Activation by serotonin and noradrenaline of vasopressin and oxytocin expression in the mouse paraventricular and supraoptic nuclei

Maternal care effects on the development of a sexually dimorphic motor system: the role of spinal oxytocin

Maternal licking in rats affects the development of the spinal nucleus of the bulbocavernosus (SNB), a sexually dimorphic motor nucleus that controls penile reflexes involved with copulation. Reduced maternal licking results in decreased motoneuron number, size, and dendritic length in the adult SNB, as well as deficits in adult male copulatory behavior. Our previous findings that licking-like tactile stimulation influences SNB dendritic development and upregulates Fos expression in the lumbosacral spinal cord suggest that afferent signaling is changed by differences in maternal stimulation. Oxytocin afferents from the hypothalamus are a possible candidate, given previous research that has shown oxytocin is released following sensory stimulation, oxytocin modulates excitability in the spinal cord, and is a pro-erectile modulator of male sex behavior. In this experiment, we used immunofluorescence and immediate early gene analysis to assess whether licking-like tactile stimulation of the perineum activated parvocellular oxytocinergic neurons in the hypothalamus in neonates. We also used enzyme immunoassay to determine whether this same stroking stimulation produced an increase in spinal oxytocin levels. We found that stroking increased Fos immunolabeling in small oxytocin-positive cells in the paraventricular nucleus of the hypothalamus, in comparison to unstroked or handled control pups. In addition, 60s of licking-like perineal stimulation produced a transient 89% increase in oxytocin levels in the lumbosacral spinal cord. Together, these results suggest that oxytocin afferent activity may contribute to the effects of early maternal care on the masculinization of the SNB and resultant male copulatory behavior.

Juvenile social experience regulates central neuropeptides relevant to emotional and social behaviors

Stressful social experiences during early-life can increase the risk of developing neuropsychiatric disorders associated with anxiety, mood, and personality. Early neglect also alters peripheral arginine vasopression (AVP) and oxytocin (OXT). We hypothesized that a lack of social stimuli should adversely affect developmental AVP and OXT systems. To test this idea, we examined changes of central AVP- and OXT-immunoreactive (ir) cell number as well as its related behaviors in socially isolated rats. Animals were weaned at 23 days of age, divided into group- or isolation-reared conditions, and maintained for at least 2 weeks. At 38-48 days of age, animals were sacrificed for immunohistochemistry, or used for two behavioral tests: elevated plus-maze test and social recognition test. The results from immunohistochemistry showed that isolation-reared males have decreased AVP-ir cells in the paraventricular nucleus hypothalamus (PVH), medial parvicellular part, ventral zone, and that isolation-reared females have decreased OXT-ir cells in the PVH, medial parvicellular part, dorsal zone, when compared with group-reared counterparts. The results from behavioral assessment showed that isolation-reared animals have difficulty with social recognition, and that isolation-reared males, but not females, have anxiogenic profile. The present study demonstrates that post-weaning social isolation results in decrease of male AVP-ir cells and female OXT-ir cells in the PVH parvocellular divisions, and supports the idea that juvenile social environment may play a critical role in neuronal and behavioral development.

Galanin and the neuroendocrine axes

Galanin has diverse physiological functions, including nociception, arousal/sleep regulation, cognition, and many aspects of neuroendocrine activities that are associated with feeding, energy metabolism, thermoregulation, osmotic and water balance, and reproduction. This review will provide a brief overview of galanin action in some major neuroendocrine processes. Most of the recent data are about the role of galanin in the central regulation of food intake and energy metabolism, and to some extent, in the regulation of reproduction. It seems that galanin plays a modulatory role rather than a regulatory one in the central and peripheral branches of the neuroendocrine systems. In the hypothalamus, it functions as a neurotransmitter/ neuromodulator. In the pituitary and the peripheral endocrine glands, it acts via its receptors in a paracrine/autocrine fashion. The development of new, selective, and potent antagonists of GALRs should keep advancing our knowledge not only in the physiology of galanin but also in its pathophysiology.

Exercise-induced neuronal plasticity in central autonomic networks: role in cardiovascular control

It is now well established that brain plasticity is an inherent property not only of the developing but also of the adult brain. Numerous beneficial effects of exercise, including improved memory, cognitive function and neuroprotection, have been shown to involve an important neuroplastic component. However, whether major adaptive cardiovascular adjustments during exercise, needed to ensure proper blood perfusion of peripheral tissues, also require brain neuroplasticity, is presently unknown. This review will critically evaluate current knowledge on proposed mechanisms that are likely to underlie the continuous resetting of baroreflex control of heart rate during/after exercise and following exercise training. Accumulating evidence indicates that not only somatosensory afferents (conveyed by skeletal muscle receptors, baroreceptors and/or cardiopulmonary receptors) but also projections arising from central command neurons (in particular, peptidergic hypothalamic pre-autonomic neurons) converge into the nucleus tractus solitarii (NTS) in the dorsal brainstem, to co-ordinate complex cardiovascular adaptations during dynamic exercise. This review focuses in particular on a reciprocally interconnected network between the NTS and the hypothalamic paraventricular nucleus (PVN), which is proposed to act as a pivotal anatomical and functional substrate underlying integrative feedforward and feedback cardiovascular adjustments during exercise. Recent findings supporting neuroplastic adaptive changes within the NTS-PVN reciprocal network (e.g. remodelling of afferent inputs, structural and functional neuronal plasticity and changes in neurotransmitter content) will be discussed within the context of their role as important underlying cellular mechanisms supporting the tonic activation and improved efficacy of these central pathways in response to circulatory demand at rest and during exercise, both in sedentary and in trained individuals. We hope this review will stimulate more comprehensive studies aimed at understanding cellular and molecular mechanisms within CNS neuronal networks that contribute to exercise-induced neuroplasticity and cardiovascular adjustments.

[André Calas, the original path of a neuroendocrinologist]

This talk, given as an introduction to a symposium organised to honor André Calas, calls forth his personality, recalls the major events in his career and summarizes the evolution of his research.

Leptin but not ciliary neurotrophic factor (CNTF) induces phosphotyrosine phosphatase-1B expression in human neuronal cells (SH-SY5Y): putative explanation of CNTF efficacy in leptin-resistant state

Growing evidences suggest that obesity is associated with hypothalamic leptin resistance, leading to the alteration of food intake control. Alternative treatment using ciliary neurotrophic factor (CNTF) has been suggested because CNTF exerts a leptin-like effect, even in leptin-resistant states, but the mechanisms by which CNTF maintains this effect are not yet understood. Both leptin and CNTF act in the hypothalamus through similar signaling pathways including janus kinase-2/signal transducer and activator of transcription (STAT)-3 pathway. To explore the differences and interactions between leptin and CNTF signaling pathways, differentiated human neuroblastoma cells (SH-SY5Y) were exposed to either leptin or CNTF and then challenged for each cytokine. Leptin pretreatment completely abolished leptin-dependent STAT-3 and ERK 1/2 phosphorylations without affecting CNTF action. The lack of cross-desensitization between leptin and CNTF signaling pathways occurred despite the induction of suppressor of cytokine signaling-3 in response to both cytokines. Interestingly, leptin as well as insulin induced the expression of phosphotyrosine phosphatase (PTP)-1B, whereas CNTF treatment did not affect its expression. In addition, acute leptin treatment but not CNTF induced PTP-1B expression in mouse hypothalamic arcuate nucleus. Furthermore, the overexpression of human PTP-1B in SH-SY5Y cells completely abolished leptin- and insulin-dependent janus kinase-2, STAT-3, and ERK 1/2 phosphorylations, but CNTF action was not altered. Collectively, our results suggest that PTP-1B constitutes a key divergent element between leptin/insulin and CNTF signaling pathways at the neuronal level, which may constitute a possible mechanism that explains the efficacy of CNTF in leptin-resistant states.

Long-term effects on hypothalamic neuropeptides after developmental exposure to chlorpyrifos in mice

BACKGROUND

Increasing evidence from animal and human studies indicates that chlorpyrifos (CPF), similar to other organophosphorus insecticides still widely used, is a developmental neurotoxicant. Developmental exposure to CPF in rodents induces sex-dimorphic behavioral changes at adulthood, including social and agonistic responses, which suggests that CPF may interfere with maturation of neuroendocrine mechanisms.

OBJECTIVES

We assessed the hypothesis that CPF affects the levels of neurohypophyseal hormones acting as modulators of social behavior in mammals, such as oxytocin (OT), arginine vasopressin (AVP), and prolactin (PRL).

METHODS

Pregnant female mice were orally administered with either vehicle (peanut oil) or 3 or 6 mg/kg CPF on gestational day (GD) 15 to GD18, and offspring were treated subcutaneously with either vehicle or 1 or 3 mg/kg CPF on postnatal days (PNDs) 11 to PND14. Dose levels were chosen to avoid systemic toxicity and inhibition of brain acetylcholinesterase. Offspring were sacrificed at 5 months of age, and expression of OT, AVP, and PRL was analyzed in the hypothalamus by Western blot or enzyme-linked immunosorbent assay (ELISA) analysis.

RESULTS

Both male and female mice showed dose-related enhancement of OT expression, with males presenting the more intense effect. AVP expression was significantly reduced in male mice at the higher prenatal and postnatal dose. We observed no significant effect on PRL expression in either sex. Overall, outcomes were mainly attributable to fetal exposure, whereas postnatal doses appeared to potentiate the prenatal effects.

CONCLUSIONS

Our data indicate that developmental exposure to CPF may permanently interfere with specific key signaling proteins of the hypothalamic peptidergic system, with time-, dose-, and sex-related effects still evident at adulthood.

A putative physiological role of hypothalamic CNTF in the control of energy homeostasis

Administration of CNTF durably reduces food intake and body weight in obese humans and rodent models. However, the involvement of endogenous CNTF in the central regulation of energy homeostasis needs to be elucidated. Here, we demonstrate that CNTF and its receptor are expressed in the arcuate nucleus, a key hypothalamic region controlling food intake, and that CNTF levels are inversely correlated to body weight in rats fed a high-sucrose diet. Thus endogenous CNTF may act, in some individuals, as a protective factor against weight gain during hypercaloric diet and could account for individual differences in the susceptibility to obesity.

Impact of gestational cocaine treatment or prenatal cocaine exposure on early postpartum oxytocin mRNA levels and receptor binding in the rat

Prior research reported decreased oxytocin levels in specific brain regions correlated with disruptions in maternal care following gestational cocaine treatment in rats. Similarly, prenatal exposure to cocaine impaired subsequent maternal behavior in adulthood, but behavioral alterations were not associated with decreases in oxytocin levels in the same brain regions as were found in their cocaine-treated rat dams. To determine if other aspects of the oxytocin system are disrupted by cocaine treatment or prenatal exposure to cocaine during critical time points associated with maternal care, oxytocin mRNA transcription and receptor binding were examined on postpartum day two in relevant brain regions following gestational treatment with, or prenatal exposure to, either cocaine or saline. We hypothesized that oxytocin mRNA levels and receptor binding would be differentially affected by cocaine in the early postpartum period of dams and their offspring. Our findings indicate that gestational cocaine treatment resulted in significant increases in oxytocin mRNA levels in only the paraventricular nucleus of cocaine-treated dams, with almost significant increases in both generations in the supraoptic nucleus, but no significant effects of cocaine on receptor binding in either generation of dams. These findings indicate that in addition to oxytocin levels, cocaine treatment or prenatal exposure primarily affects oxytocin mRNA synthesis, with little effect on receptor binding in specific brain regions associated with maternal behavior in the early postpartum period of the rat.

Vasopressinergic neurons in rats in ontogenesis: responses to salt loading and their modulation by noradrenergic afferents

Salt loading in adult mammals leads to increased vasopressin secretion by vasopressinergic neurons in the supraoptic nucleus, which is mediated by the actions of a number of hormones and neurotransmitters, including noradrenaline. The present study addressed identification of the stage of ontogenesis at which vasopressinergic neurons start to respond to salt loading and when the noradrenalinergic regulation of this process begins. Studies were performed on rats at embryonic day 21 (E21), postnatal day 3 (P3), and postnatal day 13 (P13) using immunocytochemical and in situ hybridization. Animals were subjected to salt loading, in some cases on the background of the alpha1-adrenoceptor inhibitor prazosin. Salt loading in rats of all age groups induced increases in the synthesis of vasopressin mRNA, probably accompanied by increased synthesis of vasopressin peptide. At E21 and P3, intraneuronal vasopressin levels were increased; there was no change at P13. In salt loading on the background of prazosin administration, vasopressin mRNA and vasopressin contents at E21 showed no change, while at P3 they were increased, which is evidence of the inhibitory effect of noradrenaline on vasopressin expression in the early postnatal period. Thus, vasopressinergic neurons start to respond to salt loading at the end of the prenatal period with increases in vasopressin expression; noradrenergic afferents have inhibitory influences on vasopressin expression in the early postnatal period.

Matrix metalloproteinases MMP2 and MMP9 are upregulated by noradrenaline in the mouse neuroendocrine hypothalamus

Magnocellular neurons of the hypothalamic supraoptic nuclei (SON) are involved in the synthesis and release of two major neuropeptides: oxytocin (OT) and arginine-vassopressin (AVP). Neurochemical plasticity in this system is induced by physiological conditions such as lactation, parturition and dehydration, and may be accompanied by reversible structural plasticity affecting neurons, astrocytes and the extracellular matrix (ECM). The noradrenergic system plays a critical role in triggering this chemical plasticity associated with structural plasticity. Matrix metalloproteinases (MMPs) are good candidates for involvement in the ECM remodelling observed in structural plasticity. We investigated the possible regulation of the two gelatinases, MMP2 and MMP9, by noradrenaline (NA) in the mouse neuroendocrine hypothalamus. We looked for the presence, location and activity of MMP2 and MMP9 in the SON, using an ex vivo experimental model of mouse hypothalamic slices incubated for 4 h with 10(-4) m NA. We showed that: (i) immunoreactivity for MMP2 and MMP9 was detected not only in AVP-positive and OT-positive magnocellular neurons, but also in astrocyte processes in control and NA-treated slices; (ii) the number of MMP2- and MMP9-positive cells increased after incubation with NA; (iii) MMP2 and MMP9 displayed markedly higher levels of gelatinolytic activity after NA treatment. These results suggest that both MMP2 and MMP9 are regulated by NA, and could therefore also be involved in structural plasticity within the SON.

Serotonin increases the excitability of the hypothalamic paraventricular nucleus magnocellular neurons

Recent evidence that 5-hydroxytryptamine (5-HT or serotonin) enhances the release and the gene expression of vasopressin and oxytocin in the hypothalamic paraventricular nucleus (PVN) suggests that 5-HT can excite the PVN magnocellular neurons. The objective of this study was to examine the underlying mechanisms for such excitatory action in the electrophysiologically identified hypothalamic PVN magnocellular neurons in rats using whole-cell patch-clamp. We found that 5-HT weakly depolarizes 33.3% of PVN magnocellular neurons in the presence of tetrodotoxin. A minuscule inward current was produced by 5-HT in 48% of the cells, which was attenuated when the 5-HT(4) antagonist GR113808 or the 5-HT(7) antagonist SB269970 was added. In addition, 5-HT reduced the frequency of miniature inhibitory postsynaptic currents in a dose-dependent manner. This inhibition was mimicked by the 5-HT(1B) agonist CP93129, and reversed in the presence of 5-HT(1B) antagonists cyanopindolol and SB224289. Besides, 5-HT induced a biphasic effect on the frequency of miniature excitatory postsynaptic currents, comprising a transient inhibition and a delayed concentration-dependent excitation (onset latency approximately 5 min). The facilitation was mimicked by the 5-HT(2A/2C) agonist DOI and abolished in the presence of the 5-HT(2C) antagonist RS102221. Our findings reveal that 5-HT directly increases the excitability of the PVN magnocellular neurons via multiple receptor subtypes and mechanisms. This may help understanding the regulation of 5-HT-induced hormone release and feeding behavior in the PVN.

Citalopram-induced SIADH in a hypertensive patient on salt restricted diet

Hyponatraemia is a very rare but potentially fatal complication of SSRIs and citalopram therapy, especially during the first weeks of treatment and for those who concomitantly use medications known to cause hyponatraemia. We present a 54-year-old hypertensive female patient who was admitted to the hospital with drowsiness, paresthesia, fatigue, nausea, vomiting and visual hallucinations and who was diagnosed to have syndrome of inappropriate secretion of antidiuretic hormone (SIADH) due to citalopram. All her presenting symptoms disappeared after discontinuation of citalopram therapy, fluid restriction and a careful hypertonic saline infusion. This case suggests that SIADH may develop among hypertensive patients, especially when they use diuretics or follow a salt restricted diet.

[A 67-year-old patient with somnolence and severe hyponatraemia]

A 67-year-old female patient with known depression was admitted to the intensive care unit with severe hyponatraemia (105 mmol/l) and somnolence caused by inadequate antidiuretic hormone secretion (SIADH) syndrome after starting therapy with the selective serotonin reuptake inhibitor (SSRI) Citalopram. This medication was stopped, and the hyponatraemia was carefully treated with fluid restriction and diuretics. Seven days later, the patient was discharged to a psychiatric ward with normal sodium levels and markedly improved vigilance. Given the increased use of SSRI for medical treatment of depression, the risk factors of this rare but potentially life-threatening complication and the diagnostic and therapeutic options are discussed.

The interface of oxytocin-labeled cells and serotonin transporter-containing fibers in the primate hypothalamus: a substrate for SSRIs therapeutic effects?

Oxytocin (OT) is a neuropeptide synthesized in the paraventricular (PVN) and supraoptic nuclei (SON) in the hypothalamus. Although OT is more commonly known for its role in the milk-ejection reflex, in recent years research has indicated that OT participates in the expression of social behavior, memory processing, modulation of fear, and stress responses. The demonstration that OT influences affiliative behaviors, such as parental care and reproduction, and decreases anxiety has lead to speculations that it may have a role in mood disorders. Evidence from pharmacologic studies, pointing out the modulation of the OT system by serotonin, has argued in favor of OT as a mediator of serotonin reuptake inhibitors (SSRIs) antidepressant properties. In the present study, we investigated the distribution and overlap of OT-labeled cells and serotonin transporter (5-HTT) immunoreactive (IR) fibers in the Macaque hypothalamus, utilizing immunocytochemical and double-immunofluorescent techniques. Consistent with previous reports, the distribution of OT-labeled cells in the hypothalamus is confined to the PVN and SON. In these nuclei, we demonstrate that the distribution of 5-HTT-labeled fibers follows the distribution of OT-labeled cells. Overlap of OT-labeled neurons and 5-HTT-IR fibers occurs in the parvicellular, magnocellular, dorsal, and posterior subdivisions of the PVN. In the SON, 5-HTT-labeled fibers and OT-labeled cells overlap in the ventromedial subdivision and in the 'capsular' part of the dorsolateral SON. These findings provide neuroanatomic support for the idea that SSRIs' therapeutic effects on social affiliation and anxiety may be mediated in part through components of the OT system.

Exercise training-induced remodeling of paraventricular nucleus (nor)adrenergic innervation in normotensive and hypertensive rats

Activation of oxytocin (OT)ergic projections from the hypothalamic paraventricular nucleus (PVN) to the nucleus tractus solitarii contributes to cardiovascular adjustments during exercise training (EXT). Moreover, a deficit in this central OTergic pathway is associated with altered cardiovascular function in hypertension. Since PVN catecholaminergic inputs, known to be activated during EXT, modulate PVN cardiovascular-related functions, we aimed here to determine whether remodeling of PVN (nor)adrenergic innervation occurs during EXT and whether this phenomenon is affected by hypertension. Confocal immunofluorescence microscopy and tract tracing were used to quantify changes in (nor)adrenergic innervation density in PVN subnuclei and in identified dorsal vagal complex (DVC) projecting neurons (PVN-DVC) in EXT normotensive [Wistar-Kyoto rat (WKY)] and hypertensive [spontaneously hypertensive rat (SHR)] rats. In WKY, EXT increased the density of PVN dopamine β-hydroxylase immunoreactivity (DBHir) (160%). Furthermore, the number and density of DBHir boutons overlapping PVN-DVC OTergic neurons were also increased during EXT (130%), effects that were blunted in SHR. Conversely, while DBHir in the medial parvocellular subnucleus (an area enriched in corticotropin-releasing hormone neurons) was not changed by EXT in WKY, a diminished DBHir was observed in trained SHR. Overall, these data support the concept that the PVN (nor)adrenergic innervation undergoes plastic remodeling during EXT, an effect that is differentially affected during hypertension. The functional implications of PVN (nor)adrenergic remodeling in relation to the central peptidergic control of cardiovascular function during EXT are discussed.

Neural nitric oxide gene inactivation affects the release profile of oxytocin into the blood in response to forced swimming

This study was undertaken to examine the importance of nitric oxide (NO) generated by the neural isoform of the nitric oxide synthase (nNOS) on the activity of the hypothalamic neurohypophyseal system in neural nitric oxide synthase knock-out (KO) and wild-type (WT) mice under basal conditions and in response to forced swimming. The intensity of the hybridisation signal for vasopressin (AVP) in the hypothalamic supraoptic nucleus (SON) was significantly higher in KO mice when compared with WT, whereas oxytocin (OXT) basal mRNA levels were similar in both groups. Although the basal peripheral release of AVP and OXT was equivalent in both genotypes, we observed in KO mice a significant drop of AVP and OXT plasma values 15 min after stressor onset and a robust increase in the OXT plasma concentration at 60 min. These findings suggest that in the male mouse, NO inhibits AVP gene transcription in magnocellular neurones of the SON and collaborates in maintaining constant AVP and OXT plasma levels following acute stressor exposure, exerting a bimodal regulatory action on OXT secretion. We conclude that NO is involved in the regulation of magnocellular neurones of the SON, and it is preferentially implicated in the attenuation of the peripheral release of OXT induced by acute stressor exposure.

Noradrenergic regulation in mouse supraoptic nucleus involves a nitric oxide pathway only to regulate arginine-vasopressin expression and not oxytocin expression

Noradrenalin (NA) regulates the expression of arginine-vasopressin (AVP) and oxytocin (OT) by magnocellular neurons in the supraoptic nucleus (SON) of the hypothamalus. Nitric oxide (NO) may be one of the factors involved in the NA signaling pathway regulating AVP and OT expression. To test this possibility, we used an ex vivo experimental model of mouse hypothalamus slices. Increases in AVP and OT levels in the SON were detected by immunohistochemistry and immunoenzyme assays after 1 hr and 4 hr incubations with NA (10(-4) M). There was also an increase in the expression and activity of neuronal NOS and inducible NOS in the SON as assessed by immunohistochemical and histoenzymological analysis of NADPH-diaphorase, whereas endothelial NOS was undetectable. To specify the role of NO, the slices were treated with NA and L-arginine methyl ester (L-NAME, an NOS inhibitor; 3 microM). This treatment for 1 hr abolished the NA-induced increase in AVP. Treatment with sodium nitroprusside (SNP, an NO donor; 0.1 mM) increased AVP levels, confirming that NO regulates AVP expression. Addition of 1 mM EGTA during the incubation with NA reduced the AVP increase by half, indicating that both nNOS and iNOS activities are involved in the regulation. A 1-hr treatment with L-NAME did not prevent the increase in OT induced by NA; similarly, treatment with SNP had no effect. These findings show that NO is involved in the regulation of AVP expression by NA and that NA control of OT expression is independent of NO.

Recurrent hyponatremia associated with citalopram and mirtazapine

Depression is a common problem in elderly patients and frequently is treated with antidepressants. We present the case of a 67-year-old depressed woman who began treatment with citalopram. Two months later, hyponatremia was diagnosed, most likely syndrome of inappropriate antidiuretic hormone secretion. After discontinuation of citalopram therapy, serum sodium concentrations normalized. Later, she began treatment with mirtazapine. Five months after initiating mirtazapine therapy, she developed symptomatic hyponatremia. After mirtazapine therapy was discontinued, serum sodium concentrations normalized. In this case, unlike those previously reported, hyponatremia recurred 5 months after switching from citalopram to mirtazapine, which is believed to be a safe antidepressant. In conclusion, patients older than 60 years should have baseline electrolyte measurements before starting therapy with an antidepressant, and these should be monitored not only in the first weeks of treatment, but throughout the full course.

Noradrenergic regulation of galanin expression in the supraoptic nucleus in the rat hypothalamus. An ex vivo study

Galanin is coexpressed with vasopressin and oxytocin in magnocellular neurons of the rat neuroendocrine hypothalamus. Various physiological stimuli, such as osmotic stimulation or lactation, that affect vasopressin and oxytocin expression and release also modulate galanin expression. Magnocellular neurons are highly innervated by noradrenergic inputs from the brainstem. The noradrenergic system plays a critical excitatory role in the activation of vasopressin-expressing and oxytocin-expressing neurons. Here, we have evaluated the possible regulation of Gal expression by noradrenaline in the magnocellular neurons of supraoptic nucleus in an ex vivo acute model of rat hypothalamic slices. The slices containing the supraoptic nucleus were incubated with 10(-4) M noradrenaline for 1 or 4 hr. The levels of galanin and galanin mRNA were estimated by semiquantitative immunohistochemistry and in situ hybridization, respectively. Our results show that the amount of galanin-immunopositive material in the cell bodies of the magnocellular neurons increased significantly after incubation with noradrenaline compared with control slices at the same time point and that this effect was more pronounced after 4 hr than after 1 hr. In situ hybridization showed that radiolabeling of the supraoptic nucleus with a radioactive galanin probe increased slightly after 1 hr of incubation and increased considerably after 4 hr of incubation with noradrenaline. Our study shows that galanin may be a target in the regulation of the hypothalamic magnocellular-neurohypophysial system by noradrenaline.

Hyperdopaminergia and altered locomotor activity in GABAB1-deficient mice

GABAB1-/- mice, which are devoid of functional GABAB receptors, consistently exhibit marked hyperlocomotion when exposed to a novel environment. Telemetry recordings now revealed that, in a familiar environment, GABAB1-/- mice display an altered pattern of circadian activity but no hyperlocomotion. This indicates that hyperlocomotion is only triggered when GABAB1-/- mice are aroused by novelty. In microdialysis experiments, GABAB1-/- mice exhibited a 2-fold increased extracellular level of dopamine in the striatum. Following D-amphetamine administration, GABAB1-/- mice released less dopamine than wild-type mice, indicative of a reduced cytoplasmic dopamine pool. The hyperdopaminergic state of GABAB1-/- mice is accompanied by molecular changes, including reduced levels of tyrosine hydroxylase mRNA, D1 receptor binding-sites and Ser40 phosphorylation of tyrosine hydroxylase. Tyrosine hydroxylase activity, tissue dopamine content and dopamine metabolism do not appear to be measurably altered. Pharmacological and electrophysiological experiments support that the hyperdopaminergic state of GABAB1-/- mice is not severe enough to inactivate dopamine D2 receptors and to disrupt D2-mediated feedback inhibition of tyrosine hydroxylase activity. The data support that loss of GABAB activity results in a sustained moderate hyperdopaminergic state, which is phenotypically revealed by contextual hyperlocomotor activity. Importantly, the presence of an inhibitory GABA tone on the dopaminergic system mediated by GABAB receptors provides an opportunity for therapeutic intervention.

Search for autism loci by combined analysis of Autism Genetic Resource Exchange and Finnish families

OBJECTIVE

Several genome-wide screens have been performed in autism spectrum disorders resulting in the identification of numerous putative susceptibility loci. Analyses of pooled primary data should result in an increased sample size and the different study samples have a potential to strengthen the evidence for some earlier identified loci, reveal novel loci, and even to provide information of the general significance of the locus. The objective of this study was to search for potential susceptibility loci for autism, which are supported by two independent samples.

METHODS

We performed a combined analysis of the primary genome scan data of the Autism Genetic Resource Exchange (AGRE) and Finnish autism samples to reveal susceptibility loci potentially shared by these study samples.

RESULTS

In the initial combined data analysis, the best loci (p < 0.05) were observed at 1p12-q25, 3p24-26, 4q21-31, 5p15-q12, 6q14-21, 7q33-36, 8q22-24, 17p12-q21, and 19p13-q13. The combined analysis of Finnish and AGRE families showed the most promising shared locus on 3p24-26 with nonparametric logarithm of odds (NPL) score of 2.20 (p = 0.011). The combined data analysis did not provide increased linkage evidence for the earlier identified loci on 3q25-27 or 17p12-q21. However, the 17p12-q21 locus remained promising also in the combined sample (NPL(all) =2.38, p = 0.0076).

INTERPRETATION

Our study of 314 autism families highlights the importance of further analyses on 3p24-26 locus involving comprehensive molecular genetic analyses of oxytocin receptor gene (OXTR), a positional and functional candidate gene for autism.

Thyrotrophin-releasing hormone receptor 1 and prothyrotrophin-releasing hormone mRNA expression in the central nervous system are regulated by suckling in lactating rats

BACKGROUND

The accepted function of the hypothalamic peptide, thyrotrophin-releasing hormone (TRH), is to initiate release of thyrotrophin (TSH) from the pituitary. A physiological role for TRH in lactating rats has not yet been established.

METHODS

Tissues were prepared from random-cycling and lactating rats and analysed using Northern blot, real time RT-PCR and quantitative in situ hybridisation.

RESULTS

This study demonstrates that TRH receptor 1 (TRHR1) mRNA expression is up-regulated in the pituitary and in discrete nuclei of the hypothalamus in lactating rats, while proTRH mRNA expression levels are increased only in the hypothalamus. The results were corroborated by quantitative in situ analysis of proTRH and TRHR1. Bromocriptine, which reduced prolactin (PRL) concentrations in plasma of lactating and nursing rats, also counteracted the suckling-induced increase in TRHR1 mRNA expression in the hypothalamus, but had an opposite effect in the pituitary. These changes were confined to the hypothalamus and the amygdala in the brain.

CONCLUSIONS

The present study shows that the mechanisms of suckling-induced lactation involve region-specific regulation of TRHR1 and proTRH mRNAs in the central nervous system notably at the hypothalamic level. The results demonstrate that continued suckling is critical to maintain plasma prolactin (PRL) levels as well as proTRH and TRHR1 mRNA expression in the hypothalamus. Increased plasma PRL levels may have a positive modulatory role on the proTRH/TRHR1 system during suckling.

Noradrenaline up-regulates the neuronal and the inducible nitric oxide synthase isoforms in magnocellular neurons of rat brain slices

Nitric oxide (NO) and noradrenaline (NA) are suggested to be implicated in the regulation of neuropeptide secretion in the supraoptic nuclei (SON) and the paraventricular nuclei (PVN) of the hypothalamus. Our study demonstrates short-term interactions between NA and the activity and expression of NO synthase (NOS) in magnocellular neurons, by using an ex vivo model of hypothalamic slices. In the SON as well as in the PVN, total NOS activity exhibited a time-dependant increase after an incubation with NA. In the SON, this increase of total NOS activity was in part the consequence of stimulation of the iNOS activity. Coimmunodetections showed that cells expressing the inducible form of NOS were not astrocytes but magnocellular neurons. Steady-state levels of iNOS and nNOS mRNA were dramatically enhanced by NA, particularly in the SON. Consequently, we provide new evidence that iNOS could play an important role in multiple physiological functions, including extracellular fluid balance, lactation, and parturition.

Regulation of Oxytocin Secretion

A baby sucks at a mother's breast for comfort and, of course, for milk. Milk is made in specialized cells of the mammary gland, and for a baby to feed, the milk must be released into a collecting chamber from where it can be extracted by sucking. Milk "let-down" is a reflex response to the suckling and kneading of the nipple--and sometimes in response to the sight, smell, and sound of the baby--and is ultimately affected by the secretion of oxytocin. Oxytocin has many physiological roles, but its only irreplaceable role is to mediate milk let-down: oxytocin-deficient mice cannot feed their young; the pups suckle but no milk is let down, and they will die unless cross-fostered. Most other physiological roles of oxytocin, including its role in parturition, are redundant in the sense that the roles can be assumed by other mechanisms in the absence of oxytocin throughout development and adult life. Nevertheless, physiological function in these roles can be altered or impaired by acute interventions that alter oxytocin secretion or change the actions of oxytocin. Here we focus on the diverse stimuli that regulate oxytocin secretion and on the apparent diversity of the roles for oxytocin.

Postnatal regulation by monoamines of vasopressin expression in the neuroendocrine hypothalamus of MAO-A-deficient mice

We studied the influence of noradrenaline (NA) and serotonin (5-HT) on arginine-vasopressin (AVP) expression in the mouse neuroendocrine hypothalamus during the postnatal period. We used 11-day-old transgenic Tg8 mice knock-out for the monoamine oxidase A gene, which are characterized by increased amounts of NA (two-fold) and 5-HT (nine-fold) in the brain compared with wild-type littermates. AVP expression, determined by enzyme immunoassay and in situ hybridization, was increased in the suprachiasmatic nucleus (SCN), decreased in the supraoptic nucleus (SON), and unchanged in the paraventricular nucleus of Tg8 mice compared with wild-types. Inhibiting NA synthesis by injecting alpha-methylparatyrosine to Tg8 mice, AVP levels were decreased in the SCN but increased in the SON. Moreover, the administration of parachlorophenylalanine, a 5-HT synthesis inhibitor, was associated with increased AVP contents in the SCN only. Together, these data show a marked region-specific sensitivity of AVP expression to NA and 5-HT during the postnatal period in the mouse hypothalamus.

Severe symptomatic hyponatremia during citalopram therapy--a case report

BACKGROUND

Hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone is an uncommon complication of treatment with the new class of antidepressant agents, the selective serotonin reuptake inhibitors. The risk of hyponatremia seems to be highest during the first weeks of treatment particularly, in elderly females and in patients with a lower body weight.

CASE PRESENTATION

A 61-year-old diabetic male was admitted to the hospital because of malaise, progressive confusion, and a tonic/clonic seizure two weeks after starting citalopram, 20 mg/day. On physical examination the patient was euvolemic and had no evidence of malignancy, cardiac, renal, hepatic, adrenal or thyroid disease. Laboratory tests results revealed hyponatremia, serum hypoosmolality, urine hyperosmolarity, and an elevated urine sodium concentration, leading to the diagnosis of inappropriate secretion of antidiuretic hormone. Citalopram was discontinued and fluid restriction was instituted. The patient was discharged after serum sodium increased from 124 mmol/L to 134 mmol/L. Two weeks after discharge the patient denied any new seizures, confusion or malaise. At that time his serum sodium was 135 mmol/L.

CONCLUSIONS

Because the use of serotonin reuptake inhibitors is becoming more popular among elderly depressed patients the present paper and other reported cases emphasize the need of greater awareness of the development of this serious complication and suggest that sodium serum levels should be monitored closely in elderly patients during treatment with citalopram.

Impaired somatodendritic responses to pituitary adenylate cyclase-activating polypeptide (PACAP) of supraoptic neurones in PACAP type I -receptor deficient mice

The role of pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptor (PAC1 receptor) in regulating hypothalamic supraoptic neurones was investigated using PAC1 receptor-deficient male mice (PAC1-/-). The effects of PACAP on [Ca2+]i were investigated in freshly dissociated supraoptic neurones and on the somatodendritic release of vasopressin and oxytocin, examined on intact supraoptic nuclei. In supraoptic neurones from wild-type mice (PAC1+/+), 100 nm PACAP induced an increase in [Ca2+]i and release of vasopressin and oxytocin, whereas in heterozygous (PAC1+/-) and null-mutant mice (PAC1-/-), PACAP was much less effective. PACAP had no effect on these two parameters when applied to isolated neurohypophysial nerve terminals of PAC1+/+ and PAC1-/- mice, and rats. In conclusion, the PAC1 receptor is solely responsible for the PACAP-induced [Ca2+]i signalling and secretion of vasopressin and oxytocin in the somatodendritic region of supraoptic neurones.

Methylphenidate-induced motor activity in rats: modulation by melatonin and vasopressin

Methylphenidate (MPH), a dopamine (DA) reuptake inhibitor, is well known to enhance motor activity, in part depending on the time of its application during the light-dark cycle. Moreover, after MPH administration, the hypothalamo-neurohypophysial axis including the neuropeptide vasopressin (AVP) was found influenced. Both the latter and behavioural effects of central AVP can also be modulated by the pineal gland with its light-dark-dependent activity. The present study was performed to investigate whether the pineal gland, its hormone melatonin (Mel), and AVP are involved in the MPH-evoked stimulation of activity. After application of 10 mg/kg MPH, the motor activity in pinealectomised (PE) rats was significantly higher than in sham-operated (SO) animals. After application of 250 microg Mel before MPH treatment, the stimulation of motor activity was diminished in PE rats and augmented in SO animals; however, when SO and PE rats were compared after Mel pretreatment, the reaction to MPH was nearly identical. Blocking the endogenous AVP by 25 or 1 microg of the V1a receptor antagonist d(CH(2))(5)[Tyr(Me)(2)]AVP (AAVP) before MPH treatment significantly augmented the motor activity in SO rats only and abolished the differences seen between SO and PE animals after MPH application. The present results indicate that the behavioural stimulation of MPH was modulated by both the pineal gland with its hormone Mel as well as the neuropeptide AVP.

Monoaminergic control of vasopressin and VIP expression in the mouse suprachiasmatic nucleus

We studied the effects of serotonin and noradrenaline on the expression of arginine-vasopressin (AVP) and vasoactive intestinal peptide (VIP) in the suprachiasmatic nucleus (SCN). We used transgenic Tg8 mice knockout for the MAO-A (monoamine oxidase A) gene, which are characterized by increased amounts of serotonin and noradrenaline in brain compared to wild-type mice (C3H). The MAO-A deficiency caused an increase in AVP and VIP expression (determined by immunohistochemistry, enzyme immunoassay, and in situ hybridization) compared to C3H mice. The number of peptidergic neurons was also increased. Inhibiting serotonin or noradrenaline synthesis in Tg8 mice by the administration of parachlorophenylalanine or alpha-methylparatyrosine, respectively, the amounts of AVP, VIP and their mRNAs were decreased, but not the number of peptidergic neurons. This study indicates that serotonin and noradrenaline stimulate AVP and VIP expression, and could participate in the differentiation of the neurochemical phenotype in the mouse SCN.

Reduction of hypothalamic vasopressinergic hyperdrive contributes to clinically relevant behavioral and neuroendocrine effects of chronic paroxetine treatment in a psychopathological rat model

The neuroendocrine and behavioral effects of chronic paroxetine treatment were investigated in two rat lines selectively bred for high anxiety-related behavior (HAB) or low anxiety-related behavior (LAB) emotionality. In addition to a characteristic behavioral phenotype with markedly passive stress-coping strategies, HAB rats show a hypothalamic vasopressinergic hyperdrive that is causally related to hypothalamic-pituitary-adrenocortical dysregulation as demonstrated in the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test. A total of 8 weeks of chronic paroxetine treatment induced a more active coping strategy in the forced swim test in HAB rats only. In contrast, paroxetine-treated LAB rats did not change their swimming behavior. To investigate the neuroendocrine alterations linked to these behavioral changes, a combined DEX/CRH test was performed. In HAB rats, the paroxetine-induced behavioral changes towards more active coping strategies were accompanied by a normalization of the CRH-stimulated increase in corticotropin (ACTH) and corticosterone secretion. Concomitantly, the hypothalamic vasopressinergic hyperdrive was found to be reduced in HAB but not LAB rats, as indicated by a decrease in vasopressin mRNA expression, whereas vasopressin 1a receptor binding was unaffected. These findings provide the first evidence that the vasopressinergic system is likely to be critically involved in the behavioral and neuroendocrine effects of antidepressant drugs. This novel mechanism of action of paroxetine on vasopressin gene regulation renders vasopressinergic neuronal circuits a promising target for the development of more causal antidepressant treatment strategies.

The effects of nitric oxide on magnocellular neurons could involve multiple indirect cyclic GMP-dependent pathways

Nitric oxide (NO) is known to regulate the release of arginine-vasopressin (AVP) and oxytocin (OT) by the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). The aim of the current study was to identify in these nuclei the NO-producing neurons and the NO-receptive cells in mice. The determination of NO-synthesizing neurons was performed by double immunohistochemistry for the neuronal form of NO synthase (NOS), and AVP or OT. Besides, we visualized the NO-receptive cells by detecting cyclic GMP (cGMP), the major second messenger for NO, by immunohistochemistry on hypothalamus slices. Neuronal NOS was exclusively colocalized with OT in the PVN and the SON, suggesting that NO is mainly synthesized by oxytocinergic neurons in mice. By contrast, cGMP was not observed in magnocellular neurons, but in GABA-, tyrosine hydroxylase- and glutamate-positive fibers, as well as in GFAP-stained cells. The cGMP-immunostaining was abolished by incubating brain slices with a NOS inhibitor (L-NAME). Consequently, we provide the first evidence that NO could regulate the release of AVP and OT indirectly by modulating the activity of the main afferents to magnocellular neurons rather than by acting directly on magnocellular neurons. Moreover, both the NADPH-diaphorase activity and the mean intensity of cGMP-immunofluorescence were increased in monoamine oxidase A knock-out mice (Tg8) compared to control mice (C3H) in both nuclei. This suggests that monoamines could enhance the production of NO, contributing by this way to the fine regulation of AVP and OT release and synthesis.

Inactivation of the PVN during hypoglycemia partially simulates hypoglycemia-associated autonomic failure

The anatomic connections of the paraventricular nucleus of the hypothalamus (PVN) are such that it is ideally situated to modulate and/or control autonomic responses to a variety of stressors, including hypoglycemia. In our experimental model of hypoglycemia-associated autonomic failure (HAAF), a syndrome in which the counterregulatory response to hypoglycemia is partially compromised via unknown mechanisms, activation of the PVN is blunted (15). We hypothesized that this blunted PVN activation during HAAF may be sufficient to cause the impaired counterregulatory response. To test this hypothesis, we anesthetized the PVN with lidocaine during insulin-induced hypoglycemia in rats and measured counterregulatory hormone levels. PVN inactivation decreased indexes of the sympathoadrenal response (plasma epinephrine and norepinephrine) and the hypothalamic-pituitary axis response (ACTH). Inactivation decreased the peak epinephrine response to hypoglycemia by almost half (-42 +/- 6% from control; P = 0.04) and the peak norepinephrine response by 34 +/- 5% (P = 0.01). The peak plasma ACTH levels attained were suppressed by 35 +/- 6% (P = 0.02). Adrenal corticosterone and pancreatic glucagon responses were not impaired. This pattern of neuroendocrine response is unlike that previously seen with our HAAF model. Control infusions of lidocaine >or=1 mm anterior or posterior to the PVN did not simulate this neuroendocrine pattern. Thus it appears that decreased PVN activation, as occurs with HAAF, may be involved in specific components of HAAF (i.e., blunting the sympathoadrenal and hypothalamic-pituitary-adrenocortical axis response), but not in others (i.e., blunting the glucagon response).