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Power analyses are often used to determine the number of animals required for a genome-wide association study (GWAS). These analyses are typically intended to estimate the sample size needed for at least 1 locus to exceed a genome-wide significance threshold. A related question that is less commonly considered is the number of significant loci that will be discovered with a given sample size. We used simulations based on a real data set that consisted of 3,173 male and female adult N/NIH heterogeneous stock rats to explore the relationship between sample size and the number of significant loci discovered. Our simulations examined the number of loci identified in subsamples of the full data set. The subsampling analysis was conducted for 4 traits with low (0.15 ± 0.03), medium (0.31 ± 0.03 and 0.36 ± 0.03), and high (0.46 ± 0.03) SNP-based heritabilities. For each trait, we subsampled the data 100 times at different sample sizes (500, 1,000, 1,500, 2,000, and 2,500). We observed an exponential increase in the number of significant loci with larger sample sizes. Our results are consistent with similar observations in human GWAS and imply that future rodent GWAS should use sample sizes that are significantly larger than those needed to obtain a single significant result.

BACKGROUND. Individuals with fetal alcohol spectrum disorders (FASD) often show sensory processing deficits in all sensory modalities. Using an operant light reinforcement model, we tested if prenatal ethanol exposure (PE) could alter operant responding to elicit a contingent sensory stimulus - light onset (turning on light) and habituation of this behavior in rats. We also explored if postnatal environmental enrichment could ameliorate PE-induced deficits. METHODS. Pregnant Sprague Dawley rats were gavaged twice/day with 0 or 3 g/kg/treatment ethanol (15% w/v) during gestational days 8–20, mimicking second-trimester heavy PE in humans. The offspring were reared in the standard housing condition or an enriched condition. Adult male and female offspring underwent an operant light reinforcement experiment with either a short-access or a long-access procedure. A dishabituation test was also conducted to further characterize the habituation process. RESULTS. In the short-access procedure, PE led to increased operant responding to the contingent light-onset in both sexes reared in the standard housing condition. Such an effect was not observed in rats reared in enriched condition due to an overall decrease in responding. Moreover, rats reared in enriched condition showed greater short-term habituation. In the long access procedure, PE rats showed increased responding and impaired long-term habituation. The long-access procedure facilitated both short-term and long-term habituation in control and PE rats. CONCLUSION. Prenatal ethanol exposure increases responding to contingent light-onset and impairs the long-term habituation process. The PE-induced deficits could be ameliorated by rearing in the enriched environment and increasing the duration and frequency of exposure to light-onset. The PE-induced effects are similar to increased sensation-seeking, a subtype of sensory-processing deficits, which is often observed in individuals with FASD. Our findings could inform a suitable animal model for investigating the underlying mechanisms as well as possible intervention strategies for these deficits in FASD.

Author(s): Chitre, Apurva S; Polesskaya, Oksana; Holl, Katie; Gao, Jianjun; Cheng, Riyan; Bimschleger, Hannah; Garcia Martinez, Angel; George, Tony; Gileta, Alexander F; Han, Wenyan; Horvath, Aidan; Hughson, Alesa; Ishiwari, Keita; King, Christopher P; Lamparelli, Alexander; Versaggi, Cassandra L; Martin, Connor; St Pierre, Celine L; Tripi, Jordan A; Wang, Tengfei; Chen, Hao; Flagel, Shelly B; Meyer, Paul; Richards, Jerry; Robinson, Terry E; Palmer, Abraham A; Solberg Woods, Leah C | Abstract: ObjectiveObesity is influenced by genetic and environmental factors. Despite the success of human genome-wide association studies, the specific genes that confer obesity remain largely unknown. The objective of this study was to use outbred rats to identify the genetic loci underlying obesity and related morphometric and metabolic traits.MethodsThis study measured obesity-relevant traits, including body weight, body length, BMI, fasting glucose, and retroperitoneal, epididymal, and parametrial fat pad weight in 3,173 male and female adult N/NIH heterogeneous stock (HS) rats across three institutions, providing data for the largest rat genome-wide association study to date. Genetic loci were identified using a linear mixed model to account for the complex family relationships of the HS and using covariates to account for differences among the three phenotyping centers.ResultsThis study identified 32 independent loci, several of which contained only a single gene (e.g., Epha5, Nrg1, Klhl14) or obvious candidate genes (e.g., Adcy3, Prlhr). There were strong phenotypic and genetic correlations among obesity-related traits, and there was extensive pleiotropy at individual loci.ConclusionsThis study demonstrates the utility of HS rats for investigating the genetics of obesity-related traits across institutions and identify several candidate genes for future functional testing.

Previous research has shown that rats reared in simple/impoverished environments demonstrate greater repetitive responding for sensory reinforcers (e.g., light onset). Moreover, the brains of these rats are abnormally developed, compared to brains of rats reared in more complex/enriched environments. Repetitive behaviors are commonly observed in individuals with developmental disorders. Some of these repetitive behaviors could be maintained by the reinforcing effects of the sensory stimulation that they produce. Therefore, rearing rats in impoverished conditions may provide an animal model for certain repetitive behaviors associated with developmental disorders. We hypothesize that in rats reared in simple/impoverished environments, the normal habituation process to sensory reinforcers is impaired, resulting in high levels of repetitive behaviors. We tested the hypothesis using an operant sensory reinforcement paradigm in rats reared in simple/impoverished (IC), standard laboratory (SC), and complex/enrichened conditions (EC, treatments including postnatal handling and environmental enrichment). Results show that the within-session habituation of the reinforcer effectiveness of light onset was slower in the IC and SC rats than in the EC rats. A dishabituation challenge indicated that within-session decline of responses was due to habituation and not motor fatigue or sensory adaptation. In conclusion, rearing rats in simple/impoverished environments, and comparing them to rats reared in more complex/enriched environments, may constitute a useful approach for studying certain repetitive behaviors associated with developmental disorders.

Genome-wide association studies in humans have suggested that variants of the cadherin-13 (CDH13) gene are associated with substance use disorder, subjective response to amphetamine, and attention deficit hyperactivity disorder. To examine the role of the Cdh13 and its peptide ligand adiponectin (AdipoQ) in addiction-related behaviors, we assessed Cdh13 knock-out rats and AdipoQ knock-out mice using intravenous cocaine self-administration and conditioned place preference paradigms. During intravenous cocaine self-administration, male Cdh13 heterozygous (+/−) and knock-out (−/−) rats showed increased cue-induced reinstatement compared to wild-type rats when presented with a cocaine-paired stimulus, whereas female Cdh13 rats showed no differences across genotype. Cdh13 −/− rats showed higher responding for a saccharin reinforcer and learned the choice reaction time task more slowly than wild-types. However, we found no differences between Cdh13 −/− and +/+ rats in responding for sensory reinforcement, number of premature responses in the reaction time task, tendency to approach a Pavlovian food cue, conditioned place preference and locomotor activation to cocaine (10 or 20 mg/kg). In AdipoQ −/− mice there was a significant increase in conditioned place preference to methamphetamine (1 mg/kg) but not to a range of d-amphetamine doses (0.5, 1, 2 and 4 mg/kg). Taken together, these data suggest that Cdh13 and AdipoQ regulate sensitivity to psychomotor stimulants and palatable rewards without producing major changes in other behaviors. In humans, these two genes may regulate sensitivity to natural and drug rewards, thus influencing susceptibility to the conditioned drug effects and relapse.

The stimulant, methylphenidate (MPH), is commonly used to treat attention deficit hyperactivity disorder (ADHD) and has been increasingly prescribed for school age children and adolescents. Concerns regarding its long-term effects on later substance use disorders (SUDs) have been raised. Previous animal studies have produced contradictory results regarding whether early exposure to MPH increases or protects against SUD in adulthood. The goal of our study was to determine if clinically relevant doses of MPH during adolescence alter cocaine responsiveness in adulthood in a rat model of ADHD, the spontaneous hypertensive rat (SHR). We pretreated SHRs with saline or MPH (2.5 mg/kg once or twice day) via oral gavage during their dark cycle from postnatal day 35 (p35) to p44. Adult rats (p80) were assessed in an eight-session cocaine-conditioned place preference test (CPP). Four doses of cocaine were administered via intraperitoneal injection (i.p.) during the conditioning sessions: 1, 5, 10 and 20 mg/kg. Once per day MPH treatment had a small sensitizing effect on baseline general locomotor activity in a novel environment at p80 as well as a limited suppressive effect on reward-specific locomotor activity as measured by the decreased preference to enter the cocaine-paired chamber. This treatment did not have any effect on the amount of time that rats chose to spend in the cocaine-paired chamber. Twice per day MPH treatment had no effect on locomotion or drug-preference. Our results suggest that MPH treatment of ADHD rats during adolescence does not alter preference for cocaine in adulthood.

Background Multiple factors contribute to the etiology of addiction, including genetics, sex, and a number of addiction-related behavioral traits. One behavioral trait where individuals assign incentive salience to food stimuli (“sign-trackers”, ST) are more impulsive compared to those that do not (“goal-trackers”, GT), as well as more sensitive to drugs and drug stimuli. Furthermore, this GT/ST phenotype predicts differences in other behavioral measures. Recent studies have implicated the gut microbiota as a key regulator of brain and behavior, and have shown that many microbiota-associated changes occur in a sex-dependent manner. However, few studies have examined how the microbiome might influence addiction-related behaviors. To this end, we sought to determine if gut microbiome composition was correlated with addiction-related behaviors determined by the GT/ST phenotype. Methods Outbred male (N=101) and female (N=101) heterogeneous stock rats underwent a series of behavioral tests measuring impulsivity, attention, reward-learning, incentive salience, and locomotor response. Cecal microbiome composition was estimated using 16S rRNA gene amplicon sequencing. Behavior and microbiome were characterized and correlated with behavioral phenotypes. Robust sex differences were observed in both behavior and microbiome; further analyses were conducted within sex using the pre-established goal/sign-tracking (GT/ST) phenotype and partial least squares differential analysis (PLS-DA) clustered behavioral phenotype. Results Overall microbiome composition was not associated to the GT/ST phenotype. However, microbial alpha diversity was significantly decreased in female STs. On the other hand, a measure of impulsivity had many significant correlations to microbiome in both males and females. Several measures of impulsivity were correlated with the genus Barnesiella in females. Female STs had notable correlations between microbiome and attentional deficient. In both males and females, many measures were correlated with the bacterial families Ruminocococcaceae and Lachnospiraceae. Conclusions These data demonstrate correlations between several addiction-related behaviors and the microbiome specific to sex.

ObjectiveObesity is influenced by genetic and environmental factors. Despite success of human genome wide association studies (GWAS), the specific genes that confer obesity remain largely unknown. The objective of this study was to use outbred rats to identify genetic loci underlying obesity and related morphometric and metabolic traits.MethodsWe measured obesity-relevant traits including body weight, body length, body mass index, fasting glucose, and retroperitoneal, epididymal, and parametrial fat pad weight in 3,173 male and female adult N/NIH heterogeneous stock (HS) rats across three institutions, providing data for the largest rat GWAS to date. Genetic loci were identified using a linear mixed model that accounted for the complex family relationships of the HS and covariate to account for differences among the three phenotyping centers.ResultsWe identified 32 independent loci, several of which contained only a single gene (e.g. Epha5, Nrg1 and Klhl14) or obvious candidate genes (Adcy3, Prlhr). There were strong phenotypic and genetic correlations among obesity-related traits, and extensive pleiotropy at individual loci.ConclusionsThese studies demonstrate utility of HS rats for investigating the genetics of obesity related traits across institutions and identify several candidate genes for future functional testing.

Indifferent sensory stimuli, such as light-onset, can be reinforcers (for reviews, see Berlyne, 1969; Eisenberger, 1972; Glanzer, 1958; Kish, 1966; Lockard, 1963; Tapp, 1969). In comparison to important biological reinforcers such as food and water, the reinforcing effectiveness of sensory reinforcers is weak and transient. Responding for sensory reinforcers has often been characterized as investigatory behavior. Experiments with light reinforcement were first reported by Girdner (1953), who considered the operant responding for novel light-onset analogous to investigatory loco-motor responses that expose organisms to novel environmental change (as described by Kish, 1966, p. 111). For example, exploratory activity is high when a rat is first placed into a novel locomotor chamber and then decreases within the same session. Similarly, operant responding for novel light-onset is initially high at the start of a test session and then shows a within-session decline (Gancarz, Ashrafioun, et al., 2012; Gancarz, Robble, Kausch, Lloyd, & Richards, 2012). Within-session declines in locomotor activity and responding for novel light-onset are often characterized as indicators of habituation involving memory processes. A rat, when placed in the novel chamber, forms an internal representation (memory) of the chamber and the objects within and around it (Antunes & Biala, 2012; Leussis & Bolivar, 2006). Locomotor activity decreases as a consistent internal representation of the test chamber is formed and perceived stimuli are recognized. This interpretation is consistent with memory-based explanations of habituation (Konorski, 1963; Sokolov, 1963; Wagner, 1979). According to memory-based explanations of habituation, perceived stimuli are compared with existing memory. If the perceived sensory stimuli do not match memory, they are novel and cause dishabituation. On the other hand, if the perceived stimuli match memory, then they are not novel or surprising and do not cause dishabituation. McSweeney and Murphy (2009) have argued that within-session declines in operant responding are a function of habituation to the sensory properties of repeatedly presented reinforcers. In agreement with their work, we have provided evidence that within-session declines in the effectiveness of sensory reinforcers is attributable to habituation (Lloyd, Gancarz, Ashrafioun, Kausch, & Richards, 2012). Within-session decreases in light-reinforced responding can be reasonably attributed to habituation of reinforcer effectiveness because there is a programmed contingency between responding and light-onset. In contrast, locomotor activity in a novel locomotor chamber is more likely to be described as elicited or evoked by exposure to novel environmental stimuli, suggesting that locomotor activity in a novel environment is a Pavlovian process. However, as has been previously pointed out (Berlyne, 1960), exploratory behavior can be characterized as a mixture of Pavlovian and operant processes. Novel sensory stimuli such as light-onset activate orienting or targeting reflexes that bring sensory receptors into contact with the sensory stimulus (Sokolov, 1963). Some of the sensory stimuli (e.g., localized changes in relative illumination) evoke targeting reflexes and are also reinforcers that increase the probability of the responses that produced them. It is likely that naturally occurring contingencies between responding and sensory stimulation that occur while an animal is exploring a novel environment may similarly increase locomotor activity in a novel environment. Thus, even though there are no programmed operant contingencies in a novel locomotor chamber, the habituation of the reinforcing effectiveness of inherent operant contingencies may contribute to declines in exploratory activity. This is supported by evidence from McSweeney and Swindell (1999) who showed that decreases in exploratory activity follow the same mathematical relationship as habituation in other paradigms. As was originally suggested by Girdner (1953), operant responding to produce light-onset may be an effective way to precisely measure exploratory behavior. Habituation to the reinforcing effectiveness of sensory stimuli may be mediated by decreases in dopamine (DA) neurotransmission evoked by novel or surprising sensory stimuli. Novel sensory stimuli increase phasic firing of DA neurons. This effect rapidly habituates when sensory stimuli are repeatedly presented (Ljungberg, Apicella, & Schultz, 1992). Redgrave and Gurney (2006) have hypothesized that phasic firing of DA neurons elicited by novel sensory stimuli activate the animal to repeat responses that produced the novel sensory stimulation. According to Redgrave and Gurney, this DA-mediated mechanism allows organisms to “discover” contingencies between investigatory behaviors and novel sensory events. Following initial “discovery,” phasic firing of DA neurons is cancelled by timed inhibitory input to DA as the sensory stimulus becomes predictable (familiar) through repetition. Redgrave and Gurney (2006) have described the phasic firing of DA neurons evoked by novel sensory stimulation as a sensory prediction error signal. The concept of phasic firing of DA neurons as a function of the difference between perceived and remembered stimuli fits well with memory-based explanations of habituation, where comparison of perceived and remembered stimuli leads to the identification of novel stimuli that produce dishabituation (arousal). However, instead of arousal, Redgrave and Gurney emphasize that an increase in DA neurotransmission evoked by novel stimuli determines the reinforcing effectiveness (or effects) of indifferent sensory stimuli. More specifically, they hypothesize that novelty-induced increases in DA cause the animal to repeat actions that precede novel stimuli, leading to the discovery of the action that produced it. The hypothesis that the reinforcing effects of sensory stimuli rapidly habituate, in combination with the concept of phasic DA as a sensory prediction error signal that mediates the behavioral expression of habituation, makes predictions that can be tested with both behavioral and drug manipulations. To test these predictions we have developed a method for quantitatively characterizing the rate of habituation for operant responding that takes into account relative differences in response rate so that the habituation rate (HR) measure is independent of absolute response rate measures. In Phase 1 of the current experiment, we use this method to measure the HR of the operant level of snout poking in a novel environment. Memory-based theories of habituation predict that the rate of habituation will increase with repeated exposure to the novel environment as sensory consequences of investigatory behaviors become familiar. The DA as a sensory error signal hypothesis predicts that phasic firing of DA neurons will decrease with repeated exposure, resulting in decreased activation. Both theories therefore predict that repeated exposure will lead to a decrease in measured operant level responding (snout-poking). In Phase 2, the effects of the stimulant drugs nicotine (NIC) and methamphetamine (METH) on HR are measured. The DA as a sensory error signal hypothesis predicts that stimulant drugs such as NIC and METH which artificially increase DA neurotransmission will disrupt (decrease) expression of normally occurring habituation. In Phase 3, the effects on HR of making a novel sensory stimulus contingent upon snout poking are tested. Memory-based theories of habituation predict that introduction of a novel response-contingent sensory stimulus will decrease the rate of habituation. In addition, the DA as a sensory error signal hypothesis predicts that introduction of a novel stimulus will increase DA neurotransmission and increase activation. The apparatus and procedures used in this experiment have previously been found to reliably produce light reinforced responding (Gancarz, Ashrafioun, et al., 2012; Gancarz, Robble, Kausch, Lloyd, & Richards, 2012, 2013; Lloyd, Gancarz, et al., 2012; Lloyd, Kausch, Gancarz, Beyley, & Richards, 2012). We selected 0.75 mg/kg METH for this experiment because it was within the range of known effective doses (Gancarz, Ashrafioun, et al., 2012), and we selected the NIC dose of 0.4 mg/kg because this dose was found to effectively increase light reinforced responding (Palmatier et al., 2007).

A fundamental challenge for any complex nervous system is to regulate behavior in response to environmental challenges. Three measures of behavioral-regulation were tested in a panel of eight inbred rat strains. These measures were: (1) sensation seeking as assessed by locomotor response to novelty and the sensory reinforcing effects of light onset, (2) attention and impulsivity, as measured by a choice reaction time task and (3) impulsivity as measured by a delay discounting task. Deficient behavioral-regulation has been linked to a number of psychopathologies, including ADHD, Schizophrenia, Autism, drug abuse and eating disorders. Eight inbred rat strains (August Copenhagen Irish, Brown Norway, Buffalo, Fischer 344, Wistar Kyoto, Spontaneous Hypertensive Rat, Lewis, Dahl Salt Sensitive) were tested. With n = 9 for each strain, we observed robust strain differences for all tasks; heritability was estimated between 0.43 and 0.66. Performance of the eight inbred rat strains on the choice reaction time task was compared to the performance of outbred Sprague Dawley (n = 28) and Heterogeneous strain rats (n = 48). The results indicate a strong genetic influence on complex tasks related to behavioral-regulation and indicate that some of the measures tap common genetically driven processes. Furthermore, our results establish the potential for future studies aimed at identifying specific alleles that influence variability for these traits. Identification of such alleles could contribute to our understanding of the molecular genetic basis of behavioral-regulation, which is of fundamental importance and likely contributes to multiple psychiatric disorders.

© 2016, Springer-Verlag Berlin Heidelberg. Rationale: Disorders of behavioral regulation, including attention deficit hyperactivity disorder (ADHD) and drug addiction, are in part due to poor inhibitory control, attentional deficits, and hyper-responsivity to reward-associated cues. Objectives: To determine whether these traits are related, we tested genetically variable male and female heterogeneous stock rats in the choice reaction time (CRT) task and Pavlovian conditioned approach (PavCA). Sex differences in the response to methylphenidate during the CRT were also assessed. Methods: In the CRT task, rats were required to withhold responding until one of two lights indicated whether responses into a left or right port would be reinforced with water. Reaction time on correct trials and premature responses were the operational definitions of attention and response inhibition, respectively. Rats were also pretreated with oral methylphenidate (0, 2, 4 mg/kg) during the CRT task to determine whether this drug would improve performance. Subsequently, during PavCA, presentation of an illuminated lever predicted the delivery of a food pellet into a food-cup. Lever-directed approach (sign-tracking) and food-cup approach (goal-tracking) were the primary measures, and rats were categorized as “sign-trackers” and “goal-trackers” using an index based on these measures. Results: Sign-trackers made more premature responses than goal-trackers but showed no differences in reaction time. There were sex differences in both tasks, with females having higher sign-tracking, completing more CRT trials, and making more premature responses after methylphenidate administration. Conclusions: These results indicate that response inhibition is related to reward-cue responsivity, suggesting that these traits are influenced by common genetic factors.

Recent research has suggested that intra-individual variability in reaction time (RT) distributions of children with ADHD is characterized by a particularly large rightward skew that may reflect lapses in attention. The purpose of the study was to provide the first randomized, placebo-controlled test of the effects of the stimulant methylphenidate (MPH) on this tail and other RT distribution characteristics. Participants were 49 9- to 12-year-old children with ADHD. Children participated in a 3-day double-blind, placebo-controlled medication assessment during which they received long-acting MPH (Concerta®), with the nearest equivalents of 0.3 and 0.6 mg/kg t.i.d. immediate-release MPH. Children completed a simple two-choice speeded discrimination task on and off of medication. Mode RT and deviation from the mode were used to examine the peak and skew, respectively, of RT distributions. MPH significantly reduced the peak and skew of RT distributions. Importantly, the two medication effects were uncorrelated suggesting that MPH works to improve both the speed and variability in responding. The improvement in variability with stimulant treatment is interpreted as a reduction in lapses in attention. This, in turn, may reflect stimulant enhancement of self-regulatory processes theorized to be at the core of ADHD.

Rationale Based upon extensive studies in the rat, it has been suggested that stimulus control by LSD is mediated by 5-HT2A receptors, with serotonergic receptors of the 5-HT1A and 5-HT2C subtypes playing modulatory roles. In genetically modified mice lacking the serotonin transporter (SERT), 5-HT2A receptor density is decreased and, at a functional level, the head-twitch response following the administration of DOI, an index of activation of 5-HT2A receptors, is reduced. Taken together, these studies led us to hypothesize that the efficacy of LSD in establishing stimulus control is diminished or abolished in mice lacking the serotonin transporter. Objective Determine the efficacy of LSD for establishing stimulus control in SERT knockout (KO) mice. Methods SERT KO mice and wildtype (WT) littermates were trained in a visual discrimination on a progressive fixed ratio (FR) water-reinforced task and subsequently trained on a FR10 schedule with LSD (0.17 or 0.30 mg/kg) or vehicle. To control for general deficiencies in drug discrimination, mice were trained with pentobarbital (15 or 30 mg/kg) or vehicle. Results The visual stimulus exerted control in both genotypes. LSD-induced stimulus control in 90% of WT mice but only 31% of SERT KO mice. In contrast, pentobarbital-induced stimulus control in 80% of WT mice and 54% of knockout mice. Conclusions Although SERT KO mice exhibited stimulus control by the non-serotonergic drug, pentobarbital, the efficacy of LSD in these animals was markedly decreased, suggesting that reduced density of 5-HT1A and/or 5-HT2A receptors underlies the absence of stimulus control by LSD.

In humans, prepulse inhibition (PPI) of startle is greater during attended prestimuli than it is during ignored prestimuli, whereas in rats, most work has focused on passive PPI, which does not require attention. In the work described in this article, researchers developed a paradigm to assess attentional modification of PPI in rats using motivationally salient prepulses. Water-deprived rats were either conditioned to attend to a conditioned stimulus (CS; 1-s, 7-dB increase in white noise) paired with water (CS(+) group), or they received uncorrelated presentations of white noise and water (CS0 group). After 10 conditioning sessions, startle probes (50 ms, 115 dB) were introduced, with the CS serving as a continuous prepulse. Three experiments examined PPI across a range of prepulse intensities (4-10 dB) and stimulus onset asynchronies (SOAs; 30-960 ms). PPI was consistently reduced in the CS(+) group, particularly with a 10-dB prepulse and a 60-ms SOA. Thus, PPI in rats differed between attended and ignored prestimuli, but the effect was reversed in the results of research with humans. A fourth study eliminated the group difference by reversing the CS-water contingency. Methodological and motivational hypotheses regarding the current findings are discussed.

Developing and mature midbrain dopamine (DA) neurons express fibroblast growth factor (FGF) receptor-1 (FGFR1). To determine the role of FGFR1 signaling in the development of DA neurons, we generated transgenic mice expressing a dominant negative mutant [FGFR1(TK-)] from the catecholaminergic, neuron-specific tyrosine hydroxylase (TH) gene promoter. In homozygous th(tk-)/th(tk-) mice, significant reductions in the size of TH-immunoreactive neurons were found in the substantia nigra compacta (SNc) and the ventral tegmental area (VTA) at postnatal days 0 and 360. Newborn th(tk-)/th(tk-) mice had a reduced density of DA neurons in both SNc and VTA, and the changes in SNc were maintained into adulthood. The reduced density of DA transporter in the striatum further demonstrated an impaired development of the nigro-striatal DA system. Paradoxically, the th(tk-)/th(tk-) mice had increased levels of DA, homovanilic acid and 3-methoxytyramine in the striatum, indicative of excessive DA transmission. These structural and biochemical changes in DA neurons are similar to those reported in human patients with schizophrenia and, furthermore, these th(tk-)/th(tk-) mice displayed an impaired prepulse inhibition that was reversed by a DA receptor antagonist. Thus, this study establishes a new developmental model for a schizophrenia-like disorder in which the inhibition of FGF signaling leads to alterations in DA neurons and DA-mediated behavior.

Rationale Drug-induced stimulus control has proven to be a powerful tool for the assessment of a wide range of psychoactive drugs. Although a variety of species has been employed, the majority of studies have been in the rat. However, with the development of techniques which permit the genetic modification of mice, the latter species has taken on new importance. Lysergic acid diethylamide [LSD], the prototypic indoleamine hallucinogen, has not previously been trained as a discriminative stimulus in mice. Objective To demonstrate the feasibility of LSD-induced stimulus control in the mouse and to provide a preliminary characterization of the stimulus properties of LSD in that species. Methods Male C57BL/6 mice were trained using a left or right nose-poke operant on a fixed ratio 10, water reinforced task following the injection of lysergic acid diethylamide [LSD, 0.17 or 0.30 mg/kg, SC; 15 min pretreatment] or vehicle. Results Stimulus control was established in 6 of 16 mice at a dose of LSD of 0.17 mg/kg after 39 sessions. An increase in dose to 0.30 mg/kg for the remaining mice resulted in stimulus control in an additional 5 subjects. In the low dose group, subsequent experiments demonstrated an orderly dose–effect relationship for LSD and a rapid offset of drug action with an absence of LSD effects 60 min after injection. When LSD [0.17 mg/kg] was administered in combination with the selective 5-HT2A antagonist, M100907, LSD-appropriate responding was significantly but incompletely reduced to approximately 50%; concurrently, response rates declined significantly. In mice trained with a dose of LSD of 0.30 mg/kg, full generalization to the phenethylamine hallucinogen, [−]-2,5-dimethoxy-4-methylamphetamine [DOM] was observed. Conclusions The present data demonstrate the feasibility of LSD-induced stimulus control in the mouse. The general features of stimulus control by LSD in the mouse closely resemble those observed in the rat but the present data suggest that there may be significant differences as well.

Due in part to their rich behavioral repertoire rats have been widely used in behavioral studies of drug abuse-related traits for decades. However, the mouse became the model of choice for researchers exploring the genetic underpinnings of addiction after the first mouse study was published demonstrating the capability of engineering the mouse genome through embryonic stem cell technology. The sequencing of the mouse genome and more recent re-sequencing of numerous inbred mouse strains have further cemented the status of mice as the premier mammalian organism for genetic studies. As a result, many of the behavioral paradigms initially developed and optimized for rats have been adapted to mice. However, numerous complex and interesting drug abuse-related behaviors that can be studied in rats are very difficult or impossible to adapt for use in mice, impeding the genetic dissection of those traits. Now, technological advances have removed many of the historical limitations of genetic studies in rats. For instance, the rat genome has been sequenced and many inbred rat strains are now being re-sequenced and outbred rat stocks are being used to fine-map QTLs. In addition, it is now possible to create "knockout" rats using zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALENs) and related techniques. Thus, rats can now be used to perform quantitative genetic studies of sophisticated behaviors that have been difficult or impossible to study in mice. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

UNLABELLEDPyruvate dehydrogenase (PDH) complex (PDC) deficiency is an inborn error of pyruvate metabolism causing a variety of neurologic manifestations. Systematic analyses of development of affected brain structures and the cellular processes responsible for their impairment have not been performed due to the lack of an animal model for PDC deficiency.METHODSIn the present study we investigated a murine model of systemic PDC deficiency by interrupting the X-linked Pdha1 gene encoding the α subunit of PDH to study its role on brain development and behavioral studies.RESULTSMale embryos died prenatally but heterozygous females were born. PDC activity was reduced in the brain and other tissues in female progeny compared to age-matched control females. Immunohistochemical analysis of several brain regions showed that approximately 40% of cells were PDH(-). The oxidation of glucose to CO2 and incorporation of glucose-carbon into fatty acids were reduced in brain slices from 15 day-old PDC-deficient females. Histological analyses showed alterations in several structures in white and gray matters in 35 day-old PDC-deficient females. Reduction in total cell number and reduced dendritic arbors in Purkinje neurons were observed in PDC-deficient females. Furthermore, cell proliferation, migration and differentiation into neurons by newly generated cells were reduced in the affected females during pre- and postnatal periods. PDC-deficient mice had normal locomotor activity in a novel environment but displayed decreased startle responses to loud noises and there was evidence of abnormal pre-pulse inhibition of the startle reflex.CONCLUSIONSThe results show that a reduction in glucose metabolism resulting in deficit in energy production and fatty acid biosynthesis impairs cellular differentiation and brain development in PDC-deficient mice.

The ability of locomotor activity in a novel environment (Loco) and visual stimulus reinforcement (VSR) to predict acquisition of responding for cocaine and water reinforcers in the absence of explicit audiovisual signals was evaluated.In Experiment 1 (Exp 1), rats (n = 60) were tested for VSR, followed by Loco, and finally acquisition of responding for cocaine (0.3 mg/kg/inf). In Experiment 2 (Exp 2), rats (n = 32) were tested for VSR, followed by Loco, and finally acquisition of responding for water (0.01 mL/reinforcer).There were three main findings. First, Loco and VSR were significantly associated (Exp 1: r = 0.49, p 0.00; Exp 2: r = 0.35, p 0.05). Second, neither Loco (r = .00, p = 0.998) nor VSR (r = -0.12, p = 0.352) predicted acquisition of cocaine SA. Third, in the subgroup of animals that acquired cocaine SA, VSR (r = 0.41, p 0.01) but not Loco (r = 0.28, p = 0.10) was positively associated with operant responding for cocaine. Both Loco and VSR (Loco: r = 0.37, p 0.04; VSR: r = 0.51, p 0.00) were positively associated with operant responding for water reinforcers.The results indicate that VSR is at least as good a predictor of cocaine reinforced responding as Loco. VSR was predictive of operant responding for both drug and water reinforcers, while Loco was found to be predictive of responding only for water reinforcers. In studies that present visual stimuli in association with drug delivery, Loco may be predicting acquisition of responding for VSR rather than drug.

Background Light onset can be both a sensory reinforcer (SR) with intrinsic reinforcing properties, and a conditioned reinforcer (CR) which predicts a biologically important reinforcer. Stimulant drugs, such as methamphetamine (METH), may increase the reinforcing effectiveness of CRs by enhancing the predictive properties of the CR. In contrast, METH-induced increases in the reinforcing effectiveness of SRs, are mediated by the immediate sensory consequences of the light. Methods The effects of novelty (on SRs) and METH (on both CRs and SRs) were tested. Experiment 1: rats were pre-exposed to 5 s light and water pairings presented according to a variable-time (VT) 2 min schedule or unpaired water and light presented according to independent, concurrent VT 2 min schedules. Experiment 2: rats were pre-exposed to 5 s light presented according to a VT 2 min schedule, or no stimuli. In both experiments, the pre-exposure phase was followed by a test phase in which 5 s light onset was made response-contingent on a variable-interval (VI) 2 min schedule and the effects of METH (0.5 mg/kg) were determined. Results Novel light onset was a more effective reinforcer than familiar light onset. METH increased the absolute rate of responding without increasing the relative frequency of responding for both CRs and SRs. Conclusion Novelty plays a role in determining the reinforcing effectiveness of SRs. The results are consistent with the interpretation that METH-induced increases in reinforcer effectiveness of CRs and SRs may be mediated by immediate sensory consequences, rather than prediction.

The term “sensory reinforcer” has been used to refer to sensory stimuli (e.g. light onset) that are primary reinforcers in order to differentiate them from other more biologically important primary reinforcers (e.g. food and water). Acquisition of snout poke responding for a visual stimulus (5 s light onset) with fixed ratio 1 (FR 1), variable-interval 1 min (VI 1 min), or variable-interval 6 min (VI 6 min) schedules of reinforcement was tested in three groups of rats ( n = 8/group). The VI 6 min schedule of reinforcement produced a higher response rate than the FR 1 or VI 1 min schedules of visual stimulus reinforcement. One explanation for greater responding on the VI 6 min schedule relative to the FR 1 and VI 1 min schedules is that the reinforcing effectiveness of light onset habituated more rapidly in the FR 1 and VI 1 min groups as compared to the VI 6 min group. The inverse relationship between response rate and the rate of visual stimulus reinforcement is opposite to results from studies with biologically important reinforcers which indicate a positive relationship between response and reinforcement rate. Rapid habituation of reinforcing effectiveness may be a fundamental characteristic of sensory reinforcers that differentiates them from biologically important reinforcers, which are required to maintain homeostatic balance.

The human personality trait of sensation seeking (SS) indicates an attraction to novel sensations and experiences, and is associated with greater likelihood of drug abuse. In rodents, locomotor activity in a novel environment (Loco) has been found to predict drug self-administration (SA), and has been hypothesized to be a translational model of human SS. Previously, we reported (Gancarz et al., 2011) that high responder (HR) animals responded more than low responder (LR) animals to produce a response contingent light onset. The primary goal of this paper was a detailed analysis of the association between Loco and light contingent responding in a large sample of rats (n = 93).Male rats were pre-exposed to dark operant test chambers for ten 30 min sessions and baseline levels of responding (snout poking) were determined. The pre-exposure phase was followed by 6 sessions during which active responding produced a visual sensory reinforcer (VSR; 5 s light onset) according to a variable interval 1 min schedule of reinforcement. After completion of the VSR phase, Loco was tested.The activating effects (total responding) of light were associated with Loco, but the response guiding effects (proportion of active responding) of the light were not. In addition, HR rats habituated more slowly in both the VSR and Loco tests than LR rats.These data indicate that VSR measures aspects of the rodent’s response to novel sensations and experiences that are not detected by Loco. These data provide some evidence for the use of light reinforcement as an animal model of SS.

A between-session progressive ratio (BtwPR) procedure was tested in rats responding for cocaine and water reinforcers.Experiment 1 evaluated the sensitivity of the BtwPR procedure to the magnitude of cocaine and water reinforcers. Experiment 2 compared BtwPR performance to within-session progressive ratio (WinPR) performance.In experiment 1, rats were tested on a BtwPR procedure with three doses of cocaine (0.1, 0.3, and 1.0 mg/kg/inf) or volumes of water (0.01, 0.03, and 0.1 mL/reinforcer). BtwPR test sessions began with a seeking phase, during which the animal is required to complete a fixed ratio in order to initiate a 2-h consumption phase, where the reinforcer was available according to a fixed ratio 1 (FR1) schedule. Failure to complete the seeking ratio, which was increased after each test session, determined the breakpoint (BP). In experiment 2, the same BtwPR procedure was used except that the consumption phase was a WinPR schedule of reinforcement for cocaine (1.0 mg/kg/inf) or water (0.1 mL) reinforcers.BtwPR BPs increased as a function of the magnitude of both cocaine and water reinforcers. The BtwPR produced smaller BPs than the WinPR for cocaine reinforcers. In contrast, the BtwPR produced larger BPs than the WinPR for water reinforcers. One possible explanation is that priming and response activating effects of the cocaine reinforcer increased the WinPR BP. BtwPR and WinPR procedures may measure different aspects of drug-seeking.

We describe an interresponse-time analysis of performance on a differential-reinforcement-of-low-rate 72-s schedule. This analysis compares the obtained interresponse-time distribution of individual rats to a corresponding random interresponse-time distribution. The random interresponse-time distribution is a negative exponential probability function; it predicts the relative distribution of interresponse times if the rat emitted the same number of responses randomly (i.e., with a constant probability) with respect to time. The analysis provides quantitative measures of peak location and dispersion of the interresponse times toward random performance. In Experiment 1, an unexpected outcome of this analysis was that the rats would have obtained more reinforcers had they responded at the same rate but randomly. Based on the interresponse-time analysis in Experiment 1, it was shown that rats trained on the differential-reinforcement-of-low-rate 72-s schedule could increase the number of reinforcers obtained in two ways: first, by a coherent shift of the interresponse-time distribution toward longer durations and, second, by dispersal of the interresponse times toward a random interresponse-time distribution. Experiment 2 applied the analysis described in Experiment 1 to the effects of desipramine and gepirone. Both drugs decreased response rate and increased reinforcement rate, but their effects on the distribution of interresponse times were different. The increase in reinforcement rate observed with desipramine was accompanied by a coherent shift of the reinforcement rate observed with gepirone was accompanied by dispersal of the interresponse-time distribution toward the random negative exponential prediction.

Both humans and non-humans discount the value of rewards that are delayed or uncertain, and individuals that discount delayed rewards at a relatively high rate are considered impulsive. To investigate the neural mechanisms that mediate delay discounting, the present study examined the effects of excitotoxic lesions of the nucleus accumbens (NAC) on discounting of reward value by delay and probability. Rats were trained on delay ( n = 24) or probability discounting ( n = 24) tasks. Following training, excitotoxic lesions of the NAC were made by intracranial injections of 0.5 μl 0.15 M quinolinic acid ( n = 12) or vehicle ( n = 12) aimed at the NAC (AP +1.6, ML ±1.5, DV −7.1). NAC lesions did not alter performance in animals tested with a constant delay (4 s) or probability (0.4) of reinforcement. However, when tested with between session changes in the delay (0, 1, 2, 4, and 8 s) of reinforcement, the lesioned rats had flatter discount curves than the sham group, indicating that they were less sensitive to frequent changes in the delay to reward. In contrast, the NAC lesions did not affect discounting of probabilistic rewards. NAC lesions impaired the ability to adapt to frequent between session changes in the delay to reward but did not increase or decrease discounting when the delay was held constant across sessions. NAC lesions may disrupt the ability of the animals to predict the timing of delayed rewards when the delay to reward is changed frequently.

This study investigated the acute effects of delta(9)-tetrahydrocannabinol (THC) on four behavioral measures of impulsivity in recreational marijuana users. Although impulsive behavior has been studied using several different measures of impulsivity, few studies have utilized more than one of these measures on a single cohort. In this study, 37 healthy men and women participated in three sessions, in which they received capsules containing placebo, 7.5, or 15 mg THC in randomized order under double-blind conditions. Subjects were tested on the following four tasks: the Stop task, which measures the ability to inhibit a prepotent motor response; a Go/no-go task; a Delay discounting task, which measures the value of delayed or uncertain reinforcers; and a time estimation task, which measures alterations in time perception through a time reproduction procedure. Subjects also completed mood questionnaires and general measures of performance. THC produced its expected effects on subjective measures including increases in ARCI euphoria and marijuana scales. THC increased impulsive responding on the Stop task but did not affect performance on either the Go/no-go or Delay or Probability discounting tasks. On the time reproduction task, THC increased estimates of the duration of short intervals while not affecting estimates of longer intervals. There were no significant correlations between the four tasks either before or after drug administration. These results suggest that THC may increase certain forms of impulsive behavior while not affecting other impulsive behaviors. The dissociations between the four measures of impulsivity suggest that impulsivity is an assemblage of distinct components rather than a unitary process.

This study investigated the acute behavioral effects of d-amphetamine on several behavioral indices of impulsivity. Impulsivity has been defined, variously, as difficulty in inhibiting inappropriate behaviors, inability to wait, insensitivity to delayed consequences or an alteration in the perception of time; standardized procedures have been developed to measure these behavioral dimensions. However, it is not known how drugs affect these measures, and few studies have examined more than one measure in a single study. In this study, 36 healthy men and women participated in three sessions, in which they received placebo, 10 mg, or 20 mg d-amphetamine in randomized order. On each session they performed the following five tasks: the Stop Task, which measures behavioral inhibition, a delay discounting task, which measures the relative value of immediate vs. delayed rewards, a delay of gratification task, a Go/No-Go task, and a time estimation task. Subjects also completed mood questionnaires. Amphetamine produced its expected subjective, mood-altering effects, including increases in POMS Friendliness and Elation scales, and ARCI Euphoria and Stimulant scales. On the measures of impulsivity, amphetamine decreased impulsive responding on three of the tasks: on the Stop Task it decreased Stop reaction times without affecting Go reaction time, on the Go/No-Go task, it decreased the number of false alarms, and on the delay discounting measure, amphetamine (20 mg) decreased k values indicating less discounting of delayed reward. Other measures of impulsive behavior were unaffected. These results suggest that acute doses of amphetamine decrease several forms of impulsive behavior. These findings extend and confirm previous findings in humans and laboratory animals.

Experiment I investigated the effects of reinforcer magnitude on differential-reinforcement-of-low-rate (DRL) schedule performance in three phases. In Phase 1, two groups of rats (n = 6 and 5) responded under a DRI. 72-s schedule with reinforcer magnitudes of either 30 or 300 microl of water. After acquisition, the water amounts were reversed for each rat. In Phase 2, the effects of the same reinforcer magnitudes on DRL 18-s schedule performance were examined across conditions. In Phase 3, each rat responded unider a DR1. 18-s schedule in which the water amotnts alternated between 30 and 300 microl daily. Throughout each phase of Experiment 1, the larger reinforcer magnitude resulted in higher response rates and lower reinforcement rates. The peak of the interresponse-time distributions was at a lower value tinder the larger reinforcer magnitude. In Experiment 2, 3 pigeons responded under a DRL 20-s schedule in which reinforcer magnitude (1-s or 6-s access to grain) varied iron session to session. Higher response rates and lower reinforcement rates occurred tinder the longer hopper duration. These results demonstrate that larger reinforcer magnitudes engender less efficient DRL schedule performance in both rats and pigeons, and when reinforcer magnitude was held constant between sessions or was varied daily. The present results are consistent with previous research demonstrating a decrease in efficiency as a function of increased reinforcer magnituide tinder procedures that require a period of time without a specified response. These findings also support the claim that DRI. schedule performance is not governed solely by a timing process.

An adjusting-amount procedure was used to measure discounting of reinforcer value by delay. Eight rats chose between a varying amount of immediate water and a fixed amount of water given after a delay. The amount of immediate water was systematically adjusted as a function of the rats' previous choices. This procedure was used to determine the indifference point at which each rat chose the immediate amount and the delayed amount with equal frequency. The amount of immediate water at this indifference point was used to estimate the value of the delayed amount of water. In Experiment 1, the effects of daily changes in the delay to the fixed reinforcer (100 microliters of water delivered after 0, 2, 4, 8, or 16 s) were tested. Under these conditions, the rats reached indifference points within the first 30 trials of each 60-trial session. In Experiment 2, the effects of water deprivation level on discounting of value by delay were assessed. Altering water deprivation level affected the speed of responding but did not affect delay discounting. In Experiment 3, the effects of varying the magnitude of the delayed water (100, 150, and 200 microliters) were tested. There was some tendency for the discounting function to be steeper for larger than for smaller reinforcers, although this difference did not reach statistical significance. In all three experiments, the obtained discount functions were well described by a hyperbolic function. These experiments demonstrate that the adjusting-amount procedure provides a useful tool for measuring the discounting of reinforcer value by delay.

Peak deviation analysis is a quantitative technique for characterizing interresponse-time distributions that result from training on differential-reinforcement-of-low-rate schedules of reinforcement. It compares each rat's obtained interresponse-time distribution to the corresponding negative exponential distribution that would have occurred if the rat had emitted the same number of responses randomly in time, at the same rate. The comparison of the obtained distributions with corresponding negative exponential distributions provides the basis for computing three standardized metrics (burst ratio, peak location, and peak area) that quantitatively characterize the profile of the obtained interresponse-time distributions. In Experiment 1 peak deviation analysis quantitatively described the difference between the interresponse-time distributions of rats trained on variable-interval 300-s and differential-reinforcement-of-low-rate 72-s schedules of reinforcement. In Experiment 2 peak deviation analysis differentiated between the effects of the psychomotor stimulant d-amphetamine, the anxiolytic compound chlordiazepoxide, and the antidepressant desipramine. The results suggest that peak deviation analysis of interresponse-time distributions may provide a useful behavioral assay system for characterizing the effects of drugs.

Rats were trained to turn for water reinforcement and then were given unilateral 6- hydroxydopamine lesions. After lesion, rats showed deficits in trained turning both contraand ipsilateral to the side of the lesion, with contralateral turning more severely impaired. The lesioned rats were then transplanted with fetal mesencephalic dopamine tissue into striatum. A control group of lesioned rats were sham transplanted. Four weeks after transplant, 1.5 mg/kg D-amphetamine challenge injections were used to test the functioning of the transplants. In the control rats, D-amphetamine induced ipsilateral turning; in transplanted rats, D-amphetamine slowed the rate of ipsilateral turning or reversed the direction of amphetamine-induced rotation. Only rats which reversed their, amphetamine-induced turn direction after transplant were used for the rest of the experiment. Trained turning was assessed at 4, 8, 12 and 16 weeks post transplant. Transplants did not improve learned performance at any time post transplant. When D-amphetamine was administered in conjunction with the trained turning sessions, a low dose (0.12 mg/kg) enhanced contralateral trained turn rates, without affecting ipsilateral turn rates. Higher doses of amphetamine reduced ipsilateral turn rate in the transplanted animals. The results of this study suggest that transplants alone do not reinstate performance of conditioned rotation.