ABSTRACT
The mechanisms by which natural rewards such as sugar affect synaptic transmission and behavior are largely unexplored. Here, we investigate regulation of nucleus accumbens synapses by sucrose intake. Previous studies have shown that AMPA receptor (AMPAR) trafficking is a major mechanism for regulating synaptic strength, and that in vitro, trafficking of AMPARs containing the GluA1 subunit takes place by a two-step mechanism involving extrasynaptic and then synaptic receptor transport. We report that in rat, repeated daily ingestion of a 25% sucrose solution transiently elevated spontaneous locomotion and potentiated accumbens core synapses through incorporation of Ca(2+)-permeable AMPA receptors (CPARs), which are GluA1-containing, GluA2-lacking AMPARs. Electrophysiological, biochemical, and quantitative electron microscopy studies revealed that sucrose training (7 d) induced a stable (>24 h) intraspinous GluA1 population, and that in these rats a single sucrose stimulus rapidly (5 min) but transiently (<24 h) elevated GluA1 at extrasynaptic sites. CPARs and dopamine D1 receptors were required in vivo for elevated locomotion after sucrose ingestion. Significantly, a 7 d protocol of daily ingestion of a 3% solution of saccharin, a noncaloric sweetener, induced synaptic GluA1 similarly to 25% sucrose ingestion. These findings identify multistep GluA1 trafficking, previously described in vitro, as a mechanism for acute regulation of synaptic transmission in vivo by a natural orosensory reward. Trafficking is stimulated by a chemosensory pathway that is not dependent on the caloric value of sucrose.
Subject(s)
Neurons/metabolism , Receptors, AMPA/metabolism , Sucrose/administration & dosage , Sweetening Agents/administration & dosage , Animals , Carrier Proteins , Conditioning, Operant/physiology , Dopamine beta-Hydroxylase/metabolism , Excitatory Postsynaptic Potentials/drug effects , In Vitro Techniques , Locomotion/physiology , Male , Microscopy, Electron, Transmission , Neurons/drug effects , Nucleus Accumbens/cytology , Phosphoproteins/metabolism , Post-Synaptic Density/metabolism , Post-Synaptic Density/ultrastructure , Protein Transport/drug effects , Rats , Rats, Sprague-Dawley , Subcellular Fractions/metabolism , Synaptosomes/metabolism , Synaptosomes/ultrastructureABSTRACT
Recently, many efforts have been made to develop N-methyl-D-aspartic acid receptor antagonists for treating different pathological conditions such as thrombo-embolic stroke, traumatic head injury, Huntington's, Parkinson's, and Alzheimer's diseases). However, as side-effects limit the use of most antagonists, new drugs are still required. In this work, we performed a (quantitative) structure-activity relationship analysis of 17 phenyl-amidine derivatives (1a-1q), reported as N-methyl-D-aspartic acid receptor antagonists, and used this data to rationally design the triazolyl-amidines. The best (quantitative) structure-activity relationship model constructed by multiple linear regression analysis presented high data fitting (R = 0.914) was able to explain 83.6% of the biological data variance (R(2) = 0.836), presented a satisfactory internal predictive ability (Q(2) = 0.609) and contained the descriptors (E(HOMO), Ovality and cLogP). Our assays confirmed that glutamate promotes an extensive cell death in avian neurons (77%) and 2a and 2b protected the neurons from the glutamate effect (from 77% to 27% and 45%, respectively). The results of neurotoxicity and cytotoxicity on Vero cells suggested the favorable profile of 2a and 2b. Also, the molecular modeling used to predict the activity, the interaction with the receptor and the pharmacokinetic and toxicity of the triazolyl-amidines pointed them as a promising class for further exploration as N-methyl-D-aspartic acid receptor antagonists.
Subject(s)
Amidines/chemistry , Neuroprotective Agents/chemistry , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Triazoles/chemistry , Amidines/pharmacology , Animals , Cell Death , Chlorocebus aethiops , Glutamic Acid/toxicity , Molecular Docking Simulation , Neuroprotective Agents/pharmacology , Receptors, N-Methyl-D-Aspartate/chemistry , Receptors, N-Methyl-D-Aspartate/metabolism , Retinal Neurons/cytology , Retinal Neurons/drug effects , Structure-Activity Relationship , Triazoles/pharmacology , Vero CellsABSTRACT
Glucose transporter 3 (GLUT3) is the main facilitative glucose transporter in neurons. Glucose provides neurons with a critical energy source for neuronal activity. However, the mechanism by which neuronal activity controls glucose influx via GLUT3 is unknown. We investigated the influence of synaptic stimulation on GLUT3 surface expression and glucose import in primary cultured cortical and hippocampal neurons. Synaptic activity increased surface expression of GLUT3 leading to an elevation of intracellular glucose. The effect was blocked by NMDA receptor (NMDAR) and neuronal nitric oxide synthase (nNOS) inhibition. The Akt inhibitor I (Akt-I) blocked NMDAR-induced GLUT3 surface expression while a nNOS-phosphomimetic mutant (S1412D) enhanced GLUT3 expression at cell surface. These results suggest that NMDAR/Akt-dependent nNOS phosphorylation is coupled to GLUT3 trafficking. We demonstrated that activation of cGMP-dependent protein kinase (cGK) increased the surface expression of GLUT3, which was repressed by Rp-8-pCPT-cGMPS, a potent cell-permeable inhibitor of cGKs. These studies characterize the molecular basis for activity-dependent increases in surface GLUT3 after stimulation of the NMDARs. NMDAR-induced increase in surface GLUT3 represents a novel pathway for control of energy supply during neuronal activity that is critical for maintaining glucose homeostasis during neuronal transmission.
Subject(s)
Gene Expression Regulation/physiology , Glucose Transporter Type 3/metabolism , Neurons/metabolism , 4-Aminopyridine/pharmacology , Analysis of Variance , Animals , Bicuculline/pharmacology , Biotinylation/methods , Cerebral Cortex/cytology , Cyclic GMP/analogs & derivatives , Cyclic GMP/pharmacology , Disks Large Homolog 4 Protein , Dogs , Drug Interactions , Embryo, Mammalian , Enzyme Inhibitors/pharmacology , Excitatory Amino Acid Antagonists/pharmacology , GABA-A Receptor Antagonists/pharmacology , Gene Expression Regulation/drug effects , Gene Expression Regulation/genetics , Glucose Transporter Type 3/genetics , Green Fluorescent Proteins/genetics , Hexoses/metabolism , Hippocampus/cytology , Humans , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Membrane Proteins/genetics , Membrane Proteins/metabolism , Neurons/drug effects , Neurons/ultrastructure , Nitric Oxide/metabolism , Nitric Oxide Synthase Type I/genetics , Potassium Channel Blockers/pharmacology , Protein Transport/genetics , Rats , Rats, Sprague-Dawley , Receptors, N-Methyl-D-Aspartate/genetics , Receptors, N-Methyl-D-Aspartate/metabolism , Serine/metabolism , Synapses/drug effects , Synapses/metabolism , Synaptosomes/metabolism , Thionucleotides/pharmacology , Time Factors , Transfection , Valine/analogs & derivatives , Valine/pharmacologyABSTRACT
The abundance of snail hosts and the rates of infection with Schistosoma mansoni were monitored monthly for four years in two representative localities subjected to repeated chemotherapy of infected persons. Snail abundance varied from 1.0 to 4.4 collected per person/minute/station for Biomphalaria straminea and from 0.1 to 7.0 for B. glabrata. Infection rates of snails in nature varied from 0% to 15% for the former and from 0% to 70% for the latter species. Human infection increased from 35.5% to 61.9% in the locality occupied by B. straminea, and decreased from 40.3% to 20.8% in that occupied by B. glabrata. No relationship could be detected between human infection and the snail variables. Despite seasonal variations, natural infection persisted throughout the monitoring period in both snail species. It reached remarkably high levels in B. straminea when compared to those obtained by other authors probably because of differences in methodology. It is recommended that longitudinal studies should be carried out focally and periodically to avoid underestimating the prevalence of schistosome infection in snails.
Subject(s)
Biomphalaria/parasitology , Schistosoma mansoni/isolation & purification , Animals , Brazil , Disease Vectors , Longitudinal Studies , Oxamniquine/therapeutic use , Population Density , Schistosomicides/therapeutic use , SeasonsABSTRACT
The abundance of snail hosts and the rates of infection with Schistosoma mansoni were monitored monthly for four years in two representative localities subjected to repeated chemotherapy of infected persons. Snail abundance varied from 1.0 to 4.4 collected per person/minute/station for Biomphalaria straminea and from 0.1 to 7.0 for B. glabrata. Infection rates of snails in nature varied from 0 percent to 15 percent for the former and from 0 percent to 70 percent for the latter species. Human infection increased from 35.5 percent to 61.9 percent in the locality occupied by B. straminea, and decreased from 40.3 percent to 20.8 percent in that occupied by B. glabrata. No relationship could be detected between human infection and the snail variables. Despite seasonal variations, natural infection persisted throughout the monitoring period in both snail species. It reached remarkably high levels in B. straminea when compared to those obtained by other authors probably because of differences in methodology. It is recommended that longitudinal studies should be carried out focally and periodically to avoid underestimating the prevalence of schistosome infection in snails
