Differential regulation of Ca(2+)-calmodulin stimulated and Ca(2+)-insensitive adenylyl cyclase messenger RNA in intact and denervated mouse hippocampus.

The Ca(2+)-calmodulin stimulated AC1 and Ca(2+)-insensitive AC2 are major isoforms of adenylyl cyclase, playing an important role in synaptic plasticity in the mammalian brain. We studied the pattern of expression of AC1 and AC2 genes in the hippocampus of C57BL/6 mice. We found that there were differences in their patterns of distribution in the dentate gyrus.

Paradoxical facilitatory effect of fornix lesions on acquisition of contextual fear conditioning in mice.

The present study examined the effect of fornix lesions on freezing behavior elicited by contextual and phasic conditioned stimuli. Male mice of the C57Bl/6 strain received electrolytic lesions of the fornix. Ten days following the lesion, they were submitted to acquisition of one-trial classical fear conditioning involving the pairing of an auditory conditioned stimulus (CS) with a footshock unconditioned stimuli (US).

Time-dependent reorganization of brain circuitry underlying long-term memory storage.

Retrograde amnesia observed following hippocampal lesions in humans and animals is typically temporally graded, with recent memory being impaired while remote memories remain intact, indicating that the hippocampal formation has a time-limited role in memory storage. However, this claim remains controversial because studies involving hippocampal lesions tell us nothing about the contribution of the hippocampus to memory storage if this region was present at the time of memory retrieval. We therefore used non-invasive functional brain imaging using (14C)2-deoxyglucose uptake to examine how the brain circuitry underlying long-term memory storage is reorganized over time in an intact brain.