Hotta Harumi, Suzuki Harue, Iimura Kaori, Watanabe Nobuhiro
Department of Autonomic Neuroscience, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
Front Neurosci. 2018 Feb 27;12:117. doi: 10.3389/fnins.2018.00117. eCollection 2018.
The brainstem is essential for producing micturition contractions of the urinary bladder. Afferent input from perineal skin evoked by gentle mechanical stimulation inhibits micturition contractions by decreasing both ascending and descending transmissions between the brainstem and spinal cord. Dysfunction of this inhibitory mechanism may be one cause of the increase in the prevalence of overactive bladder in old age. The aim of this study was to examine effect of aging on function of skin afferent fibers that inhibit bladder micturition contractions in rats. We used anesthetized male rats in three different age groups: young adult (4-5 months old), middle aged (6-9 months old), and aged (27-30 months old). The bladder was expanded to produce isovolumetric rhythmic micturition contractions. Skin afferent fibers were activated for 1 min either by electrical stimulation (0.5 ms, 0.2-10 V, 0.1-10 Hz) of the cutaneous branch of the pudendal nerve (CBPN) or by gentle mechanical skin stimulation with an elastomer roller. When skin afferent nerves were activated electrically, micturition contractions were inhibited in a similar manner in all age groups, with long latency inhibition induced by excitation of Aβ fibers and short latency inhibition by additional Aδ and C fiber excitation (at 1-10 Hz). On the contrary, when skin afferent nerves were activated mechanically by rolling, latency of inhibition following rolling stimulation was prolonged in aged rats. Single unitary afferent nerve activity of low-threshold mechanoreceptors (LTMs) from the cutaneous nerve was recorded. The discharge rate during rolling was not significantly reduced in Aβ units but was much lower in Aδ and C units in aged rats (0.4 and 0.5 Hz, respectively) than in young adult rats (3 and 7 Hz). These results suggest that the neural mechanism that inhibits bladder micturition contractions by skin afferent input is well maintained in old age, but the early inhibition by gentle skin stimulation is decreased because of reduced responses of Aδ- and C-LTMs.
脑干对于产生膀胱排尿收缩至关重要。轻柔机械刺激引起的会阴皮肤传入输入通过减少脑干与脊髓之间的上行和下行传递来抑制排尿收缩。这种抑制机制的功能障碍可能是老年膀胱过度活动症患病率增加的原因之一。本研究的目的是研究衰老对抑制大鼠膀胱排尿收缩的皮肤传入纤维功能的影响。我们使用了三个不同年龄组的麻醉雄性大鼠：年轻成年组（4 - 5个月龄）、中年组（6 - 9个月龄）和老年组（27 - 30个月龄）。使膀胱扩张以产生等容性节律性排尿收缩。通过电刺激阴部神经皮支（CBPN）（0.5毫秒，0.2 - 10伏，0.1 - 10赫兹）或用弹性体滚轮轻柔机械刺激皮肤来激活皮肤传入纤维1分钟。当皮肤传入神经被电激活时，所有年龄组的排尿收缩均以相似方式受到抑制，Aβ纤维兴奋诱导长潜伏期抑制，额外的Aδ和C纤维兴奋（1 - 10赫兹）诱导短潜伏期抑制。相反，当通过滚动机械激活皮肤传入神经时，老年大鼠滚动刺激后的抑制潜伏期延长。记录了来自皮神经的低阈值机械感受器（LTMs）的单单位传入神经活动。滚动过程中，老年大鼠Aβ单位的放电率没有显著降低，但Aδ和C单位的放电率（分别为0.4和0.5赫兹）比年轻成年大鼠（分别为3和7赫兹）低得多。这些结果表明，皮肤传入输入抑制膀胱排尿收缩的神经机制在老年时保持良好，但由于Aδ和C - LTMs反应性降低，轻柔皮肤刺激引起的早期抑制作用减弱。
