Impedance-voltage functions in the white rat with chronic body electrode implants

Abstract

Electrical properties of shock "punishment" delivered from implanted electrodes were studied . Subjects were six male albino rats, with four of the subjects under nembutal anesthesia and two not anesthetized. In addition, measures were taken at various times after electrode implantation so as to observe the effect, if any, of age of implant. Impedance characteristics at high and low voltages show that the rat is not a simple resistor. Anesthesia is not an important variable but age of implant seems important at low voltages. Problem Impedance measurements are reported for six male Sprague-Dawley white rats-(6-9 months old) a s a function of impressed voltage, using chronic body electrode implants . Although previous studies with rats have utilized implanted electrodes (e. g., Feirstein & Miller, 1963; Hendry & Hendry, 1963), they have not explored systematically the impedance characteristics of the organism. This has been done in the pigeon by Sidley and Schoenfeld (1963). MethodElectrodes of #30 gauge teflon coated silver wire were implanted subcutaneously in the right shoulders of the rats. The electrodes were about 3/8 in apart, and were formed by twisting together two strands of insulated wire and cutting the tips so that the exposed electrode areas consisted only of the cross-sections of the two wires. Separation of the tips was maintained by fixing them with a drop of dental acrylic cement. The electrode wires were led subcutaneously to a connector socket mounted on the skull. The socket was connected by external cable to the shock source. A shielded transformer supplied 60 cycleAC across a precision 10K ohm resistor in series with both the animal and a 1K ohm precision resistor. Applied voltage was calibrated on an oscilloscope, and voltage drop across the 1K ohm resistor was read from the oscilloscope. Impedances were calculated by Ohm's law.Eight voltages (all given in root mean square) were used: 1. 38,2.76,5.53,11.04,22 .09,44.19,88.38,176.75. At each voltage the rats were given a train of ten 60-millesec. pulses at a rate of 1 pulse per sec. Measurements were made first in an ascending, then a descending, series of voltage magnitudes. Approximately 90 sec. of "rest" separated both series and voltage values.Initial measurements were made on 4 animals under nembutal anesthesia (Rats 20, 21, 22, and 23) and on 2 non-anesthetized animals (Rats 24 and 25). The drug Psychon. Sci., 1964, Vol. 1. dosages, which included chloral hydrate supplements, were those recommended by Val en stein (1961). These first measurements were made on the several animals at varying times after implantation: Rat 20, 32 days; Rat 21, 5 days; Rat 22, 18 days; Rat 23, 20 days; Rat 24, 4 days; Rat 25, 4 days. Redeterminations were then made after the initial measurements as follows: Rat 20, 11 days (thus making a total of 43 days after implantation); Rat 21, 26 days (31 days after implantation); Rat 22, 20 days (38 days after implantation); Rat 23, 18 days (38 days after implantation); Rat 24, 9 days (13 days after implan...

Impedance-time functions in the white rat with chronic body electrode implants

“…The present data confirm and extend the data relating impedance to age of implant reported by Silver et al (1964). In contrast to the rat, however, age of implant does not seem to be an important variable with chronic implants in the pigeon.…”

“…I, there is also some variation among rats in the general level of impedance. Although differences in procedures and in electrode sizes make comparisons between absolute impedances difficult, the present levels are similar in magnitude to those reported for the rat by Hendry & Hendry (1963), and by Silver et al (1964) at low voltages.…”

“…However, with each animal's data ranked individually, the overall increase in impedance for the four rats was found to be significant (x r 2 =52.35; df=16; p<.OOl) using a Friedman two-way analysis of variance (Siegel, 1956). The data obtained on the first day were included in the statistical analysis, since Silver et al (1964) have shown that anesthesia is not an important variable affecting impedance. As mentioned above, the latter workers have also suggested that the increase in impedance with time is greatest at low voltages.…”

“…The subjects were four Charles River Caesarean delivery male albino rats about 110 days old at time of implantation. The method of implantation used was similar to that employed by Silver et al (1964). In general, the method involves passing insulated wire subcutaneously from a connector socket mounted on the skull to the rats' shoulders.…”

“…The latter have been studied in the pigeon by Azrin (1960) and more systematically in the same species by Sidley & Schoenfeld (1963). Silver et al (1964), using chronic body implants in the white rat, have found that impedance remains fairly constant over a wide range of impressed voltages and in<;:reases somewhat at low voltages. A redetermination of their first measurements by the latter workers indicated that impedance in the rat increases with age of implant, and that the greatest increase occurs at low voltages.…”