in gene expression are mitigated by E2 treatments. Contrary to this, PVN Oxtr increased with E2, and Avpr1a increased with age. In the SON, Avpr1a increased with age, Oxtr with age and timing, and Avp was altered by duration. Thus, chronological age and E2 have independent actions on gene expression, with the "critical window" hypothesis supported by the observed timing and duration effects.

Androgen and estrogen receptor-beta distribution within spinal-projecting and neurosecretory neurons in the paraventricular nucleus of the male rat

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is initiated by neurosecretory neurons residing within the medial parvicellular part of the hypothalamic paraventricular nucleus (PVN). Despite the potency by which sex steroids operate on HPA and medial parvocellular responses to stress, previous topographic and phenotypic studies suggest that gonadal steroid hormone receptors are scarcely, if at all, expressed by PVN neurons controlling anterior pituitary corticotropes. Guided by the pattern of retrograde accumulation of fluorogold, we used a direct connectional approach to define the distribution of androgen receptors (AR) and estrogen-beta receptors (ER-beta) within populations of neurosecretory vs. nonneurosecretory neurons in the PVN. Juxtaposition of AR-immunoreactivity (ir) and ER-beta mRNA to the pattern of intravenous fluorogold labeling showed these steroid hormone receptors to be concentrated within portions of the PVN devoid of neurosecretory neurons. Superimposing receptor profiles onto the pattern of spinal retrograde labeling confirmed a selective distribution of AR-ir within autonomic-related cells of the medial parvocellular division, including its dorsal, lateral, and ventral medial components. ER-beta mRNA expression was likewise concentrated within regions accumulating spinal tracer, highest within the ventral aspect of the PVN. These results indicate a direct influence of gonadal hormones on preautonomic effector neurons and remain in keeping with an indirect influence of androgens on adrenocorticotropin-regulating neurons in the PVN.

Coexpression of ER beta with ER alpha and progestin receptor proteins in the female rat forebrain: effects of estradiol treatment

Estrogen and progestin receptors (ER, PgR) play a critical role in the regulation of neuroendocrine functions in females. The neuroanatomical distribution of the recently cloned, ER beta, overlaps with both ER alpha and PgR. To determine whether ER beta is found within ER alpha- or PgR-containing neurons in female rat, we used dual label immunocytochemistry. ER beta-immunoreactivity (ER beta-ir) was primarily detected in the nuclei of cells in the periventricular preoptic area (PvPO), the bed nucleus of the stria terminalis (BNSTpr), the paraventricular nucleus, the supraoptic nucleus, and the medial amygdala (MEApd). Coexpression of ER beta-ir with ER alpha-ir or PgR-ir was observed in the PvPO, BNSTpr, and MEApd in ovariectomized rats. E2 treatment decreased the number of ER beta-ir cells in the PvPO and BNSTpr and the number of ER alpha-ir cells in the MEApd and paraventricular nucleus, and therefore decreased the number of cells coexpressing ER beta-ir and ER alpha-ir in the PvPO, BNSTpr, and MEApd. E2 treatment increased the amount of PgR-ir in cells of the PvPO, BNSTpr, and MEApd, a portion of which also contained ER beta. These results demonstrate that ER beta is expressed in ER alpha- or PgR-containing cells, and they suggest that E can modulate the ratios of these steroid receptors in a brain region-specific manner.

Developmental switch in the expression of GABA(A) receptor subunits alpha(1) and alpha(2) in the hypothalamus and limbic system of the rat

The GABA(A) receptor is a pentameric ligand gated ion channel complex assembled from a family of at least 17 different subunits encoded by distinct genes. Two subunits, alpha(1) and alpha(2), exhibit age dependent expression throughout several areas of the brain. In general, the density of immunoreactive product for alpha(1) is greatest in the adult brain, while alpha(2) is highest in younger tissue. Since the developmental switch in alpha(1) and alpha(2) coincides with the end of the sensitive period for steroid-mediated sexual differentiation of the brain, we hypothesized that GABA(A) receptor subunit expression may be involved in this process. We have examined the age-dependent expression of alpha(1) and alpha(2) in discrete regions of the hypothalamus and limbic system of males and females. While we did not detect any dramatic sex differences in alpha(1) or alpha(2) immunoreactive density, each region exhibited a unique developmental profile. In the ventromedial nucleus of neonatal animals immunoreactivity is highest for alpha(1), while in the adult the signal for alpha(2) is greater; the opposite of that observed in the ventrolateral thalamus. There is no age dependent change for alpha(1) in the preoptic area, while alpha(2) shows a small, but significant increase. Immunoreactive densities for both subunits increase in the arcuate nucleus and the hippocampus, but decrease in the lateral amygdala. We conclude that these regional differences in subunit expression across development determine individual characteristics of brain areas and may play a role in establishing unique physiological responses to GABA.

Induction of Fos-like immunoreactivity in rat oxytocin neurons following insulin injections

Double immunostaining for oxytocin (OT) and Fos was used to study the oxytocinergic system of the rat hypothalamic paraventricular nucleus (PVN) following intraperitoneal insulin injections. The expression of c-fos in the PVN appeared about 3 h after insulin treatment and was very high after 5 h while no labelling was observed in isotonic saline-injected animals. Twelve to 18% of OT neurons expressed Fos-like immunoreactivity and these activated neurons were found in both the magno- and the parvocellular compartments of the PVN suggesting that the OT neuron responses to insulin induced disturbances are complex and involve hormonal as well as autonomic pathways.

Pituitary portal plasma levels of oxytocin during the estrous cycle, lactation, and hyperprolactinemia

The median eminence receives fibers from both parvocellular and magnocellular OT neurons in the hypothalamus. The OT neuronal terminal in the median eminence is secretory and is the major source of the neuropeptide in the blood of pituitary portal vessels. The OT secretion into pituitary portal plasma increases by ovarian steroids, PRL, and the suckling stimulus. The OT secretion into the blood of pituitary portal vessels changes in parallel with the altered secretion of PRL from the pituitary. Because of correlative association between pituitary portal plasma OT and systemic plasma PRL and much abundant evidence for a direct stimulatory action of OT on PRL release, we propose that the pituitary portal vascular system serves as the window for the central OT neurotransmission to the pituitary lactotropes.

Morphometric and neurosecretory changes in supraoptic neurons after D-amphetamine treatment

Several morphological and immunochemical characteristics of the neurosecretory neurons of the supraoptic nucleus (SON) have been studied of rats treated for 1 month with D-amphetamine sulfate (AMP) (8 mg/kg weight, daily). An increase of SON volume (11%) has been observed as a consequence of the growth of the dorsoventral axis. Neurosecretory neurons increased their nucleolar area (11.4%), their nuclear area (8.3%), and their cytoplasmatic area (18.3%). Vasopressin immunoreaction did not show any differences between treated and control animals, but oxytocin immunostaining displayed an important increase (23.7%) in the neuronal cytoplasm of the treated rats. The SON hypertrophy of the AMP-treated rats corresponded to the hypertrophy/hyperfunction of its oxytocinergic neurons, and could be considered as a new mechanism of the action of the AMP. The results are discussed in relation to the plastic features of the SON and its central (neuronal) and peripheral (hormonal) function.

Oxytocin--a neuropeptide for affiliation: evidence from behavioral, receptor autoradiographic, and comparative studies

Oxytocin (OT) is a nine amino acid peptide synthesized in hypothalamic cells which project either to the neurohypophysis or to sites within the central nervous system. Although neurohypophyseal OT release has long been associated with uterine contraction and milk ejection, the function of intracerebral OT remains unclear. On the basis of behavioral, cellular, and comparative studies, this review suggests that brain OT influences the formation of social bonds. The first part of this review examines evidence linking central OT to several forms of affiliation. Central administration of OT induces maternal and reproductive behaviors in rats primed with gonadal steroids. OT antagonists and hypothalamic lesions block the initiation of maternal and reproductive behaviors but have no effects on these behaviors once established. Our new studies in rat pups demonstrate that central OT selectively decreases the separation response, an effect which mimics social contact. These studies of parental, reproductive, and attachment behaviors suggest that exogenous OT has "prosocial" effects and that endogenous OT may be essential for initiating social interaction. In a second series of experiments, we investigated the cellular mechanisms for OT's effects on social behavior by means of autoradiographic receptor binding. In the rat forebrain, OT receptors are expressed in several limbic regions believed to be involved in the integration of sensory processing. The regulation of these receptors is surprisingly resistant to either ablation of OT cells or repeated central administration of OT. However, receptors in two regions, the bed nucleus of the stria terminalis (BNST) and the ventromedial nucleus of the hypothalamus (VMN), appear selectively induced by exogenous or endogenous increases in gonadal steroids. At parturition, binding to OT receptors increases 84% in the BNST, and at estrus, binding increases 35% in the VMN. These results demonstrate that physiologic changes in gonadal steroids can alter receptor expression in anatomically discrete target fields and thereby direct responsiveness to endogenous neuropeptide release. A model for OT's effects on social behavior is proposed, which relies on the heterologous regulation of the brain OT receptor. A third series of experiments tested the hypothesis that brain OT influences affiliation by comparing prairie and montane voles, two closely related species with dichotomous systems of social organization. Although no differences appear in the presynaptic expression of the neuropeptide, OT receptors are distributed in complementary patterns in the two species. In the highly affiliative prairie vole, receptors are most evident in the BNST and one of its primary afferents, the lateral amygdala, highlighting a circuit previously implicated in maternal behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Mating alters topography and content of oxytocin immunoreactivity in male mouse brain

Sexual stimulation of males has been reported to affect hypothalamic oxytocinergic systems. In the present study we used radioimmunoassays of microdissected forebrain regions and immunocytochemical analysis of Vibratome sections to study the oxytocin systems of naive males, males killed after one mating, and males mated daily with different receptive females for 3 weeks. In males that had mated once, less oxytocin-immunoreactive neurons were observed in the paraventricular (PVN), supraoptic (SON) and periventricular (NPE) nuclei than in naive males. However, after repeated matings, the number of immunoreactive neurons and their staining intensity was increased in these regions. Furthermore, additional oxytocinergic neurons could be found in the lateral subcommissural nucleus, the zona incerta and the ansa lenticularis of repeatedly mated males. Oxytocin-immunoreactive neurons were only occasionally seen in these areas in unmated males or in animals that had been killed after initial mating. Radioimmunoassays of microdissected PVN, SON, NPE and the lateral hypothalamus confirmed the reduction in oxytocin-immunoreactive levels after a first mating by a male and the increase after repeated matings. It is likely that oxytocin secretion into peripheral and portal circulation is stimulated by the endocrine conditions associated with initial mating. These immediate effects may be followed by the activation of synthesis in oxytocin neurons in several sites of the basal forebrain.

Estrogen influences on oxytocin mRNA expression in preoptic and anterior hypothalamic regions studied by in situ hybridization

Possible estrogen influences on oxytocin mRNA expression were studied in preoptic and anterior hypothalamic regions as might be important for behavioral as well as neuroendocrine controls. In situ hybridization for oxytocin mRNA determination was supported by immunocytochemical identification and was compared with vasopressin mRNA in situ hybridization. With these techniques, oxytocin-expressing neurons were identified in medial preoptic, anterior commissural, periventricular, paraventricular, supraoptic, and perifornical nuclei as well as the bed nucleus of the stria terminalis and intersupraopticoparaventricular (internuclear) islands. Distribution and number of oxytocin mRNA-containing neurons and oxytocin mRNA levels were compared between ovariectomized control rats given cholesterol implants and ovariectomized rats given short-term (2 days) or long-term (2 months) estradiol treatment (10% estradiol, subcutaneous silastic implants). Effectiveness of long-term estrogen treatment was confirmed behaviorally. While there was a trend in several cell groups for a larger number of oxytocin-mRNA-containing neurons to be observed following 2 days of estrogen treatment, this was not statistically significant. Moreover, additional oxytocin-mRNA containing cell groups were not seen after short or long estradiol treatment. With computer-aided analysis, mean pixels per oxytocin-mRNA expressing neuron (reflecting oxytocin mRNA content) were compared between groups: In the supraoptic nucleus and the anterior commissural nucleus, these were increased both by 2 days and 2 months of estradiol treatment. These differences may be important in modulating female reproductive behavior. Present findings also suggest that estradiol can affect the oxytocinergic system via an indirect route since the cell groups influenced here by estradiol do not contain estrogen receptors. Oxytocinergic neurons may serve as a good system to compare direct transcriptional with indirect effects of hormones.

Presence of estrogen receptor immunoreactivity in the oxytocin-containing magnocellular neurons projecting to the neurohypophysis in the guinea-pig

The immunoperoxidase technique was used on adjacent sections of guinea-pig brain to compare precisely the distribution of estrogen receptor-immunoreactive cells and progesterone receptor-immunoreactive cells in the supraoptic nucleus and the paraventricular nucleus. Only estrogen receptor-immunoreactive neurons were found in the supraoptic nucleus. A large number of estrogen receptor-positive cells were observed in the periventricular magnocellular groups throughout the rostrocaudal extent of the paraventricular nucleus, whereas only a few progesterone receptor-immunoreactive cells were scattered in the anterior portion of this region. We used a combination of axonal tracing with double immunocytochemical detection to determine whether estradiol acts directly on the oxytocin-immunoreactive neurons which project to the neurohypophysis. Oxytocin-immunoreactive cells were found in the supraoptic nucleus, ventrally to the optic pathways, in subchiasmatic and retrochiasmatic areas, and in the anterior hypothalamic area. These cells were also retrogradely labeled by Granular Blue when this tracer was injected intravenously. In the paraventricular nucleus, the Granular Blue/oxytocin-positive cells were observed in the periventricular magnocellular groups whereas Granular Blue labeled neurons were found in both parvocellular and magnocellular components. We found that almost all the oxytocin-immunoreactive cells revealed estrogen receptor immunoreactivity. In conclusion, the comparative study of distribution of estrogen receptors and progesterone receptors in the guinea-pig supraoptic and paraventricular nuclei indicates that, in the supraoptic nucleus, only estrogen receptors are present and that, in the paraventricular nucleus, they are far more numerous than progesterone receptors. The present findings demonstrate that the magnocellular cells which contain estrogen receptors are oxytocinergic. In addition, these cells are retrogradely labeled pointing to a neurohypophysial projection. It is likely that estradiol controls the hypothalamo-neurohypophysial oxytocin system by direct action on the magnocellular neurons.

Quantitative immunocytochemistry shows calcitonin gene-related peptide-like immunoreactivity in lung neuroendocrine cells is increased by chronic hypoxia in the rat

We have previously shown that the vasodilator calcitonin gene-related peptide (CGRP) is increased in pulmonary neuroendocrine cells in response to hypoxia. To quantify the change, we have now examined lung of adult male Wistar rats exposed to hypoxia (FIO2 = 0.1) for 1 wk and littermate controls. Sections of lung were immunostained simultaneously using rabbit antiserum to rat alpha-CGRP with the peroxidase antiperoxidase technique. The area and integrated optical density of each group of endocrine cells were measured using an image analyzer. For each animal, the summed integrated optical density of endocrine cells divided by the sum of their areas was used as a measure of CGRP-like immunoreactivity. The intensity of immunostaining of endocrine cells in the respiratory portion of the lung was 43% greater than that of endocrine cells along the conducting airways (P less than 0.001). The intensity of staining was increased by approximately 12% (P less than 0.04) after 7 d of hypoxia with no apparent difference in the response of central and peripheral endocrine cells. Measurements of staining intensity of CGRP-coupled agarose beads indicated that a 12% change in staining intensity corresponded to a 15 to 20% change in the concentration of CGRP or CGRP-like immunoreactive material. The supra-optimal dilution technique (measurement of the increase in the number of immunoreactive cells upon sequential immunostaining with a supra-optimal and then an optimal dilution of primary antiserum) detected the increase in CGRP-like immunoreactivity after 7 d of hypoxia with a high degree of statistical significance (P less than 0.005) using the same number of sections.

Oxytocin neurons in the rat hypothalamus exhibit c-fos immunoreactivity upon osmotic stress

In order to evaluate the responses to osmotic stress of oxytocinergic neurons in vivo, we have studied oxytocin (OXY) and c-fos protein expression in the brain by means of double-immunostaining. C-fos immunoreactivity was detected in a subset of OXY neurons, as well as in other neurons non-immunoreactive for OXY, as early as 90 min after intraperitoneal injection of a hypertonic saline solution. C-fos expression was found in approx. 70% of OXY-immunoreactive neurons in the supraoptic (SON), lateral subcommisural (LSN) and paraventricular (PVN) nuclei, and not in OXY neurons in other hypothalamic areas. The expression of c-fos may be used as a means to map the circuitry by which osmotic stimulation activates OXY-containing neurons, and thus provide further insights into the functions with which OXY may be associated.

Regulation of the rat oxytocin gene by estradiol

Abstract Oxytocin (OT) plays a role in reproduction at the level of the pituitary and mammary glands and uterus. This OT is synthesized in the hypothalamo-neurohypophyseal system (HNS). A number of observations have suggested that estrogens regulate the production of OT in the HNS. In this study the effect of 17beta-estradiol on the activity of the OT gene promoter was examined as well as the effect of 17beta-estradiol in vivo on OT messenger ribonucleic acid (mRNA) and peptide revels in the rat HNS. Vasopressin (VP) and its mRNA were also determined in the in vivo studies. The direct transcriptional stimulation of OT gene expression by 17beta-estradiol was studied in two different heterologous expression systems. When a plasmid having nucleotides -363 to +16 of the rat OT gene fused to the firefly luciferase reporter gene was co-transfected with an estrogen receptor expression vector in P19 embryonal carcinoma cells, luciferase activity was stimulated 80-fold by 17beta-estradiol. In estrogen receptor containing MCF-7 cells transfected with a plasmid having nucleotides -188 to +16 of the rat OT gene fused to the chloramphenicol acetyl transferase gene, 17beta-estradiol induced the expression of the chloramphenicol acetyl transferase gene through the cloned promoter element. After in vivo treatment of ovariectomized rats with 17beta-estradiol, levels of OT mRNA and VP mRNA were measured in microdissected supraoptic and paraventricular nuclei as well as VP and OT levels in these nuclei and the pituitary gland. As compared to non-treated ovariectomized rats there was no difference in contents of OT mRNA and VP mRNA in these hypothalamic nuclei and in levels of the peptides in paraventricular nuclei and the pituitary gland. A 30% reduction of the OT content of the supraoptic nuclei only was found, while the VP content did not change. To explain the results immunocytochemical analyses of the hypothalamus were performed, showing that the estrogen receptor was absent in the magnocellular neurons of the supraoptic and paraventricular nuclei. The results demonstrate that the 5'flanking region of the OT gene confers estrogen-sensitivity to transcription of the OT gene. This potential to respond to estrogens is not used in the OT-producing neurons of supraoptic and paraventricular nuclei probably due to the absence of the estrogen receptor.

Differential localization of estrogen receptors in various vasopressin synthesizing nuclei of the rat brain

Abstract Vasopressin (VP) cells in the bed nucleus of the stria terminalis, medial amygdaloid nucleus and supraoptic and paraventricular nuclei are influenced by gonadal steroids. The present paper examined whether VP cells in the bed nucleus of the stria terminalis, medial amygdaloid nucleus, and supraoptic and paraventricular nuclei contain estrogen receptors. Brains from adult short-term castrated, colchicine-treated male rats were fixed with 4% paraformaldehyde and 0.5% glutaraldehyde. In the immunocytochemical double-staining procedure Vibratome sections were first incubated with an estrogen receptor antibody (#H222) and stained with diaminobenzidine-Ni(+). Following methanol-hydrogen peroxide washes, sections were incubated with anti-neurophysin and stained with diaminobenzidine. Parvocellular cells in the bed nucleus of the stria terminalis and medial amygdaloid nucleus were double-stained with a blue-black nucleus (indicating the estrogen receptors) surrounded by brown cytoplasm (resulting from VP-neurophysin-immunoreactivity). Our results provide the first direct anatomical evidence supporting the hypothesis that gonadal steroids' influence of parvocellular VP cells in the bed nucleus of the stria terminalis and medial amygdaloid nucleus is mediated directly via estrogen receptors localized in nuclei of VP neurons. We were unable to co-localize any estrogen receptors in VP and oxytocin cells of magnocellular size in the supraoptic, paraventricular and anterior commissural nuclei, suggesting that estrogen indirectly affects these magnocellular hypothalamic cells.

Patterns of steroid hormone effects on electrical and molecular events in hypothalamic neurons

Hypothalamic neurons with nuclear receptors for steroid hormones provide opportunities to relate individual biosynthetic and electrical changes to hormone-driven behaviors. Successful work with female rodent reproductive behavior has proven that it is possible to define a neural circuit for a vertebrate behavior. In contrast to what might be expected from an invertebrate system, results from several approaches to neuronal gene expression show the complexity of hypothalamic control, even over this simple mammalian behavior. This is not a 1 hormone-1 gene-1 behavior system. Neither is there just one mode of hormonal induction. Certain steroid hormone effects can multiply each other, showing how a clear endocrine signal could be discerned among other variations in neural activity.

In situ hybridization analysis of osmotic stimulus-induced changes in ribosomal RNA in rat supraoptic nucleus

A quantitative in situ hybridization analysis was used to investigate changes in levels of ribosomal RNA (rRNA) in neurons of the supraoptic nucleus (SON) of rats stimulated osmotically by giving 2% NaCl as drinking solution for 0 (control rats), 1, 4, and 14 days. The quantitation was autoradiographically accomplished by in situ hybridization with a nick-translated tritiated ribosomal DNA probe and with the use of computer-based image analysis system. The mean number of grains per neuron in the ventral SON was significantly increased: 1.8-fold for 1 day, 2.9-fold for 4 days, and 1.7-fold for 14 days of salt loading, whereas the mean number of grains per neuron in the dorsal SON was increased 1.3-fold for 1 day, 2.5-fold for 4 days, and 1.7-fold for 14 days. Kolmogorov-Smirnov analysis of frequency histograms of grains per neuron indicated that the amount of rRNA in neurons in the ventral and dorsal SON was significantly increased by osmotic stimulation. These increases were accompanied by increases in cell size. The subcellular location of hybridizable rRNA in magnocellular neurons was altered by osmotic stimulation. Following 1-14 days of salt-drinking, rRNAs appeared to be more unevenly distributed throughout the cytoplasm. These findings are consistent with the notion that hyperosmotic stimulation has a substantial effect on the expression of rRNA genes in neurons of both the ventral and dorsal SON.

Estradiol influences oxytocin-immunoreactive brain systems

The rat brain was examined immunocytochemically for estrogen-dependent changes of oxytocin immunoreactivity at the light microscopical level. Ovariectomized rats were treated with subcutaneous silastic implants with estradiol, or empty implants as controls for 2 days (short term treatment). Another group of rats was injected weekly for 2 months with 1 mg estradiol (long term, high dose treatment). After perfusion fixation serial Vibratome sections were stained with antibodies to oxytocin. In control animals, oxytocin immunoreactive perikarya were found in the magnocellular hypothalamic nuclei. Accessory oxytocin neurons appeared in various hypothalamic sites: immunostained neuronal processes were visible in the preoptic region, the lateral septum, the ventromedial hypothalamus and the median eminence. In short term estradiol treated animals, additional immunoreactive perikarya could be observed in the septohypothalamic nucleus, the lateral subcommissural area, the medial preoptic area, the perifornical region, the zona incerta and the ansa lenticularis. An increased number of immunostained fibers was found in the lateral septum, the preoptic region, the striatum and the amygdala. Animals treated with high doses of estradiol for 2 months showed oxytocin immunostaining only in the paraventricular and supraoptic nuclei and in the median eminence. The distribution of oxytocin immunoreactive neurons in the magnocellular nuclei did not change with changing estradiol levels. Physiological amounts of estrogen given for 2 days increased the number of oxytocinergic neurons visible outside the classical magnocellular nuclei while prolonged, high dose estrogen treatment diminished immunostaining in these oxytocinergic systems.

Effect of salt loading and salt deprivation on the vasopressin and oxytocin content of the median eminence and the neural lobe in adrenalectomized rats

In adrenalectomized rats the influence of salt loading or salt deprivation on the vasopressin and oxytocin content of the median eminence (ME) and the neural lobe (NL) was studied by means of various methods: morphometric and microphotometric analysis of aldehyde fuchsin-stained sections of ME and NL; immunohistochemical demonstration of neurophysin, oxytocin, and vasopressin in the ME and in the NL; radioimmunological measurement of oxytocin and vasopressin in the ME and in the NL. Adrenalectomy in salt-substituted rats raised the vasopressin content of the outer layer of the ME (OLME) but had no influence on the amount of vasopressin in the inner layer of the ME and in the NL. Osmotic stimulation of adrenalectomized rats by hypertonic saline markedly diminished vasopressin and oxytocin in the inner layer of the ME and in the NL but did not, or only slightly reduced vasopressin in the OLME. Withdrawal of salt supplementation in adrenalectomized rats resulted in a decrease of plasma sodium and plasma volume. It did not change the vasopressin or oxytocin content of the inner layer of the ME and of the NL, but it was correlated with a decrease of vasopressin in the OLME. The present findings may suggest that vasopressin in the OLME is involved in salt and/or volume regulation by influencing the hypophysial-adrenal axis.

Variations in concentration of oxytocin and vasopressin in the paraventricular nucleus of the hypothalamus during the estrous cycle in rats

Oxytocin (OT) and arginine-8-vasopressin (AVP) were measured by radioimmunoassay in micropunched hypothalamic neurosecretory nuclei of estrous cycling female Sprague-Dawley rats. In the paraventricular nucleus (PVN): the concentration (pg/microgram protein) of OT was significantly higher in rats in diestrus than during proestrus, estrus, or metestrus, while the concentration during metestrus was significantly greater than in proestrus and estrus; the concentration of AVP was significantly lower in animals in estrus than during the other three stages; because the paraventricular OT levels dropped before proestrus, the AVP/OT ratio was significantly greater in animals in proestrus than in diestrus, metestrus, and estrus. In the supraoptic nucleus (SON) a similar trend was noted: the concentration of OT was highest during diestrus, and AVP was lowest during estrus, though neither was significantly different from other stages. Because the OT and AVP cycles in the SON were asynchronous, the ratio of AVP to OT was significantly higher in proestrus than in metestrus or diestrus and significantly greater in estrus than during diestrus. In contrast to these two areas, peptide concentrations did not vary significantly across the estrous cycle in other sites of nonapeptide synthesis, i.e. the anterior commissural nucleus (ACN) and the suprachiasmatic nuclei (SCN).

The coexistence of oxytocin and corticotropin-releasing factor in the hypothalamus: an immunocytochemical study in the rat, sheep and hedgehog

The unlabeled antibody enzyme method has been applied on adjacent sections in order to investigate coexistence of oxytocin (OXY) and corticotropin-releasing factor (CRF) within individual neurons of the hypothalamic paraventricular nucleus of the colchicine-treated rat, sheep and hedgehog. Our results show that, although OXY and CRF immunoreactivities are both expressed by a number of cells in the rat and the sheep paraventricular nucleus, this is not the case for the hedgehog.

Lesions of the tissue surrounding the preoptic recess (AV3V region) affect neurosecretory cells in the paraventricular nuclei in the rat

Lesions of the tissue surrounding the preoptic recess (AV3V region) have severe effects on body fluid homeostasis; these include acute adipsia and failure of the antidiuretic response. Because neurosecretory cells in supraoptic nuclei comprise the major source of antidiuretic hormone (ADH) in this species, we have previously observed the fine structure of supraoptic nuclei in rats with AV3V lesions. Paraventricular nuclei are the other major source of ADH in rats. Therefore, in this investigation we compared the fine structure of paraventricular nuclei in rats which had received AV3V lesions 3 days earlier with that of control rats which had received sham lesions and either had drinking water available or had water withheld for 3 days. Degenerating axons and axon terminals were present in paraventricular nuclei of lesioned rats. The degenerating terminals were in axodendritic and less often in axosomatic synapses. Morphometric evaluation revealed that neurosecretory cells did respond to the dehydrated state of the adipsic-lesioned animals, but the response was significantly attenuated compared to that which occurred in sham-lesioned rats deprived of water for 3 days. It appears that AV3V lesions damage afferent connections and impair the response of neurosecretory cells to dehydration in paraventricular as well as supraoptic nuclei. However, in paraventricular nuclei the response is not completely prevented by AV3V lesions during the adipsic period as was observed in supraoptic nuclei. The presence of a response in paraventricular nuclei may be at least partially stimulated by reduced body fluid volume. Information from volume receptors would be carried from the medulla to paraventricular nuclei by ascending pathways which are not affected by AV3V lesions.