Unilateral destruction of dopaminergic cell bodies in the substantia nigra zona compacta (SNC) was performed in rats using either electrocoagulation or chemical lesioning (6-hydroxydopamine, 6-OHDA). Neostriatal dopamine concentration ipsilateral to an electrolytic lesion was 34% of the contralateral side 2-3 weeks after operation; serotonin and noradrenaline brain levels were not altered. In contrast, dopamine and noradrenaline forebrain concentrations ipsilateral to a 6-OHDA lesion were 20 and 31%, respectively, of the contralateral side. After 6-OHDA, dopamine concentrations in the ipsilateral neostriatum were reduced to levels below the sensitivity of the fluorometric assay; cortical, brainstem and neostriatal serotonin levels, on the other hand, were not altered after 6-OHDA. Ipsilateral circling behavior was elicited by d-amphetamine after electrolytic and chemical lesioning. In contrast, the direction of circling produced after apomorphine differed between the two lesion models: contralateral circling behavior was exhibited by 6-OHDA-lesioned rats, whereas ipsilateral circling was produced in animals with electrolytic lesions. Contralateral circling was induced in both lesion-type models by haloperidol or pimozide. S.c. atropine administration induced ipsilateral circling in rats with 6-OHDA lesions, whereas contralateral circling was observed after arecoline. Animals with electrolytic SNC lesions turn ipsilaterally after s.c. administrations of either arecoline or atropine. The data indicate that the electrolytic and 6-OHDA circling behavior models represent two different neuropharmacological states and it is, therefore, suggested that comparisons of data obtained from models using different methods of lesioning be made with caution.

Animals↗

PubMed1976

Dopaminergic-cholinergic interactions in naloxone-induced circling in morphine-dependent rats with nigral lesions.

3-4 weeks after placement of a unilateral, electrolytic lesion of the substantia nigra zona compacta, rats were highly dependent on morphine by the s.c. morphine pellet implantation technique. Following challenge with a supramaximal naloxone dose of 20 mg/kg i.p., both continuous contralateral circling behavior and severe withdrawal signs in morphine-dependent, lesioned rats were elicited. After various drug pretreatments, the contralaeral circling behavior precipitated by naloxone was: (a) reversed to ipsilateral circling by i.p. apomorphine or d-amphetamine, (b) unaltered by i.p. haloperidol or intraneostriatal arecoline administered into the intact neostriatum, and (c) reversed to ipsilateral circling by the administration of atropine into the intact neostriatum. Atropine, apomorphine and amphetamine all interfered with the manifestation of naloxone-precipitated abstinence. These data suggest that a diminution of dopaminergic or an enhancement of cholinergic activities, or both, occur at the level of the neostriatum during naloxone-precipitated withdrawal in morphine-dependent rats.

Animals↗

PubMed1976

Effect of pargyline on morphine tolerance and physical dependence development in mice.

The effects of single and repeated pargyline administration on morphine antinociception in both naive and morphine-tolerant mice and on naloxone-precipitated withdrawal in morphine tolerant-dependent animals were investigated. Adult, male Swiss-Webster mice were rendered tolerant to and dependent on morphine by the s.c. pellet implantion technique. Morphine analgesia, as assessed by the tail-flick antinociceptive test, was potentiated in tolerant animals by acute adminstration of pargyline but antagonized by repeated pargyline administration; pargyline produced similar effects in non-tolerant mice and to the same relative degree. Repeated pargyline treatment during morphine pellet implantation enhanced the withdrawal jumping response precipitated by naloxone in dependent mice. Pargyline also, after a single injection, exacerbated jumping in mice undergoing abrupt withdrawal. Neither acute nor chronic pargyline administration altered the brain distribution of injected morphine in non-tolerant mice. It was concluded that pargyline may modify acute morphine actions and withdrawal without materially altering the process(es) involved in the development of tolerance and physical dependence.

Animals↗

PubMed1976

Precipitation of abstinence-like syndrome in morphine-dependent mice by pargyline.

In mice rendered morphine-dependent by pellet implantation for 3 days, the administration of pargyline 6 hours after pellet removal intensified narcotic abstinence behavior, particularly the narcotic withdrawal jumping response. Pargyline, 75 mg/kg i.p., caused a 6- to 9-fold increase in the incidence of jumping in mice withdrawing from morphine 6 hours after removal of the pellet, whereas this effect was not observed: 1) 1 hour after the injection of pargyline or 2) in animals still implanted with the morphine pellet. The median effective dose (ED50) of pargyline required to elicit withdrawal jumping in mice implanted with morphine decreased with increasing physical dependence. The ED50 for 72 hours was about one-sixth that after 24 hours of implantation. Additionally, pargyline potentiated naloxone-precipitated withdrawal jumping as evidenced by a reduction of the naloxone ED50 by approximately one-half. Administration of other monoamine oxidase inhibitors such as pheniprazine, iproiazid or tranylcypromine failed to alter the indicence of jumping in dependent mice undergoind abrupt morphine with drawal. Further, dopamine receptor stimulation by amphetamine, pheniprazine or amantadine antagonized the pargyline-induced jumping response. These data suggest that the increased incidence of withdrawal jumping observed after pargyline in morphine-dependent mice is not related to monoamine oxidase inhibition but rather to a possible pargyline-induced decrease in dopaminergic activity.

Amantadine↗

PubMed1976

Reinitiation of sensitivity to naloxone by a single narcotic injection in postaddicted mice.

In mice implanted with a morphine pellet for 3 days and subsequently withdrawn for various periods of time, a single injection of morphine results in a rapid and marked sensitization of abstinent mice to naloxone-induced jumping behavior when compared to abstinent mice pretreated with saline or to placebo-withdrawn mice given a single morphine injection. Maximum sensitization of abstinent mice occurs at morphine doses of about 10 to 30 mg/kg and peaks at 0.5 to 2 hours after morphine administration. The ability of morphine to sensitize abstinent mice to naloxone declines with time after pellet removal and appears to consist of two components, one with a short T1/2 and one with a much longer T1/2. Abstinent mice are also sensitized to naloxone by levorphanol and methadone, but not by dextrorphan. It is proposed that the administration of a narcotic drug to abstinent mice uncovers a latent, pre-existing state of physical dependence and restores the responsiveness of this state to naloxone.

Animals↗

PubMed1976

Circling behavior after narcotic drugs and during naloxone-precipitated abstinence in rats with unilateral nigral lesions.

Unilateral lesions of the substantia nigra zona compacta (SNC) in rats were produced by electrolytic coagulation or by an injection of 6-hydroxydopamine. Two to 5 weeks later, after being preselected for amphetamine-induced ipsilateral circling behavior, the animals were administered narcotic agonists or antagonists and their circling behavior was observed. Morphine, methadone, levorphanol, nalorphine or pentazocine induced ipsilateral circling movements; both naloxone and dextrorphan were without effect. Ipsilateral circling was also observed in rats with unilateral electrolytic lesions after administration of agents that are thought to enhance central dopaminergic activities: d-amphetamine, l-dopa and apomorphine. In rats with unilateral electrolytic or 6-hydroxydopamine SNC lesions that were rendered highly morphine-dependent by multiple-morphine pellet implantation, contralateral (C) circling behavior was observed within 1 to 2 minutes after a naloxone challenge; the onset and duration of C circling behavior coincided with the initial appearance and duration of precipitated-morphine withdrawal signs. C circling was also observed after administration of putative dopamine receptor blockers, haloperidol and pimozide in rats with either unilateral electrolytic or 6-hydroxydopamine SNC lesions. Morphine pretreatment diminished both the C circling intensity and the appearance of withdrawal signs observed after a naloxone challenge in morphine-dependent, SNC-lesioned rats. The naloxone-precipitated withdrawal in unilaterally lesioned morphine-dependent rats was accompanied by a 20% elevation of neostriatal dopamine in the intact side. In contrast to the effects of a chronic SNC lesion in decreasing neostriatal dopamine, a 77% increase was observed in the lesioned side 30 minutes after electrolytic coagulation. Thus, narcotic agonists and partial agonists may enhance central dopaminergic activities and naloxone-precipitated withdrawal may involve a diminution in central dopaminergic activities of the nigroneostriatal pathway.

Animals↗

PubMed1976