Behavioral Neuroscience Copyright 1997 by the American Psychological Association, Inc. 1997, Vol. 111, No. 2,450-459 0735-7044/97/$3.00 Chorda Tympani Transection and Selective Desalivation Differentially Disrupt Two-Lever Salt Discrimination Performance in Rats Steven J. St. John, Stacy Markison, Nick A. Guagliardo, Timothy D. Hackenberg, and Alan C. Spector University of Florida Water-restricted rats were trained to press 1 of 2 levers if a sampled stimulus was NaC1 and the other lever if the stimulus was KCI (0.05, 0.1, or 0.2 M). Responses were reinforced with water. After training, the average rate of correct responses was 90%. Performance was unchanged following sham surgery. Chorda tympani (CT) transection reduced average discrimination performance to 67.7% correct, and extirpation of the sublingual and submaxil- lary salivary glands reduced average performance to 80% correct. Although selective desalivation moderately reduced discriminability, a disrupted salivary environment does not explain the effects of CT transection. More likely, the discrimination deficit in CT-transected rats reflects a loss of critical taste input conveyed by the CT about salts. A variety of behavioral evidence indicates that the chorda tympani nerve (CT) is important in coding salt taste in the rat (Breslin, Spector, & Grill, 1993, 1995; Markison, St. John, & Spector, 1995; O'Keefe, Schumm, & Smith, 1994; Slotnick, Sheelar, & Rentmeister-Bryant, 1991; Sollars & Bernstein, 1992, 1994; Sollars, Sollars, & Bernstein, 1991; Spector & Grill, 1992, 1994; Spector, Schwartz, & Grill, 1990; St. John, Markison, & Spector, 1995; Yamamoto, Shimura, Sako, Yasoshima, & Sakai, 1994). For example, CT transection elevates the detection threshold for NaC1 as much as 2 orders of magnitude (Slotnick et al., 1991; Spector et al., 1990); disrupts the specificity of depletion- induced sodium appetite (Breslin et al., 1993, 1995; Marki- son et al., 1995); can impair the expression of a presurgically conditioned taste aversion to NaC1 (Yamamoto et al., 1994); and in Fischer 344 rats reverses the uncharacteristic aversion to low concentrations of NaC1 to a preference (Sollars et al., 1991; Sollars & Bernstein, 1994). In contrast, NaC1 sensibil- ity appears to be unaffected by glossopharyngeal nerve transection (Cauthon, Garcea, & Spector, 1994; Markison et al. 1995; Sollars & Bernstein, 1994; Spector & Grill, 1992; Yamamoto et al., 1994), which denervates approximately 4 times as many taste buds as does CT transection (see Miller, 1977). Spector and Grill (1992) demonstrated that CT transection Steven J. St. John, Stacy Markison, Nick A. Guagliardo, Timothy D. Hackenberg, and Alan C. Spector, Department of Psychology, University of Florida. This research was supported, in part, by Public Health Service grants (R01-DC-01628 and R29-MH-50244), a National Science Foundation Graduate Fellowship, and a Research Career Develop- ment Award from the National Institute on Deafness and Other Communication Disorders (K04-DC-00104). Portions of this work were presented in 1996 at the 18th Annual Meeting of the Association for Chemoreception Sciences, Sarasota, Florida (St. John, Markison, Guagliardo, Hackenberg, & Spector, 1996). Correspondence concerning this article should be addressed to Alan C. Spector, Department of Psychology, University of Florida, Gainesville, Florida 32611-2250. Electronic mail may be sent to spector@psych.ufl.edu. substantially impaired performance on a presurgically learned NaCl-versus-KC1 discrimination task (see also St. John et al., 1995). Moreover, transection of the glossopharyngeal nerve did not affect discrimination performance, and CT transection did not disrupt a sucrose-versus-quinine taste discrimination. One interpretation of these results is that the CT is critical in the perception of the quality or intensity of one or both salts. Because the CT also innervates the sublingual and submaxillary salivary glands, however, the possibility could not be ruled out that the effects on taste discrimination were caused by a disruption in the salivary environment rather than by the denervation of anterior tongue taste buds. Sublingual and submaxillary salivary gland extirpation has been shown to affect rats' performance in behavioral taste tests involving salts (Brosvic & Hoey, 1990; Catala- notto & Sweeney, 1973; Cauthon, Garcea, & Spector, 1994; Markison et al., 1995; Thrasher & Fregly, 1980). For example, Brosvic and Hoey (1990) found that extirpation of the sublingual and submaxillary salivary glands reduced preference for 0.15 M NaCI and increased preference for 0.15 M KC1, relative to controls. Performance of the same rats, however, was unaffected in a conditional discrimination task in which they were trained to respond differentially to 0.068 M NaCI and other taste stimuli (including 0.068 M KC1). In the present study, we examined the possible effects of selective desalivation on NaC1 and KC1 discrimination across the same concentration range (0.05-0.2 M) used in previous studies of CT transection (Spector & Grill, 1992; St. John et al., 1995). In those salt-discrimination studies, rats were trained to lick in the presence of one salt during a 5-s trial and suppress licking in the presence of the other. Discriminability was evidenced by a high number of licks to one salt and a low number of licks to the other. However, extirpation of the sublingual and submaxillary salivary glands has been shown to disturb licking under some circumstances (Spector, Red- man, & Garcea, 1996; St. John, Garcea, & Spector, 1994; Wong & Kraintz, 1977). These nonspecific effects could potentially confound any sensory effects of removing the 450