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Newly metamorphosed individuals of the Kenyan reed frog, Hyperolius viridiflavus ferniquei, are able completely to regenerate amputated digits, including the morphologically complex digital pad. The sequence of morphological events is very similar to that seen in the typical epimorphic regeneration of amphibian extremities. Amputated forearms typically produce hypomorphic spike regenerates. Despite the lack of underlying hand and digital structures, an apical "digital" pad commonly differentiates.
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A staging system has been devised for normal regeneration from the upper arm in the mature axolotl. It consists of seven externally definable stages: (1) Wound healing (WH): (2) Dedifferentiation (DD); (3) Early bud (EB); (4) Medium bud (MB); (5) Late bud (LB); (6) Palette (Pal), and (7) Digital outgrowth (DO). Serial histological sections of 38 regenerating limbs were used to correlate gross stages with microscopic events in the regenerative process.
This study examines the allometric scaling relationships of the cetacean humerus, radius, and ulna. Bone lengths and diameters were measured for 20 species of odontocete and three species of mysticete cetaceans, representing eight of the nine extant cetacean families. The scaling of individual bone proportions (bone length vs. cranio-caudal diameter, bone length vs. dorso-ventral diameter), and of individual bone dimensions against estimated body mass, are compared to models of geometric and elastic similarity. The geometric similarity model describes the scaling relationship of bone length vs. cranio-caudal diameter and body mass vs. cranio-caudal diameter for the humerus only; geometric similarity also describes the scaling relationship of body mass vs. bone length for all three bones. None of the scaling relationships fits the elastic similarity model. The scaling relationships of bone length vs. dorso-ventral diameter for all three bones, and bone length vs. cranio-caudal diameter for the radius and ulna, exhibit negative allometry, indicating that large bones are less robust than small bones. Negative allometry of structural support elements has not been previously described for terrestrial mammals or plants. The high relative swimming speeds of small delphinids may generate sufficient stresses to require more robust bones relative to those of larger whales.
The present study examined the fiber-type proportions of 22 muscles spanning the shoulder and/or elbow joints of three Macaca mulatta. Fibers were classified as one of three types: fast-glycolytic (FG), fast-oxidative-glycolytic (FOG), or slow-oxidative (SO). In most muscles, the FG fibers predominated, but proportions ranged from 25-67% in different muscles. SO fibers were less abundant except in a few deep, small muscles where they comprised as much as 56% of the fibers. Cross-sectional area (CSA) of the three fiber types was measured in six different muscles. FG fibers tended to be the largest, whereas SO fibers were the smallest. While fiber-type size was not always consistent between muscles, the relative size of FG fibers was generally larger than FOG and SO fibers within the same muscle. When fiber CSA was taken into consideration, FG fibers were found to comprise over 50% of the muscle's CSA in almost all muscles.
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We investigated the inositol phospholipid transmembrane signaling pathway as a possible mediator of neurotrophic (mitogenic) signals in the newt limb regeneration blastema. Blastema mesoderm tissues were prelabeled with myo-[3H]inositol, treated with 10 mM LiCl and then exposed to substance P or to extracts of spinal ganglia, brain, or spinal cord. Stimulation with substance P resulted in a rapid dose-dependent reduction of [3H]phosphatidylinositol 4,5-bisphosphate and [3H]phosphatidylinositol 4-phosphate, correlated with a rapid accumulation of inositol 1,4,5-triphosphate. This effect was inhibited when the blastema tissue was treated with neomycin, a known inhibitor of inositol phospholipid turnover. In addition, substance P stimulated the incorporation of [3H]thymidine into DNA of blastema mesoderm cells, and this effect was also suppressed by neomycin, at a dose corresponding to that required to inhibit inositol phosphate accumulation. Extracts of neural tissues, especially spinal ganglia, induced the formation of inositol phosphates and extract activity was attenuated following treatment with heat or trypsin. These findings suggest a role for mitogen-activated inositol phospholipid signaling, initiating events that ultimately lead to cell proliferation.
Xenopus laevis can regenerate an amputated limb completely at early limb bud stages, but the metamorphosed froglet gradually loses this capacity and can regenerate only a spike-like structure. We show that the spike formation in a Xenopus froglet is nerve dependent as is limb regeneration in urodeles, since denervation concomitant with amputation is sufficient to inhibit the initiation of blastema formation and fgf8 expression in the epidermis. Furthermore, in order to determine the cause of the reduction in regenerative capacity, we examined the expression patterns of several key genes for limb patterning during the spike-like structure formation, and we compared them with those in developing and regenerating limb buds that produce a complete limb structure. We cloned Xenopus HoxA13, a marker of the prospective autopodium region, and the expression pattern suggested that the spike-like structure in froglets is accompanied by elongation and patterning along the proximodistal (PD) axis. On the other hand, shh expression was not detected in the froglet blastema, which expresses fgf8 and msx1. Thus, although the wound epidermis probably induces outgrowth of the froglet blastema, the polarizing activity that organizes the anteroposterior (AP) axis formation is likely to be absent there. Our results demonstrate that the lost region in froglet limbs is regenerated along the PD axis and that the failure of organization of the AP pattern gives rise to a spike-like incomplete structure in the froglet, suggesting a relationship between regenerative capacity and AP patterning. These findings lead us to conclude that the spike formation in postometamorphic Xenopus limbs is epimorphic regeneration.
In the majority of patients, spinal cord injury (SCI) results in abnormal pain syndromes in which non-noxious stimuli become noxious (allodynia). To reduce allodynia, it would be desirable to implant a permanent biological pump such as adrenal medullary chromaffin cells (AM), which secrete catecholamines and opioid peptides, both antinociceptive substances, near the spinal cord. We tested this approach using a recently developed a mammalian SCI model of chronic central pain, which results in development of mechanical and thermal allodynia. Thirty day-old male Sprague-Dawley rats were spinally hemisected at T13 and allowed 4 weeks for recovery of locomotor function and development of allodynia. Nonimmunosuppressed injured animals received either control-striated muscle (n = 7) or AM (n = 10) transplants. Nociceptive behavior was tested for 4 weeks posttransplant as measured by paw withdrawals to von Frey filaments, radiant heat, and pin prick stimuli. Hemisected animals receiving AM demonstrated statistically significant reductions in both fore- and hindlimb mechanical and thermal allodynia, but not analgesia, when compared to hemisected animals receiving striated muscle transplants (P < 0.05). Tyrosine hydroxylase immunoreactivity indicated prolonged transplant survival and production of catecholamines. HPLC analysis of cerebrospinal fluid samples from animals receiving AM transplants demonstrated statistically significant increases in levels of dopamine (sevenfold), norepinephrine (twofold), and epinephrine (threefold), compared to control values several weeks following transplant (P < 0.05). By 28 days posttransplant, however, antinociceptive effects were diminished. These results support the therapeutic potential of transplanted AM in reducing chronic central pain following spinal cord injury.
Novel neuroimaging techniques are extending the scope for studying dynamic brain function. We have developed a system which enables the repeatable imaging of rapid function in rodent primary somatosensory cortex (S-I), based on activity-related changes in its optical reflectance (intrinsic signals). The S-I cortices of anesthetized male Sprague-Dawley rats were exposed. Images were acquired with a slow-scan, cooled, charge-coupled device camera (CCD) through filters at 550, 610, and 850 nm before, during, and after contralateral stimulation (vibrissal deflection or forepaw stimulation). Images were divided by prestimulus controls and then averaged across 9-27 trials to produce maps of stimulus-related reflectance change. Optical activity had magnitude 10(-3) of baseline reflectance and consistently comprised two distinct spatiotemporal components over cortex, depending on paradigm. The diffuse signal at 610 nm begins 0.5-1 s after stimulus onset and has a duration of 4-5 s. The second signal is macrovenous and is delayed by 1 s. Similar response patterns were observed at 550 and 850 nm. Evoked potentials, recorded at sites inside and outside the zone of optical activity, confirmed the functional nature of these signals. Using a CCD we have imaged functional reflectance changes over rodent S-I which commence, peak, and extinguish over a time scale of seconds. This optical activity is consistent with the etiologies of microvascular recruitment and chromophore redox change.
The distal course of the sensory nerve fibres on the palmar side of the hand of 12-day-old mouse embryos was followed by serial ultrathin cross-sections of conventionally fixed tissue. Small nerves fibres are to be found in the space between the layer of the cutaneous blood vessels and the epidermis. A special arrangement of the tissue which is traversed by the nerve fibres is not visible. In most cases the nerve fibres are in intimate contact with fibroblasts. More distally the nerve fibres consist only of one axon encircled by a Schwann cell. The sheath of the Schwann cell decreases gradually, and finally disappears completely. The distal tips of the naked axons are a few microns ahead. In some cases they are considerably enlarged and contain only a fine fuzzy material without special cell organelles. Other axons may end in a more finger-like fashion, and contain also in the naked parts many cell organelles. Also the naked axons contact fibroblasts over long ranges. Collagen was not found aligned to the distal nerve fibres.
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