A shock harness for rats: Resistance as a function of shock intensity

Abstract

AbstraetThe efficiency of a harness device for administering consistent electric shocks to rats was evaluated by measuring changes in resistance as a function of shock intensity, both within a single shock and over the course of 15 days. Resistance within a single session was most constant at the highest shock level used (4.25 mal and did not increase significantly as a function of time at any of the four shock intensities employed. IntroductionThe several problems associated with presentation of shock through an electrified grid floor (England, 1964) have lead to the development and increasingly successful use of implanted electrodes in various species (Azrin, 1959; Silver et al, 1964). We have found that a nonavoidable and consistent shock can also be delivered to rats through a small metal harness which can be attached before each conditioning session.The efficiency of the shock harness device has been evaluated by examining changes in a rats resistance: (a) within a single shock of 0.6 sec. duration; (b) during a single session in which 100 shocks were administered and (c) over the course of 15 daily sessions. Each of these three indi ces was studied a s a function of four levels of shock ranging from 1.5 to 4.25 mao Resistance was determined from the slope of a voltage versus current curve, photographed from an oscilloscope display. The method described is equally applicable to resistance measurements with implanted electrodes and other types of harness electrodes. MethodThe shock harness consists of a flexible, stainless steel pipe clamp (45 gm in weight) which can be adjusted to the girth of the rat. A semi-circle of copper (1/2 in x 1-1/2 in x 0.02 in) is attached to and insulated from the inside of the steel band . Input leads, encased in flexible metal shielding, are attached to both the steel band and the copper strip, and joined to a connector on the roof of the experimental chamber.In order to determine the extent to which movement or possible tissue changes would alter resistance in this harness, four naive hooded rats, weighing 300-350 gm, were given 100 shocks of 0.6 sec. duration, at 20 sec. intervals, every day for 15 days . The shock source delivers 60 cycle AC current to the rat through 10,000 ohm series resistor. Four shock intensities, approximately 0.5, 1.5, 3, and 4 .25 milliamperes (rna) were used. Each rat received only one shock level throughout the experiment.Following Ohms law, it is possible to calculate the resistance of the r at during a single shock, by plotting Psychun . Sci., 196 5. Vol. 3 voltage (V) a gainst current (1) on an oscilloscope (Tektronix 502). A typical V 1 trace is shown in Fig. 1a . Similarly, both voltage changes (upper trace) and current changes (lower trace) can be plotted as a function of time within a single shock (Fig. Ib),To calculate the instantaneous resistance of an animal from an oscilloscope tracing of a V 1 curve, it is first necessary to determine the vertical and horizontal extent of the V 1 curve in centimeters. The vertical excursion, vo...