Immunoreactive neuropeptide systems in avian embryos (domestic mallard, domestic fowl, Japanese quail)

Somatostatin affects GnRH neuronal development and migration and stimulates olfactory-related fiber fasciculation

Transient expression of somatostatin (SST) has been observed in the olfactory epithelium (OE) and nerves of chick embryos. Intense expression of SST in these regions on embryonic days (E) 5-8 coincides with the migration of neurons producing gonadotropin-releasing hormone (GnRH) from the OE to the forebrain (FB), suggesting that SST plays a role in the development of GnRH neurons. Using in ovo electroporation of small interfering RNA, we found that the suppression of SST mRNA in the olfactory placode (OP) of E3.5 chick embryos significantly reduced the number of GnRH and Islet-1-immunoreactive neurons in the nasal region without affecting the entry of GnRH neurons into the FB at E5.5-6. SST knockdown did not lead to changes in the number of apoptotic, proliferating, or HuC/D-positive neuronal cells in the OE; therefore, it is possible that SST is involved in the neurogenesis/differentiation of GnRH neurons and OP-derived GnRH-negative migratory neurons. In whole OP explant cultures, we also found that SST or its analog octreotide treatment significantly increased the number of migratory GnRH neurons and the migratory distance from the explants. The co-application of an SST antagonist blocked the octreotide-induced increase in the number of GnRH neurons. Furthermore, the fasciculation of polysialylated neural cell adhesion molecule-immunoreactive fibers emerging from the explants was dependent on octreotide. Taken together, our results provide evidence that SST exerts facilitatory effects on the development of neurons expressing GnRH or Islet-1 and on GnRH neuronal migration, in addition to olfactory-related fiber fasciculation.

Olfactory placode generates a diverse population of neurons expressing GnRH, somatostatin mRNA, neuropeptide Y, or calbindin in the chick forebrain

The olfactory placode (OP) of vertebrates generates several classes of migrating cells, including hypothalamic gonadotropin-releasing hormone (GnRH)-producing neurons, which play essential roles in the reproduction system. Previous studies using OP cell labeling have demonstrated that OP-derived non-GnRH cells enter the developing forebrain; however, their final fates and phenotypes are less well understood. In chick embryos, a subpopulation of migratory cells from the OP that is distinct from GnRH neurons transiently expresses somatostatin (SS). We postulated that these cells are destined to develop into brain neurons. In this study, we examined the expression pattern of SS mRNA in the olfactory-forebrain region during development, as well as the destination of OP-derived migratory cells, including SS mRNA-expressing cells. Utilizing the Tol2 genomic integration system to induce long-term fluorescent protein expression in OP cells, we found that OP-derived migratory cells labeled at embryonic day (E) 3 resided in the olfactory nerve and medial forebrain at E17-19. A subpopulation of green fluorescent protein (GFP)-labeled GnRH neurons that remained in the olfactory nerve was considered to comprise terminal nerve neurons. In the forebrain, GFP-labeled cells showed a distribution pattern similar to that of GnRH neurons. A large proportion of GFP-labeled cells expressed the mature neuronal marker NeuN. Among the GFP-labeled cells, the percentage of GnRH neurons was low, while the remaining GnRH-negative neurons either expressed SS mRNA, neuropeptide Y, or calbindin D-28k or did not express any of them. These results indicate that a diverse population of OP-derived neuronal cells, other than GnRH neurons, integrates into the chick medial forebrain.

Characterization of the hypothalamus of Xenopus laevis during development. I. The alar regions

The patterns of expression of a set of conserved developmental regulatory transcription factors and neuronal markers were analyzed in the alar hypothalamus of Xenopus laevis throughout development. Combined immunohistochemical and in situ hybridization techniques were used for the identification of subdivisions and their boundaries. The alar hypothalamus was located rostral to the diencephalon in the secondary prosencephalon and represents the rostral continuation of the alar territories of the diencephalon and brainstem, according to the prosomeric model. It is composed of the supraoptoparaventricular (dorsal) and the suprachiasmatic (ventral) regions, and limits dorsally with the preoptic region, caudally with the prethalamic eminence and the prethalamus, and ventrally with the basal hypothalamus. The supraoptoparaventricular area is defined by the orthopedia (Otp) expression and is subdivided into rostral and caudal portions, on the basis of the Nkx2.2 expression only in the rostral portion. This region is the source of many neuroendocrine cells, primarily located in the rostral subdivision. The suprachiasmatic region is characterized by Dll4/Isl1 expression, and was also subdivided into rostral and caudal portions, based on the expression of Nkx2.1/Nkx2.2 and Lhx1/7 exclusively in the rostral portion. Both alar regions are mainly connected with subpallial areas strongly implicated in the limbic system and show robust intrahypothalamic connections. Caudally, both regions project to brainstem centers and spinal cord. All these data support that in terms of topology, molecular specification, and connectivity the subdivisions of the anuran alar hypothalamus possess many features shared with their counterparts in amniotes, likely controlling similar reflexes, responses, and behaviors.

Ontogenetic distribution of the transcription factor nkx2.2 in the developing forebrain of Xenopus laevis

The expression of the Nkx2.2 gene is involved in the organization of the alar-basal boundary in the forebrain of vertebrates. Its expression in different diencephalic and telencephalic regions, helped to define distinct progenitor domains in mouse and chick. Here we investigated the pattern of Nkx2.2 protein distribution throughout the development of the forebrain of the anuran amphibian, Xenopus laevis. We used immunohistochemical and in situ hybridization techniques for its detection in combination with other essential territorial markers in the forebrain. No expression was observed in the telencephalon. In the alar hypothalamus, Nkx2.2 positive cells were scattered in the suprachiasmatic territory, but also in the supraopto-paraventricular area, as defined by the expression of the transcription factor Orthopedia (Otp) and the lack of xDll4. In the basal hypothalamus Nkx2.2 expressing cells were localized in the tuberal region, with the exception of the arcuate nucleus, rich in Otp expressing cells. In the diencephalon it was expressed in all three prosomeres (P1–P3) and not in the zona limitans intrathalamica. The presence of Nkx2.2 expressing cells in P3 was restricted to the alar portion, as well as in prosomere P2, whereas in P1 the Nkx2.2 expressing cells were located in the basal plate and identified the alar/basal boundary. These results showed that Nkx2.2 and Sonic hedgehog are expressed in parallel adjacent stripes along the anterior–posterior axis. The results of this study showed a conserved distribution pattern of Nkx2.2 among vertebrates, crucial to recognize subdivisions that are otherwise indistinct, and supported the relevance of this transcription factor in the organization of the forebrain, particularly in the delineation of the alar/basal boundary of the forebrain.

Ontogeny of a novel decapeptide derived from POMC-A in the brain and pituitary of the rainbow trout

Trout POMC-A exhibits a unique C-terminal extension of 25-amino acids which is processed in the pituitary and hypothalamus to generate two novel decapeptides, EQWGREEGEE and ALGERKYHFQ-NH(2). The fibers containing these two decapeptides are widely distributed in the brain, suggesting that they may exert neurotransmitter or neuromodulator activities. In the present study, we have investigated the ontogeny of the decapeptide EQWGREEGEE in the trout pituitary and brain. In the pituitary of 29-day embryos and 33-day alevins, EQWGREEGEE-immunoreactive material was observed in a cluster of cells located in the central and rostral region of the gland, respectively. In 47-day alevins, a second group of cells exhibiting EQWGREEGEE-like immunoreactivity was detected in the caudal region of the pituitary and the intensity of labeling in these cells increased in 61-day fry. In the brain, EQWGREEGEE immunoreactivity was detected in 47-day alevins. In 47- and 61-day larvae, immunoreactive elements were mainly detected in the diencephalon. Characterization of the immunoreactive material by reversed-phase high-performance liquid chromatographic analysis combined with radioimmunoassay detection revealed the existence of two major forms which exhibited different retention times than synthetic EQWGREEGEE. The present study indicates that EQWGREEGEE-related peptides are present in the trout pituitary early during ontogeny and appear in the brain only later, and that processing of the C-terminal extension of POMC-A generates distinct molecular species at different developmental stages. These data suggest that alternative processing of the C-terminal domain of POMC-A gives rise to various peptide products that may exert specific activities during trout development.

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

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

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

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

Transient expression of somatostatin immunoreactivity in the olfactory-forebrain region in the chick embryo

The tissue distribution of somatostatin (SST) immunoreactivity was studied in the nasal and forebrain region in the chick embryo. On embryonic day (ED) 3, SST-immunoreactive (ir) cells were first detected in the cells migrating from the olfactory placode. Then, at ED3.5, SST-ir cells and -ir fibers appeared in the olfactory epithelium and olfactory nerve bundles. At ED6-8, one component of the SST-ir fibers was found to separate from the olfactory nerve and it entered the parenchyma of the medial forebrain surface. These SST-ir fibers extended dorsocaudally toward the preseptal area. During this same period, a few SST-ir cells were observed in the medial forebrain adjacent to the SST-ir fibers. SST immunoreactivity in the nasal and forebrain areas was most striking at ED5-8 but a reduction of SST immunoreactivity in the nasal and forebrain areas occurred at ED11 and it virtually disappeared by the day of hatching. These results indicate that the expression of SST in the nasal and forebrain regions is transient in the chick embryo. Since the SST-ir cells did not co-express luteinizing hormone-releasing hormone (LHRH), it, thus, appears that these SST-r cells belong to a different cell population from LHRH neurons that are also found in the olfactory-forebrain axis during embryonic development [23]. However, a close relationship exists between SST-ir cells and -ir neuronal fibers and LHRH neurons. This may play a role in development of LHRH neurons.

The ontogeny of luteinizing hormone-releasing hormone (LHRH) producing neurons in the chick embryo: possible evidence for migrating LHRH neurons from the olfactory epithelium expressing a highly polysialylated neural cell adhesion molecule

The development of neurons expressing luteinizing hormone-releasing hormone (LHRH) has been studied immunohistochemically in the chick embryo from the 3.5 embryonic day (ED) to the day of hatching. At ED-3.5, LHRH-immunoreactive neurons were first detected in the medial epithelium of the olfactory pit, but their appearance in the brain was delayed to ED-4.5. On EDs-6-7, cords of the LHRH-immunoreactive cells extended across the nasal septum towards the ventromedial forebrain with the olfactory nerve. By double staining for LHRH and, a highly polysialylated form of neural cell adhesion molecule (NCAM-H), the LHRH-positive neurons in the olfactory-forebrain system were found strongly NCAM-H-positive. At ED-8, a marked decrease in the number of LHRH-positive cells in the olfactory epithelium and a concomitant increase in the LHRH-positive cells in the forebrain area were noted. From ED-11 to the day of hatching, the majority of LHRH-positive neurons tended to move into their usual adult position, whereas the LHRH-positive cells had almost disappeared in the olfactory epithelium. No LHRH-immunoreactive neurons were found strongly positive to NCAM-H. These results suggest that LHRH neurons originate from the olfactory placode, then as they develop they migrate across the nasal septum and enter the forebrain with the olfactory nerve. The close association of NCAM-H with the developing LHRH neurons raises the possibility that NCAM-H plays some role in guiding the migrating LHRH neurons from the olfactory epithelium to the forebrain.

Immunocytochemical demonstration of proopiomelanocortin-derived peptides in pituitary adenomas of the pars intermedia in horses

Adenomas of the pars intermedia from 19 horses and normal pituitary glands from seven horses were evaluated histologically and immunocytochemically for adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin (beta-END), proopiomelanocortin (POMC), prolactin, neuron specific enolase, and glial fibrillary acidic protein (GFAP). The 26 horses ranged in age from 7 to 31 years. Histologically, all adenomas had a uniform pattern characterized by cords of large columnar cells forming palisades and pseudoacini separated by a delicate fibrovascular stroma. Immunostaining of adenomas derived from the pars intermedia was similar to that of non-neoplastic equine pars intermedia. An immunocytochemical evaluation revealed a diffuse, strong cytoplasmic reaction for POMC, a moderate to strong reaction for alpha-MSH and beta-END, a weak reaction for ACTH, and negative immunostaining for prolactin, GFAP, and neuron specific enolase in the adenomas. The unique clinicopathologic syndrome that develops in horses with pituitary adenomas appears to be the result of an over-production of POMC-derived peptides in addition to space-occupying effects resulting in dysfunction of the hypothalamus and neurohypophysis.

Embryonal development of arginine vasotocin/mesotocin gene expression in the chicken brain

Abstract An ontogenic series of chick embryo brains (4, 6, 9,12,14,16 and 18 days of incubation, hatching day: 21) was coronally or saggitally sectioned and investigated for expression of the arginine vasotocin (AVT)/mesotocin (MT) gene. To this end a 39mer oligonucleotide recognizing the AVT/MT encoding sequence of their respective mRNAs was constructed employing optimized codon usage and was used for in situ hybridization. AVT/MT mRNA-expressing neurons were first detected on embryonal day (E) 6 adjacent to the third ventricle. By E9 the periventricular nucleus had expanded in size but the hybridization signal was weaker. These results suggest a migration of cells in all directions away from the third ventricle into the diencephalon; some perikarya were even observed at the lateral pial surface above the optic chiasm. By E12, brain differentiation had advanced to distinct hypothalamo-neurohypophyseal nuclei (supraoptic and paraventricular nuclei) as well as to accessory groups expressing AVT/MT mRNA. Two cell types were then distinguishable in the paraventricular nucleus; the specific mRNA was expressed either as a weak or a strong hybridization signal. Comparison with other studies suggested that differentiation had almost attained adult level though cell growth and differentiation of supraoptic and paraventricular nuclei still occurred. This was complete by E18 when individual cells were larger and the intensity of the hybridization signal became very strong. RNase pretreatment depressed the signal by 100%. Northern blot hybridization of RNA extracted from newly hatched chicks verified the specificity of the probe. A single band was evident, indicating an mRNA of approximately 700 bases, which is only found in hypothalamus and not in muscle, liver or extra-hypothalamic brain, and corresponds in size closely with mammalian vasopressin mRNA. The data demonstrate a very early development (E6) of neurohypophyseal hormone gene expression in the chick embryo brain with important differentiation around E9. At E12 magnocellular neuronal arrangement resembled adult neurons but the gene expression signal increased in intensity until E18.

Proopiomelanocortin (POMC)-related peptides in the brain of the rainbow trout, Salmo gairdneri

We have investigated the presence of ACTH, alpha-MSH and beta-endorphin, three peptides which derive from the multifunctional precursor protein proopiomelanocortin (POMC) in the brain of the rainbow trout Salmo gairdneri. Using both the indirect immunofluorescence and peroxidase-antiperoxidase techniques, a discrete group of positive cells was identified in the hypothalamus, within the anterior part of the nucleus lateralis tuberis. alpha-MSH-containing neurons represented the most abundant immunoreactive subpopulation. Coexistence of alpha-MSH, ACTH and beta-endorphin was observed in the lateral part of the nucleus. ACTH- and beta-endorphin-containing cells were mainly distributed in the rostral and caudal regions of the nucleus. In the medial portion of the nucleus lateralis tuberis, numerous cells were only stained for alpha-MSH. Moderate to dense plexuses of immunoreactive fibers were observed in the ventral thalamus and the floor of the hypothalamus. Some of these fibers projected towards the pituitary. The concentrations of ACTH, alpha-MSH and beta-endorphin-like immunoreactivities were measured in microdissected brain regions by means of specific radioimmunoassays. Diencephalon, mesencephalon and medulla oblongata extracts gave dilution curves which were parallel to standard curves. The highest concentrations of POMC-derived peptides were found in the diencephalon (alpha-MSH: 4.28 +/- 0.43 ng/mg prot.; ACTH: 1.08 +/- 0.09 ng/mg prot.; beta-endorphin: 1.02 +/- 0.1 ng/mg prot.), while lower concentrations were detected in the mesencephalon, medulla oblongata and telencephalon. The present results demonstrate that various peptides derived from POMC coexist within the same cell bodies of the fish hypothalamus. Taken together, these data suggest that expression and processing of POMC in the fish brain is similar to that occurring in pituitary melanotrophs.

The ACTH-immunoreactive system in the brain of the white-crowned sparrow, Zonotrichia leucophrys gambelii (Passeriformes, Emberizidae)

The ACTH-immunoreactive (ir) system of the avian brain is particularly conspicuous in the male white-crowned sparrow (Zonotrichia leucophrys gambelii). The irperikaryal population is concentrated mainly within the tuberal region, projecting primarily in a dorsal direction: (i) into the striatum; (ii) into rostral diencephalic, septal, hyperstriatal, and thalamic areas; and (iii) into dorsal and ventral areas of the brain stem. Ir-fibers seemingly contact local non-immunoreactive neurons mainly in the accumbens nucleus, septum, dorsal thalamic nuclei, infundibular and interpeduncular nuclei, and in the rostral diencephalon. Neurohemal zones are not supplied by ACTH-ir terminals. Immunocytochemical problems arising from the complexity of the proopiomelanocortin molecule and its derived peptide components are discussed in relation to phylogenetically directed studies, and contradictory results.

Localization of avian LHRH-immunoreactive neurons in the hypothalamus of the domestic fowl, Gallus domesticus, and the Japanese quail, Coturnix coturnix

The localization of LHRH-containing perikarya and nerve fibers in the hypothalami of the domestic fowl and Japanese quail was investigated by means of the specific immunoperoxidase ABC method, using antisera against chicken LHRH-I ([Gln8]-LHRH), chicken GnRH-II ([His5-Trp7-Tyr8]-LHRH[2-10]) and mammalian LHRH ([Arg8]-LHRH). Chicken LHRH-I-immunoreactive perikarya were sparsely scattered in the nucleus preopticus periventricularis (POP), nucleus filiformis (FIL) and nucleus septalis medialis (SM), and in bilateral bands extending from these nuclei into the septal area in both species. A few reactive perikarya were also observed in the nucleus accumbens (Ac) and lobus parolfactorius (LPO). Numerous cLHRH-I-immunoreactive fibers were widely scattered in the preoptic, septal and tuberal areas, and were densely concentrated in the external layer of the median eminence and in organum vasculosum of the lamina terminalis (OVLT) in both species. Anti-mammalian LHRH serum cross-reacted weakly with perikarya and fibers immunoreactive to anti-cLHRH-I serum in normal chicken and quail. Anti-cGnRH-II[2-10] serum immunoreacted with magnocellular neurons distributed in the rostral end of the mesencephalon along the midline close to the nervus oculomotorius (N III). These perikarya were apparently different from cLHRH-I immunoreactive neurons. No immunoreactive cells and fibers against anti-cGnRH-II[2-10] were observed in the hypothalamus and median eminence of the chicken or quail. Anti-cGnRH-II[2-10] bound specifically with cGnRH-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of somatostatin immunoneutralization on growth and endocrine parameters in chickens

The effects of somatostatin immunoneutralization on growth rate, growth hormone (GH) secretion and circulating insulin-like growth factor I (IGF-I) concentrations were investigated in chickens through the use of passive and active immunization techniques. Intravenous bolus injection of goat-antisomatostatin stimulated a significant (P less than .05) increase in plasma GH levels for one hour post-injection in four and six week old male broiler chickens. The GH response to an intravenous bolus injection of hGRF44NH2 was similar in the antisomatostatin treated chicks and normal goat serum treated controls. Despite the presence of circulating somatostatin antisera after 28 hours, plasma GH levels were not different between control and antisomatostatin-treated chicks at that time. Continuous administration of somatostatin antisera by Alzet pump over a two-week period resulted in significant (P less than .05) elevations in plasma GH levels at one week post-implantation and in circulating IGF-I concentrations after two weeks of administration. Chicks which developed antibodies against somatostatin following active immunization exhibited a 7.1% increase in growth rate which was associated with a significant decrease in abdominal fat. However, neither GH nor IGF-I concentrations were elevated in the chicks which developed somatostatin antibodies. Thus, the benefits gained from somatostatin immunoneutralization may be exerted through mechanisms other than GH.

Functional development of the prenatal brain. I. Recording of extracellular action potentials from the magnocellular system of the 18-day-old chicken embryo

For the full understanding of the ontogeny of the electrical activity in the brain it is essential to record single unit activity of the fetus. However, investigations of the functional development of neuronal properties in mammals are largely limited by the inaccessibility of the prenatal brain. Therefore, we have designed a new method to record extracellular single unit activities of identified magnocellular neurones in the Nucleus paraventricularis of the chicken embryo after 18 days of incubation. One hundred and four magnocellular neurones were identified by antidromic stimulation from the neural lobe. In a high percentage of the neurones an A-B inflexion of the action potential could be observed similar to that frequently encountered in mammalian magnocellular neurones. The mean duration of the action potential was 2.8 ms with a range between less than 1 ms and 7 ms. This large range is probably due to developmental processes of the cell membrane and subsequent changes in the extra- und intracellular ion concentration. Fourty-six percent of the neurones generated spontaneous action potentials with a slow irregular firing pattern. The mean discharge frequency was estimated as approx. 1 Hz. In further 13% of the cells orthodromic action potentials could be observed only after the occurrence of several antidromic spikes. The data presented are the first recordings of single unit activity in the magnocellular system in the prenatal brain. They demonstrate that the chicken embryo may offer a suitable model to study the ontogeny of neuroendocrine systems in the fetal brain in-vivo.

Growth hormone secretion and pancreatic function following somatostatin infusion in ducks (Anas platyrhynchos)

The intravenous infusion of somatostatin (800 ng/kg min) reduced the concentration of growth hormone (GH) in the plasma of 4 to 5, 6 to 7 and 8 to 9 week-old ducklings, but not in adult ducks. The inhibition of GH secretion was not due to accompanying changes in pancreatic function, since the infusion of a lower dose of somatostatin (200 ng/kg min) increased glucagon release and decreased plasma free fatty acids (FFA), as observed with the higher dose, but had no effect on GH concentrations. The withdrawal of somatostatin inhibition resulted in rebound GH secretion in immature birds, the magnitude of which was directly related to the pre-treatment level. Following somatostatin infusion (800 ng/kg min) no modification in GH concentration was observed in adult ducks. These results demonstrate that basal GH release in young birds is not autonomous and is suppressible by somatostatin. The data provide further evidence for age-related changes in the control of avian GH and insulin release and for the independence of the effects of somatostatin on the pituitary and pancreas glands.

An immunocytochemical study of the development of central serotoninergic neurons in the chick embryo

The development of central serotoninergic neurons in the chick embryo has been investigated immunocytochemically by utilizing an antiserum to serotonin (5-HT). Immunoreactive neurons are first detected in the brainstem on embryonic day 4 (E4, stage 23), days earlier than 5-HT systems have been detected previously by biochemical techniques. The earliest 5-HT-containing cells at E4 appear rostral to the pontine flexure, yet by E5, 5-HT neuronal groups are observed throughout the brainstem from just caudal to the mesencephalic flexure to the cervical flexure. During this and subsequent phases of development, two distinct patterns of cellular migration seem to be involved in the formation of the various 5-HT neuronal groups. One pattern involves a ventral migration of 5-HT cells, which appears dependent upon the directional guidance of midline radial processes (formed by floor plate cells) that extend across the neuroepithelium. The other pattern involves a lateral migration of cells, followed by an aggregation and rearrangement of 5-HT neurons into distinct subgroups or clusters. Through these patterns of migration most components of the 5-HT neuronal system can be recognized as early as E12, with the mature organization of the 5-HT cell groups occurring by E17. One unexpected finding was the comparatively late appearance (between E9 and E12) of 5-HT neurons in the paraventricular organ of the hypothalamus. Thus, in comparison to the initial observation of the majority of brainstem 5-HT neurons at E4 to E5, the hypothalamic 5-HT cells appear after a delay of between 5 and 7 days. Such differences illustrate the fact that neurons sharing a common neurotransmitter phenotype do not necessarily share the same developmental timetable for the expression of that particular phenotype, or they may undergo neurogenesis during considerably different periods of embryogenesis.

Novel sources of descending input to the spinal cord of the hatching chick

Nuclear groups contributing supraspinal input to the spinal cord of the hatching chick (Gallus domesticus) were determined by using the enzyme tracer horseradish peroxidase processed with tetramethylbenzidine histochemistry. Five sources of projections to the spinal cord were found which have not been previously described in any species. All are probably related to autonomic function. They include ipsilateral hypothalamic projections from the lateral mamillary n., suprachiasmatic n., and n. of the lateral tubercle. There is a bilateral projection from the large interstitial cells of the mesencephalic posterior commissure, and in the myelencephalon, a mainly contralateral projection from interstitial cells of the vagus-glossopharyngeal nerve. Two other projections observed here have not been described in other avian species, one from the accessory vestibular n., the other, from the n. ambiguus. In the cerebellum, projections arise from the main and ventrolateral divisions of the fastigial n., and from "border cells" between the fastigial and interpositus n. The large-celled submedial vestibular n. projects bilaterally. Several projections previously described only in the pigeon, were confirmed here: the hypothalamic nucleus over the supramammilary decussation, the n. intercollicularis, the tangential n., and the n. alatus, a cell group between the hypoglossal and vagal nuclei. Four sources of input projected only as far as mid-cervical cord. These are n. intercollicularis, fastigial n., accessory vestibular n., and tangential n. All remaining projections reached to lower lumbosacral cord. Sources of descending input are remarkably similar in mammals and avians. Where homologous nuclei exist, virtually identical projections to the cord are present.

Peptidergic pathways in the avian brain

The results obtained by topographical studies on the immunoreactive peptide systems in the embryonic and adult avian brain (domestic fowl, domestic mallard, pigeon, Japanese quail, and zebra finch) can be realized only by means of phylogenetical comparisons. The comparative studies mainly demonstrate a fascinating constancy of the immunological properties and the spatial distribution of the neuropeptides. Independent of the development of the neopallium, and the increasing cerebral complexity, the spatial distribution of the neuropeptides, the location of their main perikaryal accumulations which are interconnected by immunoreactive fiber projections (and thereby forming widespread but continuous peptide systems) remain nearly unchanged during vertebrate evolution. The recognition of the neuropeptides as integral parts of the central nervous system is demonstrated by the fact that neuropeptidergic structures connect sensory inputs with central nervous areas as well as with the peripheral endocrinium.

Neuronal organization of the avian paraventricular nucleus: intrinsic, afferent, and efferent connections

The heterogeneous paraventricular nucleus (PVN) of birds offers favorable conditions for the analysis of intrinsic, afferent, and efferent connections of neuroendocrine systems. Paraventricular neurons are successfully impregnated with the Golgi-technique. The findings indicate a direct influence of the cerebrospinal fluid (CSF) on the magnocellular neurons that, via their axon terminals in the neural lobe of the pituitary, are also exposed to the hemal milieu. The magnocellular neurons are intermingled with parvocellular elements which may represent local interneurons. A group of parvocellular nerve cells is identified as CSF-contacting neurons. This type of cell forms a basic morphologic component of the avian neuroendocrine apparatus. Immunocytochemical and ultrastructural studies further support the concept of neuronal interactions between parvocellular and magnocellular elements. Moreover, these findings speak in favor of the existence of recurrent collaterals of the magnocellular neurons. Nerve cells giving rise to afferent connections to the PVN are located in the limbic system and autonomic areas of the upper and lower brainstem. Further afferents may originate from the subfornical organ, the organon vasculosum laminae terminalis, the ventral tegmentum, and the area postrema. Via efferent projections, the PVN is connected to the nucleus accumbens, lateral septum, several hypothalamic nuclei, the neural lobe of the pituitary, the organon vasculosum laminae terminalis, the subfornical organ, the pineal organ, the area postrema, the lateral habenular complex, and various autonomic areas of the reticular formation in the upper and lower brainstem and the spinal cord. In conclusion, the PVN may be regarded as an integral component of the neuroendocrine apparatus reciprocally coupled to the limbic system, several circumventricular organs, and various autonomic centers of the brain.

Comparative effects of somatostatin-28 and somatostatin-14 on basal growth hormone release and pancreatic function in immature ducks (Anas platyrhynchos)

The 30-min infusion of somatostatin (SRIF)-14 or SRIF-28 (800 ng/kg/min) in 7- to 8-week-old ducklings reduced the basal level of plasma growth hormone (GH). The magnitude of the GH suppression induced by SRIF-14 was similar to that elicited by SRIF-28. "Rebound" GH secretion was observed 30 min after infusion, the GH concentration being elevated above the basal level. The increase in GH secretion after SRIF-14 infusion was greater than that induced by SRIF-28. Plasma insulin and free fatty acid (FFA) levels were similarly reduced after 10 and 30 min of SRIF-14 or SRIF-28 infusion. Following infusion the FFA levels returned to the pretreatment concentration, whereas the insulin concentration in both groups remained suppressed 30 min after infusion. The insulin level was still suppressed 60 min after SRIF-14 infusion, but not after SRIF-28 infusion. The infusion of SRIF-14 resulted in a marked, progressive increase in the glucagon concentration, which was reduced in birds infused with SRIF-28 and accompanied by hypoglycaemia. Following SRIF-28 infusion a "rebound" in the glucagon concentration occurred and remained elevated for at least 60 min. These results demonstrate comparative effects of SRIF-14 and SRIF-28 on the basal release of pituitary GH and pancreatic insulin and glucagon, and in particular they suggest that SRIF-28 is more potent in inhibiting pancreatic A cell activity.

Immunohistochemical distribution of somatostatin-like immunoreactivity in the central nervous system of the adult rat

The localization and distribution of somatostatin (growth hormone release-inhibiting hormone; somatotropin release-inhibiting factor) have been studied with the indirect immunofluorescence technique of Coons and collaborators and the immunoperoxidase method of Sternberger and coworkers using specific and well-characterized antibodies to somatostatin, providing semiquantitative, detailed maps of somatostatin-immunoreactive cell profiles and fibers. Our results demonstrate a widespread occurrence of somatostatin-positive nerve cell bodies and fibers throughout the central nervous system of adult, normal or colchicine-treated, albino rats. The somatostatin cell bodies varied in size from below 10 micron up to 40 micron in diameter and could have only a few or multiple processes. Dense populations of cell somata were present in many major areas including neocortex, piriform cortex, hippocampus, amygdaloid complex, nucleus caudatus, nucleus accumbens, anterior periventricular hypothalamic area, ventromedial hypothalamic nucleus, nucleus arcuatus, medial to and within the lateral lemniscus, pontine reticular nuclei, nucleus cochlearis dorsalis and immediately dorsal to the nucleus tractus solitarii. Extensive networks of nerve fibers of varying densities were also found in most areas and nuclei of the central nervous system. Both varicose fibers as well as dot- or "dust-like" structures were seen. Areas with dense or very dense networks included nucleus accumbens, nucleus caudatus, nucleus amygdaloideus centralis, most parts of the hypothalamus, nucleus parabrachialis, nucleus tractus solitarii, nucleus ambiguus, nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. One exception is the cerebellum which only contained few somatostatin-positive cell bodies and nerve fibers. It should be noted that somatostatin-positive cell bodies and fibers did not always conform to the boundaries of the classical neuroanatomical nuclei, but could often be found in areas between these well-established nuclei or occupying, in varying concentrations, only parts of such nuclei. It was difficult to identify with certainty somatostatin-immunoreactive axons in the animals studied. Some pathways could, however, be demonstrated, but further experimental studies are necessary to elucidate the exact projections of the somatostatin-immunoreactive neurons in the rat central nervous system.