Chronic RU486 treatment reduces age-related alterations of mouse hippocampal function.

The present study investigates the protective effect of a chronic blockade of the glucocorticoid receptor (type II) by a single weekly SC injection (20 mg/kg) of RU486 (a potent antiglucocorticoid) from mid-age (12 months old) until senescence (20 to 22 months old) on perturbations of some electrophysiological parameters classically observed in CA1 hippocampal slices of aged BALB/c mice. In this CA1 hippocampal area, no electrophysiological difference was observed at a stimulation frequency of 0.3 Hz. However, an important age-related effect was observed in not-treated animals concerning the three phases of the synaptic response during and after 4 Hz repetitive stimulation ith impairment of the frequency potentiation (FP). Interestingly, this electrophysiological disturbance disappeared completely in aged animals treated previously with RU486. Furthermore, a 10 microM CORT bath application had no effect in CA1 of aged animals, while it produced the classical type II-mediated population spike (PS) decrease in adult animals. This PS amplitude decrease was maintained in aged animals previously treated with RU486. These electrophysiological findings suggest an important type II-mediated glucocorticoid action on age-related alterations of hippocampal function.

Synergistic action of corticosterone on kainic acid-induced electrophysiological alterations in the hippocampus.

The present study investigates the effect of overexposure to high doses of the stress hormone corticosterone (CORT) on the electrophysiological changes produced in the hippocampus after local microinjection of KA. Extracellular recordings were performed in the CA1 area of mouse hippocampal slices prepared after a 7-day recovery period following KA microinfusion alone or combined with 3 days overexposure to CORT. The results showed that CORT shifts the KA response profile approximately 40-fold, since animals treated with a non-toxic dose of 0.01 microgram KA and CORT exhibited epileptic activity and a shift on the paired-pulse response similar to that observed in animals treated with high doses of KA (0.4 microgram). This synergistic action of CORT on the electrophysiological changes induced by KA was antagonized by the antiglucocorticoid RU486 whereas the antimineralocorticoid spironolactone was ineffective. These results suggest that CORT may play an important role in modulating the severity of KA-induced seizures in the hippocampal structure probably by GR-receptor mediated action.

Corticosterone effects on long-term potentiation in mouse hippocampal slices.

Corticosterone (CORT) can alter several electrophysiological properties in the hippocampus. Few studies have reported the effects of CORT on hippocampal long-term potentiation (LTP). In the CA1 region of the hippocampal slice, we studied the relative increase in population spike (PS) amplitude after inducing tetanus (PS-LTP) in control conditions and in the presence of CORT (0.5 nM or 5 microM). Two perifusion mediums were used which differed in calcium concentration (M1:Ca 2.5 mM; M2: Ca 3.1 mM). In the control slices, the PS-LTP amplitude was greater in the M1 medium. With the low CORT concentration (0.5 nM), the PS-LTP amplitude was greater than in control conditions in the M2 medium only. A similar PS-LTP amplitude increase was also observed in the M2 medium after application of 0.5 nM aldosterone (type I receptor analog). With the high CORT concentration (5 microM), PS-LTP amplitude decreased in the two conditions. This effect was reversed by co-application of RU486 (type II receptor antagonist). These results demonstrate that CORT can modulate PS-LTP via its two types of hippocampal CORT receptors, depending on the concentration applied. They also showed that the extracellular calcium concentration may contribute to the functional change induced by CORT.

Regulation of the Salmonella typhimurium metF gene by the MetR protein.

The metF gene in Escherichia coli and Salmonella typhimurium is under negative transcriptional control by the MetJ repressor. Expression of an S. typhimurium metF-lacZ gene fusion is repressed up to 10-fold by methionine addition to the growth medium in E. coli hosts encoding wild-type MetJ repressor; this repression is not seen in metJ mutants. metR mutations which eliminate the MetR activator protein result in two- to threefold-more-severe repression by the MetJ repressor. In a metJ metR double mutant, however, the level of metF-lacZ expression is the same as in a metJ mutant, suggesting that MetR antagonizes MetJ-mediated methionine repression of the metF promoter. A DNA footprint analysis showed that MetR binds to a DNA fragment carrying the metF promoter and protects two separate regions from DNase I digestion: a 46-bp region from position -50 to -95 upstream of the transcription initiation site and a 24-bp region from about position +62 to +85 downstream of the transcription initiation site and within the metF structural gene. Nucleotide changes in each of the MetR-binding sites away from the consensus sequence disrupt MetR-mediated regulation of the metF-lacZ fusion.

Similar effects of aging and corticosterone treatment on mouse hippocampal function.

Cumulative exposure to corticosterone (CORT) during the lifespan plays an important role in the hippocampal aging process, and similar disturbances have been observed in chronic stress. However, there is little information on the electrophysiological changes observed in these two situations at the hippocampal level. The present study investigates the electrophysiological changes observed in control conditions and after a 10 microM CORT bath application on hippocampal slices taken from control adult BALB/c mice, from adult animals subjected to chronic overexposure to corticosterone (20 mg/kg/day during 3 months) and from aged animals. No electrophysiological difference was observed in the CA1 area of chronically CORT treated and aged groups compared to the control group. Conversely, the input/output curves from the dentate area showed a similar, statistically significant right shift in these two groups compared to the control group. Furthermore, in control subjects, a 10 microM CORT bath application produced the classical population spike amplitude decrease. However, in slices taken from chronically CORT-treated and aged mice, this effect did not occur in the CA1 while it was replaced by a population spike amplitude increase in the dentate. This increase was blocked by spironolactone. These electrophysiological alterations may indicate that a part of the aged-induced functional disturbances is mediated by glucocorticoids, and may progressively lead to impairment of neuroendocrine functions and behavioral adaptation.

Modulation of the in vitro electrophysiological effect of corticosterone by extracellular calcium in the hippocampus.

The electrophysiological effects of various concentrations of corticosterone (CORT) on the hippocampus were investigated using extracellular recordings from CA1 hippocampal slice preparations subjected to four different extracellular concentrations of calcium. In all cases, the CORT effect was manifested by a PS amplitude decrease without affecting the slope of either the input volley or the EPSP. Our results showed that, for the lowest extracellular calcium concentrations (1.3 and 2.5 mM), the inhibitory effect of CORT on the PS amplitude appeared only with the supra-physiological 10,000 nM CORT concentration, whereas for the highest ones (3.13 and 5.32 mM) this effect was observed, respectively, with 5 and 0.05 nM CORT concentrations. The antiglucocorticoid RU 486, used in combined application with CORT, blocked the electrophysiological effect of CORT. The possible involvement of calcium-dependent mechanisms at the CORT receptor level or in the final cellular response are discussed.

[In vitro functional differentiation of hippocampal corticosterone receptors by mineralo- and glucocorticoids]. / Dissociation fonctionnelle, in vitro, des récepteurs hippocampiques à la corticostérone par les minéralo- et les glucocorticoïdes.

Modulation of CA1 evoked electrophysiological properties (amplitude, latency, paired-pulse facilitation) by different concentrations of aldosterone (ALDO), spironolactone (SPI), and corticosterone (CT) was studied in hippocampal slice preparation from BALB/c mice. ALDO (5 nM) induced a prolonged increase of the population spike (PS) amplitude with a decrease of its latency and of the paired pulse facilitation. The same effect was observed with a solution of CT (0.5 nM) alone or combined with ALDO (0.5 nM), but no effect was observed with a solution of combined CT (0.5 nM) and SPI (500 nM). Implication of corticosteroid receptors in this response was discussed.

The effect of diaminoalkyl-anthraquinone derivatives on the growth of the promastigotes of Leishmania tropica minor, L. t. major, L. donovani and L. aethiopica.

By combining knowledge of polyamine biosynthesis and its inhibition by various analogues with that on the activity of synthetic anthraquinones, a series of six anthraquinone derivatives were synthesized. Their ability to inhibit the growth of leishmanial promastigotes in vitro was used as a preliminary screen to check their potential as new antileishmanial chemotherapeutics. They were tested against four strains, representing four different species; Leishmania tropica major, L. tropica minor, L. aethiopica and L. donovani, associated with four separate disease syndromes. All six derivatives exhibited a fair degree of antileishmanial activity, some being more effective than others. They all inactivated cultures at 100 micrograms/ml and some did so at 10 micrograms/ml and even 1 microgram/ml; but taking different lengths of time to achieve this. Antileishmanial activity associated with anthraquinone derivatives might provide a new approach to the chemotherapy of leishmaniasis.

Polyamines and the growth of leishmanial parasites.

The relation between the grown of leishmanial parasites and polyamine biosynthesis was studied. Polyamines, mainly putrescine and spermidine, accumulated in macrophages infected with Leishmania tropica major promastigotes grown in vitro. Similar results were obtained, when tissues of BALB/C mice infected with L. tropica major were examined. A consistent increase in cellular putrescine and spermidine levels was observed in infected skin and spleen. With the accumulation of putrescine, a concomitant increase in ornithine decarboxylase activity was detected in growing leishmanial promastigotes and in macrophages supporting the growth of leishmanial amastigotes. An increase in the activity of ornithine decarboxylase was also observed in Leishmania-infected skin and spleen from BALB/C mice.