Activation of phosphatidylinositol-linked novel D1 dopamine receptors inhibits high-voltage-activated Ca2+ currents in primary cultured striatal neurons

Evidence-based complementary and alternative medicine bioinformatics approach through network pharmacology and molecular docking to determine the molecular mechanisms of Erjing pill in Alzheimer's disease

Erjing pill, a Traditional Chinese Medicine (TCM) formulation composed of Polygonatum sibiricum and Lycium chinense, has an important role in the treatment of Alzheimer's disease (AD). However, the underlying mechanisms of the action of Erjing pill in AD have remained elusive. In the present study, the key ingredients of Erjing pill were investigated and the active components and their mechanisms of action on AD were analyzed based on networks pharmacology. By using the TCM and TCM Systems Pharmacology and databases, the components of Erjing pill were screened and the data were captured using Discovery Studio. The SwissTarget webserver database was used to predict the potential protein targets of Erjing pill components for pathologies related to AD. The data were further analyzed with the disease targets of AD based on analysis of the Online Mendelian Inheritance in Man, DiGSeE and Therapeutic Target Database. Subsequent analysis of mechanistic pathways of the screened components and protein targets allowed us to construct a network by using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes, which revealed potential molecular mechanisms of Erjing pill against AD. Finally, the protective effect of three active components on neurons was verified using an in vitro injury model of PC12 cells induced by Aβ25-35. The results indicated that 65 bioactive components of Erjing pill, including lauric acid and zederone, and 6 targets, including acetylcholinesterase, butylcholinesterase and amyloid protein precursor, were closely associated with the prevention and treatment of AD. The molecular components of Erjing pill were indicated to be involved in various biological signaling processes, mainly in synaptic signal transmission, transsynaptic signal transmission and chemical synaptic transmission. Furthermore, related pathways targeted by Erjing pill in AD included the regulation of neuroactive ligand-receptor interactions, the PI3K-Akt signaling pathway, serotoninergic synapses, calcium signaling pathways and dopaminergic synapses. A cell viability assay indicated that the compounds (polygonatine A, polygonatine C and 4',5-dihydroxyflavone) assessed were able to significantly improve the survival rate and increase the Ca2+ level in a PC12 cell model of AD induced by amyloid-β25-35. The present study revealed that the mechanisms of action of Erjing pill to prevent and treat AD included a multicompound, multitarget and multipathway regulatory network.

Task-Dependent Effects of SKF83959 on Operant Behaviors Associated With Distinct Changes of CaMKII Signaling in Striatal Subareas

BACKGROUND

SKF83959, an atypical dopamine (DA) D1 receptor agonist, has been used to test the functions of DA-related receptor complexes in vitro, but little is known about its impact on conditioned behavior. The present study examined the effects of SKF83959 on operant behaviors and assayed the neurochemical mechanisms involved.

METHODS

Male rats were trained and maintained on either a fixed-interval 30-second (FI30) schedule or a differential reinforcement of low-rate response 10-second (DRL10) schedule of reinforcement. After drug treatment tests, western blotting assayed the protein expressions of the calcium-/calmodulin-dependent protein kinase II (CaMKII) and the transcription factor cyclic AMP response element binding protein (CREB) in tissues collected from 4 selected DA-related areas.

RESULTS

SKF83959 disrupted the performance of FI30 and DRL10 behaviors in a dose-dependent manner by reducing the total number of responses in varying magnitudes. Moreover, the distinct profiles of the behavior altered by the drug were manifested by analyzing qualitative and quantitative measures on both tasks. Western-blot results showed that phospho-CaMKII levels decreased in the nucleus accumbens and the dorsal striatum of the drug-treated FI30 and DRL10 subjects, respectively, compared with their vehicle controls. The phospho-CREB levels decreased in the nucleus accumbens and the hippocampus of drug-treated FI30 subjects but increased in the nucleus accumbens of drug-treated DRL10 subjects.

CONCLUSIONS

Our results provide important insight into the neuropsychopharmacology of SKF83959, indicating that the drug-altered operant behavior is task dependent and related to regional-dependent changes of CaMKII-CREB signaling in the mesocorticolimbic DA systems.

Evidence against dopamine D1/D2 receptor heteromers

Hetero-oligomers of G-protein-coupled receptors have become the subject of intense investigation, because their purported potential to manifest signaling and pharmacological properties that differ from the component receptors makes them highly attractive for the development of more selective pharmacological treatments. In particular, dopamine D1 and D2 receptors have been proposed to form hetero-oligomers that couple to Gαq proteins, and SKF83959 has been proposed to act as a biased agonist that selectively engages these receptor complexes to activate Gαq and thus phospholipase C. D1/D2 heteromers have been proposed as relevant to the pathophysiology and treatment of depression and schizophrenia. We used in vitro bioluminescence resonance energy transfer, ex vivo analyses of receptor localization and proximity in brain slices, and behavioral assays in mice to characterize signaling from these putative dimers/oligomers. We were unable to detect Gαq or Gα11 protein coupling to homomers or heteromers of D1 or D2 receptors using a variety of biosensors. SKF83959-induced locomotor and grooming behaviors were eliminated in D1 receptor knockout (KO) mice, verifying a key role for D1-like receptor activation. In contrast, SKF83959-induced motor responses were intact in D2 receptor and Gαq KO mice, as well as in knock-in mice expressing a mutant Ala(286)-CaMKIIα that cannot autophosphorylate to become active. Moreover, we found that, in the shell of the nucleus accumbens, even in neurons in which D1 and D2 receptor promoters are both active, the receptor proteins are segregated and do not form complexes. These data are not compatible with SKF83959 signaling through Gαq or through a D1/D2 heteromer and challenge the existence of such a signaling complex in the adult animals that we used for our studies.

Activation of D1-like receptor-dependent phosphatidylinositol signal pathway by SKF83959 inhibits voltage-gated sodium channels in cultured striatal neurons

Dopamine, a key neurotransmitter mediating the rewarding effects, exerts some of its effects by modulating neuronal excitability of striatal medium spiny neurons. A D1-like dopamine receptor-dependent phosphatidylinositol signal pathway exists in the striatum, however little is known about its role in the dopaminergic modulation of striatal neuronal excitability. 3-Methyl-6-chloro-7, 8-hydroxy-1-(3-methylphenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF83959) is a selective D1 receptor agonist with high-affinity. Here, we observed its effect on the voltage-gated sodium channels (VGSCs) in primary cultured striatal neurons by whole cell patch-clamp technique. We found that SKF83959 induced an inhibition on VGSCs in a dose-dependent manner in striatal neurons (IC50 value: 3.31 ± 0.39 μM), which could be prevented by antagonist of D1 receptor, but not that of D2, α1 adrenergic, or cholinoceptor. The effect of SKF83959 on VGSCs was also prevented by pretreatment with inhibitors of phospholipase C (PLC) and protein kinases C (PKC), but the inositol-1,4,5-phosphate 3 (IP3) antagonist did not occlude SKF83959 (1μM)-induced reduction of VGSCs. These data indicate that SKF83959 inhibits VGSCs in cultured striatal neurons via D1-like receptor-phosphatidylinositol-PKC pathway, which may underlie the dopaminergic modulation on striatal neuronal excitability.

The cellular building blocks of breathing

Respiratory brainstem neurons fulfill critical roles in controlling breathing: they generate the activity patterns for breathing and contribute to various sensory responses including changes in O2 and CO2. These complex sensorimotor tasks depend on the dynamic interplay between numerous cellular building blocks that consist of voltage-, calcium-, and ATP-dependent ionic conductances, various ionotropic and metabotropic synaptic mechanisms, as well as neuromodulators acting on G-protein coupled receptors and second messenger systems. As described in this review, the sensorimotor responses of the respiratory network emerge through the state-dependent integration of all these building blocks. There is no known respiratory function that involves only a small number of intrinsic, synaptic, or modulatory properties. Because of the complex integration of numerous intrinsic, synaptic, and modulatory mechanisms, the respiratory network is capable of continuously adapting to changes in the external and internal environment, which makes breathing one of the most integrated behaviors. Not surprisingly, inspiration is critical not only in the control of ventilation, but also in the context of "inspiring behaviors" such as arousal of the mind and even creativity. Far-reaching implications apply also to the underlying network mechanisms, as lessons learned from the respiratory network apply to network functions in general.

SKF83959, an agonist of phosphatidylinositol-linked D(1)-like receptors, promotes ERK1/2 activation and cell migration in cultured rat astrocytes

Extracellular signal-regulated kinase 1/2 (ERK1/2) is a member of the mitogen-activated protein kinase family. It can mediate cell migration. Classical dopamine receptor-mediated ERK1/2 phosphorylation is widely studied in neurons. Here, we report that ERK1/2 phosphorylation is also modulated by putative phosphatidylinositol-linked D₁-like receptors in cultured rat astrocytes. 6-chloro-7,8-dihydroxy-3-methyl-1-(3-methylphenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF83959), an agonist of the putative phosphatidylinositol-linked D₁-like receptors, was found to enhance ERK1/2 phosphorylation, which then promoted the migration of cultured astrocytes. The SKF83959-induced ERK1/2 phosphorylation was found to be Ca²⁺-independent based on the following observations: i. chelating intracellular Ca²⁺ did not inhibit ERK1/2 phosphorylation and astrocyte migration; ii. blockage of the release of intracellular Ca²⁺ from the endoplasmic reticulum by an inhibitor of inositol 1,4,5-trisphosphate (IP3) receptor did not attenuate ERK1/2 phosphorylation. However, inhibition of phospholipase C (PLC), the upstream molecule of internal Ca²⁺ release, disabled SKF83959’s ability to elevate the level of ERK1/2 phosphorylation. Both non-selective protein kinase C (PKC) inhibitor and PKCδ selective inhibitor prevented ERK1/2 phosphorylation increase and astrocyte migration, but PKCα inhibitor did not. This suggests that Ca²⁺-independent and diacylglycerol-dependent PKCδ acts downstream of putative phosphatidylinositol-linked D₁-like receptor activation and mediates SKF83959-induced elevation of ERK1/2 phosphorylation in order to modulate astrocyte migration. In conclusion, our results demonstrate that SKF83959-induced increases in ERK1/2 phosphorylation and astrocyte migration are dependent on PLC-PKCδ signals. This might help us to further understand the functions of the putative phosphatidylinositol-linked D₁-like receptors in the nervous system.

Sinomenine protects against ischaemic brain injury: involvement of co-inhibition of acid-sensing ion channel 1a and L-type calcium channels

BACKGROUND AND PURPOSE

Sinomenine (SN), a bioactive alkaloid, has been utilized clinically to treat rheumatoid arthritis in China. Our preliminary experiments indicated that it could protect PC12 cells from oxygen-glucose deprivation-reperfusion (OGD-R), we thus investigated the possible effects of SN on cerebral ischaemia and the related mechanism.

EXPERIMENTAL APPROACH

Middle cerebral artery occlusion in rats was used as an animal model of ischaemic stroke in vivo. The mechanisms of the effects of SN were investigated in vitro using whole-cell patch-clamp recording, calcium imaging in PC12 cells and rat cortical neurons subjected to OGD-R.

KEY RESULTS

Pretreatment with SN (10 and 30 mg·kg(-1) , i.p.) significantly decreased brain infarction and the overactivation of calcium-mediated events in rats subjected to 2 h ischaemia followed by 24 h reperfusion. Extracellular application of SN inhibited the currents mediated by acid-sensing ion channel 1a and L-type voltage-gated calcium channels, in the rat cultured neurons, in a concentration-dependent manner. These inhibitory effects contribute to the neuroprotection of SN against OGD-R and extracellular acidosis-induced cytotoxicity. More importantly, administration of SN (30 mg·kg(-1) , i.p.) at 1 and 2 h after cerebral ischaemia also decreased brain infarction and improved functional recovery.

CONCLUSION AND IMPLICATIONS

SN exerts potent protective effects against ischaemic brain injury when administered before ischaemia or even after the injury. The inhibitory effects of SN on acid-sensing ion channel 1a and L-type calcium channels are involved in this neuroprotection.