Saumen Maitra - Academia.edu (original) (raw)

Papers by Saumen Maitra

J Biosciences, 2002

Formoguanamine (2,4-diamino-s-triazine) was known to be an effective chemical agent in inducing b... more Formoguanamine (2,4-diamino-s-triazine) was known to be an effective chemical agent in inducing blindness in poultry chicks, but not in adult birds. The present study was undertaken to demonstrate the influences, if any, of this chemical on the visual performance and retinal histology in an adult sub-tropical wild bird, the roseringed parakeet (Psittacula krameri). Formoguanamine (FG) hydrochloride was subcutaneously injected into adult parakeets at a dosage of 25 mg (dissolved in 0⋅75 ml physiological saline)/100 g body weight/day, for two consecutive days while the control birds were injected only with a placebo. The effects were studied after 10, 20 and 30 days of the last treatment of FG. Within 24 h of the treatment of FG, about 90% of the total birds exhibited lack of visual responses to any light stimulus and even absence of pupillary light reactions. The remaining birds became totally blind on the day following the last injection of FG and remained so till the end of investigation. At the microscopic level, conspicuous degenerative changes were noted in the outer pigmented epithelium and the photoreceptive layer of rods and cones in the retinas of FG treated birds. A significant reduction in the thickness of the outer nuclear layer was also found in the retinas of FG treated parakeets, compared to that in the control birds. However, the inner cell layers of the retina in the control and FG administered parakeets were almost identical. It deserves special mention that the effects of FG, noted after 30 days of last treatment, were not very different from those noted just after 10 days of treatment. Collectively, the results of the present investigation demonstrate that FG can be used as a potent pharmacological agent for inducing irreversible blindness through selective damage in retinal tissue even in the adult wild bird, thereby making FG treatment an alternative euthanasic device to a cumbersome, stressful, surgical method of enucleation of the ocular system for laboratory studies.

ABSTRACT The pineal hormone melatonin (N-acetyl-5-methoxytryptamine) is synthesized in all groups... more ABSTRACT The pineal hormone melatonin (N-acetyl-5-methoxytryptamine) is synthesized in all groups of vertebrates in a rhythmic manner and its rhythmicity is controlled chiefly by the light-dark cycle. It is the main time keeping hormone in biological system as it reflects the seasonal variation in day length. Photoperiod is the major important cue that is used by most tropical fish to dictate the time of gonadal maturation and spawn at a particular time of the year. Our earlier studies revealed that both photoperiod and melatonin play a significant role in the regulation of growth and maturation of gonad in Indian major carp, Catla catla and thereby are considered as most important in aquaculture and fisheries management. However, possible interplay between them was unknown. Accordingly, the present study aimed at demonstration of a correlation, if any, between the rate of development of oocytes and endogenous melatonin level as well as with its ovarian receptors in carp Catla catla under natural and altered photoperiods. The adult female fish were held under three different photoperiodic conditions, viz., Natural Photoperiod (NP), Long Photoperiod (LP; LD 16:08) and Short Photoperiod (SP; LD 08:16) for 30 days during the pre-spawning phase in an annual reproductive cycle. We measured the serum melatonin level by radioimmunoassay, ovarian melatonin receptor protein by western blot analysis and the rate of oocyte development by quantitative microscopic study of the relative percentage of most advanced stage of ovarian follicles. The study revealed that the oocyte development was accelerated by LP, while SP had an inhibitory effect. In SP fish, the serum melatonin level was about three times higher than that of LP carp, whereas there was no significant change in ovarian melatonin receptor profile in the fish kept under different photoperiodic regime. In NP and SP fish groups, the diurnal peak value of both melatonin and its receptors on the ovary was observed at midnight (24.00h), but in LP carp the melatonin peak was shifted to late dark phase (04.00h). Collectively, the results of the present study underline for the first time that differential role of LP and SP on the oocyte development in carp may be due to the altered profiles of endogenous melatonin, while receptors of this hormone on the ovary are free from the influences of photoperiods.

Endocrine Research, Sep 1, 2001

Journal of Photochemistry and Photobiology B Biology, Apr 1, 2010

We studied temporal organization of both the photoreceptor (rod-like opsin, alpha subunit of the ... more We studied temporal organization of both the photoreceptor (rod-like opsin, alpha subunit of the G protein transducin or alpha-TD) and melatonin generating (AANAT) proteins in the same pineal of a tropical surface dwelling free-living carp Catla catla, and analyzed possible correlation between them as well as with natural photo-thermal variables in an annual cycle. The pineal from individual fish was collected at four different time points (06.00 h, 12.00 h, 18.00 h, and 24.00 h) in a 24.00 h cycle and the same was repeated in four distinct seasons in an annual reproductive cycle to study each protein following Western blot and densitometric analyses of respective immunoblots. The rod-like opsin was represented by four distinct bands, a closely spaced doublet of 39 kDa and bands of 78 and 115 kDa. Two separate bands, one at 43 kDa and another at 65 kDa, were detected for alpha-TD, and a single band at 23 kDa for AANAT. Both the pineal photoreceptor proteins exhibited an identical pattern of diurnal variations with a peak at midday (12.00 h) and fall at midnight (24.00 h), while maximum band intensity of AANAT was noted in midnight (24.00 h) and minimum at midday (12.00 h) depicting a significant negative correlation (p&amp;lt;0.001) between them. Likewise, in an annual cycle, a significant (p&amp;lt;0.01) negative correlation was found between the expression of each pineal photoreceptor protein (being highest during the spawning phase) and AANAT (maximum during the post-spawning phase). Seasonal fluctuations of both the photoperiod and water temperature exhibited a significant (p&amp;lt;0.01) positive correlation with the expression of pineal photoreceptor proteins and a significant (p&amp;lt;0.05) negative correlation with the pineal AANAT. Collectively, the present phenological study is the first report on temporal organization of pineal photoreceptor proteins and their correlation with the melatonin rhythm-generating enzyme AANAT as well as environmental photo-thermal cues depicting their integrative role in the synthesis of proteins in the pineal in any fish. Nonetheless, importance of further experimental studies on carp is emphasized for a conclusive evidence of functional relationship between the studied variables in the pineal and the components of environment in which the fish live in.

Http Dx Doi Org 10 1080 09291019509360327, Sep 30, 2008

The effects of daily afternoon injection of melatonin (25 ug/ 100 g body wt for 45 days) on the c... more The effects of daily afternoon injection of melatonin (25 ug/ 100 g body wt for 45 days) on the cytology of the pineal were studied during the preparatory, progressive, pre‐breeding and breeding phases of the annual testicular cycle in male roseringed parakeets. The cytological responses of the pineal to the melatonin administration in either case were evaluated by comparison with the pineals in parallel groups of control and sham‐control (only ethanolic‐saline injected) birds. It was found that the pinealocyte‐response to exogenous melatonin was stimulatory to the pineal functions during the progressive phase and inhibitory during the pre‐breeding phase. But no changes in the pinealocytes of melatonin treated birds were found during the preparatory and the breeding phases. This is the first demonstration of cytological responses of the pineal to administration of its own hormone melatonin in any bird. The study implicates the involvement of hitherto unknown annual cyclic variable(s) related to the reproductive periodicity in the determination of the responses of the pinealocytes to exogenous melatonin in male roseringed parakeets.

Frontiers in endocrinology, 2015

Melatonin, following discovery in the bovine pineal gland, has been detected in several extra-pin... more Melatonin, following discovery in the bovine pineal gland, has been detected in several extra-pineal sources including gastrointestinal tract or gut. Arylalkylamine N-acetyltransferase (AANAT) is the key regulator of its biosynthesis. Melatonin in pineal is rhythmically produced with a nocturnal peak in synchronization with environmental light-dark cycle. A recent study on carp reported first that melatonin levels and intensity of a ~23 kDa AANAT protein in each gut segment also exhibit significant daily variations but, unlike pineal, show a peak at midday in all seasons. Extensive experimental studies ruled out direct role of light-dark conditions in determining temporal pattern of gut melatoninergic system in carp, and opened up possible role of environmental non-photic cue(s) as its synchronizer. Based on mammalian findings, physiological significance of gut-derived melatonin also appears unique because its actions at local levels sharing paracrine and/or autocrine functions have...

Chronobiology international, Jan 29, 2015

Influences of starvation, re-feeding and time of food supply on daily rhythm features of melatoni... more Influences of starvation, re-feeding and time of food supply on daily rhythm features of melatonin (5-methoxy-N-acetyltryptamine) and its key regulator AANAT (arylalkylamine N-acetyltransferase) protein in the gut tissues were separately evaluated in carp Catla catla. The first experiment was aimed at demonstration of duration dependent effects of starvation and re-feeding after starvation on the daily profiles and rhythm features of gut melatonin and AANAT. Accordingly, juvenile carp were randomly distributed in three groups, which were (a) provided with balanced diet daily at a fixed time, that is, 10:00 clock hour or zeitgeber time (ZT) 4 (control), or (b) starved (for 2-, 4-, 6- or 8 days), or (c) initially starved for 8 days and then re-fed (for 2-, 4-, 6-, 8-, 12- or 16 days) daily with the same food and at the time (ZT4) used for control fish. The carp in each group were sampled for collection of gut tissues at six different time points at a regular interval of 4 h in a daily...

Indian journal of experimental biology

Cell and Tissue Biology

To characterize further the functionally enigmatic "synaptic" ribbons (SR) of the mammalian pinea... more To characterize further the functionally enigmatic "synaptic" ribbons (SR) of the mammalian pineal gland and to study possible relationships to melatonin synthesis, in the present investigation rats were exposed to short pulses of light at night when both SR numbers and serotonin N-acetyltransferase (NAT) activity are high in comparison to day-time values. Male Sprague-Dawley rats were killed at 13:00 and 01:00 h, respectively, and at 01:10 and 02:00 h after exposure to light for 10 and 60 rain, respectively. The pineals were rapidly taken out and cut sagittally in half. One half was processed for electron-microscopic quantitation of SR numbers and the other half for NAT determinations. It was found that both SR numbers and NAT activity decreased significantly when the animals were exposed to light at night. Although both parameters showed corresponding changes, there was no clear-cut correlation between SR numbers and NAT activity in individual animals within a group, except after exposure to light for 60 rain when a positive correlation (R--0.939; p < 0.05) existed. After exposure to light the electron-lucent vesicles of the SR decreased in number, but the length of the SR was unchanged. These results show that numbers of pineal SR can be easily and quickly manipulated and that the presently used model may be ideal in studying the poorly understood mode in which degradation of SR occurs.

Indian journal of biochemistry & biophysics

Melatonin (N-acetyl-5-methoxytryptamine) was first purified and characterized from the bovine pin... more Melatonin (N-acetyl-5-methoxytryptamine) was first purified and characterized from the bovine pineal gland extract by Aron Lerner and co-workers in 1958. Since then, a plethora of information has piled up on its biosynthesis, metabolism, time-bound periodicity, physiological and patho-physiological functions, as well as its interactions with other endocrine or neuro-endocrine organs and tissues in the body. Melatonin has wide range of applications in physiology and biomedical fields. In recent years, a significant progress has been made in the understanding mechanism of its actions at the cellular and molecular levels. Consistent efforts have uncovered the mystery of this indoleamine, and demonstrated its role in regulation of a large as well as diverse body functions in different groups of animals in general, and in humans in particular. Current review, in commemoration of 50 years of discovery of melatonin, while revisiting the established dogmas, summarizes current information on...

Melatonin: Endogenous sources and role in the regulation of fish reproduction.

Melatonin (N-acetyl-5-methoxytryptamine) is primarily known as a hormone of pineal gland in verte... more Melatonin (N-acetyl-5-methoxytryptamine) is primarily known as a hormone of pineal gland in vertebrates, though extra-pineal melatonin is also known in several animals. This indole hormone is unique in exhibiting marked day-night variations with a nocturnal peak in both synthesis and release from the pineal gland irrespective of the habit and habitat of the species. Gastrointestinal melatonin has been studied mostly in mammals, but it remains obscure whether gut contributes to diurnal rhythmic profiles of melatonin in circulation. Accordingly, present study aims at localization of melatonin containing cells and measurement of this hormone at four different clock hours (i.e., 12:00h, 18:00h, 24:00h and 06:00h) in a light-dark cycle in different parts of gastrointestinal tract [GIT] for the first time in carp Catla catla as a representative of any fish. Immunohistochemical study reveals the presence of melatonin containing cells throughout the carp GIT. However, relative abundance of ...

The present study was performed on Indian major carp Catla catla, which because of its natural su... more The present study was performed on Indian major carp Catla catla, which because of its natural surface dwelling habit maintains close contact with environmental light and thereby considered as an ideal model for study of photo-response mechanisms in any melatonin synthesizing tissue. The study carryout on carp under natural photo-thermal conditions revealed that the concentrations of melatonin (N-acetyl-5-methoxytryptamine) and the band intensity of a ~23kDa arylalkylamine N-acetyltransferase (AANAT) protein, the key regulator of melatoninergic pathway in each (anterior, middle and hind) segment of gut irrespective of sampling months, undergo significant diurnal variations with a peak at midday, while both the variables in the pineal and melatonin in serum show a peak either in late night (in March) or at midnight (in the remaining part of year). Statistical analysis of the data for searching a temporal relationship between the profiles of melatonin in gut, pineal and serum, as well...

Frontiers in Endocrinology, 2015

The influences of serotonin (5-hydroxytryptamine) on the action of melatonin (N-acetyl-5-methoxyt... more The influences of serotonin (5-hydroxytryptamine) on the action of melatonin (N-acetyl-5-methoxytrypta-mine) in MIH (maturation inducing hormone)-induced meiotic resumption were evaluated in the oocytes of carp Catla catla using an in vitro model. Oocytes from gravid female carp were isolated and incubated separately in Medium 199 containing either (a) only melatonin (MEL; 100 pg/mL), or (b) only serotonin (SER; 100 pg/mL), or (c) only MIH (1 μg/mL), or (d) MEL and MIH (e) or MEL (4 h before) and MIH, or (f) MEL and SER, (g) or SER and MIH, or (h) SER (4 h before) and MIH, or (i) luzindole (L-antagonist of MEL receptors; 10 μM) and MEL, or (j) MEL, L and MIH, or (k) MEL (4 h before), L and MIH, or (l) metoclopramide hydrochloride (M-antagonist of SER receptors; 10 μM) and SER, or (m) M, MEL, SER, or (n) M, SER and MIH, or (o) M, SER (4 h before) and MIH, or (p) M, MEL SER and MIH, or (q) MEL, L, SER and M, or (r) MEL, L, SER, M, and MIH, or (s) MEL, SER, L and MIH. Control oocytes w...

Recent studies on several fish species, especially carp, implicated pineal hormone melatonin (N-a... more Recent studies on several fish species, especially carp, implicated pineal hormone melatonin (N-acetyl-5methoxytryptamine) as a potent candidate in the regulatory mechanism of seasonal reproduction. Under natural conditions, the temporal pattern of serum melatonin varied with daily light-dark cycle and the reproductive status of the fish as well. Carefully controlled study revealed that exogenous administration of melatonin may result in stimulation or inhibition or no influences at all on the gonadal functions depending on the reproductive status of fish. Cross-talk between the melatonin and ovarian steroid has been evident from in vitro study, in which melatonin accelerated the action of 17a,20b-dihydroxy-4-pregnen-3-one or maturation inducing hormone (MIH) on meiotic cell cycle resumption in carp oocytes by formation of maturation promoting factor (MPF) -a complex of two proteins, cyclin B and cyclin dependant kinase Cdk1. While several lines of evidence suggest melatonin effects on hypothalamo-hypophyseal-gonadal axis, localization and dynamics of a 37-kDa melatonin receptor protein in carp oocytes argued in favor of extra-hypothalamic direct action of melatonin on fish reproduction. A recent study in carp indicated that influences of an identical regimen of photoperiods in different parts of annual cycle on ovarian functions vary in relation to the profiles of serum melatonin, but not to any rhythm parameters of MT1 or MT2 receptors on the gonad or brain. The purpose of this short review is to bring together the current knowledge on the biological effects of melatonin on fish reproduction mainly focusing the recent findings on carp.

Endocrine research, 1999

In this report, we have examined the effects of lithium on testicular morphology in a male subtro... more In this report, we have examined the effects of lithium on testicular morphology in a male subtropical wild avian species, the roseringed parakeet (Psittacula krameri). Adult male birds were collected during the months of February-March, a time when the testicular gametogenic activity in these seasonally breeding birds is at its peak. They were injected, intramuscularly, twice daily (07:00 and 19:00 h) with lithium chloride (Sigma Chemical Company) at a dosage of 0.5 mEq/Kg body weight either for 5 or 10 days. A significant decrease in both the absolute and relative testicular weights was evident in the lithium-treated birds as compared to those of the saline-injected control animals. Light microscopic studies of the testis in the lithium-treated animals showed a wide range of degenerative changes. These included a) a significant reduction in the diameter of seminiferous tubules; b) necrosis and exfoliation of most of the germ cells in the seminiferous tubular lumen with the excepti...