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Intradentate colchicine impairs acquisition of a two-way active avoidance response in a Y-maze
R L McLamb1, W R Mundy, H A Tilson
1Laboratory of Molecular and Integrative Neuroscience, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709.
Abstract:
Male, Fischer-344 rats received bilateral injections of colchicine (2.0 micrograms/site) into the dorsal and ventral hippocampus to destroy dentate gyrus granule cells. Colchicine impaired the ability of rats to learn a brightness discrimination, active avoidance task in a Y-maze. Acquisition was measured in 120-trial sessions given once weekly for 3 or 4 weeks. In a second experiment, colchicine-treated rats were tested in a modified procedure in which only the tone warning stimulus and a light directional cue were presented; shock was not presented. Colchicine-treated rats showed an enhanced response bias under these conditions, selecting to go to the unlighted arm with a greater frequency than the control rats whenever the tone and light were activated. These data are consistent with other reports indicating that rats with hippocampal lesions are impaired in the acquisition of a simultaneous discrimination if a response bias exists to one of the choices.
Insights
Hippocampal lesions in rats impair learning and decision-making. Destroying dentate gyrus granule cells with colchicine disrupted brightness discrimination and led to a response bias in a Y-maze task.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Cognitive Neuroscience
Background:
- The hippocampus plays a crucial role in learning and memory.
- Dentate gyrus granule cells are key hippocampal components involved in memory formation.
Purpose of the Study:
- To investigate the effects of selective dentate gyrus granule cell destruction on learning and decision-making in rats.
- To examine how hippocampal lesions impact active avoidance and response bias in a Y-maze task.
Main Methods:
- Male Fischer-344 rats received bilateral hippocampal injections of colchicine to ablate dentate gyrus granule cells.
- Rats were trained on a brightness discrimination, active avoidance task in a Y-maze over multiple sessions.
- A modified procedure assessed response bias using auditory and visual cues without shock.
Main Results:
- Colchicine-induced hippocampal lesions significantly impaired the acquisition of the brightness discrimination task.
- Treated rats exhibited an enhanced response bias, favoring the unlighted arm when presented with tone and light cues.
- These findings suggest that hippocampal integrity is critical for tasks where response bias can interfere with learning.
Conclusions:
- Dentate gyrus granule cell ablation via colchicine disrupts hippocampal function related to learning and spatial decision-making.
- Response bias, exacerbated by hippocampal lesions, can impede the ability to acquire new discriminations.
- The study highlights the hippocampus's role in overcoming response biases for successful task acquisition.