Memantine improves memory for taste-avoidance learning in day-old chicks exposed to isolation stress.

Activation of NMDA receptors by glutamate is particularly important in the initial stages of memory consolidation. Memantine, a noncompetitive NMDA receptor antagonist, ameliorates memory impairment under certain circumstances, despite blocking the activation of NMDA receptors. The present experiments tested the hypothesis that memantine can improve memory deficits induced by isolation stress in day-old chicks (Gallus gallus domesticus) trained in a one-trial taste-avoidance task. Three experiments assessed the effects of memantine at different concentrations and in combination with isolation stress. The results of Experiment 1 indicate that, under normal, non-stressed conditions, memory in control animals is strong and 15.0 mM memantine impairs memory, similar to that seen in many studies of the effects of NMDA receptor antagonists on learning. However, the results of Experiments 2 and 3 showed that, when chicks were exposed to isolation stress during the pre-training period, memory formation for saline-injected control animals was impaired and 5.0 mM memantine significantly improved memory in an inverted U-shaped dose response function. The current results extend the findings that memantine can ameliorate memory impairment and supports the hypothesis that memantine, despite its action to reduce NMDA receptor activity, can facilitate normalized memory acquisition.

Dorsal hippocampus inhibition disrupts acquisition and expression, but not consolidation, of cocaine conditioned place preference.

Cocaine abusers may experience drug craving upon exposure to environmental contexts where cocaine was experienced. The dorsal hippocampus (DHC) is important for contextual conditioning, therefore the authors examined the specific role of the DHC in cocaine conditioned place preference (CPP). Muscimol was used to temporarily inhibit the DHC and was infused before conditioning sessions or tests for CPP to investigate acquisition and expression of cocaine CPP, respectively. To investigate consolidation, rats received intra-DHC muscimol either immediately or 6 hr after conditioning sessions. Inhibition of DHC, but not the overlying cortex, disrupted acquisition and expression of cocaine CPP. It is interesting to note that there was no effect of post-conditioning DHC inhibition. The findings suggest that the DHC is important for both acquisition and recall, but not consolidation, of context-cocaine associations.

Dorsal, but not ventral, hippocampal lesions disrupt cocaine place conditioning.

The environment in which cocaine is experienced becomes associated with the effects of the drug and can then elicit cocaine craving. This study examined whether the hippocampus is involved in such associations using the conditioned place preference model. Rats received bilateral lesions of the dorsal or ventral hippocampus and were then conditioned to associate a particular environment with cocaine. Following conditioning, rats with lesions of the dorsal, but not ventral, hippocampus failed to demonstrate conditioned place preference for the cocaine-associated environment. These findings suggest that the dorsal hippocampus plays a role in the association of environmental stimuli with the effects of cocaine and may have important implications for understanding craving elicited by cocaine-conditioned stimuli.