Effects of psychomotor stimulants, alone and in pairs, on milk drinking in the rat after intraperitoneal and intragastric administration

RW Foltin, WL Woolverton and CR Schuster

The effects of cocaine, d-amphetamine and l-cathinone, alone and in pairs, on intake of a sweetened milk solution were determined in rats. Experimental sessions consisted of 15 min access to the milk solution daily, 7 days a week. After the determination of base-line intake, rats were assigned to one of two groups. All rats in one group received i.p. injections 15 min before the session and all rats in the other group received intragastric (i.g.) infusions 30 min before the session. A series of dose-response functions were then determined by giving a dose of a drug or a pair of drug doses once every 4 days. A wide range of doses of both drugs were tested in combination to fully characterize any interactions. When given alone, all three drugs produced dose- dependent decreases in milk intake. For each drug, higher doses were required to decrease milk intake when given i.g. than when given i.p. The decreasing order of potencies was d-amphetamine, l-cathinone and cocaine after i.p. administration and l-cathinone, d-amphetamine and cocaine after i.g. administration. In nearly every case, for both routes of administration, a drug produced dose-dependent shifts to the left of the dose-response function of the drug with which it was combined. Isobolographic analysis of the interactions indicates that d- amphetamine and l-cathinone were infra-additive (i.p.) or additive (i.g.), cocaine and d-amphetamine tended toward supra-additivity by both routes and l-cathinone and cocaine were additive or infra-additive by the i.p. route. The results of the i.g. cocaine and l-cathinone interactions could not be analyzed with isobolograms. The type of interaction was dependent on the particular drug pair, the particular dose combination tested and the route of administration.

Volume 226, Issue 2, pp. 411-418, 08/01/1983
Copyright © 1983 by American Society for Pharmacology and Experimental Therapeutics