Neurons of the Ventral Tegmental Area Encode Individual Differences in Motivational "Wanting" for Reward Cues.

It has been argued that the dopaminergic system is involved in the attribution of motivational value to reward predictive cues as well as prediction error. To evaluate, dopamine neurons were recorded from male rats performing a Pavlovian approach task containing cues that have both "predictive" and "incentive" properties. All animals learned the predictive nature of the cue (illuminated lever entry into cage), but some also found the cue to be attractive and were motivated toward it ("sign-trackers," STs). "Goal-trackers" (GTs) predominantly approached the location of reward receptacle. Rats were implanted with tetrodes for neural electrophysiological recordings in the ventral tegmental area. Cells were characterized by spike waveform shape and firing rate. Firing rates and magnitudes of responses in relation to Pavlovian behaviors, cue presentation, and reward delivery were assessed. We identified 103 dopamine and 141 nondopamine neurons. GTs and STs both showed responses to the initial lever presentation (CS1) and lever retraction (CS2). However, higher firing rates were sustained during the lever interaction period only in STs. Further, dopamine cells of STs showed a significantly higher proportion of cells responding to both CS1 and CS2. These are the first results to show that neurons from the VTA encode both predictive and incentive cues, support an important role for dopamine neurons in the attribution of incentive salience to reward-paired cues, and underscore the consequences of potential differences in motivational behavior between individuals.SIGNIFICANCE STATEMENT This project serves to determine whether dopamine neurons encode differences in cued approach behaviors and incentive salience. How neurons of the VTA affect signaling through the NAcc and subsequent dopamine release is still not well known. All cues that precede a reward are predictive in nature. Some, however, also have incentive value, in that they elicit approach toward them. We quantified the attribution of incentive salience through cue approach behavior and cue interaction, and the corresponding magnitude of VTA neural firing. We found dopamine neurons of the VTA encode strength of incentive salience of reward cues. This suggests that dopamine neurons specifically in the VTA encode motivation.

Neural Activity in the Ventral Pallidum Encodes Variation in the Incentive Value of a Reward Cue.

UNLABELLED: There is considerable individual variation in the extent to which reward cues are attributed with incentive salience. For example, a food-predictive conditioned stimulus (CS; an illuminated lever) becomes attractive, eliciting approach toward it only in some rats ("sign trackers," STs), whereas others ("goal trackers," GTs) approach the food cup during the CS period. The purpose of this study was to determine how individual differences in Pavlovian approach responses are represented in neural firing patterns in the major output structure of the mesolimbic system, the ventral pallidum (VP). Single-unit in vivo electrophysiology was used to record neural activity in the caudal VP during the performance of ST and GT conditioned responses. All rats showed neural responses to both cue onset and reward delivery but, during the CS period, STs showed greater neural activity than GTs both in terms of the percentage of responsive neurons and the magnitude of the change in neural activity. Furthermore, neural activity was positively correlated with the degree of attraction to the cue. Given that the CS had equal predictive value in STs and GTs, we conclude that neural activity in the VP largely reflects the degree to which the CS was attributed with incentive salience. SIGNIFICANCE STATEMENT: Cues associated with reward can acquire motivational properties (i.e., incentive salience) that cause them to have a powerful influence on desire and motivated behavior. There are individual differences in sensitivity to reward-paired cues, with some individuals attaching greater motivational value to cues than others. Here, we investigated the neural activity associated with these individual differences in incentive salience. We found that cue-evoked neural firing in the ventral pallidum (VP) reflected the strength of incentive motivation, with the greatest neural responses occurring in individuals that demonstrated the strongest attraction to the cue. This suggests that the VP plays an important role in the process by which cues gain control over motivation and behavior.

Dynamic Encoding of Incentive Salience in the Ventral Pallidum: Dependence on the Form of the Reward Cue.

Some rats are especially prone to attribute incentive salience to a cue (conditioned stimulus, CS) paired with food reward (sign-trackers, STs), but the extent they do so varies as a function of the form of the CS. Other rats respond primarily to the predictive value of a cue (goal-trackers, GTs), regardless of its form. Sign-tracking is associated with greater cue-induced activation of mesolimbic structures than goal-tracking; however, it is unclear how the form of the CS itself influences activity in neural systems involved in incentive salience attribution. Thus, our goal was to determine how different cue modalities affect neural activity in the ventral pallidum (VP), which is known to encode incentive salience attribution, as rats performed a two-CS Pavlovian conditioned approach task in which both a lever-CS and a tone-CS predicted identical food reward. The lever-CS elicited sign-tracking in some rats (STs) and goal-tracking in others (GTs), whereas the tone-CS elicited only goal-tracking in all rats. The lever-CS elicited robust changes in neural activity (sustained tonic increases or decreases in firing) throughout the VP in STs, relative to GTs. These changes were not seen when STs were exposed to the tone-CS, and in GTs there were no differences in firing between the lever-CS and tone-CS. We conclude that neural activity throughout the VP encodes incentive signals and is especially responsive when a cue is of a form that promotes the attribution of incentive salience to it, especially in predisposed individuals.

The importance of the vaginal delivery route for antiretrovirals in HIV prevention.

The HIV/AIDS pandemic continues to be a global health priority, with high rates of new HIV-I infections persisting in young women. One HIV prevention strategy is topical pre-exposure prophylactics or microbicides, which are applied vaginally or rectally to protect the user from HIV and possibly other sexually transmitted infections. Vaginal microbicide delivery will be the focus of this review. Multiple nonspecific and specific antiretroviral microbicide products have been clinically evaluated, and many are in preclinical development, The events of HIV mucosal transmission and dynamics of the cervicovaginal environment should be considered for successful vaginal microbicide delivery. Beyond conventional vaginal formulations, intravaginal rings, tablets and films are employed as platforms in the hope to increase the likelihood of microbicide use. Furthermore, combining multiple antiretrovirals within a given formulation, combining a microbicide product with a vaginal device and integrating novel drug-delivery strategies within a microbicide product are approaches to successful vaginal-microbicide delivery.

A moral emergency and a medical problem: negotiating the control of venereal disease--the Saskatchewan Venereal Disease Protection Act, 1946.

The author examines Saskatchewan legislation that regulated venereal disease. Although venereal disease legislation was introduced in Saskatchewan in 1919, the centrepiece of this article is The Venereal Disease Prevention Act, 1946. In an attempt to understand the nuances of and underlying rationale for these laws, the author situates the legislation within its social context. The author demonstrates that the trends and contradictions apparent in society's approach to the regulation of venereal disease were reflected in the legislation. The concept of a continuum is used to illustrate the coexistence of two approaches to the control of venereal disease. On one side of the continuum, venereal disease was a moral problem and a taboo subject. Force was the key to controlling venereal disease; involuntary examinations and intrusions into people's personal lives were the solution. On the other side of the continuum, venereal disease was a medical problem. If approached rationally and openly, control of venereal disease was possible; through education and social acceptance of venereal disease as just another illness, people would voluntarily come forward for treatment. The approaches represented at the extreme ends of the continuum did not exist in isolation; these views existed simultaneously, producing contradictory and colourful rhetoric.