Characteristics and ionic processes involved in feedback spikes of turtle cones

Area of Science:

• Neuroscience
• Vision Science
• Cellular Physiology

Background:

• Cone photoreceptors in turtle retinas exhibit feedback spikes.
• These spikes are mediated by L-horizontal cells and occur with peripheral stimulation.

Purpose of the Study:

• To investigate the properties and mechanisms of feedback spikes in turtle cones.
• To determine the role of L-horizontal cells in cone excitability.

Main Methods:

• Electrophysiological recordings from turtle cone cells.
• Pharmacological manipulation using ions (Ca2+, Sr2+, Ba2+, Co2+) and neurotransmitters (GABA, glutamate, nicotine).
• Stimulation of peripheral receptive fields.

Main Results:

• Feedback spikes are regenerative, with a threshold potential, and influenced by cone membrane potential.
• Strontium (Sr2+) and barium (Ba2+) ions facilitate and stabilize feedback spikes, enabling responses to dim light.
• Cations like cobalt (Co2+) and blockers like D-600 inhibit these spikes, as do depolarizing agents acting on L-horizontal cells.

Conclusions:

• Turtle cones receive feedback input from L-horizontal cells, capable of increasing cone calcium conductance.
• This feedback mechanism appears to be regenerative and plays a significant role in cone signaling.