A study on the neural mechanism of pulsatile secretion of oxzytocin during suckling in the rat

催产素在大鼠哺乳期以脉动的方式释放。然而，产生搏动释放的神经机制及其位置尚不清楚。我们发现神经元向视上核投射，并在泌乳前在背内侧核及其附近表现出动作电位的爆发（破裂神经元）。我们测试了哺乳刺激对这些神经元背景活动的影响，发现哺乳刺激增加了神经元的放电率，而将幼崽从母亲身边带走则降低了神经元的放电率。由于催产素神经元的背景活动不受哺乳刺激的影响，因此，爆发神经元可能参与了泌乳爆发的门控机制。为了探讨催产素神经元同步泌乳的神经机制，我们在中脑半横断的哺乳期大鼠的双侧视上核（SON）上记录了催产素神经元的活动。在双侧哺乳过程中，不仅从完整侧记录的催产素神经元，而且从损伤侧记录的催产素神经元也显示出泌乳的爆发。当两侧的催产素神经元都被记录下来并显示出泌乳的爆发时，它们总是很好地同步。在下丘脑中部半横切的大鼠中，也对双侧SON进行了重新编码。完整侧记录了泌乳爆发，但未记录病变侧的爆发。因此，泌乳爆发的同步机制很可能位于中脑和中下丘脑之间的区域。

Oxytocin is known to be released in a pulsatile fashion during suckling in the latating rat. However, not only the neural mechanism to produce the pulsatile release but also its location have not been made clear. We found neurons projecting to the supraoptic nucleus and showing bursts of action potentials before milk ejection (bursting neuron) in the dorsomedial nuclers and its vicinity. We tested the effect of suckling stimuli on the background activity of those neurons and found that suckling stimuli increased the firing rate of the neuron and the removal of pups from the mother decreased it. Since the background activity of oxytocin neuron is not influenced by suckling stimuli it is suggested the bursting neuron may participate in the gating mechanism for milk ejection bursts. In order to investigate the location of the neural mechanism responsible for the synchronization of milk ejection bursts of oxytocin neurones the activity of oxytocin neurons was recorded from the supraoptic nuclei (SON) bilaterally in the lactating rats with hemitransection of the midbrain. During bilateral suckling not only the oxytocin neurones recorded from the intact side but also those recorded from the lesioned side displayd milk-ejection bursts. When oxytocin neurons could be recorded on both sides and displayd milk-ejection bursts, they were always well synchronized. Recoding from bilateral SON was also made in the rat with hemitransection in the mid-hypothalamus. Milk ejection burst were recorded from the intact side but no bursts were recorded from the lesioned side. Thus it is very likely that the synchronization mechanism for milk ejection burst is located in the region between the midbrain and the midhypothalamus.