Levels of neurotrophic factors in the hippocampus and amygdala correlate with anxiety- and fear-related behaviour in C57BL6 mice

The present study tested whether individual differences in anxiety- and fear-related behaviour are associated with between-subjects variation in postmortem brain levels of selected neurotrophic factors. Naive C57BL6/J mice of both sexes were subjected either to an elevated plus maze test or to a Pavlovian fear conditioning paradigm. Two days after behavioural assays, the mice were sacrificed for postmortem quantification of the protein levels of brain derived neurotrophic factors (BDNF), nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the hippocampus and amygdala. Significant correlations between behavioural measures and postmortem regional neurotrophic factor contents were revealed. The magnitude of anxiety-like behaviour in the elevated plus maze was positively related to dorsal hippocampal BDNF levels, but negatively related to NGF levels in dorsal hippocampus and in the amygdala. On the other hand, the expression of conditioned fear is positively related to amygdala BDNF and NGF levels, and to dorsal hippocampal NGF levels. Our results add to existing reports in human as well as in animals of correlation between anxiety trait and gross measures of hippocampal volume or activation levels. Moreover, a distinction between spontaneous and learned (or conditioned) anxiety/fear would be relevant to the identification of neurotrophin signalling mechanisms in the hippocampus and amygdala implicated in anxiety and related psychopathology.