The Activity of Single Cells in the Midbrain and Hypothalamus of the Cat during Affective Defense Behavior
Methods Page 2

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The general experimental situation consisted of two cats, a recording cat and an attacking cat, separated in a cage by a removable partition. The recording cat was implanted with a concentric microelectrode from which single cells could be recorded extracellularly. The attack cat, which was implanted in the brain with a stimulating electrode, was used simply to launch an attack upon the other cat when the partition was opened. The recording cat responded to the attack with a display of affective defense, during which time the response of one of its brain cells was recorded.

The activity of single cells during affective defense was routinely compared with activity during other manipulations of the cat including the presentation of clicks and flashes, lifting and dropping of the cat, leg retraction following extension of the cat's foreleg by the experimenter, and pinching of the tail. Following all recording from a cell, the region surrounding that cell was electrically stimulated through the barrel of the concentric electrode.


Results were obtained from 15 adult cats, selected on the basis of their response to the attacking cat. Cats which responded with affective defense, hissing or striking and ear retraction on all trials and all three combined on some trials, were selected for use in the experiment. Other cats which simply cowered or turned their backs on the attacking cat or tried to escape from the cage were not used.


The experiment was conducted in a shielded wood and plexiglas chamber divided into two compartments by a removable sliding partition. Each compartment had a separate door on the front through which the experimenter could gain access.

The electrode and mounting were especially developed for the present experiment in order to minimize the chances of losing contact with a cell during movement by the cat. There were two parts to the system as shown in Fig. 1: a bipolar, concentric, stainless steel electrode permanently mounted in a threaded nylon sleeve; and a stainless steel guide drilled longitudinally, lined with polyethylene tubing, and secured with dental cement on the cat's skull. The bared tip of the inner wire of the electrode was between 30 and 50 microns in diameter, the insulated shaft was 0.8 mm in diameter, and the barrel was bared of insulation for approximately 0.6 mm up the shaft.

Extracellular potentials were recorded differentially between the tip and barrel of the electrode and led by Microdot mininoise cab]e to a Tektronix 122 preamplifier. Frequency range of the preamplifier was at three db attenuation at eight cps for low frequencies and 20,000 cps for high frequencies. Recording was monitored by oscilloscope and audio speaker. Signals were recorded on one channel of an Ampex FR 1300 tape recorder at 60 ips. The data were later written out on a Dynograph polygraph with the tape recorder speed slowed down to 1 7/8 ips. Thus, the polygraph, which could normally follow frequencies up to 150 cps was able to follow frequencies originally recorded up to 4800 cps. In order to eliminate baseline fluctuations low frequencies were attenuated 3 db at 5.3 or 80 cps on the playback, which functioned as if filtering the original records at 175 or 2560 cps. Records made by these means were compared with identical data played back at original speed by the tape recorder into an oscilloscope and photographed on 35 mm film, and were found to be accurate for data analysis. An event marker operated by a hand switch was recorded on a second channel of the tape recorder.

Clicks were delivered through a loudspeaker placed directly above the cat's head. They were approximately 95 db SPL positive peak value. Other auditory stimuli included a "banging noise" made by striking one sheet of aluminum against another (110 db SPL), tapping the partition which separated the cats (100-105 db SPL), and scratching the shielding screen (95 db SPL). Light flashes were delivered by a Grass photostimulator set at number four intensity.

Brain stimulation was applied between the barrel of the electrode and an indifferent electrode implanted in the skull and consisted of 60 cps, 1 msec, biphasic square waves. It was passed through an isolation transformer and was monitored on an oscilloscope across a 200 ohm resistor in series with the cat.

Marking lesions of 350 μA were produced with the barrel of the electrode as anode and an indifferent electrode on the skull as cathode.

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