Biomedical subjects

Finn-Arne Weltzien

Publications and source records attributed to Finn-Arne Weltzien.

9 recordsLinked to original sources

PubMed2006

Androgen-dependent stimulation of brain dopaminergic systems in the female European eel (Anguilla anguilla).

Dopamine (DA), a neurotransmitter present in all vertebrates, is involved in processes such as motor function, learning and behavior, sensory activities, and neuroendocrine control of pituitary hormone release. In the female eel, we analyzed how gonadal steroids regulate brain expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of DA. TH mRNA levels were assayed by quantitative real-time RT-PCR. TH-positive nuclei were also localized by in situ hybridization (ISH) and immunohistochemistry, and the location of TH nuclei that project to the pituitary was determined using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindicarbocyanine perchlorate retrograde tracing. Chronic in vivo treatment with testosterone increased TH mRNA specifically in the periglomerular area of the olfactory bulbs and in the nucleus preopticus anteroventralis (NPOav). NPOav was labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindicarbocyanine perchlorate, showing that this nucleus is hypophysiotropic in the eel. The nonaromatizable 5alpha-dihydrotestosterone gave identical results in both areas, whereas 17beta-estradiol had no stimulatory effect, showing that the observed stimulatory effects of testosterone were androgen dependent. In teleosts, DA neurons originating from the NPOav directly inhibit gonadotropic function, and our results indicate an androgen-dependent, positive feedback on this neuroendocrine control in the eel. In mammals, DA interneurons in the olfactory bulbs are involved in the enhancement of olfactory sensitivity and discrimination. Our results in the European eel suggest an androgen-dependent stimulation of olfactory processing, a sensory function believed to be important in eel navigation during its reproductive migration toward the oceanic spawning grounds. To our knowledge, this is the first evidence from any vertebrate of an androgen-dependent effect on DAergic activity in the olfactory bulbs, providing a new basis for understanding the regulation by gonadal steroids of central DAergic systems in vertebrates.

Anguilla↗

PubMed2005

A quantitative real-time RT-PCR assay for European eel tyrosine hydroxylase.

Dopamine (DA) plays a key inhibitory role in pubertal development of the European eel, but how DAergic neuronal activity is regulated is not known in this species. In order to investigate the regulation of DA inhibition at the molecular level, we developed a quantitative real-time RT-PCR (qrtRT-PCR) assay, using the Light Cycler system, for the expression of eel tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. Two different reference genes were compared: the previously cloned eel cytochrome b, and eel acidic ribosomal phosphoprotein P0, the latter of which we cloned and partly sequenced. To further validate the assay, different methods of total RNA extraction were tested and compared. When applied to cDNA extracted from dissected brains of juvenile eels, the expression of TH was highest in the olfactory bulb, followed by the telencephalon including preoptic area, and the di-/mesencephalic areas excluding the optic lobes. TH expression in the optic lobes and in the medulla oblongata was low, whereas no expression could be detected in corpus cerebellum. This distribution pattern is in agreement with earlier studies on TH in the eel using immunohistochemistry, RT-PCR, and Northern blotting. The developed qrtRT-PCR assay provides a new tool for understanding the mechanisms regulating central DA inhibition of puberty in juvenile eels.

Algorithms↗

PubMed2005

Avoidance behavior and brain monoamines in fish.

The crucian carp performs a typical avoidance behavior when exposed to olfactory cues from injured skin of conspecifics. They swim rapidly to the bottom and hide in available material. This work examines the effects of skin extract exposure and availability of hiding material on this behavior, and concomitant changes in brain monoaminergic activity in crucian carp. Individual fish were exposed to skin extract in aquaria with or without hiding material. Exposure to skin extract resulted in the expected avoidance behavior consisting of rapid movement towards the bottom of the aquarium. This lasted for 1-2 min. Activity then decreased below the level observed before exposure, suggesting a "freezing" type of avoidance behavior. This behavior was independent of availability of hiding material. Brain dopaminergic activity increased in telencephalon and decreased in the brain stem following skin extract exposure, again independent of availability of hiding material. However, fish kept in aquaria without hiding material showed an elevation of serotonergic activity in the brain stem and the optic tectum compared to fish with available hiding material. Absence of hiding material increased serotonergic activity also without exposure to skin extract. In aquaria with hiding material, the fish stirred up a cloud of fine sediments and showed a more pronounced decrease in locomotor activity in agreement with this being a more efficient freezing or immobile avoidance behavior. These results show that basic components of avoidance behavior and related brain changes are present in the fish brain, in accordance with the common phylogenetic roots of avoidance behavior in all vertebrates.

Analysis of Variance↗

PubMed2004

The brain-pituitary-gonad axis in male teleosts, with special emphasis on flatfish (Pleuronectiformes).

The key component regulating vertebrate puberty and sexual maturation is the endocrine system primarily effectuated along the brain-pituitary-gonad (BPG) axis. By far most investigations on the teleost BPG axis have been performed on salmonids, carps, catfish and eels. Accordingly, earlier reviews on the BPG axis in teleosts have focused on these species, and mainly on females (e.g. 'Fish Physiology, vol. IXA. Reproduction (1983) pp. 97'; 'Proceedings of the Fourth International Symposium on the Reproductive Physiology of Fish. FishSymp91, Sheffield, UK, 1991, pp. 2'; 'Curr. Top. Dev. Biol. 30 (1995) pp. 103'; 'Rev. Fish Biol. Fish. 7 (1997) pp. 173'; 'Proceedings of the Sixth International Symposium on the Reproductive Physiology of Fish. John Grieg A/S, Bergen, Norway, 2000, pp. 211'). However, in recent years new data have emerged on the BPG axis in flatfish, especially at the level of the brain and pituitary. The evolutionarily advanced flatfishes are important model species both from an evolutionary point of view and also because many are candidates for aquaculture. The scope of this paper is to review the present status on the male teleost BPG axis, with an emphasis on flatfish. In doing so, we will first discuss the present understanding of the individual constituents of the axis in the best studied teleost models, and thereafter discuss available data on flatfish. Of the three constituents of the BPG axis, we will focus especially on the pituitary and gonadotropins. In addition to reviewing recent information on flatfish, we present some entirely new information on the phylogeny and molecular structure of teleost gonadotropins.

Animals↗

PubMed2004

[An antagonist to GnRH in the control of reproduction in teleost fish: dopaminergic inhibition. Ancestral origin and differential conservation within vertebrates?].

In mammals, the neurohormonal control of the pituitary gonadotropes is provided by the gonadoliberin GnRH. Several studies on teleost fish indicate that a single positive control by GnRH is not a general rule among vertebrates. Peter and colleagues presented the first evidence of an inhibitory neurohormonal factor, "GRIF" (gonadotropin-release inhibiting factor). They induced a preovulatory LH surge by injuring particular brain areas in the goldfish. Subsequent in vivo and in vitro studies identified dopamine as GRIF, and neuroanatomical investigations have demonstrated that dopaminergic neurones in the anterior preoptic area projecting to the pituitary represent the anatomical substrate for GRIF activity. An inhibitory role of dopamine on the control of LH and ovulation/spermiation has been evidenced in many adult teleosts, including its implications for aquaculture. However, dopamine does not play an inhibitory role in all adult teleosts. As regards the early stages of gametogenesis and especially the control of puberty, a role for dopamine has been suggested or rejected depending on species. The European eel has a unique life cycle with a long prepubertal stage, which has made it a useful model to demonstrate the key-role of dopamine in the control of puberty. Data from tetrapods suggest that the role of dopamine as a GRIF is not restricted to the teleosts, but that it may have an ancient evolutionary origin, and has been differentially conserved throughout vertebrate evolution.

Animals↗

PubMed2003

Isolation and characterization of FSH and LH from pituitary glands of Atlantic halibut (Hippoglossus hippoglossus L.).

Two gonadotropins (GtH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), were isolated and characterized from pituitary glands of Atlantic halibut (Hippoglossus hippoglossus L.). Glycoproteins were extracted in 40% ethanol followed by precipitation in 85% ethanol. Subsequently, glycoproteins were fractionated by ion-exchange chromatography on a Whatman DE-52 column using a stepwise gradient of ammonium bicarbonate (50-1000 mM). Intact FSH and LH were finally purified on rpHPLC using an AsahiPak C4P-50 column with an acetonitrile gradient (10-60%). SDS-PAGE showed a molecular mass of 33 and 32 kDa for intact FSH and LH, respectively. Final purification of subunits was performed by a subsequent purification step on rpHPLC using a Phenomenex Jupiter C18 column with an acetonitrile gradient (10-60%). FSHbeta, LHbeta, and the common alpha subunit showed molecular masses of 25, 24, and 19 kDa, respectively. Subunit identity was confirmed by N-terminal amino acid sequencing. Intact FSH and LH showed gonadotropic activity by stimulating release of 11-ketotestosterone from turbot (Scophthalmus maximus L.) testicular tissue in vitro. This provides the first purification of two distinct GtHs from an evolutionary advanced pleuronectiform teleost.

Androsterone↗

PubMed2003

Molecular characterization and expression of FSHbeta, LHbeta, and common alpha-subunit in male Atlantic halibut (Hippoglossus hippoglossus).

To elucidate the role of the gonadotropins in the multiple spawner Atlantic halibut (Hippoglossus hippoglossus) full length cDNAs encoding FSHbeta, LHbeta, and the common alpha-subunit were cloned from pituitary glands by RACE-PCR. The three cDNAs consisted of 614, 595, and 666 nucleotides encoding peptides of 131, 146, and 124 amino acids, respectively. Halibut FSHbeta and LHbeta showed unique structural features among the vertebrate glycoprotein hormones. First, in contrast to all known FSHbeta, which contain either one or two conserved N-glycosylation sites, no potential binding site was found in Atlantic halibut FSHbeta. Second, the conserved glycosylation site in the N-terminus of all vertebrate LHbeta has been substituted with a unique C-terminal binding site in Atlantic halibut LHbeta. Furthermore, a specific cysteine residue of importance for the folding and heterodimerization of mammalian FSH is lacking in the FSHbeta from Atlantic halibut as well as many other teleosts. However, teleost FSHbeta is characterized by an additional N-terminal cysteine, which has likely replaced the missing residue, implicating a modified folding pattern of this subunit. In situ hybridization of mature male pituitaries revealed that FSHbeta and LHbeta mRNA were expressed in distinct cell types throughout the proximal pars distalis of the adenohypophysis, while alpha-subunit mRNA was identified in all parts of the proximal pars distalis, and also along the periphery of pars intermedia. Consistently, Northern blot analysis of pituitary RNA from mature males showed that FSHbeta, LHbeta, and alpha-subunit mRNAs were highly expressed. In juvenile male pituitaries very few cells containing FSHbeta, LHbeta, and alpha-subunit mRNA were identified by in situ hybridization. Low mRNA levels encoding LHbeta and the alpha-subunit were also demonstrated by Northern blot analysis of the juvenile pituitaries, while no FSHbeta mRNA was detected using this less sensitive technique. The results suggest that both FSH and LH play a role during both the very early and the final reproductive stages in Atlantic halibut males.

Age Factors↗

PubMed2003

Does the lateral bundle of the medial olfactory tract mediate reproductive behavior in male crucian carp?

The olfactory tract in crucian carp (Carassius carassius) is divided into three distinct bundles: the lateral tract (LOT) and the lateral (lMOT) and medial (mMOT) bundles of the medial tract. The LOT has been shown to mediate information associated with feeding behavior, whereas the mMOT mediates information associated with alarm response. The role of the medial olfactory tract (lMOT and mMOT) in reproductive behavior is still under debate. In the present experiment, male reproductive behavior towards prostaglandin-injected females was investigated before and after cutting off the different olfactory tract bundles, to determine which of the tract bundles is essential for mediating reproductive behavior in male crucian carp. The fish were maintained in physiological saline before and after surgery to preserve the remaining tract bundles. Operations were performed symmetrically on both sides and post-operative inspections revealed the functionality of the intact tracts. Sham-operated males and males with only the lMOT intact showed typical reproductive behavior, with following of the female and inspections of the female anal papilla. However, males in which the lMOT was cut, leaving both the mMOT and the LOT intact, showed reduced reproductive behavior. Our results suggest that the lMOT mediates reproductive behavior in male crucian carp.

Animals↗

PubMed2002

Spermatogenesis and related plasma androgen levels in Atlantic halibut (Hippoglossus hippoglossus L.).

Spermatogenesis in male Atlantic halibut (Hippoglossus hippoglossus L.) was investigated by sampling blood plasma and testicular tissue from 15-39-month-old fish. The experiment covered a period in which all fish reached puberty and completed sexual maturation at least once. The germinal compartment in Atlantic halibut testis appears to be organized in branching lobules of the unrestricted spermatogonial type, because spermatocysts with spermatogonia were found throughout the testis. Spermatogenesis was characterized histologically, and staged according to the most advanced type of germ cell present: spermatogonia (Stage I), spermatogonia and spermatocytes (Stage II), spermatogonia, spermatocytes and spermatids (Stage III), spermatogonia, spermatocytes, spermatids and spermatozoa (Stage IV), and regressing testis (Stage V). Three phases could be distinguished: first, an initial phase with low levels of circulating testosterone (T; quantified by RIA) and 11-ketotestosterone (11-KT; quantified by ELISA), spermatogonial proliferation, and subsequently the initiation of meiosis marked by the formation of spermatocytes (Stage I and II). Secondly, a phase with increasing T and 11-KT levels and with haploid germ cells including spermatozoa present in the testis (Stage III and IV). Thirdly, a phase with low T and 11-KT levels and a regressing testis with Sertoli cells displaying signs of phagocytotic activity (Stage V). Circulating levels of 11-KT were at least four-fold higher than those of T during all stages of spermatogenesis. Increasing plasma levels of T and 11-KT were associated with increasing testicular mass throughout the reproductive cycle. The absolute level of, or the relation between, testis growth and circulating androgens were not significantly different in first time spawners compared to fish that underwent their second spawning season. These results provide reference levels for Atlantic halibut spermatogenesis.

Androgens↗