Ontogeny of Renin-Induced Salt Appetite in the Rat Pup MICAH LESHEM ALAN N. EPSTEIN z Biology Department and Mahoney Institute zy of Neuroscience The University of Pennsylvania Philadelphia, Pennsylvania lntracerebroventricular injections of renin in suckling rat pups increased intake of NaCl solutions when they were orally infused zyxwvut 5 hr after injection. The appetite for saline solution was evident in pups as young as zyxwvutsr 3 days, was greater in females, and was specific insofar as intake of milk, either by suckling or by oral infusion, was not affected. Three-day-old pups increased intake only to 12% NaCl, the acceptable concentration of NaCl becoming lower in older pups. These results suggest, first, that, as is true for feeding and drinking, the brain mechanism for salt appetite is competent for expression of the behavior in the very young rat pup, and second, that its angiotensinergic neural substrate is distinct from that which mediates the dipsogenic effect of the hormone. Suckling rat pups evince a precocious capacity to express adult-like ingestive behaviors when submitted to experimental challenges. Such research reveals the ontogeny of the neural substrates of regulatory behaviors. This has been shown for feeding (Friedman, 1975; Hall, 1979; Houpt zyxw & Epstein, 1973), and drinking (Bruno, 1981; Ellis, Axt, & Epstein, 1984; Leshem, Boggan, & Epstein, 1988; Leshem & Epstein, (1988); Wirth and Epstein, 1976), and recently for salt appetite where it has been demonstrated that pups as young as 12 days of age will increase their intake of a strong NaCl solution in response to depletion of body sodium by furosemide or adrenalectomy, or as a symptom of genetic hypertension (Moe, 1985; 1986a). We also know that rat pups as young as 2-5 days of age are capable of rejecting concentrated salt solutions (Bernstein & Courtney, 1987; Hall & Bryan, 1981; Moe, 1986b; Wirth and Epstein, 1976) and that after this age they begin to increase their intake of selected concentrations of NaCl. Lower concentrations of the salt are increasingly preferred until, as the pups approach weaning age (18-20 days), the preference-aversion curve is close to its adult form (Bernstein & Reprint requests should be sent to Micah Leshem, Ph.D., Psychology Department, University of Haifa, Haifa, Israel 31999. Received for publication 5 October 1987 Revised for publication 26 January 1988 Accepted at Wiley 22 February 1989 Developmental Psychobiology, 22(5):437-445 (1989) zyxwv 0 1989 by John Wiley & Sons, Inc. CCC 0012-1630/89/050437-09$04.00