7 results
Search Results
Now showing 1 - 7 of 7
PublicationArticle Immunocytochemical localization, HPLC characterization, and seasonal dynamics of vasotocin in the brain, blood plasma and gonads of the catfish Heteropneustes fossilis(Academic Press Inc., 2008) V. Singh; K.P. JoyImmunocytochemical distribution and dynamics of vasotocin (VT) were studied in the air-breathing catfish Heteropneustes fossilis in relation to the reproductive cycle. Vasotocin was localized in the brain and ovary by streptavidin-biotin immunocytochemistry. The immunoreactivity was found throughout the hypothalamo-hypophysial neurosecretory system consisting of the magnocellular and parvocellular neurons of the nucleus preopticus, neurosecretory axonal tract and neurohypophysis (NH). The VT neurons showed seasonal changes; they were numerically less in resting phase but increased during the recrudescent phase. The neurons were hypertrophied and degranulated in pre-spawning phase and heavily degranulated and vacuolated in spawning phase. In the NH, the density of VT fibers increased up to the pre-spawning phase and decreased thereafter. In the ovary, VT immunoreactivity was noticed in the follicular layer and varied with the growth of the follicles. Vasotocin was characterized and quantified by a high performance liquid chromatography with UV detection method in the brain, plasma and ovary. Brain and plasma VT concentrations were also assayed with an EIA method, which was more sensitive than the HPLC method with values about 2-fold higher. Vasotocin levels showed significant seasonal and sexual differences with higher concentrations in females in the recrudescent (preparative, pre-spawning and spawning) phase. Brain VT recorded the highest concentration in the preparative phase (both sexes) while plasma (both sexes) and ovarian VT in the spawning phase. The ovarian concentration of VT was 15- and 25-fold higher in the pre-spawning and spawning phases (when expressed per mg protein), respectively, than plasma but lower than brain levels. In testis, VT concentration was relatively low and apparently did not show any significant seasonal variation. The seasonal activity patterns and gonadal distribution of VT indicate a reproductive function of the peptide. © 2008 Elsevier Inc. All rights reserved.PublicationArticle Functional interactions between vasotocin and prostaglandins during final oocyte maturation and ovulation in the catfish Heteropneustes fossilis(Academic Press Inc., 2013) K.P. Joy; V. SinghFunctional interactions between vasotocin (VT) and prostaglandins (PGs) in the regulation of final oocyte maturation (FOM) and ovulation were investigated in the catfish Heteropneustes fossilis. Incubation of post-vitellogenic follicles with VT resulted in significant increases of both PGF2α and PGE2 at 8 and 16h intervals. The rise was higher at 16h except in the 1000nM VT group, in which the PG levels decreased compared to the 100nM group (biphasic effect). VT was more effective to increase the PG levels in comparison to hCG or IT. The co-incubation of the follicles with both hCG (20IU/ml) and VT (100nM) increased significantly PGF2α level at 8h, higher than that elicited by each when incubated alone. Pre-incubation of the follicles with V1 receptor antagonist, alone or in co-incubation with VT, significantly inhibited the VT-stimulated PGF2α and PGE2 levels. Under similar conditions, V2 receptor antagonist did not affect the PGE2 levels. Both VT (100nM) and PGs stimulated FOM (germinal vesicle breakdown) and ovulation in a dose- and duration dependent manner, PGF2α was more effective. Incubation of postvitellogenic follicles with indomethacin (a non selective cyclooxygenase inhibitor) per se did not affect FOM and ovulation but significantly decreased VT and PG effects upon pre-incubation. The results suggest that the VT stimulation of PGs may be mediated mainly through the V1 receptor though the involvement of V2 receptor cannot be excluded. The article also discussed the positive interplay of gonadotropin, maturation-inducing steroid, VT and PG during FOM and ovulation. © 2013.PublicationArticle Relative in vitro seasonal effects of vasotocin and isotocin on ovarian steroid hormone levels in the catfish Heteropneustes fossilis(Academic Press Inc., 2009) V. Singh; K.P. JoyIn the present investigation, catfish (Heteropneustes fossilis) ovarian tissues were incubated in vitro with vasotocin (VT) or isotocin (IT) to demonstrate their effects on estradiol-17β (E2), progesterone (P4), 17α-hydroxy-4-pregnene-3, 20-dione (17-P) and 17α, 20β-hydroxy-4-pregnen-3-one (17, 20β-DP). Parallel incubations with human chorionic gonadotropin (hCG) alone or in combination with VT were used for a comparison. In pre-vitellogenic phase (preparatory phase, GSI-0.48 ± 0.03%), both VT and hCG stimulated E2 significantly, VT in a biphasic manner and hCG in a dose-dependent manner. In pre-spawning (post-vitellogenic, GSI-9.05 ± 0.11%) and spawning (post-vitellogenic, GSI-8.01 ± 0.12%) phases, both hormones decreased E2 levels in a dose- and duration-dependent manner; the VT effect being biphasic in the spawning phase. The co-incubation with VT + hCG stimulated E2 in the preparatory phase but inhibited it in the pre-spawning and spawning phases. The incubations with VT or hCG increased P4 levels in a dose- and duration-dependent manner, the magnitude of the effect was higher in the pre-spawning and spawning phases. The co-incubation with VT + hCG stimulated P4 without any additive effect. The P4 derivatives (17-P and 17, 20β-DP) showed similar changes except 17-P in the spawning phase which decreased at 16 h of the incubation. The incubations with IT produced similar but low responses. In conclusion, like hCG, VT has differential effects on ovarian steroidogenesis and may be involved directly or indirectly in ovarian functions, as a paracrine/autocrine factor or a neurohormone. © 2009 Elsevier Inc.PublicationArticle An in vitro study on catecholamine modulation of ovarian steroidogenic activity in the catfish Heteropneustes fossilis(Academic Press Inc., 2014) K.P. Joy; V. Singh; R. ChaubeIn the present study, α-methylparatyrosine (α-MPT), a tyrosine hydroxylase inhibitor was used to impair ovarian catecholaminergic activity in vitro. The consequent effects on catecholamine (CA) levels were correlated with follicular steroid production. l-dihdroxyphenylalanine (l-DOPA, the precursor of CA) and human gonadotropin (hCG) were supplemented to reverse the effect of α-MPT. The experiments were conducted in two reproductive phases, namely preparatory and pre-spawning phases in female catfish Heteropneustes fossilis. The incubation with α-MPT inhibited ovarian l-DOPA, dopamine (DA), norepinephrine (NE) and epinephrine (EP) levels and the l-DOPA supplementation compensated the inhibitory effect. The level of tyramine (TR) was increased by the α-MPT treatment but inhibited by the l-DOPA supplementation. α-MPT produced stage-specific (seasonal) effects on ovarian estradiol-17β (E2); in the preparatory phase, E2 was decreased significantly at both 12 and 24h and in the pre-spawning phase, the level was stimulated over the respective control groups. The changes were higher at 24h in both phases. l-DOPA and hCG increased the E2 level significantly in the preparatory phase and reversed the inhibitory effect of α-MPT in the co-incubation groups. In the pre-spawning phase, α-MPT-stimulated the E2 level compared to the control groups, which was reversed by l-DOPA, hCG, or by both, in co-incubations. In contrast, the α-MPT treatment decreased progesterone (P4), 17-hydroxyprogesterone and 17,20β-dihydroxy-4-prenen-3-one (17,20β-DP) in a duration-dependent manner while the co-incubations with l-DOPA, hCG, or by both, significantly reversed the inhibitory effect. These results suggest that ovarian CAs (DA, NE and EP) may exert differential and stage-specific effects on E2, inhibition in the preparative phase and stimulation in the pre-spawning phase. The progestin steroids appear to be stimulated by CAs. In conclusion, this study highlights a possible direct/causal functional interaction between CA activity and gonadotropin on steroidogenic activity, and that CAs may be involved in regulating temporal secretion of the hormones through causing the shift in steroidogenic pattern. © 2013 Elsevier Inc.PublicationArticle Effects of hCG and ovarian steroid hormones on vasotocin levels in the female catfish Heteropneustes fossilis(Academic Press Inc., 2009) V. Singh; K.P. JoyEffects of hCG, ovariectomy and estradiol replacement on brain, plasma and/or ovarian vasotocin in vivo, and estradiol, progesterone, 17α, 20β-hydroxy-4-pregnen-3-one and hCG on ovarian vasotocin in vitro were investigated in the catfish. A 100 IU/fish of hCG induced ovulation and elicited both periovulatory and post-ovulatory changes in vasotocin concentrations with a significant increase up to 8 h in the brain and up to 16 h in both plasma and ovary. After stripping the fish at 16 h, the peptide concentration decreased significantly with time, up to 4 days. Ovariectomy in early pre-spawning phase resulted in a duration-dependent significant reduction of both brain and plasma vasotocin. Estradiol replacement in 3-week ovariectomized fish produced dosage-dependent biphasic effects: the lower dosage (0.1 μg/g) restored the vasotocin level while the higher dosage (0.5 μg/g) decreased it significantly below the control level. In vitro incubation of ovarian tissues with estradiol produced season-dependent effects on vasotocin. The incubation of pre-vitellogenic ovarian pieces with estradiol (1, 10, and 100 ng/ml) elevated vasotocin level in a dose- and duration-dependent manner while that of post-vitellogenic follicles resulted in a significant decrease. The incubation of intact post-vitellogenic follicles or follicular envelope with progesterone and 17α, 20β-hydroxy-4-pregnen-3-one (1 μg/ml) or hCG (20 IU/ml) for 8 and 16 h significantly increased vasotocin in a duration-dependent manner. The results show that both gonadotropin and ovarian steroids modulate vasotocin titer, which may influence follicular growth, ovulation and spawning in the catfish. © 2009 Elsevier Inc.PublicationArticle Annual and periovulatory changes in tyrosine hydroxylase activity in the ovary of the catfish Heteropneustes fossilis(Academic Press Inc., 2010) T.K. Chourasia; R. Chaube; V. Singh; K.P. JoyIn the present study, tyrosine hydroxylase (TH, the rate-limiting enzyme in catecholamine synthesis) activity was demonstrated in the ovary of the catfish to elucidate the possible physiological role of catecholamines in the gonad. The ovary is innervated by seven pairs of nerves, originating from the paired sympathetic chain lying dorsal to the posterior kidney. Ovarian TH activity showed a significant annual variation (P< 0.001, one-way ANOVA), correlating with gonado-somatic index. Activity was low from December to February (resting phase), increased from March to July (recrudescent phase) and then decreased in post-spawning phase (August-November). The annual pattern was similar to that of the brain. An intraperitoneal injection of 100. IU hCG/fish induced significant periovulatory changes in TH activity with the peak rise at 16 h, and the activity decreased after egg-stripping (P<0.001, one-way ANOVA). Brain TH activity showed similar periovulatory changes. The results suggest that catecholamine synthesis is increased during both ovarian recrudescence and spawning of the annual reproductive cycle, implying a functional role in ovarian growth, maturation and ovulation. © 2009 Elsevier Inc.PublicationArticle An involvement of vasotocin in oocyte hydration in the catfish Heteropneustes fossilis: A comparison with effects of isotocin and hCG(Academic Press Inc., 2010) V. Singh; K.P. JoyIn the present investigation, in vitro effects of vasotocin (VT) on oocyte (follicular) hydration during germinal vesicle breakdown (GVBD) and ovulation were demonstrated in hCG-primed and non-primed catfish. The data were compared with that of groups incubated with isotocin, and hCG alone or in combination with VT. The priming with hCG resulted in significant increases on percentage GVBD and ovulation, and stimulated follicular hydration, as judged by the increase in diameter, volume, water content, osmolality and Ca2+ concentration. However, Na+, K+ ATPase activity, and concentrations of Na+, K+ and Mg2+ did not alter significantly. The incubations with hCG or VT stimulated all the above parameters. In the non-primed fish, the response of hCG was significantly higher on follicular diameter, volume and osmolality, and that of VT on ovulation. In the primed fish, the VT response was significantly higher on GVBD, ovulation, Na+, K+ ATPase activity and divalent cation concentrations. The co-incubation with both hCG and VT produced maximal increases in all the parameters with significantly higher effects in the primed fish. The effects of IT on various parameters were relatively low compared to hCG or VT effects. The results indicate that VT may play an important role in oocyte (follicular) hydration, which is consistent with its role in osmoregulation of fish. © 2010 Elsevier Inc.