µ-opioid receptors in the central nucleus of the amygdala regulate food rather than water intake in rats / 南方医科大学学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Stainless 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.</p><p><b>RESULTS</b>Injections 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.</p><p><b>CONCLUSION</b>µ-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.</p>

Phorbol 12-Myristate 13-Acetate Enhances Long-Term Potentiation in the Hippocampus through Activation of Protein Kinase Cdelta and epsilon

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.

Microinjection of NMDA-type glutamate receptor agonist NMDA and antagonist D-AP-5 into the central nucleus of the amygdale alters water intake rather than food intake / 南方医科大学学报

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>Male 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.</p><p><b>RESULTS</b>Intra-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.</p><p><b>CONCLUSION</b>NMDA receptors in the CeA may participate in the control of water intake rather than food intake.</p>

Effects and mechanisms of L-glutamate microinjected into nucleus ambiguus on gastric motility in rats / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>L-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.</p><p><b>METHODS</b>A 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.</p><p><b>RESULTS</b>L-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.</p><p><b>CONCLUSIONS</b>Microinjection 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.</p>

Different glutamate receptor mechanisms in long-term depression induced by different stimulus patterns in the CA1 area of adult rat hippocampus / 生理学报

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.

Involvement of protein kinase C in NMDAR-dependent long-term potentiation in rat amygdala / 生理学报

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.

Relation between adenosine A1 receptor and NMDA receptor on synaptic transmission in dentate gyrus of hippocampus / 药学学报

<p><b>AIM</b>To observe the effect of adenosine A, receptor antagonist on synaptic transmission in the dentate gyrus of hippocampus and its relations with NMDA receptor.</p><p><b>METHODS</b>Using 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.</p><p><b>RESULTS</b>DPCPX (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.</p><p><b>CONCLUSION</b>The 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.</p>

Effect of adenosine A1 receptor antagonist on learning and memory and analysis of its mechanism / 药学学报

<p><b>AIM</b>To study the effect of blocking adenosine A1 receptors on learning and memory and the relation with cholinergic and aminoacidergic nerve.</p><p><b>METHODS</b>Using 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.</p><p><b>RESULTS</b>DPCPX 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.</p><p><b>CONCLUSION</b>The 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.</p>

D-AP5 blocks the increase of intracellular free Ca2+ induced by glutamate in isolated cochlear IHCs / 中华医学杂志(英文版)

<p><b>OBJECTIVE</b>To 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.</p><p><b>METHODS</b>When 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.</p><p><b>RESULTS</b>In 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.</p><p><b>CONCLUSIONS</b>These 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.</p>

Infusions of AP5 into the basolateral amygdala impair the formation, but not the expression, of step-down inhibitory avoidance

We evaluated the effects of infusions of the NMDA receptor antagonist D,L-2-amino-5-phosphonopentanoic acid (AP5) into the basolateral nucleus of the amygdala (BLA) on the formation and expression of memory for inhibitory avoidance. Adult male Wistar rats (215-300 g) were implanted under thionembutal anesthesia (30 mg/kg, ip) with 9.0-mm guide cannulae aimed 1.0 mm above the BLA. Bilateral infusions of AP5 (5.0 µg) were given 10 min prior to training, immediately after training, or 10 min prior to testing in a step-down inhibitory avoidance task (0.3 mA footshock, 24-h interval between training and the retention test session). Both pre- and post-training infusions of AP5 blocked retention test performance. When given prior to the test, AP5 did not affect retention. AP5 did not affect training performance, and a control experiment showed that the impairing effects were not due to alterations in footshock sensitivity. The results suggest that NMDA receptor activation in the BLA is involved in the formation, but not the expression, of memory for inhibitory avoidance in rats. However, the results do not necessarily imply that the role of NMDA receptors in the BLA is to mediate long-term storage of fear-motivated memory within the amygdala.

Involvement of hippocampal NMDA receptors in retention of shuttle avoidance conditioning in rats

The purpose of this research was to evaluate the role of hippocampal N-methyl-D-aspartate (NMDA) receptors in acquisition and consolidation of memory during shuttle avoidance conditioning in rats. Adult male Wistar rats were surgically implanted with cannulae aimed at the CA1 area of the dorsal hippocampus. After recovery from surgery, animals were trained and tested in a shuttle avoidance apparatus (30 trials, 0.5-mA footshock, 24-h training-test interval). Immediately before or immediately after training, animals received a bilateral intrahippocampal 0.5-µl infusion containing 5.0 µg of the NMDA competitive receptor antagonist aminophosphonopentanoic acid (AP5) or vehicle (phosphate-buffered saline, pH 7.4). Infusion duration was 2 min per side. Pre-training infusion of AP5 impaired retention test performance (mean Ý SEM number of conditioned responses (CRs) during retention test session was 16.47 Ý 1.78 in the vehicle group and 9.93 Ý 1.59 in the AP5 group; P<0.05). Post-training infusion of AP5 did not affect retention (mean Ý SEM number of conditioned responses during retention test session was 18.46 Ý 1.94 in the vehicle group and 20.42 Ý 2.38 in the AP5 group; P>0.10). This impairment could not be attributed to an effect on acquisition, motor activity or footshock sensitivity since AP5 affected neither training session performance measured by the number of CRs nor the number of intertrial crossings during the training session. These data suggest that NMDA receptors in the hippocampus are critical for retention of shuttle avoidance conditioning, in agreement with previous evidence showing a role of NMDA receptors in fear memory

Evidence that similar neurotransmitter mechanisms in amygdala, hippocampus and medial septum regulate memory consolidation of avoidance behavior in rats

A injeçäo de ácido DL-amino-5-fosfonopentanóico (AP5) ou escopolamina na amígdala, no septo medial ou no hipocampo, imediatamente após o treino, causa amnésia retrógrada para um aprendizado de esquiva inibitória em ratos. A picrotoxina, no entanto, causa facilitaçäo retrógrada da memória e bloqueia o efeito do AP5 e da escopolamina. O timolol näo tem efeito próprio mas cancela as açöes da picrotoxina. O AP5 é um antagonista de receptores a N-metil-D- aspartato (NMDA) dos aminoácidos excitatórios; a escopolamina é um antagonista dos receptores colinérgicos muscarínicos; a picrotoxina bloqueia o canal de cloro estimulado pelos receptores GABA-A; e o timolol é um antagonista dos ß adrenoreceptores. Os resultados indicam que, na amígdala, no septo medial e no hipocampo, receptores NMDA e muscarínicos säo necessários para a consolidaçäo da memória, receptores GABA-A inibem a açäo dos anteriores, e receptores ß noradrenérgicos modulam a açäo dos receptores GABA-A. A amígdala, o septo medial e o hipocampo operam de forma näo redundante na consolidaçäo da memória

Kynurenate and 2-amino-5-phosphonovalerate alter the spinal seizures evoked by sudden cooling of toad isolated cords

El esfriamiento brusco de la médula espinal aislada de sapos induce una convulsión característica en los miembros posteriores. En este trabajo, el kinurenato (KYN), un antagonista no competitivo de los receptores N-metil-D-aspartato (NMDA) y el 20amino-5-fosfonovalerato (APV), un antagonista competitivo de los receptores NMDA, fueron ensayados en el patrón, la latencia y la duración de esta convulsión espinal. APV, 1,3-2,5 mmol/Kg and KYN, 2,6 mmol/Kg, inhibieron la fase tónica de esta convulsión y prolongaron la duración de la fase clónica después de la administración intralinfática (i.l.). El mismo efecto fue observado después de la inyección intratecal de dosis de 10 ó 20 µmol/20 µl de cada droga. La fase clónica fue maracadamente atenuada por KYN a dosis altas de 5.3 ó 10.6 mmol/Kg, i.l., sugiriendo que receptores del tipo no NMDA podrían tener alguna mediciación en la generación de dicha fase. Ambos antagonistas retardaron el comienzo de las convulsiones, indicando que la activación de los receptores NMDA están probablemente involucrados en el comienzo de este tipo de convulsiones. Este modelo espinal podría ser una técnica útil para el ensayo de otros antagonistas de amino ácidos excitatorios