Global and Local Synchronous Spontaneous Activity in the Developing Optic Tectum
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1
Louisiana State University School of Veterinary Medicine, USA, United States
Correlated synchronous spontaneous activity in the developing brain carries a blueprint of topographic organization. To understand the development of topographic organization, thus, requires knowledge of spatio-temporal patterns of spontaneous activity. I addressed this question in the developing optic tectum of albino tadpoles, Xenopus laevis, by employing an in vivo two-photon calcium imaging technique combined with a bulk-loading cell-permeant Oregon Green BAPTA-1 AM. This technique allowed me to separately monitor spontaneous activity in the input (the neuropil consisting of ascending axons and tectal dendrites) and output (tectal cell bodies) layers of the tectum. To understand the influence of visual experience, tadpoles were separately raised in normal (visual experience) and dark (no visual experience) conditions. I found that spontaneous events in the input layer depend on the developmental stage but not visual experience, while those in the output layer depend on both developmental stage and visual experience. In the output layer of the tectum, neurons are tightly correlated with average maximum correlation coefficient of ~0.5 despite the spontaneous activity, which I refer to as hyper-synchronous spontaneous activity. Furthermore, all identified neurons and the neuropil are significantly correlated with structured temporal patterns, suggesting global synchronization. By contrast, radial glial cells, non-neuronal cells in the tectum, show more local synchronization without obvious temporal patterns, which is in a sharp contrast to global synchronization between neurons.
In terms of global synchronization, a large number of neuronal pairs (83 %) show the maximum correlation coefficients at 0 s time lag, suggesting that tectal neurons receive input from a common source to generate spontaneous activity (e.g., self-generation). To understand the source of this spontaneous activity, I directly manipulated sensory input to the tectum. The optic tectum receives input from visual and mechanosensory (e.g., lateral line, somatosensory, and auditory) systems through retino-tectal and hindbrain-tectal projections, respectively. The manipulation of each sensory input alone has a small or no effect on spontaneous events. However, the manipulation of both visual and mechanosensory inputs significantly alters frequency, magnitude, and temporal patterns of spontaneous activity, while preserving weak activity. The results suggest that spontaneous activity in tectal neurons is self-generated and enhanced by a linear combination of visual and mechanosensory inputs. This is the first study to show global hyper-synchronous spontaneous activity enhanced by a non-linear combination of visual and mechanosensory inputs in the developing brain.
Acknowledgements
I thank my collaborators, Drs. Hamilton Farris (LSUHSC) and Jonathan Shih (UCSF).
Keywords:
audition,
lateral-line,
mechanosensory,
multisensory,
somatosensory,
tadpole,
Xenopus
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Invited Symposium (only for people who have been invited to a particular symposium)
Topic:
Sensory: Vision
Citation:
Imaizumi
K
(2012). Global and Local Synchronous Spontaneous Activity in the Developing Optic Tectum.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00028
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Received:
26 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Kazuo Imaizumi, Louisiana State University School of Veterinary Medicine, USA, Baton Rouge, United States, kimaizumi@forsyth.org