Search PubMed⌕ Search

Biomedical subjects

G Rao

Publications and source records attributed to G Rao.

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

Increased electrotonic coupling in aged rat hippocampus: a possible mechanism for cellular excitability changes.

The effects of aging on the intercellular transfer of the low molecular weight fluorescent dye 5,6-carboxyfluorescein was studied in subfields fascia dentata, CA1, and CA3 of rat hippocampal slices maintained in vitro. All three areas exhibited a statistically significant increase in dye coupling with age. The increased dye coupling was accompanied by an apparent increase in postsynaptic excitability as assessed by the ratio of the population spike to EPSP components of the extracellulary recorded field potential. The possibility that artifactual dye coupling due to cell fusion contributed significantly to these results was ruled out by the demonstrations that a high molecular weight, dextran-coupled fluorescein compound did not produce multiple fills and that dye coupling with carboxyfluorescein could be prevented by prior intracellular loading with Ca++, a procedure that decouples gap junctions in other tissue. The increase in extent of electrical coupling suggested by these data may largely account for the apparent increase in cellular excitability of this tissue with age and may reflect the mechanism by which the senescent hippocampus compensates for the loss of afferent input during the course of normal aging. The additional possibility is raised that increased electrical coupling may reflect a mechanism for permanent associative storage of information in this system.

Aging↗
PubMed1987

Occlusion of hippocampal electrical junctions by intracellular calcium injection.

Low-molecular weight dyes such as Lucifer yellow or carboxyfluorescein have been used to investigate the electrical connectivity of neurons via gap junctions. The interpretation that such dye passage is mediated through intercellular channels has been controversial and difficult to corroborate with direct techniques in mammalian brain. We report here that elevated intracellular free Ca2+, a treatment shown to cause gap junction occlusion in other tissues, significantly blocks dye transfer between hippocampal cells. Furthermore, intracellular injection of FITC-dextran (which is too large to cross gap junctions) never resulted in multiple hippocampal cell fills. These data lend strong support to the argument that the extent of dye-coupling provides a good estimate of the number of intercellular communication channels, and raises the possibility that these channels may be physiologically modulated.

Animals↗
PubMed1987

Thalamic and subcortical gliosis with dementia.

We describe two cases of patients with "primary dementia" in whom autopsy showed marked astrocytosis in several subcortical nuclei, but chiefly in those of the thalamus. One patient had the onset of symptoms at 31 years of age and a subacute course. The second patient was an elderly man with a strong familial history of dementia. These cases offer further evidence that subcortical lesions, especially in the thalamus, may produce a dementia that is not always clinically distinguishable from Alzheimer's disease and other "cortical" dementias.

Adult↗
PubMed1987

Altered Electron Flow in Continuous Cultures of Clostridium acetobutylicum Induced by Viologen Dyes.

The physiological response of Clostridium acetobutylicum to methyl and benzyl viologen was investigated. Viologen dyes at low concentrations (at levels of parts per million [micrograms per milliliter]) caused significant metabolic shifts. Altered electron flow appeared to direct carbon flow from acid to alcohol production accompanied by decreased hydrogen evolution. Reducing equivalents normally released as free hydrogen were directed toward formation of NADH which, in turn, resulted in increased alcohol production. In addition, it was shown that solvent production can take place at pH 6.3. Contrary to previous reports, butanol production appears to be independent of high levels of acetate-butyrate and glucose.

Journal Article↗
PubMed1986

Intracellular fluorescent staining with carboxyfluorescein: a rapid and reliable method for quantifying dye-coupling in mammalian central nervous system.

Previous studies investigating electrotonic coupling in mammalian central nervous system have used the fluorescent marker Lucifer Yellow as an indicator of the presence of intercellular junctions between neurons. The fluorescent dye 5,6-carboxyfluorescein is known to have approximately 5 times the fluorescent yield of Lucifer Yellow. We have investigated the use of this dye as a potential alternative fluorescent marker on two types of neurons in the rat hippocampus in vitro. Unfixed hippocampal slices were mounted in a mixture of n-propyl gallate in glycerol and viewed with epifluorescence optics. Injections of small, brief hyperpolarizing currents through carboxyfluorescein-filled glass pipettes reliably produced neuronal fills of good quality. Both dendritic spines and axonal arborizations (including the thin mossy fibers of the dentate gyrus) were frequently observable. In addition to single cell fills, clusters consisting of 2-6 neurons were observed. No correlation was found between the number of cells per cluster and the ejection time. In addition, even cells exhibiting poor electrophysiological characteristics, or cells impaled only briefly, frequently exhibited good quality dye filling. This method will be particularly useful when large sample sizes are necessary to compare regional variations in the extent of electrotonic coupling in the mammalian brain.

Animals↗
PubMed1986

Long-term enhancement of hippocampal synaptic transmission and the acquisition of spatial information.

The hypothesis that memories are stored as a specific distribution of strengths in a population of modifiable synapses was examined by the bilateral induction of long-term enhancement in synapses of the main afferent fiber system to the hippocampal formation in rats. Brief, high-frequency activation of the perforant pathway in chronically prepared animals resulted in a persistent increase in the field EPSP and population spike, measured extracellularly in fascia dentata. This treatment resulted in a profound and persistent deficit in the acquisition of new spatial information in a task requiring spatial "reference" memory, and disruption of recently acquired spatial information. Well-established spatial memory was completely unaffected, however, as was the acquisition of spatial information into short-term "working" memory. These results support the hypothesis that, during the formation of "cognitive maps," spatial information must be temporarily stored at modifiable synapses at the input stage to the hippocampal formation, but that this information is not needed once the representation of the environment is well established. Spatial working memory, in a familiar environment, appears not to depend on the distribution of synaptic strengths in this system at all.

Animals↗
PubMed1985

What is the optimum A-V interval in D.D.D. pacing?

One of the programmable parameters in recent pacemakers is atrio-ventricular interval. To find out the optimum A-V interval studies were done in 14 patients. Multigated radionuclide scans were used to measure the left ventricular function, at a resting heart rate of 70/minute. Seven patients had poor left ventricles (ejection fraction less than 50%). Left ventricular ejection fraction, relative cardiac output and end diastolic counts were highest at 250 M. Sec. interval compared to 150. Ejection rates and end systolic counts were not related to A-V interval. Relative cardiac output was 27% higher in poor ventricles at 250 delay than 150. This observation was not significant in normal hearts. Optimum P-R interval is 250 M. Sec. for maximum left ventricular function.

Aged↗
PubMed1984

Thiopental treatment after global brain ischemia in pigtailed monkeys.

The authors investigated the value of high-dose thiopental (TH) therapy after 16-min complete global brain ischemia (GBI) in three groups of pigtailed monkeys, using a neck cuff model of GBI with 96 h intensive care postischemia (PI). Control group (n18): Normotension was restored within 2 min PI; paralysis/controlled ventilation was maintained for 48 h PI with 50% N2O/O2. Thiopental loading group (n13): Control treatment plus TH-loading with 90 mg/kg iv given from 5 to 65 min PI (mean peak TH plasma level 130 micrograms/ml). Thiopental anesthesia group (n14): Control treatment plus TH anesthesia with 90 mg/kg iv given over 12 h PI (sustained TH plasma levels of 25-35 micrograms/ml and EEG burst suppression). Norepinephrine requirement for blood pressure control PI was greater in the TH groups than in the control group (P less than 0.05). Lidocaine was needed for control of arrhythmias in the TH loading group. There was no significant difference in mortality or neurologic outcome between the groups. At 96 h PI seven of 11 animals were awake in the control group, compared with seven of 12 and six of 12 in the two TH groups. Neurologic deficit scores (NDS) for the survivors at 96 h PI were 23 +/- 6% (mean +/- SD) (n10) in the control group, compared with 25 +/- 9% (n11) and 26 +/- 12% (n10) in the two TH groups (NDS 100% = brain death, 0% = normal). Seizures PI (in 1-2 of each group) were associated with worse neurologic deficits.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Prolonged immobilization and controlled ventilation do not improve outcome after global brain ischemia in monkeys.

This study is a therapeutic evaluation of prolonged immobilization and controlled intermittent positive-pressure ventilation (IPPV) after global brain ischemia (GBI) in pigtailed monkeys. Sixteen min of GBI was produced with a high-pressure neck cuff, while the lungs were being continuously ventilated. Normotension was restored within 2 min postischemia (PI). The control group of 13 monkeys was weaned from IPPV 4 to 6 h PI. The treatment group of 18 animals was paralyzed and ventilated with a 50:50 nitrous oxide-oxygen mixture for 48 h PI. Intensive care was maintained for 96 h PI. In the control group, 8 of 10 animals were awake at 96 h PI compared to 7 of 11 in the treatment group. Neurologic deficit scores for the survivors in the 2 groups were also not significantly different. Histologic examination supported this conclusion. Paralysis/IPPV for 48 h post-GBI with 50% N2O facilitates control of blood gases and blood pressure, but does not improve the neurologic outcome over that achieved with only 4 to 6 h controlled ventilation.

Animals↗
PubMed1984

Amelioration of brain damage by lidoflazine after prolonged ventricular fibrillation cardiac arrest in dogs.

Calcium entry blockers can ameliorate postischemic cerebral hypoperfusion, protect the myocardium against ischemia, and may protect against early postischemic neurologic deficit. This study documents that a calcium entry blocker, given after cardiac arrest, can ameliorate late postischemic neurologic deficit (ND). Thirty-four dogs received 10 min of ventricular fibrillation, restoration of spontaneous circulation by external cardiopulmonary resuscitation, and standard postarrest intensive care. Eleven of these dogs were given lidoflazine, 1 mg/kg body weight, within 10 min postarrest and again at 8 h and 16 h. Pupillary light reflexes, EEG activity, arterial-cerebrovenous oxygen gradients (O2 demand/supply ratios) and intracranial pressure were the same in both groups. After weaning from controlled ventilation at 24 h, ND scores improved consistently through the 96-h observation period in the lidoflazine-treated dogs. In the control group, ND scores were significantly higher than in the lidoflazine-treated dogs. In the lidoflazine-treated group, 5/11 dogs achieved normal overall performance and none remained comatose, whereas all control dogs had some deficit and 4/11 remained comatose. Delayed neurologic deterioration occurred in 6/11 control and 0/11 lidoflazine-treated dogs. Total mean cerebral histopathologic damage (HD) scores at 96 h were not significantly different between the two groups; however, individual HD scores and maximum cerebro-spinal fluid (brain-specific) creatine-phosphokinase activity--which increases after brain insults--correlated well with 96-h ND scores. In the lidoflazine group, life-threatening dysrhythmias were less frequent and the norepinephrine requirement for blood pressure maintenance was the same as in the control group. Cardiac output remained at prearrest levels in the lidoflazine-treated dogs, but decreased in the control group, particularly during the first 4 h postarrest.

Animals↗
PubMed1982

Frequency of anaphylactoid reactions during intravenous urography with radiographic contrast media at two different temperatures.

One hundred randomly selected patients undergoing routine excretory urography were assigned in double-blind fashion by alternate entry pairs to receive radiographic contrast media at 37 degrees C (Group I) or room temperature (Group II). There were three anaphylactoid reactions and five nonanaphylactoid reactions in Group I, and five anaphylactoid and eight nonanaphylactoid reactions in Group II, differences that were not statistically significant. No differences were detected between reactors and nonreactors. Thus, in this study, infusion temperature had no effect on the frequency of adverse reactions to radiographic contrast media during excretory urography.

Adolescent↗