Changes in the postsynaptic density with long‐term potentiation in the dentate gyrus

Abstract

The present study documents alterations in the size of the postsynaptic density (PSD) of synapses formed by entorhinal afferents with granule cell dendritic spines with long-term potentiation (LTP). These changes appear early and persist for at least 60 minutes after LTP-inducing conditioning stimulation. Each animal received test and conditioning stimulation typical of LTP paradigms. Electron microscopic preparation of the dentate gyri from each animal followed conventional procedures. PSD trace lengths of identified asymmetric synaptic profiles were measured. The total PSD length for four categories of synaptic profiles was determined for each third of the molecular layer. PSD surface area per unit volume of tissue (SV) was then computed from these data. Statistical analysis of the SV data used multivariate analysis of variance. PSD surface area per synapse was also estimated. Total PSD surface area per unit volume does not change significantly throughout the entire molecular layer with LTP-inducing conditioning stimulation. However, in the activated portion of the molecular layer, total PSD surface area per unit volume tends to increase with conditioning stimulation. In the middle third of the molecular layer, total PSD surface area per unit volume associated with the concave spine profiles increases significantly while there is a statistically significant decrease in total PSD SV associated with the nonconcave spine profiles. The PSD surface area per synapse also increases markedly. Since it seems that there is an interconversion of spine synapses from nonconcave to concave with LTP (Desmond and Levy: J. Comp. Neurol. In press, '86a), these data suggest that potentiated synapses have larger responses because, in part, they have larger neurotransmitter receptive regions.

Interprotein Disulfide Bonds Formed During Isolation Process Tighten the Structure of the Postsynaptic Density

“…Similarly, the contents of ATPase, Nethylmaleimide-sensitive fusion protein, heat shock cognate protein-70, brain-derived neurotrophic factor receptor, and protein kinases in the PSD have been reported to increase following transient cerebral ischemia (Hu et al, 1998). That the PSD in vivo is made with proteins held together by reversible forces is also consistent with the findings that the structure of the PSD in the brain undergoes rapid alterations in response to synaptic activities (e.g., Nieto-Sampedro et al, 1982;Rees et al, 1985;Desmond and Levy, 1986;Geinisman et al, 1991; for reviews, see Lisman and Harris, 1993;Edwards, 1995).…”

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

“…Indeed, larger spines generally have larger postsynaptic densities and, presumably, more receptors and ion channels (Harris and Stevens, 1989;Lisman and Harris, 1993); increased size of the postsynaptic density has been reported by Desmond and Levy (1986b), as remarked earlier, in the subpopulation of large spines whose frequency is increased by LTP at the apparent expense of smaller spines. Alternatively, an increase in n or P-both widely considered presynaptic measures-might result from spine growth, if such growth lead to perforation of the postsynaptic density (Greenough et al, 1978) and/or coordinated changes in the presynaptic bouton (Desmond and Levy, 1986b;Schuster et al, 1990;Geinisman et al, 1992b;Lisman and Harris, 1993), or to receptor access to previously ineffectual transmitter release sites (Fig. 10).…”

Estrogen alters hippocampal dendritic spine shape and enhances synaptic protein immunoreactivity and spatial memory in female mice

“…This finding indicates that the mechanisms underlying E enhancement of synaptic proteins are conserved through evolution and, perhaps, play important roles in many aspects of brain function (19,46) In addition to effects of E, experience-induced changes in spine number and morphology have been observed in vivo and in vitro in many experimental and behavioral studies, including light deprivation (57), rearing animals in enriched environment (58), hibernation (59,60), and LTP induction in cultured neurons and intact animals (21,22,(61)(62)(63)(64)(65)(66)(67)(68). Despite controversies about the degree to which spines change under these conditions (69,70), there is a general agreement that dendritic spines change either in number or shape in response to the various experiences or environmental challenges and that such structural changes are a component of the mechanisms of functional changes.…”