Y1R may not be necessary for the cued-expression of fear, as intra-amygdalar administration of NPY robustly decreases the expression of conditioned fear,

but these effects are not replicated by Y1R agonists and are not blocked by pretreatment with a Y1R antagonist (Fendt et al., 2009). In this particular study, Y1R knockout mice showed slight elevations in freezing behavior during fear conditioning, but did not show an enhanced phenotype upon testing for the cued-expression of fear compared to wildtype mice (Fendt et al., 2009). In addition, NPY was still capable of reducing the cued-expression of fear in these Y1R deficient mice, suggesting that the Y1R may not be involved in this phase (Fendt et al., 2009). NPY can suppress the long-term incubation of conditioned fear, while delivery of NPY prior to extinction training attenuates BLU9931 ic50 freezing and enhances retention of extinguished fear memories (Gutman and et al, 2008, Lach and de Lima, 2013 and Pickens and et al, 2009). Y1R antagonism blocks NPY-induced reductions in freezing and blockade of amygdalar Y1R leads to deficient extinction retention (Gutman and et al, 2008 and Lach and de Lima, 2013). Consistent with pharmacological studies, NPY knockout mice display accelerated acquisition of conditioned fear, excessive recall of fear, and impaired fear extinction (Verma et al.,

2012). Interestingly, deletion of the Y1R has moderately similar effects, whereas knockout ZD1839 in vivo of the Y2R has no effect on fear (Verma et al., 2012). However, double Y1R and Y2R knockout mice exhibit a remarkably similar phenotype to NPY deficient mice, indicating that both receptor subtypes do play a role in aspects of fear conditioning (Verma et al., 2012). In an inescapable footshock paradigm, interactions between the NPY and CRF systems were evident as increased amygdalar CRFR1 and decreased Y1R mRNA were found concurrently in animals

displaying enhanced freezing time, and all of these effects were reversed in parallel following re-exposure to the footshock-paired environment (Hendriksen et al., 2012). Indirect evidence for NPY interactions with norepinephrine was obtained using auditory fear conditioning, in which centrally administered NPY and a Y1R agonist blunted fear-induced tachycardia (Tovote et al., 2004). These effects were blocked by a Y1R antagonist (Tovote et al., Tryptophan synthase 2004). NPY is implicated in depression-like behavior and produces antidepressant effects. For example, central administration of NPY dose-dependently reduces immobility and increases swimming time in the forced swim test (Redrobe and et al, 2005, Stogner and Holmes, 2000 and Redrobe and et al, 2002), a screening paradigm for pharmacological anti-depressant activity. Y1R agonists and Y2R antagonists also produce anti-depressant effects in forced swim (Redrobe et al., 2002), whereas Y1R antagonists block the anti-depressant effects of NPY (Redrobe et al., 2002).