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Biomedical subjects

J N Rao

Publications and source records attributed to J N Rao.

At least 19 recordsLinked to original sources
PubMed1996

Effects of photoperiod on hypothalamic and anterior pituitary tachykinins of male Siberian hamsters during development.

In previous reports from our laboratory we showed that the hypothalamus and especially the anterior pituitary gland of the Siberian hamster contain very high concentrations of substance P- and neurokinin A-like immunoreactive substances, as compared with other common laboratory rodents. It was thought, therefore, that a study of the developmental changes of these two tachykinins in the hypothalamus and anterior pituitary of male Siberian hamsters would be of interest. In addition, as this species is very sensitive to changes in environmental light, these studies were carried out in animals kept under short or long daily photoperiods. The results of this investigation show that in male Siberian hamsters, photoperiod did not markedly influence the hypothalamic concentrations of substance P- and neurokinin A-like immunoreactive substances, which steadily increased from prepuberty up to 40-50 days of age. The influence of photoperiod, however, was much more marked on tachykinin levels in the anterior pituitary gland, because the developmental increase of tachykinins in this gland was significantly more evident in animals kept under short daily photoperiods than in animals under long daily exposure to light. These results are similar to those previously obtained in female Siberian hamsters, in spite of the fact that estradiol and testosterone seem to have opposite effects on anterior pituitary tachykinin concentrations. It seems, therefore, that, in addition to gonadal steroids, other factors may be important mediators of the tachykinin response to photoperiods in the anterior pituitary of the male Siberian hamster.

Aging↗
PubMed1996

Testicular gamma-aminobutyric acid and circulating androgens in Syrian and Djungarian hamsters during sexual development.

Several factors, besides luteinizing hormone (LH), participate in the modulation of testicular function. A number of neurotransmitters are reported to be involved in this process, including a stimulatory action of gamma-aminobutyric acid (GABA) on steroidogenesis in the rat testis. The purpose of this study was to investigate the testicular pattern of GABA and glutamic acid, one of its main precursors, during sexual maturation in two seasonally breeding species: Syrian (golden) and Djungarian hamsters. Plasma androgen levels were also measured. The animals were maintained under long-day photoperiod (16:8, L:D) and were killed at 23, 30, 36, 46, 60, and 90 days of age. A different pattern of developmental changes in body and testicular weight was observed in these two species. GABA was present in the testes at all ages studied. GABA concentration and content showed a sharp elevation in the prepubertal period in golden as well as Djungarian hamsters. However, glutamic acid concentrations remained nearly constant during development in both species. Glutamic acid content increased gradually with age in the golden hamster, while a marked peak at 36 days of age was detected in the Djungarian hamster. Plasma testosterone and dihydrotestosterone levels were maximal at pubertal age in both species. The plasma levels of 5 alpha-androstane-3 alpha, 17 beta-diol increased significantly at 30 days of age in the golden hamster while in Djungarian hamsters this steroid remained unchanged. These results suggest that glutamic acid may serve as a precursor for GABA biosynthesis in the testis. In addition, changes in testicular GABA and plasma androgen levels might reflect a modulatory effect of this neurotransmitter in the acquisition of steroidogenic capability during development.

Androgens↗
PubMed1996

Variance estimation for complex surveys using replication techniques.

The analysis of survey data requires the application of special methods to deal appropriately with the effects of the sample design on the properties of estimators and test statistics. The class of replication techniques represents one approach to handling this problem. This paper discusses the use of these techniques for estimating sampling variances, and the use of such variance estimates in drawing inferences from survey data. The techniques of the jackknife, balanced repeated replication (balanced half-samples), and the bootstrap are described, and the properties of these methods are summarized. Several examples from the literature of the use of replication in analysing large complex surveys are outlined.

Analysis of Variance↗
PubMed1995

Effects of photoperiod on testicular inhibin-alpha and androgen binding protein mRNA expression during postnatal development in Siberian hamsters, Phodopus sungorus.

The effects of short photoperiod (SPP) on testicular inhibin-alpha and androgen binding protein (ABP) mRNA expression were investigated in Siberian hamsters during postnatal development. Hamsters were raised in either long photoperiod (LPP; 16L:8D) or in a SPP (6L:18D). Hamsters were sacrificed at the following developmental ages: preweaning (18-20 days), immature (28-30 days), pubertal (38-40 days), postpubertal (48-50 days) and adult (60-62 days; n = 7-12 animals per group). Body and testicular weights were determined and plasma FSH levels were measured by validated RIA. As expected, testicular weight and circulating FSH levels were significantly lower in hamsters raised in SPP than in LPP animals. Photoperiod had no significant effect on body weight except during postpubertal age. The northern analyses of inhibin-alpha and ABP expression in the testes revealed that the corresponding relative mRNA levels were higher in animals exposed to SPP than in animals from LPP. These findings suggest that the testes of hamsters exposed to a SPP can synthesize inhibin-alpha and ABP, and we speculate that the release of these proteins may be regulated by photoperiod and the role of FSH in the control of inhibin-alpha and ABP gene expression in male Siberian hamsters may be minimal.

Androgen-Binding Protein↗
PubMed1995

Developmental changes of tachykinins in the hypothalamus and anterior pituitary of female Siberian hamsters from prepuberty to adulthood.

The developmental changes of hypothalamic and anterior pituitary tachykinin concentrations were studied in female Siberian hamsters kept either under short (SD) or long (LD) daily photoperiods. The animals were killed between 15 and 70 days of age. Hypothalamic NKA sharply increased starting at 15 days up to 50 days in LD animals, and between 20 and 60 days in SD animals. Hypothalamic SP levels increased in a similar manner in SD animals, but in LD animals the increment was less pronounced, with increased levels from day 20 to 40, followed by a plateau. In the anterior pituitary gland, NKA concentrations in LD animals increased at 40 days of age, with only slight increases afterward, but overall the increment curve was considerably flatter than for hypothalamic NKA. In SD animals, the increase of anterior pituitary NKA was much steeper than in LD animals. However, the total content of NKA in the AP was similar in both SD and LD animals, because the AP weight was considerably higher in LD- than in SD-exposed hamsters. These results showed that photoperiod did not markedly affect the developmental changes in hypothalamic NKA. The developmental changes in anterior pituitary NKA concentrations were considerably smaller than in the hypothalamus in LD animals, but in SD animals they were much steeper. NKA concentrations in the anterior pituitary were markedly affected by the photoperiod. Concentrations of NKA in the anterior pituitary of the Siberian hamster at the age of 15 days of age were already higher than in the anterior pituitary of adult rats or Syrian hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Effects of tachykinins on the secretory activity of rat Sertoli cells in vitro.

In the present study we investigated the effects of various tachykinins on the secretory activity of rat Sertoli cells in vitro. Sertoli cells were isolated from testes of immature Sprague Dawley rats, cultured for 4 days and thereafter incubated with three concentrations (0.1 pM, 1 pM or 100 pM) of substance P (SP), neurokinin A (NKA), neuropeptide K (NPK) or neuropeptide gamma (NPG) for 24 h. Levels of transferrin and lactic acid were determined in the culture media and expressed per micrograms of cellular DNA. Among all the peptides studied, NPG exhibited the greatest stimulatory effect on the release of transferrin and lactate, with NKA and NPK being less potent and SP being the least potent. Also, the effects of tachykinins on the aromatase activity of cultured Sertoli cells, as reflected by their ability to metabolize testosterone to estradiol (E2), were studied. No stimulatory effect was observed at lower concentrations (1 pM), while at 100 pM both NPG and NKA increased estradiol levels in the medium. SP and NPK had no significant effect on estradiol levels in the medium. This study reveals that tachykinins are able to influence the secretory activity of Sertoli cells, and that some of these peptides can also enhance the aromatase activity. Thus there is a possibility that tachykinins may have a physiological role as modulators of the function of Sertoli cells.

Animals↗
PubMed1994

Tests for trend in developmental toxicity experiments with correlated binary data.

In this article, the operating characteristics of recently proposed tests for trend in correlated binary data arising in laboratory studies of developmental toxicity are examined using both computer-generated and experimental data. Specifically, we consider adjusted Cochran-Armitge tests based on the Rao-Scott transformation which are of the same general form as that for uncorrelated data. In addition, generalized score tests based on generalized estimating equations allowing for extrabinomial variation in the data are discussed. Specific forms of these statistics demonstrating favorable type I and type II error rates are identified and recommended for use in practice. The application of these tests is illustrated using data from studies of developmental toxicity that have been reported in the literature.

Abnormalities, Drug-Induced↗
PubMed1992

Effect of prolactin on accessory sex organs of prepuberal male albino rats: an in vitro study.

The in vitro studies on the effect of hypophysial gonadotropins (PRL, FSH, LH) on the maturation events of accessory sex organs in prepuberal male rats revealed that prolactin (PRL) alone has both direct as well as androgen mediated effect on the maturation activities. The effect of PRL is age dependent and it had higher activation on the gland system than the duct system.

Aging↗
PubMed1992

A simple method for the analysis of clustered binary data.

A simple method for comparing independent groups of clustered binary data with group-specific covariates is proposed. It is based on the concepts of design effect and effective sample size widely used in sample surveys, and assumes no specific models for the intracluster correlations. It can be implemented using any standard computer program for the analysis of independent binary data after a small amount of preprocessing. The method is applied to a variety of problems involving clustered binary data: testing homogeneity of proportions, estimating dose-response models and testing for trend in proportions, and performing the Mantel-Haenszel chi-squared test for independence in a series of 2 x 2 tables and estimating the common odds ratio and its variance. Illustrative applications of the method are also presented.

Animals↗