Biomedical subjects

S J St John

Publications and source records attributed to S J St John.

17 recordsLinked to original sources

PubMed2006

C57BL/6J and DBA/2J mice vary in lick rate and ingestive microstructure.

Fluid licking in mice is an example of a rhythmic behavior thought to be under the control of a central pattern generator. Inbred strains of mice have been shown to differ in mean or modal interlick interval (ILI) duration, suggesting a genetic-based variation. We investigated water licking in the commonly used inbred strains C57BL/6J (B6) and DBA/2J (D2), using a commercially available contact lickometer. Results from 20-min test sessions indicated that D2 mice lick at a faster rate than B6 mice (10.6 licks/s vs. 8.5 licks/s), based on analysis of the distribution of short-duration ILIs (50-160 ms). This strain difference was independent of sex, extent of water deprivation or total number of licks. D2 mice also displayed a faster lick rate when the strains were tested with a series of brief (5 s) trials. However, when ingestion over the entire 20-min session was analyzed, it was evident that D2 mice had an overall slower rate of ingestion than B6 mice. This was because of the tendency for D2 mice to have more very long pauses (>30 s) between sequences of licking bursts. Overall, it appeared that D2 mice licked more efficiently, ingesting more rapidly during excursions to the spout that were fewer and farther between.

Animals↗

PubMed2000

Neural representation of salts in the rat solitary nucleus: brain stem correlates of taste discrimination.

One mechanism of salt taste transduction by gustatory receptor cells involves the influx of cations through epithelial sodium channels that can be blocked by oral application of amiloride. A second mechanism is less clearly defined but seems to depend on electroneutral diffusion of the salt through the tight junctions between receptor cells; this paracellular pathway is insensitive to amiloride. Because the first mechanism is more sensitive to sodium salts and the second to nonsodium salts, these peripheral events could underlie the ability of rats to discriminate sodium from nonsodium salts on the basis of taste. Behavioral experiments indicate that amiloride, at concentrations that are tasteless to rats, impairs a rat's ability to discriminate NaCl from KCl and may do so by making both salts taste like KCl. In the present study, we examined the neural representation of NaCl and KCl (0.05-0.2 M), and mixtures of these salts with amiloride (0, 3, and 30 microM), to explore the neural correlates of this behavioral result. NaCl and KCl were represented by distinct patterns of activity in the nucleus of the solitary tract. Amiloride, in a concentration-dependent manner, changed the pattern for NaCl to one more characteristic of KCl, primarily by reducing activity in neurons responding best to NaCl and sucrose. The effect of amiloride concentration on the response to 0.1 M NaCl in NaCl-best neurons was virtually identical to its effect on behavioral discrimination performance. Modeling the effects of blocking the amiloride-insensitive pathway also resulted in highly similar patterns of activity for NaCl and KCl. These results suggest that activity in both the amiloride-sensitive and -insensitive pathways is required for the behavioral discrimination between NaCl and KCl. In the context of published behavioral data, the present results suggest that amiloride-sensitive activity alone is not sufficient to impart a unique signal for the taste of sodium salts.

Action Potentials↗

PubMed1999

Cellular expression of alpha-gustducin and the A blood group antigen in rat fungiform taste buds cross-reinnervated by the IXth nerve.

Although taste buds are trophically dependent on their innervation, cross-reinnervation experiments have shown that their gustatory sensitivities are determined by the local epithelium. Both the gustatory G-protein, alpha-gustducin, and the cell-surface carbohydrate, the A blood group antigen, are expressed by significantly fewer fungiform than vallate taste cells in the rat. In these experiments, one side of the anterior portion of the tongue was cross-reinnervated by the IXth nerve in order to determine whether the molecular expression of taste bud cells is determined by the epithelium from which they arise or by the nerve on which they are trophically dependent. The proximal portion of the IXth nerve was anastomosed to the distal portion of the chorda tympani (CT) nerve using fibrin glue (IX-CT rats). Control animals had the CT cut and reanastomosed using the same technique (CT-CT rats), or had the CT avulsed from the bulla and resected to prevent regeneration (CTX rats). The animals survived for 12 weeks postoperatively, and the tongues were removed, stained with methylene blue, and the fungiform taste pores counted on both sides. Tissue from the anterior 5 mm of the tongue was cut into 50-microm sections, which were incubated with antibodies against alpha-gustducin and the human blood group A antigen. In both CT-CT and IX-CT rats, there was regeneration of fungiform taste buds, although in both groups there were significantly fewer taste buds on the operated side of the tongue. The normal vallate papilla had a mean of 8.37 alpha-gustducin-expressing cells and 5.22 A-expressing cells per taste bud, whereas the fungiform papillae contained 3.06 and 0.23 cells per taste bud, respectively. In both CT-CT and IX-CT rats there was a normal number of cells expressing alpha-gustducin or the A antigen in regenerated taste buds; in the CTX animals there was a significant decrease in the expression of these markers. These results demonstrate that the molecular phenotype of taste bud cells is determined by the local epithelium from which they arise and not by properties of the innervating nerve.

ABO Blood-Group System↗

PubMed1999

Neural coding of gustatory information.

The nervous system encodes information relating chemical stimuli to taste perception, beginning with transduction mechanisms at the receptor and ending in the representation of stimulus attributes by the activity of neurons in the brain. Recent studies have rekindled the long-standing debate about whether taste information is coded by the pattern of activity across afferent neurons or by specifically tuned 'labeled lines'. Taste neurons are broadly tuned to stimuli representing different qualities and are also responsive to stimulus intensity and often to touch and temperature. Their responsiveness is also modulated by a number of physiological factors. In addition to representing stimulus quality and intensity, activity in taste neurons must code information about the hedonic value of gustatory stimuli. These considerations suggest that individual gustatory neurons contribute to the coding of more than one stimulus parameter, making the response of any one cell meaningful only in the context of the activity of its neighbors.

Acids↗

PubMed1999

Neural representation of the taste of NaCl and KCl in gustatory neurons of the hamster solitary nucleus.

NaCl and KCl are monovalent salts that can be discriminated behaviorally by hamsters on the basis of their tastes. We examined the effects of the passive Na+ channel blocker amiloride on responses to both of these salts in 34 taste-responsive neurons of the nucleus of the solitary tract (NST) in the hamster. The effects of amiloride were assessed with two different, commonly employed stimulus protocols. Additionally, concentration-response functions for each salt were measured in 37 neurons. Cells were characterized by their best response to (in M) 0. 03 NaCl, 0.1 sucrose, 0.003 HCl, 0.001 quinine hydrochloride, and 0. 1 KCl. In neurons classified as NaCl-best, amiloride reversibly blocked responses to both NaCl and KCl. In neurons classified as HCl-best, amiloride had no effect on either stimulus. In sucrose-best neurons, amiloride blocked the response to NaCl but not KCl. These results support the hypothesis that both salts are transduced by at least two different receptor mechanisms. In the NST, information arising from these different inputs is maintained in discrete populations of neurons. In addition to differences in amiloride sensitivity, the cell types also differed in their responses to the salts across concentration. At midrange salt concentrations, NaCl-best neurons were far more responsive to NaCl than KCl, whereas HCl- and sucrose-best neurons responded equivalently to the two salts at all concentrations. Because NaCl- and HCl-best cells cannot by themselves distinguish NaCl from KCl, it is the relative activity across these cell types that comprises the code for taste discrimination.

Action Potentials↗

PubMed1998

Behavioral discrimination between quinine and KCl is dependent on input from the seventh cranial nerve: implications for the functional roles of the gustatory nerves in rats.

The rat glossopharyngeal nerve (GL), which innervates posterior tongue taste buds, contains several physiologically defined taste fiber types; at least one type is primarily responsive to certain alkaloids (such as quinine), and another is primarily responsive to acids and salts. In contrast, the chorda tympani (CT), which innervates anterior tongue taste buds, does not appear to contain fibers that differentially respond to quinine relative to salts and acids. It was therefore predicted that GL transection should disrupt behavioral discriminations between quinine and either acids or salts. Water-restricted rats were trained to press one of two levers if a sampled taste stimulus was quinine (0.1-1.0 mM) and the second lever if the sampled stimulus was KCl (0.1-1.0 M). Sham surgery, GL transection, and sublingual and submaxillary salivary gland extirpation were found to have no effect relative to presurgical performance. Both CT transection and combined GL and CT transection caused a substantial and approximately equal decrement in discrimination performance. Removal of the gustatory branches of the seventh cranial nerve [CT and greater superficial petrosal (GSP)] nearly eliminated the discrimination of the taste stimuli, and combined transection of the CT, GL, and GSP unequivocally reduced performance to chance levels. Although these findings were not presaged by the known electrophysiology, they nonetheless compare favorably with other studies reporting little effect of GL transection on behavioral responses to quinine. These results, in the context of other discrimination studies reported in the literature, suggest that, in rats, the neural coding of taste quality depends primarily on the input of the facial nerve.

Alkaloids↗

PubMed1998

Amiloride does not alter NaCl avoidance in Fischer-344 rats.

Fischer-344 (F-344) rats differ from other common rat strains in that they fail to show any preference for NaCl at any concentration in two-bottle preference tests. Because 100 microM amiloride partially blocks the NaCl-evoked chorda tympani (CT) response in electrophysiological studies, we tested NaCl preference (0.068-0.273 M) in F-344 rats with and without 100 microM amiloride solution as the solvent. A third group was tested with unadulterated NaCl solutions following CT transection. Amiloride had no significant effect on the NaCl preference-aversion function, whereas CT transection significantly reduced NaCl avoidance. These results suggest that the amiloride-sensitive component of the NaCl response is not necessary for F-344 rats to display avoidance of NaCl, but the entire CT input is.

Amiloride↗

PubMed1998

Role of taste in the microstructure of quinine ingestion by rats.

The microstructure of the licking behavior of water-deprived rats presented with either water or quinine during 45-min single-bottle tests was analyzed. The chorda tympani (CT) and glossopharyngeal (GL) nerves, which innervate the taste buds of the tongue, were transected in deeply anesthetized rats to discern their contribution to the behavioral pattern of quinine drinking. Rats were presurgically habituated to the testing protocol and postsurgically tested first with water and then novel 0.2 mM quinine-HCl in a subsequent session. The substantial decrease in intake observed in sham-operated controls (n = 16) when quinine was the stimulus was entirely a function of a decrease in lick volume and burst size (a run of licks with interlick intervals <1 s). Contrary to the intake-suppressing effects of quinine, pause duration decreased and burst number increased. Combined transection of the CT and GL (n = 6) strikingly opposed all of these quinine-induced behavioral changes, whereas CT transection (n = 7) was without effect and GL transection (n = 8) had an intermediate influence. These results suggest that taste acts more on neural circuits governing burst termination as opposed to burst initiation, which, in turn, appears to be more sensitive to signals related to physiological state. These findings are discussed in terms of other known nerve transection effects on quinine responsiveness, and the implications of the microstructural results are considered with respect to probabilistic as opposed to deterministic control of licking behavior.

Animals↗

PubMed1997

Chorda tympani nerve transection disrupts taste aversion learning to potassium chloride, but not sodium chloride.

In Experiment 1, rats with chorda tympani nerve transection (CTX) acquired a LiCl-conditioned taste aversion to 0.1 M NaCl at the same rate as controls. After 3 conditioning trials, the aversion generalized to 0.03 and 0.3 M NaCl, but did not generalize to KCI (0.03, 0.1, and 0.3 M), in either the sham or CTX group. In Experiment 2, the sham group, but not the CTX group, formed an aversion to 0.1 M KCI after 1 trial. The CTX rats did form a moderate aversion after 2 conditioning trials. Following the 3rd trial, the CTX group did not suppress licking to 0.03 or 0.3 M KCI or any concentration of NaCl in relation to controls. Although there is strong evidence that CTX affects NaCl taste perception, these findings indicate that, under certain conditions, rats can nonetheless distinguish NaCl from KCI after such neurotomy. Moreover, CTX appears to have a substantial effect on the perceived intensity of KCl.

Animals↗

PubMed1997

Sucrose vs. maltose taste discrimination by rats depends on the input of the seventh cranial nerve.

Although rats treat the taste of sucrose and maltose as perceptually similar, they nonetheless appear to be able to distinguish between the two sugars, as suggested from prior work examining the cross-generalization of conditioned taste aversions. This study explictly tested whether rats could behaviorally discriminate sucrose from maltose and examined the relative importance of the gustatory input of the seventh and ninth cranial nerves in maintaining such performance. Water-restricted rats were presurgically trained in a conditioned avoidance task to suppress licking to sucrose or maltose and to maintain licking to the other sugar. Concentration (0.05, 0.1, 0.2, and 0.4 M) was varied to make intensity an irrelevant cue. Stimuli were randomly presented in 5-s trials during 50-min sessions. Bilateral transection of the chorda tympani nerve (CT) or the glossopharyngeal nerve or sham surgery did not disrupt discrimination performance. In contrast, combined transection of the CT and greater superficial petrosal nerve, which collectively removes the taste input of the seventh cranial nerve, caused severe impairments in sugar discriminability. In these rats, performance was more disturbed at the lower concentrations. These findings confirm that rats can discriminate sucrose from maltose and that this capability relies heavily on the taste input of the seventh cranial nerve. Although the input of the ninth cranial nerve is unnecessary, it may help sustain partial competence in this task, especially at high concentrations, in the combined absence of the CT and greater superficial petrosal nerve.

Animals↗

PubMed1997

Chorda tympani transection and selective desalivation differentially disrupt two-lever salt discrimination performance in rats.

Water-restricted rats were trained to press 1 of 2 levers if a sampled stimulus was NaCl and the other lever if the stimulus was KCl (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 submaxillary 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.

Animals↗

PubMed1996

Amiloride disrupts NaCl versus KCl discrimination performance: implications for salt taste coding in rats.

Amiloride, an epithelial sodium channel blocker, suppresses the responsiveness of narrowly tuned sodium-responsive taste afferents when orally applied in the rat. Broadly tuned salt-responsive taste afferents, which respond to sodium and nonsodium salts and acids, are relatively unaffected by the drug. We used amiloride treatment to examine the consequences of the specific removal of input from narrowly tuned sodium-responsive afferents on taste discrimination. Five water-restricted rats were trained in a gustometer to press one lever after licking NaCl and another lever after licking KCl across a range of concentrations (0.05, 0.1, and 0.2 M). Correct responses were rewarded with brief water access, and incorrect responses were punished with a time-out. After training, animals averaged about 90% correct responses and maintained competent performance during subsequent control sessions. Amiloride was then placed in all solutions at a given concentration (1-100 microM) for single test sessions. Control sessions were interposed between amiloride sessions. At high amiloride concentrations, overall responding was reduced to 50% correct and progressively improved as the drug concentration was lowered. The sigmoidal dose-response functions corresponded quantitatively with electrophysiological findings. Performance deficits occurred primarily with NaCl and were concentration dependent; performance during KCl trials was relatively undisturbed by amiloride adulteration. At high amiloride concentrations, rats treated NaCl as if it were KCl. Given that amiloride is tasteless to the rat, these results provide convincing evidence of the importance of narrowly tuned afferents in the discrimination between sodium and nonsodium salts and suggest that this is a general coding principle in the gustatory system.

Amiloride↗

PubMed1996

Combined glossopharyngeal and chorda tympani nerve transection elevates quinine detection thresholds in rats (Rattus norvegicus).

Using a conditioned shock avoidance procedure, behavioral quinine hydrochloride thresholds were measured before and after glossopharyngeal (GLX), chorda tympani (CTX), or combined glossopharyngeal and chorda tympani (GLX + CTX) transection, as well as after sham surgery. In Experiment 1, thresholds in the sham, CTX, and GLX rats (Rattus norvegicus) either improved (lowered) or remained the same after surgery. In Experiment 2, GLX + CTX caused a pronounced 1.5 log10 unit increase in presurgically measured thresholds. Neither the glossopharyngeal nor the chorda tympani nerve is necessary for normal sensitivity to low quinine concentrations provided the other is intact. When both of these nerve are transected, however, the remaining afferent input is not sufficient to maintain normal detection performance.

Animals↗

PubMed1995

Salt discriminability is related to number of regenerated taste buds after chorda tympani nerve section in rats.

Transection of the chorda tympani nerve (CTX) impairs taste-guided discrimination of NaCl from KCl in rats. We wanted to determine whether this discrimination recovers after chorda tympani regeneration. Experiment 1 showed that few taste buds regenerated 14 days after CTX, whereas substantial regeneration occurred 42 days after surgery. Experiment 2 demonstrated that rats trained before CTX could clearly discriminate the two salts when tested starting 49 days after surgery, whereas rats tested starting 8 days after surgery were severely impaired in this task. Rats tested starting 28 days after CTX were unimpaired, moderately impaired, or severely impaired on the discrimination task. Overall, discrimination performance was significantly related to the number of regenerated taste buds. Unilaterally transected rats tested shortly after surgery were nearly as competent as controls. These results indicate that rats can recover the ability to discriminate NaCl from KCl after regeneration of anterior tongue taste buds.

Animals↗

PubMed1995

Glossopharyngeal nerve transection does not compromise the specificity of taste-guided sodium appetite in rats.

The chorda tympani nerve (CT) has been shown to be critical in the sodium-specific drinking behavior of sodium-depleted rats, but the role of other gustatory nerves and the contribution of the major salivary glands remain to be elucidated. In this study, rats received either bilateral section of the CT (CTX) or the glossopharyngeal nerve (GLX), extirpation of the sublingual and submaxillary salivary glands (DSAL), or sham surgery. After recovery, rats were sodium depleted with furosemide and tested for their licking responses to 0.05 and 0.3 M NaCl, KCl, CaCl2, and NH4Cl, as well as distilled water in an automated gustometer. Rats that received GLX maintained a specific sodium appetite comparable to controls despite denervation of approximately 64% of the taste buds. In contrast, compared with control rats, CTX and DSAL rats had altered response profiles, showing much smaller differences in licking to NaCl relative to the other stimuli. This was accompanied by a substantially lower lick rate in DSAL rats, raising the possibility that general licking impairments contributed to the decreased NaCl responsiveness in these rats. These findings imply that the CT, but not the glossopharyngeal nerve, is necessary for the maintenance of normal sodium-specific, taste-guided behavior under sodium deplete conditions.

Animals↗

PubMed1994

Combined, but not single, gustatory nerve transection substantially alters taste-guided licking behavior to quinine in rats.

On the basis of electrophysiological studies, the glossopharyngeal nerve (GL) is far more responsive to quinine than the chorda tympani (CT) or greater superficial petrosal (GSP) nerves. The licking behavior of water-deprived rats to quinine (0.03-3.0 mM) and distilled water (10-s trails) was tested before and after various nerve transections. GL+CT section caused a substantial reduction in responsiveness. GSP+CT section had a moderate effect, and GL section alone produced only marginal impairments. Control, partially desalivated, and CT-sectioned rats were unaffected. Thus, the GL is not necessary for normal unconditioned taste-guided appetitive responsiveness to quinine, but the collective input from the GSP and CT is necessary and most likely sufficient. These data suggest that the quinine-evoked input of the GL and CT converge centrally.

Animals↗

PubMedDate not supplied

Glossopharyngeal nerve transection reduces quinine avoidance in rats not given presurgical stimulus exposure.

Behavioral studies on the effects of bilateral glossopharyngeal nerve (GL) transection on quinine responsiveness have yielded mixed results. These differences may be explained by the presence or absence of presurgical exposure with the tastant. In the present experiment we measured unconditioned licking to quinine in rats that had no exposure to quinine before surgery. Rats were water deprived and trained to lick water during 10 s trials in an automated gustometer. Next, they were divided into groups that received either GL transection or sham surgery (CON). Following recovery, the water-deprived rats were presented with seven concentrations of quinine hydrochloride (0.003-3 mM) and distilled water. The number of licks to each tastant was averaged over three days of testing. Rats with GL transection licked significantly more to the higher concentrations of quinine relative to CON rats, resulting in a 0.44 log10 unit shift in the quinine concentration-response curve. These results when considered with prior work suggest that experience before nerve transection may have a small protective effect on taste-guided behavioral responsiveness to quinine in rats.

Animals↗