Enhancement by nifedipine of cholinergic-induced depression of locomotor activity in mice

The dihydropyridine calcium channel blocker nifedipine did not affect spontaneous locomotor activity in mice when given alone but enhanced the depressant effects of the muscarinic receptor agonist oxotremorine and of the acetylcholinesterase inhibitor physostigmine. Such a behavioral depression might be due to neuronal changes induced by central calcium channel blockade combined with cholinergic activation. However, an involvement of hemodynamic factors, related to peripheral vasodilatation, cannot be excluded as locomotor depressant effects were also exerted by combinations of the two cholinomimetic agents with hydralazine, a non-calcium antagonist vasodilator.

Minaprine, but not oxiracetam, prevents desipramine-induced impairment of avoidance learning in mice

The tricyclic antidepressant desipramine impaired shuttle-box avoidance acquisition in mice of the CD-1 strain. The nootropic drug oxiracetam was unable to prevent the desipramine-induced learning impairment, while a protective action was exerted by minaprine, a psychotropic agent regarded as an atypical antidepressant drug, possessing dopaminergic and related memory-enhancing properties. It seems likely that the dopaminergic action of minaprine played a determinant role in its avoidance improving effects in desipramine treated mice, because similar effects were produced by amphetamine. However, in contrast to amphetamine, minaprine did not enhance locomotor activity and did not show signs of general behavioral stimulation.

Effect of caffeine and nicotine on avoidance learning in mice: lack of interaction

Tested alone, nicotine (0.25 or 0.5 mg kg-1) improved shuttle-box avoidance learning in mice of the CD-1 strain. Caffeine had no effect at doses of 2.5 and 5 mg kg-1 and impaired performance at a dose of 10 mg kg-1. Combinations of the two drugs did not increase avoidance responses more than nicotine alone, nor was nicotine able to attenuate performance depression induced by the highest dose of caffeine. Lack of drug interaction in the avoidance test contrasts with the occurrence of interactive effects of the two drugs in a locomotor activity test. When given in combination, caffeine and nicotine increased locomotor activity at doses ineffective by themselves. The results seem to indicate no advantage in combining caffeine and nicotine to improve active avoidance learning.

Reversal of chlorpromazine-induced avoidance depression by the N-methyl-D-aspartate antagonist, dizocilpine, in mice

The non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801 (dizocilpine) was tested, alone or in combination with chlorpromazine, in mice previously trained in the shuttlebox. The lowest doses of dizocilpine (0.02 and 0.04 mg kg-1) attenuated the disrupting action of the neuroleptic (1.5 mg kg-1) on avoidance-performance, while avoidance depression induced by 1.5 and 2 mg kg-1 chlorpromazine was completely or almost completely reversed by 0.08 mg kg-1 NMDA antagonist. The highest dose (0.16 mg kg-1) of dizocilpine did not ameliorate avoidance-performance of mice receiving 2 mg kg-1 chlorpromazine, perhaps because of ataxic effects produced by the drug combination, at these doses. The results support suggestions for a potential use of NMDA antagonists in the treatment of extrapyramidal side-effects of neuroleptics.

Shuttle-box avoidance behavior of mice treated with nifedipine in combination with nicotine or physostigmine

Nicotine and physostigmine, given alone, slightly improved shuttle-box avoidance acquisition in mice. the dihydropyridine calcium channel inhibitor nifedipine, ineffective alone, enhanced the avoidance facilitating action of nicotine, but prevented the slight improving action of physostigmine. The results confirm that calcium channel blockers can interfere with the effects of centrally acting drugs and may augment the facilitation of learning induced by some of them. However, a comparison of the effects of nifedipine with those of the noncalcium antagonist vasodilator hydralazine suggests that hypotensive action of calcium channel blockers may interfere with the behavioral action related to specific neuronal changes due to calcium channel blockade. This may be particularly important in cases in which hypotensive action is exerted by the agent used in combination with the calcium channel blocker.

Attenuation of cholinergic analgesia by nifedipine

Nociception was tested in mice receiving oxotremorine or physostigmine either after the dihydropyridine calcium channel blocker nifedipine or the non-calcium antagonist vasodilator hydralazine. Nifedipine did not change the reaction time to thermal stimulation (tail-flick test), but attenuated the prolonging action on tail-flick latencies exerted by the two cholinomimetic agents. Hydralazine had no effect alone nor modified the action of cholinomimetics. The results suggest that attenuation of cholinergic analgesia by nifedipine might be related to not yet defined neuronal changes produced by calcium channel blockade, but changes in the pharmacokinetics of oxotremorine and physostigmine cannot be ruled out.

Effects of oxiracetam, physostigmine, and their combination on active and passive avoidance learning in mice

The nootropic drug oxiracetam (50 and 100 mg/kg) had no effect on one-trial passive avoidance acquisition in CD-1 mice, while the acetylcholinesterase inhibitor physostigmine improved passive avoidance performance at doses of 0.025 and 0.05 mg/kg given either pre- or posttraining. In a multitrial avoidance task (shuttle-box), a consistent tendency to better performance was displayed by mice receiving oxiracetam (50 and 100 mg/kg) or physostigmine (0.01 and 0.025 mg/kg, but not 0.05 mg/kg). Combinations of the two drugs never improved active or passive avoidance performance more than drugs given separately. This indicates no advantage in combining nootropics and anticholinesterase inhibitors to improve learning and memory.

Facilitation of shuttle-box avoidance behaviour in mice treated with nifedipine in combination with amphetamine

The dihydropyridine calcium channel antagonist nifedipine, tested in mice of CD-1, C57BL/6 and DBA/2 strains, at doses of 2.5, 5 and 10 mg/kg IP, had no significant effect on shuttle-box avoidance acquisition. Nifedipine also failed to affect performance retention in CD-1 mice subjected to a one-trial passive avoidance task (step-through). While ineffective alone, nifedipine strongly enhanced the shuttle-box avoidance facilitating action of amphetamine (1 and 2 mg/kg IP) in low performing CD-1 mice. The results indicate that although calcium channel blockers do not affect learning in avoidance paradigms in normal animals, they can interfere with the effects of other centrally acting drugs. Calcium antagonists might interfere with neuronal changes induced by amphetamine, but at present it is difficult to explain the strong avoidance facilitation produced by combinations of nifedipine and amphetamine. A possibility that the action of nifedipine on cerebral circulation is involved in the amphetamine-nifedipine interaction cannot be excluded.

Oxiracetam prevents haloperidol-induced passive avoidance impairment in mice

The nootropic drug oxiracetam (50 mg/kg) prevented passive avoidance impairment induced by posttraining administration of haloperidol (0.25 and 0.5 mg/kg). Conversely, oxiracetam did not antagonize either locomotor depression or suppression of active avoidance responses induced by the dopamine receptor blocking agent. The results indicate that prevention of haloperidol-induced retention impairment, by oxiracetam, may be due to a not yet defined protective action, common to other nootropic agents, on different types of experimental amnesias, rather than to a specific interaction with dopaminergic mechanisms.

Neuropeptide Y-like immunoreactivity in the dogfish gastroenteropancreatic tract: light and electron microscopical study

The 36 amino acid neuropeptide Y (NPY) has been examined in mammals and is mainly located in the nerves. Its distribution in nonmammalian vertebrate and in some invertebrate nervous systems has been confirmed. Using antisera raised to porcine NPY, NPY immunoreactivity has been localized in endocrine cells of the pancreas and gastrointestinal tract of two dogfish, Scyliorhinus stellaris and Scyliorhinus canicula. Immunostained serial sections and cross-absorption experiments with related peptides, including avian and bovine pancreatic polypeptide and peptide tyrosine tyrosine, excluded any cross-reactivity. The fine structure of the cells containing NPY-like substance is described.

Enhancement by oxiracetam of passive avoidance improvement induced by the presynaptic muscarinic antagonist secoverine in mice

Post-trial administration of secoverine (0.5, 1 and 2.5 mg/kg), a presynaptic muscarinic blocker, improved retention in mice tested in a passive avoidance task. The nootropic drug oxiracetam (50 mg/kg), given before both acquisition and retention trial, had no effect alone, but significantly enhanced secoverine improving effects. Performance improvements were also found in combining ineffective doses of the two compounds. Even if not necessarily through a direct and specific action, oxiracetam might activate cholinergic function. Thus, performance improvements resulting from the combination of oxiracetam and secoverine may be due to a simultaneous activation of different cholinergic mechanisms.

A copper-thiolate polynuclear cluster in the ACE1 transcription factor

ACE1 is the transcriptional activator of the metallothionein (CUP1 locus) gene in Saccharomyces cerevisiae. Previous data had implicated the N-terminal domain of ACE1 as responsible for the Cu-dependent specific DNA binding. An expression system in Escherichia coli was constructed to enable the isolation of an ACE1 domain containing the DNA and Cu-binding regions. Here we report the purification and characterization of the Cu-ACE1 truncated molecule. Spectroscopic techniques showed that ACE1 contains an unusual type of DNA binding structure that is based on a polynuclear Cu(I)-cysteinyl thiolate cluster. The cluster consists of six or seven Cu(I) ions coordinated to cysteinyl thiolates in a trigonal geometry distorted from planarity. The Cu(I)-cysteine cluster of Cu-ACE1 exhibits structural properties analogous to the Cu(I)-thiolate polynuclear cluster in yeast Cu-metallothionein itself, suggesting an unusual mechanism for the evolution of this regulatory factor. The Cu cluster organizes and stabilizes the conformation of the N-terminal domain of ACE1 for specific DNA binding.

Effects of oxiracetam-nicotine combinations on active and passive avoidance learning in mice

Tested alone, in CD-1 mice, the nootropic drug oxiracetam (50 mg/kg) improved learning in a multitrial active avoidance task (shuttle-box), but did not affect one-trial passive avoidance acquisition. Nicotine, which was ineffective at the dose of 0.25 mg/kg, improved both active and passive avoidance at the dose of 0.5 mg/kg; 1 mg/kg nicotine still exerted facilitating effects on passive avoidance, but slightly depressed shuttle-box performance. Combinations of oxiracetam and nicotine improved passive avoidance more than either drug given separately. In the active avoidance task, a combination of oxiracetam with the lower dose of nicotine exerted improving effects never observed with nicotine alone, even at higher doses. The nootropic drug also prevented the slight depressant action exerted by 1 mg/kg nicotine. Thus, contrary to what was previously supposed, at least in mice subjected to shuttle-box avoidance training, nicotinic activation does not appear as the main neurochemical mechanism involved in the action of oxiracetam. Perhaps, oxiracetam and nicotine activate different types of cholinergic mechanisms, but it cannot be excluded that other neurotransmitters, particularly catecholamines, may be involved in the avoidance facilitating effects produced by nicotine and by combinations of the two drugs.

Avoidance learning during antidepressant withdrawal in mice

Shuttle-box avoidance acquisition, locomotor activity and density of adrenoreceptors in the cerebral cortex have been evaluated, in CD-1 mice, during withdrawal from repeated treatment with desipramine or mianserin (5 or 14 daily injections of antidepressant drug, 10 mg kg-1). Withdrawal from mianserin did not produce any behavioural or neurochemical change. Mice withdrawn from desipramine exhibited avoidance facilitation, when training started 24 h (but not 72 or 120 h) after the last injection. Locomotor activity was not affected and no change was found in the density of beta-adrenoreceptors. An up-regulation of alpha 2- and, to a lesser extent, of alpha 1-adrenoreceptors, occurred 72 h following desipramine withdrawal. However, the assessment of the role played by these neurochemical changes in the avoidance facilitation observed during withdrawal from the antidepressant treatment requires further study.

Shuttle-box avoidance facilitation by minaprine in mice

The effects on shuttle-box avoidance acquisition of the new antidepressant minaprine (1, 2.5, 5 or 10 mg/kg) and of the classical antidepressant desipramine (0.5, 1, 2.5 or 5 mg/kg) were tested, without pretreatment or after a 5 day pretreatment, in mice of the CD-1 strain, subjected to five daily 100-trial training sessions. Minaprine, recently proposed as a new nootropic agent, facilitated avoidance performance when given to pretreated animals at a dose of 10 mg/kg, which had no effect on spontaneous locomotor activity. Desipramine did not exert any significant effect on avoidance responses. The results are in agreement with previous findings showing learning improvements by minaprine, but do not clarify the mechanism involved in the avoidance facilitation.

Oxiracetam prevents mecamylamine-induced impairment of active, but not passive, avoidance learning in mice

The nicotinic antagonist mecamylamine (2.5 and 5 mg/kg/IP) depressed both active (shuttle-box) and passive (step-through) avoidance learning in mice of the DBA/2 strain. The nootropic drug oxiracetam (50 and 100 mg/kg/IP) improved acquisition in the multitrial active avoidance test, but had no effect on one-trial passive avoidance learning. When the two drugs were combined, oxiracetam did not counteract mecamylamine-induced impairment of passive avoidance learning, even if it maintained a facilitating action on shuttle-box avoidance acquisition in mice receiving the nicotinic receptor blocker. Prevention of mecamylamine-induced shuttle-box avoidance depression by oxiracetam indicates that central nicotinic mechanisms are probably involved in the improving effects exerted by nootropic drugs on learning.

Suppression of pentobarbitone-induced hyperactivity by past experience in mice

Locomotor activity of CD-1 mice, tested in an unfamiliar environment (toggle-floor box), was increased either by a subhypnotic dose (20 mg kg-1) of pentobarbitone or after recovery from pentobarbitone-induced (50 mg kg-1) anaesthesia. On the contrary, when mice were tested 6 h after a single exposure to the apparatus, pentobarbitone in either case failed to produce hyperactivity. The results demonstrate that mice recovering from barbiturate anaesthesia maintain susceptibility to the exteroceptive stimuli provided by a novel environment and knowledge of the environment acquired during past experience.

Pentobarbital-induced hyperactivity in mice: negligible role of opioid mechanisms

Subhypnotic doses (10 and 20 mg/kg) of pentobarbital significantly elevated locomotor activity measured for 30 min in CD-1 mice. The hyperactivity was also observed in mice recovering from pentobarbital-induced (50 mg/kg) sleep (measurements starting 15 min after recovery of righting reflex). Naloxone in doses up to 4 mg/kg did not affect significantly the pentobarbital-induced hyperactivity in any experiment; a dose of 8 mg/kg only partially attenuated the hyperactivity induced by a dose of 20 mg/kg of pentobarbital, but did not affect significantly either the stimulatory effect of a low subhypnotic dose (10 mg/kg) or the posthypnotic hyperactivity. This suggests a negligible involvement of opioid mechanisms in the hyperactivity induced by pentobarbital.

Avoidance facilitation by nootropics

1. The effects on avoidance acquisition of two nootropic drugs, oxiracetam and piracetam, were tested in mice subjected to five daily 100-trial training sessions in the shuttle-box. 2. Oxiracetam (25 or 50 mg/kg/i.p.) and piracetam (100 mg/kg/i.p.), given before each daily session, improved avoidance acquisition in the good performing BALB/c more than in the poor performing C57BL/6. In both cases avoidance facilitation was evident only if training was preceded by a five-day pretreatment. 3. Combinations of nootropics and methamphetamine increased avoidance responses in C57BL/6 mice more than drugs given separately. Conversely, no interaction occurred in a locomotor activity test. 4. Interactive effects in the learning situation, but not in a test of general activity, were also found when oxiracetam was combined with the anticholinergic agent scopolamine. 5. On the whole, the above results demonstrate facilitation of active avoidance acquisition by piracetam-like nootropic agents, but the neurochemical mechanisms involved in this action are not yet clear.

Effect of naloxone on the locomotor stimulatory action of chlordiazepoxide in mice

Locomotor activity was measured, during 60 min, in CD-1 mice receiving chlordiazepoxide (2.5 or 5 mg/kg) after a pretreatment with saline solution or naloxone (0.5, 1, 2.5 or 5 mg/kg). Both doses of chlordiazepoxide significantly increased locomotor activity in saline-pretreated mice. Naloxone prevented chlordiazepoxide-induced hyperactivity, at doses that did not themselves affect activity. This antagonistic action of naloxone indicates that opioid mechanisms are involved in the locomotor stimulatory effects exerted by chlordiazepoxide in mice.

Antihistaminic-opioid combination: effect on locomotor activity in mice

Various laboratory studies have been recently prompted by reports indicating abuse by heroin addicts of the narcotic agonist-antagonist pentazocine combined with the antihistaminic tripelennamine. For what concerns the effects on locomotor activity, it was demonstrated that three histamine H1 receptor antagonists, chlorpheniramine, diphenhydramine and tripelennamine enhance morphine-, but not amphetamine and scopolamine-induced hyperactivity in mice. These results suggested that antihistaminics may specifically interfere with locomotor effects of opioids. Such hypothesis was strengthened by further findings indicating enhancement by tripelennamine of the locomotor stimulation induced by buprenorphine, a drug possessing morphine-like properties.

Effects of oxiracetam-scopolamine combinations on shuttle-box avoidance acquisition in mice

The nootropic drug oxiracetam and the anticholinergic agent scopolamine were tested, alone or in combination, on shuttle-box avoidance acquisition and locomotor activity in mice of the CD-1 strain. Both drugs, given separately, slightly but significantly enhanced avoidance performance, but only scopolamine increased locomotor activity. Combinations of the 2 drugs, in some instances, enhanced avoidance performance more than drugs given separately, but the disinhibitory property of scopolamine makes it difficult to understand the role played by cholinergic mechanisms in these effects.