Prenatal lipopolysaccharide treatment enhances MK-801-induced psychotomimetic effects in rats

The aim of this study was to evaluate the effect of prenatal lipopolysaccharide (LPS) treatment, which is an animal developmental model of schizophrenia, on MK-801-induced psychotomimetic behavioral changes and brain aminergic system activity in adult offspring. Repeated LPS (1 mg/kg) injection in rats, that had started from 7th day of pregnancy and was continued every second day till delivery, resulted in a long-lasting disruption of prepulse inhibition (PPI) and elevation of locomotor activity in their offspring. The prenatally LPS-treated rats showed hypersensitivity to MK-801 (0.1 and 0.4 mg/kg) as evidenced by the enhancement of acoustic startle amplitude, reduced PPI, and enhanced locomotor activity. These behavioral changes were accompanied by a decrease in the dopamine and its metabolite, DOPAC concentration in the frontal cortex, enhanced dopaminergic system activity in the striatum and no changes in noradrenaline (NA) level. Furthermore, the significant augmentation of 5-HT and 5-HIAA content in the frontal cortex of females only was detected. No changes in the cortical NA tissue level were found. Summing up, the present study demonstrated that the activation of the immune system in prenatal period led to persistent behavioral hypersensitivity to psychotomimetic action of a non-competitive NMDA receptor antagonist, and attention/information processing deficits. The foregoing data indicate that prenatal administration of LPS model some of the clinical aspects of schizophrenia and these behavioral effects are connected with neurochemical changes.

Effect of topiramate on the kainate-induced status epilepticus, lipid peroxidation and immunoreactivity of rats

Topiramate, a new anticonvulsant, has been reported to possess neuroprotective effects in both in vivo and in vitro experiments. In the present study, the effect of topiramate (40 and 80 mg/kg ip) on the fully developed kainate-induced status epilepticus was evaluated in the rat. Injection of kainate (15 mg/kg ip) evoked recurrent limbic seizures which lasted several hours. Topiramate injected 1.5 h after kainate administration had no effect on the seizures and mortality of the animals. Biochemical study revealed that at 80 mg/kg ip, topiramate significantly attenuated the kainate-induced lipid peroxidation in the piriform cortex and showed similar tendency in the frontal cortex. Besides the central nervous system, the kainate-induced seizures evoked significant changes in immunoreactivity, such as reduction in thymus weight and the proliferative activity of splenocytes, and the splenocyte-increased production of interleukin-10, but not interferon-gamma. Topiramate did not affect the kainate-induced reduction in thymus weight, but attenuated changes in the proliferative activity of splenocytes. It is concluded that topiramate, when given during the fully developed kainate-induced status epilepticus in rats, has no effect on seizures, but attenuates lipid peroxidation in piriform cortex and prevents certain changes in immunoactivity.

Chlorpromazine inhibits the glucocorticoid receptor-mediated gene transcription in a calcium-dependent manner

Antipsychotic drugs can modulate transcription factors and also nuclear receptors, but their action on glucocorticoid receptors (GR)-members of the steroid/thyroid hormone receptor family has not been studied so far. In the present study we investigated effects of various antipsychotics on the glucocorticoid-mediated gene transcription in fibroblast cells, stably transfected with a mouse mammary tumor virus promoter (LMCAT cells). Chlorpromazine (3-100 microM) inhibited the corticosterone-induced gene transcription in a concentration- and time-dependent manner. Clozapine showed a similar, but less potent effect, while haloperidol acted only in high concentrations, and other antipsychotic drugs (sulpiride, raclopride, remoxipride) were without any effect. It was also found that a phorbol ester (an activator of protein kinase C (PKC)) and A-23187 (Ca(2+)-ionophore) attenuated the inhibitory effect of chlorpromazine on the GR-induced gene transcription. An antagonist of the L-type Ca(2+) channel, as well as an inhibitor of phospholipase C (PLC) inhibited the corticosterone-induced gene transcription, but had no effect on the chlorpromazine-induced changes. The involvement of a PKC/PLC pathway in the chlorpromazine action was confirmed by Western blot analysis which showed that the drug in question decreased the PLC-beta(1) protein level, and to a lesser extent that of the PKC-alpha protein in LMCAT cells. The aforementioned data suggest that inhibition of the glucocorticosteroid-induced gene transcription by chlorpromazine and clozapine may be a mechanism by which these drugs block some effects induced by glucocorticoids. The inhibitory effect of chlorpromazine on the corticosterone-induced gene transcription seems to depend on the inhibition of Ca(2+) influx and/or the inhibition of some calcium-dependent enzymes, e.g. phospholipase beta(1).

Effect of allopregnanolone on d-[3H]-aspartate release and [3H]-glutamate uptake in the hippocampus of kainate-treated mice

In order to determine whether the status epilepticus leads to alterations in the neurosteroid effect on excitatory amino acid transmission, we studied the influence of allopregnanolone on aspartate release and glutamate uptake in mouse hippocampus at various times after kainate administration. No significant differences in the K+-stimulated D-[3H]-aspartate release from the hippocampi of saline- and kainate-treated mice were observed; however, that parameter tended to fall in tissues collected I h after kainate administration. Allopregnanolone significantly attenuated the K+-stimulated D-[3H]-aspartate release from the hippocampi of control animals, as well at 24 h and 7 days after kainate injection; in contrast it did not affect amino acid release from the hippocampi collected 1 h after kainate administration. Kainate administration had no effect on [3H]-glutamate uptake after 1 and 24 h, but elevated that parameter on day 7. Allopregnanolone (10 and 100 microM) did not affect [3H]-glutamate uptake in control and kainate-treated mice. In conclusion, the present study indicates a loss of the inhibitory effect of allopregnanolone on the potasium-stimulated D-[3H]-aspartate release from mouse hippocampus during the kainate-induced status epilepticus; moreover, it excludes involvement of this neurosteroid in the regulation of hippocampal [3H]-glutamate uptake in both control and kainate-treated mice.

Estrone, but not 17 beta-estradiol, attenuates kainate-induced seizures and toxicity in male mice

Estrogens change the susceptibility to seizures in humans and experimental animals. In this study, the effect of estrone and 17 beta-estradiol on kainate-induced seizures and neurotoxicity was investigated in male mice. Pre-treatment with estrone (250-1000 micrograms/kg) at 24 and 2 hours before kainate (40 mg/kg) administration significantly decreased both the percentage of animals with clonic seizures and their mortality (the latter at a dose of 1000 micrograms/kg only). On the other hand, 17 beta-estradiol (10-500 micrograms/kg) had no effect on seizures, and its dose of 10 micrograms/kg increased mortality. When given alone at a dose of 1 mg/kg, tamoxifen, an antagonist at estrogene receptors, did not affect the kainate-induced seizures, but prevented the anticonvulsant effect of estrone. A histological analysis showed that 73% of mice injected with vehiculum and kainate incurred hippocampal damage. Estrone (2000 micrograms/kg) decreased the percentage of animals with hippocampal neuronal loss down to 43%, and that effect was not antagonized by tamoxifen. Pretreatment of mice with 17 beta-estradiol had no effect on the kainate-induced neuronal loss. Additionally, we found that kainate injected i.p. had a profound effect on the immune system of mice, as reflected by a decrease in the thymus weight and an increased metabolic activity of splenocytes. The anticonvulsive dose of estrone (1000 micrograms/kg) did not change the immunoreactivity of either control or kainate-treated mice. In conclusion, the obtained data indicate that estrone, but not 17 beta-estradiol, attenuates the kainate-induced seizures, mortality and excitotoxicity in male mice. Moreover, it is suggested that the suppressive effect of estrone on clonic seizures involves intracellular receptors, whereas its antineurotoxic activity seems to depend on a non-genomic mechanism.

Protective effects of TRH and its stable analogue, RGH-2202, on kainate-induced seizures and neurotoxicity in rodents

Thyrotropin-releasing hormone (TRH) has been postulated to be involved in the regulation of seizures and neural degeneration. We examined the effects of TRH and its stable analogue, RGH-2202, on the kainate-induced seizures and excitotoxicity in mice - a model of a drug-resistant temporal lobe epilepsy. We found that TRH (2.0 and 5.0 mg/kg) and RGH-2202 (2.5 and 5 mg/kg) elevated the ED(50) for kainate-induced convulsions and tended to decrease mortality. A histological analysis showed that kainate caused a neuronal loss of CA(1) and CA(3) hippocampal fields. TRH (10, 20 and 50 mg/kg) and RGH-2202 (2.5, 7.5 and 10.0 mg/kg) markedly reduced the excitotoxic effect of kainate. Further studies showed that TRH (1-100 microM) and RGH-2202 (100 microM) significantly attenuated the kainate (150 microM)-induced lactate dehydrogenase release in a primary cortical cell culture from rat embryos. In conclusion, the present study showed that TRH and RGH-2202 attenuated the kainate-induced seizures and inhibited the kainate-evoked neurotoxicity in vivo and in vitro. These results support the hypothesis of a potential utility of TRH and its analogues in the treatment of seizures and some neurodegenerative diseases.

Effects of some centrally active drugs on the allopregnanolone synthesis in rat brain

Effects of antidepressants (desipramine, amitriptyline), anticonvulsants (phenytoin, diazepam, carbamazepine) and addictive drugs (amphetamine, morphine), used at a concentration of 100 microM on the conversion of [14C]-progesterone to 5alpha-pregnane-3,20-dione and allopregnanolone in slices of the frontal cortex and olfactory bulb from rat brain were studied. The synthesis of 5alpha-pregnane-3,20-dione and allopregnanolone was stronger in the olfactory bulb than in the frontal cortex. The biosynthesis of allopregnanolone in the frontal cortex was higher by 74, 109 and 187% when stimulated by amitriptyline, desipramine and carbamazepine, respectively, and, to a lesser degree, by phenytoin and morphine. Desipramine and morphine decreased the concentration of 5alpha-pregnane-3,20-dione. In the olfactory bulb, only carbamazepine enhanced allopregnanolone production, but none of the tested drugs had any effect on 5alpha-pregnane-3,20-dione synthesis. It is concluded that some psychotropic drugs may increase allopregnanolone synthesis by stimulating the activity of the enzyme, 3alpha-hydroxysteroid dehydrogenase, in the frontal cortex, and that this neurosteroid may be partly involved in the mechanism of action of the drugs under study.

Effect of repeated desipramine and fluoxetine administration on post-adjuvant arthritis

The effects of desipramine and fluoxetine on the swelling of hind paws, radiologically-detectable bone destruction of hind paws, increase in spleen and popliteal lymph node weight, increase in metabolic activity of splenocytes and increase in proliferative activity of splenocytes and popliteal lymph node cells from right adjuvant injected paw in male C57BL/6 mice were studied on the 17th day after induction of post-adjuvant arthritis. Drugs were administered once-daily ip at a dose of 10 mg/kg. Fourteen days of desipramine administration, starting on the third day after injection of the adjuvant, significantly increased edema and radiologically assessed bone destruction, spleen and popliteal lymph node weight whereas fluoxetine induced an opposite effect, but it did not reduce edema in comparison with saline-treated control. Two-week desipramine administration significantly increased metabolic activity of splenocytes and proliferative activity of popliteal lymph node cells from the right adjuvant-injected paw, whereas 14 days of fluoxetine injection reduced proliferative activity of splenocytes in comparison with the saline-treated mice. Desipramine administration 30 days before and 17 days after adjuvant injection did not change these parameters in spite of reduction of proliferative activity of splenocytes. These findings indicate that: 1) fluoxetine has a suppressive effect on some of the local and systemic changes which occur in adjuvant-induced arthritis in mice, 2) two-week desipramine administration significantly increases whereas 47-day desipramine treatment does not change most of local and systemic parameters of post-adjuvant disease in C57BL/6 mice, 3) the action of fluoxetine differs from that of desipramine in this model of autoimmunodisease probably as a result of the distinct effect of these two drugs on corticoids levels and on the activity of a sympathetic nervous system.

Effects of pilocarpine- and kainate-induced seizures on thyrotropin-releasing hormone biosynthesis and receptors in the rat brain

The expression of mRNA coding for prepro-thyrotropin releasing hormone (preproTRH) was estimated in the rat brain in two animal models of limbic seizures, evoked by systemic administration of pilocarpine (400 mg/kg ip) or kainate (12 mg/kg ip). As shown by an in situ hybridization study, after 24h both pilocarpine- and kainate-induced seizures profoundly increased the preproTRH mRNA level in the dentate gyrus. After 72h, the preproTRH mRNA level was back to control values. Kainate-treated rats showed an elevated level of TRH in the hippocampus, septum, frontal and occipital cortex after 24 and 72h, whereas in the striatum and amygdala the TRH level was raised after 72h only. In the hypothalamus, TRH levels was lowered after 3 and 24h, and returned to the control after 72h. Pilocarpine-induced seizures also elevated the TRH level after 72h in the majority of the above structures, except for the hypothalamus and amygdala where no changes were found at any time point. A radioreceptor assay showed that kainate decreased the Bmax value of TRH receptors in the striatum and hippocampus after 3 and 24h, respectively, and had no effect on the Kd values. In contrast, pilocarpine-induced seizures lowered the Bmax of TRH receptors in the striatum, hippocampus and piriform cortex after 72h only, and decreased Kd values in the striatum, amygdala and frontal cortex. These data showed that pilocarpine- and kainate-induced seizures enhanced likewise preproTRH mRNA in the dentate gyrus; on the other hand, they differed with respect to time- and structure-related changes in TRH tissue levels and TRH receptors. These differences may have functional significance in TRH-dependent control mechanism of the seizure activity in these two models of limbic epilepsy.

Effects of pentylenetetrazole-induced kindling on thyrotropin-releasing hormone biosynthesis and receptors in rat brain

It has been postulated that changes in thyrotropin-releasing hormone biosynthesis may be involved in the mechanism of kindling--an animal model of epileptogenesis. To test this hypothesis, a time-course study was carried out to investigate the effects of pentylenetetrazole kindling (40 mg/kg i.p., daily for eight days) on the expression of gene coding for preprothyrotropin-releasing hormone, the thyrotropin-releasing hormone tissue level and thyrotropin-releasing hormone receptor parameters in rat brain. As shown by an in situ hybridization study, a single, convulsant dose of pentylenetetrazole (70 mg/kg i.p.) increased the preprothyrotropin-releasing hormone messenger RNA level in the dentate gyrus of the hippocampal formation and piriform cortex after 3 h and, to a greater extent, after 24 h. Those changes were accompanied with increases in the thyrotropin-releasing hormone level in the striatum, hippocampus, amygdala and piriform cortex. Seven days after single pentylenetetrazole administration, the thyrotropin-releasing hormone level was still significantly elevated in the piriform cortex and striatum. Acute pentylenetetrazole decreased the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum after 3 and 24 h, and increased that density in the piriform cortex and amygdala after 24 h and seven days, respectively. The thyrotropin-releasing hormone receptor affinity (Kd) was decreased in the striatum and increased in the amygdala after only 3 h. Kindled rats showed a moderate increase in the preprothyrotropin-releasing hormone messenger RNA content in the dentate gyrus of the hippocampal formation and piriform cortex after 3 and 24 h; however, a significant decrease in those parameters was found after 14 days. After 3 and 24 h, pentylenetetrazole kindling also elevated the thyrotropin-releasing hormone content in the hippocampus, piriform cortex, and striatum (in the latter structure after 24 h only), whereas in the septum the thyrotropin-releasing hormone level was decreased. After seven days, the thyrotropin-releasing hormone level was still elevated in the hippocampus and piriform cortex of kindled rats, but after 14 days it was significantly lowered in the hippocampus. The kindled rats also showed a significant decrease in the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum (after 24 h, seven and 14 days), and an increase in the piriform cortex (after seven days). The thyrotropin-releasing hormone receptor affinity (Kd) value was increased in the hippocampus after seven and 14 days, and in the piriform cortex after seven days. These results indicate that pentylenetetrazole kindling induces long-lasting alterations in the thyrotropin-releasing hormone biosynthesis and thyrotropin-releasing hormone receptor affinity in discrete regions of rat brain. These region-specific changes, in particular down-regulation of the thyrotropin-releasing hormone biosynthesis in the hippocampus, may be involved in chronic neuronal hyperexcitability associated with kindling.

The effect of N-nitro-L-arginine methyl ester on morphine-induced changes in the plasma corticosterone and testosterone levels in mice

Effects of the nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg i.p.), on morphine-induced changes in the plasma corticosterone and testosterone levels were studied in male mice. Acute morphine administration (15 and 30 mg/kg i.p.) enhanced the corticosterone level after 1 and 2 hr (at a dose of 30 mg/kg only). A 4-day treatment with increasing doses of morphine, from 15 to 50 mg/kg i.p., increased the plasma corticosterone concentration at 2 hr after the last injection. Single administration of L-NAME (30 mg/kg i.p.) had no effect on the corticosterone level, whereas its repeated injections (30 mg/kg i.p., twice a day for four days) elevated the hormone concentration at 2 hr after the last dose. Pretreatment of mice with L-NAME enhanced the stimulatory effects of both acute and repeated morphine administration on the corticosterone level. D-NAME (30 mg/kg i.p.), an inactive form of the nitric oxide synthase inhibitor, had no effect on the morphine-induced changes in the corticosterone level. Acute morphine administration had no effect on the plasma testosterone level after 1 or 2 hr, whereas repeated drug injections decreased the hormone concentration after 2 hr. Single or repeated L-NAME administration did not influence the testosterone level in either control or morphine-treated animals. The above results indicate that inhibition of nitric oxide synthase enhances the stimulatory effect of morphine on corticosterone secretion, but does not influence the inhibitory effect of repeated morphine on the plasma testosterone concentration in mice.

Effects of neurosteroids on spike-wave discharges in the genetic epileptic WAG/Rij rat

Effects of i.p. administration of the neurosteroids, allopregnanolone and pregnenolone sulfate, were studied in WAG/Rij rats, a genetic model for generalized absence epilepsy. EEG recordings showed that allopregnanolone, a positive modulator of the GABA(A) receptor, in doses ranging from 5 to 20 mg/kg, increased dose-dependently the number- and total duration of spike-wave discharges. Pregnenolone sulfate, a positive modulator of NMDA receptors, also increased those parameters, though only at the highest dose used (100 mg/kg). Significant changes in spike-wave discharges occurred during the first hour post-injection and were not accompanied with behavioral alterations. The obtained data indicate that both these neurosteroids aggravate the spike-wave activity. This finding contrasts with the anti-convulsant effects of some neurosteroids and they point to a different pharmacological profile of epilepsy with convulsive or non-convulsive seizures.

Opposite effects of inhibitory and excitatory neurosteroids on [3H]dopamine release from rat nucleus accumbens

Neurosteroids with GABAA receptor antagonistic properties increase K(+)-evoked [3H]dopamine release from rat nucleus accumbens slices, whereas neurosteroid positive modulators of GABAA exert an opposite effect.

The effect of N-nitro-L-arginine methyl ester on cocaine-induced hormonal changes in mice

Effects of the nitric oxide synthase inhibitor, N-nitroL-arginine methyl ester (L-NAME, 30 mg/kg i.p.), on cocaine-induced changes in corticosterone and testosterone plasma levels were studied in male mice. Acute (30 mg/kg i.p.) and repeated cocaine (30 mg/kg i.p., twice a day for four days) enhanced the corticosterone level after 45 min and 2 hr, respectively. Single administration of L-NAME had no effect on corticosterone level, whereas its repeated injections (30 mg/kg i.p., twice a day for four days) elevated the hormone concentration at 2 hr after the last dose. Pretreatment of mice with L-NAME enhanced the stimulatory effects of both acute and repeated cocaine on corticosterone level. D-NAME (30 mg/kg i.p.), an inactive form of the nitric oxide synthase inhibitor, was without effect on the cocaine-induced changes in corticosterone level. Acute cocaine administration (30 mg/kg) moderately decreased the testosterone plasma level after 45 min and 2 hr; however, that effect disappeared upon repeated cocaine administration. Single and repeated L-NAME administration did not influence the testosterone level in control animals. Single L-NAME injection abolished the decrease in testosterone level evoked by acute cocaine administration. The above results show that inhibition of nitric oxide synthase enhances the stimulatory effect of cocaine on corticosterone secretion, but abolishes the inhibitory effect of this psychostimulant on the plasma testosterone concentration in mice. On the other hand, a weak--if any--effect of L-NAME alone on corticosterone and testosterone levels suggests that nitric oxide plays a minor role in the tonic regulation of these hormones' secretion.

Effect of neurosteroids on glutamate binding sites and glutamate uptake in rat hippocampus

Effects of some neurosteroids on the binding of [3H]-glutamate, [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and [3H]-MK-801, as well as on the [3H]-glutamate uptake were examined in rat hippocampus. The following compounds were evaluated: (a) positive modulators of the GABA(A) receptor: 5alpha-pregnan-3alpha-ol-20-one (allopregnanolone), 5alpha-pregnane-3alpha,21-diol-20-one (allotetrahydrodeoxycorticosterone), 5alpha-pregnan-3alpha-ol-11,20-dione (alphaxalone) and 5alpha-androstan-3alpha-ol-17-one (androsterone); (b) compounds showing GABA(A)-antagonistic and/or N-methyl-D-aspartic acid (NMDA)-agonistic properties: dehydroepiandrosterone sulfate and pregnenolone sulfate; (c) a substance which, apart from its GABA(A)-agonistic potency, has a NMDA-antagonistic action: 5beta-pregnan-3alpha-ol-20-one. None of those neurosteroids tested at concentrations of 0.001-100 microM affected the binding of [3H]-glutamate, [3H]-AMPA and [3H]-MK-801 or the glutamate uptake. The present study suggests that the previously reported inhibitory effects of neurosteroids on excitatory amino acid-induced seizures and neurotoxicity can be linked neither to the direct interaction of these compounds with the above binding sites on glutamate receptor complexes, nor to the glutamate uptake mechanism.

Protective effects of neurosteroids against NMDA-induced seizures and lethality in mice

The effects of some neurosteroids on N-methyl-D-aspartic acid (NMDA)-induced seizures were examined in mice. Intraperitoneal (i.p.) administration of 5 alpha-pregnan-3 alpha-ol-20-one (5, 10 and 20 mg/kg). 5 beta-pregnan-3 alpha-ol-20-one (10 and 20 mg/kg), 5 alpha-pregnan-3 alpha-ol-11,20-dione (15 mg/kg), 5 alpha-androstan-3 alpha-ol-17-one (10 mg/kg) and dehydroepiandrosterone sulfate (25 mg/kg) significantly increased the dose of NMDA necessary to induce clonic convulsions in 50% of the tested animals (CD50). Furthermore, 5 alpha-pregnan-3 alpha-ol-20-one, 5 beta-pregnan-3 alpha-ol-20-one, 5 alpha-pregnan-3 alpha-ol-11,20-dione and 5 alpha-androstan-3 alpha-ol-17-one also protected the mice against NMDA-induced mortality. Importantly, it is only at the highest doses that neurosteroids impair motor performance of the animals, as estimated by a rotorod equilibrium procedure. The other neurosteroids tested, such as 5 alpha-pregnan-3 beta-ol-20-one (5-20 mg/kg), 5 alpha-pregnan-3 alpha,21-diol-20-one (10 and 15 mg/kg), 5 alpha-pregnan-3,20-dione (15 mg/kg) and pregnenolone sulfate (12.5-100 mg/kg) had no significant effects on the measured parameters. In another set of experiments, we evaluated the effects of neurosteroids on D-[3H]-aspartate release from rat hippocampal slices. None of the neurosteroids tested exerted a significant effect on basal D-[3H]-aspartate release. On the other hand, K(+)-stimulated D-[3H]-aspartate release was significantly attenuated by 5 alpha-pregnan-3 alpha-ol-20-one, 5 beta-pregnan-3 alpha-ol-20-one, alphaxalone, pregnenolone sulfate and dehydroepiandrosterone sulfate. The effect of 5 alpha-pregnan-3 alpha-ol-20-one was the most potent and was distinctly concentration-dependent, whereas the other compounds were effective only at the highest concentrations used. The above results indicate that some neurosteroids administered in non-sedative doses can protect mice against NMDA-induced seizures and mortality; furthermore, they inhibit D-[3H]-aspartate release in rat hippocampal slices.

Effects of neurosteroids on kainate-induced seizures, neurotoxicity and lethality in mice

In the present study we examined effects of some neurosteroids on the kainate-induced seizures, lethality and neurotoxicity in mice. We found that 5 alpha-pregnan-3 alpha-ol-20-one (allopregnanolone; 10 and 20 mg/kg) markedly elevated CD50 for kainate-induced convulsions, whereas 5 beta-pregnan-3 alpha-ol-20-one, 5 alpha-pregnan-3 alpha-ol-11,20-dione, 5 alpha-androstan-3 alpha-ol-17-one, dehydroepiandrosterone sulfate, pregnenolone sulfate and aminosteroid (U-107) were ineffective in that test. Furthermore, 5 alpha-pregnan-3 alpha-ol-20-one (5-20 mg/kg), 5 beta-pregnan-3 alpha-ol-20-one (20 mg/kg) and 5 alpha-androstan-3 alpha-ol 17-one (10 and 20 mg/kg) decreased, while dehydroepiandrosterone sulfate (25 and 50 mg/kg) and pregnenolone sulfate (25 mg/kg) elevated the kainate-induced lethality in mice. A histological analysis showed that kainate caused a dose-dependent neuronal loss of CA1 and CA3 hippocampal fields. Of the neurosteroids tested, only allopregnanolone attenuated the kainate-induced neurotoxicity. The above data indicate that neurosteroids exert moderate effects on seizures and neurotoxic effects of kainate. On the other hand, neurosteroids with a GABAA receptor agonistic or antagonistic activity decrease or increase, respectively, the kainate-evoked lethality.

Repeated cocaine administration down-regulates glucocorticoid receptors in the rat brain cortex and hippocampus

Chronic exposure to psychostimulants results in an aberrant activity of the hypothalamic-pituitary-adrenal (HPA) axis. Since this axis is under inhibitory control of corticosteroid receptors, the present study has been designed to determine the effects of repeated (15 mg/kg, ip, once an hour for 3 h, for 8 days) cocaine administration on cytosolic and nuclear glucocorticosteroid receptor (GR) levels in the hippocampus and frontal cortex of the rat. As shown by a sensitive Western blotting technique, repeated (but not single) treatment with cocaine significantly reduced the density of cytosolic GR in the frontal cortex (by ca. 23%) and to a lesser extent in the hippocampus (by ca. 10%), after 45 min and 72 h, respectively. No changes in the nuclear fraction of the GR level were found following repeated cocaine administration, whereas acute treatment enhanced the signal in the hippocampus by ca. 17%. The obtained results indicate that repeated cocaine administration decreases the level of GR in the cytosol, but does not enhance transport of these receptors into the nuclei. The down-regulation of cortical and hippocampal GR receptors may play some role in the cocaine-induced impairment of the feedback control mechanism of the HPA axis activity.