Post-light potentiation at type B to A photoreceptor connections in Hermissenda.
We investigated whether the long (approximately 30-s) or short (approximately 3-s) light stimuli that have been used during behavioral training would induce post-light potentiation (PLP) at the type B to A photoreceptor connections of the isolated nervous system of Hermissenda. We found that a single approximately 30-s light step induced PLP at these connections relative to both pre-light baseline and seawater control preparations, as did a series of nine short (approximately 3-s) light steps. In addition, a 30-s step of depolarization-elicited type B cell activity induced potentiation comparable to that induced by a approximately 30-s light step, indicating that light-elicited type B cell activity contributes to the induction of PLP. By contrast, even though a series of short (3-s) light steps induced potentiation, short steps of depolarization-evoked type B cell activity did not. Hence, light-evoked processes other than type B cell depolarization or activity (e.g., perhaps intracellular Ca2+ release) also contribute to the induction of PLP. Further results suggest that these other light-evoked processes interact nonadditively with type B cell activity to generate PLP. Some but not all instances of synaptic potentiation were accompanied by various changes in parameters of type B cell action potentials and afterhyperpolarizing potentials, suggesting diverse underlying mechanisms, including increases in neurotransmitter release. Given that the type A cells have been proposed to polysynaptically excite the motor neurons that drive phototaxis, a light-evoked potentiation of synaptic strength at the inhibitory type B to A photoreceptor connections may play a mechanistic role in light-elicited nonassociative learning.
Schultz
L M
LM
Department of bioengineering, University of Utah, Salt Lake City 84112, USA. lschultz@alumni.princeton.edu
Butson
C R
CR
Clark
G A
GA
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001245:Association Learning / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D008027:Light; D008974:Mollusca; D009415:Nerve Net / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D013569:Synapses / Q000502:physiology
D015220:Calcium Channels