An 8-day extensive elemental, but not contextual, fear conditioning potentiates hippocampal-lateral septal synaptic efficacy in mice.

Aline Desmedt, Ren� Garcia, Robert Jaffard
Synapse. 2003-06-20; 49(4): 270-278
DOI: 10.1002/syn.10243

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Previous findings have suggested a critical role for hippocampal-lateral septal
(HPC-LS) synaptic transmission in the modulation of elemental vs. contextual fear
conditioning. Pharmacologically- or electrophysiologically-induced increases in
HPC-LS neurotransmission were shown to be associated with both an increase in
elemental and a decrease in contextual fear conditioning. However, elemental
conditioning, induced by an unconditional stimulus (US) that was explicitly
paired with a simple conditional stimulus (CS), did not result in any change in
this neurotransmission when two tone CS-footshock US pairings were provided. The
present experiment was thus designed to investigate directly, in mice, whether
extensive elemental conditioning (repeated CS-US pairings) could induce an
increase in HPC-LS neurotransmission. For that purpose, over 8 days, an elemental
conditioning group was repeatedly submitted to CS-US pairings in either one
context (A) or another (B) depending on the training day. Hence, whichever the
context, the tone CS was the relevant predictive stimulus for the occurrence of
the footshock US. In contrast, a contextual conditioning group was submitted to
the same regimen except that the US was delivered only in context A and was never
paired with the CS, making, thereby, the context A the relevant predictor for the
US regardless of the occurrence of the tone CS. Results show that during
re-exposure of the animals to either context A or B, a significant increase in
HPC-LS neurotransmission was selectively associated with the repeated elemental
conditioning. This study supports the idea that changes in HPC-LS
neurotransmission may modulate the strength of simple CS-US associations, and
suggests that alterations of hippocampal functioning might be involved.


Auteurs Bordeaux Neurocampus