beta-Endorphins (beta-EP) in amphibians: higher beta-EP levels during regenerating stages of anuran life cycle and immunocytochemical localization of beta-EP in regeneration blastemata

Proteomic analysis of fibroblastema formation in regenerating hind limbs of Xenopus laevis froglets and comparison to axolotl

Background

To gain insight into what differences might restrict the capacity for limb regeneration in Xenopus froglets, we used High Performance Liquid Chromatography (HPLC)/double mass spectrometry to characterize protein expression during fibroblastema formation in the amputated froglet hindlimb, and compared the results to those obtained previously for blastema formation in the axolotl limb.

Results

Comparison of the Xenopus fibroblastema and axolotl blastema revealed several similarities and significant differences in proteomic profiles. The most significant similarity was the strong parallel down regulation of muscle proteins and enzymes involved in carbohydrate metabolism. Regenerating Xenopus limbs differed significantly from axolotl regenerating limbs in several ways: deficiency in the inositol phosphate/diacylglycerol signaling pathway, down regulation of Wnt signaling, up regulation of extracellular matrix (ECM) proteins and proteins involved in chondrocyte differentiation, lack of expression of a key cell cycle protein, ecotropic viral integration site 5 (EVI5), that blocks mitosis in the axolotl, and the expression of several patterning proteins not seen in the axolotl that may dorsalize the fibroblastema.

Conclusions

We have characterized global protein expression during fibroblastema formation after amputation of the Xenopus froglet hindlimb and identified several differences that lead to signaling deficiency, failure to retard mitosis, premature chondrocyte differentiation, and failure of dorsoventral axial asymmetry. These differences point to possible interventions to improve blastema formation and pattern formation in the froglet limb.

The axolotl as an animal model for the comparison of 3-D ultrasound with plain film radiography

We assessed the usefulness of an animal model, the axolotl (Ambystoma mexicanum), in comparing 3-D ultrasound (3-D US) and plain film radiographs. Hindlimbs were amputated from 5 animals, at either the zeugopodial or stylopodial level, and each regenerating limb was imaged 16 times with 3-D US and 14 times with plain film X ray over 315 days. US images were acquired with a Siemens Sonoline Versa Pro and a 10-MHz linear array transducer. For 3-D US images, the probe was translated in a motor-driven linear stage while images were digitized. The regenerating tibia and fibula bones were detected on 3-D US an average of 37 days earlier than on plain film radiography, and regenerating phalangeal bones were detected on 3-D US an average of 18 days earlier. After 120 days, both imaging modalities consistently showed the bones. The average bone growth rates for the tibia and fibula were 0.019 +/- 0.001 mm/day and 0.019 +/- 0.001 mm/day, respectively.

Localization of beta-endorphin-like immunoreactivity in the nervous system of the adult newt, Notophthalmus viridescens

Using indirect immunofluorescence methods, we have localized for the first time in the newt, Notophthalmus viridescens, beta-endorphin (beta-ep)-like immunoreactivity in the neurons of spinal ganglia (SPG), spinal cord (SPC), as well as in the hypothalamic region of the brain. An examination of serially sectioned SPG showed that the beta-ep-positive neurons, cell bodies, and nerve fibers were distributed at all levels of SPG. Peripheral regions of the perikarya of beta-ep-positive SPG neurons exhibited intense staining for beta-ep, the central nuclear region remaining nonreactive. In SPC, brightly staining fibers were seen entering the afferent nociceptive input areas, namely the Lissauer's tracts, substantia gelatinosa, and the dorsal ascending columns. Dot-fiber immunofluorescence pattern was observed throughout the gray matter of SPC representing beta-ep-positive, secondary sensory neurons as well as interneurons. Also, discrete cluster of neurons located deep in the gray matter of SPC stained positively to beta-ep antisera. This study not only demonstrates for the first time the presence of beta-ep like material in the newt, more specifically in SPG and SPC, but also raises the question of a possible link between beta-ep and newt limb regeneration as previous work has shown that SPG support limb regeneration in a denervated-amputated newt forelimb.

A search for immunoreactive substance P and other neural peptides in the limb regenerate of the newt Notophthalmus viridescens

Immunochemical studies demonstrate that the undecapeptide substance P (SP) may be detected by radioimmunoassay in newt limb regenerates and that SP is localized in the blastemal epidermis by immunofluorescence and peroxidase-antiperoxidase staining. Immunoreactive SP is predominantly distributed at the periphery of epidermal cells, suggesting the presence of SP binding sites on the cell surface; the basal germinative layer of the epidermis and blastemal mesenchyme cells remain unreactive. The pattern of SP immunoreactivity in the blastema was compared with that of four other tachykinin-family peptides (eledoisin, kassinin, substance K, and neuromedin K) and with three non-tachykinin neural peptides (bombesin, neurotensin, and metenkephalin). With the exception of neurotensin, which showed weak staining in the basal layer but an absence in the peripheral layers of the epidermis, none of the peptides examined exhibited immunoreactivity in the blastema epidermis comparable to that of SP.

Detection of Met-enkephalin and Leu-enkephalin in the brain of the hagfish, Eptatretus stouti, and the lamprey, Petromyzon marinus

Acid extracts of the brain of the pacific hagfish, Eptatretus stouti, and the marine lamprey, Petromyzon marinus, were each fractionated by gel filtration chromatography and aliquots of column fractions were screened with radioimmunoassays (RIAs) specific for pro-dynorphin-related end products and for pro-enkephalin-related end products. Only pro-enkephalin-related immunoreactive forms were detected. The enkephalin-sized immunoreactive material, isolated for each species, was separately fractionated by reverse-phase high-performance liquid chromatography (HPLC). Aliquots of column fractions were screened with RIAs specific for Met-enkephalin, Leu-enkephalin, Met-enkephalin-Arg-Phe, and Met-enkephalin-Arg-Gly-Leu. In the hagfish brain, immunoreactive forms with the same retention times as synthetic Met-enkephalin and Leu-enkephalin were detected in a ratio of approximately 2:1. In addition, an immunoreactive form was detected with the Met-enkephalin-Arg-Phe-specific RIA. This form had the same chromatographic properties as synthetic Met-enkephalin-Arg-Phe. Analyses with the Met-enkephalin-Arg-Gly-Leu RIA were negative. HPLC analysis of the lamprey enkephalin-related material revealed the presence of authentic Met-enkaphalin and Leu-enkephalin in a molar ratio of 3:1. C-terminally extended forms of Met-enkaphalin were not detected in the lamprey extracts. Collectively these observations indicate that pro-enkephalin-related opioid peptides are present in the brain of cyclostomes.

Opioids and the developing organism: a comprehensive bibliography, 1984-1988

A comprehensive bibliography of the literature concerned with opioids and the developing organism for 1984-1988 is presented. Utilized with companion papers (Neurosci. Biobehav. Rev. 6:439-479; 1982; 8:387-403; 1984), these articles cover the clinical and laboratory references beginning in 1875. For the years 1984, 1985, 1986, 1987, and 1988, a total of 877 citations were recorded. A series of indexes accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics, and subdivided into such topics as the type of opioid explored and the general area of biological interest (e.g., physiology).

Neuropeptides induce directional asymmetry in brain and spinal cord: facts and hypotheses

Directional behavioral and functional asymmetries (i.e., left-biased or right-biased in all or most animals of the population) induced by certain chemical substances are new types of brain and spinal cord asymmetry. The revealed asymmetry comprises: (1) left- or right-biased circle rotation in rat, (2) hind limb postural asymmetry resulting from alteration of the left or right flexion reflex in rat and cat, and (3) asymmetric alterations of the evoked potentials (EP) in the turtle visual cortex. Circle rotation of animals is induced by hypothalamic neurohormones (somatostatin, LH-RH, substance P, and TRH). Postural asymmetry develops under the effect produced by enkephalins and opioid kappa- and delta-agonists, sigma-agonist SKF 10.047, Arg-vasopressin. Endogenous peptide factors, the activity (or content) of which increased under brain and spinal cord unilateral injury, as well as the ones localized in the left or right hemisphere, also induced postural asymmetry. EP of the left and right turtle visual cortex were inhibited by enkephalins and opioid kappa-, and delta- and mu-agonists, and factors predominantly localized in the left or right turtle visual cortex in a different manner. The data reported here suggest the existence of a side-specific mechanism for a selective neurohormonal regulation of the neuronal activity and other processes in the left and right halves of brain and spinal cord which involves lateralized neuropeptides and their receptors. This mechanism might serve to maintain a certain balance between the activity of the left and right-side neurons, and other contralateral processes in the paired and bilateral structures in brain and spinal cord. Significant deviations from the balance occur most likely due to powerful unilateral stimuli, e.g., unilateral trauma. Many neuropeptides (opioid ones, somatostatin, MSH, ACTH) are, presumably, involved in the regeneration processes in the central and peripheral nervous system. In the case of brain lesions, some lateralized endogenous peptides may participate in the regulation of regeneration process on the left, whereas the other ones, on the right side of the midline, which depends on the side of the lesion. Some lateralized receptors and ligands may serve as positional markers of the left, whereas the other ones may serve as those of the right brain hemisphere. In ontogenesis, these markers are probably necessary to perform the function of the mechanism responsible for symmetrical brain formation.

Immunohistochemical localization of beta-endorphin-like material in the urodele and anuran amphibian tissues

In the present study, we have localized for the first time beta-endorphin (beta-EP)-like material in the adult and larval urodele and anuran tissues using immunohistochemical techniques. In the adult Notophthalmus viridescens and Ambystoma mexicanum, strong immunoreactivity to beta-EP antisera was observed in the region of the intermediate lobe, the latter fluorescing as a discrete body. The fluorescence was confined to the periphery of the cells, while the nuclei and the immediately surrounding cytoplasmic regions of the cells remained unstained. A few scattered cells in the anterior pituitary gland as well as the tracts in the posterior lobe also exhibited positive staining, although not as strong as the intermediate lobe. In the larval urodele, A. maculatum, beta-EP-like material was localized for the first time in the sensory ganglia and their emerging nerve fibers, in the Leydig cells of the skin, as well as in a few discrete cells scattered among stomach epithelial cells. In addition to the above, immunoreactivity to beta-EP antisera was observed in the cellular intermediate part of the neurointermediate lobe of the pituitary gland in young Xenopus laevis, the neural part of the lobe remaining nonreactive.

Plasma levels of beta-endorphin in white-tailed deer: seasonal variation and the effect of thyroxine, GnRH, dexamethasone and ACTH administration

1. A distinct seasonal cycle of beta-endorphin (beta-E) was detected in plasma of four intact, male white-tailed deer. Peak levels (around 11 pg/ml) were observed in August and minimal concentrations (around 5 pg/ml) were detected in January and February. 2. The seasonal variation (which corresponds to intensity of antler growth) was more pronounced in the two mature bucks, as compared to the immature ones. 3. Intramuscular administration of synthetic thyroxine (in doses of 500, 750 and 1000 micrograms/deer) and GnRH (100 micrograms/deer) had generally no significant effect on the beta-E levels. 4. I.v. administration of dexamethasone (5 mg/deer) as well as i.m. injection ACTH (20 Int. Units/deer) significantly reduced beta-E levels.

Localization of enkephalin immunoreactivity in diverse tissues and cells of the developing and adult rat

The distribution of enkephalin, an endogenous opioid, in tissues and cells of the developing and adult rat was determined by immunocytochemistry with antibodies to met- and leu-enkephalin. Met- and leu-enkephalin were found in all developing cells investigated, with staining generally located throughout the cytoplasm; cell nuclei were not immunoreactive. In comparison to developing cells, immunoreactive analogues to met-enkephalin were usually difficult to detect in the adult. Some notable exceptions were reaction products in leukocytes in blood, lung, and cortex of thymus, fibroblasts in the skin, and seminiferous tubules. These results, in concert with earlier reports that opioid receptors are found largely in developing, but not adult, tissues, indicate that endogenous opioids are specifically involved in biological development, particularly cell proliferation and differentiation. Immunoreactivity in adult non-neural cells may be related to their development in some cases, but also could indicate other functions.

Regenerate epithelium and skin glands of the adult newt react to the same monoclonal antibody

A search for specific proteins involved in newt limb regeneration, using monoclonal antibodies against forelimb blastemas, led to the detection of an antigen in the regenerate epithelium. Fluorescent-antibody-labeled cells first appeared just prior to blastema outgrowth. From bud through early digit stages this antibody reacted with nearly all of the regenerate epithelial cells. Other tissues also reacted, including nerve, blood vessels, and gastrointestinal tract. The behavior of the reactive cells in the regenerate epithelium, and their close association with immediately adjacent skin glands, raises several new possibilities for the origin of the regenerate epithelium.

Pattern-deficient forelimb regeneration in adult bullfrogs

This study was designed to test the ability of adult bullfrogs (Rana catesbeiana) to regenerate forelimbs, both with and without various experimental treatments. Distal humerus-level forelimb amputations provided with additional deviated (sciatic) nerve and/or repeated soft-tissue injury exhibited considerable outgrowth. However, control sham-operated forelimbs also produced regenerates with comparable frequency, size, and morphological complexity. The lengths of the regenerates ranged from 0.4 to 2.6 cm, representing an outgrowth of 10-65% of the portion removed by the distal humerus amputation plane; some regenerates exhibited an external morphology indicative of digitlike structures. Some outgrowths were flexible but only one was capable of independent movement. Victoria Blue staining of whole regenerates revealed a variety of internal cartilage elements. Staining showed a single solid mass of cartilage in some regenerates while others had several individual and variably shaped cartilages projecting distally. Histological analysis also revealed the presence of connective tissue, striated muscle, and abundant nerve fibers in addition to the individual cartilage elements. We have tentatively termed these responses pattern-deficient regeneration.