Sex, Drugs, and Adult Neurogenesis: Sex-Dependent Effects of Escalating Adolescent Cannabinoid Exposure on Adult Hippocampal Neurogenesis, Stress Reactivity, and Amphetamine Sensitization Tiffany T.-Y. Lee, 1 Steven R. Wainwright, 2 Matthew N. Hill, 3 Liisa A.M. Galea, 1,2,4 and Boris B. Gorzalka 1,2 * ABSTRACT: Cannabinoid exposure during adolescence has adverse effects on neuroplasticity, emotional behavior, cognition, and reward sensitivity in adult rats. We investigated whether escalating doses of the cannabinoid receptor 1 (CB 1 R) agonist, HU-210, in adolescence would affect adult hippocampal neurogenesis and behavioral processes puta- tively modulated by hippocampal neurogenesis, in adult male and female Sprague-Dawley rats. Escalating doses of HU-210 (25, 50, and 100 mg/kg), or vehicle were administered from postnatal day (PND) 35 to 46. Animals were left undisturbed until PND 70, when they were treated with 5-bromo-2-deoxyuridine (BrdU; 200 mg/kg) and perfused 21 days later to examine density of BrdU-ir and BrdU/NeuN cells in the dentate gyrus. In another cohort, hypothalamic-pituitary-adrenal (HPA) axis reactivity to an acute restraint stress (30 min; PND 75) and behav- ioral sensitization to d-amphetamine sulfate (1-2 mg/kg; PND 105-134) were assessed in adulthood. Adolescent HU-210 administration sup- pressed the density of BrdU-ir cells in the dentate gyrus in adult male, but not adult female rats. Adolescent HU-210 administration also induced significantly higher peak corticosterone levels and reminiscent of the changes in neurogenesis, this effect was more pronounced in adult males than females. However, adolescent cannabinoid treatment resulted in significantly higher stereotypy scores in adult female, but not male, rats. Thus, adolescent CB 1 R activation suppressed hippocam- pal neurogenesis and increased stress responsivity in adult males, but not females, and enhanced amphetamine sensitization in adult female, but not male, rats. Taken together, increased CB 1 R activation during adolescence results in sex-dependent, long-term, changes to hippocam- pal structure and function, an effect that may shed light on differing vulnerabilities to developing disorders following adolescent cannabinoid exposure, based on sex. V C 2013 Wiley Periodicals, Inc. KEY WORDS: sex difference; CB1 receptor; sur- vival; periadolescent; HPA axis INTRODUCTION Adolescence is characterized by changes in physical maturation, establishing independence, increased roles of peer interactions, and risk-taking behavior (Spear, 2000; Casey et al., 2010). Neuroplasticity during ado- lescence may facilitate the development of functional changes in cognition, decision making strategies, and social behaviors (Sisk and Zehr, 2005). Adolescent neuroplastic changes include modification of dendritic spine densities, neurotransmitter levels, myelination (Sisk and Zehr, 2005) and maturation of the hypothalamic-pituitary-adrenal (HPA) axis (Romeo, 2010a). Thus, perturbations during this period, such as stress exposure, have been shown to induce long-term changes in adult behavior and structural plasticity, such as adult hippocampal neurogenesis (McCormick et al., 2010; Barha et al., 2011). Besides stress exposure, cannabis use during adoles- cence may also alter the maturation of the nervous system and lead to long-lasting neural as well as cog- nitive and behavioral changes in adulthood (Rice and Barone, 2000; Hodes et al., 2009). Rubino and col- leagues have demonstrated long-term sex-dependent impairments in adult emotionality and cognition that coincide with neuroanatomical changes resulting from escalating doses of THC during adolescence (Rubino and Parolaro, 2008; Rubino et al., 2008; Rubino et al., 2009a,b). Clinically, adolescent cannabis use has been linked to the development of subsequent cannabis or other drug dependence (see review, Spano et al., 2010), depressive and/or anxiety disorders (Pat- ton et al., 2002), as well as schizophrenia (Cohen et al., 2008), with heavier users having the highest risk (Viveros et al., 2006). The psychoactive effects of cannabis and synthetic cannabinoids are predomi- nately mediated by the activation of central cannabi- noid 1 receptors (CB 1 R; Devane et al., 1988; Matsuda et al., 1990). These receptors are the primary central receptors of the endocannabinoid system, which is important for gating neurotransmitter release 1 Department of Psychology, University of British Columbia, Vancouver, BC, Canada; 2 Program in Neuroscience, University of British Columbia, Vancouver, BC, Canada; 3 Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; 4 Brain Research Centre, University of British Columbia, Vancouver, BC, Canada Grant sponsor: Canadian Institutes of Health Research (CIHR) and Cana- dian Consortium for the Investigation of Cannabinoids (CCIC); Grant number: 96353; Grant sponsor: CIHR; Grant number: 119502; Grant sponsors: CIHR and National Science and Engineering Reseach Council (NSERC); Grant numbers: 102568; 05099; Grant sponsors: CIHR; Grant number: 79399. Abbreviations used: AMPH, amphetamine; BrdU-ir cell, BrdU-immuno- reactive cell; CB 1 R, CB 1 receptor; GCL, granule cell layer; PND, post- natal day *Correspondence to: Boris B. Gorzalka, Ph.D., Department of Psychol- ogy, University of British Columbia, 2136 West Mall, Vancouver, B.C., Canada V6T1Z4. E-mail: bgorzalka@psych.ubc.ca Accepted for publication 8 October 2013. DOI 10.1002/hipo.22221 Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com). V C 2013 WILEY PERIODICALS, INC. HIPPOCAMPUS 00:00–00 (2013)