Hemispheric differences in protein kinase C βII levels in the rat amygdala:: Baseline asymmetry and lateralized changes associated with cue and context in a classical fear conditioning paradigm

The amygdala is critically important for fear learning, and specific kinases have been implicated as contributors to the mechanisms that underlie learning. We examined levels of protein kinase C beta II (PKC beta II) in the left and right lateral and basolateral nuclei (LA/BLA) of the amygdala from animals that were classically fear conditioned with tones as cues and footshocks. Groups consisted of animals that received neither tones nor shocks, paired tones and shocks, or unpaired tones and shocks. At 1 h after conditioning, some animals from each group were used for biochemical measurements of PKC beta II levels and other animals were given probe trials to assess freezing behavior to cue and context. The levels of PKC beta II were greater in the left hemisphere in animals receiving neither tones nor shocks and animals receiving paired tones and shocks. PKC beta II levels were greater in the right hemisphere of animals receiving randomly presented tones and shocks. Freezing times to cue were long (> 80% of probe trial time) in both the paired tone/shock and randomly unpaired tone/shock groups. Freezing times to context were long in the unpaired tone/shock group, but not the paired tone/shock group. Correlational analyses showed that freezing times to context, but not cue, precisely predicted the right/left relation of PKC beta II levels in the LA/BLA: the greater the time spent freezing to context, the greater the increase in right hemisphere PKC beta II levels. We conclude that fear conditioning causes hemisphere and input specific increases in PKC beta II in the rat LA]BLA. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.