Ketamine blocks a taste recognition memory in fetal rats

Decisions about novelty/familiarity are critical in determining whether or not information should be attended to, and possibly encoded, for long-term storage. We have reported that fetal and neonatal rats exhibit an increase in orofacial movements (e.g., perseverative mouthing and mouth movements, a nd licks) upon tasting saccharin (SAC), if it was experienced previously. E 19 rat fetuses can acquire this taste recognition memory and retain it for at least 5 days (P3). In the current study, we sought to evaluate the role of N-methyl-D-aspartate (NMDA) receptors in establishing a taste recognitio n memory. Pregnant Sprague-Dawley rats received ketamine (NMDA receptor ant agonist) (doses: 0, 50, or 100 mg/kg, ip). One-half hour later, we performe d a reversible spinal block on each pregnant dam, and E19 fetuses received an oral injection of 10 mul, 0.3% SAC or water (control) while in utero. Th e uterus was replaced and the pups were later born via a normal vaginal del ivery. On P3, all pups experienced oral lavage of 10 mul, 0.3% SAC, and mot or responses were recorded. As expected, non-drugged control neonates tasti ng familiar SAC exhibited significantly more perseverative mouth movements, as well as total mouth movements and licks, than did pups tasting novel SA C. However, this taste recognition memory response was not observed in rats exposed to ketamine in utero. The data suggest that early non-associative taste memories may be disrupted by NMDA receptor blockade. (C) 2000 Elsevie r Science Inc. All rights reserved.