Monoclonal antibody monospecific to glycine for brain immunocytochemistry

The integrity of the glycine co-agonist binding site of N-methyl-D-aspartate receptors is a functional quality control checkpoint for cell surface delivery

N-Methyl-D-aspartate receptors are a subclass of ligand-gated, heteromeric glutamatergic neurotransmitter receptors whose cell surface expression is regulated by quality control mechanisms. Functional quality control checkpoints are known to contribute to cell surface trafficking of non-N-methyl-D-aspartate glutamate receptors. Here we investigated if similar mechanisms operate for the surface delivery of NMDA receptors. Point mutations in the glycine binding domain of the NR1-1a subunit were generated: D732A, a mutation that results in an approximately 3 x 10(4) decrease in glycine binding affinity; D732E, a conservative change; and D723A, a residue in the same NR1-1a domain that has no effect on glycine binding affinity. Each NR1-1a subunit was co-expressed with NR2A in mammalian cells. Immunoblotting and immunoprecipitations showed that all mutants were expressed to similar levels as wild-type NR1-1a and associated with NR2A. Cell surface expression measured by an enzyme-linked immunosorbent assay found that whereas NR1-1a (D732E)/NR2A and NR1-1a (D723A)/NR2A trafficked as efficiently as NR1-1a/NR2A, there was a 90% decrease in surface expression for NR1-1a (D732A)/NR2A. This was confirmed by confocal microscopy imaging and cell surface biotinylation. Further imaging showed that NR1-1a (D732A) and co-transfected NR2A co-localized with an endoplasmic reticulum marker. Dichlorokynurenic acid, a competitive glycine site antagonist, partially rescued surface expression. Mutation of the NR1-1a ER retention motif showed that the ligand binding checkpoint is an early event preceding endoplasmic reticulum sorting mechanisms. These findings demonstrate that integrity of the glycine co-agonist binding site is a functional checkpoint requisite for efficient cell surface trafficking of assembled NMDA receptors.

Immunocytochemical demonstration of polyamines in nucleoli and nuclei

Although biochemical studies have shown that polyamines (PAs) occur in the nucleus, only few studies have examined the intranuclear distribution of these organic cations. By immunocytochemistry, we have previously demonstrated that PAs are located in ribosomes. We now show that PAs also are present in both nucleoli and nuclei of a variety of cell types. Detection of nucleolar and nuclear PAs required novel pretreatment procedures involving protease and/or DNase digestion of specimens prior to immunoreaction. Double fluorescence staining confirmed the localizations. This suggests that PAs may be important to the formation of ribosomes in nucleoli, as well as adds support to biochemical studies suggesting that PAs are involved in many biological events in the nucleus. Further biochemical studies will be needed to substantiate this hypothesis.

Cortex contacts both output neurons and nitrergic interneurons in the superior colliculus: direct and indirect routes for multisensory integration

The ability of cat superior colliculus (SC) neurons to integrate information from different senses is thought to depend on direct projections from regions along the anterior ectosylvian sulcus (AES). However, electrical stimulation of AES also activates SC output neurons polysynaptically. In the present study, we found that nitric oxide (NO)-containing (nitrergic) interneurons are a target of AES projections, forming a component of this cortico-SC circuitry. The dendritic and axonal processes of these corticorecipient nitrergic interneurons apposed the soma and dendrites of presumptive SC output neurons. Often, an individual cortical fiber targeted both an output neuron and a neighboring nitrergic interneuron that, in turn, contacted the output neuron. Many (46%) nitrergic neurons also colocalized with gamma-aminobutyric acid (GABA), suggesting that a substantial subset have the potential for inhibiting output neurons. These observations suggest that nitrergic interneurons are positioned to convey cortical influences onto SC output neurons disynaptically via nitrergic mechanisms as well as conventional neurotransmitter systems utilizing GABA and other, possibly excitatory, neurotransmitters. In addition, because NO also acts as a retrograde messenger, cortically mediated NO release from the postsynaptic elements of nitrergic interneurons could influence presynaptic cortico-SC terminals that directly contact output neurons.

Modulation of Chelidonii herba on glycine-activated and glutamate-activated ion currents in rat periaqueductal gray neurons

BACKGROUND

Chelidonii herba is classified as Papaver somniferum L. Aqueous extract from C. herba is traditionally used for disorders with symptoms like pain, bloating, abdominal cramp after meals.

METHODS

Modulation of C. herba on glycine-activated and glutamate-activated ion currents in the acutely dissociated periaqueductal gray (PAG) neurons was investigated by the nystatin-perforated patch-clamp technique.

RESULTS

C. herba inhibited glycine-activated ion current and increased glutamate-activated ion current. C. herba-induced inhibition on glycine-activated ion current is implicated in opioid receptors and GTP-binding proteins (G-proteins). Increased glutamate-activated ion current induced by C. herba is linked neither by opioid receptors nor GTP-binding proteins.

CONCLUSIONS

Suppressed glycine-induced response and elevated glutamate-induced response by C. herba may increase neuronal excitability in PAG, results in activation of descending pain control system, and this mechanism can be suggested as one of the analgesic actions of C. herba.

Chemoarchitecture of GABAergic neurons in the ferret superior colliculus

gamma-Aminobutyric acid (GABA)ergic neurons are thought to play a key role both in visual processing and in the complex sensory-motor transformations that take place in the mammalian superior colliculus. To understand the organization of GABAergic neurons in the ferret superior colliculus, we applied antisera to several markers of GABAergic function, including GABA, two isoforms of its synthetic enzyme glutamic acid decarboxylase (GAD-65 and GAD-67), and the GABA transporter, GAT-1. We also applied antisera to several calcium binding proteins (calbindin [CB], calretinin [CR], and parvalbumin [PV]) and neuronal nitric oxide synthase (NOS), chemical markers that colocalize with GABA in some areas of the central nervous system. The distribution of GABAergic neurons in the ferret is similar to that of other mammalian species. GABAergic neurons in the ferret superior colliculus were small, morphologically diverse, and widely distributed throughout all layers of the colliculus. As has been shown in other mammalian species, neurons expressing PV, CB, CR, and NOS were differentially distributed in layers and patches throughout the ferret colliculus. None of these markers, however, showed a distribution that mirrored that of GABAergic neurons. Furthermore, few GABAergic neurons colocalized these neurochemical markers. Only 14% of GABAergic neurons in the superficial layers and 18% of neurons in the deeper layers colocalized PV, 14% of GABAergic neurons in the superficial layers and 10% in the deeper layers colocalized CB, and only 1% of GABAergic neurons in both the superficial and deep layers colocalized nitric oxide synthase. Thus, the arrangement of GABAergic neurons in the ferret superior colliculus is broadly distributed and is distinct from other recognized organizational patterns in the superior colliculus.

Beta-alanine and taurine as endogenous agonists at glycine receptors in rat hippocampus in vitro

Electrophysiological and pharmacological properties of glycine receptors were characterized in hippocampal organotypic slice cultures. In the presence of ionotropic glutamate and GABA(B) receptor antagonists, pressure-application of glycine onto CA3 pyramidal cells induced a current associated with increased chloride conductance, which was inhibited by strychnine. Similar chloride currents could also be induced with beta-alanine or taurine. Whole-cell glycine responses were significantly greater in CA3 pyramidal cells than in CA1 pyramidal cells and dentate granule cells, while responses to GABA were similar among these three cell types. Although these results demonstrate the presence of functional glycine receptors in the hippocampus, no evidence for their activation during synaptic stimulation was found. Gabazine, a selective GABA(A) receptor antagonist, totally blocked evoked IPSCs in CA3 pyramidal cells. Glycine receptor activation is not dependent on transporter-controlled levels of extracellular glycine, as no chloride current was observed in response to sarcosine, an inhibitor of glycine transporters. In contrast, application of guanidinoethanesulfonic acid, an uptake inhibitor of beta-alanine and taurine, induced strychnine-sensitive chloride current in the presence of gabazine. These data indicate that modulation of transporters for the endogenous amino acids, beta-alanine and taurine, can regulate tonic activation of glycine receptors, which may function in maintenance of inhibitory tone in the hippocampus.

Inner ear lesion alters acoustically induced c-Fos expression in the rat auditory rhomboencephalic brainstem

The pattern of c-Fos expression was mapped in the adult rat's brain following unilateral cochlear lesions. In normal and cochlear lesioned rats, c-Fos expression was induced with sound stimuli. Acoustic stimulation consisted of pulses of four tones. An additional control group consisted of non-stimulated rats. In the cochlear nuclei (CN), c-Fos activation was scarce in isolated rats and increased strongly following sound stimulation. Following unilateral cochlear lesion, acoustically driven expression was decreased in all CN in both the lesioned and the untreated sides. The ventromedial periolivary nucleus and the rostral periolivary nucleus showed c-Fos activation in isolated conditions and were strongly activated following sound stimulation. The rest of the superior olivary complex showed no c-Fos activation in isolated rats and a weak activation following sound stimulation. Following unilateral cochlear lesions, acoustically driven expression was decreased in some, but not all superior olivary nuclei in both the lesioned and the untreated sides. In the lateral lemniscus complex, c-Fos activation was scarce in isolated rats and increased strongly after stimulation. Following unilateral cochlear lesion, acoustically driven expression decreased bilaterally in all nuclei. We have found that unilateral inner ear lesions lead to bilateral impairment of the capability of acoustic pathway neurons, to being c-Fos-activated following sound stimulation.

Effects of persistent nociception on periaqueductal gray glycine release

Glycine is a candidate nociception inhibitory transmitter in specific brain regions, like for example the spinal cord, the thalamic nuclei and the periaqueductal gray matter. However, quantitative changes in glycine released in these brain regions during peripheral inflammation episodes have not been characterized in awake animals. To address this issue, an in vivo microdialysis study was carried out in freely moving rats in order to analyse periaqueductal gray matter extracellular glycine concentration following unilateral formalin injection into the dorsal skin of the right hind-paw. The extracellular concentration of glutamine was also evaluated in order to analyse whether or not a non-neurotransmitter amino acid was equally modified. Intra-periaqueductal gray matter tetrodotoxin perfusion reduced extracellular glycine concentration (-44+/-5%), but did not change the glutamine dialysate values. Peripheral injection of formalin reduced the glycine release during the early phase (-62+/-8%) and the late phase (-36+/-6%) of hyperalgesia, although not during the analgesic period. Perfusion with naloxone (300microM) neither prevented the formalin-induced decreases in extacellular glycine concentration, nor modified the perfusate basal values of glycine and glutamine. These results show that, contrary to what has been recognized on the interactive role of opioids and GABA into the periaqueductal gray matter (i.e. opioid disinhibition), endogenous opioids seem not to modulate the activity of glycinergic neurons in the same midbrain area. In the light of these preliminary data, it is reasonable to suppose that GABA and glycine are probably not co-released at the level of periaqueductal gray matter of the rat.

Pharmacology of the vestibular system

In the past year significant advances have been made in our understanding of the neurochemistry and neuropharmacology of the peripheral and central vestibular systems. The recognition of the central importance of excitatory amino acids and their receptors at the level of the hair cells, vestibular nerve and vestibular nucleus has progressed further, and the role of nitric oxide in relation to activation of the N-methyl-D-aspartate receptor subtype is becoming increasingly clear. Increasing evidence suggests that excessive N-methyl-D-aspartate receptor activation and nitric oxide production after exposure to aminoglycoside antibiotics is a critical part of hair cell death, and new pharmacological strategies for preventing aminoglycoside ototoxicity are emerging as a result. Conversely, the use of aminoglycosides to lesion the peripheral vestibular system in the treatment of Meniere's disease has been studied intensively. In the vestibular nucleus, new studies suggest the importance of opioid, nociceptin and glucocorticoid receptors in the control of vestibular reflex function. Finally, the mechanisms of action and optimal use of antihistamines in the treatment of vestibular disorders has also received a great deal of attention.