Search PubMed⌕ Search

Biomedical subjects

S J John

Publications and source records attributed to S J John.

5 recordsLinked to original sources
PubMed2004

Cloning and characterization of a bovine genomic fragment homologous to epidermal growth factor genes.

Epidermal growth factor (EGF) is a potent mitogen for a variety of cell types. The 53-amino acid mature EGF protein is encoded by sequences in exons 20 and 21 of a gene spanning over 110 kb. In this study, we report the cloning and characterization of 7.5 kb of bovine genomic sequence homologous to exon 19 through 21 from EGF genes from other mammalian species. The cloned gene fragment had an unusual sequence composition in the form of an in-frame TGA codon in the coding sequence. The sequence was expressed at low levels in kidney tissue and the corresponding cDNA contained the TGA codon. The level of similarity between the bovine exonic sequence and the human, porcine, murine, feline, and canine corresponding sequences varied from 64% to 73%; however, when only sequences encoding the mature EGF protein were compared, the level of similarity between the bovine sequence and the sequence from these species was 59% to 66%. The sequence similarity of the deduced mature protein was lower (34% to 39%) than the sequence similarity of the deduced propeptide. Although the cloned sequences could originate from a bovine EGF pseudogene, the possibility exists that they originate from the functional EGF gene. An as yet unidentified mechanism to by-pass the stop codon would allow the synthesis of a functional EGF protein. Alternatively, the cloned sequence could originate from an EGF-like gene.

Animals↗
PubMed1998

Atrial natriuretic peptide mediated alterations in catecholamine and indoleamine turnover in the nucleus of the solitary tract of rats.

The effect of locally perfused atrial natriuretic peptide (ANP) into the nucleus of the solitary tract (NST) was studied by monitoring the changes in the extracellular neurotransmitters and the cardiovascular functions in urethane anesthetized Sprague-Dawley rats. Perfusion of ANP was accomplished by using in vivo microdialysis probe unilaterally and stereotaxically implanted into the NST area. ANP at a concentration of 4 x 10(-12) M was perfused at a constant flow rate of 1.5 microl/min. over a period of one hour and the dialysate was assayed for both catecholamines and indoleamine. Perfusion of ANP into the NST led to significant reduction in both blood pressure and heart rate. Serotonin turnover was unaffected. Both norepinephrine (NE) and methoxyhydroxyphenylglycol (MHPG) levels increased, while the dihydroxyphenylacetic acid (DOPAC) level decreased, indicating the possible interaction between ANP and the catecholaminergic system of the NST in regulating the arterial blood pressure.

Animals↗
PubMed1998

Brain natriuretic peptide-mediated changes in the extracellular neurotransmitter turnover in the rostral ventrolateral medulla.

Changes in the rostral ventrolateral medullary neurotransmitter levels and associated cardiovascular functions in response to local administration of brain natriuretic peptide were investigated in urethane-anesthetized Sprague-Dawley rats. Unilateral injections of various doses of brain natriuretic peptide into the rostral ventrolateral medulla region led to significant reductions in both blood pressure and heart rate. To identify the changes occurring in the extracellular neurochemical profile, brain natriuretic peptide was perfused at the rate of 1.5 microliters/min for a period of 1 h through a microdialysis probe implanted stereotaxically into the rostral ventrolateral medulla area and the dialysate was assayed every 15 min for both catechols and indoleamine. Both norepinephrine and epinephrine concentrations were significantly reduced. Dihydroxyphenylacetic acid concentration showed no significant change in response to brain natriuretic peptide perfusion. On the other hand, serotonin turnover estimated by the measurement of its metabolite (5-hydroxyindoleacetic acid) concentration increased during the perfusion of brain natriuretic peptide. Blood pressure and heart rate also showed significant reduction during the perfusion of brain natriuretic peptide. These results suggest that brain natriuretic peptide may be relevant in the central regulation of cardiovascular functions by modulating monoamine neurotransmitters.

Animals↗
PubMedDate not supplied

Neuronal cell types and taste quality coding.

Over the past 25 years, there have been two opposing views of how taste information is represented in the activity of gustatory neurons. One view, the across-fiber pattern (AFP) theory, postulates that taste quality is represented by the pattern of activity across the afferent population. Stimuli with similar tastes produce similar patterns of activity. The other view is that activity in a few distinct neuron types codes taste quality in a "labeled-line" fashion. Neurons responding best to sucrose, for example, would represent "sweetness," and those responding best to NaCl would code "saltiness." Some of these neuron types appear to have a biological significance, such as the NaCl-best cells, which receive input about sodium stimuli exclusively from an amiloride-sensitive epithelial ion channel. However, the relatively broad tuning of these neurons makes it unlikely that they are capable of unambiguously coding information about taste quality. Rather, these neuron types play a critical role in establishing unique AFPs that distinguish among taste stimuli. The relative activity across these cell types represent taste quality, much like the patterns of activity across broadly tuned photoreceptors code information about stimulus wavelength.

Animals↗