Protein phosphorylation and associative learning in Hermissenda

Area of Science:

• Neuroscience
• Animal Behavior
• Cellular Biology

Background:

• Phototaxis, the movement of an organism in response to light, can be modified through associative learning in the nudibranch mollusc Hermissenda crassicornis.
• Previous studies indicate that conditioning alters potassium (K+) currents and protein phosphorylation in the photoreceptors and eyes of these animals.

Purpose of the Study:

• To investigate the role of intracellular free calcium (Ca2+) and protein phosphorylation in the cellular mechanisms underlying learned changes in phototaxis.
• To test the hypothesis that conditioning increases photoreceptor Ca2+, activating phosphorylation pathways that modulate K+ channel activity.

Main Methods:

• Measuring intracellular Ca2+ levels using Arsenazo absorption following light and depolarization stimuli.
• Assessing the effects of Ca2+ on K+ current inactivation rates.
• Introducing Ca2+/calmodulin-dependent and cAMP-dependent protein kinases into cells via intracellular injection.
• Identifying the presence of Ca2+- and cAMP-dependent protein kinases in Hermissenda neural tissue.

Main Results:

• Light and depolarization stimuli were found to increase intracellular Ca2+ levels.
• Increased Ca2+ accelerated the inactivation of K+ currents, mirroring changes observed after conditioning.
• Intracellular injection of specific protein kinases reduced these K+ currents.
• Hermissenda neural tissue contains potent Ca2+- and cAMP-dependent protein kinases.

Conclusions:

• The findings support the hypothesis that conditioning-induced increases in intracellular Ca2+ activate protein kinases, leading to the modulation of K+ channel activity.
• Further research is needed to identify specific phosphorylated proteins and their relationship to K+ channel function in learned responses.