Neurochemistry of Gestation-produced Analgesia

描述(申请人提供)：妊娠的抗伤害性感觉(GSA)及其激素模拟(HSPA)是多种成分整合的结果，需要强啡肽(Dyn)/K和脑啡肽/6阿片受体(Enk/DOR)脊髓止痛系统的伴随活性。HSPA过程中脊髓Dyn释放的增强是由于伤害素失去了对诱发的Dyn释放的抑制，并将其DOR偶联抑制转变为易化。GSA和HSPA还需要通过腹下神经(HGN)的传入输入和脊髓去甲肾上腺素能受体(NAR)的激活。然而，这些变化背后的机制(S)仍不清楚。我们的生化和初步免疫组织化学(IHC)数据使我们能够制定一个作为GSA和HSPA基础的神经元相互作用的综合模型。我们假设DOR从抑制Enk释放到促进Enk释放的转变是由与Dyn神经元相反的静脉曲张增加的脊髓血管活性肠肽(VIP)释放所触发的。这单独或与Dyn神经元表达的DORs的激活一起，增加了它们的cAMP含量。我们认为，这些事件对于DOR偶联抑制的丧失和DOR偶联促进Dyn释放的出现以及通过伤害素失去其抑制是至关重要的。我们还推测，在HSP过程中，由Dyn神经元表达的脊髓a2c-NARs具有增强的Dyn释放效应。为了验证该模型，本文提出了四个主要的具体目标：(1)确定妊娠和热休克蛋白对脊髓VIP释放的影响。这将通过放射免疫分析的体外脊髓组织以及通过IHC可视化的体内VIP受体内化来进行评估。(2)确定(A)VIP受体单独激活以及与DOR联合激活对对照脊髓组织Dyn释放的调节作用，以及(B)确定a2c-NAR激动剂和拮抗剂对对照和HSP动物脊髓组织Dyn释放的影响。(3)确定体内(A)脊髓VIP受体阻断和(B)抑制脊髓蛋白激酶A对GSA和HSPA的影响。(4)确定GSA和HSPA组分之间的空间关系以及卵巢性类固醇激素对其患病率的影响。初级传入的激活预计会释放兴奋性递质，从而产生疼痛，而不是改善其知觉。然而，有数据表明，初级传入活动也可以增强阿片类药物的抗伤害感受。我们提出的实验应该为进一步理解这一悖论提供一个框架。这项拟议的研究还应该阐明卵巢性类固醇改变(内脏)损伤诱导的脊髓重塑以产生痛觉减退的能力，而不是通常在非怀孕状态下导致的神经病理性疼痛。

DESCRIPTION (provided by applicant): The antinociception of gestation (GSA) and its hormonal simulation (HSPA) result from the integration of multiple components and requires concomitant activity of dynorphin (Dyn)/K and enkephalin/6 opioid receptor (enk/DOR) spinal analgesic systems. Enhanced release of spinal Dyn during HSPA results from the loss of inhibition of evoked Dyn release by nociceptin and the conversion of its DOR-coupled inhibition to facilitation. Afferent input via the hypogastric nerve (HGN) and activation of spinal noradrenergic receptors (NARs) are also required for GSA and HSPA. However, the mechanism(s) underlying these changes remains unknown. Our biochemical and preliminary immunohistochemical (IHC) data have allowed us to formulate an integrated model of the neuronal interactions that underlie GSA and HSPA. We hypothesize that the shift from inhibition to facilitation of enk release by DOR is triggered by increased release of spinal vasoactive intestinal polypeptide (VIP) from varicosities that appose Dyn neurons. This, alone or in combination with activation of DORs that are expressed by Dyn neurons, augments their cAMP content. We contend that these events are critical for the loss of DOR- coupled inhibition and the appearance of DOR-coupled facilitation of Dyn release as well as for the loss of its inhibition via nociceptin. We also postulate that during HSP, there are enhanced Dyn releasing effects of the spinal a2c-NARs that are expressed by Dyn neurons. Four major specific aims are proposed with which to validate this model: (1) Determine the effect of pregnancy and HSP on the release of spinal VIP. This will be assessed using ex vivo spinal tissue via radioimmunoassay as well as via in vivo VIP receptor internalization visualized by IHC. (2) Determine (a) the effect of VIP receptor activation, alone and in combination with DOR activation, on the regulation of spinal Dyn release from control spinal tissue and (b) determine the effects of a2c-NAR agonists and antagonists on Dyn release from spinal tissue obtained from control and HSP animals. (3) Determine the consequences to GSA and HSPA of in vivo (a) spinal VIP receptor blockade and (b) inhibition of spinal protein kinase A. (4) Determine the spatial relationships among components of GSA and HSPA and the influence of ovarian sex steroids on their prevalence. Activation of primary afferents would be expected to release excitatory transmitters that should produce pain, not ameliorate its perception. However, there are data indicating that primary afferent activity can also enhance opioid antinociception. Our proposed experiments should provide a framework for further understanding this paradox. The proposed research should also shed light on the ability of ovarian sex steroids to alter (visceral) injury-induced spinal remodeling to produce hypoalgesia instead of the neuropathic pain that often results during the nonpregnant state.