Median eminence-afferent vasoactive intestinal peptide (VIP) neurons in the hypothalamus: localization by simultaneous tract tracing and immunocytochemistry

Metformin Treatment Attenuates Brain Inflammation and Rescues PACAP/VIP Neuropeptide Alterations in Mice Fed a High-Fat Diet

High-fat diet (HFD)-induced comorbid cognitive and behavioural impairments are thought to be the result of persistent low-grade neuroinflammation. Metformin, a first-line medication for the treatment of type-2 diabetes, seems to ameliorate these comorbidities, but the underlying mechanism(s) are not clear. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) are neuroprotective peptides endowed with anti-inflammatory properties. Alterations to the PACAP/VIP system could be pivotal during the development of HFD-induced neuroinflammation. To unveil the pathogenic mechanisms underlying HFD-induced neuroinflammation and assess metformin’s therapeutic activities, (1) we determined if HFD-induced proinflammatory activity was present in vulnerable brain regions associated with the development of comorbid behaviors, (2) investigated if the PACAP/VIP system is altered by HFD, and (3) assessed if metformin rescues such diet-induced neurochemical alterations. C57BL/6J male mice were divided into two groups to receive either standard chow (SC) or HFD for 16 weeks. A further HFD group received metformin (HFD + M) (300 mg/kg BW daily for 5 weeks) via oral gavage. Body weight, fasting glucose, and insulin levels were measured. After 16 weeks, the proinflammatory profile, glial activation markers, and changes within the PI3K/AKT intracellular pathway and the PACAP/VIP system were evaluated by real-time qPCR and/or Western blot in the hypothalamus, hippocampus, prefrontal cortex, and amygdala. Our data showed that HFD causes widespread low-grade neuroinflammation and gliosis, with regional-specific differences across brain regions. HFD also diminished phospho-AKT^(Ser473) expression and caused significant disruptions to the PACAP/VIP system. Treatment with metformin attenuated these neuroinflammatory signatures and reversed PI3K/AKT and PACAP/VIP alterations caused by HFD. Altogether, our findings demonstrate that metformin treatment rescues HFD-induced neuroinflammation in vulnerable brain regions, most likely by a mechanism involving the reinstatement of PACAP/VIP system homeostasis. Data also suggests that the PI3K/AKT pathway, at least in part, mediates some of metformin’s beneficial effects.

The anorexigenic effect of vasoactive intestinal polypeptide in Japanese quail is associated with molecular changes in the arcuate and dorsomedial hypothalamic nuclei

Vasoactive intestinal polypeptide (VIP) is involved in gastric smooth muscle relaxation, vasodilation, and gastric secretions. It is also associated with appetite regulation, eliciting an anorexigenic response in mammals, birds, and fish; however, the molecular mechanism mediating this response is not well understood. The aim of the present study was thus to investigate hypothalamic mechanisms mediating VIP-induced satiety in 7-d old Japanese quail. In experiment 1, chicks that received intracerebroventricular (ICV) injection of VIP had reduced food intake for up to 180 min after injection and reduced water intake for 90 min. In experiment 2, VIP-treated chicks that were food restricted did not reduce water intake. In experiment 3, there was increased c-Fos immunoreactivity in the arcuate (ARC) and dorsomedial (DMN) nuclei of the hypothalamus in VIP-injected quail. In experiment 4, ICV VIP was associated with decreased neuropeptide Y mRNA in the ARC and DMN and an increase in corticotropin releasing factor mRNA in the DMN. In experiment 5, VIP-treated chicks displayed fewer feed pecks and locomotor behaviors. These results demonstrate that central VIP causes anorexigenic effects that are likely associated with reductions in orexigenic tone involving the ARC and DMN.

c-Fos expression in the hypothalamic paraventricular nucleus after a single treatment with a typical haloperidol and nine atypical antipsychotics: a pilot study

Objective. The aim of the present study was to find out whether acute effect of different doses of selected antipsychotics including aripiprazole (ARI), amisulpride (AMI), asenapine (ASE), haloperidol (HAL), clozapine (CLO), risperidone (RIS), quetiapine (QUE), olanzapine (OLA), ziprasidone (ZIP), and paliperidone (PAL) may have a stimulatory impact on the c-Fos expression in the hypothalamic paraventricular nucleus (PVN) neurons.

Methods. Adult male Wistar rats weighing 280–300 g were used. They were injected intraperitoneally with vehicle or antipsychotics in the following doses (mg/kg of b.w.): ARI (1, 10, 30), AMI (10, 30), ASE (0.3), HAL (1.0, 2.0), CLO (10, 20), RIS (0.5, 2.0), QUE (10, 20), OLA (5, 10), ZIP (10, 30), and PAL (1.0). Ninety min later, the animals were anesthetized with Zoletil and Xylariem and sacrificed by a transcardial perfusion with 60 ml of saline containing 450 μl of heparin (5000 IU/l) followed by 250 ml of fixative containing 4% paraformaldehyde in 0.1 M phosphate buffer (PB, pH 7.4). The brains were postfixed in a fresh fixative overnight, washed two times in 0.1 M PB, infiltrated with 30% sucrose for 2 days at 4 °C, frozen at −80 °C for 120 min, and cut into 30 μm thick serial coronal sections at −16 °C. c-Fos profiles were visualized by nickel intensified DAB immunohistochemistry and examined under Axio-Imager A1 (Zeiss) light microscope.

Results. From ten sorts of antipsychotics tested, only six (ARI-10, CLO-10 and CLO-20, HAL-2, AMI-30, OLA-10, RIS-2 mg/kg b.w.) induced distinct c-Fos expression in the PVN. The antipsychotics predominantly targeted the medial parvocellular subdivision of the PVN.

Conclusions. The present pilot study revealed c-Fos expression increase predominantly in the PVN medial parvocellular subdivision neurons by action of only several sorts of antipsychotics tested indicating that this structure of the brain does not represent a common extra-striatal target area for all antipsychotics.

Vasoactive intestinal peptide modulates luteinizing hormone subunit gene expression in the anterior pituitary in female rat

The direct monosynaptic pathway which exists between vasoactive intestinal peptide (VIP) and GnRH neurons in the hypothalamic preoptic area provides a neuroanatomical background for the modulatory effects of VIP exerted on GnRH neurons activity. Though central microinjection of VIP revealed its involvement in the modulation of LH release pattern, there is a lack of data concerning a possible VIP influence on the alpha and LHbeta subunit gene expression in the pituitary gland. Using a model based on intracerebroventricular pulsatile peptide(s) microinjections (1 pulse/h [10 microl/5 min] over 5 h) the effect of exogenous VIP (5 nM dose) microinjection on subunits mRNA content in ovariectomized/oestrogen-pretreated rats was studied. Subsequently, to obtain data concerning the involvement of GnRH and VIP receptor(s) in the regulation of alpha and LHbeta subunit mRNA expression, OVX/estrogen-primed rats received a pulsatile microinjections of 5 nM VIP with 3 nM antide (GnRH receptor antagonist) or 5 nM VIP with 15 nM VIP 6-28 (VIP receptor antagonist). In this case, substances were given separately with a 30 min lag according to which each antagonist pulse preceded a VIP pulse. Northern-blot analysis revealed that VIP microinjection resulted in a decreased alpha and LHbeta mRNA content in pituitary gland and this effect was dependent on GnRH receptor activity. Moreover, obtained results indicated that centrally administered VIP might operate through its own receptor(s) because a receptor antagonist, VIP 6-28, blocked the inhibitory effect of VIP exerted on both LH subunit mRNA content and LH release.

Rhythmic secretion of prolactin in rats: action of oxytocin coordinated by vasoactive intestinal polypeptide of suprachiasmatic nucleus origin

Prolactin (PRL) is secreted from lactotrophs of the anterior pituitary gland of rats in a unique pattern in response to uterine cervical stimulation (CS) during mating. Surges of PRL secretion occur in response to relief from hypothalamic dopaminergic inhibition and stimulation by hypothalamic releasing neurohormones. In this study, we characterized the role of oxytocin (OT) in this system and the involvement of vasoactive intestinal polypeptide (VIP) from the suprachiasmatic nucleus (SCN) in controlling OT and PRL secretion of CS rats. The effect of OT on PRL secretion was demonstrated in cultured lactotrophs showing simultaneous enhanced secretion rate and increased intracellular Ca(2+). Neurosecretory OT cells of the hypothalamic paraventricular nucleus that express VIP receptors were identified by using immunocytochemical techniques in combination with the retrogradely transported neuronal tracer Fluoro-Gold (iv injected). OT measurements of serial blood samples obtained from ovariectomized (OVX) CS rats displayed a prominent increase at the time of the afternoon PRL peak. The injection of VIP antisense oligonucleotides into the SCN abolished the afternoon increase of OT and PRL in CS-OVX animals. These findings suggest that VIP from the SCN contributes to the regulation of OT and PRL secretion in CS rats. We propose that in CS rats the regulatory mechanism(s) for PRL secretion comprise coordinated action of neuroendocrine dopaminergic and OT cells, both governed by the daily rhythm of VIP-ergic output from the SCN. This hypothesis is illustrated with a mathematical model.

Antagonism of vasoactive intestinal peptide mRNA in the suprachiasmatic nucleus disrupts the rhythm of FRAs expression in neuroendocrine dopaminergic neurons

This study was designed to determine whether there is a functional relationship between cfos expression in vasoactive intestinal peptide (VIP) -containing neurons of the suprachiasmatic nucleus (SCN) and Fos-related antigens (FRAs) expression in neuroendocrine dopaminergic neurons of the arcuate (ARN) and periventricular (PeVN) nuclei of the hypothalamus. Brains were obtained from ovariectomized (OVX) female rats killed at 12:00 AM, 7:00 AM, 9:00 AM, 12:00 PM, and 7:00 PM (12 hours illumination beginning 6:00 AM). Antibodies against FRAs and tyrosine hydroxylase (TH) identified activated neuroendocrine dopaminergic neurons. Antibodies against cfos and VIP identified activated VIP-immunoreactive (IR) neurons in the SCN. The proportion of neuroendocrine dopaminergic neurons in the ARN and PeVN expressing FRAs was greatest and equivalent at 7:00 AM, 9:00 AM, 12:00 PM, and 12:00 AM. At 7:00 PM, the proportion of neuroendocrine dopaminergic neurons expressing FRAs was significantly lower than all other time points. In the SCN, a subpopulation of VIP-IR neurons maximally expressed cfos at 7:00 AM, which decreased through 9:00 AM. cFos was not expressed at 7:00 PM and 12:00 AM in VIP-IR neurons. Antisense VIP oligonucleotides were injected into the SCN to determine whether attenuation of VIP expression disturbs rhythms in neuroendocrine dopaminergic neuronal activity. OVX rats were infused with either antisense VIP oligonucleotides or scrambled sequence oligonucleotides bilaterally (0.5 microg in 0.5 microl of saline per side) in the SCN. Animals were killed 34 hours (7:00 PM) and 46 hours (7:00 AM) after receiving infusions, and brains were recovered. Administration of antisense VIP oligonucleotides decreased VIP protein expression in the SCN and prevented the decrease in the percentage of neuroendocrine dopaminergic neurons expressing FRAs at 7:00 PM but did not affect FRAs expression at 7:00 AM when compared with animals receiving scrambled oligonucleotides. These data suggest that VIP fibers from the SCN may relay time-of-day information to neuroendocrine dopaminergic neurons to inhibit their activity and, thus, initiate prolactin release in the evening.

Vasoactive intestinal peptide fibers innervate neuroendocrine dopaminergic neurons

Hypothalamic neuroendocrine dopaminergic neurons exhibit a diurnal rhythm. Higher level input to these neurons has not been described. In the present study, we identified fibers known to originate in the suprachiasmatic nucleus (SCN), which were associated with neuroendocrine dopaminergic neurons. Hypothalamic sections were obtained from either ovariectomized (OVX) female rats or OVX female rats implanted with estrogen and progesterone (E+P). Confocal microscopic images were acquired from the periventricular nucleus, as well as the rostral, dorsomedial, ventrolateral, and caudal regions of the arcuate nucleus. Using antibodies directed against vasoactive intestinal peptide (VIP) and tyrosine hydroxylase (TH) the rate-limiting enzyme in dopamine synthesis, fine VIP fibers in close apposition to TH-immunoreactive (IR) soma and proximal dendrites were revealed. Of the antibodies for the two VIP receptor subtypes (VIP1R and VIP2R), only VIP2R was found on TH-IR neurons. E+P significantly increased the incidence and density of neuroendocrine dopaminergic neurons expressing VIP2R, when compared to OVX animals. E+P did not affect the percent of neuroendocrine dopaminergic neurons associated with VIP fibers. No VIP fibers or VIP2R were found on dopaminergic neurons in the zona incerta. Brain sections triple labeled for Synapsin (a protein localized in synaptic vesicles) VIP, and TH demonstrated that Synapsin was colocalized with VIP fibers that were associated with TH-IR neurons in the arcuate nucleus. Double-label immuno-electron microscopy of hypothalamic sections labeled with antibodies for VIP and TH revealed VIP boutons associated with TH-IR soma and proximal dendrites. These results suggest VIPergic neurons may directly regulate neuroendocrine dopaminergic neuron activity, and ovarian steroids may play a modulatory role.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Effects of delta9-THC on VIP-induced prolactin secretion in anterior pituitary cultures: evidence for the presence of functional cannabinoid CB1 receptors in pituitary cells

Peripheral administration of cannabinoid CB1 receptor agonists to laboratory rats induce a brief rise in plasma prolactin (PRL) levels followed by a prolonged decrease in PRL secretion from the pituitary. While the inhibitory component of this biphasic response depends on the cannabinoid-induced activation of dopamine release from hypothalamic terminals located in the median eminence, the neurobiological mechanisms underlying the activation phase of PRL release remains to be explained. In the present study the possible direct effect of the cannabinoid receptor agonist delta9-Tetrahydrocannabinol (THC) on prolactin secretion and cAMP accumulation was examined in anterior pituitary cultures. THC (0.1 and 1 microM) increased cAMP levels, and induced PRL release (1 and 10 mu). THC did not affect vasoactive intestinal peptide (VIP, 0.5 microM) induced cAMP accumulation in pituitary cultures, showing additive effects at THC 1 microM concentration. However, THC did prevent VIP-dependent increases in prolactin secretion. These results indicate that THC, through a direct pituitary action, activates both the synthesis of cAMP and PRL release and interferes with intracellular mechanisms involved in PRL secretion by VIP. These actions could be mediated through cannabinoid CB1 receptors which were found to be present in anterior pituitary cells, including lactotrophs, as revealed by immunocytochemistry with a specific polyclonal antibody raised against the CB1 receptor protein.

Central administration of antiserum to vasoactive intestinal peptide delays and reduces luteinizing hormone and prolactin surges in ovariectomized, estrogen-treated rats

The present study investigated the role of hypothalamic VIP in the regulation of the LH and PRL surge using immunoneutralization of endogenous VIP in mature ovariectomized (OVX), estradiol benzoate (EB)-treated female Wistar rats. We compared the effect of intracerebroventricular (i.c.v.) injections of a VIP antiserum (VIP-Ab) with that of saline (Ctr) on LH and PRL profiles in two separate groups of rats following two subcutaneous EB injections on days 8 and 9 after OVX. VIP-Ab or Ctr injections were given during the second half of the dark period, i.e. at 22:00 h (day 9), and, in addition, the following morning, i.e. at 08:00 h (day 10), just before the expected onset of the LH surge. Hourly blood samples were collected between 09:00 and 18:00 h on day 10. In addition, we studied the reproducibility of EB-induced LH and PRL surges and compared the effect of Ctr and VIP-Ab treatment on sequential surges in individual OVX females, i.e. 10 and 23 days after OVX, using each animal as its own control. Although we observeda large variation in the height and timing of LH and PRL peak levels between EB-treated females, the characteristics of successive surges of individual rats were highly reproducible. This reproducibility suggests that differences in functioning of the suprachiasmatic nucleus as well as in the response of the hypothalamus to steroid feedback largely explain the normal variation in hormone responses between rats. The VIP-Ab treatment resulted in a significant delay in the time course and a strong reduction of the magnitude of the afternoon LH and PRL surge. When analyzed within individual females, the effect of VIP-Ab treatment was even more pronounced due to a reduction in variability when each animal was used as its own control. These results suggest that hypothalamic VIP is an important regulator of both the timing and the magnitude of the EB-induced LH and PRL surge in the OVX rat, and suggest that its role may be stimulatory in this respect.

Fatty acids and brain peptides

The role of fatty acids (FA) as a mediator and modulator of central nervous system activity in general, and peptides in particular, is only recently becoming understood. This paper reviews numerous findings concerned with the activity of fatty acids, particularly with their interaction with diverse neurochemical systems and their consequences for better understanding neurotransmitters, hormones and peptides. The effects include FA as precursors in the manufacture of neurochemical elements, including enzymes, neurotransmitters, and hormones. Of particular interest is the important changes in neuronal membrane composition that have been attributed to FA. Such changes may account for the changes in thermoregulation, learning, and other functions that accompany dietary manipulation of FA intake. While the total level of FA has been the object of many investigations, this report addresses the need to focus on the ratio of FA, especially alpha-linolenic/linoleic acid, which has been shown to be a critical factor in a number of research studies.

The cellular localization of vasoactive intestinal peptide (VIP) in the mouse median eminence by immuno-electron microscopy

The aim of this study was to examine, by use of pre-embedding immunocytochemistry, the ultrastructural localization of vasoactive intestinal peptide (VIP) immunoreactivity in the mouse median eminence. VIP immunoreactivity was observed in axonal profiles. The VIP-immunoreactive axonal profiles were in close proximity to non-immunoreactive axonal profiles that contained dense granular vesicles and clear vesicles and also to processes of tanycytes. VIP-immunoreactive terminals were observed in the proximity of the perivascular space and in the neuropil. Our results suggest that VIP-immunoreactive axon terminals may possibly interact with other non-immunoreactive axon terminals containing peptide and/or other transmitters at the level of the median eminence or may be released to the portal vasculature thereby to effect anterior pituitary cells.

The distribution of vasoactive intestinal peptide2 receptor messenger RNA in the rat brain and pituitary gland as assessed by in situ hybridization

The distribution of rat vasoactive intestinal peptide2 (VIP2) receptor messenger RNA in the brain and the pituitary gland was examined by in situ hybridization and by ribonuclease protection assay. labelled cells were found chiefly in the suprachiasmatic nucleus, the central nucleus of the amygdala and the thalamus (the lateral geniculate nucleus, and the paraventricular, mediodorsal and ventral nuclei of the thalamus). The distribution of the VIP2 receptor overlaps only in part with that of the VIP1 receptor, for example in the hippocampus, where VIP2 receptor messenger RNA was found in the pyramidal cells of the CA1-CA3 subfields and in the granule cells of the dentate gyrus. Small numbers of neurons containing high concentrations of VIP2 receptor messenger RNA were present in the brainstem in the principal sensory trigeminal nucleus and in the substantia gelatinosa of the spinal cord, suggesting a role for the VIP2 receptor in the processing of sensory information. The presence of the VIP2 receptor in the suprachiasmatic nucleus suggests that it is this receptor subtype which is involved in the control of circadian rhythms.