Quantitative correlation between barrel-field size and the sensory innervation of the whiskerpad: a comparative study in six strains of mice bred for different patterns of mystacial vibrissae

Abstract

In mice from 6 strains bred for different patterns of mystacial vibrissae, we studied the consequences of the presence of supernumerary whiskers for the sensory innervation of the vibrissal follicles and their cortical representation in the barrel field. The parameters were number of axons innervating individual vibrissal follicles, tangential area of individual barrels, and thickness of the layers in the barrel cortex. These parameters are highly constant for animals within a strain but may differ greatly between strains. For all strains, the innervation of a follicle depends on its position on the whiskerpad, the highest innervation density being at the posterolateral corner. This matches the wave of development that travels over this part of the face during embryogenesis. Although large differences exist between strains in the number of axons innervating the whiskerpad, the relative number of axons innervating the "standard" follicles of 1 row is remarkably constant. The thickness of the barrel cortex increases from posteromedial to anterolateral for all strains. This increase is due to variations in thickness of the cortical output layers (II and III, V and VI).For individual barrel-follicle pairs, we calculated the ratio between cortical barrel area and axon number. The major findings were that (1) supernumerary follicles are innervated and, given a threshold number of axons, represented by barrels; (2) barrel area per peripheral axon differs between follicles within a row and is highest for the supernumerary elements; and (3) for each strain there is a direct, linear correlation between axon number and barrel size, which differs significantly among certain, but not all, strains. The data allowed us tentatively to define some of the factors that play a role in the formation of brain maps and pointed to the existence of major genetic differences between mouse strains with respect to these factors.Since 1977 we have selectively bred a number of mouse strains that differ in number and pattern of mystacial vibrissae, starting with a selection made from a large population of albino mice from an outbred ICR stock . Thirteen bilaterally symmetric patterns were obtained, and the "improvement" of the strains in question has been the subject of recent reports Van der Loos et al., 1986). We proved that the patterns, both standard and "enriched," are genetically determined.Six strains from that group have been selected for the present

Somatosensory cortex dominated by the representation of teeth in the naked mole-rat brain

“…For example, investigations of rodent somatosensory ''barrel'' cortex have revealed a close relationship between innervation density and cortical representational area (32,33). This finding would suggest that mole-rats may have a particularly large set of densely innervated periodontal mechanoreceptors.…”

Somatosensory cortical plasticity: recruiting silenced barrels by active whiskers

“…Whisker and digit-related patterns are first established in the brainstem somatosensory nuclei, then in the VPM-VPL complex of the dorsal thalamus and finally in the neocortex (Belford and Killackey, 1980;Ma and Woolsey, 1984;Van der Loos, 1976;Woolsey and Van der Loos, 1970). The instructive role of the sensory periphery in sculpting central neural patterns has been demonstrated by whisker follicle or trigeminal nerve lesion studies performed in perinatal rodents, or in mice selectively bred for aberrant numbers of whiskers (Killackey et al, 1995;O'Leary et al, 1994;Welker and Van der Loos, 1986;Woolsey, 1990). Several lines of evidence indicate that somatosensory periphery-related neural maps and patterns are conveyed to target cells by the afferents at each synaptic relay station Jhaveri, 1990, 1992a,b;Erzurumlu and Killackey, 1983;Senft and Woolsey, 1991).…”

Structure edge and ontogenetic of the built-in cognition

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