INTERACTION BETWEEN NICOTINE AND STRESS

尼古丁对中枢神经系统既有兴奋又有抑制作用，可能 调整其对压力的反应。ACTH轴已被用作 了解尼古丁如何强烈刺激大鼠脑干-下丘脑 单位。进一步阐明尼古丁的这种刺激作用的研究和 其脱敏作用将集中在神经化学相互作用上。 儿茶酚胺起源于脑干，下丘脑促肾上腺皮质激素 释放因子(CRF)和血浆ACTH。还建议进行调查 评估尼古丁(I)是否通过改变基因组而影响大脑功能 表达，以及(Ii)抑制神经元对非尼古丁的基因组反应 刺激，如CRF，可能参与协调中枢反应 来施加压力。为了定位和量化尼古丁的抑郁效应， 我们计划利用c-fos mRNA的表达，快速、早期的产物 反应基因，作为神经元对两种刺激的基因组反应的指标： (I)美曲唑，已被证明可诱导神经元c-fos表达，以及 (Ii)CRF，我们已经证明它诱导c-fos。神经化学的研究进展 尼古丁刺激的ACTH分泌将与 大鼠下丘脑CRF与肾上腺素和去甲肾上腺素的比较 分别脑池内注射秋水仙碱或α-甲基-对酪氨酸 高效液相色谱-电化学检测儿茶酚胺。在这些研究中， 一次静脉注射。第四脑室(i.c.v.)尼古丁将会是 比较一下。儿茶酚胺耗竭或肾上腺素能拮抗剂的作用 静脉注射对CRF周转和ACTH分泌的影响。尼古丁将会是 确定。长期、重复服用尼古丁也将被研究。 阐明ACTH脱敏的神经化学基础 对尼古丁的反应。急性和慢性暴露于空气中的影响 尼古丁对下丘脑CRF信使核糖核酸水平的影响 确定长期暴露是否会导致神经元适应。在许多 研究表明，尼古丁对下丘脑和下丘脑外的影响将是 通过原位杂交或显微切割获得的组织进行比较。 最后，近端部位(S)介导尼古丁对促肾上腺皮质激素的影响 分泌物将在局部神经毒性消融或输注后确定 尼古丁进入选定的脑干细胞组。以确定是否慢性 急性尼古丁暴露对大鼠脑内c-fos基因表达的影响 对美曲唑或CRF激活神经元的反应，c-fos mRNA水平将 用斑点杂交和Northern杂交分析特异性 显微解剖的细胞核。糖皮质激素反馈在调节中的作用 尼古丁对c-fos表达的影响将在肾上腺切除后进行评估 VS糖皮质激素替代的大鼠。最后，实质内的尼古丁会 用来评价尼古丁的抑郁效应是否通过中介作用 本地的。总而言之，这些研究检验了这样的假设：单一的 暴露于尼古丁刺激大脑CRF的释放，导致ACTH 作为类似于应激反应的协调反应的一部分， 而慢性暴露会使CRF神经分泌反应减敏，并 抑制CRF刺激的c-fos反应。

Nicotine exerts both stimulant and depressant effects on the CNS which may modify its responses to stress. The ACTH axis has been used as a model to understand how nicotine acutely stimulates the rat brainstem-hypothalamic unit. Studies to further elucidate this stimulant effect of nicotine and its desensitization will focus on the neurochemical interaction between catecholamines originating in the brainstem, hypothalamic corticotropin releasing factor (CRF) and plasma ACTH. Investigations are also proposed to assess whether nicotine (i) affects brain function by altering genomic expression, and (ii) depresses neuronal genomic responses to non-nicotinic stimuli, such as CRF, which may be involved in coordinating CNS responses to stress. To localize and quantitate the depressive effects of nicotine, we plan to use the expression of c-fos mRNA, product of a rapid, early response gene, as an index of neuronal genomic responses to two stimuli: (i) metrazole, which as been shown to induce neuronal c-fos expression, and (ii) CRF, which we have shown induces c-fos. The neurochemical studies of nicotine stimulated ACTH secretion will correlate the turnover rates of hypothalamic CRF vs epinephrine and norepinephrine in rats pretreated with intracisternal colchicine or alpha-methyl-p-tyrosine, respectively, using HPLC with electrochemical detection of catecholamines. In these studies, a single dose of i.v. vs fourth ventricular (i.c.v.) nicotine will be compared. The effects of catecholamine depletion or adrenergic antagonists on CRF turnover and ACTH secretion in response to i.c.v. nicotine will be determine. Chronic, repetitive dosing with nicotine will also be studied to clarify the neurochemistry underlying desensitization of the ACTH response to nicotine. The effects of acute and chronic exposure to nicotine on the levels of hypothalamic CRF mRNA will be evaluated to determine whether chronic exposure causes neuronal adaptation. In many studies, the hypothalamic vs extra-hypothalamic effects of nicotine will be compared by in-situ hybridization or in tissue obtained by microdissection. Finally, the proximal site(s) mediating the effect of nicotine on ACTH secretion will be determine after local neurotoxic ablation or by infusing nicotine into selected brainstem cell groups. To determine whether chronic vs acute exposure to nicotine depresses the expression of c-fos mRNA in response to neuronal activation by metrazole or CRF, c-fos mRNA levels will be quantitated by dot-blot and Northern hybridization analysis of specific microdissected nuclei. The role of glucocorticoid feedback in mediating nicotine's affect on c-fos expression will be assessed in adrenalectomized vs glucocorticoid-replaced rats. Finally, intraparenchymal nicotine will be used to evaluate whether the depressive effect of nicotine is mediated locally. In summary, these studies test the hypothesis that a single exposure to nicotine stimulates the release of brain CRF, leading to ACTH secretion as part of a coordinated response similar to a stress response, whereas chronic exposure desensitizes CRF neurosecretory responses and depresses c-fos responses stimulated by CRF.