title: Synaptic remodeling in hippocampal CA1 region of aged rats correlates with better memory performance in passive avoidance test.
abstract: Aging is associated with deficits in long-term declarative memory formation, and wide differences in performance can be observed among aged individuals. The cellular substrates of these deficits and the reasons for such marked individual differences are not yet fully understood. In the present study, morphologic parameters of synapses and synaptic mitochondria in stratum molecolare of CA1 hippocampal region were investigated in aged (26- to 27-month-old) female rats after a single trial inhibitory avoidance task. In this memory protocol animals learn to avoid a dark compartment in which they received a mild, inescapable foot shock. Rats were tested 3 and 6 or 9 hours after the training, divided into good and bad responders according to their performance (retention times above or below 100 seconds, respectively) and immediately sacrificed. The number of synapses and synaptic mitochondria per cubic micrometer of tissue (numeric density), the average area of synapses and volume of synaptic mitochondria, the total area of synapses per cubic micrometer of tissue, the percentage of perforated synapses and the overall volume of mitochondria per cubic micrometer of tissue were evaluated. In the good responder group, the numeric density of synapses and mitochondria was significantly higher and the average mitochondrial volume was significantly smaller 9 hours versus 6 hours after the training. No significant differences were observed among bad responders. Thus, better performances in passive avoidance memory task are correlated with more efficient plastic remodeling of synaptic contacts and mitochondria in hippocampal CA1. Present findings indicate that maintenance of synaptic plastic reactivity during aging is a critical requirement for preserving long-term memory consolidation.
authors.affiliation: Department of Human and General Physiology, University of Bologna, Bologna, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Platano
authors.forename: Patrizia
authors.initials: P
authors.lastname: Fattoretti
authors.forename: Marta
authors.initials: M
authors.lastname: Balietti
authors.forename: Belinda
authors.initials: B
authors.lastname: Giorgetti
authors.forename: Tiziana
authors.initials: T
authors.lastname: Casoli
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Di Stefano
authors.forename: Carlo
authors.initials: C
authors.lastname: Bertoni-Freddari
authors.forename: Giorgio
authors.initials: G
authors.lastname: Aicardi
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000502:physiology*; D005260:Female; D006624:Hippocampus / Q000502:physiology* / Q000648:ultrastructure; D008568:Memory / Q000502:physiology*; D008928:Mitochondria / Q000648:ultrastructure; D009043:Motor Activity / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012153:Retention, Psychology; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure