Hippocampal asymmetry in serotonergic modulation of learning and memory in rats.

The modulation of learning and memory after left or right microinjections of the selective 5-HT1A receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist NAN190 into the hippocampal CA1 area of male Wistar rats was studied. Microinjections of 8-OH-DPAT (1 microg) into the right or left CA1 hippocampal area produced a significant decrease in the number of avoidances in a shuttle box. The impairing effect of 8-OH-DPAT was more pronounced when injected into the right hippocampus compared to the left one. Microinjections of NAN190 (1 microg) into the right or left CA1 hippocampal area produced a significant increase in the number of avoidances in a shuttle box. Right microinjections of NAN190 increased the number of avoidances more strongly than compared to left injections. These effects on learning and memory were more pronounced after injection of either of the serotonergic agents into the right CA1 hippocampal area compared to the left. The stronger memory-modulating effect after injection of 8-OH-DPAT or NAN190 into the right CA1 hippocampal area suggests a rightward bias in the rat.

CCK-8 modulates GABA-stimulated [3H]-flunitrazepam binding in vitro.

In membranes from rat cerebral cortex, cholecystokinin-8 (CCK-8) did not modulate basal [(3)H]-flunitrazepam binding at either 4 degrees C or 37 degrees C. At a concentration of 10(-6) M, CCK(-8) significantly decreased gamma-amino-butyric acid (GABA)-stimulated (10(-6) M) [(3)H]-flunitrazepam binding at 37 degrees C. Scatchard analyses suggest that the decreased GABA-stimulated binding might be due to a decrease in the affinity of benzodiazepine receptors rather than to a decrease of number of binding sites. The observed modulation of benzodiazepine receptors by CCK-8 in vitro might explain some of the functional interactions between CCK and benzodiazepine systems.

Behavioral effects of Ginkgo biloba L., Panax ginseng C.A. Mey. and Gincosan.

The behavioral effects of a standardized extract from Panax ginseng roots (G115), of a standardized extract from Ginkgo biloba leaves (GK501) and of their combination (PHL-00701) (Gincosan) were examined in experiments on rats with undisturbed memory and on rats with experimentally-impaired memory (by alcohol or by muscarinic- and dopamine-receptor antagonists), using methods for active avoidance (shuttle-box) and passive avoidance (step-down and step-through). On multiple administration G115, GK501 and PHL-00701 exerted favorable effects on learning and memory. These effects varied with the dose and administration schedules, with the rat strain and with the behavioral method. Based on earlier results, we discuss the role of changes in brain biogenic amines induced by the extracts in their mechanism of action. The present results allow for ranking G115, GK501 and their combination PHL-00701 (Gincosan) among cognition-enhancing (nootropic) drugs.

Antinociceptive effect of somatostatin microinjected into caudate putamen.

The effects of somatostatin microinjected bilaterally and unilaterally (left or right) at a dose of 10, 50 and 100 ng into the caudate putamen of male Wistar rats on nociception (analgesy-meter test) were studied. Somatostatin injected into caudate putamen resulted in analgesia. Bilateral microinjections of somatostatin significantly increased the pain threshold in a dose-dependent manner, i.e. somatostatin exerted antinociceptive effect. The pain threshold after left-side microinjections was significantly higher than that after injections into right-side. These findings suggest antinociceptive and asymmetric effects of somatostatin on pain in the caudate putamen.

Behavioral effects of somatostatin microinjected into caudate putamen.

The present study examined the behavioral responses to bilateral microinjections of somatostatin (SRIF) into caudate putamen of male Wistar rats. SRIF locally administered at doses of 10, 50 and 100 ng/side dose-dependently affected locomotor activity, as reflected in both horizontal and vertical movements. SRIF modulated locomotor activity in a biphasic manner, exerting an inhibitory and a facilitatory effect. In the elevated plus-maze experiments, SRIF at doses of 50 and 100 ng/side microinjected bilaterally into caudate putamen decreased only the total number of entries in the open and closed maze arms, confirming the suppressing effect of SRIF on locomotion at the first 5 min.

Memory effects of the Ca2+ and 5-HT antagonists dotarizine and flunarizine.

In experiments on Wistar and Long Evans rats, using behavioral methods for passive (step-down and step-through) and active (shuttle-box two-way avoidance with punishment reinforcement) the newly synthesized diphenyl-methyl-piperazine derivative with Ca2+ and 5-HT antagonistic action dotarizine (DOT) administered repeatedly at oral doses of 50 and 10 mg/kg in some cases improve memory process. Under the same experimental conditions the chemically related to dotarizine Ca2+ antagonist flunarizine significantly facilitated retention. In old (Long Evans and Wistar) rats DOT in large dose decreases values of learning criterion. Probably this is a manifestation of the inherent to drugs with nootropic action "therapeutic window". Earlier investigations of the same and other authors suggest the participation of serotonergic neurotransmission in the mechanism of the memory effects of the drug DOT.

Does nitric oxide participate in the mechanism of action of dotarizine?

Behavioral and nociceptive effects of dotarizine (DOT) and other substances acting on migrainous attacks and nitric oxide (NO) metabolism were studied in comparative experiments on rats. Behavioral effects were evaluated by the changes induced in ambulations and rearings of rats in the Opto-Varimex apparatus; effects on nociception were determined by the changes of pain threshold in growing mechanical pressure on one of the rat paw. The data showed that (1) NO did not participate directly in the mechanism of the behavioral actions of DOT. A role could be ascribed to the modulating influence of DOT on the changes in NO formation induced by other agents; (2) the NO system did not participate in the mechanisms of the responses to the painful mechanical pressure on the rat paw; (3) the behavioral effects of the substances with facilitating or inhibitory action on the migrainous process (m-CPP and ergotamine) and the influence of substances proved to affect NO formation (L-arginine, histamine, L-NAME) on these effects suggest a role for NO as a modulating but not a basic factor in the mechanisms of action of these pro- and antimigrainous substances; and (4) the behavioral effects of DOT were similar to the effects of the antimigrainous drug ergotamine and different from the promigrainous drug meta-chlorophenyl-piperazine (m-CPP)--which suggest an antimigrainous activity of dotarizine.

Behavorial responses to the 5-HT1A receptor antagonist NAN190 injected into rat CA1 hippocampal area.

1. Behavioral responses to unilateral and bilateral microinjections of the 5-HT1A receptor antagonist, NAN190 [1-(2-methoxyphenyl)-4-[4-(2-phthalimido) butyl]piperazine hydrobromide] (1 microgram), into the hippocampal CA1 area of male Wistar rats were studied. 2. NAN190 decreased locomotor activity (the number of horizontal and vertical movements). The effect was most pronounced with microinjections of NAN190 into the right hippocampus. 3. Microinjections of NAN190 facilitated learning and memory in shuttle-box testing. 4. Microinjections of NAN190 had an anxiogenic effect in elevated plus-maze experiments and Vogel's conflict test. 5. The different behavioral responses to left and right microinjections of NAN190 in some of the behavioral tests suggest functional asymmetry of 5-HT1A receptors in the CA1 hippocampal area.

Anxiolytic effects of dotarizine, a possible antimigraine drug.

In experiments on rats in elevated plus-maze and in Opto Varimex apparatus, used for studying exploratory behavior, we observed that dotarizine (DOT), a drug with Ca2+ and 5-HT1/5-HT2-receptor antagonistic action, exerted effects suggesting anxiolytic action. The 5-HT uptake inhibitor fluoxetine (FLU) produced mainly anxiogenic effects. The simultaneous administration of DOT and FLU weakened the anxiolytic effect of DOT. The effects of the 5-HT1B/5-HT1C receptor agonist with promigraine action, m-chlorophenylpiperazine (m-CPP), indicated anxiogenic action, which was increased to a certain extent when it was combined with FLU. Some of the other 5-HT-receptor agonists and antagonists tested showed anxiogenic action and others anxiolytic action. In most cases, these effects were changed when they were administered simultaneously with FLU. DOT increased general locomotor activity and when combined with FLU this effect tended to decrease. In contrast, m-CPP decreased general locomotor activity and this effect was potentiated by FLU. DOT at the two doses used did not significantly change the rate of development of habituation, while m-CPP, buspirone and ondansetron increased it. The behavioral effects of DOT observed in all cases opposite to the same effects of the promigraine drug m-CPP suggest an antimigraine action of DOT.

Participation of different 5-HT receptors in the memory process in rats and its modulation by the serotonin depletor p-chlorophenylalanine.

The memory effects of agonists and antagonists of some serotonin (5-HT) receptor subtypes were examined in experiments on rats using an active avoidance method (shuttle-box). The 5-HT receptor antagonists NAN 190 (1 mg/kg i.p.) and pindolol (6 mg/kg i.p.) improved some indices for memory; the 5-HT2 and 5-HT3 receptor antagonists ritanserin (1 mg/kg i.p.) and ondansetron (0.1 mg/kg i.p.) exerted a favourable effect on the mastering of active avoidance performance. The tryptophan hydroxylase inhibitor para-chlorophenylalanine (300 mg/kg i.p.) alone produced no significant changes in the indices for retention of learned behaviour but in combination with the 5-HT-receptor agonists and antagonists influenced some of their effects. The results obtained show different participation of 5-HT1A, 5-HT2 and 5-HT3 receptors in the mechanisms of the memory process; the nature of this involvement is modulated by the brain level of serotonin.

Effects on nociception of the Ca2+ and 5-HT antagonist dotarizine and other 5-HT receptor agonists and antagonists.

The effects of the Ca2+ and 5-HT1 and 5-HT2 receptor antagonist dotarizine and of some other agonists and antagonists of different 5-HT receptor subtypes administered alone or in combination with the 5-HT uptake inhibitor fluoxetine (FLU) on nociception were studied, using a foot-pressure method (analgesy-meter testing). Dotarizine (DOT) administered at a dose of 50 mg/kg for 3 days orally significantly increased the pain threshold. Fluoxetine (FLU) administered at a dose of 10 mg/kg for 3 days also significantly increased the pain threshold. The combination of DOT and FLU abolished the analgesic effects of the two drugs. The 5-HT1A and 5-HT1B/1C receptor agonists buspirone and m-CPP decreased the pain threshold. The antagonists of 5-HT1A(NAN-190),5-HT1/5-HT2(methysergide), 5-HT2 (ritanserin), and 5-HT3 (ondansetron) receptors as well as the agonists of 5-HT2(DOI) and 5-HT3 (mCPBG) receptors increased the pain threshold. Fluoxetine at a single dose of 10 mg/kg differently influenced the effects of the 5-HT agonists and antagonists on nociception. Comparison of the effects of dotarizine with the effects of some of the agonists and antagonists of 5-HT receptor subtypes on the nociceptive and other actions suggests the possibility of a therapeutic value of dotarizine as an antimigraine drug.

Asymmetry in behavioral responses to cholecystokinin microinjected into rat nucleus accumbens and amygdala.

The behavioral responses of rats to uni- or bilateral microinjections of the octapeptide cholecystokinin (CCK-8) into the left and/or right or both nucleus accumbens (NA) or amygdalae were studied. There were two main findings of effects of microinjections of CCK-8 into NA. First, bilateral injections of CCK-8 into NA dose-dependently decreased the horizontal activity. The second more important finding was that CCK-8 at a specific dose (0.01 micrograms) injected into the right NA increased the number of horizontal movements 6-fold as compared to the injection into the left NA. Neither uni- nor bilateral injections of CCK-8 into NA at all doses used induced changes in the vertical movements. CCK-8 injected into left, right or both amigdalae increased locomotion at the lowest dose (0.01 microgram), while at the high doses (0.5 and 1.0 microgram) it significantly decreased it. The plus-maze test confirmed the anxiogenic effect of CCK-8 (0.01 microgram) injected into amigdalae. CCK-8 exerted a favorable effect on learning and memory (shuttle-box) when injected into the left but not into the right amygdala. Injection of CCK-8 (0.01 micrograms) into left amygdala provoked a 4-fold increase of the number of avoidances as compared to the microinjection into the right amygdala.

Hippocampal asymmetry in the behavioral responses to the 5-HT1A receptor agonist 8-OH-DPAT.

The present study examined the behavioral responses of rats to unilateral and bilateral injections of the selective serotonin 1A (5-HT1A)-receptor agonist 8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT) 1 microgram into the hippocampal CA1 area of male Wistar rats. 8-OH-DPAT increased locomotor activity, which was most pronounced with injections into the left hippocampus. The agonist impaired learning and memory (shuttle-box), especially when injected into the right hippocampus. The elevated plus-maze experiments showed that neither left nor right nor bilateral hippocampal injections of 8-OH-DPAT produced any anxiogenic effect. However, with Vogel's conflict test, right injections of 8-OH-DPAT produced anxiety. The present study has revealed hippocampal asymmetry in the behavioral responses to the 5-HT1A-receptor agonist 8-OH-DPAT.

Behavioral effects of the Ca2+/5-HT antagonist dotarizine.

The diphenyl-methyl-piperazine derivatives with Ca(2+)-antagonistic effect dotarizine (DOT), Fl-6020 and flunarizine were investigated in experiments on rats. The substances tested were administered repeatedly at an oral dose of 50 mg/kg. Behavioral methods were used to study the exploratory activity when the animals were placed in an environment that was unfamiliar to them (the chamber of the Opto Varimex apparatus), the elevated plus-maze method for examining the effect on anxiety, and the method of recording changes in motor activity (using the Automex II apparatus). DOT was found to increase motor activity and to have an anxiolytic effect. Combination of DOT--a compound with Ca(2+)--and 5-HT2-receptor antagonistic action--and the 5-HT-receptor agonists and antagonists used (buspirone, NAN190, pindolol, ritanserin and ondansetron) resulted in such changes in the development of habituation and in anxiety, which suggest that the modulating effects of DOT depend but partly on its typical interaction with the 5-HT2 receptor. Apparently, the Ca(2+)-antagonistic action of DOT plays a definite role, changing its biological activity depending on the 5-HT receptor subtype at the level of which the interaction is taking place.

Memory effects of standardized extracts of Panax ginseng (G115), Ginkgo biloba (GK 501) and their combination Gincosan (PHL-00701).

In experiments on young (aged 3 months) and old (aged 26 months) rats, using some conditioned-reflex methods with punishment or positive reinforcement for active and passive avoidance (shuttle-box, step-down, step-through, and water maze), we studied the effects of the standardized extracts of Panax ginseng (G115), Ginkgo biloba (GK501) and their combination Gincosan (PHL-00701). The extracts were administered orally for 7 days before training at three increasing doses: 17, 50, and 150 mg/kg for G115; 10, 30, and 90 mg/kg for GK501; and 27, 80, and 240 mg/kg for PHL-00701. The two extracts and their combination improved the retention of learned behavior. This effect varied considerably with the extracts, with the dose and with the behavioral method used. The results suggest that the Panax ginseng G115 and the Ginkgo biloba GK501 extracts possess properties similar in every respect to those of nootropic drugs. The favorable effects on learning and memory of the combination of G115 plus GK501 and the other pharmacological activities inherent in the extracts characterize this combination, offered as Gincosan as a particularly promising drug in geriatric practice.

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--I. Frog retina, Rana ridibunda.

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, applied at two different backgrounds, were studied. Additionally, a stimulation with long-lasting stimuli (ordinarily 5 sec ON-, 5 sec OFF-) was used. Both white and coloured light stimuli were presented. 2. 150 microM 2-amino-4-phosphonobutyrate (APB) was used to separate OFF- from ON- channels. 3. Before APB application, one or two components in the impulse activity in response to a flash were observed, depending on the type of ganglion cell (ON-, OFF- or ON-OFF). the latency of the first component was 60 msec and the latency of the second one was from 160 to 430 msec on average, at different background conditions. APB abolished the first component and enhanced the second one. 4. By means of APB, two components were shown to exist in the main positive wave of the flash ERG. APB abolished the first component and did not influence or enhance the second one. 5. The data obtained show that both ON- and OFF- channels take part in the generation of the frog retinal responses to brief stimuli.

Comparative investigation of retinal responses to brief light stimuli: 2-amino-4-phosphonobutyrate studies--II. Turtle retina (Emys orbicularis).

1. Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, presented on two different backgrounds, were studied. Additionally, stimulation with long lasting stimuli (ordinarily 5 sec ON-, 15 sec OFF-) was used. 2. 2-amino-4-phosphonobutyrate (APB) at a concentration of 450 microM on average was used to separate OFF- from ON- channels. It is known, that in other species APB selectively blocks the activity of ON- channel only. 3. The existence of APB- sensitive membrane receptors was demonstrated in the turtle retina. As in other species, APB abolished the ERG b-wave and enhanced the d-wave, when long lasting stimulation was used. 4. By means of APB, two components were shown to exist in the ERG positive wave in response to a flash. APB abolished the first component and did not influence or enhanced the second one. 5. By means of APB, one or two components in the impulse activity in response to flash were demonstrated, depending on the type of ganglion cell (ON-, OFF- or ON-OFF). The latency of the first component was 70 msec and the latency of the second one 210 msec on average. APB abolished the first component, and enhanced the second one. 6. The data obtained show that both ON- and OFF- channels take part in the generation of the turtle retinal responses to brief stimuli. 7. Based on the results obtained, some peculiarities of the network organization of the ganglion cells' receptive fields are discussed.

Participation of the GABAergic system of the turtle retina in the light adaptation process.

A comparative study was made of the ERG b- and d-wave intensity-response functions before and after GABAergic blockade by means of 0.4 mmol l-1 picrotoxin. A wide range of background intensities, including part of the high photopic range, were used. The intensity-response functions of both the ERG waves fitted well to the Michaelis-Menten equation (V/Vmax = In/(In + sigma n). A sigma-value decrease and a Vmax and n increase were observed after picrotoxin treatment. The analysis of the intensity-response functions shows that, under a wide range of backgrounds, the GABAergic neurons influence the ON- and OFF-response in the distal retina in a similar way. They decrease the gain and the contrast gain of the b- and d-wave generating neuronal mechanisms and widen the intensity span of their responses under given background illumination. The GABAergic system is involved also in response 'scaling' in the ON- and OFF-channels in the distal retina. A very important effect in this respect seems to be the equalization of the range of the responses to increment stimuli under different backgrounds.

Memory effects of a group of newly-synthesized pyrrolidine derivatives with putative nootropic effect.

The original pyrrolidine derivatives with putative nootropic effect: para-chloro-phenoxyacetyl-2-pyrrolidinone (Mf-P), 1-adamantanyl-2-pyrrolidinone (A-P), 2-oxo-1-pyrrolidine-3,7-dimethylxanthine (A-T) and para-benzoyl-1,4-dipyrrolidinone (p-P), were studied. Toxicological screening performed on mice demonstrated the low toxicity of the compounds. Five- or seven-day oral administration of the substances to rats in a dose of 100 mg/kg weight facilitated the learning process and improved the memory of the rats with most of the conditioned-reflex methods used. Application of Mf-P to 2- and 24-month-old rats for 8 days induced changes in the levels of some biogenic monoamines in the brain structures studied. The results obtained, as well as the results of other studies in this laboratory, show that the pyrrolidine derivatives studied, which can be considered to be original new aniracetam analogues, improve the memory process. This effect varies strongly depending on the regime of application of the compounds studied, on the memory capacity of the experimental animals and on the experimental method used. The changes in the brain neurotransmission induced by the substances studied play an essential role in their mechanism of action.