Persistence of the extinction of fear memory requires late-phase cAMP/PKA signaling in the infralimbic cortex

Fear extinction is a form of new learning that inhibits expression of the original fear memory without erasing the conditioned stimulus-unconditioned stimulus association. Much is known about the mechanisms that underlie the acquisition of extinction, but the way in which fear extinction is maintained has been scarcely explored. Evidence suggests that protein kinase A (PKA) in the frontal cortex might be related to the persistence of extinction. Phosphodiesterase-4 (PDE4) specifically hydrolyzes cyclic adenosine monophosphate (cAMP). The present study evaluated the effect of the selective PDE4 inhibitor roflumilast (ROF; 0.01, 0.03, and 0.1 mg/kg given i.p.) on acquisition and consolidation of the extinction of fear memory in male Wistar rats in a contextual fear conditioning paradigm. When administered before acquisition, 0.1 mg/kg ROF disrupted short-term (1 day) extinction recall. In contrast, 0.03 mg/kg ROF administration in the late consolidation phase (3 h after extinction learning) but not in the early phase immediately after learning improved long-term extinction recall at 11 days, suggesting potentiation of the persistence of extinction. This effect of ROF requires the first (day 1) exposure to the context. A similar effect was observed when 9 ng ROF or 30 µM 8-bromoadenosine 3',5'-cAMP (PKA activator) was directly infused in the infralimbic cortex (IL), a brain region necessary for memory extinction. The PKA activity-dependent ROF-induced effect in the IL was correlated with an increase in its brain-derived neurotrophic factor (BDNF) protein expression, while blockade of PKA with 10 µM H89 in the IL abolished the ROF-induced increase in BDNF expression and prevented the effect of ROF on extinction recall. These effects were not associated with changes in anxiety-like behavior or general exploratory behavior. Altogether, these findings suggest that cAMP-PKA activity in the IL during the late consolidation phase after extinction learning underlies the persistence of extinction.

MODERATE INTENSITY IS A BETTER STIMULUS TO INDUCE QUADRIPECS FEMORIS POWER IN ELDERLY ADULTS

ABSTRACT Introduction: The best strategy for improving knee extensor power, a major functional capacity indicator in older adults, is power training. Nonetheless, the training intensity required to induce optimal gains is yet to be found. Objective: Our purpose was to compare knee extensor peak power responses between low, moderate, and high intensity load conditions (30%, 50% and 70% of 1RM). Methods: Thirteen sedentary elderly women performed six knee extensions in each load condition, calculating knee extensor mechanical work/power output and knee extension peak angular velocity. Results: No difference in peak power was found between the high (207.0 ± 68.1 W) and moderate (206.1 ± 71.6 W) load conditions (p = 0.994), and both had higher values (p ≤0.004) than the low intensity condition (135.6 ± 56.3 W). Conclusion: Moderate load at 50% of 1RM appears to be the preferred strategy for inducing knee extensor power output because in contrast with the high intensity condition, the moderate load yielded higher angular peak velocity, which is also a functional indicator. Level of Evidence ll; Therapeutic studies - Investigating treatment results.

Resistance to cerebral malaria in tumor necrosis factor-alpha/beta-deficient mice is associated with a reduction of intercellular adhesion molecule-1 up-regulation and T helper type 1 response

Tumor necrosis factor (TNF) induced by Plasmodium berghei ANKA (PbA) infection was suggested to play an important role in the development of cerebral malaria (CM). We asked whether TNF-alpha/beta double-deficient mice, which have a complete disruption of the TNF-signaling pathways, are protected from CM and what might be the possible mechanisms of protection. PbA infection induces fatal CM in wild-type mice, which die within 5 to 8 days with severe neurological signs. In contrast, TNF-alpha/beta-deficient mice are completely resistant to PbA-induced CM. As PbA-induced up-regulation of endothelial intercellular adhesion molecule (ICAM)-1 expression as well as the systemic release of nitric oxide is found only in wild-type mice, TNF is apparently central for the recruitment of mononuclear cells and microvascular damage. Mononuclear cell adhesion to the endothelium, vascular leak and, perivascular hemorrhage are found only in the brain of wild-type mice. By contrast, the development of parasitemia and anemia is independent of TNF. Resistance to CM in TNF-alpha/beta-deficient mice is associated with reduced interferon-gamma and interleukin-12 expression in the brain, in the absence of increased T helper type 2 cytokines. In conclusion, TNF apparently is required for PbA-induced endothelial ICAM-1 up-regulation and subsequent microvascular pathology resulting in fatal CM. In the absence of TNF, ICAM-1 and nitric oxide up-regulation are reduced, and PbA infection fails to cause fatal CM.