Evidence that the inhibitory effects of stress on reproduction in teleost fish are not mediated by the action of cortisol on ovarian steroidogenesis

Ovarian follicles of goldfish, common carp, and the sparid Pagrus auratus (New Zealand snapper) were incubated in vitro to assess the effects of cortisol (F) on ovarian steroidogenesis. Unstimulated goldfish follicles produced little testosterone (T) or 17 beta-estradiol (E2), whereas both carp and snapper follicles spontaneously produced E2 and to a lesser extent T. Goldfish follicles produced increased amounts of E2 in response to treatment with human chorionic gonadotropin (hCG), whereas carp and snapper follicles did not. However, stimulation of carp follicles with maturational carp gonadotropin (cGTH-II) resulted in dose-dependent increases in production of E2. Treatment of follicles of all three species with T resulted in E2 production to levels as high as or higher than those following treatment with hCG or cGtH-II. Cotreatment of follicles with T and hCG or cGTH-II did not result in higher E2 production than treatment with T alone. Goldfish follicles treated with 25-hydroxycholesterol showed increases in E2 production that were similar to those occurring following treatment with T. Treatment of follicles with F at a range of doses up to 1 microgram.ml-1 had no inhibitory effect on T or E2 production in any treatment combination in any of the species examined. In several cases, follicles incubated with T and/or hCG produced more E2 in the presence of F than they did without F. The results suggest either that the observed inhibitory effects of stress in a range of teleost species are not mediated by F or that they arise higher in the endocrine pathway than at the level of ovarian steroidogenesis.

Nature and distribution of gonadotropin-releasing hormone (GnRH) in the brain, and GnRH and GnRH binding activity in serum of the spotted dogfish Scyliorhinus canicula

The distribution of different molecular forms of gonadotropin-releasing hormone (GnRH) in the brain and serum of the spotted dogfish, Scyliorhinus canicula, was investigated by an indirect immunofluorescence method, using antisera against salmon (s-), chicken-II (cII-) and mammalian (m-) GnRHs, and by reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with radioimmunoassays. Five GnRH molecular forms were demonstrated on the basis of the retention time in the RP-HPLC system. The characteristics of four of these GnRH peptides are consistent with those of m-, cII-, dogfish (df-), and sGnRH. The fifth form appears to be novel. Immunoreactive sGnRH structures were confined to the diencephalon; whereas cIIGnRH and mGnRH were found in the telencephalon and diencephalon. cIIGnRH- and dfGnRH-like molecules were detected in the serum. Moreover, a specific, low-affinity GnRH binding protein (GnRH-BP) was found in the serum of the spotted dogfish. The binding of [125I]sGnRHA to the serum GnRH-BP was dependent on incubation time, equilibrium being reached within 1 hr at 4 degrees; binding was rapid and completely reversible. Scatchard analysis yielded a linear plot with a Kd of 7.9 x 10(-7) M. The presence of a GnRH-BP in spotted dogfish serum suggests a probable action of GnRH via the general circulation.

Bombesin-like immunoreactivity in the forebrain and pituitary and regulation of anterior pituitary hormone release by bombesin in goldfish

The presence and distribution of bombesin (BBS)/gastrin-releasing peptide (GRP)-like immunoreactivity (IR) was examined in the goldfish pituitary and forebrain. BBS/GRP-like IR nerve fibres were consistently observed throughout the pituitary neurointermediate lobe (NIL); occasionally, BBS/GRP-like material was localized in cells and few fibres within the pars distalis. Within the goldfish forebrain, sparse, fine-beaded BBS/GRP-like IR fibres and few perikarya were detected in the preoptic hypothalamus. BBS/GRP-like IR material was also present in the ventro-posterior hypothalamus and the hypothalamic inferior lobes, and, in particular, within the nucleus lateral tuberis pars anterioris (NLTa) and nucleus lateral tuberis pars posterioris (NLTp), nucleus anterior tuberis (NAT), nucleus recessus lateralis (NRL), nucleus recessus posterioris (NRP), and the nucleus diffusus lobi inferioris (NDLI). Several BBS/GRP-like IR perikarya were observed in periventricular regions of the NLT, NRL, and NRP. Finally, BBS/GRP-like IR material was detected in the nucleus habenularis, the nucleus rotundus, several thalamic nuclei, and the optic tectum of the dorso-posterior diencephalon. The presence of BBS/GRP-like IR material within the preoptic hypothalamus, hypophysial stalk, and in the pituitary suggests that BBS-like peptides may regulate pituitary hormone release in fish. Perifusion of goldfish pituitary fragments with initial pulses of 0.1, 10, 100 or 1,000 nM BBS stimulated both growth hormone (GH) and gonadotropin (GtH-II) release. Repeated pulses of the same dose of BBS generally stimulated GH and GtH-II release to a similar magnitude. These studies provide initial evidence that BBS/GRP-like peptides are present within the central nervous system of teleost fish. The anatomical distribution of BBS/GRP-like IR in goldfish hypothalamic feeding center supports our previous report indicating a role for BBS in the central regulation of food intake in fish. Additionally, the presence of BBS/GRP-like IR material in the pituitary and brain areas associated with the regulation of anterior pituitary hormone secretion, as well as evidence demonstrating a direct action of BBS at the level of the goldfish pituitary to modify GH and GtH-II secretion, indicates that BBS/GRP-like peptides likely act to regulate pituitary hormone release in teleosts.

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.

CCK/gastrin-like immunoreactivity in brain and gut, and CCK suppression of feeding in goldfish

The presence and distribution of cholecystokinin (CCK)/gastrin-like immunoreactive (IR) material were examined in the goldfish brain and gut. In the forebrain, CCK/gastrin-like IR fibers and perikarya were localized to nuclei of predominantly the ventral telencephalon and diencephalon; more dorsal forebrain regions contained only few, thin-beaded, sparsely distributed IR fibers. CCK/gastrin-like IR was specifically detected in the preoptic hypothalamus, including the nucleus entopeduncularis, nucleus preopticus periventricularis, and nucleus preopticus. Of all brain regions examined, the highest concentration of CCK/gastrin-like IR staining was consistently observed in nuclei of the ventroposterior and inferior lobes of the hypothalamus. Within the gut, both nerve fibers and endocrine cells contained CCK/gastrin-like IR. The abundance of CCK/gastrin-like IR material within brain areas known to represent the feeding center of fish, as well as the presence of IR material within the gut, suggests that CCK may influence feeding behavior in fish. When injected either intraperitoneally or into the third brain ventricle into goldfish, sulfated CCK-8 (CCK-8s) suppressed food intake. The nonsulfated form of CCK-8 was not as effective as CCK-8s in suppressing feeding after intraperitoneal injection. No consistent changes were observed in circulating serum growth hormone or gonadotropin levels after either intraperitoneal or intracerebroventricular injection of CCK-8s. These studies demonstrate for the first time that CCK-8s is effective in acutely suppressing feeding behavior in fish when administered either peripherally or centrally into the third brain ventricle.

Episodic growth hormone secretion in the grass carp, Ctenopharyngodon idellus (C. & V.)

The secretory pattern of growth hormone (GH) was studied in sexually immature grass carp (0.5-1.0 kg body wt). Serial blood samples were taken at 15-min intervals during 4- to 6-hr sampling periods via a dorsal aorta cannula. During each 4- to 6-hr sampling period plasma GH profiles demonstrated episodic secretion. Two patterns were observed, consisting either of one episodic of GH secretion (single or several pulses clustered) or two episodes of GH secretion during each sampling period. The interval between the two episodes of GH secretion was 2.6 hr. This is the first demonstration of episodic GH secretion in a teleost.

Receptor binding of gonadotropin-releasing hormone antagonists that inhibit release of gonadotropin-II and growth hormone in goldfish, Carassius auratus

In goldfish, GnRH stimulates gonadotropin-II (GTH-II) and growth hormone (GH) release. The two native forms of GnRH, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), bind to two classes of GnRH binding sites: high-affinity/low-capacity sites and low-affinity/high-capacity sites. Our previous in vitro perifusion studies of goldfish pituitary fragments showed that [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E), [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-sGnRH (analog C), and [Ac-D(2)Nal1, 4Cl-D-Phe2, D-(3)Pal3,6]-cGnRH-II (analog N) inhibited both sGnRH- and cGnRH-II-stimulated GTH-II and GH release. Interestingly, analog C stimulated GH release but not GTH-II release. The objectives of the present study were 1) to test the site of action of GnRH antagonists in goldfish, 2) to test the relationship between receptor binding affinity of antagonists and their in vitro inhibitory potencies and apparent duration of action, and 3) to compare the binding characteristics of analog C with its differential action on GTH-II and GH release. As in previous studies, analog E suppressed sGnRH-stimulated GTH-II and GH release from perifused pituitary fragments. Similarly, analog E suppressed both sGnRH- and cGnRH-II-stimulated GTH-II and GH release from perifused dispersed goldfish pituitary cells, indicating the direct action of GnRH antagonists at the pituitary cell level. In the receptor binding studies, analog E displaced 125I-[D-Arg6, Pro9NHEt]-sGnRH (sGnRH-A) from crude goldfish pituitary membrane preparations in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

A new gonadotropin-releasing hormone (GnRH) superagonist in goldfish: influence of dialkyl-D-homoarginine at position 6 on gonadotropin-II and growth hormone release

The two native forms of gonadotropin-releasing hormones (GnRH) present in goldfish, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate gonadotropin-II (GTH-II) and growth hormone (GH) release both in vivo and in vitro. In our previous study using perifused goldfish pituitary fragments, many mammalian GnRH antagonists, especially those with D-Arg6, showed weak to strong stimulation of GTH-II and GH release. In the present study, the dose-related stimulation of GTH-II and GH release by [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-Arg6, Trp7, D-Ala10] mGnRH (analog J) and [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-hArg(Et2)6, D-Ala10] mGnRH (analog K) was demonstrated; the stimulatory potency of both analogs was significantly lower than that of native sGnRH. In the presence of analogs J and K, cGnRH-II stimulated GTH-II release was significantly suppressed. Further, GTH-II and GH stimulation by 2 microM of analog K was significantly suppressed by a 'true' GnRH antagonist, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6] mGnRH (analog E). These results indicate that analogs J and K increase GTH-II and GH release in goldfish by acting on GnRH receptors on gonadotrophs and somatotrophs. Since analog K, having [D-hArg(Et2)6], strongly stimulated GTH-II release, the potency of [D-hArg(Et2)6] or [D-hArg(CH2CF3)2(6)] substituted analogs to stimulate GTH-II and GH release from the perifused goldfish pituitary fragments was tested. Among the peptides tested, [D-hArg(Et2)6, Pro9-NHEt] sGnRH had a higher potency in stimulating GTH-II release than any other analog tested in the present or in previous studies. For stimulation of GH release, [D-hArg(Et2)6, Pro9-NHEt] sGnRH and [D-Arg6, Pro9-NHEt] sGnRH were the most potent analogs tested; analogs of mGnRH were less potent than sGnRH, indicating the importance of Trp7, Leu8 residues in the native peptide. These results suggest the importance of [D-Arg6] or alkylated [D-Arg6] in determining the intrinsic activity and potency of GnRH peptides in goldfish.

Activin-like peptides in somatotrophs and activin stimulation of growth hormone release in goldfish

Activin and inhibin, dimeric protein hormones originally isolated from mammalian gonads, are involved in the regulation of pituitary gonadotropin secretion. Using domain-specific antibodies against activin and inhibin alpha, beta A, and beta B subunits, the present study demonstrates that immunoreactive activin and inhibin subunits, especially beta A, exist in goldfish pituitary. Immunocytochemical staining with anti-gonadotropin-II and anti-growth hormone showed that the pituitary cells containing immunoreactive activin beta subunits are somatotrophs. This is different from the situation in mammals where it is the gonadotrophs that produce activin molecules within the pituitary. The staining with anti-beta B was overall weak compared to that with anti-beta A, but both appear to localize in the same cells. Strong immunostaining with the anti-inhibin alpha subunit was also observed in the goldfish pituitary; however, the immunoreactivity is dissociated from those of beta A and beta B, and mainly associated with nerve fibers in the neurointermediate lobe. Based on this evidence, it is suggested that the goldfish pituitary predominantly produced activin-like molecules. Both porcine activin and inhibin stimulate growth hormone release from perifused goldfish pituitary fragments. Taken together with our previous findings that porcine activin stimulates gonadotropin-II release in goldfish, and the fact that the somatotrophs and gonadotrophs are in close contact with each other in the goldfish pituitary, it is hypothesized that somatotroph-derived activin may exert paracrine actions on the adjacent gonadotrophs to stimulate gonadotropin release and autocrine actions on somatotrophs to stimulate growth hormone secretion. This also provides a mechanism for communication between these two pituitary cell types.

Biomechanical effects of internal fixation of the distal tibiofibular syndesmotic joint: comparison of two fixation techniques

This biomechanical study compares two methods of internal fixation of the tibiofibular syndesmosis used in Weber type C malleolar fractures of the ankle. The transverse syndesmotic 3.5-mm screw was compared with two 1.5-mm Kirschner wires introduced obliquely across the distal tibiofibular syndesmosis. The influence of implants on distal tibiofibular joint motion and contact characteristics of the intact ankle joint were determined. Up to 1.25 mm of lateral displacement and 2 degrees of external rotation of the lateral malleolus during uninjured ankle dorsiflexion was recorded. Both techniques stabilized the injured syndesmotic joint and limited its normal motion during flexion and extension of the ankle. Pressure distribution displaced laterally in internally stabilized ankles compared with intact specimens, regardless of the type of fixation used. Therefore, both techniques alter joint biomechanics equivalently compared with the intact ankle.

Differential actions of a mammalian gonadotropin-releasing hormone antagonist on gonadotropin-II and growth hormone release in goldfish, Carassius auratus

In goldfish the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate both gonadotropin-II (GTH-II) and growth hormone (GH) release. Modifications of GnRH structure at positions 1, 2, 3, and 6 often result in an antagonist in goldfish, an observation well documented in mammalian studies. In a preliminary study in goldfish, a mammalian GnRH antagonist, [Ac-D(2)Nal1, 4Cl-D-Phe2, D(3)-Pal3,6, Arg5, D-Ala10]-mGnRH (analog L) weakly stimulated GTH-II release, and strongly inhibited GH release. The objectives of the present study were to study the dose-related actions of analog L on GTH-II and GH release in the goldfish, the specificity of inhibition of native GnRH actions, and to test whether analog L can act directly on goldfish pituitary cells. In a goldfish pituitary fragments perifusion system, analog L at different concentrations, given as 2-min pulses or as 30-min prolonged treatments, stimulated GTH-II and inhibited GH release in a dose-dependent manner. Analog L at 2 microM concentration (45 min) significantly suppressed sGnRH- and cGnRH-II-stimulated GTH-II as well as GH release. Analog L specifically inhibited GnRH-stimulated GH release, without having any significant effects on the GH release induced by either SKF38393, a dopamine D1 receptor agonist, or thyrotropin-releasing hormone. The GTH-II stimulatory and GH-inhibitory actions of analog L were significantly suppressed by a 'true' GnRH antagonist (Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6)-mGnRH. Further, analog L stimulated GTH-II release and suppressed GH release from the enzymatically dispersed goldfish pituitary cells, indicating the direct actions of analog L at the pituitary cell level. Analog L also displaced 125I-(D-Arg6, Pro9 NHEt)-sGnRH bound to crude goldfish pituitary membrane preparations in a dose-related manner. In conclusion, contrary to its action as a potent GnRH antagonist in mammals, analog L has GTH-II stimulatory action in goldfish. Analog L by acting via GnRH receptors at the pituitary cell level differentially acts on GTH-II and GH release, suggesting functional differences in the properties of the GnRH receptors on GTH and GH cells. Analog L also specifically inhibits sGnRH and cGnRH-II actions on GTH-II and GH release.

Functional evidence regarding receptor subtypes mediating the actions of native gonadotropin-releasing hormones (GnRH) in goldfish, Carassius auratus

In goldfish, two native gonadotropin-releasing hormone (GnRH) peptides, salmon GnRH (sGnRH) and chicken-II GnRH (cGnRH-II), stimulate gonadotropin (GTH-II) and growth hormone (GH) secretion. In the present study we tested whether sGnRH and cGnRH-II act through different or the same population of GnRH receptors on GTH and GH cells, using various approaches. A GnRH antagonist [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH (analog C) equally inhibited GTH-II release by sGnRH and cGnRH-II. Similarly, [Ac-D(2)Nal1,4Cl-D-Phe2,D-(3)Pal3,6]cGnRH-II (analog N) suppressed GTH-II stimulation by the two GnRH peptides equally. Further, in the continued presence of 100 nM sGnRH, a 100 nM pulse of cGnRH-II failed to cause additional GTH-II release and vice versa. Prolonged exposure of pituitary fragments to 100 nM sGnRH or cGnRH-II resulted in desensitization and reduced the GTH-II response to a subsequent pulse of either sGnRH or cGnRH-II equally. All these results indicate that both sGnRH and cGnRH-II act through the same population of GnRH receptors on gonadotrophs. Similarly, the GH responses obtained with (i) analog N treatment, (ii) pulse challenge to cGnRH-II during prolonged sGnRH treatment and vice versa, and (iii) desensitization studies suggest that both sGnRH and cGnRH-II act through the same population of GnRH receptors on somatotrophs. However, the properties of GnRH receptors on GTH-II and GH cells are different. Analog C stimulated GH release but not GTH-II release. In contrast, [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,D-Arg6]mGnRH stimulated GTH-II release but weakly suppressed GH release. These results indicate that sGnRH and cGnRH-II act on the same population of receptors on GTH cells and on a functionally distinct population of receptors on GH cells.

Neuropeptide-Y gene expression in the goldfish brain: distribution and regulation by ovarian steroids

Neuropeptide-Y (NPY) has been recently cloned from a goldfish cDNA library. Using a probe derived from this cDNA clone, the distribution and regulation of NPY mRNA in the goldfish brain were examined in the present study by in situ hybridization, Northern blot analysis, and ribonuclease protection assay. Frozen tissue sections from the goldfish brain and pituitary were hybridized with a digoxigenin-labeled RNA probe. Hybridization signal was detected mainly in fore-brain regions, particularly in the nucleus entopeduncularis of the ventral telencephalon, the preoptic area (POA), the olfactory bulbs, and various thalamic regions. In the midbrain, NPY mRNA was found in the optic-tectum and locus coeruleus. Northern blot hybridization of total RNA extracted from different brain areas with a 32P-labeled RNA probe detected a single mRNA species and confirmed that most NPY mRNA was present in telencephalon/POA and optic-tectum/thalamus. Our previous physiological studies showed that the ovarian steroids testosterone (T) and estradiol (E2) have potentiating effects on the actions of NPY on gonadotropin and GH release. Therefore, we also tested the possibility that T and E2 may modulate NPY gene expression. Fish were implanted ip with pellets containing T, E2, or no steroid (control) for 5 days, RNA was extracted, and NPY mRNA levels were estimated using a ribonuclease protection assay. Pretreatment with T or E2 induced a 2- to 3-fold increase in NPY mRNA levels in the telencephalon/POA, but not in the optic-tectum/thalamus. In situ hybridization using brains taken from T-implanted fish demonstrated that the site of steroid action is the POA. This report represents the first study on NPY gene expression in a nonmammalian species and demonstrates that 1) NPY mRNA is present in the neuroendocrine regulatory centers; and 2) ovarian steroids stimulate NPY gene expression in the POA.

Regional distribution and in vitro secretion of salmon and chicken-II gonadotropin-releasing hormones from the brain and pituitary of juvenile and adult goldfish, Carassius auratus

The content of salmon (sGnRH) and chicken-II (cGnRH-II) gonadotropin-releasing hormones was measured in discrete brain regions and pituitaries of juvenile and postspawning adult goldfish, using specific radioimmunoassays. In juveniles, the content of both peptides was low. sGnRH was the predominant form in telencephalon-preoptic area (T-POA) (sGnRH:cGnRH-II ratio = 2.06 +/- 0.66) and diencephalon (DIEN) (sGnRH:cGnRH-II ratio = 2.72 +/- 0.32), whereas cGnRH-II was predominant in cerebellum-brain stem (STEM) (sGnRH:cGnRH-II ratio = 0.47 +/- 0.05). Equal amounts of the two peptides were present in pituitary (PIT) (sGnRH:cGnRH-II ratio = 1.04 +/- 0.18). In adults, the content of both peptides in all regions was significantly increased. The increase in sGnRH exceeded that of cGnRH-II in T-POA and PIT, resulting in an increased sGnRH:cGnRH-II ratio in these tissues (T-POA, 3.55 +/- 0.26; PIT, 7.85 +/- 2.28). In DIEN and STEM, the increase in cGnRH-II content equaled or exceeded that of sGnRH; the sGnRH:cGnRH-II ratio was unchanged in STEM (0.39 +/- 0.06) and decreased in DIEN (1.23 +/- 0.13). The secretion of sGnRH and cGnRH-II was investigated under static in vitro incubation conditions. Both forms of the peptide were secreted from T-POA slices and PIT fragments from juvenile and adult fish. Secretion was significantly increased under potassium depolarizing conditions. Secretion of the two peptides was proportional to their content in tissues from both juvenile and adult goldfish.

An unusual arthroscopic discovery: an intraarticular schwannoma of the knee

This case report describes an unusual arthroscopic finding in a patient presenting with typical symptomatology of a medial meniscal tear of the right knee. Arthroscopy showed an multilobulated tumor that on histological examination was diagnosed as an intraarticular Schwannoma.

Seasonal variations in gonadotropin responsiveness, self-priming, and desensitization to GnRH peptides in the common carp pituitary in vitro

Seasonal variations of the GtH release response to salmon GnRH (sGnRH) and [D-Arg6,Pro9NEt]-sGnRH (sGnRH-A) were investigated in female common carp at different stages of the reproductive cycle using perifused pituitary fragments. The responsiveness to sGnRH and sGnRH-A varied seasonally in common carp pituitaries in vitro, with the greatest GtH release response in pituitaries from sexually mature (preovulatory) fish compared to pituitaries from sexually regressed fish. The magnitude of this seasonal change in the GtH release response was greater for sGnRH-A than for sGnRH, and sGnRH-A has a higher potency than sGnRH, particularly in pituitaries from sexually mature fish. Desensitization of perifused pituitary fragments to sGnRH and sGnRH-A, and a self-priming effect of sGnRH-A on the GtH release response, caused by repeated pulse administrations of the GnRH peptides, varied with the stage of reproductive cycle of the common carp. Using pituitaries from sexually regressed female common carp, desensitization occurred only when a high dose of sGnRH or sGnRH-A was given as repeated pulses at short time intervals, and no self-priming was observed by repeated administrations of sGnRH and sGnRH-A. Using pituitaries from sexually mature female common carp, desensitization occurred when a high dose of sGnRH and both high and low dosages of sGnRH-A were given as repeated pulses at short time intervals. Self-priming, largely due to the increase in basal GtH levels, occurred in response to repeated pulses of low dosages of sGnRH-A given at long intervals.

Bombesin acts to suppress feeding behavior and alter serum growth hormone in goldfish

The acute effects of a single injection of bombesin (BBS) on feeding behavior and serum growth hormone (GH) levels in goldfish were examined. When injected intraperitoneally (IP), BBS (0.5-100 ng/g) caused a dose-dependent decrease in food intake within 30 and 45 min of administration; maximal suppression was achieved at 50 ng/g BBS and was accompanied by an elevation in serum GH levels. Associated with IP injection of BBS was a pronounced spitting out behavior in which food pellets were taken into the oral cavity but immediately expelled. When injected into goldfish deprived of food for 72 h, 50 ng/g BBS was still potent in suppressing feeding behavior and increasing serum GH. Additionally, IP injection of BBS (10 or 100 ng/g) into groups of fish caused a significant increase in circulating serum GH levels at 1.5 h postinjection. Finally, when injected into the third brain ventricle (ICV), 60 ng/g BBS also caused a suppression in food intake and a concomitant increase in serum GH. Groups of fish injected ICV with 5 or 50 ng/g BBS also exhibited a graded increase in serum GH levels at 45 min postinjection. Overall, these data are the first to demonstrate in any lower vertebrate that a neuropeptide acts to suppress food intake and cause concomitant alterations in circulating serum GH levels, following either peripheral or central administration.

Interactions of somatostatin, gonadotropin-releasing hormone, and the gonads on dopamine-stimulated growth hormone release in the goldfish

Previously, we have demonstrated that dopamine (DA) stimulates growth hormone (GH) release from the goldfish pituitary through DA D1 receptors. In the present study, the role of DA as a GH-releasing factor was further examined in vitro by studying its interactions with other GH regulators in the goldfish. The GH-releasing effects of DA and salmon gonadotropin-releasing hormone (sGnRH) were found to be independent and additive at the pituitary cell level. Both the kinetics and the magnitude of DA-stimulated GH release were unaffected by simultaneous treatment with sGnRH and vice versa. Castration of sexually mature (or prespawning) goldfish significantly enhanced the DA-stimulated GH release, but at the same time reduced the GH responses to sGnRH. Furthermore, the GH responses to DA and the D1 agonist SKF38393 were totally abolished by somatostatin (SRIF), a known GH release inhibitor in the goldfish. These findings strongly indicate that SRIF, DA, sGnRH, and gonadal factors interact at the pituitary level to regulate GH release in the goldfish.

Identification of gonadotropin-releasing hormone and associated binding substances in the blood serum of a holocephalan (Hydrolagus colliei)

The identity of the gonadotropin-releasing hormone (GnRH) form and the presence of GnRH-binding substances in the blood serum of the holocephalan, spotted ratfish (Hydrolagus colliei), were investigated. The GnRH-like peptides in the serum were identified on the basis of relative hydrophobicity using reverse-phase HPLC. [His5,Trp7,Tyr8]GnRH (chicken GnRH-II) was the only GnRH form detected in the serum. It has been previously shown to be the only GnRH form in the brain of this species. The presence of GnRH-binding substances was inferred by anomalous HPLC elution of GnRH, ultrafiltration behavior, and by the direct binding of iodinated GnRH analogues by blood serum components. The mean GnRH concentration in the extracted blood serum was 125 +/- 11 pg ml-1 (n = 5) in males and 64 +/- 48 pg ml-1 (n = 4) and 155 +/- 26 (n = 4) in two separate groups of females. Measurement of GnRH in the blood serum is complicated by the presence of GnRH-binding substances, which may cause the coprecipitation of GnRH during extraction with organic solvents. The high concentration of GnRH and the presence of GnRH-binding substances suggest that systemic blood is the route by which GnRH reaches the gonadotropes and/or that GnRH may have a hormonal role in H. colliei.

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.

CCK/gastrin-like immunoreactivity in the goldfish pituitary: regulation of pituitary hormone secretion by CCK-like peptides in vitro

The presence and distribution of cholecystokinin (CCK)/gastrin-like immunoreactivity (IR) was examined in the goldfish pituitary. Intense CCK/gastrin-like IR was consistently observed within fibers of the proximal pars distalis (PD), with fewer IR fibers localized in the rostral PD. Within the proximal PD CCK/gastrin-like IR fibers were distributed among both the gonadotrophs and somatotrophs, suggesting a possible role for CCK-like peptides in the regulation of gonadotropin-II (GtH-II) and growth hormone (GH) secretion. Exposure of pituitary fragments from either sexually gonadal recrudescing (maturing) or regressed goldfish to three 5-min pulses of 1.0 or 10 nM sulfated CCK8 (CCK8-s), at 55-min interpulse intervals, resulted in an increased secretion of both GtH-II and GH. Independent of the dose perifused, the GtH-II release responses to the second and third pulses of CCK8-s were always of similar magnitude to the first pulse at a given dose. For GH, repeated challenges of pituitary fragments to 0.1 or 1.0 nM CCK8-s stimulated release responses of similar magnitude; however, successive pulses of 10 nM CCK8-s resulted in a desensitization in the GH release response to the second or the third pulse. Fragments from sexually regressed goldfish exhibited an overall greater release response of GtH-II to CCK8-s relative to fragments from sexually recrudescing fish, whereas the GH release responses to CCK8-s were similar between the two sexual stages. A dose-dependent release of GtH-II was present in pituitary fragments from sexually regressed goldfish following five 5-min pulses of increasing (0.1 to 100 nM) doses of CCK8-s. Finally, the sulfated forms of CCK8 and gastrin 17 (G17-s) exhibited greater stimulatory abilities than the nonsulfated form of CCK8 in releasing GtH-II and GH from fragments of sexually recrudescing fish. Additionally, CCK8-s and G17-s were equal in their capacity to stimulate the release of GtH-II, whereas G17-s was slightly more effective than CCK8-s in stimulating the release of GH. Overall, these studies are the first to provide evidence that IR CCK/gastrin-like fibers are codistributed among the gonadotrophs and somatotrophs, and that CCK-like peptides are highly effective in stimulating GtH-II and GH release from the goldfish pituitary.

In vitro characterization of gonadotropin-releasing hormone antagonists in goldfish, Carassius auratus

The two native forms of GnRH, salmon GnRH and chicken GnRH-II, in the brain and pituitary of goldfish are both active in stimulating gonadotropin-II (GTH-II) and GH release. The objective of the present study was to characterize GnRH antagonists for their ability to inhibit sGnRH- and cGnRH-II-induced GTH-II and GH release in goldfish using a pituitary fragments perifusion system. Contrary to expectations, putative GnRH antagonists with D-Arg6 stimulated GTH-II and GH release in nearly all cases. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mammalian (m) GnRH inhibited sGnRH- and cGnRH-II-stimulated GTH-II release in a dose-dependent manner, with ED50 values of 242 +/- 48 and 169 +/- 17 nM, respectively. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mGnRH also inhibited GH release stimulated by sGnRH (ED50, 128 +/- 74 nM) and cGnRH-II (ED50, 157 +/- 67 nM). The degree of inhibition was higher in sexually regressed fish compared to postspawning fish. [D-p-Glu1,D-Phe2,D-Trp3,6]mGnRH suppressed both sGnRH- and cGnRH-II-induced GTH-II release with ED50 values of 326 +/- 96 and 249 +/- 74 nM, respectively. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH inhibited sGnRH and cGnRH-II stimulated GTH-II release, but stimulated GH release. On the other hand, [Ac-D(2)-Nal1,4Cl-D-Phe2,D-(3)Pal3,6,Arg5,D-A la10]mGnRH weakly stimulated GTH-II release, but strongly inhibited basal GH release. These results indicate that [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mGnRH has clear antagonistic activity on sGnRH and cGnRH-II stimulation of GTH-II and GH release in vitro. The differential actions of a few GnRH analogs on GTH-II and GH release indicate that the properties of the GnRH receptors on GTH and GH cells may be different. The amino acid in position 6 plays an important role in determining the nature of intrinsic activity of GnRH peptides, and substitution of D-Arg6 normally produces agonistic analogs.

Characterization of D1 receptors mediating dopamine-stimulated growth hormone release from pituitary cells of the goldfish, Carassius auratus

Previously, we demonstrated that dopamine (DA) stimulates GH release from the pituitary of goldfish, and this action is mediated by D1-like receptors. In the current study, we have provided evidence for the presence of D1-specific binding sites in the pituitary cells of goldfish. These D1-binding sites were found to be saturable, stereospecific, and selective for D1 ligands. The rank order of binding affinity of these D1-binding sites is (+)SCH23390 > SKF83566 >> (-)SCH23390 > domperidone > LY171555 >> serotonin. The association of these D1-binding sites with [3H]SCH23390, a D1-specific radioligand, was rapid, reversible, and exhibited a high binding affinity in the nanomolar range. The Kd values were estimated to be 33.7 +/- 8.5 nM for mixed populations of pituitary cells and 10.9 +/- 2.5 nM for pituitary cell preparations enriched with somatotrophs. Autoradiographic studies revealed that specific binding of [3H]SCH23390 was predominantly localized in the pars distalis, not in the neurointermediate lobe of the goldfish pituitary. Furthermore, these D1-binding sites in the goldfish pituitary cells could be functionally correlated with the GH-releasing actions of DA. Since these D1-binding sites exhibited the expected pharmacological properties of mammalian D1 receptors, we conclude that DA D1 receptors are present in the goldfish pituitary and are responsible for the mediation of DA D1-stimulated GH release. The apparent similarities of the D1 receptor pharmacology between goldfish and mammals also suggests that DA D1 receptors are highly conserved during vertebrate evolution.

GABA stimulation of gonadotropin-II release in goldfish: involvement of GABAA receptors, dopamine, and sex steroids

The involvement of gamma-aminobutyric acid (GABA) in regulation of pituitary gonadotropin-II (GTH-II) release was studied in the goldfish. Intraperitoneal injection of GABA (300 micrograms/g) stimulated an increase in serum GTH-II levels at 30 min postinjection. The GABAA receptor agonist muscimol (0.1-10 micrograms/g) stimulated GTH-II in a dose-dependent manner. Baclofen, a GABAB receptor agonist, had a small but significant stimulatory effect at 1 and 10 micrograms/g; the amount of GTH-II released in response to baclofen was significantly less (P < 0.05) than that released by muscimol. Pretreatment of goldfish with bicuculline, a GABAA receptor antagonist, but not saclofen, a GABAB receptor antagonist, blocked the stimulatory effect of GABA on serum GTH-II. Elevation of brain and pituitary GABA levels with the GABA transaminase inhibitor, gamma-vinyl-GABA (GVG), decreased hypothalamic and pituitary dopamine (DA) turnover rates, indicating that GABA may stimulate GTH-II release in the goldfish by decreasing dopaminergic inhibition of GTH-II release. The release of GTH-II stimulated by muscimol and GVG was potentiated by pharmacological agents that decrease inhibitory dopaminergic tone, indicating that DA may also inhibit GABA-stimulated GTH-II release. Based on the linear 24-h accumulation of GABA in brain and pituitary after GVG injection, implantation of testosterone, estradiol, or progesterone, previously shown to regulate the serum GTH-II release response to gonadotropin-releasing hormone and GABA, was also found to modulate GABA synthesis in the brain and pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)