Projections of the medial orbital and ventral orbital cortex in the rat

Abstract

The medial orbital (MO) and ventral orbital (VO) cortices are prominent divisions of the orbitomedial prefrontal cortex. To our knowledge, no previous report in the rat has comprehensively described the projections of MO and VO. By using the anterograde tracer Phaseolus vulgaris leucoagglutinin and the retrograde tracer Fluoro-Gold, we examined the efferent projections of MO and VO in the rat. Although MO and VO projections overlap, MO distributes more widely throughout the brain, particularly to limbic structures, than does VO. The main cortical targets of MO were the orbital, ventral medial prefrontal (mPFC), agranular insular, piriform, retrosplenial, and parahippocampal cortices. The main subcortical targets of MO were the medial striatum, olfactory tubercle, claustrum, nucleus accumbens, septum, substantia innominata, lateral preoptic area, and diagonal band nuclei of the basal forebrain; central, medial, cortical, and basal nuclei of amygdala; paratenial, mediodorsal, and reuniens nuclei of the thalamus; posterior, supramammillary, and lateral nuclei of the hypothalamus; and periaqueductal gray, ventral tegmental area, substantia nigra, dorsal and median raphe, laterodorsal tegmental, and incertus nuclei of the brainstem. By comparison, VO distributes to some of these same sites, notably to the striatum, but lacks projections to parts of limbic cortex, to nucleus accumbens, and to the amygdala. VO distributes much more strongly, however, than MO to the medial (frontal) agranular, anterior cingulate, sensorimotor, posterior parietal, lateral agranular retrosplenial, and temporal association cortices. The patterns of MO projections are similar to those of the mPFC, whereas the projections of VO overlap with those of the ventrolateral orbital cortex (VLO). This suggests that MO serves functions comparable to those of the mPFC, such as goal-directed behavior, and VO performs functions similar to VLO such as directed attention. MO/VO may also serve as a link between lateral orbital and medial prefrontal cortices.

Inactivating Anterior Insular Cortex Reduces Risk Taking

“…Concerning striatal connectivity, the AIC mainly projects to ventral and lateral parts of the striatum, whereas the OFC projects more dorsally and medially (Schilman et al, 2008). Concerning frontal connectivity, the AIC has major interconnections with the anterior cingulate, prelimbic, and infralimbic cortex, whereas the OFC is mainly interconnected with the anterior cingulate cortex and has much less interconnection with prelimbic and infralimbic cortex (Hoover and Vertes, 2011). The important point of our results is that AIC and OFC inactivations had opposite effects on risk preference, and this suggests, to our knowledge for the first time, that the AIC and OFC make different contributions to risky decisions.…”

Obesity-Induced Structural and Neuronal Plasticity in the Lateral Orbitofrontal Cortex

“…The ventral OFC is thought to bridge the medial and prefrontal cortical networks (Price, 2007), with the dorsal striatum being their primary extracortical target (Hoover and Vertes, 2011). While restricted access rats serve as a non-obese control with exposure to the diet in these studies, they do exhibit disordered feeding behaviour such that they consume most of their daily energy requirement within an hour.…”

Social Play Behavior in Adolescent Rats is Mediated by Functional Activity in Medial Prefrontal Cortex and Striatum

“…Inactivation of the PrL, IL, and MO/VO may, therefore, disrupt social play behavior by interfering with cognitive flexibility and decision-making processes necessary for a proper social interaction. Studies in the past decade have found considerable anatomical (Groenewegen and Uylings, 2010;Hoover and Vertes, 2011;Vertes, 2004) and functional heterogeneity within the PFC and OFC (Chudasama et al, 2003;Gourley et al, 2010;Killcross and Coutureau, 2003;Mar et al, 2011;Peters et al, 2009). This begs the question of the exact contribution of PrL, IL, and MO/VO in social play behavior, given that their inactivation produces comparable reductions in social play.…”