Learning deficits in an odor reward-task induced by parafascicular thalamic lesions are ameliorated by pretraining D-cycloserine in the prelimbic cortex.

We investigated whether the N-methyl-D-aspartate (NMDA) receptor partial agonist D-cycloserine (DCS) infused into the prelimbic cortex (PLC) would reverse the learning deficits caused by bilateral excitotoxic lesions of the parafascicular nucleus (PFn) in an odor discrimination task (ODT). Rats with PFn lesions received a bilateral infusion of DCS (10 µg/side) into the PLC 20 min before ODT acquisition. The task retention was evaluated in a drug-free test carried out 24 h later. DCS significantly attenuated the PFn lesion-induced deficits as measured by both latency to nose-poke the rewarded odor and number of errors committed during ODT acquisition and retention. Therefore, DCS may be an enhancing memory treatment in animal models of cognitive impairment, such as PFn-lesioned rats. The PFn contribution to learning and memory may possibly be linked to its role in the modulation of glutamatergic PLC activity.

Effects of muscarinic receptor antagonism in the basolateral amygdala on two-way active avoidance.

The aim of the present study was to investigate whether the blockade of muscarinic receptors (mRs) in the basolateral amygdala (BLA), which receives important cholinergic inputs related to avoidance learning, affects the consolidation of two-way active avoidance (TWAA). In Experiment 1, adult male Wistar rats were bilaterally infused with scopolamine (SCOP, 20 µg/site) or PBS (VEH) in the BLA immediately after a single 30-trial acquisition session. Twenty-four hours later, avoidance retention was tested in an identical session. Results indicated that scopolamine in the BLA did not affect TWAA performance measured by the number of avoidance responses. Experiment 2 was conducted to test whether such a negative outcome might be due to the occurrence of overtraining during acquisition, which may indeed have a protective effect against scopolamine-induced memory deficits. In this experiment, rats were infused with scopolamine in the BLA immediately after a brief 10-trial acquisition session and tested 24 h later in a 30-trial retention session. The SCOP group showed significantly more avoidances and inter-trial crossings in the retention session than the VEH rats. Together, these results reveal that mRs blockade in the BLA does not disrupt TWAA consolidation and may even enhance avoidance performance when infused after a low number of acquisition trials. Performance factors, such as locomotor activity in the shuttle-box, may account, at least in part, for the facilitative effects of muscarinic antagonism in the BLA.

D-cycloserine in prelimbic cortex enhances relearning of an odor-reward associative task.

We investigated the effects of bilateral infusions in the prelimbic cortex of D-cycloserine (DCS), a partial agonist of the NMDA receptor-associated glycine site. Wistar rats underwent a training session (acquisition, three trials) and a 24-h test (two retention and two relearning trials) of a rapidly learned olfactory discrimination task. Rats infused with DCS (10 microg/site) prior to training exhibited a significant enhancement of performance in such odor-reward task, especially in relearning.