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Biomedical subjects

M Singer

Publications and source records attributed to M Singer.

At least 271 records · Page 15Linked to original sources
PubMed1979

Temporal locus of inference in the comprehension of brief passages: recognizing and verifying implications about instruments.

Recent investigations of language comprehension have shown that people frequently report recognizing test sentences which express ideas that were only implied in an antecedent passage. The present study asked whether the inferences underlying these false alarms are drawn when the original message is encoded or at test time. In Exp. 1, it was shown that the recognition rate for direct quotations from brief passages is clearly higher than for sentences expressing implications about the instruments used to perform actions. In Exps. 2, 3, and 4 the subjects were timed while they decided whether test sentences (a) had been heard verbatim in the passage or (b) were true concerning the passage. In all conditions, subjects needed about .2 sec. more to respond affirmatively to "implicit" sentences than to ones that quoted or paraphrased the passage. It was concluded that at least a subset of the cognitive processes associated with the inferences in question is executed at test time.

Concept Formation↗
PubMed1979

Evidence that the cholinergic enteropancreatic reflex may be independent of cholecystokinin release.

Studies were performed in four dogs with chronic gastric and pancreatic fistulas following intraduodenal perfusion with 10 mmole hr-1 of sodium oleate for 30 minutes. Radioimmunoassay (RIA) of plasma CCK LI was undertaken by an RIA method using labeled, desulfated CCK 8 I125 and an antiserum raised to CCK 8. The detection limit for the assay was 0.25 to 0.5 fmole and the lowest detectable plasma level was 5 to 10 fmoles ml-1. Since there was equal cross-reactivity to gastrin, a gastrin-specific assay also was employed to evaluate any changes in gastrin levels. After oleate infusion the plasma CCK increment above basal was 50 +/- 11 fmoles ml-1, with return to basal levels after 60 minutes. Administration of atropine significantly (P less than 0.01) inhibited the release of CCK in the first 20 minutes. Thereafter CCK release was not reduced. Plasma gastrin values did not change before and after oleate perfusion. Pancreatic protein output increased from 72 +/- 12 to 420 +/- 55 mg/10 min-1 after oleate administration. However, after atropinization the rise in pancreatic protein output was significantly lower (152 +/- 36 mg/10 min-1) (P less than 0.01). We have shown that, using our RIA method, there is a measurable rise in plasma CCK LI after intraduodenal oleate. After atropinization the CCK response was decreased significantly during the first 30 minutes, but was virtually unchanged during the second 30 minutes, when the fall in pancreatic protein output was most marked. We conclude that the cholinergic mechanism which plays a role in the endogenous stimulation of pancreatic protein secretion by intraduodenal oleate cannot be explained simply be decreased CCK release. This mechanism may be hormonal, distinct from secretin, or neural possibly, via activation of an enteropancreatic reflex.

Animals↗
PubMed1978

The role of ependyma in regeneration of the spinal cord in the urodele amphibian tail.

The new spinal cord formed during tail regeneration in the newt first develops as a caudal extension of the ependymal tube. Neuroblasts and neuroglia subsequently differentiate from cells of the ependymal tube in a proximal-caudal sweep. Descending axons from the cord rostral to the lesion and from newly differentiating neurons travel in channels which are present prior to the ingrowth of axons. The present study confirms previous observations from our laboratory and presents details of the ultrastructural relations of axons and ependymal processes within the cord. The ependymal cell surface facing channels typically forms numerous digitor sheet-like protuberances which extend into the channel lumen. As axons enter the channels in increasing numbers these protuberances partially subdivide the axons into smaller groupings, even occasionally segregating individual axons. At levels where fibers have not yet entered or have most recently entered the ependymal channesl two specializations appear on the ependymal plasmalemma facing the channels and their axons: coated membranes and hemidesmosome-like structures. At more mature levels, where many fibers have already entered the channels, axons in contact with ependymal processes sometimes show synapse-lide vesicle accumulations with associated membrane densities. Coated membranes and hemidesmosome-like structures are lacking at these levels. Our observations suggest that ependymal processes, in addition to providing substrate and direction for regenerating spinal cord axons, may also furnish or exchange more specific information at the morphologically identifiable specializations described above.

Animals↗
PubMed1978

Highly reiterated sequences of SIMIANSIMIANSIMIANSIMIANSIMIAN.

A 172-base pair segment of DNA that is repeated several million times in the genome of the African green monkey has been characterized. Sequence analysis revealed that the many repeats of this complex unit are not all identical but represent a set of closely related segments: Sequence divergence occurs at various positions in the segment in a nonrandom manner. The uncloned segment obtained from monkey DNA is compared with a cloned segment of the same DNA which was recombined into the genome of simian virus 40 during permissive infection.

Animals↗
PubMed1978

Nerve dependent macromolecular synthesis in the epidermis and blastema of the adult newt regenerate.

The present study is an analysis of neurotrophic control of DNA and protein synthesis in the separated epidermis and blastema of the early newt limb regenerate. Previous macromolecular studies employed the entire regenerate without discrimination between its two components. The results demonstrate that the specific activities of newly synthesized protein and DNA show a nerve dependence in both epidermis and blastema. There appears to be a postdenervation rise in synthesis followed by a decline to a plateau level in both components, similar to what is reported for the whole regenerate. After two days of denervation DNA synthesis in the mesenchymatous cells is more profoundly depressed, suggesting that the epidermis is less nerve dependent.

Animals↗
PubMed1978

Family cooperation and effectiveness in a cholesterol-lowering diet.

An average reduction in serum cholesterol approximating 10 per cent was achieved in a short-term, family-centered study in which intakes of cholesterol and saturated fats were decreased and sunflower oil and margarine were added as the major sources of polyunsaturated fats. Dietary Achievement Scores demonstrated shifts in food consumption between baseline and diet periods. Changes were evident in all fat-containing food groups; meat was the least altered. A high degree of cooperation was evident in participating families, implying the possibilities for complete family cooperation in preventive or therapeutic dietary programs. Approximately three months after the end of the test period, cholesterol levels had returned to pre-diet levels, indicating the need for continuation of the changed regimen if cholesterol-lowering is to be maintained.

Adolescent↗
PubMed1977

The perineural sheath in the urodele amphibian.

The perineural epithelial cells of the peripheral nerve sheath in triturus are elongated flat cells with long and thin cytoplasmic processes. Structural characteristics of the processes include a relative absence of common cytoplasmic organelles of the perinuclear cytoplasm but an abundance of vesicular profiles similar to fully formed pinocytotic vesicles. Unlike pinocytotic vesicles, vesicles of the processes often contain an 8-nm thick filament attached to their cytoplasmic face. Vesicles are also interconnected by similar filaments or by tubules. In addition, almost all vehicles appear to have openings at the cell surface, a feature not seen for pinocytotic vesicles. The concentration of exogenous peroxidase in the vesicles, and the subsequent appearance of peroxidase in the endoneural fluid, myelin sheath and axon, support the notion that the vesicles function in the exchange of substances between extraneural and endoneural fluids.

Animals↗
PubMed1977

Intraperitoneal transplants of taste buds in the newt.

Autografts of tongue onto the liver contained taste buds without nerves for up to 30 days. However, these denervated taste buds were generally smaller than normal and distorted in structure. Nerve fibers invaded the graft from the liver and after 30 days normal appearing taste buds were found only in implants of tongue which contained extensive nerve fibers. Thus it appears that certain visceral nerves can maintain and possibly induce taste bud formation in implants of tongue. This is interpreted as additional evidence for the trophic influence of nerves upon taste buds. Moreover, this ability to maintain taste buds is not restricted to gustatory nerves in the newt.

Animals↗
PubMed1977

Relation between nerve fiber number and pectoral fin regeneration in the teleost.

The number of nerve fibers per unit of amputation surface area has been determined in four teleosts capable of regenerating their fins (Gobius paganellus, Gobius minutus, Ictalurus nebulosus and Fundulus heteroclitus) and in two-non-regenerating ones (Cottus bubalis and Blennius pholis). The number of nerve fibers is about 16 in the non-regenerating fin and varies between 25 and 35 in the regenrating ones. These data, correlated with previous ones obtained on tetrapods, affirm the principle that there is a phylogenetic decline in the quantitative innervation of the vertebrate appendage. Moreover, they show that in the fish a quantitative neuronal threshold must also be satisfied in order for fin regeneration to occur. The threshold, in terms of fiber number, is higher than in the urodele amphibian. However, the fibers appear to be of smaller caliber; and so, the total amount of neuroplasm at the amputation surface which is required for regeneration may be similar to that for the amphibian.

Animals↗
PubMed1977

Neurotrophic stimulation of DNA synthesis in the regenerating forelimb of the newt, Triturus.

The effect of infusions of soluble newt brain extracts on deoxyribonucleic acid (DNA) synthesis in the denervated, regenerating newt blastema has been studied. When moderate early to early regenerates are denervated for 48 hours, DNA synthesis normally drops to about 40% of that found in contralateral, innervated blastemas. Infusion of brain extract halfway through the denervation period (at 24 hours) approximately doubles the rate of DNA synthesis in denervated regenerates.

Animals↗
PubMed1977

The effect of light on forelimb regeneration in the newt.

The forelimb of the newt, Triturus (Notophthalamus) viridescens, was bilaterally amputated and the animals subjected to different photoperiods during the period of regeneration, namely (1) continuous light, (2) 15 hours of light/day and (3) total darkness. Animals exposed to continuous light reached the palette regeneration stage four to five days before those kept in total darkness with the 15 hours of light/day animals being intermediate. The difference in regeneration rate was first evident in the moderate early stage (blastema accumulation stage); it then increased during subsequent stages and the difference persisted during the observation period. In an attempt to determine whether the retina was the receptor of light affected, some animals were blinded at the time of amputation and subjected to continuous light. Their rate of regeneration was similar to sighted animals subjected to continuous light but greater than sighted animals in total darkness. The pineal is discussed as the likely mediator of the photo effect.

Animals↗