Alkondon Manickavasagom, Pereira Edna F R, Albuquerque Edson X
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Biochem Pharmacol. 2007 Oct 15;74(8):1134-44. doi: 10.1016/j.bcp.2007.06.023. Epub 2007 Jun 21.
Protein density measurements and mRNA analysis have provided valuable information on age-dependent changes in the distribution of different nicotinic receptor (nAChR) subtypes in various areas of the rat brain, including the hippocampus. However, very little is known regarding the functional expression of nAChRs in individual neuron types at various ages. Likewise, there is paucity of information regarding the functional and pharmacological profile of nAChRs in the mature rat hippocampus. To address these issues, we used the whole-cell patch-clamp technique to record nicotinic responses from CA1 stratum radiatum (SR) interneurons in hippocampal slices from rat pups (5-19 days old) and adult rats (2-5 months old). As previously observed in the hippocampus of rat pups, CA1 SR interneurons in the hippocampus of adult rats responded to choline (10mM, 12s) with whole-cell currents that decayed to the baseline within the agonist pulse, were sensitive to inhibition by methyllycaconitine (10nM) or alpha-bungarotoxin (50 nM), and were, therefore, mediated by alpha7*(1)[1] nAChRs. Likewise, as previously observed in the hippocampus of young rats, in the adult rat hippocampus excitatory postsynaptic currents (EPSCs) were recorded from SR interneurons in response to a pulse of ACh (0.1 mM, 12s) applied in the presence of the GABA(A) receptor antagonist bicuculline. ACh-triggered EPSCs were inhibited by mecamylamine (1 microM) or choline (1 mM) and were, therefore, likely to have resulted from activation of alpha3beta4beta2* nAChR. The magnitude of alpha7* nAChR-mediated responses increased with the age of the animals. In contrast, the magnitude of alpha3beta4beta2* nAChR-mediated responses was highest at the second postnatal week. The distinct age dependency of functional expression of alpha7* and alpha3beta4beta2* nAChRs strongly suggests that the excitability of CA1 SR interneurons is differentially regulated by the nicotinic cholinergic system in the hippocampus of rat pups and adult rats.
蛋白质密度测量和mRNA分析为大鼠大脑不同区域（包括海马体）中不同烟碱型受体（nAChR）亚型分布的年龄依赖性变化提供了有价值的信息。然而，对于不同年龄段个体神经元类型中nAChRs的功能表达知之甚少。同样，关于成熟大鼠海马体中nAChRs的功能和药理学特征的信息也很少。为了解决这些问题，我们使用全细胞膜片钳技术记录了来自幼鼠（5 - 19日龄）和成年大鼠（2 - 5月龄）海马切片中CA1辐射层（SR）中间神经元的烟碱反应。正如之前在幼鼠海马体中观察到的那样，成年大鼠海马体中的CA1 SR中间神经元对胆碱（10mM，12s）的反应是全细胞电流，在激动剂脉冲内衰减至基线，对甲基lycaconitine（10nM）或α-银环蛇毒素（50 nM）的抑制敏感，因此由α7*(1)[1] nAChRs介导。同样，正如之前在幼鼠海马体中观察到的那样，在成年大鼠海马体中，在存在GABA(A)受体拮抗剂荷包牡丹碱的情况下，记录到SR中间神经元对乙酰胆碱脉冲（0.1 mM，12s）的兴奋性突触后电流（EPSCs）。乙酰胆碱引发的EPSCs被美加明（1 microM）或胆碱（1 mM）抑制，因此可能是由α3β4β2* nAChR的激活引起的。α7* nAChR介导的反应幅度随动物年龄增加而增加。相比之下，α3β4β2* nAChR介导的反应幅度在出生后第二周最高。α7和α3β4β2 nAChRs功能表达的明显年龄依赖性强烈表明，CA1 SR中间神经元的兴奋性在幼鼠和成年大鼠海马体中受到烟碱胆碱能系统的差异调节。
