Shupeng Li

Uncoupling the dopamine D1-D2 receptor complex exerts antidepressant-like effects

We report that coupling between dopamine D1 and D2 receptors was markedly increased in postmortem brain of subjects suffering from major depression. Biochemical analyses revealed that D1 and D2 receptors form heterodimers via a direct protein-protein interaction. Administration of an interfering peptide that disrupts the D1-D2 receptor complex substantially reduced immobility in the forced swim test (FST) without affecting locomotor activity, and decreased escape failures in learned helplessness tests in rats.

Uncoupling the D1-N-Methyl-D-Aspartate (NMDA) Receptor Complex Promotes NMDA-Dependent Long-Term Potentiation and Working Memory

BACKGROUND Although dopamine D1 receptors are involved in working memory, how D1 receptors contribute to this process remains unclear. Numerous studies have shown that D1 receptors have extensive functional interaction with N-methyl-D-aspartate (NMDA) receptor. Our group previously demonstrated that D1 receptors were able to regulate NMDA receptor functions through direct protein-protein interactions involving the carboxyl terminals of D1 receptors and NMDA receptor NR1a and NR2A subunits respectively. In this study, we explored the effects of the D1-NR1 interaction on NMDA receptor-dependent long-term potentiation (LTP) and working memory by using the TAT-conjugated interfering peptide (TAT-D1-t2). METHODS Miniature excitatory postsynaptic currents are recorded in rat hippocampal primary cultures. Coimmunoprecipitation and calcium/calmodulin-dependent protein kinase II (CaMKII) activity are measured in hippocampal slices and hippocampal neurons under the specified experimental conditions, respectively. Working memory was assessed using a delayed match-to-place protocol in the Morris Water Maze following administration of the TAT-D1-t2 peptide. RESULTS Electrophysiology experiments showed that activation of D1 receptor upregulates NMDA receptor-mediated LTP in a CaMKII-dependent manner. Furthermore, D1 receptor agonist stimulation promotes the NR1-CaMKII coupling and enhances the CaMKII activity; and the D1 receptor-mediated effects can be blocked by the application of the TAT-D1-t2 peptide. Interestingly, animals injected with TAT-D1-t2 peptide exhibited significantly impaired working memory. CONCLUSIONS Our study showed a critical role of NMDA-D1 direct protein-protein interaction in NMDA receptor-mediated LTP and working memory and implicated the involvement of CaMKII in this process.

Chronic nicotine and smoking treatment increases dopamine transporter mRNA expression in the rat midbrain.

Previous pharmacokinetics and electrophysiological results indicated an important role of nicotine in the modulation of dopamine transporter (DAT). To elucidate the expression changes of DAT on chronic nicotine and smoke administration, the effects of nicotine and passive cigarette smoke on DAT mRNA expression in the ventral tegmental area (VTA) and the substantia nigra (SN) area were examined using in situ hybridization and RNase protection assay. The results showed that chronic nicotine and smoke exposure highly unregulated DAT mRNA in the VTA and SN areas, including the dorsal part of substantia nigra pars compacta. Smoke for 30 min showed the highest increasing effect, whereas nicotine and smoke for 10 min only had slightly increasing effects. However, smoke for 1 h showed an increasing effect to a lesser extent than 30 min. These results revealed a new aspect of nicotines modulation on the DAT, and may have important roles in neuropsychological disorders related to the midbrain abnormalities such as drugs addiction.

A Dopamine D2 Receptor-DISC1 Protein Complex may Contribute to Antipsychotic-Like Effects

Current antipsychotic drugs primarily target dopamine D2 receptors (D2Rs), in conjunction with other receptors such as those for serotonin. However, these drugs have serious side effects such as extrapyramidal symptoms (EPS) and diabetes. Identifying a specific D2R signaling pathway that could be targeted for antipsychotic effects, without inducing EPS, would be a significant improvement in the treatment of schizophrenia. We report here that the D2R forms a protein complex with Disrupted in Schizophrenia 1 (DISC1) that facilitates D2R-mediated glycogen synthase kinase (GSK)-3 signaling and inhibits agonist-induced D2R internalization. D2R-DISC1 complex levels are increased in conjunction with decreased GSK-3α/β (Ser21/9) phosphorylation in both postmortem brain tissue from schizophrenia patients and in Disc1-L100P mutant mice, an animal model with behavioral abnormalities related to schizophrenia. Administration of an interfering peptide that disrupts the D2R-DISC1 complex successfully reverses behaviors relevant to schizophrenia but does not induce catalepsy, a strong predictor of EPS in humans.

Dopamine D1 and D2 receptor mRNA up-regulation in the caudate-putamen and nucleus accumbens of rat brains by smoking.

Nicotine, the toxic substance that is exclusively absorbed from smoking, produces a wide array of behavior and collectively propels drug-seeking behaviors when abused. The neurotransmitter dopamine (DA) is important in the reward and reinforcing properties of many addictive drugs: however, the effect of nicotine by cigarette smoking itself on the expression of DA receptors in the caudate-putamen (CPu), nucleus accumbens (NAc) and olfactory tubercle (OTu) has not been elucidated completely. Hence, the effects of smoking and nicotine on DA receptors need to be defined. In this research, the effect of smoking and nicotine addiction on the DA D1 and D2 receptors in the rat CPu, NAc and OTu were studied. Adult male Spraque-Dawley (S.D., n=50) rats were administered with cigarette smoke (passive inhaled for 10 min and 1 h, 500 ml x 3 times/day, 4 weeks) and nicotine (oral, 3 mg/day). DA D1 and D2 receptor mRNA levels were determined by in situ hybridization and RNase protection assay (RPA). In the smoking groups (10 min and 1 h), DA D1 and D2 receptor mRNA greatly increased in the CPu and NAc, and most of all in the NAc. The nicotine treated group showed increased expression of DA D1 and D2 receptor mRNA too, but statistically less than in the smoking group. In the smoking group, DA D1 and D2 receptor mRNA levels were significantly higher in the CPu and NAc than in the nicotine group (P<.01). These results suggest that smoking and nicotine administration both influence DA receptor mRNAs in the CPu, NAc and OTu, in terms of up-regulation. The up-regulation was much more evident in the smoking group than in the nicotine group. In conclusion, we believe that smoking up-regulate the DA receptor mRNA expression significantly higher in rat CPu and NAc than nicotine but only a little bit higher in OTu.

Melatonin protects SH‐SY5Y neuroblastoma cells from calyculin A‐induced neurofilament impairment and neurotoxicity

Abstract:  Hyperphosphorylation of cytoskeletal proteins seen in Alzheimers disease is most probably the result of an imbalanced regulation in protein kinases and protein phosphatases (PP) in the affected neurons. Previous studies have revealed that PP‐2A and PP‐1 play important roles in the pathogenesis. Employing human neuroblastoma cells, we found that 10 nm calyculin A (CA), a selective inhibitor of PP‐2A and PP‐1, significantly increased phosphorylation and accumulation of neurofilament (NF) in the cells. Levels of NF‐M (middle chain) and NF‐L (light chain) mRNA decreased after CA treatment. Additionally, CA led to a decreased cell viability determined by MTT and crystal violet assay. Melatonin efficiently protects the cell from CA‐induced alterations in NF hyperphosphorylation and accumulation, suppressed NF gene expression as well as decreased cell viability. It is concluded that inhibition of PP‐2A/PP‐1 by CA induces abnormalities in NF metabolism and cell survival, and melatonin efficiently arrests the lesions.

The α7nACh–NMDA receptor complex is involved in cue-induced reinstatement of nicotine seeking

Disrupting the α7nAChR–NMDAR complex blocks cue-induced nicotine seeking.

Early fetal expression of GABAB1 and GABAB2 receptor mRNAs on the development of the rat central nervous system

GABA(B) receptors are G-protein-coupled receptors that mediate slow onset and prolonged effects of GABA in the central nervous system (CNS). While they appear to influence developmental events, depending on where they are found at a synapse, little, if anything, is known as to the expression of GABA(B1) and GABA(B2) receptor mRNAs during the early developmental stages. We used in situ hybridization and RNase protection assays (RPA) to investigate the early fetal expression of GABA(B1) and GABA(B2) receptor mRNAs on the development of the rat CNS. Our in situ studies defined a pattern of early and strong GABA(B1) receptor mRNA expression in the spinal cord, medullar and cerebral cortex neuroepithelium of discrete brain regions on gestational day (GD) 11.5. On GD 12.5, GABA(B1) receptor mRNAs were found in the hippocampal formation, cerebral cortex, intermediate and posterior neuroepithelium, and the pontine neuroepithelium of whole brain. RPA results showed GABA(B1) receptor mRNA was intensely expressed on GD 11.5 and GD 12.5, when it was first detected in the ganglia, thalamus, and cerebellum. However, GABA(B2) receptor mRNA was not detected on GD 10.5, 11.5, or 12.5. We suggest that GABA(B1) receptor might have a role in the early fetal brain and spinal cord during pre- and post-synaptogenesis, neuronal maturation, proliferation, and migration, and may be more important than the GABA(B2) receptor in the early development of the rat CNS.

Direct interaction between GluR2 and GAPDH regulates AMPAR-mediated excitotoxicity

Over-activation of AMPARs (α−amino-3-hydroxy-5-methylisoxazole-4-propionic acid subtype glutamate receptors) is implicated in excitotoxic neuronal death associated with acute brain insults, such as ischemic stroke. However, the specific molecular mechanism by which AMPARs, especially the calcium-impermeable AMPARs, induce neuronal death remains poorly understood. Here we report the identification of a previously unrecognized molecular pathway involving a direct protein-protein interaction that underlies GluR2-containing AMPAR-mediated excitotoxicity. Agonist stimulation of AMPARs promotes GluR2/GAPDH (glyceraldehyde-3-phosphate dehydrogenase) complex formation and subsequent internalization. Disruption of GluR2/GAPDH interaction by administration of an interfering peptide prevents AMPAR-mediated excitotoxicity and protects against damage induced by oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia.

Chronic nicotine and smoke treatment modulate dopaminergic activities in ventral tegmental area and nucleus accumbens and the γ-aminobutyric acid type B receptor expression of the rat prefrontal cortex

Dopaminergic afferents from the mesencephalic areas, such as ventral tegmental area (VTA), synapse with the γ‐aminobutyric acid (GABA)‐ergic interneurons in the prefrontal cortex (PFC). Pharmacological and electrophysiological data show that the reinforcement, the dependence‐producing properties, as well as the psychopharmacologic effects of nicotine depend to a great extent on activation of nicotinic receptors within the mesolimbocortical dopaminergic projection. To explore further the relationship between the mesencephalic dopaminergic neurons and PFC GABAergic neurons, we investigated the effects of nicotine and passive exposure to cigarette smoke on the regulation of tyrosine hydroxylase (TH) in VTA and substantia nigra (SNC) and dopamine (DA) D1 receptor levels in nucleus accumbens (NAc) and caudate‐putamen (CPu). Also, the simultaneous changes in GABAB receptors mRNAs in the PFC were studied. The results showed that chronic nicotine and smoking treatment differentially changed the levels of TH protein in VTA and SNC and DA D1 receptor levels in Nac and CPu. GABAB1 and GABAB2 receptor mRNA levels also showed different change patterns. Ten and thirty minutes of smoke exposure increased GABAB1 receptor mRNA to a greater extent than that of GABAB2, whereas GABAB2 was greatly enhanced after 1 hr of smoke exposure. The TH levels in VTA were closely related to DA D1 receptor levels in NAc and with GABAB receptor mRNA changes in PFC. These results suggest that the mesolimbic pathway and GABAB receptor mRNA in PFC are modulated by nicotine and cigarette smoke, implying an important role in nicotines psychopharmacological effects.