Granule cell neurogenesis and LTP

成年后，大鼠、小鼠[2，8，75]和灵长类动物[53]，包括人类[44]，海马齿状回颗粒细胞层的神经元以较低的速率持续增加。最近的研究报道，丰富的环境[75，4，1,138]和空间学习[51]都增加了齿状颗粒细胞，而与年龄相关的颗粒细胞增殖减少与空间学习的下降[77,114]平行。这些发现表明，持续的颗粒细胞神经发生对正常学习和记忆是重要的。我们的研究表明，成年大鼠颗粒细胞轴突(苔藓纤维)的激活足以诱导苔藓纤维LTP，这是学习中涉及的突触可塑性机制[11，92]增加颗粒细胞神经发生[41,139]。因此，LTP和促进学习的条件都会增加成年动物的颗粒细胞。然而，调控神经发生的机制尚不清楚。本项目中提出的合作研究将确定(1)LTP诱导后的颗粒细胞神经发生是否需要LTP诱导，或者它是否是一个依赖于苔藓纤维激活和/或颗粒细胞去极化的过程，以及(2)神经发生的增加是由于前体细胞或新形成的细胞向颗粒细胞的增殖或分化增加，还是颗粒存活或分化增加。这些研究将在长期植入电极的成年大鼠体内进行，并将使用溴脱氧尿苷(BrdU)掺入，这是一种衡量神经发生的指标，结合荧光免疫细胞化学，可以对前体细胞、胶质细胞、颗粒细胞、未成熟神经元和凋亡细胞进行联合标记，以区分这些可能性。在具体目标1中，我们将确定苔藓纤维LTP诱导后神经发生最多的时间，在LTP诱导后的每天间隔使用单剂量BrdU，以及刺激后的神经发生是否是由于颗粒细胞增殖、存活、分化或对细胞死亡的反应，使用有丝分裂、细胞表型和凋亡标记的荧光标记。在特定的目标2中，我们将确定LTP在穿孔路径-颗粒细胞突触的诱导是否增加了神经发生，以及允许选择性增强穿孔路径-齿状突触、苔藓纤维-CA3突触或两者的刺激参数是否会不同地改变神经发生[136]。在具体目标3中，我们将确定阻断LTP诱导的药物治疗是否类似地阻断神经发生。在特定的目标4中，我们将确定与海马位置场形成和LTP诱导相关的新环境的探索是否也增加颗粒细胞的增殖、存活或成熟细胞向颗粒细胞的分化。研究人员的互补专业领域将提供一个互惠互利的研究项目，既可以增进对神经发生调控机制的理解，也可以加强对UTSA不同群体的本科生、研究生和博士生的培训。

Neurons are continually added at a low rate to the granule cell layer of the hippocampal dentate gyrus during adulthood in rats, mice [2,8,75] and primates [53], including humans [44]. Recent studies report that both enriched environments [75,4 1,138] and spatial learning [51] increase dentate granule cells, whereas age-related decreases in granule cell proliferation n parallel a decline in spatial learning [77,114]. These findings suggest that sustained granule cell neurogenesis is important for normal learning and memory. Our studies indicate that activation of granule cell axons (the mossy fibers) in the adult rat sufficient to induce mossy fiber LTP, a mechanism of synapticplasticity thought involved in learning [11,92] increases granule cell neurogenesis [41,139]. Thus both LTP and conditions that promote learning increase granule cells in adult animals. However, the mechanisms regulating neurogenesis are unknown. The collaborative studies proposed in this project will determine (1) if granule cell neurogenesis that follows LTP induction requires LTP induction, or if it is a process dependent on mossy fiber activation and/or granule cell depolarization, and (2) if increases in neurogenesis is the result of increase in the proliferation or differentiation of precursor or newly formed cells to granule cells, or increase in granule survival or differentiation. These studies will be conducted in vivo in adult rats with chronically implanted electrodes, and will employ bromodeoxyuridine (BrdU) incorporation, a measure of neurogenesis, in conjunction with fluorescent immunocytochemistry allowing co-labeling of precursor, glia, granule cells, immature neurons ,and apoptotic cells to distinguish among these possibilities. In Specific Aim 1, we will determine time at which neurogenesis is maximal following mossy fiber LTP induction using single doses of BrdU at daily intervals following LTP induction, and if neurogenesis following stimulation of results from an increase in granule cell proliferation, survival, differentiation, or in response to cell death using fluorescent markers for mitosis, cell phenotype, and markers for apoptosis. In Specific Aim 2, we will determine if LTP induction at perforant path-granule cell synapses increases neurogenesis, and if stimulation parameters that allow for selective potentiation of perforant path-dentate synapse, the mossy fiber-CA3 synapse, or both [136] differentially alter neurogenesis. In Specific Aim 3, we will determine if pharmacological treatments that block the induction of LTP similarly block neurogenesis. In Specific Aim 4, we will determine if exploration of novel environments, which associated with hippocampal place field formation and LTP induction [30,31] also increase granule cell proliferation, survival, or differentiation of mature cells to granule cells. The complimentary areas of expertise of the investigators will provide a mutually beneficial research program that will enhance both the understanding of mechanisms regulating neurogenesis, as well as enhance training of the diverse population of undergraduate, graduate and Ph.D. students at UTSA.