Research Report The supragenual nucleus: A putative relay station for ascending vestibular signs to head direction cells Claudinei E. Biazoli Jr. a , Marina Goto a , Ana Maria P. Campos b , Newton S. Canteras a, ⁎ a Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, Av. Lineu Prestes, 2415, CEP 05508-900 São Paulo, SP, Brazil b Department Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, Brazil ARTICLE INFO ABSTRACT Article history: Accepted 30 March 2006 Available online 8 May 2006 Head direction (HD) cells located in several regions of the brain, including the postsubiculum, retrosplenial cortex, lateral dorsal thalamic nucleus, anterior dorsal thalamic nucleus, and lateral mammillary nucleus, provide a signal of the rat's momentary directional heading. Experimental evidence suggests that vestibular inputs are critical for the maintenance these cells' directional sensitivity. However, it is still unclear how vestibular information is conveyed to the HD cell-related circuitry. In a recent study, the supragenual nucleus (SG) was suggested as a putative relay of vestibular inputs to this circuitry. In the present study, using anterograde and retrograde tract-tracing methods, we first investigated whether the SG is in a position to convey vestibular inputs. Next, we examined the projections of the SG with the Phaseolus vulgaris leucoagglutinin method. Our results indicate that the SG receives direct inputs from the medial vestibular nucleus and projects to elements of the HD cell-related circuitry, providing a massive input to the contralateral dorsal tegmental nucleus and a moderately dense projection to the shell region of the lateral mammillary nucleus. Overall, the present findings serve to clarify how vestibular inputs reach the HD cell-related circuit and point out the SG as an important interface to this end. © 2006 Elsevier B.V. All rights reserved. Keywords: Vestibular system Head direction cell Navigation Spatial cognition Mammillary nuclei Dorsal tegmental nucleus 1. Introduction Head direction (HD) cells discharge as a function of the animal's head direction in the horizontal plane and are independent of the rat's location in the environment as well as ongoing behavior. Evidence suggests that these cells participate in navigation and spatial cognition (Muller et al., 1996). The circuitry responsible for the generation and maintenance of the HD signal has been extensively studied, and HD cells have been identified in the postsubiculum (Taube et al., 1990), retrosplenial cortex (Chen et al., 1994; Cho and Sharp, 2001), lateral dorsal thalamic nucleus (Mizumori and Williams, 1993), anterior dorsal thalamic nucleus (Taube, 1995), and lateral mammillary nucleus (Blair et al., 1998; Stackman and Taube, 1998). Vestibular information plays an essential role in the generation of HD signal. Recent lesion studies (Stackman and Taube, 1997; Stackman et al., 2002) indicated that inactivation of labyrinthine inputs abolished the direction- related activity of HD cells. Unfortunately, knowledge of the BRAIN RESEARCH 1094 (2006) 138 – 148 ⁎ Corresponding author. Fax: +55 11 3091 7285. E-mail address: newton@icb.usp.br (N.S. Canteras). 0006-8993/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2006.03.101 available at www.sciencedirect.com www.elsevier.com/locate/brainres