CORTICOTROPIN-RELEASING FACTOR IN THE CAUDAL PONTINE RETICULAR NUCLEUS MEDIATES THE EXPRESSION OF FEAR-POTENTIATED STARTLE IN THE RAT

The fear-potentiated startle paradigm is a valuable model for the inve stigation of the neuronal basis of fear. Previous studies have demonst rated that the neuropeptide corticotropin-releasing factor (CRF) plays an important role in fear-related processes, notably in the potentiat ion of the acoustic startle response. The present study investigated t he role in fear-potentiated startle of CRF in the caudal pontine retic ular nucleus, a brain nucleus that mediates the acoustic startle respo nse. First, we showed that the central nucleus of the amygdala gives r ise to a CRFergic projection to the caudal pontine reticular nucleus. In the second experiment, we iontophoretically applied CRF to caudal p ontine reticular nucleus neurons and extracellularly recorded the acti vity of these neurons. CRF had a mainly excitatory effect on the tone- evoked activity of the neurons. In our third experiment, we injected t he CRF antagonist alpha-helical CRF into the caudal pontine reticular nucleus of awake rats. Here, alpha-helical CRF dose-dependently blocke d fear-potentiated startle, but had no effect on the baseline startle amplitude. The present results show that CRF-containing neurons which project from the central nucleus to the caudal pontine reticular nucle us are important for the enhancement of startle by fear, and further c haracterize the hypothetical neuronal circuitry underlying the express ion of fear-potentiated startle.