Female fear: Influence of estrus cycle on behavioral response and neuronal activation

Abstract

Our observation that male rats innate fear response differed with hormonal status, as well as the higher prevalence of fear and anxiety disorders in human females led to the current investigation of the impact of phases of the estrous cycle on innate fear responding. Female rats in different phases of the cycle were exposed to an innate fear-inducing stimulus (2,5-dihydro- 2,4,5-trimethylthiazoline, TMT odor) and monitored for changes in behavior and brain activation. Behavioral data showed freezing responses to TMT were significantly enhanced during estrus as compared to other phases of the cycle. This data was supported by significant increases in pixel intensity in cortical and sub-cortical regions in estrus compared to proestrus and diestrus. Imaging results demonstrated significant increases in brain activation in the somatosensory and insular cortices when comparing estrus to diestrus. There were significant increases in neural activity in the BNST and septum in estrus as compared to proestrus. Additionally, the hippocampus, hypothalamus, olfactory system, and cingulate cortex show significant increases in the estrus phase when compared to both diestrus and proestrus. Taken together, these results suggest that the female's hormonal status may be correlated with alterations in both neuronal and behavioral indices of fear.

Predator odor-evoked BOLD activation in the awake rat: Modulation by oxytocin and V1a vasopressin receptor antagonists

“…Most of the areas were cortical and regions such as the BNST, amygdala, septum and prefrontal cortex did not distinguish between BA and TMT. This differs somewhat from Chen et al (2009), which measured the BOLD signal response to TMT in female rats and reported increased in BOLD in BNST, septum, hypothalamic nuclei, hippocampus, in addition to similar regions reported in the present study and in Febo and Pira (2011). However, Chen et al (2009) did not include a control odor during scanning which makes it difficult to compare the studies and to discern whether the pattern of BOLD signal changes corresponds to innate fear circuitry or the neural response to an aversive odor.…”

Toxoplasma gondii influences aversive behaviors of female rats in an estrus cycle dependent manner

“…Cycle status affects anxiety [1], fear [6], and aversion in rodents [7]. Rats in receptive phases of their cycle are less anxious, spending more time in open arms of elevated plus maze and in brightly lit areas, showing decreased latency in leaving dark chambers, decreased freezing after a foot shock, and increased interaction with conspecifics, as compared to animals in diestrus.…”

Relativizing innateness: innateness as the insensitivity of the appearance of a trait with respect to specified environmental variation

“…One scientist may conclude that the trait ''is innate'' and the other that it is not, as we saw in the cowbird case. Another puzzling situation is when scientists are investigating the causes of a trait that has already been claimed to be ''innate,'' such as ''innate fear,'' which, though it does not require prior exposure to the source of fear, is nonetheless influenced by other causes worth studying, such as neonatal maternal separation or phase in the estrus cycle (Stevenson et al 2009;Chen et al 2009). Similarly, cuttlefish have been claimed to have an ''innate preference'' for shrimp because they will choose shrimp over crab at their first feeding, never having eaten either before.…”