Trace amines differentially regulate adult locomotor activity, cocaine sensitivity, and female fertility in Drosophila melanogaster

The trace biogenic amines tyramine and octopamine are found in the nervous systems of animals ranging in complexity from nematodes to mammals. In insects such as Drosophila melanogaster, the trace amine octopamine is a well-established neuromodulator that mediates a diverse range of physiological processes, but an independent role for tyramine is less clear. Tyramine is synthesized from tyrosine by the enzyme tyrosine decarboxylase (TDC). We previously reported the identification of two Tdc genes in Drosophila: the peripherally-expressed Tdc1 and the neurally-expressed Tdc2. To further clarify the neural functions of the trace amines in Drosophila, we examined normal and cocaine-induced locomotor activity in flies that lack both neural tyramine and octopamine because of mutation in Tdc2 (Tdc2(RO54)). Tdc2(RO54) flies have dramatically reduced basal locomotor activity levels and are hypersensitive to an initial dose of cocaine. Tdc2-targeted expression of the constitutively active inward rectifying potassium channel Kir2.1 replicates these phenotypes, and Tdc2-driven expression of Tdc1 rescues the phenotypes. However, flies that contain no measurable neural octopamine and an excess of tyramine due to a null mutation in the tyramine beta-hydroxylase gene (TbetaH(nM18)) exhibit normal locomotor activity and cocaine responses in spite of showing female sterility due to loss of octopamine. The ability of elevated levels of neural tyramine in TbetaH(nM18) flies to supplant the role of octopamine in adult locomotor and cocaine-induced behaviors, but not in functions related to female fertility, indicates mechanistic differences in the roles of trace amines in these processes.     

Tyramine and octopamine have opposite effects on the locomotion of Drosophila larvae

Biogenic amines are believed to play important roles in producing behaviors. Although some biogenic amines have been extensively studied in both vertebrates and invertebrates, little is known about the effects of trace amines like tyramine and octopamine. We investigated how trace amines affect behaviors using quantitative morphometric methods on Drosophila Tbetah(nM18) and iav(N) mutants that have altered levels of tyramine and octopamine. Locomotion of wild-type and mutant third instar larvae was analyzed using Dynamic Image Analysis System (DIAS) software. We found that Tbetah(nM18) mutants, with elevated tyramine levels and reduced octopamine levels, had a severe locomotion phenotype. Mutant larvae spent much more time in pausing episodes than wild-type larvae and displayed a reduction in speed and linear translocation. The locomotion phenotype was partially rescued by feeding Tbetah(nM18) larvae octopamine, an effect that could be nullified with simultaneous feeding of tyramine. Feeding Tbetah(nM18) larvae yohimbine, an agent that inhibits the activity of Drosophila tyramine receptors, also improved some locomotion parameters. Feeding both octopamine and yohimbine further improved rescue efficiency. Simultaneously reducing the octopamine and tyramine levels as in iav(N) larvae, in contrast, led to a less severe behavioral phenotype than that of Tbetah(nM18) mutants. Feeding iav(N) larvae either tyramine or octopamine exerted only a minor improvement in locomotion. These results suggest that tyramine and octopamine have opposite effects on Drosophila larval locomotion regulation and that a balance between the two is important in producing normal behavior.     

Tyramine Functions independently of octopamine in the Caenorhabditis elegans nervous system

Octopamine biosynthesis requires tyrosine decarboxylase to convert tyrosine into tyramine and tyramine beta-hydroxylase to convert tyramine into octopamine. We identified and characterized a Caenorhabditis elegans tyrosine decarboxylase gene, tdc-1, and a tyramine beta-hydroxylase gene, tbh-1. The TBH-1 protein is expressed in a subset of TDC-1-expressing cells, indicating that C. elegans has tyraminergic cells that are distinct from its octopaminergic cells. tdc-1 mutants have behavioral defects not shared by tbh-1 mutants. We show that tyramine plays a specific role in the inhibition of egg laying, the modulation of reversal behavior, and the suppression of head oscillations in response to anterior touch. We propose a model for the neural circuit that coordinates locomotion and head oscillations in response to anterior touch. Our findings establish tyramine as a neurotransmitter in C. elegans, and we suggest that tyramine is a genuine neurotransmitter in other invertebrates and possibly in vertebrates as well.     

The trace amine tyramine is essential for sensitization to cocaine in Drosophila.

BACKGROUND: Sensitization to psychostimulant drugs of abuse is thought to be an important aspect of human addiction, yet how it develops is still unclear. The development of sensitization to cocaine in the fruit fly Drosophila melanogaster is strikingly similar to that observed in vertebrates. By taking advantage of the powerful genetic approaches that are possible in Drosophila, we are able to identify and characterize mutants that fail to develop sensitization. RESULTS: We found that the Drosophila mutant inactive (iav) failed to become sensitized to cocaine. Mutant flies had reduced amounts of the trace amine tyramine in the brain because of reduced activity of the enzyme tyrosine decarboxylase (TDC), which converts tyrosine to tyramine. Furthermore, cocaine exposure induced TDC enzyme activity in a time-dependent manner that paralleled the development of behavioral sensitization. The sensitization failure of iav flies could be rescued by feeding the flies with tyramine; other biogenic amines or amine precursors did not have the same effect. CONCLUSIONS: These results indicate an essential role for tyramine in cocaine sensitization in Drosophila.     

Characterization of rice tryptophan decarboxylases and their direct involvement in serotonin biosynthesis in transgenic rice

l-Tryptophan decarboxylase (TDC) and l-tyrosine decarboxylase (TYDC) belong to a family of aromatic l-amino acid decarboxylases and catalyze the conversion of tryptophan and tyrosine into tryptamine and tyramine, respectively. The rice genome has been shown to contain seven TDC or TYDC-like genes. Three of these genes for which cDNA clones were available were characterized to assign their functions using heterologous expression in Escherichia coli and rice (Oryza sativa cv. Dongjin). The purified products of two of the genes were expressed in E. coli and exhibited TDC activity, whereas the remaining gene could not be expressed in E. coli. The recombinant TDC protein with the greatest TDC activity showed a K _m of 0.69 mM for tryptophan, and its activity was not inhibited by phenylalanine or tyrosine, indicating a high level of substrate specificity toward tryptophan. The ectopic expression of the three cDNA clones in rice led to the abundant production of the products of the encoded enzymes, tyramine and tryptamine. The overproduction of TYDC resulted in stunted growth and a lack of seed production due to tyramine accumulation, which increased as the plant aged. In contrast, transgenic plants that produced TDC showed a normal phenotype and contained 25-fold and 11-fold higher serotonin in the leaves and seeds, respectively, than the wild-type plants. The overproduction of either tyramine or serotonin was not strongly related to the enhanced synthesis of tyramine or serotonin derivatives, such as feruloyltyramine and feruloylserotonin, which are secondary metabolites that act as phytoalexins in plants.     

A tyramine receptor gene mutation causes a defective olfactory behavior in Drosophila melanogaster

We characterized molecular profiles of a new olfactory mutant line, honoka (hono), which was found among 500 viable P-element insertion lines screened first by 5-bromo-4-chloro-3-indrolyl-beta-D-galactopyranoside (X-gal) staining on the third segment of the antenna, and then by behavioral assays to several pure chemicals.The behavioral responses of hono mutants to repellents such as ethyl acetate (EA), benzaldehyde (BZ) and 4-methylcycrohexanol (MCH), were reduced compared with those of a control strain. The location of the P-element insertion was determined to be about 100bp) upstream of the first exon of the tyramine receptor gene. The level of 3.6kb tyramine receptor mRNA expression was reduced in hono compared with that of wild-type flies. The tyramine receptor cDNA hybridized to the chromosomal division 79C-D, the same locus as the P-element insertion point in hono, and not to 99A-B, previously reported by Arakawa et al. (1990. Neuron 2, 343-354).Electrophysiological responses to octopamine and tyramine were examined by measuring the excitatory junctional potential (EJP) amplitude from larval body-wall muscles of the hono mutant. The hono was impaired with responding to tyramine, while displaying normal response to octopamine. These results indicate that tyramine has a functional role in the Drosophila olfactory system as a neurotransmitter or a neuromodulator, and hono is the first tyramine receptor mutant. This study provides the first step toward understanding of the molecular genetics of tyramine-mediated neural functions in Drosophila.     

First evidence of a membrane‐bound,tyramine and β‐phenylethylamine producing,tyrosine decarboxylase in Enterococcus faecalis: A two‐dimensional electrophoresis proteomic study

The soluble and membrane proteome of a tyramine producing Enterococcus faecalis, isolated from an Italian goat cheese, was investigated. A detailed analysis revealed that this strain also produces small amounts of β‐phenylethylamine. Kinetics of tyramine and β‐phenylethylamine accumulation, evaluated in tyrosine plus phenylalanine‐enriched cultures (stimulated condition), suggest that the same enzyme, the tyrosine decarboxylase (TDC), catalyzes both tyrosine and phenylalanine decarboxylation: tyrosine was recognized as the first substrate and completely converted into tyramine (100% yield) while phenylalanine was decarboxylated to β‐phenylethylamine (10% yield) only when tyrosine was completely depleted. The presence of an aspecific aromatic amino acid decarboxylase is a common feature in eukaryotes, but in bacteria only indirect evidences of a phenylalanine decarboxylating TDC have been presented so far. Comparative proteomic investigations, performed by 2‐DE and MALDI‐TOF/TOF MS, on bacteria grown in conditions stimulating tyramine and β‐phenylethylamine biosynthesis and in control conditions revealed 49 differentially expressed proteins. Except for aromatic amino acid biosynthetic enzymes, no significant down‐regulation of the central metabolic pathways was observed in stimulated conditions, suggesting that tyrosine decarboxylation does not compete with the other energy‐supplying routes. The most interesting finding is a membrane‐bound TDC highly over‐expressed during amine production. This is the first evidence of a true membrane‐bound TDC, longly suspected in bacteria on the basis of the gene sequence.     

Induced tyramine overproduction in transgenic rice plants expressing a rice tyrosine decarboxylase under the control of methanol-inducible rice tryptophan decarboxylase promoter

Tyramine, one of the various biogenic amines found in plants, is derived from the aromatic L-amino acid tyrosine through the catalytic reaction of tyrosine decarboxylase (TYDC). Tyramine overproduction by constitutive expression of TYDC in rice plants leads to stunted growth, but an increased number of tillers. To regulate tyramine production in rice plants, we expressed TYDC under the control of a methanol-inducible plant tryptophan decarboxylase (TDC) promoter and generated transgenic T(2) homozygous rice plants. The transgenic rice plants showed normal growth phenotypes with slightly increased levels of tyramine in seeds relative to wild type. Upon treatment with 1% methanol, the transgenic rice leaves produced large amounts of tyramine, whereas no increase in tyramine production was observed in wild-type plants. The methanol-induced accumulation of tyramine in the transgenic rice leaves was inversely correlated with the tyrosine level. These data indicate that tyramine production in rice plants can be artificially controlled using the methanol-inducible TDC promoter, suggesting that this promoter could be used to selectively induce the expression of other proteins or metabolites in rice plants.     

Tyramine injections reduce locust viability

In the locust nervous system, tyramine is the direct precursor for octopamine synthesis and, as an octopamine analogue, it can activate octopamine receptors. Furthermore, the identification of specific tyramine receptors in Locusta migratoria and Drosophila melanogaster suggests that it is an important transmitter or modulator candidate. In this paper, we report that repeated tyramine injections reduced the viability of last instar larvae of Locusta and Schistocerca. In addition, a retardation of the last ecdysis was observed as a sublethal effect of the repeated tyramine treatment. Moreover, egg deposition by adult females was also retarded and/or drastically reduced. These effects show similarity to sublethal effects described for certain "insecticidal" octopamine receptor agonists, such as formamidines and phenyliminoimidazolidines. Since certain formamidine compounds were also shown to be agonists for the cloned tyramine receptors, it cannot be excluded that some lethal or sublethal consequences of tyramine administration are the result of an interaction with specific tyramine receptors.     

A new family of insect tyramine receptors

The Drosophila Genome Project database contains a gene, CG7431, annotated to be an "unclassifiable biogenic amine receptor." We have cloned this gene and expressed it in Chinese hamster ovary cells. After testing various ligands for G protein-coupled receptors, we found that the receptor was specifically activated by tyramine (EC(50), 5x10(-7)M) and that it showed no cross-reactivity with beta-phenylethylamine, octopamine, dopa, dopamine, adrenaline, noradrenaline, tryptamine, serotonin, histamine, and a library of 20 Drosophila neuropeptides (all tested in concentrations up to 10(-5) or 10(-4)M). The receptor was also expressed in Xenopus oocytes, where it was, again, specifically activated by tyramine with an EC(50) of 3x10(-7)M. Northern blots showed that the receptor is already expressed in 8-hour-old embryos and that it continues to be expressed in all subsequent developmental stages. Adult flies express the receptor both in the head and body (thorax/abdomen) parts. In addition to the Drosophila tyramine receptor gene, CG7431, we found another closely related Drosophila gene, CG16766, that probably also codes for a tyramine receptor. Furthermore, we annotated similar tyramine-like receptor genes in the genomic databases from the malaria mosquito Anopheles gambiae and the honeybee Apis mellifera. These four tyramine or tyramine-like receptors constitute a new receptor family that is phylogenetically distinct from the previously identified insect octopamine/tyramine receptors. The Drosophila tyramine receptor is, to our knowledge, the first cloned insect G protein-coupled receptor that appears to be fully specific for tyramine.     

Site-directed mutagenesis studies on the Drosophila octopamine/tyramine receptor

The cloned Drosophila octopamine/tyramine receptor can be coupled to second messenger pathways in an agonist-specific fashion by the endogenously occurring biogenic amines, octopamine and tyramine, when expressed in Chinese hamster ovary cells. We have mutated to alanine a range of receptor amino acids that could potentially form hydrogen bonds with the beta-hydroxyl group of octopamine based on homologies with alpha- and beta-adrenergic receptor subtypes. After stable expression of the mutant receptors in CHO cells we have compared the ability of octopamine and tyramine to displace [(3)H]yohimbine binding to membrane fractions from the mutant cell lines with their ability to modulate adenylyl cyclase activity in intact cells. The results suggest that none of the mutated amino acids residues, at least in isolation, are likely to be involved in interactions with the beta-hydroxyl group of the octopamine side chain. It is possible that amino acids not mutated in the present study are somehow involved in this interaction. Alternatively, it is also possible that the beta-hydroxyl group of the octopamine side chain is capable of interacting with more than one of the amino acids mutated in the present study.     

Influence of the biogenic amine tyramine on ethanol-induced behaviors in Drosophila

The biogenic amine tyramine has been implicated in drug-induced behavior. The Drosophila inactive mutant is characterized by reduced tyramine and octopamine levels and is defective in cocaine sensitization. To test whether there is an overlap in the use of the amine neurotransmitter system in ethanol- and cocaine-induced behaviors, mutant analyses were extended to the phenotypic characterization of inactive and other mutants effecting the tyramine and octopamine neurotransmitter system. The inactive mutant displays increased ethanol sensitivity and is impaired in the initial startle response upon ethanol application. Furthermore, this mutant fails to regulate its alcohol-induced hyperactivity properly. In contrast to the defects seen after cocaine application, inactive mutants develop normal ethanol tolerance and sensitize to the locomotor activating effect of ethanol. The tyramine-beta-hydroxylase mutant (TbetaH) with increased tyramine and depleted octopamine levels displays normal ethanol sensitivity, a startle repression, and hyperactivates more in response to ethanol. In addition, TbetaH mutants fail to develop a tolerance to the hyperactivating effect of ethanol. Ethanol-induced sensitization does not seem to be impaired in either mutant, suggesting that tyramine is not required for this process. The comparative analysis of the phenotypes associated with inactive and TbetaH mutants suggests that the fine tuning of ethanol-induced hyperactivity can be correlated with different tyramine levels. Defects in other aspects of ethanol-induced behaviors might be due to different molecules or mechanisms.     

Decrease in juvenile hormone level as a result of genetic ablation of the corpus allatum cells affects the synthesis and metabolism of stress related hormones in Drosophila

Previous studies have shown that juvenile hormone (JH) regulates dopamine (DA) and octopamine (OA) content in Drosophila, and we have shown the influence of an increase in JH level on DA and OA metabolism in young females of Drosophila virilis and Drosophila melanogaster. Here we investigate the effects of genetic ablation of a subset of cells in the Corpusallatum (CA, endocrine gland synthesizing JH) on the DA levels and activities of alkaline phosphatase (ALP), tyrosine hydroxylase (TH), DA-dependent arylalkylamine N-acetyltransferase (DAT) and tyrosine decarboxylase (TDC) in young D. melanogaster females under normal conditions and upon heat stress (38°С). We show that ablation of СА cells causes: (1) a decrease in ALP, TH and DAT activities, (2) an increase in DA level and (3) an increase in TDC activity in young females. The CA ablation was also found to modulate ALP, TH and TDC responses to heat stress. Mechanisms of regulation of DA and OA levels by JH in Drosophila females are discussed.     

Agonist-specific coupling of a cloned Drosophila octopamine/tyramine receptor to multiple second messenger systems.

A cloned seven transmembrane-spanning Drosophila octopamine/tyramine receptor, permanently expressed in a Chinese hamster ovary cell line, both inhibits adenylate cyclase activity and leads to the elevation of intracellular Ca2+ levels by separate G-protein-coupled pathways. Agonists of this receptor (octopamine and tyramine), differing by only a single hydroxyl group in their side chain, may be capable of differentially coupling it to different second messenger systems. Thus, a single receptor may have a different pharmacological profile depending on which second messenger system is used to assay its efficacy.     

Requirement of RBP9, a Drosophila Hu homolog, for regulation of cystocyte differentiation and oocyte determination during oogenesis

The Drosophila RNA binding protein RBP9 and its Drosophila and human homologs, ELAV and the Hu family of proteins, respectively, are highly expressed in the nuclei of neuronal cells. However, biochemical studies suggest that the Hu proteins function in the regulation of mRNA stability, which occurs in the cytoplasm. In this paper, we show that RBP9 is expressed not only in the nuclei of neuronal cells but also in the cytoplasm of cystocytes during oogenesis. Despite the predominant expression of RBP9 in nerve cells, mutational analysis revealed a female sterility phenotype rather than neuronal defects for Rbp9 mutants. The female sterility phenotype of the Rbp9 mutants resulted from defects in oogenesis; the lack of Rbp9 activity caused the germarium region of the mutants to be filled with undifferentiated cystocytes. RBP9 appears to stimulate cystocyte differentiation by regulating the expression of bag-of-marbles (bam) mRNA, which encodes a developmental regulator of germ cells. RBP9 protein bound specifically to bam mRNA in vitro, which is required for cystocyte proliferation, and the number of cells that expressed BAM protein was increased 5- to 10-fold in the germarium regions of Rbp9 mutants. These results suggest that RBP9 protein binds to bam mRNA to down regulate BAM protein expression, which is essential for the initiation of cystocyte differentiation into functional egg chambers. In hypomorphic Rbp9 mutants, cystocytes differentiated into egg chambers; however, oocyte determination and positioning were perturbed. Therefore, the concentrated localization of RBP9 protein in the oocyte of the early egg chambers may be required for proper oocyte determination or positioning.     

The Drosophila RNA-binding protein Lark is required for the organization of the actin cytoskeleton and Hu-li tai shao localization during oogenesis

Elimination of maternal expression of the Drosophila RNA-binding protein Lark results in female sterility. Here we show that this is due to a requirement during oogenesis. Developing oocytes from lark(1) germline clones (GLCs) are often smaller than normal due to defects in nurse cell cytoplasmic "dumping." Late-stage egg chambers from lark(1) GLCs contain low levels of cortical and ring canal associated actin and completely lack nurse cell cytoplasmic F-actin bundles, suggesting the "dumping" phenotype is due to a defect in the actin cytoskeleton. Localization of Hu-li tai shao (Hts) protein, a component of ring canals, is also disrupted in these mutants. In addition to the dumpless phenotype, we observed a buildup of late-stage egg chambers, a phenotype that correlates with the decrease in egg-laying observed in the mutants. We postulate that this phenotype is due to defects in the cytoskeletal integrity of eggs since retained and oviposited eggs are fragile and often deflated. These mutant phenotypes are likely due to disruption of an RNA-binding function of Lark as similar phenotypes were observed in flies carrying specific RNA-binding domain mutations. We propose that Lark functions during oogenesis as an RNA-binding protein, regulating mRNAs required for nurse cell transport or apoptosis.     

Molecular and functional characterization of an octopamine receptor from honeybee (Apis mellifera) brain

Biogenic amines and their receptors regulate and modulate many physiological and behavioural processes in animals. In vertebrates, octopamine is only found in trace amounts and its function as a true neurotransmitter is unclear. In protostomes, however, octopamine can act as neurotransmitter, neuromodulator and neurohormone. In the honeybee, octopamine acts as a neuromodulator and is involved in learning and memory formation. The identification of potential octopamine receptors is decisive for an understanding of the cellular pathways involved in mediating the effects of octopamine. Here we report the cloning and functional characterization of the first octopamine receptor from the honeybee, Apis mellifera. The gene was isolated from a brain-specific cDNA library. It encodes a protein most closely related to octopamine receptors from Drosophila melanogaster and Lymnea stagnalis. Signalling properties of the cloned receptor were studied in transiently transfected human embryonic kidney (HEK) 293 cells. Nanomolar to micromolar concentrations of octopamine induced oscillatory increases in the intracellular Ca2+ concentration. In contrast to octopamine, tyramine only elicited Ca2+ responses at micromolar concentrations. The gene is abundantly expressed in many somata of the honeybee brain, suggesting that this octopamine receptor is involved in the processing of sensory inputs, antennal motor outputs and higher-order brain functions.     

Biochemical analysis of torso and D-raf during Drosophila embryogenesis: implications for terminal signal transduction.

Determination of anterior and posterior terminal structures of Drosophila embryos requires activation of two genes encoding putative protein kinases, torso and D-raf. In this study, we demonstrate that Torso has intrinsic tyrosine kinase activity and show that it is transiently tyrosine phosphorylated (activated) at syncytial blastoderm stages. Torso proteins causing a gain-of-function phenotype are constitutively tyrosine phosphorylated, while Torso proteins causing a loss-of-function phenotype lack tyrosine kinase activity. The D-raf gene product, which is required for Torso function, is identified as a 90-kDa protein with intrinsic serine/threonine kinase activity. D-Raf is expressed throughout embryogenesis; however, the phosphorylation state of the protein changes during development. In wild-type embryos, D-Raf is hyperphosphorylated at 1 to 2 h after egg laying, and thereafter only the most highly phosphorylated form is detected. Embryos lacking Torso activity, however, show significant reductions in D-Raf protein expression rather than major alterations in the protein's phosphorylation state. This report provides the first biochemical analysis of the terminal signal transduction pathway in Drosophila embryos.     

Genetic Control of Biogenic-Amine Systems in Drosophila Under Normal and Stress Conditions

The contents of octopamine and its precursors (tyrosine and tyramine) were studied in adults of two lines of Drosophila virilis with contrasting stress responses. It was demonstrated that in individuals responding to stress by a hormonal stress reaction (line 101), the contents of octopamine and tyrosine are lower than in nonresponding flies (line 147). It was found that there is no difference between the lines in the level of tyramine under normal conditions. The dopamine response to stressor was also studied. Genetic analysis of these differences revealed that they are controlled by a single gene and that the gene is not sex-linked. The gene controlling the response was found to be linked to chromosome 6 of D. virilis.     

Influence of the biogenic amine tyramine on ethanol‐induced behaviors in Drosophila

The biogenic amine tyramine has been implicated in drug‐induced behavior. The Drosophila inactive mutant is characterized by reduced tyramine and octopamine levels and is defective in cocaine sensitization. To test whether there is an overlap in the use of the amine neurotransmitter system in ethanol‐ and cocaine‐induced behaviors, mutant analyses were extended to the phenotypic characterization of inactive and other mutants effecting the tyramine and octopamine neurotransmitter system. The inactive mutant displays increased ethanol sensitivity and is impaired in the initial startle response upon ethanol application. Furthermore, this mutant fails to regulate its alcohol‐induced hyperactivity properly. In contrast to the defects seen after cocaine application, inactive mutants develop normal ethanol tolerance and sensitize to the locomotor activating effect of ethanol. The tyramine‐β‐hydroxylase mutant (TβH) with increased tyramine and depleted octopamine levels displays normal ethanol sensitivity, a startle repression, and hyperactivates more in response to ethanol. In addition, TβH mutants fail to develop a tolerance to the hyperactivating effect of ethanol. Ethanol‐induced sensitization does not seem to be impaired in either mutant, suggesting that tyramine is not required for this process. The comparative analysis of the phenotypes associated with inactive and TβH mutants suggests that the fine tuning of ethanol‐induced hyperactivity can be correlated with different tyramine levels. Defects in other aspects of ethanol‐induced behaviors might be due to different molecules or mechanisms. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005