Investigating the sex-specific effects of socialization on voluntary ethanol self-administration in rats using the vapor chamber

ABSTRACTIntroductionPeer interactions are a crucial part of social and personal development, particularly during adolescence. Adolescence is characterized as a transitional developmental period between childhood and adulthood that is often associated with increased freedom, self-exploration, and novel experiences that are frequently peer-influenced. Due to newfound independence, there is a higher prevalence of alcohol consumption, which is in part due to the heightened social facilitating and rewarding effects of alcohol. Previous work shows that males and females who consume excessive alcohol during adolescence are at an increased risk of developing an alcohol use disorder (AUD) later in life. However, the contributions of social interaction and sexual dimorphism in alcohol consumption, two driving factors that influence AUD risk, are not fully understood. Many current rat models used to study the characteristics of alcohol use and the emergence of AUD coerce the animals into consuming liquid ethanol by the addition of a sweetener, which has been proven to confound results in adolescent rats. Here we use a novel self-administration ethanol vapor system to investigate the sexual dimorphic nature of socially facilitated ethanol consumption without the addition of sweeteners.MethodsAdolescent and adult male and female Sprague-Dawley rats underwent a novel voluntary chronic intermittent self-administration ethanol vapor paradigm. Nose poke-initiated self-administration vapor chambers (La Jolla Alcohol Research, Inc.) administered 20mg/L of vaporized ethanol or air (control) into the chamber in response to each individual nose poke. Beginning on postnatal day (PND) 30 or PND70, animals were placed in vapor chambers for 4 hours every other day for a total of 40 sessions. All animals underwent 10 sessions with their cagemate (social access) followed by 10 sessions in isolation (isolated access), a 10 day forced abstinence period, 10 sessions in isolation (isolated access), and 10 sessions with their cagemate (social access).ResultsFemale rats consumed more alcohol per body weight than age-matched males, while male rats increased ethanol preference over sessions regardless of age. In addition, all rats regardless of sex or age consumed more ethanol per body weight during the first social access session than during the subsequent isolated access sessions. Interestingly, there was an increase in ethanol consumption in adult male and females during the second social access session compared to the previous isolated access session that was not observed in either adolescent groups.ConclusionThese data demonstrate that female and male rats, regardless of age, are vulnerable to socially facilitated ethanol consumption. This is consistent with human data showing that increased levels of alcohol consumption among adolescents and young adults is associated with high levels of alcohol use within their social group (Sudhinaraset, Wigglesworth, & Takeuchi, 2016). However, only male rats demonstrate escalation across sessions. This may indicate that male rats are more vulnerable to escalated drinking and the emergence of ethanol dependence compared to females regardless of peer interaction. These data demonstrate that the self-administration ethanol vapor system is an effective alternative to other methods of voluntary ethanol administration for investigating factors that contribute to alcohol use and escalation.

Interval Timing and Motivation are Dissociable when Interval-Initiating Responses are Discriminable from Target Responses

Data have accumulated suggesting that motivation and timing are correlated processes, yet few studies have tested whether motivation and timing are procedurally dissociable. This may be attributed to the fact that the most common framework in which to study timing, the pacemaker-accumulator model, does not readily suggest a route by which to dissociate motivation and timing. In contrast, the behavioral systems framework suggests that motivation and timing could be dissociated if subjects were trained in response-initiated (RI) interval-timing procedures rather than in common externally-initiated (EI) procedures. RI procedures were predicted to enhance temporal control and yield timing performance robust to fluctuations in motivation. Experiment 1 tested this hypothesis by training rats to either initiate switch-timing trials with a single press on the lever associated with the shorter FI schedule (SL-RI), or wait for switch-timing trials to be initiated (EI). Motivation was varied through pre-feeding. SL-RI and EI rats showed similar levels of temporal control and sensitivity to pre-feeding in their switch-timing performance. Experiment 2 tested a revised RI hypothesis, the discriminative-RI hypothesis, which predicts that as the trial-initiating response becomes progressively different from target responses, motivation and timing are increasingly dissociated. This experiment replicated Experiment 1 and added a trial-initiating condition in which a nose-poke into a nose port (NP-RI) initiated trials. As predicted, the sensitivity of switching-timing performance to pre-feeding scaled such that EI > SL-RI > NP-RI. These data suggest that it is possible to dissociate timing and motivation, challenging the notion that these processes are correlated.

Novel nose poke-based temporal discrimination tasks with concurrent in vivo calcium imaging in freely moving mice

The hippocampus has been known to process temporal information as part of memory formation. While time cells have been observed in the hippocampus and medial entorhinal cortex, a number of the behavioral tasks used present potential confounds that may cause some contamination of time cell observations due to animal movement. Here, we report the development of a novel nose poke-based temporal discrimination task designed to be used with in vivo calcium imaging for the analysis of hippocampal time cells in freely moving mice. First, we developed a ten second held nose poke paradigm for use in mice to deliver a purer time metric for the analysis of time cell activity in hippocampus CA1. Second, we developed a temporal discrimination task that involves the association of held nose poke durations of differing lengths with differential spatial cues presented in arms on a linear I-maze. Four of five mice achieved successful temporal discrimination within three weeks. Calcium imaging has been successfully performed in each of these tasks, with time cell activity being detected in the 10s nose poke task, and calcium waves being observed in discrete components of the temporal discrimination task. The newly developed behavior tasks in mice serve as novel tools to accelerate the study of time cell activity and examine the integration of time and space in episodic memory formation.

Nestin Null Mice Show Improved Reversal Place Learning

The intermediate filament protein nestin is expressed by neural stem cells, but also by some astrocytes in the neurogenic niche of the hippocampus in the adult rodent brain. We recently reported that nestin-deficient (Nes−/−) mice showed increased adult hippocampal neurogenesis, reduced Notch signaling from Nes−/− astrocytes to the neural stem cells, and impaired long-term memory. Here we assessed learning and memory of Nes−/− mice in a home cage set up using the IntelliCage system, in which the mice learn in which cage corner a nose poke earns access to drinking water. Nes−/− and wildtype mice showed comparable place learning assessed as the incorrect corner visit ratio and the incorrect nose poke ratio. However, during reversal place learning, a more challenging task, Nes−/− mice, compared to wildtype mice, showed improved learning over time demonstrated by the incorrect visit ratio and improved memory extinction over time assessed as nose pokes per visit to the previous drinking corner. In addition, Nes−/− mice showed increased explorative activity as judged by the increased total numbers of corner visits and nose pokes. We conclude that Nes−/− mice exhibit improved reversal place learning and memory extinction, a finding which together with the previous results supports the concept of the dual role of hippocampal neurogenesis in cognitive functions.

Dynamics of Spatio-Temporal Binding in Rats

Time and space are commonly approached as two distinct dimensions, and rarely combined together in a single task, preventing a comparison of their interaction. In this project, using a version of a timing task with a spatial component, we investigate the learning of a spatio-temporal rule in animals. To do so, rats were placed in front of a five-hole nose-poke wall in a Peak Interval (PI) procedure to obtain a reward, with two spatio-temporal combination rules associated with different to-be-timed cues and lighting contexts. We report that, after successful learning of the discriminative task, a single Pavlovian session was sufficient for the animals to learn a new spatio-temporal association. This was seen as evidence for a beneficial transfer to the new spatio-temporal rule, as compared to control animals that did not experience the new spatio-temporal association during the Pavlovian session. The benefit was observed until nine days later. The results are discussed within the framework of adaptation to a change of a complex associative rule involving interval timing processes.

Activation of serotonin neurons promotes active exploitation in a probabilistic foraging task

The neuromodulator serotonin (5-HT) has been implicated in a variety of functions that involve patience or impulse control. For example, activation of 5-HT neurons promotes waiting for delayed rewards. Many of these effects are consistent with a long-standing theory that 5-HT promotes behavioral inhibition, a motivational bias favoring passive over active behaviors. To further test this idea, we studied the impact of 5-HT in a probabilistic foraging task, in which mice must learn the statistics of the environment and infer when to leave a depleted foraging site for the next. Critically, mice were required to actively nose poke in order to exploit a given site. We found that optogenetic activation of 5-HT neurons in the dorsal raphe nucleus increased the willingness of mice to actively attempt to exploit a reward site before giving up. These results indicate that behavioral inhibition is not an adequate description of 5-HT function and suggest that a unified account must be based on a higher-order function.

Influence of General Anesthesia on Impulsivity and Learning Ability-Experimental Study

Objective: To investigate the effect of anesthesia on rats’ ability of learning and over their impulsivity.Material and Methods: We studied eight Wistar adult male rats, test and drug naive subjects. Animals were separated in two groups, group A and B with four members each. Group A included the anesthetized animals. The combination of ketamine, xylazine and piplophen in 2ml/kg body weight dosage was used and testing was done 24 hours after anesthesia. Group B was taken as control. The study was conducted using the ”Delay discounting” apparatus. Experiments assessing impulsive behavior were conducted using automated operant chambers, equipped with two nose-poke holes (holes where pellets of food were released). Rat’s answer was considered touching the nose-poke hole. One answer was rewarded with pellets of food of 45 mg each (small reward), while another hole released five pellets of 45 mg each (high reward). Both types of rewards were presented immediately after rat’s answer and were followed for a period of 25 seconds timeout. During the training phase, rats were placed in operant chambers 30 minutes per day, 5 consecutive days. The growing percent of preference for greater reward indicates learning. For the testing phase the procedure was similar, but a delay was introduced before the release of the big reward. During this phase, the preference for higher reward was indicative for non-impulsive behaviour.Results: The results didn’t show significant statistically differences between the two groups.Conclusions: Anesthesia had no effect on learning ability nor on impulsivity.