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, and licks) upon tasting saccharin (SAC), if it was experienced previously. E19 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 recognition memory. Pregnant Sprague-Dawley rats received ketamine (NMDA receptor antagonist) (doses: 0, 50, or 100 mg/kg, i.p.). One-half hour later, we performed a reversible spinal block on each pregnant dam, and E19 fetuses received an oral injection of 10 microl, 0.3% SAC or water (control) while in utero. The uterus was replaced and the pups were later born via a normal vaginal delivery. On P3, all pups experienced oral lavage of 10 microl, 0.3% SAC, and motor responses were recorded. As expected, non-drugged control neonates tasting familiar SAC exhibited significantly more perseverative mouth movements, as well as total mouth movements and licks, than did pups tasting novel SAC. 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.