Nucleus accumbens neurons encode initiation and vigor of reward approach behavior

The nucleus accumbens (NAc) is considered an interface between motivation and action, with NAc neurons playing an important role in promoting reward approach. However, the encoding by NAc neurons that contribute to this role remains unknown. Here, we trained male rats to find rewards in an 8-arm radial maze. The activity of 62 neurons, mostly in the shell of the NAc, were recorded while rats ran towards each reward place. General linear model (GLM) analysis showed that variables related to the vigor of the locomotor approach, like speed and acceleration, and the fraction of the approach run completed were the best predictors of the firing rate for most NAc neurons. Nearly 23% of the recorded neurons, here named locomotion-off cells, were inhibited during the entire approach run, suggesting that reduction in firing of these neurons promotes initiation of locomotor approach. Another 24% of the neurons presented a peak of activity during acceleration followed by a valley during deceleration (peak-valley cells). Together, these neurons accounted for most of the speed and acceleration encoding identified in the GLM analysis. Cross-correlations between firing and speed indicated that the spikes of peak-valley cells were followed by increases in speed, suggesting that the activity of these neurons drives acceleration. In contrast, a further 19% of neurons presented a valley during acceleration followed by a peak just prior to or after reaching reward (valley-peak cells). These findings suggest that these three classes of NAc neurons control the initiation and vigor of the locomotor approach to reward.Significance StatementDeciphering the mechanisms by which the NAc controls the vigor of motivated behavior is critical to better understand and treat psychiatric conditions in which motivation is dysregulated. Manipulations of the NAc profoundly impair subjects’ ability to spontaneously approach reward-associated locations, preventing them from exerting effort to obtain reward. Here, we identify for the first time specific activity of NAc neurons in relation to spontaneous approach behavior. We discover three classes of neurons that could control initiation of movement and the speed vs. time trajectory during locomotor approach. These results suggest a prominent but heretofore unknown role for the NAc in regulating the kinematics of reward approach locomotion.

Time allocation to resources by three species of rats (Rattus spp.) in a radial arm maze

ContextIntroduced rats (Rattus spp.) can pose a serious threat to native flora and fauna, especially on islands where most species have evolved in the absence of terrestrial predators. Effective detection and eradication methods for introduced rats are essential to the maintenance of insular ecosystem integrity. Thus, it is important to better understand the behaviour of rats when they first arrive in a new setting. AimsTo determine whether rats would find some novel stimuli to be significantly more attractive than other novel stimuli. MethodsAn eight-arm radial maze was used to study the behaviour of three species of Rattus finding themselves in a novel environment with various familiar and unfamiliar stimuli. Key resultsAlthough there were some differences in responses by species and by sex, most rats sought out and spent considerable time in the den box, suggesting an immediate need for security when in an unfamiliar setting. Rats also sought out faeces of conspecifics, suggesting the need for social contact or reproduction. The rats, which had not been food deprived, did not seem interested in food sources, although there was some attraction to the water source. ImplicationsThe management implications of the present study’s results are two-fold. First, appears that detection of newly arriving rats on islands would be aided by strategic placement of den boxes that are highly acceptable to rats. Managers could then inspect the den boxes periodically (or use a remote sensing system) for evidence of rat presence. Second, the den boxes could be scented with the faeces of other rats to further attract invading rats to the den boxes. This protocol might also hold the rats near the invasion site for a longer period of time before they begin seeking other shelter, food sources or mates. These protocols could give managers increased opportunities to detect any newly invading rats, and potentially increase the available time to deploy a rapid response to the invasion, before the animals begin to widely disperse. Of course, the rats will ultimately seek a source of palatable food, so placing durable, yet palatable, rodenticide bait in the den boxes might further decrease the probability of the invaders establishing a self-sustaining population.

EFFECT OF SLEEP DEPRIVATION ON REMINISCENCE AND APPREHENSION BEHAVIOR IN WISTAR ALBINO RATS

Objective: The aim of the present study is to investigate the effect of paradoxical sleep deprivation (SD) on learning and memory impairment and anxiety-like behavior in female Wistar albino rats. Methods: Eight-arm radial maze, open-field test, and light and dark test were used to assess the animals learning and memory and anxiety-like behavior. Results: SD associated with weaker learning and memory and increased anxiety- and depressive-like behavior in animals. Conclusion: Animals were exposed to SD showed learning and memory impairment and also exhibited increased anxiety- and depressive-like behavior when compared to control animals.

Prenatal Exposure to Cadmium During Organogenesis Impairs Memory in Young Rats

Pregnant rats were treated with 0.3 and 0.6 mg cadmium (CdCl2)/kg injected subcutaneously on a daily basis from gestational day 7 to day 15 (organogenesis period). One control group was not injected and other received saline. The 45-day-old offspring were tested in a step-down inhibitory avoidance to evaluate short-term and long-term memory and in a radial maze for the study of spatial memory. These studies showed that gestational exposure to 0.6 mg Cd/kg produced in the male offspring a significant impairment in the retention of long-term memory evaluated 24 hours after training in the step-down inhibitory avoidance. The radial maze also demonstrated that the male offspring prenatally exposed to 0.6 mg Cd presented a significant deficit in the retention of spatial memory evaluated 42 days after training. These results demonstrate that the exposure to Cd during organogenesis may affect the retention of some types of memory.