Relationship between the organization of the forepaw barrel subfield and the representation of the forepaw in layer IV of rat somatosensory cortex

Abstract

We studied the organization of the forepaw barrel subfield (FBS) in layer IV of adult rat somatosensory cortex using the mitochondrial marker cytochrome oxidase and related this organization to the representation of the forepaw. The FBS is an ovoid structure consisting of barrels and barrel-like structures, the most conspicuous of which form four centrally located medio lateral running bands. Each band contains three to four barrels. These centrally located bands are bordered along their entire lateral side by a nebulous zone of undifferentiated labeling. At the anterior border, two small barrels are located laterally and one or two larger barrels are located medially. Medial to the central zone are three well-defined barrels. The posterior border consists of a nebulous field of labeling and occasional barrel-like structures. The results from our electrophysiological recording and mapping revealed that the forepaw representation was topographically organized into a single map and that the forepaw map matches almost precisely with individual barrels and barrel-like structures in the FBS. Each of the four central bands is associated with the representation of a single glabrous digit. Digit two (D2) is represented anteriorly and followed posteriorly by D3 through D5. Within each digit band the digit is somatotopically organized, with the skin over the distal phalanx represented in the two lateral barrels and the middle and proximal phalanges represented in the medial barrel(s). The dorsal hairy digit skin and dorsal hand are represented in the lateral zone. D1 is represented by two small anteriorly located barrels. Medial to the representation of the glabrous digits is the representation of the palmar pads. The representation of these pads, in turn, lies between the representations of the thenar (located anteriorly) and hypothenar (located posteriorly) pads. Posterior to the hypothenar pad representation lie the representations of the wrist and forearm. While the present results support the conclusion that individual barrels are associated with discrete locations on the forepaw, examples were found where the recording site was not precisely located within the predicted barrel. Some of these errors may be accounted for by limitations in the mapping techniques; nevertheless, the FBS offers an excellent model system to study relationships between cortical structure and function.

Nursing-Induced Somatosensory Cortex Plasticity: Temporally Decoupled Changes in Neuronal Receptive Field Properties Are Accompanied by Modifications in Activity-Dependent Protein Expression

“…A parylene-coated tungsten microelectrode (ϳ1 M⍀ at 1 kHz; World Precision Instruments, Hertfordshire, UK) was moved perpendicular to the cortical surface in Cartesian coordinates by a three-dimensional stepping micromanipulator (Märzhauser; Fine Science Tools, Vancouver, British Columbia, Canada). Using the recording artifact generated by the microelectrode contact with the cortex surface as a zero level, we advanced the electrode to a depth of ϳ650 -700 m to record responses from small clusters of neurons (two to four) in layer IV (Waters et al, 1995;Coq and Xerri, 1998). Sites of electrode penetration were identified relative to the vasculature of the cortical surface.…”

Hypergravity within a critical period impacts on the maturation of somatosensory cortical maps and their potential for use-dependent plasticity in the adult

“…The electrode was moved perpendicular to the cortical surface in Cartesian coordinates by a three-dimensional (3-D) stepping micromanipulator (Märzhäuser; FST, North Vancouver, BC, Canada). Using the recording artifact generated by the microelectrode contact with the cortex surface as a zero level, we advanced the electrode to a depth of about 650 -700 m to record responses from clusters of two to four neurons in layer IV (Coq and Xerri 1998;Waters et al 1995). The inter-electrode penetration distance was close to 70 -80 m in all groups of rats.…”

“…The barrel cortex has been extensively investigated as a model of the experience-dependent refinement of the primary somatosensory (S1) cortex during development. Damage to whisker follicles during the first few days after birth prevents the formation of barrels within layer 4 of the S1 cortex (O'Leary et al 1994;Woolsey and Wann 1976; for a review see Erzurumlu 2010;Erzurumlu and Gaspar 2012). By contrast, whisker trimming does not affect barrel-pattern formation (Fox 1992;Henderson et al 1992;Rema et al 2003;Simons and Land 1987) but impairs the neurophysiological properties of cortical neurons (Fox 1992;Rema et al 2003;Shoykhet et al 2005;Simons and Land 1987;Stern et al 2001) as well as whisker discrimination (Carvell and Simons 1996).…”

Early postnatal alcohol exposure reduced the size of vibrissal barrel field in rat somatosensory cortex (SI) but did not disrupt barrel field organization

“…The flattened cortices were sectioned tangentially on a Vibratome at 100 μm-thickness and placed in containing 0.01 M potassium phosphate buffer solution (KPBS, pH 7.4, 21°C). To visualize the barrel field, sections were reacted with cytochrome oxidase, mounted on gelatin-coated slides, and cover slipped (Waters et al, 1995;Wong-Riley and Welt, 1980).…”