The medial prefrontal cortex (mPFC) is directly involved in the integration of cognitive and autonomic functions underlying flexible goal-directed behavior (Cechetto and Saper, 1990;Neafsey et al., 1993;Loewy, 1991;Owens et al., 1999;Van Eden and Buijs, 2000;Drevets, 2000;Heidbreder and Groenewegen, 2003). In the rat, the mPFC is composed of the anterior cingulate (ACd, Brodmann area 24b), prelimbic (PL, area 32), infralimbic (IL, area 25), and peduncular (P) cortices (Neafsey et al., 1993;Gabbott et al., 2005;Resstel and Corrêa, 2006b).Anatomical and physiological evidence indicates that areas of dorsal (d) mPFC (ACd and dPL cortices) process cognitive information, whereas regions of ventromedial prefrontal cortex (vmPFC) (vPL, IL and P cortices) are also involved in autonomic and visceral functions, especially, cardiovascular and respiratory activities (Hardy and Mack, 1990;Neafsey, 1990;Loewy, 1991;Neafsey et al., 1993;Spyer, 1994;Fisk and Wyss, 2000;Uylings et al., 2003;Heidbreder and Groenewegen, 2003). Descending efferent projections from vmPFC, in particular IL cortex, innervate a wide range of subcortical autonomic centers, including the nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM), brain stem nuclei strategically involved in cardiopulmonary activities (Agarwal and Calarescu, 1992;Van Giersbergen et al., 1992;Dampney, 1994;Owens and Verberne, 1996, 2000Owens et al., 1999). Indeed, stimulation of the vPL and IL cortices is known to influence arterial blood pressure and blood flow through specific vascular beds (Owens and Verberne, 2001). As a result, the vmPFC has been considered to represent a 'visceromotor' territory of the rodent PFC (Terreberry and Neafsey, 1987;Ruit and Neafsey, 1990;Loewy, 1991;Neafsey et al., 1993; Resstel and Corrêa, 2006a,b).Although the pathways from IL cortex to autonomic centers in the brain stem have been described in previous light microscope studies (Sesack et al., 1989;Hurley et al., 1991;Takagishi and Chiba, 1991;Van Eden and Buijs, 2000;Heidbreder and Groenewegen, 2003;Vertes, 2004;Gabbott et al., 2005), the ultrastructural identities and neurochemical content of the post-synaptic target neurons have not been investigated in detail (Zagon et al., 1994;Torrealba and Müller, 1999). Of specific functional significance is that catecholaminergic neurons in the NTS and rostral ventrolateral medulla (rVLM) are strategically in-*Correspondence to: P. L. A. Gabbott, Department of Biological Sciences, The Open University, Milton Keynes, MK7 6AA UK. Tel: ϩ44-1908-659469; fax: ϩ44-1908-654167. E-mail address: p.l.gabbott@open.ac.uk (P. L. A. Gabbott). Abbreviations: ACd, dorsal anterior cingulate cortex (area 24b); B, Bregma; BDA, biotinylated dextran amine; BLA, basolateral nucleus of the amygdala; CEA, central nucleus of the amygdala; DAB, 3,3=-diaminobenzidine; DMH, dorsomedial hypothalamic nucleus; DMX, dorsal motor nucleus of the vagus; IL, infralimbic cortex (area 25