Gustatory System

Ventroposterior medialis parvocellularis (VPMpc) of thalamus, the thalamic relay nucleus for gustatory sensation, receives primary input from parabrachial nucleus, and projects to insular cortex. To reveal unique properties of gustatory thalamus in comparison to archetypical sensory relay nuclei, this study examines the morphology of synaptic circuitry in VPMpc, focusing on parabrachiothalamic driver input and corticothalamic feedback. Anterogradely visualized parabrachiothalamic fibers in VPMpc bear large swellings. At electron microscope resolution, parabrachiothalamic axons are myelinated and make large boutons, forming multiple asymmetric, adherent and perforated synapses onto large caliber dendrites and dendrite initial segments. Labeled boutons contain dense-core vesicles, and they resemble a population of calcitonin gene-related peptide containing terminals within VPMpc. As typical of primary inputs to other thalamic nuclei, parabrachiothalamic terminals are over 5 times larger than other inputs, while constituting only 2% of all synapses. Glomeruli and triadic arrangements, characteristic features of other sensory thalamic nuclei, are not encountered. As revealed by anterograde tracer injections into insular cortex, corticothalamic projections in VPMpc form a dense network of fine fibers bearing small boutons. Corticothalamic terminals within VPMpc were also observed to synapse on cells that were retrogradely filled from the same injections. The results constitute an initial survey in describing unique anatomical properties of rodent gustatory thalamus.

Section: Discussionsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Morphology and connectivity of parabrachial and cortical inputs to gustatory thalamus in rats

Holtz

Loflin

et al. 2014

“…The insula shows a dense zinc reaction throughout, with less signal seen over the underlying claustrum (Ins; Cl; Figure a); in contrast, the neocortex has much lower amounts of zinc, largely in layers 1–3, 5, and 6, and displays a distinctive wholly negative layer 4. A small prolongation of the latter indents the insular boundary, entering the presumptive granular insula; this layer 4 prolongation was previously described, and reported to contain neurons reacting to tongue temperature, but not to taste (Lundy Jr & Norgren, ). This suggests a partial tangential displacement of some neocortical neurons into nearby insula.…”

Section: Some Molecular Markersmentioning

confidence: 63%

Concentric ring topology of mammalian cortical sectors and relevance for patterning studies

Puelles

Alonso

Garcı́a-Calero

et al. 2019

146

Models aiming to explain causally the evolutionary or ontogenetic emergence of the pallial isocortex and its regional/areal heterogeneity in mammals use simple or complex assumptions about the pallial structure present in basal mammals and nonmammals. The question arises: how complex is the pattern that needs to be accounted for in causal models? This topic is also paramount for comparative purposes, since some topological relationships may be explained as being ancestral, rather than newly emerged. The mouse pallium is apt to be reexamined in this context, due to the breadth of available molecular markers and correlative experimental patterning results. We center the present essay on a recapitulative glance at the classic theory of concentric mammalian allo‐, meso‐, and neocortex domains. In its simplest terms, this theory postulates a central neocortical island (6 layers) separated by a surrounding mesocortical ring (4–5 layers) from a peripheral allocortical ring (3 layers). These territories show additional partition into regional or areal subdivisions. There are also borderline amygdalar, claustral, and septal areas of the pallium, nuclear in structure. There has been little effort so far to contemplate the full concentric ring model in current “cortex patterning” models. In this essay, we recapitulate the ring idea in mammals (mouse) and consider a potential causal patterning scenario using topologic models. Finally, we briefly explore how far this theory may apply to pallium models proposed recently for sauropsids.

“…The dorsal part of the olfactory cortex has been traditionally interpreted to cover the pallial thickening, although this depends on the species (Striedter, 1997;Bruce, 2007;Puelles, 2011;Guirado and D avila, 2002 showed radial glia fibers supporting this point in a lizard). It may also be significant in this context that Rieke and Wenzel (1978) reported some olfactory bulb projections to the mesopallium in the pigeon and chicken, whereas Shipley and Geinisman (1984) and Shipley and Adamek (1984) reported some olfactory projections to the mouse gustatory cortex, a part of the insula (Lundy and Norgren, 2004). The large olfactorecipient pallial domain of reptiles may thus reflect an independent variant saurian trend evolved on top of the ancestral situation in basal amniotes.…”

Section: Lpallmentioning

confidence: 95%

Selective early expression of the orphan nuclear receptor Nr4a2 identifies the claustrum homolog in the avian mesopallium: Impact on sauropsidian/mammalian pallium comparisons

Puelles

Ayad

Alonso

et al. 2015

180

The transcription factor Nr4a2 was recently revealed as a very early developmental marker of the claustrum (CL) proper in the mouse. The earliest claustral primordium was identified superficially, dorsal to the olfactory cortex, and was subsequently covered by the Nr4a2-negative cells of the insular cortex. Some tangentially migrating claustral derivatives (subplate cells and some endopiriform elements) also expressed this marker. The present study employs the same genetic marker to explore the presence of a comparable pallial division in chicken in which, in principle, the same pallial sectors exist as in mammals. We were indeed able to delineate an early-developing Nr4a2-positive mantle domain at the expected topologic position within the developing chicken lateral pallium. In the chicken as well as in the turtle (from data in the literature), the earliest postmitotic lateropallial cells likewise express Nr4a2 and occupy a corticoid superficial stratum of the mesopallium, which is clearly comparable in spatial and chronological profile to the mouse CL. Other cells produced in this pallial sector include various tangentially migrating Nr4a2-labeled derivatives as well as Nr4a2-negative and Nr4a2-positive local deeper subpopulations that partially interdigitate, forming mesopallial core and shell populations. We hold that the deep avian and reptilian mesopallial formation developing under the superficial corticoid CL homolog represents a field homolog of the insula, although additional studies are required to underpin this hypothesis.