A cytoarchitectonic and TH-immunohistochemistry characterization of the dopamine cell groups in the substantia nigra, ventral tegmental area and retrorubral field in the rock cavy (Kerodon rupestris) Jose ´ R.L.P. Cavalcanti a,b, *, Joacil G. Soares b , Francisco G. Oliveira b,c , Fausto P. Guzen a,b , Andre ´ L.B. Pontes d , Twyla B. Sousa b , Jeferson S. Cavalcante d , Expedito S. Nascimento Jr b , Judney C. Cavalcante b , Miriam S.M.O. Costa b a Department of Biomedical Sciences, Laboratory of Experimental Neurology, Health Science Center, University of State of Rio Grande do Norte, Mossoro ´, RN, Brazil b Department of Morphology, Laboratory of Neuroanatomy, Biosciences Center, Federal University of Rio Grande do Norte, Natal, RN, Brazil c Department of Biological Sciences, Biological Sciences and Health Center, Regional University of Cariri, Crato, CE, Brazil d Department of Physiology, Laboratory of Neurochemical Studies, Biosciences Center, Federal University of Rio Grande do Norte, Natal, RN, Brazil 1. Introduction In the 1950s, 3-hydroxytyramine/dopamine (DA) was de- scribed as a neurotransmitter in the central nervous system, in addition to its role as a precursor of the noradrenaline and adrenaline synthesis (Carlsson et al., 1958; Bjo ¨ rklund and Dunnett, 2007a). As such, DA is a monoamine included in the catecholamine group, is a major neurotransmitter in the modulation of brain function and plays a crucial role in the adaptation of animal behavior throughout evolution (Smeets and Gonza ´ lez, 2000; Jones and Pilowski, 2002; Yamamoto and Vernier, 2011). The first detailed description of the distribution of neurons containing catecholamine substances identified 12 neuronal groups, designated A1–A12 in caudorostral direction in the rat encephalon (Dahlstro ¨m and Fuxe, 1964). Subsequent studies added five more cell groups, A13–A17 (Ho ¨ kfelt et al., 1984). Of all these, the caudal groups A1–A7 are mainly noradrenergic, Journal of Chemical Neuroanatomy 55 (2014) 58–66 A R T I C L E I N F O Article history: Received 10 July 2013 Received in revised form 5 November 2013 Accepted 6 January 2014 Available online 17 January 2014 Keywords: Dopamine Retrorubral field Rock cavy Substantia nigra Tyrosine hydroxylase Ventral tegmental area A B S T R A C T The 3-hydroxytyramine/dopamine is a monoamine of the catecholamine group and it is a precursor of the noradrenaline and adrenaline synthesis, in which the enzyme tyrosine hydroxylase acts as a rate- limiting enzyme. The dopaminergic nuclei retrorubral field (A8 group), substantia nigra pars compacta (A9 group) and ventral tegmental area (A10 group) are involved in three complex circuitries named mesostriatal, mesocortical and mesolimbic, which are directly related to various behavioral manifestations such as motor control, reward signaling in behavioral learning, motivation and pathological manifestations of Parkinson’s disease and schizophrenia. The aim of this study was to describe the delimitation of A8, A9 and A10 groups and the morphology of their neurons in the brain of the rock cavy (Kerodon rupestris), a typical Brazilian Northeast rodent belonging to the suborder Hystricomorpha, family Caviidae. Coronal and sagittal sections of the rock cavy brains were submitted to Nissl staining and TH immunohistochemistry. The organization of these dopaminergic nuclei in the rock cavy brain is very similar to that found in other animals of the Rodentia order, except for the presence of the tail of the substantia nigra, which is found only in the species under study. The results revealed that, apart some morphological variations, A8, A9 and A10 groups are phylogenetically stable brain structures. ß 2014 Elsevier B.V. All rights reserved. Abbreviations: 3N, oculomotor nucleus; Aq, cerebral aqueduct; Cli, caudal linear nucleus of the raphe; cp, cerebral peduncle; csc, commissure of the superior colliculus; fr, fasciculus retroflexus; Hb, habenular nucleus; IF, interfascicular nucleus; IP, interpeduncular nucleus; ml, medial lemniscus; MN, mammilary nucleus; ns, nigrostriatal bundle; PAG, periaqueductal gray; PBP, parabrachial pigmented nucleus; pc, posterior commissure; PIF, parainterfascicular nucleus; PN, paranigral nucleus; RLi, rostral linear nucleus; RN, red nucleus; RRF/A8, retrorubral field; rs, rubrospinal tract; SN/A9, substantia nigra pars compacta (nuclear complex); SNCD, substantia nigra dorsal tier; SNCL, substantia nigra lateral cluster; SNCM, substantia nigra medial cluster; SNCV, substantia nigra ventral tier; SNR, substantia nigra reticulate; STh, subthalamic nucleus; SuM, supramammilary nucleus; tSN, tail of the substantia nigra; VTA/A10, ventral tegmental area (nuclear complex); VTAR, ventral tegmental area rostral part; ZI, zona incerta. * Corresponding author at: Department of Biomedical Sciences/Laboratory of Experimental Neurology, Health Science Center, University State of Rio Grande do Norte, 59607-360, Mossoro ´, RN, Brazil. Tel.: +55 84 33152248; fax: +55 84 33152248. E-mail addresses: rodolfolopes@uern.br, joserodolfolopes@uol.com.br (Jose ´ R.L.P. Cavalcanti). Contents lists available at ScienceDirect Journal of Chemical Neuroanatomy jo ur n al ho mep ag e: www .elsevier .c om /lo cate/jc h emn eu 0891-0618/$ – see front matter ß 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jchemneu.2014.01.002