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Dopamine antagonists produce an age-dependent increase in the responding of the young chick
1Department of Physiology and Biophysics, A.B. Chandler Medical Center, University of Kentucky, Lexington 40536-0084.
Insights
Dopamine receptor antagonists affect learning differently in 1-day-old versus 4-day-old chicks. Younger chicks showed increased responding, while older chicks showed varied responses depending on the task.
Area of Science:
- Neuroscience
- Animal Behavior
- Developmental Psychology
Background:
- Dopamine plays a crucial role in learning and behavior.
- The development of dopaminergic systems can influence cognitive functions.
- Understanding age-related differences in dopamine's effects is important for developmental neuroscience.
Purpose of the Study:
- To investigate the effects of dopamine D2 receptor antagonists on learning in young chicks.
- To compare the impact of these antagonists on response-contingent punishment and autoshape learning at different ages (1 vs. 4 days old).
- To determine if dopaminergic synaptic transmission differs functionally between 1- and 4-day-old chicks.
Main Methods:
- Three experiments were conducted using 1- and 4-day-old chicks.
- Chicks were trained on key-peck tasks for heat reward.
- Dopamine D2 receptor antagonists (haloperidol, sulpiride) or saline were administered intraperitoneally before punishment or autoshape learning sessions.
Main Results:
- 1-day-old chicks treated with haloperidol or sulpiride showed significantly increased key-peck responding in both punishment and appetitive tasks compared to saline controls.
- 4-day-old chicks treated with haloperidol or sulpiride did not show significant differences in the punishment task compared to controls.
- In the autoshape task, 4-day-old chicks treated with haloperidol showed reduced responding compared to saline controls.
Conclusions:
- Dopaminergic synaptic transmission, as assessed by dopamine D2 receptor blockers, functions differently in 1-day-old chicks compared to 4-day-old chicks.
- These findings highlight critical developmental changes in dopamine's role in learning during early chick development.
- The study provides evidence for age-dependent effects of dopamine antagonists on distinct learning paradigms.
Abstract:
In three experiments the effects of dopamine receptor antagonists on response-contingent punishment and autoshape learning of 1- and 4-day-old chicks were determined. In the first two experiments, 1- or 4-day-old chicks (N = 120) were trained to key-peck for heat reward and then injected intraperitoneally (ip) with either haloperidol (1.5, 2.5, or 5.0 mg/kg) or saline (Experiment 1) and with either haloperidol (2.0 mg/kg), sulpiride (50 mg/kg) or saline (Experiment 2) 30 min before a 96-trial response-contingent punishment session. In Experiment 3, 1- and 4-day-old chicks (N = 48) were injected ip with saline or haloperidol (2.0 mg/kg) 30 min prior to a 30-trial autoshape learning session. In both the punishment and appetitive tasks 1-day-old chicks pretreated with either haloperidol (1.5 to 2.5 mg/kg) or sulpiride showed a significant increase in key-peck responding compared with their saline injected controls. In contrast, 4-day-old chicks given either haloperidol (2.0 mg/kg) or sulpiride did not differ significantly from saline treated chicks on the punishment task, and on the autoshape task haloperidol-treated 4-day-old chicks responded on fewer trials than did their saline controls. These results indicate that dopaminergic synaptic transmission in the young chick as measured by dopamine D2 receptor blockers is functionally different at 1 compared with 4 days of age.