Excitatory Amino Acid Agonists Research Articles

Identifying interstitial lung disease associated chemicals by integrating transcriptome-wide association study and chemical-gene interaction networks.

Interstitial lung diseases (ILD) comprise a heterogeneous group of lung disease characterized by common clinical syndromes and patterns of lung injury which poses growing burden on the health and social economic consequences. Its etiology remains elusive. By integrating transcriptome-wide association studies analysis of ILD and chemical-gene interaction networks implemented by CGSEA software, we systematically evaluated the association between ILD and 11,190 chemicals in this study. We detected several chemicals significantly associated with ILD (permutated empirical P values < 0.05). Briefly, a total of 56 chemicals were detected for ILD in lung tissue, 121 in whole blood respectively. Among the chemicals identified for ILD in lung tissue and whole blood, we found 7 common chemicals, including St. Thomas' Hospital cardioplegic solution, cytarabine, ginsenoside Rg3, cholecalciferol, fluoxetine, oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine and excitatory amino acid agonists. Our findings shed lights on the underlying impact of chemical exposure on the development and progression of ILD, which will pave the way for more effective prevention and treatment strategies, ultimately improving the health outcomes and quality of life of those affected by ILD.

Physiological and Pharmacological Studies on Cervical Motor Neurons in Slices Prepared from Neonatal and Aged Mice

The effects of age on the physiological properties of cervical motor neurons were examined in slices made from an excised spinal cord graft of ICR mice from the second day after birth to age 350 days. The membrane potential of post-natal day 2 (PD2) to PD350 was about -65 mV and did not change greatly with age, although it was slightly higher at PD2. However, there were significant changes in membrane resistance, which increased with age from about 15 to 30 MΩ. The depolarization induced by the excitatory amino acid agonists, kainic acid, NMDA and AMPA, decreased with aging in spite of the increase in membrane resistance. The motor neurons of the aged mice showed delayed recovery from excitation caused by excitatory amino acid agonists. By injecting Lucifer yellow CH into motor neurons, it was observed that the dendrite trees become thin, and some of the dendrite branches were missing in older animals.

Effect of GLYX-13 on cognitive function after long-time isoflurane anesthesia in mice

Objective To evaluate the effects of GLYX-13 on cognitive function after long-time isoflurane anesthesia in mice. Methods A total of 192 healthy male C57/B6J mice, aged 8 weeks, weighing 22-25 g, were divided into 4 groups (n=48 each) using a random number table: control group (group C), isoflurane anesthesia group (group I), GLYX-13 group (group G), and isoflurane anesthesia plus GLYX-13 group (group IG). The animals were exposed to 1.5% isoflurane for 6 h in I and IG groups.GLYX-13 1 mg/kg was injected via the caudal vein at 2 h before anesthesia in G and IG groups.Novel object recognition test and contextual fear conditioning test were performed on 1st, 3rd and 7th days after anesthesia.The expression of 2B subunits-containing NMDA receptor (NR2B) and cyclic adenosine monophosphate response element-binding protein (CREB) mRNA in the hippocampus was detected by quantitative real-time polymerase chain reaction after the end of behavioral tests on 1st, 3rd and 7th days after anesthesia. Results Compared with group C, the percentage of time spent in exploring a novel object, discrimination index and percentage of freezing time were significantly decreased, and the expression of NR2B and CREB mRNA in the hippocampus was down-regulated in group I (P <0.05). Compared with group I, the percentage of time spent in exploring a novel object, discrimination index and percentage of freezing time were significantly increased, and the expression of NR2B and CREB mRNA in the hippocampus was up-regulated in group IG (P <0.05). Conclusion GLYX-13 can significantly improve the cognitive function after long-time isoflurane anesthesia in mice. Key words: Excitatory amino acid agonists; Isoflurane; Cognition disorders

Paeoniflorin inhibits excitatory amino acid agonist-and high-dose morphine-induced nociceptive behavior in mice via modulation of N-methyl-D-aspartate receptors.

BackgroundPain, the most common reasons for physician consultation, is a major symptom in many medical conditions that can significantly interfere with a person’s life quality and general functioning. Almost all painkillers have its untoward effects. Therefore, seeking for a safe medication for pain relieve is notable nowadays. Paeonia lactiflora is a well-known traditional Chinese medicine. Paeoniflorin is an active component found in Paeonia lactiflora, which has been reported to inhibit formalin-induced nociceptive behavior in mice. Aims of this present study were to investigate effects of paeoniflorin on excitatory amino acid agonist- or high-dose morphine-induced nociceptive behaviors in mice.ResultsPaeoniflorin (100, 200, 500 nmol, i.c.v.) alone and combined with glutamatergic antagonists (MK-801 14.8 pmol, or NBQX 5 nmol, i.t.) inhibited nociception. Those agents also inhibited the clonic seizure-like excitation induced by high-dose morphine (250 nmol, i.t) in mice. Antisense oligodeoxynucleotides of NMDA receptor subunits NR1, NR2A, NR2B significantly enhanced the inhibition of paeoniflorin on excitatory amino acid-and high-dose morphine-induced nociception. Docking energy data revealed that paeoniflorin had stronger binding activity in NR2A and NR2B than NR2C of NMDA receptors.ConclusionsResults of this study indicate that paeoniflorin-induced inhibition of excitatory amino acid agonist- and high-dose morphine-induced nociceptive behaviors might be due to modulation of NMDA receptors, specifically the NR2B subunit.

Manganese-Enhanced MRI Reflects Both Activity-Independent and Activity-Dependent Uptake within the Rat Habenulomesencephalic Pathway.

Manganese-enhanced magnetic resonance imaging (MEMRI) is a powerful technique for assessing the functional connectivity of neurons within the central nervous system. Despite the widely held proposition that MEMRI signal is dependent on neuronal activity, few studies have directly tested this implicit hypothesis. In the present series of experiments, MnCl2 was injected into the habenula of urethane-anesthetized rats alone or in combination with drugs known to alter neuronal activity by modulating specific voltage- and/or ligand-gated ion channels. Continuous quantitative T1 mapping was used to measure Mn2+ accumulation in the interpeduncular nucleus, a midline structure in which efferents from the medial habenula terminate. Microinjection of MnCl2 into the habenular complex using a protocol that maintained spontaneous neuronal activity resulted in a time-dependent increase in MEMRI signal intensity in the interpeduncular nucleus consistent with fast axonal transport of Mn2+ between these structures. Co-injection of the excitatory amino-acid agonist AMPA, increased the Mn2+-enhanced signal intensity within the interpeduncular nucleus. AMPA-induced increases in MEMRI signal were attenuated by co-injection of either the sodium channel blocker, TTX, or broad-spectrum Ca2+ channel blocker, Ni2+, and were occluded in the presence of both channel blockers. However, neither Ni2+ nor TTX, alone or in combination, attenuated the increase in signal intensity following injection of Mn2+ into the habenula. These results support the premise that changes in neuronal excitability are reflected by corresponding changes in MEMRI signal intensity. However, they also suggest that basal rates of Mn2+ uptake by neurons in the medial habenula may also occur via activity-independent mechanisms.

Regulation of arterial pressure by the paraventricular nucleus in conscious rats: interactions among glutamate, GABA, and nitric oxide

The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic and neuroendocrine regulation. Experiments in anesthetized animals and in vitro indicate an interaction among gamma-aminobutyric acid (GABA), nitric oxide (NO), and glutamate in the PVN. The cardiovascular role of the PVN and interactions of these neurotransmitters in conscious animals have not been evaluated fully. In chronically instrumented conscious rats, mean arterial pressure (MAP) and heart rate (HR) responses to microinjections (100 nl) in the region of the PVN were tested. Bilateral blockade of ionotropic excitatory amino acid (EAA) receptors (kynurenic acid, Kyn) in the PVN produced small but significant decreases in MAP and HR. GABAA receptor blockade (bicuculline, Bic), and inhibition of NO synthase [(NOS), N-(G)-monomethyl-L-arginine, L-NMMA] each increased MAP and HR. The NO donor sodium nitroprusside (SNP) produced depressor responses that were attenuated by Bic. NOS inhibition potentiated both pressor responses to the selective EAA agonist, N-methyl-D-aspartic acid (NMDA), and depressor responses to Kyn. Increases in MAP and HR due to Bic were blunted by prior blockade of EAA receptors. Thus, pressor responses to GABA blockade require EAA receptors and GABA neurotransmission contributes to NO inhibition. Tonic excitatory effects of glutamate in the PVN are tonically attenuated by NO. These data demonstrate that, in the PVN of conscious rats, GABA, glutamate, and NO interact in a complex fashion to regulate arterial pressure and HR under normal conditions.

Nucleus accumbens facilitates nociception

We have previously demonstrated an opioid link in nucleus accumbens (NAc) that mediates antinociception produced by a novel ascending pain modulation pathway. For example, noxious stimulation induces heterosegmental antinociception that is mediated by both mu- and delta-opioid receptors in NAc. However, spinal intrathecal administration of the mu-receptor agonist [ d-Ala 2, N-Me-Phe 4,Gly 5-ol]-enkephalin (DAMGO) also induces heterosegmental antinociception. The aim of the present study in the rat was to identify the intra-NAc opioid receptors that mediate the antinociceptive effects of spinally administered DAMGO and also to determine the effect of NAc efferent activity on nociception. Intra-NAc administration of either the mu-opioid receptor antagonist Cys 2,Tyr 3, Orn 5,Pen 7amide (CTOP) or the delta-opioid receptor antagonist naltrindole blocked the antinociceptive effect of spinally administered DAMGO on the jaw-opening reflex (JOR). Injection of quaternary lidocaine (QX-314) attenuated the JOR, suggesting that the output of NAc is pronociceptive. In support of this, intra-NAc injection of the excitatory amino acid agonist kainate enhanced the JOR. Thus, it is possible to modulate activity in NAc to bidirectionally attenuate or enhance nociception, suggesting a potential role for NAc in setting nociceptive sensitivity.

Localization, pharmacology, and organization of brain locomotor areas in larval lamprey

In larval lamprey, spinal locomotor activity can be initiated by pharmacological microstimulation from the following higher order brain locomotor areas [Paggett et al. (2004) Neuroscience 125:25–33; Jackson et al. (2007) J Neurophysiol 97:3229–3241]: rostrolateral rhombencephalon (RLR); ventromedial diencephalon (VMD); or dorsolateral mesencephalon (DLM). In the present study, pharmacological microstimulation with excitatory amino acids (EAAs) or their agonists in the brains of in vitro brain/spinal cord preparations was used to determine the sizes, pharmacology, and organization of these locomotor areas. First, the RLR, DLM and VMD locomotor areas were confined to relatively small areas of the brain, and stimulation as little as 50 μm outside these areas was ineffective or elicited tonic or uncoordinated motor activity. Second, pharmacological stimulation with NMDA, kainate, or AMPA in the VMD or DLM reliably initiated well-coordinated spinal locomotor activity. In the RLR, stimulation with all three ionotropic EAA receptor agonists could initiate spinal locomotor activity, but NMDA or AMPA was more reliable than kainate. Third, with synaptic transmission blocked only in the brain, stimulation in the RLR, VMD, or DLM no longer initiated spinal locomotor activity, suggesting that these locomotor areas do not directly activate spinal locomotor networks. Fourth, following a complete transection at the mesencephalon-rhombencephalon border, stimulation in the RLR no longer initiated spinal motor activity. Thus, the RLR locomotor area does not appear able to initiate spinal locomotor activity by neural circuits confined entirely within the rhombencephalon but requires more rostral neural centers, such as those in the VMD and DLM, as previously proposed [Paggett et al. (2004) Neuroscience 125:25–33].

Role of homocysteic acid in the guinea pig (Cavia porcellus) anterior cingulate cortex in tonic immobility and the influence of NMDA receptors on the dorsal PAG

Tonic immobility (TI) is an innate defensive behaviour elicited by physical restriction and postural inversion, and is characterised by a profound and temporary state of akinesis. Our previous studies demonstrated that glutamatergic stimulation of the dorsomedial/dorsolateral portion of periaqueductal gray matter (dPAG) decreases the duration of TI in guinea pigs (Cavia porcellus). Furthermore, evidence suggests that the anterior cingulate cortex (ACC) constitutes an important source of glutamate for the dPAG. Hence, in the current study, we investigated the effects of microinjection of the excitatory amino acid (EAA) agonist dl-homocysteic acid (DLH) and the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 into the ACC on the duration of TI in guinea pigs. We also assessed the effect of the NMDA receptor antagonist (MK-801) into the dorsal periaqueductal gray matter (dPAG) prior to DLH microinjection into the ACC on the TI duration in the guinea pig. Our results demonstrated that DLH microinjections into the ACC decreased the duration of TI. This effect was blocked by previous MK-801 microinjections into the ACC or into the dPAG. The MK-801 microinjections alone did not influence TI duration. These results provide the new insight that EAAs in the ACC can decrease the duration of TI. The mechanism seems to be dependent on the NMDA receptors present in the ACC and in the dPAG.

Descending interactions with spinal cord networks: a time to build?

Descending interactions with spinal cord networks: a time to build?

Activation of 5-HT receptors in the periaqueductal gray attenuates the tachycardia evoked from dorsomedial hypothalamus

Studies have shown that the dorsomedial hypothalamus (DMH) is a key region in the descending pathways mediating the cardiovascular response to emotional stress. We have recently demonstrated that the lateral/dorsolateral periaqueductal gray (l/dlPAG) is an important synaptic relay in mediating the tachycardic effect produced by activation of DMH neurons. This synaptic relay is mediated via NMDA excitatory amino acid receptors. In this study, our aim was to investigate, in conscious rats, whether activation of 5-Hydroxytriptamine 1A (5-HT1A) receptors in the l/dlPAG can attenuate the increases in heart rate and arterial pressure evoked by a) chemical activation of the DMH, b) air jet stress paradigm and c) chemical activation of l/dlPAG. Microinjections of the 5-HT1A receptor agonist, 8-OH-DPAT (1 nmol/100 nl), into the l/dlPAG reduced (by 62%) the increases in heart rate evoked by chemical activation of DMH neurons with the GABAA antagonist bicuculline methiodide (10 pmol/100 nl). The tachycardic and pressor responses evoked by air jet stress paradigm were also attenuated after treatment with 8-OH-DPAT in the l/dlPAG. The increases in heart rate and arterial pressure produced by microinjection of the excitatory amino acid receptor agonist, NMDA, into the l/dlPAG were largely reduced (by 94% and 73%, respectively) after treatment in the same region with 8-OH-DPAT. Taken together, our findings indicate that 5-HT1A receptors at the lateral dorsolateral PAG play a significant role in modulating the descending cardiovascular pathways from the dorsomedial hypothalamus and consequently the cardiovascular response to emotional stress.

Involvement of glutamate and cytokine pathways on antinociceptive effect of Pfaffia glomerata in mice

Ethnopharmacological relevance Pfaffia glomerata (Spreng) Pedersen (Amaranthaceae) is a medicinal plant known in Brazil as “Paratudo” and “Brazilian ginseng” and is commonly used as tonic, antidiabetic and to treat gastric disorders. Aim of the study This study evaluates the possible mechanism by which hydroalcoholic extract (HE) of Pfaffia glomerata exerts its antinociceptive effect. Materials and methods The HE was evaluated in acetic acid and glutamate models of pain or by biting behavior following intrathecal (i.t.) administration of agonists of excitatory aminoacids (EAA) receptors glutamate and pro-inflammatory cytokines, IL-1β and TNF-α in mice. Results Oral administration of HE produced dose-dependent inhibition of acetic acid-induced visceral pain and glutamate-induced pain, with ID 50 of 64.6 (47.7–87.5) mg/kg and ID 50 of 370.8 (253.4–542.7) mg/kg, respectively. The HE (300 mg/kg, p.o.) antinociception, in the acetic acid test, was not affected by i.p. treatment of animals with naloxone. In addition, HE (300 mg/kg, p.o.) inhibited the pain-related behaviors induced by i.t. injection of trans-ACPD and TNF-α, but not by NMDA, AMPA, kainate or IL-1β. Conclusions Our results suggest that inhibition of glutamatergic metabotropic receptors and TNF-α may account for the antinociceptive action reported for the HE in models of chemical pain used in this study.

Fos expression following activation of the ventral pallidum in normal rats and in a model of Parkinson’s Disease: implications for limbic system and basal ganglia interactions

The circuit-related consequences of activating the ventral pallidum (VP) are not well known, and lacking in particular is how these effects are altered in various neuropathological states. To help to address these paucities, this study investigated the brain regions affected by VP activation by quantifying neurons that stain for Fos-like immunoreactivity (ir). Fos-ir was assessed after intra-pallidal injections of the excitatory amino acid agonist, NMDA, or the GABA(A) antagonist, bicuculline in normal rats and in those rendered Parkinsonian-like by lesioning dopaminergic neurons with the neurotoxin, 6-OHDA. We hypothesized that activation of the VP will alter the activity state of brain regions associated with both the basal ganglia and limbic system, and that this influence would be modified in the Parkinsonian state. Blocking tonically activated GABA(A) receptors with bicuculline (50 ng/0.5 microl) elevated Fos-ir in the VP to 423% above the contralateral, vehicle-injected side. Likewise, intra-VP NMDA (0.23 microg or 0.45 microg/0.5 microl), dose-dependently increased the number of pallidal neurons expressing Fos-ir by 224 and 526%, respectively. At higher NMDA doses, the density of Fos-ir neurons was not elevated above control levels. This inverted U-shaped profile was mirrored by a VP output structure, the medial subthalamic nucleus (mSTN). The mSTN showed a 289% increase in Fos-ir neurons with intra-VP injections of 0.45 microg NMDA, and this response was halved following intra-VP injections of 0.9 microg NMDA. Of the 12 other brain regions measured, three showed VP NMDA-induced enhancements in Fos-ir: the frontal cortex, entopeduncular nucleus and substantia nigra pars reticulata, all regions associated with the basal ganglia. In a second study, we evaluated the NMDA activation profile in a rat model of Parkinson's Disease (PD) which was created by a unilateral injection of 6-OHDA into the rostral substantia nigra pars compacta. Comparisons of responses to intra-VP NMDA between the hemispheres ipsilateral and contralateral to the lesion revealed that Fos-ir cells in the pedunculopontine nucleus was reduced by 62%, whereas Fos-ir for the basolateral amygdala and STN was reduced by 32 and 42%, respectively. These findings support the concept that the VP can influence both the basal ganglia and the limbic system, and that that the nature of this influence is modified in an animal model of PD. As the VP regulates motivation and cognition, adaptations in this system may contribute to the mood and mnemonic disorders that can accompany PD.

Modulation of tonic immobility in guinea pig PAG by homocysteic acid, a glutamate agonist

Tonic immobility (TI) is an innate defensive behavior elicited by physical restriction and postural inversion, and is characterized by a profound and temporary state of motor inhibition. The participation of the periaqueductal gray matter (PAG) in TI modulation has previously been described. In addition, the excitatory amino acids (EAA) are important mediators involved in the adjustment of several defensive responses produced by PAG. In the present study, we investigated the effect of microinjection of the EAA agonist dl-homocysteic acid (DLH) and the N-methyl- d-aspartate (NMDA) receptor antagonist (MK-801) into the ventrolateral and dorsal PAG over the duration of TI in guinea pigs. Microinjection of 15 nmol/0.2 µl of DLH into the ventrolateral PAG (vlPAG) and 30 nmol/0.2 µl of DLH into the dorsal PAG (dPAG) promoted an increase and decrease in TI duration, respectively. These responses were blocked by prior microinjection of the NMDA receptor antagonist, MK-801 (3.6 nmol/0.2 µl) at the same site. Microinjection of MK-801 alone into the vlPAG and dPAG did not alter the duration of TI episodes. These results suggest that NMDA receptors are involved in the modulation of TI in both the vlPAG and dPAG. In addition, PAG excitatory amino acids modulate the TI response via columnar organization of the PAG. In this manner, the vlPAG facilitates TI modulation whereas dPAG has an inhibitory role in TI.

Central endocannabinoid modulation of baroreflex‐evoked sympathoinhibition in spontaneously hypertensive rats

GABAergic neurotransmission has been reported to be greater in the spontaneously hypertensive rat (SHR) as compared to normotensive Wistar Kyoto (WKY) and Sprague Dawley (SD) rats. Previously, we have shown that endocannabinoids prolong baroreflex inhibition of renal sympathetic nerve activity (RSNA) via modulation of GABAergic neurotransmission in the nucleus tractus solitarius (NTS). Thus we proposed that endocannabinoids could prolong baroreflex‐induced sympathoinhibition more in SHRs than in normotensive rats. This study characterized the physiological role of endogenously released endocannabinoids in the NTS on baroreflex control of RSNA evoked by pressor responses (phenylephrine bolus) or direct stimulation of the baroreflex (NTS microinjection of the excitatory amino acid agonist d,l‐homocysteic acid). Baroreflex responses were compared before and after a microinjection of an indirect cannabinoid 1 receptor agonist, AM404, into the barosensitive region of the NTS of adult male SD rats, WKY rats, and SHRs. AM404 microinjections into the NTS were found to significantly prolong baroreflex‐induced sympathoinhibition in SD and WKY rats, but had an insignificant effect in SHRs. This observation suggests that endocannabinoid modulation of GABAergic transmission in SHRs is reduced and could contribute to elevated sympathetic tone characteristic of this model. VA Medical Research Funds.

Brainstem sites for regulation of gill ventilation mapped by microinjection of DLH in the pre‐metamorphic bullfrog (Lithobates catesbeiana)

This study examined the role of ionotropic excitatory amino acid (EAA) receptors for regulating gill‐related respiratory rhythm in the bullfrog brainstem. Our objective was to ‘map’ the sites responsible for generating rhythmic gill burst activity by microinjection of the EAA agonist DL‐Homocysteic Acid (DLH). We used an in vitro brainstem preparation from pre‐metamorphic tadpoles (N=8; T‐K stages 8–16) that was superfused with oxygenated artificial CSF (20–22 °C) and generated spontaneous respiratory motor output measured by suction electrodes attached to cranial nerves (CN) V, X and XII. Pressure injections of small volumes (2–4 nL) of DLH in glass micropipettes were made in 7 locations from the rostral margin of CN V to the caudal margin of CN XII, lateral to the midline and at depths from 100 to 400 microns. DLH produced both inhibitory and excitatory responses. Inhibitory responses were largely confined to an area delineated by the extent of CN VII whereas excitatory responses, consisting of increases in respiratory frequency and burst amplitude, occurred in areas defined by the caudal margin of CN VIII to the rostral margin of CN XII and at most depths examined. These results indicate that EAAs have a widespread influence on gill burst activity in pre‐metamorphic bullfrogs that is not confined to a localized area of the brainstem. Supported by NIH SO6 GM48135.

Neuroprotective effects of lactation against kainic acid treatment in the dorsal hippocampus of the rat

Marked hippocampal changes in response to excitatory amino acid agonists occur during pregnancy (e.g. decreased frequency in spontaneous recurrent seizures in rats with KA lesions of the hippocampus) and lactation (e.g. reduced c-Fos expression in response to N-methyl- d, l-aspartic acid but not to kainic acid). In this study, the possibility that lactation protects against the excitotoxic damage induced by KA in hippocampal areas was explored. We compared cell damage induced 24 h after a single systemic administration of KA (5 or 7.5 mg/kg bw) in regions CA1, CA3, and CA4 of the dorsal hippocampus of rats in the final week of lactation to that in diestrus phase. To determine cellular damage in a rostro-caudal segment of the dorsal hippocampus, we used NISSL and Fluorojade staining, immunohistochemistry for active caspase-3 and TUNEL, and we observed that the KA treatment provoked a significant loss of neurons in diestrus rats, principally in the pyramidal cells of CA1 region. In contrast, in lactating rats, pyramidal neurons from CA1, CA3, and CA4 in the dorsal hippocampus were significantly protected against KA-induced neuronal damage, indicating that lactation may be a natural model of neuroprotection.

Increased calbindin-D28K immunoreactivity in rat cerebellar Purkinje cell with excitatory amino acids agonists is not dependent on protein synthesis.

The calcium binding protein Calbindin-D28K (CaBP) is abundantly expressed in cerebellar Purkinje cells and show increased immunoreactivity (CaBP-IR) when challenged with glutamate or an analog agonist for the ionotropic glutamate receptor (iGluR). Here we report that t-ACPD, a metabotropic glutamate receptor (mGluR) agonist, produced small increases in CaBP-IR which was potentiated by a mGluR antagonist The increase in CaBPIR was not due to de novo protein synthesis because the translational inhibitors (cycloheximide and emetine) or transciptional inhibitors (actinomycine-D and a-amanitine), did not prevent the EAA enhanced CaBP-IR. The CaBP-IR in the PC appears to be coupled to the ionotropic rather than the metabotropic glutamate receptors, but the latter become effective in the presence of their blocker, L-AP3. The results suggest that CaBP may increase its IR through a conformational change of the protein itself.

The mapped pattern of kainate on blood pressure responses is similar to that of l-proline in the ventrolateral medulla of the rat

Kainate is an excitatory amino acid receptor agonist with a structure similar to the amino acid L-proline. Our previous studies demonstrated that microinjections of L-proline into the ventrolateral medulla (VLM) of the rat induce a mapped pattern of blood pressure responses distinct from L-glutamate, and the depressor response to L-proline in the caudal VLM (CVLM) is abolished by the kainate/AMPA receptor antagonist CNQX. The present study investigated whether kainate produces the L-proline-mapped pattern of responses in the VLM, compared with the pattern by AMPA. Kainate is known to activate AMPA receptors at higher concentrations. Therefore, responses to kainate were investigated at a low concentration. Microinjections of AMPA or NMDA showed the pattern of the L-glutamate-type; a pressor response in the rostral VLM and caudal pressor area (CPA) and a depressor response in the CVLM. Microinjections of kainate showed depressor responses in the CVLM but minor pressor responses in the rostral VLM, suggesting the same responses to L-proline. However, the response sites in the CPA did not enable us to clearly determine the L-proline-type. Further trials at sites defined by a pressor response to L-glutamate in the CPA, successive injections of L-proline and kainate produced no response, indicating that L-glutamate responding neurons in the CPA are not sensitive to L-proline and kainate. These results suggest that kainate stimulation in the VLM produces a mapped pattern of ABP responses similar to the mapped pattern with L-proline. Kainate receptors could therefore be involved in the depressor response to L-proline in the medulla.

A potent non‐monoaminergic paradoxical sleep inhibitory system: a reverse microdialysis and single‐unit recording study

Using reverse microdialysis and polygraphic recordings in freely moving cats, we investigated the effects on sleep-waking states of application of excitatory and inhibitory amino acid agonists, cholinergic agonist and monoamines to the periaqueductal grey and adjacent mesopontine tegmentum. Single-unit recordings during behavioural states were further used to determine the neuronal characteristics of these structures. We found that muscimol, a GABAA receptor agonist, induced a significant increase in paradoxical sleep (PS) only when applied to a dorsocaudal central tegmental field (dcFTC) located just beneath the ventrolateral periaqueductal grey. In this structure, both kainic and N-methyl-aspartic acids caused a dose-dependent increase in wakefulness (W) and decrease in both slow-wave sleep (SWS) and PS. Norepinephrine and epinephrine, and to a lesser extent histamine, also increased W and decreased SWS and PS, whereas serotonin, dopamine and carbachol, a cholinergic agonist, had no effect. Two types of neurones were recorded in this structure, those exhibiting a higher rate of tonic discharge during both W and PS compared with during SWS, and those showing a phasic increase in firing rate during both active W and PS. Both types of neurones showed a gradual increase in unit activity during PS. Our study demonstrated for the first time that the ventrolateral periaqueductal grey and dcFTC play different roles in behavioural state control, that the dcFTC neurones are critically involved in the inhibitory mechanisms of PS generation, playing a central part in its maintenance, and that these neurones are under the control of GABAergic, glutamatergic, adrenergic and histaminergic systems.