Hippocampal acetylcholine increases during eyeblink conditioning in the rabbit

Area of Science:

• Neuroscience
• Neurobiology
• Behavioral Neuroscience

Background:

• The septohippocampal cholinergic system modulates the rabbit nictitating membrane reflex (NMR).
• Neurotoxins like aluminum (Al) disrupt hippocampal acetylcholine (ACh) synthesis and release, impairing cognitive functions.
• Previous research indicates that disrupting the cholinergic system hinders NMR acquisition.

Purpose of the Study:

• To test the hypothesis that NMR acquisition in rabbits is linked to hippocampal ACh release.
• To investigate the impact of aluminum intoxication on hippocampal ACh release during NMR training.

Main Methods:

• Microdialysis was used to measure hippocampal ACh release in control and Al-intoxicated rabbits during NMR training.
• NMR training involved four sessions with 100 conditioning trials each in a delay paradigm.
• A pseudoconditioning group controlled for the effects of stimulus presentation alone.

Main Results:

• Rabbits in the control group showed a significant increase in hippocampal ACh release during NMR acquisition.
• Al-intoxicated rabbits exhibited a deficit in CR acquisition and failed to show increased hippocampal ACh release.
• The pseudoconditioned group did not acquire the CR, and ACh release did not increase, indicating the observed ACh increase was specific to learning.

Conclusions:

• Hippocampal cholinergic function plays a critical role in the acquisition of the nictitating membrane reflex in rabbits.
• Aluminum-induced disruption of hippocampal ACh release impairs conditioned response learning.
• These findings support the involvement of hippocampal acetylcholine in associative learning processes.