Behavioral and electrophysiological evidence suggests that glutamatergic neurotransmission plays an important role in some of the long-term effects of cocaine and other drugs of abuse on brain function. We therefore examined the effect of repeated cocaine treatment on glutamate receptor subunit expression in central dopamine (DA) pathways implicated in many of cocaine's behavioral actions. By immunoblotting procedures using subunit-specific antibodies, we found that repeated, but not acute, cocaine treatment increased the levels of immunoreactivity of GluR1 (an AMPA receptor subunit) and NMDAR1 (an NMDA receptor subunit) in the ventral tegmental area (VTA), a nucleus containing mesolimbic DA neurons. In contrast, chronic cocaine treatment did not alter levels of GluR2 (an AMPA receptor subunit), NMDA2A/B (NMDA receptor subunits), or GluR6/7 (kainate receptor subunits) in this brain region. Moreover, GluR1 and NMDAR1 levels were not regulated in other regions of the mesolimbic or nigrostriatal DA pathways, including the substantia nigra. Because several drugs of abuse and stress can elicit common and cross-sensitizing effects on mesolimbic DA function, we next examined whether repeated morphine and stress treatments would regulate these proteins similarly in the VTA. Although morphine delivered by subcutaneous pellet implantation had no significant effect on subunit levels, morphine delivered intermittently by subcutaneous injections of escalating doses elevated GluR1 levels in the VTA. Repeated restraint stress also paradigm (2 stressors/d under variable conditions) increased both GluR1 and NMDAR1 levels in this brain region. Unlike cocaine, morphine, and stress, repeated treatment with other psychotropic drugs (haloperidol, raclopride, sertraline, and desipramine) that lack reinforcing or sensitizing properties did not regulate GluR1 or NMDAR1 subunit levels in the VTA. Increased glutamate receptor subunit expression in the VTA may represent an important molecular mechanism by which drugs of abuse and stress exert common, long-term effects on mesolimbic DA function.

Combined therapy with nadolol and isosorbide mononitrate is more effective than endoscopic ligation for the prevention of recurrent bleeding and is associated with a lower rate of major complications. A hemodynamic response to treatment is associated with a better long-term prognosis.

It is well known that cocaine blocks the dopamine transporter. This mechanism should lead to a general increase in dopaminergic neurotransmission, and yet dopamine D 1 receptors (D 1 Rs) play a more significant role in the behavioral effects of cocaine than the other dopamine receptor subtypes. Cocaine also binds to σ-1 receptors, the physiological role of which is largely unknown. In the present study, D 1 R and σ 1 R were found to heteromerize in transfected cells, where cocaine robustly potentiated D 1 R-mediated adenylyl cyclase activation, induced MAPK activation per se and counteracted MAPK activation induced by D 1 R stimulation in a dopamine transporterindependent and σ 1 R-dependent manner. Some of these effects were also demonstrated in murine striatal slices and were absent in σ 1 R KO mice, providing evidence for the existence of σ 1 R-D 1 R heteromers in the brain. Therefore, these results provide a molecular explanation for which D 1 R plays a more significant role in the behavioral effects of cocaine, through σ 1 R-D 1 R heteromerization, and provide a unique perspective toward understanding the molecular basis of cocaine addiction.receptor heteromer | drug addiction A key molecular mechanism contributing to the development of addiction by drugs of abuse consist of the increase of the extracellular levels of dopamine in the striatum, particularly in its ventral portion, the nucleus accumbens (1, 2). Cocaine causes a rapid and strong increase in striatal extracellular dopamine by its ability to bind with high affinity to the dopamine transporter (DAT) and to inhibit its function (3-5). In the striatum, dopamine signaling is mediated mainly by dopamine D 1 and D 2 receptors (D 1 Rs and D 2 Rs, respectively), which are mostly segregated in two phenotypically different subtypes of GABAergic medium-sized spiny neurons (MSNs) (6). Activation of D 1 Rs is an absolute requirement for the induction of many of the cellular and behavioral responses to cocaine, as deduced from studies performed in D 1 R KO mice and from experiments with transgenic mice in which D 1 R-or D 2 R-expressing MSNs are visualized by the expression of fluorescent proteins (7-11).The σ-1 receptor, originally proposed as a subtype of opioid receptors, is now considered to be a nonopioid receptor with two transmembrane domains, one extracellular loop and cytosolic N and C termini (12). The σ 1 R is highly expressed in the brain, including the striatum, and its association with neurons is well established (12, 13). However, its biological function and even its main endogenous neurotransmitter remain enigmatic (12). Cocaine interacts with σ 1 Rs at pharmacologically relevant concentrations (12,14). In fact, reducing brain σ 1 R levels with antisense oligonucleotides attenuates the convulsive and locomotor stimulant actions of cocaine (15, 16), and σ 1 R antagonists mitigate the actions of cocaine in animal models (12,14). A recent study showed that σ 1 R agonists not only potentiate the reinforcing effects of cocaine, but they may be self...

Quantitative blot immunolabeling techniques were used to determine the concentrations of ERK1 (M(r) 44 kDa) and ERK2 (M(r) 42 kDa), the two major extracellular signal-regulated protein kinases, in different regions of rat brain. The aggregate ERK concentrations (ERK1 and ERK2) were relatively high in each of the brain regions studied, ranging from approximately 0.35 ng/microgram protein in cerebellum to approximately 1.2 ng/microgram protein in nucleus accumbens. However, differences in the regional distributions of ERK1 and ERK2 resulted in ratios of their relative abundance that differed by close to 10-fold among the regions studied. The ratios of ERK1 protein to ERK2 protein varied along a rostral-caudal gradient from a low of 0.16 in frontal cortex to a high of 1.5 in pons/medulla. In hypotonic homogenates from regions at either extreme of the gradient, ERK1 and ERK2 were both found to be predominantly (> 80%) soluble. In subcellular fractions prepared from sucrose homogenates of frontal cortex and pons/medulla, both ERK1 and ERK2 were enriched in the synaptosomal and cytosolic fractions, whereas ERK2 was also enriched in the microsomal fraction. By contrast, in subfractions containing purified nuclei, levels of ERK1 and ERK2 were about one-third of those seen in homogenates and, in subfractions enriched in mitochondria, both ERK1 and ERK2 were barely detectable. The catalytic activity of the ERKs paralleled their protein levels in all of the brain regions except the hippocampus, in which the activity and phosphotyrosine content were disproportionately high. As a possible explanation for this apparent disparity, the regional distribution of ERK kinase (MEK), which phosphorylates and activates the ERKs, was also investigated. The levels of immunoreactivity of the M(r) 45 kDa ERK kinase band differed by about threefold among the brain regions, with the highest levels being present in nucleus accumbens, hippocampus, substantia nigra, and caudate/putamen. Therefore, a higher concentration of ERK kinase immunoreactivity did not appear to account for the disproportionate levels of ERK activity and phosphotyrosine content in the hippocampus. Potential regulation of ERK and ERK kinase levels was also investigated in rats subjected to chronic morphine treatment. ERK1 and ERK2 levels were increased selectively in locus coeruleus and caudate/putamen after chronic morphine treatment, whereas ERK kinase immunoreactivity remained unchanged in all of the brain regions analyzed. In summary, the regional differences in ERK and ERK kinase expression and the region-specific regulation of ERK expression suggest that ERK-related signaling may play an important role in CNS function and its adaptive responses.