Friend recollections, and a collection of collaborations with Nadia

In this selective review article, we showcase our collaborations with our colleague, Dr. Nadia Chaudhri. Dr. Chaudhri was an esteemed colleague and researcher who contributed greatly to our understanding of Pavlovian alcohol conditioning. From 2014 to 2019, we collaborated with Nadia. Here, we reflect on our friendship, the work we did together, and the continued impact on the field

Cue-alcohol associative learning in female rats

The ability of environmental cues to trigger alcohol seeking behaviors is believed to facilitate problematic alcohol use. We previously showed that the development of this cue-evoked alcohol approach reflects cue-alcohol learning and memory in the adult male rat; however, we do not know whether the same is true for similarly aged female rats. Consequently, adult Long-Evans female rats were allowed to drink unsweetened alcohol in the homecage (MWF 24 hr two-bottle choice, 5 weeks) and subsequently split into two experimental groups: paired and unpaired. Groups were matched for ingested doses and alcohol bottle preference across the pre-conditioning homecage period. Both groups were trained in conditioning chambers using a Pavlovian procedure. For the paired group, the chamber houselight was illuminated to signal access to an alcohol sipper. Houselight onset was yoked for the unpaired group, but access to the alcohol sipper was scheduled to occur only during the intervening periods (in the absence of light). We found that in the paired, but not unpaired group, an alcohol approach reaction was conditioned to houselight illumination, and the level of cue-conditioned reactivity predicted drinking behavior within trials. Groups experienced equivalently low but non-negligible blood alcohol concentrations over the course of conditioning sessions. We conclude that cue-triggered alcohol seeking behavior in adult female rats reflects associative learning about the relationship between alcohol availability and houselight illumination

Acute phenylalanine/tyrosine depletion of phasic dopamine in the rat brain

Dopamine plays a critical role in striatal and cortical function, and depletion of the dopamine precursors phenylalanine and tyrosine is used in humans to temporarily reduce dopamine and probe the role of dopamine in behavior. This method has been shown to alter addiction-related behaviors and cognitive functioning presumably by reducing dopamine transmission, but it is unclear what specific aspects of dopamine transmission are altered

Alcohol-associated antecedent stimuli elicit alcohol seeking in non-dependent rats and may activate the insula

Alcohol self-administration produces brain and behavior adaptations that facilitate a progressive loss of control over drinking and contribute to relapse. One possible adaptation is the ability of antecedent environmental stimuli that are consistently paired with alcohol to trigger alcohol seeking behaviors. We previously modeled this adaptation in rats using a Pavlovian conditioning procedure in which illumination of a houselight preceded the presentation of a sipper tube that produced unsweetened alcohol when licked. However, in our previous work we did not demonstrate whether this adaptation represented a consequence of repeated exposure to alcohol or the houselight, or whether it was the consequence of associative learning and memory. Thus, in the present study, we tested the associative basis of alcohol seeking in response to houselight illumination in our task using adult male rats that were not food or water deprived and were not dependent on alcohol. Separate groups of rats received houselight illumination that was explicitly paired or unpaired with presentation of the retractable sipper that provided access to unsweetened alcohol. Our primary dependent variable was appetitive alcohol-directed behavior: the frequency of movement toward and interaction with the hole in the wall of the chamber through which the sipper was presented during the period of houselight illumination trial before each sipper presentation. However, we also analyzed consummatory sipper licking behavior and blood ethanol concentration in the same rats. Finally, we explored the brain basis of cue-elicited alcohol seeking using c-Fos immunohistochemistry. Our findings confirmed the associative basis of cue-elicited alcohol seeking in our paradigm and mapped these onto the insular cortex, suggesting a role for this brain region in early stages of brain and behavior adaptation to regular alcohol us

Ethanol Seeking by Long Evans Rats Is Not Always a Goal-Directed Behavior

Background -- Two parallel and interacting processes are said to underlie animal behavior, whereby learning and performance of a behavior is at first via conscious and deliberate (goal-directed) processes, but after initial acquisition, the behavior can become automatic and stimulus-elicited (habitual). With respect to instrumental behaviors, animal learning studies suggest that the duration of training and the action-outcome contingency are two factors involved in the emergence of habitual seeking of “natural” reinforcers (e.g., sweet solutions, food or sucrose pellets). To rigorously test whether behaviors reinforced by abused substances such as ethanol, in particular, similarly become habitual was the primary aim of this study. Methodology/Principal Findings -- Male Long Evans rats underwent extended or limited operant lever press training with 10% sucrose/10% ethanol (10S10E) reinforcement (variable interval (VI) or (VR) ratio schedule of reinforcement), or with 10% sucrose (10S) reinforcement (VI schedule only). Once training and pretesting were complete, the impact of outcome devaluation on operant behavior was evaluated after lithium chloride injections were paired with the reinforcer, or unpaired 24 hours later. After limited, but not extended instrumental training, lever pressing by groups trained under VR with 10S10E and under VI with 10S was sensitive to outcome devaluation. In contrast, responding by both the extended and limited training 10S10E VI groups was not sensitive to ethanol devaluation during the test for habitual behavior. Conclusions/Significance -- Operant behavior by rats trained to self-administer an ethanol-sucrose solution showed variable sensitivity to a change in the value of ethanol, with relative insensitivity developing sooner in animals that received time-variable ethanol reinforcement during training sessions. One important implication, with respect to substance abuse in humans, is that initial learning about the relationship between instrumental actions and the opportunity to consume ethanol-containing drinks can influence the time course for the development or expression of habitual ethanol seeking behavior.Research support was provided by awards T32AA007471, F32AA018252, and R37AA011852 from the National Institute on Alcohol and Alcohol Abuse (http://www.niaaa.nih.gov) and HRD-0703584 from the National Science Foundation (www.nsf.gov). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Pharmac

Experimental groups and representative sequence of training parameters.

a<p>Values listed for the reinforcement schedules are the average of the programmed values used to determine the time interval (seconds) before a single press yielded reinforcement for the VI groups, or the number of lever presses required to yield reinforcement for the VR groups. From session 7 on, the average ratio was 5 for some VR animals (n = 2 extended training, 11 limited training).</p>b<p>Drinking solutions were always 10% sucrose (w/v), with either 0% or 10% ethanol (vol/vol), as shown. In the limited training 10S10E groups, some animals received one additional session with 10S before transitioning to 10S10E.</p>c<p>Extended training continued with the same parameters for an additional 9 sessions, and limited training with no more than 1 additional session, before extinction and retraining (depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042886#pone-0042886-g001" target="_blank">Figure 1</a> and described in Behavioral methods).</p

Limited training: Instrumental seeking behavior.

<p>(A, C, E): Lever presses (per 4 minute bin of reinforced session) for the unpaired conditions (open symbols) of the 10S10E VI (A), 10S VI (C), and 10S10E VR (E) groups, before (dashed line) and after (solid line) LiCl treatment. (B, D, F): Lever presses (per 4 minute bin of reinforced session) for the paired conditions (filled symbols) of the 10S10E VI (B), 10S VI (D), and 10S10E VR (F) groups before (dashed line) and after (solid line) LiCl treatment.</p

Extended training: Instrumental seeking behavior.

<p>(A, C, E): Lever presses (per 4 minute bin of reinforced session) for the unpaired conditions (open symbols) of the 10S10E VI (A), 10S VI (C), and 10S10E VR (E) groups, before (dashed line) and after (solid line) LiCl treatment. (B, D, F): Lever presses (per 4 minute bin of reinforced session) for the paired conditions (filled symbols) of the 10S10E VI (B), 10S VI (D), and 10S10E VR (F) groups before (dashed line) and after (solid line) LiCl treatment.</p

Extended instrumental lever press training.

<p>Total presses per session, for each group (10S10E VI, squares; 10S VI, circles; and 10S10E VR, triangles) across baseline training. Symbols filled with grey indicate sessions with 10S reinforcement; black filled symbols represent sessions with 10S10E reinforcement. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042886#pone-0042886-t001" target="_blank">Table 1</a> describes the progression of reinforcement schedules.</p

Limited training: Paired vs. unpaired LiCl treatment.

<p>(A–C): Extinction test responses (total lever presses, expressed as percent of pre-LiCl session). Paired LiCl condition (filled bars) was not different from unpaired LiCl condition (open bars), for the 10S10E VI group (A), but was for the 10S VI (B) and the 10S10E VR (C) groups. (D–F): Reacquisition test measures (totals, expressed as percent of final pre-LiCl training session): lever presses (left), reinforcers delivered (center) and licks (right). All measures were significantly reduced in the paired LiCl condition (filled bars) compared to the unpaired LiCl condition (open bars), for the 10S10E VI (D), the 10S VI (E), and the 10S10E VR (F) groups. *, P<0.05; ***, P<0.001, paired vs. unpaired. Bars represent mean+s.e.m.</p