Effects of morphine in the nucleus accumbens on stimulant-induced locomotion.

Article date: 1991/9/1

PubMed ID: 1685784

Journal name: Pharmacology, biochemistry, and behavior (ISSN: 0091-3057)


This study assessed the effects of morphine in the nucleus accumbens on motility elicited by dopaminergic and other classes of drugs, using locomotor activity as the measured response. Dopaminergic stimulants, d-amphetamine (10 micrograms) or dopamine (20 micrograms, 2 hours after nialamide, 200 mg/kg, IP) induced large increases in locomotor activity when injected into the nucleus accumbens. This response was blocked by coadministration of morphine (5 micrograms). The hypermotility response elicited by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 0.5 micrograms), an excitatory amino acid agonist, was also abolished by coadministration of morphine. Increasing the dose of AMPA to 1.5 micrograms partially overcame the morphine block, while increasing the dose of amphetamine to 50 micrograms did not. In other experiments, morphine (5 micrograms) injected into the nucleus accumbens blocked the hypermotility elicited by systemic caffeine (10 mg/kg, SC) or scopolamine (0.5 mg/kg, SC) or intra-accumbal MK-801 (5 micrograms). However, picrotoxin (0.15 or 0.5 microgram) injected into the nucleus accumbens elicited a hypermotility that was not attenuated by coinjection of morphine (5 or 10 micrograms). These data demonstrate that opiate and dopaminergic pathways have competing actions on the regulation of locomotion in the nucleus accumbens. Furthermore, the results with combinations of picrotoxin and morphine suggest the presence of two distinct locomotor pathways or a GABA receptor site “downstream” from the morphine site in a single pathway.

Author List: Layer R T, Uretsky N J, Wallace L J

Publication Types: Journal Article

Substances mentioned in the article: Central Nervous System Stimulants; Dopamine Agents; Oligopeptides; Glutamine; Picrotoxin; Ibotenic Acid; Caffeine; Scopolamine Hydrobromide; Dizocilpine Maleate; Morphine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; deltakephalin; Amphetamine;

Mesh terms: Amphetamine/pharmacology; Animals; Caffeine/antagonists & inhibitors; Central Nervous System Stimulants/pharmacology; Dizocilpine Maleate/antagonists & inhibitors; Dopamine Agents/pharmacology; Glutamine/physiology; Ibotenic Acid/analogs & derivatives; Male; Morphine/pharmacology; Motor Activity/drug effects; Neural Pathways/drug effects; Nucleus Accumbens/physiology; Oligopeptides/pharmacology; Picrotoxin/pharmacology; Rats; Scopolamine Hydrobromide/antagonists & inhibitors; Synaptic Transmission/drug effects; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid;

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