Monroe Derek C, Holmes Philip V, Koch Lauren G, Britton Steven L, Dishman Rodney K
Department of Kinesiology, University of Georgia, 330 River Road, Athens, GA 30602-6554, USA.
Psychology Department, University of Georgia, Athens, GA, USA.
Brain Res. 2014 Jul 14;1572:11-7. doi: 10.1016/j.brainres.2014.05.014. Epub 2014 May 17.
Rats selectively bred for high- and low-capacity for running on a treadmill (HCR; LCR) also differ in wheel-running behavior, but whether wheel-running can be explained by intrinsic or adaptive brain mechanisms is not as yet understood. It is established that motivation of locomotory behavior is driven by dopaminergic transmission in mesolimbic and mesostriatal systems. However, whether voluntary wheel running is associated with enkephalinergic activity in the ventral striatum is not known.
40 male (20 HCR and 20 LCR) and 40 female (20 HCR and 20 LCR) rats were randomly assigned to 3 weeks of activity wheel exposure or sedentary conditions without wheel access. After 3 weeks of activity-wheel running, rats were decapitated and brains were extracted. Coronal sections were analyzed utilizing in situ hybridization histochemistry for enkephalin (ENK) mRNA in the ventral striatum.
HCR rats expressed less ENK than LCR rats in the nucleus accumbens among females (p<0.01) and in the olfactory tubercle among both females (p<0.05) and males (p<0.05). There was no effect of wheel running on ENK mRNA expression.
Line differences in ENK expression in the olfactory tubercle, and possibly the nucleus accumbens, partly explain divergent wheel-running behavior. The lower striatal ENK in the HCR line is consistent with enhanced dopaminergic tone, which may explain the increased motivation for wheel running observed in the HCR line.
选择性培育出在跑步机上具有高跑步能力和低跑步能力的大鼠（高能力跑步大鼠；低能力跑步大鼠）在轮转行为上也存在差异，但轮转行为能否由内在或适应性脑机制来解释，目前尚不清楚。已确定运动行为的动机是由中脑边缘系统和中脑纹状体系统中的多巴胺能传递驱动的。然而，自愿轮转行为是否与腹侧纹状体中的脑啡肽能活性相关尚不清楚。
40只雄性大鼠（20只高能力跑步大鼠和20只低能力跑步大鼠）和40只雌性大鼠（20只高能力跑步大鼠和20只低能力跑步大鼠）被随机分配到3周的活动轮转暴露组或无轮转设备的久坐组。经过3周的活动轮转跑步后，大鼠被断头并取出大脑。利用原位杂交组织化学分析腹侧纹状体中脑啡肽（ENK）mRNA的冠状切片。
在雌性大鼠的伏隔核中（p<0.01），以及在雌性（p<0.05）和雄性（p<0.05）大鼠的嗅结节中，高能力跑步大鼠表达的脑啡肽比低能力跑步大鼠少。轮转跑步对脑啡肽mRNA表达没有影响。
嗅结节以及可能的伏隔核中脑啡肽表达的品系差异部分解释了不同的轮转行为。高能力跑步大鼠品系中较低的纹状体脑啡肽与增强的多巴胺能张力一致，这可能解释了在高能力跑步大鼠品系中观察到的轮转跑步动机增加的现象。
