NPY Y1 receptors differentially modulate GABAA and NMDA receptors via divergent signal-transduction pathways to reduce excitability of amygdala neurons.

Neuropeptide Y (NPY) administration into the basolateral amygdala (BLA) decreases anxiety-like behavior, mediated in part through the Y1 receptor (Y1R) isoform. Activation of Y1Rs results in G-protein-mediated reduction of cAMP levels, which results in reduced excitability of amygdala projection neurons. Understanding the mechanisms linking decreased cAMP levels to reduced excitability in amygdala neurons is important for identifying novel anxiolytic targets. We studied the intracellular mechanisms of activation of Y1Rs on synaptic transmission in the BLA. Activating Y1Rs by [Leu(31),Pro(34)]-NPY (L-P NPY) reduced the amplitude of evoked NMDA-mediated excitatory postsynaptic currents (eEPSCs), without affecting AMPA-mediated eEPSCs, but conversely increased the amplitude of GABAA-mediated evoked inhibitory postsynaptic currents (eIPSCs). Both effects were abolished by the Y1R antagonist, PD160170. Intracellular GDP-ß-S, or pre-treatment with either forskolin or 8Br-cAMP, eliminated the effects of L-P NPY on both NMDA- and GABAA-mediated currents. Thus, both the NMDA and GABAA effects of Y1R activation in the BLA are G-protein-mediated and cAMP-dependent. Pipette inclusion of protein kinase A (PKA) catalytic subunit blocked the effect of L-P NPY on GABAA-mediated eIPSCs, but not on NMDA-mediated eEPSCs. Conversely, activating the exchange protein activated by cAMP (Epac) with 8CPT-2Me-cAMP blocked the effect of L-P NPY on NMDA-mediated eEPSCs, but not on GABAA-mediated eIPSCs. Thus, NPY regulates amygdala excitability via two signal-transduction events, with reduced PKA activity enhancing GABAA-mediated eIPSCs and Epac deactivation reducing NMDA-mediated eEPSCs. This multipathway regulation of NMDA- and GABAA-mediated currents may be important for NPY plasticity and stress resilience in the amygdala.

Subendocardial increase in reactive oxygen species production affects regional contractile function in ischemic heart failure.

AIMS: Heart failure (HF) is characterized by regionalized contractile alterations resulting in loss of the transmural contractile gradient across the left ventricular free wall. We tested whether a regional alteration in mitochondrial oxidative metabolism during HF could affect myofilament function through protein kinase A (PKA) signaling. RESULTS: Twelve weeks after permanent left coronary artery ligation that induced myocardial infarction (MI), subendocardial (Endo) cardiomyocytes had decreased activity of complex I and IV of the mitochondrial electron transport chain and produced twice more superoxide anions than sham Endo and subepicardial cells. This effect was associated with a reduced antioxidant activity of superoxide dismutase and Catalase only in MI Endo cells. The myofilament contractile properties (Ca(2+) sensitivity and maximal tension), evaluated in skinned cardiomyocytes, were also reduced only in MI Endo myocytes. Conversely, in MI rats treated with the antioxidant N-acetylcysteine (NAC) for 4 weeks, the generation of superoxide anions in Endo cardiomyocytes was normalized and the contractile properties of skinned cardiomyocytes restored. This effect was accompanied by improved in vivo contractility. The beneficial effects of NAC were mediated, at least, in part, through reduction of the PKA activity, which was higher in MI myofilaments, particularly, the PKA-mediated hyperphosphorylation of cardiac Troponin I. INNOVATION: The Transmural gradient in the mitochondrial content/activity is lost during HF and mediates reactive oxygen species-dependent contractile dysfunction. CONCLUSIONS: Regionalized alterations in redox signaling affect the contractile machinery of sub-Endo myocytes through a PKA-dependent pathway that contributes to the loss of the transmural contractile gradient and impairs global contractility.

Adenosine A2A receptor induces protein kinase A-dependent functional modulation of human (alpha)3(beta)4 nicotinic receptor.

Adenosine modulates the function of nicotinic ACh receptors (nAChRs) in a variety of preparations, possibly through pathways involving protein kinase A (PKA), but these phenomena have not yet been investigated in detail. In this work we studied, using the patch clamp technique, the functional modulation of recombinant human α3ß4 nAChR by the A2A adenosine receptor, co-expressed in HEK cells. Tonic activation of A2A receptor slowed current decay during prolonged applications of nicotine and accelerated receptor recovery from desensitization. Together, these changes resulted into a more sustained current response upon multiple nicotine or ACh applications. These findings were confirmed in cultured mouse superior cervical ganglion neurones, which express nAChR containing the α3 subunit together with ß2 and/or ß4 and A2A receptor. Expression of the A2A receptor in HEK cells also increased the apparent potency of nAChR for nicotine, further supporting a general A2A-induced gain of function for nAChR. These effects were dependent on PKA since the direct activation of PKA mimicked, and its inhibition prevented almost completely, the effects of the A2A receptor. Mutations of R385 and S388 in the cytoplasmic loop of the α3 subunit abolished the functional modulation of nAChR induced by activation of A2A receptor, PKA and other Ser/Thr kinases, suggesting that this region constitutes a putative consensus site for these kinases. These data provide conclusive evidence that activation of the A2A receptor determines functional changes

Increase nitric oxide synthase activity in parotid glands from rats with experimental periodontitis.

OBJECTIVE: In this study we investigated the activity of the nitric oxide synthase (NOS) in parotid glands from rats with experimental periodontitis and controls. METHODS: Periodontitis was produced by a ligature placed around the cervix of the two lower first molar. Experiments were carried out 22 days after the ligature. RESULTS: Ligation caused an increase in parotid NOS activity. The selective blocker of the inducible isoform of the enzyme partially inhibited its activity in parotid glands from rat with ligature. In controls, the activity was partially inhibited by the antagonists of the selective neural and endothelial isoforms. NOS activity in rats with ligature was cyclic adenosine monophosphate (cAMP)-dependent while in controls it was calcium-dependent. Prostaglandin E2 concentration was increased in parotid gland from rats with ligature. The inhibitor of prostaglandin production, FR 122047, diminished both, prostaglandin production and NOS activity. In rats with ligature unstimulated amylase released is increased. Both, prostaglandin and NOS were involved in the increment of amylase release. CONCLUSION: It can be concluded that in parotid glands from ligated rats, prostaglandin E2 production is increased and, through cAMP accumulation, activates the inducible NOS isoform. The increment of nitric oxide production participates in the increase in basal amylase release.