Mixed metal nanoparticle assembly and the effect on surface enhanced raman scattering

Here we report the assembly of mixed metal nanoparticles using an oligonucleotide-templated approach. Substitution of one of the gold nanoparticle probes with an analagous silver probe to produce a hetero-metal duplex permitted surface enhanced Raman scattering of the dye label, exploiting the improved surface enhancement properties of silver nanoparticles whilst maintaining the surface chemistry benefits of gold nanoaprticle

Recent updates on incubation of drug craving: a mini-review

Cue-induced drug craving progressively increases after prolonged withdrawal from drug self-administration in laboratory animals, a behavioral phenomenon termed 'incubation of drug craving.' Studies over the years have revealed several important neural mechanisms contributing to incubation of drug craving. In this mini-review, we first discuss three excellent Addiction Biology publications on incubation of drug craving in both human and laboratory animals. We then review several key publications from the past year on behavioral and mechanistic findings related to incubation of drug craving

Different Roles of BDNF in Nucleus Accumbens Core versus Shell during the Incubation of Cue-Induced Cocaine Craving and Its Long-Term Maintenance

Brain-derived neurotrophic factor (BDNF) contributes to diverse types of plasticity, including cocaine addiction. We investigated the role of BDNF in the rat nucleus accumbens (NAc) in the incubation of cocaine craving over 3 months of withdrawal from extended access cocaine self-administration. First, we confirmed by immunoblotting that BDNF levels are elevated after this cocaine regimen on withdrawal day 45 (WD45) and showed that BDNF mRNA levels are not altered. Next, we explored the time course of elevated BDNF expression using immunohistochemistry. Elevation of BDNF in the NAc core was detected on WD45 and further increased on WD90, whereas elevation in shell was not detected until WD90. Surface expression of activated tropomyosin receptor kinase B (TrkB) was also enhanced on WD90. Next, we used viral vectors to attenuate BDNF-TrkB signaling. Virus injection into the NAc core enhanced cue-induced cocaine seeking on WD1 compared with controls, whereas no effect was observed on WD30 or WD90. Attenuating BDNF-TrkB signaling in shell did not affect cocaine seeking on WD1 or WD45 but significantly decreased cocaine seeking on WD90. These results suggest that basal levels of BDNF transmission in the NAc core exert a suppressive effect on cocaine seeking in early withdrawal (WD1), whereas the late elevation of BDNF protein in NAc shell contributes to incubation in late withdrawal (WD90). Finally, BDNF protein levels in the NAc were significantly increased after ampakine treatment, supporting the novel hypothesis that the gradual increase of BDNF levels in NAc accompanying incubation could be caused by increased AMPAR transmission during withdrawal

BDNF Contributes to Both Rapid and Homeostatic Alterations in AMPA Receptor Surface Expression in Nucleus Accumbens Medium Spiny Neurons

Brain-derived neurotrophic factor (BDNF) plays a critical role in plasticity at glutamate synapses and the effects of repeated cocaine exposure. We recently showed that intracranial injection of BDNF into the rat nucleus accumbens (NAc), a key region for cocaine addiction, rapidly increases AMPA receptor (AMPAR) surface expression. To further characterize BDNF’s role in both rapid AMPAR trafficking and slower, homeostatic changes in AMPAR surface expression, we investigated the effects of acute (30 min) and long-term (24 h) treatment with BDNF on AMPAR distribution in NAc medium spiny neurons from postnatal rats co-cultured with mouse prefrontal cortex (PFC) neurons to restore excitatory inputs. Immunocytochemical studies showed that acute BDNF treatment increased cell surface GluA1 and GluA2 levels, as well as their co-localization, on NAc neurons. This effect of BDNF, confirmed using a protein crosslinking assay, was dependent on ERK but not AKT signaling. In contrast, long-term BDNF treatment decreased AMPAR surface expression on NAc neurons. Based on this latter result, we tested the hypothesis that BDNF plays a role in AMPAR “scaling down” in response to a prolonged increase in neuronal activity produced by bicuculline (24 h). Supporting this hypothesis, decreasing BDNF signaling with the extracellular BDNF scavenger TrkB-Fc prevented the scaling down of GluA1 and GluA2 surface levels in NAc neurons normally produced by bicuculline. In conclusion, BDNF exerts bidirectional effects on NAc AMPAR surface expression, depending on duration of exposure. Furthermore, BDNF’s involvement in synaptic scaling in the NAc differs from its previously described role in the visual cortex

The PKC Inhibitor Ro31-8220 Blocks Acute Amphetamine-Induced Dopamine Overflow in the Nucleus Accumbens

Acute administration of the psychostimulant amphetamine increases extracellular levels of dopamine (DA) by reversing the DA transporter on ascending midbrain DA neurons. In vitro studies using striatal synaptosomal, slice and nucleus accumbens (NAcc) tissue preparations have implicated protein kinase C (PKC) in this effect. The present study further examined this effect in vivo by assessing the ability of the PKC inhibitor, Ro31-8220 (10 microM), to inhibit acute amphetamine-induced DA overflow when applied with this drug to the NAcc via reverse dialysis. Amphetamine was applied at a concentration of 30 microM, and the core and shell subregions of the NAcc were assayed separately in freely moving rats. These brain regions play a role in the acute locomotor-activating and motivational effects of amphetamine. Consistent with the findings of previous in vitro experiments, reverse dialysis of Ro31-8220 with amphetamine robustly attenuated the ability of this drug to increase extracellular levels of dopamine in both the core and shell subregions of the NAcc. These results confirm that amphetamine stimulates dopamine overflow via a PKC-dependent mechanism

mGlu5 Inhibition in the Basolateral Amygdala Prevents Estrous Cycle-Dependent Changes in Cue-Induced Cocaine Seeking

Drug associated cues are a common relapse trigger for individuals recovering from cocaine use disorder. Sex and ovarian hormones influence patterns of cocaine use and relapse vulnerability, with studies indicating that females show increased cue-induced craving and relapse vulnerability compared to males. In a rodent model of cocaine craving and relapse vulnerability, cue-induced cocaine seeking behavior following weeks of withdrawal from extended-access cocaine self-administration is higher in females in the estrus stage of the reproductive (estrous) cycle (Estrus Females) compared to both Males and females in all other stages (Non-Estrus Females). However, the neuronal substrates and cellular mechanisms underlying these sex differences is not fully understood. One region that contributes to both sex differences in behavioral responding and cue-induced cocaine seeking is the basolateral amygdala (BLA), while one receptor known to play a critical role in mediating cocaine seeking behavior is metabotropic glutamate receptor 5 (mGlu5). Here we assessed the effects of BLA mGlu5 inhibition following prolonged withdrawal from cocaine self-administration on observed estrous cycle-dependent changes in cue-induced cocaine seeking behavior. We found that BLA microinjections of the mGlu5 antagonist MTEP selectively reduced the enhanced cue-induced cocaine seeking normally observed in Estrus Females while having no effect on cocaine seeking in Males and Non-Estrus Females. These findings identify a unique interaction between cocaine-exposure, estrous cycle fluctuations and BLA mGlu5-dependent transmission on cue-induced cocaine seeking behavior

Distribution of AMPA Receptor Subunits and Tarps in Synaptic and Extrasynaptic Membranes of the Adult Rat Nucleus Accumbens

We characterized the distribution of AMPA receptor (AMPAR) subunits and the transmembrane AMPA receptor regulatory proteins (TARPs) γ-2 and γ-4 in adult rat nucleus accumbens (NAc) using a method that separates plasma membranes into synaptic membrane-enriched and extrasynaptic membrane-enriched fractions. We also measured GluA1 phosphorylated at serine 845 (pS845 GluA1) and serine 831 (pS831 GluA1). GluA1–3 protein levels and pS831 GluA1/total GluA1 were higher in synaptic membranes. However, pS845 GluA1/total GluA1 was higher in extrasynaptic membranes, consistent with a role for S845 phosphorylation in GluA1 insertion at extrasynaptic sites. Homeric GluA1 receptors were detected in extrasynaptic membranes, consistent with evidence for extrasynaptic Ca2+-permeable AMPARs in other systems. The TARP γ-2 was enriched in synaptic membranes, whereas γ-4 was mainly found in extrasynaptic membranes, suggesting distinct roles for these proteins in the NAc. These experiments provide fundamental information that will aid in the interpretation of studies on AMPAR-related plasticity in the NAc

Inhibition Of Camkii in the Nucleus Accumbens Shell Decreases Enhanced Amphetamine Intake in Sensitized Rats

Microinjection of the calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-93 into the nucleus accumbens (NAcc) shell impairs expression of the sensitized locomotion and NAcc dopamine (DA) overflow normally observed in psychostimulant-exposed rats. Based on these results, we investigated the effect of NAcc shell KN-93 on the enhanced amphetamine (AMPH) intake normally observed in AMPH- relative to saline-exposed rats. Rats were administered five injections of either AMPH (1.5mg/kg, i.p.) or saline, one injection every 2-3 days. Fourteen days following the last injection, they were trained to self-administer AMPH (200 microg/kg/infusion, i.v.) first on fixed ratio schedules (FR) and then on a progressive ratio schedule of reinforcement (PR). As expected, AMPH-exposed rats worked harder and obtained significantly more drug infusions than saline-exposed rats on the PR schedule. After 4 days of stable responding, all rats were bilaterally microinjected with KN-93 (1 or 10 nmol/0.5 microl/side) into the NAcc shell, 2 min prior to the beginning of the self-administration session. Inhibiting CaMKII in this site reduced the enhanced drug intake observed in AMPH-exposed rats to levels no longer significantly different from those of saline-exposed rats. Responding in these latter controls was not affected by KN-93 nor did KN-93 affect responding in AMPH-exposed rats when it was infused into the NAcc core. Thus, in a manner similar to what has been reported for sensitized locomotion and NAcc DA overflow, these results suggest that inhibiting CaMKII in the NAcc shell attenuates the enhanced motivation to obtain a drug reinforcer that is normally displayed in AMPH-exposed rats