Involvement of isoproterenol-induced intracellular Zn2+ dynamics in the basolateral amygdala in conditioned fear memory.

Beta-adrenergic receptors in the basolateral amygdala play an essential role in fear memory, while the physiological role of intracellular Zn2+ remains to be clarified. Intracellular Zn2+ level was decreased 5 min after local injection of 500 µM isoproterenol (2 µl), a nonselective beta-adrenergic receptor agonist into the basolateral amygdala, suggesting that intracellular Zn2+ dynamic is linked with beta-adrenergic receptor signaling in the basolateral amygdala. When isoproterenol was injected into the basolateral amygdala 20 min prior to long-term potentiation (LTP) induction, LTP at perforant pathway-basolateral amygdala was enhanced and conditioned fear memory was also augmented, suggesting that isoproterenol leads to utilization of Zn2+ to consolidate fear memory followed by lowering intracellular Zn2+. We postulated that synaptic Zn2+ dynamics under conditioned fear experience regulates conditioned fear memory in cooperation with beta-adrenergic receptor signaling. When either intracellular Zn2+ chelator (ZnAF-2DA) or extracellular Zn2+ chelator (CaEDTA) was locally injected into the basolateral amygdala in the same manner, LTP was also enhanced. The local injection of ZnAF-2DA augmented fear memory. It is likely that the decrease in availability of intracellular Zn2+ by Zn2+ chelators under fear experience affects the function of Zn2+-required proteins followed by augmentation of fear memory and its related LTP. The present study suggests that beta-adrenergic receptor signaling is linked with intracellular Zn2+ signaling in the basolateral amygdala to consolidate conditioned fear memory. Because intracellular Zn2+ signaling is required for fear memory, the decrease in availability of intracellular Zn2+ may augment fear memory and its related LTP under non-physiological condition.

Isoproterenol injected into the basolateral amygdala rescues amyloid ß1-42-induced conditioned fear memory deficit via reducing intracellular Zn2+ toxicity.

On the basis of amyloid ß (Aß) peptides as triggers in atrophy of structures in the limbic system, here we postulated that Aß1-42-induced intracellular Zn2+ toxicity in the basolateral amygdala contributes to conditioned fear memory. Aß1-42 increased intracellular Zn2+ level in the amygdala after local injection of Aß1-42 into the basolateral amygdala, resulting in conditioned fear memory deficit via attenuated LTP at perforant pathway-basolateral amygdala synapses. Co-injection of isoproterenol, a beta-adrenergic receptor agonist, reduced Aß1-42-mediated increase in intracellular Zn2+, resulting in rescue of the memory deficit and attenuated LTP. The present study suggests that beta-adrenergic activity induced by isoproterenol in the basolateral amygdala rescues the impairment of conditioned fear memory by Aß1-42. The rescuing effect may be linked with reducing Aß1-42-induced intracellular Zn2+ toxicity. Furthermore, Aß1-42 injection into the basolateral amygdala also attenuated LTP at perforant pathway-dentate granule cell synapses, while co-injection of isoproterenol rescued it, suggesting that Aß1-42 toxicity in the basolateral amygdala also affects hippocampus-dependent memory. It is likely that beta-adrenergic receptor activation in the basolateral amygdala rescues the limbic system exposed to Aß1-42 toxicity.

Adrenergic ß receptor activation reduces amyloid ß1-42-mediated intracellular Zn2+ toxicity in dentate granule cells followed by rescuing impairment of dentate gyrus LTP.

Adrenergic ß receptor activation prevents human soluble amyloid ß (Aß)-induced impairment of long-term potentiation (LTP) in slices. On the basis of the evidence that human Aß1-42-induced impairment of LTP is due to Aß1-42-mediated Zn2+ toxicity, we postulated that adrenergic ß receptor activation reduces Aß1-42-mediated intracellular Zn2+ toxicity followed by rescuing Aß1-42 toxicity. To test the effect of adrenergic ß receptor activation, LTP was recorded at perforant pathway-dentate granule cell synapses of anesthetized rats 60 min after Aß1-42 injection into the dentate granule cell layer. Human Aß1-42-induced impairment of LTP was rescued by co-injection of isoproterenol, an adrenergic ß receptor agonist, but not by co-injection of phenylephrine, an adrenergic α1 receptor agonist. Isoproterenol did not reduce Aß1-42 uptake into dentate granule cells, but reduced increase in intracellular Zn2+ in dentate granule cells induced by Aß1-42. In contrast, phenylephrine did not reduce both Aß1-42 uptake and increase in intracellular Zn2+ by Aß1-42. In the case of human Aß1-40 and rat Aß1-42, which do not increase intracellular Zn2+, human Aß1-40- and rat Aß1-42-induced impairments of LTP were not rescued by co-injection of isoproterenol. The present study indicates that adrenergic ß receptor activation reduces Aß1-42-mediated increase in intracellular Zn2+ in dentate granule cells, resulting in rescuing Aß1-42-induced impairment of LTP. It is likely that noradrenergic neuron activation by stimulating the locus coeruleus is effective for rescuing Aß1-42-induced cognitive decline that is caused by intracellular Zn2+ dysregulation in the hippocampus.

Asymmetric Total Synthesis of Brasilicardins.

Brasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti-syn-anti-fused perhydrophenanthrene terpenoid scaffold (ABC-ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC-ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)-vinyl copper species. The late-stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A-D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Adrenergic ß receptor activation in the basolateral amygdala, which is intracellular Zn2+-dependent, rescues amyloid ß1-42-induced attenuation of dentate gyrus LTP.

On the basis of the evidence that the basolateral amygdala (BLA) modulates hippocampal memory processes via synaptic plasticity, here we report that adrenergic ß receptor activation in the BLA rescues amyloid ß1-42 (Aß1-42)-induced attenuation of long-term potentiation (LTP) at perforant pathway-dentate granule cell (DGC) synapses. When 500 µM isoproterenol (2 µl), an adrenergic ß receptor agonist, was injected into the BLA 20 min before LTP induction, LTP was enhanced. Isoproterenol-mediated enhancement of LTP was blocked by co-injection with 100 µM ZnAF-2DA, an intracellular Zn2+ chelator, suggesting that intracellular Zn2+ is required for the intracellular signaling cascade after adrenergic ß receptor activation in the BLA. Aß1-42-induced attenuation of LTP, which was induced by Aß1-42 injection into the dentate gyrus 60 min before LTP induction, was rescued by isoproterenol injection into the BLA 20 min before LTP induction, but not by 500 µM phenylephrine (2 µl), an adrenergic α1 receptor agonist, injection into the BLA, which did not enhance LTP unlike the case of isoproterenol injection. Interestingly, Aß1-42-induced attenuation of LTP was also rescued by 100 µM isoproterenol injection into the BLA 20 min before LTP induction, which did not enhance LTP. The present study demonstrates that adrenergic ß receptor activation in the BLA, which is linked with intracellular Zn2+ signaling, rescues Aß1-42-induced attenuation of dentate gyrus LTP. It is likely that adrenergic ß receptor activation in the BLA is a strategy for rescuing Aß1-42-induced cognitive decline that is associated with hippocampal synaptic plasticity.