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Biomedical subjects

S Prabhakar

Publications and source records attributed to S Prabhakar.

At least 91 records · Page 5Linked to original sources

Organophosphorus intoxication.

In every period of history, military leaders have wrestled between a desire to gain victory by using every possible means and a revulsion from resorting to poison. During the First World War, a European country cast aside the humanitarian tradition of its poets and philosophers and attacked its enemies with a wave of chlorine gas; the same nation, 30 years later, put to death 6 million human beings in gas chambers. But out of the industry of war gases, a few organophosphorus compounds, notably tabun and sarin, later underwent large-scale development. These compounds are nowadays used primarily as insecticides. Several early citations on organophosphate compounds place this chemical class in neurological context. However, as evidenced by events during the Gulf War of 1991 and the United Nations' arsenal inspections during that war, military interests in organophosphates are medically very pertinent today, beyond just historical allusions.

Animals↗

Claisen rearrangement of allyl phenyl ether and its sulfur and selenium analogues on electron impact

The electron impact (EI) mass spectrum of allyl phenyl ether (1) includes an ion at m/z 106 that is formed mainly by the loss of CO from the molecular ion, as supported by high resolution and MS/MS data. The formation of the [M - CO](+) ion from 1 can be explained in terms of the Claisen rearrangement of 1 after ionization in the ion source of the mass spectrometer. Similarly, allyl phenyl sulfide (2) and allyl phenyl selenide (3) showed characteristic ions corresponding to [M - CH(3)](+), [M - XH](+) (X = S or Se) and [M - C(2)H(4)](+.), and the formation of these ions are explained via Claisen rearrangement of 2 and 3 in the ion source of the mass spectrometer resulting in a mixture of rearrangement products. The formation of molecular ions of 2-allyl thiophenol and 2-allyl selenophenol as intermediates, that cannot be isolated as the neutrals from the solution phase Claisen rearrangement of 2 and 3, respectively, is clearly indicated in the gas phase. The mass spectra of the rearrangement products obtained from the solution phase reaction were also consistent with the proposal of formation of these products in the ion source of the mass spectrometer. The formation of characteristic fragment ions attributed to the Claisen rearrangement products are also evident in the collision induced dissociation spectra of the corresponding molecular ions. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗

Acute disseminated encephalomyelitis and multiple sclerosis: magnetic resonance imaging differentiation.

The study was undertaken to compare the MR imaging features of acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS) in a country with a high prevalence of ADEM. Magnetic resonance scans from 33 patients diagnosed clinically with MS (14 patients) or ADEM (19 patients) were reviewed concurrently by two radiologists blinded to the clinical diagnosis. The size, site, morphology and pattern of brain and spinal cord involvement were recorded and the MR imaging diagnosis was compared with the clinical diagnosis. The MR imaging findings matched with the clinical diagnosis in 11 of 14 patients with MS (sensitivity = 78.6%), and with the clinical diagnosis in 15 of 18 patients with ADEM (sensitivity = 78.9%). Three patients had non-specific findings and in a further three patients discordant imaging features were present. One patient with imaging features typical of Balo's concentric sclerosis was diagnosed clinically as suffering from ADEM. In a country with a high prevalence of ADEM, the majority of patients with ADEM and MS can be differentiated on MR imaging.

Adolescent↗

Expression of GC-C, a receptor-guanylate cyclase, and its endogenous ligands uroguanylin and guanylin along the rostrocaudal axis of the intestine.

Members of the receptor-guanylate cyclase (rGC) family possess an intracellular catalytic domain that is regulated by an extracellular receptor domain. GC-C, an intestinally expressed rGC, was initially cloned by homology as an orphan receptor. The search for its ligands has yielded three candidates: STa (a bacterial toxin that causes traveler's diarrhea) and the endogenous peptides uroguanylin and guanylin. Here, by performing Northern and Western blots, and by measuring [125I]STa binding and STa-dependent elevation of cGMP levels, we investigate whether the distribution of GC-C matches that of its endogenous ligands in the rat intestine. We establish that 1) uroguanylin is essentially restricted to small bowel; 2) guanylin is very low in proximal small bowel, increasing to prominent levels in distal small bowel and throughout colon; 3) GC-C messenger RNA and STa-binding sites are uniformly expressed throughout the intestine; and 4) GC-C-mediated cGMP synthesis peaks at the proximal and distal extremes of the intestine (duodenum and colon), but is nearly absent in the middle (ileum). These observations suggest that GC-C's activity may be posttranslationally regulated, demonstrate that the distribution of GC-C is appropriate to mediate the actions of both uroguanylin and guanylin, and help to refine current hypotheses about the physiological role(s) of these peptides.

1-Methyl-3-isobutylxanthine↗

Episodic ataxia: a case report and review of literature.

This report describes the clinical features of a 29 year female presenting with a 3 years history of episodes of cerebellar ataxia, dysarthria and nystagmus lasting 3-5 days, recurring almost every month. Sleep disturbance and buzzing in ears were noted 3-4 days before each episode. No other precipitant factor was present. Family history was negative. She was diagnosed as a case of episodic ataxia type-2 and was successfully treated with acetazolamide, a carbonic anhydrase inhibitor. She was asymptomatic at 2 year followup.

Adult↗

Neurologic complications of dropsy: from possibility to reality.

Epidemic dropsy, which results from the accidental ingestion of mustard oil adulterated with argemone oil, has been associated with certain neurologic symptoms. The occurrence of objective neurologic involvement has, however, precluded this illness. We report two cases, who were victims of epidemic dropsy in the recent outbreak in India and showed objective neurologic deficit in the form of brachial neuritis.

Adult↗

P300 in newly diagnosed non-dementing Parkinson's disease: effect of dopaminergic drugs.

Changes in cognitive function are an integral part of the clinical presentation of Parkinson's Disease (PD). P300 potential studies in early stages of Parkinson's disease are lacking and effect of L-dopa therapy on these potentials is controversial. In this study, changes in P300 potentials in early stages of PD and effects of dopaminergic therapy were investigated. P300 waves were elicited by standard auditory 'odd ball' paradigm and were recorded before the start of therapy and 15 days, 3 and 6 months after the start of L-dopa therapy in 25 newly diagnosed patients with idiopathic PD. All patients were classified according to Hoehn and Yahr scale. Minimental status examination (MMSE) was done in all. Control group had 20 normal subjects. The P300 latency was not significantly increased in early Parkinson's disease. This latency was reduced with dopaminergic therapy on 15th day, but increased later. Implications of the data are discussed.

Adult↗

Changing scenario of cryptococcosis in a tertiary care hospital in north India.

BACKGROUND & OBJECTIVES: With the increase in the number of patients of AIDS, the incidence of cryptococcosis is on the rise in India. It was therefore considered important to evaluate the predisposing factors, laboratory investigations and outcome of patients with cryptococcosis in this changed scenario. METHODS: We assessed 58 patients with cryptococcosis retrospectively over a five year period (January 1995-December 1999) at the Nehru Hospital, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh. RESULTS: The annual incidence of cryptococcosis in PGIMER, Chandigarh has increased about 15 fold from 1970-1982 (pre AIDS era) to 1995-1999 (present series). Of the 47 patients studied for predisposing factors, 36 patients were identified with predisposing factors, HIV infection (57.4%) was the commonest followed by haematologic malignancies (6.3%) and renal transplant (4.2%). Forty one patients were diagnosed by isolation of the organism as well as antigen detection in cerebrospinal fluid/serum, 9 by isolation alone and 8 by antigen detection alone. Quantitative antigen titres were done in 38 patients and a significantly higher (P < 0.01) antigen titre (> 512) was observed in HIV positive patients as compared to HIV negative patients. All isolates tested were of Cryptococcous neoformans var neoformans biotype and no resistance to antifungal agents was noted. Twenty of 41 patients receiving treatment improved. The results were compared with other studies available from India. INTERPRETATION & CONCLUSION: The incidence of cryptococcosis is on the rise in this part of north India and this can be attributed to an increase in AIDS cases.

Adult↗

Profile of intractable epilepsy in a tertiary referral center.

This study was undertaken to find out the profile of intractable epilepsy (IE) in a tertiary referral centre. 100 patients (males 67; females 33) with IE attending the epilepsy clinic were evaluated. Detailed history, examination, investigations like EEG and CT scan and details regarding pharmacotherapy were analysed. The age of the patients ranged from 5 to 70 yrs (mean=23.2 yrs). Mean duration of seizures was 11.44 years. Commonest seizure type was partial seizures (74%). Amongst patients with generalised seizures (26%), 14% had multiple seizure types. The seizure frequency was 12.39 +/- 21.57 (mean +/- SD) per month. Fifty seven patients were in the symptomatic group with CNS infections being the leading cause (19%) of epilepsy. Fifty patients had one or more abnormal predictors of IE. There was no difference in the severity of epilepsy in patients with no abnormal feature when compared with patients having abnormal features. EEG was abnormal in 69% cases with background abnormality in 20% and focal abnormality in 36% cases. CT scan was abnormal in 41% cases with commonest abnormality being neurocysticercosis (11%) followed by gliosis (9%) and chronic infarct (9%). Sixty patients were receiving a combination of two drugs, 32 patients 3 drugs and 8 patients were on 4 drugs. There was no difference in seizure control in patients who were on 2 drugs or more than 2 drugs. Partial seizures were the commonest seizure type leading to IE; CNS infection being the leading aetiological factor. The presence or absence of predictors of intractability does not predict severity of epilepsy. Addition of third primary drug to existing combination only increases adverse effects without better control of seizures.

Adolescent↗

Risk of recurrence of seizures following single unprovoked idiopathic seizure.

A prospective study was conducted to look for various factors that could predict the risk of recurrence of a single unprovoked idiopathic seizure. Seventy six patients with a history of single episode of seizure ultimately completed the study and the data regarding age, sex, duration of seizure, time of occurrence of the ictus, interval between onset and referral, family history of seizure and alcohol consumption were analysed. All patients of symptomatic epilepsy and those with an abnormal scan were excluded. The patients were randomized into two groups, one of which received anti epileptic medication and the other did not. All patients underwent electroencephalography (EEG). Twenty two (M=16, F=6) of the 76 patients (M=56, F=20) had a recurrence of seizure. The duration of seizure at initial presentation was 10.1 +/- 5.2 min. in the recurrence group and 6.5 +/- 4.1 min. in the non-recurrence group. Twelve of the 16 patients with an abnormal EEG had a recurrence whereas only 10 of the 60 patients with a normal EEG had a recurrence (p <0.001). Of the treated cases (n=36), only 4 had a recurrence compared to 18 of the untreated cases (n=40) (p <0.002). Eighteen of the 22 cases having a recurrence did so within three months. Six of the cases with family history of seizure (n=10) had a recurrence, whereas only 16 of the cases without family history of seizure (n=16) had a recurrence (p <0.05). Patients of a single unprovoked idiopathic seizure with a normal CT scan are less likely to have a recurrence if the duration of seizure at presentation is short, EEG is normal, more than 3 months have passed since the first seizure and if treatment has been started. Family history of seizures does have a moderately significant bearing, but alcohol intake does not increase the chances of seizure.

Adolescent↗

Mass spectral study of substituted allyl aryl and allyl alkyl selenides and some analogous sulfides

The electron impact (EI) mass spectra of allyl aryl selenides showed abundant molecular ions and many fragment ions containing the selenium atom. alpha-Cleavage is the dominant process in the fragmentation of selenides, and cleavage product ions are characteristic of the substituents. In the case of 3-methyl allyl and related aryl selenides, characteristic delta-hydrogen migration to the selenium atom is observed. A McLafferty-type rearrangement is found in benzyl allyl selenides and substituted alkyl allyl selenides. The charge on the rearrangement products preferably remains on the fragments containing the phenyl group. The [M - SeH](+), [M - CH(3)](+) and [M - C(2)H(4)](+) ions are found only in the EI mass spectrum of allyl phenyl selenide, and are attributed to a Claisen rearrangement in the source of the mass spectrometer. All structurally informative fragmentation processes are supported by collision induced dissociation spectra of molecular ions. The fragmentation patterns found in methane chemical ionization (CI) spectra of the selenides were significantly different from those observed in EI. The EI and CI mass spectra of analogous sulfides showed similar behaviour to that observed in the corresponding selenides. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗

New syntheses of DNA adducts from methylated anilines present in tobacco smoke.

A new synthetic pathway for the formation of deoxyguanosine-monoarylamine adducts is described, involving the generation and use of arylnitrenes as electrophilic synthons. Photolysis of aryl azides, the most common method for generating arylnitrenes, was tested in the presence of 2'-deoxyguanosine. N-(2'-Deoxyguanosin-8-yl)monoarylamine (dG-C8-Ar) adducts were obtained, but the yields were typically low. Deoxygenation of nitro- and nitrosoarenes by triethyl phosphite in the presence of 2'-deoxyguanosine proved to be an effective method, by which dG-C8-Ar, (2'-deoxyguanosin-N1-yl)monoarylamine (dG-N1-Ar), and (2'-deoxyguanosin-O(6)-yl)monoarylamine (dG-O(6)-Ar) adducts were obtained in acceptable yields.

Aniline Compounds↗

The maize EmBP-1 orthologue differentially regulates opaque2-dependent gene expression in yeast and cultured maize endosperm cells.

In addition to the bZIP protein Opaque2 (O2), there are other maize endosperm nuclear proteins that recognize the O2 box in 22 kDa zein gene promoters. In an effort to understand the effect of these factors on 22 kDa zein expression, we have cloned one of these and identified it as the putative maize (Zea mays L.) orthologue of the wheat bZIP protein EmBP-1 (mEmBP-1). The mEmBP-1 protein exhibits 52% sequence identity and 68% similarity with the wheat protein and recognizes a similar spectrum of DNA sequences, albeit with slightly altered specificity. The mEmBP-1 gene exists as duplicate loci in maize on chromosomes 7S (mEmBP-1a) and 2L (mEmBP-1b). The mEmBP-1 genes are expressed in endosperm, embryo, immature ears, tassel, roots, and seedling shoots at low levels. Although mEmBP-1 binds to the O2 box from the 22 kDa zein gene promoter as a homodimer, it is unable to heterodimerize with O2. The mEmBP-1 protein can activate transcription from a truncated promoter containing a pentamer of the O2 site in yeast cells; however, it inhibited regulated transcription of a 22 kDa zein promoter in a transient expression assay using cultured maize endosperm cells.

Amino Acid Sequence↗

Intravenous immunoglobulin in very severe childhood Guillain-Barré syndrome.

To evaluate intravenous immunoglobulin (IVIG) therapy in children with very severe Guilain-Barré syndrome (GBS) with reference to the need for respiratory support, ICU stay and long-term outcome, we studied 33 children with very severe GBS and quadriparesis and/or respiratory muscle weakness admitted to the Pediatric Intensive Care Unit (PICU) of PGIMER, Chandigarh. Cases (n = 22, IVIG group) were enrolled prospectively, and controls (n = 11), similar to cases in age and severity of illness, retrospectively. All children received similar supportive and respiratory care. In addition, cases were given IVIG (Sandoglobulin, Sandoz) 0.4 g/kg bodyweight per day for 5 days. The mean age, duration of symptoms prior to admission and severity of illness in the two groups were similar. In the IVIG group, onset of recovery of muscle power was significantly earlier (day 14.8 (6.8) of illness vs day 20.9 (8.6), p < 0.05) and the length of PICU stay significantly shorter (20.5 (13.0) days vs 50.5 (33.3) days, p < 0.01). Sixteen (72.7%) children in the IVIG group had improved by at least one functional grade after 1 month and 15 (68%) were walking independently after 3 months compared with two (18%) and four (36%) controls, respectively (p < 0.05). The number of children who needed endotracheal intubation and mechanical ventilation and the duration of mechanical ventilation was significantly less in the IVIG-treated group. We conclude that in very severe GBS in children IVIG therapy improves outcome to a remarkable extent, reduces the need for intubation and mechanical ventilation, shortens the length of stay in ICU, and promotes ambulation sooner.

Case-Control Studies↗

Clinical profile of multiple sclerosis in north-west India.

A total of 100 patients were enrolled in this study with the clinical diagnosis of multiple sclerosis (MS). This included prospective analysis of 35 patients and retrospective analysis of 65 patients from their medical records spanning a period from January 1986 to March 1998. They were divided into 3 groups (i) overall group (ii) MRI group (where MRI was available) (iii) No MRI group (where MRI was not available). Data in terms of clinical features and laboratory investigations were compared in the three groups. MS was found to constitute 2.54% of neurology admission between January 1993 to December 1997. It was higher as compared to previous data from our institute (1.58%). Cerebellar symptoms were higher in the MRI group as compared to the non MRI group. The clinical spectrum of MS in the MRI group was comparable to that in the west. Obviously the MRI helps in early diagnosis of milder and atypical cases. Oligoclonal bands were found in 30.5% of cases only.

Adult↗

Systemic brucellosis with chronic meningitis: A case report.

A young adult presenting with 11 months history of fever, headache, vomiting was found to have CSF lymphocytic pleocytosis with increased protein. His serum tested strongly positive for Brucella (standard tube agglutination titre 1: 320) whereas CSF was weakly positive. He became asymptomatic on treatment with tetracycline, rifampicin and streptomycin with significant CSF response. This case is reported because of its rarity.

Adult↗