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Biomedical subjects

V L Trudeau

Publications and source records attributed to V L Trudeau.

At least 37 records · Page 2Linked to original sources
PubMed1998

Sex steroids and the initiation of puberty in male African catfish (Clarias gariepinus).

The effects of sex steroids on spermatogenesis and testicular androgen secretion were studied in juvenile (spermatogonia present in testes) African catfish. Fish were implanted with Silastic pellets containing 11-ketotestosterone (KT), 11beta-hydroxyandrostenedione (OHA), androstenetrione (OA), androstenedione (A), testosterone (T), 5alpha-dihydrotestosterone (DHT), or estradiol-17beta (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were incubated with African catfish luteinizing hormone (LH) and the amount of OHA secreted in vitro (the main androgen produced by African catfish testes) was quantified. Tissue fragments were then fixed for histological analysis of spermatogenesis. Treatment with KT, OHA, and OA stimulated testicular growth and spermatogenesis (spermatocytes and spermatids were found), whereas T, DHT, A, or E2 had no such effects. All steroids, except for DHT and E2, reduced OHA secretion in the absence and presence of LH to approximately 10% of the control values. Previous studies have shown that KT, OHA, and OA have little effect on circulating LH levels in juvenile male African catfish, so that these androgens probably had direct effects on the testis. Inasmuch as OHA, OA, and KT have largely similar effects and because OHA and OA are converted to KT in vivo, we suggest that KT is physiologically the most relevant androgen for the initiation of spermatogenesis in African catfish.

Androstenedione↗
PubMed1998

Gamma-aminobutyric acid up-regulates the expression of a novel secretogranin-II messenger ribonucleic acid in the goldfish pituitary.

An RNA-arbitrarily primed PCR differential display strategy was used to identify candidate genes in the pituitary that are up-regulated by endogenously activated gamma-aminobutyric acid (GABA) systems that may also be involved in the control of reproduction. Goldfish were injected with the GABA metabolism inhibitor gamma-vinyl-GABA (GVG), known for its high efficiency to specifically increase endogenous brain and pituitary GABA levels in this species, resulting in higher levels of circulating gonadotropin-II (GTH-II). Several transcripts related to hormone secretion, signal transduction pathways, and messenger RNA (mRNA) editing were shown to be up-regulated after GVG injection. Among these transcripts we characterized an mRNA coding for the secretory vesicle protein secretogranin-II (SgII), a member of the chromogranin family, which is the precursor of a novel 34 amino acid neuropeptide, goldfish secretoneurin (SN). A semiquantitative PCR developed to measure pituitary SgII mRNA levels showed a 5-fold increase in GVG treated fish vs. control fish. Moreover, GVG treatment specifically increased SgII mRNA levels in gonadotrophs, concomitant with a decrease in GTH-II cell content. In addition, i.p. injection of synthetic goldfish SN increased GTH-II release in goldfish pretreated with the dopamine antagonist domperidone. Activation of GABAergic neurons has two effects, enhancing in vivo GTH-II release and up-regulating SgII mRNA specifically in goldfish gonadotrophs. Together with our SN bioactivity data, this suggests the existence in the pituitary of an autocrine or paracrine mechanism linked to the regulated secretory pathway in the gonadotrophs.

Amino Acid Sequence↗
PubMed1997

Activin facilitates neuronal development in the rat amygdala.

The amygdala is one of the richest sources for activin receptor in the central nervous system (CNS) but the function of activin in the amygdala is unknown. An in vitro culture system was developed to study the effect of recombinant human activin-A on neuronal growth. Activin-A (1000 pM) was added continuously from day 1 in vitro and the medium changed every 2 days. Continuous visual assessment revealed that control neurones started to atrophy within 2 days of incubation in serum free N2-MEM. After 6 days in culture, cells were fixed and stained for growth-associated protein (GAP-43), a membrane-bound phosphoprotein involved in axonal elongation and synaptogenesis. Activin-A reduced the number of atrophying neurones and stimulated neuritic growth. The results presented here indicate a possible neurotrophic role for activin-A in the neonatal CNS.

Activins↗
PubMed1997

Estradiol stimulates growth hormone production in female goldfish.

The effects of estradiol (E2) on growth hormone (GH) production was investigated in gonad-intact female goldfish. It was first necessary to generate a specific antibody for use in immunocytochemistry, Western, and dot-blot analyses of GH production. To accomplish this, grass carp GH (gcGH) cDNA was cloned by the reverse transcription polymerase chain reaction (RT-PCR) and expressed in Echerichia coli and a specific polyclonal antibody to recombinant gcGH was generated in the rabbit. In Western blot, the anti-gcGH antibody specifically immunoreacted with recombinant gcGH, purified natural common carp GH, and with a single 21.5-kDa GH form from pituitary extracts of grass carp, common carp, goldfish, and zebrafish but not salmon, trout, or tilapia. Intraperitoneal injection of the recombinant gcGH enhanced the growth rates of juvenile common carp demonstrating biological activity of this GH preparation. Electron microscopic studies showed that the anti-gcGH-I antibody specifically reacted with GH localized in the secretory granules of the goldfish somatotroph. Using anti-gcGH-I in a dot-blot assay, it was found that in vivo implantation of solid silastic pellets containing E2, (100 micrograms/g body weight for 5 days) increased pituitary GH content by 150% in female goldfish. In a second, independent study employing a previously characterized anticommon carp GH antibody for radioimmunoassay, it was found that E2 increased pituitary GH content by 170% and serum GH levels by approximately 350%. The E2-induced hypersecretion of GH and increase in pituitary GH levels was not associated with changes in steady-state pituitary GH mRNA levels, suggesting that this sex steroid may enhance GH synthesis at the posttranscriptional or translational level. Previous observations indicate that GH can stimulate ovarian E2 production. The present results show that E2 can in turn stimulate GH production, indicating the existence of a novel pituitary GH-ovarian feedback system in goldfish.

Animals↗
PubMed1997

Expression of cholecystokinin messenger RNA in reciprocally-connected auditory thalamus and cortex in the rat.

Cholecystokinin exerts a potent antiepileptic action in mammalian auditory system and undergoes seizure-mediated up-regulation. The present study investigated cholecystokinin messenger RNA expression in the reciprocally-connected auditory thalamus and cortex in the rat. Immunofluorescence in situ hybridization was performed using a 24-base cholecystokinin-messenger RNA oligonucleotide probe. Corticothalamic projection neurons were identified by means of the retrograde fluorescent tracer rhodamine latex microspheres injected into the medial geniculate body. In our experiments, cholecystokinin messenger RNA transcripts were found in about 80% of neurons located within the reciprocally-connected regions of the medial geniculate body and the auditory cortices. These observations provide evidence of cholecystokinin production in the reciprocally-connected regions of the auditory thalamus and cortex, the structures which jointly create the thalamo-corticothalamic circuit which has been implicated in seizure genesis.

Animals↗
PubMed1997

Immunofluorescence in situ hybridization (IFISH) in neurones retrogradely labelled with rhodamine latex microspheres.

The method of non-radioactive in situ hybridization was developed as an alternative to radioactive assay because of the difficulties and disadvantages of the safety measures required, extensive time required for autoradiography (especially with 3H-labelled probes) and limited cellular resolution obtained using 32P- and 35S-labelled probes. This method holds great potential for studying functional anatomy of specific neuronal pathways if it can be used in conjunction with conventional tract tracing techniques. In this article we describe a simple method by which immunofluorescence in situ hybridization (IFISH) was jointly used with rhodamine latex microspheres (RLM) to trace the origin of the thalamic cholecystokininergic input in rat. RLM is a widely used retrograde fluorescence tracer and seems ideal for IFISH because: (1) it lacks aversive effect on the hybridization and immunocytochemical reactions, (2) it is resistant to the rather harsh tissue treatment required for IFISH, and (3) both the RLM and mRNA hybrids give fluorescence signals; therefore, the extent of signal co-localization can be conveniently and more accurately verified under an epifluorescence microscope. Success of the IFISH-RLM combination is chiefly limited by the quantity and availability of mRNA signals in the tissue. In our case, we used a digoxigenin (DIG)-labelled oligonucleotide probe, which through immunological amplification significantly enhanced the sensitivity of mRNA detection.

Animals↗
PubMed1997

Neuroendocrine regulation of gonadotrophin II release and gonadal growth in the goldfish, Carassius auratus.

The goldfish, a member of the carp family, is a widely used model for reproductive neuroendocrine studies of economically important fish. The two gonadotrophin (GTH) molecules released from the fish anterior pituitary, GTH-I and GTH-II, are structurally similar to tetrapod FSH and LH, respectively. Gonadotrophin II is the best studied, and in goldfish stimulates gonadal growth and steroidogenesis, ovulation and sperm release. Growth hormone also has gonadotrophic actions in fish which enhance gonadal steroidogenesis. The principal stimulatory and inhibitory systems regulating GTH-II release are the gonadotrophin-releasing hormone (GnRH) and dopamine neurones in the preoptic-hypothalamic region. In goldfish there are two native GnRH forms, salmon GnRH and chicken GnRH-I; both stimulate GTH-II release but use different signal transduction pathways. In contrast to mammals, teleost fish do not have a median eminence and the GTH-II cells are thus directly innervated by neurones producing GnRH, dopamine and other stimulatory neurohormones. For most of these factors, the ability to stimulate GTH-II release varies seasonally. The amino acid neurotransmitter, gamma-aminobutyric acid, has the most prominent stimulatory actions which enhance GnRH release and inhibit dopamine turnover in the hypothalamo-pituitary complex. Neuropeptide Y stimulates GTH-II release by a combined direct action on the gonadotroph and also by enhancing GnRH release. Positive and negative sex steroid feedback mechanisms act concurrently to regulate GTH-II release in adults of both sexes. The principal site of positive feedback is the GTH-II cell where testosterone and oestradiol potentiate GnRH-stimulated GTH-II release. Negative feedback by sex steroids involves activation of inhibitory dopamine neurones, thus maintaining tight control over circulating GTH-II concentrations.

Animals↗
PubMed1996

Regulation of growth hormone secretion by amino acid neurotransmitters in the goldfish (I): Inhibition by N-methyl-D, L-aspartic acid.

High levels of the amino acid neurotransmitter glutamate were found in the goldfish hypothalamus and pituitary using high performance liquid chromatography with fluorometric detection. A specific polyclonal antibody to glutamate was generated in the rabbit for immunocytochemistry. Localization studies demonstrated that glutamatergic neurons of undetermined origin innervate the particular part of the goldfish adenohypophysis where somatotrophs and gonadotrophs are located. Intraperitoneal and brain third ventricle injection of the glutamate agonist N-methyl-D,L-aspartic acid (NMA) inhibited GH release in vivo. The gonadal steroid estradiol plays an important role in regulating GH secretion by stimulating basal serum GH levels and enhancing the inhibitory effects of NMA on GH secretion. Taken together, these results demonstrate that glutamate is an important regulator of GH secretion in goldfish.

Animals↗
PubMed1996

Regulation of activin type-II receptor mRNA levels in rat hypothalamus by estradiol in vivo.

A solution-hybridization S1-nuclease protection assay was used to evaluate the expression of messenger RNAs for the activin beta A subunit and type II activin receptor in adult rat brain. Results indicate the presence of beta A subunit mRNA in both hypothalamus and brainstem, with approximately two-fold higher levels in brainstem. Levels of activin type II receptor mRNA were similar in the hypothalamus of young virgin and 15-day lactating females, and in females in which pups were removed after a 5-day lactation period. Male rats castrated prepubertally (30 days p.n.) had approximately 220% higher (P < 0.05) hypothalamic activin type II receptor mRNA levels than postpubertal, 3-month old age-matched sham controls. Two month treatment of castrate rats with estradiol (200 ng/g, i.p. every 2 days) reduced hypothalamic activin type II receptor mRNA expression to control levels; the same dose of testosterone had no effect. The expression of the hypothalamic activin type II receptor gene may be estrogen-regulated in vivo.

Activin Receptors↗
PubMed1996

Melatonin receptors are present in non-optic regions of the brain of a deep-sea fish living in the absence of solar light.

Pineal melatonin hormonally transduces photoperiod to influence daily and seasonal cycles in most vertebrates (1, 2). Evidence of melatonin receptors throughout the brain of several fish species (3-5), particularly in retinorecipient structures, also indicates a role in visual processing. Despite the absence of solar light many deepsea organisms show seasonality (6-8). The presence of central melatonin receptors was investigated by quantitative in vitro autoradiography in the deep-sea fish Coryphaenoides (Nematonurus) armatus. Specific, time-dependent, saturable, high affinity and guanine nucleotide sensitive, 2-[125I]iodomelatonin binding was found over the mid-brain tegmentum and hindbrain. Competing ligand potency was iodomelatonin > melatonin >> 5-HT. Although C.(N.) armatus has well developed eyes no 2-[125I]iodomelatonin binding occurred in optic tectum, cerebellum or hypothalamus. Thus melatonin involvement in processing of visual information and control of seasonal physiology via hypothalamic areas appears to be absent in this species. The presence of central G-protein coupled receptors indicates a function for melatonin unrelated to solar light.

Animals↗
PubMed1995

Expression of cholecystokinin mRNA in corticothalamic projecting neurons: a combined fluorescence in situ hybridization and retrograde tracing study in the ventrolateral thalamus of the rat.

Cholecystokinin (CCK), a well-known neuroactive peptide, has been observed in the axon endings within the thalamic reticular nucleus and the adjacent ventrolateral nucleus of the thalamus. The origin of this CCK innervation remains undefined. In this study, a fluorescence in situ hybridization (FISH) technique was used in conjunction with latex microsphere retrograde tracing to investigate whether cortical neurons may provide a source of CCK afferents to the ventrolateral thalamic nucleus. Rhodamine latex beads were injected into the ventrolateral thalamic nucleus of adult male rats to retrogradely label corticothalamic cells. After 7 days, tissues were processed for FISH using a 24-base oligonucleotide probe complementary to the 3' coding region of rat preprocholecystokinin mRNA. It was found that CCK transcripts are expressed in about 80% of identified corticothalamic projecting neurons. We therefore conclude that the descending cortical projections to the ventrolateral thalamus may provide an important source of CCK innervation to this region of the brain.

Animals↗
PubMed1994

Overexpression of activin-beta A subunit mRNA is associated with decreased activin type II receptor mRNA levels in the testes of alpha-inhibin deficient mice.

Activins and inhibins are polypeptides of the transforming growth factor-beta family that participate in differentiation and growth of diverse cell types, and are involved in endocrine/paracrine regulation of the hypothalamo-pituitary-gonadal axis. Mice with alpha-inhibin subunit gene deletion develop large testicular tumors. In these animals, a 200-fold increase in testicular expression of activin beta A subunit mRNA was detected using S1-nuclease protection analysis. Northern blot analysis demonstrated that a predominant mRNA form of approximately 6.5 kb and a second minor form of 4.5 kb were overexpressed in the testes of the alpha-inhibin deficient animals. Testicular expression of the type II activin receptor was decreased 3-fold in these mice. In contrast, hypothalamic beta A and type II activin receptor mRNA levels remained unaltered. alpha-Inhibin may play a role to suppress the expression of beta A mRNA in the mammalian testes. These results demonstrate that increased expression of activin is accompanied by a tissue specific reduction in the expression of its own receptor mRNA in vivo.

Activin Receptors↗
PubMed1994

In vivo actions of a gonadotropin-releasing hormone (GnRH) antagonist on gonadotropin-II and growth hormone secretion in goldfish, Carassius auratus.

In our previous in vitro studies, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E) suppressed both gonadotropin-II (GTH-II) and growth hormone (GH) release stimulated by sGnRH and cGnRH-II. In the present study analog E significantly inhibited the increases in plasma GTH-II levels stimulated by sGnRH in sexually mature female and sexually recrudescent goldfish. Treatment of goldfish with alpha-methyl-p-tyrosin methyl ester (alpha-MPT) inhibits dopamine synthesis and abolishes the inhibitory actions of dopamine on GTH-II release, resulting in a potentiation of the GTH-II response to sGnRH. Following alpha-MPT pretreatment, analog E significantly reduced basal plasma GTH-II levels, and suppressed both sGnRH and cGnRH-II actions on GTH-II release. Analog E also inhibited the increase in plasma GTH-II levels in sexually mature male goldfish exposed to the female sexual pheromone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha 20 beta-P), demonstrating that the increase in plasma GTH-II levels is due to release of endogenous GnRH. Analog E significantly inhibited the increases in plasma GH levels stimulated by treatment with sGnRH. Implantation of estradiol pellets increases basal plasma GH levels and increases the GH responsiveness to sGnRH in sexually recrudescent goldfish; analog E also suppressed the increase in plasma GH levels stimulated by injection of sGnRH in estradiol-treated fish. Analog E suppressed basal GTH-II and GH levels in fish that were unhandled prior to injection; however, analog E was not effective in reducing basal plasma GTH-II or GH levels in experiments in which the fish were blood sampled or subjected to some experimental manipulation prior to injection of analog E. Analog E also suppressed basal levels of GTH-II in alpha-MPT-treated fish, suggesting that stress inhibition of GTH-II release may be mediated by the dopaminergic system. In summary, the results demonstrate that (i) analog E can suppress the actions of exogenous sGnRH and cGnRH-II on GTH-II and GH release in vivo, (ii) the GnRH system mediates, at least in part, the plasma GTH-II response in sexually mature male goldfish following exposure to the female sexual pheromone 17 alpha 20 beta-P, and (iii) endogenous GnRH peptides are important in the regulation of basal plasma levels of GTH-II as well as GH, particularly in low stress conditions.

Animals↗
PubMed1993

Norepinephrine turnover in the goldfish brain is modulated by sex steroids and GABA.

It is known that norepinephrine (NE) is important in the neuroendocrine control of pituitary gonadotropin II (GTH-II) and growth hormone (GH) release but very little is known about the factors regulating NE neurons in the goldfish brain. Female gonad-intact goldfish were implanted intraperitoneally (100 micrograms/g) with testosterone (T) or estradiol (E2) to elevate serum steroid levels. High-performance liquid chromatography measurements showed that steroid implantation had no effect on NE content in the telencephalon, including preoptic area (TEL-POA), or the hypothalamus (HYP). The turnover rate of NE was estimated from the rate of depletion of NE content from tissues following inhibition of tyrosine hydroxylase by alpha-methyl-p-tyrosine (240 micrograms/g). The present study demonstrates that E2 can decrease NE turnover rates in TEL-POA and HYP of sexually regressed goldfish (August). The results in recrudescent fish (November), however, indicate a more complex interaction of E2 with NE neurons since E2 increased NE turnover in TEL-POA and HYP in these animals. Testosterone (T) has less prominent effects on NE turnover rates in TEL-POA and HYP; the only significant effect of T-implantation was a small reduction of NE turnover in the TEL-POA of sexually recrudescent fish. Elevation of endogenous brain GABA concentrations by injection of the GABA transaminase inhibitor, gamma-vinyl-GABA (300 micrograms/g), significantly reduced NE turnover in TEL-POA. These data demonstrate that goldfish NE neurons in the TEL-POA are sensitive to regulation by changes in circulating sex steroids and by increases in brain GABA.

4-Aminobutyrate Transaminase↗
PubMed1993

Interactions of gonadal steroids with brain dopamine and gonadotropin-releasing hormone in the control of gonadotropin-II secretion in the goldfish.

In goldfish it is known that intraperitoneal implantation with testosterone (T) or estradiol (E2) potentiates the serum gonadotropin-II (GtH-II) response to gonadotropin-releasing hormone (GnRH) without affecting basal GtH-II levels. Since the release of GtH-II in goldfish is under a tonic dopaminergic inhibitory tone, the possibility of sex steroids modulating brain and pituitary dopamine was examined in vivo and in vitro. Implantation of females with either T or E2 (100 micrograms/g in solid silastic pellets) also potentiated the increase in serum GtH-II in response to the dopamine antagonist, domperidone (10 micrograms/g). High-performance liquid chromatography measurements showed that steroid implantation had no effect on dopamine content in the telencephalon including preoptic area, hypothalamus, and pituitary. However, the present study demonstrates that T or E2 can increase pituitary dopamine turnover rates following tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine (240 micrograms/g). In vitro perifusion of pars distalis fragments from E2- or T-treated fish also showed a potentiation of salmon GnRH (sGnRH)-induced GtH-II release compared to controls. However, exposure to pituitary fragments from control and steroid-treated fish to increasing doses of the dopamine agonist LY 171555 did not demonstrate a significant difference in the sensitivity of the gonadotrophs to dopamine. Testosterone-induced alterations in DA turnover are dissociable from the positive action of T on pituitary responsiveness, since the potentiating effect of T implantation was not affected by severe depletion of brain and pituitary DA levels by alpha-methyl-p-tyrosine pretreatment. These data demonstrate that in gonad-intact goldfish, sex steroids enhance pituitary responsiveness to GnRH but basal serum GtH-II levels are maintained by a concomitant increase in DA turnover in the pituitary.

Animals↗
PubMed1993

Effects of sex steroid treatments on gonadotropin-releasing hormone-stimulated gonadotropin secretion from the goldfish pituitary.

The effects of gonadal steroids on the gonadotropin (GTH) release response to salmon gonadotropin-releasing hormone (sGnRH), chicken gonadotropin-releasing hormone-II (cGnRH-II), and the sGnRH analogue, [D-Arg6, Trp7, Leu epsilon, Pro9]-N-ethylamide-GnRH (sGnRH-A), were investigated using an in vitro perifusion system for goldfish pituitary fragments. Gonad-intact male and female goldfish were implanted intraperitoneally (i.p.) with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g); pituitaries were removed 5 days later for perifusion experiments. In vivo treatment with T or E2 potentiates sGnRH-, cGnRH-II-, and sGnRH-A-induced GTH secretion from pituitary fragments of sexually regressed and sexually recrudescent goldfish in vitro. Testosterone (100 nM; 24 h) treatment in vitro has a direct effect on the pituitary to increase sGnRH responsiveness, and this potentiating effect of T was blocked by the protein synthesis inhibitor cycloheximide (25 microM). In sexually regressed goldfish, in vivo T implantation enhanced the serum GTH response to sGnRH-A (0.01 microgram/g; 6 h) 7-fold. ED50 estimates for in vitro pituitary GTH responsiveness to sGnRH-A were 1.0 +/- 0.1 nM and 0.1 +/- 0.1 nM (p < 0.05) for blank and T-implanted groups, respectively. Radioligand (125I-sGnRH-A) binding studies demonstrated that enhanced pituitary responsiveness was independent of changes in pituitary GnRH receptor affinity or number. These results demonstrate that sex steroids increase pituitary sensitivity to GnRH peptides in the goldfish.

Animals↗