6-cyano-7-nitroquinoxaline-2-3-dione and anandamide

Cannabinoid receptors (CB1Rs) are present in glomeruli of the main olfactory bulb. The functions of CB1Rs and their endogenous activators, endocannabinoids, for glomerular signaling are unknown. Glomeruli contain at least three types of neurons: periglomerular (PG), external tufted (ET), and short-axon (SA) cells. PG cells form inhibitory GABAergic dendrodendritic synapses with ET cells. ET cells form excitatory glutamatergic dendrodendritic synapses with PG and SA cells. In mouse brain slices, we used whole-cell patch-clamp recordings to study the role of CB1Rs in regulating PG and ET cells. Cannabinoids displayed strong, direct inhibitory effects on PG cells and weak effects on ET cells. Single pulses or a train of pulses of depolarizing current injected into an ET cell evoked suppression of IPSCs. This suggests retrograde endocannabinoid signaling, namely, depolarization-induced suppression of inhibition (DSI) in ET cells. Our results support the hypothesis that burst firing of ET cells triggers the release of endocannabinoids which in turn directly inhibit PG cells and reduce GABA release from PG cells. This, in turn, can result in a transient reduction of PG cell inhibitory input to ET cells.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Arachidonic Acids; Benzoxazines; Cannabinoid Receptor Agonists; Cannabinoid Receptor Antagonists; Cannabinoids; Data Interpretation, Statistical; Endocannabinoids; Excitatory Amino Acid Antagonists; Female; Male; Mice; Mice, Inbred C57BL; Morpholines; Naphthalenes; Nerve Net; Neurons; Olfactory Bulb; Patch-Clamp Techniques; Piperidines; Polyunsaturated Alkamides; Pyrazoles; Receptor, Cannabinoid, CB1; Receptors, Cannabinoid; Signal Transduction; Synapses; Synaptic Transmission

Cannabinoid CB1 receptors (CB1Rs) regulate the neurodegenerative damage of experimental autoimmune encephalomyelitis (EAE) and of multiple sclerosis (MS). The mechanism by which CB1R stimulation exerts protective effects is still unclear. Here we show that pharmacological activation of CB1Rs dampens the tumor necrosis factor α (TNFα)-mediated potentiation of striatal spontaneous glutamate-mediated excitatory postsynaptic currents (EPSCs), which is believed to cogently contribute to the inflammation-induced neurodegenerative damage observed in EAE mice. Furthermore, mice lacking CB1Rs showed a more severe clinical course and, in parallel, exacerbated alterations of sEPSC duration after induction of EAE, indicating that endogenous cannabinoids activate CB1Rs and mitigate the synaptotoxic action of TNFα in EAE. Consistently, we found that mice lacking the fatty acid amide hydrolase (FAAH), and thus expressing abnormally high brain levels of the endocannabinoid anandamide, developed a less severe EAE associated with preserved TNFα-induced sEPSC alterations. CB1Rs are important modulators of EAE pathophysiology, and might play a mechanistic role in the neurodegenerative damage of MS patients.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amidohydrolases; Animals; Arachidonic Acids; Cannabinoid Receptor Modulators; Corpus Striatum; Dizocilpine Maleate; Dronabinol; Encephalomyelitis, Autoimmune, Experimental; Endocannabinoids; Etanercept; Excitatory Postsynaptic Potentials; Female; Glutamic Acid; Immunoglobulin G; Mice; Mice, Inbred C57BL; Mice, Knockout; Nerve Degeneration; Neurons; Polyunsaturated Alkamides; Receptor, Cannabinoid, CB1; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Receptors, Tumor Necrosis Factor; Tumor Necrosis Factor-alpha

The activation of transient receptor potential vanilloid receptor 1 (TRPV1) by capsaicin in rat brain stimulates gastric acid secretion via tachykinin NK2 receptors and the vagus cholinergic nerve, but the involvement of other receptor systems has not been elucidated. We investigated the role of the glutamate and gamma-amino-butyric acid (GABA) receptor systems on the capsaicin response. Gastric acid secretion stimulated by the injection of capsaicin (30 nmol) into the lateral cerebroventricle (i.c.v.) was inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an antagonist of non-N-methyl-D-aspartate (non-NMDA) receptors, 10.9 nmol, i.c.v.) and bicuculline (a GABA(A) receptor antagonist, 222 microg kg(-1) 10 min(-1), i.v. infusion). Secretion stimulated by the injection of capsaicin (50 nmol) into the fourth cerebroventricle was inhibited by CNQX and bicuculline. I.c.v. injection of anandamide (an endogenous ligand of TRPV1 and cannabinoid receptors, 30 and 100 nmol) stimulated gastric acid secretion, and the response was inhibited by an antagonist of TRPV1 and in the capsaicin-treated rats, but not by an antagonist of cannabinoid receptors. In conclusion, the TRPV1 system, which is activated by capsaicin and anandamide, is preferentially coupled with non-NMDA and GABA(A) receptor systems in the brain and stimulates gastric acid secretion in rats.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Arachidonic Acids; Bicuculline; Cannabinoid Receptor Modulators; Capsaicin; Dose-Response Relationship, Drug; Endocannabinoids; Excitatory Amino Acid Antagonists; GABA Antagonists; Gastric Acid; Gastric Mucosa; Injections, Intraventricular; Ion Channels; Male; Polyunsaturated Alkamides; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, Glutamate; Statistics, Nonparametric; TRPV Cation Channels

Glutamate-induced formation of N-acylethanolamine (NAE) and N-acylphosphatidylethanolamine (NAPE) was studied in primary cultures of mouse neocortical neurons prelabeled with [14C] ethanolamine. The formation of these two lipids was dependent on the maturity of the cell culture; i.e., no glutamate-induced formation was seen in 2-day-old cultures, whereas glutamate induced a pronounced formation in 6-day-old cultures. The calcium ionophore A23187 (2 microM) stimulated, within 2 h, formation of NAPE in 2-day-old cultures (fourfold) as well as in 6-day-old cultures (eightfold). Glutamate exerted its effect via NMDA receptors as seen by the inhibitory action of the NMDA-selective receptor antagonists D-(-)-2-amino-5-phosphonovalerate and N-(1-(2-thienyl)cyclohexyl)piperidine and the lack of effect of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate-receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In 6-day-old cultures, exposure to NMDA (100 microM for 24 h) induced a linear increase in the formation of NAPE and NAE as well as a 40-50% neuronal death, as measured by a decrease in cellular formazan formation [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay]. The increase in NAPE and NAE could be detected earlier than the neuronal death. Neither cyclic AMP, cyclic GMP, nitric oxide, protein kinase C, nor peroxidation appears to be involved in the formation of NAPE and NAE, as assessed by the use of different pharmacological agents. Exposure to 5 mM NaN3 for 8 h resulted in a >80% decrease in the cellular MTT staining and a pronounced linear increase in the formation of NAE and NAPE (reaching 25-30% of total labeling). [14C]Anandamide was also formed in [14C]arachidonic acid-labeled neurons exposed to NaN3. No NAPE formation was detected in A23187-stimulated mouse astrocytes, rat Leydig cells and cardiomyocytes, and several other cells. These results suggest that the glutamate-induced formation of NAPE and NAE was mediated by the NMDA receptor and the formation of these lipids may be associated with neuronal death.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Arachidonic Acid; Arachidonic Acids; Calcimycin; Cell Death; Cells, Cultured; Cerebral Cortex; Embryo, Mammalian; Endocannabinoids; Ethanolamine; Ethanolamines; Glutamic Acid; Ionophores; Mice; Neurons; Phencyclidine; Phosphatidylethanolamines; Polyunsaturated Alkamides; Receptors, N-Methyl-D-Aspartate; Time Factors