Background-Recent cell-based studies have found that cGMP synthesis and hydrolysis by phosphodiesterase (PDE) appear compartmentalized, with nitric oxide synthase-derived and/or PDE type 5 (PDE-5)-hydrolyzable cGMP undetected at the sarcolemmal membrane in contrast to cGMP stimulated by natriuretic peptide. In the present study, we determine the functional significance of such compartments with a comparison of ␤-adrenergic modulation by PDE-5 inhibition to that of natriuretic peptide stimulation in both cardiomyocytes and intact hearts. The potential role of differential cGMP and protein kinase G stimulation by these 2 modulators was also studied. Methods and Results-Intact C57/BL6 mouse hearts were studied with pressure-volume analysis, and adult isolated myocytes were studied with fluorescence microscopy. PDE-5 inhibition with 0.1 to 1 mol/L sildenafil (SIL) suppressed isoproterenol (ISO)-stimulated contractility, whereas 10 mol/L atrial natriuretic peptide (ANP) had no effect. ISO suppression by SIL was prevented in cells pretreated with a protein kinase G inhibitor. Surprisingly, myocardial cGMP changed little with SILϩISO yet rose nearly 5-fold with ANP, whereas protein kinase G activation (vasodilator-stimulated protein phosphorylation; ELISA assay) displayed the opposite: increased with SILϩISO but unaltered by ANPϩISO. PDE-5 and ANP compartments were functionally separated, as inhibition of nitric oxide synthase by N

-1 Receptors are endoplasmic reticulum (ER) chaperones that are implicated in the neuroplasticity associated with psychostimulant abuse. We immunocytochemically examined the distribution of -1 receptors in the brain of drug-naive rats and then examined the dynamics of -1 receptors and other ER chaperones in specific brain subregions of rats that self-administered methamphetamine, received methamphetamine passively, or received only saline injections. -1 Receptors were found to be expressed in moderate to high levels in the olfactory bulb, striatum, nucleus accumbens shell, olfactory tubercle, amygdala, hippocampus, red nucleus, ventral tegmental area, substantia nigra, and locus ceruleus. Methamphetamine, whether self-administered or passively received, significantly elevated ER chaperones including the -1 receptor, BiP, and calreticulin in the ventral tegmental area and substantia nigra. In the olfactory bulb, however, only the -1 receptor chaperone was increased, and this increase occurred only in rats that actively self-administered methamphetamine. Consistent with an increase in -1 receptors, extracellular signal-regulated kinase was found to be activated and protein kinase A attenuated in the olfactory bulb of methamphetamine self-administering rats. -1 Receptors in the olfactory bulb were found to be colocalized with dopamine D1 receptors. These results indicate that methamphetamine induces ER stress in the ventral tegmental area and substantia nigra in rats whether the drug is received actively or passively. However, the changes seen only in rats that actively self-administered methamphetamine suggest that D1 and -1 receptors in the olfactory bulb might play an important role in the motivational conditioning/learning aspects of methamphetamine self-administration in the rat.

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The -1 receptor (Sig-1R) can bind psychostimulants and was shown to be up-regulated in the brain of methamphetamine self-administering rats. Up-regulation of Sig-1Rs has been implicated in neuroplasticity. However, the mechanism(s) whereby Sig-1Rs are up-regulated by psychostimulants is unknown. Here, we employed a neuroblastoma cell line B-104, devoid of dopamine receptors and transporter, and examined the effects of psychostimulants as well as cAMP on the expression of Sig-1Rs in this cell line, with a specific goal to identify signal transduction pathway(s) that may regulate Sig-1R expression. Chronic treatments of B-104 cells with physiological concentrations of cocaine or methamphetamine failed to alter the expression of Sig-1Rs. N 6 ,2Ј-O-Dibutyryl-cAMP (dBcAMP), when used at 0.5 mM, caused a down-regulation of Sig-1Rs that could be blocked by a protein kinase A (PKA) inhibitor, N- [2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89). However, dB-cAMP, when used at 2 mM, caused an up-regulation of Sig-1Rs that was insensitive to the H-89 blockade but was partially blocked by an extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase inhibitor PD98059 (2Ј-amino-3Ј-methoxyflavone). Furthermore, 2 mM dB-cAMP induced an ERK phosphorylation lasting at least 90 min, at which time the phosphorylation caused by 0.5 mM dB-cAMP had already diminished. PD98059, applied 90 min after addition of 2 mM dB-cAMP, attenuated the Sig-1R up-regulation. Our results indicate that cAMP is bimodal in regulating Sig-1R expression: a downregulation via PKA and an up-regulation via ERK. Results also suggest that psychostimulants may manipulate the cAMP-PKA-Sig-1R and/or the cAMP-ERK-Sig-1R pathways to achieve a neuroplasticity that favors addictive behaviors.The -1 receptor (Sig-1R) is a unique intracellular nonopioid binding site with nano-to low-micromolar affinities for diverse classes of drugs including benzomorphans, antidepressants, neuroleptics, steroid hormones including progesterone, and psychostimulants such as cocaine and methamphetamine (Sharkey et al., 1988;Su et al., 1988;Snyder and Largent, 1989;Quirion et al., 1992;Nguyen et al., 2005).Sig-1Rs exist in the central and peripheral nervous systems where they modulate neurotransmitter release and cell excitability via ion channels (Monnet et al., 1990;Hayashi and Su, 2001;Aydar et al., 2002;Nuwayhid and Werling, 2003). Behavioral studies implicated Sig-1Rs in higher ordered brain functions including mood and learning and memory (Maurice et al., 2001;Meunier et al., 2004).Recently, a number of studies suggested that psychostimulant-induced behaviors involve an up-regulation of Sig-1Rs. Ujike et al. (1996) demonstrated that cocaine-induced locomotor sensitization was cross-sensitized to the Sig-1R agonist 3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and that the sensitization could be suppressed by a Sig-1R antagonist,

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