Browsing by Author "B. Senthilkumaran"

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A Turnover Study of Hypothalamic Monoamine Oxidase (MAO) and Effects of MAO Inhibition on Gonadotropin Secretion in the Female Catfish, Heteropneustes fossilis
(1995) B. Senthilkumaran; K.P. Joy
In the present study, the rate constants of degradation (k) and synthesis (S) and half-life of hypothalamic monoamine oxidase were determined to explain annual variations and biphasic effects of the enzyme to low and high doses of estradiol-17β (E2) in 3-week ovariectomized Heteropneustes fossilis . In the preparatory phase, the half-life (t1/2) of the enzyme was the longest (21.16 days) with low k (0.03275 days-1) and S (0.000845 Units/day) values, suggesting a low turnover of the enzyme. In the prespawning phase the t1/2 was the shortest (11.65 days) with high k (0.0595 days-1) and S (0.011 Units/day) values. The low and high turnovers of the enzyme, respectively, in these two seasons could be correlated to low and high profiles of plasma E2 levels. In the resting phase, the values were in between (t1/2 = 18.83 days, k = 0.0368 days-1, S = 0.00211 Units/day) but the plasma E2 level was undetectable. Three weeks of ovariectomy increased the t1/2 (19.04 days) compared to that of the control (11.61 days) with decreases in both k and S values. The administration of a low dose of E2 (0.1 μg/g BW) further increased the t1/2 (19.63 days) over that of the ovariectomized fish with a significant rise in the S value. However, a high dose of E2 (1.0 μg/g BW) decreased it (13.33 days) by reducing the S and elevating the k values. These results suggest that the stimulatory effect of low doses of E2 on the enzyme activity is produced by elevating its synthesis rate and the inhibitory effect of high doses of E2 by simultaneously decreasing the synthesis and increasing the degradation rates of the enzyme. The administration of a single dose (75 mg/kg BW) of pargyline has elevated plasma gonadotropin (GTH) level after 3 and 6 hr and 7 days in the sham-ovariectomized (control), ovariectomized, and ovariectomized low-E2-dose groups; the peak increase was found at 6 hr. On the contrary, in the ovariectomized high-E2 group the GTH level was inhibited at 3 and 6 hr postinjection. These changes in the GTH level could be correlated with changes in the profiles of hypothalamic monoamines. The data show that E2 exerts its feedback regulation of GTH by modifying monoaminergic activity at the level of oxidative deamination. © 1995 by Academic Press, Inc.
Annual and diurnal variations in, and effects of altered photoperiod and temperature, ovariectomy, and estradiol-17β replacement on catechol-O-methyltransferase level in brain regions of the catfish, Heteropneustes fossilis
(1998) K.P. Joy; B. Senthilkumaran
The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 μg/g doses of E2, and none at week 2 and 5 of OVX and after 0.5 and 1 μg/g doses of E2. The season specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.
Annual cyclic, and castration and cyproterone acetate-induced, changes in sialic acid content of the seminal vesicle of the catfish, Heteropneustes fossilis (Bloch)
(Kluwer Academic Publishers, 1993) B. Senthilkumaran; K.P. Joy
In this study, the presence of sialic acid is demonstrated in the seminal vesicle (SV) of Heteropneustes fossilis. Sialic acid levels show an annual variation that was correlated with the secretory activity of the SV (expressed as the SV somatic index (SV-SI)) with the index being lowest in resting phase (January) and highest in spawning phase (July). Sialic acid was not detectable from November to March (resting to mid-preparatory phases). Castration (3 weeks) induced a significant rise in both SV-SI and SV sialic acid content possibly due to an elevated local production of androgens under the influence of increased gonadotropin secretion. Cyproterone acetate treatment caused a significant decrease in both SV-SI and SV sialic acid content. The results suggest that secretion of sialic acid in the SV is influenced by androgens and its measurement can be used as a simple and reliable index for quantitative assessment of the functional testicular state. © 1993 Kugler Publications.
Annual Variations in Hypothalamic Serotonin and Monoamine Oxidase in the Catfish Heteropneustes fossilis with a Note on Brain Regional Differences of Day-Night Variations in Gonadal Preparatory Phase
(1993) B. Senthilkumaran; K.P. Joy
In Heteropneustes fossilis, significant annual variations in serotonin (5-HT) and monoamine oxidase (MAO) were found in the hypothalamus both at 12 and 24 hr with high values of content and turnover index (TI) during gonadal recrudescence, and low values during gonadal quiescence. The 5-HT content reached high levels during April-July (late preparatory, prespawning, and spawning phases). The TI of 5-HT showed two peaks in its midday value: a major peak occurred in March (midpreparatory phase) and a minor one in June (prespawning phase). High MAO activity was seen in June (prespawning phase) and low values during February, March, and April (preparatory phase). Significant day-night variations in 5-HT content and TI, and MAO activity were observed in the hypothalamus and telencephalon in February and March (early and midpreparatory phase), but not at other times of the year. In the whole brain and separate regions such as the thalamus, midbrain, and hindbrain no day-night patterns were seen. A comparison of the data shows that the increase in 5-HT content and TI from February to March was significantly higher in the hypothalamus than in telencephalon and the opposite is true for MAO. The results suggest that the high hypothalamic activities of 5-HT and MAO during recrudescence is related to breeding activity; the day-night variations during the early and midpreparatory phase in these variables may be related to initiation of breeding in this species. © 1993 by Academic Press, Inc.
Changes in Hypothalamic Catecholamines, Dopamine-β-hydroxylase, and Phenylethanolamine-N-methyltransferase in the Catfish Heteropneustes fossilis in Relation to Season, Raised Photoperiod and Temperature, Ovariectomy, and Estradiol-17β Replacement
(1995) B. Senthilkumaran; K.P. Joy
In Heteropneustes fossilis, contents and turnovers of hypothalamic catecholamines (CA) and activities of dopamine-β-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) showed significant seasonal variations with significantly high day values. The seasonal pattern of dopamine (DA) on one hand and that of noradrenaline (NA) and adrenaline (A) on the other hand showed an inverse relationship, the former decreasing and the latter increasing during the progress of gonadal recrudescence. The DBH and PNMT levels were low in the resting phase and increased to the peak in the prespawning (DBH) and spawning (PNMT) phases. Maintenance of the fish under long photoperiods (16L:8D) and high temperature (28 ± 2°) stimulated the NA and A, and DBH and PNMT activities, and suppressed the DA mechanism, the changes being maximal in the raised temperature groups. In the resting phase (December), ovariectomy (OVX) or estradiol-17β, (E2) replacement in 4-week ovariectomized fish did not produce any significant effects on the CA and enzyme activities. On the contrary, in the prespawning phase (May), OVX produced differential and biphasic responses on CA and the enzymes. The contents and turnovers of both NA and A increased significantly at 2-5 weeks and decreased in the sixth week. However, the reverse was true for DA. The DBH and PNMT activities (assayed only 3, 4, and 6 weeks after OVX) were elevated significantly in the third and fourth weeks but decreased in the sixth week. Plasma levels of gonadotropin (GTH) increased significantly at all durations of OVX in a bimodal pattern while the E2 levels decreased consistently. Supplementation with a low dose (0.1 μg/g BW) or E2 restored the NA and A and enzyme activities while the higher doses (0.5, 1.0, and 5.0 μg/g BW) depleted them. The reverse was true for DA. The low dose of E2 restored the GTH level while the higher ones inhibited it significantly. These results indicate that both environmental photoperiod and temperature and E2-negative feedback act on the CA to modulate GTH secretion. © 1995 by Academic Press, Inc.
Circadian Aspect of Photoperiodic Time Measurement in a Female House Sparrow, Passer domesticus
(1995) G. Ravikumar; B. Senthilkumaran; P.D. Tewary; A.K. Goel
Endogenous circadian rhythms are involved in various photoperiodic responses of birds. Investigations involving the mechanisms of photoperiodic time measurement in birds have been confined mainly to temperate zone species using males exclusively. Due to the paucity of experimental evidence on sub tropical birds that have very wide distribution, the present study was performed using subtropical female house sparrows. Photoperiodic sparrows were sub jected to various T cycles for 60 days in which a fixed 3-h photophase was combined with scotophase in cycles of 20-30 h duration. Simultaneously, two groups of birds were also exposed to short days (light:dark = 8L:16D) or long days (15L:9D) as controls. Significant ovarian growth was found only in cycles of 3L:17D, 3L:23D, 3L:25D, and 3L:27D as well as in 15L:9D, whereas no positive response was detected in 3L:19D, 3L:21D, and 8L:16D. Plasma levels of estradiol showed a close relation to ovarian growth. The results indicate that photoperio dic time measurement in house sparrows involves an endogenous circadian rhythm. © 1995, Sage Publications. All rights reserved.
Effects of administration of some monoamine-synthesis blockers and precursors on ovariectomy-induced rise in plasma gonadotropin II in the catfish Heteropneustes fossilis
(Academic Press Inc., 1996) B. Senthilkumaran; K.P. Joy
In the present study, effects of three daily ip injections of some monoamine (MA)-synthesis blockers and precursors on plasma gonadotropin (GTH- II) levels were investigated in 3-week ovariectomized catfish, and the effects were correlated with changes in hypothalamic MA contents. Administration of α-methylparatyrosine (α-MPT; 250 μg/g BW, a tyrosine hydroxylase inhibitor) significantly decreased the ovariectomy-induced rise in GTH-II compared to that of the sham control group. Injection of L- dihydroxyphenylalanine (10 μg/g BW) in the α-MPT-treated fish elevated the GTH-II level significantly over that of the sham control group but not to the level of the ovariectomized fish. Administration of noradrenaline (NA; 5 μg/g BW) in combination with α-MPT counteracted the effect of the latter and maintained the plasma GTH-II level at that of the ovariectomized fish. Plasma GTH-II level was decreased significantly in the diethyldithiocarbamate (10 μg/g BW, a dopamine-β-hydroxylase inhibitor)-injected fish compared to that of the sham and ovariectomized control groups. Administration of para- chlorophenylalanine (p-CPA; 100 μg/g BW, a tryptophan hydroxylase inhibitor) decreased the GTH-II level significantly compared to that of the ovariectomized group. Supplementation of 5-hydroxytryptophan (20 μg/g BW) with p-CPA nullified the latter's effect and maintained the GTH-II level at that of the ovariectomized fish. The administration of both p-CPA and α-MPT significantly reduced plasma GTH-II to the lowest mark compared to that of the sham, ovariectomized, and all other treatment groups. These results clearly show that the ovariectomy-induced rise in GTH-II was mediated through simultaneous activation of hypothalamic serotonergic and NA-ergic and suppression of dopaminergic mechanisms.
Effects of melatonin, p-chlorophenylalanine, and α-methylparatyrosine on plasma gonadotropin level and ovarian activity in the catfish, Heteropneustes fossilis: A study correlating changes in hypothalamic monoamines
(Kluwer Academic Publishers, 1995) B. Senthilkumaran; K.P. Joy
The effects of (ip, 10 injections over 20 days) of melatonin (75 μg 100 g-1 BW), the serotonin (5-HT)-synthesis blocker, para-cholorophenylalanine (p-CPA, 10 mg 100g-1 BW) and the catecholamine-synthesis blocker, α-methylparatyrosine (α-MPT, 10 mg 100 g-1 BW) on gonadotropin (GTH) secretion and ovarian activity were studied in Heteropneustes fossilis during late preparatory to early prespawning (April-May). The treatments resulted in significant reductions of plasma GTH and estradiol-17β levels, the gonadosomatic index, frequency distribution of vitellogenic and postvitellogenic oocytes, and ovarian and serum 32p-labelled alkali-labile phosphoprotein (a marker of vitellogenic activity). Most of the oocytes were nonvitellogenic or had undergone atretic changes. The hepatic 32-phosphoprotein content increased significantly over the saline control value. The effects were similar and pronounced in the p-CPA and melatonin-treated groups but were moderate in the α-MPT-treated group. Hypothalamic 5-HT content and turnover were significantly inhibited in the p-CPA and melatonin-treated groups but the content and turnover of catecholamines were not. The α-MPT treatment decreased significantly the content and turnover of dopamine (DA), noradrenaline (NA), and adrenaline (A) but did not influence the 5-HT content or turnover. These results suggest that 5-HT, NA and A are stimulatory to GTH secretion and that melatonin may act on the serotonergic system to inhibit the pituitary-gonadal axis. © 1995 Kugler Publications.
Effects of ovariectomy and oestradiol replacement on hypothalamic serotonergic and monoamine oxidase activity in the catfish, Heteropneustes fossilis: A study correlating plasma oestradiol and gonadotrophin levels
(BioScientifica Ltd., 1994) B. Senthilkumaran; K.P. Joy
Hypothalamic serotonin (5-HT; content and turnover) and monoamine oxidase (MAO) activity were measured in female catfish, Heteropneustes fossilis, after ovariectomy and supplementation with oestradiol-17β (OE2) in the recrudescent and quiescent phases. These factors were correlated with changes in plasma levels of OE2 and gonadotrophin. In the quiescent phase (December), neither ovariectomy nor OE2 supplementation had any significant effect on 5-HT content and MAO activity. Plasma levels of OE2 and gonadotrophin were undetectable in both control and treated fish, indicating that there was no feedback effect. In the recrudescent phase (prespawning, May), ovariectomy caused biphasic responses of MAO activity and 5-HT content. The enzyme activity decreased significantly after 2, 3, 4 and 5 weeks but increased significantly 6 weeks after ovariectomy. The 5-HT content varied in a biphasic manner with a significant increase at 2, 3 or 4 weeks and a significant decrease in week 6; there being no effect in week 5. 5-HT turnover was inhibited significantly only in week 4 after ovariectomy and did not show a biphasic pattern. In the ovariectomized groups, the OE2 level decreased significantly in a progressive manner with a maximum reduction in week 6. The plasma level of gonadotrophin showed a significant bimodal pattern of increase with the peak in week 4 after ovariectomy, indicating a strong negative feedback effect of OE2. The bimodal pattern of pituitary gonadotrophin release could be correlated with a similar pattern of increase in 5-HT content. OE2 treatment of fish which had been ovariectomized 3 weeks previously had dose-dependent effects on the enzyme; the low dose (0.1 μg/g body weight) was stimulatory and the higher doses (0.5, 1.0 and 5.0 μg/g body weight) were inhibitory. The reverse was true for 5-HT content. Serotonergic turnover increased significantly only in the groups given high doses (1.0 and 5.0 μg/g body weight). The low dose of OE2 (0.1 μg/g body weight) restored the gonadotrophin and OE2 levels to those of the sham-ovariectomized vehicle-treated control group, whereas the high doses (0.5, 1.0 and 5.0 μg/g body weight) decreased the release of gonadotrophin in a dose-dependent manner. Our results suggest that OE2 modulates MAO activity to alter hypothalamic 5-HT in a seasonally dependent manner. The ovariectomy-induced changes in plasma levels of gonadotrophin appear to be mediated, at least partly, by the feedback action of OE2 on 5-HT metabolism.
Effects of photoperiod alterations on day-night variations in hypothalamic serotonin content and turnover, and monoamine oxidase activity in the female catfish, Heteropneustes fossilis (Bloch)
(Kluwer Academic Publishers, 1994) B. Senthilkumaran; K.P. Joy
The effects of different photoperiod regimes, and total darkness on day-night variations in hypothalamic serotonin (5-HT) content and turnover index (TI), and monoamine oxidase (MAO) activity that occur exclusively during the gonadal preparatory phase (February-March) were investigated in female Heteropneustes fossilis. Exposure of the fish to long photoperiods (16L:8D; light between 06.00-22.00h, for 40 days elevated both the midphotophase and midscotophase values of 5-HT content and MAO, and abolished their day-night differences. The daily variations of 5-HT-TI was further intensified by the treatment. Under short photoperiods (4L:20D; light between 18.00-22.00h for 40 days), there was a significant decrease in both 5-HT content and TI, a reversal of the day-night variations of 5-HT content and MAO activity, and loss of the 5-HT-TI pattern. In fish maintained in total darkness the day-night variations were not found and there was a significant inhibition of 5-HT. Exposure of the fish to continuous light abolished the day-night variations of these correlates and elevated their values at both intervals. When the LD cycle was reversed, there was a corresponding shift in the day-night patterns. The gonadosomatic index (GSI) was significantly elevated in the long photoperiod and continuous illumination groups, significantly decreased in the short photoperiod and total darkness groups, and unchanged in the reversed LD cycle regime. The results indicate that the day-night variations of 5-HT and MAO are photoperiod-dependent and are controlled by the prevailing LD cycle during the gonadal preparatory phase of the annual reproductive cycle. The photoperiod effects on the gonadal activity may be mediated through the hypothalamic serotonergic system. © 1994 Kugler Publications.
Expression profile of kisspeptin2 and gonadotropin-releasing hormone2 mRNA during photo-thermal and melatonin treatments in the female air-breathing catfish Heteropneustes fossilis
(Springer Science and Business Media B.V., 2020) R. Chaube; S. Sharma; B. Senthilkumaran; S.G. Bhat; K.P. Joy
In seasonally breeding vertebrates, extrinsic factors like photoperiod and temperature are major determinants, controlling the annual reproductive cycle. In teleosts, kisspeptin, which occurs in two molecular forms: kisspeptin1 (Kiss1) and kisspetin2 (Kiss2), has been reported to alter gonadotropin (Lh and Fsh) secretion but its effect on gonadotropin-releasing hormone (Gnrh) secretion is not unequivocally proved. In the catfish Heteropneustes fossilis, we isolated and characterized kiss2 and gnrh2 cDNAs and the present work reports effects of altered photo-thermal conditions and melatonin (MT, a pineal hormone) on their expressions in the brain. The exposure of the catfish to long photoperiod (LP, 16 h light) at normal temperature (NT) or high temperature (HT, 28 °C) at normal photoperiod (NP) for 14 or 28 days stimulated both kiss2 and gnrh2 expression in both gonad resting and preparatory phases with the combination of LP + HT eliciting maximal effects. Short photoperiod (SP, 8 h light) under NT or HT altered the gene expression according to the reproductive phase and temperature. MT that mediates photo-thermal signals to the brain inhibited brain kiss2 and gnrh2 gene expression in the NP + HT, LP + NT, and SP + NT groups. The altered photo-thermal conditions elicited changes in steroidogenic pathway as evident from changes in plasma E2, progesterone, and testosterone levels. The results show that brain kiss2-gnrh2 signaling is involved in photo-thermal-mediated mechanisms controlling reproduction. © 2020, Springer Nature B.V.
Identification of kisspeptin2 cDNA in the catfish Heteropneustes fossilis: Expression profile, in situ localization and steroid modulation
(Academic Press Inc., 2020) R. Chaube; S. Sharma; B. Senthilkumaran; S.G. Bhat; K.P. Joy
Kisspeptin (Kiss) is considered an upstream regulator of gonadotropin-releasing hormone in mammals but its role in non-mammalian vertebrates is not unequivocally established. In the catfish Heteropneustes fossilis, a 605 bp long cDNA was identified from the brain by cloning as well as by retrieving from the catfish transcriptome database. The open reading frame (ORF, 93–405 bp) codes for a 113 amino acids long precursor protein. Homology and phylogenetic analyses showed that the predicted protein belongs to the vertebrate Kiss2 type with a high degree of conservation in the Kiss2-10 region (FNFNPFGLRF). The kiss2 transcripts were expressed highly in the brain and gonads in a dimorphic manner with a female bias. In the brain, kiss2 transcripts showed regional differences with higher expression in the medulla oblongata and forebrain regions. The kiss2 transcripts showed significant seasonal variations with the highest expression in the brain in spawning phase and in the gonads in prespawning phase. The kiss2 transcripts were localized in the brain (nucleus preopticus, habenular nucleus, nucleus recessus posterioris, nucleus recessus lateralis) and stratum periventriculare (radial glial cells) of optic tectum, pituitary and ovary (follicular layer and germinal vesicle). Ovariectomy (1, 2, 3 and 4 weeks) decreased brain kiss2 mRNA levels and a single injection of estradiol-17β (E2; 0.5 μg/g body weight) in 3- week ovariectomized (OVX) and sham operated fish resulted in an increase in the transcript levels after 24 h. The E2 receptor antagonist Tamoxifen (TMX) produced biphasic effects on the kiss2 expression in the dose- response study. TMX inhibited the expression in the OVX fish, but elicited a stimulatory effect in the OVX + E2-treated fish. Testosterone (T) decreased, and progesterone (P4) inhibited (resting phase) or stimulated (prespawning phase) the transcript level in 3-week OVX fish. In the 3-week sham groups, E2 increased, and TMX, T and P4 inhibited the kiss2 transcript levels. The results suggest that Kiss2 is an important regulator of the brain- pituitary- gonadal- endocrine axis, and in habenular and optic tectum functions. © 2020 Elsevier Inc.
Kisspeptins stimulate the hypothalamus - pituitary - ovarian axis and induce final oocyte maturation and ovulation in female stinging catfish (Heteropneustes fossilis): Evidence from in vivo and in vitro studies
(Elsevier B.V., 2022) R. Chaube; S. Sharma; B. Senthilkumaran; S.G. Bhat; K.P. Joy
In the present study, effects of synthetic human Kisspeptin1 (hKiss1) and catfish Kisspeptin2 (cfKiss2) on the hypothalamic - pituitary - ovarian (HPO) axis, and induction of final oocyte maturation and ovulation were investigated in prespawning female stinging catfish (Heteropneustes fossilis) under in vivo and in vitro conditions. Gene expression was quantified by real time quantitative PCR and steroids were measured by specific enzyme-linked immunoassays. Intraperitoneal (ip) injections (1, 2, 3 ng/g body weight, BW) of synthetic hKiss1 and cfKiss2 stimulated hypothalamic, pituitary and ovarian gnrh1 and gnrh2 expression at 24 h and the effect was higher after the cfKiss2 treatment. In vitro incubation of hypothalamus, pituitary and ovary pieces with the Kiss peptides (5, 10, 20 nM) produced a similar effect. GPR54 (Kiss1 receptor) antagonist peptide234, when given ip (5, 10, 20 ng/g BW) or incubated in vitro (5, 10, 20 nM), inhibited the gnrh1 and gnrh2 expression at 24 h. The supplementation with hKiss1 or cfKiss2 restored the inhibition due to peptide234 in vivo and in vitro and the effect was higher in the cfKiss2 combination group. Both hKiss1 and cfKiss2 altered the expression of pituitary gonadotropin (Gth) subunit genes follicle-stimulating hormone β (fshβ), luteinizing hormone β (lhβ) and glycoprotein α (gpα) in vivo and in vitro. The expression of fshβ was more sensitive to the treatments than lhβ expression and the effect was greater in the cfKiss2 groups. Peptide234 in vivo and in vitro inhibited the expression of the Gth genes and the effect was reversed and restored in the hKiss1 and cfKiss2 combination groups. The Kiss peptide treatments in vivo or in vitro stimulated both plasma and ovarian levels of estradiol-17β, progesterone and 17,20β-dihydoxy-4-pregnen-3-one levels. The peptide234 treatment inhibited, or elicited a decreasing trend on the steroid levels both in vivo and in vitro, and the inhibition was reversed by the hKiss1 and cfKiss2 combination treatments. Incubation of post vitellogenic follicles with hKiss1 or cfKiss2 stimulated germinal vesicle breakdown (GVBD) and ovulation. The inhibition due to peptide234 was reversed in the combination groups. Ovulation was not elicited or unaffected in the peptide234 treated groups. The data show that the Kiss peptides act downstream the HPO axis to stimulate oocyte maturation and ovulation, and cfKiss2 peptide is functionally more effective than hKiss1. © 2021 Elsevier B.V.
Methallibure-induced inhibition of hypothalamo-hypophyseal-ovarian activity in the catfish Heteropneustes fossilis involves changes in hypothalamic monoamine activity
(Springer Netherlands, 1998) B. Senthilkumaran; K.P. Joy
Administration of Methallibure, a non-steroidal gonadotropin (GTH) inhibitor 20 μg g-1 body weight; i.p., daily for 10 days, to prespawning phase female Heteropneustes fossilis inhibited the brain-pituitary-ovarian axis as indicated by significant reductions in plasma and pituitary levels of GTH-II, and plasma levels of 17β-estradiol (E2) and testosterone. Concurrently, the treatment resulted in significant reductions in the hypothalamic content of serotonin, noradrenaline (and adrenaline) that stimulate, and a significant elevation of dopamine that inhibits GTH-II release in this species. Activities of the monoamine degrading enzymes, monoamine oxidase and catechol-O-methyltransferase were significantly increased, while that of the synthesizing enzymes, dopamineβ-hydroxylase and phenylethanolamine-N-methyltransferase were significantly decreased. These results suggest that the mechanism of inhibition of GTH-II secretion includes, among others, differential actions of the drug on hypothalamic monoamine metabolism.
Molecular cloning and characterization of a gonadotropin-releasing hormone 2 precursor cDNA in the catfish Heteropneustes fossilis: Expression profile and regulation by ovarian steroids
(Academic Press Inc., 2019) R. Chaube; A. Rawat; S. Sharma; B. Senthilkumaran; S.G. Bhat; K.P. Joy
Gonadotropin-releasing hormone 2 (Gnrh2) is one of the three classes of Gnrh distributed in vertebrates and is highly conserved. In the present study, the cDNA encoding Gnrh2 was isolated and characterized in the ostariophysan catfish Heteropneustes fossilis (hf). The cDNA is 611 bp long with an open reading frame (ORF) of 261 bp that encodes a highly conserved protein of 86 amino acids. The deduced Gnrh2 precursor protein clustered with the vertebrate Gnrh2 type. The sequence identity of hfgnrh2 is 94% with African catfish (Clarias gariepinus) gnrh2 mRNA (accession no. X78047). The hfgnrh2 transcripts were expressed only in the brain and gonads with a higher expression in the female brain and ovary in both resting and prespawning phases. The expression was higher in the prespawning phase than the resting phase. The gnrh2 expression in the brain and ovary showed significant seasonal variations but with opposite patterns. In the brain, the expression was the highest in the preparatory phase, decreased progressively to low levels in the postspawning and resting phases. In the ovary, the transcript level was low in the resting and preparatory phases, increased sharply in the prespawning phase reaching the peak level in the spawning phase and declined sharply in the postspawning phase. The gnrh2 mRNA showed the highest expression in the hind brain-medulla oblongata and moderate to low expression in forebrain regions and pituitary. Ovariectomy resulted in a duration-dependent inhibition of hfgnrh2 mRNA levels in the resting and prespawning phases. Steroid (E2, testosterone and progesterone) replacement treatments (0.5 μg/g body weight) in the 3- week ovariectomized fish restored the inhibition due to ovariectomy, elevated the expression over and above the sham level in the resting phase (E2 group), and raised the levels almost to that of the sham group (testosterone and progesterone groups) in the prespawning phase. In the sham control groups, the steroid replacement resulted in a significant reduction in the mRNA levels. The expression of the gnrh2 mRNA in the brain-pituitary-gonadal axis and its regulation by gonadal steroids suggest that Gnrh2 may have a reproductive role in the catfish. © 2019 Elsevier Inc.
Periovulatory changes in catfish ovarian oestradiol-17β, oestrogen-2-hydroxylase and catechol-O-methyltransferase during GnRH analogue-induced ovulation and in vitro induction of oocyte maturation by catecholoestrogens
(2001) B. Senthilkumaran; K.P. Joy
In the catfish Heteropneustes fossilis and Clarias batrachus, ovarian oestrogen-2-hydroxylase (OE-2-H) activity increased significantly at 8 h after the injection of an ovulatory dose (0.15 μg/g body weight) of a mammalian GnRH analogue ([D-Ala6-Pro9]-LHRH ethylamide) and was restored to the 0 h (control) level after egg-stripping at 16 h. On the other hand, ovarian oestradiol-17β (OE2) level and catechol-O-methyltransferase (COMT) activity decreased significantly at 8 h. While the OE2 level was restored to the 0 h level, COMT activity increased significantly at 16 h. Changes in ovarian OE2 level and enzymes indicate higher synthesis of 2-hydroxylated catecholoestrogens and their degradation during the peri-ovulatory period. Under in vitro conditions, the synthetic catecholoestrogens (CEs, 2- and 4-hydroxylated oestradiol-17β and oestrone (OE1)) induced germinal vesicle break down (GVBD) in a dose- (0.01-10 μg/ml) and duration-(1-36 h) dependent manner, the mean values of the responses being in the order 2-OH OE2>4-OH OE2> 2-OH OE1>4-OH OE1. The CE-induced GVBD response (8 h induction) was not blocked by prior and subsequent incubations with steroid synthesis inhibitors (cyanoketone, epostane and aminoglutethimide) up to 36 h, suggesting that de novo steroidogenesis is not essential for the response. The percentage of GVBD response to 2-h induction by CEs was significantly inhibited by actinomycin D (a transcriptional inhibitor) and cyclo-heximide (a translational inhibitor), indicating the involvement of both RNA and protein synthesis. The CE-induced 8-h stimulation of GVBD was mildly blocked by propranolol, the β-adrenergic inhibitor, suggesting the response was partly mediated through a β-adrenergic receptor mechanism. Incubations with phentolamine, an α-adrenergic inhibitor, did not interfere with the CE-induced GVBD response. The results demonstrate CE-related enzymatic changes in teleost (catfish) ovaries and maturation-inducing substance activity of CEs.
Periovulatory changes in hypothalamic and pituitary monoamines following GnRH analogue treatment in the catfish Heteropneustes fossilis: A study correlating changes in plasma hormone profiles
(1998) K.P. Joy; B. Senthilkumaran; C.C. Sudhakumari
In Heteropneustes fossilis, administration of a single dose (0.15 μg/g body weight, i.p.) of [D-Ala6,Gly10]-gonadotrophin-releasing hormone analogue (GnRHa) induced ovulation (in 35 of 35 fish) when wild-stripped at 16 h. Plasma gonadotrophin II (GTH II) levels showed a highly significant increase at 2, 4, 8, 12 and 16 h with the peak at 8 h. Plasma cortisol, progesterone and testosterone showed significant elevations at 2, 4, 8 and 12 h with peaks at 8 h (cortisol and testosterone) and 4 h (progesterone). The levels declined to control values at 16 and 48 h except that of testosterone which decreased even further. In contrast, plasma levels of oestradiol-17β decreased significantly at 2, 4, 8 and 12 h, with the lowest value at 8 h, but increased at 16 and 18 h. The contents of hypothalamic and pituitary serotonin and noradrenaline increased at 8 h, coinciding with the peak GTH II rise, and decreased at 16 h. In contrast, dopamine content declined at 8 h in both the hypothalamus and pituitary, but increased at 16 h only in the hypothalamus. The hypothalamic adrenaline level decreased at 8 h but increased significantly at 16 h. Hypothalamic levels of monoamine oxidase, catechol O-methyltransferase and dopamine β-hydroxylase were elevated significantly at 8 h; the dopamine β-hydroxylase activity decreased at 16 h. Phenylethanolamine N-methyltransferase activity was elevated only at 16 h, coinciding with the rise in adrenaline content. It is inferred that the preovulatory decreased in dopamine content concomitant with rises in serotonin and noradrenaline levels, triggered by the low titre of oestradiol, might have potentiated the GnRHa/GnRH (endogenous)-induced release of GTH II for a prolonged period.
Pituitary-gonadal relationship in the catfish Clarias batrachus (L): A study correlating gonadotrophin-II and sex steroid dynamics
(Zoological Society of Japan, 2000) K.P. Joy; M.S. Singh; B. Senthilkumaran; H.J.Th. Goos
A heterologous radioimmunoassay was developed for measuring gonadotrophin-II (GTH-II) in the catfish Clarias batrachus. Serum and/or pituitary levels of GTH-II showed significant annual/seasonal variations in male and female catfish, which could be correlated with both gonadosomatic index and/or serum testosterone level. GTH-II was not detected in resting phase, increased during gonadal recrudescence to peak values in late prespawning /spawning phases, and declined to low values in postspawning phase. During gonadal recrudescence, the pituitary and serum levels of GTH-II maintained positive or inverse relationships implying differential rates of hormone release and synthesis/storage. Gonadectomy resulted in increased release of GTH-II; the release pattern varied in females and hemi-castrated or completely castrated males. In females, the GTH-II increase followed a distinct biphasic pattern with the peak rise at week 4 of ovariectomy. In males, castration resulted in significant rise of serum GTH-II levels at all duration except week 5, but the magnitude of the rise was higher in completely castrated fish (weeks 1, 2 and 3). Testosterone replacement in 3-week hemi-castrated fish restored the GTH-II level to that of the sham control vehicle group. In intact fish, administration of testosterone elicited an increase in serum GTH-II levels in the low dose (0.25 and 0.5 μg / g BW) groups and no change in the high dose (1.0 μg / g BW) group. Methallibure treatment inhibited GTH-II levels in a dose-dependent manner. The reduction was greater in males. Withdrawal of the drug treatment restored the GTH-II and testosterone levels after 15 days in the low dose group (2 μg / g BW). The results indicate that there exists a dynamic positive or negative feedback relationship between gonadal steroids and GTH-II, which is essential to control the release and availability of circulating GTH-II.
Seasonal changes in adrenal and gonadal activity in the quail, Perdicula asiatica: Involvement of the pineal gland
(Elsevier Inc., 2001) C.C. Sudhakumari; C. Haldar; B. Senthilkumaran
The present study assessed annual adrenal gland activity in the Indian tropical Jungle bush quail, Perdicula asiatica. We also elucidated the role of the annual variations in gonadal steroids and melatonin in the regulation of its activity. Increasing day length (photoperiod), ambient temperature and rainfall are positively correlated with adrenal and gonadal functions, and inversely related to pineal gland activity. Pineal, adrenal and gonadal weights showed cyclical patterns relative to environmental factors, which were also correlated with plasma melatonin, corticosterone and gonadal steroids, respectively. In both sexes of P. asiatica, pineal gland weight and/or plasma melatonin levels were inversely related to adrenal lipids, (e.g. phospholipids, free and esterified cholesterol) and plasma corticosterone levels. Melatonin levels also showed an inverse relationship with plasma testosterone and estradiol levels. These studies indicate that changes in environmental factors promote annual variations in adrenal and gonadal activity probably by modulating the pineal gland. Melatonin receptors have been localized in the pars tuberalis, adrenal gland and gonads of birds, the pineal gland may, therefore, mediate environmental stimuli indirectly and directly to down regulate adrenal and gonadal activity, which run in parallel in this species. © 2001 Elsevier Science Inc.
Seasonal dynamics in gonadotropin secretion and E2-binding in the catfish Heteropneustes fossilis
(2005) R. Kirubagaran; B. Senthilkumaran; C.C. Sudhakumari; K.P. Joy
In the present investigation, significant annual/seasonal variations were noticed in plasma and pituitary gonadotropin (GTH) which were correlated with gonado-somatic index, plasma estradiol-17β, and nuclear E2 receptor (NE2R) in the pituitary, hypothalamus and telencephalon. The NE2R concentrations and dissociation constant (kd) values showed significant seasonal variations with high values in the late preparatory phase and low values in the postspawning phase. The NE2R levels were the highest in the pituitary, followed by the hypothalamus and telencephalon in all the seasons. In the prespawning phase, ovariectomy (OVX) elicited a strong negative feedback on GTH secretion with a bimodal pattern of release and elevated the NE2R levels and kd values, without producing any significant change in the resting phase suggesting that E2 appears to exert differential feedbacks on GTH secretion. © Springer Science+Business Media B.V. 2006.