Chemosensory Cues are Essential for Mating-Induced Dopamine Release in MPOA of Male Syrian Hamsters

Abstract

The medial preoptic area (MPOA) is crucial for male sex behavior. Dopamine (DA) is released in MPOA during copulation, and contributes to the reinforcing effects of mating. The aim of the present study was to identify sensory stimuli responsible for matinginduced DA release. Specifically, we determined if chemosensory cues are essential for mating-induced MPOA DA release using in vivo microdialysis in male Syrian hamsters. Hamsters were used because chemosensory cues from the olfactory mucosa and vomeronasal organ are essential for sexual behavior in this species. Sexually experienced adult male hamsters were implanted with a microdialysis guide cannula over MPOA. At the same time, males received sham olfactory bulbectomy (Sham Bx, n ¼ 11), bilateral bulbectomy (Bibx, n ¼ 6), or unilateral bulbectomy (Ubx) ipsilateral (Ipsi Ubx, n ¼ 9) or contralateral (Contra Ubx, n ¼ 8) to the microdialysis probe. This model takes advantage of the predominantly ipsilateral projections of the olfactory bulbs. Microdialysis samples were collected from the MPOA during baseline, exposure to a receptive female, and after removal of female. Extracellular DA was measured using highperformance liquid chromatography with electrochemical detection. During mating, DA increased in MPOA of Sham Bx males (to 146.7717.5% of baseline). Bibx males did not mate, and MPOA DA did not increase (96.1715.8% of baseline). Although both groups of Ubx males mated to ejaculation, MPOA DA increased significantly only in Contra Ubx males (to 161.8735.3% of baseline), and not in males with Ipsi Ubx (107.6711.5% of baseline). The results demonstrate that chemosensory cues are essential for MPOA DA release during mating in male Syrian hamsters.

Sexual behavior in male rodents

“…nNOS-ir is co-localized with gonadal steroid receptors in the MPOA, and castration decreased nNOS-ir (Hadeishi and Wood, 1996). As in rats, extracellular DA levels rose in the MPOA of male hamsters presented with an estrous female; this increase was blocked by bilateral or ipsilateral, but not contralateral or sham, bulbectomy (Triemstra et al, 2005).…”

Male Syrian hamsters demonstrate a conditioned place preference for sexual behavior and female chemosensory stimuli

“…DA is released in the medial preoptic area (MPOA) and nucleus accumbens following copulation and exposure to chemosensory stimuli in male rodents (Asmus, 1994; Balfour et al, 2004; Damsma et al, 1992; Mas et al, 1990; Meisel et al, 1993; Mitchell and Gratton, 1992; Pfaus et al, 1990; Sato et al, 1995; Schulz et al, 2003; Wenkstern et al, 1993). In fact, the MPOA DA release in hamsters requires exposure to female chemosensory stimuli (Triemstra et al, 2005), further reinforcing the obligatory nature of chemosensory stimuli for sexual responses in this species. DA is implicated in CPP for sexual behavior in hamsters, as CPP induced by sexual behavior in female hamsters is blocked by administration of a D2 receptor antagonist (Meisel et al, 1996, but see Agmo and Berenfeld, 1990; Agustin-Pavon et al, 2007 for different findings in other rodent species).…”

Dopamine, the medial preoptic area, and male sexual behavior

“…Therefore, the ability of sexual stimuli to elicit a DA response in the MPOA is correlated with the ability of a male to copulate. Finally, hamsters with bulbectomies ipsilateral to the probe within the MPOA or bilateral bulbectomies did not show matinginduced release of DA in the MPOA; while those with sham lesions or contralateral bulbectomies displayed normal DA response, suggesting that chemosensory cues are essential for the release of DA in the MPOA during mating [93].…”