Fear, Pain and the Amygdaloid Complex
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
In classical conditioning the amygdala is a critical area for the convergence of the unconditioned (US) and conditioned stimulus (CS). During this process the CS acquires some of the properties of the US. By assessing the US properties of foot-shock, namely reflex, pain and fear, the neural systems of pain and fear were evaluated in the rat basolateral and central amygdala. The central fear state produced by footshock was compared to the central fear state expressed during the fear-potentiated startle paradigm. By analysing the similarities and differences in the fear states, the effects of GABAergic, glutamatergic, and dopaminergic systems and protein synthesis inhibition on these fear states were investigated. The basolateral amygdala was sensitive to GABAergic modulation during US and CS presentations. This was interpreted as a central fear effect. The central amygdala was sensitive to glutamate but not to GABAergic modulation. NMDA receptor antagonism prevented fear arousal to US but not CS presentation. This effect was interpreted as a deficit in pain processing. Non-NMDA receptor antagonism could significantly attenuate both US and CS fear expression. This was interpreted as an overall non-NMDA receptor inhibitory effect that affected pain and conditioned fear expression. Results of these experiments have implications for our understanding of the circuitry involved in processing the US. The basolateral amygdala appears to support emotional neural plasticity while the central amygdala appears to support pain neural plasticity. Finally and and most importantly each area processes different properties of the US.