Comparative localization of neurons containing ovine corticotropin releasing factor (CRF)-like and neurophysin-like immunoreactivity in the diencephalon of the pigeon (Columba livia domestica)

Subpopulations of corticotropin-releasing factor containing neurons and internal circuits in the chicken central extended amygdala

In mammals, the central extended amygdala is critical for the regulation of the stress response. This regulation is extremely complex, involving multiple subpopulations of GABAergic neurons and complex networks of internal and external connections. Two neuron subpopulations expressing corticotropin-releasing factor (CRF), located in the central amygdala and the lateral bed nucleus of the stria terminalis (BSTL), play a key role in the long-term component of fear learning and in sustained fear responses akin to anxiety. Very little is known about the regulation of stress by the amygdala in nonmammals, hindering efforts for trying to improve animal welfare. In birds, one of the major problems relates to the high evolutionary divergence of the telencephalon, where the amygdala is located. In the present study, we aimed to investigate the presence of CRF neurons of the central extended amygdala in chicken and the local connections within this region. We found two major subpopulations of CRF cells in BSTL and the medial capsular central amygdala of chicken. Based on multiple labeling of CRF mRNA with different developmental transcription factors, all CRF neurons seem to originate within the telencephalon since they express Foxg1, and there are two subtypes with different embryonic origins that express Islet1 or Pax6. In addition, we demonstrated direct projections from Pax6 cells of the capsular central amygdala to BSTL and the oval central amygdala. We also found projections from Islet1 cells of the oval central amygdala to BSTL, which may constitute an indirect pathway for the regulation of BSTL output cells. Part of these projections may be mediated by CRF cells, in agreement with the expression of CRF receptors in both Ceov and BSTL. Our results show a complex organization of the central extended amygdala in chicken and open new venues for studying how different cells and circuits regulate stress in these animals.

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.

New Insights Into the Evolution of Corticotropin-Releasing Hormone Family With a Special Focus on Teleosts

Corticotropin-releasing hormone (CRH) was discovered for its role as a brain neurohormone controlling the corticotropic axis in vertebrates. An additional crh gene, crh2, paralog of crh (crh1), and likely resulting from the second round (2R) of vertebrate whole genome duplication (WGD), was identified in a holocephalan chondrichthyan, in basal mammals, various sauropsids and a non-teleost actinopterygian holostean. It was suggested that crh2 has been recurrently lost in some vertebrate groups including teleosts. We further investigated the fate of crh1 and crh2 in vertebrates with a special focus on teleosts. Phylogenetic and synteny analyses showed the presence of duplicated crh1 paralogs, crh1a and crh1b, in most teleosts, resulting from the teleost-specific WGD (3R). Crh1b is conserved in all teleosts studied, while crh1a has been lost independently in some species. Additional crh1 paralogs are present in carps and salmonids, resulting from specific WGD in these lineages. We identified crh2 gene in additional vertebrate groups such as chondrichthyan elasmobranchs, sarcopterygians including dipnoans and amphibians, and basal actinoperygians, Polypteridae and Chondrostei. We also revealed the presence of crh2 in teleosts, including elopomorphs, osteoglossomorphs, clupeiforms, and ostariophysians, while it would have been lost in Euteleostei along with some other groups. To get some insights on the functional evolution of the crh paralogs, we compared their primary and 3D structure, and by qPCR their tissue distribution, in two representative species, the European eel, which possesses three crh paralogs (crh1a, crh1b, crh2), and the Atlantic salmon, which possesses four crh paralogs of the crh1-type. All peptides conserved the structural characteristics of human CRH. Eel crh1b and both salmon crh1b genes were mainly expressed in the brain, supporting the major role of crh1b paralogs in controlling the corticotropic axis in teleosts. In contrast, crh1a paralogs were mainly expressed in peripheral tissues such as muscle and heart, in eel and salmon, reflecting a striking subfunctionalization between crh1a and b paralogs. Eel crh2 was weakly expressed in the brain and peripheral tissues. These results revisit the repertoire of crh in teleosts and highlight functional divergences that may have contributed to the differential conservation of various crh paralogs in teleosts.

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.

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.

The hypothalamic supraoptic and paraventricular nuclei of the echidna and platypus

The monotremes are an intriguing group of mammals that have major differences in their reproductive physiology and lactation from therian mammals. Monotreme young hatch from leathery skinned eggs and are nourished by milk secreted onto areolae rather than through nipples. Parturition and lactation are in part controlled through the paraventricular and supraoptic nuclei of the hypothalamus. We have used Nissl staining, enzyme histochemistry, immunohistochemistry for tyrosine hydroxylase, calbindin, oxytocin, neurophysin and non-phosphorylated neurofilament protein, and carbocyanine dye tracing techniques to examine the supraoptic and paraventricular nuclei and the course of the hypothalamo-neurohypophysial tract in two monotremes: the short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). In both monotremes, the supraoptic nucleus consisted of loosely packed neurons, mainly in the retrochiasmatic position. In the echidna, the paraventricular nucleus was quite small, but had similar chemoarchitectural features to therians. In the platypus, the paraventricular nucleus was larger and appeared to be part of a stream of magnocellular neurons extending from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. Immunohistochemistry for non-phosphorylated neurofilament protein and carbocyanine dye tracing suggested that hypothalamo-neurohypophysial tract neurons in the echidna lie mainly in the retrochiasmatic supraoptic and lateral hypothalamic regions, but most neurophysin and oxytocin immunoreactive neurons in the echidna were found in the paraventricular, lateral hypothalamus and supraoptic nuclei and most oxytocinergic neurons in the platypus were distributed in a band from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. The small size of the supraoptic nucleus in the two monotremes might reflect functional aspects of monotreme lactation.

Fiber connections of the compact division of the posterior pallial amygdala and lateral part of the bed nucleus of the stria terminalis in the pigeon (Columba livia)

The compact division of the posterior pallial amygdala (PoAc) and lateral part of the bed nucleus of the stria terminalis (BSTL) are components of the limbic system in the pigeon brain. In this study, we examined the position and fiber connections of these two nuclei by using Nissl staining and tract-tracing methods. PoAc occupies a central division in the posterior pallial amygdala. BSTL faces the ventral horn of the lateral ventricle and extends between A 7.25 and A 10.50. PoAc and BSTL connect bidirectionally by the stria terminalis. PoAc connects reciprocally with two nuclear groups in the cerebrum: 1) a continuum consisting of the caudoventral nidopallium, lateral part of the caudoventral nidopallium (NCVl), subnidopallium beneath NCVl, and piriform cortex and 2) rostral areas of the hemisphere, including the frontolateral and frontomedial nidopallium and the densocellular part of the hyperpallium. Extratelencephalic projections of PoAc terminate in the dorsomedial thalamic nuclei and reach the lateral hypothalamic area via the hypothalamic part of the occipito-mesencephalic tract. BSTL also connects reciprocally with two main regions: 1) the same continuum as for PoAc projections, except the piriform cortex and 2) rostral areas of the hemisphere, including the olfactory tubercle and nucleus accumbens. Extratelencephalic reciprocal connections are with the substantia nigra, nucleus subceruleus dorsalis, parabrachial nucleus, locus coeruleus, and nucleus of the solitary tract. The dorsomedial subdivision of the hippocampal formation projects massively to PoAc and BSTL. These findings indicate that PoAc and BSTL are important components of an interconnected neural circuit involving widespread regions of the neuraxis and mediating limbic-visceral functions.

Exposure to chronic stress downregulates corticosterone responses to acute stressors

We used captive European starlings ( Sturnus vulgaris) to test whether corticosterone responses differed in birds held under normal laboratory conditions or conditions of chronic stress. Surprisingly, both basal corticosterone concentrations and corticosterone responses to acute stress were significantly reduced when birds were chronically stressed. To determine the mechanism underlying this reduced response, animals under both conditions were injected with lactated Ringer’s solution (control), adrenocorticotropin (ACTH), arginine vasotocin (AVT), or dexamethasone (DEX). ACTH increased corticosterone concentrations above stress-induced levels in both cases, although maximum responses were lower in chronically stressed birds. AVT did not augment the corticosterone response under nonchronically stressed conditions, but it did under chronically stressed conditions. DEX reduced maximal corticosterone concentrations in both cases. Neither ovine nor rat corticotropin-releasing factor (CRF) altered normal stress responses. These data indicate that changes in responsiveness of the hypothalamic-pituitary-adrenal axis to ACTH and AVT serve to downregulate corticosterone responses during chronic stress. Furthermore, these data lead to the following hypothesis: ACTH output from the pituitary limits maximum corticosterone concentrations under normal conditions, but reduced AVT release from the hypothalamus regulates lower corticosterone concentrations under chronic stress conditions.

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.

Corticotropin-releasing hormone-like immunoreactivity in the brain of the snake Bothrops jararaca

The distribution of corticotropin-releasing hormone in the brain of the snake Bothrops jararaca was studied immunohistochemically. Immunoreactive neurons were detected in telencephalic, diencephalic and mesencephalic areas such as dorsal cortex, subfornical organ, paraventricular nucleus, recessus infundibular nucleus, nucleus of the oculomotor nerve and nucleus of the trigeminal nerve. Immunoreactive fibres ran along the hypothalamo-hypophysial tract to end in the outer layer of the median eminence and the neural lobe of the hypophysis. In general, immunoreactive fibres occurred in the same places of immunoreactive neurons. In addition, immunoreactive fibres were observed in the septum, amygdala, lamina terminalis, supraoptic nucleus, nucleus of the paraventricular organ, ventromedial hypothalamic nucleus and interpeduncular nucleus. These results indicate that, as for other vertebrates, corticotropin-releasing hormone in B. jararaca brain, besides being a releasing hormone, may also act as a central neurotransmitter and/or neuromodulator.

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.

Immunocytochemical localization of corticotropin-releasing factor in the brain of the turtle, Mauremys caspica

Brain sections of the turtle, Mauremys caspica were studied by means of an antiserum against rat corticotropin-releasing factor. Immunoreactive neurons were identified in telencephalic, diencephalic and mesencephalic areas such as the cortex, nucleus caudatus, nucleus accumbens, amygdala, subfornical organ, paraventricular nucleus, hypothalamic dorsolateral aggregation, nucleus of the paraventricular organ, infundibular nucleus, pretectal nucleus, periventricular grey, reticular formation and nucleus of the raphe. Many immunoreactive cells located near the ependyma were bipolar, having an apical dendrite that contacted the cerebrospinal fluid. Immunoreactive fibers were seen in these locations and in the lamina terminalis, lateral forebrain bundle, supraoptic nucleus, median eminence, neurohypophysis, tectum opticum, torus semicircularis and deep mesencephalic nucleus. Parvocellular bipolar immunoreactive neurons from the paraventricular and infundibular nuclei projected axons that joined the hypothalamo-hypophysial tract and reached the outer zone of median eminence, and the neural lobe of the hypophysis where immunoreactive fibers terminated close to intermediate lobe cells. From these results it can be concluded that, as in other vertebrates, corticotropin-releasing factor in the turtle may act as a releasing factor and, centrally, as a neurotransmitter or neuromodulator.

Plasma adrenocorticotropin in domestic geese: effects of ether stress and endocrine manipulations

A direct radioimmunoassay for the determination of avian adrenocorticotropin (ACTH) in a small volume of plasma was developed using an antiserum specific for N-terminal region of the ACTH molecule. The sensitivity of the two stage assay is 0.1 fmol ACTH/tube. The specificity of the antiserum was tested by its cross reactions with synthetic ACTH fragments and by comparing curves obtained by dilution of different plasma specimens to that of ACTH reference standard. Adrenocorticotropin responses of chronically cannulated geese to ether stress were evaluated and compared to changes of plasma corticosterone (B) concentration over a 2-hr period. ACTH showed a maximum between 5 and 10 min after ether exposure, while B peak appeared 10-15 min later. Thirty minutes after ether inhalation plasma ACTH returned to the baseline, while B response was longer-lasting and decreased to the resting level between 60 and 120 min. Basal and stress-induced ACTH plasma levels were also investigated in male and female gonadectomized and thyroidectomized geese. Castration increased, while thyroidectomy decreased the basal ACTH concentration. These endocrine manipulations did not, however, markedly affect the stress-induced ACTH hypersecretion except in thyroidectomized ganders, where the increment of plasma ACTH 10 min after ether inhalation was significantly lower than in sham operated control geese.

The distribution of corticotropin-releasing factor--immunoreactive neurons and nerve fibers in the brain of the snake, Natrix maura. Coexistence with arginine vasotocin and mesotocin

The anatomical distribution of neurons and nerve fibers containing corticotropin-releasing factor (CRF) has been studied in the brain of the snake, Natrix maura, by means of immunocytochemistry using an antiserum against rat CRF. To test the possible coexistence of CRF with the neurohypophysial peptides arginine vasotocin (AVT) and mesotocin (MST) adjacent sections were stained with antisera against the two latter peptides. CRF-immunoreactive (CRF-IR) neurons exist in the paraventricular nucleus (PVN). In some neurons of the PVN, coexistence of CRF with MST or of CRF with AVT has been shown. Numerous CRF-IR fibers run along the hypothalamo-hypophysial tract and end in the outer layer of the median eminence. In addition, some fibers reach the neural lobe of the hypophysis. CRF-IR perikarya have also been identified in the following locations: dorsal cortex, nucleus accumbens, amygdala, subfornical organ, lamina terminalis, nucleus of the paraventricular organ, nucleus of the oculomotor nerve, nucleus of the trigeminal nerve, and reticular formation. In addition to all these locations CRF-IR fibers were also observed in the lateral septum, supraoptic nucleus, habenula, lateral forebrain bundle, paraventricular organ, hypothalamic ventromedial nucleus, raphe and interpeduncular nuclei.

Distribution of vasoactive intestinal peptide-like and neurophysin-like immunoreactive neurons and acetylcholinesterase staining in the ring dove hypothalamus with emphasis on the question of an avian suprachiasmatic nucleus

Two nuclei, termed here the medial hypothalamic nucleus and the lateral hypothalamic retinorecipient nucleus, are possible homologs of the mammalian suprachiasmatic nucleus. As the mammalian suprachiasmatic nucleus is characterized by a dense concentration of vasoactive intestinal peptide (VIP)- and neurophysin (NP)-immunoreactive neurons and an absence of acetylcholinesterase (AChE) staining, we decided to examine these factors in the ring dove hypothalamus. Neither the medial hypothalamic nucleus nor the lateral hypothalamic retinorecipient nucleus contained either VIP- or NP-like immunoreactive neurons. The lateral hypothalamic retinorecipient nucleus stained darkly for AChE. Although there was some overlap in the distribution of VIP- and NP-like immunoreactive neurons, a clustering of both types into a well defined nucleus was not observed. Therefore, an avian homolog to the mammalian suprachiasmatic nucleus must differ in its chemoarchitecture from that of mammalian species described to date.

Immunocytochemical study of the hypothalamic magnocellular neurosecretory nuclei of the snake Natrix maura and the turtle Mauremys caspica

An immunocytochemical study of the magnocellular neurosecretory nuclei was performed in the snake Natrix maura and the turtle Mauremys caspica by use of antisera against: (1) a mixture of both bovine neurophysins, (2) bovine oxytocin-neurophysin, (3) arginine vasotocin, and (4) mesotocin. Arginine vasotocin- and mesotocin-immunoreactivities were localized in individual neurons of the supraoptic and paraventricular nuclei, with a distinct pattern of distribution in both species. The same cells appeared to be stained by the anti-oxytocin-neurophysin and antimesotocin sera. The supraoptic nucleus can be subdivided into rostral medial and caudal portions. In N. maura, but not in M. caspica, neurophysin-immunoreactive neurons were found in the retrochiasmatic nucleus. No immunoreactive elements were seen in the suprachiasmatic nucleus of both species after the use of any of the antisera. A dorsolateral aggregation of neurophysin-containing cells, localized over the lateral forebrain bundle, was present in both species. Magnocellular and parvocellular neurophysin-immunoreactive neurons were present in the paraventricular nucleus of both species. In the turtle, the paraventricular neurons were arranged into four distinct layers parallel to the ependyma; these neurons were bipolar with the major axis perpendicular to the ventricle, and many of them projected processes toward the cerebrospinal-fluid compartment. In N. maura a group of large neurons of the paraventricular nucleus was found in a very lateral position. The posterior lobe of the hypophysis and the external zone of the median eminence contained arginine vasotocin- and mesotocin-immunoreactive nerve fibers. The lamina termialis of both species was supplied with a dense bundle of fibers containing immunoreactive neurophysin. Neurophysin-immunoreactive fibers were also present in the septum, some telencephalic regions, including the cortex and the olfactory tubercule, in the paraventricular organ, and the periventricular and periaqueductal gray of the brainstem.

Distribution of immunoreactive vasotocin and mesotocin in the chicken gastrointestinal tract

Immunoreactive arginine vasotocin (AVT) and mesotocin (MT) were measured in heart, breast muscle, adrenals, testes, and different parts of the gastrointestinal tract in adult male chickens. Neither of the peptides were detected in liver, testis, heart and breast muscle. The amounts of AVT and MT in the adrenals were 167 +/- 25 and 669 +/- 198 pg/gland, respectively. Considerable amounts of immunoreactive peptides were found in the gastrointestinal tract with the highest concentration in the proventriculus (4.18 +/- 0.31 ng AVT and 16.58 +/- 0.86 ng MT per organ). Dose-response curves of duodenal and proventriculus extracts were parallel with synthetic AVT and MT standards.

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.

Hypophysiotrophic function of vasopressin and oxytocin

We have investigated the effects of lesioning the hypothalamic paraventricular nucleus (PVN) on the secretion of two corticotropin-releasing neurohormones, vasopressin (VP) and oxytocin (OT), at the median eminence. The experimental model was the median eminence incubated in vitro, the secretion of neurohormones was stimulated by adding 48 mM KCl to the incubation medium. In addition, immunohistochemical staining was performed to correlate the changes in neuropeptide secretion with the distribution of VP and OT immunoreactive elements in the median eminence. Lesioning of the PVN abolished the KCl-induced release of VP 1 week after hypothalamic surgery. After a longer period of postoperative survival (6 weeks), VP release was restored towards normal. The secretion of OT was reduced by 50% at 1 week after lesioning and rose to 400% of control at six weeks. The changes in VP and OT release at the median eminence largely correlated with the immunohistochemical distribution of VP and OT immunopositive nerve fibers in the external zone of the median eminence. Most importantly, 6 weeks after the PVN lesion a dense network of OT immunoreactive varicosities was observed around primary portal capillaries, where normally OT fiber density is very low. These results demonstrate the functional and structural plasticity of VP- and OT-ergic neuronal systems that project to the median eminence. Furthermore, when taken together with earlier studies on the regulation of corticotropin secretion in long-term PVN-lesioned rats, the data indicate an important role for OT in the regulation of pituitary-adrenocortical function in PVN-lesioned rats.

Immunoreactivity to vasoactive intestinal polypeptide (VIP) and thyreotropin-releasing hormone (TRH) in hypothalamic neurons of the domesticated pigeon (Columba livia). Alterations following lactation and exposure to cold

The distribution of VIP- and TRH-immunoreactivity in neurons and processes within the hypothalamus of the pigeon was investigated with light-microscopic immunocytochemical techniques. Most of the VIP-containing neurons are concentrated in the middle and caudal parts of the hypothalamus, with the greatest concentration of perikarya occurring in the medial and lateral part of the ventromedial hypothalamic nucleus and the infundibular nucleus. These cells give rise to axons that seem to extend into the median eminence. An extensive network of VIP-immunoreactive fibers and varicosities occupy the external layer of the median eminence. The majority of TRH-containing neurons is found in the anterior hypothalamus with the greatest concentration of cells in the magnocellular preoptic, medial preoptic, suprachiasmatic and paraventricular nuclei. TRH-immunoreactive fibers and varicosities form a dense arborization in the external layer of the median eminence. Lactation seems to induce substantial changes in VIP as well as in TRH-immunostaining in the median eminence and other hypothalamic regions as compared to control, sexually active animals. Furthermore, TRH-immunoreactivity decreased in the median eminence following 60-min exposure to cold. These results suggest that VIP- and TRH-containing pathways in the pigeon hypothalamus are involved in the mediation of neuroendocrine responses.