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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(More)
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(More)
The effects of aging on the responsiveness of hippocampal neurons to iontophoretic application of L-glutamate and AMPA were studied in vitro. There were no effects of age on neuronal responses to L-glutamate; however, CA1 pyramidal cells of old rats, but not granule cells in the fascia dentata, showed both a smaller reduction in extracellularly-recorded(More)
A modulatory role for the hippocampal theta rhythm in synaptic plasticity is suggested by the observations that theta occurs during exploratory behaviors, spatial learning is impaired when the theta rhythm is disrupted, and excitation of hippocampal principal cells is phase-coupled to the theta wave. The theta phase affects the nature of the plasticity(More)
Glutamatergic fast synaptic transmission is known to be altered with age in a region-specific manner in hippocampus of memory-impaired old rats. In the present experiment, presynaptic fiber potentials and non-N-methyl-D-aspartate (NMDAR) and NMDAR-mediated synaptic responses in CA1 were compared in three ages of behaviorally characterized male F-344 rats.(More)
Hippocampal long-term potentiation (LTP) is reduced in aged relative to young F-344 rats when peri-threshold stimulation protocols (several stimulus pulses at 100-200 Hz) are used. The present study was designed to examine the possibility that this LTP-induction deficit is caused by a reduced overlap of Schaffer-collateral inputs onto CA1 pyramidal cells(More)
Previous studies have reported a lack of an age effect in the induction of long-term potentiation (LTP) at CA1 synapses, using robust (supramaximal) stimulation parameters, but an apparent age effect on the induction threshold of LTP using less robust stimulation, in the perithreshold region. These findings have led to the suggestion that old animals may(More)
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(More)
Synaptic transmission in hippocampal field CA1 is largely N-methyl-d-aspartate receptor (NMDA(R)) dependent during the early postnatal period. It becomes increasingly mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptors until an adult ratio of AMPA to NMDA receptors is achieved. It is shown here that increases in the AMPA(More)
Old, memory-deficient rats do not show a change in the threshold for long-term potentiation (LTP) induction in hippocampal region CA1. This observation suggests that defective NMDA receptor mechanisms at the Schaffer collateral-CA 1 pyramidal cell synapse cannot explain age-related LTP induction deficits that are observed under some stimulation protocols.(More)