Synthesis of multiwhisker-receptive fields in subcortical stations of the vibrissa system

This study addresses the origins of multiwhisker-receptive fields of neurons in the thalamic ventral posterior medial (VPM) nucleus of the rat. We sought to determine whether multiwhisker-receptive field synthesis occurs in VPM through convergent projections from the principalis (PrV) and interpolaris (SpVi) nuclei, or in PrV by intersubnuclear projections from the spinal trigeminal complex. We tested these hypotheses by recording whisker-evoked responses in PrV and VPM before and after electrolytic lesion of the SpVi in lightly anesthetized rats. Before the lesion PrV cells responded, on average, to 3.2 +/- 1.2 whiskers but responsiveness was reduced to 1.07 +/- 0.31 whisker after the lesion. A similar reduction of receptive field size was observed in VPM, where neurons responded, on average, to 2.94 +/- 0.95 whiskers before the lesion and to 1.05 +/- 0.22 whisker after the lesion. Thus one can conclude that intersubnuclear projections mediate surround whisker-receptive fields in PrV, and therefore in VPM. However, it has previously been shown that parasagittal brain stem transection, which severed ascending projections from SpVi, but left intersubnuclear connections intact, rendered VPM cells monowhisker responsive. We wondered whether midline brain stem lesion modified receptive field properties in SpVi. In normal rats SpVi cells responded, on average, to 7.52 +/- 4.25 whiskers, but responsiveness was dramatically reduced to 1.47 +/- 1.07 whisker after the lesion. Together these results indicate that the synthesis of surround receptive fields in subcortical stations relies almost exclusively on intersubnuclear projections from the spinal trigeminal complex to the PrV.

A desert octodontid rodent, Tympanoctomys barrerae, uses modified hairs for stripping epidermal tissue from leaves of halophytic plants

Desert rodents that consume halophytic plants must have adaptations for coping with the high salt content of the leaves. A kidney capable of excreting very concentrated urine is one method. Another is removal of the hypersaline epidermis by means of chisel-like incisors prior to ingestion of the leaves. Tympanoctomys barrerae has evolved a unique refinement of the latter adaptation. It possesses two bundles of stiffened hairs on either side of the palate just caudal to the incisors. The bundles vibrate against the lower incisors, removing the epidermis from the leaves. The efficiency of the operation is significantly greater than with the use of incisors alone. Such a device has not been described in any other mammal. The facial muscles associated with the lips, the cheek vibrissae, and the oral cavity are described in T. barrerae and the nonhalophilic octodontid Octomys mimax. M. buccinatorius pars intermaxillaris is the only muscle in direct contact with the bristle bundles. Other anatomical features found in T. barrerae that may be associated with this feeding device are: 1) a much enlarged and mobile lower labial pad operated by Mm. buccinatorius pars orbicularis oris, pars longitudinalis profunda, and mandibularis cranialis profunda; 2) two oral glands not described in other rodents; and 3) a shortened tongue. Although, taken as a whole, this epidermal stripping device is unique to T. barrerae, most of its features have evolved by modification of structures present in the facial region of more generalized rodents.

Similarities and differences in the innervation of mystacial vibrissal follicle-sinus complexes in the rat and cat: a confocal microscopic study

Our confocal three-dimensional analyses revealed substantial differences in the innervation to vibrissal follicle-sinus complexes (FSCs) in the rat and cat. This is the first study using anti-protein gene product 9.5 (PGP9.5) immunolabeling and confocal microscopy on thick sections to examine systematically the terminal arborizations of the various FSC endings and to compare them between two species, the rat and the cat, that have similar-appearing FSCs but different exploratory behaviors, such as existence or absence of whisking. At least eight distinct endings were clearly discriminated three dimensionally in this study: 1) Merkel endings at the rete ridge collar, 2) circumferentially oriented lanceolate endings, 3) Merkel endings at the level of the ring sinus, 4) longitudinally oriented lanceolate endings, 5) club-like ringwulst endings, 6) reticular endings, 7) spiny endings, and 8) encapsulated endings. Of particular contrast, each nerve fiber that innervates Merkel cells at the level of the ring sinus in the rat usually terminates as a single, relatively small cluster of endings, whereas in the cat they terminate en passant as several large clusters of endings. Also, individual arbors of reticular endings in the rat ramify parallel to the vibrissae and distribute over wide, overlapping territories, whereas those in the cat ramify perpendicular and terminate in tightly circumscribed territories. Otherwise, the inner conical body of rat FSCs contains en passant, circumferentially oriented lanceolate endings that are lacking in the cat, whereas the cavernous sinus of the cat has en passant corpuscular endings that are lacking in the rat. Surprisingly, the one type of innervation that is the most similar in both species is a major set of simple, club-like endings, located at the attachment of the ringwulst, that had not previously been recognized as a morphologically unique type of innervation. Although the basic structure of the FSCs is similar in the rat and cat, the numerous differences in innervation suggest that these species would have different tactile capabilities and perceptions possibly related to their different vibrissa-related exploratory behaviors.

Ability of transplanted cultured epithelium to respond to dermal papillae

Cultured epithelium has been used successfully in the treatment of extensive burns. Regenerated epidermis, however, lacks such as hair follicles and sweat glands that are common in mammalian skin. We attempted to determine whether cultured epithelium could be induced to form hair follicles by dermal papillae, which are most important for the morphogenesis and growth of hair follicles. We cultivated adult rat sole keratinocytes, obtained the cultured epithelium, and prepared recombinants consisting of cultured epithelium and fresh dermal papillae with or without the sole dermis. These recombinants were then transplanted underneath the dermis of the dorsal skin of syngeneic rats or athymic mice. Histologic examination revealed that the transplanted cultured epithelium formed the follicular structures with sebaceous gland-like structure following induction of the dermal papillae, especially when supported by the dermis. We concluded that transplanted cultured epithelium of adult rat sole keratinocytes can respond to growth signals from adult dermal papillae.

Morphogenesis and renewal of hair follicles from adult multipotent stem cells

The upper region of the outer root sheath of vibrissal follicles of adult mice contains multipotent stem cells that respond to morphogenetic signals to generate multiple hair follicles, sebaceous glands, and epidermis, i.e., all the lineages of the hairy skin. At the time when hair production ceases and when the lower region of the follicle undergoes major structural changes, the lower region contains a significant number of clonogenic keratinocytes, and can then respond to morphogenetic signals. This demonstrates that multipotent stem cells migrate to the root of the follicle to produce whisker growth. Moreover, our results indicate that the clonogenic keratinocytes are closely related, if not identical, to the multipotent stem cells, and that the regulation of whisker growth necessitates a precise control of stem cell trafficking.

Size gradients of barreloids in the rat thalamus

The spatial organization of the anatomical structures along the trigeminal afferent pathway of the rat conserves the topographical order of the receptor sheath: The brainstem barrelettes, thalamic barreloids, and cortical barrels all reflect the arrangement of whiskers across the mystacial pad. Although both the amount of innervation in the mystacial pad and the size of cortical barrels were shown previously to exhibit increasing gradients toward the ventral and caudal whiskers, whether similar gradients existed in the brainstem and thalamus was not known. Here, the authors investigated the size gradients of the barreloids in the ventral posteromedial nucleus of the rat thalamus. Because the angles used to cut the brain were crucial to this study, the optimal cutting angles were determined first for visualization of individual barreloids and of the entire barreloid field. Individual barreloids, arcs, and rows as well as entire barreloid fields were clearly visualized using cytochrome oxidase staining of brain slices that were cut with the optimal cutting angles. For the first five arcs (including straddlers), the length of barreloids increased in the direction of dorsal-to-ventral whiskers and of caudal-to-rostral whiskers. These gradients reveal an inverse relationship between the size of barreloids and whiskers (length and follicle diameter) along arcs and rows. The largest barreloids in the ventral posteromedial nucleus were those that represent whiskers C2-C4, D2-D4, and E2-E4, which are neither the largest nor the most innervated whiskers in the mystacial pad. This implies that the extended representation is not merely a reflection of peripheral innervation biases and probably serves an as yet unknown processing function.

Nutritional and functional blood vessels of anagen and telogen vibrissal follicles in the cat

The nutritional blood vessel system in the anagen (growing) vibrissal follicle consists of a rete capillare papillae pili, rete capillare bulbi pili, rete capillare folliculi pili, and rete capillare canalis pili. Due to degeneration of papilla and bulb during the sinus hair cycle, the basal capillary networks are absent in the telogen (resting) vibrissal follicle. Thus, nonpermanent and permanent capillary networks have to be distinguished. A functional blood vessel system originates from arterioles that enter the sinus cavernosus at its basolateral side. Blood flow continues into the sinus anularis. Efferent capillaries, originating from the apical-axial area of the sinus anularis, build up a separate network for the collection of blood from the sinuses. These capillaries continue towards the dermis, contribute to the nutritional vascularization of the sebaceous gland, and finally connect with the subepidermal capillary loops.

Adaptive differentiations of the skin of the head in a subterranean rodent, Spalax ehrenbergi

The skin of macroscopically distinct regions (hairy skin, vibrissal fields, buccal ridge, and rhinarium) of the head of the blind mole-rat, Spalax ehrenbergi, was studied by routine histological methods. Few guard and several soft vellus hairs are organized into tufts that grow from a group of hair follicles localized in an invaginated compound cavity. We suggest that this hair arrangement may be a burrowing adaptation to match frictional resistance. The follicles and the compound cavity possess either well developed complex striated musculature or errector pili muscles. There are no structural specializations (sweat glands, glomus bodies) to enhance thermoregulatory (heat dissipative) capacities in the hairy skin of the head. Vibrissae penetrate the epidermal surface as single hairs. They are microscopically normally developed and arranged in vibrissal fields according to a basal mammalian pattern. Most of them are, however, relatively short and inconspicuous. The mystacial vibrissal field is horizontally divided by a prominent buccal ridge which is probably involved in bulldozing. The hairs in the ridge leave the compound cavity singularly. The follicles of guard hairs and bristles are equipped with well developed pilo-Ruffini complexes indicating that the buccal ridge may serve also as a tactile organ. The glabrous skin of the rhinarium has a highly interdigitated dermal-epidermal interface. The dermal papillae possess simple lamellated and/or simple Meissner's corpuscles and few Merkel cell-axon-complexes indicating that the skin of the rhinarium may be particularly sensitive to perception of vibrations.

Functional architecture of the mystacial vibrissae

We investigated the transduction operation and function of the mystacial vibrissae, using a comparative morphological analysis and behavioral experiments in rats. Vibrissal architecture was documented in a series of mammals to identify evolutionary conserved features of vibrissal organization. As a result of this analysis, we distinguish between a frontal microvibrissal system and macrovibrissal system of the mystacial pad. The latter was invariably comprised of whiskers aligned in regular rows. In each row, whiskers were oriented perpendicular to the animal's rostrocaudal axis; all shared a specific dorsoventral orientation. In all species, progressing from rostral to caudal in any vibrissal row, there was a precisely exponential increase in whisker length. Each whisker appeared to act as a lever-like transducer, providing information as to whether or not--but not where--an individual vibrissa had been deflected. The rat's frontal microvibrissae system was found to have a vibrissa tip density that was about 40 times higher than that of the mystacial macrovibrissae. In behavioral studies spatial tasks and object recognition tasks were used to investigate (a) search behaviors; (b) single whisker movements; (c) object recognition ability; and (d) effects of selective macro- or microvibrissae removal on task performances. A clear distinction between the functional roles of macro- and microvibrissae was demonstrated in these studies. Mystacial macrovibrissae were critically involved in spatial tasks, but were not essential for object recognition. Microvibrissae were critically involved in object recognition tasks, but were not essential for spatial tasks. A synthesis of these morphological and behavioral data led to the following functional concept: The mystacial macrovibrissae row is a distance decoder. Its function is to derive head centered obstacle/opening contours at the various dorsoventral angles represented by vibrissal rows. This distance detector model is functionally very different from traditional concepts of whisker function, in which the mystacial whiskers were hypothesized to form a fine grain skin-like object-recognizing tactile surface.

The sensorineural specializations of the trunk tip (finger) of the Asian elephant, Elephas maximus

BACKGROUND

The dorsal extension of the tip of the trunk of Asian elephants (Elephas maximus), often referred to as "the finger," possesses remarkable mechanical dexterity and is used for a variety of special behaviors including grasping food and tactile and ultimately chemosensory recognition via the vomeronasal organ. The present study describes a unique sensory innervation of this specialized region of the trunk.

METHODS

The tip of the dorsal aspect of the trunk is referred to as the trunk tip finger and has been studied grossly in 13 living elephants. One tip from a male Asian elephant was obtained for histologic study when it was accidentally severed. The tissue was fixed in 10% neutral buffered formalin, and portions were either sectioned frozen or embedded in paraffin and serial sectioned. Sections were stained with silver in both cases.

RESULTS

The skin of the trunk tip finger differs from that of the surrounding areas; it contains a high density of free nerve endings, numerous convoluted branched small corpuscles, and vellus vibrissae that resemble vellus hairs, which do not protrude beyond the skin surface. The finger is thus densely innervated with three distinctive types of sensory terminals. Corpuscular receptors consist of small Pacinian corpuscles and convoluted branched simple corpuscles. Both are present in the superficial dermis. Abundant regular vibrissae are present in the skin surrounding the trunk tip finger. Short vibrissae that do not protrude from the skin surface, referred to as vellus vibrissae, are abundant in the finger tip. Both types of vibrissae are innervated by hundreds of axons resembling the mystacial vibrissae of rodents. Free nerve endings are numerous in the superficial dermis, often making intimate contact with the basal cells of rete pegs.

CONCLUSIONS

The dorsal finger of the trunk tip of Asian elephants has a unique sensory innervation that resembles aspects of sensory innervation of mystacial skin of rodents or lip tissue of monkeys. This dense sensory innervation can be correlated with the tactile ability of these animals to use the trunk finger to grasp small objects for feeding and to insert chemically active samples into the ductal orifices of the vomeronasal organ for subsequent chemosensory processing.

Tenascin knockout mice: barrels, boundary molecules, and glial scars

In light of a previous report suggesting that the brains of tenascin-deficient animals are grossly normal, we have studied the somatosensory cortical barrel field and injured cerebral cortex in postnatal homozygous tenascin knockout, heterozygote, and normal wild-type mice. Nissl staining, cytochrome oxidase, and Dil axonal tracing of thalamocortical axonal projections to the somatosensory cortex, all reveal the formation of normal barrels in the first postnatal week in homozygous knockout mice that cannot be distinguished from heterozygote or normal wild-type barrels. In addition to confirming the absence of tenascin in knockout animals, and reporting apparently reduced levels of the glycoprotein in barrel boundaries of heterozygote animals using well-characterized antibodies and immunocytochemistry, we also studied the DSD-1-PG proteoglycan, another developmentally regulated molecule known to be associated with transient glial/glycoconjugate boundaries that surround developing barrels; DSD-1-PG was also found to be expressed in barrel boundaries in apparently normal time frames in tenascin knockout mice. Peanut agglutinin (PNA) binding of galactosyl-containing glycoconjugates also revealed barrel boundaries in all three genotypes. We also examined the expression of tenascin-R, a paralog of tenascin-C (referred to here simply as tenascin). As previously reported, tenascin-R is prominently expressed in subcortical white matter, and we found it was not expressed in the barrel boundaries in any of the genotypes. Thus, the absence of tenascin does not result in a compensatory expression of tenascin-R in the barrel boundaries. Finally, we studied wounds of the cerebral cortex in the late postnatal mouse. The astroglial scar formed, for the most part, in the same time course and spatial distribution in the wild-type and tenascin knockout mice. However, there may be some differences in the extent of gliosis between the knockout and the wild type that warrant further study. Roles for boundary molecules like tenascin during brain pattern formation and injury are reconsidered in light of these findings on barrel development and cortical lesions in tenascin-deficient mice.

A scanning electron-microscopic analysis of the morphology of equine lower lip sinus hair

Sinus hairs, which are tactile organs of most mammals, are differentiated into cavernous and sinus types. The horse has the cavernous type. Horse lower lips were perfused in diluted Karnovsky's fixative and sinus hair processed for scanning electron microscopy. Anastomosing trabeculae of different thickness and shape originate from the internal connective tissue layer and extend to the external layer, thus forming a dense meshwork suspending the hair root like a net. However, many of the distal trabeculae do not reach the external wall of the blood sinus but end in a finger-like knob within the sinus, thus sharing some features of the sinus type. The sinus wall and trabeculae are completely covered by polygonal endothelial cells showing characteristically protruding nuclei, sparse microvilli and distinct cell borders. Endothelial cells on the trabeculae are more elongated. Openings of small blood vessels were found exclusively on the internal wall, indicating that blood exchange occurs via the internal wall only and that turnover of blood may be minimal. The supposed significance and function of the finger-like trabeculae in the distal part of the blood sinus lying close to the majority of nerve terminals is discussed.

forked proteins are components of fiber bundles present in developing bristles of Drosophila melanogaster

The forked (f) gene of Drosophila melanogaster encodes six different transcripts 6.4, 5.6, 5.4, 2.5, 1.9, and 1.1 kb long. These transcripts arise by the use of alternative promoters. A polyclonal antibody raised against a domain common to all of the forked-encoded products has been used to identify forked proteins on two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and in Drosophila pupal tissues. The antibody stains fiber bundles present in bristle cells for about 15 hr during normal pupal development. Electron microscopy shows that these fibers are present from 40 to 53 hr in bristles of wild-type flies but are absent in the null f36a mutant. The forked protein(s) thus appear to be an essential part of the bristle fibers. The phenotype of the f36a mutation can be rescued by a 13-kb fragment of the forked locus containing the coding regions for the 2.5, 1.9, and 1.1-kb transcripts, suggesting that the proteins encoded by the three large forked RNAs are dispensable during bristle development. Increasing the copy number of a P[w+,f+] construct containing the 13-kb fragment induces a hypermorphic bristle phenotype whose severity correlates with the number of copies of P[w+,f+] present. These results indicate that alterations in the ratios among the forked proteins, or between forked products and other components of the fiber, result in abnormal assembly of the fibrillar cytoplasmic structures necessary for bristle morphogenesis.

Structure, vascularization, and innervation of the mystacial pad of the rat as revealed by the lectin Griffonia simplicifolia

The mystacial pad of the rat is endowed with rows of vibrissal follicle-sinus complexes (F-SCs) that receive a dense and rich variety of innervation, much of which is C fibers. Each F-SC consists of a follicle at the core of a spindle-shaped, encapsulated vascular sinus. Previous studies have shown that the B subunit of the lectin Griffonia simplicifolia (GSA I-B4) binds selectively to a subset of small neurons in the trigeminal ganglion and to a subset of C fibers preferentially distributed to inner lamina II and outer lamina III of nucleus caudalis in the brainstem trigeminal complex in the rat. These laminae are also a major site of termination for afferents in superficial vibrissal nerves (SVNs) that innervate the upper portion of F-SCs. To determine the peripheral distribution of the afferents that bind GSA I-B4, mystacial pads from rats were prepared for fluorescence microscopy with GSA I-B4 conjugated to rhodamine. At the neck of each F-SC, numerous circumferentially oriented bundles of fine-caliber axonal profiles were labeled in the inner conical body, which receives nearly all of its innervation from the SVNs. A sparse, random distribution of fine-caliber profiles from deep vibrissal nerves was labeled at the level of the cavernous sinus in the deep half of the F-SCs. GSA I-B4 also labeled a variety of nonneural structures. By binding to vascular linings, GSA I-B4 revealed a dense, highly organized capillary system within the mesenchymal sheath that forms the inner lining of the vascular sinuses. Thus each F-SC appears to have a closed capillary system within the open vascular sinus. Trabeculae within the lumen of the cavernous sinus were also revealed to span between the sinus capsule and the mesenchymal sheath only about midway along the length of the follicle instead of the entire deeper half, as was previously believed. in addition, GSA I-B4 bound to the surface of follicular cells preferentially in the superficial half of the F-SCs. Sweat glands within the intervibrissal fur and some cells within sebaceous glands in F-SCs were also labeled as well as their ducts. The potential functional implications of these various features are discussed.

Segregation of keratinocyte colony-forming cells in the bulge of the rat vibrissa

The epidermis and its related appendages such as the hair follicle constitute the epithelial compartment of the skin. The exact location and distribution of the keratinocyte colony-forming cells within the epidermis or its appendages are unknown. We report that in the rat vibrissa, keratinocyte colony-forming cells are highly clustered in the bulge-containing region. Approximately 95% of the total colonies formed in culture from fractionated vibrissae were in this location and fewer than 4% were located in the matrix area of the follicle. Finer dissection of the bulge-containing region located the colony-forming cells in the small part containing the bulge itself. The segregation of keratinocyte colony-forming cells in the bulge confirms the hypothesis that the bulge is the reservoir of the stem cells responsible for the long-term growth of the hair follicle and perhaps of the epidermis as well.

Induction of follicle formation and hair growth by vibrissa dermal papillae implanted into rat ear wounds: vibrissa-type fibres are specified

Adult vibrissa follicle dermal papillae have the capacity to induce hair growth and follicle formation when associated with epidermis from various sources. However, the range of conditions under which hair follicle induction will take place has not been established. The question of whether or not the adult papilla carries information to impose fibre-type specificity has also not been fully answered. This study describes how the implantation of isolated papillae into small incisional cuts on the rat ear pinna resulted in the subsequent emergence of abnormally large hair fibres from the wound sites. Many of these hairs were found to display vibrissa-type characteristics. Histological observations indicated that the papillae had interacted with the edges of the wound epidermis to produce new, and particularly large follicles, while immunohistochemical staining revealed that early follicle construction was accompanied by a profusion of the basement membrane constituents laminin and type IV collagen in the subjacent dermis. These findings show that adult rat papillae retain the capacity, as displayed by embryonic dermis, to determine vibrissa specificity in induced follicles.

The morphology and innervation of facial vibrissae in the tammar wallaby, Macropus eugenii

The morphology of the vibrissal follicles on the mystacial pad of the tammar wallaby is similar to that seen in other species except that the follicles lack a ringwulst or ring sinus. Instead, the mesenchymal sheath is thickened around the central region of the hair shaft. The follicle is innervated by both deep and superficial vibrissal nerves. The deep nerve enters as 4-11 fascicles which can be in close proximity or widely distributed around the hair. C1 follicles received more myelinated nerve fibres (252 +/- 31) than the smaller C4 follicles (174 +/- 43). The deep vibrissal nerve supplies the thickened mesenchymal sheath, the narrow 'waist' region above and the majority of endings in the inner conical body (ICB), while the superficial nerves provide a sparse innervation to the ICB and rete ridge. Receptors present in the follicle were of 4 types: (1) Merkel cells, especially numerous in the outer root sheath of the 'waist' region and occasionally in the ICB and rete ridge; (2) and (3) lanceolate and lamellated endings parallel to the hair shaft in both the mesenchymal thickening and the 'waist' region where they were particularly dense; (4) free nerve endings in the mesenchymal thickening, 'waist' region and ICB. No corpuscular, bulbous or Ruffini endings were seen. The innervation of the intervibrissal fur was similar to that described in other species.

Functional asymmetries in the rodent barrel cortex

Neurophysiological and 2-deoxyglucose (2DG) studies of the rodent whisker barrel cortex have demonstrated asymmetries in its functional organization. To examine the possibility that the activity gradients observed in metabolic studies can be attributed to subtle rostral-caudal and dorsal-ventral asymmetries in electrophysiologically measured surround or cross-whisker inhibition, we compared 2DG results with predictions generated from quantitative single-cell receptive field data. Despite differences in the two experimental approaches, there is remarkable agreement between the findings. (1) The distribution of 2DG activity declines across the barrel cortex of the behaving animal from anteromedial barrels to posterolateral barrels, and is qualitatively and quantitatively similar to the values predicted from neurophysiology. (2) The strength of surround inhibition in barrel neurons predicts the twofold increase in activation of the C3 barrel following acute clipping of adjacent whiskers. And (3) within a cortical column, the decrease in metabolic activity associated with adjacent whisker stimulation is greatest in layer IV and least in the infragranular layers; this corresponds to the laminar distribution of inhibitory interactions observed electrophysiologically.

Numbers of axons innervating mystacial vibrissa follicles in newborn and adult rats

Electron-microscopic techniques were used to determine the numbers of axons in the deep vibrissal nerves innervating the C1 and C4 follicles in newborn and adult rats. All counts were made from thin sections taken after the nerve had entered the follicle capsule (FC). In newborn animals, the nerves supplying the C1 (n = 10) and C4 (n = 10) follicles contained an average (means +/- standard deviation) of 355.0 +/- 40.0 and 233.9 +/- 19.2 axons, respectively. In the adult animals (n = 10 for C1 and n = 9 for C4), the respective values were 314.4 +/- 26.2 and 233.3 +/- 34.4 axons. There were no significant differences between the values for the counts from the neonates and adults for either follicle (p greater than 0.01, independent t tests). In the vibrissal nerves of neonates, both degenerating axons and occasional growth cones were visible. Such profiles were not observed in the nerves taken from adults.

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

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 supernumerary follicles are innervated and, given a threshold number of axons, represented by barrels; barrel area per peripheral axon differs between follicles within a row and is highest for the supernumerary elements; and 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.

Mystacial vibrissae representation within the trigeminal sensory nuclei of the cat

Somatotopic arrangements of axon terminals of primary afferent fibers innervating follicles of the mystacial vibrissae were examined in the cat by the transganglionic horseradish peroxidase (HRP) method. Forty to 60 hours after injecting HRP into a single or a group of vibrissal follicles, transported HRP was visualized by the tetramethylbenzidine technique. HRP-labeled axon terminals were distributed in the ventral subnucleus of the principal sensory trigeminal nucleus (ventral Vp), in the oral and interpolar spinal trigeminal nuclei (Vo and Vi), and in the caudal spinal trigeminal nucleus (Vc) (layer I, deep part of layer II, layers III-V) with its spinal extension into the dorsal horn of the first cervical cord segment (rostral C1). In cross sections through the caudal parts of the ventral Vp, Vi, and layer IV of the Vc and rostral C1, a single mystacial vibrissa was represented in a one-to-one fashion by a patch of dense terminal arbors of primary afferent fibers. The more dorsally a horizontal row of the mystacial vibrissae was located, the more ventrally was it represented in the ventral Vp, the more ventrolaterally in the Vi, and the more ventrally in layer IV of the Vc and the rostral C1. In addition, the more anteriorly a vibrissa was located in a horizontal row of the mystacial vibrissae, the more medially was it represented in the ventral Vp, the more ventromedially in the Vi, and the more laterally in layer IV of the Vc and rostral C1; the most posteriorly located vibrissae in the horizontal rows of the mystacial vibrissae were represented along the lateral border of the ventral Vp and Vi, and most medially in layer IV of the Vc and rostral C1. Thus, the representation pattern in the ventral Vp was rotated clockwise at about 45 degrees angle in the Vi, and projected as a mirror image in layer IV of the Vc and rostral C1. It was also indicated that the anterior-posterior arrangement of the mystacial vibrissae was represented in a rostral-caudal organization within layer IV of the Vc and rostral C1. It was also indicated that the anterior-posterior arrangement of the mystacial vibrissae was represented in a rostral-caudal organization within layer IV of the Vc and rostral C1. Patchy patterns probably replicating the distribution of the vibrissae on the face of the cat were also revealed by the cytochrome oxidase histochemical staining in cross sections through the caudal parts of the ventral Vp, Vi, and layer IV of the Vc and rostral C1.

Whisker growth induced by implantation of cultured vibrissa dermal papilla cells in the adult rat

Retention of the capacity to induce the growth of hair by cultured adult rat vibrissa dermal papilla cells has been investigated. Small pellets of serially cultured papilla cells were implanted into the bases of the exposed follicular epidermis of amputated adult rat vibrissa follicles. Amputated follicles that received no cell implants or implants of cultured dorsal skin fibroblasts were used as controls. Over 50% of follicles implanted with cultured papilla cells in the passage range 1-3 grew hairs. In contrast none of the follicles that received late passage cells (range 6-15) produced hairs; and spontaneous regeneration of hair occurred in only 3% of the control follicles. These results demonstrate that cultured papilla cells of early passage numbers retain their ability to induce hair growth. Histological examination confirmed that the implanted papilla cells interacted with follicular epidermis to organize the development of new, hair-producing bulbs, each containing a discrete dermal papilla. An important observation was that aggregative behaviour leading to papilla formation was only manifested by early passage papilla cell implants. This persisting embryonic characteristic appears to be an essential functional component of papilla cell activity which operates to regulate the profound morphogenetic changes that occur during the hair growth cycle.

Is areal extent in sensory cerebral cortex determined by peripheral innervation density?

The whisker-to-barrel pathway of mice (an important component of the animal's somatosensory system) was studied in two experiments. In one, the cortical representation of a row of whiskers was caused to be larger by lesioning a neighbouring row of follicles, while the innervation density remained unchanged. In the second experiment mice, selectively bred for particular whisker and barrel patterns, showed for their supernumerary vibrissal follicles a relatively large cortical representation. On the basis of the second experiment we formulate a possible role of the sensory periphery in brain evolution.

The role of vibrissae in behavior: a status review

Vibrissae or tactile hairs are an important part of the tactile sensory apparatus of many mammals. A wide range of suggested functions found in the literature include food acquisition, prey attack, aggression and attack behavior, facial expression in intraspecies communications, dispersion of pheromones, maintaining head position in swimming, and a wide range of environmental monitoring (e.g., current detection in water, wind direction on land). There is little work done specifically on domestic animals or their feral relatives. Work on the tactile senses in general and vibrissae in particular is an open field of study. A set of general questions for study of vibrissa function in domestic animals is presented.