PubMed · 13291274
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L KRAFFT. 1955. [Practice with cito-eunarcon].. https://pubmed.ncbi.nlm.nih.gov/13291274/
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Intraperitoneal (i.p.) administration of lithium chloride (LiCl) has two effects on pain sensation: (1) it induces a transient hyperalgesia that is reversed by intracerebroventricular (i.c.v.) or intrathecal (i.t.) administration of the opioid receptor antagonist naloxone or by peripheral administration of the quaternary compound naloxone methiodide [Behav. Neurosci. 114 (2000) 1183]; (2) it produces a long-lasting (24 h) reduction in morphine analgesia and does so in the absence of hyperalgesia [Behav. Brain Res. 142 (2003) 89]. We confirmed that rats administered with LiCl showed a reduction in analgesia when administered morphine 24 h later. We also found that morphine analgesia was restored if LiCl had been preceded by i.p. or i.c.v. administration of naloxone or by i.p. administration of naloxone methiodide. However, i.p. administration of naloxone methiodide prior to testing 24 h after an injection with LiCl did not restore morphine analgesia. Thus, activity at peripheral and central opioid receptors is necessary for the inhibition of morphine analgesia by LiCl, but peripheral opioid receptors are not critical for the expression of this inhibition.
Fruit flies (Drosophila melanogaster) are typically used for genetic studies but they also could be employed for neuropharmacological research. Therefore, we designed an apparatus and developed methods to investigate how injecting antinociceptive drugs, i.e., a gamma-aminobutyric acid B receptor agonist, to adult flies affects their avoidance of noxious heat stimuli. We found a drug-induced dose-dependent increased threshold for heat avoidance and we propose Drosophila as an ethically acceptable animal model for in vivo pharmacological analgesia research.
RATIONALE: The dopamine D3 receptor has been shown to mediate conditioned effects of psychostimulants such as cocaine. The present work was aimed at determining whether drugs acting at D3 receptors alter acquisition of conditioned effects of opiates. METHODS: We have used the conditioned place preference (CPP) in mice, which permits the measurement of approach behaviour to environmental stimuli previously paired with drug effects. To assess the interaction of morphine and D3 receptor ligands during acquisition of CPP, we have used a particular procedure, in which the animals were given the choice between compartments associated with either morphine alone or the combination of morphine with the tested agent. RESULTS: D3 receptor agonists (7-OH-DPAT, quinelorane, BP 897) did not induce, alone, a significant CPP but, all of them, at the doses tested, and notably BP 897, a highly selective partial agonist, significantly enhanced acquisition of morphine-induced CPP when administered together with morphine at each conditioning session. PNU-99194A, a D3 receptor-preferring antagonist, induced a CPP itself at the dose of 10 mg/kg but not at 5 or 15 mg/kg and impaired significantly at 10 and 15 mg/kg the morphine-induced CPP. In contrast, BP 897 did not alter morphine-induced analgesia, an unconditioned effect of this drug. CONCLUSIONS: These results suggest the stimulation of D3 receptors has no rewarding effect per se, but may synergize upon opiate-induced dopamine release with stimulation of other dopamine receptor subtypes to enhance approach behaviour to morphine-associated environment.