Effects of single and long-term theophylline treatment on the threshold of mechanical nociception: contribution of adenosine A1 and alpha2-adrenoceptors.

The effects of single and long-term treatment with theophylline as well as the influence of adenosine A1 receptor agonist cyclopentyladenosine (CPA) and a-adrenergic receptor antagonists prazosin and yohimbine were assessed in the paw pressure test in rats. Both single (37.5 and 75 mg/kg) and long-term (75 mg/kg/day, 14 days i.p.) theophylline treatments exerted antinociceptive effect by increasing the mechanical pain threshold. Single treatment of theophylline (75 mg/kg) antagonized the antinociceptive effect of CPA (0.1 mg/kg); CPA (0.1 mg/kg) abolished the theophylline-induced antinociception. Chronic treatment with theophylline did not change the antinociceptive effect of CPA, while CPA decreased the theophylline antinociception. Yohimbine (0.5 mg/kg), an a 2-adrenoceptor antagonist, diminished the antinociception of a single dose (75 mg/kg) of theophylline, whereas prazocin, an a 1-adrenoceptor antagonist, did not affect it. These results suggest that adenosine A1 and a 2-adrenoceptors take part in the antinociception induced by a single dose of theophylline. The antinociception induced by chronic theophylline treatment probably has a more complex mechanism in which the involvement of adenosine A1.

Effects of peptide and non-peptide antagonists of angiotensin II receptors on drinking behavior in rats.

The effects of the non-peptide selective angiotensin II AT1 receptor antagonist DuP 753 and its metabolite EXP 3174, of the peptide ANGII analogues saralasin and sarmesin and of the newly synthesized imidazole compound (1-methyl-4,5-diphenylimidazole) on ANGII-induced drinking in rats were investigated. The effect of the AT2 selective antagonist PD 123319 on ANGII-induced drinking in rats was also studied. DuP 753, EXP 3174, saralasin and sarmesin (peptides and non-peptides) dose-dependently inhibited ANGII-induced water intake. The ID50 values of these drugs showed the following order of potency: EXP 3174 > saralasin > sarmesin > DuP 753 indicating their ability to block central AT1 receptors. The imidazole compound increased ANGII-induced water intake suggesting its AT1 receptor agonistic properties. PD 123319 inhibited ANGII-induced water intake at a higher dose (64 nmol), allowing to assume AT1 receptor agonistic properties.

Interaction of angiotensin II and adenosine receptors in pentylenetetrazol-induced kindling in mice.

The relationships of adenosine A1 receptor agonists and antagonists in combination with angiotensin II (AT II) and its analogue sarmesin in PTZ (pentylenetetrazol) kindling in ICR mice were studied. The occurrence of clonic and tonic seizures and the latency to their onset in PTZ kindled mice was determined. Combination of adenosinergic and AT II-ergic agents significantly reduced the incidence of clonic seizures in PTZ kindling without changing the latency. Pretreatment with 8-p-Sulfophenyl-theophylline (8-p-SPT) reversed the anti-convulsant effect of sarmesin.

Effects of [arginine8, glycine-OH9]-vasopressin on pentylenetetrazol seizures in mice. Interaction with adrenaline.

The effects of [arginine8, glycine-OH9]-vasopressin (AGV), alone and in combination with adrenaline, on pentylenetetrazol (PTZ) seizure threshold by timed intravenous infusion in tall vein and intensity by subcutaneous (s.c.) PTZ test (85 mg/kg) were studied in male albino mice. AGV was administered intracerebroventricularly (i.c.v.) at doses of 0.001, 0.01, 0.1, 1.0 and 5.0 ng/mouse 5, 15 and 30 min prior to PTZ AGV induced decrease of seizure threshold at middle doses (0.01 and 0.1) 5 and 15 min prior to PTZ (75 and 67% respectively vs. controls). Adrenaline (1 mg/kg, i.p.) potentiated the effect of AGV on seizure threshold. AGV also induced increase of seizure intensity at doses of 0.01 and 1.0 ng and decrease of latency of the first tonic seizure. Adrenaline (1.0 mg/kg, i.p.) enhanced the effects of AGV suggesting interactions of vasopressin with adrenergic neurotransmission in the CNS.

Effects of non-peptide angiotensin II-receptor antagonists on pentylenetetrazol kindling in mice.

The effects of non-peptide AT1- and AT2-receptor antagonists DuP 753 (losartan) and PD 123319 on the intensity of pentylenetetrazol (PTZ)-kindled seizures in mice were studied. PTZ was injected intraperitoneally at a subconvulsive dose of 40 mg/kg at 48 h until the appearance of clonic seizures. DuP 753 administered intracerebroventricularly (i.c.v.) tended to decrease seizure intensity. Successive administration of ineffective doses of DuP 753 (losartan) and AT2 (angiotensin II) significantly decreased seizure intensity. PD 123319 (i.c.v.) decreased seizure intensity. Combination of ineffective doses of PD 123319 and AT2 also significantly decreased seizure intensity. The results suggest the role of AT2 receptor and its subtypes in PTZ-kindled seizures as well as an action of DuP 753 and PD 123319 similar to the action of AT2, an AT2-receptor agonist.

Further evidence for the interactions between angiotensin II and GABAergic transmission in pentylenetetrazol kindling seizures in mice.

The effects of the GABAergic drugs nipecotic acid, Gabrene, baclofen and metatolylcarbamide (MTC), when given alone or in combination at subthreshold doses with AT II also at a subthreshold dose effective on PTZ-kindling in mice were studied. PTZ-kindling was provoked by intraperitoneal (i.p.) injections of PTZ (40 mg/kg) every other day in male albino mice until clonic seizures appeared. Nipecotic acid (100 and 200 micrograms/mouse intracerebroventricularly [i.c.v.]) tended to decrease seizure intensity. Gabrene (25, 50, 100 and 250 mg/kg i.p.) inhibited PTZ-kindled seizures. Baclofen at a doses of 2.5 and 5 mg/kg i.p. tended to decrease seizure intensity and at a dose of 10 mg/kg was ineffective at all. MTC (50 and 75 mg/kg i.p.) tended to decrease and at a dose of 100 mg/kg significantly decreased seizure intensity. Combinations of subthreshold dose of AT II (0.05 micrograms/mouse i.c.v.) and subthreshold doses of nipecotic acid (100 micrograms/mouse) or Gabrene (10 mg/kg) or baclofen (10 mg/kg) or MTC (50 mg/kg) significantly decreased the intensity of PTZ-kindled seizures in mice. The observed potentiation of the anticonvulsive activity on PTZ-kindling suggests interactions of AT II receptors with GABA receptors (GABAA, GABAB or both), effected through allosteric mechanisms.

Interactions between angiotensin II, diazepam, clonazepam and di-n-propylacetate in pentylenetetrazol kindling seizures in mice.

The effects of AT II alone and in combinations with the anticonvulsants diazepam, clonazepam and di-n-propylacetate (depakine) on PTZ-kindling in mice were studied. PTZ-kindling was provoked by intraperitoneal (i.p.) injections of PTZ (40 mg/kg) every other day in male albino mice until clonic seizures appeared. AT II in doses 0.1 and 1 microgram/mouse intracerebronventricularly (i.c.v.) decreased the intensity of seizures in PTZ-kindled mice. Diazepam (0.25 and 1 mg/kg i.p.), clonazepam (0.05 and 0.1 mg/kg i.p.) and depakine (75 mg/kg) inhibited PTZ-kindled seizures. Combinations of ineffective doses of AT II (0.05 microgram/mouse) and ineffective doses of diazepam (0.1 mg/kg) or clonazepam (0.01 mg/kg) or depakine (50 mg/kg) significantly decreased the intensity of seizures in PTZ-kindled mice. The seizure-decreasing effect of diazepam, clonazepam and depakine on PTZ-kindling in mice, which was potentiated by AT II, suggests interactions of AT II receptors with GABA and benzodiazepine receptors or with the GABA-benzodiazepine receptor-ionophore complex, probably effectuated through alsoteric mechanisms. A more efficient coupling of the GABA-benzodiazepine receptor-ionophore complex with AT II receptors might also be the reason for the decrease of the intensity of seizures in PTZ-kindled mice.

Cholinergic influence on memory facilitation induced by angiotensin II in rats.

The influence of the cholinesterase inhibitor galanthamine (Nivalin), of the cholinergic agonist oxotremorine, and of the muscarinic cholinergic antagonist scopolamine on the retention-improving effect of angiotensin II (AT II) was studied in male Wistar rats trained and tested for retention (24h later) using two paradigms: two-way active avoidance (shuttle-box) and passive (step-through) avoidance. AT II and the cholinergic agonists, administered together potentiated their retention-improving effects, while scopolamine abolished the memory effect of AT II. It is suggested that brain cholinergic neurotransmission participates in the mechanisms of the memory-facilitating effect of AT II.

Interactions between angiotensin II and baclofen in shuttle-box and passive avoidance performance.

In experiments on male rats, we established that angiotensin-II (AT II) at a dose of 0.1 micrograms injected intracerebroventricularly immediately after training improved memory when retention tests (active and passive avoidance) were given 24 hours later. Baclofen at doses of 2, 5 and 10 mg/kg injected intraperitoneally immediately after training also improved retention in both active and passive avoidance tasks. Baclofen at a dose of 20 mg/kg was without effect on active avoidance performance. Combination of AT II and baclofen (2, 5 and 10 mg/kg) facilitated memory in active avoidance as compared to controls, but impaired retention as compared to the AT II-treated group. The impairment of the AT II-improved retention was stronger when the dose of baclofen in the combination was 20 ng/kg. Combination of AT II and baclofen (10 mg/kg) did not impair retention in passive avoidance. These data favor the view that GABA receptors may interfere with the AT II effects on memory consolidation or retention and that interactions of GABA (GABAA and GABAB) receptors with AT II receptors are of importance for memory processes.

Comparative studies on the central effects of the angiotensin II analogue (Sar1 azaVal3 Ile8) AT II.

The effects of the newly-synthesized AT II analogue (Sar1 azaVal3 Ile8) AT II were investigated in comparison with the octapeptide AT II and the analogue saralazin (Sar1 Ala8) AT II, using intracerebroventricular administration, with respect to the following parameters: the level of biogenic monoamines (DA, NA and 5-HT) and the metabolites HVA and 5-HIAA in mouse forebrain; the behaviour of the animals--cataleptogenic actions of mice, PTZ convulsive--seizure threshold in mice, apomorphine stereotypy in rats and behaviour of rats in a conflict situation. The analogue (Sar1 azaVal3 Ile8) AT II, unlike saralazin and AT II, was found to induce a rise in the NA and 5-HT levels, causing also catalepsy that is different from the catalepsy induced by saralazine, AT II and haloperidol, because of its rapid onset and decline; it increases the PTZ convulsive--seizure threshold and reduces the number of punished responses to the conflict drinking test (anxiomimetic effect) in a dose 20 times lower than the dose inducing the remaining effects. This effect was antagonized by saralazine. It is concluded that the newly-synthesized analogue (Sar1 azaVal3 Ile8) AT II induces effects similar to those caused by AT II, being at the same time different to a certain extent from the effects (quantitative and qualitative) of octapeptide AT II.

Interactions between angiotensin II, GABA and diazepam in convulsive seizures.

In experiments on male mice, we studied the effects of gamma-aminobutyric acid (GABA), angiotensin II (AT II), administered intracerebroventricularly, diazepam, injected intraperitoneally, and combinations of GABA + AT II and diazepam + AT II on convulsive seizures induced by pentylenetetrazol (PTZ) (80 mg/kg subcutaneously) and 3-mercaptopropionic acid (3-MPA) (40 mg/kg intraperitoneally). The anticonvulsant effects of GABA and diazepam on PTZ-induced seizures were increased by AT II in doses which did not significantly influence seizures. AT II applied together with GABA or diazepam in ineffective doses provoked a strong anticonvulsant effect on both PTZ- and 3-MPA-induced seizures. These results indicate that the anticonvulsant effects of GABA and diazepam on PTZ- and 3-MPA-induced seizures might effectively be potentiated by the octapeptide AT II. It is suggested that AT II operates as an endocoid acting on GABA, respectively benzodiazepine recognition sites in the CNS.

Participation of angiotensin II in learning and memory. II. Interactions of angiotensin II with dopaminergic drugs.

The effect of angiotensin II (ATII) and of its interactions with dopaminergic drugs injected post-trial on retention in active avoidance tasks in shuttle-box-trained rats were studied. ATII at doses of 0.10 and 0.50 micrograms administered intracerebroventricularly (i.c.v.) immediately after training improved retention. The dopaminergic receptor agonist apomorphine at a dose of 0.10 mg/kg injected intraperitoneally (i.p.) facilitated retention whereas elymoclavine (a dopaminergic agonist) at a dose of 2.5 mg/kg i.p. had no effect. ATII at a dose of 0.10 micrograms i.c.v. administered after apomorphine 0.10 mg/kg or elymoclavine 2.5 mg/kg exerted a stronger retention-facilitating effect. The dopaminergic receptor antagonist haloperidol at a dose of 1 mg/kg i.p. markedly impaired retention. ATII at a dose of 0.50 micrograms administered after haloperidol (1 mg/kg) did not exercise its retention-facilitating effect. It is concluded that the retention facilitating effects of ATII are realized through interactions with brain dopaminergic transmission.

Comparative studies on the central effects of angiotensin II and of its fragments.

Comparative studies were carried out of the central effects of the octapeptide angiotensin II (AT II) and of its fragments: C-terminal hexapeptide (AT 3-8), middle tetrapeptide (AT 3-6) and initial tripeptide (AT 1-3). The experiments were carried out with respect to the cerebral level of the biogenic amines DA, NA, 5-HT and their metabolites HVA and 5-HIAA in intact mice and in mice pretreated with haloperidol, as well as with respect to the animals' behaviour (haloperidol catalepsy, apomorphine stereotypy, unconditioned jumping reaction, hexobarbital sleep and the threshold of convulsive seizures induced by times intravenous infusion of pentylenetetrazol). The fragments studied were found to manifest activity in the tests used. In some respects this activity is very similar to the activity of AT II. There are also effects which differ from those of AT II, as well as effects which are entirely opposite in some respects, which makes it possible to examine some of these substance as its potential natural antagonists. All this shows that the biological activity of AT II in the brain undergoes a number of qualitative and quantitative changes when its molecule broken to produce peptides with shorter chains. In the effects observed AT II and its fragments interact predominantly with the DA-ergic transmission in the brain.

Interactions of angiotensin II and GABA-ergic agents at the threshold of convulsive reactions.

The effects of angiotensin II (AT II), GABA, muscimol (administered i.c.v.) and of amino-oxiacetic acid (AOAA) and baclofen (administered i.p.), as well as of the combinations of AT II with these substances and bicuculline, were studied with respect to the threshold of the convulsive seizures induced by timed intravenous infusion of pentylenetetrazol (PTZ) in mice. It was found in the experiments that the threshold-increasing effect of GABA, muscimol and AOAA was potentiated by AT II (applied in a dose which did not change essentially the convulsive threshold). The potentiated effect of GABA, muscimol and AOAA on the convulsive threshold, when applied in combination with AT II, was antagonized by bicuculline. The threshold-increasing effect of baclofen was not affected substantially by AT II; in this case bicuculline had no effect. On the basis of the results obtained it may be assumed that AT II performs the functions of an antocoid predominantly for the GABA-A receptors in the central nervous system.

Memory effects of GABA-ergic antagonists in rats trained with two-way active avoidance tasks.

In experiments on male Wistar rats, trained and tested for memory after 24 h in a shuttle box, it was found that bicuculline applied intraperitoneally 10 min before the training in a dose of 0.5 mg/kg, improves learning and retention; bicuculline applied immediately after training in a dose of 1.0 mg/kg, improves retention. Picrotoxin, administered i.p. 20 min before training in doses of 0.25 and 0.50 mg/kg, improves learning, while in doses of 0.10-2.0 mg/kg it facilitates retention; picrotoxin, applied immediately after training in doses of 1.0 and 2.0 mg/kg, improves retention in the experimental animals. It is assumed that the GABA-ergic receptor antagonists, administered intraperitoneally, facilitate the processes of memory formation, whereby the decrease in the inhibitory effect of GABA is essential.

Central effects of angiotensin II, its fragment and analogues.

The effects of the octapeptide angiotensin II (AT II), its fragment Ile8 AT3-8 and the analogues Sar1 Ala8 AT II, Ala8 AT II and Ile8 AT II were studied with respect to: the level of biogenic amines (DA, 5-HT and their metabolites HVA and 5-HIAA) in the forebrain; the behaviour of the animals--haloperidol catalepsy, apomorphine stereotypy, unconditioned jumping reaction (UJR), convulsive threshold. Good correlation was found between the biochemical and behavioural effects. The fragment of AT II where phenylalanine is substituted at the C-terminal by Ile reduces the haloperidol-increased content of HVA, potentiates apomorphine stereotypy and reduces catalepsy, whereas the AT II analogues (where the C-terminal phenylalanine is substituted by Ala, and the N-terminal--by Sar) potentiate the effect of haloperidol increasing the HVA content, reduce apomorphine stereotypy and potentiate catalepsy; saralasine independently applied induces brief catalepsy; AT II, its fragment and analogues inhibit UJR, in combination with amphetamine and PTZ this effect becomes deeper; the duration of hexobarbital sleep is increased. The peptides investigated increase the convulsive threshold. The results show that the hexapeptide fragment has preserved the effects of AT II, whereas in the analogues (with changed C- and N-terminals) they are changed. The results obtained may be explained with the modulating influence of AT II-receptors on the DA-ergic receptors in the brain structures with which AT II and its fragment and analogues enter in contact.

Effects of single and repeated application of clonazepam and diazepam independently and in combination with cyproheptadine on apomorphine stereotypy in rats.

The effects of the benzodiazepines clonazepam (CLZ) and diazepam (DZ), introduced independently and in combination with cyproheptadine (CY) upon single and repeated application on apomorphine stereotypy in rats were studied. On single application CLZ shortened the duration of apomorphine stereotypy and DZ did not change it. On repeated application (14 days) CLZ reduced stereotypy while DZ increased it. Cyproheptadine on both single and repeated application reduced apomorphine stereotypy. On single application the combination of CLZ and CY increased stereotypy and the combination of DZ and CY increased gnawing behavior. On repeated administration the combination of CLZ and CY reduced apomorphine stereotypy to a higher extent than did CLZ when applied alone. The CLZ- and DZ-induced changes in apomorphine stereotypy were determined through a mediated effect in which 5-hydroxytryptamine plays an important role.

[Participation of GABA and other mediators in regulating the convulsive threshold]. / Uchastie GAMK i drugikh mediatorov v reguliatsii sudorozhnogo poroga.

The participation of GABA and some other transmitter systems in the regulation of the convulsive seizure threshold was studied using pharmacological tools. The convulsion were provoked by intravenous infusion of the GABAergic antagonists picrotoxin and bicuculline and, in some cases, of pentylenetetrazole and strychnine. The GABAergic transmitter mechanisms were established to play a major role in the regulation of the convulsive seizure threshold. Of some importance is also the participation of benzodiazepine receptors, cholinergic, dopaminergic, serotoninergic mechanisms, as well as of cyclic nucleotides. The interactions between the GABAergic and dopaminergic, cholinergic mechanisms, cyclic nucleotides, benzodiazepine receptors may also play a role in the convulsive threshold regulation. The changes in the threshold of convulsive reactions are closely related to the decrease or increase of both central inhibition (pre- or postsynaptic) and excitation.