fg-9041 and ifenprodil

In the visual cortex, synaptic plasticity is very high during the early developmental stage known as the critical period and declines with development after the critical period. Changes in the properties of N-methyl-D-aspartate receptor (NMDAR) and γ-aminobutyric acid type A receptor (GABAA R) have been suggested to underlie the changes in the characteristics of plasticity. However, it is largely unknown how the changes in the two receptors interact to regulate synaptic plasticity. The present study investigates the changes in the properties of NMDAR and GABAA R from 3 to 5 weeks of age in layer 2/3 pyramidal neurons of the rat visual cortex. The impact of these changes on the characteristics of long-term potentiation (LTP) is also investigated. The amplitude and decay time constant of GABAA R-mediated currents increased during this period. However, the decay time constant of NMDAR-mediated currents decreased as a result of the decrease in the proportion of the GluN2B subunit-mediated component. Induction of NMDAR-dependent LTP at 3 weeks depended on the GluN2B subunit, but LTP at 5 weeks did not. Enhancement of GABAA R-mediated inhibition suppressed the induction of LTP only at 5 weeks. However, partial inhibition of the GluN2B subunit with a low concentration of ifenprodil allowed the GABAA R-mediated suppression of LTP at 3 weeks. These results suggest that changes in the properties of NMDAR- and GABAA R-mediated synaptic transmission interact to determine the characteristics of synaptic plasticity during the critical period in the visual cortex.

Topics: 2-Amino-5-phosphonovalerate; Age Factors; Animals; Animals, Newborn; Bicuculline; Diazepam; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; GABA Modulators; GABA-A Receptor Antagonists; Gene Expression Regulation, Developmental; Long-Term Potentiation; Male; Neural Inhibition; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA; Receptors, N-Methyl-D-Aspartate; Visual Cortex

Precise control of synaptic strength is critical for maintaining accurate network activity and normal brain functions. Several major brain diseases are related to synaptic alterations in the adult brain. Detailed descriptions of the normal physiological properties of adult synapses are scarce, mainly because of the difficulties in performing whole cell patch-clamp recording in brain slices from adult animals. Here we present the portrait of excitatory synapses and intrinsic properties of medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a central structure of the mesocorticolimbic system, from youth (P14) to adulthood (P120). We found that intrinsic neuronal excitability decreased over development, mainly due to an enhancement of potassium conductance and the consequent reduction in membrane resistance. The ratio between paired-pulse synaptic responses was similar in juvenile, adolescent, and adult MSNs, suggesting that the probability of neurotransmitter release was unaltered. alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated excitatory postsynaptic currents (EPSCs) decayed more slowly in adult MSN. In contrast, the kinetic properties and the subunit composition of N-methyl-d-aspartate receptor (NMDAR)-mediated EPSC in the NAc were conserved from youth to adulthood. Changes in synaptic strength were estimated from the ratio of AMPAR to NMDAR evoked and spontaneous EPSCs (AMPAR/NMDAR ratio). Although both AMPAR and NMDAR EPSCs decreased over development, there was an increase of the AMPAR/NMDAR ratio that was linked to changes in NMDAR EPSC. Furthermore, distribution of the AMPAR/NMDAR ratio was more heterogeneous in MSNs from adults, suggesting that synaptic strength is continuously refined during life.

Topics: Age Factors; Analysis of Variance; Animals; Animals, Newborn; Biophysics; Calcium Chloride; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; In Vitro Techniques; Male; Membrane Potentials; Neurons; Nucleus Accumbens; Patch-Clamp Techniques; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Methamphetamine (METH) is a strongly addictive psychostimulant that dramatically affects the central nervous system (CNS). On the other hand, protein kinase C (PKC) plays a major role in cellular regulatory and signalling processes that involve protein phosphorylation. The purpose of this study was to investigate the role of neuronal and astrocytic PKC in changes in the central glutamatergic system induced by METH. We show here that in vitro treatment with METH caused the phosphorylation of both neuronal and astrocytic PKC and the activation of astrocytes in cortical neuron/glia co-cultures. Treatment of cortical neuron/glia co-cultures with either the PKC activator phorbol 12,13-dibutyrate (PDBu) or glutamate also caused the PKC-dependent activation of astrocytes. The PKC inhibitor chelerythrine suppressed the Ca2+ responses to glutamate in both cortical neurons and astrocytes. Moreover, a low concentration of PDBu significantly enhanced the Ca2+ responses to glutamate, but not to dopamine, in both cortical neurons and astrocytes. Notably, treatment with METH also enhanced the Ca2+ responses to glutamate in cortical neurons. The activation of astrocytes induced by METH was also reversed by co-treatment with glutamate receptor antagonists (ifenprodil, DNQX or MPEP) in cortical neuron/glia co-cultures. In the conditioned place preference paradigm, intracerebroventricular administration of glutamate receptor antagonists (ifenprodil, DNQX or MPEP) attenuated the METH-induced rewarding effect. These findings provide evidence that the changes in PKC-dependent neuronal and astrocytic glutamatergic transmission induced by METH may, at least in part, contribute to the development of psychological dependence on METH.

Topics: Amphetamine-Related Disorders; Animals; Astrocytes; Calcium; Cell Communication; Central Nervous System Stimulants; Coculture Techniques; Conditioning, Operant; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Immunohistochemistry; Male; Methamphetamine; Mice; Mice, Inbred ICR; Microscopy, Confocal; Neuroglia; Neurons; Piperidines; Pregnancy; Protein Kinase C; Pyridines; Quinoxalines; Receptors, Glutamate; Synaptic Transmission

NMDA receptors undergo drastic changes in their subunit composition during development of the mammalian neocortex. An increase in the expression of the NR2A subunit correlates with developmental changes in the properties of synaptic NMDA receptors. In this study, we investigated whether these developmental alterations are restricted to synaptic NMDA receptors or whether similar developmental changes also occur at extrasynaptic NMDA receptors. To analyse the properties of extrasynaptic receptors, glutamate-evoked ion currents mediated by extrasynaptic NMDA receptors were isolated by irreversibly blocking synaptic NMDA receptors with MK-801. Whole-cell ion currents mediated by extrasynaptic receptors showed developmental changes in their sensitivity against the NR2B subunit-specific antagonist ifenprodil similar to that of synaptic receptors. In summary, our results strongly suggest that NR2A subunit-containing NMDA receptors increasingly contribute also to extrasynaptic NMDA receptors during in vitro differentiation.

Topics: Animals; Cells, Cultured; Coculture Techniques; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Gene Expression Regulation, Developmental; Glutamic Acid; Glycine; Ion Channels; Neocortex; Neurons; Patch-Clamp Techniques; Picrotoxin; Piperidines; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Stimulation, Chemical; Synapses

Subunit composition of subsynaptic transmitter receptors is controlled presynaptically in the developing neuromuscular junction. To investigate presynaptic regulation of NMDA receptor subunit composition in the CNS, we co-cultured different types of hippocampal explants with dissociated target neurons. Postsynaptic NMDA receptors were studied using whole-cell patch-clamp recordings. After 1 week in culture with innervation by dentate gyrus (dg) explants, the kinetic and pharmacological properties of postsynaptic NMDA receptors indicated the expression of NMDA receptor subtypes containing NR2B subunits (NR1/NR2A/NR2B or NR1/NR2B or both). The properties of NMDA receptors in noninnervated neurons were similar to those of neurons innervated by dg explants. In contrast, after innervation by explants from the cornu ammonis (CA) region, we found an additional NMDA receptor subtype with properties consistent with the subunit composition NR1/NR2A. These findings indicate that presynaptic signals determine NMDA receptor subunit composition. After prolonged cultivation (11-12 d) the properties of synaptic NMDA receptors in the majority of dg-innervated neurons also indicated the expression of NR1/NR2A receptors. This suggests a delayed developmental maturation of NMDA receptors in dg-innervated neurons. Long-term plasticity of central glutamatergic synapses is critically influenced by the subunit composition of NMDA receptors, and thus presynaptic control of NMDA receptor subunit composition might regulate synaptic plasticity.

Topics: Animals; Bicuculline; Cells, Cultured; Coculture Techniques; Embryo, Mammalian; Evoked Potentials; Excitatory Amino Acid Antagonists; Hippocampus; Kinetics; Macromolecular Substances; Magnesium; N-Methylaspartate; Neuronal Plasticity; Neurons; Organ Culture Techniques; Patch-Clamp Techniques; Piperidines; Polymerase Chain Reaction; Presynaptic Terminals; Quinoxalines; Rats; Receptors, N-Methyl-D-Aspartate; Synapses