ANOTHER NEW TYPE OF CAT RETINAL GANGLION CELL? Department of Psychology, Michigan State University. East Lansing. MI 48824. U.S.A. (Recrired 7 Aprii 1975;

in

revised form 22 Au+st 1975)

Abstract-A group of cat retinal ganglion cells. termed “triggered response cells”, responded to normal visual stimuli with elevations of their firing rates lasting tens or hundreds of seconds. These sells seem different from other cells whose maintained discharges undergo long-lasting changes. In many other respects “triggered response cells” resemble Y-type cells.

A number of reports have described cat retinal ganglion cells whose maintained discharge was unusual in one way or another. One such phenomenon was an oscillation of the rate of maintained discharge with a period of 60 set or more under conditions of dim background illumination (Rodieck and Smith, 1966; Ascoli and Maffei, 1964). More recently there have been several reports of stimulus “triggered”, long lasting, sustained elevations of the maintained discharge which may outlast the stimuius by tens or hundreds of seconds (Fukada and Saito, 1971; Saito and Fukada, 1973; Cleland and Levick, 1975). A possibly related result has also been described in L~~~~iis(Wasserman, 1968). Because these cells are encountered infrequently progress toward understand~g them has been slow. Several observations are described which might guide other investigators if they encounter similar cells. METHODS Preparation The anesthesia, surgical preparation, and immobilization of adult cats were essentially like those reported in a number of other reports by other investigators (Levick and Zacks, 1970; Cleland, Dubin and Levick, 1971). Following initial induction with ethyl chloride, anesthesia was continued with ether until the cephalic vein was cannulated. Then 1% thiamyl sodium (Surital) was administered i.v. as needed until all surgical procedures were completed. A tracheal cannula was installed to permit subsequent artificial ventilation. The cervical sympathetic trunk on the side of the eye to be recorded from was severed to aid ocular stability. A rectal thermistor was installed to permit monitoring and, through a feedback-regulated heating blanket. control of body temperature at 38-39’ C. The right eye was sutured to a steel ring to aid ocular stability and to provide support for the electrode manipulator (Cleland er al., 1971). The pupi was dilated with a mixture of 1% atropine and 25% neosynepherine. Following the surgical preparation the animal was paralyzed with an initial dose of 10 mgikg of Flaxedil, and maintained on 5 mgikg hr of Flaxedil in 6% glucose solution. Anesthesia was maintained from this point by a mixture of 70% nitrous oxide. 28.5% oxygen, and 15% carbon dioxide given at 34 strokesimin. The volume/stroke was determined from the graph by Kleinman and Radford (Harvard Apparatus, Millford. Mass.) and then multiplying that value by 1.5.

Retinal

recordinq

The basic aspects of the procedures

and apparatus used for extracellular recording from retinal ganglion cell bodies or their axons were base2 on proceduies similar to those described bv Levick and Zacks (1970). and Cleland et (II. (1971). Gla&.-insulated tungsten ‘micr&lectrodes, made as described by Levick (1972). were introduced into the right eye through a cannula which penetrated the globe just forward of the equator. A hydraulic micromanipulator and positioner were used to orient and advance the electrode onto the inner surface of the retina. Details of the ampli~cation and display ~angements using an a.c. coupled, high impedence preamplifier, cathode ray oscilloscope, and audio monitor were conventional. In addition the amplified signal was fed co a Schmitt trigger where the action potentials were used to initiate a pulse of standard amplitude and duration. This pulse was used to intensify the display of the action potential to verify triggering levels, as the input to a low-pass RC filter (Cleland er al., 1971) to provide a continuous record of mean firing rate on a chart recorder, and as the input to a LINC computer which was used to control stimulus presentation and to process the resulting trains of action potentials. On-line data processing The LINC computer was used to cumulate post-stimulus time histograms (Gerstein and Kiang, 1960). A useful variation of the post-stimulus time histogram consisted of a histogram representing the sums of the numbers of action potentials observed in each of 512 successive I-set intervals. This histogram could be used either to rqresent the maintained discharge in the absence of a stimulus or to represent responses to stimulation on a coarse time scale without requiring that the assumption of stationarity required for meaningful interpretation of multiple-sweep, post-stimulus time histograms be satisfied.

Stimuli Background illumination was provided either by an incandescent tungsten lamp run from the a.c. line. or. at lower luminances, another tungsten source operated from a regulated d.c. power supply. Stimuli were produced either by a bank of fluorescent tubes which were electronically gated on and off or by an incandescent projector controlled by an electromagnetically operated shutter. Luminances of the Bashed stimuli were controlled by neutral density filters and measured with a visual photometer (SEI, Ilford Ltd.).

OnI) csils bcirh on-center. &-surrounds wre studied in detail. One off-center cell uhich It-as examined onit cursorill; seemed to share the main feature of the cells described beio

Another new type of cat retinal ganglion cell.

ANOTHER NEW TYPE OF CAT RETINAL GANGLION CELL? Department of Psychology, Michigan State University. East Lansing. MI 48824. U.S.A. (Recrired 7 Aprii 1...
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