Injections of the NMDA receptor antagonist aminophosphonopentanoic acid into the lateral nucleus of the amygdala block the expression of fear-potentiated startle and freezing
M. Fendt, Injections of the NMDA receptor antagonist aminophosphonopentanoic acid into the lateral nucleus of the amygdala block the expression of fear-potentiated startle and freezing, J NEUROSC, 21(11), 2001, pp. 4111-4115
NMDA receptors within the amygdala play an important role in the acquisitio
n and expression of conditioned fear. Because amygdaloid injections of NMDA
receptor antagonists did not block the expression of every behavioral sign
of fear, a discussion arose as to whether amygdaloid NMDA receptors play d
ifferent roles in different kinds of fear-conditioning tasks. To clarify th
e exact role of amygdaloid NMDA receptors, the present study measured the e
ffects of amygdaloid NMDA receptor blockade on the two major animal models
of conditioned fear. An experimental design was used that allowed simultane
ous measurement of fear-potentiated startle and freezing during the same te
st session after animals had undergone identical training procedures. The p
resent study clearly demonstrates that injections of the NMDA receptor anta
gonist AP-5 into the lateral nucleus of the amygdala significantly attenuat
ed both behavioral fear responses (i.e., the amygdaloid NMDA receptors are
necessary for the expression of fear-potentiated startle and freezing). The
present results together with others from the literature indicate that NMD
A receptors within the lateral amygdala are critically involved in normal s
ynaptic transmission. It appears then that NMDA receptor antagonists may bl
ock the acquisition of fear conditioning by directly interfering with norma
l synaptic transmissions in the amygdala. Possible reasons for some discrep
ant results in earlier studies are also discussed.