Ions and amino acid analysis of Cyperus articulatus L. (Cyperaceae) extracts and the effects of the latter on oocytes expressing some receptors.

Extracts from rhizomes of Cyperus articulatus L. (Cyperaceae) used in Africa and Amazonia to treat many diseases has been shown to possess sedative and anticonvulsant properties. The aim of this study is to determine the mechanism of action of Cyperus articulatus extracts. In Xenopus oocytes expressing receptors, using electrophysiological measurement, extracts of rhizomes of Cyperus articulatus (300 microg/ml) inhibited 50% of the EC(50) and EC(80) of glutamate (1.3 and 2.9 microM, respectively) induced inward current through hNMDAR1A/2A receptors. Extracts induced very small current through rGluR3 receptors. The largest current induced by the extract (30 mg/ml) represents 128% of the EC(100) of glutamate induced inward current, through rGluR3 receptors. The excess 28% current could be induced by aspartate and/or glutamate in the extracts. The effect on Xenopus oocytes expressing heteromeric GABA(B)R1b/R2 receptors and rectifying potassium channels (Kir3) is clear. A decoction and water extract of Cyperus articulatus induced a large inward current that represented 71 and 57% (respectively) of the EC(100) of gaba (30 microM) induced inward current. The water extract induced also a large current through rectifying potassium channels (Kir3). Part of the current induced through GABA(B) receptors could be related to rectifying potassium channels and GABA(B) site receptors. Cyperus articulatus extracts possessed components that could decrease excitation (NMDA receptor antagonists) and increase inhibition (GABA(B) receptor agonists) in the central nervous system.

Electrophysiological studies on the hippocampus and prefrontal cortex assessing the effects of amyloidosis in amyloid precursor protein 23 transgenic mice.

In vitro and in vivo electrophysiological studies were done to investigate the neuronal function of the hippocampus and prefrontal cortex in the amyloid precursor protein (APP) 23 transgenic mouse model for amyloidosis developed by Sturchler-Pierrat et al. [Proc Natl Acad Sci USA 94 (1997) 13287]. Brain slices were taken from 3, 6, 9, 12, 18 and 24 month old wildtype and hemizygous type APP23 mice. Extracellular field potentials were recorded from the CA1 region of the hippocampus while stimulating the Schaffer collaterals. In addition, extracellular field potentials were elicited from areas within layer V/VI of the prefrontal cortex by stimulating the same layer V/VI. Basic synaptic function in the hippocampus was reduced in hemizygous APP23 mice compared with their wildtype littermates at 12 and 18 months of age, whereas, it was unaltered within the prefrontal cortex. Long-term potentiation in the hippocampus and the prefrontal cortex of hemizygous APP23 mice was similar compared with their wildtype littermates. In vivo electrophysiological experiments were done in 3, 9, 18 and 24 month old wildtype and hemizygous APP23 mice. No differences were observed in the number of single spontaneously active units recorded within the prefrontal cortex of hemizygous APP23 mice compared with their wildtype littermates. Field potentials elicited during stimulation of cortico-cortical pathways to assess synaptic transmission and short-term synaptic plasticity were also unchanged in hemizygous APP23 mice. Furthermore, presumable antidromic field potentials recorded in the prefrontal cortex during stimulation of the striatum were similar between the hemizygous APP23 and wildtype mice at each age. The present study shows that amyloidosis impairs basic synaptic function but not long-term potentiation in the hippocampus, however, does not alter any of the neurophysiological functions measured within the prefrontal cortex. These findings suggest that amyloidosis may be involved in altering some neurophysiological functions within only certain brain structures. Although APP23 mice have impaired cognitive performance, long-term plasticity, a cellular model for memory, is not affected, raising the question on the relationship between these processes.

Positive allosteric modulation of native and recombinant gamma-aminobutyric acid(B) receptors by 2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) and its aldehyde analog CGP13501.

The compounds CGP7930 [2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol] and its close analog CGP13501 were identified as positive modulators of gamma-aminobutyric acid(B) (GABA(B)) receptor function. They potentiate GABA-stimulated guanosine 5'-O-(3-[(35)S]thiotriphosphate) (GTP gamma[(35)S]) binding to membranes from a GABA(B(1b/2)) expressing Chinese hamster ovary (CHO) cell line at low micromolar concentrations and are ineffective in the absence of GABA. The structurally related compounds propofol and malonoben are inactive. Similar effects of CGP7930 are seen in a GTP gamma[(35)S] binding assay using a native GABA(B) receptor preparation (rat brain membranes). Receptor selectivity is demonstrated because no modulation of glutamate-induced GTP gamma[(35)S] binding is seen in a CHO cell line expressing the metabotropic glutamate receptor subtype 2. Dose-response curves with GABA in the presence of different fixed concentrations of CGP7930 reveal an increase of both the potency and maximal efficacy of GABA at the GABA(B(1b/2)) heteromer. Radioligand binding studies show that CGP7930 increases the affinity of agonists but acts at a site different from the agonist binding site. Agonist affinity is not modulated by CGP7930 at homomeric GABA(B(1b)) receptors. In addition to GTP gamma[(35)S] binding, we show that CGP7930 also has modulatory effects in cellular assays such as GABA(B) receptor-mediated activation of inwardly rectifying potassium channels in Xenopus laevis oocytes and Ca(2+) signaling in human embryonic kidney 293 cells. Furthermore, we show that CGP7930 enhances the inhibitory effect of L-baclofen on the oscillatory activity of cultured cortical neurons. This first demonstration of positive allosteric modulation at GABA(B) receptors may represent a novel means of therapeutic interference with the GABA-ergic system.

Metabotropic glutamate receptor subtype 5 (mGlu5) and nociceptive function. I. Selective blockade of mGlu5 receptors in models of acute, persistent and chronic pain.

The excitatory neurotransmitter, glutamate, is particularly important in the transmission of pain information in the nervous system through the activation of ionotropic and metabotropic glutamate receptors. A potent, subtype-selective antagonist of the metabotropic glutamate-5 (mGlu5) receptor, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), has now been discovered that has effective anti-hyperalgesic effects in models of inflammatory pain. MPEP did not affect rotarod locomotor performance, or normal responses to noxious mechanical or thermal stimulation in naïve rats. However, in models of inflammatory pain, systemic administration of MPEP produced effective reversal of mechanical hyperalgesia without affecting inflammatory oedema. In contrast to the non-steroidal anti-inflammatory drugs, indomethacin and diclofenac, the maximal anti-hyperalgesic effects of orally administered MPEP were observed without acute erosion of the gastric mucosa. In contrast to its effects in models of inflammatory pain, MPEP did not produce significant reversal of mechanical hyperalgesia in a rat model of neuropathic pain.

Immunocytochemical localization of the metabotropic glutamate receptor mGluR4a in the piriform cortex of the rat.

This study evaluates the localization of the metabotropic glutamate receptor mGluR4a in the piriform cortex of rats using preembedding immunocytochemical methods. At the light microscopic level, punctate labeling was evident in layers Ia and Ib of the piriform cortex, and immunolabeled fibers were present in layers II and III. Following bilateral destruction of the olfactory bulb, the density of labeled puncta in layer Ia decreased. These results suggest that the receptor is present on the terminals of the lateral olfactory tract (LOT). Electron microscopic evaluation of layers Ia and Ib revealed that mGluR4a was localized in synaptic terminals in layers Ia and Ib. The terminals had clear, round synaptic vesicles and terminated on asymmetric synapses on dendritic spines and shafts. There was also immunolabeling of some dendritic profiles in layers Ia and Ib that were postsynaptic to unlabeled presynaptic terminals. These observations suggest that mGluR4a is present on presynaptic terminals in the layers of the piriform cortex that receive LOT and associational synapses. This is the same area in which previous studies have revealed the presence of mGluR7 and mGluR8, suggesting that all three receptors may be colocalized.

Gamma-hydroxybutyrate is a weak agonist at recombinant GABA(B) receptors.

Gamma-hydroxybutyrate (GHB) is a neuromodulator with high affinity binding sites in the mammalian brain. However, the receptor for GHB has not yet been identified. There are indications that GHB and gamma-aminobutyric acid (GABA) mediate their effects via the same receptor. We tested this hypothesis using GABA(B)R1/R2 receptors co-expressed with Kir3 channels in Xenopus oocytes. GHB activated these receptors with an EC50 of approximately 5 mM and a maximal stimulation of 69% when compared to the GABA(B) receptor agonist L-baclofen. GHB and L-baclofen did not amplify each others effect nor did they stimulate the GABA(B) receptor in a linearly additive manner. CGP54626A, 2-OH saclofen and CGP35348, three competitive GABA(B) receptor antagonists, inhibited the GHB induced response completely. A concentration of 30 mM GHB displaced [125I]CGP64213 binding at GABA(B)R1 expressed in COS cells by 21%. These results indicate that GHB is a weak partial agonist at the GABA binding site of GABA(B)R1/R2.

Developmental expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body of the rat.

A preembedding immunocytochemical method for light microscopy was used to study the postnatal development of expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body (MNTB) of the rat. Immunoreactivity for mGluR4a was localized in axonal endings wrapping the principal globular neurons in MNTB, known as calyces of Held. The percentage of calyces of Held immunoreactive for mGluR4a increased progressively from postnatal day 3 (PND3), showing the highest density of labeled calyces by PND9. From this postnatal age on, a gradual reduction in the number of mGluR4a-immunopositive calyces of Held was observed, reaching the lowest level of labeled profiles in adult tissue. The developmental expression of mGluR4a in calyces of Held correlates well with previous studies in young animals showing a modulation of synaptic neurotransmission by group III mGluRs in these giant excitatory synapses made on MNTB principal neurons. All these observations together suggest that the expression of mGluR4a mainly between PND7 and PND12 might be relevant to the maturation and modulation of synaptic transmission at the calyces of Held.