Place preference induced by nucleus accumbens amphetamine is impaired by local blockade of Group II metabotropic glutamate receptors in rats

BACKGROUND: The nucleus accumbens (NAc) plays a critical role in amphetamine-produced conditioned place preference (CPP). In previous studies, NAc basal and amphetamine-produced DA transmission was altered by Group II mGluR agents. We tested whether NAc amphetamine CPP depends on Group II mGluR transmission. RESULTS: NAc injections (0.5 μl/side) of the Group II mGluR antagonist (2 S)- a-ethylglutamic acid (EGLU: 0.01–0.8 μg but not 0.001 μg) impaired CPP. The drug did not block the acute locomotor effect of amphetamine. CONCLUSION: Results suggest that Group II mGluRs may be necessary for the establishment of NAc amphetamine-produced CPP. These receptors may also mediate other forms of reward-related learning dependent on this structure

Lifespan changes in the countermanding performance of young and middle aged adult rats

Inhibitory control can be investigated with the countermanding task, which requires subjects to make a response to a go signal and cancel that response when a stop signal is presented occasionally. Adult humans performing the countermanding task typically exhibit impaired response time, stop signal response time and response accuracy as they get older, but little change in post-error slowing. Rodent models of the countermanding paradigm have been developed recently, yet none have directly examined age-related changes in performance throughout the lifespan. Male Wistar rats (N = 16) were trained to respond to a visual stimulus (go signal) by pressing a lever directly below an illuminated light for food reward, but to countermand the lever press subsequent to a tone (stop signal) that was presented occasionally (25% of trials) at a variable delay. Subjects were tested in 1 hour sessions at approximately 7 and 12 months of age with intermittent training in between. Rats demonstrated longer go trial response time, a higher proportion of go trial errors and performed less total trials at 12, compared to 7 months of age. Consistent stop signal response time and post-error slowing were observed for rats at both ages. These results suggest that the countermanding performance of rats does vary throughout the lifespan, in a manner similar to humans, suggesting that rodents may provide a suitable model for behavioral impairment related to normal aging. These findings also highlight the importance of indicating the age at which rodents are tested in countermanding investigations

Electrical stimulation of the brain as a reinforcing stimulus

Note:In comparison with Controls that were never reinforced, rats reinforced with electrical stimulation of the brain (ESB) on interval and ratio schedules were observed to initiate responding faster without priming before each daily session; they also continued to respond for intermittent ESBs with no apparent difficulty, and persisted at responding during extinction, showing spontaneous recovery from one session to the next.ESB-reinforced rats ran faster in a runway with short intertrial intervals (ITIs) than with long ITIs while water- and sucrosereinforced rats tended to run faster with longer ITIs but all rats ran slower on the first trial of each session than on the last trial of the preceding day's session. In both paradigms, preceding the onset of ESB with a signal seemed to result in better environmental control of the response. All of these results with ESB reinforcement were observed in rats maintained on ad libitum food and water and were therefore interpreted as demonstrating hehavior based on an expectancy. In a final experiment expectancy-based responding was observed in non-deprived rats with a history of responding for foodwhile food-deprived. Theories which suggest that a homeostatic imbalance or organismic need is required to motivate behavior are inadequate to deal with these data.Des rats renforcés par stimulation électrique du cerveau (SEC) sur des programmes d'intervalle et de rapport commençaient à répondre plus vite sans stimulation de préparation avant chaque session quotidienne, comparativement aux contrôles non stimules; de plus, ils continuaient à répondre pour des SECs intermittentes sans difficulté apparente, et persistaient à répondre durant l’extinction, démontrant une récupération spontanée d'une session a l’autre. […] Dans une dernière expérience, le taux de réponse has~ sur l'attente a été observé chez des rats non privés, possédant une histoire de renforcement par nourriture, alors qu'ils 6taicnt en 6tat de privation. Los théories qui suggèrent qu'un état d'imbalance homostatique ou de besoin organismique est requis pour motiver le compartement sont inadéquate pour expliquer ces données

Neuropeptide Y: Intrastriatal injections produce contralateral circling that is blocked by a dopamine antagonist in rats

The brain is rich in neuropeptide Y (NPY) but its function is poorly understood. Previous studies have shown that intrastriatal injections of NPY stimulate dopamine (DA) release. In the present paper, behavioral studies evaluated the possibility that unilateral intrastriatal injections of NPY would produce contralateral circling that could be blocked by coinjection with a DA antagonist. Four experiments examined circling behavior in rats after unilateral intrastriatal microinjections (0.5 μl) of: 1) amphetamine alone; 2) amphetamine with the DA antagonist cis-flupenthixol; 3) NPY alone; and 4) NPY with cis-flupenthixol. Each experiment consisted of seven test sessions; the first and seventh were preceded by no injection, the second and sixth by a control injection (saline or cis-flupenthixol with saline) and the third, fourth, and fifth by drug injections. Animals were scored during two 5-min intervals of a 20-min test session that began with the central injection and placement in a circular arena (30 cm diam.). Results indicated that the 25.0- but not the 6.0- or 12.0-μg doses of amphetamine and the 0.10- but not the 0.01- or 1.0-μg doses of NPY produced contralateral circling. This directional bias was antagonized by cis-flupenthixol (20 μg in 0.5 μl) in the case of amphetamine and fully blocked in the case of NPY. Results raise the intriguing possibility that contralateral circling induced by unilateral intrastriatal NPY may be mediated by DA