Specific and Nonspecific Activities of the Visual System in Rabbits

Abstract

Although it has been shown that the rises in cortical activities by 3 and 5/sec flash stimulations verified in the frequency response of the visual cortex of unanesthetized rabbits (MIMURA and SATO, 1965) can be correlated with the excitability changes of 5/sec (BIsHOP, 1933) or 4-5/sec (PEARLMAN, 1963) in the visual cortex of the rabbit, it was not ascertained whether these excitability changes originated from the cortex itself or from subcortical structures nor was it ascertained whether it was from the specific or the nonspecific system. The present study is an attempt to solve the above problems through observations on the pattern of response to repetitive flash stimulations in the specific and non-specific systems of the cortex and subcortical structures of anesthetized and unanesthetized rabbits. METHODTen anesthetized and eleven unanesthetized rabbits weighing about 3kg were used. The anesthetized experiments were carried out under an intraperitoneal administration of sodium pentobarbital at a rate of 15mg/kg/2 hrs. The animal was mounted on the Johnson type stereotaxic instrument. Intubation to the trachea under ether anesthesia was done in unanesthetized experiments and the animal was immobilized of ter opening the skull by intraperitoneal administration of Flaxedil throughout the experiment, which necessitated artificial respiration with oxygen-mixed air.Stainless steel electrodes of 0.5mm and/or 80u diameter, insulated except at the tip, were inserted stereotaxically into the brain according to the atlases of SAWYER et al. (1954), GANGLOFF (1961) andFIFKOVA and MURsALA (1962). Surface records from the cortex were taken with 0.5mm diameter silver ball tipped electrodes. ERGs were recorded by placing the same silver ball electrode on the cornea. All recordings were monopolarly taken in relation to a reference electrode on the neck muscle. The location of the electrodes were checked histologically by the KLUVER-BARRERA staining techniques (1953) of ter each experiment.The exposed cortical surface was covered with warm mineral oil. The temperature