Rapid, Labile, and Protein Synthesis– Independent Short-Term Memory in Conditioned Taste Aversion

Abstract

Short-term memory is a rapid, labile, and protein-synthesis-independent phase of memory. The existence of short-term memory in conditioned taste aversion (CTA) learning has not been demonstrated formally. To determine the earliest time at which a CTA is expressed, we measured intraoral intake of sucrose at 15 min, 1 hr, 6 hr, or 48 h after contingent pairing of an intraoral infusion of 5% sucrose (6.6 ml over 6 min) and toxic lithium chloride injection (76 mg/kg). Rats were implanted with intraoral catheters to allow presentation of taste solutions at arbitrary times. Intraoral intake was measured under conditions of long-delay, single-trial learning typical of CTA. Rats decreased intraoral intake of sucrose at 15 min after contingent pairing of sucrose and LiCl, but not after noncontingent LiCl or sucrose. Thus CTA learning can be expressed rapidly. To determine if short-term CTA memory is labile and decays in the absence of long-term memory, we measured intraoral intake of sucrose after pairing sucrose with low doses of LiCl. Rats received an intraoral infusion of 5% sucrose (6 ml/6 min); 30 min later LiCl was injected at three different doses (19, 38, or 76 mg/kg). A second intraoral infusion of sucrose was administered 15 min, 1 hr, 3 hr, 4.5 hr, 6 hr, or 48 hr later. The formation of long-term CTA memory was dependent on the dose of LiCl paired with sucrose during acquisition. Low doses of LiCl induced a CTA that decayed within 6 hr after pairing. Central administration of the protein synthesis inhibitor cycloheximide prior to LiCl injection blocked long-term CTA expression at 6 and 48 hr, but not short-term CTA expression at 1 hr. Thus, short-term memory for CTA learning exists that is acquired rapidly and independent of protein synthesis, but labile in the absence of long-term memory formation.

Temporal and Qualitative Dynamics of Conditioned Taste Aversion Processing: Combined Generalization Testing and Licking Microstructure Analysis.

“…Eckel and Ossenkopp (1996) observed increased aversive responses 10 min after LiCl injection in intact rats. Houpt and Berlin (1999) showed that rats decreased intraoral sucrose intake 15 min after contingent pairing of intraoral sucrose and intraperitoneal LiCl. The present study reduces the time to observe CTA formation to less than 9 min.…”

“…It is interesting to note that Eckel and Ossenkopp (1996), Houpt andBerlin (1999), andSpector et al (1988) failed to observe unconditioned effects of LiCl on intake or taste reactivity responses when rats were first tested 15 or 20 min after LiCl injection. Consistent with this finding, we observed no shifts in the ILI distribution during T2 water licking after T1 LiCl in Experiment 2, as we did for LiCl and NaCl CTA conditions in both experiments.…”

Forebrain structures specifically activated by conditioned taste aversion.

“…To evaluate whether the nature of the structures engaged in CTA acquisition depends on the aversion strength, we therefore studied the relationship between Fos expression levels in strong versus weak CTA conditioning. For this purpose, we used injections of different LiCl doses during CTA acquisition, because a weak malaise induces a weak CTA, whereas a strong malaise induces a strong CTA (Houpt & Berlin, 1999; Miranda et al, 2002; Nachman & Ashe, 1973; Sakai & Yamamoto, 1997).…”

Dissociating the conditioning and the anorectic effects of estradiol in female rats.

“…It has been demonstrated that CTAs are formed rapidly following the pairing of the CS with the US. A LiCl CTA is expressed 15 minutes following the pairing of saccharin with the agent (Houpt & Berlin, 1999). If this holds true for estradiol as well, then in order for estradiol to condition on the basis of satiety, the animals must be in a state of satiation shortly following the estradiol injection.…”

“…However, administration of a US after a certain interval fails to result in CTA. For instance, CS-US intervals greater than 12 hours do not support radiation CTAs (Smith & Roll, 1967) and a 24-hour inter-stimulus interval prevents acquisition of a LiCl CTA (Houpt & Berlin, 1999).…”