The distribution of dopamine, substance P, vasoactive intestinal polypeptide and neuropeptide Y immunoreactivity in the brain of the collared dove, Streptopelia decaocto

Neuropeptide Y and maternal behavior in the female native Thai chicken

Maternal care behaviors in birds include incubation and rearing behaviors. During incubating period, the hens stop laying and eating less due to food restriction as a natural fasting when compared with the rearing hens, resulting in low production of eggs and chicks. Neuropeptide Y (NPY), a neurotransmitter/neuromodulator, is very well known to be involved in food intake regulation in birds and mammals. The objective of this study is to elucidate the association between NPY and maternal behaviors in the female native Thai chicken. The distributions of NPY-immunoreactive (-ir) neurons and fibers in the brain of the incubating (INC), nest-deprived (ND), and replaced-egg-with-chicks (REC) hens at day 6 were determined utilizing immunohistochemistry technique. The results revealed that the distributions of NPY-ir neurons and fibers were observed within the septalis lateralis, nucleus rotundus, and nucleus dorsolateralis anterior thalami, with predominantly located within the the nucleus paraventricularis magnocellularis (PVN). NPY-ir fibers were located throughout the brain and the densest NPY-ir fibers were distributed in a discrete region lying close to the ventriculus tertius (third ventricle) through the hypothalamus. Changes in the number of NPY-ir neurons within the PVN of the INC, ND, and REC hens were compared at different time points (at days 6 and 14). Interestingly, the number of NPY-ir neurons within the PVN was significantly higher (P < 0.05) in the INC hens when compared with those of the ND and REC hens at day 14 but not day 6. In addition, the number of NPY-ir neurons within the PVN of the INC hens was significantly increased (P < 0.05) from day 6 to day 14 but not the ND and REC hens. These results indicated, for the first time, the asscociation between NPY and maternal behaviors in the femle native Thai chicken. Change in the number of NPY-ir neurons within the PVN during the transition from incubating to rearing behavior suggested the possible role of NPY in the regulation of the maternal behaviors in this equatorial species. In addition, the native Thai chicken might be an excellent animal model for the study of this phenomenon.

Role of vasoactive intestinal peptide during the transition from incubation behavior to rearing behavior in the female native Thai chicken

It is well documented that vasoactive intestinal peptide (VIP) is an avian prolactin-releasing factor, regulating the reproductive cycle, that initiates and maintains incubation behavior in avian species. Native Thai chicken has strong maternal behaviors. Thus, it is an excellent animal model to study this phenomenon. Changes in the numbers of VIP neurons within the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) are associated with maternal behaviors in the native Thai chicken. The objective of this study was to elucidate the role of VIP during the transition from egg incubation to rearing behavior in this species. The distributions of VIP-immunoreactive (-ir) neurons and fibers within the nucleus septalis lateralis (SL), nucleus anterior medialis hypothalami (AM), regio lateralis hypothalami (LHy), nucleus commissurae pallii (nCPa), nucleus ventromedialis hypothalami (VMN), and IH-IN were compared between incubating (INC) hens and replaced-egg-with-chicks (REC) hens, in which eggs were replaced by 3-day-old chicks after 6, 10, and 14 d of incubation period for 3 days. Using an immunohistochemistry technique, the results revealed that VIP-ir neurons and fibers were found within the SL, AM, LHy, nCPa, VMN, and IH-IN, with the greatest expression observed in the IH-IN in both groups. The number of VIP-ir neurons in the IH-IN was markedly decreased (P < 0.05) in the REC hens when compared with those of the INC hens at 3 different time points (at d 9, 13, and 17). However, changes in the number of VIP-ir neurons between the INC and REC hens were not observed within other hypothalamic areas tested. These findings indicate that the presence of eggs and chicks affects the VIPergic system, and VIP neurons in the IH-IN might play a role in the transition from incubating to rearing behavior in the native Thai chicken.

Neuroendocrine Control of Broodiness

In the majority of vertebrates, survival of offspring to sexual maturation is important for increasing population size, and parental investment in the young is important for reproductive success. Consequently, parental care is critical for the survival of offspring in many species, and many vertebrates have adapted this behavior to their social and ecological environments. Parental care is defined as any behavior that is performed in association with one's offspring (Rosenblatt, Mayer, Siegel. Maternal behavior among nonprimate mammals. In: Adler, Pfaff, Goy, editors. Handbook of behavioral neurobiology. New York: Plenum; 1985. p. 229-98) and is well characterized in mammals and birds. In birds (class Aves), this is due to the high level of diversity across species. Parental behavior in birds protects the young from intruders, and generally involves nest building, incubation, and broody behavior which protect their young from an intruder, and the offspring are reared to independence. Broodiness is complexly regulated by the central nervous system and is associated with multiple hormones and neurotransmitters produced by the hypothalamus and pituitary gland. The mechanism of this behavior has been extensively characterized in domestic chicken (Gallus domesticus), turkey (Meleagris gallopavo), and pigeons and doves (family Columbidae). This chapter summarizes broodiness in birds from a physiology, genetics, and molecular biology perspective.

A novel relay nucleus between the inferior colliculus and the optic tectum in the chicken (Gallus gallus)

Processing multimodal sensory information is vital for behaving animals in many contexts. The barn owl, an auditory specialist, is a classic model for studying multisensory integration. In the barn owl, spatial auditory information is conveyed to the optic tectum (TeO) by a direct projection from the external nucleus of the inferior colliculus (ICX). In contrast, evidence of an integration of visual and auditory information in auditory generalist avian species is completely lacking. In particular, it is not known whether in auditory generalist species the ICX projects to the TeO at all. Here we use various retrograde and anterograde tracing techniques both in vivo and in vitro, intracellular fillings of neurons in vitro, and whole-cell patch recordings to characterize the connectivity between ICX and TeO in the chicken. We found that there is a direct projection from ICX to the TeO in the chicken, although this is small and only to the deeper layers (layers 13-15) of the TeO. However, we found a relay area interposed among the IC, the TeO, and the isthmic complex that receives strong synaptic input from the ICX and projects broadly upon the intermediate and deep layers of the TeO. This area is an external portion of the formatio reticularis lateralis (FRLx). In addition to the projection to the TeO, cells in FRLx send, via collaterals, descending projections through tectopontine-tectoreticular pathways. This newly described connection from the inferior colliculus to the TeO provides a solid basis for visual-auditory integration in an auditory generalist bird. J. Comp. Neurol. 525:513-534, 2017. © 2016 Wiley Periodicals, Inc.

Distribution of hypothalamic vasoactive intestinal peptide immunoreactive neurons in the male native Thai chicken

Avian prolactin (PRL) secretion is under stimulatory control by the PRL-releasing factor (PRF), vasoactive intestinal peptide (VIP). The neuroendocrine regulation of the avian reproductive system has been extensively studied in females. However, there are limited data in males. The aim of this study was to elucidate the VIPergic system and its relationship to PRL and testosterone (T) in the male native Thai chicken. The distributions of VIP-immunoreactive (-ir) neurons and fibers were determined by immunohistochemistry. Changes in VIP-ir neurons within the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) areas were compared across the reproductive stages. Plasma levels of PRL and T were determined by enzyme-linked immunosorbent assay and then compared across the reproductive stages. The results revealed that the highest accumulations of VIP-ir neurons were concentrated only within the IH-IN, and VIP-ir neurons were not detected within other hypothalamic nuclei. Within the IH-IN, VIP-ir neurons were low in premature and aging males and markedly increased in mature males. Changes in VIP-ir neurons within the IH-IN were directly mirrored with changes in PRL and T levels across the reproductive stages. These results suggested that VIP neurons in the IH-IN play a regulatory role in year-round reproductive activity in males. The present study also provides additional evidence that VIP is the PRF in non-seasonal, continuously breeding equatorial species.

Distribution of vasotocin- and vasoactive intestinal peptide-like immunoreactivity in the brain of blue tit (Cyanistes coeruleus)

Blue tits (Cyanistes coeruleus) are songbirds, used as model animals in numerous studies covering a wide field of research. Nevertheless, the distribution of neuropeptides in the brain of this avian species remains largely unknown. Here we present some of the first results on distribution of Vasotocine (AVT) and Vasoactive intestinal peptide (VIP) in the brain of males and females of this songbird species, using immunohistochemistry mapping. The bulk of AVT-like cells are found in the hypothalamic supraoptic, paraventricular and suprachiasmatic nuclei, bed nucleus of the stria terminalis, and along the lateral forebrain bundle. Most AVT-like fibers course toward the median eminence, some reaching the arcopallium, and lateral septum. Further terminal fields occur in the dorsal thalamus, ventral tegmental area and pretectal area. Most VIP-like cells are in the lateral septal organ and arcuate nucleus. VIP-like fibers are distributed extensively in the hypothalamus, preoptic area, lateral septum, diagonal band of Broca. They are also found in the bed nucleus of the stria terminalis, amygdaloid nucleus of taenia, robust nucleus of the arcopallium, caudo-ventral hyperpallium, nucleus accumbens and the brainstem. Taken together, these results suggest that both AVT and VIP immunoreactive structures show similar distribution to other avian species, emphasizing evolutionary conservatism in the history of vertebrates. The current study may enable future investigation into the localization of AVT and VIP, in relation to behavioral and ecological traits in the brain of tit species.

Immunohistochemical mapping of neuropeptide Y in the tree shrew brain

Day-active tree shrews are promising animals as research models for a variety of human disorders. Neuropeptide Y (NPY) modulates many behaviors in vertebrates. Here we examined the distribution of NPY in the brain of tree shrews (Tupaia belangeri chinensis) using immunohistochemical techniques. The differential distribution of NPY-immunoreactive (-ir) cells and fibers were observed in the rhinencephalon, telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon of tree shrews. Most NPY-ir cells were multipolar or bipolar in shape with triangular, fusiform, and/or globular perikarya. The densest cluster of NPY-ir cells were found in the mitral cell layer of the main olfactory bulb (MOB), arcuate nucleus of the hypothalamus, and pretectal nucleus of the thalamus. The MOB presented a unique pattern of NPY immunoreactivity. Laminar distribution of NPY-ir cells was observed in the MOB, neocortex, and hippocampus. Compared to rats, the tree shrews exhibited a particularly robust and widespread distribution of NPY-ir cells in the MOB, bed nucleus of the stria terminalis, and amygdala as well as the ventral lateral geniculate nucleus and pretectal nucleus of the thalamus. By contrast, a low density of neurons were scattered in the striatum, neocortex, polymorph cell layer of the dentate gyrus, superior colliculus, inferior colliculus, and dorsal tegmental nucleus. These findings provide the first detailed mapping of NPY immunoreactivity in the tree shrew brain and demonstrate species differences in the distribution of this neuropeptide, providing an anatomical basis for the participation of the NPY system in the regulation of numerous physiological and behavioral processes.

Increased STAT5 signaling in the ring dove brain in response to prolactin administration and spontaneous elevations in prolactin during the breeding cycle

Prolactin acts on target cells in the central nervous system (CNS) to stimulate behavioral changes associated with parental care in birds, but the signaling mechanisms that mediate these actions have not been characterized. In mammals, the Janus Kinase 2-Signal Transducer and Activator of Transcription 5 (JAK2-STAT5) signaling pathway mediates many of the actions of prolactin. To assess the importance of this pathway in prolactin-sensitive target cells in the avian brain, we measured changes in activated (phosphorylated) STAT5 (pSTAT5) in the forebrain of female ring doves sampled as plasma prolactin levels change during the breeding cycle and in prolactin-treated, non-breeding females. The anatomical distribution of cells exhibiting pSTAT5 immunoreactivity in dove brain closely paralleled the distribution of prolactin receptors in this species. The density of pSTAT5 immunoreactive (pSTAT5-ir) cells was highest in the preoptic area, the suprachiasmatic, paraventricular, and ventromedial hypothalamic nuclei, the lateral and tuberal hypothalamic regions, the lateral bed nucleus of the stria terminalis, and the lateral septum. Mean pSTAT5-ir cell densities in these eight brain areas were several fold higher in breeding females during late incubation/early post-hatching when plasma prolactin levels have been observed to peak than in non-breeding females or breeding females sampled at earlier stages when prolactin titers have been reported to be lower. Similar differences were observed between prolactin-treated and vehicle-treated females in all three of the forebrain regions that were compared. We conclude that JAK2-STAT5 signaling is strongly activated in response to prolactin stimulation in the ring dove brain and could potentially mediate some of the centrally-mediated behavioral effects of this hormone.

Evolution of a vertebrate social decision-making network

Animals evaluate and respond to their social environment with adaptive decisions. Revealing the neural mechanisms of such decisions is a major goal in biology. We analyzed expression profiles for 10 neurochemical genes across 12 brain regions important for decision-making in 88 species representing five vertebrate lineages. We found that behaviorally relevant brain regions are remarkably conserved over 450 million years of evolution. We also find evidence that different brain regions have experienced different selection pressures, because spatial distribution of neuroendocrine ligands are more flexible than their receptors across vertebrates. Our analysis suggests that the diversity of social behavior in vertebrates can be explained, in part, by variations on a theme of conserved neural and gene expression networks.

The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis

All animals evaluate the salience of external stimuli and integrate them with internal physiological information into adaptive behavior. Natural and sexual selection impinge on these processes, yet our understanding of behavioral decision-making mechanisms and their evolution is still very limited. Insights from mammals indicate that two neural circuits are of crucial importance in this context: the social behavior network and the mesolimbic reward system. Here we review evidence from neurochemical, tract-tracing, developmental, and functional lesion/stimulation studies that delineates homology relationships for most of the nodes of these two circuits across the five major vertebrate lineages: mammals, birds, reptiles, amphibians, and teleost fish. We provide for the first time a comprehensive comparative analysis of the two neural circuits and conclude that they were already present in early vertebrates. We also propose that these circuits form a larger social decision-making (SDM) network that regulates adaptive behavior. Our synthesis thus provides an important foundation for understanding the evolution of the neural mechanisms underlying reward processing and behavioral regulation.

The avian subpallium: new insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

The subpallial region of the avian telencephalon contains neural systems whose functions are critical to the survival of individual vertebrates and their species. The subpallial neural structures can be grouped into five major functional systems, namely the dorsal somatomotor basal ganglia; ventral viscerolimbic basal ganglia; subpallial extended amygdala including the central and medial extended amygdala and bed nuclei of the stria terminalis; basal telencephalic cholinergic and non-cholinergic corticopetal systems; and septum. The paper provides an overview of the major developmental, neuroanatomical and functional characteristics of the first four of these neural systems, all of which belong to the lateral telencephalic wall. The review particularly focuses on new findings that have emerged since the identity, extent and terminology for the regions were considered by the Avian Brain Nomenclature Forum. New terminology is introduced as appropriate based on the new findings. The paper also addresses regional similarities and differences between birds and mammals, and notes areas where gaps in knowledge occur for birds.

Dopamine and mesotocin neurotransmission during the transition from incubation to brooding in the turkey

We investigated the neuroendocrine changes involved in the transition from incubating eggs to brooding of the young in turkeys. Numbers of mesotocin (MT; the avian analog of mammalian oxytocin) immunoreactive (ir) neurons were higher in the nucleus paraventricularis magnocellularis (PVN) and nucleus supraopticus, pars ventralis (SOv) of late stage incubating hens compared to the layers. When incubating and laying hens were presented with poults, all incubating hens displayed brooding behavior. c-fos mRNA expression was found in several brain areas in brooding hens. The majority of c-fos mRNA expression by MT-ir neurons was observed in the PVN and SOv while the majority of c-fos mRNA expression in dopaminergic (DAergic) neurons was observed in the ventral part of the nucleus preopticus medialis (POM). Following intracerebroventricular injection of DA or oxytocin (OT) receptor antagonists, hens incubating eggs were introduced to poults. Over 80% of those injected with vehicle or the D1 DA receptor antagonist brooded poults, while over 80% of those receiving the D2 DA receptor antagonist or the OT receptor antagonist failed to brood the poults. The D2 DA/OT antagonist groups also displayed less c-fos mRNA in the dorsal part of POM and the medial part of the bed nucleus of the stria terminalis (BSTM) areas than did the D1 DA/vehicle groups. These data indicate that numerous brain areas are activated when incubating hens initially transition to poult brooding behavior. They also indicate that DAergic, through its D2 receptor, and MTergic systems may play a role in regulating brooding behaviors in birds.

Chicken lateral septal organ and other circumventricular organs form in a striatal subdomain abutting the molecular striatopallidal border

The avian lateral septal organ (LSO) is a telencephalic circumventricular specialization with liquor-contacting neurons (Kuenzel and van Tienhoven [1982] J. Comp. Neurol. 206:293-313). We studied the topological position of the chicken LSO relative to molecular borders defined previously within the telencephalic subpallium (Puelles et al. [2000] J. Comp. Neurol. 424:409-438). Differential expression of Dlx5 and Nkx2.1 homeobox genes, or the Shh gene encoding a secreted morphogen, allows distinction of striatal, pallidal, and preoptic subpallial sectors. The chicken LSO complex was characterized chemoarchitectonically from embryonic to posthatching stages, by using immunohistochemistry for calbindin, tyrosine hydroxylase, NKX2.1, and BEN proteins and in situ hybridization for Nkx2.1, Nkx2.2, Nkx6.1, Shh, and Dlx5 mRNA. Medial and lateral parts of LSO appear, respectively, at the striatal part of the septum and adjacent bottom of the lateral ventricle (accumbens), in lateral continuity with another circumventricular organ that forms along a thin subregion of the entire striatum, abutting the molecular striatopallidal boundary; we called this the "striatopallidal organ" (SPO). The SPO displays associated distal periventricular cells, which are lacking in the LSO. Moreover, the SPO is continuous caudomedially with a thin, linear ependymal specialization found around the extended amygdala and preoptic areas. This differs from SPO and LSO in some molecular aspects. We tentatively identified this structure as being composed of an "extended amygdala organ" (EAO) and a "preoptohypothalamic organ" (PHO). The position of LSO, SPO, EAO, and PHO within a linear Dlx5-expressing ventricular domain that surrounds the Nkx2.1-expressing pallidopreoptic domain provides an unexpected insight into possible common and differential causal mechanisms underlying their formation.

Feeding behavior after metergoline or GR-46611 injections into the paraventricular nucleus of the hypothalamus in the pigeon

The present study examined changes in spontaneous behavior of free-feeding pigeons in response to local injections of metergoline (MET, an antagonist of 5-HT(1/2) receptors; 5, 10 and 20 nmol), GR-46611 (GR, a 5-HT(1B/1D) agonist; 0.6 and 6 nmol) or vehicle into the paraventricular hypothalamic nucleus (PVN). When infused into the PVN, MET and GR promptly and reliably elicited feeding at their higher doses, without affecting drinking or non-ingestive behaviors (locomotion, exploration, preening, sleep) during the first hour after injection. Both GR- and MET-evoked ingestive responses were associated only with an increase in feeding duration, with no changes in latency to start feeding. In a second series of experiments, the effective doses of MET (20 nmol) and GR (6 nmol) were injected into other diencephalic areas. This exploratory study revealed that intense feeding responses to both MET and GR local injections are also observed in the n. medialis hypothalami posterioris and in the adjacent n. lateralis hypothalami posterioris (PMH/PLH complex, in the caudoventral hypothalamus) and in the n. magnocellularis preopticus (PPM, in the caudal preoptic region). The behavioral profiles associated with these hyperphagic responses were nucleus-specific: in the PMH/PLH, MET-induced feeding was accompanied by an increase in total feeding duration and by a reduction in the latency to start feeding, while ingestive responses evoked by MET in the PPM were associated only with an increase in feeding duration (similar to that observed in the PVN experiments). No ingestive effects were observed after intracerebroventricular (ICV, lateral ventricle) injections of MET (10, 30, 100 or 300 nmol), while ICV injections of GR (3, 15 or 30 nmol) increased feeding only at the higher dose [Da Silva RA, De Oliveira ST, Hackl LPN, Spilere CI, Faria MS, Marino-Neto J, Paschoalini MA. Ingestive behaviors and metabolic fuels after central injections of 5-HT1A and 5-HT1D/1B receptors agonists in the pigeon. Brain Res, 2004;1026:275-283]. These data indicate the presence of a tonic inhibitory influence on feeding behavior exerted by 5-HT afferents on these hypothalamic areas, and suggest that these inputs, possibly mediated by non-rodent-type 5-HT1D/1B receptors, can affect both satiety and satiation mechanisms.

Evidence for increased neuropeptide Y synthesis in mediobasal hypothalamus in relation to parental hyperphagia and gonadal activation in breeding ring doves

Like lactating mammals, male and female ring dove parents increase their food consumption to meet the energetic challenges of provisioning their young. To clarify the neurochemical mechanisms involved, the present study investigated the relationship between parental hyperphagia and changes in activity of the potent orexigen neuropeptide Y (NPY) in the hypothalamus of breeding doves. Changes in NPY-immunoreactive (NPY-ir) cell numbers in the tuberal hypothalamus of male and female doves were examined by immunocytochemistry at six stages of the breeding cycle. Parallel NPY mRNA measurements were recorded in mediobasal hypothalamus (which includes the tuberal hypothalamus) by semiquantitative reverse transcription-polymerase chain reaction using 18S rRNA as the internal standard. NPY mRNA changes were also measured in the mediobasal hypothalamus of nonbreeding doves following intracranial administration of prolactin, an orexigenic hormone that is elevated in the plasma of parent doves, and in response to food deprivation, which mimics the negative energy state that develops in parents as they provision their growing young. NPY-ir cell numbers in the tuberal hypothalamus and NPY mRNA levels in the mediobasal hypothalamus were significantly higher in breeding males and females during the period of parental hyperphagia after hatching than during the late incubation period when food intake remains unchanged. In nonbreeding doves, food deprivation and prolactin treatment increased NPY mRNA in this region by two- to three-fold, which suggests that NPY expression is sensitive to hormonal and metabolic signals associated with parenting. We conclude that NPY synthesis is increased in the mediobasal hypothalamus during the posthatching period, which presumably supports increased NPY release and resulting parental hyperphagia. NPY-ir and mRNA were also high in the mediobasal hypothalamus prior to egg laying when food intake remained unchanged. Several lines of evidence suggest that this elevation in NPY supports the increased gonadal activity that accompanies intense courtship and nest building interactions in breeding doves.

Identification of dopamine, gonadotrophin-releasing hormone-I, and vasoactive intestinal peptide neurones activated by electrical stimulation to the medial preoptic area of the turkey hypothalamus: a potential reproductive neuroendocrine circuit

The neural and neurochemical substrates regulating reproduction in birds remain vaguely defined. The findings that electrical stimulation in the medial preoptic area (ES/MPOA) or intracerebroventricular infusion of dopamine (DA) stimulated luteinising hormone (LH) and prolactin (PRL) release in female turkeys, led to the suggestion that ES/MPOA might help to clarify the DA circuitry regulating LH and PRL. We used c-fos mRNA and tyrosine hydroxylase immunoreactivity as measured by double in situ hybridisation/immunocytochemistry (ISH/ICC) to determine which group/subgroup of DA neurones was activated following unilateral ES/MPOA. To establish that the reproductive neuroendocrine system was activated, double ISH/ICC was also conducted on c-fos/gonadotrophin-releasing hormone-I (GnRH-I) and c-fos/vasoactive intestinal peptide (VIP). Changes in circulating LH and PRL were determined by radioimmunoassay. Unilateral ES/MPOA (100 microA, right side) of anaesthetised laying turkeys for 30 min increased circulating LH and PRL levels. It also induced c-fos mRNA expression on the ipsilateral side by all GnRH-I neurones within the septopreoptic region, implying that GnRH-I neurones in this region share similar circuitry. VIP neurones within the nucleus infundibularis were the only VIP group to show c-fos mRNA expression, suggesting their involvement in ES/MPOA induced PRL release. c-fos mRNA expression was also observed in a subgroup of DA neurones in the nucleus mamillaris lateralis (ML). To our knowledge, the present study is the first to show that activation of DAergic cells in the ML is associated with the activation of GnRH-I and VIP neurones and the release of LH and PRL. It is likely that ES/MPOA activated VIP/GnRH-I neurones via activation of DA neurones in the ML, as this was the only DA subgroup that showed c-fos mRNA expression.

Monoaminergic markers in the optic tectum of the domestic chick

The avian optic tectum has become a reliable model system to study the basic mechanisms that underlie the computation of visual stimuli. Many aspects of its cytoarchitecture, chemoarchitecture, connectivity and development are thoroughly characterized. However, knowledge about its monoaminergic innervation is still incomplete. As a prerequisite to understand a possible functional role of the monoaminergic neurotransmitters, the serotonergic, noradrenergic, and dopaminergic innervation of the optic tectum as well as the distribution of serotonin 2A receptors, the dopamine- and cAMP-regulated phosphoprotein DARPP-32 and calbindin D-28K was studied in domestic chicks by immunohistochemical techniques. Serotonergic, noradrenergic, and tyrosine hydroxylase positive axons and axon terminals were present in all layers of the optic tectum. Generally, the highest densities of serotonergic, noradrenergic, and tyrosine hydroxylase positive fibers were found in the superficial tectal layers 1-8, whereas only moderate densities of serotonergic, noradrenergic, and tyrosine hydroxylase positive fibers became obvious in the deep tectal layers 9-15. Serotonergic fibers were particularly abundant in layers 4, 5a and 7 and serotonin 2A receptors in layer 13. Noradrenergic fibers were densest in layers 4 and 5a, whereas tyrosine hydroxylase positive fibers showed a slightly different distribution pattern with additional dense labeling in layer 7. As revealed by double-labeling immunohistochemistry, serotonergic fibers were closely related to the cell bodies of calbindin-positive horizontal cells in layer 5b and tyrosine hydroxylase positive fibers often contacted DARPP-32+ dendritic shafts in layers 9 and 10. These findings indicate that the catecholaminergic innervation of the optic tectum consists of a noradrenergic and a dopaminergic component and that the noradrenergic, serotonergic, and dopaminergic system may be potentially involved in the modulation of retinal input in the superficial layers of the optic tectum as well as in the modulation of tectal output via the deep tectal layers.

Neuropeptide Y in the olfactory system, forebrain and pituitary of the teleost, Clarias batrachus

Distribution of neuropeptide Y (NPY)-like immunoreactivity in the forebrain of catfish Clarias batrachus was examined with immunocytochemistry. Conspicuous immunoreactivity was seen in the olfactory receptor neurons (ORNs), their projections in the olfactory nerve, fascicles of the olfactory nerve layer in the periphery of bulb and in the medial olfactory tracts as they extend to the telencephalic lobes. Ablation of the olfactory organ resulted in loss of immunoreactivity in the olfactory nerve layer of the bulb and also in the fascicles of the medial olfactory tracts. This evidence suggests that NPY may serve as a neurotransmitter in the ORNs and convey chemosensory information to the olfactory bulb, and also to the telencephalon over the extrabulbar projections. In addition, network of beaded immunoreactive fibers was noticed throughout the olfactory bulb, which did not respond to ablation experiment. These fibers may represent centrifugal innervation of the bulb. Strong immunoreactivity was encountered in some ganglion cells of nervus terminalis. Immunoreactive fibers and terminal fields were widely distributed in the telencephalon. Several neurons of nucleus entopeduncularis were moderately immunoreactive; and a small population of neurons in nucleus preopticus periventricularis was also labeled. Immunoreactive terminal fields were particularly conspicuous in the preoptic, the tuberal areas, and the periventricular zone around the third ventricle and inferior lobes. NPY immunoreactive cells and fibers were detected in all the lobes of the pituitary gland. Present results describing the localization of NPY in the forebrain of C. batrachus are in concurrence with the pattern of the immunoreactivity encountered in other teleosts. However, NPY in olfactory system of C. batrachus is a novel feature that suggests a role for the peptide in processing of chemosensory information.

Centrifugal visual system of Crocodylus niloticus: a hodological, histochemical, and immunocytochemical study

The retinopetal neurons of Crocodylus niloticus were visualized by retrograde transport of rhodamine beta-isothiocyanate or Fast Blue administered by intraocular injection. Approximately 6,000 in number, these neurons are distributed in seven regions extending from the mesencephalic tegmentum to the rostral rhombencephalon, approximately 70% being located contralaterally to the injected eye. None of the centrifugal neurons projects to both retinae. The retinopetal neurons are located in rostrocaudal sequence in seven regions: the formatio reticularis lateralis mesencephali, the substantia nigra, the griseum centralis tectalis, the nucleus subcoeruleus dorsalis, the nucleus isthmi parvocellularis, the locus coeruleus, and the commissura nervi trochlearis. The greatest number of cells (approximately 93%) is found in the nucleus subcoeruleus dorsalis. The majority are multipolar or bipolar in shape and resemble the ectopic centrifugal visual neurons of birds, although a small number of monopolar neurons resembling those of the avian isthmo-optic nucleus may also be observed. A few retinopetal neurons in the griseum centralis tectalis were tyrosine hydroxylase (TH) immunoreactive. Moreover, in the nuclei subcoeruleus dorsalis and isthmi parvocellularis, both ipsilaterally and contralaterally, approximately one retinopetal neuron in three (35%) was immunoreactive to nitric oxide synthase (NOS), and a slightly higher proportion (38%) of retinopetal neurons were immunoreactive for choline acetyltransferase (ChAT). Some of them contained colocalized ChAT and NOS/reduced nicotinamide adenine dinucleotide phosphate-diaphorase. Fibers immunoreactive to TH, serotonin (5-HT), neuropeptide Y (NPY), or Phe-Met-Arg-Phe-amide (FMRF-amide) were frequently observed to make intimate contact with rhodamine-labeled retinopetal neurons. These findings are discussed in relation to previous results obtained in other reptilian species and in birds.

Fiber connections of the hippocampal formation and septum and subdivisions of the hippocampal formation in the pigeon as revealed by tract tracing and kainic acid lesions

The organization of the pigeon hippocampal formation was examined by tract tracing by using biotinylated dextran amine (BDA) and cholera toxin B subunit (CTB) and by injections of kainic acid to produce excitotoxic lesions. The hippocampal formation was divided into seven subdivisions based on Nissl staining and intrinsic and septal connections: dorsomedial (DM), dorsolateral (DL), triangular (Tr), V-shaped layer, magnocellular (Ma), parvocellular, and cell-poor regions. DL was composed of dorsal and ventral portions and sent associational fibers to DM, the V-shaped layer, and Tr. DL had strong reciprocal connections with the densocellular part of the hyperpallium (HD) and projected to the dorsolateral corticoid area. DM had reciprocal fiber connections with the V-shaped layer, Ma, and DL as well as with several subdivisions of the arcopallium. DL and DM, but not the V-shaped layer, projected fibers to the septum where those from DM exceeded in number those from DL. These projections further extended to the hypothalamus, particularly the lateral hypothalamic area. The lateral and medial septal nuclei projected back a very small number of ascending fibers to the hippocampal formation. Intraventricular injections of kainic acid induced neuronal loss widely in the hippocampal formation and subsequently produced gliosis in DM. These results indicate that DL receives its main afferents from HD and in turn sends inputs to an intrinsic circuit composed of hippocampal subdivisions DM, Ma, Tr, and the V-shaped layer; and also that DM is the main exit to the septum and hypothalamus. It is suggested that neurons in the V-shaped layer are intrinsic. Together, the results suggest that the V-shaped layer is comparable to the dentate gyrus of the mammalian hippocampal formation and that DM incorporates components comparable to both Ammon's horn and the subiculum.

Hypothalamic circadian organization in birds. I. Anatomy, functional morphology, and terminology of the suprachiasmatic region

In mammals, the "master clock" controlling circadian rhythmicity is located in the hypothalamic suprachiasmatic nuclei (SCN). Until now, no comparable structure has been unambiguously described in the brain of any nonmammalian vertebrate. In birds, early anatomical and lesioning studies described a SCN located in the anterior hypothalamus, but whether birds possess a nucleus equivalent to the mammalian SCN remained controversial. By reviewing the existing literature it became evident that confusion in delineation and nomenclature of hypothalamic cell groups may be one of the major reasons that no coherent picture of the avian hypothalamus exists. In this review, we attempt to clarify certain aspects of the organization of the avian hypothalamus by summarizing anatomical and functional studies and comparing them to immunocytochemical results from our laboratory. There is no single cell group in the avian hypothalamus that combines the morphological and neurochemical features of the mammalian SCN. Instead, certain aspects of anatomy and morphology suggest that at least two anatomically distinct cell groups, the SCN and the lateral hypothalamic nucleus (LHN), bear some of the characteristics of the mammalian SCN.

The central mesencephalic grey in birds: nucleus intercollicularis and substantia grisea centralis

The question discussed in this paper is, whether the dorsomedial part of the intercollicular nucleus and central mesencephalic grey of birds are comparable to (parts of) the periaqueductal grey in mammals. The mammalian periaqueductal grey, and the avian dorsomedial part of the intercollicular nucleus + central mesencephalic grey are each part of pathways in control of functions such as vocalization and sexual behavior. The connectivity and histochemical features of the dorsomedial intercollicular nucleus and central mesencephalic grey are partly different and also differ partly from those of the mammalian periaqueductal grey. It is suggested that these areas in mammals and birds form comparable links in the emotional motor pathway that has been defined before in mammals.