Shankaranarayana Rao B S, Laxmi T R, Meti B L, Raju T R
Department of Neurophysiology, National Institute of Mental Health and Neurosciences, PO Box 2900, Hosur Road, 560 029, Bangalore, India.
Neuroscience. 2001;102(2):319-27. doi: 10.1016/s0306-4522(00)00462-0.
The subiculum is a major source of output projections from hippocampus to cortical and subcortical regions. Our previous studies have demonstrated the selective loss of CA1 pyramidal neurons of the hippocampus, and operant and spatial learning impairment in subicular lesioned rats [Govindaiah et al. (1997) Brain Res. 745, 121-126; Laxmi et al. (1999) Brain Res. 816, 245-148]. In the present study, the effect of ibotenate lesions of the subiculum on the dendritic morphology of CA1 and CA3 pyramidal neurons of the hippocampus was investigated in 30-day-old male Wistar rats. The ventral subiculum was lesioned bilaterally with multiple injections of ibotenic acid, stereotaxically. The dendritic branching points and intersections were studied in apical and basal dendrites up to 320 and 160 microm, respectively, in Golgi-impregnated CA1 and CA3 pyramidal neurons of the hippocampus. The results revealed a significant (P<0.001) decrease in the number of dendritic branching points, intersections and total number of dendrites in both apical and basal dendrites of CA1, as well as CA3 pyramidal neurons of the hippocampus. It is surprising that the subicular lesions caused dendritic atrophy of CA3 neurons without affecting the cell density. The results of the present study demonstrate the dendritic atrophy of hippocampal neurons following selective subicular lesions. This might be responsible for the impairments in operant and spatial learning tasks in these rats as observed in our earlier studies. In addition, hippocampal damage is also associated with an impairment in the process of the active monitoring of movements in space, rather than place learning per se [Whishaw (1998) Neurosci. biobeh. Rev. 22, 209-220]. Accordingly, further studies are required to correlate the differential effect of subicular lesions on impairments in learning and movement in space in rats.
海马下脚是海马向皮质和皮质下区域输出投射的主要来源。我们之前的研究已经证明，海马CA1锥体神经元会选择性丧失，且海马下脚损伤的大鼠存在操作性和空间学习障碍[戈文达亚等人（1997年），《脑研究》745卷，第121 - 126页；拉克希米等人（1999年），《脑研究》816卷，第245 - 148页]。在本研究中，我们在30日龄雄性Wistar大鼠中研究了海马下脚的鹅膏蕈氨酸损伤对海马CA1和CA3锥体神经元树突形态的影响。通过立体定位向双侧腹侧海马下脚多次注射鹅膏蕈氨酸造成损伤。在经高尔基染色的海马CA1和CA3锥体神经元中，分别对顶树突和基底树突长达320微米和160微米的树突分支点和交叉点进行了研究。结果显示，海马CA1以及CA3锥体神经元的顶树突和基底树突中的树突分支点数量、交叉点数量和树突总数均显著减少（P<0.001）。令人惊讶的是，海马下脚损伤导致CA3神经元树突萎缩，却不影响细胞密度。本研究结果表明，选择性海马下脚损伤后海马神经元会出现树突萎缩。这可能是我们早期研究中观察到的这些大鼠操作性和空间学习任务受损的原因。此外，海马损伤还与空间中运动的主动监测过程受损有关，而不是与位置学习本身有关[惠肖（1998年），《神经科学与生物行为评论》22卷，第209 - 220页]。因此，需要进一步研究来关联海马下脚损伤对大鼠学习和空间运动障碍的不同影响。
