Cortical Regulation of Striatal Neuropeptide Y (NPY)-Containing Neurons in the Rat

This study examined the functional relationships established by nigral, cortical, and thalamic striatal afferent pathways with neuropeptide Y (NPY)-containing neurons in the rat rostral striatum by coupling selective deafferentation procedures and NPY immunohistochemistry. Previous experiments have shown that after unilateral 6-hydroxydopamine (6-OHDA)-induced degeneration of nigrostriatal dopaminergic neurons, the mean number of NPY-immunoreactive (Ir) neurons per frontal section was increased in the striatum ipsilateral to the lesion side and unaltered in the contralateral striatum. The present topographical analysis of the 6-OHDA lesion effects led us to state that the increase in NPY-Ir neuron density occurs in restricted ventral and medial zones of the ipsilateral striatum. Unilateral ablation of the frontoparietal cerebral cortex by thermocoagulation was moreover shown to elicit, 20 - 30 days later, a significant bilateral increase in the number of striatal NPY-Ir cells. The increase was more marked in the striatum ipsilateral to the hemidecortication where it was similar in amplitude to that induced by the 6-OHDA lesion. The topographical analysis of the cortical lesion effects also revealed an uneven striatal response, but, in contrast to that observed for the 6-OHDA lesion, changes were restricted to dorsolateral areas of the striatum in both brain sides, revealing an apparent complementarity of nigral dopaminergic and cortical influences over striatal NPY neuronal system. Combined unilateral nigral and cortical lesions surprisingly counteracted in a survival time dependent manner the effects of each lesion considered separately. In that condition topographical changes related to the 6-OHDA lesion totally disappeared and those related to the cortical lesion were attenuated but still present. These results suggest that expression of striatal dopamine - NPY interaction is dependent on corticostriatal transmission. Interestingly lesion of thalamic areas projecting to the striatum did not significantly modify the mean number of NPY-Ir neurons determined per section from the whole striatal surface, but selectively increased the NPY neuron density in the mediodorsal region of the striatum, suggesting that the striatal NPY-containing neuronal system is also influenced by thalamostriatal projections.     

Neuropeptide Y (NPY) and C-flanking peptide of NPY in the pineal gland of normal and ganglionectomized sheep.

The present immunohistochemical study describes the presence and distribution of nerve fibers containing neuropeptide Y (NPY), and C-Flanking Peptide Of NPY (CPON) in the pineal gland of the sheep. Nerve fibers were detected by using a series of antisera directed against NPY or against CPON. Many positive immunoreactive nerve fibers were identified in the pial capsule of the pineal, in connective septae and in the parenchyma between pinealocytes. The intraparenchymal fibers were particularly evident and created an extensive network throughout the gland. Nerve fibers immunoreactive for all the peptides were also observed in the posterior commissure and in the stria medullaris thalami. No NPY- or CPON-positive neurons were found in the pineal gland. In order to study the site of origin of NPY- and CPON-immunoreactive nerve fibers, the superior cervical ganglia were bilaterally removed in a series of animals. Sympathetic denervation was checked by using an antiserum against tyrosine hydroxylase (TH). Nearly all TH-immunoreactive elements disappeared in the pineal glands of animals sacrificed 15 days after surgery. Also the density of NPY- and CPON-immunoreactive nerve fibers decreased in the animals after the ganglionectomy. However, a number of nerve fibers still remained in the gland. These data indicate that some NPY- and CPON-immunoreactive nerve fibers of the sheep pineal gland derive from an extrasympathetic origin. The very dense innervation of the sheep pineal gland with nerve fibers containing NPY and CPON strongly indicates a functional role for this family of peptides in the pineal gland of this species.     

Neuropeptide Y (NPY) and vasopressin (AVP) in the hypothalamo-neurohypophysial axis of salt-loaded or Brattleboro rats

A close anatomical relationship between nerve terminals containing neuropeptide Y (NPY) and vasopressin (AVP) has been demonstrated in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). Furthermore, injections of NPY into the SON increased plasma concentrations of AVP in the rat. These data suggest a potential involvement of hypothalamic NPY in fluid homeostasis in the rat. Therefore, we have studied the effect of elevated plasma osmolality on the concentration of NPY and AVP in the hypothalamus and neurointermediate lobe (NIL) of the pituitary gland. Furthermore, we measured the concentration of NPY in the AVP-deficient Brattleboro rat, which suffers from diabetes insipidus and hyperosmolality. Salt-loading increased plasma osmolality and the concentration of AVP from 2.0 +/- 0.5 to 4.1 +/- 0.6 pg/ml after 7 days. The concentration of NPY in the NIL doubled after 7 days of salt-loading, from 7.9 +/- 0.6 ng/mg protein to 15.2 +/- 1.4 ng/mg protein, whereas AVP concentrations fell from 2285.7 +/- 210.9 ng/mg protein to 187.5 +/- 2.5 ng/mg protein. AVP concentrations in the ME increased transiently after 2 days of salt-loading and returned to control levels after 7 days. In contrast, NPY concentrations in the ME were unchanged at 2 days and were increased 61% after 7 days. NPY concentrations also were significantly elevated after 7 days of salt-loading in the preoptic area (POA) and mediobasal hypothalamus (MBH). The concentration of NPY in the NIL of the homozygous Brattleboro rat was 2-fold greater than in the heterozygous Brattleboro rat and 4-fold greater than in Sprague-Dawley rats used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuropeptide Y (NPY) and the central nervous system: distribution effects and possible relationship to neurological and psychiatric disorders

1. NPY is a 36 amino acid tyrosine-rich peptide. It is one of the most abundant and widely distributed neuropeptides known today within the central nervous system with particularly high concentrations in the hypothalamus and in several limbic regions. 2. NPY seems to coexist with other on neurotransmitters like somatostatin, galanin, GABA and the catecholamines noradrenaline and adrenaline in discrete brain regions. 3. NPY binding sites are widely distributed in the brain. However they do not always overlap with the distribution of NPY-like immunoreactivity. 4. NPY is suggested to be involved in a large number of neuroendocrine functions, stress responses, circadian rhythms, central autonomic functions, eating and drinking behaviour, and sexual and motor behaviour. 5. Psychotropic drugs and neurotoxins can alter the NPY concentrations in discrete brain regions. 6. It is possible that NPY is related to various neurological and psychiatric illnesses, like Huntington's chorea, Alzheimer's disease, Parkinson's disease, eating disorders, and major depressive illness.     

Ontogeny of a novel peptide, neuropeptide Y (NPY) in rat brain

Changes in the concentration of a newly discovered peptide, neuropeptide Y (NPY) have been determined in the developing rat brain using a recently developed radioimmunoassay and chromatographic analysis. NPY was present in the brain stem (14.8 ± 5.6 pmol/g) and diencephalon (12.1 ± 12.1 pmol/g) in the earliest embryos studied (14 days postconception), but appeared only on the 19th day postconception in the cerebral cortex. The concentrations of NPY showed a rapid postnatal rise in all regions examined. The finding of NPY early in the development of the embryonic rat brain and particularly in caudal regions has some similarities to the pattern of development of the catecholaminergic system.     

Neuropeptide Y (NPY) May Integrate Responses of Hypothalamic Feeding Systems and the Hypothalamo-Pituitary-Adrenal Axis

Neuropeptide Y (NPY) is a powerful stimulus to food intake in the rat. Exogenous NPY given into the third ventricle or into the paraventricular nucleus (PVN) of the hypothalamus stimulates both food consumption as well as the hypothalamus-pituitary-adrenal (HPA) axis. Presumably NPY activates the adrenocortical system through direct stimulation of CRF containing cells in the PVN. Food intake is also a major regulator of adrenocortical activation. Rhythms in HPA axis activity follow rhythms in food consumption, and rats that have been food deprived overnight have inhibited HPA axis responses to restraint stress and corticosteroid feedback the following morning. To investigate the interaction of NPY with both feeding and HPA axis activation three sets of experiments were performed: Animals fed ad lib were injected icv with NPY (2.5 μg) and allowed access to food or not post injection; animals were fasted overnight prior to NPY injection; finally, dose response experiments were performed to examine the relative sensitivities of feeding and HPA axis activation to exogenous NPY. Ad lib fed animals allowed access to food after NPY injection had slightly greater ACTH responses to NPY while glucocorticoid and insulin responses were not significantly different from ad lib fed animals not allowed access to food post injection. Animals allowed to eat post injection had significantly decreased food consumption the night following injection, however, total 24 h food consumption was not different between these animals and those given food 8 h post NPY injection. In overnight fasted animals NPY injections produced ACTH responses of equal magnitude to those in ad lib fed animals. Insulin responses to NPY were significantly elevated compared to CSF controls in overnight fasted animals. Dose response studies revealed that the adrenocortical system responds to icv NPY with at least as great sensitivity as feeding systems. NPY is discussed as a potential integrator of feeding and responsiveness in the HPA axis.     

Neuropeptide Y (NPY) mRNA in rat brain tissue: effects of decapitation and high-energy microwave irradiation on post mortem stability

mRNA recovery from brain tissue is affected by time-interval from death to inactivation of tissue, and may depend on sacrificial method. Sacrifice by high-energy microwave irradiation increases recovery of intact neuropeptides and proteins, and it has been suggested that this may be valid also for neuropeptide mRNAs. We therefore compared post-mortem NPY mRNA recovery following decapitation or microwave irradiation. Total RNA yield was significantly higher in tissue from decapitated rats. A decline in NPY mRNA (amol/mg tissue) over time, presumably reflecting degradation, was found in frontal cortex, hippocampus and striatum. Following high-energy microwaves, NPY message levels were higher in occipital cortex, lower in the hypothalamus, and unaltered in the other brain regions examined. These results show that post-mortem processes contribute to estimates of NPY mRNA levels obtained using standard methods for obtaining brain tissue from experimental animals and raise the question whether different pools of NPY mRNA might be differentially affected by post-mortem degradation. A general protective effect of high-energy radiation against degradation is not supported.     

Neuropeptide Y (NPY) in tumor growth and progression: Lessons learned from pediatric oncology

Neuropeptide Y (NPY) is a sympathetic neurotransmitter with pleiotropic actions, many of which are highly relevant to tumor biology. Consequently, the peptide has been implicated as a factor regulating the growth of a variety of tumors. Among them, two pediatric malignancies with high endogenous NPY synthesis and release – neuroblastoma and Ewing sarcoma – became excellent models to investigate the role of NPY in tumor growth and progression. The stimulatory effect on tumor cell proliferation, survival, and migration, as well as angiogenesis in these tumors, is mediated by two NPY receptors, Y2R and Y5R, which are expressed in either a constitutive or inducible manner. Of particular importance are interactions of the NPY system with the tumor microenvironment, as hypoxic conditions commonly occurring in solid tumors strongly activate the NPY/Y2R/Y5R axis. This activation is triggered by hypoxia-induced up-regulation of Y2R/Y5R expression and stimulation of dipeptidyl peptidase IV (DPPIV), which converts NPY to a selective Y2R/Y5R agonist, NPY_3–36. While previous studies focused mainly on the effects of NPY on tumor growth and vascularization, they also provided insight into the potential role of the peptide in tumor progression into a metastatic and chemoresistant phenotype. This review summarizes our current knowledge of the role of NPY in neuroblastoma and Ewing sarcoma and its interactions with the tumor microenvironment in the context of findings in other malignancies, as well as discusses future directions and potential clinical implications of these discoveries.     

Electron microscope immunocytochemical localization of neuropeptide Y (NPY) in the rat brain

In order to identify the neuronal structures as well as the intracellular organelles which contain the newly discovered brain peptide, neuropeptide Y (NPY), we have localized this peptide by immunoelectron microscopy in brain areas containing high levels of NPY. Ultrastructural studies using both the pre- and post-embedding immunoperoxidase techniques have shown that NPY-like immunoreactivity could be observed in neuronal cell bodies, dendrites and axonal processes. In terminals, the reaction product was associated with the large dense core vesicles. Only a small percentage of the positive terminals were seen making synaptic contacts. These results support the hypothesis that NPY can act as a neurotransmitter or neuromodulator.     

Neuropeptide Y (NPY) in the area of the hypothalamic paraventricular nucleus activates the pituitary-adrenocortical axis in the rat

Immunocytochemical studies have documented the presence of neuropeptide Y (NPY) in the hypothalamic paraventricular nucleus (PVN) which harbours a large number of neurones that contain corticotrophin-releasing factor (CRF). In this study the close morphological association between NPY fibres and CRF cell bodies in the PVN was confirmed. The localization of NPY terminals in the vicinity of CRF neurones forms a morphological basis for an action of NPY in the hypothalamic control of the pituitary-adrenocortical axis. We therefore microinjected NPY into the area of the PVN of both conscious, freely moving and anaesthetized rats and noted a powerful stimulatory effect on adrenocorticotropic hormone (ACTH) and corticosterone release as measured by radioimmunoassay. In experiments with conscious, freely moving rats, higher ACTH and corticosterone levels were detected following injection of NPY into the area of the PVN than following control injection (desamidated NPY). Intracerebroventricular injection of NPY produced a small, albeit significant, increase in circulating corticosterone levels as compared to control (saline-injected) rats. Anaesthetized rats responded to NPY (but not to saline) injected into the area of the PVN with elevated ACTH and corticosterone levels, while injection of NPY into the neocortex failed to affect the blood concentration of either ACTH or corticosterone. In conclusion, we have demonstrated an activating effect of NPY on the pituitary-adrenocortical axis both in conscious and anaesthetized rats which may reflect the anatomical relationship between NPY fibres and CRF neurones in the PVN.     

Characterization of 14 microsatellite loci for the pan-oriental narrow-mouthed toad,Microhyla ornata (Amphibia: microhylidae)

Conservation Genetics Resources - Fourteen polymorphic microsatellite loci were isolated in the pan-oriental narrow-mouthed toad, Microhyla ornata, which is one of the smallest anuran species. We...     

Neuropeptide Y (NPY) Y2 receptors mediate behaviour in two animal models of anxiety: evidence from Y2 receptor knockout mice

The behavioural phenotype of mice lacking neuropeptide Y (NPY) Y(2)-type receptors was assessed in two well documented animal models of anxiety: namely, the elevated plus maze and the open field. NPY Y(2)-/- mice made more entries into, and spent significantly more time on, the open arms of the elevated plus maze when compared to their wild-type Y(2)+/+ controls (P<0.001). This effect was not due to non-specific changes in locomotor activity as the number of closed arm entries did not differ between groups. In addition, NPY Y(2)-/- mice displayed increased preference for the central area of the open field when compared to Y(2)+/+ animals (P<0.01), whereas total entries did not differ between groups. This study suggests that NPY Y(2) receptors may play an inhibitory role and supports the hypothesis that Y(2) receptors are involved in the regulation of anxiety-like behaviours by NPY.     

Galanin-neuropeptide Y (NPY) interactions in central cardiovascular control: involvement of the NPY Y receptor subtype

The interactions between neuropeptide Y (NPY), specifically through NPY Y(1) and Y(2) receptor subtypes, and galanin [GAL(1-29)] have been analysed at the cardiovascular level. The cardiovascular effects of intracisternal coinjections of GAL(1-29) with NPY or NPY Y(1) or Y(2) agonists, as well as quantitative receptor autoradiography of the binding characteristics of NPY Y(1) and Y(2) receptor subtypes in the nucleus of the solitary tract (NTS), in the presence or absence of GAL(1-29), have been investigated. The effects of coinjections of GAL(1-29) and the NPY Y(1) agonist on the expression of c-FOS immunoreactivity in the NTS were also studied. The coinjection of NPY with GAL(1-29) induced a significant vasopressor and tachycardic action with a maximum 40% increase (P < 0.001). The coinjection of the NPY Y(1) agonist and GAL(1-29) induced a similar increase in mean arterial pressure and heart rate as did NPY plus GAL(1-29), actions that were not observed with the NPY Y(2) agonist plus GAL(1-29). GAL(1-29), 3 nm, significantly and substantially (by approximately 40%) decreased NPY Y(1) agonist binding in the NTS. This effect was significantly blocked (P < 0.01) in the presence of the specific galanin antagonist M35. The NPY Y(2) agonist binding was not modified in the presence of GAL(1-29). At the c-FOS level, the coinjection of NPY Y(1) and GAL(1-29) significantly reduced the c-FOS-immunoreactive response induced by either of the two peptides. The present findings suggest the existence of a modulatory antagonistic effect of GAL(1-29) mediated via galanin receptors on the NPY Y(1) receptor subtype and its signalling within the NTS.     

Neuropeptide Y attenuates NMDA-induced phase shifts in the SCN of NPY Y1 receptor knockout mice in vitro

Neuropeptide Y (NPY) blocks the effect of light on the mammalian circadian clock during the subjective night. The present study explores the role of the NPY Y1 receptor in this interaction. The effect of NPY when co-applied with NMDA, a glutamate agonist that can mimic the effect of light, was examined in NPY Y1-/- mice (background strain 129SVXBalb/c) using electrophysiology. Cells in the suprachiasmatic nucleus (SCN), the master circadian pacemaker, show a circadian rhythm in spontaneous firing rate that can be recorded in vitro. The results demonstrated that NPY attenuated the phase shifts to NMDA in both the Y1-/- mice and control mice, indicating that the Y1 receptor does not mediate the NPY blockade of photic-like phase shifts. The peak in frequency in the untreated control brain slices from Y1-/- mice was advanced by approximately 1 h as compared to the Y1+/+ mice. The Y1 receptor may contribute to a functional model of circadian rhythms, but apparently is not essential for the effects of NPY on photic phase shifts.     

Neuropeptide Y Y1 receptor mRNA in rodent brain: distribution and colocalization with melanocortin-4 receptor

The central neuropeptide Y (NPY) Y1 receptor (Y1-R) system has been implicated in feeding, endocrine, and autonomic regulation. In the present study, we systematically examined the brain distribution of Y1-R mRNA in rodents by using radioisotopic in situ hybridization histochemistry (ISHH) with a novel sensitive cRNA probe. Within the rat hypothalamus, Y1-R-specific hybridization was observed in the anteroventral periventricular, ventromedial preoptic, suprachiasmatic, paraventricular (PVH), dorsomedial, ventromedial, arcuate, and mamillary nuclei. In the rat, Y1-R mRNA expression was also seen in the subfornical organ, anterior hypothalamic area, dorsal hypothalamic area, and in the lateral hypothalamic area. In addition, Y1-R hybridization was evident in several extrahypothalamic forebrain and hindbrain sites involved in feeding and/or autonomic regulation in the rat. A similar distribution pattern of Y1-R mRNA was observed in the mouse brain. Moreover, by using a transgenic mouse line expressing green fluorescent protein under the control of the melanocortin-4 receptor (MC4-R) promoter, we observed Y1-R mRNA expression in MC4-R-positive cells in several brain sites such as the PVH and central nucleus of the amygdala. Additionally, dual-label ISHH demonstrated that hypophysiotropic PVH cells coexpress Y1-R and pro-thyrotropin-releasing hormone mRNAs in the rat. These observations are consistent with the proposed roles of the central NPY/Y1-R system in energy homeostasis.     

[Leu,Pro]Neuropeptide Y (NPY), but not NPY 20–36, produces discriminative stimulus effects similar to NPY and induces food intake

Rats were trained to discriminate between an intracerebroventricular injection of 1.15 nmol of Neuropeptide Y (NPY) and a sham injection. Rats rapidly learned to press the appropriate lever during training. NPY's discriminative stimulus effects were compared to those of saline, and 1.15–3.45 nmol [Leu³¹,Pro³⁴]NPY, a Y₁ receptor agonist and NPY 20–36, Y₂ receptor agonist. [Leu³¹,Pro³⁴]NPY resulted in NPY-appropriate responding, whereas saline and NPY 20–36 did not. [Leu³¹,Pro³⁴]NPY also increased food intake, but NPY 20–36 did not. This suggests that NPY's discriminative stimulus and orexigenic effects involve the Y₁, but not the Y₂, receptor.     

Neuropeptide Y: regional distribution chromatographic characterization and immunohistochemical demonstration in post-mortem human brain

Using a neuropeptide Y (NPY)-directed radioimmunoassay the post-mortem stability of NPY was assessed in both rat and human brain samples. The regional distribution of NPY-like immunoreactivity in human brain was determined. The NPY-like immunoreactivity in human brain separated on Sephadex G-50 columns and ¹⁸C reverse phase at the position expected for NPY. Immunohistochemical staining using the NPY-directed antiserum revealed a characteristic population of cortical and striatal neurons containing NPY-like immunoreactivity.     

Neuropeptide Y (NPY) delays the oestrogen-induced luteinizing hormone (LH) surge in the ovariectomized ewe: further evidence that NPY has a predominant negative effect on LH secretion in the ewe

Studies in rats suggest that neuropeptide Y (NPY) plays a stimulatory role in the generation of the preovulatory luteinizing hormone (LH) surge, via the Y1 receptor. We have investigated this issue using the oestradiol benzoate (EB)-treated ovariectomized (OVX) ewe which is a model for the preovulatory LH surge. A Y1 receptor antagonist (BIBO3304) was infused (25 microg/h) into the third cerebral ventricle (III-V) from 2 h before EB injection for 24 h, and had no effect on the ensuing LH surge. Using in situ hybridization, we then examined expression of NPY mRNA in the arcuate nucleus during the luteal, follicular and oestrous phases of the oestrous cycle, and found that levels were greatest during the luteal phase. Thus, reduced NPY synthesis might be an integral factor in the events leading to the cyclic preovulatory LH surge. This was tested by infusion of NPY (25 microg/h) into the III-V (as above). The NPY infusion delayed the LH surge until the infusion was ceased. High levels of NPY expression during the luteal phase of the oestrous cycle may be caused by progesterone. Thus, we determined whether NPY cells possess progesterone receptors (PR) and whether progesterone treatment up-regulates NPY mRNA expression in the arcuate nucleus. Immunohistochemistry for NPY and PR was performed in OVX, oestrogen-treated ewes, but no NPY cells of the arcuate nucleus were seen to colocalize PR. In situ hybridization for NPY was performed in OVX and OVX ewes treated with progesterone. There was no significant effect of progesterone treatment on NPY mRNA expression in the arcuate nucleus. We conclude that chronically elevated levels of NPY block the preovulatory surge of gonadotropin-releasing hormone/LH secretion in sheep, but high levels of NPY mRNA expression in the luteal phase of the oestrous cycle cannot be explained by an action of progesterone.     

Distribution of NPY Y5-like immunoreactivity in the rat brain

The pharmacology and brain mRNA distribution of the neuropeptide Y (NPY) rat Y5 (rY5) receptor has led to the hypothesis that this receptor might mediate the hypothalamic feeding response to NPY in addition to many other physiologic functions. However, through the use of autoradiographic techniques, only very low levels of Y5-like immunoreactive (Y5-ir) binding are detected in the rat brain. To localize the Y5 protein in the rat brain, polyclonal antibodies were raised to the carboxyl terminus of the rY5 receptor. The resulting antisera were affinity purified and characterized by specific binding to HEK293 cells that had been stably transfected with the rY5 receptor. Utilizing immunohistochemical techniques, we found a discrete pattern of Y5-ir in the rat brain. In initial studies, very low levels of Y5-ir were detected, and TSA amplification was required to visualize the staining. Areas with the highest levels of expression in clude the piriform cortex, supraoptic nucleus, and hippocampus. Areas with moderate levels of expression include the lateral septum, amygdala, arcuate nucleus, paraventricular hypothalamic nucleus, locus coeruleus, and cerebellum. With several exceptions, this pattern of distribution is consistent with earlier reports of rY5 mRNA and receptor protein expression.