Modulatory effects of caffeine on behavioral and neural visual contrast sensitivity of rats

[Speaker] Keisuke Tsunoda:1
[Co-author] Akinori Sato:1, Ryo Mizuyama:1, Satoshi Shimegi:1,2
1:Graduate school of Frontier Biosciences, Osaka University, Japan, 2:Graduate school of Medicine, Osaka University, Japan

Caffeine (1, 3, 7-trimethylxanthine) is a well-known CNS stimulant, affecting positively arousal and attention by antagonism of adenosine receptors. The action is thought to be exerted by antagonism of adenosine receptors, thereby, the adenosinergic inhibitory effects on CNS activity is disinhibited and the releases of neuromodulators including acetylcholine are also altered significantly.
This suggests that caffeine modulates various CNS functions including visual function. However, it remains unclear whether and how caffeine modulates visual ability such as contrast sensitivity (CS) and CS-spatial frequency (SF) relationship. To investigate these points, we tested the effects of caffeine on the behavioral CS of freely moving rats. Long Evans rats were trained to perform a two-alternative forced-choice visual grating detection task (2AFC). After the animal's learning, the CS was measured with or without an intraperitoneal injection of caffeine using the 2AFC combined with a staircase method. The grating contrast was decreased or increased step-by-step according to animal's correct or miss response in the prior trial. Caffeine improved the CS at low SF (0.1 cycles/degree), suggesting that neuronal visual information processing is modulated by caffeine presumably via adenosine receptors.
Moreover, in the head-fixed and passively viewing condition of awake rats, the same treatment of caffeine was found to shift upwardly the contrast-response functions in neurons of the primary visual cortex (V1), which is called a baseline control. However, baseline control enhances not only visual responses as a signal but also spontaneous discharges as a noise, and those behavioral and electrophysiological studies were conducted separately.
Therefore, it remains unknown whether and how behavioral CS improvement by caffeine could be mediated by the neuronal modulation in V1. To answer these questions, we newly established a simultaneous measurement system for behavioral and neural CSs, in which neural activities were recorded in V1 of head-fixed rats performing visual detection task in Go-No-Go paradigm. By using this system, we measured CS-SF relationship, confirming that the SF tuning of the CS is low-pass which is the same as our previous results. We are currently performing the multi-unit recordings from V1 of task-performing rats with or without administration of caffeine and acetylcholine.

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