Memory consolidation of a habituation task: role of N-methyl-D-aspartate, cholinergic muscarinic and GABA-A receptors in different brain regions.

1. The immediate post-training microinjection of the N-methyl-D-aspartate receptor antagonist amino-5-phosphonopentanoic acid (5 micrograms) or of scopolamine, the cholinergic muscarinic antagonist (2 micrograms), into the dorsal hippocampus of rats caused retrograde amnesia for habituation to a novel environment, as measured by the number of rearings and crossings performed in a test session. In contrast, picrotoxin (0.08 microgram), the indirect GABA-A antagonist, caused retrograde memory facilitation. 2. Receptor agonists administered into the hippocampus had effects opposite to those of the respective antagonists: glutamate (5 micrograms) and oxotremorine (2 micrograms) enhanced memory and muscimol (0.03 microgram) was amnestic. 3. Aminophosphonopentanoic acid, scopolamine and picrotoxin had no effect when injected into the amygdala or medial septum. Our result contrasted with the recent report of an inhibitory avoidance task in which these drugs, at the doses used here, were effective when injected post-training into any of the three structures. 4. These findings suggest that similar neurotransmitter mechanisms operate in different brain regions in order to regulate memory consolidation processes; however, there is a specialization of these brain regions in relation to different types or components of memory.