Medial Prefrontal Cortex

Abstract

Abstract-The infralimbic (IL) 'visceromotor' area of the rat medial prefrontal cortex projects to strategic subcortical nuclei involved in autonomic functions. Central among these targets are the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (rVLM). By combining tract-tracing using the anterograde tracer biotinylated dextran amine (BDA) with immunolabeling for tyrosine hydroxylase (TH; an enzyme marker of catecholaminergic neurons), a limited proportion of BDA-labeled IL axonal boutons in the NTS and rVLM was found to be closely associated with TH immunopositive (؉) target structures. Such structural appositions were mainly located proximally over the labeled dendritic arbors of identified TH؉ neurons.Quantitative ultrastructural examination revealed that in NTS, TH؉ dendritic shafts comprised 7.0% of the overall post-synaptic target population innervated by BDA-labeled IL boutons, whereas TH؉ dendritic spines represented 1.25% of targets. In rVLM, TH؉ shafts represented 9.0% and TH؉ spines 2.5% of IL targets. Labeled IL boutons established exclusively asymmetric Gray Type 1 (presumed excitatory) synaptic junctions.The results indicate that subpopulations of catecholaminergic neurons in the NTS and rVLM are among the spectrum of post-synaptic neurons monosynaptically innervated by descending 'excitatory' input from IL cortex. Such connectivity, albeit restricted, identifies the potential direct influence of IL cortex on the processing and distribution of cardiovascular, respiratory and related autonomic information by catecholaminergic neurons in the NTS and VLM of the rat. 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, stimulati...