The impact of maternal separation and isolation stress during stress hyporesponsive period on fear retention and extinction recall memory from 5-week- to 1-year-old rats
The purpose of the present study was to determine whether age would disrupt fear retention and extinction memory in rats pre-exposed to maternal separation and isolation stress; these rats are called MS rats. MS stress was induced by exposing rat pups into maternal separation followed by isolation stress from peer groups (MS) daily/6 h during stress hyporesponsive period, while controls rats that were undisturbed during this period are called NMS rats. 5, 8, 15 and 52 weeks later, these animals were exposed to classical fear conditioning test by pairing auditory stimulus (conditioned stimulus, CS+) with electric footshock. 24 h later, conditioned freezing response to CS+ was measured during fear retention, extinction and extinction recall trials. The normal ageing per se did not affect the formation of fear memory, retention and fear extinction memory. MS stress, on the other hand, disrupted fear memory at young adulthood age exhibiting increased freezing response to CS+ during retention test and reduced during fear extinction memory test when compared to NMS groups. On the other hand, rats at adolescence age exhibited reduced freezing during fear retention and enhanced freezing response to CS+ during extinction recall test. However, MS-induced changes in freezing response during fear retention and extinction tests were not seen in adulthood and 1-year-old age groups. These data demonstrate the young adulthood age is highly vulnerable to fear memory and extinction processes. The differences in freezing response to CS+ during fear conditioning from adolescence to old age, thus, appear to be related to the maturation of the limbic circuit.
KeywordsMaternal separation stress and isolation stress Stress hyporesponsive period 5 week 8 week 15 week 1 year Fear retention Fear extinction memory
This study was funded by ICMR New Delhi and CSIR New Delhi.
Compliance with ethical standards
Conflict of interest
The author declares that no competing interests exist.
- Flandreau EI, Ressler KJ, Owens MJ, Nemeroff CB (2012) Chronic overexpression of corticotropin-releasing factor from the central amygdala produces HPA axis hyperactivity and behavioral anxiety associated with gene-expression changes in the hippocampus and paraventricular nucleus of the hypothalamus. Psychoneuroendocrinology 37:27–38CrossRefGoogle Scholar
- Lajud N, Roque A, Cajero M, Gutiérrez-Ospina G, Torner L (2012) Periodic maternal separation decreases hippocampal neurogenesis without affecting basal corticosterone during the stress hyporesponsive period, but alters HPA axis and coping behavior in adulthood. Psychoneuroendocrinology 37:410–420CrossRefGoogle Scholar
- Toda H, Boku S, Nakagawa S, Inoue T, Kato A, Takamura N, Song N, Nibuya M, Koyama T, Kusumi I (2014) Maternal separation enhances conditioned fear and decreases the mRNA levels of the neurotensin receptor 1 gene with hypermethylation of this gene in the rat amygdala. PLoS One 9:e97421CrossRefGoogle Scholar