n-3脂肪酸對母鼠HPA axis壓力反應和回饋調控及焦慮憂鬱和學習記憶行為表現之影響

Abstract

二十二碳六烯酸(docosahexaenoic acid, DHA, 22:6n-3)是n-3多元不飽和脂肪酸，主要富含於腦部，對神經發育生長及功能的影響十分重要。腦部DHA含量主要在大腦發育時期迅速堆積，即親代母體的懷孕泌乳期，由母體提供DHA會透過胎盤及泌乳的方式給予子代。本實驗室先前研究發現懷孕泌乳期母鼠餵食n-3脂肪酸缺乏飼料，會因子代在大腦發育期的大量需求，而使母鼠腦部的DHA含量大量被剝奪流失。本論文主要探討親代腦部DHA流失是否影響其母性泌乳照顧行為，且在懷孕泌乳時期母體內下視丘-腦下垂體-腎上腺路徑(Hypothalamus-pituitary-adrenal axis, HPA axis)對壓力的反應及負回饋調控，產後焦慮憂鬱情緒表現及學習記憶行為的影響。母鼠在懷孕泌乳期分別餵食葵花油n-3脂肪酸缺乏飼料以及葵花油和魚油混合n-3脂肪酸充足飼料，而同年紀的virgin雌鼠攝取與母鼠相同的實驗飼料。 若與懷孕泌乳期母鼠餵食n-3脂肪酸充足飼料相比，母鼠攝取n-3脂肪酸缺乏飼料會顯著降低其腦部DHA含量，減少licking/grooming、arched back及lied on back等母性照顧泌乳行為，在強迫游泳及十字迷宮測試中，增加了憂鬱及焦慮的程度，而在水迷宮測試的空間參考記憶、空間探針記憶、空間工作記憶也都顯著較差，在主動閃避測試中也降低了恐懼記憶。但懷孕泌乳期母鼠餵食n-3脂肪酸充足或缺乏飼料之間，在束縛壓力時肛溫變化以及壓力前後血清中corticosterone濃度都無差異。而HPA axis負回饋調控在給予Dexamethasone後再利用Restraint及Corticotropin-releasing hormone(CRH)方式去刺激血清中corticosterone的濃度，發現母鼠攝取n-3脂肪酸充足或缺乏飼料之間無差異。 若比較懷孕泌乳期母鼠及virgin雌鼠之間，發現母鼠在束縛壓力下肛溫變化較小，且降低產後焦慮及憂鬱情緒表現，但在被動閃避恐懼記憶、空間參考記憶以及空間探針記憶的行為測試中母鼠都顯著比virgin雌鼠差，而空間工作記憶及主動閃避恐懼記憶在兩組之間則無差異。另外HPA axis負回饋調控在血清中corticosterone濃度變化，母鼠與virgin雌鼠之間無差異。 若與virgin雌鼠餵食n-3脂肪酸充足飼料相比，virgin雌鼠攝取n-3脂肪酸缺乏飼料增加了焦慮及憂鬱的程度，在被動閃避恐懼記憶、空間探針記憶以及空間工作記憶的行為測試中n-3脂肪酸缺乏virgin雌鼠都比n-3充足雌鼠差，而空間參考記憶及主動閃避恐懼記憶在virgin兩組之間則無差異。在給予束縛壓力時肛溫變化以及壓力前後血清中corticosterone的濃度，發現virgin雌鼠攝取n-3脂肪酸充足或缺乏飼料之間無差異，而在HPA axis負回饋調控的血清中corticosterone濃度變化，virgin雌鼠攝取n-3脂肪酸充足或缺乏飲食之間無差異。 綜合以上所述，母鼠攝取n-3脂肪酸缺乏飼料會降低其腦部DHA含量、較低的母性泌乳照顧行為、容易有產後焦慮及憂鬱情緒表現且有較差的學習記憶能力。懷孕泌乳期母鼠與virgin雌鼠相比，母鼠對於HPA axis的壓力反應較低，不易有焦慮及憂鬱情緒表現，但會降低其學習記憶能力。然而是否經歷懷孕泌乳時期或者飲食中有無攝取n-3脂肪酸缺乏飼料則對HPA axis負回饋調控影響不大。

Docosahexaenoic acid (DHA, 22:6n-3), an n-3 polyunsaturated fatty acid (PUFA), is mainly enriched in the brain and is essential for normal neurological function. Most DHA accumulation in the brain occurs during brain development in the perinatal period and is supplied via the placenta to the fetus and in the breast-fed milk to the pup. We previous found that maternal brain DHA levels are depleted via maternal n-3 PUFA deficient diet during pregnancy and lactation due to meeting the high demand of the developing nervous system in the offspring. The aim of this study was to examine effects of depleted maternal brain DHA levels on maternal care behaviors and evaluated effects of the reproductive cycle on the hypothalamus-pituitary-adrenal (HPA) axis activity and negative feedback regulation as well as postpartum anxiety, depression and learning memory performance. Pregnant rats were fed during pregnancy and lactation with a sunflower oil-based n-3 PUFA deficient diet or sunflower oil mixed with fish oil as an n-3 PUFA adequate diet, age-matched virgin rats being fed the same diets. We found that compared to the maternal rats fed an n-3 PUFA adequate diet, the maternal rats fed n-3 PUFA deficient diet showed significant lower licking/grooming, arch-back and lie on back nursing behaviors and significant decreased brain DHA levels, and enhanced depressive-like behavior in the forced-swimming test and anxiety-like behavior in the plus-maze test, and poor spatial learning memory, memory retention and working memory in water maze and poor fear learning memory in active avoidance test, but no difference in changes in colonic temperature and serum corticosterone during or after restraint-induced stress and no effect on HPA regulation in Dexamethasone suppression following CRH stimulation test or restraint-induced stress test.. In both set of postpartum rats compared to those in virgin females showed significantly decreased restraint stress-induced changes in colonic body temperature, and less anxiety-like and depression-like behaviors, poor fear memory in the passive avoidance test, poor spatial learning memory and memory retention in Morris water maze, but no difference in working memory in Morris water maze and fear memory in active avoidance test and no effect on HPA negative feedback regulation in Dexamethasone suppression following CRH stimulation test or restraint-induced stress test. Compared to the virgin rats fed an n-3 fatty acid adequate diet, the virgin rats fed n-3 PUFA deficient diet showed more anxiety-like and depression-like behavior, poor learning memory in passive avoidance test, poor memory retention in probe test, and poor working memory in Morris water maze but no difference in spatial learning memory in Morris water maze and fear memory in active avoidance test, as well as no difference in changes in colonic temperature and serum corticosterone during or after restraint-induced stress and no difference in HPA negative feedback regulation in Dexamethasone suppression following CRH stimulation test or restraint-induced stress test. These results suggest that the maternal rats fed an n-3 PUFA deficient diet showed decreased brain DHA levels, less maternal care behavior, more anxiety and depression as well as poor learning memory performance. The postpartum rats presented hypo-activity of HPA axis response to stress and less anxiety and depression but with poor memory performance. The reproductive cycle or n-3 PUFA diet had no effect on HPA negative feedback regulation.