Calcium-deprived rats sham-drink CaCl2 and NaCl

Behavioral and Neural Responses to Vitamin C Solution in Vitamin C-deficient Osteogenic Disorder Shionogi/Shi Jcl-od/od Rats

To investigate the appetite for vitamin C (VC), we conducted behavioral and neural experiments using osteogenic disorder Shionogi/Shi Jcl-od/od (od/od) rats, which lack the ability to synthesize VC, and their wild-type controls osteogenic disorder Shionogi/Shi Jcl- +/+ (+/+) rats. In the behavioral study, rats were deprived of VC for 25 days and then received two-bottle preference tests with a choice between water and 10 mM VC. The preference for 10 mM VC solution of od/od rats was significantly greater than that of +/+ rats. In the neural study, the relative magnitudes of the whole chorda tympani nerve (CTN) responses to 100-1000 mM VC, 3-10 mM HCl, 100-1000 mM NaCl, and 20 mM quinine▪HCl in the VC-deficient rats were significantly smaller than those in the nondeficient ones. Further, we conducted additional behavioral experiments to investigate the appetite for sour and salty taste solutions of VC-deficient od/od rats. Preference scores for 3 mM citric acid increased in od/od rats after VC removal, compared with before, whereas preference scores for 100 and 150 mM NaCl were decreased in VC-deficient od/od rats. The preference for 300 mM NaCl was not changed. Hence, our results suggest that the reduction of the aversive taste of VC during VC deficiency may have involved the reduction of CTN responses to acids. Overall, our results indicate that VC-deficient rats ingest sufficient VC to relieve their deficiency and that VC deficiency causes changes in peripheral sensitivity to acids, but nongustatory factors may also affect VC intake and choice.

Parabrachial lesions in rats disrupt sodium appetite induced by furosemide but not by calcium deprivation

An appetite for CaCl2 and NaCl occurs in young rats after they are fed a diet lacking Ca or Na, respectively. Bilateral lesions of the parabrachial nuclei (PBN) disrupt normal taste aversion learning and essentially eliminate the expression of sodium appetite. Here we tested whether similar lesions of the PBN would disrupt the calcium-deprivation-induced appetite for CaCl2 or NaCl. Controls and rats with PBN lesions failed to exhibit a calcium-deprivation-induced appetite for CaCl2. Nevertheless, both groups did exhibit a significant calcium-deprivation-induced appetite for 0.5M NaCl. Thus, while damage to the second central gustatory relay in the PBN disrupts the appetite for 0.5M NaCl induced by furosemide, deoxycorticosterone acetate, and polyethylene glycol, the sodium appetite induced by dietary CaCl2 depletion remains intact.

Influence of cross-fostering on preference for calcium chloride in C57BL/6J and PWK/PhJ mice

We investigated whether maternal influences during the suckling period alter the avidity for calcium, using as models mice from the calcium-preferring PWK/PhJ strain and the calcium-avoiding C57BL/6J strain. We found that milk collected from PWK/PhJ dams had higher calcium concentrations than did milk collected from C57BL/6J dams. Despite this, cross-strain fostering had no effect on adult calcium preferences relative to mice of the same strain that were within-strain fostered or not fostered. Our results indicate that calcium avoidance by C57BL/6J mice and acceptance by PWK/PhJ mice are unaffected by maternal environment during the suckling period.

T1R3: a human calcium taste receptor

Many animals can detect the taste of calcium but it is unclear how or whether humans have this ability. We show here that calcium activates hTAS1R3-transfected HEK293 cells and that this response is attenuated by lactisole, an inhibitor of hT1R3. Moreover, trained volunteers report that lactisole reduces the calcium intensity of calcium lactate. Thus, humans can detect calcium by taste, T1R3 is a receptor responsible for this, and lactisole can reduce the taste perception of calcium by acting on T1R3.

Chorda tympani nerve modulates the rat's avoidance of calcium chloride

Calcium intake depends on orosensory factors, implying the presence of a mechanism for calcium detection in the mouth. To better understand how information about oral calcium is conveyed to the brain, we examined the effects of chorda tympani nerve transection on calcium chloride (CaCl(2)) taste preferences and thresholds in male Wistar rats. The rats were given bilateral transections of the chorda tympani nerve (CTX) or control surgery. After recovery, they received 48-h two-bottle tests with an ascending concentration series of CaCl(2). Whereas control rats avoided CaCl(2) at concentrations of 0.1mM and higher, rats with CTX were indifferent to CaCl(2) concentrations up to 10mM. Rats with CTX had significantly higher preference scores for 0.316 and 3.16 mM CaCl(2) than did control rats. The results imply that the chorda tympani nerve is required for the normal avoidance of CaCl(2) solution.

Comparison of differences between PWD/PhJ and C57BL/6J mice in calcium solution preferences and chorda tympani nerve responses

We used the C57BL/6J (B6) and PWD/PhJ (PWD) mouse strains to investigate the controls of calcium intake. Relative to the B6 strain, the PWD strain had higher preferences in two-bottle choice tests for CaCl(2), calcium lactate (CaLa), MgCl(2), citric acid and quinine hydrochloride, but not for sucrose, KCl or NaCl. We also measured taste-evoked chorda tympani (CT) nerve activity in response to oral application of these compounds. Electrophysiological results paralleled the preference test results, with larger responses in PWD than in B6 mice for those compounds that were more highly preferred for the former strain. The strain differences were especially large for tonic, rather than phasic, chorda tympani activity. These data establish the PWD strain as a "calcium-preferring" strain and suggest that differences between B6 and PWD mice in taste transduction or a related peripheral event contributes to the differences between the strains in preferences for calcium solutions.

Vegetable bitterness is related to calcium content

In the U.S. and Europe, most people do not consume the recommended amounts of either calcium or vegetables. We investigated whether there might be a connection; specifically, whether the taste of calcium in vegetables contributes to their bitterness and thus acceptability. We found a strong correlation between the calcium content of 24 vegetables, based on USDA Nutrient Database values, and bitterness, based on the average ratings of 35 people (r = 0.93). Correlations between the content of other nutrients and bitterness were lower and most were not statistically significant. To assess whether it is feasible that humans can detect calcium in vegetables we tested two animal models known to display a calcium appetite. Previous work indicates that calcium solutions are preferentially ingested by PWK/PhJ mice relative to C57BL/6J mice, and by rats deprived of dietary calcium relative to replete controls. In choice tests between collard greens, a high-calcium vegetable, and cabbage, a low-calcium vegetable, the calcium-favoring animals had higher preferences for collard greens than did controls. These observations raise the possibility that the taste of calcium contributes to the bitterness and thus acceptability of vegetables.

Involvement of T1R3 in calcium-magnesium taste

Calcium and magnesium are essential for survival but it is unknown how animals detect and consume enough of these minerals to meet their needs. To investigate this, we exploited the PWK/PhJ (PWK) strain of mice, which, in contrast to the C57BL/6J (B6) and other inbred strains, displays strong preferences for calcium solutions. We found that the PWK strain also has strong preferences for MgCl2 and saccharin solutions but not representative salty, sour, bitter, or umami taste compounds. A genome scan of B6 x PWK F2 mice linked a component of the strain difference in calcium and magnesium preference to distal chromosome 4. The taste receptor gene, Tas1r3, was implicated by studies with 129.B6ByJ-Tas1r3 congenic and Tas1r3 knockout mice. Most notably, calcium and magnesium solutions that were avoided by wild-type B6 mice were preferred (relative to water) by B6 mice null for the Tas1r3 gene. Oral calcium elicited less electrophysiological activity in the chorda tympani nerve of Tas1r3 knockout than wild-type mice. Comparison of the sequence of Tas1r3 with calcium and saccharin preferences in inbred mouse strains found 1) an inverse correlation between calcium and saccharin preference scores across primarily domesticus strains, which was associated with an I60T substitution in T1R3, and 2) a V689A substitution in T1R3 that was unique to the PWK strain and thus may be responsible for its strong calcium and magnesium preference. Our results imply that, in addition to its established roles in the detection of sweet and umami compounds, T1R3 functions as a gustatory calcium-magnesium receptor.

Calcium taste preferences: genetic analysis and genome screen of C57BL/6J x PWK/PhJ hybrid mice

To characterize the genetic basis of voluntary calcium consumption, we tested C57BL/6J mice (B6; with low avidity for calcium), PWK/PhJ mice (PWK; with high avidity for calcium) and their F(1) and F(2) hybrids. All mice received a series of 96-h two-bottle preference tests with a choice between water and the following: 50 mm CaCl(2), 50 mm calcium lactate, 50 mm MgCl(2), 100 mm KCl, 100 mm NH(4)Cl, 100 mm NaCl, 5 mm citric acid, 30 microm quinine hydrochloride and 2 mm saccharin. Most frequency distributions of the parental and F(1) but not F(2) groups were normally distributed, and there were few sex differences. Reciprocal cross analysis showed that B6 x PWK F(1) mice had a non-specific elevation of fluid intake relative to PWK x B6 F(1) mice. In the F(2) mice, trait correlations were clustered among the divalent salts and the monovalent chlorides. A genome screen involving 116 markers showed 30 quantitative trait loci (QTLs), of which six involved consumption of calcium chloride or lactate. The results show pleiotropic controls of calcium and magnesium consumption that are distinct from those controlling consumption of monovalent chlorides or exemplars of the primary taste qualities.

Forty mouse strain survey of voluntary calcium intake, blood calcium, and bone mineral content

We measured voluntary calcium intake, blood calcium, and bone mineral content of male and female mice from 40 inbred strains. Calcium intakes were assessed using 48-h two-bottle tests with a choice between water and one of the following: water, 7.5, 25, and 75 mM CaCl(2), then 7.5, 25, and 75 mM calcium lactate (CaLa). Intakes were affected by strain, sex, anion, and concentration. In 11 strains females consumed more calcium than did males and in the remaining 29 strains there were no sex differences. Nine strains drank more CaLa than CaCl(2) whereas only one strain (JF1/Ms) drank more CaCl(2) than CaLa. Some strains had consistently high calcium intakes and preferred all calcium solutions relative to water (e.g., PWK/PhJ, BTBR T(+)tf/J, JF1/Ms). Others had consistently low calcium intakes and avoided all calcium solutions relative to water (e.g., KK/H1J, C57BL/10J, CE/J, C58/J). After behavioral tests, blood was sampled and assayed for pH, ionized calcium concentration, and plasma total calcium concentration. Bone mineral density and content were assessed by DEXA. There were no significant correlations between any of these physiological measures and calcium intake. However, strains of mice that had the highest calcium intakes generally fell at the extremes of the physiological distributions. We conclude that the avidity for calcium is determined by different genetic architecture and thus different physiological mechanisms in different strains.

Calcium: taste, intake, and appetite

This review summarizes research on sensory and behavioral aspects of calcium homeostasis. These are fragmented fields, with essentially independent lines of research involving gustatory electrophysiology in amphibians, ethological studies in wild birds, nutritional studies in poultry, and experimental behavioral studies focused primarily on characterizing the specificity of the appetite in rats. Recently, investigators have begun to examine potential physiological mechanisms underlying calcium intake and appetite. These include changes in the taste perception of calcium, signals related to blood calcium concentrations, and actions of the primary hormones of calcium homeostasis: parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D. Other influences on calcium intake include reproductive and adrenal hormones and learning. The possibility that a calcium appetite exists in humans is discussed. The broad range of observations documenting the existence of a behavioral limb of calcium homeostasis provides a strong foundation for future genetic and physiological analyses of this behavior.

Calcium deprivation alters gustatory-evoked activity in the rat nucleus of the solitary tract

Calcium-deprived rats develop a compensatory appetite for substances that contain calcium. To investigate the role of gustatory factors in calcium appetite, we recorded the extracellular activity of single neurons in the nucleus of the solitary tract of calcium-deprived and replete rats. The activity evoked by a broad array of taste stimuli was examined in 51 neurons from replete rats and 47 neurons from calcium-deprived rats. There were no differences between the groups in the responses of all neurons combined. However, neurons with sugar-oriented response profiles gave significantly larger responses to 3, 10, and 100 mM CaCl(2) in the calcium-deprived group than did corresponding cells in the replete group. This difference in taste-evoked responding may underlie an increase in the palatability of CaCl(2) and, in turn, contribute to the expression of calcium appetite.