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Behavioural effects of (-)naloxone in mice from four inbred strains
Abstract:
To study the role of endogenous opioid peptides in the regulation of behavioural responses to novelty, male mice from the inbred strains SRH, SRL, C57BL/6, and DBA/2 were injected IP with either saline alone, or the opiate antagonist naloxone, dissolved in saline, in dosages of 4 or 8 mg/kg. After 10 min, the animals were placed individually for 20 min in a novel environment and some 12 behavioural components were recorded. Naloxone reduced grooming and incipient rearing in all four strains and it reduced sniffing, leaning against the wall, and locomotor activity in some of them. Object-sniffing, object-learning, defecation, freezing, and Straub tail elevation remained unaffected. The results for grooming and locomotor activity are largely in agreement with reports from others. Rather unexpectedly, the drug enhanced rearing responses in all strains. Although in several cases, a genotype-treatment interaction became apparent, the observed strain differences usually persisted and the correlations found between the behavioural components did not alter much. The naloxone-induced reductions in sniffing, leaning, locomotion, and grooming suggest endogenous opioid involvement in the control of behavioural activation in a novel situation. The increases in rearing possibly result from an additional agonist action of naloxone.
Insights
The opiate antagonist naloxone affects mouse behavior in novel environments. Naloxone reduced grooming and locomotion but unexpectedly increased rearing, suggesting opioid peptide involvement in behavioral regulation.
Area of Science:
- Neuroscience
- Behavioral Science
- Pharmacology
Background:
- Endogenous opioid peptides play a role in regulating behavioral responses.
- Understanding these peptides is crucial for comprehending complex behaviors, particularly in novel situations.
Purpose of the Study:
- To investigate the role of endogenous opioid peptides in regulating behavioral responses to novelty.
- To examine the effects of the opiate antagonist naloxone on mouse behavior in a novel environment.
Main Methods:
- Male mice from four inbred strains (SRH, SRL, C57BL/6, DBA/2) were administered saline or naloxone (4 or 8 mg/kg) intraperitoneally.
- Following injection, animals were placed in a novel environment for 20 minutes, and 12 behavioral components were recorded.
- Behavioral data were analyzed to assess the effects of naloxone across different strains.
Main Results:
- Naloxone significantly reduced grooming and incipient rearing in all tested mouse strains.
- Reduced sniffing, wall-leaning, and locomotor activity were observed in some strains following naloxone administration.
- Unexpectedly, naloxone enhanced rearing responses across all strains, while object-sniffing, learning, defecation, freezing, and Straub tail elevation remained unaffected.
Conclusions:
- The naloxone-induced reductions in specific behaviors suggest endogenous opioid involvement in controlling behavioral activation in novel situations.
- The observed increase in rearing may indicate an additional agonist action of naloxone.
- Strain differences in behavioral responses to naloxone persisted, highlighting genetic influences on opioid peptide function.