Hypothalamic galanin-immunoreactive neurons projecting to the posterior lobe of the rat pituitary: a combined retrograde tracing and immunohistochemical study

Responsiveness of pituitary to galanin throughout the reproductive cycle of male European sea bass (Dicentrarchus labrax)

The neuropeptide galanin (Gal) is a putative factor regulating puberty onset and reproduction through its actions on the pituitary. The present study investigated the pituitary responsiveness to galanin and the patterns of galanin receptors (Galrs) expression throughout the reproductive cycle of two years old male European sea bass (Dicentrarchus labrax), an important aquaculture species. Quantitative analysis of pituitary and hypothalamus transcript expression of four galr subtypes revealed differential regulation according to the testicular developmental stage, with an overall decrease in expression from the immature stage to the mid-recrudescence stage. Incubation of pituitary cells with mammalian 1-29Gal peptide induced significant changes in cAMP concentration, with sensitivities that varied according to the testicular development stages. Furthermore 1-29Gal was able to stimulate both follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) release from pituitary cell suspensions. The magnitude of the effects and effective concentrations varied according to reproductive stage, with generalized induction of Fsh and Lh release in animals sampled in January (full spermiation). The differential expression of galrs in pituitary and hypothalamus across the reproductive season, together with the differential effects of Gal on gonadotropins release in vitro strongly suggests the involvement of the galaninergic system in the regulation the hypothalamus-pituitary-gonad axis of male sea bass. This is to our knowledge the first clear evidence for the involvement of galanin in the regulation of reproduction in non-mammalian vertebrates.

DiI tracing of the hypothalamic projection systems during perinatal development

The hypothalamus is the higher neuroendocrine center of the brain and therefore possesses numerous intrinsic axonal connections and is connected by afferent and efferent fiber systems with other brain structures. These projection systems have been described in detail in the adult but data on their early development is sparse. Here I review studies of the time schedule and features of the development of the major hypothalamic axonal systems. In general, anterograde tracing experiments have been used to analyze short distance projections from the arcuate and anteroventral periventricular nuclei (Pe), while hypothalamic projections to the posterior and intermediate pituitary lobes (IL) and median eminence, mammillary body tracts and reciprocal septohypothalamic connections have been described with retrograde tracing. The available data demonstrate that hypothalamic connections develop with a high degree of spatial and temporal specificity, innervating each target with a unique developmental schedule which in many cases can be correlated with the functional maturity of the projection system.

Galanin and galanin-like peptide modulate vasopressin and oxytocin release in vitro: the role of galanin receptors

Galanin (Gal) and galanin-like peptide (GALP) may be involved in the mechanisms of the hypothalamo-neurohypophysial system. The aim of the present in vitro study was to compare the influence of Gal and GALP on vasopressin (AVP) and oxytocin (OT) release from isolated rat neurohypophysis (NH) or hypothalamo-neurohypophysial explants (Hth-NH). The effect of Gal/GALP on AVP/OT secretion was also studied in the presence of galantide, the non-selective galanin receptors antagonist. Gal at concentrations of 10(-10 )M and 10(-8 )M distinctly inhibited basal and K(+)-stimulated AVP release from the NH and Hth-NH explants, whereas Gal exerted a similar action on OT release only during basal incubation. Gal added to the incubation medium in the presence of galantide did not exert any action on the secretion of either neurohormone from NH and Hth-NH explants. GALP (10(-10 )M and 10(-9 )M) induced intensified basal AVP release from the NH and Hth-NH complex as well as the release of potassium-evoked AVP from the Hth-NH. The same effect of GALP has been observed in the presence of galantide. GALP added to basal incubation medium was the reason for stimulated OT release from the NH as well as from the Hth-NH explants. However, under potassium-stimulated conditions, OT release from the NH and Hth-NH complexes has been observed to be distinctly impaired. Galantide did not block this inhibitory effect of GALP on OT secretion. It may be concluded that: (i) Gal as well as GALP modulate AVP and OT release at every level of the hypothalamo-neurohypophysial system; (ii) Gal acts in the rat central nervous system as the inhibitory neuromodulator for AVP and OT release via its galanin receptors; (iii) the stimulatory effect of GALP on AVP and OT release is likely to be mediated via an unidentified specific GALP receptor(s).

Novel galanin receptors in teleost fish: identification, expression and regulation by sex steroids

In fish, the onset of puberty, the transition from juvenile to sexually reproductive adult animals, is triggered by the activation of pituitary gonadotropin secretion and its timing is influenced by external and internal factors that include the growth/adiposity status of the animal. Kisspeptins have been implicated in the activation of puberty but peripheral signals coming from the immature gonad or associated to the metabolic/nutritional status are also thought to be involved. Therefore we hypothesize the importance of the galinergic system in the brain and testis of pre-pubertal male sea bass as a candidate to translate the signals leading to activation of testicular maturation. Here, the transcripts for four galanin receptors (GALR), named GALR1a, 1b, 2a and 2b, were isolated from European sea bass, Dicentrarchus labrax. Phylogenetic analysis confirmed the previously reported duplication of GALR1 in teleost fish, and unravelled the duplication of GALR2 in teleost fish and in some tetrapod species. Comparison with human showed that the key amino acids involved in ligand binding are present in the corresponding GALR1 and GALR2 orthologs. Transcripts for all four receptors are expressed in brain and testes of adult fish with GALR1a and GALR1b abundant in testes and hardly detected in ovaries. In order to investigate whether GALR1 dimorphic expression was dependent on steroid context we evaluated the effect of 11-ketotestosterone and 17β-estradiol treatments on the receptor expression in brain and testes of pre-pubertal males. Interestingly, steroid treatments had no effect on the expression of GALRs in the brain while in the testes, GALR1a and GALR1b were significantly up regulated by 11KT. Altogether, these results support a role for the galaninergic system, in particular the GALR1 paralog, in fish reproductive function.

Galanin influences on vasopressin and oxytocin release: in vitro studies

Galanin (Gal) acts in the central nervous system as the neuromodulator of the hypothalamo-neurohypophysial system function. Present investigations in vitro were undertaken to study the influence of Gal, added to the incubative media at the concentrations of 10(-10), 10(-9), 10(-8) or 10(-7) M, on AVP and OT release from isolated rat hypothalamus (Hth), neurohypophysis (NH) and hypothalamo-neurohypophysial system (Hth-NH). The present results showed that Gal at the concentrations of 10(-10), 10(-9) and 10(-8) M inhibited basal AVP secretion from the all incubated tissues as well as OT release from the NH and Hth-NH explant. On the contrary, 10(-10) M Gal was the reason of intensified basal hypothalamic OT secretion. The presence of Gal at the concentrations of 10(-10) and 10(-8) M in the incubative media enriched in potassium ions excess was the cause of diminished AVP release from the NH and from the Hth-NH explant, respectively. Any effect of Gal on AVP release from the Hth has been observed. All the concentrations of Gal did not exert any effect on OT release from the NH as well as Hth-NH explants. However, the K(+)-evoked OT release from the Hth was distinctly intensified under influence of 10(-10)M as well as 10(-8) M Gal. It may be concluded that: * Gal modifies AVP and OT release in vitro at every level of Hth-NH system. * Gal has been supposed to perform the role of central inhibitory neuromodulator for AVP release from the Hth-NH system. * Gal exerts inhibitory effect on OT release in vitro from NH as well intact Hth-NH system but stimulatory influence on OT secretion at the level of Hth.

Deciphering the mechanisms of homeostatic plasticity in the hypothalamo-neurohypophyseal system—genomic and gene transfer strategies

The hypothalamo-neurohypophyseal system (HNS) is the specialised brain neurosecretory apparatus responsible for the production of a peptide hormone, vasopressin, that maintains water balance by promoting water conservation at the level of the kidney. Dehydration evokes a massive increase in the regulated release of hormone from the HNS, and this is accompanied by a plethora of changes in morphology, electrical properties and biosynthetic and secretory activity, all of which are thought to facilitate hormone production and delivery, and hence the survival of the organism. We have adopted a functional genomic strategy to understand the activity dependent plasticity of the HNS in terms of the co-ordinated action of cellular and genetic networks. Firstly, using microarray gene-profiling technologies, we are elucidating which genes are expressed in the HNS, and how the pattern of expression changes following physiological challenge. The next step is to use transgenic rats to probe the functions of these genes in the context of the physiological integrity of the whole organism.

Distribution of galaninergic immunoreactivity in the brain of the mouse

The distribution of galaninergic immunoreactive (-ir) profiles was studied in the brain of colchicine-pretreated and non-pretreated mice. Galanin (GAL)-ir neurons and fibers were observed throughout all encephalic vesicles. Telencephalic GAL-ir neurons were found in the olfactory bulb, cerebral cortex, lateral and medial septum, diagonal band of Broca, nucleus basalis of Meynert, bed nucleus of stria terminalis, amygdala, and hippocampus. The thalamus displayed GAL-ir neurons within the anterodorsal, paraventricular, central lateral, paracentral, and central medial nuclei. GAL-ir neurons were found in several regions of the hypothalamus. In the midbrain, GAL-ir neurons appeared in the pretectal olivary nucleus, oculomotor nucleus, the medial and lateral lemniscus, periaqueductal gray, and the interpeduncular nucleus. The pons contained GAL-ir neurons within the dorsal subcoeruleus, locus coeruleus, and dorsal raphe. In the medulla oblongata, GAL-ir neurons appear in the anterodorsal and dorsal cochlear nuclei, salivatory nucleus, A5 noradrenergic cells, gigantocellular nucleus, inferior olive, solitary tract nucleus, dorsal vagal motor and hypoglossal nuclei. Only GAL-ir fibers were seen in the lateral habenula nucleus, substantia nigra, parabrachial complex, cerebellum, spinal trigeminal tract, as well as the motor root of the trigeminal and facial nerves. GAL-ir was also observed in several circumventricular organs. The widespread distribution of galanin in the mouse brain suggests that this neuropeptide plays a role in the regulation of cognitive and homeostatic functions.

Projections from the hypothalamus to the posterior lobe in rats during ontogenesis: 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate tracing study

The objective of this study was to determine the schedule of the arrival of the axons from the hypothalamus to the posterior lobe of the pituitary (PL) in rats during ontogenesis by using the fluorescent lipophilic carbocyanine dye 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (DiI) as a retrograde tracer. After preliminary fixation of the brain, DiI crystals were implanted in the PL on embryonic day 15 (E15), E16, E17, and E19 as well as on postnatal day 2 (P2) and P9. This was followed by a DiI retrograde diffusion along the plasma membrane and subsequent staining of hypothalamic neuronal cell bodies. The supraoptic nucleus (SO) contained an accumulation of fluorescent cells that extended toward the diamond-like swelling of the third ventricle as early as E15. These data suggest that the magnocellular neurons of the SO send their axons to the PL at the very beginning of differentiation, perhaps even before reaching their final position. The initial axons of the neurons of the paraventricular nucleus proper (PV) appeared to reach the PL significantly later, at E17. In addition to the SO and the PV, accessory magnocellular nuclei contributed to the innervation of the PL in perinatal rats. The neurons of the retrochiasmatic accessory nucleus first sent their axons to the PL on E16-E17. Axons that originated from other accessory hypothalamic nuclei reached the PL after birth, suggesting a delay in their involvement in the regulation of visceral functions compared with other magnocellular nuclei. Thus, the axons of magnocellular neurons reach the PL unexpectedly early in embryogenesis, raising the possibility of the functional significance of vasopressin and oxytocin as fetal neurohormones.

Subcellular localization of preprogalanin messenger RNA in perikarya and axons of hypothalamo-posthypophyseal magnocellular neurons: an in situ hybridization study

The subcellular compartmentalization and axonal transport of oxytocin and vasopressin messenger RNAs have recently been reported in the rat hypothalamo-posthypophyseal system using in situ hybridization. So far, no data are available concerning the intracellular distribution of co-localized peptide transcripts, for example of galanin, which is synthesized in the vasopressinergic magnocellular neurons of the rat and which is up-regulated in these neurons under different conditions, including salt loading and colchicine injection. In the present study, using non-radioactive in situ hybridization and immunohistochemistry at the light and electron microscope levels, preprogalanin messenger RNA and galanin-like immunoreactivity were localized in the hypothalamo-posthypophyseal system. After salt loading, preprogalanin transcripts were found throughout the perikaryal cytoplasm, especially in the peripheral cytoplasm and in the perinuclear area. Since immunohistochemistry also showed galanin-like immunoreactivity preferentially in the perinuclear area of control rats, galanin synthesis may occur mainly in this cytoplasmic domain. Preprogalanin messenger RNA was also clustered in dendrites containing rough endoplasmic reticulum. The use of a new in situ hybridization method involving tyramide signal amplification, based on catalysed reporter deposition, allowed visualization of preprogalanin messenger RNA in axonal projections running through the internal layer of the median eminence after salt loading, but not in control or in colchicine-injected animals. The negative results obtained after colchicine injection indicate that the mechanism of messenger RNA transport may require an intact cytoskeleton. The labelling was found in non-dilated axon segments as well as in a subset of axonal swellings in the rostral aspect of the median eminence, but was restricted to a few swellings in its caudal part, with no labelling in the posterior pituitary. Thus, preprogalanin messenger RNA was segregated in the axons. The functional significance of messenger RNAs' exportation into axons is not known, but our results suggest that this phenomenon may not be limited to the two principal magnocellular hormone messenger RNAs, but may also involve co-existing peptide messenger RNAs.

Growth hormone inhibits the hypophysectomy-induced expression of galanin in hypothalamic neurons of the toad (Bufo arenarum hensel)

The expression of the neuropeptide galanin was analyzed by immunohistochemistry in magnocellular and preoptic hypothalamic neurons of toads following hypophysectomy (HPX) and pars distalectomy (PDX). There was a marked increase in the galanin-like immunoreactive expression in magnocellular hypothalamic cells 3 days after HPX, followed by a decrease to normal levels after 7 days. No changes in the expression of galanin were detected after PDX in these neurons when compared to controls. Moreover, 7 days after HPX or PDX the number of cells expressing galanin was significantly increased in the preoptic area, where numerous intraependymal cells were intensely immunoreactive. The hypophysis grafts into the hind limb in HPX or PDX animals prevented increased galanin-like immunoreactivity in preoptic cells but not in magnocellular neurons. Similarly, PDX toads given growth hormone showed no GAL-LI in the intraependymal preoptic cells. These results suggest the presence of a region regulation of galanin expression in the preoptic area by hypophyseal hormones, in particular growth hormone.

The prepubertal ontogeny of galanin-like immunoreactivity in the male Meishan pig brain

Galanin (GAL) is a neuropeptide found in the mammalian brain and is involved in numerous functions including the control of feeding, growth and reproduction, and therefore may be an important peptide to study in agricultural species. We describe the immunohistochemical localization of GAL throughout prepubertal development in the Meishan pig, a Chinese breed known for its superior reproductive characteristics, but slow growth rate and abundant adipose tissue. Brains of animals from gestational day (g) 30, 50, 70, 90 and 110 and postnatal day (pn) 1, 10, 20 and 50 (duration of pregnancy averaged 114 days) were processed using a standard immunohistochemical technique utilizing a commercially available rabbit anti-porcine GAL antibody. Galanin-like immunoreactivity (GAL-IR) in cell bodies and fibers was evident in the brain at g30, primarily in the hypothalamus. Throughout prenatal development, cell bodies containing GAL-IR generally increased in number and distribution in the brain. During postnatal development, the number of cell bodies displaying GAL-IR decreased, particularly in hypothalamic areas. The distribution of GAL-IR in fibers became more widespread throughout gestational development, showing a pattern by pn1 that continued during later postnatal ages. The intensity of GAL-IR in fibers also increased throughout gestation. Some additional increases in immunoreactivity occurred postnatally, especially in the periventricular hypothalamus. The results of this study indicate that the distribution of GAL-IR in cell bodies and fibers in the Meishan pig brain was similar to that seen in other species, including the rat. These results support the hypothesis that GAL participates in the control of feeding, growth and reproduction in the pig.

Distribution of galanin-like immunoreactive elements in the brain of the adult lamprey Lampetra fluviatilis

Galanin is a brain-gut peptide present in the central nervous system of vertebrates and invertebrates. The distribution of galanin-like immunoreactive perikarya and fibers in the brain of the river lamprey Lampetra fluviatilis (Agnatha) has been studied immunocytochemically by using antisera against rat and porcine galanin. Galanin-like immunoreactive perikarya were seen in the telencephalon and mediobasal diencephalon. In the telencephalon, they were present in the nucleus olfactorius anterior, nucleus basalis, and especially, in the nucleus commissurae anterioris. The diencephalon contained most of the immunoreactive neurons. They were located in the nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus commissurae postinfundibularis, nucleus ventralis thalami, and nucleus dorsalis thalami pars medius. Most of the galanin-like immunoreactive infundibular neurons showed apical processes contacting the cerebrospinal fluid. Immunoreactive fibers and terminals were widely distributed throughout the neuraxis. In the telencephalon, the richest galaninergic innervation was found in the nucleus olfactorius anterior, lobus subhippocampalis, corpus striatum, and around the nucleus septi and the nucleus praeopticus. In the diencephalon, the highest density of galanin-like immunoreactive fibers was seen in the nucleus commissurae postopticae, nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus dorsalis hypothalami, and neurohypophysis. In the mesencephalon and rhombencephalon, the distribution of immunoreactive fibers was heterogeneous, being most pronounced in a region between the nucleus nervi oculomotorii and the nucleus interpeduncularis mesencephali, in the nucleus isthmi, and in the raphe region. A subependymal plexus of immunoreactive fibers was found throughout the ventricular system. The distribution of immunoreactive neurons and fibers was similar to that of teleosts but different to those of other vertebrate groups. The possible hypophysiotropic and neuroregulatory roles of galanin are discussed.

Localization of preprogalanin messenger RNA in rat brain: identification of transcripts in a subpopulation of cerebellar Purkinje cells

Galanin, a 29 amino acid peptide, is widely distributed throughout both the peripheral and central nervous systems and is thought to be involved in multiple physiological functions including smooth muscle relaxation, stimulation of feeding, blood pressure regulation, control of hormone secretion and modulation of nociception. Galanin has been shown to co-exist with several neurotransmitters throughout the neuroaxis and in some cases to modify their presynaptic and postsynaptic actions. In the present study, the anatomical distribution of preprogalanin messenger RNA in rat brain was examined by in situ hybridization histochemistry using specific 35S-labelled oligonucleotide probes. Neurons expressing preprogalanin messenger RNA were found throughout the brain and were particularly abundant in the hypothalamus. High densities of preprogalanin messenger RNA-positive neurons were found in the anteroventral preoptic, supraoptic, paraventricular and dorsomedial nuclei of the hypothalamus, in the locus coeruleus and in the nucleus of the solitary tract. Moderate densities of preprogalanin messenger RNA-positive cells were apparent in the periventricular and arcuate nuclei of the hypothalamus, in the dorsal raphe and dorsal cochlear nuclei. Low densities of preprogalanin messenger RNA-expressing neurons were observed in the piriform cortex, medial septum and the retrochiasmatic area. These findings are consistent with results of previous in situ localization studies of preprogalanin messenger RNA and also with studies reporting the distribution of galanin-like immunoreactivity in rat brain. A novel finding, however, was the detection of preprogalanin messenger RNA in Purkinje cells in the caudal cerebellar vermis (lobules 6 to 10) and the flocculus and paraflocculus of the lateral hemispheres of the cerebellum. Galanin is presumably co-localized in these cells with GABA, which is normally present in Purkinje cells and possibly with tyrosine hydroxylase, which has recently been detected in a similar subpopulation of cerebellar Purkinje cells in both rat and mouse. Thus, the present study reveals a previously unreported site of galanin gene expression in the cerebellum which represents a novel, putative site of action for galanin to add to its already varied physiological roles.

Immunohistochemical mapping of neuropeptides in the premamillary region of the hypothalamus in rats

The topographical distribution of neuropeptide-containing cell bodies, fibers and terminals was studied in the premamillary region of the rat hypothalamus using light microscopic immunohistochemistry. Alternate coronal sections through the posterior third of the hypothalamus of normal and colchicine-treated male rats were immunostained for 19 different neuropeptides and their distributions were mapped throughout the following structures: the ventral and dorsal premamillary, the supramamillary, the tuberomamillary and the posterior hypothalamic nuclei, as well as the premamillary portion of the arcuate nucleus and the postinfundibular median eminence. Seventeen of the investigated neuropeptides were present in neuronal perikarya, nerve fibers and terminals while the gonadotropin associated peptide and vasopressin occurred only in fibers and terminals. Growth hormone-releasing hormone-, somatostatin-, alpha-melanocyte stimulating hormone-, adrenocorticotropin-, beta-endorphin- and neuropeptide Y-immunoreactive neurons were seen exclusively in the premamillary portion of the arcuate nucleus. Thyrotropin-releasing hormone-, dynorphin A- and galanin-containing neurons were distributed mainly in the arcuate and the tuberomamillary nuclei. A high number of methionine- and leucine-enkephalin-immunoreactive cells were detected in the arcuate and dorsal premamillary nuclei, as well as in the area ventrolateral to the fornix. Substance P-immunoreactive perikarya were present in very high number within the entire region, in particular in the ventral and dorsal premamillary nuclei. Cell bodies labelled with cholecystokinin- and calcitonin gene-related peptide antisera were found predominantly in the supramamillary and the terete nuclei, respectively. Corticotropin-releasing hormone-, vasoactive intestinal polypeptide- and neurotensin-immunoreactive neurons were scattered randomly in low number, mostly in the arcuate and the ventral and dorsal premamillary nuclei. Peptidergic fibers were distributed unevenly throughout the whole region, with each peptide showing an individual distribution pattern. The highest density of immunoreactive fibers was presented in the ventral half of the region including the arcuate, the ventral premamillary and the tuberomamillary nuclei. The supramamillary nucleus showed moderately dense fiber networks, while the dorsal premamillary and the posterior hypothalamic nuclei were poor in peptidergic fibers.

Galanin in the hypothalamus of fed and fasted lean and obese Zucker rats

Galanin (GAL), a 29 aminoacid peptide, is widely distributed in the central nervous system and especially in the hypothalamus. It strongly stimulates food intake when it is injected in the paraventricular nucleus (PVN) of normal rats. The obese Zucker rat with a well-established hyperphagia is characterized by a general dysregulation of some important neuropeptides involved in the regulation of feeding behavior e.g. neurotensin, NPY or CCK and the aim of this study was to measure GAL in different microdissected brain areas in lean (Fa/Fa) and obese (fa/fa) male Zucker rats. As feeding status may modulate the central peptide concentrations, it was measured in ad libitum fed rats and in 48-h fasted rats of both genotypes. GAL was measured by a specific radioimmunoassay in the arcuate nuclei (ARC) and parvocellular (PVNp) and magnocellular (PVNm) parts of the PVN as well as in the median eminence (ME), median preoptic area (MPOA), supraoptic (SON) and dorsomedian (DMN) nuclei. Two-way analysis of variance revealed a very significant effect of genotype in the PVNp (P < 0.001), SON (P < 0.001) and in the ME (P < 0.02). No significant variations at all were noted in the ARC, PVNm, MPOA and DMN. GAL concentrations were more than doubled in the PVNp and SON of ad lib obese rats when compared to the ad lib lean rats (P < 0.005). On the other hand, in the ME where GAL concentration was about 4-fold greater than in the other areas, there was a 20 to 30% decrease in GAL concentrations in the obese rat (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Localisation of mRNA encoding the protein precursor of galanin in the monkey hypothalamus and basal forebrain

The hypothalamic and basal forebrain sites of synthesis of preprogalanin mRNA were identified in three adult monkeys (Macaca fascicularis) by in situ hybridisation performed with a radiolabelled cRNA probe transcribed from human preprogalanin cDNA. With stringent hybridisation conditions, the cRNA probe was hybridised to free-floating sections containing structures contiguous with the rostral hypothalamus through to the caudal limit of the hypothalamus as defined by the mammillary bodies. Specific hybridisation of the preprogalanin cRNA probe occurred throughout the hypothalamus but was particularly intense in the arcuate, paraventricular (parvicellular and magnocellular portions), and dorsomedial nuclei. Moderate hybridisation was found in the periventricular nucleus and scattered hybridisation in the medial preoptic nucleus. The medial preoptic area and the anterior and lateral hypothalamic areas showed moderate to intense hybridisation in scattered cells. A few cells in the tuberal portion and dorsal cap of the anterior portion of the supraoptic nucleus were labelled. Isolated cells were also labelled in the zona incerta. There was little labelling in the dorsal hypothalamic area but moderate labelling in the posterior hypothalamic area. Structures contiguous with the rostral hypothalamus including the diagonal band of Broca, bed nucleus of stria terminalis, substantia innominata, and basal nucleus of Meynert showed intense hybridisation. These data indicate a widespread distribution of preprogalanin mRNA in the monkey hypothalamus. A comparison with the previously reported distribution of preprogalanin mRNA in the rat, as well as with the distribution of galanin-like immunoreactivity in the rat and human, suggests some important species differences. Of particular interest were differences in the supraoptic, suprachiasmatic, and dorsomedial nuclei. The intense hybridisation throughout the paraventricular nucleus and in the rostral arcuate nucleus suggests that galanin may play a role in the regulation of both posterior and anterior pituitary function.

Immunocytochemical localization of a galanin-like peptidergic system in the brain of two urodele and two anuran species (Amphibia)

Galanin-like immunoreactivity was localized in the brain of Urodela (Ambystoma, Pleurodeles) and Anura (Bufo, Xenopus) by immunocytochemistry with anti-porcine galanin antiserum. In the four species, immunoreactive perikarya were observed in the telencephalon (striatum, amygdala), diencephalon preoptic area mainly along the anterodorsal wall of the preoptic recessus, suprachiasmatic nucleus, lateral hypothalamus, ventral and dorsal infundibular nuclei, paraventricular organ, and rhombencephalon (nucleus of the solitary tract). Galaninergic fibres extended in similar regions and in the medial septum, ventral telencephalon, ventral hypothalamus, median eminence, and various mesencephalic and rhombencephalic regions. Contacts with the cerebrospinal fluid cavity occurred along the preoptic recessus (Ambystoma) and the ventral infundibular wall (all species). Fibres were scarce in the neurohypophysis. The distal and intermediate lobes of the pituitary were virtually devoid of immunoreactivity. The galaninergic system appeared more developed in adult amphibia than in young animals, suggesting the stimulating influence of sex steroids on the expression of galanin as previously described in Anguilla. The extensive distribution of the galanin-like immunoreactive neurons in amphibian brains suggests that this peptide may act as a neuromodulatur and/or neurotransmitter.

Anatomical organization of the hypophysiotrophic systems in the electric fish, Apteronotus leptorhynchus

The organization of afferents to the pituitary was investigated by applying DiI crystals to the pituitary or pituitary stalk of the gymnotiform electric fish, Apteronotus leptorhynchus. Most hypophysiotrophic cells were found in the hypothalamus and were distributed throughout its rostrocaudal extent: nucleus preopticus periventricularis, pars anterior and posterior; suprachiasmatic nucleus; anterior, dorsal, ventral, lateral, and caudal hypothalamic nuclei; and nucleus tuberis lateralis, pars anterior and posterior. In addition a small number of retrogradely labeled cells were found in the ventral telencephalon (area ventralis, pars ventralis) and, most surprisingly, in a thalamic nucleus (nucleus centralis posterioris). The nucleus preopticus periventricularis pars posterior and the anterior hypothalamic nucleus appear to correspond to the parvicellular and magnocellular divisions of the nucleus preopticus of other teleosts. Integration of these results with immunohistochemical localization of monoamines and neuropeptides in the apteronotid brain suggests many homologies between the hypophysiotrophic nuclei of teleosts and other vertebrates, including mammals. Apteronotus communicates electrically during agonistic and sexual interactions. There are numerous anatomical links between the hypophysiotrophic systems and the brain areas related to electrocommunication.

Organization of galanin-like immunoreactive neuronal systems in weakly electric fish (Apteronotus leptorhynchus)

Immunohistochemical procedures were used to investigate the distribution of galanin-like immunoreactive neuronal somata, fiber pathways and apparent termination fields in the gymnotiform brain. Immunoreactive somata were observed only in the hypothalamus and were confined to preoptic, lateral and caudal hypothalamic regions. Within these areas, positive cells tended to be most concentrated in juxtaventricular nuclei. Dense immunoreactive fiber systems originating from hypothalamic regions were seen to project in separate or coalescing fiber bundles to the basal telencephalan, thalamus/tuberal diencephalon, midbrain and brainstem. The density of positive axons and boutons was quite variable, but regions which displayed the most massive network of axons included structures within the hypothalamus itself (anterior periventricular preoptic nucleus, caudal and lateral hypothalamus), ventral telencephalon (superior and ventral subdivisions), thalamic/tuberal areas (central posterior nucleus and tuberal neuropil within the ventral territory of the prepacemaker nucleus) and brainstem nuclei (dorsal reticular nucleus and the medial paralemniscal nucleus). Within these areas axons appeared more randomly distributed and varicose than along fiber tracs, and in counterstained sections were occasionally seen in apposition to unstained neuronal cell bodies and dendrites. In addition, a system of fibers was seen in the neurointermediate lobe of the pituitary. It is concluded that galanin-like immunoreactive neurons in the gymnotiform brain have a more restricted distribution than those in mammals, and that the major fiber systems emanating from the hypothalamus resemble the diverse projections of the tuberomammillary nucleus of higher vertebrates. The anatomy of galanin-like immunoreactive systems in the apteronotid brain suggests a role in neuroendocrine regulation and an involvement with anatomical areas controlling aggressive and courtship behaviour.

Investigations of origins of serotonergic projection to developing rat visual cortex: a combined retrograde tracing and immunohistochemical study

The present study investigated whether the raphe neurons which give rise to the transient serotonergic fibers in the visual cortex of neonatal rats persist or disappear as the rats mature. Three experiments were performed employing the WGA-apoHRP-Au retrograde transport technique in conjunction with 5-HT or WGA-HRP immunohistochemical staining. WGA-apoHRP-Au was injected into the primary visual cortex of all rats 9 days postnatally. In the first experiment, the animals were examined after 2 days; retrogradely labeled cells were observed in the dorsal raphe nucleus (DR), the median raphe nucleus (MR), and in the B9 and B6 cell groups; the majority (82.5%) of the cells was serotonergic. In the second experiment, the examinations took place following a survival time of 8 weeks: virtually all of the original raphe-visual cortical serotonergic neurons were found to the present. In the third experiment, also performed after 8 weeks relabeling the raphe-visual cortical neurons by WGA-HRP, it was found that 37.2% of the raphe neurons which had projected to the neonatal visual cortex no longer possessed such projections.

Ultrastructural localization of galanin immunoreactivity in the rat median eminence

The aim of this study was to examine, by use of a pre-embedding immunoperoxidase technique, the ultrastructural localization of galanin immunoreactivity in the external layer of the rat median eminence. Galanin immunoreactivity was only observed in axonal profiles. Immunoreactive fibers were found in contact with the following non-immunoreactive structures: (1) axonal profiles that contain dense granular vesicles and clear vesicles, (2) axonal profiles that contain predominantly clear vesicles, (3) glial cell bodies, and (4) processes of tanycytes. Labeled terminals were also observed in the proximity of the perivascular space of the portal vessels. The results suggest possible interactions between galanin-immunoreactive terminals and other terminals containing peptide and/or other transmitters in the external layer of the median eminence.

Immunocytochemical localization of a galanin-like peptidergic system in the brain and pituitary of some teleost fish

Immunostaining of brain and pituitary sections of teleost fishes (eels, salmonidae, cyprinidae, gourami, sculpin, mullet) with anti porcine galanin (GAL) revealed the presence of immunoreactive (ir) perikarya and a rich network of fibers. Ir-perikarya were located rostrodorsally to the recessus preopticus, and in the posterior tuberal hypothalamus. Ir-fibers were abundant in basal telencephalon and around diencephalic ventricular recesses but never contacted their lumen. Furthermore, they were observed in basal hypothalamus, brainstem and ventral medulla. Ir-fibers passed along corticotropic (ACTH), gonadotropic cells and somatotropes (GH cells) in eel and trout pars distalis, but rarely ended in caudal neurohypophysis. In goldfish pituitary ir-fibers occurred in neural digitations and among different cell types which however did not contain a GAL-like peptide. The relation GAL fibers/GH cells appeared more evident in species with a high growth rate. The other species showed a similar distribution of brain GAL. In eels and trout, ir-perikarya were not observed in areas containing somatostatin, GH- and ACTH-releasing factor, and ACTH-like perikarya, suggesting that GAL did not coexist with these peptides. The widespread distribution of a GAL-like peptide in teleost brain suggests that it could play a role of neurotransmitter and/or neuromodulator and regulate the secretion of adenohypophysial hormone(s).

Centrally administered galanin inhibits osmotically stimulated arginine vasopressin release in conscious rats

The effect of centrally administered galanin on arginine vasopressin (AVP) release was investigated in conscious rats. Intracerebroventricular injection of porcine galanin suppressed hypertonic saline-induced increase in plasma AVP in a dose-dependent manner (12.5-100 pmol/rat) at 10 min after the injection. Pretreatment with subcutaneous injection of naloxone (1 mg/100 g b.wt.) partially blocked the galanin-induced effect on plasma AVP. These results suggest that central galanin inhibits osmotically stimulated AVP release and endogenous opioids are, at least in part, involved in the mechanism.

Evidence for a colocalization of oxytocin mRNA and galanin in magnocellular hypothalamic neurons: a study combining in situ hybridization and immunohistochemistry

The possible colocalization of oxytocin (OT) and galanin (GAL) was studied by combining, on the same cryostat sections, in situ hybridization (ISH) for OT mRNA with a tritiated oligonucleotide probe and immunohistochemistry (ICC) of GAL. Many cells were either labelled by ISH (OT mRNA containing cells), or by ICC (GAL containing cells). Moreover, some magnocellular neurons in the supraoptic and paraventricular nuclei were labelled for both OT mRNA and GAL. These results demonstrate that some magnocellular neurons of the rat hypothalamus contain both GAL and OT. This approach is suitable for studying the intracellular distribution of OT gene expression and mature GAL under different physiological or experimental conditions.