Immunocytochemical demonstration of separate vasotocinergic and mesotocinergic neurons in the amphibian hypothalamic magnocellular neurosecretory system

Arginine Vasotocin, the Social Neuropeptide of Amphibians and Reptiles

Arginine vasotocin (AVT) is the non-mammalian homolog of arginine vasopressin (AVP) and, like vasopressin, serves as an important modulator of social behavior in addition to its peripheral functions related to osmoregulation, reproductive physiology, and stress hormone release. In amphibians and reptiles, the neuroanatomical organization of brain AVT cells and fibers broadly resembles that seen in mammals and other taxa. Both parvocellular and magnocellular AVT-containing neurons are present in multiple populations located mainly in the basal forebrain from the accumbens-amygdala area to the preoptic area and hypothalamus, from which originate widespread fiber connections spanning the brain with a particularly heavy innervation of areas associated with social behavior and decision-making. As for mammalian AVP, AVT is present in greater amounts in males in many brain areas, and its presence varies seasonally, with hormonal state, and in males with differing social status. AVT's social influence is also conserved across herpetological taxa, with significant effects on social signaling and aggression, and, based on the very small number of studies investigating more complex social behaviors in amphibians and reptiles, AVT may also modulate parental care and social bonding when it is present in these vertebrates. Within this conserved pattern, however, both AVT anatomy and social behavior effects vary significantly across species. Accounting for this diversity represents a challenge to understanding the mechanisms by which AVT exerts its behavioral effects, as well are a potential tool for discerning the structure-function relationships underlying AVT's many effects on behavior.

Plasticity of melanotrope cell regulations in Xenopus laevis

This review focuses on the plasticity of the regulation of a particular neuroendocrine transducer cell, the melanotrope cell in the pituitary pars intermedia of the amphibian Xenopus laevis. This cell type is a suitable model to study the relationship between various external regulatory inputs and the secretion of an adaptive endocrine message, in this case the release of α-melanophore-stimulating hormone, which activates skin melanophores to darken when the animal is placed on a dark background. Information about the environmental conditions is processed by various brain centres, in the hypothalamus and elsewhere, that eventually control the activity of the melanotrope cell regarding hormone production and secretion. The review discusses the roles of these hypothalamic and extrahypothalamic nuclei, their neurochemical messengers acting on the melanotrope, and the external stimuli they mediate to control melanotrope cell functioning.

In Vivo Induction of Glial Cell Proliferation and Axonal Outgrowth and Myelination by Brain-Derived Neurotrophic Factor

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family of neuronal cell survival and differentiation factors but is thought to be involved in neuronal cell proliferation and myelination as well. To explore the role of BDNF in vivo, we employed the intermediate pituitary melanotrope cells of the amphibian Xenopus laevis as a model system. These cells mediate background adaptation of the animal by producing high levels of the prohormone proopiomelanocortin (POMC) when the animal is black adapted. We used stable X. transgenesis in combination with the POMC gene promoter to generate transgenic frogs overexpressing BDNF specifically and physiologically inducible in the melanotrope cells. Intriguingly, an approximately 25-fold overexpression of BDNF resulted in hyperplastic glial cells and myelinated axons infiltrating the pituitary, whereby the transgenic melanotrope cells became located dispersed among the induced tissue. The infiltrating glial cells and axons originated from both peripheral and central nervous system sources. The formation of the phenotype started around tadpole stage 50 and was induced by placing white-adapted transgenics on a black background, i.e. after activation of transgene expression. The severity of the phenotype depended on the level of transgene expression, because the intermediate pituitaries from transgenic animals raised on a white background or from transgenics with only an approximately 5-fold BDNF overexpression were essentially not affected. In conclusion, we show in a physiological context that, besides its classical role as neuronal cell survival and differentiation factor, in vivo BDNF can also induce glial cell proliferation as well as axonal outgrowth and myelination.

Modulation of rhythmic motor activity by pyrokinin peptides

Pyrokinin (PK) peptides localize to the central and peripheral nervous systems of arthropods, but their actions in the CNS have yet to be studied in any species. Here, we identify PK peptide family members in the crab Cancer borealis and characterize their actions on the gastric mill (chewing) and pyloric (filtering) motor circuits in the stomatogastric ganglion (STG). We identified PK-like immunolabeling in the STG neuropil, in projection neuron inputs to this ganglion, and in the neuroendocrine pericardial organs. By combining MALDI mass spectrometry (MS) and ESI tandem MS techniques, we identified the amino acid sequences of two C. borealis pyrokinins (CabPK-I, CabPK-II). Both CabPKs contain the PK family-specific carboxy-terminal amino acid sequence (FXPRLamide). PK superfusion to the isolated STG had little influence on the pyloric rhythm but excited many gastric mill neurons and consistently activated the gastric mill rhythm. Both CabPKs had comparable actions in the STG and these actions were equivalent to those of Pevpyrokinin (shrimp) and Leucopyrokinin (cockroach). The PK-elicited gastric mill rhythm usually occurred without activation of the projection neuron MCN1. MCN1, which does not contain CabPKs, effectively drives the gastric mill rhythm and at such times is also a gastric mill central pattern generator (CPG) neuron. Because the PK-elicited gastric mill rhythm is independent of MCN1, the underlying core CPG of this rhythm is different from the one responsible for the MCN1-elicited rhythm. Thus neuromodulation, which commonly alters motor circuit output without changing the core CPG, can also change the composition of this core circuit.

Brain-derived neurotrophic factor in the brain of Xenopus laevis may act as a pituitary neurohormone together with mesotocin

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, occurs abundantly in the brain, where it exerts a variety of neural functions. We previously demonstrated that BDNF also exists in the endocrine melanotroph cells in the intermediate lobe of the pituitary gland of the amphibian Xenopus laevis, suggesting that BDNF, in addition to its neural actions within the brain, can act as a hormone. In the present study, we tested whether BDNF, in addition to its neural and hormonal roles, can be released as a neurohormone from the neural pituitary lobe of X. laevis. By light immunocytochemistry, we show that BDNF is present in perikarya, in ventrolaterally projecting axons of the hypothalamic magnocellular nucleus and in the neural lobe of the pituitary gland, and that it coexists in these structures with the amphibian neurohormone, mesotocin. The neural lobe was studied in detail at the ultrastructural level. Two types of neurohaemal axon terminals were observed, occurring intermingled and in similar numbers. Type A is filled with round, moderately electron-dense secretory granules with a mean diameter of approximately 145 nm. Type B terminals contain electron-dense and smaller, ellipsoid granules (long and short diameter approximately 140 and 100 nm, respectively). BDNF is exclusively present in secretory granules of type A axon terminals. Double gold-immunolabelling revealed that BDNF coexists in these granules with mesotocin. Furthermore, we demonstrate in an superfusion study performed in vitro that mesotocin stimulates peptide release from the endocrine melanotroph cells. On the basis of these data, we propose that BDNF can act on these cells as a neurohormone.

Co-localization of mesotocin and opsin immunoreactivity in the hypothalamic preoptic nucleus of Xenopus laevis

The purpose of the present investigation was to provide a detailed description of the encephalic photoreceptors of Xenopus laevis at the light microscopic level and to determine their relationship with the neurosecretory cells of the hypothalamus in order to further our understanding of photoperiodic regulation of seasonal rhythms. Numerous opsin-positive neurons were found in the hypothalamic magnocellular preoptic nucleus and their axonal processes were seen to run laterally towards the basal regions of the brain, reaching the neural lobe of the hypophysis. Analysis of labelling with different antisera in adjacent sections, as well as double-immunolabelling carried out on the same section, revealed that mesotocin immunoreactivity was present in most of the opsin-positive neurons; however, no evidence for opsin and vasotocin coexpression was found in any of the sections analysed. The close localization of LHRH and opsin/mesotocin fibers in some regions of the brain, such as the median eminence, suggests that some interaction between these two systems might exist. In conclusion, in this study we provide the first strong evidence that the hypothalamic mesotocinergic neurons, which have been proved to be connected to the GnRH system in other species, are directly involved in photoreception in Xenopus laevis. These findings represent a novel contribution to our understanding of how light influences the seasonal reproductive cycles in lower vertebrates.

The distribution of vasotocin and mesotocin immunoreactivity in the brain of the snake, Bothrops jararaca

Polyclonal antibodies against vasotocin (AVT) and mesotocin (MST) were used to explore the distribution of these peptides in the brain of the snake Bothrops jararaca. Magnocellular AVT- and MST-immunoreactive (ir) perikarya were observed in the supraoptic nucleus (SON), being AVT-ir neurons more numerous. A portion of the SON, in the lateroventral margin of the diencephalon ventrally to optic tract, showed only AVT-ir perikarya and fibers. However, the caudal most portion displayed only mesotocinergic perikarya. Parvocellular and magnocellular AVT- and MST-ir perikarya were present in the paraventricular nucleus (PVN) being AVT-ir fibers more abundant than MST-ir. Vasotocinergic perikarya were also found in a dorsolateral aggregation (DLA) far from the PVN. Mesotocinergic perikarya were also present in the recessus infundibular nucleus and ependyma near to paraventricular organ. Nerve fibers emerging from supraoptic and paraventricular nuclei run along the diencephalic floor, internal zone of the median eminence (ME) to end in the neural lobe. Also a dense network of AVT- and MST-ir fibers was present in the external zone of the ME, close to the vessels of the hypophysial portal system. As a rule, all regions having vasotocinergic and mesotocinergic perikarya also showed immunoreactive fibers. Vasotocinergic and mesotocinergic fibers but not perikarya were found in the lamina terminalis (LT). Moreover AVT-ir fibers were present in the nucleus accumbens and MST-ir fibers in the septum. In mesencephalon and rhombencephalon MST-ir fibers were more numerous than AVT-ir fibers. Vasotocinergic and mesotocinergic fibers in extrahypothalamic areas suggest that these peptides could function as neurotransmitters and/or neuromodulators in the snake B. jararaca.

Anatomical and biochemical evidence for the synthesis of unconjugated and sulfated neurosteroids in amphibians

Various studies have shown that, in mammals, neurons and glial cells are capable of synthesizing bioactive steroids, or neurosteroids, which regulate the activity of the central nervous system (CNS). However, although steroid hormones are involved in the regulation of behavioral and neuroendocrine processes in amphibians, neurosteroid biosynthesis has never been studied in the CNS of non-mammalian vertebrates. Reviewed here are several data sets concerning the production of unconjugated and sulfated neurosteroids in amphibians. These data were obtained by investigating the immunohistochemical localization and activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and hydroxysteroid sulfotransferase (HST), in the frog brain. Numerous 3beta-HSD-immunoreactive neurons were detected in the anterior preoptic area, nucleus of the periventricular organ, posterior tuberculum, ventral and dorsal hypothalamic nuclei. 17beta-HSD-like immunoreactivity was found in ependymal gliocytes bordering the lateral ventricles of the telencephalon. Two populations of HST-immunoreactive neurons were localized in the anterior preoptic area and the dorsal magnocellular nucleus of the hypothalamus. High amounts of progesterone (PROG), 17-hydroxyprogesterone (17OH-PROG), testosterone (T) and dehydroepiandrosterone sulfate (DHEAS) were measured in the frog brain by combining HPLC analysis of tissue extracts with radioimmunoassay detection. Incubation of telencephalic or hypothalamic explants with tritiated pregnenolone ([3H]PREG) yielded the synthesis of various metabolites including PROG, 17OH-PROG, DHEA and T. Incorporation of [35S]3'-phosphoadenosine 5'-phosphosulfate ([35S]PAPS) and [3H]PREG or [3H]DHEA into frog brain homogenates led to the formation of [3H,35S]pregnenolone sulfate ([3H,35S]PREGS) or [3H,35S]DHEAS, respectively. Altogether, these results demonstrate that the process of neurosteroid biosynthesis occurs in amphibians as previously seen in mammals.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Colocalization of arginine-vasotocin and chicken luteinizing hormone-releasing hormone-I (cLHRH-I) in the preoptic-hypothalamic region of the chicken

To characterize a possible relationship between chicken luteinizing hormone-releasing hormone-I (cLHRH-I) and arginine-vasotocin (AVT) we performed immunocytochemical double-stainings throughout the preoptic-hypothalamic region of the chicken brain. This study clearly reveals a partial colocalization between both neuropeptides. Single-labeled neurons, containing either cLHRH-I or AVT are found intermingled with double stained cells, immunoreactive (ir) for both peptides. A significant number of double-labeled perikarya is found in the preoptic area, more specifically in the ventral and external portion of the supraoptic nucleus (SOv and SOe) and in the medial preoptic nucleus (MPOv). At the level of the anterior hypothalamus, double-labeled cells are predominantly observed near the third ventricle in the nucleus paraventricularis magnocellularis (PVN) and the nucleus periventricularis hypothalami (PHN). Next to this colocalization, a number of cLHRH-I-ir cell bodies are found in close apposition to AVT-ir fiber profiles in the very same areas. Taken together, these data are the first to provide morphological evidence indicating that the AVT system might be involved in the regulation of cLHRH-I release and thus of reproductive functions in birds.

Comparative neuroanatomy of vasotocin and vasopressin in amphibians and other vertebrates

This review focuses on the neuroanatomical distribution of vasotocin (VT) and vasopressin (VP) and presents a comparative analysis of brain areas in which VT and VP cell bodies have been reported in fish, amphibians, reptiles, birds and mammals. A comparison of information from previous neuroanatomical studies of VT and VP with findings from a recent study of VT in an amphibian (Taricha granulosa) supports the conclusions that the VT/VP system can be subdivided into identifiable groups of cell bodies, based on neuroanatomical and cell morphology characteristics, and that these cell groups are not necessarily delimited by classical neuroanatomical boundaries. The comparative neuroanatomy of the distribution of VT and VP cell bodies also indicates that the neuroanatomy of the VT/VP system is fairly conserved among vertebrates. The review uses comparative data to present a series of tentative hypotheses about the homology of the VT cell groups and VP cell groups in the different vertebrate taxa.

Background adaptation by Xenopus laevis: a model for studying neuronal information processing in the pituitary pars intermedia

This review is concerned with recent literature on the neural control of the pituitary pars intermedia of the amphibian Xenopus laevis. This aquatic toad adapts skin colour to the light intensity of its environment, by releasing the proopiomelanocortin (POMC)-derived peptide alpha-MSH (alpha-melanophore-stimulating hormone) from melanotrope cells. The activity of these cells is controlled by brain centers of which the hypothalamic suprachiasmatic and magnocellular nuclei, respectively, inhibit and stimulate both biosynthesis and release of alpha-MSH. The suprachiasmatic nucleus secretes dopamine, GABA, and NPY from synaptic terminals on the melanotropes. The structure of the synapses depends on the adaptation state of the animal. The inhibitory transmitters act via cAMP. Under inhibition conditions, melanotropes actively export cAMP, which might have a first messenger action. The magnocellular nucleus produces CRH and TRH. CRH, acting via cAMP, and TRH stimulate POMC-biosynthesis and POMC-peptide release. ACh is produced by the melanotrope cell and acts in an autoexcitatory feedback on melanotrope M1 muscarinic receptors to activate secretory activity. POMC-peptide secretion is driven by oscillations of the [Ca2+]i, which are initiated by receptor-mediated stimulation of Ca2+ influx via N-type calcium channels. The hypothalamic neurotransmitters and ACh control Ca2+ oscillatory activity. The structural and functional aspects of the various neural and endocrine steps in the regulation of skin colour adaptation by Xenopus reveal a high degree of plasticity, enabling the animal to respond optimally to the external demands for physiological adaptation.

Neuroanatomical distribution of vasotocin in a urodele amphibian (Taricha granulosa) revealed by immunohistochemical and in situ hybridization techniques

Immunohistochemical and in situ hybridization techniques were used to investigate the neuroanatomical distribution of arginine vasotocin-like systems in the roughskin newt (Taricha granulosa). Vasotocin-like-immunoreactive neuronal cell bodies were identified that, based on topographical position, most likely, are homologous to groups of vasopressin-immunoreactive neuronal cell bodies described in mammals, including those in the bed nucleus of the stria terminalis, medial amygdala, basal septal region, magnocellular basal forebrain-including the horizontal limb of the diagonal band of Broca, paraventricular and supraoptic nuclei, suprachiasmatic nucleus, and dorsomedial hypothalamic nucleus. Several additional vasotocin-like-immunoreactive cell groups were observed in the forebrain and brainstem regions; these observations are compared with previous studies of vasotocin- and vasopressin-like systems in vertebrates. Arginine vasotocin-like-immunoreactive fibers and presumed terminals also were widely distributed with high densities in the basal limbic forebrain, the ventral preoptic and hypothalamic regions, and the brainstem ventromedial tegmentum. Based on in situ hybridization studies with synthetic oligonucleotide probes for vasotocin and the related neuropeptide mesotocin, as well as double-labeling studies with combined immunohistochemistry and in situ hybridization, we conclude that the vasotocin immunohistochemical procedures used identify vasotocin-like, but not mesotocin-like, elements in the brain of T. granulosa. The distribution of arginine vasotocin-like systems in T. granulosa is greater than the distribution previously reported for any other single vertebrate species; however, it is consistent with an emerging pattern of distribution of vasotocin- and vasopressin-like peptides in vertebrates. Complexity in the vasotocinergic system adds further support to the conclusion that this peptide regulates multiple neurophysiological and neuroendocrinological functions.

Development of arginine vasotocin innervation in two species of anuran amphibian: Rana catesbeiana and Rana sylvatica

Arginine vasotocin (AVT) is a neurotransmitter in the amphibian central nervous system and is released from the neurohypophysis in the regulation of hydromineral balance and other homeostatic functions. Many amphibians experience drastic changes in habitat with respect to water availability during their transformation from aquatic larvae to terrestrial adults. To examine whether metamorphosis is accompanied by a reorganization of central vasotocinergic neurons, the developmental organization of vasotocin neurons and nerve fibers was studied with immunocytochemistry in the brains of bullfrogs (Rana catesbeiana) and woodfrogs (R. sylvatica). In bullfrogs, early limb-bud-stage tadpoles had AVT-immunoreactive neurons and nerve fibers in the lateral septal nucleus, amygdala, preoptic hypothalamus, suprachiasmatic nucleus, and posterodorsal tegmentum. Woodfrog larvae showed similar patterns of hypothalamic AVT immunoreactivity, although neuronal staining in the amygdala did not appear until metamorphic climax, and never appeared in septal neurons or in the posterodorsal tegmentum. Whereas the highly terrestrial R. sylvatica adults must adapt to an adult habitat with prolonged periods of dehydration, R. catesbeiana adults remain semiaquatic and, as such, need not develop extreme mechanisms for water retention. Nonetheless, vasotocinergic pathways showed developmental similarities in the two species. The early appearance of AVT innervation in both Rana suggests that AVT has neuroregulatory functions well before metamorphosis.

Distribution of two molecular forms of gonadotropin-releasing hormone (GnRH) in the central nervous system of the frog Rana ridibunda

Two molecular forms of gonadotropin-releasing hormone (GnRH) have been recently characterized in the brain of the frog Rana ridibunda i.e. mammalian GnRH (mGnRH) and chicken GnRH-II (cGnRH-II). Using highly specific antisera against each form of GnRH, we have investigated the distribution of these two neuropeptides in the frog brain by the indirect immunofluorescence and the peroxidase-antiperoxidase techniques. mGnRH-immunoreactive cell bodies were restricted to a well defined region corresponding to the septal-anterior preoptic area. mGnRH-containing fibers projected through the ventral diencephalon and ended in the median eminence. In contrast, cGnRH-II-immunoreactive structures were widely distributed in the frog brain. In the telencephalon cGnRH-II-positive elements formed a ventromedial column extending from the olfactory bulb to the septal area, a pathway which corresponds to the terminal nerve. A dense accumulation of cGnRH-II-immunoreactive cell bodies was also found in the septal-anterior preoptic area; these neurons sent processes towards the median eminence via the hypothalamus. Double immunostaining revealed that, in this area, mGnRH- and cGnRH-II-like immunoreactivity co-existed in the same neurons. In the mid-diencephalon, numerous cGnRH-II-immunoreactive perikarya were found, surrounding the third ventricle, in the posterior preoptic and infundibular areas. Many of these neurons sent processes towards the ventricular cavity. More caudally, a dense population of cGnRH-II-immunoreactive perikarya was also observed in the nucleus of the paraventricular organ and the posterior tubercle. Dorsally, the thalamus, the tegmentum, the tectum and the granular layer of the cerebellum were richly innervated by cGnRH-II-positive fibers. In the medulla oblongata, numerous cGnRH-II-immunoreactive perikarya were seen in several cranial nerve nuclei. Ventrally, a dense plexus of immunoreactive fibers projected rostrocaudally into the spinal cord. The occurrence of mGnRH- and cGnRH-II-like immunoreactivity in the septal-anterior preoptic area and the hypothalamo-pituitary pathway supports the view that both peptides act as hypophysiotropic neurohormones. The widespread distribution of cGnRH-II-immunoreactive elements in the central nervous system of the frog strongly suggests that this peptide may also exert neuromodulator and/or neurotransmitter activities.

Immunohistochemical double-labeling study of gonadotropin-releasing hormone (GnRH)-immunoreactive cells and oxytocin-immunoreactive cells in the preoptic area of the dwarf gourami, Colisa lalia

The distribution of gonadotropin-releasing hormone (GnRH)-immunoreactive (ir) cells in the preoptic area (POA) of the dwarf gourami, Colisa lalia, was immunohistochemically studied. These neurons form cell columns on both sides of the common ventricle, and their axons project to the pituitary gland by forming distinct bundles. Also examined was the distribution of isotocin (IST) cells in the POA by using an anti-oxytocin (OXT) serum which has been proven to crossreact with IST. These two kinds of immunoreactive cells were distributed quite similarly in the POA. However, by using an immunofluorescence double-labeling method on thinner sections we found that a population of small IST cells in the ventral POA were also immunoreactive to GnRH, but that large IST cells in the dorsal POA were not immunoreactive to GnRH, and small GnRH-ir cells in the most ventral POA were not immunoreactive to the OXT antiserum. In the pituitary gland, GnRH-ir fibers were found in both the neurohypophysis and proximal pars distalis, but IST fibers were found only in the neurohypophysis.

Involvement of retinohypothalamic input, suprachiasmatic nucleus, magnocellular nucleus and locus coeruleus in control of melanotrope cells of Xenopus laevis: a retrograde and anterograde tracing study

The amphibian Xenopus laevis is able to adapt the colour of its skin to the light intensity of the background, by releasing alpha-melanophore-stimulating hormone from the pars intermedia of the hypophysis. In this control various inhibitory (dopamine, gamma-aminobutyric acid, neuropeptide Y, noradrenaline) and stimulatory (thyrotropin-releasing hormone and corticotropin-releasing hormone) neural factors are involved. Dopamine, gamma-aminobutyric acid and neuropeptide Y are present in suprachiasmatic neurons and co-exist in synaptic contacts on the melanotrope cells in the pars intermedia, whereas noradrenaline occurs in the locus coeruleus and noradrenaline-containing fibres innervate the pars intermedia. Thyrotropin-releasing hormone and corticotropin-releasing hormone occur in axon terminals in the pars nervosa. In the present study, the neuronal origins of these factors have been identified using axonal tract tracing. Application of the tracers 1,1'dioctadecyl-3,3,3',3' tetramethyl indocarbocyanine and horseradish peroxidase into the pars intermedia resulted in labelled neurons in two brain areas, which were immunocytochemically identified as the suprachiasmatic nucleus and the locus coeruleus, indicating that these areas are involved in neural inhibition of the melanotrope cells. Thyrotropin-releasing hormone and corticotropin-releasing hormone were demonstrated immunocytochemically in the magnocellular nucleus. This area appeared to be labelled upon tracer application into the pars nervosa. This finding is in line with the idea that corticotropin-releasing hormone and thyrotropin-releasing hormone stimulate melanotrope cell activity after diffusion from the neural lobe to the pars intermedia. After anterograde filling of the optic nerve with horseradish peroxidase, labelled axons were traced up to the suprachiasmatic area where they showed to be in contact with suprachiasmatic neurons. These neurons showed a positive reaction with anti-neuropeptide Y and the same held for staining with anti-tyrosine hydroxylase. It is suggested that a retino-suprachiasmatic pathway is involved in the control of the melanotrope cells during the process of background adaptation.

Immunocytochemical localization of atrial natriuretic factor (ANF)-like peptides in the brain and heart of the treefrog Hyla japonica: effect of weightlessness on the distribution of immunoreactive neurons and cardiocytes

The localization of atrial-natriuretic factor (ANF)-like immunoreactivity was investigated in the brain and heart of the treefrog Hyla japonica by the indirect immunofluorescence technique. Concurrently, the effect of weightlessness on the distribution of ANF-containing neurons and cardiocytes was studied in frogs that were sent into space for 9 days on the space station "MIR." In control animals, the amygdala contained the most prominent group of ANF-immunoreactive cells and fibers. ANF-positive neurons and nerve processes were also detected in other areas of the telencephalon such as the nucleus olfactorius, the pallium mediale, and the striatum. In "space frogs," the intensity of labeling of the amygdala and nucleus olfactorius was similar to that seen in control animals. In contrast, the pallium and the striatum of "space frogs" were totally devoid of positive cell bodies. In the diencephalon, of all animals, numerous ANF-immunoreactive perikarya and fibers were seen in the hypothalamus, the anterior thalamus, the infundibulum, and the median eminence. ANF-positive cell bodies were also noted in the lateral forebrain bundle of control frogs but were absent in "space frogs." The major difference between control and "space frogs" was observed in the posterior nuclei of the thalamus. In "space frogs," the nucleus posterocentralis thalami and the nucleus posterolateralis thalami exhibited large ANF-immunoreactive perikarya, while, in control frogs, these nuclei only contained scarce positive nerve fibers. In the mesencephalon, ANF-positive cell bodies and nerve processes were seen in the nucleus tegmenti mesencephali, the interpeduncular nucleus, and the nucleus cerebelli of all animals. However, stained perikarya were only observed in the nucleus reticularis isthmi of control frogs. In the heart, atrial cardiocytes exhibited intense ANF-like immunoreactivity. ANF-positive myocytes were also detected in the subpericardial region of the ventricle. The density and distribution of the staining were identical in the heart of control and "space frogs." These data support the concept that prolonged exposure to microgravity affects biosynthesis and/or release of ANF-related peptides in discrete regions of the amphibian brain.

Ultrastructural radioautographic analysis of neurogenesis in the hypothalamus of the adult frog, Rana temporaria, with special reference to physiological regeneration of the preoptic nucleus. II. Types of neuronal cells produced

Light- and electron-microscopic radioautography was used to identify the newly formed neuronal cells in the hypothalamic preoptic area of the frog. Adult Rana temporaria that had been caught in May/June received repeated 3H-thymidine injections and were sacrificed 30 days later. Heavily labeled cells were found in 1-micron plastic coronal sections of the preoptic area and then analysed in electron-microscopic radioautographs of neighbouring thin sections. The cells were identified as newly generated by the presence of 3H-thymidine label over the nucleus. All frogs showed considerable numbers of new peptidergic neurosecretory cells, small conventional neurons, and glia in the preoptic area. Some new ependymally located cells contacting the cerebrospinal fluid displaying ultrastructural characteristics of monoaminergic cells were also revealed. We conclude that prominent ventricular neurogenesis normally exists in the intact adult frog hypothalamus. The birth of small hypothalamic neurons seems to represent a case of sustained growth leading to a net increase in neuron numbers without loss. Conversely, the birth of large peptidergic neurosecretory cells, in which the increased secretory activity often leads to natural death of some cells, is considered as a neuronal replacement phenomenon, referred to as physiological regeneration of the magnocellular preoptic nucleus. The possible significance of this phenomenon in adult Anamnia is discussed.

Sexual dimorphism in the vasotocin system of the bullfrog (Rana catesbeiana)

Arginine vasotocin (AVT) is widespread in amphibian brains, where its levels have been correlated with reproductive behaviors. To better understand which neural systems are involved in central actions of AVT, we used immunocytochemistry to compare the distribution of AVT in the brains of male and female bullfrogs (Rana catesbeiana). AVT-immunoreactive cells were observed in the septal nucleus, amygdala pars lateralis, magnocellular preoptic area, suprachiasmatic nucleus, and hypothalamus. AVT-immunoreactive cells were also found in the pretrigeminal nucleus, but only in animals killed in the fall. Immunoreactive fibers were broadly distributed in hypothalamic and extrahypothalamic areas. The most obvious sex differences were found in the amygdala pars lateralis, where the density of immunoreactive cells and fibers was significantly greater in male than in female bullfrogs. In addition, in the habenular nucleus, males had a denser distribution of AVT-immunoreactive fibers than females. In the suprachiasmatic nucleus, AVT-immunoreactive cells were larger in females than in males but did not differ in number. Since the areas that showed sex differences in AVT distribution have also been implicated in control of reproductive behaviors, they may form the neural substrates for the effects of AVT on sexually dimorphic behaviors in amphibians.

Distribution of vasotocin- and mesotocin-like immunoreactivities in the brain of the South African clawed frog Xenopus-laevis

In order to obtain more insight into primitive and derived conditions of neuropeptidergic systems in vertebrates, in particular amphibians, we have studied immunohistochemically the distribution of vasotocin (AVT) and mesotocin (MST) neuronal elements in the brain of the South African clawed frog Xenopus laevis. Apart from a well-developed hypothalamohypophysial system, the antibodies revealed the existence of extrahypothalamic AVT- and MST-immunoreactive cell groups as well as extensive extrahypothalamic networks of immunoreactive fibres, thus confirming the phylogenetic constancy of this condition in vertebrates. The wide distribution of AVT- and MST-immunoreactive fibres throughout the brains of amphibians suggests that the two neuropeptidergic systems are involved not only in hypothalamohypophysial interactions, but also, as in mammals, in a variety of other brain functions. In particular, the relationship of AVT- and MST-immunoreactive fibres with catecholaminergic cell bodies was noted. The present study has underscored once again that considerable differences in relative densities of AVT- and MST-immunoreactive fibres occur between species, even within a single order of vertebrates.

Evolutionary precedents for behavioral actions of oxytocin and vasopressin

It is clear that the behavioral actions of oxytocin and vasopressin in mammals are not newly acquired, but have evolutionary antecedents. Injection studies with fish, amphibians, reptiles, and birds indicate that AVT can activate certain reproductive behaviors. The strongest evidence that AVT acts centrally to control reproductive behaviors comes from research on T. granulosa. In this amphibian, injections of AVT agonists activate courtship behaviors (amplectic clasping) in males and egg-laying behaviors in females, whereas injections of AVT antagonists inhibit the behaviors. Also, in Taricha males, AVT concentrations in specific brain areas are associated with the expression of courtship behaviors. Several conclusions about steroid-peptide interactions can be drawn, based on research with this amphibian. First, gonadal steroid hormones act to maintain the behavioral actions of AVT in both males and females. In Taricha, gonadectomy abolishes and steroid implants restore AVT-induced courtship in males and egg-laying in females. Second, gonadal steroids maintain the behavioral actions of AVT, in part, by modulating AVT receptor numbers on target neurons. In Taricha males and females, gonadectomy reduces AVT receptor concentrations (but not binding affinity) in certain brain areas (amygdala pars lateralis) and not others. Third, the type of gonadal steroid determines whether AVT elicits male-like or female-like reproductive behaviors. Ovariectomized Taricha females respond to AVT injections with egg-laying behaviors when implanted with estradiol and with male-like amplectic clasping when implanted with dihydrotestosterone. Fourth, the masculinization of AVT-induced behaviors in females most likely reflects site-specific actions of androgens on AVT-synthesizing neurons. In Taricha, AVTir concentrations in the optic tectum are sexually dimorphic (higher in males than females) and reach peak levels in males during the breeding season. Fifth, AVT content in specific brain areas increase as a function of performing the behaviors. In Taricha, AVTir concentrations in DPOA, CSF, and ventral infundibulum are higher in males that exhibit courtship behaviors than in males that do not. These conclusions illustrate how steroid-peptide interactions in the control of behaviors entail multiple neuroanatomical sites and neurochemical actions.

Comparative analysis of the vasotocinergic and mesotocinergic cells and fibers in the brain of two amphibians, the anuran Rana ridibunda and the urodele Pleurodeles waltlii

To obtain more insight into the vasotocinergic and mesotocinergic systems of amphibians and the evolution of these neuropeptidergic systems in vertebrates in general, the distribution of vasotocin (AVT) and mesotocin (MST) was studied immunohistochemically in the brains of the anuran Rana ridibunda and the urodele Pleurodeles waltlii. In Rana, AVT-immunoreactive cell bodies are located in the nucleus accumbens, the dorsal striatum, the lateral and medial part of the amygdala, an area adjacent to the anterior commissure, the magnocellular preoptic nucleus, the hypothalamus, the mesencephalic tegmentum, and in an area adjacent to the solitary tract. In Pleurodeles, AVT-immunoreactive somata are confined to the medial amygdala, the preoptic area, and an area lateral to the presumed locus coeruleus. In both species, the distribution of MST-immunoreactive cell bodies is more restricted: in the frog, MST-immunoreactive somata are present in the medial amygdala and the preoptic area, whereas, in the urodele, cell bodies are found only in the preoptic area. Both in Rana and Pleurodeles, AVT- and MST-immunoreactive fibers are distributed throughout the brain and spinal cord. A major difference is that in Rana the number of MST-immunoreactive fibers is evidently higher than that of AVT-immunoreactive fibers, whereas the opposite is found in Pleurodeles. This holds, in particular, for the forebrain and the brainstem. The presence of several extrahypothalamic AVT-immunoreactive cell groups and the existence of well-developed extrahypothalamic networks of AVT- and MST-immunoreactive fibers are features that amphibians share with amniotes. However, this study has revealed that major differences exist not only between species of different classes of vertebrates, but also within a single class. In order to determine whether features of these neuropeptidergic systems are primitive or derived, a broad selection of species of each class of vertebrates is needed.

Distribution of galanin-like immunoreactivity in the brain of Rana esculenta and Xenopus laevis

The immunocytochemical distribution of galanin-containing perikarya and nerve terminals in the brain of Rana esculenta and Xenopus laevis was determined with antisera directed toward either porcine or rat galanin. The pattern of galanin-like immunoreactivity appeared to be identical with antisera directed toward either target antigen. The distribution of galanin-like immunoreactivity was similar in Rana esculenta and Xenopus laevis except for the absence of a distinct laminar distribution of immunoreactivity in the optic tectum of Xenopus laevis. Galanin-containing perikarya were located in all major subdivisions of the brain except the metencephalon. In the telencephalon, immunoreactive perikarya were detected in the pars medialis of the amygdala and the preoptic area. In the diencephalon, immunoreactive perikarya were detected in the caudal half of the suprachiasmatic nucleus, the nucleus of the periventricular organ, the ventral hypothalamus, and the median eminence. In the mesencephalon, immunoreactive perikarya were detected near the midline of the rostroventral tegmentum, in the torus semicircularis and, occasionally, in lamina A and layer 6 of the optic tectum. In the myelencephalon, labelled perikarya were detected only in the caudal half of the nucleus of the solitary tract. Immunoreactive nerve fibers of varying density were observed in all subdivisions of the brain with the densest accumulations of fibers occurring in the pars lateralis of the amygdala and the preoptic area. Dense accumulations of nerve fibers were also found in the lateral septum, the medial forebrain bundle, the periventricular region of the diencephalon, the ventral hypothalamus, the median eminence, the mesencephalic central gray, the laminar nucleus of the torus semicircularis, several laminae of the optic tectum, the interpeduncular nucleus, the isthmic nucleus, the central gray of the rhombencephalon, and the dorsolateral caudal medulla. The extensive system of galanin-containing perikarya and nerve fibers in the brain of representatives of two families of anurans showed many similarities to the distribution of galanin-containing perikarya and nerve fibers previously described for the mammalian brain.

[The intermediate lobe of the pituitary, model of neuroendocrine communication]

The intermediate lobe of the pituitary is composed of a homogeneous population of endocrine cells, the melanotrophs, which secrete several bioactive peptides including alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin. In contrast to most endocrine glands which are richly vascularized, the intermediate lobe of the pituitary contains very few blood vessels; in some species, the pars intermedia is virtually totally avascular. In contrast, pituitary melanotrophs are richly supplied by nerve fibers originating from the hypothalamus. The pars intermedia thus appears as a pure model of neuroendocrine communication, i.e. it is an archetype of the mode of transducing interface between the central nervous system and endocrine effectors. In mammalian species, different types of nerve terminals containing dopamine, norepinephrine, gamma-aminobutyric acid (GABA) and serotonin have been identified. In lower vertebrates, particularly in fish and amphibians, the pars intermedia is also innervated by peptidergic fibers which are though to take part in regulation of the secretory activity of the melanotroph. In these animals, the pars intermedia is regarded as a major center of neuroendocrine integration and an exceptional model to investigate the process of communication between the brain and the endocrine glands. The purpose of the present review is to summarize our current knowledge on the synthesis, processing and release of peptide hormones from pars intermedia cells and to survey the multiple regulatory mechanisms which are involved in the control of the activity of pituitary melanotrophs. Proopiomelanocortin, a multifunctional precursor. Pituitary melanotrophs synthetise a major precursor protein called proopiomelanocortin (POMC) which generates through proteolytic cleavage several biologically active peptides including adrenocorticotropic hormone (ACTH), endorphins and MSHs. In lower vertebrates, alpha-MSH is generally considered as the major hormone secreted by melanotrophs, in that it is involved in the process of skin colour adaptation. The post-translational processing of POMC, which yields to the mature hormones released by melanotrophs, includes a number of steps: glycosylation, phosphorylation, tissue-specific proteolytic cleavage, amidation and acetylation. Some of these posttranslational modifications can be regulated by neuroendocrine factors. For instance, in frogs, it has been shown that dopamine inhibits acetylation of alpha-MSH and thus reduces the secretion of the biologically active form of the peptide. The intermediate lobe of the pituitary: a model of neuroendocrine integration. In most vertebrate species, the intermediate lobe of the pituitary is innervated by catecholamine-containing fibers. In particular, the presence of dopaminergic nerve fibers has been observed in the pars intermedia of mammals and poikilotherms.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of vasotocin on locomotor activity in bullfrogs varies with developmental stage and sex

Although neurohypophysial peptides are present in many regions of the developing and adult bullfrog (Rana catesbeiana) brain, the function of these peptides remains unclear. To investigate possible behavioral actions, we examined locomotor activity following peptide injection in bullfrogs at various developmental stages. An intraperitoneal (ip) injection of arginine vasotocin (AVT) in tadpoles (stages V, X, or XVII) produced an immediate and dose-dependent inhibition of locomotor activity. On the other hand, AVT stimulated activity when administered ip to juvenile or adult female bullfrogs, but did not influence activity in juvenile or adult males. The minimum effective dose of AVT, when injected directly into the brain of tadpoles, was 100-fold less than that observed when injected ip, suggesting a central nervous system site of action for this peptide. A vasopressin receptor antagonist (d(CH2)5[Tyr(Me)2]AVP administered ip or icv) significantly increased locomotor activity in tadpoles, compared to controls. Oxytocin, vasopressin, and AVP4-9 inhibited activity in tadpoles while mesotocin, des Gly(NH2)AVP, and pressinoic acid had no significant effect. Injection of PGF2 alpha also significantly decreased activity levels in tadpoles. However, pretreatment of tadpoles with indomethacin, a prostaglandin synthesis inhibitor, did not prevent the behavioral effects of AVT, suggesting that prostaglandin synthesis is not required for this response. In summary, AVT influenced locomotor activity in bullfrog tadpoles and female frogs. This effect shifted during development from an inhibitory action in tadpoles to a stimulatory effect in metamorphosed female frogs. The effect of AVT on juvenile and adult frog locomotion was sexually dimorphic, as this peptide altered female behavior but not male behavior.

Distribution and co-existence of Met-enkephalin-like and mesotocin-like immunoreactivity in the neural lobe of the pituitary of the frog

Content and distribution of Met-enkephalin (Met-ENK)-like immunoreactivity in the hypothalamo-hypophysial system of bovine, rat and frog were examined using specific radioimmunoassay and immunohistochemistry. Ultrastructural localization and co-existence of Met-ENK-, mesotocin (MT)- and vasotocin (VT)-like immunoreactivity in the neural lobe of the frog pituitary was examined by a method combining pre-embedding peroxidase-antiperoxidase immunostaining for Met-ENK with post-embedding immunocolloidal gold staining for MT or VT. The highest concentrations of immunoassayable Met-ENK were present in the neural lobe of the pituitary of the frog. In addition to nerve fibers showing only MT-like or Met-ENK-like immunoreactivity, nerve fibers containing neurosecretory granules showing both MT- and Met-ENK-like immunoreactivities were very rich. But VT-like and Met-ENK-like immunoreactivity was confirmed separately in different axon terminals.

Co-existence of TRH with mesotocin in the same axon terminals of the bullfrog pars nervosa as revealed by double labeling immunocytochemistry

The co-existence of thyrotropin-releasing hormone (TRH)- and mesotocin (MT)-like immunoreactivities in single axon terminals in the frog pars nervosa was observed using a method combining pre-embedding peroxidase-antiperoxidase for TRH with post-embedding immunocolloidal gold staining for MT. Both TRH- and MT-like immunoreactivities were localized in the same large dense elementary granules 130-220 nm in diameter (170 nm mean diameter). A few axons contained only TRH-like immunoreactive small granular vesicles 80-120 nm in diameter (92 nm mean diameter). Axon terminals containing both TRH- and MT-like immunoreactive granules were in direct contact with the perivascular basal lamina of blood capillaries.

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.

Immunohistochemical localization of gonadotropin-releasing-hormone-associated peptide in the brain of the frog

Gonadotropin-releasing-hormone (GnRH)-associated peptide (GnRH-AP) is a 56 amino acid neuropeptide derived from the GnRH prohormone. GnRH-AP corresponds to the C-terminal fragment flanking the GnRH peptide. Using an antiserum raised against human GnRH-AP [1-56], or against human GnRH, we have investigated the neuronal systems containing either peptide in the central nervous system of the frog Rana ridibunda by immunohistological techniques. A main group of GnRH-AP-containing perikarya was found in a dorsoventral orientation of the supra anterior preoptic area (SAPA) just in front of the preoptic recess. Fibers originating from these perikarya projected rostrally toward the medial septal nucleus and the diagonal band of Broca. A network of GnRH-AP-immunoreactive (ir) fibers runs caudally from the SAPA toward the ventral hypothalamus. A high density of GnRH-AP-ir terminals was found in the median eminence. A few positive fibers were detected in the neural lobe of the pituitary, particularly in the region bordering the pars intermedia. Labelling of consecutive sections by either GnRH-AP or GnRH antibodies showed that GnRH and GnRH-AP-like irs were contained in the same cells of the SAPA. The double-staining technique with electrophoretic elution confirmed the colocalization of GnRH and GnRH-AP within the same neurons. Such a coexistence indicates that frog GnRH originates from a high molecular weight precursor which is closely related to rat pro-GnRH. The relative preservation of the C-terminal sequence of the pro-GnRH during evolution suggests that GnRH-AP may possess intrinsic biological activity. The high density of GnRH-AP-containing neurons projecting through the external zone of the median eminence would support the concept that GnRH-AP is involved in the modulation of pituitary hormone secretion.

Immunocytochemical studies of vasotocin, mesotocin, and neurophysins in the Xenopus hypothalamo-neurohypophysial system

Mesotocinergic and vasotocinergic neurons, which constitute the principal neurons in the hypothalamo-neurohypophysial system in Xenopus, were studied by immunocytochemical techniques. Antibodies that could unequivocally distinguish mesotocin, vasotocin, and their respective neurophysins were used in these studies. A monoclonal antibody directed at rat oxytocin-associated neurophysin (PS-36) detected an antigen that was colocalized with vasotocin, whereas a monoclonal antibody to rat vasopressin-associated neurophysin (PS-45) crossreacted with an antigen in mesotocinergic cells. As vasotocin is regarded as an evolutionary precursor of vasopressin, and as mesotocin is usually associated with oxytocin, we were surprised to see this apparent eptitope switch in the associated neurophysins. One interpretation of this epitope switch is that the final exons encoding for the carboxy-terminals of the mammalian neurophysins, which contain the PS-45 and PS-36 antibody epitopes, are in reversed positions in Xenopus. Approximately 4,000 mesotocinergic and vasotocinergic neurons and their fibers were topographically mapped in the Xenopus hypothalamus. The two types of neurons were intermingled and scattered throughout a large contiguous region including but not limited to the preoptic recess. Small, medium size, and large cells contained these antigens. Immunoreactive fibers were seen in the preoptic area, the neurohypophysial tract, the median eminence, and the neural lobe of the pituitary. The neurophysin-specific monoclonal antibodies have several advantages as phenotypic markers in development; i.e., high titer, low background, and affinity for the prohormone forms as well as for the fully processed neurophysin polypeptides. Their antigens are related gene products whose expression is central to the identity of the two cell types and whose expression is differentially controlled in development. This characterization of their adult distribution provides a basis for future studies of the development of peptidergic phenotype in the central nervous system of Xenopus.

Ontogeny of the hypothalamo-neurohypophysial system in the toad, Bufo melanostictus: an immunohistochemical study

Employing unlabeled antibody enzyme technique, the development of the hypothalamo-neurohypophysial system of the common Indian toad, Bufo melanostictus, has been studied by using antiserum raised in rabbit against bovine neurophysin. Immunoreactivity to the antiserum is first observed at stage 22 (Gosner, 1960) in the presumptive preoptic nucleus and at stage 23 in the presumptive median eminence and pars nervosa. As development proceeds, progressive increase in the immunoreactivity in all the components of the hypothalamo-neurohypophysial system is observed. The detection of neurohypophysial hormones (stages 22-23) much before the appearance of limb buds (stages 25-26) may be due to the greater sensitivity of the immunohistochemical technique.

Organization of tyrosine-hydroxylase immunopositive neurons in the brain of the crested newt, Triturus cristatus carnifex

The localization of neurons, fibers, and terminals containing tyrosine hydroxylase (TH)-like immunoreactivity was studied in the brain of the crested newt by using an antiserum to rat phaeochromocytoma tyrosine hydroxylase. Immunoreactive cells and fibers were found in the spinal cord, the medulla oblongata (lateral periventricular areas), and the acousticolateral area. In the tegmentum mesencephali, two bilateral clusters of labelled cells were localized in the ventrolateral periventricular gray extending toward the caudal hypothalamus. In the hypothalamic tuberal lobes, the TH-like reactive neurons, frequently of CSF-contacting type, lined the dorsal wall of the lateral infundibular recesses. A thick network of TH-like reactive nerve fibers and terminals was observed in the perivascular zone of the median eminence and in the adenohypophysial pars intermedia. A number of labelled cell bodies were also found in the dorsal thalamus (pars intercalaris diencephali), the paraventricular organ, and the ventral wall of the preoptic recess. In the telencephalon, immunoreactive innervation was identified in the striatum, together with immunopositive cell bodies in the olfactory bulbs. The pattern of organization of TH-immunoreactive systems in the newt showed, except for some peculiarities (e.g., the labelled cell bodies in dorsal thalamus), close similarities to the arrangement typical of mammals.

Correlation between immunoreactive vasotocin in optic tectum and seasonal changes in reproductive behaviors of male rough-skinned newts

Previous studies have shown that intracranial administration of the amphibian neuropeptide arginine vasotocin (AVT) to male rough-skinned newts (Taricha granulosa) can stimulate masculine sexual behaviors. The present study was conducted to determine whether concentrations of endogenous AVT in specific brain areas are correlated with seasonal changes in sexual behavior. Immunoreactive (ir) AVT was measured in the dorsal preoptic area and in the optic tectum throughout the course of the reproductive cycle. In the optic tectum, irAVT levels were low throughout the summer, fall, and winter, but rose over fivefold in the spring when sexual behaviors are most prevalent in male newts. In contrast, irAVT levels in the dorsal preoptic area were high in the summer, but declined in the fall and fluctuated widely during the winter and spring. Thus, there are site-specific changes in irAVT concentrations in the brain of male newts during the seasonal reproductive cycle. The finding that irAVT concentrations in the optic tectum are seasonally correlated with newt sexual behaviors provides further evidence that AVT in this brain area may be important in the expression of sexual behavior.

An immunohistochemical study of seasonal changes in luteinizing hormone-releasing hormone and vasotocin in the forebrain and the neurohypophysis of the toad, Bufo japonicus

Seasonal changes in luteinizing hormone-releasing hormone (LH-RH) and arginine vasotocin (AVT) were examined immunohistochemically in the toad forebrains and neurohypophyses. Strongly immunoreactive (ir-) LH-RH perikarya, from which dense ir-LH-RH fibers project to the median eminence, were localized in the medial septal nucleus and the nucleus of the diagonal band of Broca in the animals captured in the spring and the autumn. While, in the animals collected in the summer, ir-LH-RH perikarya and fibers were sparse, and immunoreactivity in the median eminences was weak. Artificially induced hibernation decreased the density of ir-LH-RH in the median eminence, in contrast with strong immunoreactivity in the control animals kept at room temperature. The amounts of ir-LH-RH in the median eminences of hibernating toads which were captured shortly before the breeding period varied conspicuously among individuals. The median eminences in migrating toads showed relatively weak LH-RH immunoreactivity. After the breeding, the immunoreactivity returned to the strong level that was observed in the spring and the autumn. These seasonal changes in ir-LH-RH seem to correspond to seasonal reproductive activity in this species. However, significant seasonal variations were not found in ir-AVT.

Opiomelanocorticotropic-like hormones in Vipera aspis pituitary

By using immunohistochemical techniques (indirect immunofluorescence and PAP) adrenocorticotropic-like hormone (ACTH), alpha-melanocyte stimulating-like hormone (alpha-MSH), beta-lipotropic-like hormone (beta-LPH), and beta-endorphin-like (beta-EP) have been localized in the pituitary gland of newborn and adult Vipera aspis. The immunolocalization have been compared with the classical histochemical staining and the data show that the opiomelanocorticotropic-like cells resembles the B3 cells of the current literature. In the intermediate lobe both in adults and in newborns the same cells exhibit immunoreactivity for all the peptides considered, while in the rostral region of the pars distalis a difference has been observed between adults and newborns. In the adults, the cells immunostain for ACTH, beta-LPH, and beta-EP but not for alpha-MSH while in the newborns, the same cells show immunoreactivity for ACTH, beta-LPH, alpha-MSH but not for beta-EP. It has been hypothesized that in Vipera during maturation the pars distalis and the intermediate lobe can differently process the common precursor molecule.

Phylogenetic cross-reactivities of monoclonal antibodies produced against rat neurophysin

Previously described mouse monoclonal antibodies against rat neurophysins [Ben-Barak, Y., et al. (1985); Whitnall, M. H., et al. (1985)] were studied here for their cross-reactivities to neurophysins (NPs) from other vertebrate species. Posterior pituitary extracts from various mammals (rat, mouse, cow, human) and lower vertebrates (frog, ratfish) were studied. The monoclonal antibodies displayed several distinct patterns of cross-reactivity to the various species, indicating that the epitopes which they recognized were different. PS 67 bound strongly to rat pituitary extract in solid-phase radioimmunoassay (RIA) but showed no cross-reactivity with extracts from any of the other species tested, including the mouse. PS 36 cross-reacted with mouse and frog extracts but showed almost no cross-reactivity with cow and none to ratfish extracts. PS 41 cross-reacted with mouse, cow, and frog extracts. PS 45 was the most cross-reactive antibody and recognized an antigen in extracts from mouse, cow, frog, and ratfish pituitaries. Electrophoresis of proteins extracted from posterior pituitaries, followed by immunoblot staining with either PS 36 or PS 45, demonstrated that the NP-like molecules within each species are heterogeneous, i.e., more than two bands stained in each species. The frog NP stained by PS 45 was about twice the molecular weight of the mammalian NPs. The possible valve of the PS 45 antibody for future molecular cloning experiments on the arginine vasotocin precursor in lower vertebrates is discussed.

Immunohistochemical localization of corticotropin-releasing factor (CRF)-like immunoreactivity in the hypothalamus of the newt, Triturus cristatus

The distribution of corticotropin-releasing factor (CRF) immunoreactivity was investigated in the hypothalamus and preoptic area of the newt by single and double immunocytochemical procedures. CRF immunopositive cell bodies were seen in the preoptic area (from the anterior wall of the preoptic recess to the dorsal parts of the preoptic nucleus) and in the tuberal portions of the posterior hypothalamus. Abundant nerve fibres are seen in the outer zone of the median eminence, while the pars nervosa lacks CRF-immunoreactivity. CRF immunoreactive material is seemingly separated from neurophysins- and somatostatin immunoreactive cell bodies and fibres.

Oxytocin/vasopressin-like immunoreactivity is present in the nervous system of hydra

Nerve cells have been found in hydra, which react with antisera to oxytocin, vasopressin and mesotocin. These nerve cells have a high density in the ectoderm of basal disk and tentacles and lower density in the ectoderm of peduncle, gastric region and hypostome. A very small number of nerve cells occur also in the endoderm of foot, gastric region and hypostome. By using a technique for simultaneous visualisation of nerve cells reacting with antisera to oxytocin and vasopressin, it can be shown that these nerve cells belong to a single population. In agreement with this, the staining of the nerve cells can be abolished by absorbing each antiserum with either oxytocin, vasopressin, [Lys8]vasopressin, vasotocin, mesotocin or isotocin, indicating that the antigenic determinant of hydra cross-reacts with those antibody subpopulations, which recognize common portions (sequence 1-2, 5-7, 9) of the oxytocin/vasopressin-like peptides. With radioimmunoassays that are specific for either oxytocin or vasopressin, only very low amounts of immunoreactivity were measured. In addition, the dilution curves in these assays were not parallel to the standards, indicating that the antigenic determinant of hydra is not oxytocin or vasopressin. The presence of oxytocin/vasopressin-like material in coelenterates, shows that this family of peptides is of great antiquity.

Immunohistochemical analysis of magnocellular elements in rat hypothalamus: distribution and numbers of cells containing neurophysin, oxytocin, and vasopressin

A cell-by-cell analysis of the magnocellular elements in hypothalami of fifty Long-Evans (normal) and Brattleboro (diabetes insipidus) rats was done using the unlabeled antibody enzyme technique (PAP) with primary antisera directed against oxytocin (OXY), vasopressin (ADH), and the neurophysins. The magnocellular neurons of the hypothalamus were found in the supraoptic (SON), paraventricular (PVN), and anterior commissural (ACN) nuclei, a number of accessory nuclei, and as individual cells in the anterior hypothalamic area. SON was divided by the optic tract into the principal part and retrochiasmatic SON. In retrochiasmatic SON a majority of the cells contained vasopressin. Within the principal part of SON oxytocin-producing cells tended to be found rostrally and dorsally, while the vasopressin cells were more common caudally and ventrally. PVN was divided into three subnuclei, the medial, lateral, and posterior subnuclei, on the basis of cellular morphology and peptide content. The magnocellular cells of the medial and lateral PVN were closely packed together and nearly round, while those of posterior PVN were more separated and fusiform in shape with their long axis running in a medio-lateral direction. Medial PVN consisted primarily of oxytocin-producing cells, while lateral PVN was formed by a core of vasopressin-producing cells with a rim of oxytocin cells. Posterior PVN contained largely oxytocin-producing cells. Both ADH and OXY cells were found in the accessory nuclei. In the Long-Evans rat the SON had, on the average, 1443 OXY and 3236 ADH cells; the PVN had 1174 OXY and 976 ADH cells; and the accessory magnocellular groups in the hypothalamus (including the ACN) had 1286 OXY and 552 ADH cells. The Brattleboro strain animal had similar numbers of cells in these nuclei. (The cells which contain ADH in normal animals were identified in the Brattleboro rat as large, neurophysin-negative cells.) Thus, a large fraction of the magnocellular oxytocin- and vasopressin-producing cells in the rat were located outside of the PVN and SON. One accessory cell group in particular, ACN, had 616 OXY cells, or about 50% as many as PVN. In each nucleus the sum of the numbers of OXY and ADH cells was approximately the number of neurophysin cells.