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Biomedical subjects

C Nicholson

Publications and source records attributed to C Nicholson.

62 records · Page 4Linked to original sources
PubMed1972

Calcium transient in presynaptic terminal of squid giant synapse: detection with aequorin.

Microinjection of aequorin, a bioluminescent protein sensitive tocalcium, into the presynaptic terminal of the squid giant synapse demnonstrated an increase in intracellular calcium ion concentration during repetitive synaptic transmission. Although no light flashes synchronous with individual presynaptic : tion potentials were detected, the results are considered consistent with the hypothesis that entry of calcium into the presynaptic terminal triggers release of e synaptic transmitter substance.

Action Potentials↗
PubMed1969

Preferred centripetal conduction of dendritic spikes in alligator Purkinje cells.

Dendritic action potentials in alligator Purkinje cells tend to have a unidirectional preference which favors centripetal over centrifugal propagation. This unidirectional tendency funnels the peripherally evoked dendritic spikes into the lower dendrites and soma of these cells, and it allows the peripheral dendritic branches to operate to a certain extent as partially independent functional units.

Action Potentials↗
PubMedDate not supplied

Age differences in responses to facial trauma.

This study examines age differences in causes, characteristics, and outcomes of facial trauma seen in a major trauma hospital. A retrospective analysis was undertaken of 615 cases of facial trauma that had occurred during a 5-year period. The greatest proportion of patients were aged 20 to 29; those older than age 60 represented just 6.8% of the total cases. Gender differences were not observed in the oldest age groups. The oldest patients (older than 70 years) were more likely to have had pedestrian accidents and less likely to have been assaulted than other age groups. Older patients had more multiple injuries but fewer treatment procedures than other age groups. Significant differences were found in death rates; the older patients were more likely to die as a result of their injuries. Implications for patient management based on age and treatment needs are discussed.

Accidental Falls↗
PubMedDate not supplied

Issues involved in the transmission of chemical signals through the brain extracellular space.

Two classes of substances exist within the extracellular space: energetic and informational. Examples of the former are glucose, dissolved oxygen and CO2 while the latter include excitatory amino acids, cathecholamines and opiates. The simple ions Na+ and Cl- are generally associated with energetic processes while extracellular K+ and Ca2+ tend to be informational in function. Local release of an informational substance brings about a concentration gradient that causes the substance to be dispersed in the extracellular space by diffusion. This process is modified relative to a free aqueous medium by the constraints of volume fraction, tortuosity and uptake. Volume fraction is defined simply as the fraction of a brain region that is extracellular. If a given quantity of substance is released into a region with a reduced volume fraction then the substance will reach a higher concentration than it would in a free medium. Tortuosity is related to the increase in the path length of the random walk of a diffusing particle due to the necessity to navigate around cellular obstructions. Tortuosity manifests itself as a decrease in the diffusion coefficient. Uptake represents the movement of a substance from the extracellular space to the intracellular. Since initially a concentration gradient exists in this direction and all membranes have some permeability some concentration-dependent uptake always occurs. In addition there exist specific carrier-mediated uptake processes for some substances such as amino acids or catecholamines. In some regions the dispersal process can be dominated by uptake rather than diffusion. While volume fraction, tortuosity and uptake have all been demonstrated by a technique based on the use of radiolabels and other methods, these classical techniques have limited spatial and temporal resolution. The advent of methods based on micro-injection of substances by iontophoresis or pressure and subsequent detection with ion-selective microelectrodes (ISMs) or voltammetric microsensors (VMs) has opened a new window onto the dynamic local behavior of the extracellular space. In the last decade our laboratory and others have studied the migration of the test substances tetramethylammonium, tetraethylammonium, AsF6- and alpha naphthalene sulfonate, the endogenous ions K+ and Ca2+, the epileptogenic agent penicillin and the neurotransmitter dopamine. These studies have been carried out on the cerebellum and some other regions in a variety of species that include rat, turtle, skate and an intervertebrate, the cuttlefish.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗