Kramer A C, Mirto A J, Austin K J, Roselli C E, Alexander B M
University of Wyoming, Department of Animal Science, Dept 3684, 1000 E. University Ave., Laramie, WY 82071, United States.
Oregon Health & Science University, Department of Physiology & Pharmacology, 3181 SW Sam Jackson Park Road, Portland, OR 97239, United States.
Anim Reprod Sci. 2017 Dec;187:152-158. doi: 10.1016/j.anireprosci.2017.10.019. Epub 2017 Oct 31.
Dopamine synthesis in the ventral tegmental area (VTA) is necessary for the reinforcement of sexual behavior. The objective of this study determined if sexual stimuli initiates reward, and whether reward is attenuated in sexually inactive rams. Sexually active rams were exposed to urine from estrous (n=4) or ovariectomized (n=3) ewes with inactive rams (n=3) exposed to urine from estrous ewes. Following exposure, rams were exsanguinated and brains perfused. Alternating sections of the VTA were stained for Fos related antigens (FRA), tyrosine hydroxylase, and dopamine beta-hydroxylase activity. Forebrain tissue, mid-sagittal ventral to the anterior corpus callosum, was stained for dopamine D receptors. Concentrations of cortisol was determined prior to and following exposure. Exposure to ovariectomized-ewe urine in sexually active rams did not influence (P=0.6) FRA expression, but fewer (P<0.05) neurons were positive for tyrosine hydroxylase in the VTA. Sexually inactive rams had fewer (P<0.05) FRA and tyrosine hydroxylase positive neurons in the VTA than sexually active rams following exposure to estrous ewe urine. VTA neurons staining positive for dopamine beta-hydroxylase did not differ by sexual activity (P=0.44) or urine exposure (P=0.07). Exposure to stimulus did not influence (P=0.46) numbers of forebrain neurons staining positive for dopamine D2 receptors in sexually active rams, but fewer (P=0.04) neurons stain positive in inactive rams. Serum concentrations of cortisol did not differ (P≥0.52) among rams prior to or following stimulus. In conclusion sexual inactivity is unlikely due to stress, but may be partially a result of decreased tyrosine hydroxylase and/or the response to dopamine.
腹侧被盖区（VTA）中的多巴胺合成对于性行为强化至关重要。本研究的目的是确定性刺激是否引发奖赏，以及在性不活跃的公羊中奖赏是否减弱。将性活跃的公羊暴露于发情母羊（n = 4）或去势母羊（n = 3）的尿液中，性不活跃的公羊（n = 3）暴露于发情母羊的尿液中。暴露后，对公羊进行放血并灌注大脑。VTA的交替切片用于Fos相关抗原（FRA）、酪氨酸羟化酶和多巴胺β-羟化酶活性染色。胼胝体前部腹侧的前脑组织用于多巴胺D受体染色。在暴露前后测定皮质醇浓度。性活跃的公羊暴露于去势母羊尿液中不影响（P = 0.6）FRA表达，但VTA中酪氨酸羟化酶阳性的神经元较少（P < 0.05）。性不活跃的公羊在暴露于发情母羊尿液后，VTA中FRA和酪氨酸羟化酶阳性神经元比性活跃的公羊少（P < 0.05）。多巴胺β-羟化酶染色阳性的VTA神经元在性活动（P = 0.44）或尿液暴露方面没有差异（P = 0.07）。暴露于刺激对性活跃公羊中多巴胺D2受体染色阳性的前脑神经元数量没有影响（P = 0.46），但在不活跃的公羊中染色阳性的神经元较少（P = 0.04）。刺激前后公羊血清皮质醇浓度没有差异（P≥0.52）。总之，性不活跃不太可能是由于应激，但可能部分是酪氨酸羟化酶减少和/或对多巴胺反应降低的结果。
