Brain Research 988 (2003) 139–145 www.elsevier.com / locate / brainres
Research report
Medial preoptic area dopaminergic responses to female pheromones develop during puberty in the male Syrian hamster Kalynn M. Schulz a , Heather N. Richardson a,c , Russell D. Romeo a,c , John A. Morris c , Keith J. Lookingland b,c , Cheryl L. Sisk a,c , * a
b
Department of Psychology, Michigan State University, East Lansing, MI 48824, USA Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA c Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA Accepted 15 July 2003
Abstract Chemosensory cues from receptive females do not elicit similar reactions before and after puberty in male hamsters. While pheromones facilitate a complex display of reproductive behavior in adults, prepubertal males do not engage in these same behaviors. Dopamine (DA) released from the medial preoptic area (MPOA) in response to a receptive female or her odors is an important component of the neural events underlying adult male rat sexual behavior. The current experiment investigated whether increased dopaminergic activity occurs in the adult male hamster MPOA in response to female pheromones, and if so, whether this response is absent in prepubertal males, which ¨ prepubertal and adult male hamsters were exposed to cotton swabs with or without pheromone from an do not mate. Sexually naıve estrous female for 0, 5, 15, or 25 min, after which brains were collected and frozen on dry ice. The MPOA was micropunched from frozen coronal sections (500 mm), and concentrations of DA and its primary metabolite DOPAC were determined by high-performance liquid chromatography–electrochemical detection. DOPAC was used as an index of dopaminergic activity. DOPAC levels significantly increased in adults after 15 min exposure to pheromone. In contrast, MPOA DOPAC concentrations did not increase in prepubertal males exposed to pheromone. These data demonstrate that the neural processing of sexually relevant chemosensory stimuli matures during puberty. The absence of a DA response to female pheromones prior to puberty may contribute to the inability of prepubertal males to display reproductive behavior. 2003 Elsevier B.V. All rights reserved. Theme: Neural basis of behaviour Topic: Monoamines and behaviour Keywords: Dopamine; Pheromone; Reproductive behavior; Puberty; Medial preoptic area
1. Introduction Puberty is the developmental stage during which male rodent reproductive behaviors emerge. In the adult male Syrian hamster, full expression of reproductive behavior relies on both the presence of gonadal steroid hormones and exposure to female pheromones [10,26]. These pheromonal cues and steroidal signals are integrated within a forebrain neural circuit consisting of the medial *Corresponding author. Department of Psychology and Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824, USA. Tel.: 11-517-355-5253; fax: 11-517-352-2744. E-mail address: sisk@msu.edu (C.L. Sisk). 0006-8993 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0006-8993(03)03358-4
amygdala (Me), the bed nucleus of the stria terminalis (BNST) and nuclei within the medial preoptic area (MPOA) [26]. While the neural circuitry underlying chemosensory processing and the hormonal regulation of reproductive behavior are well studied in the adult male Syrian hamster, how these steroid-sensitive circuits develop during puberty to permit the expression of adult behavior is not clear. Unlike adults, prepubertal males do not mate with a receptive female, even when treated with adult levels of gonadal steroids [9,16,20]. Surprisingly, differences in neural responses to steroid hormones do not seem to account for these behavioral differences. For example, both testosterone and dihydrotestosterone increase brain an-