Pape J R, Tramu G
Laboratoire de Neurocytochimie fonctionnelle, URA CNRS 339, Université de Bordeaux I, Talence, France.
Neuroendocrinology. 1996 Jun;63(6):540-9. doi: 10.1159/000127083.
Hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC)-derived peptides located in the arcuate nucleus (ARC) have been postulated to be good candidates to play a modulatory role during lactation. In the present study, we first quantified, by in situ hybridization, lactation-induced changes in NPY and POMC gene expression throughout the ARC. In a second phase of the study, we attempted to determine whether any relationship exists between neuropeptide gene expression and the suckling stimulus itself. For this, we used experimental groups of animals submitted to suppression of the suckling stimulus by removal of pups and the subsequent restoration of the suckling stimulus by the return of the litter. Since lactation is characterized by an estrogen-deficient status [15], we attempted using ovariectomized (2 or 21 days) diestrous females to describe the changes in NPY gene expression observed during lactation. Since the suckling stimulus induces a strong prolactin (PRL) release, we completed this study by using an intravenous injection of PRL antiserum in order to discriminate the effects of PRL per se on the observed suckling-induced changes in neuropeptide gene expression. Freely nursing lactating females exhibited a large increase in NPY mRNA expression as compared to diestrous females (10.10 +/- 0.50 vs. 4.51 +/- 0.35). After suppression of the suckling stimulus by removal of pups, this increase intensified during short-term suppression of 16 h (15.37 +/- 0.67) and was reversed following long-term suppression of 36 h (12.35 +/- 0.61). Ovariectomized diestrous animals showed significant changes in NPY mRNA expression as compared to lactating females (5.25 +/- 0.42 vs. 10.10 +/- 0.50). Lactating females submitted to PRL immunoneutralization by PRL antiserum showed a slight increase in NPY mRNA expression as compared to non-injected lactating females (13.75 +/- 0.51 vs. 12.95 +/- 0.59). Freely nursing lactating females showed a decrease in POMC mRNA expression (8.27 +/- 0.33) whereas suppression of suckling by removal of the pups (9.52 +/- 0.45) resulted in a return to diestrous POMC mRNA levels (10.77 +/- 0.36). We showed that restoration of suckling by the return of the litter induced an increase in POMC gene expression (12.55 +/- 0.66). By lowering circulating levels of PRL with PRL antiserum after restoration of suckling, we observed a decrease in POMC mRNA expression (9.81 +/- 0.46). Results of this study showed that the increase in NPY mRNA in the medial ARC during lactation did not appear to be due either to gonadal steroid-deficient status or to the suckling-induced hyperprolactinemia. If freely nursing lactating females showed a moderate decrease in POMC gene expression, restoration of the suckling stimulus by return of the pups provoked an increase in POMC gene expression which seemed to depend on high endogenous levels of PRL.
位于弓状核（ARC）的下丘脑神经肽Y（NPY）和源自阿黑皮素原（POMC）的肽被认为是在哺乳期间发挥调节作用的良好候选者。在本研究中，我们首先通过原位杂交定量了整个ARC中NPY和POMC基因表达的泌乳诱导变化。在研究的第二阶段，我们试图确定神经肽基因表达与哺乳刺激本身之间是否存在任何关系。为此，我们使用了实验组动物，通过移除幼崽来抑制哺乳刺激，并随后通过放回幼崽来恢复哺乳刺激。由于泌乳的特征是雌激素缺乏状态[15]，我们试图使用去卵巢（2或21天）的动情期雌性动物来描述泌乳期间观察到的NPY基因表达变化。由于哺乳刺激会诱导强烈的催乳素（PRL）释放，我们通过静脉注射PRL抗血清来完成本研究，以区分PRL本身对观察到的哺乳诱导的神经肽基因表达变化的影响。与动情期雌性动物相比，自由哺乳的泌乳雌性动物的NPY mRNA表达大幅增加（10.10±0.50对4.51±0.35）。通过移除幼崽抑制哺乳刺激后，这种增加在16小时的短期抑制期间加剧（15.37±0.67），并在36小时的长期抑制后逆转（12.35±0.61）。与泌乳雌性动物相比，去卵巢的动情期动物的NPY mRNA表达有显著变化（5.25±0.42对10.10±0.50）。通过PRL抗血清对泌乳雌性动物进行PRL免疫中和后，与未注射的泌乳雌性动物相比，其NPY mRNA表达略有增加（13.75±0.51对12.95±0.59）。自由哺乳的泌乳雌性动物的POMC mRNA表达降低（8.27±0.33），而通过移除幼崽抑制哺乳（9.52±0.45）导致POMC mRNA水平恢复到动情期水平（10.77±0.36）。我们发现，放回幼崽恢复哺乳会诱导POMC基因表达增加（12.55±0.66）。在恢复哺乳后用PRL抗血清降低循环中的PRL水平，我们观察到POMC mRNA表达降低（9.81±0.46）。本研究结果表明，泌乳期间内侧ARC中NPY mRNA的增加似乎既不是由于性腺类固醇缺乏状态，也不是由于哺乳诱导的高催乳素血症。如果自由哺乳的泌乳雌性动物的POMC基因表达适度降低，放回幼崽恢复哺乳刺激会导致POMC基因表达增加，这似乎取决于内源性PRL的高水平。
