Differential impairment of auditory and contextual fear conditioning by protein synthesis inhibition in C57BL/6N mice

A 1-trial fear conditioning was used to investigate the temporal developmen t of fear responses expressed as increase of freezing or heart rate and its impairment by the protein synthesis inhibitor cycloheximide (CHX) in male C57/BL/6N mice. Heart rate was measured with an implanted transmitter. In t he memory tests, mice were exposed to tone and context provided either as f oreground or background stimulus during training. The fear responses develo ped differently from 0 to 24 hr after training under these 3 conditions. A single pretraining CHX injection impaired both memory forms, whereas a sing le posttraining CHX injection impaired tone but not context-dependent memor y, with the context provided as background stimulus. It was concluded that consolidation of tone-, foreground context-, and background context-depende nt fear conditioning may be mediated by partly different neuronal or partly different biochemical pathways, or both.