Blockade of ethanol induced conditioned taste aversion by 3-amino-1,2,4-triazole: evidence for catalase mediated synthesis of acetaldehyde in rat brain

This investigation seeks to present evidence for the oxidation of ethanol in the brain via the peroxidatic activity of catalase and simultaneously provide evidence for the role of central acetaldehyde (ACH) in the mediation of an ethanol-induced conditioned taste aversion (CTA). Ethanol is capable of inducing a conditioned taste aversion. Pretreatment with the catalase inhibitor, 3-amino-1,2,4-triazole (AT), shows an attenuation of this ethanol-induced CTA. Animals receiving ethanol injections showed a CTA to a novel solution paired with a drug administration, while ethanol injected animals pretreated with AT did not show a CTA to ethanol administration. This effect of AT appears to be specific to the effects of ethanol as CTA's to morphine and lithium chloride were not affected by AT pretreatment. Peripheral levels of ethanol were the same in all animals regardless of pretreatment indicating that AT had no effect on peripheral levels of ethanol. These data increase support for the notion that acetaldehyde is produced directly in the brain and that it may be the agent mediating some of the psychopharmacological properties of ethanol.     

Convergent analysis of cDNA and short oligomer microarrays, mouse null mutants and bioinformatics resources to study complex traits

Gene expression data sets have recently been exploited to study genetic factors that modulate complex traits. However, it has been challenging to establish a direct link between variation in patterns of gene expression and variation in higher order traits such as neuropharmacological responses and patterns of behavior. Here we illustrate an approach that combines gene expression data with new bioinformatics resources to discover genes that potentially modulate behavior. We have exploited three complementary genetic models to obtain convergent evidence that differential expression of a subset of genes and molecular pathways influences ethanol-induced conditioned taste aversion (CTA). As a first step, cDNA microarrays were used to compare gene expression profiles of two null mutant mouse lines with difference in ethanol-induced aversion. Mice lacking a functional copy of G protein-gated potassium channel subunit 2 (Girk2) show a decrease in the aversive effects of ethanol, whereas preproenkephalin (Penk) null mutant mice show the opposite response. We hypothesize that these behavioral differences are generated in part by alterations in expression downstream of the null alleles. We then exploited the WebQTL databases to examine the genetic covariance between mRNA expression levels and measurements of ethanol-induced CTA in BXD recombinant inbred (RI) strains. Finally, we identified a subset of genes and functional groups associated with ethanol-induced CTA in both null mutant lines and BXD RI strains. Collectively, these approaches highlight the phosphatidylinositol signaling pathway and identify several genes including protein kinase C beta isoform and preproenkephalin in regulation of ethanol- induced conditioned taste aversion. Our results point to the increasing potential of the convergent approach and biological databases to investigate genetic mechanisms of complex traits.     

Perception of sweet taste is important for voluntary alcohol consumption in mice

To directly evaluate the association between taste perception and alcohol intake, we used three different mutant mice, each lacking a gene expressed in taste buds and critical to taste transduction: α-gustducin ( Gnat3 ), Tas1r3 or Trpm5 . Null mutant mice lacking any of these three genes showed lower preference score for alcohol and consumed less alcohol in a two-bottle choice test, as compared with wild-type littermates. These null mice also showed lower preference score for saccharin solutions than did wild-type littermates. In contrast, avoidance of quinine solutions was less in Gnat3 or Trpm5 knockout mice than in wild-type mice, whereas Tas1r3 null mice were not different from wild type in their response to quinine solutions. There were no differences in null vs. wild-type mice in their consumption of sodium chloride solutions. To determine the cause for reduction of ethanol intake, we studied other ethanol-induced behaviors known to be related to alcohol consumption. There were no differences between null and wild-type mice in ethanol-induced loss of righting reflex, severity of acute ethanol withdrawal or conditioned place preference for ethanol. Weaker conditioned taste aversion (CTA) to alcohol in null mice may have been caused by weaker rewarding value of the conditioned stimulus (saccharin). When saccharin was replaced by sodium chloride, no differences in CTA to alcohol between knockout and wild-type mice were seen. Thus, deletion of any one of three different genes involved in detection of sweet taste leads to a substantial reduction of alcohol intake without any changes in pharmacological actions of ethanol.     

Genetic differences in ethanol-induced hyperglycemia and conditioned taste aversion.

Genetic differences in the hyperglycemic response to acute ethanol exposure and ethanol-induced conditioned taste aversion were examined using inbred mice. Adult male C57BL/6J and DBA/2J mice were injected with ethanol (0-6 g/kg, I.P.) and blood glucose levels determined over 4 h. C57 mice demonstrated greater dose-dependent elevations in blood glucose compared to DBA mice. In a conditioned taste aversion procedure, water deprived mice received ethanol injections (1-4 g/kg, I.P.) immediately after access to a NaCl flavored solution. DBA mice developed aversion to the ethanol-paired flavor at a lower dose (2 g/kg) than C57 mice. These results provide further support for a possible inverse genetic relationship between sensitivity to ethanol-induced hyperglycemia and sensitivity to conditioned taste aversion.     

Lesions of the Lateral Habenula Increase Voluntary Ethanol Consumption and Operant Self-Administration,Block Yohimbine-Induced Reinstatement of Ethanol Seeking,and Attenuate Ethanol-Induced Conditioned Taste Aversion

The lateral habenula (LHb) plays an important role in learning driven by negative outcomes. Many drugs of abuse, including ethanol, have dose-dependent aversive effects that act to limit intake of the drug. However, the role of the LHb in regulating ethanol intake is unknown. In the present study, we compared voluntary ethanol consumption and self-administration, yohimbine-induced reinstatement of ethanol seeking, and ethanol-induced conditioned taste aversion in rats with sham or LHb lesions. In rats given home cage access to 20% ethanol in an intermittent access two bottle choice paradigm, lesioned animals escalated their voluntary ethanol consumption more rapidly than sham-lesioned control animals and maintained higher stable rates of voluntary ethanol intake. Similarly, lesioned animals exhibited higher rates of responding for ethanol in operant self-administration sessions. In addition, LHb lesion blocked yohimbine-induced reinstatement of ethanol seeking after extinction. Finally, LHb lesion significantly attenuated an ethanol-induced conditioned taste aversion. Our results demonstrate an important role for the LHb in multiple facets of ethanol-directed behavior, and further suggest that the LHb may contribute to ethanol-directed behaviors by mediating learning driven by the aversive effects of the drug.     

Ontogenetic characteristics of the acquisition and extinction of a taste aversion in dogs following damage to the dorsal area of the hippocampus

In 2-9 months dogs the influence was studied of ablation of the hippocampus dorsal area on formation and preservation of conditioned taste aversion (CTA), elaborated by combination of 30% sucrose solution with i.p. injection of 0.28 M LiCl solution. Lesion of the hippocampus dorsal area does not prevent acquisition after the first pairing of conditioned taste aversion in puppies and adult dogs. Heterogeneous influences are observed after hippocampus lesions on the process of CTA extinction in animals of different ages. Acquaintance with conditioned stimulus before CTA acquisition accelerates the process of its extinction in hippocampectomized indiviuals, but less than in animals with an intact hippocampus.     

Is glycine "sweet" to mice? Mouse strain differences in perception of glycine taste

Glycine is an amino acid tasting sweet to humans. In 2-bottle tests, C57BL/6ByJ (B6) mice strongly prefer glycine solutions, whereas 129P3/J (129) mice do not, suggesting that they differ in perception of glycine taste. We examined this question using the conditioned taste aversion (CTA) generalization technique. CTA was achieved by injecting LiCl after drinking glycine, and next its generalization to 10 taste solutions (glycine, sucrose, saccharin, D-tryptophan, L-tryptophan, L-alanine, L-proline, L-glutamine, NaCl, and HCl) was examined by video recording licking behavior. Both B6 and 129 mice generalized the aversion to sucrose, saccharin, L-alanine, and L-proline and did not generalize it to NaCl, HCl, and L-tryptophan. This indicates that both B6 and 129 mice perceive the sweetness (i.e., a sucrose-like taste) of glycine. Thus, the lack of a glycine preference by 129 mice cannot be explained by their inability to perceive its sweetness. Strain differences were observed for CTA generalization to 2 amino acids: 129 mice generalized aversion to L-glutamine but not D-tryptophan, whereas B6 mice generalized it to D-tryptophan but not L-glutamine. 129.B6-Tas1r3 congenic mice with 2 genotypes of the Tas1r3 locus (B6/129 heterozygotes and 129/129 homozygotes) did not differ in aversion generalization, suggesting that the differences between 129 and B6 strains are not attributed to the Tas1r3 allelic variants and that other, yet unknown, genes are involved in taste perception of amino acids.     

Ethanol-induced activation and rapid development of tolerance may have some underlying genes in common

Ethanol exerts biphasic effects on behavior, stimulant at low doses and depressant at higher doses. In the present study we used two mouse genetic models to investigate the relationships among activating and depressant responses to alcohol. The first model was a panel of nine isogenic genotypes. FAST and SLOW mice, selectively bred for high and low ethanol-induced motor activation, respectively, were used as a second model. We used loss of righting reflex to assess initial sensitivity and acute functional tolerance to a hypnotic dose of ethanol (3 g/kg, 20% v/v). Blood ethanol concentration at the onset of loss of righting reflex was used as an estimate of initial sensitivity, while the difference between concentration values at the recovery and loss of righting represented an acute functional tolerance score. Mean initial sensitivity and acute functional tolerance values of the nine strains were correlated with a previously obtained measure of ethanol-induced locomotor activation. Activation correlated significantly with both initial sensitivity ( r _g = 0.80; P < 0.05) and acute functional tolerance ( r _g = 0.77; P < 0.05). Thus, inbred genotypes that were activated more by a low dose of ethanol were also more sensitive to and developed more acute tolerance to a high dose. FAST mice had initial sensitivity values similar to those of SLOW mice, but developed more pronounced tolerance, indicating that ethanol-induced activation and acute functional tolerance may be regulated by some common genetic mechanisms. In summary, these results supported a genetic association between ethanol-induced activation and rapid development of tolerance.     

Molecular signaling during taste aversion learning

Behavioral and neural assessment tools have been used to identify cellular and molecular events that occur during taste aversion acquisition. Studies described here include an assessment of taste information processing and taste-illness association using fos-like immunoreactivity (FLI) to mark populations of cells that react strongly to the taste conditioned stimulus (CS), the illness unconditioned stimulus (US), or the pairing of CS and US. Exposure to a novel, but not a familiar, CS taste (saccharin) was found to induce robust increases in FLI in some, but not all, brain regions previously implicated in taste processing or taste aversion learning. Striking effects of taste novelty on FLI were found in central amygdala (CNA) and insular cortex (IC) but not in basolateral amygdala (BLA), pontine parabrachial nucleus (PBN), or nucleus of the solitary tract (NTS). Of those regions responding to taste novelty, only CNA showed significant elevations in FLI in response to the US, LiCl. In additional studies, FLI was examined after an effective training experience, novel CS-US pairing, and compared with an ineffective one, familiar CS-US pairing. After CS-US pairing, taste novelty modulated FLI in virtually all the regions previously implicated in conditioned taste aversion (CTA) learning, including PBN, CNA, BLA, IC, as well as NTS. Thus, a distributed and interdependent neural CTA circuit is mapped using this method, and the use of localized lesion and inactivation studies promises to further define the functional role of structures within this circuit.     

Parabrachial unit activities after the acquisition of conditioned taste aversion to a non-preferred HCl solution in rats

Abstract In a behavioral experiment, rats reliably acquired a taste aversion to non-preferred 0.01 M HCl that had been previously paired with intraperitoneal injection of 0.15 M LiCl. These rats showed aversions to other acidic solutions such as malic acid and tartaric acid. In a neurophysiological experiment, the neuronal activities of the parabrachial nucleus (PBN) were recorded after the acquisition of conditioned taste aversion (CTA) to 0.01 M HCl in urethane-anesthetized rats. Neuronal responses to the conditioned stimulus (CS) did not change on the whole but decreased in the dorsal region to the brachium conjunctivum. The proportion of HCl-best to NaCl-best units was lower in the CTA group than in controls. The spontaneous firing rate was lower in the CTA group than in controls. Correlation coefficients between the HCl CS and normally preferred tastes (sucrose and NaCl) were more negative and those between HCl and quinine were more positive in the CTA group than in the controls. These results may be explained by the notion that gustatory responses of PBN neurons are concerned with alterations in taste hedonics after the acquisition of conditioned taste aversions.     

Neuropeptide FF (NPFF) reduces the expression of morphine- but not of ethanol-induced conditioned place preference in rats

Neuropeptide FF (NPFF) has been described as an anti-opioid peptide. It plays a role in opioid antinociception, dependence and tolerance. Previous study has indicated that 1DMe ([D-Tyr(1), (NMe)Phe(3)]NPFF), a stable analog of NPFF, inhibits acquisition of the rewarding effect of morphine but not of ethanol in mice. The rewarding effects of these drugs were measured in the unbiased paradigm of conditioned place preference (CPP). The present study examines the influence of NPFF on the expression of morphine- and ethanol-induced CPP in the biased procedure in rats. Our experiments showed that NPFF, given intracerebroventricularly (i.c.v.) at the doses of 5, 10 and 20 nmol, inhibited the expression of morphine-induced CPP. NPFF gave itself, neither induced place preference nor aversion, although a tendency to aversive effect was seen at the highest dose of 20 nmol. NPFF did not indicate fear behavior in the elevated plus maze test, and did not disturb locomotor activity of rats. However, NPFF was unable to inhibit the expression of ethanol-induced CPP. Probably this effect is due to the fact that ethanol reward is a more complex process and apart from the role of opioids, there are other neurotransmitters also involved in this mechanism. These results suggest that NPFF is involved in the expression of morphine reward. Moreover, our study supports an anti-opioid character of this peptide.     

Conditioned taste aversion by lithium and saline: a methodological evaluation

Conditioned taste aversion (CTA) to saccharin induced by orallithium chloride and normal saline were investigated in 270Wistar rats in a CTA paradigm. They were trained to drink for20-min sessions per day in a two-bottle choice, providing saccharinand water simultaneously. Saccharinn neophobia was replacedby a preference with two more exposures. Saccharin was withheldfor 2 days following force-feeding of lithium or saline in orderto assess lithium-illness. Lithium-fed rats showed signs ofillness followed by a strong CTA to saccharin persisting for3–4 days. Saline-fed rats did not suffer from any illnessbut showed a weak and inconsistent CTA lasting for a day ortwo. Scopolamine injections prior to force-feeding did not affectthe pattern of aversion in either group, but significantly suppressedthe revocation of CTA in the saline-fed rats by a second oraldose of saline.     

Monosodium glutamate and sweet taste: discrimination between the tastes of sweet stimuli and glutamate in rats

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.     

Enhanced extinction of aversive memories by high-frequency stimulation of the rat infralimbic cortex

Electrical stimulation of the rodent medial prefrontal cortex (mPFC), including the infralimbic cortex (IL), immediately prior to or during fear extinction training facilitates extinction memory. Here we examined the effects of high-frequency stimulation (HFS) of the rat IL either prior to conditioning or following retrieval of the conditioned memory, on extinction of Pavlovian fear and conditioned taste aversion (CTA). IL-HFS applied immediately after fear memory retrieval, but not three hours after retrieval or prior to conditioning, subsequently reduced freezing during fear extinction. Similarly, IL-HFS given immediately, but not three hours after, retrieval of a CTA memory reduced aversion during extinction. These data indicate that HFS of the IL may be an effective method for reducing both learned fear and learned aversion.     

Genotype modulates age‐related alterations in sensitivity to the aversive effects of ethanol: an eight inbred strain analysis of conditioned taste aversion

Adolescent individuals display altered behavioral sensitivity to ethanol, which may contribute to the increased ethanol consumption seen in this age‐group. However, genetics also exert considerable influence on both ethanol intake and sensitivity. Currently there is little research assessing the combined influence of developmental and genetic alcohol sensitivities. Sensitivity to the aversive effects of ethanol using a conditioned taste aversion (CTA) procedure was measured during both adolescence (P30) and adulthood (P75) in eight inbred mouse strains (C57BL/6J, DBA/2J, 129S1/SvImJ, A/J, BALB/cByJ, BTBR T⁺tf/J, C3H/HeJ and FVB/NJ). Adolescent and adult mice were water deprived, and subsequently provided with access to 0.9% (v/v) NaCl solution for 1 h. Immediately following access mice were administered ethanol (0, 1.5, 2.25 and 3 g/kg, ip). This procedure was repeated in 72 h intervals for a total of five CTA trials. Sensitivity to the aversive effects of ethanol was highly dependent upon both strain and age. Within an inbred strain, adolescent animals were consistently less sensitive to the aversive effects of ethanol than their adult counterparts. However, the dose of ethanol required to produce an aversion response differed as a function of both age and strain.     

Ethanol-induced hypothermia. Cross tolerance with morphine

The development of tolerance to ethanol-induced hypothermia and hypnosis, and cross-tolerance with morphine was studied in mice and rats. Ethanol significantly decreased the body temperature in rats (3.0 and 3.2 g/kg) and in mice (3.5 and 4.0 g/kg). Chronic administration of ethanol resulted in the tolerance not only to ethanol hypothermia but also to hypothermic effects of morphine in examined animals. Implantation of morphine pellets caused the development of cross tolerance to ethanol-induced hypothermia in rats but not in mice. The hypnotic effect of ethanol was significantly shorter in chronic alcoholized rats but not in morphine-implanted rats. Neither chronic ethanol administration nor implantation of morphine pellets changed the duration of ethanol-induced hypnosis in mice. These results seem to support the hypothesis on the opiate-like mechanism of ethanol action.     

Behavioral discrimination between glutamate and the four basic taste substances in mice

1. Behavioural studies using the conditioned taste aversion (CTA) paradigm in mice showed that aversion conditioned to monosodium L-glutamate (MSG), which elicits a unique taste in humans, did not strongly generalize to any of the four basic taste stimuli, suggesting that mice could behaviourally discriminate between MSG and the four basic taste stimuli. 2. Denervation of bilateral glossopharyngeal nerve significantly increased behavioural similarities (the strength of generalization in the CTA paradigm) between MSG and sodium salts. This was not the case after destruction of the bilateral chorda tympani nerve. 3. These results suggest that taste information of glossopharyngeal nerve plays a more important role in the behavioural discrimination between MSG and the four basic tastes than does that of the chorda tympani nerve.     

咸味觉厌恶模型大鼠鼓索神经对味觉刺激的电生理反应特性

目的:探索大鼠咸味觉厌恶建立后外周鼓索神经(CT)对咸味觉及其他味觉刺激的电生理反应特性的改变。方法:将14只SD成年雄性大鼠分为咸味觉厌恶模型组(CTA)和对照组(n=7/group)。实验第1日给予大鼠30min的0.1mol/LNaCl饮食,随后CTA组和对照组大鼠分别腹腔注射2ml0.15mol/LLiCl和同等量生理盐水。在第2、3和4日,测量两组大鼠每天30min内对NaCl和蒸馏水饮用量。于第4日行为学测试后,分别记录CTA组大鼠和对照组大鼠CT对口内给予系列浓度NaCl溶液、0.3mol/LNaCl与0.1mmol/L阿米洛利(一种舌上皮钠通道阻断剂)混合液和其他四种基本味觉刺激溶液的电生理反应。结果:与对照组相比,CTA组大鼠CT对系列浓度NaCl和其他4种基本味觉刺激的电生理反应特性没有发生明显变化(P>0.05);舌上皮钠通道阻断剂阿米洛利强烈抑制CTA大鼠对NaCl的反应(P<0.01)。结论:条件性咸味觉厌恶模型大鼠CT对各种味觉刺激的电生理反应特性没有发生明显改变。     

Formation of taste aversions in the rat

The presence of correlation between the initial attitude of animals to a certain taste agent and the intensity of conditioned taste aversion (CTA) after LiCl poisoning was studied in nonlineal male white rats. 4 types of behavioural reactions were revealed: 1) the nonspecific inhibitory reaction to the situation in which CTA was elaborated; 2) specific associative-adaptive connection of CTA with the taste agent used (0,1% saccharine solution); 3) complex reaction consisting of the two first ones; 4) the same drinking behaviour as that before CTA elaboration. Moreover, a correlation was found between the initial attitude of animals to certain taste agent and the intensity of CTA after pairing of this agent with subsequent poisoning.     

An analysis of 5'-inosine and 5'-guanosine monophosphate taste in rats

Inosine monophosphate (IMP) and guanosine monophosphate (GMP) elicit an umami taste in humans and synergistically increase the intensity of the umami taste of monosodium glutamate (MSG). Conditioned taste aversion (CTA) studies in rodents indicate that these nucleotides and MSG elicit quite similar tastes, but recent physiological evidence suggests that these nucleotides and MSG may not activate the same population of taste receptors and therefore may not elicit identical taste qualities. This study reports the findings of several behavioral experiments with rats that compared the taste properties of IMP and GMP with each other and with those of MSG. Well-trained rats were able to detect both nucleotides at nanomolar concentrations, but they did not respond to either nucleotide in two-bottle preference tests or brief-access CTA tests at concentrations less than 0.5 mM. Discrimination experiments found that the tastes of these nucleotides could not be discriminated from each other, but both could be discriminated from MSG, even when the taste of Na(+) was controlled. Overall, these experiments indicate the taste properties of the two 5'-ribonucleotides are quite similar to each other, and even though they may elicit an umami sensation, these sensations are not identical to the taste of MSG.