Suppression of behavior by food pellet-lithium chloride pairings in squirrel monkeys.

Responding by squirrel monkeys was maintained under a 30-response fixed-ratio schedule of food presentation; during different sessions responding produced either sucrose-flavored or banana-flavored food pellets. Pre-session administration of doses of lithium chloride (LiCl) less than 3.0 mEq/kg did not alter rates of responding whereas pairing either type of pellet with post-session injections of 1.8 mEq/kg LiCl suppressed both lever pressing and consumption during subsequent sessions in which that pellet type was available. When post-session injections of LiCl were discontinued, responding recovered within 14 sessions. The suppression of responding, but not pellet consumption, was then reliably reproduced in each monkey by pairing post-session LiCl with the previously non-paired type of pellet. Pre-session administration of chlordiazepoxide (CDAP, 3.0-17.0 mg/kg) increased rates of suppressed responding in a dose-related manner, but did not increase pellet consumption. These data indicate that different mechanisms may be involved in the suppression of responding and the suppression of consumption of food by post-session injections of drugs. The suppression of responding by post-session injections of drugs in primates appears to be qualitatively similar to the suppression of responding by other noxious stimuli such as electric shock in that it is reversible, it can be reinstated by re-exposure to post-session drug injections, and it can be attenuated by pre-session administration of CDAP.