Postnatal development of hypothalamic inputs to the dorsal vagal complex in rats Linda Rinaman * Department of Neuroscience, University of Pittsburgh, 446 Crawford Hall, Pittsburgh, PA 15260, USA Received 4 February 2003; accepted 4 February 2003 Abstract The hypothalamus is critically involved in energy homeostasis and is an appropriate focus for research investigating the central neural underpinnings of obesity, anorexia and normal food intake. However, little is known regarding pathways and mechanisms that convey relevant hypothalamic signals to the brainstem circuits that ultimately control ingestive behavior. This brief review highlights work investigating the postnatal development of hypothalamic inputs to the hindbrain dorsal vagal complex (DVC). Research findings indicate that these inputs are both structurally and functionally immature in newborn rats. The progressive postnatal maturation of descending projections to the DVC occurs in concert with newly emerging physiological and behavioral responses to osmotic dehydration, which inhibits gastric emptying and food intake in adult animals but not in neonates. The postnatal emergence of other intake controls might also reflect progressive engagement of DVC neural circuits, whose intrinsic components and output pathways are envisioned as being critical for initiating and terminating ingestive behavior. D 2003 Elsevier Science Inc. All rights reserved. Keywords: Hypothalamus; Dorsal vagal complex; Rats 1. Introduction Newborn mammals obtain water and nutrients by suck- ling milk from their dams. In the proper experimental environment, however, newborn rats will independently ingest milk from saturated towels placed beneath them [1]. The controls of such early independent ingestion are rel- atively simple and few but appear to be developmentally continuous with the more numerous and complex controls that emerge later [2]. At any age, a given factor can control intake only if it leads to altered neural activity in brain circuits that initiate and/or terminate motor components of ingestive behavior. Findings in adult decerebrate rats indic- ate that some food intake controls can alter ingestive behavior by recruiting neural circuits contained entirely within the brainstem (e.g., taste, gastric distension and cholecystokinin), whereas other controls appear to require forebrain components (e.g., energy deficits and conditioned aversions) (for a recent review, see Ref. [3]). To better understand the central controls of ingestive behavior, researchers generally have focused on determining how intrinsic hypothalamic circuits and signaling pathways are engaged by endogenous and exogenous factors that alter intake. However, little is known regarding the mechanisms responsible for conveying hypothalamic signals to relevant effector circuits in the brainstem. Anatomical, physiological and behavioral data collected primarily in rodents support the view that central modulation of ingestive behavior is largely achieved by recruitment of neural circuits that relay through the hindbrain dorsal vagal complex (DVC). The DVC comprises the dorsal motor nucleus of the vagus (DMV), nucleus of the solitary tract (NST) and area post- rema (AP). As summarized in Fig. 1, many features of the DVC make it ideally suited as a brainstem integration and command center for ingestive behavior: 1. The DVC contains parasympathetic vagal motor neurons that regulate digestive (i.e., gastric, intestinal, pancreatic, hepatic and biliary) functions. 2. DVC neurons receive direct and relayed synaptic input from taste and visceral afferents that convey pre- and postabsorptive signals generated by ingested substances. 0031-9384/03/$ – see front matter D 2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S0031-9384(03)00105-7 * Tel.: +1-412-624-6994; fax: +1-412-624-9198. E-mail address: Rinaman@pitt.edu (L. Rinaman). Physiology & Behavior 79 (2003) 65 – 70