Subsequent anxiety-related behavior in rats exposed to low-dose methadone during gestation, lactation or both periods consecutively Felicity M. Daly, Robert N. Hughes ⁎, Lianne J. Woodward Department of Psychology, University of Canterbury, Christchurch, New Zealand abstract article info Article history: Received 24 November 2011 Received in revised form 11 May 2012 Accepted 21 May 2012 Available online 24 May 2012 Keywords: Methadone Gestation Lactation Rat Activity Anxiety In order to assess the long-term behavioral consequences of exposing rats to methadone during gestation, lactation or both periods consecutively, pregnant Wistar dams were provided with drinking water containing approximately 2.39 mg/kg/day methadone. Soon after birth, litters of offspring were assigned to methadone- naïve foster mothers. Half of these foster mothers were then provided with drinking water containing meth- adone (approximately 2.86 mg/kg/day), while the other half received unadulterated water. Maternal weight gain, pregnancy duration, litter sizes, sex ratios and average pup weights were recorded. Following weaning on postnatal day (PND) 28, individual rats were weighed and inspected for physical abnormalities and stress reactions at PND20, 60 and 120. At these same ages, observations were also made of the rats' behavior in an emergence apparatus, and an open field. Apart from a smaller number of full-term pregnancies, there were no effects of any type of methadone treatment on physical measurements recorded at any age. Nor were there any behavioral effects of gestational methadone experienced on its own. However, methadone experienced during lactation (without gestational exposure) decreased emergence speed at PND30, and for all testing ages combined, increased open-field ambulation (males only), walking, rearing and occupancy of the center of the apparatus. Exposure to methadone during both gestation and lactation decreased emer- gence latencies at PND30 and, for all ages combined, decreased ambulation (males only), center occupancy and defecation. The subsequent behavioral effects of methadone were largely confined to lactational expo- sure and, when combined with gestational exposure, suggested increased anxiety. © 2012 Elsevier Inc. All rights reserved. 1. Introduction Methadone maintenance programs for the management of opioid dependence have been operating for over 40 years when they were first introduced by Dole et al. (1966) for the treatment of heroin addiction. The question of whether or not infants born to women on methadone maintenance while pregnant might experience neuro- behavioral deficits has attracted interest from behavioral teratologists since the advent of its use. Findings suggest that methadone exposed infants are at increased risk of neonatal withdrawal, reduced head circumference, irritability, disorganized cry, state dysregulation, poor quality of movements and depressed interactive behavior (Bada et al., 2002; Chasnoff et al., 1984; Hans, 1989; Malpas et al., 1995; Quick et al., 2009; Rosen and Johnson, 1988; Serane and Kurian, 2008). Similar abstinence symptoms (Hutchings, 1990) are also evident in neonate rats (Barr et al., 1998). However, while short term effects have been demonstrated, findings from longer term follow-up studies are limited, but nevertheless suggest that risks may be ongoing and span attentional and cognitive problems (Bandstra et al., 2010; Hans, 1989; Hickey et al., 1995; Hutchings, 1990; Rosen and Johnson, 1988). Many women enrolled in methadone maintenance treatment dur- ing their pregnancies continue with treatment post delivery and while breastfeeding their offspring. Consequently, there is the possibility that prenatal exposure to the drug will be supplemented by postnatal exposure during lactation. However, even though methadone is ex- creted unchanged in breast milk, the very low concentration is gener- ally regarded as unlikely to be problematic for the infant (Jansson et al., 2004, 2008). On the contrary, it may play a part in reducing the severity of neonatal abstinence symptoms in both humans (Ballard, 2002; Malpas et al., 1997) and rats (Kunko et al., 1996). One of the most striking aspects of research into the consequences of prenatal (or gestational) and lactational exposure to methadone is the relative lack of long term studies. Most human research does not follow up effects on offspring much beyond about 2 years of age. Sim- ilarly, animal research is generally confined to a few weeks after birth although Grove et al. (1979) followed their rats through to 65 days after birth. The first goal of the present study was to assess the effects of ges- tational exposure to methadone provided in rat dams' drinking water on pregnancy and birth outcomes. Then the offspring of these dams Pharmacology, Biochemistry and Behavior 102 (2012) 381–389 ⁎ Corresponding author. Tel.: +64 3 364 2879; fax: +64 3 364 2181. E-mail address: robhughes@canterbury.ac.nz (R.N. Hughes). 0091-3057/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.pbb.2012.05.010 Contents lists available at SciVerse ScienceDirect Pharmacology, Biochemistry and Behavior journal homepage: www.elsevier.com/locate/pharmbiochembeh