Localization of corticotropin-releasing factor-containing neurons in the brain of the domestic fowl. An immunohistochemical study

Mapping of corticotropin-releasing factor, receptors, and binding protein mRNA in the chicken telencephalon throughout development

Understanding the neural mechanisms that regulate the stress response is critical to know how animals adapt to a changing world and is one of the key factors to be considered for improving animal welfare. Corticotropin-releasing factor (CRF) is crucial for regulating physiological and endocrine responses, triggering the activation of the sympathetic nervous system and the hypothalamo-pituitary-adrenal axis (HPA) during stress. In mammals, several telencephalic areas, such as the amygdala and the hippocampus, regulate the autonomic system and the HPA responses. These centers include subpopulations of CRF containing neurons that, by way of CRF receptors, play modulatory roles in the emotional and cognitive aspects of stress. CRF binding protein also plays a role, buffering extracellular CRF and regulating its availability. CRF role in activation of the HPA is evolutionary conserved in vertebrates, highlighting the relevance of this system to help animals cope with adversity. However, knowledge on CRF systems in the avian telencephalon is very limited, and no information exists on detailed expression of CRF receptors and binding protein. Knowing that the stress response changes with age, with important variations during the first week posthatching, the aim of this study was to analyze mRNA expression of CRF, CRF receptors 1 and 2, and CRF binding protein in chicken telencephalon throughout embryonic and early posthatching development, using in situ hybridization. Our results demonstrate an early expression of CRF and its receptors in pallial areas regulating sensory processing, sensorimotor integration and cognition, and a late expression in subpallial areas regulating the stress response. However, CRF buffering system develops earlier in the subpallium than in the pallium. These results help to understand the mechanisms underlying the negative effects of noise and light during prehatching stages in chicken, and suggest that stress regulation becomes more sophisticated with age.

Telencephalic regulation of the HPA axis in birds

The hypothalamo-pituitary-adrenal (HPA) axis is one of the major output systems of the vertebrate stress response. It controls the release of cortisol or corticosterone from the adrenal gland. These hormones regulate a range of processes throughout the brain and body, with the main function of mobilizing energy reserves to improve coping with a stressful situation. This axis is regulated in response to both physical (e.g., osmotic) and psychological (e.g., social) stressors. In mammals, the telencephalon plays an important role in the regulation of the HPA axis response in particular to psychological stressors, with the amygdala and part of prefrontal cortex stimulating the stress response, and the hippocampus and another part of prefrontal cortex inhibiting the response to return it to baseline. Birds also mount HPA axis responses to psychological stressors, but much less is known about the telencephalic areas that control this response. This review summarizes which telencephalic areas in birds are connected to the HPA axis and are known to respond to stressful situations. The conclusion is that the telencephalic control of the HPA axis is probably an ancient system that dates from before the split between sauropsid and synapsid reptiles, but more research is needed into the functional relationships between the brain areas reviewed in birds if we want to understand the level of this conservation.

Incubation temperature affects the expression of young precocial birds' fear-related behaviours and neuroendocrine correlates

The influence of embryonic microclimate on the behavioural development of birds remains unexplored. In this study, we experimentally tested whether chronic exposure to suboptimal temperatures engendered plasticity in the expression of fear-related behaviours and in the expression of the corticotropin-releasing factor in the brains of domestic chicks (Gallus g. domesticus). We compared the neurobehavioural phenotypes of a control group of chicks incubated in an optimal thermal environment (37.8 °C) with those of a group of experimental chicks exposed chronically in ovo to suboptimal temperatures (27.2 °C for 1 hour twice a day). Chronic exposure to a suboptimal temperature delayed hatching and decreased growth rate and experimental chicks had higher neophobic responses than controls in novel food and novel environment tests. In addition, experimental chicks showed higher expression of corticotropin-releasing factor than did controls in nuclei of the amygdala, a structure involved in the regulation of fear-related behaviours. In this study, we report the first evidence of the strong but underappreciated role of incubation microclimate on the development of birds’ behaviour and its neurobiological correlates.

Anatomical and functional implications of corticotrophin-releasing hormone neurones in a septal nucleus of the avian brain: an emphasis on glial-neuronal interaction via V1a receptors in vitro

Previously, we showed that corticotrophin-releasing hormone immunoreactive (CRH-IR) neurones in a septal structure are associated with stress and the hypothalamic-pituitary-adrenal axis in birds. In the present study, we focused upon CRH-IR neurones located within the septal structure called the nucleus of the hippocampal commissure (NHpC). Immunocytochemical and gene expression analyses were used to identify the anatomical and functional characteristics of cells within the NHpC. A comparative morphometry analysis showed that CRH-IR neurones in the NHpC were significantly larger than CRH-IR parvocellular neurones in the paraventricular nucleus of the hypothalamus (PVN) and lateral bed nucleus of the stria terminalis. Furthermore, these large neurones in the NHpC usually have more than two processes, showing characteristics of multipolar neurones. Utilisation of an organotypic slice culture method enabled testing of how CRH-IR neurones could be regulated within the NHpC. Similar to the PVN, CRH mRNA levels in the NHpC were increased following forskolin treatment. However, dexamethasone decreased forskolin-induced CRH gene expression only in the PVN and not in the NHpC, indicating differential inhibitory mechanisms in the PVN and the NHpC of the avian brain. Moreover, immunocytochemical evidence also showed that CRH-IR neurones reside in the NHpC along with the vasotocinergic system, comprising arginine vasotocin (AVT) nerve terminals and immunoreactive vasotocin V1a receptors (V1aR) in glia. Hence, we hypothesised that AVT acts as a neuromodulator within the NHpC to modulate activity of CRH neurones via glial V1aR. Gene expression analysis of cultured slices revealed that AVT treatment increased CRH mRNA levels, whereas a combination of AVT and a V1aR antagonist treatment decreased CRH mRNA expression. Furthermore, an attempt to identify an intercellular mechanism in glial-neuronal communication in the NHpC revealed that brain-derived neurotrophic factor (BDNF) and its receptor (TrkB) could be involved in the signalling mechanism. Immunocytochemical results further showed that both BDNF and TrkB receptors were found in glia of the NHpC. Interestingly, in cultured brain slices containing the NHpC, the use of a selective TrkB antagonist decreased the AVT-induced increase in CRH gene expression levels. The results from the present study collectively suggest that CRH neuronal activity is modulated by AVT via V1aR involving BDNF and TrkB glia in the NHpC.

A second corticotropin-releasing hormone gene (CRH2) is conserved across vertebrate classes and expressed in the hindbrain of a basal neopterygian fish, the spotted gar (Lepisosteus oculatus)

To investigate the origins of the vertebrate stress-response system, we searched sequenced vertebrate genomes for genes resembling corticotropin-releasing hormone (CRH). We found that vertebrate genomes possess, in addition to CRH, another gene that resembles CRH in sequence and syntenic environment. This paralogous gene was previously identified only in the elephant shark (a holocephalan), but we find it also in marsupials, monotremes, lizards, turtles, birds, and fishes. We examined the relationship of this second vertebrate CRH gene, which we name CRH2, to CRH1 (previously known as CRH) and urocortin1/urotensin1 (UCN1/UTS1) in primitive fishes, teleosts, and tetrapods. The paralogs CRH1 and CRH2 likely evolved via duplication of CRH during a whole-genome duplication early in the vertebrate lineage. CRH2 was subsequently lost in both teleost fishes and eutherian mammals but retained in other lineages. To determine where CRH2 is expressed relative to CRH1 and UTS1, we used in situ hybridization on brain tissue from spotted gar (Lepisosteus oculatus), a neopterygian fish closely related to teleosts. In situ hybridization revealed widespread distribution of both crh1 and uts1 in the brain. Expression of crh2 was restricted to the putative secondary gustatory/secondary visceral nucleus, which also expressed calcitonin-related polypeptide alpha (calca), a marker of parabrachial nucleus in mammals. Thus, the evolutionary history of CRH2 includes restricted expression in the brain, sequence changes, and gene loss, likely reflecting release of selective constraints following whole-genome duplication. The discovery of CRH2 opens many new possibilities for understanding the diverse functions of the CRH family of peptides across vertebrates.

Identification of arginine vasotocin (AVT) neurons activated by acute and chronic restraint stress in the avian septum and anterior diencephalon

Effects of acute and chronic psychological stress in the brain of domestic avian species have not been extensively studied. Experiments were performed using restraint stress to determine groups of neurons activated in the septum and diencephalon of chickens. Using FOS immunoreactivity six brain structures were shown activated by acute stress including: the lateral hypothalamic area (LHy), ventrolateral thalamic nucleus (VLT), lateral septum (LS), lateral bed nucleus of the stria terminalis (BSTL), nucleus of the hippocampal commissure (NHpC) and the core region of the paraventricular nucleus (PVNc). Additionally, the LHy and PVNc showed increased FOS immunoreactive (-ir) cells in the birds chronically stressed when compared to controls. In contrast, the NHpC showed decreased FOS-ir cells following the 10day chronic stress imposed. Thereafter, restraint stress experiments were performed to identify activated arginine vasotocin (AVT) neurons (parvocellular or magnocellular) using immunocytochemistry. Of the six FOS activated structures, the PVN was known to contain distinct size groups of AVT-ir neurons, parvocellular (small), medium sized and magnocellular (large). Using dual immunostaining (AVT/FOS), AVT-ir parvocellular neurons in the PVNc were found activated in both acute and chronic stress. To determine whether these AVT-ir parvocellular neurons are co-localized with corticotropin releasing hormone (CRH), an attempt was made to visualize CRH-ir neurons using colchicine. Although AVT-ir and CRH-ir parvocellular neurons occur in the PVNc, only a few neurons were shown co-localized with AVT and CRH after acute restraint stress. Results of this study suggest that the NHpC, LS, VLT, BSTL, LHy and AVT-ir parvocellular neurons in the PVNc are associated with psychological stress in birds.

Central injection of urocortin-3 but not corticotrophin-releasing hormone influences the ghrelin/GHS-R1a system of the proventriculus and brain in chicks

Ghrelin, the endogenous ligand for growth hormone secretagogue receptor 1a (GHS-R1a), stimulates food intake in mammals centrally and peripherally. In contrast, central injection of ghrelin inhibits feeding in neonatal chicks (Gallus gallus), which is thought to be mediated by the corticotrophin-releasing hormone (CRH) system, indicating that the mechanisms underlying ghrelin's action are different in chicks and mammals. However, the interaction between the ghrelin system and the CRH system has not been fully clarified in chicks. In the present study, we examined the effect of intracerebroventricular (ICV) injection of CRH and urocortin-3 (UCN-3), a CRH family peptide and an endogenous ligand for the CRH type-2 receptor (CRH-R2), on synthesis and secretion of ghrelin in chicks. Intracerebroventricular injection of UCN-3 but not CRH increased plasma ghrelin concentration (P < 0.05), diencephalic mRNA expression of ghrelin, and GHS-R1a (P < 0.05) and tended to decrease ghrelin (P = 0.08) and GHS-R1a (P = 0.10) mRNA expression in the proventriculus. Moreover, ICV injection of UCN-3 tended to increase diencephalic mRNA expression of CRH-R2 (P = 0.08) and CRH had no effect on it. In addition, ICV injection of CRH but not UCN-3 increased plasma corticosterone concentration (P < 0.05) and decreased the diencephalic mRNA expression of CRH-R1 (P < 0.05). These results clearly indicate that the roles of the CRH system for the ghrelin system are divided. The present study suggests that UCN-3 is mainly involved in the ghrelin system in chicks perhaps through the CRH-R2.

Calcitonin receptor bindings in the hen hypothalamus before and after oviposition

To demonstrate the presence of a receptor for calcitonin (CT) in the hen hypothalamus and to determine when CT acts on this tissue during the oviposition cycle, bindings of (125)I labeled CT in the plasma membrane fraction of the hen hypothalamus were measured by radioligand binding assay. The specific CT binding component in the plasma membrane fraction of the hypothalamus containing the preoptic area (HPOA) possessed properties of a receptor: binding specificity to CT, saturable binding, high affinity, and limited capacity. As for the median eminence area, no specific binding component was found in the present study. Therefore, the binding component for CT in the plasma membrane fraction of HPOA is likely to be a receptor for CT. In laying hens, the binding affinity of CT receptor increased at 30 min before oviposition and the binding capacity was decreased at 30 min before oviposition but not changed in nonlaying hens during a 24-h period. These results suggest that the action of CT on the hen HPOA may increase 30 min before oviposition.

The anatomy and physiology of the avian endocrine system

The endocrine system of birds is comparable to that of mammals, although there are many unique aspects to consider when studying the anatomy, physiology, and biochemistry. Avian endocrinology is a field of veterinary medicine that is unfamiliar to many practitioners; however, it is important to have a comprehensive understanding when evaluating companion birds in clinical practice. This article covers the anatomy and physiology of the normal avian, and readers are referred to other articles for a more detailed explanation of altered physiology and pathology.

Regulation of behavioral responses by corticotropin-releasing factor

In the wild, animals survive by responding to perceived threats with adaptive and appropriate changes in their behaviors and physiological states. The exact nature of these responses depends on species-specific factors plus the external context and internal physiological states associated with the stressful condition. The neuroendocrine mechanisms that control context-dependent stress responses are poorly understood for most animals, but some progress has been made recently. Corticotropin-releasing factor (CRF) plays an important role in mediating neuroendocrine, autonomic, and behavioral responses to stress. Across many vertebrate taxa, CRF not only stimulates the HPA axis by increasing the secretion of ACTH and glucocorticoid hormones, but also acts centrally by modifying neurotransmitter systems and behaviors. CRF or one of several CRF-related neuropeptides acts to stimulate locomotor activity during periods of acute stress. This behavioral activation consists of anxiety-related non-ambulatory motor activity, ambulatory locomotion, or swimming depending on the species and context. CRF-related neuropeptides increase swimming behaviors in amphibians and fish, apparently by activating brainstem serotonergic systems because the administration of fluoxetine (a selective serotonin re-uptake inhibitor) greatly enhances CRF-induced locomotor activity. Thus, our working model is that CRF, in part via interactions with brainstem serotonergic systems, modulates context-dependent behavioral responses to perceived threats, including both anxiety-related risk assessment behaviors and fight-or-flight locomotor responses.

Anorexigenic effects of pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide in the chick brain are mediated by corticotrophin-releasing factor

Intracerebroventricular (ICV) injection of pituitary adenylate cyclase-activating polypeptide-38 (PACAP) or vasoactive intestinal peptide (VIP) inhibits feeding in chicks. However, the underlying anorexigenic mechanism(s) has not yet been investigated. The present study investigated whether these peptides influence the activity of corticotrophin-releasing factor (CRF) neural pathways in the brain of chicks. Firstly, we found that ICV injections of PACAP and VIP increased plasma corticosterone concentrations. The corticosterone-releasing effect of PACAP was completely attenuated by co-injection of astressin, a CRF receptor antagonist, but this effect was only partial for VIP. These results demonstrated that CRF neurons mediate the actions of PACAP and, to a lesser extent, VIP, and suggest that the signaling mechanisms differ between the two peptides. This difference may arise from the two peptides interacting with different receptors because the corticosterone-releasing effect of PACAP, but not VIP, was completely attenuated by co-injection of PACAP (6-38), a PACAP receptor antagonist. Finally, we examined the effect of ICV co-injection of astressin on the anorexigenic effects of PACAP and VIP and found that the effects of both peptides were attenuated by astressin. Overall, the present study suggests that the anorexigenic effects of PACAP and VIP are mediated by the activation of CRF neurons.

Distribution and acute stressor-induced activation of corticotrophin-releasing hormone neurones in the central nervous system of Xenopus laevis

In mammals, corticotrophin-releasing hormone (CRH) and related peptides are known to play essential roles in the regulation of neuroendocrine, autonomic and behavioural responses to physical and emotional stress. In nonmammalian species, CRH-like peptides are hypothesized to play similar neuroendocrine and neurocrine roles. However, there is relatively little detailed information on the distribution of CRH neurones in the central nervous system (CNS) of nonmammalian vertebrates, and there are currently no comparative data on stress-induced changes in CRH neuronal physiology. We used a specific, affinity-purified antibody raised against synthetic Xenopus laevis CRH to map the distribution of CRH in the CNS of juvenile South African clawed frogs. We then analysed stress-induced changes in CRH immunoreactivity (CRH-ir) throughout the CNS. We found that CRH-positive cell bodies and fibres are widely distributed throughout the brain and rostral spinal cord of juvenile X. laevis. Strong CRH-immunoreactivity (ir) was found in cell bodies and fibres in the anterior preoptic area (POA, an area homologous to the mammalian paraventricular nucleus) and the external zone of the median eminence. Specific CRH-ir cell bodies and fibres were also identified in the septum, pallium and striatum in the telencephalon; the amygdala, bed nucleus of the stria terminalis and various hypothalamic and thalamic nuclei in the diencephalon; the tectum, torus semicircularis and tegmental nuclei of the mesencephalon; the cerebellum and locus coeruleus in the rhombencephalon; and the ventral horn of the rostral spinal cord. To determine if exposure to an acute physical stressor alters CRH neuronal physiology, we exposed juvenile frogs to shaking/handling and conducted morphometric analysis. Plasma corticosterone was significantly elevated by 30 min after exposure to the stressor and continued to increase up to 6 h. Morphometric analysis of CRH-ir after 4 h of stress showed a significant increase in CRH-ir in parvocellular neurones of the anterior preoptic area, the medial amygdala and the bed nucleus of the stria terminalis, but not in other brain regions. The stress-induced increase in CRH-ir in the POA was associated with increased Fos-like immunoreactivity (Fos-LI), and confocal microscopy showed that CRH-ir colocalized with Fos-LI in a subset of Fos-LI-positive neurones. Our results support the view that the basic pattern of CNS CRH expression arose early in vertebrate evolution and lend further support to earlier studies suggesting that amphibians may be a transitional species for descending CRH-ergic pathways. Furthermore, CRH neurones in the frog brain exhibit changes in response to a physical stressor that parallel those seen in mammals, and thus are likely to play an active role in mediating neuroendocrine, behavioural and autonomic stress responses.

Cloning and tissue distribution of the chicken type 2 corticotropin-releasing hormone receptor

We report the cloning of the complete coding sequence of the putative chicken type 2 corticotropin-releasing hormone receptor (CRH-R2) by rapid amplification of cDNA ends (RACE). The chicken CRH-R2 is a 412-amino acid 7-transmembrane G protein-coupled receptor, showing 87% identity to the Xenopus laevis and Oncorhynchus keta CRH-R2s, and 78-80% to mammalian CRH-R2s. The distribution of CRH-R2 mRNA was studied by RT-PCR analysis and compared to CRH-R1 distribution. Both CRH-R1 and CRH-R2 mRNA are expressed in the main chicken brain parts. In peripheral organs, CRH-R1 mRNA shows a more restricted distribution, whereas CRH-R2 mRNA is expressed in every tissue investigated, indicating that a number of actions of CRH and/or CRH-like peptides remain to be discovered in the chicken as well as in other vertebrates.

Comparison of brain arginine-vasotocin and corticotrophin-releasing factor for physiological responses in chicks

Arginine-vasotocin (AVT), a non-mammalian homologue of mammalian arginine-vasopressin, is a stress-related peptide in the brain of birds. The aim of the present study was to determine the effects of intracerebroventricular (ICV) injection of AVT on feeding behavior, body temperature, corticosterone release and several behavioral parameters in chicks. These effects were compared with those of corticotrophin-releasing factor (CRF), another stress-related peptide. The ICV injection of AVT inhibited feeding behavior, increased rectal temperature, and increased plasma corticosterone concentrations, but these effects were weaker than those of CRF. AVT induced hypoactivity as evidenced by decreased vocalization and stepping while CRF induced hyperactivity. The present results demonstrate that some functions of brain AVT are similar to those of CRF, although these effects are weaker than those induced by CRF. However, some AVT-induced behaviors were different from CRF, indicating that the physiological roles of AVT in the regulation of stress behavior are different from those of CRF in chicks.

Distribution of corticotropin-releasing factor-immunoreactive neurons in the central nervous system of the domestic chicken and Japanese quail

In birds, as in mammals, corticotropin-releasing factor (CRF) is present in a number of extrahypothalamic brain regions, indicating that CRF may play a role in physiological and behavioral responses other than the control of adrenocorticotropin hormone release by the pituitary. To provide a foundation for investigation of the roles of CRF in the control of avian behavior, the distribution of CRF immunoreactivity was determined throughout the central nervous system of the domestic chicken (Gallus domesticus) and Japanese quail (Coturnix japonica). The distribution of CRF-immunoreactive (-ir) perikarya and fibers in the chicken and quail brain was found to be more extensive than previously reported, notably in the telencephalon. Numerous CRF-ir perikarya and fibers were present in the hyperstriatum, hippocampus, neostriatum, lobus parolfactorius, and archistriatum, as well as in the nucleus taeniae, nucleus accumbens, and bed nucleus of the stria terminalis, which exhibited the strongest immunolabeling in the telencephalon. The presence of dense populations of CRF-ir perikarya in the medial lobus parolfactorius, nucleus of the stria terminalis, and paleostriatum ventrale, apparently giving rise to CRF-ir projections to the mesencephalic reticular formation, the parabrachial/pericerulear region, and the dorsal vagal complex, suggests that these telencephalic areas may constitute part of the avian "central extended amygdala." These results have important implications for understanding the role of extrahypothalamic CRF systems in emotional responses in birds.

Centrally administered norepinephrine modifies the behavior induced by corticotropin-releasing factor in neonatal chicks

We previously reported that glucagon-like peptide-1 decreased corticotropin-releasing factor (CRF)-induced behaviors in neonatal chicks, and such an effect is hypothesized to act through norepinephrine (NE). Experiments were designed to explore the effect of the NE on CRF-induced behaviors. In experiment 1, the chicks were intracerebroventricularly (i.c.v.) administered saline, 0.1 microg of CRF, 50.0 microg of NE, or 0.1 microg of CRF with 50.0 microg of NE. Behavior was monitored for the 10 min immediately after i.c.v. injection, and plasma corticosterone was analyzed at the end of behavior tests. Compared with the control, chicks were excited by CRF as evidenced by increased spontaneous activity and distress vocalizations (DVs). NE decreased the spontaneous activity of chicks, and the differences diverged with time. DVs completely disappeared in the presence of NE, and sleep-like (sitting with eyes closed) behavior was observed in the same birds. NE-treated birds spent most of the time in a sleep-like posture irrespective of CRF treatment. CRF-treated chicks had increased plasma corticosterone, whereas NE injection caused a decrease in corticosterone. In experiment 2, the effect of NE was further studied using i.c.v. administration with either 0.1 microg of CRF alone or 0.1 microg of CRF plus 12.5, 25.0, or 50.0 microg of NE. NE dose dependently modified the CRF-induced locomotor activity in the open field, and DVs disappeared when chicks were given any dose of NE with CRF. With these findings taken together, it is suggested that central NE interacts the CRF-induced behaviors in neonatal chicks.

Interaction of corticotropin-releasing factor and glucagon-like peptide-1 on behaviors in chicks

Both corticortropin-releasing factor (CRF) and glucagon-like peptide-1 (GLP-1) inhibit food intake of chicks, but they also produce other behaviors. The present experiments were undertaken to clarify the interaction of CRF and GLP-1 regarding their anorectic actions as well as other behaviors. In Experiment 1, birds were injected intracerebroventricularly (i.c.v.), following a 3-h fast, with either saline, 0.1 microg of CRF, 0.1 microg of CRF+0.1 microg of GLP-1 or 0.1 microg of CRF+1 microg of GLP-1, and food intake was measured for 2 h. The injection of CRF decreased food intake, and CRF injected with GLP-1 suppressed food intake for up to 2 h. Birds were treated similarly in Experiment 2 in which the doses of CRF and GLP-1 were reversed. GLP-1 strongly suppressed food intake, and this effect was augmented by coadministration of CRF. In Experiment 3, the behaviors of chicks injected with saline, CRF (0.1 microg), GLP-1 (0.1 microg) or CRF (0.1 microg)+GLP-1 (0.1 microg) were monitored for the numbers of steps, vocalization and locomotion. Chicks were excited, moved more and vocalized loudly following injection of CRF, whereas an opposite response was seen with GLP-1. The behaviors were intermediate following the coinjection of the two peptides. In conclusion, CRF and GLP-1 interact in the chick brain, but the response depends on the behavior being measured.

Evolution and physiology of the corticotropin-releasing factor (CRF) family of neuropeptides in vertebrates

Corticotropin-releasing factor (CRF), urotensin-I, urocortin and sauvagine belong to a family of related neuropeptides found throughout chordate taxa and likely stem from an ancestral peptide precursor early in metazoan ancestry. In vertebrates, current evidence suggests that CRF on one hand, and urotensin-I, urocortin and sauvagine, on the other, form paralogous lineages. Urocortin and sauvagine appear to represent tetrapod orthologues of fish urotensin-I. Sauvagine's unique structure may reflect the distinctly derived evolutionary history of the anura and the amphibia in general. The physiological actions of these peptides are mediated by at least two receptor subtypes and a soluble binding protein. Although the earliest functions of these peptides may have been associated with osmoregulation and diuresis, a constellation of physiological effects associated with stress and anxiety, vasoregulation, thermoregulation, growth and metabolism, metamorphosis and reproduction have been identified in various vertebrate species. The elaboration of neural circuitry for each of the two paralogous neuropeptide systems appears to have followed distinct pathways in the actinopterygian and sarcopterygian lineages of vertebrates. A comparision of the functional differences between these two lineages predicts additional functions of these peptides.

Inhibition of food intake by CRF in chickens

The effect of intracerebroventricular (i.c.v.) injection of corticotrophin releasing factor (CRF) on food and water intake and on body temperature in chickens was determined. Both broiler and Leghorn type chickens were utilized in this experiment. A stainless steel guide cannula was surgically implanted into the right lateral ventricle of each bird. The i.c.v. injection of CRF significantly decreased food intake in both fed and overnight-fasted broilers and Leghorns. Water intake was decreased by CRF in Leghorns but not broilers. When CRF was injected into Leghorns given access to water, but not food, water intake was not affected. Body temperature was not affected by the i.c.v. injection of CRF. These results suggest that CRF acts within the central nervous system of chickens to decrease food intake while having no affect on water intake or body temperature.

Hypothalamic and extrahypothalamic sauvagine-like immunoreactivity in the bullfrog (Rana catesbeiana) central nervous system

In the present study, immunocytochemistry and radioimmunoassay were used to investigate the presence of sauvagine in both hypothalamic and extrahypothalamic areas of the central nervous system (CNS) of the bullfrog (Rana catesbeiana) using a specific antiserum raised against synthetic non-conjugated sauvagine (SVG), a frog (Phyllomedusa sauvagei) skin peptide of the corticotropin-releasing factor (CRF) family. Sauvagine-immunoreactive (SVG-ir) bipolar neurons were found in the nucleus of the fasciculus longitudinalis medialis located in the rostral mesencephalic tegmentum. In the tectal mesencephalon, beaded SVG-ir fibres were present in the optic tectum, and in the torus semicircularis. Abundant SVG-ir varicose fibres were seen in the granulosa layer of the cerebellum, the nucleus isthmi, and the obex of the spinal cord. SVG-ir fibres were also seen by the alar plate of the rombencephalon. In the diencephalon, the antiserum stained parvocellular neurons of the preoptic nucleus (PON) which extended their dendrites into the cerebro-spinal fluid (CSF) of the third ventricle and projected their ependymofugal fibres to the zona externa (ZE) of the median eminence. Immunopositive fibres were also present in the medial forebrain bundle at the chiasmatic field, the posterior thalamus, the pretectal gray, and the ventrocaudal hypothalamus. In the telencephalon (forebrain), SVG-ir fibres were seen in the medial septum, the lateral septum, and the amygdala. The SVG immunoreactivity could not be detected after using the SVG antiserum previously immunoabsorbed with synthetic SVG (0.1 microM), but immunoblock of the antiserum with sucker (Catostomus commersoni) urotensin I (sUI), sole (Hippoglossoides elassodon) urotensin I, sucker CRF, rat/human CRF, or ovine CRF (0.1-10 microM) did not eliminate visualization of the immunoreactivity. In radioimmunoassay, the SVG antiserum did not crossreact with sUI, or the SVG fragments SVG1-16, SVG16-27, and SVG26-34, but it recognized the C-terminal fragment SVG35-40. Crossreaction with mammalian ovine CRF and rat/human CRF was negligible. Both hypothalamic and mesencephalic extracts gave parallel displacement curves to SVG. The results suggest the presence in the bullfrog brain of a SVG-like neuropeptide, i.e., a peptide of the CRF family, that either is SVG or shares high homology with the C-terminus of that peptide. The function of this neuropeptide in amphibians is not known at this time, but based on its anatomical distribution to the ZE it could affect the release of adrenocorticotropin (ACTH) or other substances from the amphibian pars distalis. Involvement of the SVG-like peptide in behavioural (forebrain), visual (thalamus-tegmentum mesencephali-pretectal gray-optic tectum), motor coordination (cerebellum), and autonomic (spinal) functions, as well as an undefined interaction with the CSF in the bullfrog, seems likely.

Topographical distribution of CRF immunoreactivity in the pigeon brain

The distribution of corticotropin-releasing factor (CRF) immunoreactivity was demonstrated by immunocytochemistry in intact and colchicine-treated pigeons. Colchicine injections were administered at different times related to the circadian activity of the CRF-adrenocorticotropin (ACTH)-corticosterone axis. Three CRF antisera were used, two directed against synthetic rat CRF and one directed against synthetic ovine CRF. No fundamental differences appeared in the pigeon brain with respect to the specific CRF antiserum used. The most effective colchicine injection times corresponded to hypersecretion in the corticotropic axis. CRF-immunopositive neurons were scattered throughout the pigeon brain. In addition to the paraventricular hypothalamic system, which is involved in adenohypophysial ACTH regulation, several other hypothalamic and extrahypothalamic areas showed CRF neurons. The distribution suggests that CRF may also act as a modulator and a neurotransmitter. Two hypothalamic paraventricular nucleus-median eminence CRF pathways are described here. Moreover, CRF-immunopositive reactions were observed in specific areas of cerebral ventricle walls, suggesting that CRF may be released into the cerebral fluid.

Immunohistochemistry of the hypothalamic neuropeptides and anterior pituitary cells in the Japanese quail

The pars distalis of the avian adenohypophysis consists of well-defined cephalic and caudal lobes which are distinct in their cellular constituents. Immunocytochemical investigations on the pituitary hormones of the pars distalis of the Japanese quail reveal five types of secretory cells, adenocorticotropin (ACTH) cells, prolactin (PRL) cells, thyroid-stimulating hormone (TSH) cells, growth hormone GH (STH) cells, and FSH/LH (gonadotropic) cells. The ACTH cells, TSH cells, and PRL cells are restricted to the cephalic lobe, and GH (STH) cells are confined to the caudal lobe, while FSH/LH cells are distributed throughout the cephalic and caudal lobes. The median eminence of birds has distinct anterior and posterior divisions, each with different neuronal components. The avian hypophysial portal vessels also consists of two groups, anterior and posterior. The peculiar arrangement and distribution of the avian hypophysial portal vessels are possibly related to the distribution of neuropeptides in the two divisions of the median eminence and to the cytological and functional differentiation of two lobes of the pars distalis. The localization of perikarya and fibers containing luteinizing hormone releasing hormone (LHRH), somatostatin, vasotocin, mesotocin, corticotropin-releasing factor (CRF), vasoactive intestinal polypeptide (VIP), glucagon, metenkephalin, and substance P in the hypothalamus and median eminence of the Japanese quail has been investigated by means of immunohistochemistry using antisera against the respective neuropeptides. LHRH-, somatostatin-, VIP-, met-enkephalin-, and substance P-immunoreactive fibers are localized in the external layer of the anterior and posterior divisions of the median eminence, while CRF- and vasotocin-reactive fibers are demonstrated only in the external layer of the anterior division of the median eminence. The metenkephalin fibers are thicker in the anterior median eminence but the substance P fibers are more abundant in the posterior division. Mesotocin fibers occur only in the internal layer of the median eminence and neural lobe.