Drugs of abuse are rewarding to addicted and nonaddicted subjects, but they trigger craving and compulsive intake only in addicted subjects. Here, we used positron emission tomography (PET) and [18F]deoxyglucose to compare the brain metabolic responses (marker of brain function) of cocaine-addicted subjects ( n = 21) and controls ( n = 15) to identify brain regions that are uniquely activated in addicted subjects by intravenous methylphenidate (a drug that cocaine-addicted subjects report to be similar to cocaine). In parallel, we also measured the changes in dopamine (DA) induced by intravenous methylphenidate (using PET and [11C]raclopride) in the striatum and in the thalamus. Metabolic responses between groups differed significantly only in the right medial orbital prefrontal cortex [Brodmann's area (BA) 25 and medial BA 11], where methylphenidate increased metabolism in addicted subjects but decreased metabolism in controls. These changes were associated in all subjects with increased “desire for methy...

Action potential firing or depolarization of the postsynaptic neuron can induce a transient suppression of inhibitory synaptic inputs to the depolarized neuron in the cerebellum and hippocampus. This phenomenon, termed depolarization-induced suppression of inhibition (DSI), is initiated postsynaptically by an elevation of intracellular Ca2+ concentration ([Ca2+]i) and is expressed presynaptically as a suppression of the transmitter release. It is, therefore, thought that some retrograde signal must exist from the depolarized postsynaptic neurons to the presynaptic terminals. Recent studies on hippocampal neurons have revealed that endogenous cannabinoids (endocannabinoids) play a key role as a retrograde messenger. There are, however, conflicting reports that glutamate may be a candidate retrograde messenger for cerebellar DSI that acts on presynaptic group II metabotropic glutamate receptors (mGluRs). In this study, we examined whether endocannabinoids mediate retrograde signal for cerebellar DSI. We reco...

The G-protein-coupled metabotropic glutamate receptor subtype 7a (mGluR7a) is a member of group III metabotropic glutamate receptors that plays an important role as a presynaptic receptor in regulating transmitter release at glutamatergic synapses. Here we report that the protein interacting with C-kinase (PICK1) binds to the C terminus (ct) of mGluR7a. In the yeast two-hybrid system, the extreme ct of mGluR7a was shown to interact with the PSD-95/Discs large/ZO-1 (PDZ) domain of PICK1. Pull-down assays indicated that PICK1 was retained by a glutathione S -transferase fusion of ct-mGluR7a. Furthermore, recombinant and native PICK1/mGluR7a complexes were coimmunoprecipitated from COS-7 cells and rat brain tissue, respectively. Confocal microscopy showed that both PICK1 and mGluR7a displayed synaptic colocalization in cultured hippocampal neurons. PICK1 has previously been shown to bind protein kinase C α-subunit (PKCα), and mGluR7a is known to be phosphorylated by PKC. We show a relationship between these t...

Cannabinoid effects on sustained conductances that control neuronal excitability have not been investigated in brain. Here, intracellular voltage-clamp recordings were performed using the rat hippocampal slice preparation to study the postsynaptic effect of cannabinoid agonists on CA1 pyramidal neurons. Superfusion of the cannabimimetics WIN55212–2 or methanandamide onto CA1 neurons elicited an inward steady-state current that reversed near the equilibrium potential for K+ and voltage-dependently activated from a threshold of approximately −70 mV. The cannabinoid receptor (CB1) antagonist SR141716 did not alter membrane properties but prevented this effect. Further investigation revealed that the inward current elicited by cannabinoids was caused by a decrease of the noninactivating voltage-dependent K+ M-current ( I M). Cannabinoids had no effect in slices pretreated with the M-channel blocker linopirdine. Assessment of the I M relaxation indicated that cannabinoids decreased I M in a concentration-depend...

Desensitization of cannabinoid receptor signaling by a G-protein coupled receptor kinase (GRK) was examined using the Xenopus oocyte expression system. Application of a CB1 agonist, WIN 55,212-2, evoked a concentration-dependent increase in K+ conductance (Kir3) in oocytes coexpressing rat CB1 with the G-protein-gated, inwardly rectifying K+ channels Kir3.1 and Kir3.4. Desensitization was slight during continuous agonist application in the absence of GRK and arrestin. However, coexpression of GRK3 and β-arrestin 2 (β-arr2) caused profound homologous CB1 receptor desensitization, supporting the hypothesis that GRK3 and β-arr2 effectively produce CB1 receptor desensitization. To identify the regions of the CB1 receptor responsible for GRK3- and β-arr2-mediated desensitization, we constructed several CB1 receptor mutants. Truncation of the C-terminal tail of CB1 receptor at residue 418 (Δ418) almost completely abolished desensitization but did not affect agonist activation of Kir3. In contrast, truncation at ...

We have found that phosphorylation of a G-protein-coupled receptor by protein kinase C (PKC) disrupts modulation of ion channels by the receptor. In AtT-20 cells transfected with rat cannabinoid receptor (CB1), the activation of an inwardly rectifying potassium current (Kir current) and depression of P/Q-type calcium channels by cannabinoids were prevented by stimulation of protein kinase C by 100 nm phorbol 12-myristate 13-acetate (PMA). In contrast, activation of Kir current by somatostatin was unaffected, and inhibition of calcium channels was only modestly attenuated. The possibility that PKC acted by phosphorylating CB1 receptors was confirmed by demonstrating that PKC phosphorylated a single serine (S317) of a fusion protein incorporating the third intracellular loop of CB1. Mutating this serine to alanine did not affect the ability of CB1 to modulate currents, but it eliminated disruption by PMA, demonstrating that PKC can disrupt ion channel modulation by receptor phosphorylation.

Following the discovery of the antidepressant properties of ketamine, there has been a recent resurgence in the interest in this NMDA receptor antagonist. Although detailed animal models of the molecular mechanisms underlying ketamine's effects have emerged, there are few MEG/EEG studies examining the acute subanesthetic effects of ketamine infusion in man. We recorded 275 channel MEG in two experiments ( n = 25 human males) examining the effects of subanesthetic ketamine infusion. MEG power spectra revealed a rich set of significant oscillatory changes compared with placebo sessions, including decreases in occipital, parietal, and anterior cingulate alpha power, increases in medial frontal theta power, and increases in parietal and cingulate cortex high gamma power. Each of these spectral effects demonstrated their own set of temporal dynamics. Dynamic causal modeling of frontoparietal connectivity changes with ketamine indicated a decrease in NMDA and AMPA-mediated frontal-to-parietal connectivity. AMPA-...

Social decision-making is fundamental for successful functioning and can be affected in psychiatric illness and by serotoninergic modulation. The Prisoner's Dilemma is the archetypal paradigm to model cooperation and trust. However, the effect of serotonergic enhancement is poorly characterized, and its influence on the effect of variations in opponent behavior unknown. To address this, we conducted a study investigating how the serotonergic enhancer 3,4-methylenedioxy-methamphetamine (MDMA) modulates behavior and its neural correlates during an iterated Prisoner's Dilemma with both trustworthy and untrustworthy opponents. We administered 100 mg MDMA or placebo to 20 male participants in a double-blind, placebo-controlled, crossover study. While being scanned, participants played repeated rounds with opponents who differed in levels of cooperation. On each round, participants chose to compete or cooperate and were asked to rate their trust in the other player. Cooperation with trustworthy, but not untrustw...

In the nucleus accumbens (NAc), a key structure to the effects of all addictive drugs, presynaptic cannabinoid CB1 receptors (CB1Rs) and postsynaptic metabotropic glutamate 5 receptors (mGluR5s) are the principal effectors of endocannabinoid (eCB)-mediated retrograde long-term depression (LTD) (eCB-LTD) at the prefrontal cortex-NAc synapses. Both CB1R and mGluR5 are involved in cocaine-related behaviors; however, the impact of in vivo cocaine exposure on eCB-mediated retrograde synaptic plasticity remains unknown. Electrophysiological and biochemical approaches were used, and we report that a single in vivo cocaine administration abolishes eCB-LTD. This effect of cocaine was not present in D1 dopamine receptor (D1R) -/- mice and was prevented when cocaine was coadministered with the selective D1R antagonist 8-chloro-2,3,4,5-tetrahydro-3-5-1h-3-benzazepin-7-ol (0.5 mg/kg) or with the NMDA receptor (NMDAR) blocker (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate (1 mg/kg), suggestin...

Dravet syndrome (DS) is a catastrophic form of pediatric epilepsy mainly caused by noninherited mutations in the SCN1A gene. DS patients suffer severe and life-threatening focal and generalized seizures which are often refractory to available anti-seizure medication. Antisense oligonucleotides (ASOs) based approaches may offer treatment opportunities in DS. MicroRNAs are short noncoding RNAs that play a key role in brain structure and function by post-transcriptionally regulating gene expression, including ion channels. Inhibiting miRNA-134 (miR-134) using an antimiR ASO (Ant-134) has been shown to reduce evoked seizures in juvenile and adult mice and reduce epilepsy development in models of focal epilepsy. The present study investigated the levels of miR-134 and whether Ant-134 could protect against hyperthermia-induced seizures, spontaneous seizures and mortality (SUDEP) in F1. Scn1a( +/− )tm1kea mice. At P17, animals were intracerebroventricular injected with 0.1–1 nmol of Ant-134 and subject to a hyper...