Comparative neurophysiological study of the nootropic drugs piracetam and centrophenoxine

Effects of nootropic drugs on transcallosal evoked potential (TEP) and EEG spectra of the animal brain cortex and hippocamp were studied. It was found that piracetam and centrophenoxine exert similar effects on the amplitude of the primary TEP components, produce its increase and also a rise and stabilization of the predominant peak in distribution of EEG power spectrum that corresponds to the improvement of theta rhythm organization. The drugs exert different effects on the secondary positive TEP component; centrophenoxine induces a change in non-basic rhythm of EEG in rats. Based on the results obtained, the authors consider possible neurophysiological mechanisms of the nootropic effect and make a comparative analysis of the actions of the drugs.     

Biogenic monoamine uptake by rat brain synaptosomes during aging. Effects of nootropic drugs

1. In experiments on young (3–5-month-old), adult (10–11-month-old) and old (21–22-month-old) rats, it was found that significant age-related changes occurred in the high-affinity uptake of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) by cortical and striatal synaptosomes.2. Changes in DA, NA and 5-HT uptake during aging are suggested to be neurochemical correlates of cognition and memory deficits that develops in senescence.3. The in vitro effects of the nootropic drugs piracetam, aniracetam, meclofenoxate and adafenoxate on the DA, NA and 5-HT uptake by cortical and striatal synaptosomes from young rats were studied. Administered in increasing concentrations (1 × 10⁻⁴ to 5 × 10⁻³ M) these drugs inhibited monoamine uptake.4. Adafenoxate proved to be a more potent monoamine uptake inhibitor than the other three drugs; it inhibited the uptake in the frontal cortex and striatum without selectivity for either monoaminergic system. It is suggested that adafenoxate affects cognition through the involvement of central neurotransmission and particularly through the inhibition of monoamine uptake systems.     

Dissociation of the anti-amnesic and antihypoxic effects of nootropic and antihypoxic preparations

In experimental studies on mice it was shown that piracetam, Cleregil, centrophenoxine, pyritinol possessed the most pronounced anti-amnestic activity. A close effect was noted with Euclidan, 3-hydroxypyridine and ionol. GABAergic agents (sodium oxybutyrate, phenibut, pantogam), gutimine, nicotinoyl-GABA eliminated amnesia to a lesser extent. The antihypoxic effect on the model of hypobaric hypoxia was exerted by typical antihypoxic agents (gutimine, sodium oxybutyrate, 3-hydroxypyridine). The antihypoxic activity of nootropic drugs (centrophenoxine, pyritinol, phenibut) could be determined only at a significant increase of doses. No interrelationship and the presence of dissociation in manifestation of anti-amnestic and antihypoxic effects were revealed.     

Influence of nootropic drugs on the learning- and memory-impairing effect of diethyldithiocarbamate in albino rats

The effects of four nootropic drugs (piracetam, aniracetam, meclofenoxate and fipexide) on the impaired cognitive functions by the dopamine-beta-hydroxylase inhibitor diethyldithiocarbamate (DDC) were investigated in albino rats. The changes in learning and memory were studied by the two-way active avoidance with punishment reinforcement (shuttle box). DDC injected intraperitoneally at a dose of 300 mg/kg in the course of the 5-day shuttle box training significantly impaired learning and retention. The 10-day treatment (5 days before and 5 days during training) with piracetam 600 mg/kg, aniracetam 50 mg/kg, meclofenoxate 100 mg/kg and fipexide 10 mg/kg completely abolished the learning- and memory-impairing effect of DDC. The role of the NA-ergic neurotransmitter system for the DDC-induced disturbances in cognition as well as for the protective effects of nootropic drugs was discussed.     

Influence of nootropic drugs on the memory-impairing effect of clonidine in albino rats

The effects of four nootropic drugs (piracetam, aniracetam, meclofenoxate and fipexide) on cognitive functions impaired by the antihypertensive drug clonidine were investigated in albino rats. The changes in learning and memory were studied by two-way active avoidance with punishment reinforcement (shuttle box). Clonidine injected intraperitoneally at a dose of 0.1 mg/kg immediately after a one-day shuttle box training significantly impaired retention. A 5-day treatment before the training session with piracetam 600 mg/kg, aniracetam 50 mg/kg, meclofenoxate 100 mg/kg and fipexide 10 mg/kg completely abolished the memory-impairing effect of clonidine. The role of the NAergic neurotransmitter system in the clonidine-induced disturbances of cognition, as well as in the protective effects of nootropic drugs, was discussed.     

Protection of cell proteins against free-radical attack by nootropic drugs: scavenger effect of pyritinol confirmed by electron spin resonance spectroscopy

The potency of nootropic drugs to protect cell proteins and lipids against free radical attack was studied. In an in vitro system, generating hydroxyl radicals by a Fenton-type reaction, the soluble proteins (bovine serum albumin and cytosol protein from brain) were quickly insolubilized and precipitated. Pyritinol (and tamitinol) exhibited the best protection against insolubilization of protein while centrophenoxine (meclophenoxate) and its dimethylaminoethanol moiety were less effective, piracetam (and oxiracetam) being without effect. The lipid peroxidation induced by free radicals from cyclic redox reactions of iron-ascorbate was not influenced by pyritinol, indicating the selectivity of its scavenger action. The efficient scavenging of hydroxyl radicals by pyritinol was confirmed by electron spin resonance spectroscopy measurement of hydroxyl radicals entrapped by spin trap. Millimolar concentrations of pyritinol competitively decreased the formation of spin adducts. The results suggest that the protective effect of pyritinol against free-radical induced derangement of cell proteins may be an important part of its antirheumatic, as well as nootropic, action.     

Enhanced amphetamine-mediated dopamine release develops in PC12 cells after repeated amphetamine treatment

The present study tests the activity of nootropic drugs in a behavioral test linked to depression. This test measures the reduction of submissive behavior in a competition test as the relative success of two food-restricted rats to gain access to a feeder. Nootropic drugs tested include piracetam (2-oxo-1-pyrrolidineacetamide), aniracetam (1-(4-methoxybenzoyl)-2-pyrrolidinone), the Ampakine, Ampalex, 1-(quinoxalin-6-ylcarbonyl)piperidine, and analogs were compared to the antidepressants, fluoxetine ((+/-)-N-methyl-gamma-(4-[trifluoromethyl]phenoxy)-benzenepropanamine) and desimpramine (5H-dibenz[b,f]azepine-5-propanamine, 10,11-dihydro-N-methyl-, monohydrochloride), while the anxiolytic diazepam (7-chloro-1-methyl-5-phenyl-3H-1,4-benzodiazepin-2(1H)-one) served as a control. Drugs were given intraperitoneally for 3 weeks. The antidepressant and nootropic drugs reduced submissive behavior over time. The effect was dose dependent as measured for fluoxetine and Ampakines. The reduction of submissive behavior by Ampakines gradually faded after cessation of treatment and had a more rapid onset of activity (during the 1st week of treatment) than fluoxetine (after 2 weeks). The results suggest that Ampakines may have antidepressant activity. The potential of depression treatment with memory-enhancing drugs is hypothesized and the link between cognition and depression is discussed.     

DM235 (sunifiram): a novel nootropic with potential as a cognitive enhancer

DM235 (sunifiram), a new compound structurally related to piracetam, prevented the amnesia induced by scopolamine (1.5 mg kg(-1) i.p.), after intraperitoneal (0.001-0.1 mg kg(-1)) or oral (0.01-0.1 mg kg(-1)) administration, as shown by a passive avoidance test in mice. The antiamnesic effect of DM235 was comparable to that of well-known nootropic drugs such as piracetam (30-100 mg kg(-1) i.p.), aniracetam (100 mg kg(-1) p.o.) or rolipram (30 mg kg(-1) p.o.). DM235 also prevented mecamylamine (20 mg kg(-1) i.p.)-, baclofen (2 mg kg(-1) i.p.)- and clonidine (0.125 mg kg(-1) i.p.)-induced amnesia in the same test. In the Morris water maze test with rats, scopolamine (0.8 mg kg(-1) i.p.) inhibited the reduction of escape latency in both acquisition and retention/retraining tests. DM235 (0.1 mg kg(-1) i.p.), 20 min before each daily acquisition training, prevented the scopolamine-induced memory impairment. DM235 (1 mg kg(-1) i.p.) also reduced the duration of pentobarbitone-induced hypnosis in mice without modifying the induction time of hypnosis. At the highest effective doses, the investigated compound neither impaired motor coordination (rota-rod test), nor modified spontaneous motility and inspection activity (Animex and hole board tests).These results indicate that DM235, a compound structurally related to piracetam, is a novel nootropic endowed with the capability to prevent cognitive deficits at very low doses. Indeed, its potency is about 1,000 times higher than that of the most active piracetam-like compounds.     

The neurochemical and behavioral effects of the novel cholinesterase-monoamine oxidase inhibitor, ladostigil, in response to L-dopa and L-tryptophan, in rats

The novel drugs, ladostigil (TV3326) and TV3279, are R and S isomers, respectively, derived from a combination of the carbamate cholinesterase (ChE) inhibitor, rivastigmine, and the pharmacophore of the monoamine oxidase (MAO) B inhibitor, rasagiline. They were developed for the treatment of comorbidity of dementia with Parkinsonism. In the present study, we determined the effects of these drugs on both aminergic neurotransmitter levels and motor behavioral activity in na?ve and in L-dopa- or L-tryptophan-induced rats. Chronic treatment of rats with ladostigil (52 mg kg(-1) for 21 days) inhibited hippocampal and striatal MAO A and B activities by >90%, increased striatal levels of dopamine and serotonin, and inhibited striatal ChE activity by approximately 50%. Chronic TV3279 (26 mg kg(-1) for 21 days) similarly inhibited approximately 50% of striatal ChE activity, but did not affect MAO activity or amine levels. In sharp contrast to the inductive effect of the MAO A/B inhibitor, tranylcypromine (TCP), on stereotyped hyperactivity in response to L-dopa (50 mg kg(-1)) or L-tryptophan (100 mg kg(-1)), ladostigil completely inhibited these behavioral hyperactivity syndromes. Accordingly, acute rivastigmine (2 mg kg(-1)) and chronic TV3279 abolished the ability of TCP to initiate L-dopa-induced hyperactivity, while scopolamine (0.5 mg kg(-1)) reversed the inhibitory effect of chronic ladostigil on L-dopa-induced hyperactivity, suggesting that ladostigil may attenuate successive locomotion by activating central cholinergic muscarinic receptors.Finally, while chronic ladostigil administration to na?ve rats resulted in preserved spontaneous motor behavior, acute treatment with ladostigil decreased motor performance, compared to control animals. In contrast, chronic as well as acute treatments with TV3279 reduced spontaneous motor activity. Thus, the aminergic potentiation by ladostigil may counteract its cholinergic inhibitory effect on spontaneous motor behavior. Our results suggest that potentiation of both aminergic and cholinergic transmission systems by ladostigil contributes equally to motor behavior performance, which is substantially impaired in comorbidity of dementia with Parkinsonism including dementia with Lewy bodies (DLB).     

Piracetam and TRH analogues antagonise inhibition by barbiturates, diazepam, melatonin and galanin of human erythrocyte D-glucose transport

1 Nootropic drugs increase glucose uptake into anaesthetised brain and into Alzheimer's diseased brain. Thyrotropin-releasing hormone, TRH, which has a chemical structure similar to nootropics increases cerebellar uptake of glucose in murine rolling ataxia. This paper shows that nootropic drugs like piracetam (2-oxo 1 pyrrolidine acetamide) and levetiracetam and neuropeptides like TRH antagonise the inhibition of glucose transport by barbiturates, diazepam, melatonin and endogenous neuropeptide galanin in human erythrocytes in vitro. 2 The potencies of nootropic drugs in opposing scopolamine-induced memory loss correlate with their potencies in antagonising pentobarbital inhibition of erythrocyte glucose transport in vitro (P<0.01). Less potent nootropics, D-levetiracetam and D-pyroglutamate, have higher antagonist Ki's against pentobarbital inhibition of glucose transport than more potent L-stereoisomers (P<0.001). 3 Piracetam and TRH have no direct effects on net glucose transport, but competitively antagonise hypnotic drug inhibition of glucose transport. Other nootropics, like aniracetam and levetiracetam, while antagonising pentobarbital action, also inhibit glucose transport. Analeptics like bemigride and methamphetamine are more potent inhibitors of glucose transport than antagonists of hypnotic action on glucose transport. 4 There are similarities between amino-acid sequences in human glucose transport protein isoform 1 (GLUT1) and the benzodiazepine-binding domains of GABAA (gamma amino butyric acid) receptor subunits. Mapped on a 3D template of GLUT1, these homologies suggest that the site of diazepam and piracetam interaction is a pocket outside the central hydrophilic pore region. 5 Nootropic pyrrolidone antagonism of hypnotic drug inhibition of glucose transport in vitro may be an analogue of TRH antagonism of galanin-induced narcosis.     

Can nootropic drugs be effective against the impact of ethanol teratogenicity on cognitive performance?

Rats exposed pre- (PA) and postnatally (PNA) to ethanol at a dose of 1 g/kg for 24 h developed fetal alcohol effects (FAE). This was measured using a condition-reflex method for active avoidance with punishment reinforcement (shuttle-box) in which pronounced learning and memory deficits in 3-month-old rats were found after ethanol exposure (Vaglenova and Petkov, 1998. Fetal alcohol effects in rats exposed pre- and postnatally to a low dose of ethanol. Alcohol. Clin. Exp. Res. 22(3), 697--703). In the present study the effects of piracetam (Pyramem) at a dose of 600 mg/kg body weight, aniracetam at 50 mg/kg, and meclophenoxate (Centrophenoxine) at 100 mg/kg were studied. The drugs were administered orally during 10 days to separate groups of naive and pre- and postnatally exposed to ethanol rats. All the investigated nootropic drugs showed a significant possibility to alleviate learning and memory disability of rats with FAE. Aniracetam was administered to 1-month-old rats, demonstrating a prolonged (2 months) therapeutic effect, observed in rats aged 3 months. As previously reported (Vaglenova and Petkov, 1998), between male rats with FAE and controls, 66 and 33% were 'poor learners', respectively. In all nootropic treatment groups the percentage of 'poor learners' dropped to 28%. The positive effects of piracetam, aniracetam and meclophenoxate suggest that these drugs could be used for both treatment and prophylactic of FAE-connected disturbances of cognition.     

Design of the novel dipeptide neuropsychotropic drug preparations

The paper considers a new strategy in the field of neuropsychotropic dipeptide drug design, the main points being as follows: (i) determination of the structural elements of dipeptides, such as fragments of amino acid side radicals and peptide bonds, in nonpeptide drugs; (ii) design of peptide analogs topologically close to the drug; (iii) synthesis and activity testing of these analogs; (iv) determination of the corresponding endogenous neuropeptide among the known neuropeptides or identification of the new neuropeptides in the brain of experimental animals. Using this approach, new pyroglutamyl- and prolyl-containing dipeptides were obtained based on the structure of the well-known classical nootropic drug piracetam. The new drugs exhibit nootropic activity in doses 100-10,000 times lower than those of piracetam. The structure of most active pyroglutamyl dipeptide pGlu-Asn-NH2 coincides with that of the N-end fragment of the endogenous memory peptide AVP(4-9). Noopept (N-phenylacetylprolylglycine ethyl ester), patented in Russia and USA as a new nootropic drug, is currently under stage 2 of successful clinical trials. The main metabolite of noopept, cyclo-Pro-Gly, is identical to the endogenous dipeptide designed in this work and is most close analog of piracetam with respect to pharmacological activity. The universal character of the proposed strategy is demonstrated by the design of active dipeptide analogs of an atypical neuroleptic drug sulpiride. As a result, a potential dipeptide neuroleptic dilept was obtained, which has been patented in Russia and now passes broad preclinical trials.     

Radioelectroencephalographic characterization of tenilsetam (CAS 997), a putative nootropic compound,in the freely behaving rat

Recording, telemetric trandmission, and spectral analysis of field potentials from frontal cortex, hippocampus, striatum, and reticular formation of the rat brain were used to monitor the effect of tenilsetam (CAS 997) and piracetam on the central nervous in delta and alpha₂ power in all brai areas. Dose-dependent decreases in alpha₁ power were seen in the frontal cortex, striatum, and reticular formation, whereas the hippocampal alpha₁ activity increased (100 mg/kg) or remained unaffected. These effects were dose-dependent and lasted for at least 90 min. In the presence of piracetam, changes in brain electrical activity were dominated by an overall decrease in alpha₁ activity and by less pronounced effects on beta₁ activity. The spectral pattern profile induced by tenilsetam was compared to the “fingerprints” of a great number of different drugs from our data base. Some similarities to the action of fluvoxamine and SK&F 38393 point to changes in serotonergic and dopaminergic transmission. The present data show the functional outcome of interactions with different aspects of neurotranmission and suggest that the “nootropic” drug tenilsetam enhances vigilance by shifting the balance of neurotransmission to a status resembling low serotonergic and, at the same time, high dopaminergic activity. These drugs obviously not only improve brain function under pathological conditions but can also affects electrical activity of the intact brain.     

The nootropic concept and its prospective implications

Giurgea, C.E. : The nootropic concept and its prospective implications. Drug. Dev. Res. 2:441–446, 1982. The nootropic concept emerged about 10 years ago essentially from the unusual pharmacology of piracetam, which later on was confirmed and extended to human pharmacoclinics and therapeutics. A nootropic drug is characterized by a direct functional activation of the higher integrative brain mechanisms that enhances cortical vigilance, a telencephalic functional selectivity, and a particular efficiency in restoring deficient higher nervous activity. In contradistinction to other psychotropic drugs, nootropics do not induce direct reticular, limbic, or other subcortical events. Little is known with regard to nootropic, neurochemical mechanisms of action except that they interact with factors that contribute to the neuronal membrane stability, and possibly with the brain 5-HT. Main therapeutical indications seem to be in children with speech disorders, in the posttraumatic, and posthypoxic sequelae, in vertigo of central origin, and in geriatric, moderately impaired, possibly dysmnesic patients. Other drugs, such as pyritinol, meclofenoxate, and, to some extent, hydergine and vincamine, do show partially nootropic activities. The nootropic line of research is by now multifaceted to deepen the neurochemical and neurophysiologic comprehension of nootropics' mode of action; to make clearer their clinical differential profile; to enlarge the nootropic framework to some other existing drugs, clinically if not pharmacologically related to piracetam; and to find new, more potent, and possibly more selective nootropic agents. The general aim of nootropic research is to find new drugs capable of enhancing directly the efficiency of the cognitive, noetic activity of the brain, thus compensating various neuro-psychologic deficits such as, but not exclusively, those related to aging.     

Different in vivo properties of three new inhibitors of catechol O-methyltransferase in the rat.

1. We compared three new catechol O-methyltransferase (COMT) inhibitors (OR-611, Ro 40-7592 and CGP 28014; 10 and 30 mg kg-1, i.p.) in male rats given levodopa (L-DOPA, 50 mg kg-1, i.p.) and carbidopa ((-)-L-alpha-methyl dopa, 50 mg kg-1, i.p.). In some studies pretreatment with pargyline (80 mg kg-1, i.p.) was used to block the function of monoamine oxidase (MAO). 2. Decreases of hypothalamic and striatal 3-O-methyl-dopa (3-OMD) levels were used as measures of the inhibition of peripheral COMT. The inhibition of brain COMT activity was estimated by decreases of hypothalamic and striatal homovanillic acid (HVA) and 3-methoxytyramine (3-MT; after pargyline) levels. 3. The three COMT inhibitors studied had different individual characteristics. OR-611 was primarily a peripherally acting COMT inhibitor, decreasing 3-OMD levels in the striatum (to 31-52%) and in the hypothalamus (to 16-27%) both in the control and pargyline-treated animals at 1 and 3 h. It did not have any effect on brain HVA and 3-MT. 3. Ro 40-7592 was a broad spectrum COMT inhibitor decreasing striatal and hypothalamic 3-OMD (always to less than 30%), HVA (to less than 50%) and 3-MT levels (to less than 23%) significantly both at 1 and 3 h. It was more potent than OR-611. 4. CGP 28014 functioned as a weak COMT inhibitor in the periphery inhibiting 3-OMD formation only at 3 h. In contrast, it was fairly potent in decreasing the brain HVA and 3-MT levels at 1 h (to 37-22% and 42-35% in the striatum, and to 57-33% and 64-35% in the hypothalamus, respectively) but not at 3 h. Since CGP 28014, unlike OR-611 and Ro 40-7592, did not generally increase the brain DOPA, dopamine or DOPAC levels, it was not a typical COMT inhibitor.     

Novel aspects of dopamine oxidative metabolism (confounding outcomes take place of certainties)

Abstract: Understanding dopamine (DA) oxidative metabolism allows to get a deeper insight into neurologic and psychiatric disorders featured by an altered DA neurotransmission as well as developing appropriate therapeutic strategies. Oxidative DA deamination is carried out by two highly conserved isoenzymes: monoamine oxidase (MAO) A and B; these isoenzymes both metabolize DA to dihydroxyphenylacetaldehyde (DOPALD), which, in turn, is converted to dihydroxyphenylacetic acid (DOPAC). In the past twenty years most studies on MAO activity were performed using brain dialysis in freely moving rats and measuring DA and DOPAC levels after administration of specific MAO inhibitors. This led to concepts on DA metabolism grounded on a single brain area (striatum) investigated, almost exclusively, in a single animal species (rat). These experiments were based on measurement of striatal levels of DOPAC which represents the indirect product of MAO activity. At present, the specific role of each MAO isoform appears to differ significantly depending on varying experimental conditions such as measuring the direct product of DA metabolism. In particular, recent studies allowed the estimate of the first metabolite (DOPALD) formed by MAO, showing that DOPAC levels do not necessarily reflect MAO activity. Again, the relative contribution of the two MAO iso forms in sustaining DA metabolism varies considerably, depending on the animal species and the specific brain area (either striatum or substantia nigra) under investigation. In this article we will briefly review these concepts in light of new evidence derived from innovative approaches: improved in vivo analysis of direct MAO metabolic products; measurement of oxidative metabolism in different parts of the DA nigrostriatal pathway; measurement of MAO activity in various animal species including MAO knock-out mice.     

Novel Aspects of Dopamine Oxidative Metabolism (Confounding Outcomes Take Place of Certainties

Abstract: Understanding dopamine (DA) oxidative metabolism allows to get a deeper insight into neurologic and psychiatric disorders featured by an altered DA neurotransmission as well as developing appropriate therapeutic strategies. Oxidative DA deamination is carried out by two highly conserved isoenzymes: monoamine oxidase (MAO) A and B; these isoenzymes both metabolize DA to dihydroxyphenylacetaldehyde (DOPALD), which, in turn, is converted to dihydroxyphenylacetic acid (DOPAC). In the past twenty years most studies on MAO activity were performed using brain dialysis in freely moving rats and measuring DA and DOPAC levels after administration of specific MAO inhibitors. This led to concepts on DA metabolism grounded on a single brain area (striatum) investigated, almost exclusively, in a single animal species (rat). These experiments were based on measurement of striatal levels of DOPAC which represents the indirect product of MAO activity. At present, the specific role of each MAO isoform appears to differ significantly depending on varying experimental conditions such as measuring the direct product of DA metabolism. In particular, recent studies allowed the estimate of the first metabolite (DOPALD) formed by MAO, showing that DOPAC levels do not necessarily reflect MAO activity. Again, the relative contribution of the two MAO iso forms in sustaining DA metabolism varies considerably, depending on the animal species and the specific brain area (either striatum or substantia nigra) under investigation. In this article we will briefly review these concepts in light of new evidence derived from innovative approaches: improved in vivo analysis of direct MAO metabolic products; measurement of oxidative metabolism in different parts of the DA nigrostriatal pathway; measurement of MAO activity in various animal species including MAO knock‐out mice.     

Inhibition of rodent brain monoamine oxidase and tyrosine hydroxylase by endogenous compounds - 1,2,3,4-tetrahydro-isoquinoline alkaloids

Four different noncatecholic and one catecholic tetrahydroisoquinolines (TIQs), cyclic condensation derivatives of beta-phenylethylamine and dopamine with aldehydes or keto acids, were examined for the inhibition of rat and mouse brain monoamine oxidase (MAO) and rat striatum tyrosine hydroxylase (TH) activity. Simple noncatecholic TIQs were found to act as moderate (TIQ, N-methyl-TIQ, 1-methyl-TIQ) or weak (1-benzyl-TIQ), MAO B and MAO A inhibitors. 1-Methyl-TIQ inhibited more potently MAO-A than MAO-B; the similar but more modest effect was exerted by salsolinol. Only salsolinol markedly inhibited TH activity, being competitive with the enzyme biopterin cofactor. The inhibition of MAO and TH by TIQs is discussed in relation to their ability to regulate monoamine metabolism.     

In vivo monoamine oxidase inhibition by d-amphetamine

In vitro, d- and l-amphetamine (AMPH) are reversible monoamine oxidase (MAO) type A inhibitors, the d-form being approximately five times more potent. Experiments were conducted in rats to determine whether MAO inhibition occurs in vivo. d-AMPH was more effective than l-AMPH at decreasing striatal 3,4-dihydroxyphenylacetic acid (DOPAC). However, assays of striatal MAO activity following administration of AMPH in vivo failed to show MAO inhibition. In other experiments, rats were treated with d-AMPH (zero time) followed by phcnelzine (1 hr), an irreversible MAO inhibitor, and were killed at 25 hr. MAO activity was determined in vitro for the striatum and the rest of the brain using serotonin (MAO-A) and phenylethylaminc (MAO-B) as substrates. d-AMPH provided significant protection against MAO-A inhibition by phenelzine, whereas l-AMPH and cocaine (used instead of AMPH) were without effect. d-AMPH failed to protect against MAO-B inhibition by phenelzine. Thus, d-AMPH appears to inhibit reversibly MAO type A in vivo. However, using the same ‘protection protocol’, d-AMPH failed to oppose phenelzine-induced lowering of striatal DOPAC. Experiments were undertaken to determine whether the protective effect of d-AMPH on MAO type A would influence striatal dopamine depletion by RO4-1284, a rapidly acting reserpine-like agent. RO4-1284-induced depletion of dopamine was inhibited by phenelzine. Prior treatment with d-AMPH reduced significantly the protective effect of phenelzine, suggesting reversible, intraneuronal MAO inhibition by d-AMPH in vivo. The possible neuronal mechanisms for these events are discussed.     

A possible intraneuronal site of action of thymoleptics

The uptake of catecholamines (CAs) into crude mitochondria preparations (P₂ fractions) and vesicle preparations from rat hypothalamus and striatum were compared in terms of the inhibition by thymoleptics and other drugs.Thymoleptics preferentially inhibited the uptake of CAs into hypothalamic P₂ fractions, while ATPase inhibitors preferentially inhibited the uptake of dopamine into striatal P₂ fractions. When the preparation obtained from rats pretreated with reserpine was used, the preferential inhibition of hypothalamic uptake by thymoleptics was entirely abolished. When P₂ fractions from both regions were incubated with 10^-6M ¹⁴C-imipramine, the intrasynaptosomal distribution of labeled imipramine revealed its affinity not only to the synaptosomal membrane, but also to the synaptic vesicles. Accumulated ³H-norepinephrine (NE) could be released by a hypoosomotic shock from striatal P₂ fractions, but not from hypothalamic P₂ fractions. The ATP-Mg²⁺-dependent uptake of ³H-NE into the synaptic vesicles from rat brain stem was inhibited by desipramine.These results indicate that the inhibition of CA uptake by thymoleptics in the hypothalamus is predominantly due to the inhibition at the synaptic vesicle, while in the striatum the uptake at the synaptosomal membrane is predominantly inhibited.