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Notes: Abstract: The effects of γ-aminobutyric acid (GABA) on the spontaneous release of endogenous glutamic acid (Glu) or aspartic acid (Asp) and the effects of Glu on the release of endogenous GABA or [3H]GABA were studied in superfused rat cerebral cortex synaptosomes. GABA increased the outflow of Glu (EC5017.2 μM) and Asp (EC50 18.4 μM). GABA was not antagonized by bicuculline or picrotoxin. Neither muscimol nor (-)-baclofen mimicked GABA. The effects of GABA were prevented by GABA uptake inhibitors and were Na+ dependent. Glu enhanced the release of [3H]GABA (EC50 11.5 μM) from cortical synaptosomes. Glu was not mimicked by the glutamate receptor agonists N-methyl-d-aspartic, kainic, or quisqualic acid. The Glu effect was decreased by the Glu uptake inhibitor D-threo-hydroxyaspartic acid (THA) and it was Na+ sensitive. Similarly to Glu, D-Asp increased [3H]GABA release (EC50 9.9 μM), an effect blocked by THA. Glu also increased the release of endogenous GABA from cortex synaptosomes. In this case the effect was in part blocked by the (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist 6-cyano-7-nitroquinoxaiine-2, 3-dione, whereas the 6-cyano-7-nitroquinoxaline- 2, 3-dione-insensitive portion of the effect was prevented by THA. GABA increased the [3H]D-Asp outflow (EC50 13.7 μM) from hippocampal synaptosomes in a muscimol-, (-)- baclofen-, bicuculline-, and picrotoxin-insensitive manner. The GABA effect was abolished by blocking GABA uptake and was Na+ dependent. Glu increased the release of [3H]- GABA from hippocampal synaptosomes (EC50 7.1 μM) in an N-methyl-d-aspartic acid-, kainic acid-, or quisqualic acid-insensitive way. The effect of Glu was prevented by THA and was Na+ dependent. As in the cortex, the effect of Glu was mimicked by D-Asp in a THA-sensitive manner. It is proposed that high-affinity GABA or Glu heterocarriers are sited respectively on glutamatergic or GA- BAergic nerve terminals in rat cerebral cortex and hippocampus. The uptake of GABA may modulate Glu and Asp release, whereas the uptake of Glu may modulate the release of GABA. The existence of these heterocarriers is in keeping with the reported colocalization of GABA and Glu in some cortical and hippocampal neurons. Preliminary data suggest that these mechanisms may also be present in rat cerebellum and spinal cord.

Notes: Abstract: The ability of γ-aminobutyric acid (GABA) and glycine (Gly) to modulate each other's release was studied in synaptosomes from rat spinal cord, cerebellum, cerebral cortex, or hippocampus, prelabeled with [3H]GABA or [3H]-Gly and exposed in superfusion to Gly or to GABA, respectively. GABA increased the spontaneous outflow of [3H]Gly (EC50, 20.8 μM) from spinal cord synaptosomes. Neither muscimol nor (-)-baclofen, up to 300 μM, mimicked the effect of GABA, which was not antagonized by either bicuculline or picrotoxin. However, the effect of GABA was counteracted by the GABA uptake inhibitors nipecotic acid and N-(4,4-diphenyl-3-butenyl)nipecotic acid. Moreover, the GABA-induced [3H]Gly release was Na+ dependent and disappeared when the medium contained 23 mM Na+. The effect of GABA was Ca2+ independent and tetrodotoxin insensitive. Conversely, Gly enhanced the outflow of [3H]-GABA from rat spinal cord synaptosomes (EC50, 100.9 μM). This effect was insensitive to both strychnine and 7-chlorokynurenic acid, antagonists at Gly receptors, but it was strongly Na+ dependent. Also, the Gly-evoked [3H]-GABA release was Ca2+ independent and tetrodotoxin insensitive. GABA increased the outflow of [3H]Gly (EC50, 11.1 μM) from cerebellar synaptosomes; the effect was not mimicked by either muscimol or (—)-baclofen nor was it prevented by bicuculline or picrotoxin. The GABA effect was, however, blocked by GABA uptake inhibitors and was Na+ dependent. Gly increased [3H]GABA release from cerebellar synaptosomes (EC50, 110.7 μM) in a strychnine- and 7-chlorokynurenic acid-insensitive manner. This effect was Na+ dependent. The effects of GABA on [3H]Gly release seen in spinal cord and cerebellum could be reproduced also with cerebrocortical synaptosomes. However, in cortex, the effect of Gly on [3H]GABA release was much lower than in spinal cord or cerebellum, although it was partly Na+ dependent. No changes of [3H]Gly release were observed in hippocampal synaptosomes exposed to GABA. It is suggested that transporters specific for GABA or Gly are colocalized on the same nerve terminal in rat spinal cord, cerebellum, and cerebral cortex, but not in hippocampus. Moreover, GABA uptake modulates Gly release and, at least in spinal cord and cerebellum, Gly uptake modulates GABA release. These conclusions are compatible with the reported coexistence of GABA and Gly in spinal and cerebellar neurons.

Notes: Rat cerebral cortex synaptosomes were exposed in superfusion to various depolarizing stimuli and the release of somatostatin-like immunoreactivity (SRIF-LI) was measured by means of a radioimmunoassay procedure. High KC1 (9-50 mM) concentration dependently evoked SRIF-LI release; the evoked overflow reached a plateau at 25 mM KC1 and was completely abolished when Ca2+ ions were omitted from the superfusion medium, independently of the concentration of KC1 used. The 15 mM K+-evoked release of SRIF- LI increased sharply as the Ca2+ concentration was raised to 0.8 mM, then leveled off and reached a plateau at 1.2 mM. The 15 mM K+-evoked overflow, but not the spontaneous outflow, was partially decreased (50%) by 1 μM tetrodotoxin. The presence in the superfusion fluid of a mixture of peptidase inhibitors did not improve the recovery of SRIF-LI both in the absence and in the presence of high K+. Exposure of synaptosomes to veratrine (1-50 μM) induced release of SRIF-LI in a concentration-dependent way. The effect of the alkaloid was strictly Ca2+ and tetrodotoxin sensitive. Replacement of extracellular Na+ by sucrose caused an acceleration of the spontaneous SRIF-LI outflow that was inversely correlated to the Na+ content in the superfusion medium. The release evoked by the sodium-deprived media did not exhibit any calcium dependence. HPLC analysis of the samples collected during superfusion showed that 〉90% of the SRIF-LI released either during the spontaneous outflow or by 15 mM KC1 was represented by SRIF-14 (SRIF-2814-28). These values reflected the ratio SRIF-14/SRIF-28 found in synaptosomes at the end of the experiments.

Notes: Abstract: Release-regulating heterocarriers exist on brain nerve endings. We have investigated in this study the mechanisms involved in the neurotransmitter release evoked by GABA heterocarrier activation. GABA increased the basal release of [3H]acetylcholine and [3H]noradrenaline from rat hippocampal synaptosomes and of [3H]dopamine from striatal synaptosomes. These GABA effects, insensitive to GABA receptor antagonists, were prevented by inhibiting GABA uptake but not by blocking noradrenaline, choline, or dopamine transport. Lack of extracellular Ca2+ or addition of tetrodotoxin selectively abolished the GABA-evoked release of [3H]noradrenaline, leaving unaffected that of [3H]acetylcholine or [3H]dopamine. 1,2-Bis(2-aminophenoxy)-ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA-AM) or vesamicol attenuated the release of [3H]acetylcholine elicited by GABA. Reserpine, but not BAPTA-AM, prevented the effect of GABA on [3H]dopamine release. Autoreceptor activation inhibited the GABA-evoked release of [3H]noradrenaline but not that of [3H]acetylcholine or [3H]dopamine. It is concluded that (a) the release of [3H]noradrenaline consequent to activation of GABA heterocarriers sited on noradrenergic terminals meets the criteria of a conventional exocytotic process, (b) the extracellular [Ca2+]-independent releases of [3H]acetylcholine and [3H]dopamine appear to occur from vesicles possibly through involvement of intraterminal Ca2+, and (c) autoreceptor activation only affects heterocarrier-mediated vesicular release linked to entry of extracellular Ca2+.

Notes: Cyclooxygenases (COX) are a family of enzymes involved in the biosynthesis of prostaglandin (PG) and thromboxanes. The inducible enzyme cyclooxygenase-2 (COX-2) is the major isoform found in normal brain, where it is constitutively expressed in neurons and is further up-regulated during several pathological events, including seizures and ischaemia. Emerging evidence suggests that COX-2 is implicated in excitotoxic neurodegenerative phenomena. It remains unclear whether PGs or other products associated to COX activity take part in these processes. Indeed, it has been suggested that reactive oxygen species, produced by COX, could mediate neuronal damage. In order to obtain direct evidence of free radical production during COX activity, we undertook an in vivo microdialysis study to monitor the levels of PGE2 and 8-epi-PGF2α following infusion of N-methyl-d-aspartate (NMDA). A 20-min application of 1 mm NMDA caused an immediate, MK-801-sensitive increase of both PGE2 and 8-epi-PGF2α basal levels. These effects were largely prevented by the specific cytosolic phospholipase A2 (cPLA2) inhibitor arachidonyl trifluoromethyl ketone (ATK), by non- selective COX inhibitors indomethacin and flurbiprofen or by the COX-2 selective inhibitor NS-398, suggesting that the NMDA-evoked prostaglandin synthesis and free radical-mediated lipid peroxidation are largely dependent on COX-2 activity. As several lines of evidence suggest that prostaglandins may be potentially neuroprotective, our findings support the hypothesis that free radicals, rather than prostaglandins, mediate the toxicity associated to COX-2 activity.

Notes: We have previously shown that protein kinase C (PKC) activity is up-regulated in nerve terminals of animals that have been subjected to targeted cellular ablation of cortical and hippocampal neurons by treatment with methylazoxymethanol (MAM), which results in impaired long-term potentiation (LTP) and cognitive deficit. In this study we investigated the consequences of increased membrane-bound PKC in the regulation of release of glutamate, the major excitatory transmitter involved in LTP. We show that nerve terminals of MAM-treated rats show higher PKC activity, as monitored by the in situ phosphorylation of B-50/GAP-43, in both basal and phorbol ester-stimulated conditions. In these animals, hippocampal nerve endings release a greater amount of glutamate than those of controls, both in basal conditions and when synaptosomes are stimulated with KCI or 3,4–diaminopyridine. The potentiation observed in MAM-treated rats was counteracted by the PKC blocker H-7 and the clostridial tetanus toxin. On the contrary, GABA release was not significantly up-regulated, either in basal or in depolarization-evoked conditions. Therefore our data show that the increase in synaptosomal PKC activity is paralleled by increased glutamate but not GABA release in this animal model. Whether this reflects specific up-regulation of membrane PKC activity in glutamatergic terminals or an alteration in the regulation of glutamate release remains to be determined.

Notes: Background : Anti-Helicobacter pylori therapy has been reported to cause regression of low-grade gastric mucosa-associated lymphoid tissue lymphoma in a high percentage of patients. However, in some patients, these lesions persist despite antibiotic treatment.Aim : To determine the various endosonographic findings that may predict the regression of low-grade gastric mucosa-associated lymphoid tissue lymphoma post-antibiotics.Methods : Seventy-six patients with Helicobacter pylori-positive gastric mucosa-associated lymphoid tissue lymphoma were studied. Follow-up data were available on 51 patients. All patients were treated with antibiotics. Participants underwent pre- and post-anti-Helicobacter pylori therapy endoscopy with gastric biopsies, followed by endoscopic ultrasonography examination of the stomach.Results : Helicobacter pylori was eradicated in 45 of 51 (88%) patients. At the 2-year follow-up, complete regression of mucosa-associated lymphoid tissue lymphoma was seen in 28 of 51 (55%) patients: 12 of 16 (75%) patients in stage T1m N0, 11 of 19 (58%) patients in stage T1sm N0, four of eight (50%) patients in stages T1m N1 and T1sm N1, and one of four (25%) patients in stage T2 N0. None of the stage T2 N1 patients achieved clinical regression.Conclusions : Endoscopic ultrasonography evaluation of gastric mucosa-associated lymphoid tissue lymphoma plays a pivotal role in the initial staging and post-treatment follow-up evaluation of these lesions. Accurate staging is essential in the determination of the optimal treatment modality.