Effects of corticotropin releasing factor on spontaneous burst activity in the piriform–amygdala complex of in vitro brain preparations from newborn rats

The amygdala is an important higher regulatory center of the autonomic nervous system, involved in respiratory and cardiovascular control, and it also plays a role in the formation of emotions. Corticotropin-releasing factor (CRF) is a neuropeptide involved in stress responses. We have examined the effects of CRF on the spontaneous burst activity in the piriform–amygdala complex of rat brain preparations in vitro. Limbic–brainstem–spinal cord preparations of 0- to 1-day-old Wistar rats were isolated under deep ether anesthesia, and were superperfused in a modified Krebs solution. Bath application of 50 nM CRF substantially increased the frequency of burst activity in the piriform–amygdala complex, whereas this polypeptide exerted only minor effects on C4 inspiratory activity. The excitatory effect of CRF on the amygdala burst was effectively blocked by the CRF1 antagonist, antalarmin, but not the CRF2 antagonist, astressin-2B, suggesting that CRF1 mediated the excitatory effect. The spatio-temporal pattern of the burst activity according to optical recordings was basically identical to the controls; the burst activity initially appeared in the piriform cortex and then propagated to the amygdala. The present experimental model could be useful for the study of role of the limbic system, including the amygdala, in stress responses.