Center for Molecular and Behavioral Neuroscience, Rutgers University, Newark, New Jersey 07102, USA.
J Comp Neurol. 2013 Aug 1;521(11):2538-50. doi: 10.1002/cne.23297.
The perirhinal cortex plays a critical role in recognition and associative memory. However, the network properties that support perirhinal contributions to memory are unclear. To shed light on this question, we compared the synaptic articulation of short- and long-range inputs from the perirhinal cortex or temporal neocortex with perirhinal neurons in rats. Iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) were performed at different rostrocaudal levels of the ventral temporal neocortex or perirhinal cortex, and electron microscopic observations of anterogradely labeled (PHAL(+)) axon terminals found at perirhinal sites adjacent to or rostrocaudally distant from the injection sites were performed. After neocortical injections, the density of PHAL(+) axons in the perirhinal cortex decreased steeply with rostrocaudal distance from the injection sites, much more so than following perirhinal injections. Otherwise, similar results were obtained with neocortical and perirhinal injections. In both cases, most (76-86%) PHAL(+) axon terminals formed asymmetric synapses, typically with spines (type A, 83-89%) and less frequently with dendritic profiles (type B, 11-17%). The remaining terminals formed symmetric synapses with dendritic profiles (type C, 14-23%). Type B and C synapses were 2.4-2.6 times more frequent in short- than long-range connections. The postsynaptic elements in type A-C synapses were identified with immunocytochemistry for CAMKIIα, a marker of glutamatergic cortical neurons. Type A and C terminals contacted CAMKIIα-positive principal cells, whereas type B synapses contacted presumed inhibitory neurons. Overall, these results suggest that principal perirhinal neurons are subjected to significantly more inhibition from short- than from long-range cortical inputs, an organization that likely impacts perirhinal contributions to memory.
颗粒下皮质在识别和联想记忆中起着关键作用。然而，支持颗粒下皮质对记忆贡献的网络特性尚不清楚。为了阐明这个问题，我们比较了来自颗粒下皮质或颞叶新皮质的短程和长程输入与大鼠颗粒下神经元的突触表达。在腹侧颞叶新皮质或颗粒下皮质的不同头尾部水平进行了植物凝集素（PHA）的顺行示踪注射，并对颗粒下部位的顺行标记（PHA（+））轴突末梢进行了电子显微镜观察，这些部位与注射部位相邻或头尾部距离较远。在新皮质注射后，颗粒下皮质中 PHA（+）轴突的密度随注射部位的头尾部距离急剧下降，下降幅度远大于颗粒下皮质注射后的情况。否则，新皮质和颗粒下皮质注射后均得到类似的结果。在这两种情况下，大多数（76-86%）PHA（+）轴突末梢形成不对称突触，通常与棘突（A型，83-89%）形成突触，较少与树突轮廓（B 型，11-17%）形成突触。其余的末端与具有树突轮廓的对称突触（C 型，14-23%）形成突触。B 型和 C 型突触在短程连接中比长程连接更常见 2.4-2.6 倍。在 A-C 型突触中，后突触元素通过 CAMKIIα的免疫细胞化学鉴定，CAMKIIα是谷氨酸皮质神经元的标志物。A 型和 C 型末端接触 CAMKIIα阳性主细胞，而 B 型突触接触假定的抑制性神经元。总的来说，这些结果表明，主颗粒下神经元受到来自短程皮质输入的抑制作用明显大于来自长程皮质输入的抑制作用，这种组织可能会影响颗粒下皮质对记忆的贡献。
