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Variations of motor activity following intraventricular (D-Pen2, D-Pen5)-enkephalin administration: interaction with
1Unit for Behavioural Medicine and Psychopharmacology, Carleton University, Ottawa, Ontario, Canada.
Abstract:
The effects of intraventricular administration of (D-Pen2, D-Pen5)-enkephalin (DPDPE) (0.005, 1.0, and 2.5 micrograms/microlitter in a 1-microlitter vol.) on horizontal activity, rearing, and exploratory head dipping were assessed among CD-1 mice exposed to acute uncontrollable foot-shock 15 min following stressor termination. Foot-shock reduced horizontal activity, rearing, and exploratory head dipping during the immediate 15-min poststressor interval. Mice challenged with 0.005 micrograms DPDPE were behaviorally indistinguishable from vehicle-treated subjects. The 1.0-microgram dose of DPDPE increased horizontal activity in stressed and nonstressed subjects. Intraventricular infusion of 2.5 micrograms DPDPE potentiated horizontal activity in previously stressed mice but had no effect in nonstressed animals. The suppression of rearing and exploratory head dipping following uncontrollable foot-shock was not ameliorated by the delta-receptor agonist, and DPDPE was without effect on rearing and exploratory head dipping in nonstressed animals. Potential neurochemical mechanisms associated with the expression of these stressor associated behaviors are discussed.
Insights
The delta-receptor agonist (D-Pen2, D-Pen5)-enkephalin (DPDPE) did not reverse stress-induced behavioral suppression in mice. However, DPDPE modulated horizontal activity in both stressed and non-stressed subjects.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
- Stress Research
Background:
- Acute uncontrollable stress significantly impacts animal behavior.
- Opioid peptides, like enkephalins, play a role in modulating stress responses.
- The delta-opioid receptor system's role in stress-induced behavioral changes requires further investigation.
Purpose of the Study:
- To investigate the effects of intraventricular administration of (D-Pen2, D-Pen5)-enkephalin (DPDPE) on behavioral responses to acute uncontrollable foot-shock stress in mice.
- To determine if DPDPE can ameliorate stress-induced suppression of horizontal activity, rearing, and exploratory head dipping.
- To explore dose-dependent effects of DPDPE on behavior in both stressed and non-stressed conditions.
Main Methods:
- CD-1 mice were exposed to acute uncontrollable foot-shock.
- DPDPE was administered intraventricularly at doses of 0.005, 1.0, and 2.5 micrograms.
- Behavioral assessments included horizontal activity, rearing, and exploratory head dipping during the post-stressor interval.
Main Results:
- Foot-shock stress reduced horizontal activity, rearing, and head dipping.
- A low dose (0.005 micrograms) of DPDPE had no significant effect compared to vehicle controls.
- Higher doses (1.0 and 2.5 micrograms) of DPDPE increased horizontal activity in stressed mice, with the 2.5 microgram dose also affecting non-stressed mice.
- DPDPE did not ameliorate the suppression of rearing or exploratory head dipping in stressed mice.
Conclusions:
- The delta-opioid receptor agonist DPDPE did not reverse stress-induced behavioral deficits in rearing and exploration.
- DPDPE demonstrated a dose-dependent effect on horizontal activity, increasing it in stressed and non-stressed mice at higher doses.
- These findings suggest a complex role for delta-opioid receptors in the behavioral manifestations of stress, particularly concerning activity levels versus exploratory behaviors.