The effect of monoamine oxidase inhibition on formation, fixation and reproduction of temporary connections]

An administration of 100 to 300 mg/kg doses of iprazid to rats and mice leads in 24 hours to a considerably higher serotonin and noradrenaline content in the brain. Defensive conditioning against this background proceeds in the same way as in control animals but the retention of elaborated reflexes is sharply disturbed. A similar effect is produced by 5-oxytryptophane. An iprazid administration after conditioning does not disturb the retention and subsequent achievement of the reflex. Inclusion of S35-methionine in the total proteins of the mice brain does not change under the influence of iprazid. A conclusion has been drawn that inhibition of monoaminoxidase by iprazid does not prevent the formation and reproduction of temporary connections, but deeply disturbs their fixation. It is suggested that the revealed disturbances of fixation of temporary connections are due to the accumulation of serotonin in the brain, which suppresses the protein synthesis in the synaptosomes or that of specific proteins.     

The effect of a decrease in cerebral noradrenaline concentrations on the formation and fixation of temporary connections]

A sharp drop in the noradrenaline content (Na) in the brain of mice does not prevent the elaboration and fixation of relatively simple conditioned reflexes, but considerably disturbs the elaboration of more complex conditioned reflexes with delayed reinforcement. The decrease in the NA content in the brain does not appear to influence directly the process of consolidation of temporary connections; impaired fixation of relatively more complex forms of temporary connections is of a secondary nature and is due to disturbances in their formation.     

The effect of temporary hypoxia on prostaglandin synthesis in mouse brain cell cultures during development

Cultures of dissociated brain cells of new born mice represent a model for the study of brain development. One and two weeks old, they correspond in regard to oligodendrocyte differentiation to about the developmental stage of a human newborn and a six months old infant respectively. Such cultures were used to establish the developmental prostaglandin pattern and to study early and late recovery of prostaglandin synthesis from temporary hypoxia. Basal and bradykinin stimulated prostaglandin release were examined. Most prominently in stimulated release, the developmental prostaglandin pattern at one week showed a prevalence of PGE2 (33 +/- 4%) over PGD2 (12 +/- 5%), which in two weeks old cultures changes to an opposite distribution (PGE2 10 +/- 4%; PGD2 25 +/- 6%). This change goes parallel with the number and differentiation of oligodendrocytes. During the first day post hypoxia, imposed at the end of one week, the production of 6 oxo PGF1 alpha, PGE2, PGD2 and TXB2 was significantly decreased in two study series and increased compared to control in another. Since the arachidonic acid uptake was the same in all three series, this differential observation indicates differential early recovery. 8 days post hypoxia (late recovery), PG release was not different from control, indicating complete recovery at that time. During early recovery from hypoxia on 14 days old cultures, basal PG release was not significantly different from control, however bradykinin stimulated release was significantly inhibited in all three series. This may indicate that mainly regulatory influences on PG release in older cultures are compromised by hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of an excess of serotonin in the brain on consolidation of temporary connections]

As a result of intravenous administration of 100 mg/kg of 5-oxytryptophane (5-OTP) to mice, the serotonin content in the brain rises in ten minutes by 35 to 37 per cent, and in an hour, by 58 to 60 per cent, and declines in a day to its initial level. In case of elaboration of passive avoidance reflexes (PAR) an hour after 5-OTP injection, their preservation considerably decreases in a day's time, while 5-OTP administration immediately following PARs elaboration does not affect their preservation. However, 5-OTP injected after PARs elaboration to animals subjected to preliminary cooling, sharply deteriorates their preservation. These facts in conjunction with the previously obtained date attest that excess of serotonin in the brain has a negative effect on the earliest stages of consolidation. When the animals are cooled and the brain temperature is reduced, the consolidation processes are retarded; as a result, the temporary connections prove to be still vulnerable to the action of serotonin excess set up after PAR elaboration.     

Effect of scopolamine on formation and fixation of temporary connections in rats with altered brain serotonin levels

The influence of scopolamine on elaboration and maintenance of conditioned reflexes of two-way avoidance was studied in rats under conditions of excess and deficit of serotonin in the brain. Administration of scopolamine to intact rats accelerated conditioning and did not prevent fixation of the reflex. Administration of scopolamine to animals with a lowered level of serotonin in the brain (by means of para-chlorophenylalanine) impaired conditioning and induced amnesia. In animals with ablated raphe nuclei, the same dose of scopolamine did not prevent elaboration and maintenance of conditioned reflexes. Accumulation of scopolamine in the brain by means of 5-oxytryptophan abolished acceleration of conditioning, which is specific for scopolamine, and affected the preservation of the reflexes. Against the background of the action of iprozid, scopolamine impaired the conditioning and tended to deteriorate the maintenance of conditioned reflexes. It is assumed that the serotoninergic system exerts a modulating influence on the activity of the brain cholinergic and cholinoreactive mechanisms.     

Intra-analyzer temporary connections in the visual system]

The possibility of setting up intraanalyser temporary connections integrating the activity of various elements within the central part of the visual analyser at a neuronal level was studied in acute experiments on unanaesthetized immobilized cats. In the given model of temporary connection the unit activity in the lateral geniculate bodies (LGB) was investigated. Electrical stimulation of the superior colliculi was used as a conditioned stimulus, and illumination of the receptive fields of the studied LGB neurones, as an unconditioned one. In the process of conditioning, 10 to 11% of learning elements were revealed in LGB. The possibility is discussed of integration of learning elements into a definite microsystem achieving the process of temporary connection closing in the visual analyser in the course of conditioning.     

The antiarrhythmic effect of prostaglandin E2 on catecholamine-induced arrhythmias

The antiarrhythmic effect of PGE2 as compared with the adrenergic beta-receptor blocking substance propranolol and the unspecific antiarrhythmic agent ajmaline was examanined on catecholamine-induced arrhythmias of the guinea-pig after preliminary sensibilisation by means of chloroform. Prophylactic administration of the tested substances resulted in a decrease in severity of arrhythmia by 91% after propranolol, by 37% after PGE2 and by 34% after ajmaline. Onset and duration of the arrhythmia were affected only to a negligible degree. The possible mode of action is still under discussion.     

Involvement of GTP-regulatory protein in brain prostaglandin E2 receptor and separation of the two components

The specific binding protein for prostaglandin (PG) E2 solubilized from porcine brain was sensitive to guanine nucleotides. GTP inhibited the association and enhanced the dissociation of the specific [3H]PGE2 binding. Scatchard analyses showed that GTP (10 microM) decreased the binding affinity more than 3-fold without major change in the number of binding site. Gel filtration separated the binding site from GTP-regulatory component (N). The separated binding protein had a reduced affinity to PGE2 and lost its sensitivity to GTP. The addition of the separated N restored its responsiveness to GTP, and also increased the binding affinity to the original level. These results provide direct evidence for the molecular interaction between the PGE2 binding protein and N in the brain.     

Mechanical stress and prostaglandin E2 synthesis in cartilage

Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE2) is one of the main catabolic factors involved in OA in which metalloproteinase (MMP) is crucial for cartilage degradation. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy-prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE2. Among the isoforms described, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. We investigated the regulation of the COX, PGES and 15-PGDH and MMP-2, MMP-9 and MMP-13 genes by mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) from 2 to 24 h. After determination of the PGE2 release in the media, mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blot respectively. Mechanical compression of cartilage explants significantly increased PGE2 production in a time dependent manner. This was not due to the synthesis of IL-1, since pretreatment with IL1-Ra did not alter the PGE2 synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE2 synthesis after 18 hours suggesting that PGE2 synthesis could be altered by the induction of 15-PGDH expression. MAPK are involved in signaling, since specific inhibitors partially inhibited COX-2 and mPGES-1 expressions. Lastly, compression induced MMP-2, -9, -13 mRNA expressions in cartilage. We conclude that dynamic compression induces pro-inflammatroy mediators release and matrix degradating enzymes synthesis. Notably, compression increases mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.     

Intracellular-specific colocalization of prostaglandin E2 synthases and cyclooxygenases in the brain

Prostaglandin E2 (PGE2) is the major primary prostaglandin generated by brain cells. However, the coordination and intracellular localization of the cyclooxygenases (COXs) and prostaglandin E synthases (PGESs) that convert arachidonic acid to PGE2 in brain tissue are not known. We aimed to determine whether microsomal and cytosolic PGES (mPGES-1 and cPGES) colocalize and coordinate activity with either COX-1 or COX-2 in brain tissue, particularly during development. Importantly, we found that cytosolic PGES also associates with microsomes (cPGES-m) from the cerebrum and cerebral vasculature of the pig and rat as well as microsomes from various cell lines; this seemed dependent on the carboxyl terminal 35-amino acid domain and a cysteine residue (C58) of cPGES. In microsomal membranes from the postnatal brain and cerebral microvessels of mature animals, cPGES-m colocalized with both COX-1 and COX-2, whereas mPGES-1 was undetectable in these microsomes. Accordingly, in this cell compartment, cPGES could coordinate its activity with COX-2 and COX-1 (partly inhibited by NS398); albeit in microsomes of the brain microvasculature from newborns, mPGES-1 was also present. In contrast, in nuclei of brain parenchymal and endothelial cells, mPGES-1 and cPGES colocalized exclusively with COX-2 (determined by immunoblotting and immunohistochemistry); these PGESs contributed to conversion of PGH2 into PGE2. Hence, contrary to a previously proposed model of exclusive COX-2/mPGES-1 coordination, COX-2 can coordinate with mPGES-1 and/or cPGES in the brain, depending on the cell compartment and the age group.     

The effect of inhibition of protein synthesis on some biochemical and functional activities of the brain in chick embryos]

By means of radioautographic and biochemical methods, it has been shown that cycloheximide administration to the brain in a dose of 76 mug significantly decreases protein synthesis within 30 min, the decrease being maximal after 2 hours. RNA synthesis in neuronal cytoplasm is blocked within 4 hours. Changes in biopotentials of the forebrain and midbrain structures were observed already 15-20 minutes after cycloheximide treatment. Application of cycloheximide (12.5-25 mug) to the area of vascular brannching of the foetal membranes of a 17-day embryo inhibits motor activity within 20 min.; in 28-day embryos, this effect is observed at a dose of 75 mug. Therefore, inhibition of protein synthesis in the brain results in sharp changes of the electrical activity of the brain and inhibits motor activity of the chick embryo.     

The effect of prostaglandin E2 (PGE2) on amino acid uptake and protein formation by lung fibroblasts

The effect of prostaglandin E2 (PGE2) on the utilization of extracellular amino acids by fetal lung fibroblasts was examined. PGE2 decreased the uptake of proline and aminoisobutyric acid (AIB) by quiescent fibroblasts in culture. The uptake of AIB by serum-activated cultures was also dramatically decreased by PGE2. The PGE2-induced decrease in the uptake of AIB was first observed at 4 h following the addition of the effector molecule to the cultures. PGE2 did not affect the uptake of leucine. The addition of cycloheximide also resulted in a decrease in the uptake of proline, similar to that induced by PGE2 at 5 X 10(-8) M. The combination of cycloheximide and PGE2 resulted in a further decrease in proline uptake. Kinetic analysis of AIB uptake following a 24-h PGE2 treatment showed an increase in the apparent Km as compared with untreated cultures. The prostaglandin remained active for at least 72 h after the addition of the molecule. Removal of the PGE2 was followed by an influx of proline into the cells. The decrease in proline uptake was associated with a decrease in the amount of intracellular free proline and an overall decrease in the amount of cell-associated protein. While PGE2 is known to increase intracellular protein degradation, the effect of PGE2 on amino acid uptake was not the result of an increase in the intracellular concentration of amino acids (transinhibition).     

Several mechanisms of acetylcholine participation in the processes of formation and fixation of temporary connections

Microphoretic application of acetylcholine (ACH) to the neurones of the rabbit sensorimotor cortex elicits changes of spontaneous and evoked activity which do not correlate with one another and which persist up to two minutes after the end of ACH application. Following the formation of a defensive conditioned reflex to sound, the reactions to ACH in units involved in the formation of the temporary connection are intensified as compared with their reactions before conditioning and with reactions of those neurones which did not elaborate a temporary connection. The possible mechanisms of ACH participation in the processes of elaboration and fixation of temporary connections are discussed.     

In vitro effect of eicosapentaenoic and docosahexaenoic acids on prostaglandin E2 synthesis in a human lung carcinoma

The capacity to synthesize both prostaglandins E1 (PGE1) and E2 (PGE2) has been determined in human lung mucoepidermoid carcinoma homogenates when [14C]-fatty acid precursors were added to the incubation medium. Only 10% of the total radioactivity recovered in PGs was found in PGF1 alpha and PGF2 alpha. The experiments were principally focused to inhibit the PGE2 synthesis either with pure eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids or with mixtures of both n-3 fatty acids obtained from fish oil. The results demonstrated that significant inhibitions were found when using 25 microM or a higher concentration of pure EPA or DHA in the incubation medium; however, 5 microM of mixtures of different EPA/DHA ratio caused the same inhibition. The results suggest that EPA and DHA, when added together, may enforce their inhibitory effect on PGE2 synthesis.