Valentincic T, Koce A
Department of Biology, University of Ljubljana, Slovenia.
Pflugers Arch. 2000;439(3 Suppl):R193-5.
At present, the principles of coding and codes for individual odorants are not known; however, several coding properties and their limitations emerged. The olfactory code for different odorants must be different to enable olfactory discrimination. We studied elements of the olfactory code that are accessible to combined microelectrode and behavioral techniques. A random sample of spontaneously active olfactory receptor neurons (ORNs) responded to a 15 component mixture of amino acids with suppression, excitation and no change in their activity in the ratio of 6:1:8; ORNs responded to L-arginine (L-Arg) in the ratio of 5:5:60 and to L-cysteine (L-Cys) in the ratio of 10:1:27. ORNs provide information that enables nearly an unlimited behavioral discrimination of single odorants. Underwater electro-olfactogram (EOG) recordings from the olfactory organ measure the odorant-induced summed dc potential change from all the olfactory receptor neurons. In behavioral studies, the more (most) stimulatory component of the binary (ternary) mixture determined in EOG recordings was its better-perceived component; however, discrimination conditioning--repeated presentation of the conditioned mixture and its more stimulatory component alone--enabled the discrimination of the conditioned binary and ternary mixtures from their more (most) stimulatory components. In large multimixtures (13 components), where one amino acid is the more potent EOG stimulus than the other less stimulatory but equipotent components, catfish discriminated all single components from the conditioned multimixture. These results indicate that the multi-mixture is not detected as its most stimulatory component. Catfish also do not learn to discriminate a 13 component multimixture from a 12 component multimixture comprising 12 of the same components. Taken together, these findings indicate that the capacity for parallel transfer of mixture component information is limited in the catfish olfactory system. The finding of a limited capacity of multimixture component detection in catfish also supports the hypothesis of across nerve pattern coding of odorants and eliminates the sole existence of entirely specialized olfactory receptor neurons and labeled lines.
目前，关于单个气味剂的编码原则和代码尚不清楚；然而，一些编码特性及其局限性已经显现出来。不同气味剂的嗅觉编码必须不同，以便能够进行嗅觉辨别。我们研究了联合微电极和行为技术可触及的嗅觉编码元素。一个自发活动的嗅觉受体神经元（ORN）随机样本对15种氨基酸组成的混合物有反应，其活动受到抑制、兴奋，且活动无变化的比例为6:1:8；ORN对L-精氨酸（L-Arg）的反应比例为5:5:60，对L-半胱氨酸（L-Cys）的反应比例为10:1:27。ORN提供的信息几乎能够对单一气味剂进行无限的行为辨别。从嗅觉器官记录的水下电嗅图（EOG）测量了气味剂引起的所有嗅觉受体神经元的直流电位变化总和。在行为研究中，EOG记录中二元（三元）混合物中刺激性更强（最强）的成分是其更容易被感知的成分；然而，辨别条件作用——反复呈现条件混合物及其单独的刺激性更强的成分——使得能够将条件二元和三元混合物与它们的刺激性更强（最强）的成分区分开来。在大型多混合物（13种成分）中，其中一种氨基酸是比其他刺激性较小但等效的成分更强效的EOG刺激物，鲶鱼能够从条件多混合物中辨别出所有单一成分。这些结果表明，多混合物并非作为其刺激性最强的成分被检测到。鲶鱼也没有学会从包含12种相同成分的12种成分多混合物中辨别出13种成分的多混合物。综上所述，这些发现表明鲶鱼嗅觉系统中混合物成分信息的并行传递能力是有限的。鲶鱼中多混合物成分检测能力有限的发现也支持了气味剂跨神经模式编码的假设，并排除了完全专门化的嗅觉受体神经元和标记线路的唯一存在。
