Reproductive Plasticity in Oxytocin Neurons

描述（由申请人提供）：催产素（OT）在分娩和哺乳中作为激素发挥作用，在大脑中作为神经调质发挥作用。OT受体存在于OT神经元上，它们在体树突OT释放期间自动调节。在妊娠和哺乳期间，OT释放是脉动的，而不是连续的，这种模式对于避免OT受体脱敏和确保子宫和乳腺中靶平滑肌的适当激素功能至关重要。视上核（SON）和室旁核（PVN）中的神经元在妊娠晚期和哺乳期经历显著的可塑性，包括神经胶质-神经元重排和突触活动的增加。我们已经发现在这两个时期增强尖峰后超极化（AHPs）。AHPs在塑造来自OT神经元的短（~4秒）高频（~50 Hz）爆发中至关重要，这些爆发是这种脉动的基础，这些爆发产生OT向血流中的团注释放，以最大限度地收缩子宫平滑肌或乳腺肌上皮。 SON和PVN的生殖相关可塑性取决于妊娠期间卵巢类固醇释放的模式和OT的体树突释放。我们提出的第一个体内证据表明，中央OT受体是至关重要的钙依赖性AHPs的增强通常表现在怀孕后期。一个特定的OT拮抗剂长期管理的第三脑室在妊娠晚期阻断这种形式的可塑性，VP神经元没有影响。此外，我们通过将OT应用于妊娠（E18-19）大鼠的下丘脑切片来模仿这种可塑性。本提案的目标是了解OT神经元进行这种适应的机制，以及它如何塑造OT神经元放电以最大限度地释放激素，从而确保婴儿发育的正常分娩和哺乳。了解OT神经元的中枢OT受体转导机制对于理解OTR在脑功能中的更广泛作用具有重要的应用。有三个具体目标：具体目标1。确定OT引起的OT神经元AHPs增强是否特异于OT神经元和OT受体激活，是否特异于妊娠动物，以及是否是由于潜在电流的Ca 2+敏感性变化所致。具体目标2。为了测试OT是否对 AHPs是通过pERK 1/2-MAPK级联介导的，以及它是否与AHPs通道和/或已知调节AHPs Ca 2+敏感性的酶CK 2和PP 2a的表达增加有关。具体目标3。确定增强的AHP如何调节OT神经元爆发，并确定缺失兴奋性活动的重新插入是否以OT依赖性方式差异性地改变哺乳期大鼠与未孕大鼠的OT放电模式。

DESCRIPTION (provided by applicant): Oxytocin (OT) functions as a hormone in labor and lactation and as a neuromodulator in the brain. OT receptors are present on OT neurons, which they autoregulate during somatodendritic OT release. During pregnancy and lactation, OT release is pulsatile, not continuous, and this pattern is critical to avoid OT receptor desensitization and insure proper hormone function at target smooth muscle in uterus and mammary gland. Neurons in the supraoptic (SON) and paraventricular nuclei (PVN) undergo remarkable plasticity during late pregnancy and lactation, including a glial-neuronal rearrangement and increases in synaptic activity. We have found enhanced spike afterhyperpolarizations (AHPs) during both periods. AHPs are critical in sculpting the short (~4 sec) high frequency (~50 Hz) bursts from OT neurons underlying this pulsatility, bursts that produce a bolus release of OT into the bloodstream to maximally contract uterine smooth muscle or mammary gland myoepithelium. Reproductive-associated plasticity in the SON and PVN depends on the pattern of ovarian steroid release during pregnancy and on the somatodendritic release of OT. We present the first in vivo evidence showing that central OT receptors are critical for the enhancement of the calcium-dependent AHPs normally manifest at late pregnancy. A specific OT antagonist administered chronically to the third ventricle during late pregnancy blocked this form of plasticity with no effect on VP neurons. In addition, we mimicked this plasticity by applying OT to hypothalamic slices from pregnant (E18-19) rats. The goal of this proposal is to understand the mechanisms of this adaptation made by OT neurons, and how it shapes OT neuronal firing to maximize hormone release and thereby insure normal parturition and lactation for infant development. Understanding the mechanisms of central OT receptor transduction at the OT neuron will have important applications for understanding the wider roles of OTRs in brain function. There are Three Specific Aims: Specific Aim 1. To determine if the enhancement of AHPs in OT neurons by OT is specific to OT neurons and OT receptor activation, whether it is specific to pregnant animals, and whether it is due to a change in the Ca2+ sensitivity of the underlying currents. Specific Aim 2. To test whether OT's effects on AHPs are mediated through a pERK 1/2-MAPK cascade, and whether it is associated with an increase expression of the AHP channels and/or the enzymes CK2 and PP2a, known to modulate AHP Ca2+ sensitivity. Specific Aim 3. To determine how enhanced AHPs modulate OT neuronal bursts, and to determine whether the reinsertion of missing excitatory activity differentially alters OT firing pattern in lactating vs. virgin rats, in an OT-dependent manner.