Amygdala kindling disrupts trace and delay fear conditioning with parallel changes in Fos protein expression throughout the limbic brain.
Amygdala kindling is well known to increase unconditioned fear and anxiety. However, relatively little is known about whether this form of kindling causes functional changes within the neural circuitry that mediates fear learning and the retrieval of fear memories. To address this issue, we examined the effect of short- (i.e., 30 stimulations) and long-term (i.e., 99 stimulations) amygdala kindling in rats on trace and delay fear conditioning, which are aversive learning tasks that rely predominantly on the hippocampus and amygdala, respectively. After memory retrieval, we analyzed the pattern of neural activity with Fos, the protein product of the immediate early gene c-fos. We found that kindling had no effect on acquisition of the trace fear conditioning task but it did selectively impair retrieval of this fear memory. In contrast, kindling disrupted both acquisition and retrieval of fear memory in the delay fear conditioning task. We also found that kindling-induced impairments in memory retrieval were accompanied by decreased Fos expression in several subregions of the hippocampus, parahippocampus, and amygdala. Interestingly, decreased freezing in the trace conditioning task was significantly correlated with dampened Fos expression in hippocampal and parahippocampal regions whereas decreased freezing in the delay conditioning task was significantly correlated with dampened Fos expression in hippocampal, parahippocampal, and amygdaloid circuits. Overall, these results suggest that amygdala kindling promotes functional changes in brain regions involved in specific types of fear learning and memory.
Department of Psychology, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada.
J J
JJ
Botterill
Department of Psychiatry, Yale University School of Medicine, Yale University, New Haven, CT 06508, USA.
N M
NM
Fournier
Department of Psychology, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada.
A J
AJ
Guskjolen
Department of Psychology, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada.
A L
AL
Lussier
Department of Psychology, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada.
W N
WN
Marks
Department of Medicine, University of Saskatchewan, Saskatoon, SK S7N 5A5, Canada. Electronic address: lisa.kalynchuk@usask.ca.
L E
LE
Kalynchuk
D000679:Amygdala / Q000378:metabolism* / Q000503:physiopathology; D000818:Animals; D001921:Brain / Q000378:metabolism; D003214:Conditioning, Classical / Q000502:physiology; D004558:Electric Stimulation; D005239:Fear / Q000502:physiology*; D007696:Kindling, Neurologic / Q000502:physiology*; D008032:Limbic System / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans
D016760:Proto-Oncogene Proteins c-fos
amygdala; fear conditioning; hippocampus; kindling; memory; temporal lobe epilepsy