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Biomedical subjects

L Singh

Publications and source records attributed to L Singh.

At least 145 records · Page 8Linked to original sources
PubMed1987

The use of Y-chromosome-specific repeated DNA sequences in the analysis of testis development in an XX/XY mouse.

A study, by means of Y-chromosome-specific repeated DNA probes, of mouse (ST) with small testes is reviewed. Mouse ST was shown to be a somatic mosaic of 10% XY and 90% XX cells. The cellular composition of the azoospermic testis reflected the overall proportions of XX and XY cells but it was found that XY cells predominated in the Sertoli cells of the testis tubules. These findings have been interpreted to indicate a fundamental role for the Sertoli cell in inducing testis organization in the indifferent gonadal rudiment, involving the expression of the Y chromosome.

Animals↗
PubMed1986

Chronic antidepressant treatment reduces central beta-adrenoceptor sensitivity in a behavioural test.

The ability of beta-adrenoceptor agonists to potentiate the head-twitch response to 5-hydroxytryptophan (5-HTP) in mice was used to assess the in vivo sensitivity of beta-adrenoceptors 48 h after cessation of acute or chronic administration of desmethylimipramine (DMI) or iprindole (IPD). Neither acute nor chronic antidepressant administration significantly altered the head-twitch response to 5-HTP alone. Forty-eight hours after withdrawal from chronic but not acute pretreatment with DMI or IPD the potentiating effects of dobutamine, prenalterol and salbutamol were significantly decreased. This is consistent with a reduction in beta-adrenoceptor density and suggests that the 'spare' beta-adrenoceptor pool is small enough for this to result in functional subsensitivity. Implications of these findings are discussed.

5-Hydroxytryptophan↗
PubMed1986

Involvement of noradrenaline in potentiation of the head-twitch response by GABA-related drugs.

The involvement of noradrenaline in the potentiation of head-twitching by drugs acting at GABA and related receptors has been examined in mice. The direct 5-HT agonist 5-methoxy-N,N-dimethyltryptamine was used to induce the head-twitch. The dopamine beta-oxidase inhibitor FLA-63 depleted whole brain noradrenaline by 90% and potentiated head-twitching when this was measured 4 h after injection. The GABAA-receptor agonists muscimol and 3-aminopropanesulphonic acid (3-APS), a low dose of pentobarbitone, diazepam and picrotoxin (PTX) potentiated control head-twitch rates but had no further effect when head-twitching had been potentiated by FLA-63. The potentiating action of FLA-63 was prevented by the beta-adrenoceptor antagonist metoprolol; the latter having no effect on control head-twitch rates. Muscimol and diazepam potentiation was examined and found to be blocked by metoprolol. The GABAB-receptor agonist baclofen reduced head-twitching. This was also prevented by FLA-63. The role of beta-adrenoceptors in modulating these actions of GABA-related drugs is discussed.

Adrenergic beta-Antagonists↗
PubMed1986

The modulation of head-twitch behaviour by drugs acting on beta-adrenoceptors: evidence for the involvement of both beta 1- and beta 2-adrenoceptors.

Drugs selective for either the beta 1- or beta 2-adrenoceptor have been investigated for their effects on the head-twitch behaviour induced by L-5-hydroxytryptophan (L-5-HTP) in mice. All four agonists, dobutamine and prenalterol (beta 1-), and salbutamol and procaterol (beta 2-), potentiated the effect of L-5-HTP although they were ineffective in inducing the head-twitch when administered alone. The corresponding antagonists, practolol and metoprolol (beta 1-) and butoxamine and ICI 118,551 (beta 2-), were without effect on the L-5-HTP head-twitch. The antagonists each significantly reduced the effect of the corresponding agonists but, while butoxamine and ICI 118,551 were inactive against dobutamine and prenalterol potentiation, both practolol and metoprolol reduced the effect of salbutamol and procaterol. Thus it is argued that dobutamine and prenalterol potentiation is due to an action at beta 1-adrenoceptors, while at least a component of the potentiating effect of salbutamol and procaterol is exerted through beta 2-adrenoceptors. The lack of effect of the antagonists alone is discussed.

5-Hydroxytryptophan↗
PubMed1986

Bkm sequences are polymorphic in humans and are clustered in pericentric regions of various acrocentric chromosomes including the Y.

Probes of uncloned Bkm satellite DNA and a Drosophila clone 2 (8), consisting mainly of GATA repeats related to a major sequence component in Bkm, have been used to probe Southern blots of human male and female DNAs obtained from a Caucasian and an Australian aboriginal population and to human chromosomes in situ. Hybridization was observed to a distinct and an indistinct series of bands against a smeared background. The same distinct bands are identified in the DNA samples with both probes, but are most readily detected using the uncloned Bkm probe. Most restriction bands are common to both populations and some are polymorphic. However, certain bands appear to be characteristic of the Australian aboriginal samples. There are no distinct sex-linked patterns. However all of the small acrocentric human chromosomes, including the Y chromosome show hybridization to uncloned Bkm in situ.

Centromere↗
PubMed1986

Involvement of the locus coeruleus in the potentiation of the quipazine-induced head-twitch response by diazepam and beta-adrenoceptor agonists.

Head-twitching in rats induced by quipazine was reduced by bilateral lesions of the locus coeruleus (LC) produced by 6-hydroxydopamine. Both beta 1-and beta 2-adrenoceptor agonists potentiated the head-twitch induced by quipazine in sham-operated controls. Lesions of the locus coeruleus increased the responses to the beta 1-adrenoceptor agonists, prenalterol and dobutamine, but reduced the response to the beta 2-adrenoceptor agonists, salbutamol and procaterol. Diazepam (0.25 mg/kg) also potentiated the response to quipazine and this was reversed to inhibition by lesions of the locus coeruleus. These results suggest that the beta 1-adrenoceptors involved are postsynaptic and the beta 2-adrenoceptors are presynaptic to neurones of the locus coeruleus and indicate a dual action of diazepam on the head-twitch induced by quipazine. Possible mechanisms for these effects are discussed.

Adrenergic beta-Agonists↗
PubMed1985

Modulation of 5-hydroxytryptamine-induced head-twitch response by drugs acting at GABA and related receptors.

The effects of drugs acting at the gamma-aminobutyric acid (GABA) receptors and other chloride ionophore-related sites have been studied for their ability to modulate the head-twitch induced by 1-5-hydroxytryptophan (5-HTP) in the mouse. The GABAa receptor agonists, muscimol, imidazoleacetic acid and 3-aminopropanesulphonic acid, produced a dose-related potentiation, while bicuculline inhibited the head-twitch. The GABAb receptor agonist, baclofen, produced dose-related inhibition. Diazepam potentiated the head-twitch while the 'inverse' benzodiazepine receptor agonist ethyl-beta-carboline-3-carboxylate inhibited the head-twitch. The antagonist Ro15-1788 also produced inhibition. Ro05-4864, a ligand for the benzodiazepine 'acceptor' site, potentiated the head-twitch. Pentobarbitone and pentylenetetrazol potentiated the 5-HTP-induced head-twitch at low doses, changing to inhibition as the dose was increased. Picrotoxin in subconvulsant doses, produced only potentiation. More than one site may be involved in the action of these substances. GABA, amino-oxyacetic acid and 1-2-4-diaminobutyric acid inhibited the head-twitch, while the GABA-depletor, 3-mercaptopropionic acid potentiated it. Of all the agents tested, only muscimol produced head-twitching when given alone. It was concluded that both GABAa and GABAb receptors modulate the head-twitch response to 5-HTP.

5-Hydroxytryptophan↗
PubMed1985

Serum proteins among Dusads of Bihar.

Horizontal starch gel electrophoresis has been employed for the detection of haptoglobin, transferrin and albumin phenotypes among 88 Dusads of Bihar. No variant of the haptoglobins or transferrins has been found in this sample, whereas one individual showed bisalbuminemia.

Blood Proteins↗
PubMed1984

The conserved nucleotide sequences of Bkm, which define Sxr in the mouse, are transcribed.

We have recovered a conserved transcribed component of the snake W chromosome satellite DNA (Bkm) from Drosophila and male mouse libraries. This consists of repeats of the tetranucleotide GATA that are concentrated in the sex-determining region of the Y chromosome of mouse, on the W chromosome of snakes, and in the proximal region of the X chromosome of D. melanogaster, and it appears to be transcribed in a sex-specific and developmentally regulated manner. Sequencing studies show that, unlike most other transcribed repeats, the GATA repeats potentially contain open reading frames. These encode mainly the amino acids leucine, serine, isoleucine, and tyrosine but with occasional variant codons that differ in different clonal isolates. Transcription is exclusive to the GATA strand in different tissues of the same organism and in different unrelated organisms. The complementary strand CTAT contains stop codons in all reading frames. The possible developmental significance of these sequences is discussed.

Amino Acids↗
PubMed1984

Reproductive performance of Bhotia women of Mana Valley.

This paper reports the preliminary findings on the reproductive performance of 52 Bhotia women from the Mana Valley (Uttar Pradesh; elevation 10 560 ft.), who had approached menopause. The total amount of time available for reproduction and the total time used for effective reproduction as well as the period, which has been wasted as a result of sociocultural and biological factors, have been calculated. The total time available to Bhotia women for reproduction is found to be 1584 years, out of which 1563 years (98.67%) were used for effective reproduction. The reproductive wastage as a result of socio-economic and biological circumstances is calculated as 21 years only or 0.40 years per woman. All pregnancies as well as lactation operate to reduce fecundability. The various family limiting methods also lower the reproductive performance. A comparison has been made with the results of similar studies in other populations.

Abortion, Spontaneous↗
PubMed1983

Age at menarche among the Bhotias of Mana Valley.

The mean menarcheal age of the Bhotia girls of Mana Valley (Uttar Pradesh) has been found to be 16.38 +/- 1.53 years, which is the highest value so far reported from Indian populations. It is observed that altitude and nutritional status have a great bearing on the onset of menarche. The results obtained are compared with those from other Indian populations.

Adolescent↗
PubMed1982

Sex reversal in the mouse (Mus musculus) is caused by a recurrent nonreciprocal crossover involving the x and an aberrant y chromosome.

Satellite DNA (Bkm) from the W sex-determining chromosome of snakes, which is related to sequences on the mouse Y chromosome, has been used to analyze the DNA and chromosomes of sex-reversed (Sxr) XXSxr male mice. Such mice exhibit a male-specific Southern blot Bkm hybridization pattern, consistent with the presence of Y-chromosome DNA. In situ hybridization of Bkm to chromosomes of XXSxr mice shows an aberrant concentration of related sequences on the distal terminus of a large mouse chromosome. The XYSxr carrier male, however, shows a pair of small chromosomes, which are presumed to be aberrant Y derivatives. Meiosis in the XYSxr mouse involves transfer of chromatin rich in Bkm-related DNA from the Y-Y1 complex to the X distal terminus. We suggest that this event is responsible for the transmission of the Sxr trait.

Animals↗