Mother–infant separation leads to hypoactive behavior in adolescent Holtzman rats

Abstract

This is the first study of the effects of mother-infant separation (MS) on adolescent behavior of Holtzman rats. Different rat strains, such as Harlan Sprague-Dawley and Holtzman, share a common origin. However, MS may lead to hypoactive behavioral effects in Holtzman rats because of their greater susceptibility to show depressive-like responses to stress. Sixty Holtzman pups were divided into 3 groups at postnatal day 2 (P2). For 10 days, the MS group was separated 6 hours daily and the early handled (EH) group 15 min daily. A standard facility reared (SFR) group was not separated. Animals were tested for novel open-field activity (P28), defensive withdrawal in a light-dark (LD) apparatus (P29) and familiar open-field (P30). Behavioral measures were classified into general activity (ambulatory and short movement time), orienting (rearing time) and risk-taking (velocity and exposed zone time). MS rats displayed reductions in general activity and risk-taking, and increases in orienting time. In contrast, EH favored risk-taking behavior, which may be consistent with previous findings implicating early handling as beneficial in coping with stress. Sex differences in these behaviors were limited. This study suggests a genetic predisposition in Holtzman rats for predominantly hypoactive/anxiety-like behaviors when exposed to an early life stressor.

Maternal separation disrupts dendritic morphology of neurons in prefrontal cortex, hippocampus, and nucleus accumbens in male rat offspring

“…However, Marin and Planeta (2004) found an increase in locomotor activity in novel environment before puberty. Meanwhile, several authors have reported undisturbed locomotor activity in novel environment at postpubertal age (Marin and Planeta, 2004;Knuth and Etgen, 2007;Renard et al, 2007;Spivey et al, 2008), which agrees with the results of the present study. In contrast, Lippmann et al (2007) reported reductions in locomotor activity and Slotten et al (2006) reported increases in locomotion in novel environments.…”

“…In our study, we found a decreased locomotor activity in MS rats at PND35, and no changes in activity at a post-pubertal age. In agreement with this finding, a recent report found decrements in locomotor activity at a prepubertal age (Spivey et al, 2008). However, Marin and Planeta (2004) found an increase in locomotor activity in novel environment before puberty.…”

Adolescent female rats are more resistant than males to the effects of early stress on prefrontal cortex and impulsive behavior

“…Renard, Rivarola & Suarez (2007) have proposed that female rats are more resistant than males to certain adverse effects of MS, which is supported by previous MS studies (Ruedi-Bettschen, Zhang, Russig, Ferger, Weston, Pedersen, Feldon, & Pryce, 2006; Spivey, Barrett, Padilla, & Gonzalez-Lima, 2008) and other stress-related manipulations such as restraint stress (Conrad, Jackson, Wieczorek, Baran, Harma, Wright, & Korol, 2004) and learned helplessness (Dalla, Edgecomb, C., Whetstone, A. S., & Shors, T. J., 2008). …”

“…While other rat strains, such as Holtzman, have been reported to show reduced or even reversed direction of sex differences in certain OF behaviors (Spivey et al, 2008a), the overall review of the literature provides a picture in which females are described to be more active and ambulatory than males (Blizard, Lippman & Chen, 1975; Slob, Bogers, & van Stolk, 1981; Slob, Huizer & van der Werff ten Bosch, 1986). It is therefore not surprising that in the current study, SFR and EH females had higher scores in measures of activity (both horizontal and vertical) than males.…”

Early maternal separation affects ethanol-induced conditioning in a nor-BNI insensitive manner, but does not alter ethanol-induced locomotor activity

“…There are few studies that, instead of imposing a substantial delay until testing on adulthood, analyzed the effects of chronic maternal separation immediately after termination of this treatment during infancy (Arnold & Sivy, 2002) or adolescence (Spivey et al, 2008). …”