Neuropeptide Y: stimulation of feeding and drinking by injection into the paraventricular nucleus

Neuropeptide Y (NPY), a peptide contained within numerous presynaptic terminals in the hypothalamic paraventricular nucleus (PVN), was injected directly into the PVN of satiated, brain-cannulated rats, and food and water intake were measured 0.5, 1, 2 and 4 hrs postinjection. Neuropeptide Y (24 and 78 pmoles/0.3 microliter isotonic saline) caused a dose-dependent increase in food intake, as well as a small, dose-dependent increase in water intake. This effect on feeding occurred even when food was not presented until 4 hrs postinjection. To determine the behavioral specificity of this effect, the impact of PVN injection of NPY (78 pmoles) on various behaviors was observed. With food available, only feeding and drinking behavior were affected. No change in other behaviors, including grooming, rearing, sleeping, resting or different levels of activity, was observed. With food absent, NPY still elicited drinking, suggesting that this is a primary effect, rather than secondary to the feeding. In addition to drinking, NPY reliably increased activity while decreasing sleep and grooming. These results suggest an important role for hypothalamic NPY, or a structurally-related peptide, in the regulation of feeding and drinking behavior.     

Neuropeptide FF and neuropeptide VF inhibit GABAergic neurotransmission in parvocellular neurons of the rat hypothalamic paraventricular nucleus

Neuropeptide FF (NPFF) and neuropeptide VF (NPVF) are octapeptides belonging to the RFamide family of peptides that have been implicated in a wide variety of physiological functions in the brain, including central autonomic and neuroendocrine regulation. The effects of these peptides are mediated via NPFF1 and NPFF2 receptors that are abundantly expressed in the rat brain, including the hypothalamic paraventricular nucleus (PVN), an autonomic nucleus critical for the secretion of neurohormones and the regulation of sympathetic outflow. In this study, we examined, using whole cell patch-clamp recordings in the brain slice, the effects of NPFF and NPVF on inhibitory GABAergic synaptic input to parvocellular PVN neurons. Under voltage-clamp conditions, NPFF and NPVF reversibly and in a concentration-dependent manner reduced the evoked bicuculline-sensitive inhibitory postsynaptic currents (IPSCs) in parvocellular PVN neurons by 25 and 31%, respectively. RF9, a potent and selective NPFF receptor antagonist, blocked NPFF-induced reduction of IPSCs. Recordings of miniature IPSCs in these neurons following NPFF and NPVF applications showed a reduction in frequency but not amplitude, indicating a presynaptic locus of action for these peptides. Under current-clamp conditions, NPVF and NPFF caused depolarization (6-9 mV) of neurons that persisted in the presence of TTX but was abolished in the presence of bicuculline. Collectively, these data provide evidence for a disinhibitory role of NPFF and NPVF in the hypothalamic PVN via an attenuation of GABAergic inhibitory input to parvocellular neurons of this nucleus and explain the central autonomic effects of NPFF.     

Effects of steroid hormones on the neuropil of the hypothalamic paraventricular nucleus of male chickens

Summary Testosterone and corticosterone, administered in doses of 0.5 mg/day for two weeks to three-day-old male chickens, induced alterations in the distributional pattern and in the number of synapses in the rostral neuropil of the hypothalamic paraventricular nucleus. This avian nucleus is a target area for both above-mentioned hormones and also one of the most important centers involved in the regulation of behavioral patterns related to reproduction. Testosterone increased the number of synapses in the rostral paraventricular nucleus, while corticosterone altered their distributional pattern causing an increase in type-B terminals; according to morphological criteria the latter are regarded to represent aminergic endings. Similar results were induced by simultaneous administration of both testosterone and corticosterone. Precocious sexual behavior was also provoked by double treatment.Preliminary results have been presented on the occasion of the 5th ENA meeting (Liège, Belgique, Sept. 1981) and the 1st Italian Meeting of Cell Biology (Rimini, Italy, April 1982)This study was supported by CNR bilateral grants (82.00215.04 & 83.00492.04), MPI 40% and European Training Program in Brain and Behaviour Researchs (twinning grant)     

Arginine vasopressin in hypothalamic paraventricular nucleus is transferred to the caudate nucleus to participate in pain modulation

Arginine vasopressin (AVP), which is synthesized and secreted in the hypothalamic paraventricular nucleus (PVN), is the most important bioactive substance in the pain modulation. Our pervious study had shown that AVP plays an important role in pain modulation in caudate nucleus (CdN). The experiment was designed to investigate the source of AVP in CdN by the nucleus push-pull perfusion and radioimmunoassay. The results showed that: (1) pain stimulation increased the AVP concentration in the CdN perfusion liquid, (2) PVN decreased the effect of pain stimulation which was stronger in both sides than in one side of PVN cauterization; and (3) L-glutamate sodium would excited the PVN neurons by the PVN microinjection that could increase the AVP concentration in the CdN perfusion liquid. The data suggested that AVP in the CdN might come from the PVN in the pain process, i.e., AVP in the PVN might be transferred to the CdN to participate in the pain modulation.     

Lesions of the hypothalamic paraventricular nucleus and norepinephrine turnover in rats

The effects of bilateral lesions of the hypothalamic paraventricular nuclei (PVN), of rats with a mean weight of 260 g body, on eating habits and body weight, as well as on sympathetic nervous system (SNS) activity in interscapular brown adipose tissue (IBAT) were investigated. In 59 of 131 Sprague-Dawley female rats, PVN lesions resulted in hyperphagia and obesity. Although lesions were considered successful when more than 50% of the PVN was destroyed histologically, such lesions were observed in 35.9% (47/131) of all lesioned rats and all of these 47 rats were obese. Therefore, in this study, these 47 rats which were confirmed histologically, were designated as "PVN-lesioned rats". Plasma insulin levels in these 47 PVN-lesioned ats were more than double those of the controls. However, no significant differences were observed between plasma glucose levels in PVN-lesioned and control groups. Norepinephrine turnover, a reliable indicator of SNS activity, in IBAT, heart and pancreas was similar in PVN-lesioned and sham-operated control animals, even under contrasting conditions of feeding (ad libitum and fasting) and temperature (22 degrees C and 4 degrees C). It is concluded that PVN lesions produce hyperphagia, obesity and hyperinsulinemia in rats with an average body weight of 260g without affecting the SNS activity in IBAT, heart or pancreas.     

Feeding inhibition by urocortin in the rat hypothalamic paraventricular nucleus

Ventricular administration of urocortin (UCN) inhibits feeding, but specific site(s) of UCN action are unknown. In the current studies we examined the effect of UCN in the hypothalamic paraventricular nucleus (PVN) on feeding. We tested UCN administered into the PVN in several paradigms: deprivation-induced, nocturnal, and neuropeptide Y (NPY)-induced feeding. We compared the effect of equimolar doses of UCN and corticotrophin releasing hormone (CRH) on NPY-induced and nocturnal feeding, determined whether UCN in the PVN produced a conditioned taste aversion (CTA) and induced changes in c-Fos immunoreactivity (c-Fos-ir) after UCN and NPY administration in the PVN. UCN in the PVN significantly decreased NPY and nocturnal and deprivation-induced feeding at doses of 1, 10, and 100 pmol, respectively. UCN anorectic effects lasted longer than those attributed to CRH. Ten and thirty picomoles UCN did not induce a CTA, whereas 100 pmol UCN produced a CTA. UCN (100 pmol) in the PVN neither increased c-Fos-ir in any brain region assayed nor altered c-Fos-ir patterns resulting from PVN NPY administration. These data suggest the hypothalamic PVN as a site of UCN action.     

Neuropeptide FF (NPFF) control of magnocellular neurosecretory cells of the rat hypothalamic paraventricular nucleus (PVN)

Neuropeptide FF (NPFF) is an octapeptide belonging to an extended family of RF amide peptides that have been implicated in a wide variety of physiological functions in the brain. NPFF and its receptors are abundantly expressed in the rat brain and spinal cord including the hypothalamic paraventricular nucleus (PVN), an autonomic nucleus critical for the secretion of neurohormones and the regulation of sympathetic outflow. In this study, we sought to examine the effects of NPFF on GABAergic inhibitory synaptic input to magnocellular neurosecretory cells (MNCs) of the PVN, which secrete the neurohormones, vasopressin and oxytocin from their terminals in the neurohypophysis. Whole cell patch clamp recordings under voltage clamp conditions were performed from PVN MNCs in the brain slice. Bicuculline-sensitive inhibitory postsynaptic currents (IPSCs) were isolated in the presence of glutamate receptor blockers. In tetrodotoxin, NPFF (5 microM) caused an increase in frequency, but not amplitude of miniature inhibitory postsynaptic currents (mIPSCs) in MNCs indicating a presynaptic locus of action for this peptide. Intracerebroventricular application of NPFF resulted in an activation of GABAergic neurons located adjacent to the PVN as revealed by immunohistochemistry for Fos protein and in situ hybridization for glutamic acid decarboxylase (GAD67) mRNA. Based on these observations we conclude that NPFF facilitates inhibitory input to MNCs of the PVN via GABAergic interneurons located in immediate vicinity of the nucleus. These findings provide a cellular and anatomic basis for the NPFF-induced inhibition of vasopressin release has been reported consequent to hypovolemia and hyperosmolar stimulation.     

Arginine vasopressin in hypothalamic paraventricular nucleus is transferred to the nucleus raphe magnus to participate in pain modulation

Hypothalamic paraventricular nucleus (PVN) is one of the main sources of arginine vasopressin (AVP) synthesis and secretion. AVP is the most important bioactive substance in PVN regulating pain process. Our pervious study has pointed that pain stimulation induced AVP increase in the nucleus raphe magnus (NRM), which plays a role in pain modulation. The present study was designed to investigate the source of AVP in the rat NRM during pain process using the methods of nucleus push–pull perfusion and radioimmunoassay. The results showed that pain stimulation increased the AVP concentration in the NRM perfusion liquid, PVN cauterization inhibited the role that pain stimulation induced the increase of AVP concentration in the NRM perfusion liquid, and PVN microinjection of l-glutamate sodium, which excited the PVN neurons, could increase the AVP concentration in the NRM perfusion liquid. The data suggested that AVP in the PVN might be transferred to the NRM to participate in pain modulation.     

Neuropeptide Y effect on food intake in broiler and layer chicks

Broiler chicks eat more food than layer chicks. In this study, we examined the involvement of orexigenic peptide neuropeptide Y (NPY) in the difference in food intake between broiler and layer chicks (Gallus gallus). First, we compared the hypothalamic mRNA levels of NPY and its receptors (Y1 and Y5 receptors) between these strains at 1, 2, 4, and 8 days of age. Daily food intake was significantly higher in broiler chicks than layer chicks after 2 days of age. However, the hypothalamic NPY mRNA level was significantly lower in broiler chicks than layer chicks except at 8 days of age. In addition, the mRNA levels of NPY receptors were also significantly lower in broiler chicks than layer chicks at 2 and 4 days of age (Y1 receptor) or 2 days of age (Y5 receptor). These results suggest that the differences in the expressions of hypothalamic NPY and its receptors do not cause the increase in food intake in broiler chicks. To compare the orexigenic effect of NPY between broiler and layer chicks, we next examined the effects of central administration of NPY on food intake in these strains. In both strains, central administration of NPY significantly increased food intake at 2, 4 and 8 days of age. All our findings demonstrated that the increase in food intake in broiler chicks is not accompanied with the over-expression of NPY or its receptor.     

Role of AgRP on Ghrelin-induced feeding in the hypothalamic paraventricular nucleus

MT II, agonist for MC3/4-Rs, inhibited Ghrelin's orexigenic effect in the paraventricular nucleus of the hypothalamus (PVN). To further investigate the role of the melanocortin system as mediator of ghrelin's orexigenic actions, we explored the involvement of AgRP in Ghrelin's orexigenic effect by testing the effect on food intake after their co-administration in the PVN, during the light and dark phases of feeding in rats. During both the phases of feeding, co-administration of Ghrelin with either AgRP 50 or AgRP 100 pmol into the PVN did not produce a synergistic effect on the food intake, suggesting that ghrelin induction of feeding occurs by recruiting Agrp as one of the obligatory mediators of its orexigenic effect.     

The neurosteroid allopregnanolone modulates oxytocin expression in the hypothalamic paraventricular nucleus

Virgin, ovariectomized rats exposed to 2 wk of sequential estradiol (E(2)) and progesterone (P) followed by P withdrawal have increased hypothalamic oxytocin (OT) mRNA and peptide levels relative to sham-treated animals. This increase is prevented if P is sustained. In the central nervous system, P is metabolized to the neurosteroid allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), which exerts effects by acting as a positive allosteric modulator of GABA(A) receptor/Cl(-)-channel complexes. In the present study, ovariectomized rats that received sequential E(2) and P for 2 wk followed by P withdrawal were administered allopregnanolone at the time of P withdrawal. Hypothalamic and plasma allopregnanolone concentrations, serum E(2) and P concentrations, and hypothalamic OT mRNA levels were measured at death. Steroid-induced increases in OT mRNA were attenuated in animals treated with allopregnanolone at the time of P withdrawal. The results suggest that allopregnanolone plays an important modulatory role in steroid-mediated increases in hypothalamic OT.     

Purinergic and glutamatergic interactions in the hypothalamic paraventricular nucleus modulate sympathetic outflow

P2X receptors are expressed on ventrolateral medulla projecting paraventricular nucleus (PVN) neurons. Here, we investigate the role of adenosine 5′-triphosphate (ATP) in modulating sympathetic nerve activity (SNA) at the level of the PVN. We used an in situ arterially perfused rat preparation to determine the effect of P2 receptor activation and the putative interaction between purinergic and glutamatergic neurotransmitter systems within the PVN on lumbar SNA (LSNA). Unilateral microinjection of ATP into the PVN induced a dose-related increase in the LSNA (1 nmol: 38 ± 6 %, 2.5 nmol: 72 ± 7 %, 5 nmol: 96 ± 13 %). This increase was significantly attenuated by blockade of P2 receptors (pyridoxalphosphate-6-azophenyl-20,40-disulphonic acid, PPADS) and glutamate receptors (kynurenic acid, KYN) or a combination of both. The increase in LSNA elicited by L-glutamate microinjection into the PVN was not affected by a previous injection of PPADS. Selective blockade of non-N-methyl-D-aspartate receptors (6-cyano-7-nitroquinoxaline-2,3-dione disodium salt, CNQX), but not N-methyl-D-aspartate receptors (NMDA) receptors (DL-2-amino-5-phosphonopentanoic acid, AP5), attenuated the ATP-induced sympathoexcitatory effects at the PVN level. Taken together, our data show that purinergic neurotransmission within the PVN is involved in the control of SNA via P2 receptor activation. Moreover, we show an interaction between P2 receptors and non-NMDA glutamate receptors in the PVN suggesting that these functional interactions might be important in the regulation of sympathetic outflow.     

Agouti-related protein in the hypothalamic paraventricular nucleus: effect on feeding

Agouti-related protein (Agrp) is an endogenous melanocortin-4 receptor antagonist implicated in the regulation of food intake. Effects of Agrp on feeding under varying conditions were investigated. Agrp (10 to 100 pmol) was injected into the hypothalamic paraventricular nucleus of satiated (a.m. and p.m. injections) and food-deprived rats, or was co-administered with 117 pmol Neuropeptide Y (NPY). Agrp significantly stimulated light-phase feeding by 24 h post-injection. However, Agrp stimulated dark-phase and deprivation-induced feeding by 4 and 2 h, respectively. Animals receiving NPY and Agrp consumed more than animals receiving either peptide alone, the effect remaining by 24 h.     

The renin-angiotensin-aldosterone system excites hypothalamic paraventricular nucleus neurons in heart failure

The paraventricular nucleus (PVN) of the hypothalamus has critical homeostatic functions, including the regulation of fluid balance and sympathetic drive. It has been suggested that altered activity of this nucleus contributes to the progression of congestive heart failure (HF). We hypothesized that forebrain influences of the renin-angiotensin-aldosterone system augment the activity of PVN neurons in HF. The rate of PVN neurons (n = 68) from rats with ischemia-induced HF was higher than that of PVN neurons (n = 42) from sham-operated controls (8.7 +/- 0.8 vs. 2.7 +/- 0.3 spikes/s, P < 0.001, HF vs. SHAM). Forebrain-directed intracarotid artery injections of the angiotensin type 1 receptor antagonist losartan, the angiotensin-converting enzyme inhibitor captopril, and the mineralocorticoid receptor antagonist spironolactone all significantly (P < 0.05) reduced PVN neuronal activity in HF rats. These findings demonstrate that the renin-angiotensin-aldosterone system drives PVN neuronal activity in HF, likely resulting in increased sympathetic drive and volume accumulation. This mechanism of neurohumoral excitation in HF is accessible to manipulation by blood-borne therapeutic agents.     

Neuropeptide Y receptor agonists: Multiple effects on spontaneous activity in the paraventricular hypothalamus

In vitro rat hypothalamic slices were used to examine the ability of neuropeptide Y (NPY), and the putative Y₁ and Y₂ receptor agonists [Pro³⁴]NPY, and [C²]NPY, to modify spontaneous single-neuron discharge in the paraventricular nucleus (PVN). NPY and [Pro³⁴]NPY, at high concentrations (1500 nM), decreased discharge rates. At intermediate concentrations (150 nM) these peptides produced multiple effects, including increases, decreases, and biphasic changes. At lower concentrations (0.15–15 nM), they typically increased discharge rates. In contrast, [C²]NPY, at all concentrations (1.5–1500 nM), predominantly increased discharge rates. Thus, these NPY sybtype agonists have multiple effects on discharge rate, which may be due to action on multiple NPY receptor subtypes.     

Reaction of specific cell populations of hypothalamic paraventricular nuclei of the rat to carbohydrate loading and fasting

The structural correlates of the cell responses in subnuclei of the hypothalamic paraventricular nuclei (PVN) in fasting and carbohydrate loaded adult male rats were studied using light microscopic morphometric methods. The data obtained revealed difference in responsiveness of the subnuclei studied to alternative shifts in the carbohydrate homeostasis: histophysiological features in five of ten cell-divisions, distinguished in the rat RVN, demonstrated their dependence on impaired carbohydrate homeostasis.     

Glucocorticoids regulate peptidyl-glycine alpha-amidating monooxygenase gene expression in the rat hypothalamic paraventricular nucleus

Peptidyl-glycine alpha-amidating monooxygenase (PAM) is a posttranslational processing enzyme which catalyzes the formation of biologically active alpha-amidated peptides. The two major neuropeptides involved in the regulation of ACTH secretion [CRF and arginine vasopressin (AVP)], synthesized in the parvocellular part of the hypothalamic paraventricular nucleus (PVN), are amidated, and their synthesis and/or release is negatively regulated by glucocorticoids. In this study, using in situ hybridization, we have shown that PAM mRNA is abundantly expressed in the hypothalamic paraventricular and supraoptic nucleus. Surgical adrenalectomy (ADX) induced increases in PAM, CRF, and AVP mRNA in the parvocellular part of the PVN, while corticosterone treatment normalized these values. PAM and AVP gene expression were not changed in the magnocellular part of the PVN or in the supraoptic nucleus. These observations suggest that in addition to stimulation of CRF and AVP synthesis, ADX induces an increase in PAM synthesis in the PVN and, thus, support the hypothesis of increased secretion of both CRF and AVP after ADX.     

Circannual rhythms of ground squirrels: role of the hypothalamic paraventricular nucleus

Female golden-mantled ground squirrels, maintained in an LD 14:10 photoperiod at 23 degrees C, sustained lesions of the paraventricular nucleus (PVN) or sham operations. Body weight and reproductive status were recorded weekly pre- and postoperatively. Bilateral lesions of the PVN did not eliminate, phase-shift, or otherwise disrupt the circannual rhythms of body mass or reproduction. Absolute levels of body weight were unaffected by PVN ablation. The PVN is not an essential component of the oscillatory system that generates circannual cycles in ground squirrels.