PT  - JOURNAL ARTICLE
AU  - Jami, Shekib A.
AU  - Wright, William G.
AU  - Glanzman, David L.
TI  - Differential Classical Conditioning of the Gill-Withdrawal Reflex in <em>Aplysia</em> Recruits Both NMDA Receptor-Dependent Enhancement and NMDA Receptor-Dependent Depression of the Reflex
AID  - 10.1523/JNEUROSCI.2581-06.2007
DP  - 2007 Mar 21
TA  - The Journal of Neuroscience
PG  - 3064--3068
VI  - 27
IP  - 12
4099  - http://www.jneurosci.org/content/27/12/3064.short
4100  - http://www.jneurosci.org/content/27/12/3064.full
SO  - J. Neurosci.2007 Mar 21; 27
AB  - Differential classical conditioning of the gill-withdrawal response (GWR) in Aplysia can be elicited by training in which a conditioned stimulus (CS) delivered to one side of the siphon (the CS+) is paired with a noxious unconditioned stimulus (US; tail shock), while a second conditioned stimulus (the CS−), delivered to a different siphon site, is unpaired with the US. NMDA receptor (NMDAR) activation has been shown previously to be critical for nondifferential classical conditioning in Aplysia. Here, we used a semi-intact preparation to test whether differential classical conditioning of the GWR also depends on activation of NMDARs. Differential training produced conditioned enhancement of the reflexive response to the CS+ and a reduction in the response to the CS−. Comparison of the results after differential training with those after training in which only the two CSs were presented (CS-alone experiments) indicated that the decrement in the response to CS− after differential training was not caused by habituation. Surprisingly, differential training in the NMDAR antagonist APV (dl-2-amino-5-phosphonovalerate) blocked not only the conditioned enhancement of the GWR, but also the conditioning-induced depression of the GWR. We suggest that differential conditioning involves an NMDAR-dependent, competitive interaction between the separate neural pathways activated by the CS+ and CS−.