Coronas V, Krantic S, Jourdan F, Moyse E
Neurosciences et Systèmes Sensoriels, CNRS UPRESA 5020, Université Claude Bernard-Lyon, Villeurbanne, France.
Neuroscience. 1999 Apr;90(1):69-78. doi: 10.1016/s0306-4522(98)00460-6.
Dopamine binding sites of D1 and D2/D3 subtypes had been detected in the rat peripheral olfactory system and postulated to account for dopamine-dependent enhancement of olfactory memory and retro-inhibition of olfactory input within the olfactory bulb, respectively. We further assessed, in the present study, the mechanisms of these dopamine actions by using adenylyl cyclase activity assay and [35S]GTP radioautography in rat olfactory bulb and mucosa. The D1 agonist SKF 38393 increased adenylyl cyclase activity on membranes of the olfactory bulb, but not on those of the olfactory mucosa. Stimulation of adenylyl cyclase by SKF 38393 in the olfactory bulb was dose dependent, with a half-maximal effect (EC50) at 0.16 microM SKF 38393, reaching 40% over basal adenylyl cyclase activity, and was blocked by the D1 antagonist SCH 23390. The D2 agonists bromocriptine and quinpirole inhibited both basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. These adenylyl cyclase inhibitions were dose dependent, with EC50 values of 0.1-0.3 microM for bromocriptine and 1-3 microM for quinpirole, equal to 25% of basal enzyme activity at concentrations of 1-10 microM, and were blocked by the D2 antagonist eticlopride. The D2 antagonist was devoid of any effect on basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. Odorant-induced stimulation of adenylyl cyclase was blocked by D2 agonist in olfactory mucosa membranes, which suggests dopaminergic regulation of odor detection in the olfactory mucosa. By using microdissected fractions of the olfactory mucosa, D2 agonist-induced inhibition of adenylyl cyclase was shown to occur only in lamina propria, thus co-localizing with D2 binding sites. [35S]GTP radioautography on tissue sections revealed D2 agonist-induced G-protein activation in olfactory nerve and glomerular layers of the olfactory bulb, and in the chorion of the olfactory mucosa. Taken together, these data demonstrate functional coupling of the dopamine receptors with adenylyl cyclase in both the olfactory bulb and mucosa, and document novel aspects of dopamine's physiological involvement in olfaction and of D2-mediated signal transduction.
在大鼠外周嗅觉系统中已检测到D1和D2/D3亚型的多巴胺结合位点，推测它们分别与多巴胺依赖的嗅觉记忆增强和嗅球内嗅觉输入的逆向抑制有关。在本研究中，我们通过对大鼠嗅球和黏膜进行腺苷酸环化酶活性测定和[35S]GTP放射自显影，进一步评估了这些多巴胺作用的机制。D1激动剂SKF 38393可增加嗅球膜上的腺苷酸环化酶活性，但对嗅黏膜膜上的活性无影响。SKF 38393在嗅球中对腺苷酸环化酶的刺激呈剂量依赖性，在0.16 microM SKF 38393时达到半数最大效应（EC50），比基础腺苷酸环化酶活性高出40%，且被D1拮抗剂SCH 23390阻断。D2激动剂溴隐亭和喹吡罗可抑制嗅球和黏膜中基础及福斯高林刺激的腺苷酸环化酶活性。这些对腺苷酸环化酶的抑制呈剂量依赖性，溴隐亭的EC50值为0.1 - 0.3 microM，喹吡罗为1 - 3 microM，在1 - 10 microM浓度下相当于基础酶活性的25%，且被D2拮抗剂依替必利阻断。D2拮抗剂对嗅球和黏膜中基础及福斯高林刺激的腺苷酸环化酶活性无任何影响。气味剂诱导的腺苷酸环化酶刺激在嗅黏膜膜中被D2激动剂阻断，这表明多巴胺能对嗅黏膜中的气味检测进行调节。通过使用显微解剖的嗅黏膜部分，发现D2激动剂诱导的腺苷酸环化酶抑制仅发生在固有层，因此与D2结合位点共定位。组织切片上的[35S]GTP放射自显影显示，D2激动剂可诱导嗅球的嗅神经层和肾小球层以及嗅黏膜绒毛中的G蛋白激活。综上所述，这些数据证明了多巴胺受体在嗅球和黏膜中均与腺苷酸环化酶存在功能偶联，并记录了多巴胺在嗅觉生理参与及D2介导的信号转导方面的新情况。
