Effect of psychological stress on [35S]TBPS binding in rat brain.

This study was designed to determine whether psychological stress alters the function of the GABAergic synapse, examined as biochemical changes of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding, in unwashed membranes of rat cerebral cortex. Psychological stress increased the number of [35S]TBPS binding sites by 22%. This enhancement was very similar to that after acute foot shock (24%). Psychological stress was induced very rapidly, because only 1 day after previous foot shock exposure, [35S]TBPS binding was increased by 23%. Diazepam [3 mg/kg intraperitoneally (subcutaneously)] and ipsapirone (5 mg/kg subcutaneously), injected 30 min before psychological stress, antagonized the enhancement of [35S]TBPS binding. This result suggests that psychological stress is a good animal model for investigating the various biochemical changes related to stress, avoiding the physical components associated with most of the normally used stressors and mimicking only emotional state alterations.

Effects of chronic treatment with fluoxetine and citalopram on 5-HT uptake, 5-HT1B autoreceptors, 5-HT3 and 5-HT4 receptors in rats.

The effect in rats of chronic treatment with two specific 5-HT reuptake inhibitors (SSRI) with antidepressant properties, citalopram (10 mg/kg, i.p. twice a day for 14 days, one day washout) and fluoxetine (15 mg/kg, p.o. twice a day for 21 days, 7 days washout), was evaluated on some mechanisms involved in central 5-HT neurotransmission. No adaptive modifications of brain 5-HT uptake (sites) were found by measuring functional [3H]5-HT uptake and [3H]citalopram binding in cortical and hippocampal synaptosomes, and by [3H]citalopram binding autoradiography in the raphe nuclei (5-HT cell bodies) and the ventral tegmental area (5-HT axonal pathway). Chronic treatments had no effect on presynaptic 5-HT1B autoreceptors, functionally evaluated by measuring 5-HT1B-mediated inhibition of depolarization-induced [3H]5-HT release from cortical and hippocampal synaptosomes. Chronic citalopram or fluoxetine did not significantly affect the binding of [3H]BRL-43694 to 5-HT3 receptors in the rat brain cortex. Citalopram had no effect on [125I]SB-207710 binding to 5-HT4 receptors, measured by autoradiography in the substantia nigra. Negative results, such as those reported in the present study, could be due to a number of variables including the animal species, the treatment schedule or the brain areas considered, thus explaining the differences from some previous reports of significant effects of SSRI. However, our negative data are in agreement with many other published studies, suggesting that adaptive modifications of brain 5-HT transporters, terminal 5-HT1B receptors, 5-HT3 and 5-HT4 receptors may not be a general effect induced by all SSRI.

[125I][Tyr14]Orphanin binding to rat brain: evidence for labelling the opioid-receptor-like 1 (ORL1).

[125I][Tyr14]Orphanin binds to a number of saturable non-interacting binding sites in rat brain cortical membrane preparations, with a density of 510 fmol/mg protein and affinity 0.9 nM. This high affinity, saturable [125I][Tyr14]orphanin binding was not inhibited by leu-enkephalin and by other ligands for opiate and neurotransmitter receptors both in membrane preparations and brain sections. In rat brain sections, the highest density of binding was found in the outer and medial cortical layers, subiculum, hippocampus and nucleus accumbens; intermediate binding densities were found in the inner cortical layer, pontine nuclei, thalamus and hypothalamus. Very low specific binding was seen in the cerebellum and striatum, according to the described distribution of ORL1 transcripts. These results suggest that [125I][Tyr14] orphanin binding in rat brain occurs to the described ORL1 receptor.

DHEAS inhibits TNF production in monocytes, astrocytes and microglial cells.

We previously reported that neurosteroids, including dehydroepiandrosterone sulfate (DHEAS), inhibit the production of TNF in vitro and in vivo. In this paper we evaluated the effect of DHEAS on TNF production by cultured rat astrocytes and murine glial cell clones, and compared it with the effect on monocytic THP-1 cells. We found that DHEAS at a concentration of 10(-4)-10(-7) M inhibits TNF production induced by lipopolysaccharide (LPS, 1 microgram/ml) in these cells. Since the inhibitory effect of DHEAS is not mediated by the glucocorticoid (GC) receptor and DHEAS is an allosteric antagonist of the GABAA receptor, we investigated the possible role of GABAA receptors in this effect. The results showed that the inhibitory effect of DHEAS (10(-6) M) on TNF production by THP-1 cells was completely reversed by addition of 10(-6) M GABA. However, a GABAA receptor antagonist (bicuculline) did not mimic the action of DHEAS. In conclusion, DHEAS can inhibit TNF production in astrocytic and microglial cells suggesting it could be an endogenous regulator of TNF production in the brain.

Effects of repeated administration of selective adenosine A1 and A2A receptor agonists on pentylenetetrazole-induced convulsions in the rat.

The protective effects of the selective adenosine A1 receptor agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA), the selective adenosine A2A receptor agonist, 2-hexynyl-5'-N-ethylcarboxamidoadenosine (2HE-NECA), and the non-selective agonist, 5'-N-ethylcarboxamidoadenosine (NECA) were studied against lethal seizures induced by intraperitoneal (i.p.) injection of pentylenetetrazole (80 mg/kg). In acute studies there was a dose-dependent reduction of lethal seizures, as shown by the low dose's protecting 50% of animals (PD50): 0.11, 0.05 and 0.05 mg/kg i.p. for CCPA, 2HE-NECA and NECA, respectively. In the repeated administration studies the animals received either vehicle or drug i.p. twice daily for 12 days. The drug doses were twice the PD50 value: 0.3 mg/kg for CCPA or 0.1 mg/kg for both 2HE-NECA and NECA. 2HE-NECA and NECA maintained their protective activity against pentylenetetrazole-induced seizures (63% or 60% vs. 60% or 58% in acute studies, respectively). Conversely, repeated treatment with CCPA resulted in a marked decrease of its effects (67% vs. 30% in acute studies; P < 0.05). The data indicate that in addition to adenosine A1 the A2A receptors also appear to be involved in the protection from seizures. The anticonvulsant effects induced by repeated stimulation of adenosine A1 receptors are subject to tolerance, whereas effects depending on adenosine A2A receptor activation are maintained.

NMDA receptor function is enhanced in the hippocampus of aged rats.

The density and functional activity of the N-methyl-D-aspartate (NMDA)-sensitive glutamate receptor was examined in various brain areas of 3-, 18- and 24-month-old rats. The total numbers of binding sites for the NMDA receptor antagonists [3H]CGP 39653 and [3H]MK 801 binding sites were decreased in the hippocampus, cerebral cortex and striatum of 18- and 24-month-old rats, relative to 3-month-old animals. In the hippocampus of 18-month-old rats, the reduced number of NMDA receptors was associated with an increased sensitivity of [3H]MK 801 binding to the stimulatory action of glycine and glutamate. Thus, 10 microM glycine and 10 microM glutamate increased [3H]MK 801 binding in the hippocampus of 18-month-old rats by 75 and 160%, respectively; in 3-month-old animals, the same concentration of these amino acids increased binding by 37 and 95%, respectively. The sensitivity of [3H]MK 801 binding to glycine and glutamate was not increased in the cerebral cortex and striatum of aged rats. Moreover, an increased efficacy of glycine and glutamate in stimulating the binding of [3H]MK 801 in the hippocampus was no longer apparent in the 24-month-old rats. The increased sensitivity of [3H]MK 801 binding to glycine and glutamate in the hippocampus of 18-month-old rats may reflect an increase in NMDA receptor activity to compensate for the decrease in receptor number.

Failure of flumazenil to precipitate a withdrawal syndrome in cats chronically treated with the new anxioselective beta-carboline derivative abecarnil.

The effect of chronic administration of the novel anxiolytic beta-carboline derivative, abecarnil (isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate), was examined and compared with the capability of diazepam to induce physical dependence in cats. The acute administration of the benzodiazepine receptor antagonist, flumazenil (20mg/kg i.p.), to cats treated for 2 weeks with diazepam (7mg/kg i.p., three times daily), induced a severe withdrawal syndrome characterized by the appearance of severe physical signs. Within minutes all cats displayed tremors, increased muscle tone, fear response, repeated vocalization and salivation. On the contrary, in all cats treated chronically (2 weeks) with abecarnil (7mg/kg i.p. three times daily) the challenge dose of flumazenil failed to precipitate a clear abstinence syndrome. In fact, a pupillary dilatation and a mild fear response were the only signs present 15-30min after flumazenil administration. This finding indicates that abecarnil, a new potential therapeutic agent for anxiety disorders and seizures, might have advantages over classical benzodiazepines with regard to development of physical dependence.

Pharmacology of gamma-aminobutyric acidA receptor complex after the in vivo administration of the anxioselective and anticonvulsant beta-carboline derivative abecarnil.

In rodents, the effect of the beta-carboline derivative isopropyl-6- benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate (abecarrnil), a new ligand for benzodiazepine receptors possessing anxiolytic and anticonvulsant properties, was evaluated on the function of central gamma-aminobutyric acid (GABA)A receptor complex, both in vitro and in vivo. Added in vitro to rat cortical membrane preparation, abecarnil increased [3H]GABA binding, enhanced muscimol-stimulated 36Cl- uptake and reduced the binding of t-[35S]butylbicyclophosphorothionate ([35S]TBPS). These effects were similar to those induced by diazepam, whereas the partial agonist Ro 16-6028 (tert-butyl-(S)-8-bromo-11,12,13,13a-tetrahydro-9-oxo-9H- imidazo[1,5-a]-pyrrolo-[2,1-c][1,4]benzodiazepine-1-carboxylate) showed very weak efficacy in these biochemical tests. After i.p. injection to rats, abecarnil and diazepam decreased in a time-dependent and dose-related (0.25-20 mg/kg i.p.) manner [35S]TBPS binding measured ex vivo in the cerebral cortex. Moreover, both drugs at the dose of 0.5 mg/kg antagonized completely the convulsant activity and the increase of [35S]TBPS binding induced by isoniazide (350 mg/kg s.c.) as well as the increase of [35S]TBPS binding induced by foot-shock stress. To better correlate the biochemical and the pharmacological effects, we studied the action of abecarnil on [35S]TBPS binding, exploratory motility and on isoniazid-induced biochemical and pharmacological effects in mice. In these animals, abecarnil produced a paralleled dose-dependent (0.05-1 mg/kg i.p.) reduction of both motor behavior and cortical [35S]TBPS binding. Moreover, 0.05 mg/kg of this beta-carboline reduced markedly the increase of [35S]TBPS binding and the convulsions induced by isoniazid (200 mg/kg s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)