PII S0031-9384(97)00310-7 The Newborn Rat Ingests Fluids through a Surrogate Nipple: A New Technique for the Study of Early Suckling Behavior EVGENIY S. PETROV, ELENA I. VARLINSKAYA AND WILLIAM P. SMOTHERMAN Laboratory of Perinatal Neuroethology, Center for Developmental Psychobiology, Department of Psychology, State University of New York at Binghamton, Binghamton, NY 13902-6000 Received 15 January 1997; Accepted 14 May 1997 PETROV, E. S., E. I. VARLINSKAYA AND W. P. SMOTHERMAN. Feeding of the newborn rat with a surrogate nipple: A new technique for the experimental study of early suckling behavior. PHYSIOL. BEHAV. 62(5) 1155–1158, 1997.—In this report we describe an apparatus and procedure that permits a newborn rat pup to ingest test fluids including milk through a surrogate nipple. The surrogate nipple represents a new testing situation for the experimental study of sensory and neurochemical controls of suckling behavior immediately after birth. © 1997 Elsevier Science Inc. Surrogate nipple Artificial feeding Suckling Rat pup Milk Development STUDY of the infant rat has served as a focus of psychobio- logical research for nearly three decades (6) and has provided a foundation for investigating the development of suckling be- havior (1,2). Nevertheless, experimental study of the first suck- ling episode including the physiological and biochemical mech- anisms that regulate early behavior at the nipple can benefit from a simple and reliable technique where newborn rat pups ingest milk and other fluids from a surrogate nipple. With this technique, psychobiologists, physiologists and nutritionists can assess initial responses of the newborn rat to stimuli present in the suckling context, including milk and the surrogate nipple itself. Experiments can take place under controlled conditions and be conducted apart from active maternal care. The new technique will compliment existing strategies for studying early behavior at the nipple including suckling tests conducted on the ventral surface of an anesthetized female (1) or presentation of milk through an oral cannula (5,8). In this report, we describe the apparatus and procedures that permit the newborn rat pup to ingest fluids through a surrogate nipple. The surrogate nipple feeding technique will provide a unique testing situation for investigating the control and development of behavior that appears in the context of suckling and becomes functionally important immediately after birth. THE SURROGATE NIPPLE APPARATUS The surrogate nipple apparatus consists of three main parts: the surrogate nipple, the fluid reservoir and the glove box (Fig. 1). The surrogate nipple is constructed from a block of soft vinyl material (Carolina Biological Supply, Burlington, NC) and fashioned with a sanding disk attached to a high speed dental drill. The surrogate nipple is 25 mm long and tapers to a 1-mm diameter at the rounded tip. The surrogate nipple has a round plate (1.5 mm thick; 5 mm diameter) made from the same soft vinyl material that is positioned 5 mm from the tip of the nipple. The plate provides a contact point for the snout when the pup exhibits an oral grasp response of the surrogate nipple (10) (Smotherman, W. P.; Petrov, E. S.; Varlin- skaya, E. I. Experimental study of the first suckling episode: Rat pups ingest fluids through a surrogate nipple. Submitted for pub- lication). The base of the surrogate nipple is attached to the end of an angled dental probe to facilitate manual presentation by the experimenter. A length of PE 10 tubing (0.58 mm inner diameter) extends through the center and ends flush with the rounded tip of the nipple. The PE 10 tubing is connected to a fluid reservoir made from a 5-mL disposable syringe. The syringe is anchored in a test tube holder and positioned so as to be level with the head of the experimental subject. The syringe-tubing-surrogate nipple sys- tem, when filled with a test fluid, represents an open hydraulic To whom requests for reprints should be addressed. E-mail: SMOTHER@BINGHAMTON.EDU Physiology & Behavior, Vol. 62, No. 5, pp. 1155–1158, 1997 © 1997 Elsevier Science Inc. All rights reserved. Printed in the U.S.A. 0031-9384/97 $17.00 + .00 1155