Infusion of methylphenidate into the basolateral nucleus of amygdala or anterior cingulate cortex enhances fear memory consolidation in rats

The psychostimulant methylphenidate (MPD; also called Ritalin) is a blocker of dopamine and norepi-nephrine transporter. It has been clinically used for treatment of Attention Deficit and Hyperactivity Disorder (ADHD). There have been inconsistent reports regarding the effects of systemically adminis-tered MPD on learning and memory, either in animals or humans. In the present study, we investigated the effect of direct infusion of MPD into the basolateral nucleus of amygdala (BLA) or the anterior cin-gulate cortex (ACC) on conditioned fear memory. Rats were trained on a one-trial step-through inhibi-tory avoidance task. MPD was infused bilaterally into the BLA or the ACC, either at ‘0’ or 6 h post-training. Saline was administered as control. Memory retention was tested 48 h post-training. In-tra-BLA or intra-ACC infusion of MPD ‘0’ h but not 6 h post-training significantly improved 48-h memory retention: the MPD-treated rats had significant longer step-through latency than controls. The present results indicate that action of MPD in the BLA or the ACC produces a beneficial effect on the consoli-dation of inhibitory avoidance memory.

Investigating the inhibition of NMDA glutamate receptors in the basolateral nucleus of the amygdala on the pain and inflammation induced by formalin in male Wistar rats

BACKGROUND： The role of the amygdala in controlling emotional pain has been emphasized in several studies. In this study, the role of the NMDA glutamate receptors in the basolateral nucleus of the amygdala （BLA） in regulating inflammation and emotional pain, induced by formalin, was studied in male rats. METHODS： Male Wistar rats, weighing 250±0 g, were injected with 20 μL of 2% formalin into the paw of the right hind limb. Memantine, at doses of 1 and 5 μg/rat, was injected bilaterally into the BLA five minutes prior to injecting formalin. Following the injection, the pain and inflammation of the paws were measured using Dubbison-Dennis and mercury immersion methods, respectively. The behavior of the animals, including licking time and foot volume, was assessed. RESULTS： The results showed that the inactivation of the NMDA receptors in the BLA in the acute phase of pain reduced the licking time （the emotional aspect of pain）. However, at a high dose （5μg/rat）, memantine exacerbates the pain induced by formalin in the chronic phase. Additionally, the inhibition of the NMDA receptors in the BLA by memantine enhanced the formalin-induced increase in foot volume （inflammation） in a dose-dependent manner. CONCLUSION： The study showed that the NMDA glutamate receptors in the BLA are crucial for the emotional pain and inflammation in both chronic and acute phases of formalin-induced pain. However, their roles are more pronounced in the chronic phase than in the acute phase of pain.