Long-lasting morphological changes in dendritic spines of dentate granular cells following stimulation of the entorhinal area

Abstract

Stimulation of the perforant path induces a long-lasting increase in the area of dendritic spines, which are sites of termination of the stimulated pathway in the distal third of the dentate molecular layer. No enlarged spines were found in the proximal third of the dentate molecular layer, where the commissural afferents terminate. Following a single tetanic stimulus of 30 sec duration at 30/sec, spines became significantly larger by 15%, 38%, 35% and 23% within poststimulation intervals of 2-6 min, 10-60 min, 4-8 h, and 23 h, respectively. Axon terminals decreased their area by 15% within the 2-6 min interval and the vesicle density was decreased by 19% within the 10-60 min interval. Both changes were reversible and terminals resumed their prestimulation condition at longer intervals (greater than 4 h). The initial enlargement of spines was interpreted as being due to a glutamate-induced increase in the sodium permeability of the spine membrane, whereas for the long-lasting enlargement an increase in protein synthesis was postulated. The long-lasting enlargement of dendritic spines in the dentate molecular layer following a short train of stimuli delivered to the perforant path, supports the postulate which links such a change to the mechanism of long-lasting postactivation potentiation observed in this pathway.

Repeated confocal imaging of individual dendritic spines in the living hippocampal slice: evidence for changes in length and orientation associated with chemically induced LTP

“…10). It has been suggested that the number and size of functional vesicular release sites increases in proportion with the size of the terminal bouton (Pierce and Lewin, 1994), and there is ev-idence from fixed tissue of activity-dependent presynaptic structural changes in the hippocampus (Fifkova and Van Harreveld, 1977;Chang and Greenough, 1984;Applegate et al, 1987;Meshul and Hopkins, 1990;Represa and Ben-Ari, 1992). Note that physical coupling of pre-and postsynaptic membranes (postsynaptic densities are commonly observed bound to isolated synaptosomes) could obviate an obligatory role for diffusible retrograde messengers in triggering presynaptic expression of LTP (Lisman and Harris, 1993).…”

“…Evidence of such alterations has been found in fixed CNS tissue from animals of several species reared in complex versus simple environments, or exposed to various training or stimulation regimens (reviewed by Globus, 1975;Greenough and Bailey, 1988;Bailey and Kandel, 1993;Horner, 1993;Harris and Kater, 1994). Changes in dendritic spines after induction of long-term potentiation (LTP), a widely studied experimental model of learning (Bliss and Lomo, 1973;Bliss and Collingridge, 1993), have been reported by a number of investigators (e.g., Van Harreveld and Fifkova, 1975;Fifkova and Van Harreveld, 1977;Lee et al, 1979Lee et al, , 1980Levy, 1983, 1986a,b;Chang and Greenough, 1984;Petukhov and Popov, 1986;Schuster et al, 1990;Geinisman et al, 1991Geinisman et al, , 1992bWallace et al, 1991). Indeed, the long duration of LTP (Bliss and Gardner-Medwin, 1973;Racine et al, 1983) suggests a structural basis for its maintained expression.…”

Immunocytochemical localization of actin and microtubule-associated protein MAP2 in dendritic spines.

“…The above-mentioned studies and many others have contributed to the emerging hypothesis that spines are dynamic structures that are capable of very rapid structural modifications, which, in turn, alter synaptic efficacy (2,(4)(5)(6)(7)(8)(9). How these shape changes are brought about is of considerable interest.…”

“…It has long been recognized that spines in various brain regions can be modified by experience, presumably in response to variations in the patterns of activity over the presynaptic fibers (2)(3)(4). Furthermore, brief periods of electrical activity that induce changes in synaptic efficacy (long-term potentiation) also result in dramatic changes in spine shape (5,6). Because the size and shape of a spine would be expected to result in severe attenuation of current flow between the synapse and the parent dendrite during a transient depolarization (7), a change in spine shape could bring about changes in synaptic efficacy as a consequence of changes in current flow during synaptic activation.…”

Actinfilin, a Brain-specific Actin-binding Protein in Postsynaptic Density

“…Activity-induced actin assembly and disassembly is thought to play a critical role in shaping the dendritic spine, a subcellular protrusion that is found in more than 90% of glutamatergic synapses. The changes in number, size, and morphology of spines are linked to long-term memory (1)(2)(3)(4)(5)(6). Increasing evidence suggests that the dynamic reorganization of actin filament is probably mediated by several classes of molecules including small second messages and regulatory protein factors that interact with G-or F-actin.…”