Steroids synthesized in the periphery or de novo in the brain, so called ‘neurosteroids’, exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the γ-aminobutyric acid type A (GABA_A) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA_A receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (σ) receptors. Recent studies particularly demonstrated that the σ₁ receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the σ₁ receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the σ₁-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective σ₁ drugs.

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Vascular smooth muscle contraction is mediated by activation of extracellular signal-regulated kinase (ERK) 1/2, an isoform of mitogen-activated protein kinase (MAPK). However, the role of stress-activated protein kinase/c-Jun N-terminal kinase (JNK) in vascular smooth muscle contraction has not been defined. We investigated the role of JNK in the contractile response to norepinephrine (NE) in rat aortic smooth muscle. NE evoked contraction in a dose-dependent manner, and this effect was inhibited by the JNK inhibitor SP600125. NE increased the phosphorylation of JNK, which was greater in aortic smooth muscle from hypertensive rats than from normotensive rats. NE-induced JNK phosphorylation was significantly inhibited by SP600125 and the conventional-type PKC (cPKC) inhibitor Gö6976, but not by the Rho kinase inhibitor Y27632 or the phosphatidylinositol 3-kinase inhibitor LY294002. Thymeleatoxin, a selective activator of cPKC, increased JNK phosphorylation, which was inhibited by Gö6976. SP600125 attenuated the phosphorylation of caldesmon, an actin-binding protein whose phosphorylation is increased by NE. These results show that JNK contributes to NE-mediated contraction through phosphorylation of caldesmon in rat aortic smooth muscle, and that this effect is regulated by the PKC pathway, especially cPKC.

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We investigated the effects of bifemelane, a nootropic drug, on the intracellular calcium concentration ([Ca²⁺]_i) in rat cerebral astrocytes using a Ca²⁺ imaging device. At concentrations of 10 – 30 μM, bifemelane induced a slow onset and small increase in the [Ca²⁺]_i, while at higher concentrations (100 – 300 μM), it induced a rapid transient increase in the [Ca²⁺]_i during administration and a second large increase was seen during drug washout. The first peak was observed in Ca²⁺-free medium, but its onset was significantly delayed, and no second peak was seen. Neither of these effects was seen in cells treated with thapsigargin, a specific inhibitor of endoplasmic reticulum Ca²⁺-ATPase, in Ca²⁺-free medium. When thapsigargin-treated astrocytes were returned to normal medium containing Ca²⁺ (1.8 mM), the [Ca²⁺]_i increased significantly, and this effect was reversely inhibited by bifemelane. We conclude that bifemelane causes the first peak by stimulating release from intracellular Ca²⁺ stores and the second by capacitive entry through store–operated Ca²⁺ channels. Although the detail mechanisms of action of the drug are still unknown, bifemelane will be provided as a pharmacological tool for basic studies on astrocytes.

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In this study, we examined the inhibitory mechanism of monensin on high K⁺-induced contraction in guinea-pig urinary bladder. The relaxant effect of monensin (0.001 – 10 μM) was more potent than those of NaCN (100 μM – 1 mM) and forskolin (3 – 10 μM). Monensin (0.1 μM), NaCN (300 μM), or forskolin (10 μM) inhibited high K⁺-induced contraction without decreasing [Ca²⁺]_i level. Monensin and NaCN remarkably decreased creatine phosphate and ATP contents. Monensin and NaCN inhibited high K⁺-induced increases in flavoprotein fluorescence, which is involved in mitochondrial respiration. Forskolin increased cAMP content but monensin did not. Monensin increased Na⁺ content at 10 μM but not at 0.1 μM that induced maximum relaxation. In the α-toxin-permeabilized muscle, forskolin significantly inhibited the Ca²⁺-induced contraction, but monensin did not affect it. These results suggest that the relaxation mechanism of monensin in smooth muscle of urinary bladder may be an inhibition of oxidative metabolism.

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In this study, we investigated the effect of vesicular zinc on ischemic neuronal injury. In cultured neurons, addition of a low concentration (under 100 μM) of zinc inhibited both glutamate-induced calcium influx and neuronal death. In contrast, a higher concentration (over 150 μM) of zinc decreased neuronal viability, although calcium influx was inhibited. These results indicate that zinc exhibits biphasic effects depending on its concentration. Furthermore, in cultured neurons, co-addition of glutamate and CaEDTA, which binds extra-cellular zinc, increased glutamate-induced calcium influx and aggravated the neurotoxicity of glutamate. In a rat transient middle cerebral artery occlusion (MCAO) model, the infarction volume, which is related to the neurotoxicity of glutamate, increased rapidly on the intracerebral ventricular injection of CaEDTA 30 min prior to occlusion. These results suggest that zinc released from synaptic vesicles may provide a protective effect against ischemic neuronal injury.

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Hyperproliferation of phenotypically modified vascular smooth muscle cells (VSMCs) is one of the major factors in the development of atherosclerosis and restenosis. Previously it was demonstrated that benidipine, a dihydropyridine-calcium channel antagonist, reduced neointimal formation in a rat balloon-injury model. In the present study, we examined the effect of benidipine on the phenotypic modulation and proliferation of VSMCs, using primary cultures of rat VSMCs. In the absence of drug treatment, protein levels of the smooth muscle specific markers, such as smooth muscle myosin heavy chain-1 (SM1), calponin 1, and α-actin, decreased during culture. However, treatment of VSMCs with benidipine (3 – 10 μmol/L) for 1 week reversed the effect in a concentration-related manner so that high levels of marker proteins were maintained. The expression of calponin mRNAs was reduced markedly during 1-week culture, and treatment with benidipine (3 μmol/L) significantly inhibited the reduction. Treatment with benidipine for 2 days increased the level of p21 protein and partially reduced p70 S6 kinase 1 (p70S6K1) activity. These data suggest that benidipine may arrest the growth of VSMCs, thereby preventing cell dedifferentiation. These additional properties of benidipine suggest that the drug should provide useful therapy for atherosclerosis and restenosis.

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Generalizations of NMDA-receptor antagonists to the discriminative stimulus effects of κ-opioid receptor agonists in rats were examined. Phencyclidine, MK-801, and ketamine, non-competitive NMDA-receptor antagonists, generalized to the discriminative stimulus effects of U-50,488H, but not those of TRK-820, whereas (±)-3-(2-carbaxypiperazine-4-yl) propyl-1-phosphonic acid (CPP), a competitive NMDA-receptor antagonist, and ifenprodil, an NR1/NR2B NMDA-receptor antagonist, did not, suggesting that non-competitive NMDA-receptor antagonists possess U-50,488H-like discriminative stimulus effects in rats. Since U-50,488H and phencyclidine both induce aversive effects, our findings indicate that the cue of the discriminative stimulus effects of U-50,488H and non-competitive NMDA-receptor antagonists may be associated with their aversive effects.

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Heme oxygenase-1 (HO-1) is a stress-inducible isoform of HO with potential cytoprotective effects. Monocyte activation/migration mediated by monocyte chemoattractant protein-1 (MCP-1) is one of the earliest and important events in the pathogenesis of atherosclerosis. We examined the effect of HO-1 on the production of lysophosphatidylcholine (Lyso-PC)-induced MCP-1 in the human promonocytic cell line U937. Increased HO-1 induction by hemin resulted in a significant decrease in the Lyso-PC-mediated induction of MCP-1 mRNA expression. SnPP (IX), the specific inhibitor of HO-1 enzymatic activity, prevented the hemin-mediated attenuation of MCP-1 mRNA expression. These results suggest that HO-1 may work as an anti-atherogenic agent through the attenuation of MCP-1 production.

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