Changes in pressing for intracranial stimulation (ICS) after prolonged ICS

Abstract

Rats, fixed with two chronically indwelling electrodes, pressed daily for fixed intensities of ICS while press rates were tabulated. As daily testing for press rates continued, there were sessions in which 20-sec trains of low-intensity (20 j.U\ or less of 60-Hz sine waves) were imposed at some electrode sites. These trains of ICS led to reduced pressing rates for the fixed ICS, but 20 sec of intermittent ICS (.25 sec on, .25 sec off) or zero ICS did not. It was concluded that 20 sec ICS of low intensity, an ICS frequently used in studies of motivation, reduced the capacity of ICS to sustain pressing, probably by disrupting the tissue of ICS.A number of procedures involve programming durations of intracranial stimulation (ICS) of 20 sec or greater. Using these prolonged trains of ICS, Amit, Stern, and Wise (1970), as well as others following their lead, have demonstrated that daily hypothalamic ICS can lead to increased voluntary consumption of ethanol solutions. The typical procedure is to program 20 sec trains of ICS (6O-Hz sine waves of about 30 ,.,A), with intervals between trains of 20 sec, for 30 min a day. In a rat's home cage, an ethanol solution (typically 20"10 ethanol, v Iv) and tap water are presented while amounts consumed during day-long periods are tabulated. Rats that received ICS consumed considerable quantities of ethanol (sometimes taking the ethanol solutions almost exclusively) and furthermore maintained high levels of consumption beyond the days during which ICS was programm€!d.The finding that hypothalamic ICS can lead to increased consumption of ethanol is interesting and is, in part, the impetus for development of new theory and, in turn, for deriving new treatment practices for alcoholism (Amit & Sutherland, 1975; Amit, Levitan, & Sutherland, Note 1). The finding that ICS leads to heightened ethanol consumption, however, has not been found by everyone (e.g~, Martin & Myers, 1972), suggesting that subtle procedural difference between studies might account for differences in outcomes. Some of the potentially relevant variables have been studied and certain parametric manipulations of germane variables have been accomplished (Wise & James, 1974). The interpretation of the finding of enhanced ethanol consumption with ICS will, of course, vary depending on the circumstances under which the phenomenon is achieved.This research was supported by Grant DA 01049, National Institute of Drug Abuse, DHEW, and by a grant from the Distilled Spirits Council of the United States. 58One potentially relevant variable that has not been inspected is the possibility that the ICS used in these studies may be disrupting the tissue at the electrode tip. Recently collected data (Magnuson, Tadeusik, & Reid, 1976; Terando, Mirza, Zipnick, Overmier, Rossi, & Reid, Note 2) lead to the suggestion that intensities of ICS used in many studies of intracranial selfstimulation are sufficiently intense to disrupt the tissue as indexed by downward shifts in pressing for low-intensity ICS. The purpose of this study was to de...