title: Effects of unconditioned and conditioned aversive stimuli in an intense fear conditioning paradigm on synaptic plasticity in the hippocampal CA1 area in vivo.
abstract: Repeated vivid recalls or flashbacks of traumatic memories and memory deficits are the cardinal features of post-traumatic stress disorder (PTSD). The underlying mechanisms are not fully understood yet. Here, we examined the effects of very strong fear conditioning (20 pairings of a light with a 1.5-mA, 0.5-s foot shock) and subsequent reexposure to the conditioning context (chamber A), a similar context (chamber B), and/or to the fear conditioned stimulus (CS) (a light) on synaptic plasticity in the hippocampal CA1 area in anesthetized Sprague-Dawley rats. The conditioning procedure resulted in very strong conditioned fear, as reflected by high levels of persistent freezing, to both the contexts and to the CS, 24 h after fear conditioning. The induction of long-term potentiation (LTP) was blocked immediately after fear conditioning. It was still markedly impaired 24 h after fear conditioning; reexposure to the conditioning chamber A (CA) or to a similar chamber B (CB) did not affect the impairment. However, presentation of the CS in the CA exacerbated the impairment of LTP, whereas the CS presentation in a CB ameliorated the impairment so that LTP induction did not differ from that of control groups. The induction of long-term depression (LTD) was facilitated immediately, but not 24 h, after fear conditioning. Only reexposure to the CS in the CA, but not reexposure to either chamber A or B alone, or the CS in chamber B, 24 h after conditioning, reinstated the facilitation of LTD induction. These data demonstrate that unconditioned and conditioned aversive stimuli in an intense fear conditioning paradigm can have profound effects on hippocampal synaptic plasticity, which may aid to understand the mechanisms underlying impairments of hippocampus-dependent memory by stress or in PTSD.
authors: Mental Health Institute of the 2nd Xiangya Hospital, Central South University, Changsha 410011, Hunan, People's Republic of China.
authors: Zexuan
authors: Z
authors: Li
authors: Qixin
authors: Q
authors: Zhou
authors: Lingjiang
authors: L
authors: Li
authors: Rongrong
authors: R
authors: Mao
authors: Meina
authors: M
authors: Wang
authors: Wenhua
authors: W
authors: Peng
authors: Zhifang
authors: Z
authors: Dong
authors: Lin
authors: L
authors: Xu
authors: Jun
authors: J
authors: Cao
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000502:physiology; D003213:Conditioning, Psychological / Q000502:physiology*; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000009:adverse effects; D005239:Fear / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology*; D008569:Memory Disorders / Q000209:etiology / Q000503:physiopathology; D009473:Neuronal Plasticity / Q000502:physiology*; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013313:Stress Disorders, Post-Traumatic / Q000150:complications / Q000503:physiopathology; D009435:Synaptic Transmission / Q000502:physiology*