Acute intrahippocampal administration of melanin-concentrating hormone impairs memory consolidation and decreases the expression of MCHR-1 and TrkB receptors.

Interest in the role of melanin-concentrating hormone (MCH) in memory processes has increased in recent years, with some studies reporting memory-enhancing effects, while others report deleterious effects. Due to these discrepancies, this study seeks to provide new evidence about the role of MCH in memory consolidation and its relation with BDNF/TrkB system. To this end, in the first experiment, increased doses of MCH were acutely administered in both hippocampi to groups of male rats (25, 50, 200, and 500 ng). Microinjections were carried out immediately after finishing the sample trial of two hippocampal-dependent behavioral tasks: the Novel Object Recognition Test (NORT) and the modified Elevated Plus Maze (mEPM) test. Results indicated that a dose of 200 ng of MCH or higher impaired memory consolidation in both tasks. A second experiment was performed in which a dose of 200 ng of MCH was administered alone or co-administered with the MCHR-1 antagonist ATC-0175 at the end of the sample trial in the NORT. Results showed that MCH impaired memory consolidation, while the co-administration with ATC-0175 reverted this detrimental effect. Moreover, MCH induced a significant decrease in hippocampal MCHR-1 and TrkB expression with no modification in the expression of BDNF and NMDA receptor subunits NR1, NR2A, and NR2B. These results suggest that MCH in vivo elicits pro-amnesic effects in the rat hippocampus by decreasing the availability of its receptor and TrkB receptors, thus linking both endogenous systems to memory processes.

Hyperactivity induced by the dopamine D2/D3 receptor agonist quinpirole is attenuated by inhibitors of endocannabinoid degradation in mice.

The present study was designed to investigate the effect of pharmacological inhibition of endocannabinoid degradation on behavioural actions of the dopamine D2/D3 receptor agonist quinpirole in male C57Bl/6J mice. In addition, we studied the effects of endocannabinoid degradation inhibition on both cocaine-induced psychomotor activation and behavioural sensitization. We analysed the effects of inhibition of the two main endocannabinoid degradation enzymes: fatty acid amide hydrolase (FAAH), using inhibitor URB597 (1 mg/kg); monoacylglycerol lipase (MAGL), using inhibitor URB602 (10 mg/kg). Administration of quinpirole (1 mg/kg) caused a temporal biphasic response characterized by a first phase of immobility (0-50 min), followed by enhanced locomotion (next 70 min) that was associated with the introduction of stereotyped behaviours (stereotyped jumping and rearing). Pretreatment with both endocannabinoid degradation inhibitors did not affect the hypoactivity actions of quinpirole. However, this pretreatment resulted in a marked decrease in quinpirole-induced locomotion and stereotyped behaviours. Administration of FAAH or MAGL inhibitors did not attenuate the acute effects of cocaine. Furthermore, these inhibitors did not impair the acquisition of cocaine-induced behavioural sensitization or the expression of cocaine-induced conditioned locomotion. Only MAGL inhibition attenuated the expression of an already acquired cocaine-induced behavioural sensitization. These results suggest that pharmacological inhibition of endocannabinoid degradation might exert a negative feedback on D2/D3 receptor-mediated hyperactivity. This finding might be relevant for therapeutic approaches for either psychomotor disorders (dyskinesia, corea) or disorganized behaviours associated with dopamine-mediated hyperactivity.

Prefrontal inositol triphosphate is molecular correlate of working memory in nonhuman primates.

Working memory (WM) is a process of actively maintaining information in the mind for a relatively short period of time, and prefrontal cortex (PFC) has been thought to play a central role in its function. However, our understanding of underlying molecular events that translate into WM behavior remains elusive. To shed light on this issue, we have used three distinct nonhuman primate models of WM where each model represents three WM conditions: normal control, WM-deficient, and recuperated to normal from WM deficiency. Based on the hypothesis that there is a common molecular substrate for the coding of WM behavior, we have studied the relationship of these animals' performance on a WM task with their PFC levels of molecular components associated with Gq-phospholipase C and cAMP pathways, with the idea of identifying the footprints of such biomolecules. We observed that in all of the primate models WM deficiency was strongly related to the reduced concentration of IP(3) in PFC, whereas recuperation of WM-deficient animals to normal condition was associated with the normalization in IP(3) level. However, this correlation was absent or weak for cAMP, active protein kinase A, dopamine D(1) receptor, and Gq protein. In addition, WM deficiency related not only to pharmacological conditions but also to aging. Thus, it is suggested that optimal IP(3) activity is essential for normal WM function and the maintenance of intracellular IP(3)-mediated Ca(2+) level in PFC may serve as biochemical substrate for the expression of WM behavior.