Ontogeny of urine preference and its relationship to NH₄Cl preference and sodium hunger in suckling rat pups

We chart the postnatal ontogeny of urine preference in the suckling rat. Twelve-day-old sucklings, when offered urine, NH₄Cl, or NaCl, ingest more urine and NH₄Cl than NaCl. When rendered sodium hungry by ivc renin or by sodium depletion, these sucklings prefer urine and NH₄Cl to NaCl, dilute urine, or an NaCl and KCl mineral mix equimolar to urine; however, by 18 days of age, urine and NH₄Cl are no longer preferred to NaCl. Hence, urine preference in the suckling may be specific and preparatory for the variety of purposes urine preference serves in the adult rat, and it might guide the pup to urinary sodium in the nest. Since preference for urine and NH₄Cl covary during postnatal development, the high preference for NH₄Cl in midterm sucklings might be because its ammonium flavor is similar to urine.