Apomorphine sensitization: evoking conditions, context dependence, effect persistence and conditioned nature.

Area of Science:

• Neuroscience
• Animal Behavior
• Pharmacology

Background:

• Repeated administration of apomorphine (Apo) induces behavioral sensitization in pigeons, similar to rodents.
• This sensitization manifests as an increased pecking response and is partly dependent on the environmental context of drug administration.

Purpose of the Study:

• To investigate the influence of inter-drug administration intervals on apomorphine sensitization.
• To determine the minimal exposure time to a distinct environment required for maximal context-dependent sensitization.
• To assess the long-term persistence of apomorphine sensitization and the role of environmental conditioning.

Main Methods:

• Pigeons received repeated apomorphine injections with varying intervals and post-injection exposures to distinct cages.
• Behavioral responses (pecking) were measured in both experimental and standard cages.
• Control groups were used to rule out novelty effects.

Main Results:

• Inter-Apo administration intervals between 3 hours and 5 days yielded comparable sensitization.
• 20-minute exposures to a distinct cage were sufficient for maximal context-dependent sensitization.
• Pigeons showed significantly stronger sensitization when consistently exposed to the same cage compared to different cages.
• Sensitization persisted for at least 2 years, waning to 50% of the initial response.

Conclusions:

• Apomorphine sensitization in pigeons is substantially driven by conditioning to the environmental context and the drug state.
• Environmental context plays a critical role in the development and expression of drug-induced behavioral sensitization.