title: A study on fear memory retrieval and REM sleep in maternal separation and isolation stressed rats.
abstract: As rapid brain development occurs during the neonatal period, environmental manipulation during this period may have a significant impact on sleep and memory functions. Moreover, rapid eye movement (REM) sleep plays an important role in integrating new information with the previously stored emotional experience. Hence, the impact of early maternal separation and isolation stress (MS) during the stress hyporesponsive period (SHRP) on fear memory retention and sleep in rats were studied. The neonatal rats were subjected to maternal separation and isolation stress during postnatal days 5-7 (6h daily/3d). Polysomnographic recordings and differential fear conditioning was carried out in two different sets of rats aged 2 months. The neuronal replay during REM sleep was analyzed using different parameters. MS rats showed increased time in REM stage and total sleep period also increased. MS rats showed fear generalization with increased fear memory retention than normal control (NC). The detailed analysis of the local field potentials across different time periods of REM sleep showed increased theta oscillations in the hippocampus, amygdala and cortical circuits. Our findings suggest that stress during SHRP has sensitized the hippocampus-amygdala-cortical loops which could be due to increased release of corticosterone that generally occurs during REM sleep. These rats when subjected to fear conditioning exhibit increased fear memory and increased fear generalization. The development of helplessness, anxiety and sleep changes in human patients, thus, could be related to the reduced thermal, tactile and social stimulation during SHRP on brain plasticity and fear memory functions.
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Dayalan
authors.initials: D
authors.lastname: Sampath
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: K R
authors.initials: KR
authors.lastname: Sabitha
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Preethi
authors.initials: P
authors.lastname: Hegde
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: H R
authors.initials: HR
authors.lastname: Jayakrishnan
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Bindu M
authors.initials: BM
authors.lastname: Kutty
authors.affiliation: National Center for Biological Sciences (NCBS), GKVK Campus, Bangalore 560065, India.
authors.forename: Sumantra
authors.initials: S
authors.lastname: Chattarji
authors.affiliation: Indian Institute of Science (IISc), Bangalore 560012, India.
authors.forename: Govindan
authors.initials: G
authors.lastname: Rangarajan
authors.affiliation: National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore 560029, India. Electronic address: trlaxmi@nimhans.kar.nic.in.
authors.forename: T R
authors.initials: TR
authors.lastname: Laxmi
mesh_terms: D000818:Animals; D001921:Brain / Q000503:physiopathology*; D058256:Brain Waves; D003214:Conditioning, Classical; D005239:Fear / Q000502:physiology*; D005260:Female; D008297:Male; D008426:Maternal Deprivation; D011939:Mental Recall / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012895:Sleep, REM / Q000502:physiology*; D012934:Social Isolation; D013315:Stress, Psychological / Q000503:physiopathology*
keywords: Amygdala; Early maternal separation stress; Fear memory; Hippocampus; Prefrontal cortex; Sleep; Theta–gamma oscillations