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P DiScenna

Publications and source records attributed to P DiScenna.

6 recordsLinked to original sources
PubMed1994

Multideterminant role of calcium in hippocampal synaptic plasticity.

Hippocampal CA1 cells possess several varieties of long-lasting synaptic plasticity: two different forms of long-term potentiation (LTP) and at least one form of long-term depression (LTD). All forms of synaptic plasticity are induced by afferent activation, all involve Ca2+ influx, all can be blocked by Ca2+ chelators, and all activate Ca(2+)-dependent mechanisms. The question arises as how different physiological responses can be initiated by activation of the same second messenger. We consider two hypotheses which could account for these phenomena: voltage-dependent differences in cytosolic Ca2+ concentration acting upon Ca2+ substrates of differing Ca2+ affinities and compartmentalization of the Ca2+ and its substrates.

Animals↗
PubMed1993

alpha-Difluoromethylornithine decreases inhibitory transmission in hippocampal slices independently of its inhibitory effect on ornithine decarboxylase.

We tested the effect of DL-alpha-(difluoromethyl)ornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC), on recordings in area CA1 of rat hippocampal slices. In the concentration range in which it is used as an ODC inhibitor, DFMO increased neuronal excitability and blocked paired-pulse inhibition. The effect of DFMO was reversed by perfusing the slice with normal bathing solution. These effects were not attenuated by the simultaneous addition of putrescine; thus the activity of DFMO was not related to a decrease in putrescine caused by the inhibition of ODC. Mediation by the N-methyl-D-aspartate (NMDA) receptor was ruled out because DL-2-amino-5-phosphonovalerate (APV), an NMDA antagonist, did not block the effect of DFMO. Intracellular and extracellular recordings of pharmacologically isolated IPSPs supported the notion that DFMO depressed GABAergic transmission. DFMO has frequently been used as a tool to study the role of the ODC-polyamine system in neural preparations. This report suggests that the results from such studies must be interpreted with caution. In addition, our findings raise questions about the proposed use of DFMO as a neuroprotective agent against excitotoxicity.

2-Amino-5-phosphonovalerate↗
PubMed1986

The hippocampal memory indexing theory.

The hippocampal formation (comprising the hippocampus proper, the dentate gyrus, and the subiculum) has been repeatedly implicated in information storage models of the mammalian brain. The precise nature of the hippocampal role in the storage of information has, however, remained elusive. Here it is proposed that the role of the hippocampus is to form and retain an index of neocortical areas activated by experiential events. The hippocampal index, thus, represents those unique cortical regions activated by specific events. The neuronal mechanism underlying the memory index is hypothesized to be long-term potentiation. It is asserted that the reactivation of the stored hippocampal memory index will serve to also reactivate the associated unique array of neocortical areas and thus will result in a memorial experience. This hippocampal reactivation of a neocortical array may also be involved in establishing a cortically based memory trace.

Animals↗
PubMed1985

The role of hippocampus in memory: a hypothesis.

The role of the hippocampus in memory storage in the mammalian brain is examined. The intrinsic anatomical organization of the hippocampus is such that a multidimensional mapping of other brain regions is represented. Emerging knowledge of the cortico-limbic-subcortical anatomy suggests that the hippocampal representations preserve the topological features of the targets and possess reciprocal connectivity. Long-Term Potentiation (LTP) is a prominent physiological characteristic of hippocampal synapses and is a promising candidate mnemonic device. The hypothesis is advanced that the pattern, or index, of specific neocortical (and other) areas activated by an experiential event is represented, or indexed, in the hippocampus by means of LTP. This hypothesis, termed the Memory Indexing Theory, suggests that experiential events are initially stored in an index of neocortical locations maintained in hippocampus. Subsequently, other regions, notably neocortex itself, permanently encode these experiential events and the interrelationships between them.

Animals↗
PubMed1984

The topological anatomy of the hippocampus: a clue to its function.

The anatomy of the hippocampus and dentate gyrus is considered with respect to the topology of its afferents and efferents. The topological attributes of the hippocampal formation represent a four-dimensional array with the demensions being: the afferent input to laminated dendritic zones, the intrinsic tri-synaptic hippocampal system, the longitudinal and commissural association systems, and time. Within this four-dinmensional array, active foci can vary dynamically in space and time, depending upon the pattern of afferent activity. The features of hippocampal topology may relate to the role of the hippocampal formation in information storage and processing.

Animals↗