Larsson Max, Broman Jonas
Department of Experimental Medical Science, Division of Neuroscience, Lund University, BMC F10, SE-221 84 Lund, Sweden.
Eur J Neurosci. 2005 May;21(9):2445-58. doi: 10.1111/j.1460-9568.2005.04081.x.
Postsynaptic autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) at Thr286/287 is crucial for the induction of long-term potentiation at many glutamatergic synapses, and has also been implicated in the persistence of synaptic potentiation. However, the availability of CaMKII phosphorylated at Thr286/287 at individual glutamatergic synapses in vivo is unclear. We used post-embedding immunogold labelling to quantitatively analyse the ultrastructural localization of CaMKII phosphorylated at Thr286/287 (pCaMKII) at synapses formed by presumed nociceptive and low-threshold mechanosensitive primary afferent nerve endings in laminae I-IV of rat spinal cord. Immunogold labelling was enriched in the postsynaptic densities of such synapses, consistent with observations in pre-embedding immunoperoxidase-stained dorsal horn. Presynaptic axoplasm also exhibited sparse immunogold labelling, in peptidergic terminals partly associated with dense core vesicles. Analysis of single or serial pCaMKII-immunolabelled sections indicated that the large majority of synapses formed either by presumed peptidergic or non-peptidergic nociceptive primary afferent terminals in laminae I-II of the spinal cord, or by presumed low-threshold mechanosensitive primary afferent terminals in laminae IIi-IV, contained pCaMKII in their postsynaptic density. However, the postsynaptic levels of pCaMKII immunolabelling at low-threshold primary afferent synapses were only approximately 50% of those at nociceptive synapses. These results suggest that constitutively autophosphorylated CaMKII in the postsynaptic density is a common characteristic of glutamatergic synapses, thus potentially contributing to maintenance of synaptic efficacy. Furthermore, pCaMKII appears to be differentially regulated between high- and low-threshold primary afferent synapses, possibly reflecting different susceptibility to synaptic plasticity between these afferent pathways.
Ca2+/钙调蛋白依赖性蛋白激酶II（CaMKII）在苏氨酸286/287位点的突触后自磷酸化对于许多谷氨酸能突触处长期增强的诱导至关重要，并且也与突触增强的持续性有关。然而，体内单个谷氨酸能突触处苏氨酸286/287位点磷酸化的CaMKII的可用性尚不清楚。我们使用包埋后免疫金标记法，定量分析了大鼠脊髓I-IV层中假定的伤害性和低阈值机械敏感初级传入神经末梢形成的突触处苏氨酸286/287位点磷酸化的CaMKII（pCaMKII）的超微结构定位。免疫金标记在这类突触的突触后致密物中富集，这与包埋前免疫过氧化物酶染色的背角中的观察结果一致。突触前轴质也表现出稀疏的免疫金标记，在部分与致密核心囊泡相关的肽能终末中。对单个或连续的pCaMKII免疫标记切片的分析表明，脊髓I-II层中由假定的肽能或非肽能伤害性初级传入终末形成的绝大多数突触，或IIi-IV层中由假定的低阈值机械敏感初级传入终末形成的突触，其突触后致密物中含有pCaMKII。然而，低阈值初级传入突触处pCaMKII免疫标记的突触后水平仅约为伤害性突触处的50%。这些结果表明，突触后致密物中组成型自磷酸化的CaMKII是谷氨酸能突触的一个共同特征，因此可能有助于维持突触效能。此外，pCaMKII在高阈值和低阈值初级传入突触之间似乎受到不同的调节，这可能反映了这些传入通路之间对突触可塑性的不同敏感性。
