Mercaptoacetate decreases latency to initiate independent ingestion, but not suckling, in preweanling rats.

Altering oxidation of fatty acids by administration of mercaptoacetate (MA) or methyl palmoxirate has been demonstrated to stimulate independent ingestion in rat pups by 12 to 15 days of age. However, in other work, neither agent has been demonstrated to affect intake in the context of suckling. In the present experiments, we tested the effects of MA on both suckling and independent ingestive behavior by examining changes in latency to initiate suckling or independent ingestion and by measuring intake in short-term (30 min) and longer term (4 hr) suckling and independent ingestion tests in pups aged 12 to 15 days of age. The results demonstrated that (a) MA does not affect suckling intake in short- or longer term tests; (b) MA does not affect latency to attach to a nipple, most likely due to floor effects on latency to attach in control pups; (c) MA stimulates independent ingestion in short-term, but not longer terms tests; and (d) MA reduces the latency to initiate independent ingestion. These results suggest that administration of MA preferentially stimulates the initiation of independent ingestion over suckling, and that this response develops at an age just prior to the time at which independent ingestion is typically first expressed by rat pups.