Classical conditioning-induced changes in low-molecular-weight GTP-binding proteins in rabbit hippocampus

Area of Science:

• Neuroscience
• Molecular Biology
• Comparative Psychology

Background:

• Classical conditioning in the mollusk Hermissenda involves paired light-rotation events.
• This conditioning leads to a decrease in a 20-kDa G protein (cp20).
• The presence of similar proteins in vertebrates remained uninvestigated.

Purpose of the Study:

• To investigate the existence of a 20-kDa G protein similar to cp20 in vertebrates.
• To determine if classical conditioning affects G protein levels in the rabbit hippocampus.
• To explore the molecular underpinnings of associative learning in mammals.

Main Methods:

• Rabbits were trained using classical conditioning, associating a tone with periorbital electrical stimulation.
• G proteins were analyzed using photoaffinity labeling with [alpha-32P]GTP-azidoanilide.
• Levels of specific proteins were quantified in the hippocampus.

Main Results:

• A 20-kDa G protein, analogous to Hermissenda's cp20, decreased by 36% in the hippocampus of trained rabbits.
• This decrease was specific to the paired tone-electrical stimulation group, not observed in unpaired controls.
• Learning-specific reductions were also noted in the amount of ras protein.

Conclusions:

• A 20-kDa G protein, similar to that found in invertebrates, is modulated by classical conditioning in the vertebrate hippocampus.
• These findings suggest a conserved molecular mechanism for associative learning.
• The study highlights the role of G proteins and ras protein in learning processes across different species.