Hippocampal Damage Disrupts Eyeblink Conditioning in Mice Lacking Glutamate Receptor Subunit δ2.

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Synaptic Plasticity

Background:

• Cerebellar long-term depression (LTD) is implicated in classical eyeblink conditioning.
• Mutant mice lacking glutamate receptor subunit δ2 (GluRδ2) lack cerebellar LTD and show impaired delay conditioning with CS-US overlap.
• These mutants can still learn conditioning without CS-US overlap, suggesting an alternative learning pathway.

Purpose of the Study:

• To investigate the role of the hippocampus in cerebellar LTD-independent eyeblink conditioning.
• To determine if the hippocampus is essential for learning in GluRδ2 mutant mice when cerebellar LTD is absent.

Main Methods:

• Examined delay eyeblink conditioning without CS-US overlap in GluRδ2 mutant mice.
• Administered scopolamine or performed hippocampal lesions in mutant and wild-type mice.
• Compared learning performance between treated and control groups.

Main Results:

• GluRδ2 mutant mice treated with scopolamine or hippocampal lesions showed severe learning impairment.
• Control mutant mice and all wild-type mice learned normally, irrespective of treatment.
• These findings highlight the hippocampus's necessity for LTD-independent learning.

Conclusions:

• The hippocampus plays a critical role in cerebellar LTD-independent eyeblink conditioning.
• This study identifies a novel function for the hippocampus in trace conditioning paradigms.
• Disrupting the hippocampus impairs learning in GluRδ2 mutants, underscoring its importance in alternative learning mechanisms.