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Notes: Abstract: The effects of corticostriatal deafferentation (de-cortication) and destruction of intrinsic neurons (intrastriatal kainate injection) on the extracellular concentration, and veratrine-releasable pools, of endogenous amino acids in the rat striatum were examined using the in vivo brain dialysis technique. Intracellular amino acid content was also determined. Decortication reduced selectively intra-and extracellular levels of glutamate (Glu) and aspartate (Asp). Extracellular changes were more pronounced than those in tissue content. γ-Aminobutyric acid (GABA), tau-nne (Tau), and phosphoethanolamine (PEA) levels were not affected, whereas nonneuroactive amino acids were increased at 1 week but not at 1 month postlesion. The intracellular pool of Glu and Asp was also reduced in kainate-lesioned striata. However, extracellular levels of these compounds were not affected significantly by this treatment. The tissue content of all other amino acids was decreased, the most prominent change being in the concentration of GABA. Extracellular GABA concentration was also reduced dramatically, whereas the concentrations of nonneuroactive amino acids were increased to varying degrees. These data suggest that transmitter pools of neuroactive amino acids are an important supply for their extracellular pools. Lesion-induced alterations in nonneuroactive amino acids are discussed with regard to the loss of metabolic pools, glial reactivity, and changes in blood-brain bamer transport. Veratrine induced a massive release of neuroactive amino acids such as Glu, Asp, GABA, and Tau into the extracellular fluid, and a delayed increase in PEA. Extracellular levels of neuroactive amino acids were raised slightly. Decortication reduced, selectively, the amounts of Glu and Asp released by veratrine. GABA, Tau, and PEA effluxes were also decreased in kainate-lesioned striata. These findings are consistent with the proposed roles of an acidic amino acid as the corticostriatal transmitter, and of GABA as a transmitter in intrinsic striatal neurons. The existence of releasable pools of Tau and PEA within kainate-sensitive striatal neurons would also appear to be likely.

Notes: Abstract: The effect of severe insulin-induced hypoglycemia on the extracellular levels of endogenous amino acids in the rat striatum was examined using the brain microdialysis technique. A characteristic pattern of alterations consisting of a 9–12-fold increase in aspartate (Asp), and more moderate increases in glutamate (Glu), taurine (Tau), and γ-aminobutyric acid (GABA), was noted following cessation of electroencephalographic activity (isoelectricity). Glutamine (Gln) levels were reduced both during and after the isoelectric period and there was a delayed increase in extracellular phosphoethanolamine (PEA) content. The effects of decortication and excitotoxin lesions on the severe hypoglycemia-evoked efflux of endogenous amino acids in the striatum were also examined. Decortication reduced the release of Glu and Asp both 1 week and 1 month post-lesion. The efflux of other neuroactive amino acids was not affected significantly. In contrast, GABA, Tau, and PEA efflux was attenuated in kainate-lesioned striata. Glu and Asp release was also reduced under these conditions, and a smaller decrease in extracellular Gln was noted. These data suggest that GABA, Glu, and Asp are released primarily from their transmitter pools during severe hypoglycemia. The releasable pools of Tau and PEA appear to be located in kainate-sensitive striatal neurons. The significance of these results is discussed with regard to the excitotoxic theory of hypoglyce-mic cell death.

Notes: Abstract: Prostaglandin E2 (PGE2) delivered to the spinal cord produces an increased sensitivity to noxious (hyperalgesia) and innocuous (allodynia) stimuli. The mechanisms that underlie this effect remain unknown, but a PGE2-evoked enhancement of spinal neurotransmitter release may be involved. To address this hypothesis, we examined the effect of PGE2 on CSF concentrations of amino acids and also the modulatory effect of PGE2 on capsaicin-evoked changes of spinal amino acid concentrations using a microdialysis probe placed in the lumbar subarachnoid space. Amino acids were quantified using HPLC with fluorescence detection. Addition of 1 mM, but not 10 or 100 µM, PGE2 to the perfusate for a 10-min period (flow rate, 5 µl/min) evoked an immediate increase (80–100%) in glutamate (Glu), aspartate (Asp), taurine (Tau), glycine (Gly), and γ-aminobutyric acid (GABA) concentrations. Similarly, capsaicin infusion (0.1–10 µM) induced a dose-dependent increase in Glu, Asp, Tau, Gly, GABA, and ethanolamine levels. Significant increases in amino acid levels evoked by PGE2 or capsaicin were associated with a touch-evoked allodynia. The combination of PGE2 (10 µM) and capsaicin (0.1 or 1.0 µM) at concentrations that individually had no effect together evoked a significant increase (60–100%) in Glu, Asp, Tau, Gly, and GABA concentrations and produced tactile allodynia. These data demonstrate that spinally delivered PGE2 or capsaicin substantially elevates CSF concentrations of both excitatory and inhibitory amino acids. The capacity of PGE2 to enhance and prolong capsaicin-evoked amino acid concentrations may be one of the mechanisms by which spinal PGE2 produces hyperalgesia and allodynia.

Notes: Abstract: The in vivo effects of kainate (1 mM) on fluxes of 45Ca2+, and endogenous amino acids, were examined in the rat striatum using the brain microdialysis technique. Kainate evoked a rapid decrease in dialysate 45Ca2+, and an increase in the concentration of amino acids in dialysates in Ca2+-free dialysates. Taurine was elevated six-to 10-fold, glutamate two-to threefold, and aspartate 1.5-to twofold. There was also a delayed increase in phosphoethanolamine, whereas nonneuroactive amino acids were increased only slightly. The kainic acid-evoked reduction in dialysate 45Ca2+ activity was attenuated in striata lesioned previously with kainate, suggesting the involvement of intrinsic striatal neurons in this response. The increase in taurine concentration induced by kainate was slightly smaller under these conditions. Decortication did not affect the kainate-evoked alterations in either dialysate 45Ca2+ or amino acids. These data suggest that kainate does not release acidic amino acids from their transmitter pools located in corticostriatal terminals.

Notes: Abstract: Cavernous angiomas are vascular malformations that cause neurodegeneration and symptoms including epileptiform seizures, headache, and motor deficits. Following neurosurgical removal of the angiomas, patients mostly recover well and become seizure-free. This study reports on the levels of certain amino acids in angiomas, obtained from 13 patients. Distinct zones of the angiomas were analyzed, from the thrombotic core, via gliotic, hemosiderin-infiltrated intermediate zones, to a periphery without macroscopic abnormalities. The neurotransmitter amino acids glutamate, aspartate, and GABA as well as phosphoethanolamine displayed decreasing levels from the periphery to the core, reflecting the gradual neuronal loss. Compared with normal brain tissue, there was a marked increase in the levels of serine (fivefold), glycine (10-fold), and ethanolamine (20-fold) in the peripheral zone of the cavernous angiomas. The results are discussed in relation to seizures and NMDA receptor activation, neuron-glia interactions, membrane phospholipids, and blood-brain barrier function.

Notes: Abstract: The aim of the study was to evaluate how implantation of a dialysis probe influences the blood-brain barrier. Leakage of endogenous serum albumin was evaluated by Evans blue/albumin staining and by immunohistochemistry. The passage from blood to dialysate of two substances that normally do not pass into the brain, [3H]inulin and glutamate, was studied 3 and 24 h after insertion of a dialysis probe. Evans blue, given 20 min before rats were killed, was observed around the probe and surrounding brain tissue. Albumin immunoreactivity was seen at considerable distance from the probe with larger spread at 24 h than at 3 h after probe insertion. Glutamate and [3H]inulin were detected in the dialysate with no significant further increase of radioactivity after intracarotid infusion of protamine sulfate that enhances the permeability over the blood-brain barrier. When protamine was followed by infusion of glutamate, the concentrations of taurine increased in the dialysate in four of eight rats. That plasma constituents have access to the brain around the dialysis probe is essential to consider, particularly in studies using substances and drugs that do not pass an intact blood-brain barrier.

Notes: Abstract: Injection of kainic acid (KA) into the rat hippocampus reduced the phosphorylation-related immunoreactivity of the heavy subunit of neurofilament proteins (NF-H). The effect was demonstrated quantitatively with a dot-immunobinding assay and qualitatively by immunoblotting with monoclonal antibodies against phosphorylation-dependent and nonphosphorylation-related epitopes of NF-H. The KA-induced reduction affected 50% of the phosphorylated NF-H in half of the hippocampus after 48 h. At the same time, the nonphosphorylation-related NF-H immunoreactivity increased as revealed by immunoblotting, indicating a shift from phosphorylated to nonphosphorylated NF-H. The effects on NF-H preceeded a decrease in content of the neuron-specific enolase, a soluble neuronal cytoplasmic protein. No alterations of the light subunit of neurofilament proteins occurred, suggesting that KA has a preferential effect on NF-H phosphorylation. N-Methyl-D-aspartate administered similarly did not lead to a rapid dephosphorylation of NF-H. We propose that kainate receptor-mediated dephosphorylation in NF-H is involved in the signal transduction of excitatory amino acids with consequences for neuronal functions dependent on intermediary filament phosphorylation.

Notes: Abstract: This article evaluates the influence of an opening of the blood-brain barrier (BBB) on compounds in brain extracellular fluid. The concentrations of amino acids and some other primary amines were determined in dialysates sampled from the right parietal cortex of rats before and after an intracarotid infusion of protamine sulfate. Extravasated plasma proteins were visualized by Evans blue/albumin and immunohistochemistry. CSF albumin— an indicator of blood-CSF barrier opening—was quantified with immunoelectrophoresis. The brains were macroscopically edematous after 10 mg but not after 5 mg of protamine sulfate. The higher dose led to a 50% death rate. The concentrations of amino acids did not change 10 min after the BBB opening. No significant alterations in the amino acid concentrations were observed after the lower dose. The concentrations of glutamate, aspartate, GABA, glycine, taurine, and phosphoethanolamine increased significantly within 50–80 min after the infusion of 10 mg of protamine sulfate. CSF albumin levels were significantly increased 1 h after infusion. We conclude that a dysfunction of the BBB, of a degree known to induce brain edema (10 mg of protamine sulfate), significantly increases the extracellular concentration of excitatory amino acids, GABA, taurine, and phosphoethanolamine in the extracellular space.

Notes: Abstract: The effect of in vivo administration of kainic acid into the rabbit hippocampus was studied with brain dialysis and subsequent determination of the Ca2+ concentration in the dialysate. When included in the perfusing medium, kainic acid as well as veratridine induced a decrease in extracellular Ca2+. The effect of kainic acid (but not of veratridine) was insensitive to tetrodotoxin. In vitro studies revealed no effect of kainic acid on 45Ca2+ uptake by isolated astrocytes, but showed an enhancement of synaptosomal 45Ca2+ accumulation. This was, however, only 25% of the stimulatory effect of high K+ depolarization. Glutamate activated synaptosomal Ca2+ uptake, whereas dihydrokainate had no effect. The up take evoked by kainate and glutamate was independent of the K+ level in the medium which indicates the involvement of other than voltage-sensitive Ca2+ channels. The results confirm previous findings that kainic acid promotes the uptake of Ca2+ in brain cells. Kainate affects Ca2+ fluxes pre- and postsynaptically. Presynaptic Ca2+ influx may be mediated by chemically gated mechanisms.