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

Brain RFamide Neuropeptides in Stress-Related Psychopathologies

The RFamide peptide family is a group of proteins that share a common C-terminal arginine-phenylalanine-amide motif. To date, the family comprises five groups in mammals: neuropeptide FF, LPXRFamides/RFamide-related peptides, prolactin releasing peptide, QRFP, and kisspeptins. Different RFamide peptides have their own cognate receptors and are produced by different cell populations, although they all can also bind to neuropeptide FF receptors with different affinities. RFamide peptides function in the brain as neuropeptides regulating key aspects of homeostasis such as energy balance, reproduction, and cardiovascular function. Furthermore, they are involved in the organization of the stress response including modulation of pain. Considering the interaction between stress and various parameters of homeostasis, the role of RFamide peptides may be critical in the development of stress-related neuropathologies. This review will therefore focus on the role of RFamide peptides as possible key hubs in stress and stress-related psychopathologies. The neurotransmitter coexpression profile of RFamide-producing cells is also discussed, highlighting its potential functional significance. The development of novel pharmaceutical agents for the treatment of stress-related disorders is an ongoing need. Thus, the importance of RFamide research is underlined by the emergence of peptidergic and G-protein coupled receptor-based therapeutic targets in the pharmaceutical industry.

NPFF Decreases Activity of Human Arcuate NPY Neurons: A Study in Embryonic-Stem-Cell-Derived Model

Restoring the control of food intake is the key to obesity management and prevention. The arcuate nucleus (ARC) of the hypothalamus is extensively being studied as a potential anti-obesity target. Animal studies showed that neuropeptide FF (NPFF) reduces food intake by its action in neuropeptide Y (NPY) neurons of the hypothalamic ARC, but the detailed mode of action observed in human neurons is missing, due to the lack of a human-neuron-based model for pharmacology testing. Here, we validated and utilized a human-neural-stem-cell-based (hNSC) model of ARC to test the effects of NPFF on cellular pathways and neuronal activity. We found that in the human neurons, decreased cAMP levels by NPFF resulted in a reduced rate of cytoplasmic calcium oscillations, indicating an inhibition of ARC NPY neurons. This suggests the therapeutic potential of NPFFR2 in obesity. In addition, we demonstrate the use of human-stem-cell-derived neurons in pharmacological applications and the potential of this model to address functional aspects of human hypothalamic neurons.

An Inhibitory Circuit From Brainstem to GnRH Neurons in Male Mice: A New Role for the RFRP Receptor

RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal, and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges, such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found (1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly rectifying potassium channels), (2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, (3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and (4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

Evidence for the Direct Effect of the NPFF Peptide on the Expression of Feeding-Related Factors in Spotted Sea Bass (Lateolabrax maculatus)

Neuropeptide FF (NPFF) is a family member of RF-amide peptides, which are suggested to be involved in the control of vertebrate feeding behavior. However, little is known about the effect of the NPFF peptide on feeding-related processes in basal vertebrates. In this study, four full-length cDNAs, npff, npffr1, npffr2-1, and npffr2-2, were cloned from spotted sea bass and characterized. The conserved NPFF peptide is biologically active because it functionally interacts with different receptors expressed in cultured eukaryotic cells to enhance CRE promoter activity. Tissue distribution analysis showed that the highest npff mRNA expression occurred in the telencephalon, hypothalamus, medulla, gonad and muscle, but the npffrs mRNAs were mainly distributed within the central nervous system (CNS). In situ hybridization (ISH) detected npff-expressing cells in several specific regions ranging across the telencephalon and midbrain to the hypothalamus. Incubation of the spotted sea bass conserved NPFF peptide significantly increased the expression of orexin (orx) and neuropeptide Y (npy) mRNA and decreased the expression of leptin (lep), somatostatin (ss), and cholecystokinin (cck) mRNA in brain cells. Similarly, the conserved NPFF peptide also heightened the expression of gastrin (gas), ghrelin (ghrl), and motilin (mtl) mRNA and significantly reduced the expression of cck mRNA in the intestine and stomach. Taken together, these data suggest that the NPFF peptide may play a stimulating role in regulating feeding-related processes in spotted sea bass.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

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.

Neuropeptide FF2 receptor distribution in the human brain. An immunohistochemical study

Human neuropeptide FF2 (hFF2) receptor has been postulated to mediate central autonomic regulation by virtue of its ability to bind with high affinity to many amidated neuropeptides. In the present immunohistochemical study, we identified hFF2 positive neurons in the forebrain and medulla oblongata of individuals, who died suddenly of mechanical trauma or hypothermia. Morphologically, these neurons demonstrated features identified with both projection neurons and interneurons. In the forebrain, the highest density of hFF2 expressing neurons was observed in the anterior amygdaloid area and dorsomedial hypothalamic nucleus, especially in its caudal part. A lesser density of hFF2 neurons was identified in the ventromedial hypothalamic nucleus, lateral and posterior hypothalamic areas whereas few cells were visualized in the paraventricular hypothalamic nucleus, perifornical nucleus, horizontal limb of the diagonal band, ventral division of the bed nucleus of the stria terminalis, nucleus basalis of Meynert and ventral tegmental area. In the medulla, significant numbers of hFF2 neurons were observed in the dorsal motor nucleus of vagus and to a lesser extent in the area of catecholaminergic cell groups, A1/C1. These data provide first immunohistochemical evidence of hFF2 localization in the human brain, which is consistent with that reported for tissue distribution of FF2 mRNA and FF2 binding sites within the brain of a variety of mammalian species. The distribution of hFF2 may help in identifying the role of amidated neuropeptides in the human brain within the context of central autonomic and neuroendocrine regulation.

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

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

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.

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.

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

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

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.

Changes in neuropeptide FF and NPY immunohistochemical patterns in rat brain under heroin treatment

Immunohistochemical distribution patterns of neuropeptide FF (NPFF) and neuropeptide tyrosine (NPY) were studied in the brain of rats submitted to two different protocols of heroin treatment. In drug-naive rats, acutely injected heroin significantly depleted NPFF-immunoreactive material within the neurons of the nucleus of solitary tract (NTS), significantly decreased the density of NPFF-immunoreactive nerve fibers within the median eminence, pituitary stalk, and neurohypophysis, and markedly increased NPY-immunoreactive neurons and nerve fibers in the thalamic paraventricular nucleus and bed nucleus of stria terminalis. In drug-sensitized rats, heroin significantly increased the number and immunostaining intensity of the NPFF-immunoreactive neurons within the NTS and induced minor changes in the NPFF-immunoreactive nerve fiber network of the median eminence, pituitary stalk, and neurohypophysis and a relatively minor increase in NPY neurons in the thalamic paraventricular nucleus and bed nucleus of stria terminalis. These heroin-induced changes suggest that NPFF is involved in regulating the effects of the heroin injection and in the mechanisms underlying behavioral sensitization. They also add further support to the key role of NPY in any conditions tending to change the animal homeostasis.

Neuropeptide ff, but not prolactin-releasing peptide, mRNA is differentially regulated in the hypothalamic and medullary neurons after salt loading

Hypothalamic paraventricular and supraoptic nuclei are involved in the body fluid homeostasis. Especially vasopressin peptide and mRNA levels are regulated by hypo- and hyperosmolar stimuli. Other neuropeptides such as dynorphin, galanin and neuropeptide FF are coregulated with vasopressin. In this study neuropeptide FF and another RF-amide peptide, the prolactin-releasing peptide mRNA levels were studied by quantitative in situ hybridization after chronic salt loading, a laboratory model of chronic dehydration. The neuropeptide FF mRNA expressing cells virtually disappeared from the hypothalamic supraoptic and paraventricular nuclei after salt loading, suggesting that hyperosmolar stress downregulated the NPFF gene transcription. The neuropeptide FF mRNA signal levels were returned to control levels after the rehydration period of 7 days. No changes were observed in those medullary nuclei that express neuropeptide FF mRNA. No significant changes were observed in the hypothalamic or medullary prolactin-releasing peptide mRNA levels. Neuropeptide FF mRNA is drastically downregulated in the hypothalamic magnocellular neurons after salt loading. Other neuropeptides studied in this model are concomitantly coregulated with vasopressin: i.e. their peptide levels are downregulated and mRNA levels are upregulated which is in contrast to neuropeptide FF regulation. It can thus be concluded that neuropeptide FF is not regulated through the vasopressin regulatory system but via an independent pathway. The detailed mechanisms underlying the downregulation of neuropeptide FF mRNA in neurons remain to be clarified.

Activation of spinal neuropeptide FF and the neuropeptide FF receptor 2 during inflammatory hyperalgesia in rats

Several lines of evidence suggest that neuropeptide FF (NPFF) is involved in nociception and in the modulation of opioid-mediated analgesia. Following the identification of the precursor protein for NPFF, two NPFF receptors and a second PQRF-NH(2) containing peptide, termed NPVF, were identified. To further explore the functional role of PQRF-NH(2) peptides, we have studied their distribution and also the regulation of NPFF and NPVF systems in the spinal cord of rats with peripheral inflammation. The distribution of NPFF gene expression is very similar to that of NPFF immunoreactive peptide but is distinct from NPVF gene expression. In the rat spinal cord, gene expression of NPFF but not that of NPVF was up-regulated by persistent pain induced by carrageenan inflammation. The distribution of NPFF receptor 2 gene expression is very similar to that of the NPFF peptide with a striking localization in the superficial layer of spinal cord. In rats with carrageenan inflammation of the hind paw, expression of both NPFF and NPFF receptor 2 genes was up-regulated in the spinal cord, while expression of NPVF and NPFF receptor 1 genes was not affected. The results of this study demonstrate a coordinated involvement of the spinal NPFF system in the persistent nociceptive pain states. Several studies have found a potentiation and prolongation of morphine analgesia by NPFF, therefore, it is highly possible that the endogenous spinal NPFF system contributes to the enhanced analgesic potency of morphine in animals with peripheral inflammation.

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.

Central administration of neuropeptide FF causes activation of oxytocin paraventricular hypothalamic neurones that project to the brainstem

Neuropeptide FF (NPFF), a morphine modulatory peptide, is emerging as an important neuromodulator in the context of central autonomic and neuroendocrine regulation. NPFF immunoreactivity and receptors have been identified in discrete autonomic regions within the brain and spinal cord, including the hypothalamic paraventricular nucleus (PVN). In this study, we examined the effects of intracerebroventricular (i.c.v.) administration of NPFF on activation of chemically identified PVN neurones that project to the brainstem nucleus of the solitary tract (NTS). In conscious rats, i.c.v. NPFF at a dose of 10 micro g, but not 8 micro g, caused an increase in arterial blood pressure. Immunohistochemical analysis revealed a dose-dependent increase in activated (Fos positive) PVN neurones following i.c.v. NPFF administration compared to controls receiving i.c.v. saline. Activated PVN neurones were located predominantly in the parvocellular compartment of the nucleus with relatively few Fos positive cells in the magnocellular subdivision. Chemical identification of activated neurones revealed significant number of activated cells to be oxytocin positive, whereas only few vasopressin, tyrosine hydroxylase (TH) or corticotrophin-releasing factor (CRF) neurones were double-labelled. Injection of the retrograde tracer fluorogold into the NTS resulted in labelling of significant numbers of parvocellular oxytocin, but not vasopressin, TH or CRF, PVN neurones. We conclude that centrally administered NPFF stimulates brainstem-projecting oxytocin PVN neurones. Oxytocin released from terminals within the NTS oxytocin thus modulate the activity of ascending visceral autonomic pathways that synapse initially within the NTS.

Isolation, characterization, and distribution of a novel neuropeptide, Rana RFamide (R-RFa), in the brain of the European green frog Rana esculenta

A novel neuropeptide of the RFamide peptide family was isolated in pure form from a frog (Rana esculenta) brain extract by using reversed-phase high performance liquid chromatography in combination with a radioimmunoassay for mammalian neuropeptide FF (NPFF). The primary structure of the peptide was established as Ser-Leu-Lys- Pro-Ala-Ala-Asn-Leu-Pro-Leu- Arg-Phe-NH(2). The sequence of this neuropeptide, designated Rana RFamide (R-RFa), exhibits substantial similarities with those of avian LPLRFamide, gonadotropin-inhibitory hormone, and human RFRP-1. The distribution of R-RFa was investigated in the frog central nervous system by using an antiserum directed against bovine NPFF. In the brain, immunoreactive cell bodies were primarily located in the hypothalamus, i.e., the anterior preoptic area, the suprachiasmatic nucleus, and the dorsal and ventral hypothalamic nuclei. The most abundant population of R-RFa-containing neurons was found in the periependymal region of the suprachiasmatic nucleus. R-RFa- containing fibers were widely distributed throughout the brain from the olfactory bulb to the brainstem, and were particularly abundant in the external layer of the median eminence. In the spinal cord, scattered immunoreactive neurons were found in the gray matter. R-RFa-positive processes were found in all regions of the spinal cord, but they were more abundant in the dorsal horn. This study provides the first characterization of a member of the RFamide peptide family in amphibians. The occurrence of this novel neuropeptide in the hypothalamus and median eminence and in the dorsal region of the spinal cord suggests that, in frog, R-RFa may exert neuroendocrine activities and/or may be involved in the transmission of nociceptive stimuli.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Development and distribution of FMRFamide-like immunoreactivity in the toad (Bufo bufo) brain

By using immunohistochemistry, we studied the development and distribution of the FMRFamide-like immunoreactive (ir) neuronal system in the toad brain during the ontogeny. In addition to this, experimental evidence was provided to show that the rostral forebrain-located FMRFamide neurons originate in the olfactory placode and then migrate into the brain along the olfactory pathway. During early development, within the brain, FMRFamide-ir perikarya first appeared in the periventricular hypothalamus. Later in development, FMRFamide-ir cells were visualized in the rostralmost forebrain simultaneously with similar ir cells in the developing olfactory mucosa. Selective ablation of the olfactory placode(s), prior to the appearance of the first FMRFamide-ir cells in the brain, resulted in the total absence of ir cells in the telencephalon (medial septum and mediobasal telencephalon) of the operated sides(s). The preoptic-suprachiasmatic-infundibular hypothalamus-located FMRFamide-ir neurons were not affected by olfactory placodectomy, arguing that they do not originate in the placode. This result points to the placode as the sole source of such neurons in the rostral forebrain.

Immunocytochemical mapping of endomorphin-2-immunoreactivity in rat brain

Endomorphin-2 (Tyr-Pro-Phe-Phe-NH(2)) is a novel endogenous opioid with high affinity and selectivity for the mu-opioid receptor. Immunocytochemical studies have located this peptide in spinal cord, brainstem and selected brain regions. However, there are disagreements regarding its distribution between published reports. Furthermore, the distributions reported for the endomorphins resemble that of neuropeptide FF, suggesting that some of the previous findings might be due to cross-reactivity with the latter substance. In the present study, the distribution of endomorphin-2-immunoreactivity (ir) was examined throughout the entire rat brain using an affinity-purified antiserum that appeared not to cross-react with neuropeptide FF. Endomorphin-2-ir cell somata were most prominent in the hypothalamus and the nucleus of the solitary tract (NTS). Endomorphin-2-ir varicose fibers were observed in such areas as the bed nucleus of the stria terminalis, the septal nuclei, the periaqueductal gray, the locus coeruleus, the lateral parabrachial nucleus, the NTS, and the substantia gelatinosa of the medulla. More modest immunoreactivity was seen in substantia nigra, nucleus raphe magnus, the ventral tegmental area, the pontine nuclei and the amygdala. Fibers were also observed in the ventral cerebellum. Of note was the negligible immunoreactivity in the striatum, a region known to express high levels of mu-opioid receptors. Thus, endomorphin-2-ir was widely, but not uniformly, distributed throughout the central nervous system and was associated largely, but not exclusively, with regions expressing mu-opioid receptors. Based on its distribution, it may have a role in the control of neuroendocrine, cardiovascular and respiratory functions, and mood, feeding, sexual behavior and pain.

FMRFamide immunoreactivity and the invasion of adenohypophyseal cells into the neural lobe in the developing pituitary of the tree shrew Tupaia belangeri

Ontogenetic development of FMRFamide immunoreactivity in the cells and nerve fibers of the pituitary was studied in the tree shrew Tupaia belangeri. Up to the 26th day of gestation (E26), no FMRFamide immunoreactivity was visible. From E27 onwards it increased continuously until prenatally, on E41, the adult pattern was reached in the adenohypophysis, although at a lower intensity. In the adult Tupaia, as in the other mammals studied so far, a finely stained FMRFamide-immunoreactive fiber network was visible in the neural lobe and the infundibular stalk. As in several other adult mammals including man, endocrine cells in the pars intermedia and numerous scattered cells in the pars distalis were labeled, in contrast to several reports on rats and our studies on Galago, showing no FMRFamide-immunoreactive cells in these locations of the pituitary. With reference to the 'basophil invasion', we found FMRFamide-immunoreactive endocrine cells invading the neural lobe from the pars intermedia during the pituitary development. The distribution pattern of FMRFamide immunoreactivity in Tupaia indicates that the mammalian counterparts of FMRFamide may function as neuromodulators, neurotransmitters or as hormones already in defined prenatal stages.

Astroglial modulation of neurotransmitter/peptide release from the neurohypophysis: present status

Reviewed in this article are those studies that have contributed heavily to our current conceptualizations of glial participation in the functioning of the magnocellular hypothalamo-neurohypophysial system. This system undergoes remarkable morphological and functional reorganization induced by increased demand for peptide synthesis and release, and this reorganization involves the astrocytic elements in primary roles. Under basal conditions, these glia appear to be vested with the responsibility of controlling the neuronal microenvironment in ways that reduce neuronal excitability, restrict access to neuronal membranes by neuroactive substances and deter neuron neuron interactions within the system. With physiological activation, the glial elements, via receptor-mediated mechanisms, take up new positions. This permissively facilitates neuron neuron interactions such as the exposure of neuronal membranes to released peptides and the formation of gap junctions and new synapses, enhances and prolongs the actions of those excitatory neurotransmitters for which there are glial uptake mechanisms, and facilitates the entry of peptides into the blood. In addition, subpopulations of these glia either newly synthesize or increase synthesis of neuroactive peptides for which their neuronal neighbors have receptors. Release of these peptides by the glia or their functional roles in the system have not yet been demonstrated.

The magnocellular neurons of the hypothalamo-neurohypophyseal system display remarkable neuropeptidergic phenotypes leading to novel insights in neuronal cell biology

For decades the magnocellular neurons of the hypothalamo-neurophypophyseal system (HNS), in which either vasopressin or oxytocin are produced and released into the bloodstream, have been playing a pivotal role in fundamental discoveries in the nervous system. The primary structure of vasopressin and oxytocin was the first of all neuropeptides to be published, i.e., in the 1950s by the Nobel prize laureate Du Vigneaud. Moreover, many trend-setting discoveries have their origin in the HNS, which abundantly expresses vasopressin and oxytocin, clearly displays its function and is relatively easily to manipulate. Examples are the phenomenon of coexpression of neuropeptides, patch-clamping of nerve endings, axonal transport of RNA, neuroglia interactions and the behavioral effects. An extraordinarily intriguing example is the homozygous Brattleboro rat, which lacks vasopressin by a germ-line mutation, and has disclosed many of the fundamental characteristics of peptidergic neurons, and neurons in general. In this chapter we will discuss a few of them, in particular the recent data on mutations in vasopressin RNA. It is to be expected that the HNS will retain its informative role in the next decades.

Blood concentrations of vasopressin, neuropeptide FF and prolactin are increased by high-dose right unilateral ECT

Electroconvulsive therapy (ECT) is known to stimulate subcortical brain regions and release hormones from the anterior and the posterior pituitary. To enhance the subcortical effect of ECT and the neuroendocrinological response we used high dose right unilateral ECT (RUL-ECT) in 11 depressive patients and studied its effect on the release of vasopressin, prolactin and neuropeptide FF. The RUL ECT stimulus for all studied patients was 5 times the individual seizure threshold and it led to immediate release of vasopressin in all studied patients. The release of prolactin was less uniform however in accordance with results from earlier studies. The ECT also stimulated a NPFF secretion peak that came approximately 5 min after ECT stimulus and preceded the prolactin peak. The maximal elevations in circulating vasopressin and prolactin concentrations were 680% and 950%, respectively. The neuropeptide FF concentration increased by 100% after ECT. There was a second rise in NPFF concentration at 25 min after the ECT treatment. The increases in all peptide concentrations were significant, but were not correlated with each other. The neuropeptide FF concentration returned to baseline level at 10 min and the vasopressin concentration at 25 min after ECT. The prolactin concentration remained increased during the 30 min follow up period. Our results complete earlier finding on ECT stimulated vasopressin and prolactin release and show that high intensity RUL-ECT releases neuropeptide FF into human blood. The modest rise of circulating NFFF most likely represents leakage from the CNS.

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.

The effect of FMRFamide analogs on [35S]GTP-gamma-S stimulation in squid optic lobes

Pharmacological study of Phe-Met-Leu-Phe-amide (FMRFa) receptors is hindered by the lack of selective ligands. The classification of these selective ligands is further hampered by the limited availability of functional assays. In this study, we evaluated several synthetic FMRFa analogs for agonist and antagonist activity by measuring their abilities to produce [35-S]-GTP-gamma-S stimulation or to inhibit FMRFa-induced [35S]-GTP-gamma-S binding in squid optic lobes. Analogs included acetyl-Phe-norLeu-Arg-Phe-amide (acFnLRFa), desamino-Tyr-Phe-Leu-Arg-amide (daYFLRa), desamino Tyr-Phe-norLeu-Arg-Phe-amide (daYFnLRFa), desamino Tyr-Phe-norLeu-Arg-[TIC]-amide (daYFnLR[TIC]a), desamino Tyr-Trp-norLeu-Arg-amide (daYWnLRa), (D)-Tyr-Phe-norLeu-Arg-Phe-amide (D)-YFnLRFa), Phe-Leu-Arg-Phe-amide (FLRFa), and the D-amino acid analogs of FMRFa (D-FMRFa, F-(D)-MRFa and FM-(D)-RFa). For agonist studies, full dose-response curves were generated and analyzed for potency and efficacy (maximal percent effect). FMRFamide as well as analogs ac-FnLRFa, daYFnLRFa, daYFnLR[TIC]a, D-YFnLRFa, FLRFa, and (D)-FMRFa stimulated [35S]-GTP-gamma-S binding. Analogs daYWnLRa, daYFLRa, F-(D)-MRFa, and FM-(D)-RFa failed to stimulate either [35S]-GTP-gamma-S binding or to inhibit FMRFa-induced [35S]-GTP-gamma-S binding. The rank order of potency was daYFnLRFa > or = daYFnLRF[TIC]a > acFnLRFa > (D)YFnLRFa > FLRFa > or = FMRFa >> (D)-FMRFa. The order of efficacy was daYFnLRFa = acFnLRFa = (D)-YFnLRFa > FLRFa = FMRFa > or = (D)-FMRFa > or = daYFnLRF[TIC]a. Peptide analog daYFnLR[TIC]a was less efficacious (59% maximal stimulation) than analogs daYFnLRFa, acFnLRFa, and (D)-YFnLRFa (113-146% maximal stimulation). A maximal concentration of daYFnLR[TIC]a (10 microM) reduced daYFnLRFa, acFnLRFa, and (D)-YFnLRFa induced [35S]-GTP-gamma-S stimulation, indicating that daYFnLR[TIC]a is a partial agonist at the receptor stimulated by the FMRFamide analogs. Analysis of the structural requirements needed for promoting [35S]-GTP-gamma-S binding show that elongation (i.e., daYFnLRFa, D-YFnLRFa) or modification of Phe1 (ac-FnLRFa) leads to increased efficacy and potency. Moreover, elimination of the C-terminal Phe (daYWnLRa, daYFLRa,) leads to a loss of biological activity. However, substitution with L-1,2,3,4 tetrahydroisoquinoline-3-carboxylic acid, a rigid analog of the C-terminal Phe (daYFnLR[TIC]a), leads to decreased efficacy but not loss of potency. The data suggest that immobilization or modification of the C-terminal Phe may produce highly selective and potent FMRFamide antagonists. These results agree with published receptor radioligand studies and indicate that the [35S]GTP-gamma-S assay may be useful in classifying novel FMRFamide-selective ligands.

Pulsatile secretion of neuropeptide FF into human blood

Neuropeptide FF (NPFF) is a peptide with opioid modulating and cardioexcitatory effects, it is present in the central nervous system and in the periphery of several mammalian species. Using a sensitive and specific radioimmunoassay for NPFF-like immunoreactivity (NPFFir) we observed that the peptide concentration fluctuated in a pattern compatible with pulsatile secretion of the peptide in human blood. When NPFF samples were collected every 2 or 5 min for a 95 min period in healthy volunteers the basal NPFF concentration in human blood was 2.2 +/- 0.5 pg/ml and the NPFF pulses (14.6 +/- 10.6 pg/ml) represented a 526 +/- 280% increase over baseline. The NPFF pulses where short, suggesting a rapid degradation of NPFF in the circulation. We observed no twenty-four hour rhythm of NPFF in human blood when NPFF samples were taken during one day every four hours. Fluctuations in NPFF levels found in the 95 min and the 24 h studies did not correlate with plasma vasopressin levels. Our study did not support the concept that vasopressin and NPFF may be co-released from the pituitary. However, the pulsatile character of NPFF secretion in itself suggests a biologic role for neuropeptide FF in humans.

Lack of translation of normal 7B2 mRNA levels in hypothalamic mutant vasopressin cells of the homozygous Brattleboro rat

The homozygous Brattleboro rat (di/di) synthesizes a vasopressin (VP) precursor with an aberrant C-terminus, which causes a hypothalamic form of diabetes insipidus. The neuroendocrine polypeptide 7B2 is present in VP and oxytocin (OT) neurons of the supraoptic and paraventricular nucleus of the hypothalamus in wild type rats. However, in the di/di rat 7B2 immunoreactivity is absent in the VP cell population, whereas 7B2 levels within the OT cells are unaffected. Remarkably, there is no obvious difference in 7B2 transcript levels between VP and OT neurons in the di/di rat hypothalamus. This study shows that the presence of mRNA does not automatically result in the subsequent synthesis of its protein. Cellular mechanisms underlying this discrepancy are discussed.

Peptide GEGLSS-like immunoreactivity in the rat central nervous system

A rabbit antiserum was raised against the N-terminal fragment peptide, GEGLSS (Gly-Glu-Gly-Leu-Ser-Ser) of bovine neuropeptide AF (NPAF, A18Famide). NPAF is an octadecapeptide isolated from the bovine brain together with neuropeptide FF (NPFF). GEGLSS-like immunoreactivity was localized with immunofluorescence technique in colchicine-treated rats in neuronal cell bodies of the supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei. A few neurons were also observed in the retrochiasmatic part of the SON. GEGLSS-like immunoreactivity was also localized to nerve terminals of the posterior pituitary. No GEGLSS-ir neuronal cell bodies were observed in the medial hypothalamus, in an area that contains NPFF-ir neurons. GEGLSS immunoreactivity was also seen in the fibers and terminals of nucleus of the solitary tract. We injected a retrograde tracer, fluorogold, to the posterior pituitary gland and visualized GEGLSS-ir neuronal cell bodies double-labeled with the tracer in SON, PVN, and SOR. The pituitary stalk transsection totally abolished the GEGLSS-ir structures from the posterior pituitary. Our results suggest that GEGLSS immunoreactivity in the rat brain has a more limited distribution than NPFF immunoreactivity. GEGLSS immunoreactivity was partially colocalized with arginine-vasopressin and oxytocin in neuronal cell bodies in the SON and PVN. Considering the fact that the known rat NPFF-NPAF precursor does not contain GEGLSS structure, the detected GEGLSS immunoreactivity may be derived from a previously unknown precursor.

Presence of neuropeptide FF receptors on primary afferent fibres of the rat spinal cord

A radioiodinated analogue of neuropeptide FF, [125I][D. Tyr1,(NMe) Phe3]neuropeptide FF, was used as a selective probe to label neuropeptide FF receptors in the rat spinal cord. Following neonatal capsaicin treatment, dorsal rhizotomy or sciatic nerve section, the distribution and possible alterations of spinal cord specific [125I][D.Tyr1,(NMe)Phe3]neuropeptide FF binding sites were evaluated using in vitro quantitative receptor autoradiography. In normal rats, the highest densities of sites were observed in the superficial layers of the dorsal horn (laminae I-II) whereas moderate to low amounts of labelling were seen in the deeper (III-VI) laminae, around the central canal, and in the ventral horn. Capsaicin-treated rats showed a bilateral decrease (47%) in [125I][D.Tyr1,(NMe)Phe3]neuropeptide FF binding in all spinal areas. Unilateral sciatic nerve section and unilateral dorsal rhizotomy induced significant depletions (15-27%) in [125I][D.Tyr1,(NMe)Phe3]neuropeptide FF labelling in the ipsilateral dorsal horn. These results suggest that a proportion of neuropeptide FF receptors is located on primary afferent terminals of the dorsal horn and could thus play a role in the modulation of nociceptive transmission.

Increased light intensity prevents the age related loss of vasopressin-expressing neurons in the rat suprachiasmatic nucleus

We investigated whether increased light input can counteract the age-related decrease in vasopressin- (AVP) and vasoactive intestinal polypeptide (VIP)-expressing neurons of the suprachiasmatic nucleus (SCN) by determining the numbers of these neurons in rats of different ages, housed under low or high intensities of light. The significant age-related decrease for AVP was prevented in old animals after high light housing. For VIP, no effects were found.

Neuropeptide FF-containing efferent projections from the medial hypothalamus of rat: a Phaseolus vulgaris leucoagglutinin study

Neuropeptide FF (FMRFamide-like peptide, morphine-modulating peptide) is an octapeptide isolated from the bovine brain. There is evidence that neuropeptide FF participates in the modulation of nociceptive mechanisms. Neuropeptide FF acts through its own receptors which are distinct from the opiate receptors. In the rat brain neuropeptide FF is found in two major cell populations. We have studied the efferent connections of the hypothalamic neuropeptide FF-containing cell group, which is located in the medial hypothalamus between the dorsomedial, ventromedial and periventricular hypothalamic nuclei. By using an anterograde tracing method (Phaseolus vulgaris leucoagglutinin) combined with double-staining immunohistochemistry we characterized the connections of this cell group with the limbic system, certain hypothalamic nuclei, periaqueductal gray and with the solitary tract nucleus. In the limbic system, the major targets were the lateral septal nucleus, bed nucleus of stria terminalis and certain subnuclei in the amygdala. These connections suggest that neuropeptide FF may act, in addition to its well-characterized action in the sensory system, in limbic functions. Efferent connections to the periaqueductal gray suggest that neuropeptide FF may modulate the opiate mediated analgesia at this site. Good correlation between our results and receptor autoradiography support the idea that the terminal areas which our results show are target areas of the neuropeptide FF-containing system.

Distribution of FMRFamide-like immunoreactivity in the brain of the lungfish Protopterus annectens

The distribution of FMRFamide-like immunoreactive peptides was studied in the brain of the African lungfish, Protopterus annectens, using the indirect immunofluorescence technique. The main populations of FMRFamide-positive cell bodies were detected in the forebrain and in the mesencephalic tegmentum. In the telencephalon, only a small number of FMRFamide-immunoreactive neurons was localized at the level of the subpallium, in the nucleus septi medialis. The diencephalon contained two prominent groups of FMRFamide-positive cell bodies located in the preoptic and periventricular preoptic nuclei. The thalamus exhibited only scattered FMRFamide-immunoreactive perikarya in its ventral part. In the mesencephalon, a group of positive cell bodies was identified in the caudal region of the tegmentum. A strong immunoreaction was also detected in the nervus terminalis. In the pituitary, most of the cells of the intermediate lobe were brightly stained. FMRFamide-like immunoreactive fibers and nerve terminals were widely distributed in the brain. In the telecephalon, numerous fibers were observed in several regions of the pallium and subpallium. A dense plexus of fibers was found in the hypothalamus and the thalamus. Immunoreactive fibers were seen coursing along the ventral wall of the infundibular cavity and terminating in the pars nervosa of the pituitary. The tectum and the ventral mesencephalon were also densely innervated. In contrast, the caudal brainstem only showed scarce immunoreactive processes. Coexistence of FMRFamide- and neuropeptide Y-like immunoreactivity was observed in the preoptic nucleus and in the nervus terminalis. The widespread distribution of FMRFamide-immunoreactive neurons in the brain and pituitary of P. annectens suggests that the peptide may exert both neuromodulator and neuroendocrine functions. The similarity between the distribution patterns of FMRFamide and neuropeptide Y in the brain of lungfish and amphibians supports the concept of a close phylogenetic link between these two groups.

Neuron-glia interactions in the release of oxytocin and vasopressin from the rat neural lobe: the role of opioids, other neuropeptides and their receptors

The release of the neurohormones oxytocin and vasopressin from the neural lobe into the circulation is regulated in a complex manner, which has only been partly elucidated. At the level of the neural lobe, regulation of release can occur by various endogenous compounds that act on specific receptors present on the nerve terminals themselves. In addition, release may be modulated by an alternative pathway in which the local glia cells, the pituicytes, are involved. It is especially the latter pathway that is discussed in detail in this commentary.

Distribution of FMRFamide-like immunoreactivity in the brain of the lizard Podarcis sicula

The distribution of FMRFamide-like immunoreactive peptides was investigated in the brain of the lizard, Podarcis sicula, using the indirect immunofluorescence technique. The main populations of FMRFamide-immunoreactive cell bodies were located in the forebrain. In the telencephalon, FMRFamide-containing neurons were found both in the pallium and subpallium, namely in the medial cortex, the anterior olfactory nucleus, the nucleus accumbens, the septal nuclei, the nucleus of the medial forebrain bundle, and the nucleus of the diagonal band of Broca. In the diencephalon, a dense accumulation of FMRFamide-immunoreactive neurons was observed in the area preoptica lateralis, the nucleus suprachiasmaticus, the nucleus periventricularis hypothalami, the area lateralis hypothalami, and the dorsal region of the nucleus geniculatus lateralis. In the midbrain, sparse immunoreactive perikarya were found in the tegmentum of the mesencephalon. FMRFamide-immunoreactive fibers were visualized in all regions containing positive cell bodies. In particular, dense bundles of immunoreactive processes were seen in the area preoptica lateralis, in the hypothalamus, and in the median eminence. The tectum and the basal mesencephalon were also densely innervated. Conversely, the caudal brain stem only exhibited scarce immunoreactive processes. The distribution pattern of FMRFamide-immunoreactive neurons in the brain of Podarcis sicula exhibits a number of similarities with that reported in mammals, but significantly differs from that reported in amphibians and fish, suggesting that the neuromodulatory functions of FMRFamide may have diverged during the emergence of terrestrial life.