Exogenous Glutamate-Induced Modulation of Neurosecretory Process in Nerve Terminals Obtained from the Rat Brain

We studied intracellular processes in nerve terminals of neurons of the rat brain in response to application of exogenous glutamate. Using a рН-sensitive fluorescence probe, acridine orange (AO), and labeled gammaaminobutyric acid ([³Н]GABA), we estimated the effect of application of glutamate on the level of acidification of synaptic vesicles and also on the release of GABA from nerve terminals (synaptosomes) obtained from hippocampal tissue. Our experiments showed that glutamate in a dose-dependent manner stimulated the [³Н]GABA release from nerve terminals, and then we observed re-uptake of this neurotransmitter. A selective blocker of GABA transporters, NO-711, completely blocked the uptake of neurotransmitter but did not influence its release; this observation indicates that the glutamate-induced GABA release was from the vesicular, not cytosolic, pool. We confirmed that glutamate stimulates the process of exocytosis in experiments using AO, where we obtained data indicating that this process is two-phase. The first phase, which reflects probably calcium-induced exocytosis, looked like a “burst” of fluorescent signal typical of the response of synaptosomes to the action of KCl applied in depolarization concentration. Both phases of the response were completely blocked or significantly suppressed in calcium-free medium or in the presence of 25 μM Cd²⁺. The second (slow) phase of the response developed after a certain lag period and was characterized by a gradual increase in the intensity of fluorescent signal. This phase was completely dependent on the presence of sodium in the extracellular medium and completely blocked when sodium was replaced by choline or N-methyl-D-glucamine. We hypothesize that the second phase of the response can reflect either spontaneous unstimulated exocytosis or dissipation of the proton gradient in synaptic vesicles induced by the entry of Na⁺ into the nerve terminal.     

The Peptides Mimicking the Third Intracellular Loop of 5-Hydroxytryptamine Receptors of the Types 1B and 6 Selectively Activate G Proteins and Receptor-Specifically Inhibit Serotonin Signaling via the Adenylyl Cyclase System

The third intracellular loop (ICL3) of G protein-coupled receptors has, as a rule, a key role in their interaction with heterotrimeric G proteins. We synthesized peptides corresponding to the C-terminal region of the ICL3 (C-ICL3) of 5-hydroxytryptamine receptors of the type 1B (5-HT_1BR) and 6 (5-HT₆R) and studied their influence on the functional activity of adenylyl cyclase signaling system (ACSS) in synaptosomal membranes isolated from the rat brain. The 5-HT_1BR-peptide ARERKATKTL^307–316K-amide mimicking agonist-activated 5-HT_1BR reduced forskolin-stimulated adenylyl cyclase (AC) activity and activated pertussis toxin-sensitive G proteins. It lowered inhibitory effects of serotonin and 5-HT_1BR-agonists on forskolin-stimulated AC activity and their stimulating effects on GTP binding. This was not the case in the presence of 5-HT_1BR-antagonists. The 5-HT₆R-peptides mimicking 5-HT₆R activated both the basal AC activity and GTP binding of cholera toxin-sensitive G proteins. They lowered the stimulating effect of serotonin and 5-HT₆R-agonists on AC and G_s proteins, but in the presence of 5-HT₆R-antagonists their action was blocked. Of all the 5-HT₆R-peptides with linear and dimeric structure we studied the palmitoylated peptide KHSRKALKASL^258–268K(Pal)A-amide had a most pronounced effect both on the basal and 5-HT₆R-agonist-stimulated ACSS. The data was obtained indicating that the peptides corresponding to C-ICL3 of 5-HT_1BR and 5-HT₆R selectively activate G_i and G_s proteins, respectively, and in a receptor-specific manner reduce signal transduction via serotonin-sensitive ACSS in the rat brain. The results of the study give strong evidence in favor of active participation of C-ICL3 of these 5-HTRs in their coupling with the G proteins.     

Terpenoids in Buddleja: relevance to chemosystematics,chemical ecology and biological activity

The terpenoids reported from Buddleja species are described. The antifungal activity of chloroform extracts of B. cordata and B. davidii stembark against the soil fungi Fusarium culmorum and Sordari fimicola is reported, with buddledin A shown to be the major compound responsible. The terpenoids present support the view that the Buddlejaceae should be classified in a taxon with Scrophulariaceae rather than Loganiaceae. Ecological aspects of the terpenoids are considered in relation to insects and soil fungi and the role of terpenoids in the chemical basis of the use of Buddleja in traditional medicine is also discussed, especially with regard to their anti-inflammatory properties.     

Ca2+-Dependent and Ca2+-Independent [3H]GABA Release from Rat Brain Synaptosomes: the Effect of Temperature

The main inhibitory neurotransmitter GABA in the mammalian brain is distributed in the nerve terminals between two pools, vesicular (synaptic vesicles) and cytosolic. GABA is released from these pools by different mechanisms; there are calcium-activated exocytotic release and calcium-independent sodium-dependent release from the cytosolic pool (resulting from the membrane GABA transporter reversal). We investigated the influence of temperature on [³H]GABA release from rat brain synaptosomes, which was induced by stimulation of both these processes. In addition, we used -latrotoxin as a stimulant of [³H]GABA release. Synaptosomes from the rat brain were used in the experiments. 4-Aminopyridine (4-AP) and high [KCl] were applied to stimulate calcium-activated and calcium-independent [³H]GABA release, respectively. 4-AP-evoked [³H]GABA release was of the same intensity at 37 and 25°C (10.1 ± 1.2 and 10.1 ± 0.8% of total [³H]GABA incorporated into the synaptosomes, respectively). The effect of 4-AP on the ⁴⁵Ca²⁺ influx into synaptosomes was also temperature-independent: 0.775 ± 0.075 and 0.725 ± 0.100 nmol/min/mg of protein at 37 and 25°C, respectively. A drop in the effect of 4-AP was observed only at 15°C. When synaptosomes were depolarized with 50 mM KCl, a temperature decrease from 37°C to 25°C resulted in a twofold drop in the [³H]GABA release, from 20.5 ± 1.4 to 10.3 ± 0.7%; at 15°C [³H]GABA release dropped to less than one-third of the norm (6.0 ± 0.5%). -Latrotoxin-stimulated [³H]GABA release was diminished from 32.5 ± 2.5 at 37°C to 17.2 ± 1.3 at 25°C and 5.9 ± 0.4% at 15°C and was not affected by the presence or absence of calcium in the medium. It seems likely that the observed effect of temperature can be interpreted as based on the temperature dependence of the -latrotoxin insertion into the membrane. It is suggested that the pattern of the temperature sensitivity of GABA release from the synaptosomes can be used as a criterion for identification of the mode of neurotransmitter release.     

A fallacy in phytochrome pelletability due to in vitro instability of the phytochrome-particle association

Two fractionation procedures were used to study the phenomenonof phytochrome pelletability or binding to a particulate fractionof maize coleoptiles. Using a revised procedure, we were unableto show an increase of phytochrome pelletability during darkincubation of red irradiated plant tissue, reported by Manabeand Furuya for pea seedlings (6), and the P_fr-enhanced affinityfor P_r in R/FR irradiated tissue as reported by Quail et al.(11). However, we were able to match these reported observationsusing a procedure which we have regarded as standard. In thestandard procedure, the irradiated tissue is homogenized andthe brei permitted to incubate in the dark at 0?C before fractionationby differential centrifugation prior to measurements of phytochromepelletability. In the revised procedure this incubation is eliminatedand fractionation and measurement follow directly on tissuehomogenization. A progressive decrease of particulate phytochromewas observed during dark incubation at 0?C of the brei fromred irradiated tissue, but no substantial decrease was observedduring dark incubation of the red irradiated tissue at 0?C.The decrease was not dependent on in vitro P_frP_r reversion.In the case of R/FR irradiated tissues, phytochrome pelletabilitywas found to decrease during dark incubation of both the irradiatedtissue and its brei at 0?C. With these results and a recognitionof the tendency of phytochrome to dissociate from the particulatefraction in vitro, we have thus rationalized the results ofQuail et al. (11) and Manabe and Furuya (6). (Received August 12, 1976; )     

Immunological mechanisms of the radioprotective effects of ceruloplasmin

The aim of the work was to examine immunotropic features of celluroplasmine++ (Cp) and estimate its capacity as radioprotector. The pulse radiolysis method was used to set the mechanism of elementary reactions, which were responsible for antioxidant activity, and to demonstrate a particular role of reversible oxycomplexis, Cp...O2. Within in vitro test-systems the effects of Cp were examined on the model of interaction between lymphocytes from Shelter staff which constantly contacts with ionizing irradiation, and autologous erythrocytes in rosset-forming phenomenon (223 Shelter employees in comparison with 253 donors of Kyiv blood transfucion station). Expression of this Index in the presence of antigens with known poly-specificity was determined (antigens were taken from cortical and pyramid sections of kidney, liver, lungs, myocard, pancreatic gland, grey matter and aorta). Simultaneously the presence of analogous autoantibodies was determined (ELISA). It has been shown that Cp can reprogram the level of expression of immunovaluable receptors towards to norm. It has been also defined that Cp presence in blood irradiated in vitro (1-15 rem) promotes the masking of active centers of autoantibodies of different tissue specificity.