Dysgranular Insular Areas Research Articles

Complementary circuits connecting the orbital and medial prefrontal networks with the temporal, insular, and opercular cortex in the macaque monkey

The origin and termination of axonal connections between the orbital and medial prefrontal cortex (OMPFC) and the temporal, insular, and opercular cortex have been analyzed with anterograde and retrograde axonal tracers, injected in the OMPFC or temporal cortex. The results show that there are two distinct, complementary, and reciprocal neural systems, related to the previously defined "orbital" and "medial" prefrontal networks. The orbital prefrontal network, which includes areas in the central and lateral part of the orbital cortex, is connected with vision-related areas in the inferior temporal cortex (especially area TEav) and the fundus and ventral bank of the superior temporal sulcus (STSf/v), and with somatic sensory-related areas in the frontal operculum (OPf) and dysgranular insular area (Id). No connections were found between the orbital network and auditory areas. The orbital network is also connected with taste and olfactory cortical areas and the perirhinal cortex and appears to be involved in assessment of sensory objects, especially food. The medial prefrontal network includes areas on the medial surface of the frontal lobe, medial orbital areas, and two caudolateral orbital areas. It is connected with the rostral superior temporal gyrus (STGr) and the dorsal bank of the superior temporal sulcus (STSd). This region is rostral to the auditory parabelt areas, and there are only relatively light connections between the auditory areas and the medial network. This system, which is also connected with the entorhinal, parahippocampal, and cingulate/retrosplenial cortex, may be involved in emotion and other self-referential processes.

NMDA and non-NMDA receptors mediate taste afferent inputs to cortical taste neurons in rats.

Two main subclasses of ionotropic receptors for excitatory amino acids (EAAs), N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors, are involved in neurotransmission in the cortex of mammals. To examine whether EAAs are transmitters at the cortical taste area (CTA) in rats and to elucidate which types of the two ionotropic receptors operate at these synapses, we studied the effects of microiontophoretic administration of EAA antagonists on the responses of 64 taste cortical neurons to four basic taste stimuli in urethane-anesthetized rats. Both D-2-amino-5-phosphonovalerate (APV), a selective antagonist for NMDA receptors, and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a selective antagonist for non-NMDA receptors, suppressed most of the taste responses. The percentage of neurons suppressed by APV (70.3%) was almost the same as that suppressed by CNQX (64.1%). These suppressive effects were independent of the effects of background discharges during the prestimulus, water-rinsing period. The percentage of neurons suppressed by the antagonists did not differ between any pairs of taste stimuli. The number of neurons possessing both receptors was larger in the granular insular area (area GI), one of the two CTAs, than in the dysgranular insular area (area DI). In addition, taste responses were suppressed by CNQX or by both APV and CNQX in area GI in a significantly larger number of layer V neurons than in area DI. The present results indicate that normal excitatory transmission of taste afferents in the CTA in rats was mediated by both NMDA and non-NMDA receptors. The finding that a large fraction of neurons in the CTA in rats mediated taste information through NMDA receptors in normal transmission might be related to the higher potency of the plasticity observed in the CTA.

Taste area in granular and dysgranular insular cortices in the rat identified by stimulation of the entire oral cavity

While applying natural stimulation to the entire oral cavity, we recorded responses from 489 neurons (400 mechanoreceptive, 84 taste and 5 cold neurons) in the insular cortex of urethane-anesthetized rats. Intermingled with the mechanoreceptive neurons was a major group of taste neurons located in the granular or dysgranular insular area at levels of 2.55-1.20 mm anterior to the bed nucleus of the anterior commissure as stereotaxically located. Most of the taste neurons were also sensitive to mechanical stimulation of the oral and/or perioral tissue.