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Biomedical subjects

C A Barnes

Publications and source records attributed to C A Barnes.

At least 127 records · Page 7Linked to original sources
PubMed1983

Renal oncocytoma and its congeners.

Although the morphologic criteria for separating renal oncocytomas from renal carcinomas with overlapping features are not established completely, the distinction is crucial because of the marked difference in prognosis. Of the 247 renal carcinomas observed at our hospital since 1947, six had sufficient morphologic features of oncocytoma to pose potential difficulty in diagnosis. We term this group the "congeners of renal oncocytoma." Both the congeners and our 10 oncocytomas were well-circumscribed tumors, varied considerably in size, and were composed of cells with granular, pink-red cytoplasm. The congeners lacked the diffuse organoid packeting of cells, characteristic of oncocytoma. Additional features that helped separate individual congeners from oncocytomas included yellow-tan rather than brown-red gross color, necrosis, pleomorphism, ballooned cytoplasm, or clear cells. Our studies indicate that some renal carcinomas have fields identical to oncocytoma, and frozen section, needle biopsy, or aspiration cytology from such an area could lead to a misdiagnosis.

Adenoma↗
PubMed1982

Long-term synaptic enhancement in hippocampus is not regulated by postsynaptic membrane potential.

The contributions of membrane potential and postsynaptic discharge during afferent fibre tetanization to the generation of long-lasting synaptic enhancement was studied by intra- and extracellular recording in the CAl region of hippocampal slices. Neither parameter affected the magnitude of intracellular synaptic enhancement. Thus, if postsynaptic integration is involved in the control of the enhancement process, the integration must be chemically rather than electrically mediated.

Animals↗
PubMed1980

Physiological compensation for loss of afferent synapses in rat hippocampal granule cells during senescence.

1. The effects of senescence on the input-output characteristics of the perforant path projection to granule cells of the fascia dentata were studied in rats using extracellular techniques in vivo, and both extra- and intracellular recording in vitro. 2. Senescent animals exhibited a significant reduction in the perforant path excitatory synaptic field potential at all stimulus intensities tested. This was associated with a reduction in the size of the afferent fibre response, although there was no apparent change in the threshold for fibre activation. These data support the anatomical literature which indicates a loss of afferent synapses with advanced age. 3. For a given magnitude of afferent fibre response, however, the old animals exhibited a larger synaptic field potential, suggesting that the remaining synapses were in fact more powerful. Furthermore, the magnitude of the extracellular population spike, an index of the number of discharging granule cells, was greater in the old animals when plotted as a function of extracellular e.p.s.p. amplitude. 4. Intracellular recording from a total of 190 granule cells in the transverse hippocampal slice preparation revealed a 17% reduction in the voltage threshold for synaptically elicited granule cell discharge, and a 13% reduction in the latency of the action potential in old compared to young rats. Resting potentials, action potential amplitudes, whole neurone time constants, the relations between applied current and input resistance, and the discharge threshold following depolarizing current pulses, were not different between age groups. 5. These data indicate that granule cells could partly compensate for a loss of synapses during senescence by an increase in their electrical responsiveness to synaptic activation and possibly by an increase in synaptic efficacy.

Action Potentials↗
PubMed1979

Memory deficits associated with senescence: a neurophysiological and behavioral study in the rat.

Neurophysiological and behavioral measures were obtained from 32 senescent (28--34 mo) and 32 mature adult (10--16 mo) rats. Extracellularly recorded synaptic responses were obtained from electrodes chronically implanted in the fascia dentata and perforant path. The rats were first tested on a circular platform, which favored the use of spatial cues for its solution, and the senescent rats were shown to exhibit poorer memory for the rewarded place. When granule cell synaptic responses were recorded after a single session of very brief high-frequency stimulation, the amount of elevation and time course of decline were equivalent between age groups. Af ter three repetitions, however, the young rats maintained the increased synaptic strength for at least 14 days, whereas the old rats declined after the first session. The amount of synaptic enhancement was statistically correlated with the ability to perform the circular platform task both within and between groups. Furthermore, the aftereffects of the high-frequency stimulation selectively impaired the old rats' spontaneous alternation behavior on a T-maze. Certain other neurophysiological and electroencephalographic measures did not distinguish between age groups. The results are discussed in terms of the synaptic theory of memory formation and of their relevance to the aging process.

Age Factors↗
PubMed1979

Neurophysiological comparison of dendritic cable properties in adolescent, middle-aged, and senescent rats.

Relative dendritic atrophy has been reported in hippocampal granule cells of senescent (25 month) as compared to young (3 month) rats. An electrophysiological study of synaptic response waveform was un;ertaken to determine whether these anatomical changes have physiological correlates of functional significance to the integrative capacity of the granule cells. The variable of interest was the rist time of the extracellularly recorded population synaptic response because this parameter (under appropriate conditions) has been shown to reflect relative electrotonic distance of active synapses from the spike generating zone located near the cell body. By selectively stimulating small subsets of perforant path fibers along its medio-lateral axis, synapses at increasing distances from the soma may be activated and the response waveform recorded. Systematic observations were made on both hemispheres of 3 adolescent (2 months), three middle-aged (12 months), and 3 senescent (28 months) rats. There were no significant differences in the mean, variance, or range of the frequency distributions of synaptic response rise times. However, the medians of the distributions revealed a small shift towards lower values with advanced age. Although the latter finding is consistent with the anatomical changes, the magnitude of the differences were so small as to make their functional significance dubious.

Aging↗
PubMed1977

Physiological identification and analysis of dentate granule cell responses to stimulation of the medial and lateral perforant pathways in the rat.

Stimulation of the dorsomedial or ventrolateral perforant pathways resulted in quantitatively different extracellularly recorded EPSPs in the fascia dentata of the rat. The two potentials differed in latency to peak and in width at half amplitude in a manner consistent with the different locus of termination of the two pathways on the granule cell dendrites. Both potentials were able to follow brief stimulus trains of 100 Hz, which suggests that they are monosynaptic. Medially elicited responses had their peak negativity approximately 100 to 180 micrometer deeper in the molecular layer than laterally elicited responses. Stimulation at short intervals along a dorsomedial to ventrolateral track in the angular bundle yielded a step function rather than a continuum of EPSP peak latency and half-width, in agreement with Hjorth-Simonsen's ('72) evidence for the separateness of the two pathways. Both pathways were able to induce granule cell discharge. Laterally elicited spikes, however, were delayed. Stimulation at intermediate locations frequently elicited double spikes from the granule cell population. Population spikes elicited by either pathway were inhibited for as long as 100 msec after a single discharge. Both pathways showed facilitation with double stimuli at short intervals, and both showed post-tetanic potentiation lasting at least 30 minutes. Under conditions where it could be shown that the two pathways at least partially converged onto the same granule cells, the response of one pathway did not increase when long lasting potentiation was induced on the other.

Animals↗
PubMed1977

Circadian rhythm of synaptic excitability in rat and monkey central nervous system.

Synaptic responses in hippocampal granule cells to stimulation of their afferent fibers from the entorhinal cortex fluctuate with a 24-hour period. The phase of this cycle for rats and monkeys depends on whether the animal is naturally nocturnal or diurnal. In a rat blinded by enucleation, the rhythm persists but drifts out of phase with the rhythm of sighted controls.

Action Potentials↗