Responses of single chorda tympani taste fibers of the calf (Bos taurus)

Abstract

In spite of a wealth of information on feed and nutrition in cattle, there little is published of what they actually can taste. Here, we attempt to remedy some of this deficiency by presenting recordings of the chorda tympani proper nerve of young Holstein calves during stimulation of approximately 30 compounds. Hierarchical cluster analysis of 46 single taste fibers separated 4 fiber clusters: N (salt best), H (sour best), and 2 clusters, which could not be related to any human taste quality. The N fibers responded best to LiCl, NaCl, urea, monosodium glutamate, and KCl, whereas the H fibers responded strongly to citric and ascorbic acid. Interestingly, propionic and butyric acid stimulated best the 3rd cluster, whereas the 4th cluster responded best to denatonium benzoate and only to a small extent to quinine hydrochloride. Sweeteners stimulated moderately all clusters. Beginning with the largest response to sweet, the order between the responses was: acesulfame-K, saccharin, D-phenylalanine, glycine, sucrose, fructose, erythritol, cyclamate, and lactose. Alitame, aspartame, and super-aspartame evoked no or little responses. Three and 5 M ethanol stimulated all clusters. Comparison with taste fibers in other species suggests that the taste world of cattle is quite different from other species'.

Figure 1

Averaged responses of the summated CT nerve recording from 4 calves. The stimuli have been arranged in the general order of salty, sour, bitter, and sweet, as judged by humans. The amplitudes of the columns are measured in arbitrary units and represent maximum responses.

Figure 2

Recordings of a CT filament, single fiber CA9N11G during stimulation with sucrose, NaCl, citric acid, QHCl, and urea. Onset and offset of stimuli are shown as change of the top horizontal line. Stimulation time was 10 s, and the stimulation was preceded and followed by a flow of artificial saliva over the tongue for 40 s. Of interest is the difference in latency of response between NaCl and urea.

Figure 3

An overview of the response profiles of 46 CT taste fibers of calves. The area of the circles represents impulse frequency over the first 5 s of stimulation. Absence of a mark shows that data are missing. The stimuli were arranged along the short axis in order of stimuli: salty, sour, bitter, and sweet. The fibers were arranged along the longer axis in order of increasing responses to: NaCl, citric acid, and QHCl.

Figure 4

Recordings of the temporal intensity or profile of 7 CT fibers before, during, and after stimulation are shown. The impulse activity of each fiber is displayed during 5 s of rinsing with artificial saliva, followed by 10 s of stimulation and then by 5 s of renewed rinsing with the artificial saliva. The vertical traces show the response to each stimulus listed on top of the graph: QHCl, DB, urea, caffeine, saccharin, acesulfame-K, sucrose, NaCl, and citric acid. Some of the features mentioned in Figure 1 are shown. Thus, it is evident that a response to QHCl is poorly correlated with the response to denatonium or a response to acesulfame-K with the response to sucrose.

Figure 5

Results of hierarchical cluster analysis of the response profile of 46 CT fibers. Intercluster similarity was measured with the Pearson correlation coefficient, and the cluster analysis proceeded according to the average linking method. The identity of the fiber is listed on the left side and response category on the basis of its best response to the 4 basic solutions is entered on the right side. The analysis distinguished 2 major clusters consisting of 17 N fibers and 19 H fibers and 2 clusters that could not be categorized according to human taste qualities. N stands for NaCl and H for citric acid.

Figure 6

Average response profiles of from the top the N cluster, the H cluster, the 3rd and 4th clusters. The error bars show the SE. The horizontal line drawn in each plot illustrates 2 SD of the averaged spontaneous activity.

Figure 7

The 2D space, showing location of 22 taste stimuli, was obtained from the MDS analysis. The distribution was calculated with Pearson correlation coefficient between stimuli across 46 CT fibers. The value of stress is 0.057. The plot shows that the stimuli did not group according to human taste qualities. For example, the compounds that to humans share the quality of being sweet do not form one group but are distributed among all the other stimuli; citric and ascorbic acid are located away from the other 2 acids, butyric and propionic acid; QHCl is distant from DB; urea in the vicinity of NaCl and LiCl.