Galanin-like immunoreactive nerve fibres in the anterior pituitary of the normal and adrenalectomized rat

Organization of the galaninergic neuronal system in the brain of the gecko Hemidactylus frenatus

Galanin (GAL) is a 29 amino acid peptide present in the central nervous system (CNS) as well as peripheral tissues in vertebrates. However, the brain distribution pattern of GAL is understudied in reptiles. The aim of this study was to determine the organization of galaninergic neuronal system in the brain of the gecko Hemidactylus frenatus, a tropical and sub-tropical lizard, using rabbit anti-galanin antibody. In the telencephalon, GAL-ir perikarya and fibres were found in the lateral septal nucleus, but only GAL-ir fibres were observed in the striatum, nucleus accumbens, anterior commissure, nucleus centralis amygdalae, dorsal and medial septal nuclei, nucleus of the diagonal band of Broca and in the optic chiasma. In the preoptic region, a cluster of GAL-ir cells and fibres was observed in the periventricular preoptic area and lateral preoptic area. GAL-ir perikarya and fibres were observed in hypothalamic areas such as the supraoptic nucleus, suprachiasmatic nucleus, paraventricular nucleus, periventricular nucleus of the hypothalamus, infundibular recess nucleus and in the median eminence, whereas GAL-ir fibres were present in the pars distalis of the pituitary gland. In the thalamus, GAL-ir fibres were observed in the dorsomedial, dorsolateral, and medial thalamic nuclei. GAL-ir fibres were also detected in mesencephalic areas such as the optic tectum, torus semicircularis, ventral tegmental area and substantia nigra, brain stem as well as the spinal cord. The organization of GAL-ir cells and fibres throughout the gecko brain suggests several neuroendocrine, neuromodulatory and behavioural functions for GAL in lizards. The study provides new insights into the evolutionarily conserved nature of GAL peptide in squamate reptiles and forms a valuable basis for future comparative studies.

Coordinated Targeting of Galanin Receptors on Cholangiocytes and Hepatic Stellate Cells Ameliorates Liver Fibrosis in Multidrug Resistance Protein 2 Knockout Mice

Galanin (Gal) is a peptide with a role in neuroendocrine regulation of the liver. In this study, we assessed the role of Gal and its receptors, Gal receptor 1 (GalR1) and Gal receptor 2 (GalR2), in cholangiocyte proliferation and liver fibrosis in multidrug resistance protein 2 knockout (Mdr2KO) mice as a model of chronic hepatic cholestasis. The distribution of Gal, GalR1, and GalR2 in specific liver cell types was assessed by laser-capture microdissection and confocal microscopy. Galanin immunoreactivity was detected in cholangiocytes, hepatic stellate cells (HSCs), and hepatocytes. Cholangiocytes expressed GalR1, whereas HSCs and hepatocytes expressed GalR2. Strategies were used to either stimulate or block GalR1 and GalR2 in FVB/N (wild-type) and Mdr2KO mice and measure biliary hyperplasia and hepatic fibrosis by quantitative PCR and immunostaining of specific markers. Galanin treatment increased cholangiocyte proliferation and fibrogenesis in both FVB/N and Mdr2KO mice. Suppression of GalR1, GalR2, or both receptors in Mdr2KO mice resulted in reduced bile duct mass and hepatic fibrosis. In vitro knockdown of GalR1 in cholangiocytes reduced α-smooth muscle actin expression in LX-2 cells treated with cholangiocyte-conditioned media. A GalR2 antagonist inhibited HSC activation when Gal was administered directly to LX-2 cells, but not via cholangiocyte-conditioned media. These data demonstrate that Gal contributes not only to cholangiocyte proliferation but also to liver fibrogenesis via the coordinate activation of GalR1 in cholangiocytes and GalR2 in HSCs.

Excitatory and inhibitory effects of prolactin release activated by nerve stimulation in rat anterior pituitary

BACKGROUND

A series of studies showed the presence of substantial amount of nerve fibers and their close relationship with the anterior pituitary gland cells. Our previous studies have suggested that aside from the classical theory of humoral regulation, the rat anterior pituitary has direct neural regulation on adrenocorticotropic hormone release. In rat anterior pituitary, typical synapses are found on every type of the hormone-secreting cells, many on lactotrophs. The present study was aimed at investigating the physiological significance of this synaptic relationship on prolactin release.

METHODS

The anterior pituitary of rat was sliced and stimulated with electrical field in a self-designed perfusion chamber. The perfusate was continuously collected in aliquots and measured by radioimmunoassay for prolactin levels. After statistic analysis, differences of prolactin concentrations within and between groups were outlined.

RESULTS

The results showed that stimulation at frequency of 2 Hz caused a quick enhancement of prolactin release, when stimulated at 10 Hz, prolactin release was found to be inhibited which came slower and lasted longer. The effect of nerve stimulation on prolactin release is diphasic and frequency dependent.

CONCLUSIONS

The present in vitro study offers the first physiological evidence that stimulation of nerve fibers can affect prolactin release in rat anterior pituitary. Low frequency stimulation enhances prolactin release and high frequency mainly inhibits it.

Effects of bilateral adrenalectomy on systemic kainate-induced activation of the nucleus of the solitary tract. Regulation of blood pressure and local neurotransmitters

Glutamatergic transmission through metabotropic and ionotropic receptors, including kainate receptors, plays an important role in the nucleus of the solitary tract (NTS) functions. Glutamate system may interact with several other neurotransmitter systems which might also be influenced by steroid hormones. In the present study we analyzed the ability of systemic kainate to stimulate rat NTS neurons, which was evaluated by c-Fos as a marker of neuronal activation, and also to change the levels of NTS neurotransmitters such as GABA, NPY, CGRP, GAL, NT and NO by means of quantitative immunohistichemistry combined with image analysis. The analysis was also performed in adrenalectomized and kainate stimulated rats in order to evaluate a possible role of adrenal hormones on NTS neurotransmission. Male Wistar rats (3 month-old) were used in the present study. A group of 15 rats was submitted either to bilateral adrenalectomy or sham operation. Forty-eight hours after the surgeries, adrenalectomized rats received a single intraperitoneal injection of kainate (12 mg/kg) and the sham-operated rats were injected either with saline or kainate and sacrificed 8 hours later. The same experimental design was applied in a group of rats in order to register the arterial blood pressure. Systemic kainate decreased the basal values of mean arterial blood pressure (35%) and heart rate (22%) of sham-operated rats, reduction that were maintained in adrenalectomized rats. Kainate triggered a marked elevation of c-Fos positive neurons in the NTS which was 54% counteracted by adrenalectomy. The kainate activated NTS showed changes in the immunoreactive levels of GABA (143% of elevation) and NPY (36% of decrease), which were not modified by previous ablation of adrenal glands. Modulation in the levels of CGRP, GAL and NT immunoreactivities were only observed after kainate in the adrenalectomized rats. Treatments did not alter NOS labeling. It is possible that modulatory function among neurotransmitter systems in the NTS might be influenced by steroid hormones and the implications for central regulation of blood pressure or other visceral regulatory mechanisms control should be further investigated.

Intercellular communication within the rat anterior pituitary: XIV electron microscopic and immunohistochemical study on the relationship between the agranular cells and GnRH neurons in the dorsal pars tuberalis of the pituitary gland

Although numerous investigators in 1970s to 1980s have reported the distribution of LH-RH nerve fibers in the median eminence, a few LH-RH fibers have been shown to be present in the pars tuberalis. The significance of the finding remains to be elucidated, and there are few studies on the distribution of LH-RH neurons in the pars tuberalis, especially in the dorsal pars tuberalis (DPT). Adult male Wistar-Imamichi rats were separated into two groups: one for electron microscopy and the other for immunohistochemistry to observe LH-RH and neurofilaments. Pituitary glands attached to the brain were fixed by perfusion, and the sections were prepared parallel to the sagittal plane. The typical glandular structure of the pars tuberalis was evident beneath the bottom floor of the third ventricle, and the thick glandular structure was present in the foremost region. Closer to the anterior lobe, the glandular structure changed to be a thin layer, and it was again observed at the posterior portion. Then the pituitary stalk was surrounded with the dorsal, lateral, and ventral pars tuberalis. LH-RH and neurofilaments fibers were noted in the bottom floor, and some of them vertically descended to the gland. Adjacent to the glandular folliculostellate cells in the pars tuberalis, Herring bodies with numerous dense granules invading into the gland were present between the pituitary stalk and DPT. It was postulated that the "message" carried by LH-RH might have been transmitted to the cells in the DPT to aid in the modulation of LH release.

Development of galanin-like immunoreactivity in the brain of the brown trout (Salmo trutta fario), with some observations on sexual dimorphism

The development of galanin-like immunoreactive (GAL-ir) cells and fibers was investigated in the brain of brown trout embryos, alevins, juveniles, and adults (some spontaneously releasing their gametes). The earliest GAL-ir neurons appeared in the preoptic region and the primordial hypothalamic lobe of 12-mm embryos. After hatching, new GAL-ir neurons appeared in the lateral, anterior, and posterior tuberal nuclei, and in late alevins, GAL-ir neurons appeared in the area postrema. In juveniles, further GAL-ir populations appeared in the nucleus subglomerulosus and magnocellular preoptic nucleus. The GAL-ir neuronal groups present in juveniles were also observed in sexually mature adults, although the area postrema of males lacked immunoreactive neurons. Moreover, spawning males exhibited GAL-ir somata in the olfactory bulb and habenula, which were never observed in adult females or in developing stages. In adults, numerous GAL-ir fibers were observed in the ventral telencephalon, preoptic area, hypothalamus, neurohypophysis, mesencephalic tegmentum, ventral rhombencephalon, and area postrema. Moderate to low GAL-ir innervation was seen in the olfactory bulbs, dorsomedial telencephalon, epithalamus, medial thalamus, optic tectum, cerebellum, and rhombencephalic alar plate. There were large differences among regions in the GAL-ir innervation establishment time. In embryos, GAL-ir fibers appeared in the preoptic area and hypothalamus, indicating early expression of galanin in hypophysiotrophic centers. The presence of galanin immunoreactivity in the olfactory, reproductive, visual, and sensory-motor centers of the brain suggest that galanin is involved in many other brain functions. Furthermore, the distribution of GAL-ir elements observed throughout trout development indicates that galaninergic system maturation continues until sexual maturity.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Suppression of adrenocorticotropic hormone release by stimulation of the nerve fibres in the anterior pituitary

With the recent revelation of considerable peptidergic innervation of the anterior pituitary in several mammalian species, including man, it becomes imperative to elucidate the physiological significance of such a morphological entity. We addressed this issue by employing an anterior pituitary slice in vitro superfusion system coupled with electrical field stimulation. Anterior pituitary slices of 0.8 mm were perfused with Krebs-Ringer bicarbonate-bovine serum albumin buffer in a superfusion chamber for 30 min before electrical field stimulation. A square current of 30 mA, 10 Hz and 0.5 ms was then applied for 10 min. The perfusate was collected every 10 min and measured for adrenocorticotropic hormone (ACTH) by radio-immunoassay. It was found that under the experimental condition the basal release of ACTH was suppressed by electrical field stimulation of the nerve fibres in the anterior pituitary. Furthermore, vasopressin was added as a secretagogue. The suppression of ACTH by electrical field stimulation became even more marked. This is the first physiological evidence of the effect of stimulation of the nerve fibres innervating the anterior pituitary on its secretory activity.

Evidence for direct neural regulation of the mammalian anterior pituitary

1. The mammalian anterior pituitary was not known to be directly regulated by nervous elements until recently. Although it is generally acknowledged that there are a small number of nerve fibres in the anterior pituitary, they are considered to be autonomic in nature and are not directly involved in the regulation of the activities of the gland cells. 2. A growing body of evidence has been accumulated in the past decade, mainly from our laboratory, indicating that the anterior pituitary can be directly regulated by nerve fibres innervating it. The present article reviews the evidence for the hypothesis that there is neural-humoral dual regulation of the mammalian anterior pituitary. 3. Human, macaque monkey, dog and rat anterior pituitaries have been used for immunocytochemical studies at light and electron microscopic levels. Studies of the changes in the nerve fibres in the anterior pituitary following adrenalectomy or ovariectomy have been conducted on rats. The effects of electrical stimulation of the nerve fibres in the anterior pituitary on adrenocorticotropic hormone (ACTH) secretion have also been studied. 4. There are substantial amounts of nerve fibres in the anterior pituitary. They are in close proximity to the gland cells, including forming synapses. The number of nerve terminals are large. Adrenalectomy or ovariectomy induces an active response of the nerve fibres and electrical stimulation of the nerve fibres changes ACTH secretion. 5. It has been concluded that the anterior pituitary can be directly regulated by the innervating nerve fibres.