Efferent connections of dorsal and ventral agranular insular cortex in the hamster, Mesocricetus auratus

Abstract

The anterior portion of rodent agranular insular cortex consists of a ventral periallocortical region (AIv) and a dorsal proisocortical region (AId). Each of these two cortical areas has distinct efferent connections, but in certain brain areas their projection fields are partially or wholly overlapping. Bilateral projections to layers I, III and VI of medial frontal cortex originate in the dorsal agranular insular cortex and terminate in the prelimbic, anterior cingulate and medial precentral areas; those originating in ventral agranular insular cortex terminate in the medial orbital, infralimbic and prelimbic areas. The dorsal and ventral regions of the agranular insular cortex project topographically to the ipsilateral cortex bordering the rhinal fissure, which includes the posterior primary olfactory, posterior agranular insular, perirhinal and lateral entorhinal areas. Fibers to these lateral cortical areas were found to travel in a cell-free zone, between cortical layer VI and the claustrum, which corresponds to the extreme capsule. The dorsal and ventral regions send commissural projections to layer I, lamina dissecans and outer layer V, and layer VI of the contralateral homotopical cortex, via the corpus callosum. Projections from the ventral and dorsal regions of the agranular insular cortex to the caudatoputamen are topographically arranged and terminate in finger-like patches. The ventral, but not the dorsal region, projects to the ventral striatum and ventral pallidum. The thalamic projections of the ventral and dorsal regions are largely overlapping, with projections from both to the ipsilateral reticular nucleus and bilaterally to the rhomboid, mediodorsal, gelatinosus and ventromedial nuclei. The heaviest projection is that to the full anteroposterior extent of the medial segment of the mediodorsal nucleus. Brainstem areas receiving projections from the ventral and dorsal regions include the lateral hypothalamus, substantia nigra pars compacta, ventral tegmental area and dorsal raphe nucleus. In addition, the ventral region projects to the periaqueductal gray and the dorsal region projects to the parabrachial and ventral pontine nuclei. These efferent connections largely reciprocate the afferent connections of the ventral and dorsal agranular insular cortex, and provide further support for the concept that these regions are portions of an outer ring of limbic cortex which plays a critical role in the expression of motivated, species-typical behaviors.

The trajectory of sensory pathways from the lamina terminalis to the insular and cingulate cortex: a neuroanatomical framework for the generation of thirst

“…The distribution of putative first-order (directly projecting) PRV-positive neurons within the thalamus of rats infected for 2 days that project to either the insular or cingulate cortices in this study are largely consistent with previous monosynaptic tracing studies (2,9,23,28,43,(51)(52)(53)68). The majority of the overlapping regions of the thalamus that project to both the insular and cingulate cortex are localized to the midline thalamic region (2,9,28,43,(51)(52)(53)68).…”

“…The emotional aspects of thirst therefore reflect the arousal and affect associated with the generation of thirst and the motivation to obtain satiation. Thirst has been considered in many physiological studies (36,48,69,70); however, the effector regions responsible have only been alluded to (18,19,21,48) and therefore require further investigation.The thalamus has been implicated as having a role in the translation of viscerosensory information into signals of arousal and affect (9, 47, 56, 71) through intricate thalamocortical connections (9,23,28,43,(51)(52)(53)68). Two cortical regions implicated in the emotional aspects of thirst, the activity of which is altered by hyperosmotic stimulation or dehydration, are the insular and cingulate cortex (17,20,21,48,54).…”

“…The thalamus has been implicated as having a role in the translation of viscerosensory information into signals of arousal and affect (9, 47, 56, 71) through intricate thalamocortical connections (9,23,28,43,(51)(52)(53)68). Two cortical regions implicated in the emotional aspects of thirst, the activity of which is altered by hyperosmotic stimulation or dehydration, are the insular and cingulate cortex (17,20,21,48,54).…”

Ventral Pallidum Firing Codes Hedonic Reward: When a Bad Taste Turns Good

“…Those VP functions may arise partly from its connection with other reward structures such as amygdala (Galaverna et al 1993;Napier 1992), orbitofrontal and insular cortex (Reep and Winans 1982;Zahm 2006), ventral tegmentum, and parabrachial nucleus (Groenewegen et al 1993;Grove 1988a,b;Kalivas et al 1999;Mitrovic and Napier 1998;Napier and Mitrovic 1999). VP also acts as the chief target for efferent projections from the nucleus accumbens, which itself codes reward information (Gulley et al 2002;Peoples et al 2004), and serves as a centripetal final common output path for mesocorticolimbic circuits (Groenewegen et al 1999;Usuda et al 1998;Zahm 2006).…”

The Periaqueductal Gray: From Longitudinal columns to defensive behaviour

“…The function of the amygdala would be to synthesize the various stimulus inputs from the environment and then signal to the PAG according to the degree of threat represented to the organism (LeDoux, 1994, LeDoux, et al, 1988, McNaughton and Corr, 2004. A series of retrograde studies revealed that the projections to the PAG arise predominantly from the medial prefrontal cortex wall and a few selected orbital/anterior insular prefrontal cortex regions (Floyd, et al, 2000, Reep andWinans, 1982). In addition, injections of anterograde tracers into each PAG-projecting prefrontal region revealed distinct columnar patterns in the PAG.…”