Differential patterns of performance impairment result from changed reinforcer efficacy or distracting stimulation in a two-choice rodent spatial signal detection task

Chronic Administration of Δ9-Tetrahydrocannabinol Alters Brain Glucose Uptake and Improves Waiting Impulsivity in the Rat

Introduction: Δ9-Tetrahydrocannabinol (THC) acts as an agonist at cannabinoid receptors. Its chronic intake affects many behaviors, including cognitive processes. The aims of this study in rats are to assess the chronic effects of THC on impulsivity and on regional brain glucose uptake. Materials and Methods: For the determination of "waiting impulsivity," a total of 20 male Lister Hooded rats were trained to perform a reaction time task, followed by a baseline test of impulsivity and baseline glucose uptake measurements with [18F]-fluoro-2-deoxy-D-glucose and positron emission tomography (PET). Then, 10 rats each received 3 mg/kg THC or vehicle injected intraperitoneally daily for 21 days. Subsequently, a second behavioral test and PET measurements were performed, and blood THC concentrations were determined. Analyses of variance of brain regions of the impulsivity network with the parameter "standardized uptake value" regarding glucose uptake and correlation analyses of the collected parameters were carried out. Discussion: After chronic THC treatment, decreased glucose uptake (p-values <0.05) was found in cingulate cortex, hippocampus, amygdala, thalamus, and cerebellar cortex, as compared with vehicle-treated rats. The number of correct no-go responses (increased waiting time) significantly increased (p<0.05) in THC-treated rats. Furthermore, correct no-go responses correlated positively and strongly with the THC blood concentrations (Spearman's ρ=0.79, p<0.01). Conclusion: These findings reflect a specific reduction in impulsive behavior after chronic THC treatment, showing a functionally relevant influence of THC on "waiting impulsivity" with reduced selective glucose uptake at the same time.

Intracerebroventricular administration of galanin decreases free water intake and operant water reinforcer efficacy in water-restricted rats

The 29/30 amino acid neuropeptide galanin coexists with vasopressin in the hypothalamus and has been shown to inhibit the actions of vasopressin and aldosterone, suggesting an inhibitory role for galanin in physiological water retention mechanisms and water seeking and water consumption behavior. Little work, however, has examined a role for galanin in water intake regulation. Furthermore, many experiments that have reported galanin-induced impairments in the performance of tasks thought to measure learning and memory have used water restriction routines and water reinforcers to maintain responding. Therefore, the present study examined the effects of intracerebroventricularly administered galanin (5.0-20.0 microg/5 microl) on free water consumption during a 10 min test session and a follow up open field exploration, an operant progressive ratio (PR) schedule, a test used to assess reinforcer strength, and an operant fixed time schedule (FT 20) in 23.5h water restricted rats. Finally, in an additional experiment that was designed to simulate the effects of a galanin-induced decrease in water reinforcer efficacy, the rats were allowed access to water prior to testing in an operant delayed non-matching to position (DNMTP) task. A galanin-induced decrease in water consumption was observed in both the free access test and the FT 20 at the 20 microg dose, but no significant galanin-induced alterations in open field behavior. A decrease in responses emitted and rewards received was observed on the PR schedule at the 5, 10, and 20 microg doses. Pre-session access to water significantly reduced the number of trials per session in the DNMTP but did not reduce accuracy. This study is the first to observe a galanin-induced reduction in water intake and reinforced operant behavior, and suggests that galanin may play a role in regulating water intake and reinforcement. However, the present data also suggest that DNMTP choice accuracy deficits observed previously cannot be attributed to a galanin-induced change in reinforcer efficacy.

Signal detection behavior in humans and rats: a comparison with matched tasks

Animal models of human cognitive processes are essential for studying the neurobiological mechanisms of these processes and for developing therapies for intoxication and neurodegenerative diseases. A discrete-trial signal detection task was developed for assessing sustained attention in rats; a previous study showed that rats perform as predicted from the human sustained attention literature. In this study, we measured the behavior of humans in a task formally homologous to the task for rats, varying two of the three parameters previously shown to affect performance in rats. Signal quality was manipulated by varying the increment in the intensity of a lamp. Trial rate was varied among values of 4, 7, and 10 trials/min. Accuracy of signal detection was quantified by the proportion of correct detections of the signal (P(hit)) and the proportion of false alarms (P(fa), i.e. incorrect responses on non-signal trials). As with rats, P(hit) in humans increased with increasing signal intensity whereas P(fa) did not. Like rats, humans were sensitive to the trial rate, though the change in behavior depended on the sex of the subject. These data show that visual signal detection behavior in rats and humans is controlled similarly by two important parameters, and suggest that this task assesses similar processes of sustained attention in the two species.