Impact of maternal morphine and saline injections on behavioral responses to a cold water stressor in adult male and female progeny Romana S ˇ lamberova ´ a , Cheryl J. Schindler b , Ilona Vathy a,b, * a Department of Psychiatry and Behavioral Sciences, Albert Einstein College of Medicine, Bronx, NY, USA b Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA Received 12 October 2001; received in revised form 20 December 2001; accepted 25 January 2002 Abstract The purpose of the present study was to test the effects of maternal morphine and saline injections on chronic cold water stress responses in three groups of adult male and female rats: prenatally morphine-exposed adult progeny, prenatally saline-exposed adult progeny, and control groups. All male rats were gonadally intact, and female rats were ovariectomized (OVX) in adulthood, and half of them were injected with estradiol benzoate (EB). All animals were exposed to a cold water stressor daily for 2 weeks and tested before (baseline) and after (stress effects) the chronic cold water stressor in a swim test and an open field test. In the swim test, both adult males and OVX, EB-treated adult females born to mothers injected with morphine or saline displayed more floating behavior during the swim test than their controls, both before and after the cold water stressor. Male rats exposed to morphine or saline prenatally also spent more time struggling during the swim tests than controls, and this was further increased after the cold water stressor. In the open field test, males and OVX, EB-treated females born to morphine- or saline-injected mothers were less active and displayed fewer rearings than controls. No differences were observed in OVX females as a result of prenatal injections. Thus, the present study demonstrates that maternal injections, regardless of injection content, induce long-lasting effects on stress responsiveness in adult progeny. D 2002 Elsevier Science Inc. All rights reserved. Keywords: Prenatal morphine; Prenatal saline; Cold water stressor; Open field; Swim test; Gonadal hormones 1. Introduction Our previous work demonstrated that prenatal morphine exposure has sexually dimorphic, long-lasting effects on neurobehavioral development in adult rats [1–7]. The work of others showed that in adult rats, there is an interaction between morphine- and stress-induced behavioral changes [8–11]. Morphine injection (5–10 mg/kg) in adult males increases locomotor activities in the open field after repeated stress including restraint, handling, or social defeat [10]. Further, acute or chronic morphine injections, as well as restraint stress, increase immobility in the swim test, and these effects can be blocked by the nonspecific opiate antagonist, naloxone [9,11]. Naltrexone, the long-acting opiate antagonist, decreases immobility in swim tests [8]. Thus, the data suggest that stress [12] and morphine can induce immobility [9,11] during the swim test in adult animals, possibly through the endogenous opioid system. Whether exposure to morphine during fetal development affects stress responses, such as immobility, in the adult progeny is not known. Behavioral changes in adult offspring may also be produced by prenatal stress caused by saline injections and handling of their mothers [13,14]. Peters [14] showed that adult male rats, born to mothers exposed to crowding and daily saline injections during pregnancy, exhibited increased locomotion and rearing in an open field. Maternal restraint also increased initial locomotor activity in the adult offspring tested in the open field [15]. Vallee et al. [15] showed that adult offspring of mothers exposed to restraint during pregnancy spent more time in the corners of the open field, which is considered a type of anxiety-like behavior. Higher anxiety in prenatally stressed, adult male rats has also been demonstrated by a reduction in time spent on the open arms of an elevated plus maze [15]. In addition, during a Porsolt swim test, a maternal restraint stressor [16] and a maternal cold water stressor [17] increased immobility in 0031-9384/02/$ – see front matter D 2002 Elsevier Science Inc. All rights reserved. PII:S0031-9384(02)00669-8 * Corresponding author. Department of Psychiatry and Behavioral Sciences, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Ull. 111, Bronx, NY 10461, USA. Tel.: +1-718-430-3386; fax: +1-718- 430-8772. E-mail address: vathy@aecom.yu.edu (I. Vathy). Physiology & Behavior 75 (2002) 723 – 732