Distribution and characterization of two putative endogenous opioid antagonist peptides in bovine brain

Neuropeptide FF (NPFF)-positive nerve cells of the human cerebral cortex and white matter in controls, selected neurodegenerative diseases, and schizophrenia

We quantified and determined for the first time the distribution pattern of the neuropeptide NPFF in the human cerebral cortex and subjacent white matter. To do so, we studied n = 9 cases without neurological disorders and n = 22 cases with neurodegenerative diseases, including sporadic amyotrophic lateral sclerosis (ALS, n = 8), Alzheimer's disease (AD, n = 8), Pick's disease (PiD, n = 3), and schizophrenia (n = 3). NPFF-immunopositive cells were located chiefly, but not exclusively, in the superficial white matter and constituted there a subpopulation of white matter interstitial cells (WMIC): Pyramidal-like and multipolar somata predominated in the gyral crowns, whereas bipolar and ovoid somata predominated in the cortex surrounding the sulci. Their sparsely ramified axons were unmyelinated and exhibited NPFF-positive bead-like varicosities. We found significantly fewer NPFF-immunopositive cells in the gray matter of the frontal, cingulate, and superior temporal gyri of both sporadic ALS and late-stage AD patients than in controls, and significantly fewer NPFF-positive cells in the subjacent as well as deep white matter of the frontal gyrus of these patients compared to controls. Notably, the number of NPFF-positive cells was also significantly lower in the hippocampal formation in AD compared to controls. In PiD, NPFF-positive cells were present in significantly lower numbers in the gray and white matter of the cingulate and frontal gyrii in comparison to controls. In schizophrenic patients, lower wNPFF cell counts in the neocortex were significant and global (cingulate, frontal, superior temporal gyrus, medial, and inferior gyri). The precise functions of NPFF-positive cells and their relationship to the superficial corticocortical white matter U-fibers are currently unknown. Here, NPFF immunohistochemistry and expression characterize a previously unrecognized population of cells in the human brain, thereby providing a new entry-point for investigating their physiological and pathophysiological roles.

The hypothalamic neuropeptide FF network is impaired in hypertensive patients

BACKGROUND

The human hypothalamus contains the neuropeptide FF (NPFF) neurochemical network. Animal experiments demonstrated that NPFF is implicated in the central cardiovascular regulation. We therefore studied expression of this peptide in the hypothalamus of individuals who suffered from essential hypertension (n = 8) and died suddenly due to acute myocardial infarction (AMI), and compared to that of healthy individuals (controls) (n = 6) who died abruptly due to mechanical trauma of the chest.

METHODS

The frozen right part of the hypothalamus was cut coronally into serial sections of 20 μm thickness, and each tenth section was stained immunohistochemically using antibody against NPFF. The central section through each hypothalamic nucleus was characterized by the highest intensity of NPFF immunostaining and thus was chosen for quantitative densitometry.

RESULTS

In hypertensive patients, the area occupied by NPFF immunostained neuronal elements in the central sections through the suprachiasmatic nucleus (SCh), paraventricular hypothalamic nucleus (Pa), bed nucleus of the stria terminalis (BST), perinuclear zone (PNZ) of the supraoptic nucleus (SON), dorso- (DMH), ventromedial (VMH) nuclei, and perifornical nucleus (PeF) was dramatically decreased compared to controls, ranging about six times less in the VMH to 15 times less in the central part of the BST (BSTC). The NPFF innervation of both nonstained neuronal profiles and microvasculature was extremely poor in hypertensive patients compared to control.

CONCLUSIONS

The decreased NPFF expression in the hypothalamus of hypertensive patients might be a cause of impairment of its interaction with other neurochemical systems, and thereby might be involved in the pathogenesis of the disease.

RFamide Peptides in Early Vertebrate Development

RFamides (RFa) are neuropeptides involved in many different physiological processes in vertebrates, such as reproductive behavior, pubertal activation of the reproductive endocrine axis, control of feeding behavior, and pain modulation. As research has focused mostly on their role in adult vertebrates, the possible roles of these peptides during development are poorly understood. However, the few studies that exist show that RFa are expressed early in development in different vertebrate classes, perhaps mostly associated with the central nervous system. Interestingly, the related peptide family of FMRFa has been shown to be important for brain development in invertebrates. In a teleost, the Japanese medaka, knockdown of genes in the Kiss system indicates that Kiss ligands and receptors are vital for brain development, but few other functional studies exist. Here, we review the literature of RFa in early vertebrate development, including the possible functional roles these peptides may play.

The recent progress in research on effects of anesthetics and analgesics on G protein-coupled receptors

The exact mechanisms of action behind anesthetics and analgesics are still unclear. Much attention was focused on ion channels in the central nervous system as targets for anesthetics and analgesics in the 1980s. During the 1990s, major advances were made in our understanding of the physiology and pharmacology of G protein coupled receptor (GPCR) signaling. Thus, several lines of studies have shown that G protein coupled receptors (GPCRs) are one of the targets for anesthetics and analgesics and especially, that some of them inhibit the functions of GPCRs, i.e,, muscarinic receptors and substance P receptors. However, these studies had been focused on only G(q) coupled receptors. There has been little work on G(s)- and G(i)-coupled receptors. In the last decade, a new assay system, using chimera G(i/o)-coupled receptor fused to Gq(i5), has been established and the effects of anesthetics and analgesics on the function of G(i)-coupled receptors is now more easily studied. This review highlights the recent progress of the studies regarding the effects of anesthetics and analgesics on GPCRs.

The anorectic effect of neuropeptide AF is associated with satiety-related hypothalamic nuclei

Neuropeptide AF (NPAF), a member of the RFamide family, is encoded by the same gene as neuropeptide FF (NPFF), which causes short-term anorexia. However, reports on the role of NPAF on appetite-related process are lacking. Thus, i.c.v. injections of 4.0, 8.0 and 16.0 nmol NPAF were administered to chicks to observe its effect on food and water intake. Chicks treated with 8.0 and 16.0 nmol i.c.v. NPAF decreased both their food and water intake. Additionally, all doses of NPAF injected caused a similar reduction in whole blood glucose concentration 180 min after injection. In a second experiment, chicks that received i.c.v. NPAF had an increased number of c-Fos immunoreactive cells in the dorsomedial, paraventricular (magnocellular and parvicellular parts) and ventromedial nuclei. The arcuate nucleus and lateral hypothalamic area were not affected. In a third experiment, NPAF-treated chicks exhibited fewer feeding pecks and spent less time perching, whereas they spent an increased time in deep rest. Other behaviours, including exploratory pecking, escape attempts, defecations, distance moved, and time spent standing, sitting and preening, were not affected by NPAF injection. We conclude that NPAF causes anorectic effects that are associated with the hypothalamus.

Pharmacological aspects of the effects of tramadol on G-protein coupled receptors

Tramadol is an analgesic that is used worldwide, but its mechanisms of action have not been elucidated. It has been speculated that tramadol acts primarily through the activation of micro-opioid receptors and the inhibition of monoamine reuptake. The majority of studies to date have focused on ion channels in the central nervous system as targets of anesthetics and analgesics. During the past decade, major advances have been made in our understanding of the physiology and pharmacology of G-protein coupled receptor (GPCR) signaling. Several studies have shown that GPCRs and ion channels are targets for analgesics and anesthetics. In particular, tramadol has been shown to affect GPCRs, including muscarinic acetylcholine receptors and 5-hydroxytryptamine receptors. Here, the effects of tramadol on monoamine transporters, GPCRs, and ion channels are presented, and recent research on the pharmacology of tramadol is discussed.

Neuropeptide FF distribution in the human and rat forebrain: a comparative immunohistochemical study

Neuropeptide FF (NPFF) is an octapeptide implicated in a variety of physiological functions, including nociception, cardiovascular responses, and neuroendocrine regulation. The NPFF gene and its mRNA are highly conserved across species. A comparative study of NPFF distribution in the human and rat forebrain was carried out by using single NPFF and double NPFF + vasopressin (VP) immunohistochemistry. NPFF is extensively localized within neurochemical circuits of human and rat forebrain. Semiquantitative analysis revealed that the densities of NPFF cells and fibers in many forebrain nuclei in the human correlate well with those observed for the same structures in the rat. High numbers of NPFF positive neurons in the dorsomedial hypothalamic nucleus and a dense plexus of NPFF fibers surrounding the fornix within the bed nucleus of the stria terminalis were identified in the human and rat forebrain. Within the hypothalamus of both species, dense NPFF innervation was observed in the perinuclear zone of the supraoptic nucleus (SO) just dorsolateral to the VP-positive neurons. Extensive NPFF innervation of ventricular ependyma and brain microvasculature were common for both species. At the same time, obvious differences in NPFF localization between the two species were also apparent. For example, in contrast to the rat SO, no NPFF- or NPFF- + VP-immunostained cells were observed in the human SO. Knowledge of NPFF neuroanatomical localization in the human brain and the relationship of these observations to those in the rat brain may provide insight into the role of this peptide in central cardiovascular and neuroendocrine regulation.

Modulatory roles of the NPFF system in pain mechanisms at the spinal level

The possible roles of the NPFF system in pain processing are summarized from the viewpoints of (1) biological activities of NPFF, (2) anatomical distribution of NPFF and its receptor(s) and (3) the regulation of NPFF and receptor(s) in animal models of pain. NPFF and NPFF analogues were found to have analgesic, pronociceptive and morphine modulating activities. Since the isolation of NPFF, several other RF-NH2 peptides have been identified and some of them were found to have nociceptive or morphine modulating activity. Depending on the pharmacological doses and locations of administration, NPFF may exhibit the biological activities of other structurally related RF-NH2 peptides thus complicating NPFF bioactivity studies and their interpretation. Acid sensing ion channels were found to respond to RF-NH2 peptides including NPFF, raising the possibility that interaction of NPFF and acid sensing ion channels can modulate nociceptive activity. NPFF and NPFF receptor mRNAs are highly expressed and localized in the superficial layers of the dorsal cord, the two genes are also in dorsal root ganglia though at much lower level. The spinal NPFF system is up-regulated by peripheral inflammation in the rat. Furthermore, immunohistochemically, NPFF receptor 2-protein was demonstrated to be increased in the primary afferents in the spinal cord of rats with peripheral inflammation. Regulation and localization of spinal NPFF systems, taken together with the analgesic bioactivity of intrathecally administered NPFF, strongly suggest involvement of spinal NPFF system in pain processing.

Distribution of neuropeptide FF-like immunoreactive structures in the lamprey central nervous system and its relation to catecholaminergic neuronal structures

The neuropeptide FF (NPFF) is an octapeptide of the RFamide-related peptides (FaRPs) that was primarily isolated from the bovine brain. Its distribution in the CNS has been reported in several mammalian species, as well as in some amphibians. Therefore, in order to gain insight in the evolution on the expression pattern of this neuropeptide in vertebrates, we carried out an immunohistochemical study in the sea lamprey, Petromyzon marinus. The distribution of NPFF-like-immunoreactive (NPFF-ir) structures in the lamprey brain is, in general, comparable to that previously described in other vertebrate species. In lamprey, most of the NPFF-ir cells were found in the hypothalamus, particularly in two large populations, the bed nucleus of the tract of the postoptic commissure and the tuberomammillary area. Numerous NPFF-ir cells were also observed in the rostral rhombencephalon, including a population in the dorsal isthmic gray and the reticular formation. Additional labeled neurons were found inside the preoptic region, the parapineal vesicle, the periventricular mesencephalic tegmentum, the descending trigeminal tract, the nucleus of the solitary tract, as well as in the gray matter of the spinal cord. The NPFF-ir fibers were widely distributed in the brain and the spinal cord, being, in general, more concentrated throughout the basal plate. The presence of NPFF-ir fibers in the lamprey neurohypophysis suggests that the involvement of NPFF-like substances in the hypothalamo-hypophyseal system had emerged early during evolution.

Spatiotemporal sequence of appearance of NPFF-immunoreactive structures in the developing central nervous system of Xenopus laevis

Neuropeptide FF-like immunoreactive (NPFFir) cells and fibers were analyzed through development of Xenopus laevis. The first NPFFir cells appeared in the embryonic hypothalamus, which projected to the intermediate lobe of the hypophysis, the brainstem and spinal cord. Slightly later, scattered NPFFir cells were present in the olfactory bulbs and ventral telencephalon. In the caudal medulla, NPFFir cells were observed in the nucleus of the solitary tract only at embryonic and early larval stages. Abundant NPFFir cells and fibers were demonstrated in the spinal cord. The sequence of appearance observed in Xenopus shares many developmental features with mammals although notable differences were observed in the telencephalon and hypothalamus. In general, NPFF immunoreactivity developed earlier in amphibians than in mammals.

Distribution of Neuropeptide FF-Like Immunoreactivity in the Brain of Dermophis mexicanus (Amphibia; Gymnophiona): Comparison with FMRFamide Immunoreactivity

Neuropeptide FF (NPFF) is an FMRFamide-related peptide widely distributed in the mammalian brain. NPFF immunohistochemistry labeled cell bodies in a few locations and dense fiber networks throughout the brain. Recently, the distribution of NPFF immunoreactive (NPFF-ir) cells and fibers in the brain of anuran and urodele amphibians was studied and, as in mammals, significant species differences were noted. To further assess general and derived features of the NPFF-containing neuron system in amphibians, we have investigated the distribution of NPFF-ir cell bodies and fibers in the brain of the gymnophionan Dermophis mexicanus by means of an antiserum against bovine NPFF. This distribution was compared to that of FMRFamide immunoreactivity. Major traits shared with anurans and urodeles were the abundant fiber labeling in the ventral telencephalon, hypothalamus, isthmus, ventrolateral medulla and dorsal spinal cord. In addition, in the three amphibian orders the majority of the NPFF-ir cells were located in the preoptic-hypothalamic region. However, distinct particular features were present in the gymnophionan such as the lack of NPFF-ir cells in the telencephalon, brainstem and spinal cord and the absence of NPFF-ir fibers in the hypophysis and the olfactory bulbs. This pattern was distinct from that observed for FMRFamide distribution. Striking differences were noted in the pallium, caudal hypothalamus and midbrain tegmentum where FMRFamide-containing cells were localized. The present results in Dermophis support the idea that data from gymnophionans must be included when stating the amphibian condition of a given system because important variations are obvious when gymnophionans are compared with anurans and urodeles.

Distribution of neuropeptide FF-like immunoreactivity in the brain of the lizardGekko gecko and its relation to catecholaminergic structures

The present study provides a detailed description of the distribution of neuropeptide FF (NPFF)-like immunoreactivity in the brain of the lizard Gekko gecko. NPFF is found to be involved in nociception, cardiovascular regulation, and endocrine function. Because of its known relationship with catecholamines in mammals, double staining with tyrosine hydroxylase (TH) antibodies was used to corroborate this for reptiles. The present study revealed that NPFF-like-immunoreactive (NPFF-ir) cells and fibers were widely distributed throughout the brain. Major NPFF-ir cell groups were observed in the diagonal band nucleus of Broca, hypothalamus, and dorsal horn of the spinal cord. Additional cells were found in the anterior olfactory nucleus, lateral and dorsal cortices, dorsolateral septum, and diencephalic intergeniculate leaflet formation. Dense plexuses of NPFF-ir fibers were identified in the diagonal band nucleus of Broca, septum, preoptic and hypothalamic areas, isthmic region, ventrolateral tegmentum, solitary tract nucleus, and dorsolateral funiculus of the spinal cord. Extensive fiber staining also occurred in the nucleus accumbens and the midbrain tectum. Although an intimate relationship between NPFF-ir and TH-ir structures was obvious at many places in the brain, colocalization of these two substances was not observed. In conclusion, the distribution of NPFF in the brain of Gekko shares more features with anamniotes in terms of number of cell groups, more elaborate networks of fibers, and lack of colocalization with catecholamines than with mammals, suggesting a decrease in the distribution of this peptide in the latter vertebrate group.

Neuropeptide FF receptor 2 (NPFF2) is localized to pain-processing regions in the primate spinal cord and the lower level of the medulla oblongata

Studies have suggested that NPFF-like peptides and their receptors play important roles in physiological and pathological conditions. Here, we show, using multiple expression modalities, that the type 2 NPFF receptor (hNPFF2) is expressed in regions of the primate spinal cord and brainstem mediating pain sensation. In situ hybridization using an NPFF2 riboprobe, and immunohistochemistry using a novel NPFF2 antibody, demonstrated strong NPFF2 expression in the superficial layer of the dorsal horn, and in the spinal trigeminal nucleus of the brainstem of the African green monkey (AGM). In addition, autoradiography using a radiolabeled NPFF analog ([125I]1DMe) revealed dense binding signal in the superficial layer of the dorsal horn in the spinal cord. The distribution pattern of hNPFF2 in the AGM spinal cord and the lower level of the brainstem are consistent with a hypothesized potential role for NPFF peptides in modulation of sensory input, opioid analgesia and morphine tolerance through spinal and supraspinal mechanisms.

Comparative analysis of neuropeptide FF-like immunoreactivity in the brain of anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians

The neuropeptide FF (NPFF) is a member of the RFamide related peptides (FaRPs) that share the dipeptide Arg-Phe-NH2 at their C-terminal. It was originally isolated from bovine brain and its wide distribution has been demonstrated in the brain of several mammalian species. By means of an NPFF antiserum we have investigated the distribution pattern of NPFF-like immunoreactive cells and fibers in the brain of anuran and urodele amphibians. In both amphibian orders, the most conspicuous labeled cell population was found in the preoptic area and hypothalamus, primarily in the suprachiasmatic region. Numerous fibers reached the median eminence and the intermediate lobe of the hypophysis. Only in the anuran brain cells were observed in the pallium and septum. In the urodele, cells and fibers of the terminal nerve were distinctly labeled. Cell bodies were widely distributed in the reticular formation of anurans and, in both orders, a large cell population was found in the nucleus of the solitary tract and the spinal cord. Comparable fiber distribution between both orders exists in which the basal telencephalon (mainly the amygdaloid complex), the hypothalamus and the spinal cord are the regions most richly innervated. The distribution pattern of NPFF-like immunorective elements in the brain of amphibians, which only partly overlaps with those of other FaRPs, supports the notion that a NPFF-like peptide exists in amphibians. On the basis of its localization, this peptide may act as a hypophysiotropic neurohormone and be involved in background adaptation. Its wide distribution in similar zones of the brain in amphibians and mammals suggests that functional roles of this peptide have been conserved in vertebrate evolution.

Analysis of human neuropeptide FF gene expression

As an initial step to study the function of the gene encoding the human neuropeptide FF (NPFF), we cloned a 4.7-kb sequence from the promoter region. Primer extension and 5'-rapid amplification of cDNA ends revealed multiple transcription initiation sites. Northern blot analysis of the mRNA expression revealed a specific signal only in poly(A) + RNA from medulla and spinal cord. Chimeric luciferase reporter gene constructs were transiently transfected in A549, U-251 MG, SK-N-SH, SK-N-AS and PC12 cells. The promoter activity was directly comparable with the level of endogenous NPFF mRNA as determined by real-time quantitative RT-PCR. The highest promoter activity was measured when a region from - 552 to - 830 bp of the 5'-flanking region was fused to the constructs, and a potential silencer element was localized between nucleotides -220 and -551. A twofold increase in NPFF mRNA was observed after 72 h of nerve growth factor stimulation of PC12 cells and the region between - 61 and - 214 bp of the 5'-flanking region was found to be responsive to this stimulation. We postulate that control of human NPFF gene expression is the result of both positive and negative regulatory elements and the use of multiple transcription initiation sites.

New central projections of neuropeptide FF: colateral branching pathways in the brainstem and hypothalamus in the rat

Neuropeptide FF (NPFF), a morphine modulatory peptide, has been identified within discrete autonomic regions in the brainstem and hypothalamus. Triple fluorescence labelling was employed to identify collateral branching projections of NPFF neurons located within the nucleus tractus solitarius (NTS) and in the region of the hypothalamus between the dorsomedial and ventromedial hypothalamus. Injections of two retrograde tracers, rhodamine- and fluorescein-labelled latex microspheres into the pontine parabrachial nucleus (PBN) and the ventrolateral medulla resulted in labelling of NPFF neurons in the NTS that contained one (double-labelled) or both (triple-labelled) tracers. Within the NTS, most double- and triple-labelled NPFF neurons were localized at the level of the area postrema or just rostral to it and within the medial and dorsomedial subdivisions of the nucleus. Injections of tracers into the PBN and hypothalamic paraventricular nucleus revealed double- and triple-labelled NPFF neurons, a majority of which were located in a zone between the dorsomedial and ventromedial hypothalamus. These results indicate that NPFF neurons in the brainstem and hypothalamus may simultaneously transmit signals to their target nuclei in the brainstem and forebrain. This coordinated signalling may lead to synchronized responses of NPFF target sites and provide insights into the role of this peptide in cardiovascular and nociceptive responses.

Neuropeptide FF and FMRFamide potentiate acid-evoked currents from sensory neurons and proton-gated DEG/ENaC channels

Acidosis is associated with inflammation and ischemia and activates cation channels in sensory neurons. Inflammation also induces expression of FMRFamidelike neuropeptides, which modulate pain. We found that neuropeptide FF (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe amide) and FMRFamide (Phe-Met-Arg-Phe amide) generated no current on their own but potentiated H+-gated currents from cultured sensory neurons and heterologously expressed ASIC and DRASIC channels. The neuropeptides slowed inactivation and induced sustained currents during acidification. The effects were specific; different channels showed distinct responses to the various peptides. These results suggest that acid-sensing ion channels may integrate multiple extracellular signals to modify sensory perception.

Unilateral joint inflammation induces bilateral and time-dependent changes in neuropeptide FF binding in the superficial dorsal horn of the rat spinal cord: implication of supraspinal descending systems

Using quantitative autoradiography, the effects of acute and chronic inflammation on specific 125I-1DMethyl-FLFQPQRFamide binding were investigated in the rat spinal cord dorsal horn superficial layers, at 6 and 24 h and 2, 4, 6 and 12 weeks after induction of monoarthritis produced by injection of killed Mycobacterium butyricum suspended in Freund adjuvant in one tibio-tarsal joint. Six hours after monoarthritis induction, no modification in specific 125I-1DMethyl-FLFQPQRFamide binding was observed, whereas a significant bilateral increase occurred after 24 h and 2 weeks in L4/L5 dorsal horns, with a return to control values at 4, 6 and 12 weeks. Specific 125I-1DMethyl-FLFQPQRFamide binding was also investigated 24 h after monoarthritis induction in rats submitted 4 days before the induction to spinal cord lesions at the thoracic level (T9-T10). Hemisection of the spinal cord contralateral to the affected ankle prevented the transient bilateral increase in specific 125I-1DMethyl-FLFQPQRFamide binding, whereas total spinal cord section induced a significant bilateral decrease. All of these modifications were restricted to the spinal segments receiving afferent input from the arthritic ankle (L4/L5); no modifications were found at the levels L1 or C6-C8. These data suggest that FLFQPQRFamide is involved in spinal nociceptive processing during sustained peripheral nociceptor activation. The effects of spinal cord lesions in monoarthritic rats indicate that the modifications seen in the FLFQPQRFamide system activity, during sustained peripheral inflammation, depend on afferent fiber activation as well as on supraspinal controls.

Evidence for neuropeptide FF (FLFQRFamide) in rat dorsal root ganglia

By using specific antibodies and radioimmunological and immunohistochemical methods, we here show that neuropeptide FF (NPFF) occurs in cervical and lumbar dorsal root ganglia cells. Levels in the ganglia were low because they were detectable only after colchicine treatment or after unilateral dorsal rhizotomy. Similar high-performance liquid chromatography profiles were obtained from dorsal root ganglia and spinal cord extracts, indicating that the NPFF-immunoreactivity in the dorsal root ganglia represented similar molecular forms to that in the spinal cord. Immunocytochemistry localized NPFF-immunoreactivity in small- and medium-sized cells. These data suggest that low levels of NPFF present in fine diameter primary afferent fibers could be involved in the treatment of nociceptive information from fore- or hindlimb.

Neuropeptide FF in the rat adrenal gland: presence, distribution and pharmacological effects

Neuropeptide FF (NPFF, FLFQPQRFamide) is an FMRFamide-like octapeptide exhibiting antiopiate activity. The presence of both NPFF-immunoreactivity (NPFF-IR) and NPFF-specific receptors has been described in the mammalian central nervous system (CNS). The peripheral effects of NPFF indicate that NPFF-IR material is present outside the CNS. Biochemical and immunohistochemical methods enabled us to determine the presence and distribution of NPFF-IR in the rat adrenal gland. The amount of NPFF-IR material in whole gland was estimated by radioimmunoassay to be 19.00 +/- 4.00 fmol/gland. High performance liquid chromatography analysis of adrenal extracts revealed a single molecular form which coeluted with authentic NPFF. Demedullation decreased adrenal NPFF-IR content, indicating that NPFF-IR was present in both cortex and medulla. Light microscopy revealed NPFF-IR in beaded fibers confined in the outer part of the cortex and in medullary cells. Double-labeling with antityrosine-hydroxylase and anti-NPFF antibodies showed NPFF-IR in cortical catecholaminergic postganglionic fibers restricted to the subcapsular and glomerulosa zonae. NPFF-IR was also located in medullary chromaffin cells and in rays and islets of chromaffin cells dispersed throughout the cortex. Insulin-induced hypoglycemia did not alter NPFF-IR content. Denervation lowered adrenal NPFF-IR content. These data indicate that this peptide is present in nerve fibers of extrinsic origin. In vitro approaches using adrenal slices have shown that NPFF inhibited aldosterone release in a dose-dependent manner. Taken together, these data suggest that NPFF may participate in the control of aldosterone production and adrenal blood supply.

Antiserum against neuropeptide FF augments vasopressin release in conscious rats

We previously reported that centrally administered neuropeptide FF (NPFF) inhibited arginine vasopressin (AVP) release. In this study, immunoneutralization of central NPFF was performed to evaluate the role of endogenous NPFF in the regulation of AVP release. Intracerebroventricular (ICV) injection of antiserum against NPFF (Anti-NPFF) significantly augmented the plasma AVP increase induced by hyperosmolality [intraperitoneal injection of hypertonic saline (600 mOsm/kg, 2% BW)] at 60 min after ICV injection compared with normal rabbit serum (NRS) (NRS: 4.20+/-0.30 pg/ml, Anti-NPFF: 5.83+/-0.46 pg/ml, p < 0.01). Anti-NPFF did not cause significant change in plasma osmolality, plasma volume or arterial blood pressure. This evidence indicates that endogenous NPFF might be physiologically involved in osmoregulation of the plasma AVP level through its inhibitory action.

Regulation of mu binding sites after chronic administration of antibodies directed against specific anti-opiate peptides

There is some indication that anti-opiate peptides (AOP) modulate opioid receptor systems by altering mu-receptor density. To further characterize this phenomenon, we investigated the effects of continuous infusion of anti-AOP IgG on mu binding sites in the brains of rats. Specifically, male Sprague-Dawley rats received intracerebroventricular (i.c.v.) infusions for 13 days of either control (rabbit) IgG or test IgGs: anti-dynorphin A IgG, anti-dynorphin A1-8 IgG, anti-alpha-MSH IgG, or the monoclonal anti-NPFF IgG. Administration of anti-NPFF IgG or the anti-dynorphin1-8 IgG significantly increased mu labeling by 40-70% in several brain regions at the caudate level. Contrary to these findings, anti-alpha-MSH IgG decreased (19-32%) [125I]-DAMGO labeling in several thalamic nuclei. The results suggest that the density of mu-opioid receptors is regulated in part by anti-opiate peptides in the extracellular fluid of the brain.

A human gene encoding morphine modulating peptides related to NPFF and FMRFamide

FMRFamide-related peptides have been isolated from both invertebrates and vertebrates and exhibit a wide range of biological effects in rats. We show here that in humans 2 FMRFamide-related peptides are encoded by a single gene expressed as a spliced mRNA. The larger predicted peptide (AGEGLNSQFWSLAAPQRFamide) differs from the peptide isolated from bovines (AGEGLSSPFWSLAAPQRFamide) by the substitutions of 2 amino acids. The shorter predicted peptide (NPSF, SQAFLFQPQRFamide) is 3 amino acids longer than the bovine 8 amino-acid NPFF (FLFQPQRFamide) or the human NPFF peptide isolated from serum [5], suggesting that the encoded protein is subject to cleavage by a tripeptidyl peptidase or by a novel processing mechanism. On rat spinal cord, the larger peptide is indistinguishable in activity from the equivalent bovine peptide whereas the smaller extended peptide is inactive.

Light-modulated release of RFamide-like neuropeptides from nervus terminalis axon terminals in the retina of goldfish

The nervus terminalis of teleosts, a cranial nerve anatomically associated with the olfactory system, projects to visual system targets including retina and optic tectum. It is known to contain gonadotropin-releasing hormone and RFamide-like peptides, but its function remains unknown. We have probed nervus terminalis function in goldfish by measuring peptide content in retina and tectum with a radioimmunoassay for A18Famide (neuropeptide AF; bovine morphine-modulating peptide). We found that retinal peptide content increased in the dark and decreased in the light, whereas tectal peptide content decreased in the dark and increased in the light. In addition, RFamide-like peptide content in the retina was transiently decreased by severing both olfactory tracts, increased in light-adapted eyes treated with a GABAergic agonist (isoguvacine), and decreased in dark-adapted eyes treated with GABAergic antagonists (bicuculline and picrotoxin). We also found that RFamide-like peptide release could be induced in dark-adapted isolated-superfused retinas by exposure to light or a high concentration (102.5 mM) of potassium ions. We interpret the increase and decrease in peptide content as reflecting a decrease and increase, respectively, in rate of peptide release. We propose that the release and accumulation of RFamide-like peptides in axon terminals of nervus terminalis processes in the retina are modulated primarily by neurons intrinsic to the retina and regulated by light. Peptide release appears to be inhibited tonically in the dark by GABA acting through GABAA receptors; light facilitates peptide release by disinhibition due to a reduction in GABA release. In addition, we propose that electrical signals originating outside the retina can override these intrinsic release-modulating influences.

Migration of GnRH-immunoreactive neurons from the olfactory placode to the brain: a study using avian embryonic chimeras

Previous studies suggest that gonadotropin-releasing hormone (GnRH) neurons appear in the olfactory placode and subsequently migrate into the brain during embryonic development. The aim of the present study was to obtain direct evidence for migration of GnRH neurons from the olfactory placode into the brain. Olfactory placodes from quail embryos were transplanted isotopically and isochronically, to replace the unilaterally ablated olfactory placodes of chick embryos. The chimeric embryos were allowed to develop for several days until they reached the embryonic stages when GnRH neurons are seen in the brain in normal embryos. Quail olfactory epithelia were formed in the host chick embryos. Quail olfactory nerves were also formed and reached the olfactory bulb or primordial olfactory bulb. GnRH-immunoreactive cells of quail origin revealed by a triple staining method were observed in the quail olfactory epithelium, quail olfactory nerve, chick olfactory bulb, and septo-preoptic area. These results indicate that GnRH neurons originate in the olfactory placode and migrate into the telencephalon including the septo-preoptic area. A migratory route of GnRH neurons was well documented by the use of a quail neuron-specific antibody, QN. The migratory route in the brain is discussed with special reference to the terminal nerve. A GnRH-immunoreactive neuronal group of chick origin appeared in the diencephalon of chimeric embryos. These diencephalic neurons may be of non-placodal origin. FMRFamide-immunoreactive neurons of quail origin were also found in the quail olfactory nerve and the host olfactory bulb, suggesting that FMRFamide neurons also originate in the olfactory placode and migrate into the brain.

Effects of neuropeptide FF on intracellular Ca2+ in mouse spinal ganglion neurons

Intracellular Ca2+ was measured in freshly dissociated mouse dorsal root ganglion neurons by using Fluo3 as fluorescent Ca2+ probe. Short perifusions (5-10 s) with 30 mM K+ induced a sharp rise in fluorescence due to the entry of Ca2+ ions, in particular through L and N voltage sensitive Ca2+ channels opened by the action potentials that were triggered by depolarization. Perifusions with 1 or 10 nM (1DMe)Y8Fa (DYL(NMe)FQPQRFamide), a neuropeptide FF analog, suppressed the rise in fluorescence induced by short (5-10 s) K+ perifusions within 30 min. However, when K+ perifusions of longer duration were applied, Fluo3 fluorescence rose after an increased latency. Two other analogs, (2DMe)Y8Fa (DYDL(NMe)FQPQRFamide) and (3D)Y8Fa (DYDLDFQPQRFamide), had the same effect; similarly neuropeptide FF (FLFQPQRFamide, 1 nM, 30 min) reduced intracellular Ca2+ rise during depolarization. These features indicate that neuropeptide FF and its analogs exert their pharmacological effects by reducing the [Ca2+]i transient induced by short depolarizations.

Characterization of the RFamide-like neuropeptides in the nervus terminalis of the goldfish (Carassius auratus)

FMRFamide-immunoreactivity has been demonstrated in the CNS of many vertebrate species. We sought to further characterize this immunoreactivity in nervus terminalis retinal efferents of the goldfish using an antiserum raised against a bovine morphine modulating peptide (A18Famide). This antiserum robustly labels nervus terminalis efferents to the retina, as well as a sub-population of retinal amacrine cells. Under immunocytochemical conditions the antiserum cross-reacted with neuropeptide Y-like as well as A18Famide-like peptides, but under conditions of radioimmunoassay it was highly specific for A18Famide-like peptides. High pressure liquid chromatography, gel permeation chromatography and radioimmunoassay showed that at least two different RFamide-like peptides, approximately the same size as the bovine RFamide-like peptides, are present in the goldfish nervus terminalis.

Cardiovascular effects induced by the stimulation of neuropeptide FF receptors in the dorsal vagal complex: an autoradiographic and pharmacological study in the rat

Previous studies have suggested that central administration of neuropeptide FF-related peptides may modulate cardiovascular parameters in the rat. In the present study, we investigated the role of dorsal vagal complex neuropeptide FF receptors in the central regulation of cardiovascular parameters. The fate of neuropeptide FF receptors in normal and nodose ganglionectomized rats was investigated using an autoradiographic approach with 125I-[DTyr1, (NMe)Phe3]NPFF as ligand for these receptors. We showed that neuropeptide FF binding sites are preferentially located postsynaptically with respect to the vagal afferent fibers in the nucleus tractus solitarius. Thus, ganglionectomy reduced by only 30% and 17% the density of peptide binding sites in the rostral and caudal regions of this nucleus, respectively. Bilateral microinjection of neuropeptide FF (1 nmol) into the commissural nucleus tractus solitarius produced an increase in blood pressure (+13.8 +/- 0.8 mmHg, n = 6), bradycardia (-29.0 +/- 3.2 bpm) and a significant inhibition (-47.6 +/- 3.1%) of the cardiac component of the baroreceptor reflex. Further studies with doses below 1 nmol indicate that NTS microinjections of the neuropeptide produced a dose-dependent decrease in heart rate. Similar cardiovascular effects were observed after bilateral NTS microinjections of one analog neuropeptide FF receptor agonist, [DTyr1, (NMe)Phe3]NPFF (1 nmol). Pretreatment with prazosin (100 micrograms/kg), an alpha 1-adrenoreceptor antagonist, inhibited the neuropeptide FF-evoked blood pressure effect. In addition, the neuropeptide FF-induced heart rate decrease was abolished by pretreatment with atropine (30 micrograms/kg), a muscarinic receptor antagonist. Taken together, these anatomical and pharmacological data suggest that neuropeptide FF receptors within the nucleus tractus solitarius, preferentially located on the postsynaptic component, are involved in the central reflex regulation of cardiovascular parameters.

Distribution of neuropeptide FF (FLFQPQRFamide) receptors in the adult rat spinal cord: effects of dorsal rhizotomy and neonatal capsaicin

By using quantitative autoradiography and highly selective iodinated ligands, we quantified modifications in neuropeptide FF binding sites in the superficial layers (laminae I and II) of the cervical (C6-C8 segments) and lumbar (L3-L5 segments) enlargements in two models: (i) rats neonatally treated with capsaicin; (ii) rat submitted 15 days before to unilateral dorsal rhizotomies. We comparatively analysed the distribution of mu-opioid binding sites in the same animals. We have shown that the [125I]YLFQPQRFamide (neuropeptide FF sites) labelling is not significantly modified following selective damage of fine afferent fibres by neonatal capsaicin treatment. In the cervical and lumbar enlargements, capsaicin-treated/control binding ratios for [125I]YLFQPQRFamide were 0.90 and 0.86, respectively. While unilateral dorsal rhizotomy induced a drastic decrease in [125I]FK-33-824 labelling in the side ipsilateral to the lesion as compared to the intact side of (yielding ratios of 0.29 and 0.31 for cervical and lumbar levels, respectively), [125I]YLFQPQRFamide labelling was not significantly modified, yielding ratios of 0.98 and 0.91 for cervical and lumbar levels, respectively. These data suggest that, in contrast with a majority of mu-opioid receptors, neuropeptide FF receptors are not located on fine primary afferent fibers carrying nociceptive information from the fore- or hindlimb in the rat. This preferential postsynaptic localization, together with the reported "morphine modulating" action of this peptide, support the proposal of a role for neuropeptide FF in intraspinal modulation of nociceptive input.

Neuropeptide FF-like immunoreactivity in human plasma

In order to examine whether neuropeptide FF (NPFF), an octapeptide with pain-modulating and blood pressure-raising properties in the rat, is present in circulating human blood, a radioimmunoassay (RIA) was established. Using this highly specific and sensitive RIA, the mean concentration of NPFF in human plasma was 2.9 pg/ml +/- 1.1 (n = 111). The concentration did not correlate with age or sex. Reversed-phase high pressure liquid chromatography (HPLC) followed by RIA using two different antisera for NPFF showed that plasma NPFF eluted in a position identical to that of synthetic NPFF. In view of published Kd values (0.06 mM) for NPFF receptor, the concentrations detected of NPFF in human plasma may be too low for systemic actions. Thus, plasma NPFF may represent leakage of the peptide from nervous tissue.

Ontogeny of neuropeptide FF pharmacology and receptors in mouse brain

The postnatal ontogeny of neuropeptide FF (NPFF) receptors in mouse brain was mapped by quantitative autoradiography using [125I](1DME)Y8Famide as selective radioligand. By day 14, the adult distribution of NPFF sites was established in almost all brain areas. The density of NPFF receptors reached adult levels between 14 and 28 days after birth, earlier than did mu or delta opioid receptors. During ontogeny, morphine analgesia was measured in hindpaw, forepaw and tail immersion tests (57 degrees C). An antinociceptive effect of morphine in the forepaw and tail immersion test was evident in 14-day-old but not in 7-day-old mice. In 14 and 21 day-old mice, the influence of (1DME)Y8Famide on morphine analgesia depended on the dose and on the particular test. A low dose of (1DME)Y8Famide inhibited morphine analgesia in the tail or hindpaw test, whereas a higher dose had either no effect (tail test) or increased morphine activity (hindpaw test). In adult mice, only the inhibition of morphine antinociception by (1DME)Y8Famide was observed. These observations revealed the establishment of an equilibrium between NPFF and opioid functions during ontogeny.

Immunocytochemical localization of neuropeptide FF (FMRF amide-like peptide) in the hypothalamo-neurohypophyseal system of Wistar and Brattleboro rats by light and electron microscopy

Neuropeptide FF (F8Famide, FMRFamide-like, or morphine modulating peptide) immunoreactivity was localized by light and electron microscopy in the hypothalamo-neurohypophyseal system of Wistar and Brattleboro rats. In Wistar rats neuropeptide FF was present in part of the magnocellular neurones of the paraventricular and supraoptic nuclei in which it was coexpressed with vasopressin. Neuropeptide FF containing fibres were present in the paraventricular and the supraoptic nuclei, and in the central part of the neural lobe. At the electron microscopic level, neuropeptide FF containing nerve terminals in the neural lobe formed synaptoid contacts exclusively with pituicytes. No neuropeptide FF containing neurovascular contacts or contacts with other neuronal structures were observed. In contrast with Wistar rats, neuropeptide FF was almost completely absent in cell bodies of the paraventricular and supraoptic nuclei, and in fibres of the neural lobe in Brattleboro rats. Only a few solitary cells could be observed in these structures. The present results demonstrate that neuropeptide FF coexists with vasopressin within the hypothalamo-neurohypophyseal system. As we did not observe neuropeptide FF containing neurovascular contacts, neuropeptide FF containing nerve terminals probably have a local function within the neural lobe. Neuropeptide FF may be involved in the modulation of oxytocin and vasopressin release, with the pituicyte as an intermediate cell.

Distribution and characterization of neuropeptide FF-like immunoreactivity in the rat nervous system with a monoclonal antibody

Monoclonal antibodies against neuropeptide FF were produced and characterized. The antibodies are directed and highly specific to neuropeptide FF, and reactivity requires the C-terminal dipeptide of neuropeptide FF (Arg-Phe-NH2). Tissue extracts from bovine spinal cord, rat spinal cord and hypothalamus were analysed by high-pressure liquid chromatography coupled with radioimmunoassay using the characterized monoclonal antibody. Only one immunoreactive peptide was detected and it coeluted with authentic neuropeptide FF. Using this highly specific monoclonal antibody, the distribution of neuropeptide FF-like immunoreactivity was further studied by indirect immunohistochemistry. Immunoreactivity was seen in two major cell groups in the rat brain. The largest cell group was located in the medial hypothalamus between the dorsomedial and ventromedial nuclei. The other one was found in the nucleus of the solitary tract. Fibres immunoreactive for neuropeptide FF were located in the lateral septal nucleus, amygdala, different hypothalamic areas, nucleus of the solitary tract, ventral medulla, trigeminal complex and the dorsal horn of the spinal cord. Spinal and sympathetic ganglia were non-reactive. No neuropeptide FF immunoreactivity was seen in the gut autonomic nervous system or endocrine cells. The results show that neuropeptide FF-like immunoreactivity has a clearly more limited distribution in the nervous system than typical brain-gut peptides.

Neuropeptide FF (FLQPQRFamide) and IgG from neuropeptide FF antiserum affect spatial learning in mice

There is evidence indicating that the mammalian octapeptide FLQPQRFamide (F8Fa or neuropeptide FF, NPFF) is an endogenous modulator ('anti-opioid') of opioid systems. There is also substantial evidence implicating opioid systems in the mediation of spatial learning and memory. In the present study determinations were made of the effects of NPFF and IgG from antiserum against NPFF on the spatial performance of male mice in a water maze task, whereby over one day in six blocks of four trials the animals had to acquire the location of a submerged hidden platform using distal visual cues. Pretraining intracerebroventricular (i.c.v.) injection of NPFF-IgG, impaired spatial acquisition and retention, while i.c.v. administration of 1.0 microgram of NPFF marginally improved, and 10 micrograms of NPFF significantly reduced spatial acquisition. These results suggest that NPFF may have a modulatory influence on spatial acquisition.

Effects of F8Famide analogs on intestinal transit in mice

In an attempt to establish the role of F8Famide in opioid activity modulation, we examined the effects of intracerebroventricular administration of the F8Famide analogs (1DME)Y8Fa and (3D)Y8Fa on intestinal transit in mice. (1DME)Y8Fa (0.88 to 22 nmol) inhibited intestinal transit as did F8Famide and morphine. An IP injection of naloxone (2 mg/kg) decreased the morphine effect but had no effect on the response to (1DME)Y8Fa. In contrast, a subthreshold dose of morphine (0.22 nmol) inhibited the response to (1DME)Y8Fa, (3D)Y8Fa delayed intestinal transit only at large dose (22 nmol) but decreased (1DME)Y8Fa and morphine effects at lower ineffective doses. Our findings demonstrate that although F8Famide and morphine could induce the same pharmacological effect, F8Famide receptor activity was modulated by a low-level stimulation of opioid receptors. Furthermore, (3D)Y8Fa should be a useful probe to elucidate neuronal mechanisms controlled by opioids.

Analog of neuropeptide FF attenuates morphine tolerance

Previous studies suggest that neuropeptide FF (NPFF) plays a role in opiate dependence and subsequent abstinence syndrome. Endogenous NPFF also appears to play a role in opiate tolerance since third ventricle injection of IgG from NPFF antiserum selectively restores morphine sensitivity in morphine-tolerant rats. The NPFF analog, desamino YFLFQPQRamide (daY8Ra) has previously antagonized behavioral effects of NPFF and has attenuated morphine dependence. The present study assessed whether daY8Ra could similarly attenuate morphine tolerance. Third ventricle (i.c.v.) injection of daY8Ra restored the analgesic response to i.c.v. morphine in morphine-tolerant rats (radiant heat tail flick test). Saline injection failed to produce this effect. In opiate-naive rats, however, the same treatment with daY8Ra did not affect the analgesic response to i.c.v. morphine. Thus, daY8Ra appears to selectively restore morphine sensitivity in opiate-tolerant animals. These results further support the hypothesis that endogenous NPFF contributes to opiate tolerance.

Analogues of F8Famide resistant to degradation, with high affinity and in vivo effects

Four analogues of Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2, a mammalian FMRFamide-like peptide with antiopiate properties, were synthesized with N-terminus modifications and were shown to have high affinity for F8Famide binding sites. The degradation rate of these analogues in mouse brain slices was 3 times lower than that of the natural peptide. One analogue, (2DME)Y8Fa (D.Tyr-D.Leu-[N-Me]Phe-Gln-Pro-Gln-Arg-Phe-NH2), produced a clear hyperalgic effect and inhibited morphine analgesia in the mouse tail-flick test at lower doses than did the parent compound. (3D)Y8Fa (D.Tyr-D.Leu-D.Phe-Gln-Pro-Gln-Arg-Phe-NH2) and (2D)Y8Fa (D.Tyr-D.Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) in contrast did not decrease morphine analgesia but were analgesic alone. The analgesic effects of 22 nmol (2D)Y8Fa and (3D)Y8Fa were decreased by (1DME)Y8Fa (D.Tyr-Leu-[N-Me]Phe-Gln-Pro-Gln-Arg-Phe-NH2) or (2DME)Y8Fa and were reversed by naloxone. These results indicate opioid modulating properties of F8Famide. These analogues may prove to be useful tools for studying the modulation of pain by F8Famide.

Release of neuropeptide FF (FLFQPQRF-NH2) from rat spinal cord

Neuropeptide FF (FLFQPQRF-NH2), originally isolated from bovine brain, is an FMRF-NH2-like peptide with morphine-modulating activity. Neuropeptide FF (NPFF) is highly localized in the dorsal spinal cords where there are also specific NPFF binding sites. Furthermore, there have been studies indicating that NPFF may participate in the regulation of pain threshold in the spinal cord. However, whether NPFF can be released from the spinal cord is not known. The present experiments, using an in vitro superfusion of an isolated whole rat spinal cord, demonstrated that high concentrations of KCl or substance P caused a release of NPFF immunoreactive material (IR) from the spinal cord into the perfusion medium in a calcium-dependent manner. Substance P (1-11) also produced a detectable release of NPFF-IR in vivo although the response was quite variable. The released NPFF-IR was analyzed by an HPLC study and found to consist of NPFF and other minor immunoreactive peptides. Further studies with substance P-related peptides showed that the in vitro release of NPFF-IR could also be induced by substance P (1-7) but not by [pGlu5,Me-Phe8,Sar9]-substance P (5-11) or substance K. These results suggest that the specific substance P receptor (SP-N), which is recognized by both substance P (1-11) and substance P (1-7) rather than the tachykinin receptor, is involved in NPFF secretion from the spinal cord. In view of the role of substance P (1-11) and substance P (1-7) in sensory transmission, the results of this study further support the role of NPFF in the modulation of antinociception in the spinal cord.

Autoradiographic distribution of receptors to FLFQPQRFamide, a morphine-modulating peptide, in rat central nervous system

The neuropeptide FLFQPQRFamide is a structure related to FMRFamide which is able to inhibit the effects of both endogenous and exogenous opiates. This morphine-modulating activity is mediated via the stimulation of specific FLFQPQRFamide receptors, different from opiate receptors. In vitro quantitative receptor autoradiography was performed on frozen sections of rat central nervous system to characterize binding properties and visualize FLFQPQRFamide receptors using the specific ligand [125I]YLFQPQRFamide, a radio-iodinated analogue of FLFQPQRFamide. [125I]YLFQPQRFamide appeared to interact reversibly with a single class of binding sites (KD = 0.2 nM). The specific binding represented 80% of the total binding at 0.05 nM, the FLFQPQRFamide concentration used in this mapping study. Sites labelled with [125I]YLFQPQRFamide were distributed heterogeneously within the brain and spinal cord. A high density of FLFQPQRFamide binding sites was detected in the most external layers of the dorsal horn of spinal cord and various nuclei of pons and medulla including trigeminal, dorsal tegmental and reticular nuclei. Nucleus of solitary tract, parabrachial, ambiguous and facial nuclei are also intensively labelled. Some structures of mesencephalon and diencephalon exhibited a high density of FLFQPQRFamide binding sites: central gray, raphe nuclei and thalamic nuclei such as parafascicular, laterodorsal, central median, paratenial and paraventricular nuclei. Suprachiasmatic and mammillary nuclei, lateral, posterior and anterior areas of hypothalamus and medial preoptic area exhibited high labelling. FLFQPQRFamide binding sites were also seen in some structures of the dopaminergic meso-cortico-limbic system including ventral tegmental area, cingulate cortex, lateral septum and the head of the caudate-putamen. Dense labelling appeared in the presubiculum of hippocampus. The dissimilar mapping of FLFQPQRFamide and opiate brain receptors confirms our previous pharmacological findings in FLFQPQRFamide binding studies on rat spinal cord membranes, showing that FLFQPQRFamide receptors are different from opiate receptors. There was a good correspondence between localization of binding sites and that of the putative endogenous peptide. Both occur in brain areas previously associated with analgesic action of opiates. However, the mapping of FLFQPQRFamide receptors in the central nervous system suggests that the FLFQPQRFamide system could be implicated in other physiological functions.

Sex differences in the effects of neuropeptide FF and IgG from neuropeptide FF on morphine- and stress-induced analgesia

There is evidence suggesting that the endogenous mammalian octapeptide FLFQPQRFamide (F8Fa or neuropeptide FF, NPFF) has modulatory effects on opioid-mediated analgesia in rodents. There is also substantial evidence for sex differences in opioid analgesia, whereby male rats and mice display greater levels of opioid-mediated analgesia than females. In the present study, determinations were made of the effects of NPFF and IgG from antiserum against NPFF on morphine- and restraint stress-induced opioid analgesia in male and female deer mice. Intracerebroventricular (ICV) administrations of NPFF (0.10-10 micrograms) reduced in a dose-dependent manner morphine- and stress-induced analgesia in both male and female mice, with NPFF having markedly greater antagonistic effects in the male than female mice. Additionally, ICV administrations of NPFF-IgG increased the levels of morphine- and stress-induced analgesia and significantly reduced basal nociceptive sensitivity in male mice, whereas, in female mice, NPFF-IgG had no significant effects on either opioid-mediated analgesia or nociceptive sensitivity. These results indicate that there are sex differences in the modulatory effects of NPFF on opioid-mediated analgesia.

IgG from neuropeptide FF antiserum reverses morphine tolerance in the rat

Previous studies suggest that neuropeptide FF (NPFF) plays a role in opiate dependence and subsequent abstinence syndrome. The present study assessed the role of NPFF in opiate tolerance. Third ventricular injection of IgG from NPFF antiserum restored the analgesic response to i.c.v. morphine in morphine-tolerant rats (radiant heat tail flick test). IgG from control serum failed to produce this effect. In opiate-naive rats, however, the same treatment with IgG from NPFF antiserum did not affect the analgesic response to i.c.v. morphine. Thus, immunoneutralization of NPFF appears to selectively restore morphine sensitivity in opiate-tolerant animals. These results support the hypothesis that endogenous NPFF contributes to opiate tolerance.

Effects of mammalian FMRF-NH2-related peptides and IgG from antiserum against them on aggression and defeat-induced analgesia in mice

The effects of two endogenous mammalian FMRFamide (Phe-Met-Arg-Phe-NH2)-related peptides, an octapeptide F8Fa (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) and an octadecapeptide A18Fa (Ala-Gly-Glu-Gly-Leu-Ser-Ser-Pro-Phe-Trp-Ser-Leu-Ala-Pro-Gln-Arg-Phe-NH2 ), and IgG from serum against them on the responses to aggression and defeat-induced analgesia were examined in subordinate mice in "resident-intruder" pairings. Intracerebroventricular (ICV) administrations of F8Fa and A18Fa (0.10-10 micrograms) reduced, in a dose-dependent manner, the number of bites to obtain defeat in the subordinate mice during the agonistic encounters, as well as attenuating defeat-induced analgesia, with F8Fa having a greater inhibitory effect than A18Fa. Peripheral administration of naloxone (1.0 mg/kg) had a similar inhibitory effect on the number of bites to defeat and the level of defeat-induced analgesia. In contrast, ICV administrations of F8Fa-IgG and A18Fa-IgG antisera increased the number of bites to defeat and augmented the levels of defeat-induced analgesia, with F8Fa-IgG having a greater effect than A18Fa-IgG. These results provide further evidence that the peptides, F8Fa and A18Fa, are involved in the modulation of opioid-mediated analgesia accompanying biological stressors and suggest that these endogenous FMRF-NH2-related peptides may also be associated with the expression of opioid-sensitive components of aggressive behavior.

Ontogeny of the F8Famide-like (morphine-modulating) peptides in the central nervous system of rats

FLFQPQRF-NH2 (F8Famide; FMRFamide-like peptide; morphine-modulating peptide) is a peptide isolated from bovine brain. It has some opiate analgesia modulating effects. In an adult rat central nervous system, F8Famide-like immunoreactivity is found in high concentrations in the posterior pituitary, hypothalamus, pons, medulla, and dorsal spinal cord. By using immunohistochemistry and radioimmunoassay, we studied the development of the F8Famide-immunoreactive system in the rat central nervous system during the ontogeny. F8Famide-immoreactive fibers and terminals first appeared in the median eminence on the twentieth embryonal day. Postnatally the F8Famide-immunoreactive system developed rapidly both in the brain and spinal cord, the immunoreactive structures having an adultlike distribution by the age of 1 week. A transient increase of the F8Famide-immunoreactive material was observed during the third and fourth postnatal weeks. By the age of 4 weeks, the F8Famide-containing neuronal system was adultlike both in distribution and quantity. The results suggest that the F8Famide-like peptides may act as neurotransmitters or neuromodulators from the time of their appearance in the brain and spinal cord. The early appearance and the distribution of the F8Famide-like immunoreactivity suggest that these peptides may participate, in addition to nociceptive mechanisms, in the regulation of blood pressure, feeding behaviour, and endocrine functions.

Central neuronal pathways containing FLFQPQRFamide-like (morphine-modulating) peptides in the rat brain

Octapeptide FLFQPQRFamide (FMRFamide-like peptide; morphine-modulating peptide), isolated from bovine brain, has some opiate analgesia modulating effects. Octapeptide FLFQPQRFamide-like immunoreactivity is found in high concentrations in the posterior pituitary, hypothalamus, pons-medulla, and dorsal spinal cord. Octapeptide FLFQPQRFamide-immunoreactive neurons of the brain are localized in the medial hypothalamus and in the nucleus of the solitary tract. High densities of octapeptide FLFQPQRFamide-immunoreactive nerve terminals are found in the median eminence, lateral parabrachial nucleus, and nucleus of the solitary tract. By using the retrograde tract tracing method combined with immunohistochemistry, we studied the central pathways interconnecting the octapeptide FLFQPQRFamide-immunoreactive structures. The octapeptide FLFQPQRFamide-immunoreactive neurons of the hypothalamus sent projections bilaterally to the nucleus of the solitary tract. The octapeptide FLFQPQRFamide-immunoreactive neurons of the nucleus of the solitary tract projected to the contralateral side of the same nucleus, to the lateral parabrachial nuclei bilaterally, and to the ipsilateral periambigual region. The results give neuroanatomical evidence of interacerebral pathways containing recently identified FLFQPQRFamide-like peptides, which may belong to a larger family of peptides. These neuroanatomical findings support the previous pharmacological studies, suggesting that the mammalian FMRFamide-like peptides may, in addition to modulatory effects on nociceptive mechanisms, participate in the regulation of blood pressure, feeding behaviour and endocrine functions.

Characterization and localization of a putative morphine-modulating peptide, FLFQPQRFamide, in the rat spinal cord: biochemical and immunocytochemical studies

The bovine octapeptide Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (FLFQPQRFamide), originally detected by antisera raised against the invertebrate peptide, Phe-Met-Arg-Phe-NH2, is a neuropeptide which antagonizes the actions of endogenous and exogenous opiates. Using a sensitive radioreceptor assay, we show that rat spinal cord extracts were able to inhibit binding of FLFQPQRFamide, suggesting that a biologically active FLFQPQRFamide-like material exists in the rat spinal cord. We also raised antibodies against the peptide and used them, together with radioimmunological and immunohistochemical methods, to characterize this material further and analyse its cellular and subcellular localization in this area of the central nervous system. Radioimmunoassay showed that extracts from cervical and thoracolumbar levels contained measurable amounts of FLFQPQRFamide-immunoreactive material (about 3 ng/g tissue), present essentially in the dorsal horn. Analytical reverse-phase chromatography revealed that this material existed in several molecular forms. One of these fractions (about 20% of the total immunoreactivity) had the elution characteristics of synthetic FLFQPQRFamide. Light microscopic immunohistochemistry showed FLFQPQRFamide immunoreactivity at all spinal levels, localized mainly in a dense plexus of fibers in the superficial layers of the dorsal horn. Immunoreactive profiles were also seen in the lateral funiculi and around the central canal at all levels and in the intermediolateral columns; some rare immunoreactive fibers were also noted in the ventral horn at cervical and thoracic levels. FLFQPQRFamide-positive cell bodies were never detected in any of our sections. Electron microscopy of ultrathin sections of the dorsal horn and central gray treated with our antisera and a post-embedding immunogold procedure revealed that the immunoreactivity, at least within these areas, was restricted to dense-cored vesicles (90-120 nm in diameter) in axonal and terminal profiles. As seen by radioimmunoassay and immunohistochemistry, unilateral rhizotomy of all dorsal roots between segments C4 and T2 did not change the levels of FLFQPQRFamide immunoreactivity in the ipsilateral C6-C8 segments. Taken together with our recent data showing the existence of specific FLFQPQRFamide receptors at the spinal cord level, our present observations suggest that the dorsal horn of the rat spinal cord may be a site where vertebrate Phe-Met-Arg-Phe-like peptides, and in particular, FLFQPQRFamide, may exert opiate modulating activities.

The effects of two FMRFamide related peptides (A-18-F-amide and F-8-F-amide; 'morphine modulating peptides') on the endocrine and exocrine rat pancreas

The effects of two recently isolated mammalian FMRFamide related peptides (A-18-F-amide and F-8-F-amide) on the encocrine and exocrine rat pancreas were investigated. A-18-F-amide (10, 100, 1000 pM) inhibited concentration dependently glucose (10 mM)- and arginine (10 mM)-induced insulin secretion from the isolated perfused rat pancreas during the first (controls: 100%; 10 pM: 114%; 100 pM: 63%, p less than 0.05; 1000 pM: 31%, p less than 0.05) and the second secretion phase (controls: 100%; 10 pM: 102%; 100 pM: 78%; 1000 pM: 27%, p less than 0.05). The inhibitory actions of A-18-F-amide on pancreatic D-cell secretion were more pronounced during the first than the second phase (first phase: controls: 100%; 10 pM: 95%; 100 pM: 37%, p less than 0.05; 1000 pM: 39%, p less than 0.05%; second phase: controls: 100%; 10 pM: 113%; 100 pM: 72%; 1000 pM: 59%, p less than 0.05). F-8-F-amide (at 1000 pM) inhibited stimulated insulin (controls: 100%; first phase: 26%, p less than 0.05%; second phase: 20%, p less than 0.05) and somatostatin release (controls: 100%; first phase: 14%, p less than 0.05; second phase: 29%, p less than 0.05). Both peptides were without effect on basal and CCK-8-stimulated amylase release from isolated incubated rat pancreatic acini.