Oxytocinergic Neurons Research Articles

Oestradiol Potentiates Hormone Secretion and Neuronal Activation in Response to Hypertonic Extracellular Volume Expansion in Ovariectomised Rats

Secretion of vasopressin (VP), oxytocin (OT) and atrial natriuretic peptide (ANP) is an essential mechanism for the maintenance of hydromineral homeostasis. Secretion of these hormones is modulated by several circulating factors, including oestradiol. However, it remains unclear how oestradiol exerts this modulation. In the present study we investigated the participation of oestradiol in the secretion of VP, OT and ANP and in activation of vasopressinergic and oxytocinergic neurones of the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus in response to extracellular volume expansion (EVE). For this purpose, ovariectomised (OVX) rats treated for 7 days with vehicle (corn oil, 0.1 ml/rat, OVX+O group) or oestradiol (oestradiol cypionate, 10 μg/kg, OVX+E group) were subjected to either isotonic (0.15 m NaCl, 2 ml/100 g b.w., i.v.) or hypertonic (0.30 m NaCl, 2 ml/100 g b.w., i.v.) EVE. Blood samples were collected for plasma VP, OT and ANP determination. Another group of rats was subjected to cerebral perfusion, and brain sections were processed for c-Fos-VP and c-Fos-OT double-labelling immunohistochemistry. In OVX+O rats, we observed that both isotonic and hypertonic EVE increased plasma OT and ANP concentrations, although no changes were observed in VP secretion. Oestradiol replacement did not alter hormonal secretion in response to isotonic EVE, but it increased VP secretion and potentiated plasma OT and ANP concentrations in response to hypertonic EVE. Immunohistochemical data showed that, in the OVX+O group, hypertonic EVE increased the number of c-Fos-OT and c-Fos-VP double-labelled neurones in the PVN and SON. Oestradiol replacement did not alter neuronal activation in response to isotonic EVE, but it potentiated vasopressinergic and oxytocinergic neuronal activation in the medial magnocellular PVN (PaMM) and SON. Taken together, these results suggest that oestradiol increases the responsiveness of vasopressinergic and oxytocinergic magnocellular neurones in the PVN and SON in response to osmotic stimulation.

Neuroanatomical evidence for reciprocal regulation of the corticotrophin-releasing factor and oxytocin systems in the hypothalamus and the bed nucleus of the stria terminalis of the rat: Implications for balancing stress and affect

Activation of corticotrophin releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) is necessary for establishing the classic endocrine response to stress, while activation of forebrain CRF neurons mediates affective components of the stress response. Previous studies have reported that mRNA for CRF2 receptor (CRFR2) is expressed in the bed nucleus of the stria terminalis (BNST) as well as hypothalamic nuclei, but little is known about the localization and cellular distribution of CRFR2 in these regions. Using immunofluorescence with confocal microscopy, as well as electron microscopy, we demonstrate that in the BNST CRFR2-immunoreactive fibers represent moderate to strong labeling on axons terminals. Dual-immunofluorescence demonstrated that CRFR2-fibers co-localize oxytocin (OT), but not arginine-vasopressin (AVP), and make perisomatic contacts with CRF neurons. Dual-immunofluorescence and single cell RT-PCR demonstrate that in the hypothalamus, CRFR2 immunoreactivity and mRNA are found in OT, but not in CRF or AVP-neurons. Furthermore, CRF neurons of the PVN and BNST express mRNA for the oxytocin receptor, while the majority of OT/CRFR2 neurons in the hypothalamus do not. Finally, using adenoviral-based anterograde tracing of PVN neurons, we show that OT/CRFR2-immunoreactive fibers observed in the BNST originate in the PVN. Our results strongly suggest that CRFR2 located on oxytocinergic neurons and axon terminals might regulate the release of this neuropeptide and hence might be a crucial part of potential feedback loop between the hypothalamic oxytocin system and the forebrain CRF system that could significantly impact affective and social behaviors, in particular during times of stress.

In vitro functionality of isolated embryonic hypothalamic vasopressinergic and oxytocinergic neurons: modulatory effects of brain-derived neurotrophic factor and angiotensin II

There are only a few studies on the ontogeny and differentiation process of the hypothalamic supraoptic-paraventriculo-neurohypophysial neurosecretory system. In vitro neuron survival improves if cells are of embryonic origin; however, surviving hypothalamic neurons in culture were found to express small and minimal amounts of arginine-vasopressin (AVP) and oxytocin (OT), respectively. The aim of this study was to develop a primary neuronal culture design applicable to the study of magnocellular hypothalamic system functionality. For this purpose, a primary neuronal culture was set up after mechanical dissociation of sterile hypothalamic blocks from 17-day-old Sprague-Dawley rat embryos (E17) of both sexes. Isolated hypothalamic cells were cultured with supplemented (B27)-NeuroBasal medium containing an agent inhibiting non-neuron cell proliferation. The neurosecretory process was characterized by detecting AVP and OT secreted into the medium on different days of culture. Data indicate that spontaneous AVP and OT release occurred in a culture day-dependent fashion, being maximal on day 13 for AVP, and on day 10 for OT. Interestingly, brain-derived neurotrophic factor (BDNF) and Angiotensin II (A II) were able to positively modulate neuropeptide output. Furthermore, on day 17 of culture, non-specific (high-KCl) and specific (Angiotensin II) stimuli were able to significantly (P<0.05) enhance the secretion of both neuropeptides over respective baselines. This study suggests that our experimental design is useful for the study of AVP- and OT-ergic neuron functionality and that BDNF and A II are positive modulators of embryonic hypothalamic cell development.

Systemically administered oxytocin decreases methamphetamine activation of the subthalamic nucleus and accumbens core and stimulates oxytocinergic neurons in the hypothalamus

Recent preclinical evidence indicates that the neuropeptide oxytocin may have potential in the treatment of drug dependence and drug withdrawal. Oxytocin reduces methamphetamine self-administration, conditioned place preference and hyperactivity in rodents. However, it is unclear how oxytocin acts in the brain to produce such effects. The present study examined how patterns of neural activation produced by methamphetamine were modified by co-administered oxytocin. Male Sprague-Dawley rats were pretreated with either 2 mg/kg oxytocin (IP) or saline and then injected with either 2 mg/kg methamphetamine (IP) or saline. After injection, locomotor activity was measured for 80 minutes prior to perfusion. As in previous studies, co-administered oxytocin significantly reduced methamphetamine-induced behaviors. Strikingly, oxytocin significantly reduced methamphetamine-induced Fos expression in two regions of the basal ganglia: the subthalamic nucleus and the nucleus accumbens core. The subthalamic nucleus is of particular interest given emerging evidence for this structure in compulsive, addiction-relevant behaviors. When administered alone, oxytocin increased Fos expression in several regions, most notably in the oxytocin-synthesizing neurons of the supraoptic nucleus and paraventricular nucleus of the hypothalamus. This provides new evidence for central actions of peripheral oxytocin and suggests a self-stimulation effect of exogenous oxytocin on its own hypothalamic circuitry. Overall, these results give further insight into the way in which oxytocin might moderate compulsive behaviors and demonstrate the capacity of peripherally administered oxytocin to induce widespread central effects.

Hypothalamic oxytocin mediates adaptation mechanism against chronic stress in rats

Accumulation of continuous life stress (chronic stress) often causes gastric symptoms. Although central oxytocin has antistress effects, the role of central oxytocin in stress-induced gastric dysmotility remains unknown. Solid gastric emptying was measured in rats receiving acute restraint stress, 5 consecutive days of repeated restraint stress (chronic homotypic stress), and 7 consecutive days of varying types of stress (chronic heterotypic stress). Oxytocin and oxytocin receptor antagonist were administered intracerebroventricularly (icv). Expression of corticotropin-releasing factor (CRF) mRNA and oxytocin mRNA in the paraventricular nucleus (PVN) of the hypothalamus was evaluated by real-time RT-PCR. The changes of oxytocinergic neurons in the PVN were evaluated by immunohistochemistry. Acute stress delayed gastric emptying, and the delayed gastric emptying was completely restored after 5 consecutive days of chronic homotypic stress. In contrast, delayed gastric emptying persisted following chronic heterotypic stress. The restored gastric emptying following chronic homotypic stress was antagonized by icv injection of an oxytocin antagonist. Icv injection of oxytocin restored delayed gastric emptying induced by chronic heterotypic stress. CRF mRNA expression, which was significantly increased in response to acute stress and chronic heterotypic stress, returned to the basal levels following chronic homotypic stress. In contrast, oxytocin mRNA expression was significantly increased following chronic homotypic stress. The number of oxytocin-immunoreactive cells was increased following chronic homotypic stress at the magnocellular part of the PVN. Icv injection of oxytocin reduced CRF mRNA expression induced by acute stress and chronic heterotypic stress. It is suggested that the adaptation mechanism to chronic stress may involve the upregulation of oxytocin expression in the hypothalamus, which in turn attenuates CRF expression.

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, 60 s 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.

Hypothalamic gonadotropin-releasing hormone receptor activation stimulates oxytocin release from the rat hypothalamo-neurohypophysial system while melatonin inhibits this process

The present study was undertaken to investigate the influence of gonadotropin-releasing hormone (GnRH) and its agonist and antagonist on oxytocin (OT) release from the rat hypothalamo-neurohypophysial (H-N) system. An additional aim was to determine whether the possible response of oxytocinergic neurons to these peptides could be modified by melatonin through a cAMP-dependent mechanism. The results show that the highly selective GnRH agonist (i.e., [Des-Gly 10, d-His(Bzl) 6,Pro-NHEt 9]-LHRH; Histrelin) stimulates the secretion of OT from an isolated rat H-N system. Melatonin significantly inhibited basal and histrelin-induced release of OT in vitro, and displayed no significant influence on OT release in the presence of GnRH or its antagonist. Addition of melatonin to a medium containing forskolin resulted in significant reduction of OT secretion from the H-N system. On the other hand, addition of forskolin to a medium containing both histrelin and melatonin did not further alter the inhibitory influence of melatonin on the histrelin-dependent secretion of OT in vitro. Intracerebroventricular ( icv) infusion (experiment in vivo) of a GnRH antagonist resulted in substantial inhibition of OT release, thus revealing the stimulatory action of endogenous GnRH. In melatonin-treated animals, blood plasma OT levels were not changed in comparison to the vehicle. Our present data strongly suggests that activation of the GnRH receptor in the hypothalamus is involved in stimulation of OT secretion from the rat H-N system. It has also been shown, under experimental in vitro conditions, that melatonin fully suppresses the response of oxytocinergic neurons to the GnRH agonist – histrelin. The effect of melatonin on OT release is mediated by the cAMP-dependent mechanism, although other mechanisms of action are also possible.

Different antipsychotics elicit different effects on magnocellular oxytocinergic and vasopressinergic neurons as revealed by Fos immunohistochemistry

Acute administration of antipsychotics elicits regionally distinct patterns of Fos expression in the rat brain. Stimulation of oxytocin (OXY) and vasopressin (AVP) release in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei indicates that antipsychotics may play a role in autonomic, neuroendocrine, and behavioral processes. This study was focused to reveal the responsiveness of hypothalamic OXY- and AVP- producing magnocellular neurons, in terms of quantitative and topographical distinctions, to antipsychotics displaying different pharmacological profiles. Naive male Wistar rats were injected intraperitoneally with haloperidol (1 mg/kg), clozapine (30 mg/kg), olanzapine (30 mg/kg), risperidone (2mg/kg), and vehicle (5% chremophor) and were sacrificed 60 min later by a fixative. Fos, Fos/OXY, and Fos/AVP labelings were visualized by immunohistochemistry in the SON, 5 accessory (ACS) cell groups, and 4 distinct PVN subdivisions using a computerized light microscope. Most apparent activation of single Fos, Fos/OXY, and Fos/AVP cells was induced by clozapine and olanzapine; effects of risperidone and haloperidol were substantially lower; no colocalizations were revealed in naive or vehicle treated control rats. The data indicate the existence of a substantial diversity in the stimulatory effect of the selected antipsychotics on quantity of Fos, Fos/OXY, and Fos/AVP immunostainings with the preferential action of the atypicals clozapine over olanzapine and little effects of risperidone and haloperidol. Variabilities in Fos distribution in the PVN, SON, and ACS induced by antipsychotics may be helpful to understand more precisely the extent of their extra-forebrain actions with possible presumption of their functional impact and side effect consequences.

Prolactin induces Egr-1 gene expression in cultured hypothalamic cells and in the rat hypothalamus

Prolactin (PRL), the major lactogenic hormone, acts also as neuromodulator and regulator of neuronal and glial plasticity in the brain. There is an increase in synthesis and release of PRL within the hypothalamus during peripartum and in response to stress. To identify mechanisms by which PRL induces neuroplasticity, we studied the ability of PRL to induce the transcription factor Egr-1 in the hypothalamic cell line, 4B, in vitro, and in specific neuronal cell types of the hypothalamus in vivo. PRL induced Egr-1 mRNA expression in 4B cells, an effect which was prevented by the MEK inhibitor, U0126. In vivo, intracerebroventricular PRL (1 μg) increased Egr-1 mRNA levels in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON) of female rats. The increase in mRNA paralleled elevated Egr-1 protein expression in the PVN and SON. Double staining immunohistochemistry revealed Egr-1 localization in oxytocin neurons of the PVN and SON, but not in vasopressin neurons in these regions. In the dorsomedial PVN, a population of non-oxytocin or vasopressin cells localized in a region corresponding to corticotropin-releasing hormone neurons also showed marked Egr-1 immunoreactivity. The data suggest that PRL modulates plasticity in oxytocinergic neurons, through MAP kinase-dependent induction of Egr-1.

From here to paternity: Neural correlates of the onset of paternal behavior in California mice ( Peromyscus californicus)

In a minority of mammalian species, including humans, fathers play a significant role in infant care. Compared to maternal behavior, the neural and hormonal bases of paternal care are poorly understood. We analyzed behavioral, neuronal and neuropeptide responses towards unfamiliar pups in biparental California mice, comparing males housed with another male (“virgin males”) or with a female before (“paired males”) or after (“new fathers”) the birth of their first litter. New fathers approached pups more rapidly and spent more time engaging in paternal behavior than virgin males. In each cage housing two virgin males, one was spontaneously paternal and one was not. New fathers and paired males spent more time sniffing and touching a wire mesh ball containing a newborn pup than virgin males. Only new fathers showed significantly increased Fos-like immunoreactivity in the medial preoptic nucleus (MPO) following exposure to a pup-containing ball, as compared to an empty ball. Moreover, Fos-LIR in the bed nucleus of the stria terminalis (STMV and STMPM) and caudal dorsal raphe nucleus (DRC) was increased in new fathers, independent of test condition. No differences were found among the groups in Fos-LIR in oxytocinergic or vasopressinergic neurons. These results suggest that sexual and paternal experiences facilitate paternal behavior, but other cues play a role as well. Paternal experience increases Fos-LIR induced by distal pup cues in the MPO, but not in oxytocin and vasopressin neurons. Fatherhood also appears to alter neurotransmission in the BNST and DRC, regions implicated in emotionality and stress-responsiveness.

Alpha2-adrenergic impact on hypothalamic magnocellular oxytocinergic neurons in long evans and brattleboro rats: effects of agonist and antagonists.

We have previously demonstrated that alpha2-adrenoceptors regulate hypothalamic magnocellular oxytocinergic (OXY) neurons in Sprague Dawley rats. Here we investigated whether activation/inhibition of alpha2-adrenoceptors may similarly trigger/downregulate the activity of OXY neurons in control Long Evans (+/+) and permanently osmotically stressed Brattleboro (di/di) rats. The effect of alpha2-adrenoceptor agonist, xylazine (XYL) and alpha2-adrenoceptor antagonists, atipamezole (ATIP), and idazoxan (IDX) were evaluated in the supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei. Saline (SAL, 0.1 ml/100 g), XYL (10 mg/kg), ATIP, (1 mg/kg), and IDX (10 mg/kg) and IDX or ATIP followed by XYL were applied intraperitoneally. Rats were sacrificed 90 min later and Fos/OXY co-labelings analyzed in microscope. In control +/+ rats no or few Fos/OXY co-labelings occurred in SON and PVN. XYL significantly increased Fos incidence in OXY neurons in both nuclei. ATIP significantly suppressed the effect of XYL in both nuclei and IDX only in SON. In di/di controls 81% of OXY neurons in SON and 44% in PVN revealed Fos presence and XYL did not further elevate Fos number in SON OXY neurons and slightly increased Fos number in PVN. ATIP or IDX only partially reduced Fos in SAL or XYL treated di/di rats. Our data indicate that: (1) XYL stimulation is not effective in di/di rats because of sustained upregulation of OXY neurons activity and (2) neither ATIP nor IDX reduced significantly the OXY activity in control di/di rats. These findings suggest that alpha2-adrenoceptors have only a limited impact in maintaining OXY cells activity upregulation in PVN and SON of di/di rats.

Involvement of oxytocin and its receptor in nociceptive modulation in the central nucleus of amygdala of rats

Studies have demonstrated that oxytocin plays important roles in pain modulation in the central nervous system. Oxytocin-ergic neurons are found in paraventricular nucleus and supraoptic nucleus of the hypothalamus. The oxytocin-ergic neurons send fibers from hypothalamus to amygdala and high density of oxytocin receptors are found in the central nucleus of amygdala (CeA). The present study was performed to investigate the influences of oxytocin and its receptors on nociceptive responses in the CeA of rats. Intra-CeA injection of 0.1, 0.5 or 1 nmol of oxytocin induced dose-dependent increases in the handpaw withdrawal latency induced by noxious thermal and mechanical stimulation in rats. The oxytocin-induced anti-nociception could be blocked by the selective oxytocin antagonist 1-deamino-2- d-Tyr-(Oet)-4-Thr-8-Orn-oxytocin. The present study demonstrated that oxytocin and its receptors are involved in nociceptive modulation in the CeA of rats.

Vasopressine et angiogenèse

In adult mammals, the CNS vasculature remains essentially quiescent, excepted for specific pathologies. In the seventies, it was reported that proliferation of astrocytes and endothelial cells occurs within the hypothalamic magnocellular nuclei when strong metabolic activation of the vasopressinergic and oxytocinergic neurons was induced by prolonged hyperosmotic stimulation. Using more appropriate techniques, we first demonstrated that in these nuclei, the proliferative response to osmotic stimulus is essentially associated with local angiogenesis. We then showed that hypothalamic magnocellular neurons express vascular endothelial growth factor (VEGF), a potent angiogenic factor, that plays a major rôle in the angiogenesis induced by osmotic stimuli. We then demonstrated a correlation between increased VEGF secretion and local hypoxia. In AVP-deficient Brattleboro rats, the dramatic activation of magnocellular hypothalamic neurons failed to induce hypoxia, VEGF expression or angiogenesis suggesting a major role of hypothalamic AVP. Lastly we showed that 1) hypoxia and angiogenesis were not observed in non-osmotically stimulated Wistar rats in which circulating AVP was increased by the prolonged infusion of exogenous AVP, 2) contractile arterioles afferent to the magnocellular nuclei were strongly constricted by the perivascular application of AVP via V1a receptors (V1a-R) stimulation, and 3) following the intracerebral administration of selective V1a-R antagonist to osmotically stimulated rats, hypothalamic hypoxia and angiogenesis were inhibited. Together, these data strongly suggest that the angiogenesis induced by osmotic stimulation relates to tissue hypoxia resulting from the constriction of local arterioles, via the stimulation of perivascular V1a-R by AVP locally released from dendrites.

Effects of Estrogen on Stress‐induced Activation of Peptide Neurons in PVN of Ovariectomized Rats

Estrogen has been implicated in brain function related to stress responses. We investigated whether estrogen affects psychological stress-induced activation of peptide-containing or nitric oxide-producing neurons in the paraventricular hypothalamic nucleus (PVN) in ovariectomized (OVX) rats, both placebo-treated (OVX + Pla) and estrogen-treated (OVX + E2) by comparison of c-Fos expression using immunohistochemistry. Cage-switch stress increased activation in oxytocinergic neurons in the parvocellular PVN (pPVN) in OVX + Pla, but not in that of OVX + E2, rats. Moreover, the stress-induced activation in NADPH-diaphorase-positive neurons in the pPVN was larger in the OVX + E2 than in the OVX + Pla group. These findings suggest that estrogen attenuates the activation of oxytocinergic neurons in the pPVN, at least in part via nitric oxide.

Activity of Oxytocinergic Neurons in the Supraoptic Nucleus under Stimulation of α2‐Adrenoceptors in Brattleboro Rats

Vasopressin (AVP) deficient homozygous Brattleboro rats exhibit severe osmotic challenges due to waterless chronic hypernatremia and hyperosmolality. We investigated the effect of xylazine, an alpha2-adrenoceptor agonist, on the activity of oxytocinergic (OXY) neurons in the supraoptic nucleus (SON) of homozygous (di/di), heterozygous (di/+), and control (+/+) rats. Ninety minutes after saline (0.1 mL/100 g b.w., i.p.) or xylazine injection (10 mg/kg, i.p.) rats were anaesthetized with pentobarbital (50 mg/kg i.p.) and sacrificed by transcardial perfusion with fixative. Activity of OXY neurons was evidenced by nuclear Fos protein immunoreactivity. Fos/OXY colabelings were analyzed on 40-mum thick coronal sections using computerized light microscope. As expected, plasma osmolality and water intake revealed high heterogenity within the di/di group of rats. Fos expression in SON of di/di rats was correlated with osmolality of each rat. In saline-treated rats, maximum activation of Fos reached around 4% in +/+, 20% in di/+ rats, and as much as 60% in di/di rats. Xylazine activated in SON about 70% of OXY-ergic neurons in +/+, 60% in di/+ rats, and more than 80% in di/di rats. The present findings indicate that in spite of the high spontaneous activity of SON OXY-ergic neurons due to the AVP deficiency in di/di rats, many of the silent OXY-ergic neurons in the SON remained acceptable for alpha2-adrenoceptor stimulation.

Cerebral abscess in term newborn with perinatal asphyxia: The importance of cerebral ultrasound monitoring

Potentiating social, cognitive, and sensorimotor stimulations the Environmental Enrichment (EE) increases levels of novelty and complexity experienced by individuals. Growing evidence demonstrates that parental EE experience, even occurring in the pre-reproductive phase, affects behavioral and neural developmental trajectories of the offspring.To discover how the accumulation of early maternal complex experiences may inform and shape the social behavior of the following generation, we examined the effects of pre-reproductive enrichment of dams (post-natal days 21–72) on the play performances of their male and female adolescent offspring. Furthermore, we examined the effects of pre-reproductive enrichment on maternal behavior (during post-partum days 1–10) and male intruder aggression (on post-partum day 11). Since oxytocin modulates maternal care, social bonding, and agonistic behavior, the number of oxytocinergic neurons of the paraventricular (PVN) and supraoptic (SON) nuclei was examined in both dams and offspring.Results revealed that enriched females exhibited higher levels of pup-oriented behaviors, especially Crouching, and initiated pup-retrieval more quickly than standard females after the maternal aggression test. Such behavioral peculiarities were accompanied by increased levels of oxytocinergic neurons in PVN and SON. Moreover, pre-reproductive maternal EE cross-generationally influenced the offspring according to sex. Indeed, male pups born to enriched females exhibited a reduced play fighting associated with a higher number of oxytocinergic neurons in SON in comparison to male pups born to standard-housed females.In conclusion, pre-reproductive EE to the mothers affects their maternal care and has a cross-generational impact on the social behavior of their offspring that do not directly experiences EE.This article is part of the Special Issue entitled “Neurobiology of Environmental Enrichment”.

CNTF receptor alpha is expressed by magnocellular neurons and expression is upregulated in the rat supraoptic nucleus during axonal sprouting

Ciliary neurotrophic factor (CNTF) is expressed by glial cells at multiple levels of the magnocellular neurosecretory system (MNS). CNTF is present in astrocytes in the hypothalamic supraoptic nucleus (SON) as well as in perivascular cells in the neurohypophysis, and a several fold increase in CNTF immunoreactivity occurs in the SON following either axotomy of magnocellular neurons or during axonal sprouting by intact magnocellular neurons. CNTF also promotes survival and stimulates process outgrowth from magnocellular neurons in vitro. While these findings suggest that CNTF may act as a growth factor in support of neuronal plasticity in the MNS, little is known regarding possible expression of receptors for CNTF in the MNS. We have therefore used immunocytochemistry and in situ hybridization to examine the expression of CNTF receptor alpha (CNTFRα) in the rat MNS. Robust immunoreactivity for CNTFRα was observed associated with oxytocinergic and vasopressinergic neurons distributed throughout the SON. Astrocytes located within the ventral glial lamina (VGL) of the SON were also immunoreactive for CNTFRα. Robust hybridization of an anti-sense [ 35S]-cRNA probe to CNTFRα mRNA was observed throughout the SON, while binding of a control sense probe was much lower. Grains were found clustered predominantly over neuronal somata, indicative of expression by magnocellular neurons within the SON. We next examined changes in expression of CNTFRα mRNA by magnocellular neurons 7 days following unilateral transection of the hypothalamo-neurohypophysial tract. The level of CNTFRα mRNA was increased 32% (compared to age-matched intact controls; p < 0.05) in magnocellular neurons in the SON contralateral to the lesion, which are undergoing extensive collateral axonal sprouting, but was unchanged in axotomized magnocellular neurons in the SON ipsilateral to the lesion. These findings suggest that CNTF produced by MNS glia and acting via CNTFRα may exert neurotrophic effects on magnocellular neurons.

Brief daily suckling shifts locomotor behavior and induces PER1 protein in paraventricular and supraoptic nuclei, but not in the suprachiasmatic nucleus, of rabbit does

Nursing in the rabbit is a circadian event during which mother and pups interact for a period of < 5 min every day. Here we explored behavioral and neuronal changes in the mother by analyzing the suprachiasmatic nucleus (SCN), and oxytocinergic (OT) neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). We maintained lactating does in a light-dark cycle (lights on at 07 : 00 hours; ZT0); they were scheduled to nurse during either the day (ZT03) or the night (ZT19). Groups of intact and nursing females was perfused, one at each 4-h point through a 24-h cycle. We explored, by immunohistochemistry, the PER1 expression and double-labeling, with OT antibody, of neurons in the PVN and SON at lactation on day 7. In the SCN, intact and lactating groups had peak PER1 expression at ZT11; however, there was a reduction in PER1 at peak time in the nursing groups. There was a locomotor activity rhythm with increased activity around the time of lights-on in intact subjects and around the time of suckling in lactating does. There was an induction of PER1 in OT cells in the PVN and SON that shifted in phase with timing of nursing. We further explored the maintenance of the PER1 expression in OT cells in nursing-deprived does and found a significant decrease at 24 and 48 h after the last nursing. We conclude that suckling induced PER1 in the PVN and SON, but not in the SCN, in nursing does, and also shifted their locomotor behavior.

Distribution of glucagon-like peptide-1 immunoreactivity in the hypothalamic paraventricular and supraoptic nuclei

Glucagon-like peptide-1 (GLP-1) plays a role in modulating neuroendocrine and autonomic function. The hypothalamic paraventricular nucleus (PVN) contains aggregations of GLP-1 fibers and expresses GLP-1 receptors, making it a likely site of action for GLP-1 signaling. The current study was designed to establish domains of GLP-1 action, focusing on axosomatic appositions on different neuroendocrine and autonomic cell populations in the PVN. The data indicate abundant GLP-1-immunoreactive terminal appositions on corticotropin-releasing hormone neurons in the medial parvocellular PVN. GLP-1 positive boutons can also be observed in apposition to oxytocinergic neurons and on retrogradely labeled pre-autonomic neurons projecting to the region of the nucleus of the solitary tract. In contrast, there were very few vasopressinergic neurons with GLP-1 appositions. Overall, the data indicate that the central GLP-1 system preferentially targets neurons in hypophysiotrophic zones of the PVN, consistent with excitatory actions of GLP-1 on adrenocorticotropin release. GLP-1 is also in position to influence oxytocin secretion and control outflow to brainstem cardiovascular relays.

Involvement of neuromedin S in the oxytocin release response to suckling stimulus

We recently identified neuromedin S (NMS) from the rat hypothalamus as an endogenous ligand for the FM-4/TGR-1 receptor distinct from neuromedin U. In the present study, we examined the role of NMS in the oxytocin release response to suckling stimulation by rat pups. Intracerebroventricular (icv) injection of NMS induced cFos expression in the paraventricular nucleus and supraoptic nucleus. Double immunohistochemical analysis revealed induction of cFos expression in a proportion of oxytocinergic neurons in both nuclei. In addition, icv injection of NMS stimulated oxytocin release dose-dependently in intact rats, and increased milk secretion in lactating rats. On the other hand, icv injection of anti-NMS antiserum into lactating rats significantly suppressed suckling-induced milk ejection. These results suggest that, in the rat, endogenous NMS plays an important role in the oxytocin release response to the suckling stimulus.