A new role for photoresponsive neurons called simple photoreceptors in the sea slug Onchidium verruculatum: Potentiation of synaptic transmission and motor response.
The simple photoreceptors Ip-1 and Ip-2 are intrinsically light-sensitive neurons that exist in the abdominal ganglion of the sea slug Onchidium verruculatum. Using isolated ganglia and semi-intact or intact animal preparations, the present studies examined the light-sensing and physiological roles of Ip-1 and Ip-2 cells, which respond jointly to light by inducing a slow hyperpolarizing receptor potential. First, the synaptic inputs received by Ip-1 and Ip-2 and the axonal branches arising from their cell bodies were investigated. We found that these cells are not only first-order photosensory neurons, but also second-order neurons (interneurons), relaying inhibitory synaptic inputs such as water pressure and/or tactile senses. The amphibian Onchidium opens a pneumostome at low tide in order to aero-breathe. This pneumostome opening; i.e., aero-breathing behavior, was produced by spike discharges of Ip-1 and Ip-2 cells. Furthermore, the present results suggested that the hyperpolarizing photoresponse of Ip-1 and Ip-2 cells operates in the potentiation of inhibitory sensory synaptic transmission. Thus, we conclude that the simple photoreceptors of Onchidium play a role in the long-lasting potentiation of synaptic transmission and the subsequent behavioral response and so may be involved in a new photosensory modality, non-image-forming vision.
Shimotsu
Kyoko
K
Laboratory for Neuroanatomy, Department of Neurology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan.
Nishi
Takako
T
Nakagawa
Shiro
S
Gotow
Tsukasa
T
D000818:Animals; D001522:Behavior, Animal; D017952:Ganglia, Invertebrate / Q000502:physiology; D049851:Gastropoda / Q000502:physiology*; D042541:Intracellular Space / Q000502:physiology; D008027:Light; D017774:Long-Term Potentiation / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009043:Motor Activity / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000502:physiology*; D013057:Spectrum Analysis; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*