Subbarrel patterns of thalamocortical innervation in rat somatosensory cortical barrels: Organization and postnatal development

Abstract

Barrel hollows in the posteromedial barrel subfield of adult rat somatosensory cortex typically encompass two or three metabolically and structurally distinct regions, termed subbarrels. We used immunohistochemical staining for vesicular glutamate transporter 2 and the neuronal serotonin transporter, in conjunction with cytochrome oxidase (CO) histochemistry, to investigate the distribution of thalamocortical (TC) axon terminals in relation to subbarrel domains. We found, first, that CO-dark subbarrels are more intensely immunoreactive for thalamocortical terminals than the CO-light clefts that separate them. Second, during the first postnatal week, immunoreactivity for markers of TC terminals is relatively homogeneous throughout the barrel hollow; subbarrel patterns of distribution only become recognizable between P-8 and P-10. These observations extend previous findings that subbarrels denote barrel regions enriched in synaptic contacts. The data also indicate that allocation of TC terminals into subbarrel domains does not occur immediately upon thalamic axon ingrowth. Instead, refinement of TC arbors into subbarrels is a gradual process, the outcome of which is not manifest until the second week of postnatal life.

Subcortical barrelette-like and barreloid-like structures in the prosimian galago ( Otolemur garnetti )

“…In mice, the barreloids have a cell-poor core surrounded by a cell dense perimeter three to four cells thick (3). Later investigations have been able to visualize the barreloids as areas of dense staining for a variety of other reaction products, such as succinic dehydrogenase, CO, and vGluT2 (5,36). Our procedures did not reveal clear cell-hollow cylinders and only faintly labeled CO clusters; however, we found clear vGluT2 dense clusters.…”

Sensory deprivation during early development causes an increased exploratory behavior in a whisker‐dependent decision task

“…This metabolic staining overlaps with staining using Vglut‐2 (Louderback et al. ) to stain for thalamocortical synapses. The size of the barrel column using CO‐staining can thus be used to indicate changes in the neural circuitry that can occur as a result of sensory deprivation or deafferentation (Fox ; Schlaggar et al.…”

“…; Kaneko and Fujiyama ) is correlated with the metabolic CO‐staining, the size of the CO‐barrel staining can be interpreted as showing the area innervated by thalamocortical synapses (Louderback et al. ). A change in the CO‐stained barrel area is shown for the P0 group where the barrel area ratio of spared (C+D row)/deprived (A+B row) increased.…”

Subbarrel Patterns in Somatosensory Cortical Barrels Can Emerge from Local Dynamic Instabilities

“…). Subbarrel patterns also appear to be organized with respect to growing thalamocortical axons, with the patterns developing gradually and becoming recognizable in the second week of postnatal life, after the initial in-growth of the axons and the emergence of the larger barrel structure [11]. During this time, thalamocortical axon arbors become more geometrically complex, progressing from a relatively simple and sparse branching to a dense mesh work of overlapping branches [21].…”

“…Viewed with cytochrome oxidase staining, individual barrels themselves appear heterogeneous, with regions of intense staining separated by narrow, often sinuous zones of less dense reactivity [9]. The cytochrome dense regions form “subbarrel” domains that correspond to cyto- and myeloarchitecture and that are enriched with thalamocortical axon terminals [10],[11]. Interestingly, subbarrels comprise a limited number of spatial patterns, with certain patterns more likely to appear in barrels corresponding to some whiskers than in others.…”