Short-term changes in natripheric and hydrosmotic water fluxes across the skin and in urine production due to increases in the osmolarity of the external environment in the toad

1. Sudden decreases in the osmotic gradient across the skin due to the replacement of water of the bath by 115 mM NaCl had no effect on water uptake of intact or hypophysectomized toads. 2. A concomitant decrease in the urine production was observed in intact but not in hypophysectomized animals. 3. Addition of amiloride chlorydrate (0.25 mM) to the 115 mM NaCl bath induced a significant decrease in water uptake both in intact and in hypophysectomized toads. 4. The osmotic permeability coefficient (LPD) increased significantly during the osmotic gradient reduction with 115 mM NaCl plus 0.25 mM amiloride or 230 mM sucrose in both groups. 5. No changes in the plasmatic osmolarity were detected during the development of these responses to the osmotic gradient reduction. 6. These results are consistent with the hypothesis of short-term changes in the natripheric and hydrosmotic fluxes of water across the skin and in urine production triggered by the osmotic gradient reduction. The possible participation of arginine vasotocin in these responses is discussed.     

Antidiuretic responses to osmotic cutaneous stimulation in the toad,Bufo arenarum

Summary Osmotic stimulation of the skin of the toadBufo arenarum with isotonic (115 mM) or hypertonic (400 mM) NaCl solutions produced a marked and reversible antidiuresis within 5 min. No changes in plasma osmolarity were detected in the course of this response.Hypophysectomized animals exhibited a lower and delayed antidiuresis when exposed to a hypertonic environment (400 mM NaCl). This antidiuretic response was drastically reduced in normal toads after ten consecutive days of administration of the sympatoplexic guanethidine.The existence of a feed-forward control of urine production initiated by cutaneous osmotic sensors and involving an adrenergic component is proposed.     

The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis

El Mofty M. M. and Sadek I. A. 1973. The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis. International Journal for Parasitology3: 425–431. Adrenaline injections induced encystation in the opalinids of normal, hypophysectomized, and gonadectomized toads in the pre-breeding and post-breeding seasons. In normal and gonadectomized male and female toads, adrenaline injections may stimulate the release of ACTH of the anterior pituitary which in turn induces the secretion of androgenic steroids from the interrenal tissue. It is speculated that the breakdown products of these androgenic steroids cause the encystation of the parasites. In hypophysectomized male and female hosts, the injected adrenaline may stimulate the interstitial tissue of the testes and ovaries to secrete androgens, the breakdown products of which induce encystation of the opalinids. Adrenaline or ACTH gave negative results in vitro. Urine of male or female toad injected with adrenaline, ACTH, or testosterone propionate induced encystation in Opalina sudafricana m vitro.     

The effect of salt acclimation of the water uptake and osmotic permeability of the skin of the toad (Bufo viridis, L.)

1. Water uptake in vivo, and water fluxes across the isolated skin were studied in salt (NaCl) acclimated toads. 2. Water uptake of acclimated toads maintained in the solution of acclimation, decreased with the environmental salinity. 3. The osmotic water permeability (Pos) of the skin increased upon salt (NaCl) acclimation, both in vivo and in vitro. 4. Pos of the skin of toads acclimated to non-permeant solutes such as sucrose (230 mmol/l) or mannitol (400 nmol/l), was greatly reduced. 5. Oxytocin (syntocinon) increased the Pos both in tap water and salt acclimated toads. In high salt (greater than 200 mmol/l NaCl) acclimated toads however, the increased Pos and water flux at larger osmotic gradients, could not be stimulated further by the hormone. 6. The adaptive nature of the selective changes in the permeability properties of the skin under salt acclimation conditions is discussed.     

Oxidation-reduction and production of molecular hydrogen by Escherichia coli in the hyperosmotic medium

It was shown that Escherichia coli is able to grow in anaerobic conditions in hyperosmotic media containing 0.5 M sodium chloride or equivalent amount of sucrose. However, in the presence of 0.5 M NaCl, bacterial growth rate and the intensity of oxidation-reduction processes decrease, and the production of molecular hydrogen is absent. Growth rate in the presence of 0.5 M NaCl is four times lower than that in the presence of sucrose. Under hyperosmotic stress by 0.5 M NaCl but not by equivalent amount of sucrose, the uptake of K+ with a high rate is observed. Proline is able to increase the growth rate and the intensity of oxidation-reduction processes and to restore the production of molecular hydrogen as well as to induce the uptake of K+ with a high rate under a hyperosmotic stress. Such effects are observed at pH 7.5 and are absent at pH 5.5. Proline also increases cell size independently of medium pH. It is likely that the effect of proline on oxidation-reduction processes and production of H2 is mediated through the accumulation of K+ in bacteria.     

Effects of dehydration on plasma osmolality, thirst-related behavior, and plasma and brain angiotensin concentrations in Couch's spadefoot toad, Scaphiopus couchii

Under dehydrating conditions, many terrestrial vertebrates species exhibit increases in plasma osmolality and their drinking behavior. Under some circumstances, this behavioral change is accompanied by changes in plasma and central angiotensin concentrations, and it has been proposed that these changes in angiotensin levels induce the thirst-related behaviors. In response to dehydration, the spadefoot toad, Scaphiopus couchii, exhibits thirst-related behavior in the form of cutaneous drinking. This behavior has been termed water absorption response (WR) behavior. Spadefoot toads live in harsh desert environments and are subject annually to dehydrating conditions that may induce thirst-related behavior. We tested the hypothesis that an increase in WR behavior is associated with both an increase in plasma osmolality and an increase in plasma and brain angiotensin concentrations. First, we determined the degree of dehydration that was necessary to initiate WR behavior. Animals dehydrated to 85% of their standard bladder-empty weight via deprivation of water exhibited WR behavior more frequently than control toads left in home containers with water available. Next, using the same dehydration methods, we determined the plasma osmolality and sodium concentrations of dehydrated toads. Toads dehydrated to 85% standard weight also had a significant increase in plasma osmolality, but exhibited no overall change in plasma sodium concentrations, indicating that while an overall increase in plasma osmolality appears to be associated with WR behavior in S. couchii, changes in sodium concentrations alone are not sufficient to induce the behavior. Finally, plasma and brain angiotensin concentrations were measured in control toads and toads dehydrated to 85% standard weight. Plasma and brain angiotensin concentrations did not increase in dehydrated toads, indicating that dehydration-induced WR behavior that is associated with changes in plasma osmolality may not be induced by changes in endogenous angiotensin concentrations in S. couchii.     

The effects of fasting, diabetes, and hypophysectomy on adipose lactic dehydrogenase isozymes.

Lactic dehydrogenase isozyme distributions have been examined in epididymal adipose tissue of fasting, diabetic, and hypophysectomized rats. In each of these conditions the electrophoresis patterns show an enhancement of H subunits relative to M subunits suggestive of an induction of H subunits. Careful assessment of the total lactic dehydrogenase activity of adipose tissue from fasted, diabetic, and hypophysectomized rats reveals, however, that these conditions decrease total lactic dehydrogenase activity to approximately one-half those of normal animals. When this factor and the relative activity of the M and H subunits are taken into consideration it is apparent that the pattern shift from normal in these three states is due to a disproportionate loss of M subunits. An explanation for these shifts is that some degradative process, possibly activation of a protease, is induced by each of these stress conditions which selectively degrades M subunits. An interesting reversal by phosphate of the electrophoresis patterns of fasting, hypophysectomized, and diabetic rats is demonstrated.     

Drinking induced by cellular dehydration in the quail, Coturnix coturnix japonica

1. Drinking was induced in water-replete quail 5-10 min after intravenous injection of hypertonic NaCl (0.69 osmol/l) or sucrose (1.06 osmol/l), but hypertonic urea (2.78 osmol/l) failed to induce drinking. 2. The birds drank approximately the amount required to dilute the injected solutes to isotonicity for each given dose of NaCl or sucrose. 3. The plasma angiotensin II level decreased after injection of 7% NaCl (2.5 osmol/l), but it increased after injection of an equi-osmolar solution of sucrose (65%). 4. Plasma osmolality and Na+ concentration returned quickly to control levels, and then decreased further, after injection of 7% NaCl or 65% sucrose. 5. Blood volume and blood pressure increased immediately after injection of 7% NaCl or 65% sucrose. 6. These results show that drinking is induced after injection of hypertonic solutions exclusively by cellular dehydration, and other regulatory mechanisms for thirst, such as extracellular dehydration and the renin-angiotensin system, are rather inhibitory after injection of hypertonic NaCl.     

The neural activities of the greater superficial petrosal nerve of the rat in response to chemical stimulation of the palate

A comparison of the integrated responses of the rat's greatersuperficial petrosal (GSP) and chorda tympani (CT) nerves toa number of taste stimuli was studied. The GSP nerve of therat was very responsive to the chemical stimulation of the oralcavity. Among the selected stimuli related to the four basictaste qualities, 0.5 M sucrose produced the greatest neuralresponse in the GSP nerve, whereas, 0.1 M NaCl produced thegreatest in the CT nerve. The GSP nerve integrated responseto 0.5 M sucrose solution was approximately three times as greatin magnitude as that to a 0.1 M NaCl solution. The neural responsemagnitude of the GSP and CT nerves were as follows: GSP nerve;0.5 M sucrose >0.02 M Na-saccharin >0.05 M citric acid>0.1 M NaCl > 0.01 M quinine-HCl. CT nerve; 0.1 M NaCl> 0.05 M citric acid > 0.02 M Na-saccharin > 0.01 Mquinine-HCl >0.5 M sucrose. The response magnitudes of theGSP nerve to 0.3 M chloride salt solutions were: LiCl > CaCl₂> NaCl > NH₄Cl > KCl, whereas the response magnitudesof the CT nerve to the above salts were: LiCl > NaCl >NH₄Cl > CaCl₂ > KCl. All 0.5 M solutions of the selectedsugars (sucrose, rhamnose, galactose, lactose, fructose, -methyl-D-glucoside,xylose, mannose, arabinose, maltose, sorbose and glucose) evokedneural responses in both GSP and CT nerves. The order of theresponse magnitudes of the GSP nerve to the selected sugarswas similar to that of the CT nerve but the absolute magnitudesof the GSP nerve were greater.     

Intracranial renin alters gustatory neural responses in the nucleus of the solitary tract of rats

Activation of the renin-angiotensin system in the brain is considered important in the arousal and expression of sodium appetite. To clarify the effects of directly activating this hormonal cascade, taste neurons in the nucleus of the solitary tract of rats were tested with a battery of sapid stimuli after intracerebroventricular injection of renin or its vehicle. The rats were chronically prepared but lightly anesthetized during the recording procedure. Eighty-five taste neurons were tested: 46 after renin injections and 39 after vehicle. Neural activity was counted for 5.0-s periods without stimulation (spontaneous) and during stimulation with water and sapid chemicals. The averaged responses to each of the standard stimuli (0.1 M NaCl, 0.3 M sucrose, 0.01 M citric acid, and 0.01 M quinine hydrochloride) did not differ significantly between the two conditions. When the rats were tested with a concentration range of NaCl, however, after renin the average responses to the hypertonic 0.3 and 1.0 M stimuli were reduced to 74 and 70%, respectively, compared with those after vehicle injections. A similar tendency was evident for the subsample of neurons that responded best to NaCl, but the effect was smaller. These data are consistent with, but not as dramatic as, those reported after dietary-induced sodium appetite.     

Physiology of feeding-preference patterns of female black blowflies (Phormia regina Meigen): Modification in responsiveness to salts subsequent to salt feeding

Behavioural experimentation on Phormia regina shows that females previously fed only sucrose, and thus in a state of yeast preference, will ingest single-salt-sucrose mixtures in volumes similar to that of 10% yeast (Rachman et al., 1982). In particular, females will ingest NaCl 0.1 M in 0.2 M sucrose in volumes not statistically different from 10% yeast. In the experiments reported here, groups of females were given ad libitum access to both 0.2 M sucrose and NaCl 0.1 M in 0.2 M sucrose from days 0–4 after eclosion. Potassium and sodium salts were added to 0.2 M sucrose over a spectrum of concentrations and presented to the flies on day 6. The flies rejected all single-salt-sucrose mixtures offered. Even when the pre-test sodium salt was changed to a potassium salt during days 0–4, the flies still rejected the single-salt-sucrose mixtures offered subsequently. However, when sodium and potassium salts were mixed together in 0.2 M sucrose, females ingested the solutions in amounts similar to 10% yeast. Several different concentrations of the double-salt-sucrose solutions were ingested in volumes not statistically different from 10% yeast. Results support the underlying hypothesis that activity in the salt-sensitive chemosensory neurones is involved in protein preference.     

Peripheral and central interactions between sugar,water, and salt receptors of the blowfly, Phormia regina

The peripheral and central nervous interactions between the sugar, water, and salt receptors of the blowfly were investigated electrophysiologically by simultaneously recording from the labellar chemoreceptors and the extensor muscle of the haustellum. Simultaneous stimulation of two water receptors with 10 mM LiCl resulted in a motor response even though stimulating the same two sensilla separately with 10 mM LiCl did not. There was a linear decrease in the motor response to two sensilla stimulation as the salt concentration in the stimulating solution increased. Although stimulating two sensilla simultaneously with 200 mM NaCl gave no motor response, simultaneously stimulating two sensilla with 10 mM LiCl and a third with 200 mM NaCl gave a greater response than did two sensilla stimulation with 10 mM LiCl alone, indicating cross-channel summation between the water and salt receptors. Similarly, simultaneously stimulating one sensillum with 100 mM sucrose and another with 10 mM LiCl or 500 mM NaCl gave a larger response than did 100 mM sucrose stimulation alone. The cross-channel summation between the sugar and water receptors was not affected by feeding the flies water. A central excitatory state (CES) which previously had been demonstrated behaviourally was investigated. A stimulation of one sensillum with 10 mM LiCl which previously had been ineffective gave a motor response if proceeded by a stimulation with 1 M sucrose on another sensillum. The effect of the time interval between the sugar and water stimuli was tested, but for intervals of 100 msec to 4 sec no definite correlation was found. In addition, CES with respect to the sugar receptor was demonstrated. The motor response to stimulation of a single sensillum with 100 mM sucrose was enhanced by preceding it with 1 M sucrose stimulation of another sensillum. The motor response to stimulation of two water receptors with 10 mM LiCl was partially inhibited by simultaneously stimulating a third sensillum with 4 M NaCl. Inhibition was also seen when a single sensillum was stimulated with a mixture of 10 mM LiCl and 10 mM sucrose and an adjacent sensillum was simultaneously stimulated with 1 M NaCl. Behavioural experiments showing inhibition of CES by salt were confirmed. Interposing a salt stimulus of 4 M NaCl between the 1 M sucrose and 10 mM LiCl stimuli reduced but did not totally eliminate the motor response to 10 mM LiCl. The basis for peripheral control of the relative activities of the water and salt receptors is discussed. A model is proposed to account for all the receptor interactions in the central nervous system.     

Physiology of feeding-preference patterns of female black blowflies (Phormia regina Meigen): Alterations in responsiveness to salts

Electrophysiological recordings of tarsal and labellar contact chemosensilla in Phormia regina females demonstrate activation of sugar-, cation-, and possibly anion-sensitive cells in response to 10% yeast extract. Yeast extract is a proteinaceous food source that supports full egg development. Though some protein is required for egg maturation in Phormia, a blowfly not normally autogenous, purified proteins alone neither activate the chemosensilla nor promote egg development. In experiments reported here, groups of females were given ad lib access to either 0.2 M sucrose or 0.2 M sucrose and 10% yeast for four days after eclosion. The sucrose diet induced a ‘protein’ preference but no egg development. Potassium and sodium salts were added to 0.2 M sucrose and presented to the flies on day six. The volumes of salt-sucrose mixtures taken were greater than those of 0.2 M sucrose for flies raised on 0.2 M sucrose, though yeast was preferred over all but one salt solution. For sucrose-and-yeast-fed flies, volumes of 0.05 and 0.1 M salt mixtures consumed did not differ from 0.2 M sucrose; however, sucrose alone was favoured over more concentrated salt mixtures. All salt-sucrose mixtures tested were significantly more effective stimuli for sucrose-and-yeast-fed flies than yeast. It is suggested that varying sensitivity in the salt-sensitive contact chemosensilla plays a role in reported food preference shifts associated with reproduction.     

Gustatory sensitivities of the hamster's soft palate

The response properties of taste receptors distributed on thesoft palate of the hamster were studied by recording integratedresponses from the greater superficial petrosal (GSP) nerveStimuli were concentration series of sucrose, NaCl, HCl andquinine hydrochloride (QHCl), and several other 0.1 M saltsand 0.5 M sugars. For comparison, integrated responses wererecorded from the chorda tympani (CT) nerve in many of the sameanimals from which recordings were made from the GSP. Responsesin each preparation were scaled relative to the phasic responseto 0.1 M NaCl and were then expressed for each nerve as a proportionof the total response magnitude (TRM)—the sum of all theresponses to the four concentration series. In this way, therelative response of each nerve to all of the stimuli couldbe evaluated. There were significant differences between theGSP and CT nerves in the responses to NaCl, QHCl and sucrose.Both the phasic and tonic responses to sucrose were larger inthe GSP than in the CT, whereas the tonic responses to NaCland QHCl were smaller. The slopes of the concentration-responsefunctions for NaCl, HCl and sucrose were significantly differentbetween the two nerves. The responses to 0.1 M sodium and lithiumsalts were significantly greater in the CT than in the GSP;whereas the 0.5 M sugars elicited responses in the GSP thatwere 2–3 times greater than in the CT nerve. A comparisonof the relative responsiveness to 0.3M sucrose, 0 3 M NaCl,0.01 M QHCl, 0.01 M HCl and distilled water among the GSP, CT,glossopharyngeal (IXth) nerve and superior laryngeal nerve (SLN)indicated that the vast majority of information about sucroseand NaCl is transmitted to the brainstem by the VIIth nerve. ¹Present address: Department of Oral Physiology, Kagoshima UniversityDental School, Kagoshima 890, Japan     

Hydroxyapatite-mediated transfer of DNA on nitrocellulose filters in dot-hybridization experiments

The method of hydroxylapatite-mediated rapid and effective transfer of DNA onto nitrocellulose filters for following dot-hybridization was elaborated. The analysed DNA occurred initially in diluted and large volume solutions (from 1 to 10 ml) with various composition (2 M NaCl; 4 M LiCl--8 M urea; 4 M CsCl; 5 and 20% sucrose) was adsorbed on hydroxylapatite and quantitatively transferred onto nitrocellulose after hydroxylapatite solubilization in a small volume of acid (usually, 200 microliters of 10% TCA). As exemplified by the hybridization of total rat liver DNA with the plasmid ph22 DNA containing a cluster of sea urchin histone genes, the method presented appears to be not only simple and useful for handling multiple probes of diluted DNA solutions with high concentrations of salts, sucrose and urea but also more sensitive than some convenient DNA dot-hybridization methods.     

The peripheral inhibition of the tarsal sugar receptor by sodium chloride in the proboscis extension response of the blowfly,Phormia regina M.

Summary The proboscis extension reponse of the blowfly during stimulation of the tarsal sugar receptors was inhibited by the presence of NaCl. Acceptance thresholds for sucrose in various concentrations of NaCl were measured. The median acceptance thresholds for sucrose in mixtures of 0.01, 0.25, 0.5 and 1.0 M NaCl were 1.8 × 10^–3, 6.0 × 10^–3, 1.2 × 10^–2, and 2.0 × 10^–2 M, respectively. Concentration-response curves for sucrose in the tarsal D-type sugar receptor shifted to the right under the existence of high concentration of NaCl. Number of impulses per D-type sugar receptor at the median acceptance thresholds described above were 7.5, 8.4, 6.8 and 10.4 for the first 0.1 s of stimulation, respectively. The average number was 8.2 impulses per 0.1 s. Comparisons were made between the behavioral acceptance thresholds (1) on one leg exposed to sucrose mixed with 0.01 M NaCl and (2) on two contralateral legs, one of which was exposed to sucrose in 0.01 M NaCl and the other to 0.5 M NaCl alone. The acceptance thresholds from two experiments agreed with each other. The median threshold value was 1.7 × 10^–2 M sucrose. Behavioral inhibition by NaCl in mixtures with sucrose can be explained by its peripheral inhibition of sugar receptors.This research was supported in part by ITO foundation and Scientific Research Fund from the Ministry of Education of Japan.     

Cell kinetics in the epidermis of the toad Bufo bufo bufo (L.) after partial hypophysectomy followed by corticotrophin treatment (an autoradiographic study)

1. Cell kinetic parameters in the epidermis of partially hypophysectomized, ACTH-treated toads whose moulting frequency was increased threefold were studied using labelled thymidine and the autoradiographic technique. 2. The labelling index, length of S-phase and cycle time of stratum germinativum cells changed slowly as a function of the number of ACTH injections, and so did the migration of cells from stratum germinativum to stratum corneum. 3. A cell production in stratum germinativum of normal toads in excess of cell loss, as demonstrated by Levi & Nielsen (1982) should make it possible to maintain a status quo over a limited period of time following ablation of pars distalis and ACTH treatment.     

Electrical properties and gustatory responses of various taste disk cells of frog fungiform papillae

We compared the electrical properties and gustatory response profiles of types Ia cell (mucus cell), Ib cell (wing cell), and II/III cell (receptor cell) in the taste disks of the frog fungiform papillae. The large depolarizing responses of all types of cell induced by 1 M NaCl were accompanied by a large decrease in the membrane resistance and had the same reversal potential of approximately +5 mV. The large depolarizing responses of all cell types for 1 mM acetic acid were accompanied by a small decrease in the membrane resistance. The small depolarizing responses of all cell types for 10 mM quinine-HCl (Q-HCl) were accompanied by an increase in the membrane resistance, but those for 1 M sucrose were accompanied by a decrease in the membrane resistance. The reversal potential of sucrose responses in all cell types were approximately +12 mV. Taken together, depolarizing responses of Ia, Ib, and II/III cells for each taste stimulus are likely to be generated by the same mechanisms. Gustatory depolarizing response profiles indicated that 1) each of Ia, Ib, and II/III cells responded 100% to 1 M NaCl and 1 mM acetic acid with depolarizing responses, 2) approximately 50% of each cell type responded to 10 mM Q-HCl with depolarizations, and 3) each approximately 40% of Ia and Ib cells and approximately 90% of II/III cells responded to 1 M sucrose with depolarizations. These results suggest that the receptor molecules for NaCl, acid, and Q-HCl stimuli are equivalently distributed on all cell types, but the receptor molecules for sugar stimuli are richer on II/III cells than on Ia and Ib cells. Type III cells having afferent synapses may play a main role in gustatory transduction and transmission.     

Taste confusions following chlorhexidine treatment.

Chlorhexidine, a bitter bis-biguanide antiseptic, is the only known blocker of the human salty taste. In order to characterize the effects of chlorhexidine on stimulus identification, taste confusion matrix (TCM) performance was measured for subjects treated with 1.34 mM chlorhexidine gluconate (n = 9) and water controls (n = 9). Ten stimuli [water, 0.1 M NaCl, 0.1 M KCl, 0.1 mM quinine-HCl (QHCl), 0.1 M monosodium glutamate (MSG), 3 mM citric acid, 0.3 M sucrose and mixtures of NaCl, QHCl and citric acid with sucrose] were presented in 10 replicates for identification from a list of 10 stimulus names. T(10), a measure of performance consistency from information theory, was lower for chlorhexidine-treated subjects (2.02 +/- 0.11 bits) than controls (2.73 +/- 0.11 bits) (P < 0.0001). T(2), an indirect measure of pairwise stimulus discrimination, approached chance levels (0.40 bit) in chlorhexidine-treated subjects for all possible pairs of NaCl, KCl, QHCl and water, as well as pairs composed of sucrose and the NaCl-sucrose and quinine-sucrose mixtures. In controls T(2) values approached perfect scores (1.00 bit) for all stimulus pairs except NaCl-KCl and NaCl-MSG. The results demonstrate a decreased ability to identify taste stimuli that is consistent with alterations in the ability of stimuli to elicit salty and bitter taste perceptions. As a selective, effective, persistent and reversible blocker of taste perceptions, chlorhexidine should prove useful in defining taste mechanisms in humans.     

Low-dose furosemide modulates taste responses in the nucleus of the solitary tract of the rat

Taste-evoked neural responses in the nucleus of the solitary tract (NST) are subject to both excitatory and inhibitory modulation by physiological conditions that influence ingestion. Treatments that induce sodium appetite predominantly reduce NST gustatory responsiveness to sapid stimuli. When sodium appetite is aroused with 10 mg of the diuretic furosemide (Furo), however, NST gustatory neurons exhibit an enhanced responsiveness to NaCl. In addition to inducing a sodium appetite, 10 mg Furo supports a conditioned taste aversion (CTA). A lower, 2-mg dose of Furo induces an equivalent sodium appetite, but not a CTA. To determine whether the anomalous electrophysiological results reflected the adverse effects of the 10-mg dose, we replicated the original experiment but instead used 2 mg of Furo. In chronically prepared, lightly anesthetized rats, the responses of 49 single NST neurons to 12 taste stimuli were recorded after subcutaneous injections of either 2 mg Furo or saline. There was no effect of treatment on NST neural responses to the four standard taste stimuli. In the NaCl concentration series, however, 2 mg Furo evoked significantly higher responses to the two highest concentrations of NaCl. There was no effect of treatment in the sucrose concentration series. Thus, unlike other methods that induce a sodium appetite, Furo increases NST neural responsiveness to NaCl. At least as far as the first central relay, sodium appetite apparently does not depend on specific changes in the sensory neural code for taste.