Impulsive rats are less maternal.

Early life environment and maternal care can have long-lasting effects on behavior and physiology. Previously, we found that compared to mother-reared (MR) female rats, rats reared without mothers, siblings, and nest, through artificially rearing (AR), show reduced levels of maternal behavior when they grow up. These effects can be reversed if AR pups are provided with extra “licking-like” tactile stimulation during the preweaning period [Gonzalez et al. [2001] Developmental Psychobiology, 38(1), 11–42]. We also found that AR rats are more action impulsive and have reduced attentional capacities in comparison to their MR siblings [Lovic, Fletcher, & Fleming, in preparation; Lovic & Fleming [2004] Behavioural Brain Research 148: 209–219]. However, it is unknown whether increased impulsivity contributes to reduced levels of maternal behaviors. The purpose of this study was to assess the relationship between impulsivity and maternal behavior in AR and MR rats. Female rats were reared with (MR) or without mothers (AR) and half of the AR rats received additional stroking stimulation. As adults, AR and MR rats were mated and maternal behavior towards their own pups was assessed. In addition, rats were assessed on impulsive action (differential reinforcement of low-rate schedule; DRL-20s). Consistent with previous findings, AR rats were both less maternal and more action impulsive than MR rats. Partial correlations revealed that impulsivity was inversely related to pup licking-impulsive rats were less maternal. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53: 13–22, 2011.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78484/1/20481_ftp.pd

Quantifying Individual Variation in the Propensity to Attribute Incentive Salience to Reward Cues

If reward-associated cues acquire the properties of incentive stimuli they can come to powerfully control behavior, and potentially promote maladaptive behavior. Pavlovian incentive stimuli are defined as stimuli that have three fundamental properties: they are attractive, they are themselves desired, and they can spur instrumental actions. We have found, however, that there is considerable individual variation in the extent to which animals attribute Pavlovian incentive motivational properties (“incentive salience”) to reward cues. The purpose of this paper was to develop criteria for identifying and classifying individuals based on their propensity to attribute incentive salience to reward cues. To do this, we conducted a meta-analysis of a large sample of rats (N = 1,878) subjected to a classic Pavlovian conditioning procedure. We then used the propensity of animals to approach a cue predictive of reward (one index of the extent to which the cue was attributed with incentive salience), to characterize two behavioral phenotypes in this population: animals that approached the cue (“sign-trackers”) vs. others that approached the location of reward delivery (“goal-trackers”). This variation in Pavlovian approach behavior predicted other behavioral indices of the propensity to attribute incentive salience to reward cues. Thus, the procedures reported here should be useful for making comparisons across studies and for assessing individual variation in incentive salience attribution in small samples of the population, or even for classifying single animals

The Effects of Maternal Deprivation, Through Artificial Rearing, on Impulsiveness in Rats

Mammalian brain and behaviour are plastic, particularly early in development when offspring are under the care of their mothers. Adverse early life events, such as maternal and social deprivation, have short- and long-term consequences for neurobiology and consequently for behaviour. The purpose of this thesis was to investigate the effects of maternal and social deprivation, through artificial rearing (AR), on adult impulsive behaviour. Rats were raised in isolation from mothers and siblings (AR) or with their mothers and siblings in the nest [maternal rearing (MR)]. In addition, half of the AR rats were provided with replacement somatosensory stimulation designed to simulate mothers’ licking (see Gonzalez et al., 2001). As adults, rats were tested on impulsive action using the differential reinforcement of low rates (DRL) operant task and locomotor activity. Both male and female AR rats were more impulsive than MR rats; they made more responses and they were less efficient at earning rewards. In addition, they displayed greater levels of locomotor activity. These effects were partially reversed by replacement somatosensory stimulation. Furthermore, impulsivity was positively correlated with locomotor activity. Impulsive choice was then assessed using a delay discounting operant schedule. On this task, AR rats were less likely to discount the value of large-delayed reward, suggesting that they were better able to tolerate delays to large reward and were less impulsive. However, performance on a modified version of delay discounting revealed that AR rats were less efficient at switching their responses; that is, they displayed reduced behavioural flexibility. To address this finding, impulsive choice was next assessed in fixed consecutive chain operant schedule of reinforcement, but there were no differences between AR and MR animals. Finally, the relationship between impulsive action and a species-characteristic behaviour, maternal behaviour, was investigated. Consistent with the literature, AR rats were less maternal and more impulsive. Moreover, there was a negative correlation between impulsivity and maternal behaviour. Overall, this set of studies demonstrates that maternal and social deprivation produces an increase in impulsive action without an effect on impulsive choice. Furthermore, increased action impulsiveness is a significant moderator of disrupted maternal behaviour observed in artificially reared rats.Ph

Functionally distinct dopamine signals in nucleus accumbens core and shell in the freely moving rat

Dynamic signaling of mesolimbic dopamine (DA) neurons has been implicated in reward learning, drug abuse, and motivation. However, this system is complex because firing patterns of these neurons are heterogeneous; subpopulations receive distinct synaptic inputs, and project to anatomically and functionally distinct downstream targets, including the nucleus accumbens (NAc) shell and core. The functional roles of these cell populations and their real-time signaling properties in freely moving animals are unknown. Resolving the real-time DA signal requires simultaneous knowledge of the synchronized activity of DA cell subpopulations and assessment of the down-stream functional effect of DA release. Because this is not yet possible solely by experimentation in vivo, we combine computational modeling and fast-scan cyclic voltammetry data to reconstruct the functionally relevant DA signal in DA neuron subpopulations projecting to the NAc core and shell in freely moving rats. The approach provides a novel perspective on real-time DA neuron firing and concurrent activation of presynaptic autoreceptors and postsynaptic targets. We first show that individual differences in DA release arise from differences in autoreceptor feedback. The model predicts that extracellular DA concentrations in NAc core result from constant baseline DA firing, whereas DA concentrations in NAc shell reflect highly dynamic firing patters, including synchronized burst firing and pauses. Our models also predict that this anatomical difference in DA signaling is exaggerated by intravenous infusion of cocaine.Lundbeck FoundationUniversity of Copenhagen (2016 Excellence Programme for Interdisciplinary Research (DSIN))National Institute on Drug Abuse (P01 DA031656

Correlations between Lever Contacts, CS Food Cup Entries, Inter-trial Interval (ITI) Food Cup Entries, and the PCA Scores on Day 1 (top) and Day 5 (bottom) of Pavlovian training.

<p>Legend: Numbers indicate Pearson's correlation coefficient (r) and those that are Italicized numbers indicate statistically significant correlations (ps<0.01) are italicized. The number inside parentheses denotes the day of Pavlovian training.</p

The distribution of PCA Index Scores in a sample of 1,878 rats. STs, GTs and INs are classed according to the criteria presented in Fig. 5.

<p>It is clear, based on these criteria, that STs and GTs represent different subpopulations of animals.</p

The distribution of PCA Scores across each of the 5 days of Pavlovian training, using the formula given in Table 1.

<p>The number of rats are binned according to their PCA Scores, which ranges from +1 to −1, with 0.1 bin sizes. The PCA Scores range from +1 to −1. Thus, the vertical axis shows the number of rats in each bin, and the horizontal axis the PCA Score. Note that PCA Score reveals two subpopulations of animals by Days 4 and 5 of training.</p

The propensity to approach a lever-CS predicts the ability of the same lever-CS to support learning a new instrumental response to get it (i.e., the ability of the lever-CS to act as a conditioned reinforcer).

<p>Data from Lomanowska et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038987#pone.0038987-Lomanowska1" target="_blank">[25]</a> were used to compare the effectiveness of the rank-order split and PCA Index methods to predict the ability of the CS to act as a conditioned reinforcer. For the rank-order split method, rats were classed as STs and GTs by totaling the number of lever contacts over 5 days of Pavlovian training and dividing the sample of animals tested into thirds. Panel A shows the correlation between active nose-pokes (minus inactive nose-pokes) on the test for conditioned reinforcement, as a function of total lever contacts. Panel B shows the same data, but when each animal's PCA Index Score was calculated and used to class animals. In both Panels red filled symbols indicate GTs, white symbols INs, and blue filled symbols STs, classed the two different ways. Horizontal lines depict group means. (Note that the sample sizes differ for the groups between the two methods; an equal number of STs and GTs cannot be assumed when using the PCA Index.).</p

Formulas for deriving the PCA Index Score.

<p>(n) = any particular test session.</p><p>x¯ = averaged Latency.</p><p>p| = probability.</p><p>Legend: The overall PCA Index Score, used for phenotype classification (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038987#pone-0038987-g006" target="_blank">Fig. 6</a>), was derived by averaging the individual PCA Scores for Days 4 and 5 of training. The PCA Score for each session was derived by averaging the three individual measures (Response Bias, Probability Difference, and Latency Score) for that particular session. Responses Bias is a proportion of lever presses/food cup entries in relation to the total number of responses. The Probability Difference was derived by subtracting the probability of food cup entries from the probability of lever presses. Latency score was the (averaged) difference between latencies to make food cup and lever responses (divided by the length of the CS duration; in this case 8 s).</p