Effect of benzquinamide on conditioned avoidance response and brain monoamine levels in the cat

Summary A concomitant decrease of the catecholamine levels of the brain and conditioned avoidance response (CAR) in cats was observed after small doses of benzquinamide. The CAR was restored by d-DOPA and (+)-amphetamine. The possible modes of action of benzquinamide are discussed.     

Evidence that the central action of (+)-amphetamine is mediated via catecholamines

Summary The ability of reserpine (0.1 mg/kg) to disrupt conditioned avoidance response (CAR) in cats could be completely reversed by (+)-amphetamine (2 mg/kg calculated as the bitartrate). However, if the animals received the tyrosine-hydroxylase inhibitor alfa-methyl tyrosine (alfa-MT) (25 or 50 mg/kg) 2 hours before the (+)-amphetamine, the action of the latter drug was blocked. This was true even if the dose of (+)-amphetamine was increased fivefold. The activity of (+)-amphetamine could be restored by subthreshold doses of L-DOPA (5 to 25 mg/kg). The data support the view that (+)-amphetamine for its central action requires the presence of catecholamines in low concentrations. Presumably (+)-amphetamine acts by releasing catecholamines from nerve terminals in the brain.     

Comparison of tyrosine hydroxylase and dopamine-Β-hydroxylase inhibition with the effects of various 6-hydroxydopamine treatments on d-amphetamine induced motor activity

The significance of central noradrenergic and dopaminergic neural systems for the locomotor stimulant effects of d-amphetamine were investigated in rats with depletions of norepinephrine, dopamine, or both catecholamines produced by treatment with either reserpine, L--methyl-tyrosine (-MPT), 6-hydroxydopamine (6-OHDA), or the dopamine--hydroxylase inhibitor 1-phenyl-3-(2-thiazolyl)-2-thiourea (U-14,624). In animals pretreated with reserpine, amphetamine-stimulated locomotor activity was blocked by -MPT but not by U-14,624 when amphetamine was given l h after these catecholamine synthesis inhibitors. In rats with chronic depletions of brain norepinephrine, dopamine, or both catecholamines produced by different 6-OHDA treatments, both amphetamine-stimulated motor activity and stereotyped behavior were antagonized by treatments reducing dopamine or both catecholamines but not in animals in which brain norepinephrine was reduced. Results are consistent with the view that the locomotor stimulation and stereotyped behaviors produced by d-amphetamine are dependent upon functional dopaminergic neural systems in brain.     

Effects of α-methyl-Dopa on conditioned behaviour in the cat

Summary After -methyl-DOPA (-MD) administration to cats a significant decrease of a conditioned avoidance response (CAR) was observed 8 hours later. In reserpine-pretreated cats -MD caused a pronounced reduction of CAR which was not reversed by (+)-amphetamine. A subsequent administration of l-DOPA resulted in a dose-dependent CAR reversal. Different possibilities of the central action exerted by -MD are discussed.     

The disruption of conditioned avoidance response following selective depletion of brain catechol amines

Summary Selective depletion of catechol amines (CA) in brain—with little or no depletion of 5-hydroxytryptamine-was induced by -methyl-tyrosine methylester-HCl. Concomitant disruption of conditioned avoidance responses (CAR) was observed in cats (Shuttle box) and rats (Skinner box). Restoration of the CA levels in the brain by l-DOPA resulted in a restoration of CAR. The data support the view that the CA of the brain are essential for CAR. The relative importance of noradrenaline and dopamine is discussed.     

Biochemical differentiation of amphetamine vs methylphenidate and nomifensine in rats

Amphetamine-like stimulants were divided into two groups, one in which the stereotyped behaviour was not antagonized by reserpine [(+)-amphetamine, (-)-amphetamine, methamphetamine, phenmetrazine and phenethylamine] and another group in which the behavioural effects were blocked by reserpine (methylphenidate, nomifensine, pipradrol and amfonelic acid (NCA; Win 25978)). Both groups increased homovanillic acid (HVA) in whole brain 2 h after administration. The ‘methylphenidate group’ also increased brain 3,4-dihydroxy-phenylacetic acid (DOPAC) in naive rats; whereas the ‘(+)-amphetamine group’ decreased DOPAC in naive rats, as well as in reserpinized rats, α-methyl-p-tyrosine-treated rats, and after acute hemisection. The reserpine antagonism of the ‘methylphenidate group’-induced stereotyped behaviour was partially reversed by type A monoamine oxidase inhibition. The ‘(+)-amphetamine group’-induced stereotyped behaviour was not blocked by short time pretreatment with α-methyltyrosine, only by longer pretreatment intervals. The mechanisms by which the two groups are differentiated biochemically is discussed with special attention to possible intra-neuronal inhibition of dopamine oxidation by the ‘(+)-amphetamine group’.     

Central effects of an inhibitor of tyrosine hydroxylation

Summary The selective decrease of noradrenaline and dopamine content in the brain of mice and rats caused by the methylester of Dl--methyltyrosine (H 44/68) (an inhibitor of the biosynthesis of these amines) is accompanied by a lowered conditioned avoidance response (CAR) in trained animals.These two effects have the same time curve and reach a minimum within 8–16 hours. A small dose of d-DOPA refills the dopamine and noradrenaline storage sites in the brain of animals pretreated with H 44/68 and causes an improvement in the conditioned avoidance response.     

Effect of (+)-Amphetamine on the Retention of 3H-Catecholamines in Slices of Normal and Reserpinized Rat Brain and Heart

Abstract The effect of reserpine on the inhibition by (+)-amphetamine and cocaine of the accumulation of ³H-dopamine (DA) in striatal slices and ³H-noradrenaline (NA) in slices of cerebral occipital cortex and heart atrium of rats and the release of the ³H-amines from these tissues were examined. Reserpine (5 mg/kg intraperitoneally) was injected 18 hours before the experiments. It was found that reserpine markedly enhanced the in vitro potency of amphetamine in the striatum and heart but only slightly in the cortex. After administration in vivo (+)-amphetamine was about 10 times more potent in reducing the amine accumulation in the cortex as in the striatum. Reserpine enhanced the effect in both regions. The inhibitory potency of cocaine in vitro was unchanged by reserpine in the striatum but was reduced in the cortex and heart. Reserpine did not change the inhibitory potency of desipramine in the cortex and heart. The release of the ³H-amines by (+)-amphetamine was enhanced by reserpine in the striatum and heart but the small release produced in the cortex was not increased. The release produced by cocaine was similarly enhanced by reserpine but cocaine was much less active than (+)-amphetamine. The results indicate that (+)-amphetamine and cocaine inhibit the amine accumulation by different mechanisms.     

Lithium prevention of amphetamine-induced ‘manic’ excitement and of reserpine-induced ‘depression’ in mice: Possible role of 2-phenylethylamine

Repeated treatment of mice with lithium chloride (45 mg/kg, i.p., daily for 8 days) reduced the jumping, fighting, stereotypies, and hyperactivity induced by d-amphetamine (5 mg/kg, i.p.). Lithium also reduced the hypoactivity observed 1–3 h after reserpine (0.75 mg/kg, i.p.). In biochemical studies we found that 8-day treatment with lithium markedly reduced (to 45% of control) the recovery from brain of labelled 2-phenylethylamine (PEA) following i.p. injection of labelled L-phenylalanine, while decreasing recovery from brain of labelled PEA following its i.p. injection to 63% of control. In saline-treated mice, d-amphetamine appeared to increase PEA synthesis and to accelerate its disposition, whereas reserpine enhanced PEA synthesis and reduced disposition; all of these effects were antagonized by lithium pretreatments. Since PEA appears to be one of the most powerful behavioral stimulants among endogenous neuroamines, and because its deaminated metabolites are behavioral depressants, such antagonism of brain PEA metabolism may significantly contribute to the prophylactic action of lithium against both manic and depressive behavior.     

Simultaneous measurement of tyrosine and tryptophan hydroxylase activities in brain in Vivo using an inhibitor of the aromatic amino acid decarboxylase

Summary DOPA and 5-HTP accumulated in vivo in rat brain after decarboxylase inhibition with NSD 1015 (3-hydroxybenzylhydrazine). This accumulation was linear for the first 30 min and occurred in several brain regions over a wide range of NSD 1015 doses. After a peripheral decarboxylase inhibitor much less, if any, DOPA or 5-HTP accumulated in the brain. The accumulation of DOPA was prevented by H 44/68 (methylester of -methyl para-tyrosine), a tyrosine hydroxylase inhibitor. DOPA, which accumulated before H 44/68 was given, appeared stable for at least 20 min. There were no significant changes in the levels of NA, DA, 5-HT or tryptophan shortly after NSD 1015 administration, but a rise in tyrosine was noted. Increased brain tyrosine after l-tyrosine administration did not alter the DOPA accumulation, however. These data as well as the distribution of the accumulated amino acids suggest that the accumulation of DOPA and 5-HTP after decarboxylase inhibition occurs intraneuronally, that the decarboxylase enzyme is completely inhibited, and that the accumulated products are not appreciably metabolized or transported from the region studied. Amine synthesis rates and rate constants were calculated from the data and compare well with similar values determined by other methods. Thus this accumulation appears to be a reliable measure of the in vivo hydroxylation of tyrosine and tryptophan.     

Specific opioid-amphetamine interactions in the caudate putamen

Bilateral microinjection of morphine (0.003–3 g/side) into the caudate putamen enhances the behavior induced by the IP injection of 1 mg/kg d-amphetamine phosphate in a dose-related manner. The duration of activity was prolonged and ambulation was changed to d-amphetamine stereotypy, a behavior normally associated with higher doses of d-amphetamine. The opioid activity was stereospecific in that levorphanol was active, whereas dextrorphan was not. The enhancement of d-amphetamine-induced behavior by the opioids was blocked by naloxone. d-ala²-met-Enkephalin also enhanced the amphetamine-induced behavior. This enhancement appears to be specific to the caudate putamen because the oral stereotypy observed appears to be a unique action of amphetamine in this region of the brain.     

Amphetamine induced release of endogenous dopamine in vitro is not reduced following pretreatment with reserpine

Summary The release of endogenous dopamine evoked by electrical stimulation or by exposure to (+)-amphetamine (10 M) was determined in superfused striatal slices of the rat.The spontaneous and the electrically-evoked release of dopamine were significantly increased in the presence of nomifensine (10 M). After reserpine pretreatment (5 mg/kg, s.c., 24 h), the striatal dopamine content was reduced by about 90%. Exposure to 10 M (+)-amphetamine during 2 min released similar amounts of dopamine from striatal slices of untreated or reserpine pretreated rats. Similar results were obtained when monoamine oxidase activity was inhibited in vivo with pargyline.Pretreatment with reserpine does not modify the (+)-amphetamine-induced release of dopamine, in spite of the marked reduction of the striatal dopamine content. These results provide direct evidence for the view that (+)-amphetamine releases dopamine from a special, reserpine-resistant pool of newly synthetized transmitter.Some of the results described in this publication have been presented at the British Pharmacological Society Meeting (Arbilla et al. 1984a)     

A comparison of circling models for the detection of antiparkinson activity

Apomorphine, d-amphetamine, methylphenidate, nomifensine, ET495 and amantadine each induced a dose-dependent stereotyped behaviour in the rat. l-Dopa was inactive in the absence of any pretreatment. The behaviour induced by apomorphine, methylphenidate, nomifensine and amantadine persisted following pretreatment with -methylparatyrosine. However, only the effect of apomorphine developed following combined pretreatment with reserpine/ -methylparatyrosine. The effects of all Stereotypic agents were inhibited by haloperidol, apomorphine, methylphenidate and nomifensine being most resistant.All agents, including l-Dopa, induced a dose-dependent contralateral circling behaviour in animals with asymmetric lesion of the medial raphé nucleus and a dose-dependent ipsilateral circling after unilateral lesion of the substantia nigra. Following unilateral lesions in the ventromedial area of the medial forebrain bundle (medial to the substantia nigra and carrying 5-hydroxytryptamine neurones) amphetamine caused an ipsilateral circling behaviour, amantadine a behaviour which was characterised by definite bursts in either direction, and all other agents caused contralateral circling.     

Locomotor stimulation by l-Dopa: Relative importance of noradrenaline receptor activation

The importance of brain noradrenaline synthesis and receptor activation for the hyperkinesia induced by carbidopa plus l-Dopa in reserpine-treated or normal mice was analyzed in four different models. After pretratment with reserpine and the monoamine oxidase inhibitor nialamide, the hyperkinesia induced by l-Dopa (25 mg/kg i.p.) was partly mediated via stimulation of noradrenaline receptors since it was significantly antagonized by the noradrenaline receptor-blocking agent phenoxybenzamine. Treatment with reserpine plus l-Dopa (125 mg/kg i.p.) produced an increase in motor activity probably due to stimulation of dopamine receptors since it was not accompanied by an accumulation of noradrenaline and it was not inhibited by phenoxybenzamine. The hyperkinesia following treatment with reserpine and a higher dose of l-Dopa (250 mg/kg i.p.) was probably due to stimulation of both dopamine and noradrenaline receptors since the dopamine--hydroxylase inhibitor FLA-63 partly reduced the effect of l-Dopa. Phenoxybenzamine potentiated the motor stimulation by l-Dopa (125 mg/kg i.p.) in mice not pretreated with reserpine, perhaps depending on a slight enhancement of the net accumulation of brain dopamine. Thus, noradrenaline receptor activation is of importance for the l-Dopa-induced hyperkinesia, at least after high doses or after monoamine oxidase inhibition.     

The effect of amantadine and (+)-amphetamine on motility in rats after inhibition of monoamine synthesis and storage

The effect of amantadine and (+)-amphetamine on motility was investigated by subcutaneous administration to rats. Amantadine 50 and 100 mg/kg induced a moderate increase of motility. (+)-amphetamine 1, 2.5 and 5 mg/kg showed a more potent locomotor stimulant effect. A stereotyped licking was found during the hypermotility induced by (+)-amphetamine 5 mg/kg.Pretreatment with the catecholamine synthesis inhibitor -methyl-p-tyrosine inhibited the effect of (+)-amphetamine but not that of amantadine. Reserpine potentiated the effects of both amantadine and (+)-amphetamine. Tetrabenazine antagonized the hyperactivity produced by (+)-amphetamine but potentiated amantadine induced hyperactivity. The locomotor stimulant effect of amantadine seems to differ in certain respects from that of amphetamine.     

Effects of alpha-methyl tyrosine and adrenergic blocking agents on the facilitating action of amphetamine and nicotine on learning in rats

dl-amphetamine sulphate (2 mg/kg) and nicotine (0.2 mg/kg) showed a facilitatory action on the acquisition of a conditioned response in a shuttle-box by rats and this was reversed by pretreatment with -MT (30 mg/kg).Pretreatment with dibenamine (10 mg/kg) impaired the action either of amphetamine or nicotine. Nethalide (5–10 mg/kg) exerted a partial protection on the depressant effect produced by the interaction between dibenamine and nicotine.Animals treated with -MT (30 mg/kg) and kept in the cold (4–6° C for 3 h) also showed a depressed learning capacity. dl-Dopa (200 mg/kg) provided a partial protection on the depressive effects caused by the interaction of -MT with amphetamine, nicotine or cold. It is suggested that the facilitatory learning action of amphetamine and nicotine involves a common adrenergic mechanism. The depressant effects of amphetamine, nicotine or cold after -MT treatment are attributed to depletion of functional pools of catecholamines.This work was supported by grant N 2911/67 from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina (O. A. Orsingher).     

Role of catecholaminergic mechanisms in the expression of the morphine abstinence syndrome in rats

The effect of various drugs affecting catecholaminergic mechanisms on the precipitated morphine withdrawal syndrome was studied in rats which had developed a medium degree of dependence. Administration of low doses of d-amphetamine, cocaine, and L-Dopa shortly before precipitating withdrawal by levallorphan induced a dose-dependent increase of dominant withdrawal signs such as jumping and a decrease of recessive signs such as wet dog shaking; signs such as diarrhea and ptosis decreased, whereas rhinorrhea, salivation and lacrimation increased. A qualitatively very similar change in withdrawal signs occurred when withdrawal was precipitated in extremely highly dependent rats and/or increasing doses of the antagonist were administered. Therefore, the effects of the above drugs are interpreted as potentiation of withdrawal. Pretreatment with higher doses of the same drugs provoked strong stereotyped behaviour which obviously suppressed the occurrence of other motor signs.Activation of noradrenergic or dopaminergic mechanisms with desipramine or apomorphine induced an increase in the intensity of withdrawal, which was, however, much more pronounced after the former than the latter drug. When catecholamines (CA) were previously depleted by alpha-methyl-para-tyrosine (AMT), apomorphine lost a great part of its effectiveness. Blockade of CA synthesis by AMT alone resulted in decreased jumping while at the same time writhing largely increased, thus, inducing a profile of signs characteristic for a weak withdrawal. Selective inhibition of noradrenaline synthesis by FLA-63 resulted in a reduction in withdrawal intensity. Ro 4-4602 + L-Dopa, given after AMT, antagonized and reversed the reduction of withdrawal, but this effect was not so pronounced when by additional pretreatment with FLA-63 NA levels remained low. It is concluded that of both brain CA especially noradrenaline is involved in the manifestation of the morphine withdrawal syndrome.     

Biochemical differentiation of amphetamine vs methylphenidate and nomifensine in rats.

Amphetamine-like stimulants were divided into two groups, one in which the stereotyped behaviour was not antagonized by reserpine [(+)-amphetamine, (-)-amphetamine, methamphetamine, phenmetrazine and phenethylamine] and another group in which the behavioural effects were blocked by reserpine (methylphenidate, nomifensine, pipradrol and amfonelic acid (NCA; Win 25978)). Both groups increased homovanillic acid (HVA) in whole brain 2 h after administration. The 'methylphenidate group' also increased brain 3,4-dihydroxyphenylacetic acid (DOPAC) in naive rats; whereas the '(+)-amphetamine group' decreased DOPAC in naive rats, as well as in reserpinized rats, alpha-methyl-p-tyrosine-treated rats and after acute hemisection. The reserpine antagonism of the 'methylphenidate group'-induced stereotyped behaviour was partially reversed by type A monoamine oxidase inhibition. The '(+)-amphetamine group'-induced stereotyped behaviour was not blocked by short time pretreatment with alpha-methyltyrosine, only by longer pretreatment intervals. The mechanisms by which the two groups are differentiated biochemically is discussed with special attention to possible intra-neuronal inhibition of dopamine oxidation by the '(+)-amphetamine group'.     

The role of catecholamines in behavioral arousal during ontogenesis

Effect of catecholamine depletion on normal hyperactivity in the neonatal rat was examined. Both -methyl-para-tyrosine and reserpine significantly depressed behavioral arousal at 15 days postpartum, the age of greatest excitability. Heightened activity could be restored in drug-treated animals by administration of l-Dopa. These results indicate that the ontogenetic hyperactivity effect is a result of accelerated catecholamine function.This work was supported in part by National Institute of Mental Health Grants MH01562 and MH08501 to Byron A. Campbell.     

The transport of (+)-amphetamine by the neuronal noradrenaline carrier

Summary PC-12 cells (a clonal line of rat phaeochromocytoma cells) take up noradrenaline by a transport system which is identical with the neuronal amine transport system (uptake₁). The uptake of ³H-noradrenaline into reserpine-pretreated PC-12 cells (monoamine oxidase inhibited) was saturable (K_m=0.6±0.1 mol/l), dependent on sodium and chloride, and competitively inhibited by (+)-amphetamine (K_i=0.18±0.04 mol/l), cocaine (K_i=0.55±0.15 mol/l) and desipramine (K_i=4.3±0.6 nmol/l). The uptake and accumulation of ³H (+)-amphetamine showed characteristics comparable to those of ³H-noradrenaline, since the uptake of ³H (+)-amphetamine (0.1 mol/l) was reduced by omission of sodium or chloride from the incubation medium. The sodium-sensitive component of uptake and accumulation of ³H (+)-amphetamine was fully inhibited by cocaine and desipramine. The IC₅₀ of desipramine for inhibition of the sodium-sensitive component of the 1-min uptake of ³H (+)-amphetamine (20 nmol/l) was about 2 nmol/l, i.e., identical with the K_i for inhibition of uptake of ³H-noradrenaline. At concentrations above 1 mol/l, desipramine additionally caused an inhibition of the sodium-independent permeation of ³H (+)-amphetamine into PC-12 cells.Hence, by using a homogeneous population of cells endowed with uptake₁, it is possible to demonstrate — besides a pronounced lipophilic entry — a carrier-mediated uptake of ³H (+)-amphetamine.Some of the results were communicated to the German Pharmacological Society (Bönisch 1981). This study was supported by the Deutsche Forschungsgemeinschaft (Bo 521)