The mechanism of long-term potentiation (LTP) in basolateral amygdala (BLA) was explored using field potential recording in rat brain slice preparation. Field potentials (field excitatory post-synaptic potentials, fEPSPs) in BLA were evoked with sharpened steel bipolar stimulating electrodes placed in the external capsule (EC). Two theta burst stimulations (TBS, interval=10 min) induced LTP in BLA. TBS-induced synaptic potentiation lasted for more than 30 min after the second TBS. LTP in BLA was input-specific and was blocked by N-methyl-D-aspartate receptor (NMDAR) antagonist 2-amino-5-phosphonovaleric acid (APV). The effect of protein kinase C (PKC) on LTP was then determined using PKC inhibitor chelerythrine chloride. Bath application of chelerythringe chloride had no effect on basic field potentials and paired-pulse ratio (PPR). However, in the presence of chelerythrine chloride, two TBS failed to induce LTP. In contrast, bath application of chelerythrine chloride 10 min after the second TBS did not affect the maintenance of LTP in BLA. These results indicate that LTP is NMDAR-dependent and PKC is involved in the induction and early maintenance of LTP in BLA.
2-Amino-5-phosphonovalerate ; pharmacology ; Amygdala ; enzymology ; Animals ; Electric Stimulation ; In Vitro Techniques ; Long-Term Potentiation ; Protein Kinase C ; metabolism ; Rats ; Receptors, N-Methyl-D-Aspartate ; metabolism ; Synaptic Potentials

Many intracellular proteins and signaling cascades contribute to the sensitivity of N-methyl-D-aspartate receptors (NMDARs). One such putative contributor is the serine/threonine kinase, protein kinase C (PKC). Activation of PKC by phorbol 12-myristate 13-acetate (PMA) causes activation of extracellular signal-regulated kinase (ERK) and promotes the formation of new spines in cultured hippocampal neurons. The purpose of this study was to examine which PKC isoforms are responsible for the PMA-induced augmentation of long-term potentiation (LTP) in the CA1 stratum radiatum of the hippocampus in vitro and verify that this facilitation requires NMDAR activation. We found that PMA enhanced the induction of LTP by a single episode of theta-burst stimulation in a concentration-dependent manner without affecting to magnitude of baseline field excitatory postsynaptic potentials. Facilitation of LTP by PMA (200 nM) was blocked by the nonspecific PKC inhibitor, Ro 31-8220 (10microM); the selective PKCdelta inhibitor, rottlerin (1microM); and the PKCepsilon inhibitor, TAT-epsilonV1-2 peptide (500 nM). Moreover, the NMDAR blocker DL-APV (50microM) prevented enhancement of LTP by PMA. Our results suggest that PMA contributes to synaptic plasticity in the nervous system via activation of PKCdelta and/or PKCepsilon, and confirm that NMDAR activity is required for this effect.
2-Amino-5-phosphonovalerate ; Acetophenones ; Benzopyrans ; Excitatory Postsynaptic Potentials ; Hippocampus ; Indoles ; Long-Term Potentiation ; Nervous System ; Neurons ; Phorbols ; Phosphotransferases ; Protein Isoforms ; Protein Kinases ; Proteins ; Receptors, N-Methyl-D-Aspartate ; Spine

BACKGROUNDL-glutamate (L-GLU) is a major neurotransmitter in the nucleus ambiguus (NA), which can modulate respiration, arterial pressure, heart rate, etc. This study investigated the effects and mechanisms of L-GLU microinjected into NA on gastric motility in rats.

METHODSA latex balloon connected with a pressure transducer was inserted into the pylorus through the forestomach for continuous recording of the gastric motility. The total amplitude, total duration, and motility index of gastric contraction waves within 5 minutes before microinjection and after microinjection were measured.

RESULTSL-GLU (5 nmol, 10 nmol and 20 nmol in 50 nl normal saline (PS) respectively) microinjected into the right NA significantly inhibited gastric motility, while microinjection of physiological saline at the same position and the same volume did not change the gastric motility. The inhibitory effect was blocked by D-2-amino-5-phophonovalerate (D-AP5, 5 nmol, in 50 nl PS), the specific N-methyl-D-aspartic acid (NMDA) receptor antagonist, but was not influenced by 6-cyaon-7-nitroquinoxaline-2,3-(1H,4H)-dione (CNQX) (5 nmol, in 50 nl PS), the non-NMDA ionotropic receptor antagonist. Bilateral subdiaphragmatic vagotomy abolished the inhibitory effect by microinjection of L-GLU into NA.

CONCLUSIONSMicroinjection of L-GLU into NA inhibits the gastric motility through specific NMDA receptor activity, not non-NMDA receptor activity, and the efferent pathway is the vagal nerves.

2-Amino-5-phosphonovalerate ; pharmacology ; 6-Cyano-7-nitroquinoxaline-2,3-dione ; pharmacology ; Animals ; Gastrointestinal Motility ; drug effects ; Glutamic Acid ; administration & dosage ; pharmacology ; Male ; Medulla Oblongata ; drug effects ; metabolism ; Rats ; Rats, Wistar ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors ; Vagotomy

AIMTo study the effect of blocking adenosine A1 receptors on learning and memory and the relation with cholinergic and aminoacidergic nerve.

METHODSUsing step through test, spectrophotometry and HPLC method, the effect of selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.3, 0.15, 0.075, 0.03, 0.015 microgram, icv) on memory impairment by scopolamine (Scop, 3 mg.kg-1 i.p.) or 2-amino-5-phosphonovaleric (AP5, 2.5 ng, icv), acetylcholinesterase (AChE) activity and aminoacid level in brain of mice was studied.

RESULTSDPCPX was shown to significantly improve scopolamine-induced memory impairment, but not AP5-induced. The activity of AChE in mouse brain was significantly inhibited by large doses of DPCPX in vitro and in vivo test. DPCPX(0.3 microgram, icv) was shown to significantly increase the content of glutamate and aspartic acid in brain of mice. DPCPX (0.3, 0.15 microgram, icv) significantly decrease GABA and increase Glu/GABA in brain of mice.

CONCLUSIONThe selective adenosine A1 receptor antagonist DPCPX was shown to significantly improve scopolamine but not AP5-induced memory impairment. Large doses of DPCPX was shown to influence the AChE activity and the changes in aminoacid level in brain, especially increase Glu/GABA.

2-Amino-5-phosphonovalerate ; metabolism ; Acetylcholine ; metabolism ; Adenosine A1 Receptor Antagonists ; Animals ; Brain ; drug effects ; metabolism ; Female ; Glutamic Acid ; metabolism ; Learning ; drug effects ; Male ; Mice ; Random Allocation ; Scopolamine Hydrobromide ; Xanthines ; pharmacology ; gamma-Aminobutyric Acid ; metabolism

2-Amino-5-phosphonovalerate ; pharmacology ; Animals ; Animals, Newborn ; Cells, Cultured ; Cerebral Cortex ; cytology ; physiology ; Hydrogen-Ion Concentration ; Hypothermia, Induced ; Neurons ; drug effects ; Nimodipine ; pharmacology ; Protons ; Random Allocation ; Rats ; Rats, Wistar

AIMTo observe the effect of adenosine A, receptor antagonist on synaptic transmission in the dentate gyrus of hippocampus and its relations with NMDA receptor.

METHODSUsing electrophysiological technique to record the long-term potentiation (LTP), the relation between selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and NMDA receptor agonist/antagonist, in both basic synaptic transmission and 200 Hz high-frequency stimulation (HFS) induced LTP of the dentate gyrus of hippocampus in anesthetized rats, was studied.

RESULTSDPCPX (6 mg x L(-1), 5 microL, icv) or NMDA (0.2 mg x L(-1), 5 microL, icv) was shown not to affect the synaptic transmission in the dentate gyrus in rats. DPCPX was found not to affect the keeping of LTP induced by HFS after icv NMDA. But the basic synaptic transmission and the magnitude of LTP induced by HFS in the dentate gyrus after icv NMDA could be enhanced significantly by icv DPCPX in advance. DPCPX could not affect the magnitude of LTP inhibited by AP5 (0.5 mg x L(-1), 5 microL) NMDA receptor antagonist, but the inhibitory effect of AP5 on LTP could be antagonized by icv DPCPX in advance.

CONCLUSIONThe selective adenosine A1 receptor antagonist DPCPX could not affect the synaptic transmission in the dentate gyrus of hippocampus, but could significantly enhance the effect of NMDA receptor in both basic synaptic transmission and HFS induced LTP in the dentate gyrus of hippocampus in anesthetized rats.

2-Amino-5-phosphonovalerate ; pharmacology ; Adenosine A1 Receptor Antagonists ; Animals ; Dentate Gyrus ; drug effects ; physiology ; Long-Term Potentiation ; drug effects ; Male ; N-Methylaspartate ; pharmacology ; Rats ; Rats, Wistar ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors ; Synaptic Transmission ; drug effects ; Xanthines ; pharmacology

Previous reports suggested that a novel stimulus pattern of multi-train stimulus at low-frequency (2-Hz or 5-Hz) could induce stable long-term depression (LTD) in the CA1 area of adult rat hippocampus. In the present study, in order to determine the mechanism in LTD induced by the two novel tetanus patterns, changes in the population spikes (PS) in the hippocampal CA1 area of adult rats following the multi-train stimulus in the presence of AP5 [antagonist of N-methyl-D-aspartate receptors (NMDARs)] or MCPG [antagonist of type I/II metabotropic glutamate receptors (mGluRs)] were recorded. The results showed that both AP5 and MCPG inhibited the LTD induced by 2-Hz multi-train stimulus. The mean amplitude of population spikes (PSA) normalized to the baseline was (96.0±3.5)% after applying AP5 (n=10) and (95.7±4.1)% after applying MCPG (n=8), respectively, measured at 20 min post-tetanus. While 5-Hz multi-train tetanus failed to induce LTD in the presence of MCPG. The mean PSA was (73.6±4.4)% (n=10) and (98.2±8.9)% (n=8) in the presence of AP5 and MCPG, respectively, measured at 35 min post-tetanus. So it is suggested that LTD induced by 2-Hz multi-train tetanus involves co-activation of NMDARs and mGluRs, while LTD induced by 5-Hz multi-train tetanus is only related to activation of mGluRs.
2-Amino-5-phosphonovalerate ; pharmacology ; Animals ; CA1 Region, Hippocampal ; physiology ; Glycine ; analogs & derivatives ; pharmacology ; Long-Term Synaptic Depression ; Rats ; Receptors, Metabotropic Glutamate ; antagonists & inhibitors ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors

OBJECTIVETo investigate the effect of µ-opioid receptors (µ-ORs) in the central nucleus of the amygdala (CeA) on feeding and drinking behaviors in rats and evaluate the role of glutamate signaling in opioid-mediated ingestive behaviors.

METHODSStainless steel cannulas were implanted in the unilateral CeA for microinjection of different doses of the selective µ-OR agonist DAMGO in satiated or water-deprived male SD rats. The subsequent food intake or water intake of the rats was measured at 60, 120, and 240 min after the injection. The rats receiving microinjections of naloxone (NTX, a nonselective opioid antagonist) or D-AP-5 (a selective N-methyl-D-aspartic acid-type glutamate receptor antagonist) prior to DAMGO microinjection were tested for food intake at 60, 120, and 240 min after the injections.

RESULTSInjections of DAMGO (1-4 nmol in 0.5 µl) into the CeA significantly increased food intake in satiated rats, but did not affect water intake in rats with water deprivation. NTX (26.5 nmol in 0.5 µl) injected into the CeA antagonized DAMGO-induced feeding but D-AP-5 (6.3-25.4 nmol in 0.5 µl) injections did not produce such an effect.

CONCLUSIONµ-ORs in the CeA regulate food intake rather than water intake in rats, and the orexigenic role of µ-ORs is not dependent on the activation of the NMDA receptors in the CeA.

2-Amino-5-phosphonovalerate ; pharmacology ; Animals ; Central Amygdaloid Nucleus ; physiology ; Drinking ; physiology ; Eating ; physiology ; Enkephalin, Ala(2)-MePhe(4)-Gly(5)- ; pharmacology ; Excitatory Amino Acid Antagonists ; pharmacology ; Male ; Naloxone ; pharmacology ; Narcotic Antagonists ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, mu ; physiology

OBJECTIVETo investigate the role of N-Methyl-D-aspartic acid (NMDA)-type glutamate receptors in the central nucleus of the amygdale (CeA) in food and water intake.

METHODSMale Sprague-Dawley rats with stainless steel cannulae implanted unilaterally into the CeA were used. The prototypic NMDA receptor agonist NMDA, or the selective NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP-5) was microinjected into the CeA of satiated and euhydrated rats.

RESULTSIntra-CeA injection of 8.50, 17.00, or 34.00 nmol NMDA did not alter food intake but significantly increased water intake 0-1 h after the injection (F(3,32)=3.191, P=0.037) independent of food intake. Without affecting the food intake, injection of 6.34, 12.70, or 25.40 nmol D-AP-5 into the CeA significantly decreased water intake 0-1 h after the injection (F(3,28)=3.118, P=0.042) independent of food intake.

CONCLUSIONNMDA receptors in the CeA may participate in the control of water intake rather than food intake.

2-Amino-5-phosphonovalerate ; pharmacology ; Amygdala ; drug effects ; Animals ; Drinking ; drug effects ; Eating ; drug effects ; Excitatory Amino Acid Agonists ; pharmacology ; Excitatory Amino Acid Antagonists ; pharmacology ; Injections, Intraventricular ; Male ; N-Methylaspartate ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; agonists ; antagonists & inhibitors

OBJECTIVETo investigate the effect of D-AP5 (D-2-amino-5-phosphonopentanoate, a specific NMDA-antagonist) on the increase of intracellular free Ca2+ concentration ([Ca2+]i) induced by glutamate in isolated cochlear inner hair cells (IHCs), and to detect the autoreceptors of the IHC membrane.

METHODSWhen a laser scanning confocal microscope (LSCM) was used, the exogenous glutamate (Glu)-induced changes in [Ca2+]i of isolated IHCs and OHCs of guinea pig cochlea were observed with fluo-3, a fluorescent probe for [Ca2+]i. After D-AP5 or CNQX (6--cyano--7--nitroguinoxaline--2, 3--dione, a specific AMPA- antagonist) was administered, the exogenous glutamate (Glu)-induced changes in [Ca2+]i of isolated IHCs were recorded.

RESULTSIn the presence of a low concentration Glu (3.85 mumol/L), there was an increase of [Ca2+]i in IHCs, whereas there was no change in OHCs. When 50 mumol/L of D-AP5 was administrated in advance, Glu did not induce a corresponding increase in [Ca2+]i in IHCs, and 50 mumol/L of CNQX did not completely block the increase of [Ca2+]i in IHCs.

CONCLUSIONSThese results suggest that the autoreceptors existing in the IHC membrane are mainly of NMDA type, while there are relatively few AMPA receptors. Exogenous Glu is capable of increasing [Ca2+]i in IHCs by acting on the NMDA autoreceptor of IHCs in a positive feedback manner.

2-Amino-5-phosphonovalerate ; pharmacology ; 6-Cyano-7-nitroquinoxaline-2,3-dione ; pharmacology ; Animals ; Calcium ; metabolism ; Excitatory Amino Acid Antagonists ; pharmacology ; Glutamic Acid ; pharmacology ; Guinea Pigs ; Hair Cells, Auditory, Inner ; drug effects ; metabolism ; In Vitro Techniques ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors