Woo N H, Duffy S N, Abel T, Nguyen P V
Department of Physiology, University of Alberta School of Medicine, Edmonton, Alberta T6G 2H7, Canada.
J Neurophysiol. 2000 Dec;84(6):2739-45. doi: 10.1152/jn.2000.84.6.2739.
cAMP-dependent protein kinase (PKA) is believed to play a critical role in the expression of long-lasting forms of hippocampal long-term potentiation (LTP). Can distinct patterns of synaptic activity induce forms of LTP that require different isoforms of PKA? To address this question, we used transgenic mice that have genetically reduced hippocampal PKA activity, and a specific pharmacological inhibitor of PKA, Rp-cAMPS. Transgenic mice [R(AB) mice] that express an inhibitory form of a particular type of regulatory subunit of PKA (type-Ialpha) showed significantly reduced LTP in area CA1 of hippocampal slices as compared with slices from wild-type mice. This impairment of LTP expression was evident when LTP was induced by applying repeated, temporally spaced stimulation (4 1-s bursts of 100-Hz applied once every 5 min). In contrast, LTP induced by applying just 60 pulses in a theta-burst pattern was normal in slices from R(AB) mice as compared with slices from wild-type mice. We found that Rp-cAMPS blocked the expression of LTP induced by both spaced tetra-burst and compressed theta-burst stimulation in hippocampal slices of wild-type and R(AB) mice, respectively. Since Rp-cAMPS is a PKA inhibitor that is not selective for any particular isoform of PKA and these R(AB) mice show reduced hippocampal PKA activity resulting from genetic manipulation of a single isoform of PKA regulatory subunit, our data support the idea that distinct patterns of synaptic activity can produce different forms of LTP that significantly engage different isoforms of PKA. In particular, theta-burst LTP significantly recruits isoforms of PKA containing regulatory subunits other than the mutant RIalpha subunit, whereas tetra-burst LTP requires PKA isoforms containing the mutant RIalpha subunit. Thus, altering both the total amount of imposed synaptic activity and the temporal spacing between bursts of imposed activity may subtly modulate the PKA dependence of hippocampal LTP by engaging distinct isoforms of PKA. In a broader context, our findings suggest that synaptic plasticity in the mammalian brain might be importantly regulated by activity-dependent recruitment of different isoforms of key signal transduction molecules.
环磷酸腺苷（cAMP）依赖性蛋白激酶（PKA）被认为在海马体长期增强效应（LTP）的长期形式表达中起关键作用。不同模式的突触活动能否诱导出需要不同PKA亚型的LTP形式呢？为了解决这个问题，我们使用了基因改造后海马体PKA活性降低的转基因小鼠，以及一种PKA的特异性药理抑制剂Rp-cAMPS。表达特定类型PKA调节亚基（Iα型）抑制形式的转基因小鼠[R(AB)小鼠]，与野生型小鼠脑片相比，其海马体CA1区的LTP显著降低。当通过施加重复的、时间间隔的刺激（每5分钟施加一次4个1秒的100赫兹脉冲串）诱导LTP时，LTP表达的这种损伤很明显。相比之下，与野生型小鼠脑片相比，R(AB)小鼠脑片中以θ波爆发模式施加仅60个脉冲诱导的LTP是正常的。我们发现，Rp-cAMPS分别阻断了野生型和R(AB)小鼠海马体脑片中由间隔四脉冲串和压缩θ波爆发刺激诱导的LTP的表达。由于Rp-cAMPS是一种对PKA的任何特定亚型都无选择性的PKA抑制剂，并且这些R(AB)小鼠由于对PKA调节亚基的单一亚型进行基因操作而表现出海马体PKA活性降低，我们的数据支持这样一种观点，即不同模式的突触活动可以产生不同形式的LTP，这些LTP显著涉及不同的PKA亚型。特别是，θ波爆发LTP显著募集了含有除突变型RIα亚基之外的调节亚基的PKA亚型，而四脉冲串LTP需要含有突变型RIα亚基的PKA亚型。因此，改变施加的突触活动总量以及施加活动脉冲之间的时间间隔，可能通过涉及不同的PKA亚型来微妙地调节海马体LTP对PKA的依赖性。在更广泛的背景下，我们的研究结果表明，哺乳动物大脑中的突触可塑性可能通过关键信号转导分子不同亚型的活动依赖性募集而受到重要调节。
