Threat bias in mice with inactivating mutations of Prkar1a

Abstract

Anxiety disorders are associated with abnormalities in the neural processing of threat-related stimuli. However, the neurobiological mechanisms underlying threat bias in anxiety are not well understood. We recently reported that a Prkar1a heterozygote (Prkar1a+/-) mouse with haploinsufficiency for the main regulatory subunit (R1α) of protein kinase A (PKA) exhibits an anxiety-like phenotype associated with increased cAMP signaling in the amygdala. Prkar1a+/- mice provide a novel model to test the direct effect of altered PKA expression and subsequent anxiety-like behavioral phenotype on the response to threat. We hypothesized that Prkar1a+/-mice would exhibit a bias in threat detection since increased amygdala activity during emotional stimuli is associated with a maladaptive response. We measured behavior and PKA activity in brain areas after exposure to predator or control odor exposure in male Prkar1a+/- and wild-type (WT) littermates. Indeed, there were significant differences in the behavioral response to threat detection; WT mice showed the expected response of decrease in exploratory behavior during predator vs. control odor exposure, while Prkar1a+/- mice did not alter their behavior between conditions. Basal and total PKA activity was independently associated with genotype, with an interaction between genotype and threat condition. Prkar1a+/- mice had higher PKA activity in amygdala and ventromedial hypothalamus in response to predator odor. In contrast, WT mice had higher PKA activity in amygdala and orbitofrontal cortex after exposure to control odor. Dysregulated PKA activity in the amygdala- prefrontal cortex circuitry in Prkar1a+/- mice is associated with behavioral phenotype of anxiety and a bias for threat. This is likely related to a failure to inhibit the amydgala response, which is an effect of the genotype. These results suggest that the alteration in PKA signaling in Prkar1a+/- mice is not ubiquitous in the brain; tissue-specific effects of the cAMP/PKA pathway are related to threat detection and fear sensitization.

Studies of mice with cyclic AMP-dependent protein kinase (PKA) defects reveal the critical role of PKA’s catalytic subunits in anxiety

“…All behavioral testing was performed, as previously reported [31-33], between the hours of 1300-1700 h. One behavioral test per day was performed, with a span of at least two days between tests. The order of behavioral tests was randomly assigned [27]. Two scorers performed behavioral testing and obtained scoring of all results in a blinded fashion (without knowledge of the genotypes of the mice under observation).…”

“…Elevated plus maze (EPM) testing was performed as described previously [24, 27, 32, 33]. Mice were transported in their home cages to the testing room two hours prior to acclimate prior to testing.…”

“…Thus, we crossed Prkar1a +/- and Prkaca +/- mice to generate double heterozygous Prkar1a +/- /Prkaca +/- mice and expected a reversal of the anxiety phenotype that we observed previously [24, 27] in Prkar1a +/- mice, consistent with what has been reported in PKA activity regulation [25, 26]. The data perhaps not unexpectedly support attenuation but not elimination of the anxiety phenotype noted in Prkar1a +/- knockout mice (given the variable expression of other PKA subunits in brain) and highlight the importance of even modest changes in total PKA activity in the regulation of anxiety behaviors and the fact that Cα is not the sole determinant of PKA's cAMP signaling effects.…”

“…These regions of the amygdala coordinate fear- and anxiety-like behavioral responses [24-27] as well as external cues, responding to threats via direct and indirect projections to the paraventricular nucleus of the hypothalamus (PVH) and brainstem regions [27-29]. PKA activity is increased in Prkar1a +/- mice because of a deficiency in overall Cα inhibition, although the net effect varies widely in different tissues [25-30].…”

The Role of Protein Kinase A in Anxiety Behaviors

“…Our research with a mouse model with the loss of one Prkar1a allele showed augmentation of anxiety-like behaviors associated with an increase in PKA activity in the BLA and CEA and an increase in threat bias [115,116]. Functionally, loss of Prkar1a is associated with excess PKA signaling, and these findings highlight the importance of cAMP/PKA signaling in neural areas relevant to the emotional processing of threat (i.e.…”