Saumen Kumar Maitra

Annual testicular cycle of blossomheaded parakeet, Psittacula cyanocephala (Aves, Psittacidae), under natural environmental conditions

Abstract Histophysiological studies of the annual testicular events in an Indian Psittaciform bird, blossomheaded parakeet Psittacula cyanocephala, under natural environmental conditions revealed that the bird is a seasonal breeder with a single peak in a year. Active spermatogenesis takes place only during February and March, but maximum seasonal maturation of the Leydig cells occurs at least one month before the onset of active production of sperm. Comparison of the annual cycles of reproductive parameters with those of different climatological variables could show that duration of solar‐day, in contrast to ambient temperature and rainfall, through its cyclicity parallels, though in part, the gonadal cycle of male blossomheaded parakeet.

Cytological studies of the pineal in relation to the annual cycles in the testis and climatological variables of free‐living roseringed parakeets (Psittacula krameri)

Abstract Cytological studies of the pineal and the testes in free‐living roseringed parakeets (Psittacula krameri) show that the activities of both organs undergo definite annual changes. The features of hyperactivity of pinealocytes were noted during the months of April through September, after which a gradual loss of the signs of cellular activity occurred till March, when the pineal appeared to be highly regressed, followed by an abrupt change in the opposite direction in April to repeat the cycle. On the other hand, studies of the testes indicated that the species attains maximum testicular maturation during March, after which sudden regression occurs and the testes remain in the quiescent state till September when recovery of spermatogenesis takes place and steady growth and development towards the annual peak follow. A significant negative correlation was found between the seasonal values for nuclear diameter of the pinealocytes and each of the studied parameters of testes. Among the considered clim...

Importance of Photoperiods in Determining Temporal Pattern of Annual Testicular Events in Rose-Ringed Parakeet (Psittacula krameri )

Male rose-ringed parakeets (Psittacula krameri) were transferred to a long photoperiod (LP; LD 16:8) or a short photoperiod (SP; LD 8:16) for 45 or 90 days on four dates corresponding to the beginnings of different reproductive phases in an annual testicular cycle, and testicular responsiveness was evaluated by comparison with the testicular volume, weight, seminiferous tubular diameter, and germ cell profiles of birds in a natural photoperiod (NP). Exposure of birds to LP during the progressive phase (November) led to precocious maturation of testes after 45 days, but induced regression at 90 days. After showing retarded gametogenic functions at 45 days, parallel (November) SP birds exhibited an accelerated rate of germ cell formation at day 90. During the prebreeding phase (January), there were no remarkable differences in any features of testes among NP, LP, and SP birds at 45 days, but gonadal involution in LP parakeets and active spermatogenesis in SP birds occurred after 90 days. The testes did not show any response to LP or SP for 45 and 90 days when the birds were transferred to altered photoperiods during the breeding (March) and preparatory (June) phases, indicating that the parakeets were photorefractory for at least 6 months (March through September). The results also suggest that initiation and termination of seasonal gametogenic activity in parakeets are possibly functions of endogenous rhythmicity or extraphotoperiodic environmental factors. Duration of light may have certain influences on the attainment of annual peak in spermatogenesis, but in all probability the species has a low photoperiod threshold for induction of testicular growth.

Role of light in the mediation of acute effects of a single afternoon melatonin injection on steroidogenic activity of testis in the rat

Young adult male rats, maintained either in an LD 12: 12 or in continuous illumination (LL) for one week, were given a single injection of 25 μg melatonin/100 g body wt or ethanolic-saline (control) at 17.00 h. Animals from each group were sacrificed at 11.00 h on the following day. The activity of two important steroidogenic enzymes, 17β-hydroxysteroid dehydrogenase (17β-HSD) and Δ5-3β-hydroxysteroid dehydrogenase (Δ5-3β-HSD), and serum concentrations of testosterone, were measured following highly specific and sensitive spectrophotometric techniques and RIA, respectively. A significant decrease in the activity of both the steroidogenic enzymes was noted in the testes of melatonin-treated rats maintained under normal light-dark schedules, but this response was found to be lacking in the LL rats. However, no significant changes in the level of serum testosterone were noted in either group of melatonin-treated rats from the values in respective groups of ethanolic saline-administered LD and LL rats. Exposure of ethanolic saline-injected rats to continuous light also did not cause any change in the steroidogenic activity of the testis from those in LD rats. The study indicates that continuous light as such does not affect the endocrine function of testis but abolishes suppressive effects of melatonin on the steroidogenic activity of the testis in rat.

Castration and testosterone induced changes in the pinealocytes of Roseringed Parakeet, Psittacula krameri, during different phases of the annual testicular cycle

The pinealocytes in male roseringed parakeets (Psittacula krameri) were studied following bilateral castration and/or therapeutic administration of testosterone during the preparatory (June-July), progressive (Nov.-Dec.), pre-breeding (Jan.-Feb.) and breeding (March-April) phases of the annual testicular cycle. The responses of the pineal to either treatment were found to be almost identical throughout the investigation. In each reproductive phase, the pineal appeared to be hypertrophied following castration and the effect was reversed by therapeutic administration of testosterone, while hormonal treatment to the intact parakeets induced regressive changes in the pinealocytes. Collectively, the results of the current study support the hypothesis that the testis through its hormone testosterone exerts inhibitory influences on the activity of pineal, and may thus be considered as being involved in the determination of an inverse relationship between the pineal and the testis during the annual cycle of free-living parakeets.

Seasonal changes in the adrenal medulla of male blossomheaded parakeet in relation to environmental and reproductive cycles

Abstract The adrenal medulla of male blossomheaded parakeets undergoes seasonal cycles in hormonal concentrations and in the relative number of epinephnne (E) and norepinephrine (NE) cells. NE, but not E, concentrations and cells become significantly (P < 0.001) higher in March than in September and October respectively. The one environmental factor that parallels, though only in part, the annual cycle of the chromaffin tissue is the photoperiod. However, consideration of the sexual periodicity of the parakeet leads to a tentative hypothesis to be tested that active gametogenesis in the testis is correlated with the periodic activity of the adrenal medulla.

Histophysiological changes in the adrenal cortex of male blossomheaded parakeet in relation to the annual testicular and environmental cycles

Abstract Annual histophysiological changes in the adrenal cortex of free‐living blossomheaded parakeets were studied in relation to the gametokinetic activities in the testes and periodic climatic variables to evaluate possible interrelationship, if any, between these endogenous and exogenous cyclic factors. Observations involving histometry, karyometry and lipid cytochemistry of adrenal cortex along with quantitative estimation of tissue cholesterol demonstrate the annual rhythmic pattern in the activity of adrenocortical tissue with an annual peak in February followed by regressive changes till August. Steady progressive changes towards annual peak occur only after November. Results show that the seasonality of the histophysiological features in the adrenal cortex coincides better with the periodic sexual activities of the bird than with any of the surrounding environmental factors.

Pinealocyte‐response in roseringed parakeets (Psittacula krameri) to melatonin administration varies in relation to the reproductive phase of the annual testicular cycle

Abstract 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 t...

Cytologic variation in the pineal organ of roseringed parakeets (Psittacula krameri) with respect to artificial photoperiods and annual cyclicity in testicular functions

Abstract Adult male roseringed parakeets were transferred to 16L: 8D (LP), or 8L: 16D (SP) for 45 or 90 days on four particular dates corresponding to the different phases of an annual testicular cycle and the cytological responses of the pineal were studied comparing them with the features in respective natural photoperiodic (NP) birds. Different cytological characteristics including the values of nuclear diameter in pinealocytes indicated that LP for 45 days during the pre‐breeding phase and for 90 days during each phase resulted in an increased pineal activity, while SP for 45 and 90 days induced inhibitory responses of the pineal during each, but not the progressive phase of the annual testicular cycle. During the latter phase, none of the artificial photoperiodic schedules, other than LP for 90 days, influenced the cytological features of the pineal. The results suggest that the photosensitivity of the pineal in these parakeets varies in relation to the testicular functions in an annual testicular cy...

Influence of the pineal and melatonin administration on the day‐night changes in the adrenal catecholamines of young chicks

Abstract The effects of pinealectomy with or without substitutive administration of melatonin on the concentrations of epinephrine (E) and norepinephrine (NE) in the adrenals of young chicks were studied at mid‐day and mid‐night. The two‐week old chicks were either non‐operated (NO), or sham‐operated (SO), or pinealectomized (Px) and maintained in LD 12: 12 for 15 days. During this period, half of the total number of NO, SO, and Px chicks were injected daily in the afternoon with melatonin (Mel; 10 ug/100 g body wt) and the remaining birds from the same groups were administered daily only with the vehicle (V; ethanol‐saline) of the hormone. The control (Con) birds were maintained under natural conditions without any treatment. In the adrenals of both the Con and NO‐V birds, a significant nocturnal increase in the concentration of E was noted compared to the same at mid‐day. But the night‐time value of adrenal E was lowered in SO‐V birds and raised in SO‐Mel chicks. Exogenous melatonin in intact (NO‐Mel) a...