piperidines and alpha-methyl-4-carboxyphenylglycine

Astrocytes show a complex structural and physiological interplay with neurons and respond to neuronal activation in vitro and in vivo with intracellular calcium elevations. These calcium changes enable astrocytes to modulate synaptic transmission and plasticity through various mechanisms. However, the response pattern of astrocytes to single neuronal depolarization events still remains unresolved. This information is critical for fully understanding the coordinated network of neuron-glial signaling in the brain. To address this, we developed a system to map astrocyte calcium responses along apical dendrites of CA1 pyramidal neurons in hippocampal slices using single-neuron stimulation with channelrhodopsin-2. This technique allowed selective neuronal depolarization without invasive manipulations known to alter calcium levels in astrocytes. Light-evoked neuronal depolarization was elicited and calcium events in surrounding astrocytes were monitored using the calcium-sensitive dye Calcium Orange. Stimulation of single neurons caused calcium responses in populations of astrocytes along the apical axis of CA1 cell dendrites. Calcium responses included single events that were synchronized with neuronal stimulation and poststimulus changes in calcium event frequency, both of which were modulated by glutamatergic and purinergic signaling. Individual astrocytes near CA1 cells showed low ability to respond to repeated neuronal depolarization events. However, the response of the surrounding astrocyte population was remarkably accurate. Interestingly, the reliability of responses was graded with respect to astrocyte location along the CA1 cell dendrite, with astrocytes residing in the primary dendrite subregion being most responsive. This study provides a new perspective on the dynamic response property of astrocyte ensembles to neuronal activity.

Topics: Action Potentials; Analysis of Variance; Animals; Animals, Newborn; Aspartic Acid; Astrocytes; Bacterial Proteins; Benzoates; Benzoxazines; Calcium; Calcium Channel Blockers; Carbenoxolone; Channelrhodopsins; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; Glial Fibrillary Acidic Protein; Glycine; Green Fluorescent Proteins; Hippocampus; In Vitro Techniques; Luminescent Proteins; Male; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Models, Biological; Morpholines; Naphthalenes; Neurons; Patch-Clamp Techniques; Peptide Fragments; Phosphopyruvate Hydratase; Photic Stimulation; Piperidines; Pyrazoles; Pyridines; Sodium Channel Blockers; Statistics, Nonparametric; Tetanus Toxin; Tetrodotoxin; Transduction, Genetic

Endocannabinoids and their receptor CB1 play key roles in brain function. Astrocytes express CB1Rs that are activated by endocannabinoids released by neurons. However, the consequences of the endocannabinoid-mediated neuron-astrocyte signaling on synaptic transmission are unknown. We show that endocannabinoids released by hippocampal pyramidal neurons increase the probability of transmitter release at CA3-CA1 synapses. This synaptic potentiation is due to CB1R-induced Ca(2+) elevations in astrocytes, which stimulate the release of glutamate that activates presynaptic metabotropic glutamate receptors. While endocannabinoids induce synaptic depression in the stimulated neuron by direct activation of presynaptic CB1Rs, they indirectly lead to synaptic potentiation in relatively more distant neurons by activation of CB1Rs in astrocytes. Hence, astrocyte calcium signal evoked by endogenous stimuli (neuron-released endocannabinoids) modulates synaptic transmission. Therefore, astrocytes respond to endocannabinoids that then potentiate synaptic transmission, indicating that astrocytes are actively involved in brain physiology.

Topics: Animals; Animals, Newborn; Astrocytes; Benzoates; Biophysics; Calcium; Cannabinoid Receptor Modulators; Chelating Agents; Drug Interactions; Egtazic Acid; Electric Stimulation; Endocannabinoids; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glycine; Hippocampus; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Knockout; Patch-Clamp Techniques; Photolysis; Piperidines; Pyramidal Cells; Pyrazoles; Pyridines; Receptor, Cannabinoid, CB1; Resorcinols; Synaptic Transmission; Thapsigargin

Developmental changes can occur in the dynamic properties of synapses, known as short-term plasticity. Using rat acute hippocampal slices at room temperature, we have previously shown a decrease in short-term facilitation at Schaffer collateral synapses from young adults compared with juveniles in response to temporally complex natural stimulus patterns such as synapses receive in vivo. Here we show that this developmental decrease in facilitation is also seen at 32 degrees C and investigate the underlying mechanism. Addition of the mGluR1 antagonist LY367385 increases short-term facilitation in response to the natural stimulus pattern, showing that mGluR1 is activated by synaptically released glutamate. Although synaptic activation of mGluR1 occurs at both ages, the effect is larger in young adults. Furthermore, blocking mGluR1 eliminates most of the developmental decrease in short-term facilitation during the natural stimulus pattern. We investigated possible retrograde/downstream messengers involved after synaptic activation of mGluR1. Blocking cannabinoid receptors has no effect on the response during the natural stimulus pattern, indicating that the reduction in facilitation during synaptic activation of mGluR1 does not occur through release of endocannabinoids. We find that blocking GABA(B) receptors increases facilitation during the natural stimulus pattern and occludes the effect of the mGluR1 antagonist, indicating a role for the modulation of GABA release from inhibitory interneurons by mGluR1 activation. These data suggest a model where synaptic activation of mGluR1 on inhibitory interneurons causes an increase in GABA release by inhibitory interneurons, which activates GABA(B) receptors on Schaffer collateral synapses and inhibits short-term facilitation during the natural stimulus pattern.

Topics: Action Potentials; Age Factors; Analysis of Variance; Animals; Animals, Newborn; Benzoates; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Glycine; Hippocampus; Phosphinic Acids; Piperidines; Propanolamines; Pyrazoles; Rats; Rats, Long-Evans; Receptors, Metabotropic Glutamate; Synapses; Temperature

This study was undertaken to analyze the involvement of periaqueductal gray (PAG) cannabinoid or group I metabotropic glutamate receptors in the formalin-induced changes on the rostral ventromedial medulla (RVM) ON- and OFF-cells activities. S.c. injection of formalin into the hind paw produced a transient decrease (4-6 min) followed by a longer increase (25-35 min) in tail flick latencies. Formalin also increased basal activity in RVM ON-cells (42+/-7%) and decreased it in OFF-cells (35+/-4%). Intra-PAG microinjection of (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2) (2 nmol/rat), a cannabinoid receptor agonist, prevented the formalin-induced changes in RVM cell activities. Higher dosages of WIN 55,212-2 (4-8 nmol/rat) increased the tail flick latencies, delayed the tail flick-related onset to ON-cell burst, and decreased the duration of OFF-cell pause. Furthermore, WIN 55,212-2 at a dosage of 8 nmol/rat decreased RVM ON-cell (57+/-7%) and increased OFF-cell ongoing activities (26+/-4%). These effects were prevented by N-piperidino-5-(4-chlorophenyl)-1-(2,4dichlorophenyl)-4-methyl-3-pyrazolecarboxamide SR141716A, (1 pmol/rat), a CB1 cannabinoid receptor antagonist, or by 2-methyl-6-(phenylethynyl)pyridine (MPEP 20 nmol/rat), a selective mGlu5 glutamate receptor antagonist. T7-(hydroxyimino) cyclopropa[b]chromen-1alpha-carboxylate ethyl ester (CPCOOE/50 nmol/rat) and (S)-(+)-alpha-amino-4-carboxy-2-methylbenzeneacetic acid (LY367385, 20 nmol/rat), selective mGlu1 glutamate receptor antagonists, were ineffective in preventing the WIN-induced effects. This study suggests that s.c. injection of formalin modifies RVM neuronal activities and this effect is prevented by PAG cannabinoid receptor stimulation. Moreover, the physiological stimulation of PAG mGlu5, but not mGlu1 glutamate receptors, seems to be required for the cannabinoid-mediated effect.

Topics: Action Potentials; Analgesics; Animals; Benzoates; Benzoxazines; Chromones; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Formaldehyde; Glycine; Injections, Subcutaneous; Male; Medulla Oblongata; Morpholines; Naphthalenes; Neurons; Pain Measurement; Periaqueductal Gray; Piperidines; Pyrazoles; Pyridines; Rats; Rats, Wistar; Reaction Time; Receptor, Cannabinoid, CB1; Receptors, Metabotropic Glutamate; Rimonabant

The involvement of metabotropic glutamate (mGlu) receptors in the modulatory actions of a novel cognition enhancer, (+)-5-oxo-D-prolinepiperidinamide monohydrate (NS-105), on adenylyl cyclase activity in rat cerebrocortical membranes and primary neuronal cultures was investigated using selective antagonists and antisense oligodeoxynucleotides for mGlu receptor subclasses. In rat cerebrocortical membranes, the inhibitory action of NS-105 (0.1 microM) on forskolin-stimulated cAMP formation was blocked by a group II mGlu receptor antagonist, (+/-)-alpha-ethylglutamic acid, and by a group III antagonist, (+)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP-4), but not by a group I antagonist, (+/-)-1-aminoindan-1,5-dicarboxylic acid (AIDA), whereas the facilitation of cAMP formation by NS-105 (1 microM) in pertussis toxin-pretreated membranes was abolished by AIDA but not by (+/-)-alpha-ethylglutamic acid or MAP-4. In primary cultured neurons of mouse cerebral cortex, the inhibitory action of NS-105 on adenylyl cyclase activity disappeared after treatment with antisense oligodeoxynucleotides for group II (mGlu(2) and mGlu(3) receptors) and group III (mGlu(4) and mGlu(7) receptors) but not group I (mGlu(5) receptor) mGlu receptor subclasses. These findings suggest that the inhibitory action of NS-105 on adenylyl cyclase activity is mediated through group II and group III mGlu receptor subclasses while the facilitatory action is dependent on the group I mGlu receptor subclass.

Topics: Adenylyl Cyclases; Animals; Benzoates; Cells, Cultured; Cerebral Cortex; Colforsin; Cyclic AMP; Excitatory Amino Acid Antagonists; Fetus; Gene Expression Regulation; Glycine; Male; Membranes; Neurons; Nootropic Agents; Oligodeoxyribonucleotides, Antisense; Oligonucleotides; Piperidines; Proline; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; RNA, Messenger