Ilene Bernstein - US grants

The objective of this project is to evaluate the contribution of learned food aversions to the appetite and weight loss induced by tumors and anti-tumor therapy. The proposed studies are based on our recent demonstrations (a) that learned aversions to specific foods can occur in cancer patients receiving GI toxic chemotherapy; and (b) that in animals, tumor growth alone, in the absence of any aversive therapy, can produce aversions to the available diet. Using an experimental animal model we intend to (a) define the conditions under which aversions to foods are acquired as a consequence of tumor growth and/or chemotherapy; (b) evaluate whether learned food aversions contribute to anorexia; and (c) evaluate intervention approaches for minimizing or eliminating these learned food aversions. In the clinic we intend (a) to continue to define the conditions under which learned food aversions are acquired as a consequence of GI toxic chemotherapy as well as to evaluate their impact on the nutritional status of cancer patients; and (b) to evaluate the effectiveness of selected intervention methods in preventing learned food aversions in cancer patients receiving GI toxic chemotherapy.

The objective of these studies is to to identify causes of developmental changes in taste preference in the rat. Using salt (NaCl) preferences as a model system, two factors in early development will be examined which may affect intake and preference. The first is age-related changes in taste sensitivity which may contribute to changes in taste preference. The second is preweaning taste exposure which may influence adult taste sensitivity and/or preference. The proposed studies are based on our reent work indicating that immature rats express elevated preference for hypertonic saline solutions compared to adults, and that one factor likely to contribute to this elevated saline intake is a relative insensitivity of the weanling's taste system to hypertonic saline concentrations. The proposed studies involve developing behavioral paradigms for evaluating threshold and suprathreshold sensitivity to tastants in weanling and adult rats without reliance on preference or hedonic measures. These studies will then be extended to an examination of the contribution of early taste experiences to taste development. The long term objective of this project is to understand the causes of elevated salt preference because high salt intake in humans has been implicated in the development and maintenance of essential hypertension. In examining the normative development of salt sensitivity and preference we will utilize two techniques for assessing taste sensitivity----(i) an operant taste discrimination task; and (ii) a procedure which takes advantage of the high degree of concentration specificity of the "preexposure effect" in taste aversion conditioning. We will also compare the development of salt sensitivity to that of sour and sweet. Taste function of rats exposed to neonatal taste deprivation or selective taste exposure will then be examined to determine whether early experience influences the course of taste development. Reductions in taste stimulation will be accomplished by an artificial rearing procedure which uses chronic intragastric cannulas and allows rat pups to be reared in the total absence of nursing from Postnatal Days 4 through 18.

The long range goal of this project is to identify factors which contribute to variations in salt preference and intake. Salt preference refers to the ingestion of sodium or sodium chloride (NaCl) in the absence of physiological need and is of particular Interest because high salt Intake has been Implicated In the development and maintenance of essential hypertension in humans. Previous work in our laboratory has defined situations in which rats show significant departures from the "species typical norm" of salt preference. Two rat models have been examined where salt preference deviates sharply from this norm. One --the Infant rat- - could be characterized as a salt glutton, since it does not avoid hypertonic NaCl solutions at concentrations as high as 4% and 6%, which would be totally avoided by adult rats. The other --an inbred strain known as the Fischer-344 rat-- displays an unusual distaste for NaCl solutions. Adult Fischer-344 rats fall to prefer even isotonic or hypotonic NaCl solutions to water. These behaviors are at the extremes on a continuum of salt preference. Although a number of factors are likely to be involved, a focus of this proposal is the hypothesis that age and strain differences in amiloride-sensitive sodium transport at the tests bud contribute to the wide variations in NaCl preference displayed by these rats. Behavioral studies of taste preference in short and long term tests will be utilized to characterize the salt aversion displayed by Fischer-344 rats as well as examine its ontogeny. The ingestive behavior displayed by 10-day-old Long Evans rats toward salts will also be examined. Behavioral and electrophysiological approaches will be utilized to assess the hypothesis that strain and age differences in amiloride-sensitive sodium transport mechanisms at the taste bud are involved both in the aversion to salt displayed by Fischer-344 rats and in the emergence of avoidance of hypertonic NaCl solutions during the suckling period Behavioral studies of amiloride sensitivity delivery amiloride and measure licking behavior to NaCl solutions in brief access tests with a lickometer, electrophysiological studies examine multiunit activity of the chorda tympani nerve to NaCl solutions after water or amiloride pretreatment.

The long range goal of this project is to identify factors which contribute to variations in salt (NaCl) intake and preference. Salt preference refers to the ingestion of sodium or NaCl in excess of physiological need and is of particular interest because high salt intake has been implicated in the development and maintenance of essential hypertension in humans. Two models have been identified in which rats show significant departures from the "species typical norm" of salt preference. One, the neonatal rat, freely ingests NaCl solutions as high as 2% and 41% which are avoided by adult rats. In contrast, an inbred strain, the Fischer-344 (F-344) rat, fails to prefer even isotonic or hypotonic NaCl solutions to water. These two models represent opposite extremes on a continuum of salt preference. Electrophysiological, surgical and behavioral approaches will be utilized to define the gustatory mechanisms which underlie these behaviors. A focus of this proposal is the hypothesis that strain and age differences in amiloride-sensitive sodium transport at the taste bud contribute to wide variations in salt preference. Electrophysiological recordings of multiunit activity of the chorda tympani nerve in response to NaCl stimuli, before and after amiloride pretreatment, will be used to assess amiloride-sensitive sodium transport mechanisms. This approach will be combined with a genetic one, cosegregation analysis, to evaluate the role of enhanced amiloride-sensitvity of taste buds in the NaCl aversion of F-344 rats. Transection of the chorda tympani nerve, which has been found to dramatically eliminate the NaCl aversion of F-344 rats, will be employed to assess the contribution of peripheml gustatory signals to NaCl preference and intake. Behavioral studies will include intraoral infusions in neonatal rats; measures of licking behavior to NaCl solutions in brief access tests as well as traditional two-bottle preference testing methods.

The long range goal of this project is to identify factors which contribute to variations in salt (NaCl) intake and preference. Salt preference refers to the ingestion of sodium or NaCl in excess of physiological need and is of particular interest because high salt intake has been implicated in the development and maintenance of essential hypertension in humans. Two models have been identified in which rats show significant departures from the "species typical norm" of salt preference. One, the neonatal rat, freely ingests NaCl solutions as high as 2% and 41% which are avoided by adult rats. In contrast, an inbred strain, the Fischer-344 (F-344) rat, fails to prefer even isotonic or hypotonic NaCl solutions to water. These two models represent opposite extremes on a continuum of salt preference. Electrophysiological, surgical and behavioral approaches will be utilized to define the gustatory mechanisms which underlie these behaviors. A focus of this proposal is the hypothesis that strain and age differences in amiloride-sensitive sodium transport at the taste bud contribute to wide variations in salt preference. Electrophysiological recordings of multiunit activity of the chorda tympani nerve in response to NaCl stimuli, before and after amiloride pretreatment, will be used to assess amiloride-sensitive sodium transport mechanisms. This approach will be combined with a genetic one, cosegregation analysis, to evaluate the role of enhanced amiloride-sensitvity of taste buds in the NaCl aversion of F-344 rats. Transection of the chorda tympani nerve, which has been found to dramatically eliminate the NaCl aversion of F-344 rats, will be employed to assess the contribution of peripheml gustatory signals to NaCl preference and intake. Behavioral studies will include intraoral infusions in neonatal rats; measures of licking behavior to NaCl solutions in brief access tests as well as traditional two-bottle preference testing methods.

DESCRIPTION: The long range goal of this project is to identify factors which contribute to the ingestion of sodium or NaCl in excess of physiological need. The determinants of salt preference are of particular interest because high salt intake has been implicated in the development and maintenance of essential hypertension in humans. In the rat NaCl preference varies as a function of age and genetic characteristics, and these variations are associated with differences in signaling in gustatory pathways, in particular, amiloride-sensitive sodium signals conveyed by the chorda tympani nerve. Neonatal rats, of a variety of strains, prefer and freely ingest solutions containing remarkably high concentrations of NaCl, and their gustatory neural sensitivity to NaCl is relatively low. In contrast, the Fisher 344 (F344) rat fails to prefer NaCl solutions to water and avoids them at concentrations preferred by other strains. F344 rats show an amplified neural response to NaCl stimulation and this elevation appears to be due entirely to greater amiloride sensitivity. When the pathway carrying these signals is transected, the aversion disappears and F344 rats display a clear preference for NaCl. In addition, the recent finding of an anomalous preference for NH4Cl in adult rats which received CTX as neonates is reminiscent of the paradoxical NH4Cl preference of neonates, demonstrating the striking plasticity of the developing gustatory system as well as the involvement of multiple interacting pathways. Thus the studies in this proposal focus on determining the nature of these interactions and their potential for modification using these genetic and developmental variants as model systems. Studies will determine the effect on the microstructure of licking for NaCl of: strain; need state; nerve transection; and treatments which increase and decrease amiloride-sensitive sodium transport in taste buds. Studies of adult rats which received transections as neonates will determine whether their anomalous preference for NH4Cl is associated with an impaired ability to discriminate NH4Cl from NaCl. Additional studies will terminal fields of remaining gustatory nerves. Additional studies will define the relationship between maturation of gustatory pathways and developmental changes in taste preference using an assessment technique, taste reactivity, which can be applied with common methods across a wide range of ages.

DESCRIPTION (provided by applicant): A central issue in behavioral neuroscience is how alterations in neural pathways mediate the durable behavior changes involved in learning. Taste aversion conditioning provides an excellent model for studying the neural changes which underlie learning because conditioning can occur in a single trial, despite lengthy delays between conditioned and unconditioned stimuli. It is also a form of learning which occurs in humans as a result of illness or treatment for illness, with deleterious effects on appetite. The proposed studies are based on identification of cell groups and neural circuitry activated during taste aversion learning. Neural activation will be assessed by immunostaining for the protein product of the immediate early gene, c-fos. Proposed studies will address both taste aversion acquisition and expression. In addressing taste aversion expression, studies will determine whether cells in the nucleus of the solitary tract which are activated during expression project to the pontine parabrachial nucleus and/or the paraventricular nucleus of the hypothalamus as part of a circuit involved in the generation of visceral conditioned reactions to the aversive taste. Studies will also determine whether activation of these cells, as well as behavioral expression of the taste aversion, require input from discrete regions of amygdala and parabrachial nucleus. Studies addressing taste aversion acquisition will use knockout mouse models with specific deletions of protein kinase A (PKA) genes. Preliminary studies using mice with a specific deletion of a PKA gene, R11B have demonstrated that these mice are unable to acquire a conditioned taste aversion and show a specific defect in the induction of cFos protein in basolateral amygdala in response to LiCl. Proposed studies will determine whether the activation of c-fos expression by cells within the basolateral amygdala, in response to the unconditioned stimulus, LiCl, is required for acquisition and whether the observed defect in taste aversion learning in null mutant mice is limited to the long-term, but not the short-term, version of their taste aversion memory. Additional mouse strains with other selective deficits in PKA genes will be assessed for their learning and the induction of cFos protein in basolateral amygdala. By defining the neural pathways and cell types involved in conditioned taste aversion learning this project will provide the groundwork for eventually characterizing the plastic changes within and between cells which underlie this robust form of gustatory learning.

DESCRIPTION (provided by applicant): Salt intake and preference are of particular interest because high salt intake has been implicated in the etiology of hypertension. Salt appetite is a behavioral response to a sodium deficit and is expressed as avid consumption of hypertonic NACl solutions. Salt appetite is subject to sensitization, namely episodes of sodium depletion lead to increased salt appetite following subsequent depletions. Additionally, episodes of acute sodium depletion, in rats, cause an alteration in neuronal morphology with increased dendritic branches and spines in neurons in the nucleus accumbens. Strikingly, these neuronal alterations are remarkably similar to those observed in association with the sensitization to certain addictive drugs. The proposed studies will examine the relationship between sensitization of sodium appetite by prior sodium depletions and altered dendritic morphology in the nucleus accumbens and will assess the relationship of these changes to those associated with drug sensitization. Behavioral and physiological manipulations will involve administration of the natriuretic/diuretic agent, furosemide to produce sodium depletion and promote a sodium appetite. Morphology of neurons in the nucleus accumbens will be analyzed in Golgi stained material and include assessment of total dendritic length, branch length and number as well as spine number and density. The long range goal is to examine the hypothesis that neuronal alterations common to salt and drug sensitization represent a general neuronal response to a strong physiological challenge that provides a mechanism for an enhanced behavioral response to subsequent exposures to that challenge.